JP6223957B2 - Foam rubber composition for seal material and seal material comprising the foam rubber composition - Google Patents

Description

  The present invention crosslinks a foamed rubber composition for a sealing material containing a foaming agent, a filler, and an ethylene-propylene-diene terpolymer (EPDM) as a rubber component, and the foamed rubber composition. The present invention relates to a sealing material molded into a predetermined shape.

  Rubber has been used for sealing materials such as joint seals, gaskets, and weather strips for automobiles for a long time, but in recent years, foamed rubber containing bubbles is being used from the viewpoint of cost reduction and weight reduction. For example, Patent Document 1 discloses a weather strip in which a rubber composition contains heat-expandable microcapsules for the purpose of weight reduction, and bubbles are formed by expanding the microcapsules with heat during vulcanization.

JP-A-6-183305

  However, it is desirable that the sealing material not only prevents moisture and dust from entering, but also has excellent cushioning properties. On the other hand, in Patent Document 1, since the bubbles are formed by the microcapsule, the sealing material becomes harder than the case where the bubbles are formed by the foaming agent, and the compression set, that is, the cushioning property is lowered.

  Moreover, in order to improve various physical properties, this type of foamed rubber is often blended with fillers such as silica and clay. However, these fillers cannot be expected to effectively improve compression set. Moreover, some of these fillers have a large specific gravity of the filler itself, which inevitably increases the specific gravity of the sealing material. On the other hand, carbon black is a filler that has a small specific gravity and is effective in improving compression set. However, when carbon black is blended in the sealing material, blackening is inevitable. With this, it is almost impossible to make color variations of the sealing material.

  Accordingly, the present invention solves the above-described problem, and provides a foamed rubber composition for a sealant that can provide a sealant having a good compression set, a low specific gravity, and a color that can be selected. It aims at providing the sealing material which consists of a rubber composition.

  As a means for that purpose, the present invention is a foamed rubber composition for a sealing material containing a foaming agent, a filler (filler), and an ethylene-propylene-diene terpolymer (EPDM) as a rubber component. , Wherein the filler contains silitin.

  The content of silytin is preferably 45 to 170 parts by weight with respect to 100 parts by weight of the rubber component. In the present invention, “XX to XX” indicating a numerical range means “XX or more and XX or less” unless otherwise specified.

  It is also possible to provide a sealing material obtained by crosslinking and molding the foamed rubber composition.

  According to the present invention, since the bubbles are formed by the foaming agent, the cushioning property is better than when bubbles are formed by the thermally expandable microcapsules. In addition, if silytin is used as the filler, it is possible to improve the compression set of the sealing material molded into a predetermined shape while avoiding a significant increase in specific gravity. In addition, if silytin is used as the filler, it is basically unnecessary to add a conventionally known general filler, and the cost can be reduced as compared with the conventional one. In particular, it is not always necessary to add carbon black. Here, since silytin is white, the foamed rubber composition of the present invention and the sealing material using the same are basically white. Therefore, it is possible to add colors other than black by appropriately blending colorants such as pigments and dyes, and it is also possible to select the color variation of the obtained sealing material. Furthermore, if EPDM is used for the rubber component as the main component (base), the fundamental physical properties as a sealing material are better than when other rubber components are used as the main component.

<Rubber component>
An ethylene-propylene-diene terpolymer (EPDM) is used as an essential component for the rubber component as the main (base) component. EPDM is obtained by copolymerizing ethylene, propylene, and a third component having an unsaturated bond in the side chain. Specifically, an ENB-based EPDM in which the third component is 5-ethylidene-2-norbonene (ENB), the third component is exo-dicyclopentadiene (DCP), endo-dicyclopentadiene (EDCP), and di- Examples thereof include DCP-based EPDM such as cyclopentadiene (DCPD). These EPDMs may be used alone or in combination of two or more.

  In the foamed rubber composition, IR (isoprene rubber), NBR (butadiene acrylonitrile rubber), SBR (styrene butadiene rubber) are used as long as the effects of the present invention are not impaired, assuming that EPDM is an essential main component. ), CSM (chlorosulfonated polyethylene), ACM (acrylic rubber), Q (silicone rubber), FKM (fluororubber), U (urethane rubber), and the like can also be mixed.

<Foaming agent>
As the foaming agent, various chemical foaming agents can be used. Specifically, 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), azodicarbonamide (ADCA), and N, N′-dinitrosopentamethylenetetramine (DPT), which are organic decomposition foaming agents, are used. be able to. These foaming agents may be used alone or in combination of two or more. OBSH is preferable in that the odor of the generated gas is small, but ADCA is preferable from the viewpoint of reducing compression set, and ADCA is relatively easy to control the bubble diameter and easily forms open cells. If the bubbles in the obtained foamed rubber molded body are open cells, the restoring force after compression is superior to the case of closed cells (single bubbles).

  The addition amount of the foaming agent can be appropriately adjusted in consideration of the specific gravity of the obtained sealing material (foamed rubber molded product), the amount of gas generated from the foaming agent, etc., but is 1 to 100 parts by weight of the rubber component. It may be 5 parts by weight. If the content of the foaming agent is less than 1 part by weight with respect to 100 parts by weight of the rubber component, the effect of reducing the weight is difficult to obtain, and if it is more than 5 parts by weight, physical properties such as strength deteriorate.

<Filler>
Silytin is added as an essential component to the foamed rubber composition in order to improve the compression set of the resulting sealing material. In addition, when silitin is added, it also tends to be superior in volume resistivity (insulating property) than when carbon black is added. Silitin is a spherical, hidden microcrystalline Neuburg Silysian earth (silica earth), also called a silicocolloid, and is an aggregate of amorphous (amorphous) silica and plate-like kaolinite. It is also preferable to appropriately treat the silitin with a surface modifier such as a silane coupling agent as necessary.

  The added amount of silytin is at least 45 to 170 parts by weight, preferably 45 to 130 parts by weight, and more preferably 50 to 110 parts by weight with respect to 100 parts by weight of the rubber component (total amount). When the content of silytin is less than 45 parts by weight with respect to 100 parts by weight of the rubber component, the specific gravity of the obtained sealing material is light, but compression set and molding processability deteriorate. On the other hand, when the amount exceeds 170 parts by weight, not only the compression set and molding processability of the resulting sealing material deteriorate, but also the specific gravity increases.

  The foamed rubber composition of the present invention basically only needs to contain silitin as a filler, and other fillers do not necessarily need to be added, but do not impair the effects of the present invention. In order to improve various physical properties such as strength, other fillers can be added. As other fillers, known ones that have been conventionally added to rubber moldings can be used without particular limitation. Specific examples include at least one selected from the group consisting of carbon black, silica, kaolin clay, talc, mica, and calcium carbonate, or two or more.

<Crosslinking agent>
The foamed rubber composition also contains a rubber component crosslinking agent. A typical example of the crosslinking agent is sulfur, but an organic peroxide can also be used for EPDM. What is necessary is just to let the addition amount of a crosslinking agent be 0.1-5 weight part with respect to 100 weight part of rubber components. When the content of the crosslinking agent is less than 0.1 parts by weight with respect to 100 parts by weight of the rubber component, the rubber component is not accurately crosslinked, and various physical properties of the obtained sealing material are deteriorated. On the other hand, if it exceeds 5 parts by weight, the degree of crosslinking is too high, which causes a decrease in various physical properties of the sealing material.

  For crosslinking of the rubber component, an atmospheric hot air heating furnace (HAV), a fluidized bed heating furnace (LCM), a microwave heating furnace (UHF), or the like can be used.

<Other additives>
In addition, other additives such as a softening agent, a crosslinking accelerator, and a pigment can be added to the foamed rubber composition as necessary. The softening agent is for facilitating kneading when the rubber component and the additive are mixed, and examples thereof include paraffinic oil. The crosslinking accelerator acts together with the organic peroxide crosslinking agent to increase the crosslinking rate in a small amount, and examples thereof include stearic acid and triallyl isocyanurate. These various additives may add only 1 type and can also mix 2 or more types.

  The sealing material can be formed into a predetermined shape by extrusion molding or the like while crosslinking the foamed rubber composition at a predetermined temperature. The obtained sealing material is suitable as a sealing material for doors, doors, can pails, etc., in addition to weather strips along the mounting parts of automobile wind moldings, over fenders, front grills, side moldings and the like.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, it is not limited to this. Each raw material shown in Table 1 was blended at a ratio shown in Table 1 and kneaded using an open roll to prepare a foamed rubber composition. Each foamed rubber composition obtained was continuously supplied to an extrusion continuous vulcanization molding apparatus having a PCM vulcanization facility, extruded and vulcanized at 200 ° C. for 10 minutes, and a cylindrical (φ5 × 100 mm) sealing material ( Examples and Comparative Examples) were obtained. Table 1 shows the moldability at that time. In Table 1, the numerical value indicating the blending amount is parts by weight. Moreover, the evaluation criteria of moldability are as follows.
◎: There is no problem at the time of open roll kneading, the surface of the extruded vulcanized molded article is smooth, and it is excellent as a product. No △: The composition is difficult to be assembled when kneading the open roll, and the surface of the extrusion vulcanized molded product has irregularities, making it difficult to form. Unusable as a product due to severe unevenness

The following were used as each raw material.
Rubber component: Ethylene-propylene-diene terpolymer (EPDM), manufactured by Mitsui Chemicals
"EPT8120"
Siritin: “Siritin Z86” manufactured by Hoffman Minerals (no surface treatment)
"Actividyl MM" manufactured by Hoffman Minerals (mercaptosilane treatment)
Carbon black: “SRF” manufactured by Asahi Carbon
Foaming agent: Azodicarbonamide (ADCA), “Cellmic CAP” manufactured by Mitsui Chemicals, Inc.
Cross-linking accelerator: Dipentamethylene thiuram tetrasulfide (DPTT), Ouchi Emerging
“Noxeller TRA” manufactured by Gaku Kogyo Co., Ltd.
2-Mercaptobenzothiazole (MBT) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Xceller M "
Zinc dimethyldithiocarbamate (ZnMDC) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
"Noxeller PZ"
Lubricant: “Emaster 510P” manufactured by Riken Vitamin

About the obtained sealing material of each Example and the comparative example, specific gravity and compression set were measured by the following method. The results are also shown in Table 1.
(specific gravity)
Using a specific gravity measuring machine “MD-300S” manufactured by Alpha Mirage, the measurement was performed based on JIS K 6268.
(Compression set)
Based on JIS K6262, compression rate was 50%, test condition: measured at 70 ° C. for 22 hours.

From the results shown in Table 1, the examples in which silytin was added as a filler were inferior in compression set, specific gravity, and workability in comparison with Comparative Example 3 in which carbon black was added. On the other hand, Comparative Examples 1 and 2 were all inferior in specific gravity, compression set, and molding processability as compared with the Examples because only fillers other than general siltin were conventionally added. In addition, in Comparative Examples 1 and 2, when 100 parts by weight of the filler was added to 100 parts by weight of the rubber component, the composition became rough and could not be formed as a rubber molded body. Comparative Example 3 to which carbon black was added was good in compression set, specific gravity, and processability, but became a black seal material, so it was difficult to color in other colors. In Comparative Example 4, since no filler was added, the specific gravity was small, but the moldability was greatly reduced. In Comparative Example 5, although the improvement of compression set was confirmed by adding silytin, there was a problem in molding processability. In Comparative Example 6, the specific gravity, compression set, and moldability were poor because of the excessive amount of silytin added.

Claims (3)

A foamed rubber composition for a sealing material containing a foaming agent, a filler, and an ethylene-propylene-diene terpolymer (EPDM) as a rubber component,
Containing silitin as the filler ,
A foamed rubber composition for a sealing material , wherein the content of the silytin is 50 to 150 parts by weight with respect to 100 parts by weight of the rubber component . The foamed rubber composition for a sealing material according to claim 1, wherein the silitin is silicin subjected to mercaptosilane treatment. A sealing material comprising the foamed rubber composition according to claim 1.