Ethylene acrylate rubber composition and molded article thereof

Abstract

We provide an ethylene acrylate rubber composition that exhibits a good balance of oil resistance, heat resistance, and hydrolysis resistance after molding and crosslinking, and a molded article made from a crosslinked product of the ethylene acrylate rubber composition. The ethylene acrylate rubber composition contains 100 parts by mass of ethylene acrylate rubber, 10 to 50 parts by mass of a plasticizer having an SP value of 7 or more, and 0.05 to 30 parts by mass of a crosslinking agent selected from aliphatic polyhydric primary amines and their derivatives, and is characterized in that the content of the plasticizer having an SP value of less than 7 is less than 0.1 part by mass. We also provide a molded article made from a crosslinked product of the ethylene acrylate rubber composition.

Description

[Technical field]

[0001] The present invention relates to an ethylene acrylate rubber composition and a molded article thereof. [Background technology]

[0002] Acrylic rubber has excellent oil and heat resistance, and is cheaper than fluororubber, so it is widely used in sealing products such as oil seals, gaskets, O-rings, etc. However, acrylic rubber is prone to hydrolysis reactions due to water (acids and bases), and its water resistance is inferior to other synthetic rubbers such as nitrile rubber and fluororubber.

[0003] Meanwhile, various machine oils, including engine oil, are present around the engine of an automobile, where acrylic rubber-based sealants are often used. These machine oils may contain a small amount of moisture due to condensation caused by temperature changes when the engine is running and stopped, rain, etc. Furthermore, moisture generated by fuel combustion in the engine may be mixed into the engine oil.

[0004] Therefore, sealing materials using acrylic rubber are exposed to moisture in the usage environment and deteriorate due to hydrolysis, which may result in the sealing function being unable to be maintained.

[0005] Therefore, as a method for improving the hydrolysis resistance of acrylic rubber, ethylene acrylate rubber has come to be used as a rubber having a similar chemical structure and higher hydrolysis resistance than acrylic rubber, but the ethylene acrylate rubber has a problem of being slightly inferior to acrylic rubber in terms of oil resistance.

[0006] There are various known attempts to improve the performance of ethylene acrylate rubber compositions by adding a third component. For example, in Patent Document 1, an ester compound having a specific chemical structure is added to achieve both heat resistance and cold resistance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-12821 Summary of the Invention [Problem to be solved by the invention]

[0008] However, little is known about the prior art that aims to achieve compatibility between oil resistance, heat resistance, and hydrolysis resistance in an ethylene acrylate rubber composition after molding and crosslinking.

[0009] The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide an ethylene acrylate rubber composition having a good balance of oil resistance, heat resistance and hydrolysis resistance after molding and crosslinking, and a molded article made of a crosslinked product of the ethylene acrylate rubber composition. [Means for solving the problem]

[0010] The present inventors have found that by adding an appropriate amount of a plasticizer and a crosslinking agent to an ethylene acrylate rubber, it is possible to obtain both oil resistance and hydrolysis resistance while maintaining heat resistance after molding and crosslinking, and have arrived at the present invention. The present invention has the following features.

[0011] The ethylene acrylate rubber composition of the present invention contains 100 parts by mass of ethylene acrylate rubber, 10 to 20 parts by mass of a plasticizer having an SP value of 7 or more, 0.05 to 30 parts by mass of a crosslinking agent selected from aliphatic polyvalent primary amines and their derivatives, and 0.05 to 20 parts by mass of a crosslinking accelerator which is 1,8-diazabicyclo[5.4.0]undec-7-ene, wherein the plasticizer having an SP value of 7 or more is one or more selected from polyether ester plasticizers, trimellitic acid ester plasticizers, and hydrogenated hydrocarbon plasticizers, the composition at least contains a trimellitic acid ester plasticizer, and the content of plasticizers having an SP value of less than 7 is less than 0.1 part by mass. After molding and crosslinking, the rubber was treated with 1% by mass of ZnCl 2 When immersed in an aqueous solution at 150°C for 200 hours, the difference in hardness before and after immersion measured using a durometer type A is +9 or less. It is a composition.

[0012] The ethylene acrylate rubber composition of the present invention preferably contains at least one of 20 to 150 parts by mass of carbon black and 20 to 150 parts by mass of silica.

[0013] In addition, in the ethylene acrylate rubber composition of the present invention, the plasticizer having an SP value of 7 or more is preferably one or more selected from polyether ester plasticizers, trimellitic ester plasticizers, pyromellitic ester plasticizers, and hydrogenated hydrocarbon plasticizers.

[0014] The molded article of the present invention is made of a crosslinked product of the ethylene acrylate rubber composition. The molded article of the present invention is preferably a sealing material. Effect of the Invention

[0015] The ethylene acrylate rubber composition of the present invention has a good balance of oil resistance, heat resistance and hydrolysis resistance after molding and crosslinking, and the molded article of the present invention has a good balance of oil resistance, heat resistance and hydrolysis resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, the scope of the present invention is not limited to the embodiments described below.

[0017] The ethylene acrylate rubber composition of the present invention contains an ethylene acrylate rubber, a plasticizer having an SP value of 7 or more, and a crosslinking agent selected from aliphatic polyvalent primary amines and derivatives thereof. Each component constituting the ethylene acrylate rubber composition of the present invention will be described below.

[0018] (Ethylene acrylate rubber) Ethylene acrylate rubber is also called ethylene-acrylic rubber or AEM. Ethylene acrylate rubber is a polymer made by copolymerizing ethylene and acrylic acid alkyl ester as main monomer components with crosslinkable monomers having crosslinkable groups, and is preferably a terpolymer.

[0019] Examples of alkyl acrylates include alkyl acrylates having an alkyl group with 1 to 20 carbon atoms. Specific examples include methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, propyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, etc. Among these, preferred are methyl acrylate, ethyl acrylate, and n-butyl acrylate, and more preferred is methyl acrylate.

[0020] As the ethylene acrylate rubber, an ethylene acrylate rubber having a crosslinkable group that is crosslinked by an aliphatic polyvalent primary amine or its derivative is used. Therefore, the crosslinkable group of the crosslinkable monomer that constitutes the ethylene acrylate rubber must be a crosslinkable group that is crosslinked by an aliphatic polyvalent amine or its derivative. Such crosslinkable groups include carboxyl groups, epoxy groups, halogen groups, etc. Among these, it is preferable that the crosslinkable group is a carboxyl group.

[0021] Examples of the crosslinkable monomer having a carboxyl group include monoalkyl esters of unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, etc., such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, etc., and unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, etc. These crosslinkable monomers having a crosslinkable group are used in a copolymerization ratio of about 0.5 to 10% by mass in the ethylene acrylate rubber.

[0022] Commercially available examples of the ethylene acrylate rubber include Vamac (registered trademark) G and Vamac GLS manufactured by DuPont Dow Elastomers Co., Ltd. These ethylene acrylate rubbers can be used alone or in combination of two or more different types of rubber.

[0023] (Plasticizer) The present inventors presumed that it is important to select an appropriate plasticizer in order to achieve a good balance between oil resistance, heat resistance, hydrolysis resistance, and processability of an ethylene acrylate rubber composition after molding and crosslinking. That is, they considered it important to select a plasticizer that has excellent compatibility with the ethylene acrylate rubber and can be present stably in the composition, and at the same time, is moderately incompatible with both oil and water, and compensates for the oil resistance of the ethylene acrylate rubber.

[0024] The SP value is a parameter used to evaluate the compatibility of two components. The SP value is the solubility parameter, and is known as a measure of intermolecular forces. It is generally known that the smaller the difference between the SP values ​​of two components, the higher the compatibility.

[0025] Therefore, we tried to select a plasticizer using this SP value as a clue. The SP value of ethylene acrylate rubber depends on the grade, so it is not possible to obtain a definite numerical value, but it is estimated to be 8 or more. Therefore, we prepared prototypes of compositions with ethylene acrylate rubber using various plasticizers with different SP values, and evaluated the oil resistance, heat resistance, and hydrolysis resistance of the molded products after molding and crosslinking. As a result, we found that plasticizers with an SP value of 7 or more are effective. It is more preferable for the SP value of the plasticizer to be 8 or more.

[0026] The type of plasticizer having an SP value of 7 or more is preferably one or more selected from polyether ester plasticizers, trimellitic ester plasticizers, pyromellitic ester plasticizers, and hydrogenated hydrocarbon plasticizers. Among these, trimellitic ester plasticizers, which have excellent kneading processability, are preferred.

[0027] Specific examples of the polyether ester plasticizer include Adeka Cizer RS735 (manufactured by Adeka Corporation) and Adeka Cizer RS700 (manufactured by Adeka Corporation).

[0028] Specific examples of trimellitic acid ester plasticizers include tri(2-ethylhexyl) trimellitate, tri-n-octyl trimellitate, triisodecyl trimellitate, triisononyl trimellitate, and mixed higher alcohol esters of trimellitic acid.

[0029] Specific examples of pyromellitic acid ester plasticizers include tetra(2-ethylhexyl) pyromellitate, tetra-n-octyl pyromellitate, and pyromellitic acid mixed higher alcohol esters.

[0030] Specific examples of hydrogenated hydrocarbon plasticizers include the Durasyn series manufactured by INEOS.

[0031] The plasticizer having an SP value of 7 or more is blended in an amount of 10 to 50 parts by mass relative to 100 parts by mass of the ethylene acrylate rubber. The content of the plasticizer having an SP value of 7 or more is preferably 10 to 30 parts by mass, and more preferably 10 to 20 parts by mass. When the plasticizer having an SP value of 7 or more is in the above content, it is possible to achieve a good balance between processability, heat resistance, oil resistance, and hydrolysis resistance.

[0032] As the plasticizer, a plasticizer with an SP value of 7 or more and a plasticizer with an SP value of less than 7 can be used in combination, but there is a risk that the plasticizer with an SP value of less than 7 will bleed out and reduce processability. Therefore, when using a mixture of both, the content of the plasticizer with an SP value of less than 7 is less than 0.1 part by mass for 10 to 50 parts by mass of the plasticizer with an SP value of 7 or more.

[0033] (Crosslinking agent) As described above, the ethylene acrylate rubber used is an ethylene acrylate rubber crosslinked by an aliphatic polyvalent primary amine or its derivative. Therefore, a crosslinking agent selected from an aliphatic polyvalent primary amine and its derivative is used as the crosslinking agent.

[0034] Examples of aliphatic polyvalent primary amines that can be used as crosslinking agents include aliphatic polyamines such as hexamethylenediamine, N,N'-dicinnamylidene-1,6-hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, ethylenediamine, and 1,4-diaminobutane.

[0035] In addition, examples of derivatives of aliphatic polyvalent primary amines include hexamethylenediamine carbamate, etc. These aliphatic polyvalent primary amines or their derivatives may be used alone or in combination of two or more kinds.

[0036] The crosslinking agent selected from aliphatic polyvalent primary amines and their derivatives is blended in an amount of 0.05 to 30 parts by mass relative to 100 parts by mass of the ethylene acrylate rubber. The blending amount of the crosslinking agent is preferably 0.1 to 10 parts by mass, and more preferably 0.3 to 1 part by mass.

[0037] (Crosslinking accelerator) In addition to the crosslinking agent, a crosslinking accelerator can be used in combination. It is preferable to use a basic crosslinking accelerator in combination. As the basic crosslinking accelerator, a guanidine compound, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]nonene-5, etc. are used. Commercially available products include Vulcofac ACT55 manufactured by Safic Alcan. The crosslinking accelerator is preferably blended in an amount of 0.05 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the ethylene acrylate rubber.

[0038] The ethylene acrylate rubber composition preferably contains at least one of 20 to 150 parts by mass of carbon black and 20 to 150 parts by mass of silica relative to 100 parts by mass of the ethylene acrylate rubber.

[0039] (Carbon Black) Carbon black is blended to reinforce the ethylene acrylate rubber composition. The type of carbon black is not particularly limited, and examples of carbon black include SRF, GPF, FEF, HAF, MAF, ISAF, SAF, FT, and MT, with MAF and SRF being preferred. These carbon blacks may be used alone or in combination of two or more types. Commercially available products include the product name: Seast GS, manufactured by Tokai Carbon Co., Ltd.

[0040] The carbon black is preferably blended in an amount of 20 to 150 parts by mass per 100 parts by mass of the ethylene acrylate rubber. If the carbon black content is less than 20 parts by mass, it may be difficult to maintain the tensile strength of the ethylene acrylate rubber. If the carbon black content exceeds 150 parts by mass, it may be difficult to knead and mold the rubber. The carbon black content is more preferably 30 to 100 parts by mass.

[0041] (silica) Silica is compounded to reinforce the ethylene acrylate rubber composition. Specific examples of silica include precipitated silica, colloidal silica, vapor phase silica, and organosilica sol. Among these, precipitated silica is preferred. Commercially available precipitated silica products include, for example, the Nipsil series manufactured by Tosoh Silica Corporation. Commercially available colloidal silica products include, for example, the Snowtex series manufactured by Nissan Chemical Industries, Ltd. Commercially available vapor phase silica products include, for example, the Aerosil series manufactured by Nippon Aerosil Co., Ltd. Commercially available organosilica sol products include, for example, the Snowtex series manufactured by Nissan Chemical Industries, Ltd.

[0042] The silica is preferably contained in an amount of 20 to 150 parts by mass relative to 100 parts by mass of the ethylene acrylate rubber. If the silica content is less than 20 parts by mass, it may be difficult to maintain the tensile strength of the ethylene acrylate rubber. If the silica content exceeds 150 parts by mass, it may be difficult to knead and mold the rubber. The silica content is more preferably 20 to 80 parts by mass.

[0043] In addition to the above-mentioned components, the ethylene acrylate rubber composition may contain, as necessary, known compounding agents such as processing aids, reinforcing agents, fillers, acid acceptors, antioxidants, stabilizers, etc. Examples of such compounds include processing aids such as stearic acid, and acid acceptors such as zinc oxide and magnesium oxide.

[0044] (Cross-linked molded product of ethylene acrylate rubber composition) In order to manufacture a crosslinked molded product using an ethylene acrylate rubber composition, a predetermined crosslinking agent, a crosslinking accelerator, etc. are added to the ethylene acrylate rubber to form an ethylene acrylate rubber composition, which is then molded and crosslinked. The order of the molding step and the crosslinking step of the ethylene acrylate rubber composition is not particularly limited and may be selected according to the shape of the member, etc. The molding step may be performed before the crosslinking step, the crosslinking step may be performed before the molding step, or the molding step and the crosslinking step may be performed simultaneously.

[0045] As a kneader for preparing the uncrosslinked ethylene acrylate rubber composition (rubber compound), a known kneader such as a single screw extruder, a twin screw extruder, a roll, a Banbury mixer, a kneader, a high shear mixer, etc. The method and order of adding each component constituting the ethylene acrylate rubber composition to the kneader are not particularly limited.

[0046] The method for molding the ethylene acrylate rubber composition into a molded article is not particularly limited, and any method such as compression molding, injection molding, extrusion molding, and transfer molding can be used.

[0047] The crosslinking process for crosslinking the uncrosslinked ethylene acrylate rubber composition may be carried out in one step, or may be divided into two steps, a primary crosslinking and a secondary crosslinking. By carrying out the secondary crosslinking after the primary crosslinking, crosslinking can be ensured to the inside. The crosslinking conditions are generally about 150 to 230°C, and pressurized crosslinking for about 0.5 to 30 minutes. When carrying out the secondary crosslinking, it is generally carried out by heating in an oven at about 150 to 250°C for about 0.5 to 24 hours.

[0048] Molded articles made of crosslinked products of ethylene acrylate rubber compositions can be widely used in a wide range of fields, such as transportation machinery such as automobiles, general machinery, electronic and electrical equipment, building materials, hoses, etc. They are particularly useful as sealing materials such as gaskets, O-rings, packings, oil seals, and bearing seals. EXAMPLES

[0049] The present invention will be described in more detail below using examples (Examples 1 to 4, Comparative Examples 1 to 3). The raw materials of the ethylene acrylate rubber compositions used in the examples and comparative examples are as follows. Ethylene acrylate rubber (AEM): DuPont, Vamac Ultra HT-OR, high temperature oil resistant grade Acrylic rubber (ACM): Unimatec, Noxtite PA522HF Plasticizer: Trimellitic acid ester plasticizer, manufactured by ADECA, Adeka Cizer C-9N, SP value: 8.5 Plasticizer: Polyetherester plasticizer, manufactured by ADECA, Adeka Cizer RS700, SP value: 8.9 Plasticizer: Hydrogenated hydrocarbon plasticizer, INEOS, Durasyn 164, SP value: 7.9 Plasticizer: Paraffin-based, Idemitsu Kosan Co., Ltd., Diana Process Oil PW380, SP value: 6.6 Carbon black: SRF carbon black, manufactured by Tokai Carbon Co., Ltd., Seast GS Silica: Tosoh Silica, Nipsil E74P Crosslinker: Hexamethylenediamine carbamate Crosslinking accelerator: DBU (diazabicycloundecene)

[0050] Using an internal mixer and an open roll, the components shown in Table 1 were mixed to prepare a dough of an ethylene acrylate rubber composition. The obtained rubber dough was pressed to produce an uncrosslinked rubber sheet of about 3 mm thickness. Thereafter, the rubber was press-crosslinked under crosslinking conditions of 180°C for 6 minutes, and then secondary crosslinking was carried out under crosslinking conditions of 175°C for 15 hours to produce a crosslinked rubber sheet of 2 mm thickness.

[0051] <Performance evaluation of cross-linked rubber sheets> (1) Processability It was judged whether or not significant bleeding of the plasticizer was observed in the uncrosslinked material, the crosslinked rubber during press crosslinking, and the crosslinked rubber after secondary crosslinking. When the bleeding of the plasticizer was small, it was marked with ○, and when the bleeding of the plasticizer was large, it was marked with ×.

[0052] (2) Oil resistance The difference in hardness and the rate of change in volume were measured before and after immersion at 150°C for 70 hours using JIS No. 3 oil in accordance with JIS K 6258. A durometer (A type) was used to measure the hardness. Evaluation criteria for oil resistance: Good when the difference in hardness is -20 or less, and good when the volume change rate is +30% or less.

[0053] (3) Hydrolysis resistance The specimens were immersed in the aqueous solution under two conditions, and the difference in hardness and the rate of change in volume were measured before and after immersion in accordance with JIS K 6258. A durometer (type A) was used to measure the hardness. Immersion conditions for hydrolysis resistance 1: Immersed in a 1 mass % ZnCl2 aqueous solution at 120°C for 480 hours, and then dried at 120°C for 70 hours. Immersion conditions for hydrolysis resistance 2: Immersed in a 1% by mass ZnCl2 aqueous solution at 150°C for 200 hours.

[0054] Evaluation criteria for hydrolysis resistance 1: ○: Hardness difference is +20 or less, ×: Hardness difference is more than +20 Evaluation criteria for hydrolysis resistance 2: Good when the difference in hardness is +20 or less, and good when the volume change rate is +50% or less.

[0055] The evaluation results of the crosslinked rubber sheet are shown in Table 1.

[0056] [Table 1]

[0057] As can be seen from the results in Table 1, the crosslinked rubber sheets of Examples 1 to 4 were made using Vamac Ultra HT-OR, a high-temperature oil-resistant grade ethylene acrylate rubber, and by adding a plasticizer with good compatibility and an SP value of 7 or more, it was possible to improve hydrolysis resistance without significantly impairing oil resistance. The crosslinked rubber sheet of Comparative Example 1 was inferior in oil resistance to the crosslinked rubber sheet of acrylic rubber of Comparative Example 3 because no plasticizer was blended therein. The crosslinked rubber sheet of Comparative Example 2 contained a paraffin-based plasticizer that had a low SP value and poor compatibility with ethylene acrylate rubber, and therefore significant bleeding of the plasticizer was observed in both the uncrosslinked sheet and the crosslinked sheet, resulting in poor processability. The crosslinked rubber sheet of Comparative Example 3 used acrylic rubber, and was significantly inferior in hydrolysis resistance compared to ethylene acrylate rubber.

Claims

1. 100 parts by mass of ethylene acrylate rubber, 10 to 20 parts by mass of a plasticizer having an SP value of 7 or more, 0.05 to 30 parts by mass of a crosslinking agent selected from aliphatic polyvalent primary amines and their derivatives, and 0.05 to 20 parts by mass of a crosslinking accelerator which is 1,8-diazabicyclo[5.4.0]undec-7-ene. Contains the plasticizer having an SP value of 7 or more is one or more selected from a polyether ester plasticizer, a trimellitic acid ester plasticizer, and a hydrogenated hydrocarbon plasticizer, and includes at least a trimellitic acid ester plasticizer; The content of a plasticizer having an SP value of less than 7 is less than 0.1 parts by mass, An ethylene acrylate rubber composition, characterized in that when a molded and crosslinked rubber is immersed in a 1 mass % ZnCl 2 aqueous solution at 150° C. for 200 hours, the difference in hardness before and after immersion, as measured using a durometer type A, is +9 or less.

2. 2. The ethylene acrylate rubber composition according to claim 1, further comprising at least one of 20 to 150 parts by mass of carbon black and 20 to 150 parts by mass of silica.

3. A molded article comprising a crosslinked product of the ethylene acrylate rubber composition according to any one of claims 1 to 2.

4. 4. The molded article according to claim 3, which is a sealing material.

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