CA1305270C - Thermoplastic elastomer composition - Google Patents

Abstract

Title of the Invention THERMOPLASTIC ELASTOMER COMPOSITION

Abstract of the Disclosure A thermoplastic elastomer composition having a low compression set and excellent weatherability com-prising an acrylate elastomer containing at least 10% by weight of a gel insoluble in methyl ethyl ketone, a vinyl chloride resin and a plasticizer. When a carboxyl-con-taining vinyl chloride resin is used as the vinyl chloride resin and a compound of a monovalent or divalent metal is included as an additional component, the composition further has excellent rebound.

Description

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This invention relates to a thermoplastic elas-tomer composition, and more specifically, to a thermo-plastic elastomer composition having a low compression set and excellent weatherability.
Acrylate elastomers find extensive use in vari-ous fields including automotive parts by utilizing their excellent thermal resistance and weatherability. In order for them to exhibit these properties, they have first to be vulcanized.
On the other hand, vinyl chloride resins con-taining plasticizers, known as flexible vinyl chloride reqins, have a flexible rubbery feel and better mold-ability, weatherability and colorability and lower costs than vulcanized rubber, and are widely used. Since, however, their compression set is higher than that of vulcaniz-d rubber, their use at high temperatures is limited~ To improve their compression set, it i8 the practic- to add a crosslinked nitrile rubber to a vinyl chloride ee~in containing a gel ~for example, Japane~e Laid-Open Patent Publlcation Nos. 215442/1983 and 51933/1984). This method certainly improves compression set, but at the same time, reduces weatherability. Hence, products obtained by it have only limited applications.
It has been desired therefore to develop a thermoplaBtic ela8tomer which can be thermoplastically processed and has compression set close to that of a vulcanized rubber and yet excellent weatherability.

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It is an object oÇ this invention to provide such a thermoplastic elastomer.
The present inventors have extensively worked in order to achieve the above object, and have now ound that a composition compeising an actylate elastomer containing a specific amount of a gel, a vinyl chloride resin and a plasticizer as essential components can be thermoplas-tically proceqsed and give molded article~ having markedly improved weatherability and compre~sion 6et.
Thu~, according to this invention, there iB
provided a thermoplastic ela~tomer composition comp~ising an acrylate elastomer containing at lea6t 10~ by weight of a gel insoluble in methyl ethyl ketone, a vlnyl chloride resin and a pla~ticizer.
~ he present inventors have also found that when a carboxyl-containing vinyl chloeide resin i8 used as the vinyl chloride in the above co~position and a compound of a monovaleDt or divalent metal is included as an addi-tional component, the composition can give molded articles having excellent rebound at high temperatures as well as excellent weatherability and compression set.
Thus, one perferred embodiment nf this invention provid~ a thermopla~tlc olastomer compositlon compci~ing an acrylate elastomer containing at lea~t 10~ by weight of a gel insoluble in methyl ethyl ketone, a carboxyl-con-taining vinyl chloride re~in, a co~pound of a monovalent or divalent metal and a pla8ticizer.

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Illustrative of the acrylate elastomer used in this invention are an ac~ylate homopolymer elastomer, an ethylene/acrylate copolymer elastomer, an ethylene/vinyl acetate/acrylate copolymer elastomer, an acrylate/acrylo-S nitrile coplolymer elastomer, an acrylate/vinyl acetate/acrylonitrile copolymer elastomer, and an acrylate/
butadiene/acrylonitrile copolymer elastomer. It is not limited to these particular examples.
A gel may be included into the acrylate elas-tomer by any suitable method, for example by copolymeriz-ing an acrylate monomer with a mono~er having a multi-plicity of double bondfi in the molecule, such as divinyl-benzene, diallyl phthalate, diallyl maleate, trimethylol-propane tri~meth)acrylate or triallyl trimellitate, in the preparation of the acrylate elastomer, or by post-treating the acrylate elastomer using a peroxide or the like to form an intermolecular cros~linkage.
The ~gel in~oluble in methyl ethyl ketone~
denotes a residue obtained by adding 0.2 g of the acrylate ela~tomer masticated for 10 minutes by a water-cooled roll to 100 ml of methyl ethyl ketone, allowing the mixture to stand at room temperature for 24 hours to dissolve the elastomer, and then filtering it through an 80-mesh wire gauze. The amount of the gel is at least 10% by weight, preferably at least 30~ by weight. If the gel content is less than 10~ by weight, the compression set of the elastomer i~ not fully improved.

~30SZ70 When acrylate elastomer containing 0 05 to 20 by weight, pceferably 0 2 to 10~ by weight, of carboxyl groups introduced therein i~ used as the acrylate elas-tomer t~e resulting composition has improved rebound at high temperatures Introduction of carboxyl groups into the acrylate elastomer may be carried out by, for example, copolymerizing a copolymerizable alpha,beta-unsaturated carboxylic acids copolymerizing an alpha,beta-unsaturated carboxylic acid estee followed by hydrolysis; or subject-ing the acrylate ela~tomer produced to addition-reaction with a carboxylic acid-containing compound A bomopolymer of vinyl chloride, or copolymer~
of a major amount of vinyl chloride and a minor amount of monomers copolymerizabl- with it may be used as the vinyl chloride re~in in the first invention ~xamples of the oth-r monomer copolymerizabl- with vinyl chloride include vlnyl ~t-r- ~u¢h a~ vinyl ac-tato and vinyl stearate, -~ olefin~ ~uch a~ thyl-n- and propyl-n-, vinyl ethers such a~ isobutyl vinyl th-r, 2-ethylhoxyl vinyl ther and lauryl vinyl ther, accylic acid esters ~uch as ethyl acrylate, n-butyl acrylate and 2-ethylh-xyl acrylate, and maleic acid ster~ such a~ dibutyl mal-ate and di-(2-ethylhexyl) mal-at- ~h- av-rage d-gcee of polymerization of the vinyl chlorid- r-sin is not particularly limited Usually, it is 500 to S,000 Vinyl chloride re~ins con-taining a gel insoluble in tetrahydrofuran may also be u~ed :,,', ' ." , ' ' ' ' , ' ~:

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The carboxyl-containing vinyl chloride re~in in the second invention may, for example, be (1) resins obtained by copolymerizing vinyl chloride with mono-carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and cinnamic acid, dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid and citraconic acid, or monoesters of dicarboxylic acids ~uch as mono-methyl maleate, monoethyl maleate, monobutyl maleate, monomethyl itaconate, monoethyl itaconate and monobutyl itaconate; ~2) copolymerizing vinyl chloride with alpha,beta-unsaturated carboxylic acid esters and hydrolyzing the products; and (3) subjecting vinyl chloride polymers produced by an ordinary method to addition-reaction with carboxylic acid-containing com-pounds.
The carboxyl group content of the carboxyl-containing vinyl chloride resin i8 usually 0.05 to 20~ by weight, prefeeably 0.2 to 10% by weight. Rebound at high temperatures is improved by adjusting the carboxyl group content to at least 0.05~ by weight. Carboxyl group contents of more than 20% by weight are insignificant and in many cases, deleterious on other properties. There is no particular limitation on the average degree of poly-merization of the carboxyl-containing vinyl chloride re8in. Usually, it is 500 to 5,000.
Plasticizers generally used in flexible applications of vinyl chloride may be used singly or in 13~5~Z7~

combination as the plasticizer in the compositions of this invention. Examples of such plasticizers include phtha-lates such as 2-ethylhexyl phthalate, di-n-octyl phtha-late, diisodecyl phthalate, dibutyl phthalate and dihexyl phthalate; straight-chain dibasic acid esters such as dioctyl adipate and dioctyl sebacate; trimellitic acid esters; polyester-type polymeric plasticizers; epoxy-type plasticizers such as epoxidized soybean oil and epoxidized linseed oil; and phosphoric acid esters such as triphenyl pho8phate and tricresyl phosphate.
Illustrative of the compound of a monovalent or divalent metal used in the second invention are oxides, hydroxides, carboxylstes ~e.g., acetates, propionates, octylates, caprylates, stearates and naphthenate~), thio-lS carboxylates, sulfonate~, and phospbates of metals such asLi~, Na~, X~, Mgl~, C8 1~ ~ Ba~+, Zn++ and Cd++. Complex salts of those metals with acetylacetone may also be cited as example8. Theso compounds may be used singly or in combination. The amount of the metal compound is pee-ferably 0.1 molar equivalent to 3 molar equivalent to thetotal amount of carboxyl groups in the acrylate elastomer and the vinyl chloride resin. It is assumed that the metal compound acts as an ionic crosslinking agent which roacts ionically with the carboxyl groups in the acrylate elastomer and the vinyl resin to crosslink the acrylate elastomer and the vinyl chloride resin.
The mixing ratio of the acrylate elastomer to : ' ' , ~3(~SZ~fO

the vinyl chloride is in the range of from 5:95 to 90:10, preferably from lo:so to 80:20. If the mixing ratio is less than 5:95, the effect of improving permanent com-pression set is not sufficient. If it exceeds 90:10, the resulting composition has reduced melt flowability and is limited in the method of processing.
The amount of the plasticizer used is properly selected depending upon the hardness of the desired pro-duct. To obtain a flexible rubber-like product, it is preferably 20 to 300 parts by weight per 100 parts by weight of the vinyl chloride resin.
In the preparation of the thermoplastic elas-tomer composition of this invention, it i8 possible, as required, to add various additives such as a stabilizer, a lubricant, a filler, an antioxidant, an ultraviolet absorber, a processing aid, a blowing agent, a pigment, a fire retardant and an impact resisting aid as in the production of general vinyl chloride resins. Other polymers may also be mixed with the composition of this $nvention.
Molded articles having a low compression set and excellent weatherability and sometimes, excellent rebound at high temperatures can be obtained by molding the thermoplastic elastomer composition of this invention in accordance with processing method~ for ordinary vinyl chloride resins, for example extrusion, compression molding, calendering, blow molding and injection molding.

' ~30SZ70 These molded articles may be suitably used as automobile windshields, cable and wire sheaths, packings, etc. which require the aforesaid properties.
The following examples illu~trate the present invention more specifically. All parts and percentages in these examples are by weight unless otherwise specified.

In each run, each of the acrylate elastomers whose types and amounts are indicated in Table 1, each of the vinyl chloride resins whose types and amounts are indicated in Table 1, 100 parts of di-2-ethylhexyl phthalate and 4 parts of dibutyltin maleate were kneaded for 10 minutes by a hot roll at 160C to form a sheet.
The sheet wa~ hot-pressed at 175C for 10 minutes to prepare a test sample having a predetermined thickness.
The test sample was tested for compression set and weatherability. Compression set i~ expre~ed by the permanet deformation ~) which occurred after the test sample wa~ compressed to an extent of 25~ at 100C for 70 hours in accordance with JIS K-6301. Weatherability was measured by subjecting the test sample to a sunshine-type weatherometer for 500 hours and then observing the state of color change in the ~ample. The results are shown in Table 1.

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(*2): Butyl acrylate homopolymer produced by using triallyl trimellitate as a gel content adjusting agent.
(*3): Copolymer of butyl acrylate and methyl methacrylate in a weight ratio of 80:20.
(~4): Copolymer of butyl acrylate and acrylo-nitrile in a weight ratio of 75:25.
~*S): Copolymer of acrylonitrile and butadiene in a weight ratio of 33:67.
~*6): O : No color change; X: Turned brown.

In eacb run, Example 1 was repeated except that 100 parts of a butyl acrylate/acrylonitrile copolymer containing 90~ of a gel insoluble in methyl ethyl ketone ~butyl acryalte~acrylonitrile=75:25 by weight), 100 parts 2~ Of a vinyl chloride resin having an average d~gree of polymerization of 2,500, 4 parts of dibutyltin maleate, and each of the plasticizers whose types and amounts are indicated in Table 2 were used. The compression sets of the resulting compositions are shown in Table 2.

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Table 2 _ Run Plasticizer Compres-_ sion set _ Type A ount ~4~

1 Di-2-hexyl phthalte 150 5s 2 Trioctyl trimellitate 100 57 o 3 Dioctyl adipate 70 58 4 Polyester-type polymeric plasticizer (PN-250, a 80 59 S product of Adeka-Argus _ _ Co., Ltd.) Compa- None 96 rison _ In each run, each of the acrylate elastomers whose types and amounts are indicated in Table 3, each of the vinyl chloride re~ins whose types and amounts are indicated in Table 3, 100 parts of di-2-ethylhexyl phthalate, 4 parts of dibutyltin maleate and magnesium acetylacetonate in each of the amounts indicated in Table 3 were kneaded for 10 m1nutes by a hot roll at 160C to form a sheet. The sheet was hot-pressed at 175C for 10 minutes to prepare a test sample having a predetermined thickne~.
Rebound, compression set and weatherability were measured on the resulting test samples. Rebound is the percentage of rebound which was measured at 140C by a ~3Q5270 Dunlop trypsometer in accordance with BS.903 Part A
8:1963. Compression set and weatherability were measured in the same way as in Example 1. The results are shown in Table 3.

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In each run, Example 3 was repeated except that 100 parts of a butyl acrylate/acrylonitrile copolymer containing 90% of a gel insoluble in methyl ethyl ketone ~butyl acryalte:acrylonitrile=75:25 by weight), 100 parts of a vinyl chloride resin having an average degree of polymerization of 2,500 and a carboxyl group content of 1.8%, 4 parts of dibutyltin maleate, each of the metal compounds whose types and amounts are indicated in Table 4 and each of the plasticizers whose types and amounts are indicated in Table 4. The rebounds and compression sets of the resulting compositions are shown in Table 4.

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In each run, each of the acrylate elastomers whose types and amounts are indicated in Table 5, each of the vinyl chloride resins whose types and amounts are indicated in Table S, 100 parts of di-2-ethylhexyl phthalate, 4 parts of dibutyltin maleate and magnesium acetylacetonate in each of the amounts indicated in Table 5 were kneaded for 10 minutes by a hot roll at 160C to form a sheet. The sheet was hot-pressed at 175C for 10 minutes to prepare a test sample having a predetermined thickness.
The rebounds, compre~sion sets and weather-abilities of the resulting samples were measured as in Example 3, and the results aee shown in Table 5.

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Note to Table 5 (*1): Triallyl trimellitate was added dueing production of the acrylate elastomer, and the gel content was adjusted by its amount. The carboxyl group content was adjusted by the amount of acrylic acid copolymerized.
~ *2): Butyl acrylate homopolymer produced by using triallyl trimellitate as a gel content adjusting agent and acrylic acid as a modifier for introduction of carboxyl groups.
1*3): Copolymer of butyl acrylate and methyl acrylate in a weight ratio of 80:20.
~ *4): Copolymer of butyl acrylate and acrylo-nitrile in a weight ratio of 75:25.
(*5): Copolymer of acrylonitrile and butadiene in a weight ratio of 33:67.
(*6)s 0 s No color change; X: Turned brown.
EXAMPL~ 6 In each run, Example 4 was repeated except that 100 parts of a butyl acrylate/acrylonitrile copolymer containing 90~ of a gel insoluble in methyl ethyl ketone ~butyl acryaltesacrylonitrile~75:25 by weight), 100 parts of a vinyl chloride resin having an average degree of polymerization of 2,500 and a carboxyl group content of 1.8~, 4 parts of dibutyltin maleate, each of the metal compound8 who8e type~ and amounts are indicated in Table 6 and each of the plasticizers whose types and amounts are indicated in $able 6 were used. The rebounds and com-pression sets of the resulting compositions are shown in Table 6.

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Claims (19)

1. A thermoplastic elastomer composition comprising an acrylate elastomer containing at least 10% by weight of a gel insoluble in methyl ethyl ketone, a vinyl chloride resin and a plasticizer, wherein the acrylate elastomer and the vinyl chloride resin are contained in a weight ratio of from 5:95 to 90:10.

2. The composition of claim 1 wherein the gel-containing acrylate elastomer is an elastomer obtained by copolymerizing an acrylate monomer with a monomer having at least two double bonds per molecule, or an elastomer obtained by forming an intermolecular crosslinkage in an acrylate elastomer by a post-treatment reaction.

3. The composition of claim 1 wherein the amount of the plasticizer is 20 to 300 parts per 100 parts by weight of the vinyl chloride resin.

4. The composition of claim 2 wherein the amount of the plasticizer is 20 to 300 parts per 100 parts by weight of the vinyl chloride resin; and the acrylate elastomer is a member selected from the group consisting of an acrylate homopolymer elastomer, an ethylene/acrylate copolymer elastomer, an ethylene/vinyl acetate/acrylate copolymer elastomer, an acrylate/acrylonitrile copolymer elastomer, an acrylate/vinyl acetate/ acrylonitrile copolymer elastomer, and an acrylate/

22a 67566-1043 butadiene/acrylonitrile copolymer elastomer.

5. A thermoplastic elastomer composition comprising an acrylate elastomer containing at least 10% by weight of a gel insoluble in methyl ethyl ketone, a carboxyl-containing vinyl chloride resin, a compound of a monovalent or divalent metal and a plasticizer.

6. The composition of claim 5 wherein the gel-containing acrylate elastomer is an elastomer obtained by copolymerizing an acrylate monomer with a monomer having at least two double bonds per molecule, or an elastomer obtained by forming an intermolecular cross linkage in an acrylate elastomer by a post-treatment reaction.

7. The composition of claim 5 wherein the carboxyl-containing vinyl chloride resin is selected from the group consisting of 11) copolymers of vinyl chloride with mono-carboxylic acids, dicarboxylic acids or monoesters of dicarboxylic acids, (2) copolymers obtained by copoly-merizing vinyl chloride with alpha,beta-unsaturated carboxylic acid esters and hydrolyzing the products, and (3) copolymers obtained by addition reaction of vinyl chloride polymers with carboxylic acid-containing com-pounds.

8. The composition of claim 5 wherein the carboxyl group content of the carboxyl-containing vinyl chloride resin is 0.05 to 20% by weight.

9. The composition of claim 5 wherein the compound of a monovalent or divalent metal is selected from the group consisting of oxides, hydroxides, carboxylates, thiocarboxylates, sulfonates, phosphates and complex salts of monovalent or divalent metals.

10. The composition of claim 5 wherein the mixing ratio of the acrylate elastomer to the vinyl chloride resin is from 5:95 to 90:10.

11. The composition of claim 5 wherein the amount of the plasticizer is 20 to 300 parts by weight per 100 parts by weight of the vinyl chloride resin.

12. The composition of claim 5 wherein the amount of the metal compound is 0.1 to 3 molar equivalents based on the carboxyl group content of the vinyl chloride resin.

13. The composition of claim 5 wherein the acrylate elastomer contains carboxyl groups.

14. The composition of claim 13 wherein the carboxyl group content of the acrylate elastomer is 0.05 to 20% by weight.

15. The composition of claim 13 wherein the carboxyl groups of the acrylate elastomer are introduced by (1) copolymerization with an alpha,beta-unsaturated carboxylic acid, (2) copolymerization with an alpha,beta-unsaturated carboxylic acid ester followed by hydrolysis, or (3) addition reaction of a carboxylic acid-containing compound with the elastomer.

16. The composition of claim 13 wherein the amount of the metal compound is 0.1 to 3 molar equivalents based on the total amount of carboxyl groups in the acrylate elastomer and the vinyl chloride resin.

17. The composition of any one of claims 6 to 9 and 11 to 16 which contains the acrylate elastomer and the vinyl chloride resin in a weight ratio of from 5:95 to 90:10.

18. An article made by molding the composition as defined in any one of claims 1 to 16, the said article having a low compression set and good weatherability.

19. The article of claim 18, which is an automobile windshield, a cable or wire sheath or a packaging.