Indian Journal of Chemical TechnologyVol. 11, May 2004, pp 357-366

Studies of printing inks on starch blended and surface grafted polyethylenefilm for flexible packagingR N Ghosh', B Adhikari'< & B C Ray"

"Department of Chemistry, Jadavpur University, Kolkata 700 032, India

b Materials Science Centre, Il'T, Kharagpur 721 302, India

Received 21 March 2003; revised received 5 December 2003; accepted 10 February 2004Grafted vinyl acetate surface of starch blended biodegradable polyethylene film was printed with industry standard

printing inks based on polyamide resin and organic solvents. Various print and packaging properties were studied to findsuitability of the use of such grafted polyethylene film in comparison to ungrafted starch blended polyethylene film andindustry standard corona treated polyethylene film. The use of such grafted film was also comparatively studied inpolyethylene laminate packaging. Prints and laminates using industrial standard grade polyethylene, starch blendedbiodegradable polyethylene and grafted starch blended polyethylene film, were put on soil burial test and studied forbiodegradable properties.

IPC Code: C09D 11/02

Keywords: Printing ink, grafted polyethylene film, tlexible packaging, biodegradable

Over the past couple of decades a rapid increase in theuse of polyethylene film in flexible packaging hasbeen observed. Large-scale use of polyethylene filmin various packaging applications I has created atremendous detrimental effect to human living, asthese polymers are not biodegradable. Polyethylene,when blended with starch, has been found to beinadequate for printing and packaging applications,although it is encouraging for biodegradationproperties. This necessitated the surface modificationof starch-blended polyethylene for anchorage of inkand coating materials.

Printing inks for flexible packaging are coloredliquids or pastes, which produce a graphic, whensuitably applied by a printing. process or press.Printing ink consists of dispersions of pigments orsolutions of dyes, resin solutions and additives.Printing ink, when transferred onto a printing surface(substrate), colorants (pigments, dyes, etc.) along withresins and other additives, is seen as a print. The printconveys a message, provides protection in the form ofa resinous film and gives a decorative effect to thepolyethylene substrate. The colored coating, thusdeveloped on the substrate, will characterize the print

* For correspondence(E-mail: ba@matsc.iitkgp.ernet.in)

with respect to print appeal and specific packaging. 2properties .

The objective of this work is to look intopossibilities of offering printing and packagingproperties on the vinyl acetate grafted, starch basedbiodegradable polyethylene film:1.4.This work dealswith fast evaporating solvent-based gravure printingink, which is specific to polyethylene substrate. Theseinks are fluid in nature, which allow them to enter intorecessed cells of engraved cylinder for onwardtransfer onto the substrate to form the image. Thevolatile solvents used in ink formulations, evaporatequickly and printing is done reel to reel. Besidesgraphic formation, protection and decorative aspects,the ink should adhere well with the substrate film e.g.polyethylene. The adhesion is achieved by rightselection of resin, colorants, and additives in the inkand ensuring the right surface character ofpolyethylene. This adhesion is primarily controlled bythe film forming ability of the resin, present in the inkcomposition and the surface character of thepolyethylene. The use of polyamide, nitrocelluloseand vinyl resins are known in the industry and theyhave been used in this work as main structural resinsof the ink systems to study the packaging propertiesalong with biodegradation character'", Interactions ofprinting inks and polyethylene films are interpreted"

358 INDIAN J CHEM TECHNOL, VOL II , MAY 2004

in terms of surface printing properties e.g. printability,ink adhesion, gloss and solvent retention in the print,etc. Besides surface printing properties, the reverseprinting and lamination properties e.g. laminate bond,heat sealability, solvent retention etc. also have beenstudied where the polyethylene films act as sealablelayer in polyester/polyethylene laminates.

Prints and laminates using industrial standardgrade polyethylene, starch blended biodegradablepolyethylene and grafted starch blended polyethylenefilm, were subjected to soil burial tests. When allthese print properties and the printed film degradationin soil are satisfactory, there opens up the possibilityof use of such grafted biodegradable polyethylenefilm for flexible packages.

Experimental ProcedureMaterials

Current industrial standard packaging films:Untreated low-density polyethylene film (UTP)(Indian Petrochemicals Corporation Limited (IPCL»,Corona treated (at 38 to 40 dynes/ern) low-densitypolyethylene (STP), IPCL and unprimed, uncoatedpolyester film (PET), Garware Plastics & PolyesterLimited were used.

Starch blended polyethylene (SBP): SBP used inthis work was produced by IPCL.

Vinyl acetate grafted starch blendedbiodegradable polyethylene film (CBP): Vinyl acetategrafting modified the surface of the SBP film.

Laminating adhesives: Two-pack polyurethaneadhesi ve grade CAC 2511 and catalyst CAC 151 1A,Converter Adhesives and Chemicals Limited.

Printing inks: Polyamide resin based and vinylchloride-vinyl acetate copolymer resin based inkswere used.Preparation of printing inks and adhesive

Formulations of inks, varnishes are given inTables 1 and 2. The inks were made in laboratoryvibroshaker. In this work two types of printing inkshave been studied - blue Ink I for polyethylenesurface printing, and blue Ink 2 for reverse printing onpolyester film for subsequent lamination withadhesive onto polyethylene film. Blue pigment(phthalocyanine ~ blue) was dispersed by vibroshakerin the resin solution as per formulations of Ink I andInk 2, given in Table I. The pigment, resin solutionand solvents were weighed as per formulation. For100 g of above mixture, 100 g glass beads (I mm dia)were added in a stainless steel, lever lid container.

Table I - Printing ink and laminating adhesive torrnulationx

Components Ink I Ink 2 Laminating(pbw) (pbw) adhesive

(pbw)

Mill basePigment blue 10 10

Polyamide varnish 50

Toluene 5 10

Maleic resin varnish 6

Vinyl varnish 30

Thinning base

EVA varnish 30

Denatured ethyl alcohol 9

Ethyl acetate 10

Methyl isobutyl ketone 10

lso propyl alcohol 10

n-Buranol <)

Micronised polyethylene wax

Adhesive components

CAC 2511 46.5

CAC 1511A 7.0

Ethyl acetate 46.5

Total 100 100 100

The container was then put on a vibroshaker.Approximately 2 h milling led to a satisfactorydispersion level at maximum 9 ~lm on a grindinggauge, which was taken as mill base. To the mill base,other components of the recipe were added and finalinks were made for printing and packaging studies.The formulation of adhesive is given in Table I.Details of raw materials including sources are givenin Table 3.

Gravure print and laminate sample preparation

By dilution with solvents, viscosity of each of thetwo inks were set at 20 s, by Ford Cup B4 at 30°C,and gravure printing was done with Gravure Proofer(M/s R.K. Proofer, UK). Prints of inks were taken atroom temperature (30°C). The gravure printing wasdone in following steps.

GHOSH et al.: STUDIES OF PRINTING INKS 359

Table 2- Varnish formulations

Polyamide varnish Vinyl varnish Maleic varnish EVA varnish(pbw) (pbw) (pbw) (pbw)

40

25

50

25

45

10

5 15 60

20 15

40

50

100 parts 100 parts 100 parts 100 parts

Components

Cosolvent polyamide resin

Vinyl resin

Maleic resin

EVA resin

Iso propyl alcohol

n-Butanol

Toluene

Ethyl acetate

Methyl isobutyl ketone

Denatured ethyl alcohol

Total

Raw material

Table 3 - Raw materials used in making inks and laminating adhesive

Pigment Blue

Polyamide resin

Vinyl resin

EVA resin

Chemical description

Phthalocyanine Beta Blue, PB 15.3

N-230, Cosolvent grade

Vinyl chloride 1 vinyl acetate (86114) copolymer VAGH grade

Ethylene - vinyl acetate (60/40) copolymer

Denatured ethyl alcohol

Ethyl acetate

Toluene

MIBK

IPA

Methyl isobutyl ketone

Iso propyl alcohol

n-Butanol

Wax Micronised polythene wax

CAC 2511, CAC 1511A2 Component adhesive

Source

Sudarshan Chemical Industries Ltd.

Noble Synthetics Ltd.

Union CarbidelDow Chemicals

DuPont

Hindusthan Sugar Mill

Indian Organics

Cochin Refinery

NOCIL

NOCIL

NOCIL

Micro Powders

Converter Adhesives and Chemicals

Fixed the solid 'A' type plate (screen 150 lines/in)on Gravure Proofer,

Adjusted pressure on rubber roller to 4 mm usingmicrometer,

Adjusted pressure on Doctor Blade by setting 7mm clearance using micrometer,

Pasted a pre-cut (220x150 mm) substrate on therubber roller with cellotape,

Finally print was takenat standard speed mark of'5' of the Gravure Proofer.

For surface pnntmg, Ink 1 was used for UTP,STP, SBP and GBP. For reverse printing, Ink 2 wasused on PET following the above-mentioned printingmethod. Then the adhesive was applied by the samemethod onto the PET print and dried with hot airblower. The second substrate (polyethylene) wasplaced onto the printed and adhesive coated polyesterfilm. The two film layers were pressed together withan ani lox roller (R. K. Proofer, UK) taking care toexclude air bubbles, if there were any. This formed alaminate i.e., sandwich of PET film, ink, adhesive,

360 INDIAN J CHEM lECHNOL, VOL II, MAY 2004

and low-density polyethylene (LDPE) film.Lamination bond strength, which is a numerical valueassigned to describe the relative strength to peel aparttwo layers involving ink and adhesive, was measuredby Bond Strength Tester LRX, (J. J. Loyd, UK) aftercuring the laminate for 24 h at room temperature. Apiece of the laminate was cut at 15 mm width. Thelaminate was gripped between the jaws of the bondstrength tester to determine bond or peel strength.

Evaluations of film surface, print and laminate properties

Blue Ink 1 was printed on polyethylene filmsUTP, STP, SBP and GBP. The surface prints wereassessed on GBP in comparison to prints on STP andSBp9

. The films and prints were tested for thefollowing properties:

Surface tension measurement

The method for determining surface tension,which is a measure of surface energy, is known aswetting tension test 10. For this experiment, a series ofsolutions of ethyl cellosolve and formamide weremade with gradually increasing surface tension. Thevarious solutions were applied onto polyethylenesurface with a cotton bud until a particular solutionjust wets the film surface. The surface tension of thepolyethylene film is approximately equal to thesurface tension of that particular solution. The testsolutions used to judge the surface tension of UTP,STP, SBP and GBP are given in Table 4.

Contact angle measurement

The evaluation of surface energy values of solidpolymer surfaces by contact angle measurements iswidely accepted. The sessile drop method" usingwater and formamide as the probe liquids wasfollowed for contact angle measurements. Theexperiments were carried out on a plastic plate havingdimensions of lOxlOxO.3 mm in vapor-saturated air at25 ± 2°C in a closed box of the contact angle meter,Kernco Model G Il. Each value reported is the meanof five measurements with a maximum error in e of±0.5°. Time for measurement was 5 min after puttingthe liquid drop. Surface energy of a pure phase (Ys) isthe sum of the contributions from the dispersion (Ysd)and polar (y/) cornponents'",

d PYs= Ys + Y8 ... (1 )

For a solid-liquid system, different components ofthe surface energy can be calculated from thef II' . '3 '4o owmg equation .. ,

Table 4 - Compositions of test solutions to measure surfacetension

Fonnamide Cellosolve Surface tension(volume %) (volume %) (dynes/em)

0 100 30

2.5 97.5 31

10.5 89.5 32

19 81 33

26.5 73.5 34

35 65 35

42.5 57.5 36

48.5 51.5 37

59 41 39

63.5 36.5 40

67.5 32.5 41

71.5 28.5 42

where, s and I represent the solid and liquidphases respectively and e is the contact angle of theliquid with the solid surface. Using equation (2) thepolar and dispersion components of the surfaceenergy of the films UTP, SBP and GBP werecalculated after measuring the contact angle values forwater and formamide. The standard surface energiesof these two liquids are as follows:

Water: y, = 72.8 rnl/rn', y,d = 21.8 ml/rn", yi' =51.0 ml/rn'

Formamide: y, = 58.2 ml/rrr', y,U = 39.5 ml/m', YIP

= 18.7 mJ/m2

Finally using Eq. (I), Ys of the polyethylene filmsUTP, SBP and GBP were calculated from ysd and ys"values.

Adhesion measurement

Scotch tape adhesion of dried ink on polyethylenefilm, was assessed by laying the adhesive side of 1.0in wide tape on the print surface and then peelingaway from the print. Ink removal due to peeling, ifany, was recorded on a scale of I (complete removalof ink) to 10 (no ink removal). The adhesionproperties were studied everyday for a period of 7

GHOSH et al.: STUDIES OF PRINTING INKS 361

.days, from the day of printing. The average ratings of7 days are reported.

Gloss measurement

The print gloss was measured by GlossometerBYKlGARDNER - Microgloss 75°, which reads thelight, reflected by a print surface at angle 75°. Threereadings were taken and average gloss value wasrecorded.

Solvent retention measurement

Gas Chromatograph 5890 HP Series II, HewlettPackard and Headspace analyzer HS-40, Perkin-Elmer, were used to estimate solvents in the printsand laminates. Blue Ink 2 was printed on PET film.Lamination characteristics of GBP were also assessedas second web in comparison to STP and SBP films.This was done by laminating GBP, SBP and STP togravure reverse printed with Ink 2 on polyester film.The laminates were studied for the lamination bondand heat seal properties in addition to retained solventestimation.

Lamination bond measurement

Lamination bond strength, which is a numericalvalue assigned to describe the relative strength to peelapart two layers involving ink and adhesive, wasmeasured by Bond Strength Tester, after curing thelaminate for 24 h at room temperature. A piece of thelaminate was cut at 15 mm width. The laminate wasgripped between the jaws of the bond strength testerto determine bond or peel strength.

Heat-sealing test

Heat sealing properties of the polyester-polyethylene laminate was measured by a heat sealer,to form a pouch, where polyethylene layers of twolaminate pieces were pressed under jaws, at a settemperature of 120°C and pressure of 2 kg/ern' forI s. If in sealing test it is noticed that the two layersare not peeled apart, satisfactory sealing wasrecorded. If the film layers open up, the laminate failsin sealing test.

Soil burial test

The printed films and laminates were put in soilburial test where soil based microorganisms andenzymes are active. A pit of approximately 20 inlength, lOin breadth and lOin depth was dug in ahouse garden in the city of Kolkata, India. The soil ofthe pit was made free of brick chips, stones,polymeric materials, etc. The surface prints of STP,SBP and GBP and laminates of STP, SBP and GBP

were kept at the bottom of the pit. The pit was filledup with loose, moist and soft soil.Isolation of microorganisms in soil burial pit

The soil sample from the testing field wascharacterized for its types of microbes present.Microbial densities were determined by the dilutionplate count technique". Soil (lOg) was suspended insterile distilled water (90 mL) and shaken vigorouslyfor 15 min. Appropriate series of 10 fold dilutionswere performed and aliquots of 1 mL were placed inpetri dishes containing different media. The plateswere incubated at 30-32°C for 10 days. Single isolatedcolonies were counted after 10 days of incubation andsoil microbial population was calculated in terms ofcolony forming units per gram of soil. For bacteria,actinomycetes and fungi, nutrient agar, glycerol-asparagine agar and potato dextrose agar were usedrespectively. All media were sterilized by autoclavingat 15 psi for 15 min.Evaluation of films, prints and laminates after keeping in soil

The printed films and laminates were kept undersoil burial for a total period of twelve months. Atevery three months interval, the printed films andlaminates were taken out after digging the pit. Theprinted films and laminates were cleaned with tapwater, dried by keeping at room temperature and thentested/photographed to record the progress ondegradation status. After the testing on each interval,the prints and laminates were put back into the soil asmentioned above. The STP, SBP and GBP films werestudied before and after twelve months soil burial byATR spectroscopy, using Thermonicolet FTIRspectrometer, model NEXUS 870.

Results and Discussion

Film surface properties

Surface tension of the films was measured bywetting tension test or Dyne Solutions method, usingcellosolve and formamide mixtures at different ratiosfor different surface energy values (Table 4). Theresults of surface tension test are shown in Table 5.The surface energy of GBP film was found to be ashigh as that of corona treated LDPE film (STP),which is industry standard, and hence encouraging forprinting purpose. In general, no single theory can beused to predict adhesion of the ink resins, onto thevarious polyethylene film surfaces. It is useful to lookat wetting and its role in adhesion mechanism.Wetting of the polymer surface is described as theextent to which the liquid ink spreads when applied

362 INDIAN 1 CHEM TECHNOL, VOL II, MAY 2004

onto the surface. Contact angle of the liquid inkdroplet with the plane of the polymer surface is usedas a measure of the wettability. Young's Eq. (3) hasbeen used to describe the relationship between thecontact angle e and energy of the relevant interfaces.The relative contact angle between the droplet and thefilm surface was measured and compared.

YSV - YLS = YLV cas e ... (3)

where, Ysv is surface energy of solid/vaporinterface, YSL is surface energy of solid/liquid interfaceand YLV is surface energy of liquid/vapor interface.When the angle e tends towards 00

, the wetting ishigh or good. Conversely as the angle e tends towards1800

, wetting is low or poor. Contact angles of waterand formamide on the three polyethylene films UTP,SBP and GBP are reported in Table 5.

The significant drop of contact angle on thegrafted surface of starch blended polyethylene film is

important finding. The dispersion (Ys<I) and polar (Y/)components of surface energy were calculated as perthe Eq. (2) and then the surface energies of UTP, SBPand GBP films were calculated from Eq. (I). Thesurface energy increased in SBP from plain UTP.Further increase of surface energy was noticed invinyl acetate grafted film GBP. The increase is foundmore in polar component of the surface energy. Thesurface energy level of 39.8 mJ/m2 of GBP indicates abetter chance of adherence of printing ink and coatingmaterial onto GBP film.Printability and adhesion

Surface printing properties are given in Table 6.Printability is essentially a surface wetting property ofink on the polymer film whereas adhesion ensures thebonding of dried ink onto the film. The results inTable 6 characterize the adhesion properties ofprinting ink on four types of polyethylene films understudy UTP, STP, SBP and GBP. The adhesionproperties have been studied everyday for a period of

Table 5 - Contact angle, surface energy and surface tension of the polyethylene films

Films Contact angle Contact angle Ysd y/ Total surface Surface(degrees) (degrees) m1/m2 mJ/m2 energy tension.

water formamide Ys ml/rrr' dynes/em

Plain untreated polyethylene (UTP) 85 64 25 1.8 26. 8 < 32

Starch blended polyethylene (SBP) 83 58 32.4 4.0 36.4 32

Vinyl acetate grafted SBP (GBP) 64 51 27.7 12.2 39. 8 40

Corona treated polyethylene (STP) 40

Table 6 - Adhesion and surface printing properties of Ink I

Print Adhesion Retained solvent in print Glossometer Surface energy Printabilitysubstrate (I - 10) (rng/rrr') readings Dyne/ern (I - 10)

Major single solvents Total solvent

UTP < 32 10

STP 10 n-Butanol 1.30 5.56 81.9 40 10

Toluene 3.36

SBP 3 Isopropanol 9.80 56.68 29 32

Toluene 14.40

n-Butanol 16.36

GBP 8 n-Butanol 10.51 29.97 56.3 >40 9

Toluene 5.27

[Scale: I (poor) - \0 (excellent)]

GHOSH et al.: STUDIES OF PRINTING INKS 363

7 days, from the day of printing. The average ratingsare given in Table 6.

Photographs, given in Fig. 1, were taken todemonstrate peeling off the ink from prints on UTP,STP, SBP and GBP by scotch tape adhesion test. GBPoffers satisfactory printability and adhesion with InkI, based on co-solvent polyamide, which is veryencouraging, whereas the SBP does not. The higherdegree of adhesion onto the GBP film is influenced bysurface modification through vinyl acetate grafting.UTP, however, does not show any anchorage of inkon the polyethylene film. Proper adhesion ensures thecolor retention on the printed film. During printing,ink and polyethylene surface come in contact witheach other. This forms an interface whose propertiesdepend on the surface properties of both ink and film.In order to achieve good printability, printing inkshould have lower surface tension. Low surfacetension of ink is necessary for good polyethylenesurface wetting i.e. good ink lay. Solvent based inkshave inherently low surface tension" due to solventsused with surface tension around 22 dynes/em, Out ofvarious components in ink formulation, the resinand/or mixture of resins plays crucial role foradhesion. Polyamide resin is known to adhere on tothe surface treated polyethylene film.

One method of increasing the surface energy ofthe polyethylene film is electrical discharge or coronatreatment. During corona discharge excited gas

hu:"'n~BP

.. 'L I n c,.;

~~ ,.t' .~

Fig. 1- Printing ink adhesion on UTP, STP, SBP and GBP fi-lmsurfaces -

molecules attack polyolefin surface causing chemicalmodification through the formation of functional

I f 1718 Th . d .groups on po ymer sur ace '. e excite speciescan be ions, electrons or neutrals. Corona discharge isgenerated using high voltage (20 kV) and highfrequency (10-20) kHz. This increases surfaceoxidation of the film, breaking chemical bonds toproduce more - OH, >C = 0, peroxide linkages andnitrate groups'". These groups provide the active sitesfor chemical anchorage with inks and adhesives,hence, enhance adhesion. Higher surface energy ofthe film and lower surface energy of the ink andcoating materials ensure wetting and adhesiorr".

The forces of adhesion" can be characterized infour groups - mechanical, chemical, secondary anddiffusion. Mechanical forces are those created whenthe ink or adhesive flows into the micro crevices ofthe polymer surface and set up frictional orinterlocking forces. Both SBP and GBP films havedifferent surface characteristics than that of STP filmsdue to blending with starch (SBP) and vinyl acetategrafting on SBP (GBP). Due to the presence of somesurface roughness on both SBP and GBP filmsmechanical forces can operate for promotingadhesion. Higher degree of adhesion in GBP film thanSBP film is more attributed to other three forces,chemical, secondary and diffusion. Better adhesioncan also be explained by the formation of hydrogenbonds between polyamide resin in ink with the vinylacetate grafted surface of GBP film. Diffusion forcesset up when diffusion occurs across the interface e.g., ~the diffusion of ink into the in-line coating of thesubstrate polymer. The diffusion of chlorinatedpolypropylene into polypropylene film wasestablished by using radio labeller chlorinatedpolyethylene/Y", The improvement in ink adhesion isnoticeable on print of GBP in comparison to print ofSBP film, which shows the utility of vinyl acetategrafted surface.Solvent retention in prints

Table 6 shows the retained solvents present inthree printed films STP, SBP and GBP. Highersolvent retention in the print is not a desirablepackaging property. The lower the retained orentrapped value, the better it is. Very high retentionlevel of solvents found in SBP is due to the presenceof starch in the film. However, grafting with vinylacetate on GBP caused lowering of solvent retention _to a great extent, where the grafted polyvinyl acetatelayer on the film prevented solvent penetration.

364

intervals, after keeping the prints and laminates undersoil for one year. Degradation of starch blendedpolyethylene film was reported by Goheen et at?4. Onkeeping such film in soil, the report confirms starchremoval from the blend and degradation that tookplace in the polyethylene matrix. The photographs ofthe prints of STP, SBP and GBP after every threemonths keeping in soil are shown in Fig. 2 for STP,SBP and GBP. The STP prints do not show any lossof print color and polyethylene film. The prints onSBP show number of pores, developed after sixmonths and the pores have increased with time. Thedevelopment of pores indicates the disintegration ofSBP film. The prints on GBP also have shown thepores development indicating the much-desireddisintegration of the GBP film ..

The photographs of polyester laminates with thethree polyethylene films STP, SBP and GBP areshown in Fig. 3 at every three months interval ofkeeping under soil for one year. The laminates did notundergo any major change. The laminate of STPremained mostly unchanged.· The printed polyesterdid not undergo any change. The laminates of SBPand GBP, unlike that of STP, however, have showndelamination, which separates out the polyethylenepart from the printed PET film. The separatedpolyethylene from laminates of SBP and GBP filmshave shown development of pores.

INDIAN J CHEM TECHNOL, VOL II , MAY 2004

Gloss of surface prints

Table 6 also shows the gloss values of the printson STP, SBP and GBP. Very low gloss value of SBPfilm was resulted from nonuniforrnity in surfacecharacter of SBP. The gloss value on GBP hasincreased by surface regularity achieved with vinylacetate grafting on the surface.Laminate properties

Table 7 shows that laminate of Ink 2-printed PETand GBP has increased lamination bond values incomparison to the laminate using SBP film. Thelaminate bond of 500 g indicates the positive resultsof ink adhesion with GBP film. Higher solventretention in both SBP and GBP laminates areattributed to starch and polyvinyl acetate components.The polyethylene films in all the three laminates ofSTP, SBP and GBP have shown heat seal ability,which is a requirement for pouch making. However,further work on ink solvents can help minimizing theretention values, as laminate bond and sealingproperties are encouraging for GBP laminate.Microorganisms in soil

The bacteria, microbes, water, etc. present in t!!~

soil were evaluated by the culture of the soil. Themicrobes and their colony forming units are give» inTable 8. The isolation and identification of microbe"actinomycetes and fungi by type and colony formingunits characterize the nature of the soil. The data alsoopens up further microbial work on the subject.Characterization of films, prints and laminates after soil burial

Characterization of degradation or loss in theprints and laminates was studied at every 3 months

Table 7 - Laminate properties using Ink 2

Laminate Laminate bond Retained solvent Heat sealingg/l5 mm mg/ m2

PET + STP 2377 8.46 Satisfactory

PET + SBP 163 22.30 - do -

PET + GBP 504 37.63 - do-

Table 8 - Microbes in soil, types and measures

Microbe Type Colony FormingUnitlg of soil

Bacteria 10 7.97xlO-('

Actinomycetes 5 1.16xlO - (,

Fungi 3 1.2xlO -6Fig. 2-Surface prints on soil burial test (a) STP;(b) SBP

and (c) GBP

GHOSH et al.: STUDIES OF PRINTING INKS 365

•

•

Fig. 3 - Printed laminates on soil burial test: (a) STP, (b) SBPand c)GBP

The ATR spectroscopy studies of the three filmsSTP, SBP and GBP before and after keeping themunder soil for one year were done. The spectra of eachfilm before and after keeping one year under soil aremarked as BI STP, B2 SBP, B3 GBP before soilburial and AI STP, A2 SBP, A3 GBP after soil burialand shown in Fig. 4. Valuable indications in ATRspectra are found, showing major absence of bandsand appearance of new bands in the films due to oneyear burying the films under soil. STP film showsabsence of absorbance at 2915, 2847, 1462 cm-I aftersoil buriaI25,26. SBP shows no absorbance at 2847,1462,729,755 em", but it shows new peaks at 1041,1471, 1669 cm-I. The GBP film also showed similarphenomenon like SBP indicating the changes inpolyethylene matrix.

ConclusionThe results on ink adhesion, print gloss,

lamination bonds, etc. with GBP film areencouraging. This opens up the possibility of usingstarch-blended polyethylene in flexible packaging,when vinyl acetate grafting modifies suchpolyethylene surface. As both surface and laminateproperties are encouraging, packaging options withGBP film has a potential. The degradation of printed

8c€ H-t---'--+---.r.---"\)I1'------"i~~rr-~~~~~~==~~ri

4000 3500 3000 2~ 2000 1~Wave numbers (ern")

1000 soo

Fig. 4-ATR spectra before and after soil burial on STP, SBPand GBP films

SBP and GBP films and the laminates when keptunder soil is significant which is a desiredphenomenon. The soil burial test also clearlyestablishes the inertness of STP film towardsdegradation. In the laminates, the base polyester filmdid not show any degradation. Only the laminates ofSBP and GBP films that were delaminated with timehave shown degradation. Hence, both surface prints ofGBP film, the polyester laminate with GBP film aredesirable findings towards making of biodegradableflexible packaging.

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