CA1083749A - Vinylidene chloride copolymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Copolymers comprising at least about 88 weight %
vinylidene chloride, about 2 to 4 weight % methacrylonitrile, about 3 to 6 weight % methyl methacrylate, and less than about 5 weight % methacrylic acid, the weight ratio of meth-acrylonitrile to methyl methacrylate being less than 1, use-ful as heat-sealable barrier coatings for transparent packag-ing films such as regenerated cellulose and polyester.

Description

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~; Background of the Inventlon - This invention covers improvements ln and relating ... ~....................................................................... .
~ to vinylidene choride polymers~ and more particularly~ to such .:.
polymers containing units o~ methacrylonltrile, methyl methacrylate, and methacrylic acid.
-~- Brltish Patent 1,333~566 to H:Lnkamp et al. describes .~.. . .
copolymers containing 88 to 93 mole percent vinylidene chlorlde -S (VC12) and 12 to I mole percent o~ another monomer. A wide ', variety o~ other comonomers are mentioned among which are methacrylonitrlle (MAN~, methyl methacrylate (MMA) and ~ methacryllc acid (MAA), which can be used alone or in ,~ comblnation with each other. Especially mentioned are polymers wherein the mole ratlo of MAN to MMA is 2 to 1, with or with-~:, ' out small amounts of acrylic or ltaconlc acld. The disclosure ;~ teaches the use Or a ca~alyst to iniitate polymerization and ,, ,".I
~ specifies that the reaction temperature be maintained between Xi 50 to 65C- The polymers are alleged to have good barrier ~"I properties and enhanced solubility in organic solvents.
U. S. Patent 3,310,514 to Troflmow et al, describes , copolymers containing 80 to 94 weight percent VC12, 1 to 5 welght percent MAN, and at least a third comonomer which can ,l be MMA. Copolymers containing methyl acrylate and having ratio~ Or MAN to MMA of less than one are disclosed along with others having MAN to MMA ratios o~ one and greater than qi one. The polymerizatlon is catalyst initiated and the ~i reaction temperature is 35C. The polymer is described as ;~ havln~ improved barrier properties and decreased tendency ,~ toward blocking.
`, U. S. Patent 2,570,478 to Pitzl describes copolymers - 30 containing 35 to 96.5 ~eight percent vinylidene chloride, ,', , :, ',1 .

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~` 3 to 40 weight percent of at least one other comonomer which ~. i may include MAN and MMA, and 0.5 to 25 weight percent of i~ itaconlc acld. The polymers~ when used as coatlngs, are described as having improved adherence and anchorage to base films and improved heat-seal characteristics.
Summary o~ the Invention According to the present invention, there are provided improved copolymers of vinylidene chloride, .. ...
methacrylonltr~le, methyl methacrylate and methacrylic acid ` 10 which comprise at least about 88% by weight vinylidene :
chloride, about 2 to 4% by weight methacrylonitrile, about

3 to 6% by weight methyl methacrylate, and less than about 5% by weight methacrylic acidg the welght ratio of : ,:',' ~ methacrylonitrile to methyl methacrylate being less than 1, . .
the copolymer having been prepared by a thermally initiated . .:
polymerization reaction at a temperature within the range Or about 70 to 85C.
Preferred copolymers Or the lnvention are those having no more than about 92% by weight vinylidene chloride, and about 2.5 to 4.5~ by weight methacryl~c acid.
The invention also includes coated films wherein i~ the above copolymers are the principal component of coatings on a base film.

Detailed Descriptlon o~ the Invention The polymers of the invention constitute improved heat-sealable barrier coatings for transparent packaging films.
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They possess a combination of propertles whlch makes them especially useful for this purpose. To begin with, they have excellent barrier properties in respect to water vapor and oxygen.

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`~ They also have excel}ent heat-seal characteristics . ~....................................................................... .
at both ambient and high humidities. A particular advantage i`'~
o~ these polymers is that they possess a broad heat ~ealing range, exhibiting good heat seals at low sealing temperatures . ~ , .
when compared to those of previously known polymers of closely -~ related composition. For example, the polymers of the inven-tion provide consistently good heat seals at temperatures as ,......................................................................... .
- low as 90C.~ whlle slmilar copolymers having an MAN to MMA
ratio greater than 1 do not do so.
: ,, Furthermore, of the ~our monomers which are used ~o make the instant copolymer~, the most expenslYe one is methacrylonitrile. Accordlngly, the polymers of the invention, ,.....
~ which have an MAN/~MA ratlo o~ less than 1 have an economic :i advantage over closely related polymers having an MAN/MMA
~; ratio of greater than 1. That the instant polymers provide property advantages at lower cost is a significant advance.
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~ Additionally, while it is known to incorporate ... .
monomers containing rree carboxylic acld groups into inylldene chloride copolymers ~or the purpose of impro~ing ;j~ 20 their adherance to base films under both wet and dry conditions and their heat-sealing characterlstics, the instant copolymers whlch employ methacrylic acld (MAA) for this purpose o~er advantages over closely related copolymers whlch contain itaconlc acid (IA) or acrylic acld ~Ad).
For example, polymers contalning MAA can be made at higher productlon rates than those containing IA, because IA acts as a mild polymerization inhibitor. Accordlngly, MAA can be lncorporated in greater amounts than IA, which is ordlnarlly used at levels below 0.5% because of lts lnhlblting erfect, and thus polymers containing MAA can ... .

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attain better and more consistent improvement in adherence `; characteristics. Also, polymers containing MAA possess ~.
improved solubility over those conta~ning IA, which may be ,,~;
due in part to the fact that when IA ls used an accumulation of unreacted monomer develops and subsequent drifts in ;.
composltion occur, while such is more easily avolded with MAA. ~urther, polymers containing MAA have better barrier properties than those containlng AA, for equivalent amounts ; o~ the two.
The polymers o~ the inventlon can be made by suspenslon polymerlzation in water, uslng an emulsi~ier to ~- aid in dispersing the monomers and to stabilize the resulting r,, polymer emulslon, wlth thermal initiation o~ polymerlzation ``; at 70 to 85C. Operable catalysts include the known persul~ates~
peroxides and azo initiators, and are generally used in an amount of about 0.1 to 0.5% by weight o~ the monomers to be ; polymerized.
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c The polymers can be coated onto base ~ilms either -;~-*~ directly by dlspersion-coating with the aqueous dispersion so made (usually 30 to 50% solids), or by solution coatlng techniques a~ter isolation of the polymer from the aqueous dispersion and dissolution in an organic solvent (ordinarily 16 to 21% by weight solutions), followed by dryin~, such as ; with hot air or infrared heaters. In either case, the ~ ;
coating composition can be applied to either one or both sides of the substrate using any conventional coating technique including, for example, kiss coating, doctor rolls, gravure rolls, immersion coating techniques, spraylng and the like, with or without such expedients as Mayer rods or air doctor knives. In the case o~ an aqueous dispersion, :~ :
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, ~ within a few days after preparation, excellent coatings have `~ been prepared with these dispersions after storage for ".,-; several months. The coating ~hlckness should be such as to give a uniform and continuou~ distribution of the polymer in ~; the range of about 0.5 to 20 grams per square meter.
It is generally beneficial to incorporate, as is ! ,: i,/, known in the art, one or more of various waxes, such as carnauba, candelilla, or microcrystalline paraffin wax, and finely divlded particulate materlals, such as talc, silica, alumino silicates, polyvinyl chloride or polystyrene particles, ~or the purpose o~ improving the surface properties of the film, such as coefficlent of friction and winding characterlstics.
The copolymers of the invention are useful ~or coatlng films of organic polymers in general, and are especlally useful as coatings for regenerated cellulose films and for polyester films, particularly oriented polyethylene . ~ . .
terephthalate. Other base films, for example, polyethylene, polypropylene, ionomer and nylon, especially such films when oriented, can also be used.
Test Methods In the examples to follow~ the coated films were evaluated with the following test methods.
Heat seal strength is measured by cutting a piece the coated film 4 inches by 10 inches with the grain or ~; machine direction of the film running ln the long dimension ~ of the sample into 2 pieces 4 inches by 5 inches each. The ;~ 2 pieces are superimposed so that opposite surfaces are in .
contact and then sealed together at each end at rlght angles to the grain by applying a 1 inch wlde sealing bar under ,.' . .

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A ~ ~ care~ully controlled conditions o~ -temper&ture ~100,110, or 120C. as indicated), preæ~ure (5 p~s.i.~ and contac-t tlme (1/4 second). The sealed sheet~ are then cut in hal~
at right angles to the gr~in. From the center o~ each o~
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the two resulting piecesg two 1 inch wide ~trip~ parallel to .:
~ the grain are cut. The re~ulting 1~ set~ of strips are :. ~
tested by opening each set at the ~ree end, placing them in a Suter*testing m~chine, and pulling them apart at a rate o~
20 inches per minute. The highest force in grams re~uired to pull the s-trips apart ls ta~en as a mea6ure o~ the heat ~eal bond strength. Heat ~eals are measured on the coated ; ~ilm as is, and/or a~ter conditloning rOr 16 hours a-t 35%
or 81~ relative humidity (RH), the latter test belng a more severe test of the quality of the ~ilm coating.
IPV or initial permeability value ~s a ~ea~ure o~
the water vapor permeability of the coated ~ilm using the tes-t set forth in U.S. Patent 2~147,180 isæued February 14g 1939. me IPV is a measure o~ the grams o~ water permeating ~, .. . .
; through 100 square meters o~ ~ilm per hour at 39.5C.
O~ygen permeability (OPV) was measured uæing an "Ox-tran* 100" apparatus commercially available from Modern ; Controls, Inc.
The ~ol}owing e~ampl~s are speci~ic embodiment~ o~
the invention, wherein all parts and percentages are by weight unless otherwise indicated, Example 1 A mixture o~ 306 g of sodium dodecyl sulfate in 3800 g o~ diætilled water was heated to 75C in a stirred glass-lined autoclave under a nltrogen atmosphere, and 1.8 g o~ ammonium persul~ate in ~00 g o~ water was added. A~ter three minutes the ~ollowing monomer mixture was added at the * denotes trade mark .. :

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rate of 12 g/min., the temperature being controlled at . .
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~ onomers Wei~ht~ ) Percent - Vinylidene Chloride 2373 89 Methacrylonitrile 80 3 ` Methylmethacrylate 134 5 Methacrylic Acid 80 3_ Total 2667 100.0 ~"~
~- After all the monomer mixture was added, the pressure was released during about 2 minutes and the dispersion was cooled to room temperature.
~, The polymer was lsolated from part of the dispersion by freezing at 0C, thawing, washing the polymer several times ';, with water, and finally drying to a residual mositure level ,~ of less than 1%.
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A coating bath o~ the polymer in coating solvent, 65/35 tetrahydrofuran (THF~/toluene by weight, was prepared , ~;,. . .
; by slurrylng 240 g of the polymer in 476 ml o~ toluene at . ., ., 35-40~C and then addlng 860 ml o~ THF to achlenve the 65/35 :. !
~ 20 ratlo; 4.~ g of behenic acid and 1.5 g of talc (Mistron*
. . , , HG0;55) were added to the bath. Polymer solids content in the bath was 17.3% by weight.
Coated regenerated cellulose film was made by dipping a regenerated cellulose base sheet in the coating bath and removlng excess ba~h by passing the coated ~ilm j,! through doctor rolls. The film was dried by passing heated .,; . .

~1 air over the surface.
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The coated ~llm was evaluated in accordance with the test methods described above, and found to have the properties summarized ln the table.
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--~ Examples 2-5 . ~
: Four additlonal polymers according to the invent~on were prepared and isolated similarly to that of Example 1, and further similarly coated onto regenerated cellulose film. ~ .
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;- summarized in the table. .
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; . Ex~ le 6 , i . , To part of the aqueous dispersion o~ 89/3/5/3 YC12/MAN/~/MAA polymer prepared in Example 1 was added . su~icient 10% aqueous dispersion of carnauba wax and additional water to provide a 36~ solids dispersion having ::~ lO 1% by weight carnauba wax based on the polymer weight. The -resulting dlspersion was coated onto biaxially oriented poly- :~
ethylene terephthalate film and dried. The proper~ties of the :
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; Coatlng Weight 4.9 g~m2 IPV 26 g/lOOm2/hr OPV (dry) 0.5 cc/lO0 in2/24 hr . (wet) l.0 cc/lO0 in2/24 hr : Heat Seal (l/4 sec, 5 psi) (g/inch of seal width) -,; 140 , 35% RH 235 140 , 81% RH 250 '`,:
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Claims (5)

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

1. In a copolymer of vinylidene chloride, methacrylo-nitrile, methyl methacrylate, and methacrylic acid, wherein the weight percentage of vinylidene chloride units is at least about 88%, the improvement wherein:
(a) the weight percentage of methacrylonitrile units is about 2 to 4%, (b) the weight percentage of methyl methacrylate units is about 3 to 6%, and (c) the weight percentage of methacrylic acid units is less than about 5%, the weight ratio of methacrylonitrile units to methyl methacrylate units being less than 1, said copolymer having been prepared by a thermally initiated polymerization reaction at a temperature within the range of about 70° to 85°C.

2. The copolymer of claim 1 wherein the weight percentage of vinylidene chloride units is no greater than about 92%, and the weight percentage of methacrylic acid units is about 2.5 to 4.5%.

3. A coated film comprising a base film of an organic polymer having on at least one side thereof a coating comprising a copolymer of claim 1.

4. The coated film of claim 3 wherein the base film is a regenerated cellulose film.

5. The coated film of claim 3 wherein the base film is an oriented polyethylene terephthalate film.