Thermoplastic Vinyl Chloride Polymer Compositions With Improved Processing Properties

The present invention relates to thermoplastic compositions based on vinyl chloride polymers, which contain a copolymer of an acrylic acid ester or methacrylic acid ester, for the purpose of improving the processing properties.

Polyvinyl chloride is a very useful thermoplastic which, because of its good mechanical properties, its resistance to chemicals and weathering, and its high transparency, can be employed for many different purposes. However, in an unplasticized form polyvinyl chloride is very difficult to process and mold, and gives products having poor surface characteristics.

The addition of acrylic ester polymers in order to avoid these disadvantages and improve the processability has been disclosed. For calendering polyvinyl chloride, the addition of copolymers of acrylic acid esters and N-vinyllactams, according to German Pat. No. 1,081,659, has proved particularly advantageous. Such additives prevent sticking of the polyvinyl chloride to the calender bowl and thus permit trouble-free processing and the manufacture of films of improved surface quality, without at the same time excessively affecting the transparency. The addition of copolymers of acrylic acid esters and N-vinyl-lactams however does have an adverse effect on the heat stability of the polyvinyl chloride mixture. Above all, the heat stability of the polyvinyl chloride mixture deteriorates rapidly with increasing proportion of N-vinyl-lactam in the copolymer.

The deterioration of the heat stability can be avoided if an acrylic acid ester polymer which does not contain any N-vinyl-lactam as copolymerized units is added, as a processing assistant, to the polyvinyl chloride. It is true that in most cases the non-stick action of the polymer, during calendering, still persists, but the transparency of the mixture is greatly reduced and hence the material is less suitable for the manufacture of films. It is an object of the present invention to improve the processability of vinyl chloride polymers without significantly impairing the other properties of the polyvinyl chloride, above will its heat stability and its good transparency. The products obtained should in addition also have good surface characteristics.

We have found that this object is achieved if small amounts of a special acrylate copolymer or methacrylate copolymer, which contains lactone ring structures in copolymerized units, are admixed to the vinyl chloride polymer.

Accordingly, the present invention relates to thermoplastic compositions which comprise a mixture of

A. from 99.9 to 80 parts by weight of a homopolymer of vinyl chloride or a copolymer of vinyl chloride with up to 30 per cent by weight of one or more other monomers copolymerizable with vinyl chloride, and

B. from 0.1 to 20 parts by weight of a copolymer of an acrylic acid ester or a methacrylic acid ester, in which compositions the copolymer (B) of an acrylic acid ester or methacrylic acid ester contains

1. from 99.9 to 60 per cent by weight of copolymerized units of an acrylic acid alkyl ester or methacrylic acid alkyl ester of 2 to 6 carbon atoms in the alcohol component,

2. from 0.1 to 30 per cent by weight of units which contain a lactone ring structure and

3. from 0 to 39.9 per cent by weight of units of one or more other copolymerizable monomers, the percentages being based on the copolymer.

The component A of the thermoplastic compositions of the invention is a homopolymer or copolymer of vinyl chloride. The vinyl chloride homopolymers preferably have a K value (according to DIN 53,726) of from 55 to 80. Examples of monomers which are copolymerizable with vinyl chloride and which may be employed for the manufacture of the vinyl chloride copolymers are vinylidene chloride, vinyl esters, preferably vinyl acetate and vinyl propionate, acrylic acid alkyl esters and methacrylic acid alkyl esters, acrylonitrile, styrene and olefins, especially ethylene and propylene. The vinyl chloride copolymers may contain, as copolymerized units, up to 30 percent by weight of the monomers which are copolymerizable with vinyl chloride, but preferably the proportion of the comonomers does not exceed 15 percent by weight. In general, it is preferred to use homopolymers of vinyl chloride.

The homopolymers and copolymers of vinyl chloride may be manufactured in accordance with any known conventional polymerization process, eg. by polymerizing the monomers in bulk, solution, suspension or emulsion. In general, the polymerization is carried out at from 30.degree. to 75.degree. C in the presence of initiators which form free radicals, and depending on the polymerization medium conventional additives and assistants may be used. Vinyl chloride polymers which have been manufactured in aqueous suspension or emulsion are preferred.

Component B of the thermoplastic compositions of the invention is a copolymer made up of recurring units of an acrylic acid ester or methacrylic acid ester (B1) and units (B2) which contain a lactone ring structure. The lactone ring may be in the main chain of the copolymer or may be present as a side group bonded to the main chain. In addition, the copolymer of component B may optionally contain further monomers (B3) as copolymerized units. The copolymer thus consists of from 60 to 99.9% by weight, preferably from 70 to 98% by weight, of the units (B1) of the acrylic acid alkyl ester or methacrylic acid alkyl ester, from 0.1 to 30% by weight, preferably from 2 to 30% by weight, of the units (B2) which contain a lactone ring structure, and from 0 to 39.9% by weight, preferably from 0 to 28% by weight, of other copolymerized monomers (B3). Copolymers which are composed of from 95 to 80% by weight of the acrylate units or methacrylate units (B1) and from 5 to 20% by weight of the units (B2) containing a lactone ring structure, and in which the proportion of other copolymerizable monomers (B3) in the copolymer may, if present, be up to 10% by weight, are particularly advantageous.

The acrylic acid esters and methacrylic acid esters which are present as copolymerized units (B1) in the copolymer (B) to be employed according to the invention, are alkyl esters of acrylic acid or methacrylic acid, of 2 to 6 carbon atoms in the alkyl radical. Examples are ethyl acrylate, propyl acrylate, butyl acrylate and hexyl acrylate and the corresponding methacrylates. Ethyl acrylate, butyl acrylate, ethyl methacrylate and butyl methacrylate are preferred, and of these butyl acrylate and butyl methacrylate are particularly advantageous. Copolymers (B) which contain, as copolymerized units (B1), higher alkyl acrylates or methacrylates of more than six carbon atoms in the alkyl radical result in incompatibility and cloudiness of the mixture with the vinyl chloride polymers. Copolymers (B) which contain methyl acrylate or methyl methacrylate as copolymerized units (B1) are no longer very effective as processing assistants for calendering, since they only reduce the sticking of the polyvinyl chloride mixture to the calender bowls to an inadequate degree.

As already mentioned, the lactone ring can be contained in various ways in the units (B2), which contain a lactone ring structure, of the copolymer (B). Thus, the lactone ring can either occupy a side position, ie. it can be bonded, as a side chain, to the main chain of the polymer, or it can form a direct part of the polymer main chain. Usually, the lactone rings present in the copolymer have a five-membered or six-membered structure, ie. they are generally .gamma.- or .delta.-lactones.

To manufacture the copolymers (B) which contain the lactone rings in side positions, vinyl-lactones are used as a starting material. The term vinyl-lactones denotes, for the purposes of the invention, lactones which contain side chains with polymerizable olefinic double bonds. Such vinyl-lactones are adequately known and may be manufactured, eg., by reduction of unsaturated .delta.-keto-carboxylic acids with sodium borohydride, using the process described in Chemische Berichte 94 (1961), 2,401 - 2,405. Examples of such vinyl-lactones are the alkylene-.delta.-lactones, eg. the lactone of 5-hydroxy-8-decenoic acid or the lactone of 5-hydroxy-8-dodecenoic acid. To manufacture the copolymers (B) which are to be used according to the invention, the acrylic acid alkyl ester or methacrylic acid alkyl ester is copolymerized with the vinyl-lactone, in which reaction the vinyl-lactone undergoes polymerization by virtue of the olefinic double bond in the side chain, so that the lactone ring is preserved and, in the polymer, the lactone ring is present as a side group linked to the polymer main chain. Accordingly, in this case the unit (B2), containing a lactone ring structure, of the copolymer (B) is to be understood as a copolymerized unit of the vinyl-lactone.

The copolymerization of the acrylic acid ester or methacrylic acid ester with the vinyl-lactone may be carried out in accordance with conventional polymerization processes, bulk polymerization or solution polymerization being preferred. In general, the polymerization is carried out at from 30.degree. to 120.degree. C, in the presence of initiators which form free radicals, eg. the conventional peroxides or azo compounds. Of course, reaction conditions and additives which are known to cause scission or removal of the lactone ring must be avoided. The copolymerization of the acrylic acid ester or methacrylic acid ester with the vinyl-lactone can also be carried out in the presence of further copolymerizable monomers (B3). Examples of suitable copolymerizable monomers (B3) are other vinyl compounds, eg. allyl alcohols, vinyl esters, vinyl ethers, styrene, acrylonitrile, vinyl chloride and especially other acrylic acid esters or methacrylic acid esters, eg. methyl acrylate, methyl methacrylate, benzyl acrylate and the like.

The monomer ratio for the copolymerization is chosen in accordance with the desired composition of the copolymer (B). Preferably, the copolymerization of the acrylic acid ester or methacrylic acid ester (B1) with the vinyl-lactone (B2) and, if appropriate, the other copolymerizable monomers (B3) is carried out in such a way that the resulting copolymer contains from 70 to 98% by weight of acrylic acid alkyl ester or methacrylic acid alkyl ester (B1), from 2 to 20% by weight of vinyl-lactone (B2) and from 0 to 10% by weight of other monomers (B3), as copolymerized units. Particularly preferred copolymers contain from 80 to 95% by weight of acrylic acid ester or methacrylic acid ester (B1) and from 5 to 20% by weight of vinyl-lactone (B2) as copolymerized units, and no additional monomers (B3).

Copolymers (B) in which the lactone ring is directly contained in the polymer chain are preferred for use in the thermoplastic compositions of the invention. In such copolymers, the units (B2) which contain lactone rings in general have the following structure: ##STR1## where the substituents R may be hydrogen or lower alkyl. More particularly, R.sup.1 is hydrogen or methyl, but preferably hydrogen, R.sup.2 and R.sup.3 are hydrogen or substituted or unsubstituted alkyl, and may be identical or different and may together contain up to 6, and preferably up to 4, carbon atoms, it being particularly advantageous if R.sup.2 and R.sup.3 are hydrogen or substituted or unsubstituted methyl or ethyl, and more especially advantageous if at least R.sup.2, but preferably R.sup.2 and R.sup.3, is hydrogen, R.sup.4 is hydrogen or methyl, but preferably hydrogen, and R.sup.5 and R.sup.6 are hydrogen or alkyl of 1 to 4 carbon atoms, and may be identical or different, and can also be linked to one another to form a cycloaliphatic ring of 5 to 7 carbon atoms, but preferably are hydrogen or methyl or ethyl, in which case advantageously only R.sup.5 is hydrogen.

The copolymers (B) which contain the lactone ring directly in the polymer chain may be manufactured in various ways. One possible method is to copolymerize unsaturated lactones, especially .delta.-lactones, which contain a polymerizable olefinic double bond in the lactone ring, with the acrylic acid alkyl ester or methacrylic acid alkyl ester (B1) and, optionally, further monomers (B3); this copolymerization can be carried out under conventional and known conditions. However, as a rule these copolymers (B) are manufactured advantageously by copolymerizing the acrylic acid alkyl ester or methacrylic acid alkyl ester (B1) with an unsaturated alcohol or a monomer which forms such an alcohol and lactonizing the resulting copolymer during and/or after the polymerization.

For this purpose, the acrylic acid alkyl ester or methacrylic acid alkyl ester (B1) is preferably polymerized in the presence of an .alpha.,.beta.-olefinically unsaturated alcohol of the general formula ##STR2## where the substituents R.sup.2 to R.sup.6 have the meanings given above. Examples of such alcohols are allyl alcohol, butenols, such as but-1-en-3-ol, but-2-en-1-ol, but-2-ene-1,4-diol, 3-methylbut-2-en-1-ol and 3-methylbut-1-en-3-ol, pentenols, eg. pent-1-en-3-ol, 3-methylpent-1-en-3-ol and 3-methylpent-2-ene-1,5-diol, 1-vinyl-1-hydroxy-cyclohexane and others. The use of .alpha.,.beta.-olefinically unsaturated alcohols where R.sup.4 is hydrogen is preferred, and in that case the copolymerization is preferably carried out with an acrylic acid ester rather than a methacrylic acid ester. Allyl alcohol and but-1-en-3-ol have proved particularly advantageous. However, to manufacture the copolymer (B) to be employed according to the invention, the acrylic acid alkyl ester or methacrylic acid alkyl ester (B1) can also be copolymerized with a monomer which is able to form an alcohol group, ie. with monomers which, under the lactonizing conditions, form hydroxyl groups, which can then undergo lactonization with the ester groups of the acrylic acid ester or methacrylic acid ester units. Such monomers capable of forming alcohol groups are, in particular, vinyl esters, eg. vinyl acetate or vinyl propionate, and allyl esters, eg. allyl acetate.

The copolymerization of the acrylic acid alkyl ester or methacrylic acid alkyl ester (B1) with the .alpha.,.beta.-olefinically unsaturated alcohol, or the monomer which forms an alcohol group, may be carried out in accordance with conventional processes, by bulk polymerization, solution polymerization, suspension polymerization or emulsion polymerization of the monomers in the presence of initiators which form free radicals, eg. the conventional peroxides or azo compounds, advantageously at from 30.degree. to 150.degree. C, as described, eg., in German Patent No. 870,034. Bulk polymerization or solution polymerization are preferred, and for the latter the conventional solvents, eg. aromatic hydrocarbons, ethers, esters and ketones may be used. To obtain copolymers particularly rich in alcohol groups it is advantageous to take the unsaturated alcohol or the monomer which forms an alcohol group and to run the acrylic acid alkyl ester or methacrylic acid alkyl ester in slowly in step with the progress of the polymerization. The copolymerization can in that case also be carried out in the presence of other copolymerizable monomers, suitable monomers being, in particular, other acrylic acid esters or methacrylic acid esters, eg. methyl acrylate and methyl methacrylate, but also, eg., styrene, acrylonitrile and vinyl chloride.

The copolymers resulting from the polymerization of the acrylic acid ester or methacrylic acid ester with the .alpha.,.beta.-olefinically unsaturated alcohol or the monomer which forms an alcohol group, and, optionally, the further monomers, are then lactonized entirely or partially, by conventional methods, so as to arrive at a copolymer containing a lactone ring structure in copolymerized units which is employed as component B according to the invention. Suitable processes for lactonizing these copolymers are described, eg., in German Laid-Open Application No. 2,126,357 and U.S. Pat. No. 3,515,706. According to these publications, lactonizing can be effected by heating the copolymer, in the presence or absence of relatively high-boiling inert organic solvents, at not less than 100.degree. C, preferably at from 150.degree. to 250.degree. C, and removing the volatile compounds produced, if appropriate under reduced pressure. The lactonizing can be accelerated substantially by adding small amounts of conventional esterification catalysts, eg. inorganic or organic acids, such as hydrochloric acid, phosphoric acid or toluenesulfonic acid, or other esterification catalysts, eg. sodium methylate, which in general are added in amounts of from 0.01 to 0.1% by weight, based on the copolymer. If bulk polymerization or solution polymerization is used, the lactonizing may be carried out directly after the polymerization. However, depending on the chosen polymerization conditions, lactonizing may at least partially already occur during polymerization and can in that case, if necessary, be continued, to the desired degree, after the polymerization. The degree of lactonizing may be controlled by conventional methods, eg. by choice of the temperature at which the treatment is carried out, or of its duration.

The copolymers (B) manufactured in this way contain the lactone ring directly in the polymer chain and consist of units (B1) of copolymerized acrylic acid alkyl ester or methacrylic acid alkyl ester, of lactone ring units (B2) of the general structure (I) and/or (II) given above, and, optionally, of units (B3) of other copolymerized monomers. The units (B3) may be either the copolymerized .alpha.,.beta.-olefinically unsaturated alcohols, or copolymerized monomers which form alcohol groups, which have not undergone lactonization, or may be units of other monomers which have optionally been used as additional constituents during the polymerization. The composition of these copolymers (B) with the lactone ring in the polymer chain is thus determined both by the composition of the original monomer mixture and by the degree of lactonizing. Preferably, these copolymers contain from 70 to 98% by weight of the acrylate or methacrylate units (B1), from 2 to 30% by weight of the lactone ring units (B2), and up to 28% by weight, and preferably up to 10% by weight, of the units (B3) of the other monomers. The use of copolymers comprising from 80 to 95% by weight of units (B1), from 5 to 20% by weight of units (B2) and optionally up to 10% by weight of units (B3) is particularly advantageous.

To manufacture the thermoplastic compositions of the invention, the acrylic acid ester or methacrylic acid ester copolymer containing lactone ring structures in copolymerized units (component B) is mixed with the vinyl chloride polymer (component A). Mixing of the component can be effected in various ways, by conventional methods, eg. by mixing the solid components on conventional mixing equipment, eg. extruders, kneaders or mills, or by mixing solutions or aqueous dispersions of the individual components and then removing the solvent or dispersing agent by conventional methods.

The mixtures should contain from 99.9 to 80 parts by weight, preferably from 99.5 to 95 parts by weight, of component A, and from 0.1 to 20 parts by weight, preferably from 0.5 to 5 parts by weight, of component B. Copolymers having a weight average molecular weight (determined by viscosity measurements) of from 10,000 to 50,000 are employed preferentially as component B. However, copolymers (B) having a higher molecular weight, eg. up to 100,000 or above, may also be employed. Furthermore, the thermoplastic compositions can contain the conventional additives for vinyl chloride polymers, eg. stabilizers, fillers, colorants and the like.

The thermoplastic compositions of the invention may be processed by conventional thermoplastic processing methods, eg. extrusion and calendering, and may be used for the manufacture of sheets, films and the like. The compositions of the invention exhibit good processability and show no tendency to stick to the calender bowls during calendering. Moldings manufactured from the thermoplastic compositions have good surface characteristics; films are of good quality and good transparency. A deterioration of the heat stability of the vinyl chloride polymers, such as is found when polyvinyl chloride is mixed with an acrylate/vinyl-lactam copolymer, is not observed in the case of the thermoplastic compositions of the invention. The other advantageous processing characteristics of polyvinyl chloride are also preserved.

In the Examples, parts and percentages are by weight

100 parts of butyl acrylate are polymerized in the presence of 10 parts of the .alpha.,.beta.-olefinically unsaturated alcohols shown in Table 1, using 0.3 part of azodiisobutyronitrile and 0.4 part of ditert.-butyl peroxide, in the course of about 5 hours at about 110.degree. C. After distilling off the volatile constituents, the residue is diluted with methanol to about 60% solids content. The resulting copolymer contains about 60% of the copolymerized unsaturated alcohol in a lactonized form.

100 parts of suspension polyvinyl chloride of K value 61 and 5 parts of the copolymer (calculated as solids) are mixed on a mill, the conventional stabilizers being added. To determine the heat stability, a part of the mill hide is stored in an oven at 180.degree. C. To determine the transparency, the mixture is pressed to give 4 mm thick sheets, and the light transmission at 450 nm is measured. The effect on the calendering characteristics was assessed from the tendency of the mixture to stick to the calender bowls, minimum sticking being desirable. The results are summarized in Table 1.

100 parts of a suspension polyvinyl chloride of K value 61 are mixed with 5 parts of an acrylic ester polymer and with the conventional stabilizers on a mill, as described for Examples 1 to 5. In the present case, however, it is not an acrylic ester copolymer containing lactone ring structures in copolymerized units, in accordance with the invention, which is used, but instead, in Comparative Experiment A, a homopolymer of butyl acrylate, manufactured in emulsion, and, in Comparative Experiment B, an acrylic ester/N-vinyl-lactam copolymer according to German Patent No. 1,081,659, which has been manufactured by polymerizing a mixture of 100 parts of butyl acrylate and 10 parts of N-vinylpyrrolidone under the conditions indicated for Examples 1 to 5. The properties of these mixtures are also shown in Table 1.

It is found that the polyvinyl chloride mixtures show no tendency to stick to the processing equipment, adequate transparency and adequate stability on storage only if the copolymers to be employed according to the invention, which contain lactone ring structures in copolymerized units, are added.

Example 1 is repeated, but in the manufacture of the copolymer, instead of using 100 parts of butyl acrylate, 100 parts of the monomers or monomer mixtures indicated in Table 2 are polymerized in the presence of 10 parts of but-1-en-3-ol. The properties of the corresponding polyvinyl chloride mixtures are shown in Table 2.

Example 1 is repeated, but in the manufacture of the copolymer, instead of using 100 parts of butyl acrylate, 100 parts of the monomers or monomer mixtures indicated in Table 2 are polymerized in the presence of 10 parts of but-1-en-3-ol, so that the resulting products are not the copolymers to be employed according to the invention. The properties of the corresponding polyvinyl chloride mixtures are also shown in Table 2.