POLYVINYLIDENE FLUORIDE RESIN POWDER FOR MELT …

Note: Within nine months of the publication of the mention of the grant of the European patent in the European PatentBulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with theImplementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has beenpaid. (Art. 99(1) European Patent Convention).

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(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention of the grant of the patent: 04.05.2011 Bulletin 2011/18

(21) Application number: 05795766.4

(22) Date of filing: 13.10.2005

(51) Int Cl.:C08F 14/22 (2006.01) B29B 9/12 (2006.01)

B29C 45/00 (2006.01) B29K 27/12 (2006.01)

C08F 14/18 (2006.01)

(86) International application number: PCT/JP2005/019244

(87) International publication number: WO 2006/043609 (27.04.2006 Gazette 2006/17)

(54) POLYVINYLIDENE FLUORIDE RESIN POWDER FOR MELT MOLDING AND PROCESS FOR PRODUCING MOLDING FROM THE RESIN POWDER

POLYVINYLIDENFLUORIDHARZPULVER ZUR SCHMELZEFORMGEBUNG UND VERFAHREN ZUR HERSTELLUNG EINES FORMKÖRPERS AUS DEM HARZPULVER

POUDRE DE RÉSINE FLUORURE DE POLYVINYLIDÈNE POUR MOULAGE PAR FUSION ET PROCÉDÉ DE FABRICATION DE PRODUITS MOULÉS À PARTIR DE LADITE POUDRE DE RÉSINE

(84) Designated Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI SK TR

(30) Priority: 20.10.2004 JP 2004305747

(43) Date of publication of application: 04.07.2007 Bulletin 2007/27

(73) Proprietor: Kureha CorporationTokyo 103-8552 (JP)

(72) Inventors: • IKEDA, Tsukasa,

Kureha CorporationIwaki-shi, Fukushima 974-8686 (JP)

• SUZUKI, Yasuhiro,Kureha CorporationIwaki-shi, Fukushima 974-8686 (JP)

• IWABUCHI, Kenichi,Kureha CorporationIwaki-shi, Fukushima 974-8686 (JP)

• KATSURAO, Takumi,Kureha CorporationTokyo 103-8552 (JP)

(74) Representative: Albrecht, ThomasKraus & Weisert Patent- und Rechtsanwälte Thomas-Wimmer-Ring 1580539 München (DE)

(56) References cited: EP-A- 0 526 216 EP-A- 1 227 109EP-A- 1 380 605 EP-A- 1 452 550EP-A- 1 621 573 JP-A- 2 029 402JP-A- 3 185 007 JP-A- 11 080 216JP-A- 51 005 386

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Description

TECHNICAL FIELD

[0001] The present invention relates to polyvinylidene fluoride resin powder for melt molding, and more particularly topolyvinylidene fluoride resin powder capable of being molded by press-fit technique such as injection molding or extrusionmolding while retaining the form of the powdery resin as it is without pelletizing the powder.[0002] The present invention also relates to a process for producing a molding by feeding the polyvinylidene fluorideresin powder for melt molding to an injection molding machine or extrusion molding machine (extruder) while retainingthe form thereof, melting the resin powder and then injecting the resin melt into a mold.

BACKGROUND ART

[0003] A polyvinylidene fluoride resin (hereinafter abbreviated as "PVDF resin") is a crystalline resin having a lowglass transition temperature and is excellent in heat resistance, chemical resistance, mechanical properties (for example,tensile strength, flexural modulus, flexural strength, compressive strength and impact resistance), abrasion resistance,flame retardancy and weatherability. The PVDF resin also develops extremely specific electrical properties in cooperationwith a feature that a dipole moment of a C-F bond in its molecular structure is high.[0004] Other basic properties of the PVDF resin include good melt processability. In other words, the PVDF resin hasa wide processable temperature range from its melting point to its decomposition point and exhibits good melt-flowcharacteristics.[0005] As described above, the PVDF resin has well balanced physical properties and good processability in combi-nation, and application fields thereof extend to a wide variety of fields of abrasion-resistant materials, weatherablematerials, electric and electronic materials, leisure materials.[0006] The PVDF resin is excellent in the suitability for secondary processing such as machining, bending or weldingafter primary processing. For example, a machining stock such as a thick-wall round bar or plate is produced by extrusionmolding making use of the PVDF resin. The machining stock is machined into a desired shape by milling, perforating,cutting, combinations thereof.[0007] However, the PVDF resin has a drawback that a molten resin is colored when a molding temperature becomeshigh in melt molding such as injection molding or extrusion molding. In order to avoid the coloring of the molten resin,the molding temperature in the injection molding or extrusion molding is generally controlled in such a manner that thetemperature of the molten resin is 280°C or lower.[0008] In the injection molding or extrusion molding, pellets of the PVDF resin are generally used. For example, whena molding such as a wafer carrier, joint or valve is molded by injection molding, a screw injection molding machine isordinarily used. The pellets are fed into a heated cylinder of the injection molding machine by rotation of a screw. Thepellets are fed by the screw and at the same time, evenly melted. The molten resin is injected into a mold from theinjection molding machine.[0009] In the extrusion molding, the pellets are fed into a heated cylinder of an extrusion molding machine by rotationof a screw, and the molten resin is extruded into a shape of, for example, a rod, plate or pipe from a forming die installedin the tip of an extruder.[0010] In such a conventional melt molding process, the PVDF resin is subjected to thermal history upon the formationof pellets and further subjected to thermal history even upon the melt molding, so that it is difficult to prevent the coloringof the resulting molding by only controlling the molding temperature upon the melt molding low. An extrusion-moldedproduct used as a machining stock, to say nothing of an injection-molded product, is required to have a beautiful colortone and be little colored. In recent years, there has been a strong demand for provision of a PVDF resin molding havinghigh performance and high quality, and so it is required to develop a new technique for inhibiting coloring upon meltmolding.[0011] More specifically, PVDF resins can be synthesized by various polymerization processes. In industrial production,however, the resins are synthesized by an emulsion polymerization process and a suspension polymerization process.A PVDF resin synthesized is collected in the form of resin powder. Powder characteristics of the resin powder such asaverage particle diameter, particle size distribution and evenness of particle shape vary according to the kind and amountof a polymerization initiator, the kind and amount of a suspending agent or emulsifier, the kind of a reaction medium, apolymerization temperature and a manner of combining them. In the emulsion polymerization process, a latex having asmall particle diameter of 0.2 to 0.5 Pm is formed and is subjected to a granulation treatment using a flocculant after thepolymerization.[0012] When it has been intended to produce moldings with PVDF resin powder by melt molding such as injectionmolding or extrusion molding, it has been impossible or extremely difficult to obtain moldings having a fixed shape andquality because the powder has been unable to be stably fed into a cylinder of a molding machine, or an extrusion rate

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has become unstable.[0013] Therefore, the PVDF resin powder has heretofore been not fed to injection molding or extrusion molding as itis in a state of resin powder, but fed after melt processing into pellets (for example, US 6,846,436 B1). A pelletizing stephas been considered to be necessary even for evenly kneading the PVDF resin powder with various kinds of additives.[0014] When the PVDF resin powder is pelletized, the PVDF resin is subjected to thermal history in addition to thefact that it takes time, and the cost becomes high. Therefore, when the resultant pellets are used to conduct melt molding,the pellets are subjected again to thermal history at a high temperature, so that such pellets have involved a problemthat the resultant molding is colored even when the molding temperature is controlled low.[0015] However, no PVDF resin powder capable of being stably melt-molded has heretofore been proposed. A PVDFresin for melt molding is marketed in the form of pellets. Some PVDF resins are marketed in the form of resin powder.It has however been general that when injection molding or extrusion molding is conducted, the resin powder is pelletizedand then fed into a molding machine.[0016] Since the pellets are not a final molding, there is no need to strictly control a scatter of shape. Accordingly, asingle-screw or twin-screw extruder is ordinarily used in pelletizing of the PVDF resin. However, the processing conditionsmay not be strictly controlled because the resin is melt-extruded into a fine strand from a die nozzle and cut into a propersize, or a resin ejected is only cut on the tip of an extruder unlike general melt molding into a molding.[0017] On the other hand, in injection molding or extrusion molding of the PVDF resin, it is necessary to use a moldingmachine suitable for it, stably feed a resin material to the molding machine and strictly control an extrusion rate andmolding conditions so as to mold a molding having a fixed quality.

DISCLOSURE OF THE INVENTION

[0018] It is an object of the present invention to provide polyvinylidene fluoride resin powder capable of stably fed toan injection molding machine or extrusion molding machine in the form of the resin powder and providing moldings,which are excellent in various properties like a case where pellets are used, and inhibited from coloring compared withthe case where pellets are used.[0019] Another object of the present invention is to provide a process for producing a molding, by which a molding,which is excellent in various properties and inhibited from coloring, can be stably and cheaply produced by injection-molding or extrusion-molding polyvinylidene fluoride resin powder obtained by polymerization and having specific powdercharacteristics in a state of the resin powder without pelletizing the powder.[0020] The present inventors have carried out an extensive investigation with a view toward achieving the aboveobjects. As a result, it has been found that polyvinylidene fluoride resin powder, which has specific particle size distributioncharacteristics, is high in bulk density (bulk specific gravity) and low in angle of repose, is excellent in flowability andgood in intermesh with a screw installed in a cylinder of an injection molding machine or extrusion molding machine.[0021] Many of powdery PVDF resins currently marketed are low in bulk density and high in angle of repose, or smallin average particle diameter, or broad in particle size distribution, or small in average particle diameter, low in bulk densityand high in angle of repose. When such conventional PVDF resin powder is fed to an injection molding machine orextrusion molding machine, the intermesh of the resin powder with a screw in a cylinder is poor, so that the stable feedis difficult in itself, and moreover it is impossible to injection-mold it in a fixed amount or continuously extrude it.[0022] On the other hand, since the PVDF resin powder according to the present invention has specific powdercharacteristics, it is excellent in flowability, can be stably fed to a molding machine and can be precisely and stablyweighed and molded like pellets thereof. A molding obtained by melting the PVDF resin powder according to the presentinvention and conducting transfer molding into a mold is inhibited from coloring by heating compared with a moldingobtained by melt molding after pelletizing and is comparable even from the viewpoint of mechanical properties.[0023] According to the production process of the present invention, a pelletizing step can be omitted because thePVDF resin powder having the specific powder characteristics is used, so that production cost can be reduced.[0024] The present invention has been led to completion on the basis of these findings.[0025] A Polyvinylidene fluoride resin powder for melt molding having such powder characteristics (a) to (c) that

(a) the resin powder exhibits, as determined by a dry sieving method in accordance with JIS K 0069, such particlesize distribution characteristics that

i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulative distributionis 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight, andiv) a value [(D80 - D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) represented by adifference between a 80% cumulative value (D80) and a 20% cumulative value (D20) in the particle size cumulative

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distribution by the 50% cumulative value (D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity in accordancewith JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by a measuring method described in the specification in whicha bulk specific gravity measuring device prescribed in JIS K 6721 is used.

[0026] According to the present invention, there is also a process for producing a polyvinylidene fluoride resin molding,which comprises the following Steps 1 to 3:

1) Step 1 of feeding, to a melt molding machine, polyvinylidene fluoride resin powder for melt molding, which hassuch powder characteristics (a) to (c) that

(a) the resin powder exhibits, as determined by a dry sieving method in accordance with JIS K 0069, suchparticle size distribution characteristics that

i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulativedistribution is 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight, andiv) a value [(D80 -D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) represented by adifference between a 80% cumulative_ value (D80) and a 20% cumulative value (D20) in the particle sizecumulative distribution by the 50% cumulative value(D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity inaccordance with JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by measuring method described in the specification in whicha bulk specific gravity measuring device prescribed in JIS K 6721 is used,in a state of the resin powder;

2) Step 2 of heating and melting the resin powder in the melt molding machine into a resin melt; and3) Step 3 of injecting the resin melt into a mold to mold the resin melt.

[0027] According to the present invention, there is also the use of polyvinylidene fluoride resin powder for melt moldingby press-fit techniques selected from the group consisting of injection molding and extrusion molding while retaining theform of the powdery resin as it is without pelletizing the powder, wherein the polyvinylidene fluoride resin powder formelt molding has such powder characteristics (a) to (c) that


i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulative distributionis 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least_ 355 Pm is at most 5.0% by weight, andiv) a value [(D80 - D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) represented by adifference between a 80% cumulative value (D80) and a 20% cumulative value (D20) in the particle size cumulativedistribution by the 50% cumulative value (D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity in accordancewith JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by a measuring method described in the specification in whicha bulk specific gravity measuring device prescribed in JIS K 6721 is used.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] A polyvinylidene fluoride resin (PVDF resin) is a homopolymer of vinylidene fluoride or copolymers of vinylidenefluoride and monomer(s) copolymerizable therewith, comprising vinylidene fluoride as a principal structural unit.

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[0029] Examples of the vinylidene fluoride copolymer include vinylidene fluoride-hexafluoropropylene copolymers,vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers, vinylidene flu-oride-trifluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymers and vinyli-dene fluoride-chlorotrifluoroethylene-hexafluoropropylene terpolymers.[0030] These vinylidene fluoride copolymers are crystalline thermoplastic resins, in which the copolymerization ratioof comonomers such as hexafluoropropylene is 15 mol% or lower, preferably 10 mol% or lower, more preferably 5 mol%or lower. The lower limit of the proportion of the comonomer is preferably 1 mol%.[0031] The homopolymer (PVDF) of vinylidene fluoride is a crystalline resin. When the crystallinity thereof is brokenby copolymerization to form an elastomer, it is necessary to increase the copolymerization ratio of the comonomer suchas hexafluoropropylene. In a commercially available elastomer, the copolymerization ratio of the comonomer is actually20 mol% or higher. The PVDF resin used in the present invention is a polymer having a specific crystal structure of αtype, β type, γ type, αp type.[0032] Among the PVDF resins, a polyvinylidene fluoride homopolymer (PVDF) and vinylidene fluoride-hexafluoro-propylene copolymers containing hexafluoropropylene in a proportion of 15 mol% or lower are preferred from the view-points of melt moldability, mechanical properties, stain resistance, solvent resistance and secondary processability.[0033] The PVDF resin powder according to the present invention can be prepared by a suspension polymerizationprocess or emulsion polymerization process. In the emulsion polymerization, a chemically stable fluorinated emulsifieris used to conduct polymerization using, as a polymerization initiator, an inorganic peroxide, organic peroxide or organicpercarbonate compound. After the emulsion polymerization, a latex having a fine particle diameter of sub-micron unit isprecipitated and aggregated with a flocculant, thereby collecting the powder as resin particles having a proper size.[0034] The PVDF resin powder is preferably prepared by the suspension polymerization process from the viewpointof powder characteristics such as bulk density and angle of repose. In the suspension polymerization for the PVDF resin,polymerization is conducted by using a suspending agent such as methyl cellulose and dispersing a vinylidene fluoridemonomer and comonomers such as hexafluoropropylene in an aqueous medium.[0035] A process, in which an organic percarbonate (for example, di-n-propyl peroxydicarbonate) having activity at alow temperature is used as a polymerization initiator in the suspension polymerization to initiate a polymerization reactionat a temperature not higher than a critical temperature of 30.1°C, preferably 10 to 30°C, more preferably 20 to 28°C,thereby forming polymer particles (primary particles), and the temperature is raised to 30 to 90°C, preferably 40 to 80°Cto continue the polymerization reaction, is preferred from the viewpoint of obtaining polymer particles high in bulk densityand low in angle of repose. A chain transfer agent may be used to control the molecular weight of the resulting PVDF resin.[0036] Polymerization conditions such as the proportion of the suspending agent used to the monomers, the amountof the monomers charged into the aqueous medium, the droplet diameter of monomer droplets in the aqueous medium,the polymerization temperature and the polymerization time are controlled, whereby the powder characteristics of thepolymer to be formed, such as the particle size distribution including the average particle diameter, the bulk density andthe angle of repose can be adjusted. The particle size distribution characteristics can also be adjusted by classifying theresin powder obtained by the polymerization so as to fall within a desired range.[0037] The inherent viscosity of the PVDF resin is preferably 0.70 to 1.50 dl/g, more preferably 0.80 to 1.30 dl/g. Theinherent viscosity of the PVDF resin is a logarithmic viscosity at 30°C of a solution with 4 g of the resin dissolved in 1liter of N,N-dimethylformamide and measured by means of an Ubbelohde viscometer. The melting point of the PVDFresin is preferably 130 to 177°C. The melting point of the PVDF resin is a value measured by means of a differentialscanning calorimeter (DSC).[0038] The PVDF resin powder for melt molding according to the present invention has the following powder charac-teristics (a) to (c):


i) the average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulative distributionis 80 to 250 Pm,ii) the proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight, andiii) the proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight,

(b) the bulk density is 0.30 to 0.80 g/cm3, and(c) the angle of repose is at most 40°.

[0039] The particle size distribution characteristics of the PVDF resin according to the present invention are derivedon the basis of the particle size distribution measured by the dry sieving method in accordance with JIS K 0069-3.1.More specifically, they are particle size distribution characteristics measured by a measuring method described in EX-

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AMPLES, which will be described subsequently.[0040] The average particle diameter (D50) of the PVDF resin powder for melt molding according to the presentinvention is 80 to 250 Pm, preferably 100 to 230 Pm, more preferably 130 to 210 Pm. If the average particle diameterof the PVDF resin powder is too small, such powder tends to deteriorate the flowability or lower the stability of feedingto a molding machine. If the average particle diameter of the PVDF resin powder is too small or too great, the amountof finely divided particles or coarse particles formed increases, so that the particle size distribution becomes broad.When the particle size distribution of the PVDF resin particles becomes broad, a difference occurs in a molten statebetween resin particles in a cylinder of a molding machine, so that the molten state is liable to be varied. As a result, anextrusion rate varies to encounter difficulty upon provision of a molding having a fixed shape and quality.[0041] The PVDF resin powder for melt molding according to the present invention exhibits such a sharp particle sizedistribution that a value [(D80 - D20)/D50] (hereinafter referred to as "normalized value of particle size distribution")obtained by dividing a particle diameter breadth (D80 - D20) represented by a difference between a 80% cumulativevalue (D80) and a 20% cumulative value (D20) in the particle size cumulative distribution by the 50% cumulative value(D50; average particle diameter) is at most 0.8, more preferably at most 0.6. The PVDF resin powder is small in thenormalized value of the particle size distribution and sharp in the particle size distribution, whereby such powder can beevenly melted upon melt molding to provide a high-quality molding having a fixed shape.[0042] The proportion of PVDF resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight.The proportion of the PVDF resin powder having a particle diameter of at most 45 Pm can be reduced to often 2.0% byweight or lower, further 1.0% by weight or lower. The lower limit of the proportion of the PVDF resin powder having aparticle diameter of at most 45 Pm is of the order of generally 0.01% by weight, often 0.1% by weight.[0043] If the proportion of the PVDF resin powder having a particle diameter of at most 45 Pm is too high, electrostaticcling is easy to occur in a feeder or loading port (hopper), which forms the main cause of unstable feeding. If the proportionof the PVDF resin powder having a particle diameter of at most 45 Pm is high, finely divided powder tends to be meltedin the vicinity of a feed opening of a cylinder, so that an extrusion rate becomes unstable, which form the main causeof a surging phenomenon.[0044] The proportion of PVDF resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight.The proportion of the PVDF resin powder having a particle diameter of at least 355 Pm can be reduced to often 4.0%by weight or lower, further 3.0% by weight or lower. The lower limit of the proportion of the PVDF resin powder havinga particle diameter of at least 355 Pm is of the order of generally 0.05% by weight, often 0.1% by weight.[0045] The resin powder having a particle diameter of at least 355 Pm is slow in the heat transfer rate up to the centralportion thereof, so that such resin powder may possibly become unmelted in the molten resin within a cylinder of amolding machine in the process of the present invention in which the PVDF resin powder is fed to the molding machine.When a molten resin containing unmelted matter is subjected to injection molding or extrusion molding, such unmeltedmatter forms the main cause of appearance defect and deterioration of physical properties in the resulting molding.[0046] The bulk density (bulk specific gravity) of the PVDF resin powder for melt molding according to the presentinvention is 0.30 to 0.80 g/cm3, preferably 0.35 to 0.75 g/cm3, more preferably 0.40 to 0.70 g/cm3. If the bulk density ofthe PVDF resin powder is too low, the amount of air entrained in a molding machine is increased. As a result, deaerationbecomes insufficient, so that voids are generated in the resulting molding, or bubbling is caused during molding. Thebulk density is a value measured by a method described in EXAMPLES, which will be described subsequently.[0047] The angle of repose of the PVDF resin powder for melt molding according to the present invention is at most40°, preferably at most 38°, more preferably at most 35°. If the angle of repose of the PVDF resin powder is too high,the flowability of such resin powder is poor, and it is difficult to feed a fixed amount of the resin powder from a feeder.If the angle of repose of the PVDF resin powder is too high also, bridging is easy to occur in a loading port of the rawmaterial. The lower limit of the angle of repose of the PVDF resin powder is generally 20°, often 23°. The angle of reposeis a value measured by a method described in EXAMPLES, which will be described subsequently.[0048] The PVDF resin powder for melt molding according to the present invention has powder characteristics suchas particle size distribution, bulk density and angle of repose, which permit stable feeding to an injection molding machineor extrusion molding machine, and can be fed to the molding machine while retaining the form of the powdery resin asit is without pelletizing the powder to subject it to melt molding such as injection molding or extrusion molding.[0049] The process according to the present invention for producing a molding is a process for producing a molding,which comprises feeding the PVDF resin powder having the specific powder characteristics to a melt molding machinein the form of the resin powder, melting the resin powder and injecting the resultant resin melt into a mold to mold it.[0050] More specifically, the process according to the present invention for producing a molding comprises the followingSteps 1 to 3:

1) Step 1 of feeding, to a melt molding machine, polyvinylidene fluoride resin powder for melt molding, which hassuch powder characteristics (a) to (c) that

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i) the average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulativedistribution is 80 to 250 Pm,ii) the proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight, andiii) the proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight,

(b) the bulk density is 0.40 to 0.70 g/cm3, and(c) the angle of repose is at most 40°,in a state of the resin powder;


[0051] The resin melt obtained by melting in the melt molding machine is preferably injected into the mold under apressure of 50 to 500 MPa.[0052] The melt molding machine includes an injection molding machine. In this case, an injection mold is used asthe mold. The melt molding machine also includes an extrusion molding machine. In this case, the mold is a forming dieinto which the resin melt ejected from a nozzle on the tip of the extrusion molding machine is filled.[0053] In order to conduct injection molding using the PVDF resin powder according to the present invention, thePVDF resin powder is fed to an inlet of a heated cylinder of a screw type injection molding machine. The PVDF resinpowder fed into a hopper by a loader is fed to the inlet of the cylinder directly from the hopper or through a feeder. Inorder to stabilize an extrusion rate and provide a molding having a fixed shape and quality, it is particularly desirable tofeed the resin powder at such a feed rate that a screw can be seen at the inlet of the cylinder through the feeder, i.e.,by starved feeding.[0054] The highest temperature within the cylinder is controlled to generally 190 to 280°C, preferably 200 to 250°C.The PVDF resin powder melted by being subjected to heating and shearing force within the cylinder is extruded as aresin melt from the cylinder and injected into a mold under an injection pressure within the cylinder of preferably 50 to500 MPa, more preferably 150 to 300 MPa. The temperature of the nozzle on the tip of the cylinder, from which the resinmelt is injected, is controlled to preferably 200 to 250°C. The mold temperature is controlled to generally 80 to 150°C,preferably 90 to 130°C.[0055] Accordingly, when a molding is produced with the PVDF resin powder according to the present invention bythe injection molding, it is preferable to adopt a process comprising:

in Step 1, feeding the polyvinylidene fluoride resin powder for melt molding in a state of the resin powder to the inletof the cylinder equipped with a screw in the injection molding machine,in Step 2, heating and melting the resin powder in the cylinder controlled to a temperature of 190 to 280°C into aresin melt, andin Step 3, injecting the resin melt into the mold controlled to a temperature of 80 to 150°C from the nozzle on thetip of the cylinder under an injection pressure within the cylinder of 50 to 500 MPa to mold the resin melt.

[0056] It is also preferable to adopt a process comprising, in Step 1, feeding the PVDF resin powder for melt moldingin the state of the resin powder to the inlet of the cylinder from a feeder by starved feeding at such a feed rate that thecylinder can be seen at the inlet of the cylinder.[0057] In order to conduct solidification extrusion molding with the PVDF resin powder according to the present inventionby means of a forming die, the PVDF resin powder is fed into a heated cylinder of an extruder. The PVDF resin powderfed into a hopper by a loader is fed to the inlet of the cylinder directly from the hopper or through a feeder. In order tostabilize an extrusion rate and provide a molding having a fixed shape and quality, it is particularly desirable to feed theresin powder at such a feed rate that a screw can be seen at the inlet of the cylinder through the feeder, i.e., by starvedfeeding.[0058] The temperature within the cylinder is controlled to generally 50 to 280°C, preferably 50 to 250°C, more pref-erably 50 to 220°C. The PVDF resin powder melted by being subjected to heating and shearing force within the cylinderis extruded from a die nozzle on the tip of the extruder. The temperature of the die nozzle is controlled to generally 190to 280°C, preferably 200 to 250°C.[0059] In the solidification extrusion molding process, an extrusion molding machine with the die nozzle on the tip ofthe extruder linked to the forming die is used. The forming die is a die having a structure that is equipped with a coolingdevice on an external portion thereof and with a passage linked to a passage of the die nozzle in an internal portion

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thereof. An extrudate in a molten state, which has been extruded from the die nozzle, is guided to the forming die andcooled and solidified in the interior thereof. Accordingly, the extrudate extruded from the forming die arranged on the tipof the extrusion molding machine is extruded in a solidified state to the outside.[0060] When the resin melt is injected into the forming die from the die nozzle, the pressure (measured as an externalpressure of die) of the forming die is controlled so as to amount to preferably 50 to 500 MPa, more preferably 150 to400 MPa. A specific example of an extrusion molding machine suitable for use in such solidification extrusion moldingincludes that disclosed in, for example, Japanese Patent Application Laid-Open No. 61-185428.[0061] According to the result of the investigation by the present inventors, it has been found that the PVDF resinpowder having the specific powder characteristics is subjected to the solidification extrusion molding, whereby an extrudedproduct suitable for use in machining such as milling, perforating or cutting, thick in wall, free of voids and excellent inthe color tone of the surface and sectional surface thereof can be obtained.[0062] More specifically, the production process according to the present invention includes a process for producinga molding, which comprises using the PVDF resin powder having the specific powder characteristics as a raw materialand subjecting the resin powder to solidification extrusion molding in accordance with the following Steps I to III:

(I) Step I of feeding the PVDF resin powder to an extrusion molding machine linked to a mold device composed ofa die nozzle and a forming die equipped with a cooling device on an external portion thereof and with a passagelinked to a passage of the die nozzle in an internal portion thereof;(II) Step II of melting the resin powder by the extrusion molding machine into a resin melt; and(III) Step III of extruding the resin melt from the die nozzle and injecting it into the forming die shaped in a desiredform to cool and solidify the extrudate in the molten state in the interior of the forming die.

[0063] Examples of the molding include round bars, plates and pipes. Accordingly, in order to obtain these continuousmoldings by the solidification extrusion molding, the above-described Steps I to III are continuously carried out. In StepsII and III in particular, while melting the resin powder by the extrusion molding machine into the resin melt, the resin meltis continuously extruded from the die nozzle and injected into the forming die. The main body of the extrusion moldingmachine is a cylinder with a built-in screw. In Step I, it is preferable to adopt a process comprising feeding the PVDFresin powder for melt molding in the state of the resin powder to the inlet of the cylinder from a feeder by starved feedingat such a feed rate that the cylinder can be seen at the inlet of the cylinder.[0064] In the injection molding and solidification extrusion molding making use of the PVDF resin powder, it is desirablethat the PVDF resin powder is fed by the starved feeding to prevent the resin powder from being fed in excess, wherebythe intermesh of the resin powder with the screw is stabilized to prevent surging and stabilize an injection rate or extrusionrate.[0065] As the screw, may be used a generally marketed screw for injection molding or extrusion molding. As anexample of a screw design includes a design of L/D = 20 to 24, a compression ratio = 2 to 3, a feed zone = 10 to 14D,a compression zone = 3 to 4D and a metering zone = 6 to 7D. However, the present invention is not limited to such a design.[0066] The injection-molded product and extrusion-molded product obtained by the production process according tothe present invention are preferably heated to a temperature from 100°C to a temperature at which the solidified statecan be retained, preferably a temperature close to the softening point of the PVDF resin to remove residual stress. Thetime required for this heat treatment is generally at least 30 minutes, preferably from 1 hour to 24 hours. The moldingsare cooled after the heat treatment. This heat/cooling treatment is referred to as annealing. The heat treatment may beconducted by, for example, leaving the molding to stand in a heating oven.[0067] According to the melt molding process using the PVDF resin powder according to the present invention, amolding improved in yellowness index (YI) and having a good color tone compared with the case where melt moldingis conducted after pelletizing can be obtained. On the other hand, the molding obtained by conducting the melt moldingusing the PVDF resin powder has mechanical properties equivalent to those of a molding obtained by conducting themelt molding after pelletizing and is excellent in dimensional stability and free of voids.

EFFECTS OF THE INVENTION

[0068] The PVDF resin powder for melt molding according to the present invention can be stably fed to an injectionmolding machine or extrusion molding machine in the form of the resin powder and can provide moldings, which areexcellent in various properties like a case where pellets are used, and inhibited from coloring compared with the casewhere pellets are used.[0069] According to the production process of the present invention, the PVDF resin powder obtained by polymerizationand having the specific powder characteristics is used, whereby injection molding or extrusion molding can be conductedin the form of the resin powder without pelletizing the powder. According to the production process of the presentinvention, moldings, which are excellent in various properties and inhibited from coloring, can be stably and inexpensively

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produced.

EXAMPLES

[0070] The present invention will hereinafter be described more specifically by the following Examples and ComparativeExamples.[0071] Measuring methods for characteristics or properties and physical properties in the present invention are asfollow.

1. Characteristics of resin powder

(a) particle size distribution

[0072] The particle size distribution of PVDF resin powder was measured by a dry sieving method in accordance withJIS K 0069-3.1 by means of a Ro-Tap II type Sieve Shaker D Model manufactured by Heiko Seisakusho K.K. Theaverage particle diameter was calculated and determined by a logarithmic normal distribution method based on themeasured result of the particle size distribution. The average particle diameter was determined to be a particle diameterindicating a 50% cumulative value (D50) in the particle size cumulative distribution. A value [(D80 - D20)/D50] obtainedby dividing a particle diameter breadth (D80 - D20) represented by a difference between the 80% cumulative value (D80)and the 20% cumulative value (D20) by the 50% cumulative value (D50) was used as an index to the spread of the particlesize distribution.

(b) Bulk density

[0073] The bulk density of PVDF resin powder was measured in accordance with a measuring method for "BulkSpecific Gravity" in JIS K 6721-3.3. More specifically, about 120 ml of a powder sample fully stirred and mixed wasplaced in a funnel, into which a damper of a bulk specific gravity measuring device had been inserted, and the damperwas then quickly pulled up to drop the sample on a receiver. After a sample portion protuberant from the receiver wasrubbed off by a glass rod, the mass of the receiver, on which the sample had placed, was precisely weighed to 0.1 g todetermine a bulk density in accordance with the following equation.

wherein S: bulk density (g/cm3)A: mass of the receiver (g)B: internal volume of the receiver (cm3)C: mass of the receiver, on which the sample had placed (g).[0074] The measurement was conducted 3 times to calculate out an average value. The result of the test was indicatedby rounding a value measured down to the third decimal place to three decimal places.

(c) Angle of repose

[0075] The angle of repose of PVDF resin powder was determined by a method in which 100 ml of resin powder fullystirred and mixed is placed in a funnel, into which a damper of a bulk specific gravity measuring device prescribed inJIS K 6721 is inserted, and the damper is quickly pulled up to drop the sample on a sample plate having a diameter of80 mm from a height of 100 mm, thereby measuring an angle of repose of the resin powder deposited on the sampleplate. The measuring temperature was 22°C.

2. Mechanical properties

(1) Bending test

[0076] A bending test was carried out at a measuring temperature of 23°C, a distance between the supports of 50mm and a crosshead speed of 1.5 mm/min by means of a 2T Autograph AG2000 System manufactured by ShimadzuCorporation in accordance with ASTM D-790. By this bending test, a flexural modulus (deflection = 1.2 mm) (unit = MPa)and flexural strength (maximum stress; unit = MPa) were measured. A specimen was annealed by a method that the

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specimen is heated and held for 5 hours at 150°C and then gradually cooled to room temperature.

(2) Tensile test

[0077] A tensile test was carried out at a measuring temperature of 23°C, a gauge length of 50 mm and a crossheadspeed of 5 mm/min by means of a 2T Autograph AG2000 System manufactured by Shimadzu Corporation in accordancewith ASTM D-638. By this tensile test, tensile strength (tensile yield strength; MPa) was measured. A specimen wasannealed by a method that the specimen is heated and held for 5 hours at 150°C and then gradually cooled to roomtemperature.

3. Measurement of color tone

[0078] The measurement of color tone was conducted by measuring an L value and a YI value by means of a colordifference meter (ZE2000 manufactured by Nippon Denshoku Kogyo K.K.) in accordance with ASTM D-1925. A specimenwas annealed by a method that the specimen is heated and held for 5 hours at 170°C and then gradually cooled to roomtemperature. The measured values indicate that coloring is little as the YI value is small, and the L value is large. Uponthe measurement, a white plate was arranged on the back of the specimen.

Example 1

1. Synthesis of polyvinylidene fluoride resin powder (A)

[0079] An autoclave having an internal volume of 20 liters was charged with 10,730 g of ion-exchanged water, 2.10g of methyl cellulose, 92.2 g of ethyl acetate, 25.1 g of di-n-propyl peroxydicarbonate and 4,190 g of vinylidene fluorideto conduct a reaction for 5.5 hours at 26°C. The temperature was then raised to 40°C to conduct a reaction for 7 hours.After the suspension polymerization reaction was completed, a slurry containing a polymer formed was dehydrated,washed with water, dehydrated and then dried for 20 hours at 80°C to obtain polyvinylidene fluoride resin powder (A)at a yield of 90%.[0080] The inherent viscosity of the thus-obtained polyvinylidene fluoride resin powder (A) was 1.01 dl/g, and its meltingpoint was 175°C. The particle size distribution of this resin powder (A) was such that the average particle diameter was172 Pm, the proportion of powder having a particle diameter of at most 45 Pm was 0.7% by weight, and the proportionof powder having a particle diameter of at most 355 Pm was 1.0% by weight. The bulk density of the resin powder (A)was 0.45 g/cm3, and the angle of repose was 32°.[0081] In this polyvinylidene fluoride resin powder (A), a value [(D80 - D20)/D50] obtained by dividing a particle diameterbreadth (D80 - D20) represented by a difference between the 80% cumulative value (D80) and the 20% cumulative value(D20) by the 50% cumulative value (D50) was 0.52.

2. Injection molding

[0082] The polyvinylidene fluoride resin powder (A) synthesized above was fed through a constant volume feederinstalled in an injection molding machine (IS25EP-1YV manufactured by Toshiba Machine Co., Ltd.) at such a feed rate(i.e., by starved feeding) that a screw can be slightly seen at the inlet of a heated cylinder.[0083] The resin powder was melted under conditions that a revolution speed of an extruder screw within the heatedcylinder was 96 revolutions/min, and the cylinder temperature was 200 to 230°C, and the resultant resin melt was injectedinto a mold through a nozzle controlled to a temperature of 230°C under conditions of an injection pressure of 246 MPa,a mold temperature of about 100°C, a filling time of 6.4 seconds, an injection time of 20 seconds and a cooling time of30 seconds, thereby producing specimens for bending test, tensile test and color tone. The injection mold is a moldcapable of molding specimens suitable for ASTM D-790, D-638 and D-1925 at the same time. The measured resultsare shown in Table 1.

Comparative Example 1

1. Commercially available polyvinylidene fluoride resin powder

[0084] The particle size distribution of commercially available polyvinylidene fluoride resin powder (product of ATOFINACHEMICALS INC., trade name "Kynar 741") was measured. As a result, the average particle diameter was 167 Pm,the proportion of powder having a particle diameter of at most 45 Pm was 3.5% by weight, the proportion of powderhaving a particle diameter of at most 355 Pm was 1.9% by weight, and the normalized value [(D80 - D20)/D50] of particle

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diameter was 1.08. The bulk density of this resin powder was 0.22 g/cm3, and the angle of repose was 45°. In otherwords, this commercially available polyvinylidene fluoride resin powder was low in bulk density and high in angle of repose.


[0085] The above-described polyvinylidene fluoride resin powder (Kynar 741) was used to try injection molding underthe same conditions as in Example 1. As a result, the resin powder did not flow from the constant volume feeder intothe heated cylinder even when the screw revolution speed of the constant volume feeder was variously changed. Further,the resin powder was fed directly into the heated cylinder from a hopper without passing through the constant volumefeeder. However, the intermesh of the resin powder with an extruder screw was poor, so that the resin powder couldnot be smoothly fed. The revolution speed of the extruder screw was variously changed from 96 revolutions/min. however,the resin powder could still not smoothly fed, so that the injection molding could not be normally conducted. The measuredresults are shown in Table 1.

Comparative Example 2

1. Pelletizing

[0086] The polyvinylidene fluoride resin powder (A) synthesized in Example 1 was melt-extruded at 230°C by meansof LS-20 manufactured by Toyo Seiki Co., Ltd., and the resultant extrudate was cut into a size of about 3 mm in diameterand 3 mm in length to produce pellets.


[0087] Injection molding was conducted under the same conditions as in Example 1 except that the above-describedpellets were used, thereby producing the respective specimens. The measured results are shown in Table 1.

Example 2

1. Synthesis of polyvinylidene fluoride resin powder (B)

[0088] An autoclave having an internal volume of 20 liters was charged with 10,730 g of ion-exchanged water, 1.26g of methyl cellulose, 28.1 g of ethyl acetate, 25.1 g of di-n-propyl peroxydicarbonate, 4,085 g of vinylidene fluoride and105 g of hexafluoropropylene to conduct a reaction for 17.5 hours at 26°C. The temperature was then raised to 40°C toconduct a reaction for 4 hours. In the course of the suspension polymerization reaction, 132 g of ethyl acetate wasadditionally charged at the time 5 hours had elapsed from the beginning of the polymerization.[0089] After the suspension polymerization reaction was completed, a slurry containing a polymer formed was dehy-drated, washed with water, dehydrated and then dried for 20 hours at 80°C to obtain polyvinylidene fluoride resin powder(B) at a yield of 88%. The inherent viscosity of the polyvinylidene fluoride resin powder (B) was 1.05 dl/g, and its meltingpoint was 172°C. The particle size distribution of the resin powder (B) was such that the average particle diameter was195 Pm, the proportion of powder having a particle diameter of at most 45 Pm was 0.3% by weight, the proportion ofpowder having a particle diameter of at most 355 Pm was 3.0% by weight, and the normalized value [(D80 - D20)/D50]of particle diameter was 0.52. The bulk density of the resin powder (B) was 0.42 g/cm3, and the angle of repose was 28°.

2. Solidification extrusion molding

[0090] The polyvinylidene fluoride resin powder (B) synthesized above was fed to a heated cylinder of a single-screwextruder (30 mm in diameter, L/D =10) through a constant volume at such a feed rate (i.e., by starved feeding) that ascrew can be slightly seen at the inlet of the heated cylinder. The resin powder was melted under conditions that arevolution speed of a screw was 47 revolutions/min, and the cylinder temperature was 50 to 220°C, and the resultantresin melt was extruded into a forming die controlled to a temperature of 210°C and a die external pressure of 360 MPato mold a round bar having a diameter of 150 mm at a molding speed of 100 mm/hr.[0091] The resultant round bar had good color tone. This round bar was cut at intervals of 50 cm in its longitudinaldirection to investigate its section. As a result, it was confirmed that neither pores (shrink voids) nor microvoids wereobserved at all the sections, and so the round bar was homogeneous.

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3. Color tone and mechanical properties

[0092] Polyvinylidene fluoride resin powder (B) synthesized by the same process as described above was used toproduce specimens for bending test, tensile test and color tone by injection molding under the same conditions as inExample 1. The results are shown in Table 1.

[0093] When the results of Example 1 and Comparative Example 1 (marketed product) are compared with each other,it is understood that the polyvinylidene fluoride resin powder (Example 1), which has the specific particle size distributionand is sharp in particle size distribution, high in bulk density and low in angle of repose, is excellent in injection moldabilitycompared with the polyvinylidene fluoride resin powder (Comparative Example 1), which is broad in particle size distri-bution, low in bulk density and high in angle of repose.[0094] When the results of Example 1 and Comparative Example 2 (pellets) are compared with each other, it isunderstood that when the polyvinylidene fluoride resin powder (Example 1), which has the specific particle size distributionand is sharp in particle size distribution, high in bulk density and low in angle of repose, is fed to an injection moldingmachine in the form of the resin powder as it is, thereby conducting injection molding, the resultant molding doessubstantially not have a difference in mechanical properties and moreover is small in both L value and YI value comparedwith the case where the same resin powder is pelletized and then fed to the injection molding machine (ComparativeExample 2), so that a molded product good in color tone is provided.[0095] Even when the polyvinylidene fluoride resin powder obtained in Example 2 is used, such resin powder exhibitsexcellent melt processing ability, so that an injection-molded product good in color tone and excellent in mechanicalproperties can be provided (the specimens are produced by injection molding).[0096] In addition, the polyvinylidene fluoride resin powder obtained in Example 2 is used to conduct solidificationextrusion molding, whereby an extruded product good in color tone and free of voids can be provided.

INDUSTRIAL APPLICABILITY

[0097] The PVDF resin powder according to the present invention can be molded into various kinds of moldings by

Table 1

Example Comparative Example

1 2 1 2

Kind of PVDF PVDF (A) PVDF(B) Marketed product PVDF(A)

Powder characteristics of PVDF Powder Powder Powder PelletsAverage particle diameter (Pm) 172 195 167 -At most 45 Pm (wt.%) 0.7 0.3 3.5 -At least 355 Pm (wt.%) 1.0 3.0 1.9 -Bulk density (g/cm3) 0.45 0.42 0.22 -Angle or repose (°) 32 28 45 -(D80 - D20)/D50 0.52 0.52 1.08 -

Injection molding Possible Possible Impossible Possible

Properties before annealingL value 52.74 54.55 - 52.99YI 0.31 0.25 - 1.58Flexural modulus (MPa) 1804 1700 - 1809Flexural strength (MPa) 60 57 - 60Tensile strength (MPa) 55 52 - 55

Properties after annealingL value 52.02 54.01 - 52.22YI 5.85 5.65 - 8.22Flexural modulus (MPa) 1900 1750 - 1890Flexural strength (MPa) 61 58 - 61Tensile strength (MPa) 55 52 - 55

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melt molding such as injection molding or extrusion molding. The moldings obtained by the production process accordingto the present invention are good in color tone and excellent in mechanical properties, so that they can be utilized in awide variety of application fields such as electric and electronic materials, machining stocks and others.

Claims

1. Polyvinylidene fluoride resin powder for melt molding having such powder characteristics (a) to (c) that


i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulativedistribution is 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight, andiv) a value [(D80 - D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) represented by adifference between a 80% cumulative_ value (D80) and a 20% cumulative value (D20) in the particle sizecumulative distribution by the 50% cumulative value (D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity inaccordance with JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by a measuring method described in the specification inwhich a bulk specific gravity measuring device prescribed in JIS K 6721 is used.

2. The polyvinylidene fluoride resin powder for melt molding according to claim 1, wherein the average particle diameterindicated by the 50% cumulative value (D50) is 130 to 210 Pm.

3. The polyvinylidene fluoride resin powder for melt molding according to claim 1, wherein the angle of repose is 23 to 35°.

4. A process for producing a polyvinylidene fluoride resin molding, which comprises the following Steps 1 to 3:

1) Step 1 of feeding, to a melt molding machine, polyvinylidene fluoride resin powder for melt molding, whichhas such powder characteristics (a) to (c) that


i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulativedistribution is 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least 355 Pm is at most 5.0% by weight,andiv) a value [(D80 - D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) representedby a difference between a 80% cumulative_ value (D80) and a 20% cumulative value (D20) in the particlesize cumulative distribution by the 50% cumulative value (D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity inaccordance with JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by a measuring method described in the specificationin which a bulk specific gravity measuring device prescribed in JIS K 6721 is used,in a state of the resin powder;


5. The production process according to claim 4, wherein the average particle diameter indicated by the 50% cumulativevalue (D50) is 130 to 210 Pm.

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6. The production process according to claim 4, wherein the angle of repose is 23 to 35°.

7. The production process according to claim 4, wherein in Step 3, the resin melt is injected into the mold under apressure of 50 to 500 MPa.

8. The production process according to claim 4, wherein the melt molding machine is an injection molding machine,and the mold is an injection mold.

9. The production process according to claim 8, wherein in Step 1, the polyvinylidene fluoride resin powder for meltmolding is fed in a state of the resin powder to the inlet of a cylinder equipped with a screw in the injection moldingmachine,in Step 2, the resin powder is heated and melted in the cylinder controlled to a temperature of 190 to 280°C into aresin melt, andin Step 3, the resin melt is injected into the mold controlled to a temperature of 80 to 150°C from a nozzle on the tipof the cylinder under an injection pressure within the cylinder of 50 to 500 MPa to mold the resin melt.

10. The production process according to claim 4, wherein the melt molding machine is an extrusion molding machine,and the mold is a forming die into which the resin melt ejected from a die nozzle on the tip of the extrusion moldingmachine is filled.

11. The production process according to claim 4, wherein the Steps 1 to 3 comprise the following Steps I to III:

(I) Step I of feeding the polyvinylidene fluoride resin powder for melt molding to an extrusion molding machinelinked to a mold device composed of a die nozzle and a forming die equipped with a cooling device on anexternal portion thereof and with a passage linked to a passage of the die nozzle in an internal portion thereof;(II) Step II of melting the resin powder by the extrusion molding machine into a resin melt; and(III) Step III of extruding the resin melt from the die nozzle and injecting it into the forming die shaped in a desiredform to cool and solidify the extrudate in the molten state in the interior of the forming die.

12. The production process according to claim 11, wherein in Step I, the polyvinylidene fluoride resin powder for meltmolding is fed in a state of the resin powder to the inlet of a cylinder equipped with a screw in the extrusion moldingmachine,in Step II, the resin powder is heated and melted in the cylinder controlled to a temperature of 50 to 280°C into aresin melt, andin Step III, the resin melt is extruded from the die nozzle controlled to a temperature of 190 to 280°C and injectedinto the forming die under a pressure of 50 to 500 MPa to conduct solidification extrusion molding.

13. Use of polyvinylidene fluoride resin powder for melt molding by press-fit techniques selected from the group consistingof injection molding and extrusion molding while retaining the form of the powdery resin as it is without pelletizingthe powder, wherein the polyvinylidene fluoride resin powder for melt molding has such powder characteristics (a)to (c) that


i) an average particle diameter indicated by a 50% cumulative value (D50) in a particle size cumulativedistribution is 80 to 250 Pm,ii) a proportion of resin powder having a particle diameter of at most 45 Pm is at most 3.0% by weight,iii) a proportion of resin powder having a particle diameter of at least_ 355 Pm is at most 5.0% by weight, andiv) a value [(D80 - D20)/D50] obtained by dividing a particle diameter breadth (D80 - D20) represented by adifference between a 80% cumulative value (D80) and a 20% cumulative value (D20) in the particle sizecumulative distribution by the 50% cumulative value (D50) is at most 0.8,

(b) a bulk density is 0.40 to 0.70 g/cm3 as determined by a measuring method for Bulk Specific Gravity inaccordance with JIS K 6721-3.3, and(c) an angle of repose is at most 35° as determined by a measuring method described in the specification inwhich a bulk specific gravity measuring device prescribed in JIS K 6721 is used.

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14. Use of polyvinylidene fluoride resin powder for melt molding according to claim 13, wherein injection molding com-prises a step of feeding the polyvinylidene fluoride resin powder to a injection molding machine, and a step ofinjecting a resin melt into a mold.

15. Use of polyvinylidene fluoride resin powder for melt molding according to claim 13, wherein extruding molding issolidification extrusion molding comprising a step of feeding the polyvinylidene fluoride resin powder to an extrusionmolding machine, and a step of extruding a resin melt into a forming die.

Patentansprüche

1. Polyvinylidenfluorid-Harzpulver zur Schmelzformung, das die Pulvercharakteristika (a) bis (c) aufweist:

(a) das Harzpulver weist solche Partikelgrößen-Verteilungscharakteristika, wie sie durch ein Trockensiebver-fahren gemäß JIS K 0069 bestimmt werden, auf, dass

i) der durchschnittliche Partikeldurchmesser, angegeben durch einen 50%-Summenwert (D50) in einerPartikelgrößen-Summenverteilung, 80 bis 250 Pm ist,ii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von höchstens 45 Pm hat, höchstens3,0 Gew.-% ist,iii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von wenigstens 355 Pm hat, höch-stens 5,0 Gew.-% ist undiv) der Wert [(D80 - D20)/D50], der durch Dividieren eines Partikeldurchmesser-Bereichs (D80 - D20), darge-stellt durch die Differenz zwischen einem 80%-Summenwert (D80) und einem 20%-Summenwert (D20) inder Partikelgrößen-Summenverteilung, durch den 50%-Summenwert (D50) erhalten wird, höchstens 0,8 ist,

(b) die Schüttdichte 0,40 bis 0,70 g/cm3 ist, wie sie durch ein Messverfahren für spezifisches Schüttgewichtgemäß JIS K 6721-3.3 bestimmt wird, und(c) der Böschungswinkel höchstens 35° ist, wie er durch ein Messverfahren bestimmt wird, das in der Spezifi-kation beschrieben ist, in der eine Messvorrichtung für das spezifische Schüttgewicht, vorgeschrieben in JIS K6721, verwendet wird.

2. Polyvinylidenfluorid-Harzpulver zur Schmelzformung gemäß Anspruch 1, wobei der durchschnittliche Partikeldurch-messer, angegeben durch den 50%-Summenwert (D50), 130 bis 210 Pm ist.

3. Polyvinylidenfluorid-Harzpulver zur Schmelzformung gemäß Anspruch 1, wobei der Böschungswinkel 23 bis 35° ist.

4. Verfahren zur Herstellung eines Polyvinylidenfluoridharz-Formteils, das die folgenden Schritte 1 bis 3 umfasst:

1) Schritt 1 des Beschickens einer Schmelzformungsmaschine mit Polyvinylidenfluorid-Harzpulver zur Schmelz-formung, das die Pulvercharakteristika (a) bis (c) aufweist:

(a) das Harzpulver weist solche Partikelgrößen-Verteilungscharakteristika, wie sie durch ein Trockensieb-verfahren gemäß JIS K 0069 bestimmt werden, auf, dass

i) der durchschnittliche Partikeldurchmesser, angegeben durch einen 50%-Summenwert (D50) in einerPartikelgrößen-Summenverteilung, 80 bis 250 Pm ist,ii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von höchstens 45 Pm hat, höch-stens 3,0 Gew.-% ist,iii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von wenigstens 355 Pm hat,höchstens 5,0 Gew.-% ist undiv) der Wert [(D80 - D20)/D50], der durch Dividieren eines Partikeldurchmesser-Bereichs (D80 - D20),dargestellt durch die Differenz zwischen einem 80%-Summenwert (D80) und einem 20%-Summenwert(D20) in der Partikelgrößen-Summenverteilung, durch den 50%-Summenwert (D50) erhalten wird, höch-stens 0,8 ist,

(b) die Schüttdichte 0,40 bis 0,70 g/cm3 ist, wie sie durch ein Messverfahren für spezifisches Schüttgewichtgemäß JIS K 6721-3.3 bestimmt wird, und

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(c) der Böschungswinkel höchstens 35° ist, wie er durch ein Messverfahren bestimmt wird, das in derSpezifikation beschrieben ist, in der eine Messvorrichtung für das spezifische Schüttgewicht, vorgeschrie-ben in JIS K 6721, verwendet wird,in einem Zustand als Harzpulver;

2) Schritt 2 des Erwärmens und Schmelzens des Harzpulvers in der Schmelzformungsmaschine zu einer Harz-schmelze und3) Schritt des Einspritzens der Harzschmelze in eine Form, um die Harzschmelze zu formen.

5. Herstellungsverfahren gemäß Anspruch 4, wobei der durchschnittliche Partikeldurchmesser, der durch den 50%-Summenwert (D50) angegeben wird, 130 bis 210 Pm ist.

6. Herstellungsverfahren gemäß Anspruch 4, wobei der Böschungswinkel 23 bis 35° ist.

7. Herstellungsverfahren gemäß Anspruch 4, wobei in Schritt 3 die Harzschmelze unter einem Druck von 50 bis 500MPa in die Form gespritzt wird.

8. Herstellungsverfahren gemäß Anspruch 4, wobei die Schmelzformungsmaschine eine Spritzgießmaschine ist unddie Form ein Spritzgießwerkzeug ist.

9. Herstellungsverfahren gemäß Anspruch 8, wobei in Schritt 1 das Polyvinylidenfluorid-Harzpulver zur Schmelzfor-mung in einem Zustand des Harzpulvers zu der Einlassöffnung eines Zylinders, der mit einer Schnecke ausgestattetist, in die Spritzgießmaschine geführt wird,in Schritt 2 das Harzpulver in dem Zylinder, der auf eine Temperatur von 190 bis 280°C reguliert ist, erwärmt undzu einer Harzschmelze geschmolzen wird undin Schritt 3 die Harzschmelze in das Spritzgießwerkzeug, das auf eine Temperatur von 80 bis 150°C kontrolliertwird, aus einer Düse an der Spitze des Zylinders unter einem Spritzdruck innerhalb des Zylinders von 50 bis 500MPa gespritzt wird, um die Harzschmelze zu formen.

10. Herstellungsverfahren gemäß Anspruch 4, wobei die Schmelzformungsmaschine eine Extrudierformungsmaschineist und die Form ein Formungswerkzeug ist, in das die Harzschmelze aus einer Werkzeugdüse an der Spitze derExtrudierformungsmaschine gefüllt wird.

11. Herstellungsverfahren gemäß Anspruch 4, wobei die Schritte 1 bis 3 die folgenden Schritte I bis III umfassen:

(I) Schritt I des Beschickens des Polyvinylidenfluorid-Harzpulvers zur Schmelzformung in eine Extrudierfor-mungsmaschine, die mit einer Formvorrichtung verbunden ist, welche aus einer Werkzeugdüse und einemFormungswerkzeug besteht, das mit einer Kühlungsvorrichtung an einem äußeren Teil davon und mit einemKanal, der mit einem Kanal der Werkzeugdüse in einem inneren Teil davon verbunden ist, ausgestattet ist;(II) Schritt II des Schmelzens des Harzpulvers durch die Extrudierformungsmaschine zu einer Harzschmelze und(III) Schritt III des Extrudierens der Harzschmelze aus der Werkzeugdüse und Spritzen derselben in das For-mungswerkzeug, das in einer gewünschten Form gestaltet ist, unter Kühlen und Verfestigen des Extrudats imgeschmolzenen Zustand im Inneren des Formungswerkzeugs.

12. Herstellungsverfahren gemäß Anspruch 11, wobei in Schritt I das Polyvinylidenfluorid-Harzpulver zur Schmelzfor-mung in einem Zustand des Pulvers zu der Einlassöffnung eines Zylinders, der mit einer Schnecke ausgestattet ist,in die Extrudierformungsmaschine geführt wird,in Schritt II das Harzpulver in dem Zylinder, der auf eine Temperatur von 50 bis 280°C reguliert ist, erwärmt und zueiner Harzschmelze geschmolzen wird undin Schritt III die Harzschmelze aus der Werkzeugdüse, die auf eine Temperatur von 190 bis 280°C kontrolliert wird,extrudiert wird und in das Formungswerkzeug unter einem Druck von 50 bis 500 MPa gespritzt wird, um ein Verfe-stigungsextrudierformen durchzuführen.

13. Verwendung von Polyvinylidenfluorid-Harzpulver zur Schmelzformung durch Presspassungstechniken, ausgewähltaus der Gruppe, bestehend aus Spritzgießen und Extrudierformen, während die Form des pulvrigen Harzes, wiees ist, ohne Pelletisieren des Pulvers, beibehalten wird, wobei das Polyvinylidenfluorid-Harzpulver zur Schmelzfor-mung die Pulvercharakteristika (a) bis (c) aufweist:

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(a) das Harzpulver weist solche Partikelgrößen-Verteilungscharakteristika, wie sie durch ein Trockensiebver-fahren gemäß JIS K 0069 bestimmt werden, auf, dass

i) der durchschnittliche Partikeldurchmesser, angegeben durch einen 50%-Summenwert (D50) in einerPartikelgrößen-Summenverteilung, 80 bis 250 Pm ist,ii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von höchstens 45 Pm hat, höchstens3,0 Gew.-% ist,iii) der Verhältnisanteil von Harzpulver, das einen Partikeldurchmesser von wenigstens 355 Pm hat, höch-stens 5,0 Gew.-% ist undiv) der Wert [(D80 - D20)/D50], der durch Dividieren eines Partikeldurchmesser-Bereichs (D80 - D20), darge-stellt durch die Differenz zwischen einem 80%-Summenwert (D80) und einem 20%-Summenwert (D20) inder Partikelgrößen-Summenverteilung, durch den 50%-Summenwert (D50) erhalten wird, höchstens 0,8 ist,

(b) die Schüttdichte 0,40 bis 0,70 g/cm3 ist, wie sie durch ein Messverfahren für spezifisches Schüttgewichtgemäß JIS K 6721-3.3 bestimmt wird, und(c) der Böschungswinkel höchstens 35° ist, wie er durch ein Messverfahren bestimmt wird, das in der Spezifi-kation beschrieben ist, in der eine Messvorrichtung für das spezifische Schüttgewicht, vorgeschrieben in JIS K6721, verwendet wird.

14. Verwendung von Polyvinylidenfluorid-Harzpulver zur Schmelzformung gemäß Anspruch 13, wobei Spritzgießeneinen Schritt des Zuführens des Polyvinylidenfluorid-Harzpulvers zu einer Spritzgießformungsmaschine und einenSchritt des Spritzens einer Harzschmelze in die Form umfasst.

15. Verwendung von Polyvinylidenfluorid-Harzpulver zur Schmelzformung gemäß Anspruch 13, wobei eine Extrudier-formung eine Verfestigungsextrudierformung ist, die einen Schritt des Zuführens des Polyvinylidenfluorid-Harzpul-vers zu einer Extrudierformungsmaschine und einen Schritt des Extrudierens einer Harzschmelze in ein Formungs-werkzeug umfasst.

Revendications

1. Poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion ayant les caractéristiques de poudre(a) à (c) suivantes :

(a) la poudre de résine présente, comme déterminé par un procédé de tamisage à sec conforme à la normeJIS K 0069, des caractéristiques de distribution de taille de particule selon lesquelles

i) un diamètre moyen de particule indiqué par une valeur cumulative à 50 % (D50) dans une distributioncumulative de taille de particule vaut de 80 à 250 Pm,ii) une proportion de poudre de résine ayant un diamètre de particule d’au plus 45 Pm est d’au plus 3,0 %en poids,iii) une proportion de poudre de résine ayant un diamètre de particule d’au moins 355 Pm est d’au plus 5,0% en poids, etiv) une valeur [(D80-D20)/D50] obtenue en divisant une largeur de diamètre de particule (D80-D20) représentéepar une différence entre une valeur cumulative à 80 % (D80) et une valeur cumulative à 20 % (D20) de ladistribution cumulative de taille de particule par la valeur cumulative à 50 % (D50) est d’au plus 0,8,

(b) une masse volumique apparente est de 0,40 à 0,70 g/cm3, comme déterminé par un procédé de mesurede densité apparente en conformité avec la norme JIS K 6721-3.3, et(c) un angle de repos est d’au plus 35°, comme déterminé par un procédé de mesure décrit dans la spécificationdans laquelle est utilisé un dispositif de mesure de densité apparente prescrit dans la norme JIS K 6721.

2. Poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion selon la revendication 1, dans laquellele diamètre moyen de particule indiqué par la valeur cumulative à 50 % (D50) vaut de 130 à 210 Pm.

3. Poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion selon la revendication 1, dans laquellel’angle de repos vaut de 23 à 35°.

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4. Procédé de production d’un moulage de résine de poly(fluorure de vinylidène), qui comprend les étapes 1 à 3suivantes :

1) l’étape 1 consistant à fournir à une machine de moulage par fusion une poudre de résine de poly(fluorurede vinylidène) pour un moulage par fusion, qui présente des caractéristiques de poudre (a) à (c) selon lesquelles


i) un diamètre moyen de particule indiqué par une valeur cumulative à 50 % (D50) dans une distributioncumulative de taille de particule vaut de 80 à 250 Pm,ii) une proportion de poudre de résine ayant un diamètre de particule d’au plus 45 Pm est d’au plus3,0 % en poids,iii) une proportion de poudre de résine ayant un diamètre de particule d’au moins 355 Pm est d’au plus5,0 % en poids, etiv) une valeur [(D80-D20)/D50] obtenue en divisant une largeur de diamètre de particule (D80-D20)représentée par une différence entre une valeur cumulative à 80 % (D80) et une valeur cumulative à20 % (D20) de la distribution cumulative de taille de particule par la valeur cumulative à 50 % (D50) estd’au plus 0,8,

(b) une masse volumique apparente est de 0,40 à 0,70 g/cm3, comme déterminé par un procédé de mesurede densité apparente en conformité avec la norme JIS K 6721-3.3, et(c) un angle de repos est d’au plus 35°, comme déterminé par un procédé de mesure décrit dans laspécification dans laquelle est utilisé un dispositif de mesure de densité apparente prescrit dans la normeJIS K 6721,dans un état de la poudre de résine ;

2) l’étape 2 consistant à chauffer et à faire fondre la poudre de résine dan la machine de moulage par fusionen une résine fondue ; et3) l’étape 3 consistant à injecter la résine fondue dans un moule pour mouler la résine fondue.

5. Procédé de production selon la revendication 4, dans lequel le diamètre de moyen de particule indiqué par la valeurcumulative à 50 % (D50) vaut de 130 à 210 Pm.

6. Procédé de production selon la revendication 4, dans lequel l’angle de repos vaut de 23 à 35°.

7. Procédé de production selon la revendication 4, dans lequel, dans l’étape 3, la résine fondue est injectée dans lemoule sous une pression de 50 à 500 MPa.

8. Procédé de production selon la revendication 4, dans lequel la machine de moulage par fusion est une machine demoulage par injection, et le moule est un moule à injection.

9. Procédé de production selon la revendication 8, dans lequel, dans l’étape 1, la poudre de résine de poly(fluorurede vinylidène) pour un moulage par fusion est fournie dans un état de la poudre de résine à l’admission d’un cylindreéquipé d’une vis dans la machine de moulage par injection,à l’étape 2, la poudre de résine est chauffée et fondue dans le cylindre régulé à une température de 190 à 280 °Cdans une résine fondue, età l’étape 3, la résine fondue est injectée dans le moule régulé à une température de 80 à 150 °C par une buse àl’extrémité de cylindre sous une pression d’injection dans le cylindre de 50 à 500 MPa pour mouler la résine fondue.

10. Procédé de production selon la revendication 4, dans lequel la machine de moulage par fusion est une machine demoulage par extrusion, et le moule est une filière de formage dans laquelle la résine fondue éjectée par une busede filière à l’extrémité de la machine de moulage par extrusion est chargée.

11. Procédé de production selon la revendication 4, dans lequel les étapes 1 à 3 comprennent les étapes I à III suivantes :

I) l’étape I consistant à fournir la poudre de résine de poly(fluorure de vinylidène) pour un mélange par extrusionà une machine de moulage par extrusion reliée à un dispositif de moule composé d’une buse de filière et d’une

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filière de formage équipée d’un dispositif de refroidissement sur une portion externe de celle-ci et avec unpassage relié à un passage de la buse de filière dans une portion interne de celle-ci ;II) l’étape II consistant à faire fondre la poudre de résine par la machine de moulage par extrusion en une résinefondue ; etIII) l’étape III consistant à extruder la résine fondue par la buse de filière et à l’injecter dans la filière de formageformée à la forme souhaitée pour refroidir et solidifier l’extrudat à l’état fondu à l’intérieur de la filière de formage.

12. Procédé de production selon la revendication 11, dans lequel, dans l’étape I, la poudre de résine de poly(fluorurede vinylidène) pour un moulage par fusion est fournie dans un état de la poudre de résine à l’admission d’un cylindreéquipé d’une vis dans la machine de moulage par extrusion,dans l’étape II, la poudre de résine est chauffée et fondue dans le cylindre régulé à une température de 50 à 280°C en une résine fondue, etdans l’étape III, la résine fondue est extrudée par la buse de filière régulée à une température de 190 à 280 °C etinjectée dans la filière de formage sous une pression de 50 à 500 MPa pour conduire un moulage par extrusion-solidification.

13. Utilisation d’une poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion par des techniquesd’ajustement par pression choisies dans le groupe constitué par le moulage par injection et le moulage par extrusiontout en retenant la forme de la résine en poudre telle quelle sans pastillage de la poudre, où la poudre de résine depoly(fluorure de vinylidène) pour un moulage par fusion présente les caractéristiques de poudre (a) à (c) selonlesquelles


i) un diamètre moyen de particule indiqué par une valeur cumulative à 50 % (D50) dans une distributioncumulative de taille de particule vaut de 80 à 250 Pm,ii) une proportion de poudre de résine ayant un diamètre de particule d’au plus 45 Pm est d’au plus 3,0 %en poids,iii) une proportion de poudre de résine ayant un diamètre de particule d’au moins 355 Pm est d’au plus 5,0% en poids, etiv) une valeur [ (D80-D20) /D50] obtenue en divisant une largeur de diamètre de particule (D80-D20) repré-sentée par une différence entre une valeur cumulative à 80 % (D80) et une valeur cumulative à 20 % (D20)de la distribution cumulative de taille de particule par la valeur cumulative à 50 % (D50) est d’au plus 0,8,

(b) une masse volumique apparente est de 0,40 à 0,70 g/cm3, comme déterminé par un procédé de mesurede densité apparente en conformité avec la norme JIS K 6721-3.3, et(c) un angle de repos est d’au plus 35°, comme déterminé par un procédé de mesure décrit dans la spécificationdans laquelle est utilisé un dispositif de mesure de densité apparente prescrit dans la norme JIS K 6721.

14. Utilisation d’une poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion selon la revendication13, dans laquelle le moulage par injection comprend une étape de fourniture de la poudre de résine de poly(fluorurede vinylidène) à une machine de moulage par injection, et une étape consistant à injecter une résine fondue dansun moule.

15. Utilisation d’une poudre de résine de poly(fluorure de vinylidène) pour un moulage par fusion selon la revendication13, dans laquelle le moulage par extrusion est un moulage par extrusion-solidification comprenant une étape con-sistant à fournir la poudre de résine de poly(fluorure de vinylidène) à une machine de moulage par extrusion, et uneétape consistant à extruder une résine fondue dans une filière de formage.

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the Europeanpatent document. Even though great care has been taken in compiling the references, errors or omissions cannot beexcluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 6846436 B1 [0013] • JP 61185428 A [0060]

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