CA1088817A

CA1088817A - Coated polyolefin film

Info

Publication number: CA1088817A
Application number: CA259,751A
Authority: CA
Inventors: Shigeyuki Takahashi; Yuichi Harada; Tetsuo Ishihara
Original assignee: Daicel Corp
Current assignee: Daicel Corp
Priority date: 1975-08-25
Filing date: 1976-08-24
Publication date: 1980-11-04
Also published as: JPS5226584A; US4121006A

Abstract

COATED POLYOLEFIN FILM
ABSTRACT OF THE DISCLOSURE
A polyolefin film is coated with an undercoat consisting essentially of polyvinylidene chloride or its copolymer containing at least 88 percent by weight of vinylidene chloride monomer units and a chlorinated polypropylene or its graft polymer at the weight ratio in the range between 99/1 and 90/10, and a topcoat consisting essentially of a vinylidene chloride copolymer containing not more than 88 percent by weight of vinylidene chloride monomer units.

Description

t BACKGROU~D OF INVENTION
FIELD OF INVENT:[:ON
The present invention relates to a polyolefin film is coated with an undercoat consisting essentially of polyvinylidene chloride or its copolymer containing at least 88 percent by weight of vinylidene chloride monomer units and a chlorinated !~
polypropylene or its graft polymer at the weight ratio in the range between 99S1 and 90/10, and a topcoat consisting essen-tially of a vinylidene chloride copolymer containing not more than 88 percent by weight of vlnylidene chloride monomer units. ¦
More particularly, the invention relates to coated polyolefin films which are excellent in the low-temperature heat-sealing property, the barrier property to oxygen gas and water vapor, the adhesive cellophane tape peel strength of the coating and the transparency. j~
DESCRIPTION OF PRIOR ARTS
BiaxialIy stretched films o~ isotactic polypropylene now attract attention in the art because of high mechanical prop-erties and excellent transparency.~ However, ~hese films are inferior in the oxygen gas barrier property and since they are highly crystalline and are biaxially stretched, thermal shrinkage is caused at high temperatures and the heat-sealing property is quite insufficient.
As means ~or improving the oxygen gas barrier property and the heat-seallng property, there has ~een proposed a process ;~
comprising coating such polypropylene film with a mixture of a vlnylidene chloride type resin and a chlorinated polypropylene resin or a chlorinated polypropylene resin grafted with a vinyl monomer such as styrene (see Japanese Pa-tent PublicatiGns No. 16316/68, No. 26085/68, No. 277/70 and 8400/72). In this .
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method, however, ~ilms having a ~ood heat-sealing l)roperty canno~ be obtained, because a vinyiidene chlor-ide resin havlng a relatively high vinylidene chloride content is used in order to improve the oxygen gas barrier property.
As means for improving the low-temperature heat-sealing property, there have been adopted a method in which a vinylidene chloride type resin having a vinylidene chloride content reduced to some extent is employed and a method in which a third component having a low melting point is incorporated. According to these methods, a good low-temperature heat-sealing property can be attained, but the oxygen gas barrier proper~y is insufficient.
This invention relates to a polyolefin film coated with ^
I. an undercoat consisting essentially of a mixture of (a) polyvinylidene chloride or vinylidene chloride copolymer ~-;
containing at least 88 weight percent of vinylidene chloride -~
monomer units, and (b) a chlorinated polypropylene having a chlorine content of from 15 to 55 percent by weight and an intrinsic viscosity of from 0.3 to 3.0 dQ/g, wherein intrinsic viscosity is ~i `
determined by measuring the viscosity of a solution of 0.2 to 0.5 percent by weight of said chlorinated polypropylene in decalin at 135~C or a graft polymer of said chlorinated polypropylene having grafted thereto from 2 to 30 percent by ;
weight, based on the weight of the graft polymer, of an ethyl-enically unsaturated vinyl monomer, wherein the weight ratio of a/b is from 99tl to 90/10, and II. a top coat consisting essentially of a vinylidene chloride copolymer containing from 35 to 88 weight percent of vinylidene chloride monomer units.
In view of the state of the art set out above we have made various research works and have now completed coated polyolefin ~ilms which are `30 excellent in all of the foregoing properties. More specifically, in accordance with the present invention, there is provided coated polyolefin films obtained by coating a polyolefin film with an undercoat liquid composition ~ ~`

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comprising as main components 9~ to 90 par-ts by weight of a vinylidene chloride type resin conta:ining at least 88% of vinylidene chloride and 1 to 10 parts by weight of a chlorinated polypropylene resin or an ethylenically unsaturated vinyl monomer-grafted chlorinated polypropylene resin, and coating the coated surface of -the film with a topcoat liquid composition comprising as a main component a vinylidene chloride type resin containing vinylidene chloride in an amount of from 35 to 88% by weight, preferably from 50 to 85%
by weight.
As the chlorinated polypropylene, a product obtained by chlorinating crystalline or non-crystalline polypropylene can be used in the present invention It is preferred that the ., `. ' ~.';' '~ .., ' `' ~'' ' C - 3a _ a~

intrinsic viscosity of ~he startin~ polypropylene be in the range of 0.3 to 3.0 dQ/g.
If the intrinsic viscosity of the starting polypropylene is lower than 0.3 dQ/g, the film-forming property is bad and the heat seal strength o the coated polyolefin film is reduced.
If the intrinsic viscosity is higher than 3.0 dQ/g, the coating solution becomes too viscous and the adoptability to the coat-ing operation is insufficient~ Further, ~he heat seal strength of the coated polyolefin film tends to be reduced. An especially preferred intrinsic viscosity is in the range of 0.5 ~o 1.5 dQ/g.
In the instant specification, the intrinsic viscosity is a value determined based on the viscosity of a dilution of a polymer in decalin as measured at 135C, and at the concen-tration of from 0.2 to 0.5 wt ~.
It is preferred that the chlorine content in the chlorinated polypropylene be in the range of 15 to 55% by weight. If the chlorine content is lower than 15% by weight, the solubility in an organic solvent and the compatibility with a vinylidene , .
chloride type resin are insufficient. If the chlorine content is higher than 55% by weight, the thermal stability is rçduced and the heat seal strength of the coated polyolefin film is degraded.
Chlorinated polypropylene can be prepared by chlorinating polypropylene in the solution state, the suspension state or the solid dispersion state according to customary procedures. ';
These methods are described, for example, in J. Polymer Sci., 55, 169 (1961~ and Kobunshi, 9, 903 (1960). : ~-As the ethylenically unsaturated vinyl monomer-grafted chlorinated polypropylene (hereinafter referred to merely as "grafted polymer"), there is preferably employed a product obtained by graftiny a vinyl monomer in an amount oE 2 to 30% by weight (based on the grafted polymer) to a chlorinated polypropylene having a chlorine conkent of 15 to 55~ by weight, which is obtained by chlorinating polypropylene having an intrinsic viscosity of 0.3 to 3 dQ/g.
Graft polymerization of monomers to chlorinated polypro-pylenes can be performed, for example, according to a method disclosed in Kokashi, 64, 172 (1961).
Any of emulsion polymerization, suspension polymerization and solution polymerization systems may be adopted for this graft polymerization. In view of the homogeneous grafting effect, the solution polymerization system is most pre~erred.
Any of solvents capable of dissolving therein chlorinated polypropylene can be used as the solvent for the graft poly-merization. Aromatic hydrocarbon such as benzene and toluene and chlorinated hydrocarbons such as carbon tetrachloride and chloroform are especially preferred~
Various catalysts may be used for the graft polymerization.
For example, these may be employed known radical polymerization catalysts such as peroxides, azo compounds and persulfates, and redox catalysts comprising a radical polymeri2ation catalyst as mentioned above and a reducing agent such as ascorbic acid, formaldehyde or sodium sul~oxylate. Further, recently proposed matal chelate compounds, for example, chelates of 1,3-dicarbonyl compounds with transition metals of the groups I and VI to VIII
of the Per~odic Table, may be used as the graft polymerization catalyst. Recently, it was reported that a mixture of an acti-vated metal and an organic halogen compound has a polymerization-initiating activity [for example, Polymer Letters, 5, 697 (1967)].
We noted that chlorinated polypropylene has a carbon-to-chlorine , linkage, and we made investigations on the co~bination of chlorinated polypropylene and an activated metal. As a result, it was found that activated metals are able to cause graft polymerization of chlorinated polypropylene. Accordingly, activated metals such as reduced copper, iron, nickel and cobalt can be used as the graft polymerization initiator.
The polymerization catalyst may be used in an amount of 0.1 to 5 mole % (based on the monomer), preferably 0.2 to 2~mole ~.
The activated metal is used in an amount of 0.5 to 15~ by weight (based on the monomer), preferably 1 to 8% by weight.
The temperature and time for the gra~ting reaction may be changed in broad ranges, but in general, it is especially preferred that the grafting reaction be carried out at 20 to 100C for 1 to 24 hours. Needless to say, various chain trans-fer agents may be used for the grafting reaction.
As the vinyl monomer to be graft-polymerized, there can be mentioned, for example, styrene type monomers, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl propionate, I,3-butadiene, acrylonitrile, methacrylonitrile, acrolein, acrylates and methacrylates. It is preferred that the content of the grafted vinyl monomer in the grafted polymer be in the range of 2 to 30~ by weight. If the grafted monomer content is lower than 2~ by weight, no substantial effect can be obtained. If the grafted monomer content is higher than 30~ by weight, the heat seal strength tends to be reduced.
Any of known vinylidene chloride resins can be used in the present invention. For example, there may be employed vinylidene chloride-acrylonitrile copolymers, vinylidene chlorlde-vinyl chloride copolymers, vinylidene chloride-vinyl acetate copolymers, vinylidene chloride-acrylate copolymers, g~

vinylidene chloride-acrylic acid copolymers and products obtained by copolymerizing a third componen-t such as acrylic acid, methacrylic acid or the like with the above-mentioned copolymers. Use of a vinylidene chloride homopolymer is not preferred, because no good results are obtained with respect to the thermal stability, the wheatherability and the softness of the coating.
Crystalline polyolefin films, crystalline poly-4-methylpentene-l films ana the like can be used as the polyolefin film in the present invention. A biaxially stretched crystalline polypropylene film is especially preferred because it has a high melting point, a high transparency, high mechanical properties and a high packaginy adaptability.
It lS known that in order to improve the adhesiveness at the coating step, various surface treatments may be applied to polyolefin films. Also in the present invention, these known sur~ace treatments, for example, corona discharge, high frequency wave, flame and chromium-containing liquid treatments may be adopted, but it must be noted that one of characteristic features of the present invention is that very excellent results can be obtained even if such pre-treatment is not conducted.
In the present invention, coating devices customarlly used for the production of moisture-proof cellophanes, such as a dip coater, a roller coater and a gravure coater, can be used.
In the vinylidene chloride resin that is used for the undercoat liquid composition, the vinylidene chloride resin content is at least 88%. In view of -the oxygen gas barrier property, it is preferred that the vinylidene chloride content be at least 90%.

In the undercoat liquid composition, the weight ratio of the vinylidene chloride resin to the chlorinated polypropylene or ethylenically unsaturated monomer-grafted chlorinated poly-propylena is preferably in the range of 99/1 to 90/10, especially preferably in the range of 99/1 to 95/5. If this ratio is higher than 99/1, no substantial effect of improving the heat-sealing property is attained. If this ratio is lower than gO/10, the effect of improving the gas barrier property is reduced.
The undercoat liquid composition referred to in the instant specification includes a homogeneous solution formed by dissolv-ing the vinylidene chloride type resin in a solvent for the resin or a mixture of a solvent for the resin and a rlon-solvent for the resin, and a heterogeneous liquid system formed by dispersing or emulsifying the vinylidene chloride type resin in a non-solvent such as water.
In the vinylidene chloride resin for the topcoat liquid composition, the vinylidene chloride content is:from 35 to ..
88 wt ~. In view of the low-temperature heat-sealing property, it is especially preferred that the vinylidene chloride content be from 50 to 85 wt %.
As is well-known in the art, additives such as antioxidants, dyes, pigments, lubricants, antistatic agents, blocking prevent-ing agents and ultraviolet stabilizers may be incorporated into~ !
the coating composition.
The thickness of the coating layer is preferably in therange o~ 1 to 10 ~, especially 2 to 5 ~.
The coated film prepared according to the process o~ the present invention may be used as a wrapping material as it is or after it has been formed into a big. Further, it may be laminated and used as a packaging material. More particularly, :. ~ . . ..

the film of the present invention is especially suitable for packaging snack foods such as cookies, crackers and potato chips, oily and fatty foods such as chocolates and sponge cakes, and fried rice cakes, dried lavers, sprinkling food additives, peenuts, tobaccos, cut tabaccos, roast coffee beans~
handkerchiefs, gauzes, woven fabrics r soaps, detergents, dry cells and unfinished machine parts.

BRIEF DESCRIPTION OF DRAWING:
The drawing illustrates the relation between the heat-sealing temperature and the heat seal strength in the ooated polyolefin fi~m.
The present invention will now be described in detail by reference to the following illustrative examples that by no means limit the scope of the invention.
In the examples, properties of coated ~ilms were tested i according to the following methods.
(l) Adhesive cellophane tape test:
According to a method similar to the so-called Scotch lB Tape test, a pressure-sensitive adhesive cellophane tape having a size of 24 mm x 200 mm was applied to the resin-coated surface and the entire tape surface was pressed repeatedly to bond the tape tightly to the resin-coated surface. Then, the adhesive tape was violently peeled at an angle of 90~. The state of peeling of the coating was examined ana the peel strength was evaluated according to the following scale:
Excellent: the resin coating was not peeled at all.
Good: the resin-peeled area was less than 10% o~
the total area.
Fair: the resin-peeled area was lO to 20% of the total area.
Bad: the resin-peeled area was larger than 20%
of the total area.

r~c~e ~

(2) Haat seal streng-th test:
T~lo coated films were superimposed ~o that the coated surfaces confronted each other, and they were heat-sealed at a heater temperature of 120C under a pxe5sure of 2 Xg/cm2 or 2 seconds by using a har-type heat sealer. A sample having a size of 10 mm x 150 mm was taken out a~d the pulling peel strength of the heat-sealed area was tested at a pulling speed of 300 mm/min by using a Tensilon tester. When the rela-tion between the heat-sealing temperature and the heat seal stren~th was examined, the heater tempera~ure was changed in the above method, ~3) ~ater vapor permeability:
The water vapor permeability was tested at a temperature of 40C and a relati~e humidity of 90% by using a cup indicated in JIS Z-0208.
(41 Gxygen gas permeability:
The measurement was carried out at 20C by using oxygen gAS having a humidity o~ 0~ and helium gas according to~the gas chromatograph test method using Lyssy Gas PermeabiIity Testing Apparatus I-66.
~5) Transparency:
The transparency was e~aluated with the naXed eye according to the ~ollowing scale:
Excellent: equal to the transparency of a biaxially stretched polypropylene film.
Good: slightly inferior to the transparency of a biaxially stretched polypropy~ene film~
Fair: con~iderahly in~erior to the transparency of a biax-ially stretched polypropylene film but slightly ~ superior to ~hat o~ low ~ensity polyethylene.

llb~

~ad: equal or inferlor to the transparency of low density polyethylene.
(61 Blocking resistance:
Several ~ilms having a size o 100 mm x 100 mm were inserted between two glass sheets, ana they were allowed to stand still at 40C under compre~sion o~ 0.5 Kg/cm for 8 hours and then naturally cooled to room tempexature.
The blocking resistance was evaluated according to the following scale: i Excellent: the films could be separated into the re-spective films without application of a force.
Good: the films could be separated under application of a small force.
Pair: the films could be separa~ed under application of a force bu~ the coated resin layar wa~ partially damaged.
Bad: the films could not be separated without fracture of the films because the films were formed into a hard blockO
Exam~
The chlorinated polypropylene used in this example was prepared in the follo~Ying manner.
Accoxding to a customary method, isotactic polypropylene having an intrlnsic viscosity of 1.5 dQ~g was dissolved in tetrachloroethylene at 120C and chlorine gas was blown in the solution to obtain a chlorinated polypropylene having a chlorina content of 30~ by weight and an intrinsic vlscosity o~ 1.2 dQ/g.
The so obtained chlorinated polypropylena and a vinylidene chloride-vinyl chloride copolymer ~having a vinylidene chloride ~t~ 7 content of 90%) were dissolved at a mixing ratio shown in Table 1 into a toluene: tetrahydro~uran mixed solvent (1 :1 mixin~ weight ratio) to form an undercoat composition. The composition was coated by a Mayer bar on ~he surface o~
a biaxially stretched polypropylene i7m ~20 ~ in thickness) 1, that had been subjected to the corona discharge treatment to have a contact an~le of 650 to water, and the coated surface wa~ dried a~ llO~C for 1 minu~e. In each ca~e, ~he amount o~
the coating after drying was 201 tD 2.5 g/m2~ Then, a topcoat composition (recipe ~) described below, comprising as the main component a vinylidene chloride-acrylic acid ester copolymer emulsion (vinylidene chloxide con~ent - 85%), was coated on the undercoated su.rface by using a Mayer bar, and the coated ! ilm was dried for 1 minute in an oven maintained a~ 115C.
The total amount o the undercoat and topcoat ~as 4.5 to 5.1 g/m . In Table 1, Comparative Examples 1 to 3 were out~ide the scope of the present ~nvention, and they are shown only for comparison. Xn Comparative Examples 2 and 3, the topcoat composition was prepared according to the reClp2 B described bnlow.
Topcoat Composition ¦Recipe A).

Vinylidene chloride/acrylic acid 97.9 parts by weight ester copolymer (85/15) emulsion Wax emulsion (melting point of ~5C) 2 parts by weight Calcium carbonate 0.1 part by weiyht ~opcoat Composition ~Recipe B): .
Vinylidene chloride/acrylic acid 97.9 p~rts by weight ester copolymer (90/I0) emulsion Wax emulsion ~melting point of 65C~ 2 parts by weight Calcium carbonate 0.1 part by weight Properties o the so obtained ~ilms ar~ shown in Table 2.

T ble 1 Underco~ Composi~ion Topcoa~ I
Compo~ition I -Amount (parts by Amount ~parts weight) of vinyl- by weight) o~
idene chloride/ chlorinated ~inyl chloride polypropylene , copol~mer . ~ .

Comparative 100 0 Recipe A
Example 1 Example 1-1 ~8 2 ~ Recipe A
Example 1-2 37 3 ~ecipe A
Example 1-3 96 4 Recipe A
Example 1-4 ~ 93 ~ 7 Recipe~
Comparative 98 : 2 ~ Recipe B I -Example Z
Comparative 97 . 3 Recipe B ~:
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The relation between the h~at-seal:Lng temperatur~ and the heat seal str~ngth, which was observed in Example 1-2 and Comparative Examples 1 and 3, wa5 shown in the drawing, in w~ich curves a, b and c illustrate results of Example 1-2, Comparative Example 1 and Comparative ~xample 3, respectively.
From these results, it will readily be understood that the film of the present invention is much superior to comparati~e films with reSpect to the low-tempexature hea~-~ealing property.
Example 2 The grafted polym~r used in this Example was prepared in the following manner.
In a l-liter capacity autoclave, 100 g of the same chlorinated polypxopylene as used in Example 1 was charged, and 500 g of toluene was added and the mixture was sufficiently agitated to form a solution, Then, 50 g of vinyl chloride and

3.5 g of benzoyl peroxide were added to the solution and the temperature was elevated to 60C. The reaction was conducted ~or 10 hours in an oxygen-free atmosphera, and the reaction at product was puri~ied by re-precipitation to obtain 115 ~ of a pol~mer.
When the vlnyl chloride content in this polymer was calculat~d ~rom results of the nuclear magnetic resonance speatrum analysis, it was found that the vinyl chloride content was 13.8~
By utili~ing the fac that ohlorinated polypropylene is soluble in carbon tetxachloride and poly~inyl chloride is hardly soluble in carbon te~rachloride, the resul~ing polymer was dissolved in carbon te~rachloride, and ~he insoluble substance was xemoved by ~iltratLon and the purified polymer was reco~ered by re-precipitation. In the purified polymer, . - 15 -.. .

~he vinyl chloricle con-kent was 12.4~, and lt was estimated ~hat the majority of vinyl chloride containea in the purified polymer was bonded to the chlorinated polypropylene in the s-tate grafted thereto~
The grated polymer prepared by the abo~e-mentioned method and the same vinylidene chloride-vinyl chloride copolymer ~inylidene chloride content = 90~) as used for the undercoat composition in E~ample 1 were dissolved at a mixing ratio indicated in Table 3 in a toluene/tetrahydrofuran mixed sol~ent ~1/1 weight ratio) to orm an undercoat composition.
The composition was coated by a Mayer bar on ~he surfaces of a bia~lally stretched polypropylene film ~thickness - 20 ~) i whic~ had been subjected to the corona discharge treatment to have a con~act an~la o~ 65 to water (Example 2-1) and a biax-ially stretched polypropylene film ~thickness - 20 ~ which had not bean subjected to the corona discharge treatment and had a conkact angle of 90 to water (Example ~-2)~ and the coated surfaces were dried at 110C for 1 minute. The amount of the coatlng after drying was 2,2 to 2.3 g/m~ in each case. Then, a topcoat composition (recipe A) was coated on each undercoated surface by a Mayer bar. The coated films were dried for 1 minute in an oven maintained at 115C. The total amount o~
the undercoat and topcoat after drying was 5.3 to 5.~ ~m~.
Properties o~ the ~o obtained coated ~ilms are shown in Table ~

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Table 4 ~ Exam~le 2-2 Corona discharge ~reatment effected not effected ~dhesive cellophane tapeaxcellenteffected test Heat seal strength (~/15 mm~ 237 ~19 Water vapor permeability5.5 5.5 ~g/m2-24 hrs) Oxygen gas permeability 19 17 ~cc/m2 2~ hrs) Transparency excellen~ excellent Example_3 The same undercoat composition and topcoat composition (recipe A) as used in Example 2 were coated on the same biaxially stretched film (su~jected to ~he corona discharge treatment and haviny a thickness of 20 ~) as used in Example 2-1, while changin~ the amounts coated of the compositions as indicated in Tables S-l and S-2. Properties of the result-ing coated film~ are shown in Tables 5-1 and 5-2.

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The same undercoat composition as used in Ex~mple 2 was coated by a Mayer bar on the surface o~ a biaxiall~ stretched film (thickness = 20 ~) which had been subjected to the corona discharge treatment ko have a contact angle of 650 to water, and the coated surface was dried at 110C ~or 1 m$nute. Then, a topcoat compo~ition ~having recipe C indicated below) in the state dissolved in mathylethyl ketone was coated on the undercoated surface by a Mayer bar, and the coated ~ilm wa~
dried for 1 minute in an oven maintained at 110C, Topcoat Composition (recipe C):
Vinylidene chloride/vinyl chloride/ 97.9 parts by weight acrylic acid ester cspolymer (30/S0/20) Wax (melting point - 60~C~ 2 parts b~ weight Calcium carhonate 0.1 part by weight ,''.

Properties of the so obtained coated ~ilm~ are shown in Table 6.
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~a~ple 5 The styrene-~ra~ted chlorina-ted polypropylene used in this Example was prepared in the following manner.
According to a customary method, isotactic polypropylene having an intrinsic viscosity of 1.0 d/dQ was dissolved in tetrachloroethylene at 120~C and ~hlorine was blo~m in the solution to obtain a chlorinated polypropyliene ha~ing a chlorine content of 30~ by wei~h~ and an intrinsic viscosity of 0.8 dQ/g.
A l-liter capacity polymerization ~essel was charged with 120 g of the so obtained chloxinated polypropylene, 0.7 Q of benzene and 120 g o~ styrene and the mixture was sufficiently agitated to foxm a solution. Then, 2.8 g of benzoyl peroxide was added to the solution, and the temperature wa5 elevated tv 70C and the reaction was carried ou~ in a nitxogen atmosphere for an appropriate time. The product was purified by re~precipi-tation. By using a calibration cur~e prepared rom an infrared absorption spectrum of a blend of chlorinated polypropylene and polystyrene, ~he styrene content in each of the resulting pol~mers was calculated. It was found that the styrene ~ontent was 3.5, 7.8, 14.6 or ~0.5%.
It wa~ construed that the majority of the polymerized styrene wa~ bonded to the chlorinated polyp~opylane in the state gra~ted thereto.
Each of the so obtained grafted polymers and a vinylidene chloride/acryloni~rile copolymer (vinylidene chloride content i-90%) were dissolved at a mixing rat1o indicated in Table 7 in a tetrahydrofuran/toluene mixed sol~ent ~ eight ra~io) to ~orm an undercoat composition. The undercoat composition was coated by a Mayer bar on the surface of a blaxially s~retched polypropylene film (having a thickness~of 20 ~) which had been .

subjected to thc corona discharge treatmen~, and the coated sur~ace was dried at 110C ~or 1 minute. The amount of the undercoat aL ter drying was 2.1 to 2.4 g/m2. ~rhen, a topcoat composition (recipe D inclicated below) was coated on the undercoated sur~ace by a Mayer bar and the coated film was dried at 115C for 1 minute in an oven. The to~al amount of the undercoat and topcoat after dryin~ was 4.6 to 5.1 g/m2.
Topcoat Composition (Recipe D) Vinylidene chloride~vinyl chloride~ 97.9 parts by weight acrylic acid ester copolymer (84/10/6) Wax (melting point - 60C) 2 parts ~y weight Calcium carbonate ~.1 part by weight Properties of the so obtained coated films are shown in Table 8.

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The grafted polymer used in this Example w~s prepared ln the ~ollowing manner. I
Isotactic polypropylene havin~ an intrinsic viscosity of 1.0 Q/g was dissolved in tetrachloroethylene at 120C and chlorine gas was blown ~n the solution to e~ect chlorina~ion, chlorinated polypropylenes having chlorine contents of 18, 25 and ~0~ by weight, respact~ely, were obtained by chan~in~
- the chlorination time. Grated p~lymer~ were prepared from these polymers in the same manner as in Example 5. The styrene contents w2re 11.0~, 10.2% and 10.6%, respectively~
Each of the so ohkained grafted polymers and ~he same vinylidene chloride/acrylonitrile copolymPr as used for the undercoat composition in Example 5 wexe dissolved at a mixing ratio indicated in Table 9 into a tetrahydrofuran~oluene mixed sol~ent ~1 :1 weight ratio) to form an undercoat compositLonO
Tha composition was coated by a Mayer ~ar on the surface o~
a biaxially stretched polypropylene film (~hickness ~ 20 y) which had been subj~cted to the corona.discharge treatment, 2Q and the coated surface wa~ dried at 110C ~or 1 minute. The amount of ~he undercoat a~ter drying was 2.3 to 2.6 ~/m2~ ' Then, in the same manner as in Example 5, the topcoat compo-sition ~recip~ ~) was coated on the undercoated surface, and the coated surface was dried. ~he total amount o~ the under-coat and topcoat was 4.5 to 5.3 g/m2. In Examples 6 4 to 6 - 6, the non~grafted chlorinated polypropylene was used.
Properties of the resulting films are shown in Table 10.

.. . . .

o D ~ O U U U O

O ~ ~O
O O O C:~ O
~ O~ o ~-rl h O ~ H
O ~
Q- h co L') O ~010 0 ~ .,~ ~ ~ aJ
O ~i ~ O ~i .~ ~0 ~ 1 ~
~1 .~ h 0 a~ O ~ o ~:!
~q ~ ~ 1:
, ~ ~ ~ ~
.~ E~ rl : ! ~.~
1;1 ~1~ S a~
8 o ~ a~ 3 o t:: ~3 ~I h U1 ~ : j ~' P ~ ':
~1 ~ ~ ~ .

~ : ~ I ' , : :

0 5. o u~
~ O ~ 0 ~ ~ :
J~ O O ~ ~

~ .

:: , :

: ~ .

.: :

u ~ ~ ~ x -V R
~ O I ~
O Pl --,~
ji ,.
o ~> R ~ u~ n o O ~ . ;
_I h Q ~

~ , : / -~ ~ ~ ~ .
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:
Q) U ~ I ~ X X

Q~ :
I N ~ er Ul ~O -X ZO

:
~ .~

. . .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A polyolefin film coated with I. an undercoat consisting essentially of a mixture of (a) polyvinylidene chloride or vinylidene chloride copolymer containing at least 88 weight percent of vinylidene chloride monomer units, and (b) a chlorinated polypropylene having a chlorine content of from 15 to 55 percent by weight and an intrinsic viscosity of from 0.3 to 3.0 d?/g, wherein intrinsic viscosity is determined by measuring the viscosity of a solution of 0.2 to 0.5 percent by weight of said chlorinated polypropylene in decalin at 135°C or a graft polymer of said chlorinated polypropylene having grafted thereto from 2 to 30 percent by weight, based on the weight of the graft polymer, of an ethyl-enically unsaturated vinyl monomer, wherein the weight ratio of a/b is from 99/1 to 90/10, and II. a top coat consisting essentially of a vinylidene chloride copolymer containing from 35 to 88 weight percent of vinylidene chloride monomer units.

A coated film as claimed in Claim 1, wherein the substrate film is selected from a group consisting of polypropylene and poly-4-methylpentene-1.

A coated film as claimed in Claim 1 wherein the intrinsic viscosity of said chlorinated polypropylene is from 0.5 to 1.5 ??/g.

Claim Page 1 4. A coated film as claimed in claim 1 wherein the substrate film is a biaxially stretched polypropylene Film.
5. A coated film as claimed in claim 1 wherein the combined thickness of the undercoat and the topcoat is from 1 to 10 microns.
6. A coated film as claimed in claim 1 wherein the weight ratio of a/b is from 99/1 to 95/5.
7. A process for preparing coated polyolefin film, which comprises coating polyolefin film with an undercoating liquid mostly consisting of a mixture of (a) polyvinylidene chloride or its copolymer containing at least 88 weight percent of vinylidene chloride monomer units and (b) a chlorinated polypropylene having a chlorine content of from 15 to 55 percent by weight and an intrinsic viscosity of 0.3 to 3.0 d?/g, wherein intrinsic viscosity determined as in claim l or a graft polymer of said chlorinated polypropylene having grafted thereto from 2 to 30 percent by weight, based on the weight of the graft polymer, of an ethylenically unsaturated vinyl monomer; wherein the weight ratio of a/b is from 99/1 to 90/10, and then with a topcoating liquid consisting mostly of a vinylidene chloride copolymer containing from 35 to 88 weight percent of vinylidene chloride monomer units.