JP2008127518A - Acrylic rubber composition for sealing member of compressor, crosslinked product of the same and sealing member for compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealing member for compressor satisfying strength, permanent compression set and heat-aging resistance and excellent in resistance to polyalkyleneglycol based synthetic lubricating oil. <P>SOLUTION: There is provided the acrylic rubber composition composed of an acrylic rubber containing ≥50 wt.% of alkoxyalkylacrylate monomer units and a crosslinking agent, for sealing member of compressor using a synthetic lubricating oil selected from the group composed of a polyalkylene glycol based lubricating oil, an ester modified polyalkylene glycol based lubricating oil, and an ester based lubricating oil. There is provided the crosslinked product obtained by crosslinking the acrylic rubber composition. There is provided the sealing member for compressor composed of the crosslinked product. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acrylic rubber composition, a crosslinked product thereof, and a compressor seal member comprising the same. More specifically, it is suitable for an acrylic rubber composition containing an acrylic rubber having a specific composition and a crosslinking agent, a crosslinked product thereof, and a compressor using a synthetic lubricant such as a polyalkylene glycol based composition. The present invention relates to a seal member.

As a heat medium for a compressor used in a car air conditioner, a home air conditioner, a commercial air conditioner, a refrigerator, etc., in recent years, from the consideration of the global environment, it has been converted from CFCs to CFC substitutes.
Correspondingly, as a machine oil for a compressor, instead of mineral oil, a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil or an ester-based lubricating oil (hereinafter referred to as these) having good compatibility with an alternative chlorofluorocarbon gas. Are sometimes collectively referred to as “polyalkylene glycol synthetic lubricating oil”).

Nitrile rubber is excellent from the viewpoint of lubricating oil resistance as a seal member for a compressor that employs this alternative fluorocarbon-polyalkylene glycol synthetic lubricating oil combination.
However, depending on the application of the sealing member, high heat resistance is required. For example, the sealing member for a car air conditioner compressor, etc. It has been pointed out that heat resistance is insufficient in a nitrile rubber sealing member because the use atmosphere in the room is high.
It is known that heat resistance is improved by hydrogenating nitrile rubber to form hydrogenated nitrile rubber, but it is not economically advantageous to apply this to a seal member.
Patent Document 1 discloses the use of acrylate-modified butadiene-acrylonitrile rubber as a sealing member. This sealing member is said to be excellent in sealing performance, heat resistance, mechanical strength, oil resistance, creep resistance, polyalkylene glycol resistance, and the like.
However, as a result of investigation by the present inventors, it has been found that the heat resistance is not sufficient, and in particular, it cannot be used continuously at a high temperature.

Patent Document 2 discloses a compressor gasket comprising an inorganic filler other than asbestos, a carbodiimide resin, a rubber material reactive with polycarbodiimide, and a fiber component added as desired. .
However, in the production of this gasket, after making a sheet at room temperature from the emulsion rubber and carbodiimide resin, it must be hot-press molded above the softening point of polycarbodiimide resin (about 200 ° C. or higher) Further, in order to knead the polycarbodiimide resin and the rubber, it is not efficient because it is necessary to knead while cooling to 30 ° C. or lower.

JP-A-8-48968 JP-A-7-216342

  Accordingly, an object of the present invention is to satisfy the basic properties as a sealing member, ie, strength, compression set and heat aging resistance, and also resistance to polyalkylene glycol synthetic lubricating oil (hereinafter referred to as “PAG resistance”). The present invention is to provide a seal member for a seal compressor which is superior to the above.

  As a result of diligent research to achieve the above object, the present inventor satisfies the above characteristics by using a composition obtained by blending an acrylic rubber having a specific monomer unit composition with a crosslinking agent. It has been found that a seal member can be obtained, and the present invention has been completed based on this finding.

Thus, according to the present invention, a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil comprising an acrylic rubber having an alkoxyalkyl acrylate monomer unit content of 50% by weight or more and a crosslinking agent, and An acrylic rubber composition for a seal member for a compressor that uses a synthetic lubricant selected from the group consisting of ester-based lubricants is provided.
In the acrylic rubber composition for a seal member of the present invention, the monomer constituting the alkoxyalkyl acrylate monomer unit is preferably 2-methoxyethyl acrylate or 2-ethoxyethyl acrylate.
In the acrylic rubber composition for a seal member of the present invention, the acrylic rubber preferably contains 4 × 10 ⁻⁴ to 4 × 10 ⁻¹ equivalents of carboxy group or epoxy group per 100 g.
In the acrylic rubber composition for a seal member of the present invention, the acrylic rubber preferably has a butenedionic acid monoalkyl ester monomer unit.

In the acrylic rubber composition for a seal member of the present invention, the monomer constituting the butenedionic acid monoalkyl ester monomer unit is preferably mono-n-butyl maleate or mono-n-butyl fumarate. .
In the acrylic rubber composition for a seal member of the present invention, the cross-linking agent is preferably a polyamine compound.
The acrylic rubber composition for a seal member of the present invention is suitable for a compressor using polyalkylene glycol as a lubricating oil.
The acrylic rubber composition for sealing members of the present invention can be suitably used when the maximum temperature during continuous use is 130 ° C. or higher.

Furthermore, according to this invention, the acrylic rubber composition crosslinked body for sealing members formed by bridge | crosslinking the acrylic rubber composition for sealing members for compressors of the said invention is provided.
Furthermore, according to the present invention, a synthetic lubricant selected from the group consisting of a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil and an ester-based lubricating oil, comprising the crosslinked acrylic rubber composition for a seal member of the present invention. A seal member for a compressor using oil is provided.

Acrylic rubber composition for a seal member for a compressor using a synthetic lubricating oil selected from the group consisting of a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil and an ester-based lubricating oil of the present invention (hereinafter simply referred to as “this” The “acrylic rubber composition for sealing member of the invention” is sometimes referred to as “) containing an acrylic rubber having an alkoxyalkyl acrylate monomer unit content of 50% by weight or more and a crosslinking agent.
In the present invention, the “monomer unit” refers to a unit derived from a monomer that is included in the polymer by polymerizing the monomer.

The acrylic rubber composition for a seal member of the present invention is suitable for a seal member for a compressor using a polyalkylene glycol synthetic lubricating oil as a machine oil.
Here, the polyalkylene glycol synthetic lubricating oil refers to a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil, and an ester lubricating oil.

  The polyalkylene glycol lubricant is a lubricant composed of a linear or branched alkylene oxide ring-opening (co) polymer having 2 to 5, preferably 2 to 3, carbon atoms of an alkylene group. As the alkylene oxide, ethylene oxide, propylene oxide, butylene oxide and a mixture thereof are used, and preferably, ethylene oxide or propylene oxide is used. Suitable alkylene oxides are polyethylene glycol and polypropylene glycol, the molecular weight range of which is 100 to 2,000, preferably 200 to 1,000.

The ester-modified polyalkylene glycol lubricating oil is obtained by esterifying one or both terminal hydroxyl groups of the polyalkylene glycol.
The ester-based lubricating oil is a lubricating oil composed of a polyol ester, and examples thereof include polyesters or partial esters of aliphatic polyhydric alcohols and linear or branched fatty acids.
Here, as the aliphatic polyhydric alcohol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or the like is used. The fatty acids are preferably those having 5 to 12 carbon atoms, monocarboxylic acids such as valeric acid, hexanoic acid, heptanoic acid, 2-butyloctanoic acid; succinic acid, adipic acid, sebacic acid, undecanedioic acid, dodecane And dicarboxylic acids such as diacids.

The ester-based lubricating oil may be an ester of an aliphatic or aromatic polycarboxylic acid and an alcohol. Examples of the aliphatic polyvalent carboxylic acid include the above dicarboxylic acids, and examples of the aromatic polyvalent carboxylic acid include phthalic acid and isophthalic acid. Examples of the alcohol component include monovalent alcohols such as methanol, ethanol and butanol; polyhydric alcohols such as glycerin and trimethylolpropane; and adducts of alkylene oxides such as propylene oxide.
Further, the ester-based lubricating oil may be a carbonate ester.

The acrylic rubber used in the present invention has an alkoxyalkyl monomer unit content of 50% by weight or more. The content of the alkoxyalkyl acrylate monomer unit is preferably 50 to 85% by weight, and more preferably 60 to 72% by weight.
When the alkoxyalkyl acrylate monomer unit content is too small, the PAG resistance of a seal member (hereinafter, simply referred to as “seal member”) obtained using the acrylic rubber composition for seal members is lowered. Sometimes.

The alkoxyalkyl acrylate monomer is not particularly limited. The alkoxyalkyl acrylate monomer is preferably an ester of an alkoxyalkyl alcohol having 2 to 8 carbon atoms and acrylic acid, but the synthesis method is not limited.
Specific examples of the alkoxyalkyl acrylate monomer include 2-methoxymethyl acrylate, 2-ethoxymethyl acrylate, 1-ethoxyethyl acrylate, 2-butoxyethyl acrylate, 1-methoxyethyl acrylate, acrylic acid Examples include 2-propoxyethyl, 3-methoxypropyl acrylate, 4-methoxybutyl acrylate, etc., and these monomers may be used in combination of two or more.
Among the above-mentioned alkoxyalkyl acrylate monomers, 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferable.

The acrylic rubber used in the present invention preferably contains 4 × 10 ⁻⁴ to 4 × 10 ⁻¹ equivalents of carboxy group or epoxy group per 100 g. The amount of these groups is more preferably 2 × 10 ⁻³ to 2 × 10 ⁻¹ equivalents, and particularly preferably 4 × 10 ⁻³ to 1 × 10 ⁻¹ equivalents. By using the acrylic rubber containing such an amount of carboxy group or epoxy group, the sealing member of the present invention excellent in various properties can be obtained. The acrylic rubber used in the present invention is preferably an acrylic rubber containing a carboxy group in terms of more excellent compression set.
If the amount of these groups is too small, crosslinking does not proceed sufficiently, so that the shape of the seal member cannot be maintained. On the other hand, if the content is too large, the sealing member becomes too hard and loses rubber elasticity.

The monomer containing a carboxy group that can be used in the present invention is not particularly limited, but a butenedionic acid monoalkyl ester monomer is preferred.
A butenedionic acid monoalkyl ester monomer is a butenedionic acid, that is, a monoester compound obtained by reacting one of two carboxy groups of fumaric acid or maleic acid with an alkyl alcohol. The butenedionic acid monoalkyl ester monomer has an effect of imparting a crosslinking point to the acrylic rubber.

Specific examples of the butenedionic acid monoalkyl ester monomer include monomethyl maleate, monoethyl maleate, mono-n-butyl maleate, monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate and the like.
Two or more of these compounds may be used in combination.
Of the above, mono-n-butyl maleate and mono-n-butyl fumarate are particularly preferable.

The content of the butenedionic acid monoalkyl ester monomer unit in the acrylic rubber used in the present invention is preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight.
If the content of the butenedionic acid monoalkyl ester monomer unit is too small, the crosslinking density of the resulting seal member becomes insufficient, and good mechanical properties tend not to be obtained. On the other hand, when there is too much content, scorching will become early and there exists a possibility that a burn etc. may occur at the time of fabrication.

The monomer containing an epoxy group that can be used in the present invention is not particularly limited, and specific examples thereof include glycidyl acrylate, glycidyl methacrylate, vinyl glycidyl ether, allyl glycidyl ether, methallyl glycidyl ether, and the like. These compounds may be used alone or in combination of two or more.
Among the above-mentioned compounds, glycidyl acrylate and glycidyl methacrylate are particularly preferable.

The content of the monomer unit containing an epoxy group in the acrylic rubber used in the present invention is preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight.
If the content of the monomer unit containing an epoxy group is too small, the crosslinking density of the obtained seal member becomes insufficient, and good mechanical properties tend not to be obtained. On the other hand, when there is too much content, scorching will become early and there exists a possibility that a burn etc. may occur at the time of fabrication.

The acrylic rubber used in the present invention may contain monomer units other than the monomer units described above.
As an example of the monomer which comprises such a monomer unit, acrylic acid ester and methacrylic acid ester other than the monomer which has an alkoxyalkyl acrylate and a carboxy group or an epoxy group can be mentioned.
Of these, acrylic acid alkyl esters are preferred. Among them, those having an alkyl group having 8 or less carbon atoms are more preferable, those having 4 or less carbon atoms are more preferable, and butyl acrylate and ethyl acrylate are particularly preferable.

The content of the ethyl acrylate monomer unit in the acrylic rubber used in the present invention is preferably 5 to 40% by weight, and more preferably 20 to 30% by weight.
If the content of the ethyl acrylate monomer unit in the acrylic rubber is too small, the strength of the sealing member may be lowered, and if it is too much, cold resistance and PAG resistance may be lowered.
The content of the n-butyl acrylate monomer unit in the acrylic rubber used in the present invention is preferably 5 to 15% by weight, and more preferably 7 to 12% by weight.
If the content of the butyl acrylate monomer unit in the acrylic rubber is too small, the flexibility and cold resistance of the sealing member may be lowered, and if it is too much, the PAG resistance may be lowered. .

The acrylic rubber used in the present invention can be obtained by radical polymerization of a monomer mixture comprising the above-mentioned alkoxyalkyl acrylate monomer and other monomers used in combination therewith.
As the polymerization method, any of an emulsion polymerization method, a suspension polymerization method, a bulk polymerization method and a solution polymerization method can be used. Among these, the emulsion polymerization method under normal pressure, which is conventionally used as a method for producing acrylic rubber, is preferable because the polymerization reaction can be easily controlled. Moreover, what is necessary is just to use what is generally used for a polymerization initiator, a polymerization terminator, an emulsifier, etc. at this time.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the acrylic rubber used in the present invention is preferably 10 to 80, more preferably 20 to 70. If the Mooney viscosity is too small, the molding processability and the mechanical strength of the crosslinked product after crosslinking are inferior. On the other hand, if the Mooney viscosity is too large, the molding process is difficult and it may not be possible to mold into a normal shape.

The rubber composition for a seal member of the present invention contains the above-mentioned acrylic rubber and a crosslinking agent.
As a crosslinking agent, the compound generally used as a crosslinking agent of acrylic rubber can be used.
When the acrylic rubber contains a carboxy group, an amine compound and a polyfunctional isocyanate compound can be used, but an amine compound is preferable and a polyvalent amine compound is most preferable. An amine compound, particularly a polyvalent amine compound, is a compound that can form a crosslinked structure relatively easily with the carboxy group of the butenedionic acid monoester monomer unit.

The polyvalent amine compound may be either an aliphatic polyvalent amine or an aromatic polyvalent amine, but those having a non-conjugated nitrogen-carbon double bond such as a guanidine compound are not suitable.
Specific examples of the aliphatic polyvalent amine include hexamethylene diamine, hexamethylene diamine carbamate, N, N′-dicinnamylidene-1,6-hexane diamine and the like.
Specific examples of the aromatic polyvalent amine include 4,4′-methylenedianiline, m-phenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4 ′-(m-pheny Range isopropylidene) dianiline, 4,4 ′-(p-phenylenediisopropylidene) dianiline, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, 4,4′-diaminobenzanilide, 4 , 4′-bis (4-aminophenoxy) biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 1,3,5-benzenetriaminomethyl and the like.

  Specific examples of the diisocyanate compound that can be used as a crosslinking agent when the acrylic rubber contains a carboxy group include hexamethylene diisocyanate, dimethyldiphenylene diisocyanate, isophorone diisocyanate, blocked isocyanate, and dicyclohexylmethane diisocyanate.

Moreover, when an acrylic rubber contains an epoxy group, a polyamine compound, an organic ammonium compound, and a polyvalent acid can be used as a crosslinking agent.
Specific examples of the polyamine compound may be the same as those used for the acrylic rubber having a carboxy group.
Specific examples of the organic ammonium compound include ammonium benzoate, ammonium adipate, and ammonium isocyanurate.
Moreover, tetradecanedioic acid etc. can be shown as a specific example of a polyvalent acid.

  The amount of the crosslinking agent is 0.05 to 20 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 0.3 to 2 parts by weight with respect to 100 parts by weight of the acrylic rubber. If the blending amount of the crosslinking agent is too small, crosslinking is insufficient and it is difficult to maintain the shape of the crosslinked product. On the other hand, if too much, the cross-linked product becomes hard and loses its elasticity as rubber.

In the acrylic rubber composition used in the present invention, a crosslinking accelerator may be used in combination with the crosslinking agent.
The crosslinking accelerator is not limited, but as the crosslinking accelerator that can be used in combination with the polyvalent amine crosslinking agent, those having a base dissociation constant in water at 25 ° C. of 10 ⁻¹² to 10 ⁶ are preferable. Examples of such crosslinking accelerators include guanidine compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, weak acid alkali metal salts, and the like.
Specific examples of the guanidine compound include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine and the like.
Specific examples of the imidazole compound include 2-methylimidazole and 2-phenylimidazole.
Specific examples of the quaternary onium salt include tetra n-butylammonium bromide, octadecyltri n-butylammonium bromide and the like.
Specific examples of the tertiary phosphine compound include triphenylphosphine and tri-p-tolylphosphine.
Specific examples of weak acid alkali metal salts include sodium or potassium phosphates, inorganic weak acid salts such as carbonates, and organic weak acid salts such as stearates and laurates.
The amount of the crosslinking accelerator used is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, and particularly preferably 0.3 to 10 parts by weight per 100 parts by weight of the acrylic rubber. When there are too many crosslinking accelerators, the crosslinking rate may become too fast at the time of crosslinking, the bloom of the crosslinking accelerator on the surface of the crosslinked product may occur, or the crosslinked product may become too hard.

Further, the acrylic rubber composition can be further blended with a monoamine compound to improve the workability by making the composition difficult to adhere to a metal in roll processing or Banbury processing before crosslinking.
Examples of such monoamine compounds include aromatic monoamine compounds and aliphatic monoamine compounds. These may be any of primary amine compounds, secondary amine compounds, and tertiary amine compounds.
These monoamine compounds can be used singly or in combination of two or more, but when used alone, primary monoamines are preferred, and when used in combination of two or more, fat It is preferable to use a combination of an aliphatic secondary monoamine and an aliphatic tertiary monoamine.
The compounding quantity of a monoamine compound is 0.05-20 weight part in total with respect to 100 weight part of acrylic rubbers, Preferably it is 0.1-10 weight part.
In particular, when a primary monoamine is used alone, it is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, an aliphatic secondary monoamine and an aliphatic tertiary. When used in combination with monoamine, the total amount is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 7 parts by weight.

  In the acrylic rubber composition used in the present invention, reinforcing agents such as carbon black and silica; fillers such as calcium carbonate and talc; anti-aging agents; light stabilizers; plasticizers; lubricants; An additive such as a lubricant, a flame retardant, an antifungal agent, an antistatic agent, a colorant, and the like may be blended.

Moreover, you may mix | blend acrylic rubber other than acrylic rubber whose acrylic-alkyl-alkoxyalkyl monomer unit content is 50 weight% or more with an acrylic rubber composition as needed.
Furthermore, rubbers other than acrylic rubber, elastomers, resins and the like can be blended.
Specific examples include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like; olefin elastomer, styrene elastomer, vinyl chloride elastomer, polyester elastomer, polyamide elastomer, Examples include elastomers such as polyurethane elastomers and polysiloxane elastomers; polyolefin resins, polystyrene resins, polyacrylic resins, polyphenylene ether resins, polyester resins, polycarbonate resins, polyamide resins, and the like. .

The acrylic rubber composition of the present invention can be obtained by mixing an acrylic rubber and a crosslinking agent.
In mixing, an appropriate mixing method such as roll mixing, Banbury mixing, screw mixing, or solution mixing can be employed. The blending procedure is not particularly limited. First, after sufficiently mixing components that are unlikely to cause reaction or decomposition due to heat, components that are likely to cause reaction or decomposition due to heat, such as a cross-linking agent, do not cause reaction or decomposition. It is preferable to take the procedure of mixing in a short time.

The acrylic rubber composition for a seal member of the present invention can be formed into a molded body by any method.
The molding method is not particularly limited, and a generally-used rubber molding method can be employed. Specifically, a molding method such as compression molding, injection molding, injection molding, extrusion molding, or transfer molding may be selected as necessary.

The acrylic rubber composition crosslinked body for sealing members of the present invention is a crosslinked body of the acrylic rubber composition for sealing members of the present invention.
Crosslinking of the acrylic rubber composition for sealing members of the present invention can be carried out by heating the acrylic rubber composition.
The time of crosslinking may be before or after the acrylic rubber composition for a seal member of the present invention is molded.
The heating temperature is preferably 130 to 220 ° C, more preferably 140 to 200 ° C, and the heating time is usually 30 seconds to 5 hours.
As a heating method, a method generally used for crosslinking of rubber, such as press heating, steam heating, oven heating, hot air heating, etc. may be appropriately selected.
Further, after cross-linking, post-cross-linking may be performed in order to reliably cross-link to the inside of the cross-linked body. What is necessary is just to select suitably the heating method and heating temperature for post-crosslinking. Although heating time changes with heating methods, heating temperature, the shape of a crosslinked body, etc., it is 1 to 48 hours normally.

The acrylic rubber composition of the present invention is excellent in heat resistance after crosslinking, PAG oil resistance and compression set characteristics. Therefore, a crosslinked product obtained by crosslinking the acrylic rubber composition can be suitably used as a seal member for a compressor that is used in contact with a polyalkylene glycol synthetic lubricating oil by utilizing these characteristics.
In particular, the acrylic rubber composition for a seal member of the present invention is suitable for a seal member having a maximum temperature of 130 ° C. or higher during continuous use, such as a seal member used in an engine room of an automobile.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but it goes without saying that the scope of the present invention is not limited to these examples. In addition, the part and% in an Example and a comparative example are mass references | standards unless there is particular notice. Various physical properties in Examples and Comparative Examples were measured by the following methods.

[Carboxy group equivalent]
The acetone solution in which acrylic rubber is dissolved is titrated with a potentiometric titrator COMMITE-101 (manufactured by Hiranuma Sangyo Co., Ltd.) using a 0.01N ethanol solution of potassium hydroxide, and the number of carboxy groups (number of moles, unit) relative to 100 g of rubber. Ephr).
[Mooney viscosity]
The Mooney viscosity ML _{1 + 4} at a measurement temperature of 100 ° C. is measured according to the Mooney viscosity test of the uncrosslinked rubber physical test method of JIS K6300.

[Normal properties]
The rubber composition was molded and subjected to primary crosslinking by compression molding at 170 ° C. for 20 minutes to produce a sheet having a length of 15 cm, a width of 15 cm, and a thickness of 2 mm. The sheet was further left in an electric oven at 170 ° C. for 4 hours. Subsequent crosslinking gave a sheet-like crosslinked product. Next, the tensile strength and elongation were measured according to JIS K6251 at room temperature using a test piece produced by punching this sheet-like cross-linked product with a No. 3 dumbbell, and the hardness was measured according to JIS K6253 (durometer type A). taking measurement.

〔Heat-resistant〕
A test piece obtained in the same manner as the test piece for measuring normal physical properties was placed in an environment at a temperature of 150 ° C. for 72 hours, and then the tensile strength and elongation were measured according to JIS K6251, and also according to JIS K6253 (durometer type A). Each hardness is measured.
For the tensile strength and elongation, the difference (change amount) in the measured values before and after heating is obtained, and the percentage of the difference with respect to the measured values in the normal physical property measurement is calculated. Moreover, about hardness, the difference (change amount) of the measured value after a heating and the measured value in a normal-state physical property measurement is calculated | required.
The closer these values are to 0, the better the heat resistance.

〔Compression set〕
Except for using a cylindrical shape having an inner diameter of 29 mm and a height of 12.5 mm, a cylindrical cross-linked product is prepared as a test piece in the same manner as the cross-linked product for measuring normal physical properties. The obtained test piece is placed in an environment of 150 ° C. for 70 hours in a state of being compressed by 25% according to JIS K6262, and then the compression is released to measure the compression set rate.
The smaller the compression set, the more difficult it is to deform and the better.

[PAG resistance]
A sheet-like cross-linked product having a thickness of 2 mm is produced in the same manner as the cross-linked product for measurement of normal state properties, and this sheet-like cross-linked product is punched into a rectangle of 50 mm length × 20 mm width to obtain a test piece. Using the obtained test piece, according to JIS K6258, after being immersed in polyalkylene glycol of 150 ° C. (trade name “No. 8” manufactured by Nippon Denso Co., Ltd.) for 70 hours, it is taken out and dried naturally. About the test piece, hardness is measured by JIS K6253 (durometer type A), and the difference (change amount) in hardness before and after immersion is obtained. The closer this value is to 0, the better the PAG resistance.
Moreover, the volume of the test piece after immersion is measured, the amount of change from the volume before immersion is obtained, and the rate of change is calculated. The closer this value is to 0, the better the PAG resistance.

(Production Example 1)
In a polymerization reactor equipped with a thermometer and a stirrer, 200 parts of ion-exchanged water, 3 parts of sodium lauryl sulfate, 28 parts of ethyl acrylate, 10 parts of mono-n-butyl acrylate, 60 parts of 2-methoxyethyl acrylate and fumar 2 parts of mono n-butyl acid were charged. After removing oxygen sufficiently by performing degassing under reduced pressure and nitrogen substitution twice, 0.005 part of cumene hydroperoxide and 0.002 part of sodium formaldehydesulfoxylate are added, and emulsion polymerization is carried out at a temperature of 30 ° C. under normal pressure. The reaction was started until the polymerization conversion reached 95% by weight. The obtained polymerization solution was coagulated with an aqueous calcium chloride solution, filtered, washed with water and dried to obtain a carboxyl group-containing acrylic rubber (Polymer A).
The obtained polymer A had a carboxy group equivalent of 0.012 (ephr) and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 35.

(Example 1)
100 parts of polymer A, 60 parts of FEF carbon black (reinforcing agent, manufactured by Tokai Carbon Co., Ltd., trade name “SEAST SO”), 1 part of stearic acid (processing aid) and 4,4′-bis (α, α-dimethylbenzyl) ) 2 parts of diphenylamine (anti-aging agent) (trade name “NOCRACK CD”, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) were placed in a Banbury mixer and kneaded at 50 ° C. Subsequently, it moved to an open roll, hexamethylene diamine carbamate (crosslinking agent) (made by Showa Denko KK, trade name “Diak No. 1”) 0.5 part and 1,3-di-o-tolylguanidine (crosslinking accelerator) ) (Trade name “Noxeller DT” manufactured by Ouchi Shinsei Chemical Co., Ltd.) was added and kneaded at 40 ° C. to prepare a rubber composition A.
With respect to the obtained rubber composition A, normal properties (tensile strength, elongation and hardness), heat resistance and compression set were evaluated. The results are shown in Table 1.

(Production Example 2)
The same procedure as in Production Example 1 except that the monomer composition was changed to 38 parts ethyl acrylate, 30 parts mono n-butyl acrylate, 30 parts 2-methoxyethyl acrylate and 2 parts mono n-butyl fumarate. A carboxy group-containing acrylic rubber (Polymer B) was obtained.
The obtained polymer B had a carboxy group equivalent of 0.012 (ephr) and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 35.

(Comparative Example 1)
A rubber composition B was prepared in the same manner as in Example 1 except that the amount of the crosslinking agent hexamethylenediamine carbamate was 0.6 parts using the polymer B, and normal properties (tensile strength, elongation and hardness) were obtained. The heat resistance and compression set were evaluated. The results are shown in Table 1.

(Comparative Example 2)
100 parts of modified NBR (JSR, trade name “N640H”), 45 parts of basic silica (reinforcing agent, trade name “Carplex # 1120”, manufactured by Shionogi & Co.), stearic acid (processing aid) 1 part and 2 parts of 4,4′-bis (α, α-dimethylbenzyl) diphenylamine (anti-aging agent) (Ouchi Shinsei Chemical Co., Ltd., trade name “NOCRACK CD”) were mixed at 50 ° C. using a banbury. Kneaded. 40 parts of the resulting kneaded product, 3 parts of an organic peroxide (Nippon Yushi Co., Ltd., trade name “Park Mill D-40”) and 10 parts of magnesium oxide (Kyowa Chemical Industry Co., Ltd., trade name “Kyowa Mug # 150”) And kneading with an open roll to obtain a rubber composition C.
Using this rubber composition C, a sheet-like crosslinked product was obtained in the same manner as in Example 1. However, the compression molding conditions were 180 ° C. for 5 minutes, and the secondary crosslinking temperature was 150 ° C. Evaluation was conducted in the same manner as in Example 1 using this sheet.
Further, from the rubber composition C, a cylindrical cross-linked body having an inner diameter of 29 mm and a height of 12.5 mm was prepared under the same compression molding and cross-linking conditions as those for the above-mentioned sheet-like cross-linked body, and the compression set was evaluated for this. Was done.
These evaluation results are shown in Table 1.

From the results shown in Table 1, the following can be seen.
An acrylic rubber composition crosslinked body for a seal member using an acrylic rubber having an alkoxyalkyl acrylate monomer unit content of 30% by weight (50% by weight or more) deviating from the scope of the present invention (Comparative Example 1) It can be seen that the hardness and volume are greatly changed by immersion in polyalkylene glycol.
On the other hand, it turns out that the acrylic rubber composition crosslinked body for sealing members of the present invention (Example 1) is excellent in PAG resistance. Moreover, it turns out that it is excellent in the balance of compression set, heat resistance, and PAG resistance compared with the bridge | crosslinking body for sealing members obtained using NBR.

Claims (10)

  From the group consisting of polyalkylene glycol lubricating oil, ester-modified polyalkylene glycol lubricating oil and ester-based lubricating oil, comprising an acrylic rubber having an alkoxyalkyl acrylate monomer unit content of 50% by weight or more and a crosslinking agent. An acrylic rubber composition for a seal member for a compressor using a selected synthetic lubricant.   The acrylic rubber composition for sealing members according to claim 1, wherein the monomer constituting the alkoxyalkyl acrylate monomer unit is 2-methoxyethyl acrylate or 2-ethoxyethyl acrylate. The acrylic rubber composition for sealing members according to any one of claims 1 to 2, wherein the acrylic rubber contains 4 x 10 ^-4 to 4 x 10 ^-1 equivalents of carboxy group or epoxy group per 100 g.   The acrylic rubber composition for a seal member according to any one of claims 1 to 3, wherein the acrylic rubber has a butenedionic acid monoalkyl ester monomer unit.   The acrylic rubber composition for sealing members according to claim 4, wherein the monomer constituting the butenedionic acid monoalkyl ester monomer unit is mono-n-butyl maleate or mono-n-butyl fumarate.   The acrylic rubber composition for sealing members according to any one of claims 1 to 5, wherein the crosslinking agent is a polyamine compound.   The acrylic rubber composition for a seal member according to any one of claims 1 to 6, which is an acrylic rubber composition for a seal member for a compressor using polyalkylene glycol as a lubricating oil.   The acrylic rubber composition for a seal member according to any one of claims 1 to 7, wherein the maximum temperature during continuous use is 130 ° C or higher.   A cross-linked acrylic rubber composition for a seal member obtained by cross-linking the acrylic rubber composition for a seal member according to any one of claims 1 to 8.   A compressor using a synthetic lubricating oil selected from the group consisting of a polyalkylene glycol lubricating oil, an ester-modified polyalkylene glycol lubricating oil, and an ester-based lubricating oil, comprising the crosslinked acrylic rubber composition for a seal member according to claim 9. Sealing member.