JP2008106131A - Rubber composition and molded article using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition excellent in chlorine resistance and water resistance. <P>SOLUTION: This rubber composition comprises an ethylene-propylene rubber and hydrophobic silica. Thereby, problems of rubber deterioration caused by residual chlorine and water, such as the release of rubber itself or carbon compounded with the rubber, the outflow of black foreign matter into tap water, and water leak due to the swelling of the rubber and the loss of self-sealing property can be solved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition containing ethylene propylene rubber and a molded article using the same.

A rubber composition containing ethylene propylene rubber is widely used as a molding material for sealing materials such as packing because it is excellent in chemical resistance, ozone resistance, heat resistance and the like. However, since the water quality of rivers and lakes has been polluted due to recent environmental deterioration, a large amount of chlorine has been introduced into tap water using these as water sources. As a result, there has been a problem of rubber deterioration due to residual chlorine, which could not be predicted in the past. For example, the rubber itself and the carbon blended with it are detached and flow into black water as black foreign matter, or water leakage occurs due to loss of self-sealing due to rubber deterioration. It became so.
For such problems, fluororesins and fluororubbers may be used, but these are extremely expensive products and are not suitable for general purpose applications. There are problems such as inferior properties such as low temperature characteristics and high temperature steam resistance compared to rubber.

In order to solve such a problem, a rubber composition composed of a blend of ethylene propylene rubber and alkaline silica has been proposed and is said to be excellent in resistance to chlorine deterioration (Patent Document 1).
JP-A-2005-343492

However, in the conventional rubber composition, water resistance is not necessarily sufficient because it easily swells in water. Therefore, there is still room for improvement as a rubber composition that can be put to practical use.
The present invention has been made in view of such circumstances, and a problem to be solved is to provide a rubber composition excellent in chlorine resistance and water resistance and a molded product using the same.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the knowledge that the cause of the water resistance deterioration of the conventional rubber composition is the silica having alkalinity blended with the ethylene propylene rubber. It was. That is, since silica having alkalinity is produced by a wet method such as a sedimentation method, the surface has many hydroxyl groups and the hydrophilicity is improved. As a result, it has been found that the silica has a tendency to swell when contacted with water. . As a result of further research, the present inventors have found that silica to be blended with ethylene-propylene rubber is produced by a dry process with fewer hydroxyl groups on the surface compared to the wet process, or hydrophobic treatment ( The inventors have found that the above problems can be solved by using a compound in which a hydroxyl group is chemically substituted with a methyl group, and have completed the present invention.

That is, the present invention is as follows.
(1) A rubber composition comprising ethylene propylene rubber and hydrophobic silica.
(2) A molded product comprising the rubber composition as described in (1) above.
(3) The molded product according to (2), which is a sealing material.
(4) The molded article according to (2) or (3), which is used in contact with chlorine-containing water.

  According to the present invention, it is possible to provide a rubber composition that is excellent not only in chlorine resistance but also in water resistance at low cost. As a result, if the rubber composition of the present invention is used as a constituent material of a molded product used in contact with chlorine-containing water or water, rubber deterioration caused by residual chlorine or water, for example, the rubber itself or this The long life of molded products made from such rubber compositions is solved because problems such as carbon detachment, leakage of black foreign matter into tap water, swelling of rubber, and water leakage due to loss of self-sealing are solved. Can be realized. Therefore, for example, it is particularly useful as a molded product such as packing, O-ring, and expansion joint used for the purpose of supplying tap water or stopping water.

Hereinafter, embodiments of the present invention will be described in detail.
The rubber composition of the present invention is characterized by containing ethylene propylene rubber and hydrophobic silica. Hereinafter, each component which comprises the rubber composition of this invention is demonstrated.

  In the present invention, “ethylene propylene rubber” means ethylene-propylene rubber (EPM) which is a binary copolymer of ethylene and propylene, ethylene-propylene rubber which is a terpolymer of ethylene, propylene and a diene monomer for crosslinking. It is a concept including propylene-diene rubber (EPDM) and a mixture thereof. Further, EPDM is commercially available in various synthetic rubbers depending on the type and amount of the crosslinking diene monomer. Examples of the diene monomer used include ethylidene norbornene, dicyclopentadiene, 1,4-hexadiene, Examples include methyltetrahydroindene, 5-methylene-2-norbornene, and cyclooctadiene. Among them, ethylidene norbornene and dicyclopentadiene are preferable. Furthermore, the content of the diene monomer is not particularly limited, and is usually 1.5 to 9.0% by weight, preferably 4.5 to 8.0% by weight. The diene monomer may be used alone or in combination of two or more. In addition, EPM and EPDM are obtained by a normal polymerization means, and the means is not particularly limited.

Examples of the “hydrophobic silica” in the present invention include the following (1) and (2).
(1) Dry silica: Silica produced by a high-temperature gas phase reaction, that is, a so-called dry method, has almost no hydroxyl group on its surface and is acidic. The silica production method is not particularly limited as long as it is classified as a dry method, and may be an indirect method or a direct method.
(2) Wet process hydrophobic silica: Silica produced by a wet process using a liquid phase reaction, whose surface has hydroxyl groups reduced by calcination, or substituted with hydrophobic groups such as methyl groups by chemical treatment Silica.

  In order to improve the dispersibility of the hydrophobic silica in the ethylene propylene rubber, it is desirable to use one having an average particle diameter of usually 1 to 40 nm, preferably 4 to 20 nm. If it is smaller than 1 nm, the reinforcing property to ethylene propylene rubber is strong and the elongation tends to be small, and if it exceeds 40 nm, a large amount must be blended, and the permanent strain tends to decrease. In addition, an average particle diameter means the average particle diameter of a primary particle.

  The amount of hydrophobic silica blended can be selected as appropriate in consideration of the properties (hardness, tensile strength, elongation, compression set, etc.) given to the ethylene propylene rubber, but it depends on the total weight of the ethylene propylene rubber. On the other hand, it is usually 1 to 200% by weight, preferably 5 to 80% by weight, more preferably 10 to 50% by weight. If it is less than 1% by weight, the tensile strength tends to decrease, and if it exceeds 200% by weight, the elongation tends to decrease and the compression set tends to decrease.

  Thus, in the present invention, by adding hydrophobic silica to the ethylene propylene rubber, it is possible to improve the compression set, the tensile strength, and the elongation while being excellent in chlorine resistance and water resistance. Specifically, the rubber composition in the present invention has a compression set (70 ° C. × 22 hours, 25% compression) measured according to JIS K 6262, for example, 8 to 30% (preferably 8 to 16%). Further, when the hardness of the rubber composition is adjusted to about A50 / S, the tensile strength measured in accordance with JISK 6251 is, for example, 5 to 25 MPa (preferably 10 to 20 MPa), and the elongation is increased. Is, for example, 150 to 800% (preferably 500 to 750%).

  The rubber composition of the present invention includes additives known in the art, for example, a vulcanizing agent, a cross-linking agent, an anti-aging agent, an antioxidant, a silane cup, within a range that does not impair the object of the present invention. A ring agent, a plasticizer, a metal oxide, a lubricant, and a colorant can be appropriately blended, but 2 to 5 parts by weight of a vulcanizing agent and 0 to 4 of an anti-aging agent with respect to 100 parts by weight of ethylene propylene rubber. It is desirable to add 0 to 5 parts by weight of the silane coupling agent and 0 to 50 parts by weight of the plasticizer.

  The rubber composition is, for example, ethylene propylene rubber and hydrophobic silica, and if necessary, additives are kneaded using a kneader such as intermix, kneader, banbury mixer, open roll, etc., and then vulcanized press, compression molding machine It can be prepared by heating and vulcanizing usually at 150 to 200 ° C. for about 3 to 60 minutes using an injection molding machine or the like. If desired, secondary vulcanization can be carried out at 120 to 200 ° C. for 1 to 24 hours. Also good.

  In that case, it can be molded into a desired shape by a vulcanizing press, a compression molding machine, an injection molding machine or the like. The shape and size of the molded product are not particularly limited and are appropriately selected according to the purpose of use. However, since the rubber composition of the present invention has improved chlorine resistance and water resistance, it comes into contact with chlorine-containing water. Particularly useful are seal materials such as O-rings, packings, shaft seals, and expansion joints. The chlorine-containing water may be any of clean water, sewage, and waste water.

  Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

(Examples 1-5 and Comparative Examples 1-2)
Each component described in Table 1 was kneaded with an open roll, and further press vulcanized at 175 ° C. for 10 minutes to prepare a 2.0 mm thick sheet-like rubber composition. In addition, the compounding quantity of a silica and a plasticizer was adjusted so that the hardness of the sheet-like rubber composition measured based on JISK 5253 may be set to about A50 / S. Moreover, the compounding quantity of each component in Table 1 means a weight part.

The compounding components used in this example are as follows.
1) Dry process hydrophobic silica: Aerosil R-972 (product name, manufactured by Degussa Co., Ltd.)
2) Wet process hydrophilic silica: Carplex # 1120 (product name, manufactured by Nishimura Co., Ltd.)
3) Dry process hydrophilic silica: Aerosil 200 (product name, manufactured by Degussa Co., Ltd.)
4) Wet process calcined silica: Carplex CS-7 (product name, manufactured by Shionogi Co., Ltd.)
5) Wet process hydrophobic silica: Nip seal SS-30V (product name, manufactured by Tosoh Silica Co., Ltd.)
6) Wet process hydrophobic silica: Sipernat D17 (product name, manufactured by Degussa)

(Evaluation test)
The following tests were conducted on the sheet-like rubber compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2.
(1) Normal state physical property The No. 3 dumbbell piece based on JISK6251 was produced using the obtained rubber composition, and hardness, tensile strength, and elongation were evaluated. The results are shown in Table 2.

(2) Compression set The compression set (70 ° C. × 22 hours, 25% compression) of the cylindrical rubber composition was measured by a method based on JIS K 6262. The results are shown in Table 2.

(3) Water resistance The sheet-like rubber composition was immersed in 70 degreeC ion-exchange water for 168 hours, and the weight change rate of the sheet before and after immersion was measured. The results are shown in Table 2.

(4) Chlorine resistance A sodium hypochlorite aqueous solution having a chlorine concentration of 50 ppm was prepared, the sheet rubber composition was immersed in chlorine water at 60 ° C. for 500 hours, and the appearance change before and after immersion was visually observed to determine residual chlorine. The effect of was evaluated. The results are shown in Table 2.

The rubber compositions of Examples 1 to 5 were confirmed to have appropriate tensile strength and elongation, small compression set, and good chlorine resistance and water resistance.
In contrast, the rubber composition of Comparative Example 1 has substantially the same tensile strength, elongation, and compression set as Example 1, but the surface is rough in the chlorine resistance test and is black when rubbed with a finger. The adhesion of the powder was confirmed.
In the rubber composition of Comparative Example 2, the tensile strength, elongation, compression set and chlorine resistance were almost the same as in Example 1, but it was confirmed that the rubber composition was greatly swollen with water and inferior in water resistance.

Claims (4)

  A rubber composition comprising ethylene propylene rubber and hydrophobic silica.   A molded article comprising the rubber composition according to claim 1.   The molded product according to claim 2, which is a sealing material.   The molded product according to claim 2 or 3, which is used in contact with chlorine-containing water.