JP2011144364A - Acrylic rubber composition and molded product of the same - Google Patents

Abstract

An acrylic rubber composition excellent in heat resistance, oil resistance and grease resistance, and a molded product thereof are provided.
A carboxyl group-containing acrylic rubber is mixed with at least one filler and a foil-like filler.
[Selection figure] None

Description

  The present invention relates to an acrylic rubber composition and a molded article thereof.

  The acrylic rubber composition is a rubber composition mainly composed of an acrylate ester, and is known as a rubber composition excellent in heat resistance, weather resistance, compression set resistance, and oil resistance. Molded products are used in various sealing materials such as O-rings, oil seals, packings, gaskets, washer seals, bearing seals and the like that require these performances.

  In general, acrylic rubber compositions have crosslinking points such as halogen groups and epoxy groups, and crosslinking agents and crosslinking accelerators suitable for the respective crosslinking points are used. Among them, an acrylic rubber composition having a halogen group as a rubber composition and a rubber composition using a triazine derivative as a cross-linking agent are comprehensive in terms of physical properties such as heat resistance, weather resistance, compression set resistance, and oil resistance. However, there are still problems in processability, particularly storage stability. An acrylic rubber composition having an epoxy group is generally inferior in physical properties such as heat resistance and compression set resistance, and has a very slow vulcanization rate and inferior productivity.

On the other hand, an acrylic rubber composition having a carboxyl group as a crosslinking point has characteristics superior in heat resistance and compression set resistance to conventional acrylic rubber using an epoxy group, a halogen group or the like.
In recent years, with the improvement in performance of engines such as automobiles and higher rotation of bearings, the surrounding environment of the use parts of the above-mentioned various sealing materials becomes a high temperature of around 180 ° C. Materials with improved properties are desired.
The above-mentioned acrylic rubber composition containing a carboxyl group can be said to be a material that meets these needs, but its use is expanding and its demand is increasing more and more in recent years.

Patent Document 1 listed below discloses a rubber composition used for a vibration damping sheet for suppressing vibrations of home appliances and the like. Here, for the purpose of adjusting the Young's modulus of the acrylic rubber composition, mica, clay, diatomaceous earth, carbon black, silica, talc, barium sulfate, calcium carbonate, magnesium carbonate, metal oxide, graphite, aluminum hydroxide, etc. It describes that a scaly inorganic filler is blended.
Patent Document 2 listed below describes a composition containing a resinous polymer of ethylene or propylene for the purpose of resistance to deterioration oil.

JP-A-11-257424 JP 2001-342321 A

By the way, it is used by applying or filling oil or grease that can withstand high temperatures to the use site of the various sealing materials as described above. In particular, for example, an organic or inorganic metal salt that is an additive for oil. In addition, some urea compounds that are grease thickeners, for example, reduce the elasticity of acrylic rubber or cure when used for a long time at high temperatures.
Therefore, even if it is known that the acrylic rubber composition containing a carboxyl group is excellent in heat resistance, the performance of a molded article made of the acrylic rubber composition is significantly lowered by contact with oil or grease in a high temperature atmosphere. For this reason, it is difficult to use the molded product at a site where oil or grease is used.

  Although the thing of the said patent document 1 can adjust a Young's modulus by mix | blending a filler and can suppress a time-dependent change, it does not have heat resistance, oil resistance, and grease resistance.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an acrylic rubber composition excellent in heat resistance, oil resistance, and grease resistance, and a molded product thereof.

The acrylic rubber composition according to the present invention is characterized in that a carboxyl group-containing acrylic rubber is mixed with at least one filler and a foil-like filler. Further, when the composition contains an ethylene vinyl acetate copolymer, further effects can be obtained.

In the present invention, the mixing ratio of the foil-like filler may be 20% by weight or more and 80% by weight or less based on the total amount of the filler and the foil-like filler mixed.
In the present invention, the filler may be at least one selected from silica, diatomaceous earth, calcium silicate, clay, calcium carbonate, and carbon black.
Furthermore, in the present invention, the foil filler may be at least one selected from plate-like clay, talc, bentonite, mica, and sericite.
In this invention, you may further contain 1-15 weight part ethylene vinyl acetate copolymer with respect to 100 weight part of carboxyl group-containing acrylic rubber.
In the present invention, a molded product can be obtained by vulcanizing and molding the acrylic rubber composition described above. Such molded products include various seals such as an O-ring, an oil seal, a packing, a gasket, a washer seal, and a bearing seal. It can be a material.

According to the acrylic rubber composition of the present invention, while being excellent in heat resistance, it can be excellent in oil resistance and grease resistance against a medium such as oil or grease.
Moreover, according to the molded article by the acrylic rubber composition of this invention, it can be used in the seal | sticker site | part by which heat resistance, oil resistance, and grease resistance are requested | required.

Embodiments of the present invention will be described below.
The acrylic rubber composition according to the present invention is obtained by mixing a carboxyl group-containing acrylic rubber with at least one filler and a foil-like filler.

Examples of the carboxyl group-containing acrylic rubber used in the present invention include (a) methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, and the like. For example, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group, or alkyl groups and alkylene groups such as methoxymethyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, butoxyethyl acrylate, etc. At least one acrylic ester selected from alkoxyalkyl acrylates having one carbon atom, and (b) acrylic acid, methacrylic acid, paravinylbenzoic acid, vinylacetic acid, crotonic acid, 2-hexenoic acid, monomethyl maleate, maleate Two compounds copolymerizable with the above component (a) such as monobutyl acid, mono-2-ethylhexyl maleate, monoethyl fumarate, monobutyl fumarate, monoethyl itaconate, monobutyl itaconate, 2-norbornene-5-carboxylic acid, etc. It is a rubber obtained by copolymerizing one or more compounds having both a heavy bond and a carboxyl group for crosslinking reaction.
(C) The above (a) (b) such as acrylonitrile, methacrylonitrile, ethylene, vinyl chloride, ethyl vinyl ether, hydroxyethyl acrylate, tetrafluoroethylene, hexafluoropropene, styrene, divinylbenzene, ethylene glycol dimethacrylate, etc. One or more compounds having a double bond copolymerizable with the component) may be optionally copolymerized.
The content of (c) is preferably 20% or less of the whole polymer, and if it exceeds 20%, various physical properties such as heat resistance and oil resistance, which are characteristics of acrylic rubber, may be lowered.

  As the filler used in the present invention, for example, carbon black and an inorganic filler excluding a foil-like filler as described later can be used. Specifically, silica, diatomaceous earth, calcium silicate, clay, carbonate At least one kind is selected from calcium and the like. Since at least one type of filler is selected here, it goes without saying that two or more types may be combined, for example, from the above.

  Examples of the foil-like filler used in the present invention include inorganic scale-like or plate-like fillers, and at least one kind is selected from plate-like clay, talc, bentonite, mica, sericite, and the like. Also, since at least one type of foil-like filler is selected here, it goes without saying that, for example, two or more types may be combined from the above.

The filler used in the present invention is used by mixing at least one kind of filler and foil-like filler, and the total amount of the mixed filler and foil-like filler is 100 parts by weight of acrylic rubber. 20 to 200 parts by weight, preferably 40 to 130 parts by weight. If it is less than 20 parts by weight, the rubber hardness tends to be insufficient, and if it exceeds 200 parts by weight, desired physical properties tend not to be obtained.
The blending ratio of the foil-like filler is 20% by weight or more and 80% by weight or less, preferably 30% by weight or more, based on the total amount of the mixed filler and the foil-like filler.
When the blending ratio of the foil-like filler is 20% by weight or less with respect to the total amount of the mixed filler and the foil-like filler, the heat resistance, oil resistance, and grease resistance tend to be inferior, and 80% by weight or more. Then, the desired tensile strength or elongation tends not to be obtained.

  The filler and foil-like filler used in the present invention may be surface-treated with a coupling material typified by silane or titanium, fatty acid or higher alcohol. By performing surface treatment, physical properties can be improved.

  The vulcanizing agent for the carboxyl group-containing acrylic rubber used in the present invention is preferably a polyvalent amine compound. For example, an aliphatic polyvalent amine compound typified by hexamethylene diamine, hexamethylene diamine carbamate, N, N′-dicinnamylidene-1,6-hexane diamine, 4,4′-methylene dianiline, m-phenylene diamine, There are aromatic polyamine compounds represented by 4,4′-diaminodiphenyl ether, 4,4′-bis (4-aminophenoxy) biphenyl, m-xylylenediamine, 1,3,5-benzenetriamine and the like.

The carboxyl group-containing acrylic rubber used in the present invention may contain a vulcanization accelerator together with a vulcanizing agent. As the vulcanization accelerator, a base that does not react with the carboxyl group of the acrylic rubber or a conjugate base is preferable.
For example, guanidine compounds represented by 1,3-diphenylguanidine, 1,3-dioltolylguanidine, 2-methylimidazole, imidazole compounds represented by 2-phenylimidazole, tetra-n-butylammonium bromide, octadecyl Quaternary ammonium salts typified by tri-n-butylammonium bromide, triethylamine, tertiary amines typified by 1,8-diazabicyclo [5,4,0] undecene-7, Grade phosphine compounds, inorganic weak acid salts, organic weak acid salts and the like.

The ethylene vinyl acetate copolymer used in the present invention has a vinyl acetate content of 10% by weight or more. When the vinyl acetate content is less than 10% by weight, the grease resistance is inferior and the volume change rate is increased. Moreover, the compounding quantity of ethylene vinyl acetate copolymer is 1-15 weight part with respect to 100 weight part of carboxyl group-containing acrylic rubber, Preferably it is 3-10 weight part. If the amount is less than 1 part by weight, the effect on the hardness change is not observed, and if it exceeds 10 parts by weight, the volume change rate increases.
The acrylic rubber composition of the present invention is a reinforcing material, a lubricant, a processing aid, a plasticizer, a coupling agent, a vulcanization retarder, an anti-aging agent, a plasticizer, and a coloring, as necessary, within a range that does not inhibit the effect. A general compounding agent such as an agent can be added according to the purpose. If necessary, rubbers, elastomers, resins and the like other than the present invention may be blended.
The acrylic rubber composition of the present invention has a vulcanization condition of 150 to 200 ° C, preferably 160 to 180 ° C, and may be post-cured as necessary.

Hereinafter, the acrylic rubber composition of the present invention will be described more specifically with reference to examples. However, these are examples of the present invention and are not limited thereto.
The composition shown in Table 1 was kneaded using a sealed kneader or an open roll, and the resulting mixture was compression molded at 170 ° C. for 10 minutes, and further vulcanized at 170 ° C. for 4 hours to obtain a thickness. A 2 mm vulcanized sheet was obtained. Using the vulcanized sheet thus obtained as a test piece, each physical property measurement was performed in accordance with JIS standards as follows.

Example 1
Carboxyl group-containing acrylic rubber ... 100 parts by weight plate-like clay (foil-like filler) ... 70 parts by weight clay (filler) ... 30 parts by weight stearic acid (lubricant) ... 2 parts by weight octyl Diphenylamine (anti-aging agent) 3 parts by weight Hexamethylenediamine carbamate 1 part by weight Diortolyl guanidine 2 parts by weight (Example 2)
In Example 1, 50 parts by weight of talc was used instead of plate-like clay, and 30 parts by weight of silica was used instead of clay.
(Example 3)
In Example 1, 25 parts by weight of plate-like clay, 50 parts by weight of sericite, and 20 parts by weight of silica instead of clay were used.
Example 4
In Example 1, 5 parts by weight of an ethylene vinyl acetate copolymer (Ultrasen 640: manufactured by Tosoh Corporation) having a vinyl acetate content of 25% by weight was further added.
(Example 5)
In Example 1, 20 parts by weight of ethylene vinyl acetate copolymer (Ultrasen 530: manufactured by Tosoh Corporation) having a vinyl acetate content of 6% by weight was further added.
(Comparative Example 1)
In Example 1, 100 parts by weight of only plate-like clay was used, and no clay was used.
(Comparative Example 2)
In Example 1, no platy clay was used, and only 100 parts by weight of clay was used.

(1) Normal state physical properties: JIS K6253, 6251 conformity The hardness of a test piece of a predetermined size was measured according to JIS K6253.
The tensile strength and elongation of a test piece of a predetermined size were measured according to JIS K6251.
The larger the tensile strength, the more difficult it is to break, indicating that the mechanical strength is high.
(2) Air heating aging test: JIS K 6257 compliant The test piece was heat-treated at 175 ° C. for 168 hours using an air heating aging tester, and then the test piece was taken out and measured for hardness, tensile strength and elongation. It was measured. It can be said that the smaller the change in the measured value, the better the heat resistance. In addition, the hardness change, the tensile strength change rate, and the elongation change rate described in Table 1 are values calculated on the basis of (1) measured values in normal physical properties.
(3) Oil resistance test: JIS K 6258 compliant (automatic fluid, 175 ° C x 168h)
After immersing the test piece in automatic fluid oil at 175 ° C. × 168 h, the hardness, tensile strength and elongation were measured. The smaller the change in the measured value, the better the oil resistance. In addition, the hardness change, the tensile strength change rate, and the elongation change rate described in Table 1 are values calculated on the basis of (1) measured values in normal physical properties.
(4) Grease resistance test: JIS K 6258 compliant (Urea grease, 175 ° C x 168h)
After immersing the test piece in urea-based grease at 175 ° C. × 168 h, the hardness, tensile strength, elongation and volume were measured. The smaller the change, the better the grease resistance. In addition, the hardness change, the tensile strength change rate, the elongation change rate, and the volume change rate shown in Table 1 are values calculated on the basis of (1) measured values in normal physical properties.

[result]
As can be seen from the test results in Table 1, according to those obtained by blending Examples 1 to 5, an acrylic rubber composition having excellent heat resistance, oil resistance, and grease resistance can be obtained.
Specifically, it is as follows.
(1) From the test results of normal physical properties, it can be seen that good results were obtained in Examples 1 to 5. From these results, molded products obtained by vulcanization molding of these acrylic rubber compositions have physical properties that can be used for various sealing materials such as O-rings, oil seals, packings, gaskets, washer seals and bearing seals. It can be said. Comparative Example 1 is poor in tensile strength and elongation and cannot be said to have the desired physical properties, and cannot be said to be the above-described various sealing materials. Comparative Example 2 shows the same results as in Examples 1 to 5 in terms of normal physical properties. However, as described later, Comparative Example 2 is inferior in heat resistance, oil resistance, and grease resistance.

(2) From the results of the air heating aging test, it can be seen that good results were obtained in Examples 1 to 5.
Comparative Example 1 seems to have obtained inferior results when comparing only numerical values with Examples 1 to 5. However, for Comparative Example 1, the numerical value of the test result of (1) normal physical properties is very high. The numerical values in Table 1 of (2) Air heat aging test to (4) Grease resistance test are values calculated based on this. Therefore, it cannot be said that Comparative Example 1 is excellent in heat resistance, oil resistance, and grease resistance.
Further, Comparative Example 2 is poor in hardness change, tensile strength change rate, and elongation change rate. From this result, even if it is a carbosyl group-containing acrylic rubber that is originally recognized as a material having heat resistance, It can be seen that the desired heat resistance cannot be obtained depending on the filler to be blended.

(3) From the results of the oil resistance test, it can be seen that good results were obtained in Examples 1 to 5. In all of Examples 1 to 5, the change in hardness is small, and it can be said that the oil resistance is excellent as judged comprehensively. Comparative Example 1 is as described above. In Comparative Example 2, the hardness change, the tensile strength change rate, and the elongation change rate all have large numerical values and cannot be said to be excellent in oil resistance.
From this result, when the foil-like filler is mixed with the carbosyl group-containing acrylic rubber composition, the foil-like pieces (scale-like or plate-like pieces) of the foil-like filler are oriented in a plate shape (layer shape) in the same direction. Since they are stacked, they are considered to play a role of preventing the penetration and permeation of oil into the acrylic rubber composition when immersed in oil. However, from the results of Comparative Example 1, even if only a foil-like filler is blended as the filler, the desired tensile strength and elongation cannot be obtained in terms of normal physical properties, and the molded product is used as various sealing materials. I find it difficult. That is, from this result, it is understood that it is not only necessary to blend the foil-like filler, but it is important to mix the filler and the foil-like filler.

(4) From the results of the grease resistance test, it can be seen that good results were obtained in Examples 1 to 5. In any case, there are no numerical values that cause problems in hardness change, tensile strength change rate, and elongation change rate, and it can be said that the grease resistance is excellent. Comparative Example 1 is as described above. In Comparative Example 2, the values of hardness change, tensile strength change rate, and elongation change rate are all large, and the elongation change rate is particularly large, so it cannot be said that the grease resistance is excellent.
From this result, the foil-like piece of the foil-like filler mixed with the carbosil group-containing acrylic rubber is oriented in the same direction as in the oil resistance test, so when immersed in grease It is considered that it plays a role of preventing the penetration and penetration of grease into the acrylic rubber composition. However, even if only the foil-like filler is blended as the filler from the results of Comparative Example 1, the desired tensile strength and elongation cannot be obtained in terms of normal physical properties, and the foil-like filler may be simply blended. That is not the same as described above.

Claims (5)

  An acrylic rubber composition comprising a carboxyl group-containing acrylic rubber mixed with at least one filler and a foil-like filler. In the acrylic rubber composition according to claim 1,
The acrylic rubber composition is characterized in that the amount of the foil filler is 20 wt% or more and 80 wt% or less with respect to the total amount of the filler and the foil filler. In the acrylic rubber composition according to claim 1 or 2,
The filler is selected from silica, diatomaceous earth, calcium silicate, clay, calcium carbonate, and carbon black, and the foil filler is selected from plate-like clay, talc, bentonite, mica, and sericite. Acrylic rubber composition. In the acrylic rubber composition according to any one of claims 1 to 3,
The acrylic rubber composition further comprising 1 to 15 parts by weight of ethylene vinyl acetate copolymer with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber.   A molded article formed by vulcanization molding of the acrylic rubber composition according to any one of claims 1 to 4.