Vulcanizable elastomer composition

Abstract: A vulcanizable elastomer composition comprising an epoxy group-containing elastomer, and blended there­ with, (l) an organic compound having at least two bonds of the following formula wherein X and Y are both oxygen or sulfur atoms, or one of X and Y is an oxygen atom and the other is a sulfur atom, in the molecule, and (2) a quaternary compound selected from quaternary ammonium salts and quaternary phosphonium salts, and optionally (3) a compound having one >N- -N< bond wherein Z represents an oxygen or sulfur atom in the molecule.

Description: This invention relates to a vulcanizable epoxy group-containing elastomer composition. More specifically, it relates to a curable epoxy group-containing elastomer composition having superior processing stability (scorch stability) and storage stability, rapid vulcanizability, excellent compression set and excellent heat aging resistance. Polyamines, diamine carbamates, ammonium salts of organic carboxylic acids, dithiocarbamate salts, and imidazoles are generally in widespread use as vulcanization systems for epoxy group-containing elastomers having epoxy groups as crosslinking sites. With polyamines or diamine carbamates, however, premature cure is difficult to inhibit, and the vulcanizable composition has poor storage stability. When ammonium salts of organic carboxylic acids, dithiocarbamate salts or imidazoles are used, the resulting vulcanizable compositions have good processing stability and storage stability, but require post-vulcanization for relatively long periods of time since the rate of vulcanization is slow. FR-A-2 567 899 describes a vulcanizable elastomer composition comprising an epoxy group-containing elastomer, a polycarboxylic acid and quaternary ammonium or phosphonium salts. DE-A-1 942 895 describes the use of an acyl substituted urea derivative as a vulcanizing agent of polyepoxy compounds. DE-A-1 912 281 discloses a process to produce a denatured linear epoxide group-containing adduct which is a precursor of a resin. This adduct is produced by heating a low molecular weight polyepoxide compound having epoxide group at the molecular terminal, and a mononuclear N-heterocyclic compound. In order to solve these problems, the present inventors extensively worked on vulcanization systems for elastomers having epoxy groups as crosslinking sites. This work led to the discovery of a vulcanization system composed of a polycarboxylic acid and a quaternary ammonium salt and/or a quaternary phosphonium salt (US-A-4 650 834). The present inventors furthered their work on various vulcanization systems in order to improve the performance of this vulcanization system. Consequently, the present inventors have found that when a vulcanization system composed of a low-molecular-weight organic compound having specific bonds in the molecule and a quaternary ammonium salt and/or a quaternary phosphonium salt is used, there can be obtained better processing stability (scorch stability) and storage stability than in the case of using the previously discoverd vulcanization system, and excellent rapid vulcanizability, compression set and heat aging resistance. Thus, according to this invention there is provided a vulcanizable elastomer composition comprising an epoxy group-containing elastomer, and blended therewith (1) an organic compound having at least two bonds of the following formula wherein X and Y are both oxygen or sulfur atoms, or one of X and Y is an oxygen atom and the other is a sulfur atom, in the molecule, and (2) a quaternary compound selected from quaternary ammonium salts and quaternary phosphonium salts. The epoxy group-containing elastomer used in this invention is an elastomer which can be obtained by (1) epoxidizing an elastomer, or (2) copolymerizing 0.1 to 10% by weight, preferably 0.5 to 3% by weight, of a monomer containing an epoxy group as a crosslinking site and 90 to 99.9% by weight, preferably 97 to 99.5% by weight, of at least one monomer having a polymerizable terminal vinyl or vinylidene group by a known polymerization method such as emulsion polymerization, suspension polymerization, solution polymerization or bulk polymerization. Examples of the epoxy group-containing monomer used as a crosslinking site are glycidyl acrylate, glycidyl methacrylate, vinyl glycidyl ether, allyl glycidyl ether and methacryyl glycidyl ether. Glycidyl acrylate and glycidyl methacrylate are peferred. Examples of the monomer having a terminal vinyl or vinylidene group copolymerizable with the epoxy group-containing monomer include acrylates and corresponding methacrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, n-octyl acrylate, methoxymethyl acrylate, methoxyethyl acrylate and ethoxyethyl acrylate; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; vinyl ketones such as methyl vinyl ketone and ethyl vinyl ketone; vinyl aromatic compounds such as styrene, alpha-methylstyrene and vinyltoluene; conjugated dienes such as butadiene and isoprene; alpha-monolefins such as ethylene, propylene and 1-butene; vinyl monomers having a hydroxyl group such as beta-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; and vinyl and vinylidene monomers containing a nitrile group such as acrylonitrile, methacrylonitrile and betacyanoethyl acrylate. These monomers may be used singly or in combination with each other. Specific examples of the elastomer containing an epoxy group include epoxy group-containing acrylate copolymer elastomers, epoxy group-containing ethylene/vinyl acetate copolymer elastomer, epoxy group-containing ethylene/acrylate copolymer elastomers, epoxy group-containing ethylene/vinyl acetate/acrylate copolymer elastomer, epoxy group-containing ethylene/propylene copolymer elastomer, epoxy group-containing acrylate/acrylonitrile copolymer elastomers, epoxy group-containing butadiene/acrylonitrile copolymer elastomer, epoxy group-containing butadiene/styrene copolymer elastomer, epoxy group-containing butadiene/acrylonitrile/acrylate copolymer elastomers. The organic compound having at least two bonds of the formula wherein X and Y are as defined hereinabove, in the molecule which is used as a vulcanizer in this invention is a heterocyclic, aromatic or aliphatic compound having the aforesaid bonds. The possession of at least two such bonds means not only the presence of at least two such bonds independently from each other, but also the presence of at least two such bonds as a unit as in the case of The above bonds may also exist outside the ring as substituents on the heterocyclic compound. Examples of the heterocyclic compound include parabanic acid, alloxan, alloxantin, alloxan-5-oxime, barbituric acid, 5-hydroxybarbituric acid, 5-benzalbarbituric acid, 5-aminobarbituric acid, 5-hydroxyiminobarbituric acid, 5,5-diethylbarbituric acid, 5-ethyl-5-phenylbarbituric acid, 5-(1-methylbutyl)-5-(allyl)barbituric acid, 5,5-diallylbarbituric acid, isocyanuric acid and pseudouric acid, and compounds resulting from replacing the oxygen atom of of the above heterocyclic compounds by a sulfur atom, such as 2,4-dithiobarbituric acid and 2-thiobarbituric acid. Examples of the aromatic compound are pyromellitic diimide, mellitic triimide and 1,4,5,8-naphthaldiimide, and the corresponding thioimides. Examples of the aliphatic compound are triuret, 1-methyltriuret, 1,1-diethyltriuret and tetrauret and the corresponding thiourets. The organic compound (1) may be added during or after the polymerization reaction for forming the epoxy group-containing elastomer. Alternatively, it may be added to the elastomer together with other compounding chemicals such as a reinforcing agent by a kneader of the type normally used in the rubber industry. The amount of the organic compound (1) used is usually 0.1 to 10 parts by weight per 100 parts by weight of the elastomer, and the optimal amount is selected from the above range from the standpoint of the rate of vulcanization, the mechanical properties and compression set of the vulcanizate. If it is less than 0.1 part by weight, the resulting vulcanizate has a low crosslinking density and cannot be practical. If, on the other hand, it exceeds 10 parts by weight, the rate of vulcanization of the elastomeric composition is markedly low, and no vulcanizate is obtained which is practical. The preferred amount of the organic compound (1) is 0.2 to 5 parts by weight. The quaternary ammonium salt and the quaternary phosphonium salt used in this invention are compounds represented by the general formulae wherein each of R₁, R₂, R₃ and R₄ represents a hydrocarbon group having about 1 to 25 carbon atoms, such as an alkyl, aryl, alkylaryl or polyoxyalkylene group, provided that two or three of these groups R₁ to R₄ may form a heterocyclic structure together with the nitrogen or phosphorus atom; and X represents an anion derived from an inorganic or organic acid in which acidic hydrogen is bonded to halogen or oxygen. Examples of preferred anions are Cl, Br, I, HSO₄, H₂PO₄, P₅COO, R₅OSO₃, R₅SO and R₅OPO₃H (R₅ is the same hydrocarbon group as R₁ to R₄). Specific examples of the quaternary ammonium salt include tetraethyl ammonium bromide, tetrabutyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium iodide, n-dodecyltrimethyl ammonium bromide, cetyldimethylbenzyl ammonium chloride, methylcetyldibenzyl ammonium bromide, cetyldimethylethyl ammonium bromide, octadecyltrimethyl ammonium bromide, cetyl pyridium chloride, cetyl pyridium bromide, 1,8-diaza-bicyclo(5,4,0)undecene-7-methyl ammonium methosulfate, 1,8-diaza-bicyclo(5,4,0)undecene-7-benzyl ammonium chloride, cetyltrimethyl ammonium alkylphenoxypoly(ethyleneoxy)ethyl phosphate, cetyl pyridium iodide, cetyl pyridium sulfate, tetraethyl ammonium acetate, trimethylenzyl ammonium benzoate, trimethylbenzyl ammonium p-toluenesulfonate and trimethylbenzyl ammonium borate. Examples of the quaternary phosphonium salt include triphenylbenzyl phosphonium chloride, triphenylbenzyl phosphonium bromide, triphenylbenzyl phosphonium iodide, triphenylmethoxymethyl phosphonium chloride, triethylbenzyl phosphonium chloride, tricyclohexylbenzyl phosphonium chloride, trioctylmethyl phosphonium dimethylphosphate, tetrabutyl phosphonium bromide, and trioctylmethyl phosphonium acetate. The quaternary ammonium salts or the quaternary phosphonium salts may be used singly or in combination. They may be used usually in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the epoxy group-containing elastomer. The optimal amount of the quaternary ammonium salt or the quaternary phosphonium salt may be selected from the above range from the standpoint of the rate of vulcanization, processing stability, storage stability, and the mechanical properties and compression set of the vulcanizate. If it is less than 0.1 part by weight, vulcanization hardly proceeds. On the other hand, if it exceeds l0 parts by weight, the rate of vulcanization becomes too fast, and the processing stability and storage stability are impaired. The preferred amount of the quaternary ammonium or phosphonium salt is 0.1 to 5 parts by weight. Thus, according to this invention, there is further provided a vulcanizable elastomer composition comprising an epoxy group-containing elastomer, and blended therewith, (1) an organic compound having at least two bonds of the following formula wherein X and Y are both oxygen or sulfur atoms, or one of X and Y is an oxygen atom and the other is a sulfur atom, in the molecule, (2) a quaternary compound selected from quaternary ammonium salts and quaternary phosphonium salts, and (3) a compound selected from urea compounds and thiourea compounds. The elastomer composition of this invention having such a vulcanization system incorporated therein has further improved processing stability and storage stability. Examples of the compound (3) include aliphatic ureas such as urea, N-methylurea, N-ethylurea, N,N-dimethylurea, N,N-diethylurea, N,N'-diethylurea, N,N'-ethylideneurea, N-acetylurea, N-acetyl-N'-methylurea, N,N'-dimethylolurea, tetramethylurea, carbamylurea and carbamoylcarbamide acid and the corresponding aliphatic thioureas; aromatic ureas such as phenylurea, benzylurea, N-ethyl-N'-phenylurea, N,N'-diphenylurea, N,N-diphenylurea, N-acetyl-N-phenylurea, N-benzoylurea, tetraphenylurea, N,N-dimethyl-N',N'-dichlorophenylurea, and the corresponding aromatic thioureas; and heterocyclic ureas such as ethyleneurea, glycolylurea, dimethylparabanic acid, benzoylimidazolone and 5-methyluracil and the corresponding heterocylclic thioureas. These compounds (3) may be used singly or in combination in an amount of usually 0.1 to 10 parts by weight per 100 parts by weight of the epoxy group-containing elastomer. The optimal amount of the compound (3) is selected from the above range from the standpoint of processing stability and the mechanical properties and compression set of the vulcanizate. If it is less than 0.1 part by weight, the effect of adjusting the rate of vulcanization is not sufficient. On the other hand, if it exceeds 10 parts by weight, the rate of vulcanization is extremely slow, and is undesirable in practical applications. The preferred amount of the compound (3) is 0.1 to 5 parts by weight. The composition of this invention is prepared by mixing the epoxy group-containing elastomer with the vulcanization system composed of the organic compound (1) and the quaternary compound (2) and optionally the compound (3) with a reinforcing agent, a filler, a plasticizer, an antioxidant, a stabilizer, a processing aid, etc. which are normally used in the rubber industry by means of ordinary kneaders. The composition is molded into a shape conforming to the purpose of use, and then vulcanized to form a final product. Vulcanization is carried out usually at a temperature of at least 120°C, preferably about 150 to 220°C, for about 1 to 30 minutes. The vulcanizable elastomer composition of the invention has excellent processing (scorch) stability and storage stability, and shows excellent performance in respect of rapid vulcanizability, and the mechanical properties, compression set and heat aging resistance of the vulcanizate. Conventional vulcanization systems for the epoxy group-containing elastomer normally require post-vulcanication for relatively long periods of time. Such post-vulcanization may be omitted or drastically shortened in the present invention because the vulcanization system in accordance with this invention can give a vulcanizate having excellent compression set. Vulcanizates of the epoxy group-containing elastomer obtained by using the vulcanization system in accordance with this invention have superior properties such as heat aging resistance, compression set and water resistance, and can be effectively used as various sealing materials (such as gaskets, O-rings, packings and oil seals), various hoses, belts and rolls by utilizing these desirable properties. The following examples illustrate the present invention more specifically. In these examples, all percentages and parts are by weight. Figs. 1 to 3 of the accompanying drawings are cure curves measured in Example 1. The numbers attached to the curves indicate run numbers. EXAMPLE 1 In each run, 100 parts of epoxy group-containing acrylate copolymer elastomer A (having the composition shown in Table 1) synthesized by an ordinary emulsion polymerization method, 1 part of stearic acid, 60 parts of MAF carbon black (Seast 116, a product of Tokai Carbon Co., Ltd.), 1 part of an amine-type anti-oxidant (NAUGARD 445, a product of Uniroyal Inc.) and a predetermined amount of each of the various vulcanizers indicated in Table 2 were kneaded by means of a 6-inch roll to prepare a composition. The Mooney scorch time of the resulting composition was measured in accordance with JIS K-6300. The composition was also press-cured at 170°C for 20 minutes, and then post-cured for 4 hours in a Geer's oven at 150°C. The properties of the resultilng vulcanizate were measured in accordance wiht JIS K-6301. To evaluate the storage stability of the composition, its Mooney scorch time was measured after it was left to stand at room temperature for 4 weeks. The results are summarized in Table 3. The cure curves at 1.70°C of the compositions obtained in Example 1, which were measured by an oscillating disc rheometer (made by Toyo Seiki K. K.), are shown in Figures 1 to 3. These results show that the vulcanization systems in accordance with the present invention had better scorch stability than the conventional vulcanization system (Run No. 13) and also possessed rapid vulcanizability. It is also seen that the vulcanization characteristics of comparative compounds (Runs Nos. 11 and 12) having only one bond in the molecule are poor. The compositions comprising the vulcanization systems of this invention showed a vulcanization behavior not greatly different from the as-prepared compositions even after they were left to stand at room temperature for 4 weeks, and this indicates excellent storage stability. Furthermore, the vulcanization systems in accordance with this invention show excellent compression set values even after press curing at 170°C for as short as 20 minutes. This indicates that post-curing can be omitted. EXAMPLE 2 In each run, 100 parts of the epoxy group-containing acrylate elastomer B (see Table 1), 1 part of stearic acid, 60 parts of MAF carbon black, 1 part of an amine-type antioxidant (NAUGARD 445, a product of Uniroyal Inc.) and a predetermined amount of each of the vulcanizers shown in Table 4 were kneaded by means of a 6-inch roll to prepare a composition. The Mooney scorch time of the resulting composition was measured. The composition was press-cured at 170°C for 20 minutes, and then post-cured for 4 hours in a Geer's oven at 150°C. The properties of the vulcanizate were measured as in Example 1. The results are shown in Table 5. The results show that the vulcanization systems in accordance with this invention give excellent compression set values even when the elastomer has a relatively small epoxy group content. It is also seen that in a comparison in which a vulcanization system composed of a dicarboxylic acid and a quaternary ammonium salt is used (Run No. 17) and a comparison in which ammonium benzoate alone is used as a vulcanization system (Run No. 18), the compression set becomes poor when the epoxy group content of the elastomer is small. EXAMPLE 3 In each run, 100 parts of the epoxy group-containing acrylate elastomer A (see Table 1), 1 part of stearic acid, 60 parts of MAF carbon black, 1 part of an amine-type antioxidant (NAUGARD 445, a product of Uniroyal Inc.) and a predetermined amount of each of the vulcanizers shown in Table 6 were kneaded by means of a 6-inch roll to prepare a composition. The Mooney scorch time of the resulting composition was measured. The composition was press-cured at 170°C for 20 minutes, and then post-cured for 4 hours in a Geer's oven at 150°C. The properties of the vulcanizate were measured as in Example 1. The results are shown in Table 7. The results obtained show that the increase of the amount of the quaternary ammonium salt shortens the scorch time; the incorporation of an excess of the imidodicarbonyl group-containing compound retards the rate of vulcanization and thus impairs the various properties of the resulting vulcanizate; if either one of the quaternary ammonium salt and the imidodicarbonyl group-containing compound is lacking (Runs Nos. 23 and 24), the degree of vulcanization does not increase and the compositions are not suitable for practical applications; and that various quaternary ammonium salts and quaternary phosphonium salts can be used as vulcanizers in this invention. EXAMPLE 4 In each run, 100 parts of en epoxy group-containing ethylene/acrylate copolymer elastomer [composition (% by weight) determined from the chemical shifts of ¹³C-NMR: ethylene 40, methyl acrylate 58.2, glycidyl methacrylate 1.8 (Mooney viscosity ML₁+₄, 100 °C, 18.0)], 1 part of stearic acid, 45 parts of MAF carbon black, 1 part of an amine-type antioxidant (NAUGARD 445, a product of Uniroyal Inc.) and a predetermined amount of each of the vulcanizers shown in Table 8 were kneaded by means of a 6-inch roller to prepare a composition. The Mooney scorch time of the composition was measured. The composition was cured as in Example 1, and the properties of the vulcanizate were measured. The results are shown in Table 9. EXAMPLE 5 In each run, 100 parts of epoxy group-containing butadiene/acrylonitrile copolymer elastomer [composition (% by weight) determined by the chemical shifts of ¹³C-NMR: butadiene 65.2, acrylonitrile 33, glycidyl methacrylate 1.8 (Mooney viscosity ML₁+₄ , 100 °C, 60)], 1 part of stearic acid, 40 parts of MAF carbon black and a predetermined amount of each of the vulcanizers shown in Table 10 were kneaded by means of a 6-inch roll to prepare a composition. The composition was press-cured at 160 °C for 20 minutes, and the properties of the vulcanizates were measured in accordance with JIS K-6301. The results are shown in Table 11. EXAMPLE 6 In each run, 100 parts of the acrylate elastomer A described in Example 1, 1 part of stearic acid, 60 parts of MAF carbon black (Seast 116, a product of Tokai Carbon Company), 1 part of an amine-type antioxidant (NAUGARD 445, a product of Uniroyal Inc.) and a predetermined amount of each of the vulcanizers shown in Table 12) were kneaded by means of a 6-inch roll to prepare a composition. The Mooney scorch time of the resulting composition was measured in accordance with JIS K-6300. The composition was press-cured at 170 °C for 20 minutes, and the properties of the vulcanizate were measured in accordance with JIS K-6301. To evaluate the storage stability of the composition, the Mooney scorch time of the composition which had been left to stand at room temperature for 4 weeks was measured. The results are shown in Table 13. The results obtained show that the vulcanization systems comprising the compound having at least two bonds in the molecule, the quaternary ammonium salt and urea (invention) give better scorch stability than the vulcanization system of Run No. 44 not containing the urea (comparison); and that the vulcanization systems in accordance with this invention show very good compression set values after press-curing at 170 °C for as short as 20 minutes. It can be seen from the results that post-curing can be omitted in this invention. EXAMPLE 7 In each run, a composition was prepared by using the same acrylate elastomer and compounding recipe as in Example 4 except that each of the vulcanizers shown in Table 14 was used in the amount indicated. The Mooney scorch time of the composition was measured. The composition was cured, and the properties of the vulcanizate were measured, as in Example 1. The results are shown in Table 15. EXAMPLE 8 In each run, a composition was prepared by using the elastomer and compounding recipe shown in Example 5 except that each of the vulcanizers indicated in Table 16 was used in the amount indicated. The composition was press-cured at 160 °C for 20 minutes, and the properties of the vulcanizate were measured in accordance with JIS K-6301. The results are also shown in Table 16.

Claims: A vulcanizable elastomer composition comprising an epoxy group-containing elastomer, and blended therewith, (1) an organic compound having at least two bonds of the following formula wherein X and Y are both oxygen or sulfur atoms, or one of X and Y is an oxygen atom and the other is a sulfur atom, in the molecule, and (2) a quaternary compound selected from quaternary ammonium salts and quaternary phosphonium salts. A vulcanizable elastomer composition comprising an epoxy group-containing elastomer, and blended therewith, (1) an organic compound having at least two bonds of the following formula wherein X and Y are both oxygen or sulfur atoms, or one of X and Y is an oxygen atom and the other is a sulfur atom, in the molecule, (2) a quaternary compound selected from quaternary ammonium salts and quaternary phosphonium salts, and (3) a compound selected from urea compounds and thiourea compounds. The composition of claim 1 comprising 0.1 to 10 parts by weight of the organic compound and 0.1 to 10 parts by weight of the quaternary compound (2) per 100 parts by weight of the epoxy group-containing elastomer. The composition of claim 2 comprising 0.1 to 10 parts by weight of the organic compound (1), 0.1 to 10 parts by weight of the quaternary compound (2) and 0.1 to 10 parts by weight of the compound (3) per 100 parts by weight of the epoxy group-containing elastomer. The composition of claim 1 or 2 wherein the organic compound (1) is selected from heterocyclic compounds, aromatic compounds and aliphatic compounds each containing at least two said bonds in the molecule. The composition of claim 1 or 2 wherein the quaternary compound (2) is a compound represented by the formula wherein Y is a nitrogen or phosphorus atom, each of R₁, R₂, R₃ and R₄ represents a hydrocarbon group, and two or three of these groups R₁ to R₄ may form together with Y a heterocyclic ring in which at least two ring atoms are carbon atoms and the remainder are oxygen, nitrogen, phosphorus or sulfur atoms, and X is an anion. The composition of claim 1 or 2 wherein the compound (3) is selected from the group consisting of aliphatic urea compounds, aliphatic thiourea compounds, aromatic urea compounds, aromatic thiourea compounds, heterocyclic urea compounds and heterocyclic thiourea compounds each containing one said bond.

Inventors: YAGISHITA SHIGERU, YAGISHITA, SHIGERU
Applicants: NIPPON ZEON CO, NIPPON ZEON CO., LTD.
Application year: 1987
Main classification: C08G59
IPC codes: C08G59