JP2007270023A - Foamed rubber composition and foamed rubber molded item - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the discoloration problem of metallic coating by blending OBSH, to prevent the crosslinking density decrease (moldability decrease) caused by a large mount blend of OBSH and to prevent cracks at the time of release by improving the high-temperature elongation. <P>SOLUTION: This foamed rubber composition is obtained by blending 5-14 pts.mass of OBSH as a foaming agent and 1-7 pts.mass of a sulfur-giving vulcanizing agent as a vulcanizing agent with a rubber component whose dien amount of EPDM is 5-6.9 mass%. The elongation of its foamed rubber molded item after foaming and molding (e.g. a die formed section 12 of a door weather strip 10) at 150°C is not less than 100%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a foamed rubber composition and a foamed rubber molded body such as a molded part of an automotive weather strip foam-molded with the composition.

  As shown in FIG. 1, a weather strip 50 for an automobile has solid rubber at the end portions of an extruded product 51 extruded with solid rubber and / or foam rubber at portions corresponding to the corner shape portion of the automobile. In many cases, they are manufactured by being connected by a mold forming part 52 molded with foamed rubber. In the weather strip, there is the following two problems in the molded part 52 molded with foamed rubber.

(1) Discoloration of metallic coating film When this weather strip (for example, the door weather strip 50 shown in FIG. 1) is attached to an attachment portion of an automobile (door 1 in FIG. 2), a mold forming portion 52 formed of foamed rubber is formed. There was a phenomenon in which the metallic coating film 3 on the contact portion (for example, the body 2 around the door) of the automobile that was in contact was discolored black and turned into a discolored portion 4 as shown in FIG. The reason is that ammonia, which is a decomposition component of the foaming agent contained in the foamed rubber, and urea, which is the foaming aid, alter the fine aluminum pieces in the metallic coating (oxidation, etc.). I know it. Conventionally, the foaming agent often used for this foamed rubber is azodicarbonamide (ADCA), and ammonia decomposes when it decomposes.

(2) Insufficiency of high temperature elongation and cracking at the time of mold release The molded part 52 molded by foamed rubber is likely to crack at the time of mold release after mold forming. The reason is that the conventional foamed rubber composition has low elongation characteristics at high temperatures (for example, the elongation is less than 100% at 150 ° C.), and therefore, the product breaks at the time of release at a high product temperature. For example, as shown in FIG. 3B, the mold forming portion 52 has a slit 53 for removing a core (not shown) for forming a hollow portion after the mold forming, and the slit 53 is opened when in use. A connecting portion 54 is provided in the middle of the slit to prevent the crack, but a crack 55 is generated in the connecting portion 54 at the time of mold release and is torn. Therefore, it is necessary to eliminate the connecting portion 54 and to bond a joint portion corresponding to the connecting portion 54 with an adhesive after molding.

Therefore, conventionally, as a countermeasure against the discoloration of the (1) metallic coating film, a prescription with a small amount of generated ammonia and a method of neutralizing ammonia are used. In addition, the use of p, p′-oxybis-benzenesulfonylhydrazide (OBSH) as a foaming agent that does not generate ammonia even when decomposed has been studied. For example,
Patent Document 1 describes a foamed rubber roller in which EPDM is blended with 2.5 to 15 parts of foaming agent OBSH and 1 to 4 parts of sulfur.
Patent Document 2 describes an automotive sealing material in which OBSH is blended with EPDM having a non-conjugated diene content of 7 wt% or more.
Patent Document 3 describes a foamed rubber blend in which OBSH is further blended with EPDM blended with dithiocarbamic acid, thiazole, thiourea, morpholine, and thiuram vulcanization accelerators.
JP 2005-257881 A JP 2005-097478 A JP-A-10-204201

  However, when a large amount of OBSH is added as a foaming agent for foamed rubber, there is a problem that the cross-linking density is lowered. In addition, no measures have been taken for the above-mentioned (2) lack of high-temperature elongation and cracking problems at the time of mold release.

  Therefore, the object of the present invention is not only to solve the problem of discoloration of the metallic coating film by blending OBSH, but also to suppress the decrease in crosslink density (decrease in moldability) due to the large amount of OBSH blending, and to increase the high temperature elongation. It is to improve and prevent cracking during mold release.

  The present invention adopts the following means (1) to (6) in order to solve the above-mentioned problems.

(1) Foam in which 5 to 14 parts by mass of OBSH as a foaming agent is blended with 1 to 7 parts by mass of a sulfur-donating vulcanizing agent in an EPDM rubber component having a diene content of 5 to 6.9% by mass Rubber composition.
(2) In the above (1), a foamed rubber composition in which sulfur as a vulcanizing agent is blended together with the sulfur donating vulcanizing agent, and the sulfur donating vulcanizing agent / sulfur = 0.5 to 3 (weight ratio). object.
(3) The foamed rubber composition according to (1) or (2), wherein the sulfur-donating vulcanizing agent is a morpholine vulcanizing agent.
(4) A foamed rubber composition in which 5-14 parts by mass of OBSH as a foaming agent is blended with the EPDM rubber component, and the foamed rubber molded body after foam molding has an elongation at 150 ° C. of 100% or more.
(5) A foamed rubber molded article foamed with the foamed rubber composition according to any one of (1) to (4).
(6) A foamed rubber molded product, wherein the foamed rubber molded product of (5) is a molded part of a weather strip for automobiles.

[Action]
The operation according to the present invention is considered as follows.
(A) FIG. 4A shows a thermal decomposition mechanism of OBSH. OBSH as a foaming agent has a foaming action when nitrogen gas is generated during thermal decomposition (decomposition by heating: decomposition temperature about 160 ° C.). On the other hand, ammonia is not generated during the decomposition, so even if the blending amount of OBSH is as large as 5 parts by mass or more, the aluminum fine pieces in the metallic coating film are not altered (oxidized or the like).

(B) On the other hand, when the amount of OBSH is as large as 5 parts by mass or more, the crosslinking density is lowered. However, when 1 part by mass or more of the sulfur-donating vulcanizing agent is blended, the crosslinking density is increased, so that a decrease in the crosslinking density can be suppressed. Explaining this mechanism:
(B1) As shown in FIG. 4A, when OBSH is thermally decomposed, an acidic substance (p, p′-oxybisbenzenesulfinic acid) is generated together with nitrogen gas. On the other hand, zinc white (ZnO) is blended in the sulfur vulcanized foam rubber composition as an essential vulcanization acceleration aid. However, since a part of zinc white reacts with the acidic substance (p, p′-oxybisbenzenesulfinic acid) to form a zinc salt, the vulcanization promoting action that zinc white should originally play is weakened. It is considered that the vulcanization reaction does not proceed easily. That is, since the acidic substance inhibits vulcanization, it is considered that the crosslinking density decreases as the blending amount of OBSH increases. Further, it has been difficult to improve the reduction in vulcanization torque due to the blending of a large amount of OBSH with a general rubber additive.

(B2) However, when 1 part by mass or more of a sulfur-donating vulcanizing agent (for example, morpholine vulcanizing agent) is blended, the crosslinking density increases due to a phenomenon opposite to the conventional knowledge as described below. It was found.
The active sulfur content of the morpholine vulcanizing agent shown in FIG. 4B (the example shown is 4,4′-dithio-bis-dimorpholine, manufactured by Ouchi Shinsei Chemical Co., Ltd., trade name “Varnock R”) is 27. 0.1% (sulfur: 1 part by mass corresponds to morpholine vulcanizing agent: 3.7 parts by mass). Therefore (in the case where OBSH is not blended), in general, when the same amount of sulfur is substituted for the sulfur-donating vulcanizing agent, the vulcanization speed is slow (t90 becomes large). there were.

However, under a large amount of OBSH as in the present invention, a phenomenon opposite to the conventional knowledge, that is, a sulfur-donating vulcanizing agent (for example, morpholine vulcanizing agent) is more effective for the crosslinking reaction than sulfur. It was confirmed that there was. The reason is considered to be due to the following estimation 1 and / or estimation 2.
[Estimation 1] In the presence of other rubber compounding agents, the decomposition temperature of the vulcanizing agent and the blowing agent is relatively low, but sulfur (simple) is 159 ° C, which is almost the same as the OBSH (simple) decomposition temperature (160 ° C). To open active sulfur. Therefore, the generation of an acidic substance (p, p'-oxybis-benzenesulfinic acid) that is an OBSH decomposition component overlaps with the timing of generation of active sulfur. On the other hand, as shown in FIG. 4B, the morpholine vulcanizing agent decomposes at a temperature (238 ° C.) considerably higher than the OBSH decomposition temperature (160 ° C.) and releases active sulfur. For this reason, the morpholine-based vulcanizing agent has an acidic substance (p, p'-oxybis-benzenesulfinic acid) produced by the decomposition of OBSH, as shown in FIG. After being decomposed into thiophenylbenzenesulfonyl ether, active sulfur is released. Therefore, it is presumed that it is not easily affected by acidic substances (p, p′-oxybis-benzenesulfinic acid).
[Estimation 2] As shown in FIG. 4 (b), morpholine (basic substance), which is a decomposition product of morpholine vulcanizing agent, is an acidic substance (p, p'-oxybis) produced by the decomposition of OBSH.・ It is presumed to have a neutralizing effect on benzenesulfinic acid).

(C) When a large amount of sulfur-donating vulcanizing agent (for example, morpholine-based vulcanizing agent) is blended, the elongation (including elongation at high temperature) of the foamed rubber molded product tends to decrease. When the upper limit of the compounding amount of the mold vulcanizing agent is 7 parts by mass and the diene content of EPDM is 5 to 6.9% by mass, the elongation is improved. For example, the elongation at 150 ° C is 100% or more. Achievable. Thereby, for example, when forming the slit and the connecting portion in the foamed rubber molded body, the connecting portion is not torn at the time of mold release, so the connecting portion is excluded as in the prior art and corresponds to the connecting portion after molding. The process of adhering the joint with an adhesive is not necessary.

The mode of each element in the means will be exemplified next.
1. EPDM rubber The amount of diene in EPDM is preferably 5 to 6.9% by mass. When the amount is less than 5 parts by mass, the crosslinking density required for the product cannot be obtained, and when it exceeds 6.9 parts by mass, the elongation (including elongation at high temperature) of the foamed rubber molded product tends to decrease.

2. It is preferable that 5-14 mass parts of foaming agents OBSH are mix | blended, More preferably, it is 7-12 mass parts. When the amount is less than 5 parts by mass, the foaming action is weakened, and when it exceeds 14 parts by mass, the foaming action becomes excessive and the crosslinking density tends to decrease.
Moreover, it is allowed to mix other foaming agents within the range not inhibiting the discoloration of the coating film, ensuring the crosslinking density, and improving the high temperature elongation, which are the problems of the present invention.

3. Vulcanizing agent It is preferable that 1 to 7 parts by mass of the sulfur-donating vulcanizing agent is blended, and more preferably 1 to 5 parts by mass. If this is less than 1 part by mass, the crosslinking density tends to be low, and if it exceeds 7 parts by mass, the elongation tends to decrease.
Examples of the sulfur-donating vulcanizing agent include morpholine-based 4,4′-dithio-di-morpholine, thiuram-based tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, and the like.
Moreover, it is preferable to use a sulfur-donating vulcanizing agent and sulfur together, and it is more preferable that sulfur-donating vulcanizing agent / sulfur = 0.5 to 3 (weight ratio).
Moreover, it is permitted to mix other vulcanizing agents within the range not inhibiting the discoloration of the coating film, ensuring the crosslinking density and improving the high temperature elongation, which are the problems of the present invention.

4). Foamed rubber moldings Specific products of foamed rubber moldings are not particularly limited, but are extrusion moldings or mold moldings of automotive weather strips (door weather strips, opening trims, window weather strips, glass runs, etc.). Part (particularly a molded part having a large blending amount of foaming agent), mud guard, packing and the like can be exemplified.

  According to the present invention, not only the problem of discoloration of the metallic coating film is solved by blending OBSH, but also a decrease in crosslinking density (decrease in moldability) due to a large amount of OBSH can be suppressed, and further, high temperature elongation can be achieved. Can be improved to prevent cracking during mold release.

  A rubber component having a diene content of EPDM of 5 to 6.9% by mass contains 5 to 14 parts by mass of OBSH as a foaming agent, and 1 to 7 parts by mass of a sulfur-donating vulcanizing agent as a vulcanizing agent ( Preferably, a foamed rubber composition in which 1 to 5 parts by mass of a morpholine vulcanizing agent and 0.5 to 4 parts by weight of sulfur are blended in a morpholine vulcanizing agent / sulfur = 0.5 to 3 (weight ratio). The elongation at 150 ° C. of the foamed rubber molding after foam molding is 100% or more.

  FIG. 1 shows a mold formation in which the end portions of an extruded product 11 extruded with solid rubber and / or foam rubber are molded with the foam rubber composition of the present invention at a portion corresponding to a corner shape portion of an automobile. A weather strip 10 (for example, a door weather strip) manufactured by being connected by a portion 12 is shown.

  As shown in FIG. 2 (a), the door weather strip 10 is attached to the mounting portion of the automobile (the door 1 in FIG. 2 (b)). The metallic coating 3 on the contact portion (for example, the body 2 around the door) of the automobile contacted with the molded portion 12 molded with the foamed rubber composition of the present invention is maintained without being discolored as shown in FIG. Is done.

  The molded part 12 molded with the foamed rubber composition of the present invention is less susceptible to cracking during mold release after molding. Since the elongation property at high temperature is high (elongation at 150 ° C. is 100% or more), even when the product temperature is still high, it does not break at tensile. For this reason, as shown in FIG. 3A, the mold forming part 12 includes a slit 13 for extracting a core (not shown) for forming a hollow part after mold forming, and the slit 13 is in use. A connecting portion 14 in the middle of the slit for preventing the opening is provided, but the connecting portion 14 is not cracked when released. Therefore, the process of excluding the joint part 14 and bonding the joint part corresponding to the joint part 14 with an adhesive after molding becomes unnecessary.

The foamed rubber compositions of the respective formulations of Examples 1 to 9 shown in Table 1 and Comparative Examples 1 to 13 shown in Table 2 and Table 3 were prepared.
In these tables, the compounding amount of each compound from the EPDM rubber component to the foaming agent is part by mass.
The numerical value in parentheses for each EPDM rubber name is the content (mass%) of the diene (specifically, ethylidene norbornene (ENB)), and the diene content described in the column below it is not the compounding amount. ) Value for the entire rubber component.

  Using the foamed rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 13, test pieces for the following tests were foam-molded as necessary, and the respective tests were performed. The results are also shown in Tables 1 to 3.

1. Discoloration of coating film Vulcanized rubber was pressure-bonded to a coated plate with a clip and stored in a thermostatic bath at 80 ° C. for 72 hours. Thereafter, the rubber was removed from the coated plate, immersed in warm water at 50 ° C. for 24 hours, and then the presence or absence of discoloration was visually determined.

2. Moldability Molding was performed at 180 ° C. for 3 minutes (thickness 2 mm). The material is opened 3 minutes after loading the molding machine. The case where the molded product was stuck to the upper mold and the lower mold and was torn was rated as x.

3. Elongation in the atmosphere at 150 ° C. In accordance with JIS K6251, a test was conducted with a vulcanized rubber punched out in a dumbbell shape No. 2. The tensile test was carried out in a constant temperature bath at 150 ° C. and kept at 150 ° C. for 12 minutes until the vulcanized rubber was pulled.

4). Vulcanization torque test (MH)
In accordance with JIS K6300-2, the test was performed under measurement conditions of 180 ° C. × 8 minutes.

5). Vulcanization speed (t90)
In accordance with JIS K6300-2, the test was performed under measurement conditions of 180 ° C. × 8 minutes.

  For example, as can be seen from the comparison between Example 1 and Comparative Example 1, there was a coating discoloration in Comparative Example 1 using ADCA as the foaming agent, but in Example 1 using OBSH as the foaming agent. There was no.

  Further, as can be seen from the comparison between Examples 2 to 6 and Comparative Examples 2 to 9, for example, Comparative Example 2 in which a morpholine vulcanizing agent is not blended as a vulcanizing agent or even if blended is less than 1 part by mass. -9, while the crosslinking density is low, there are problems such as poor moldability and slow vulcanization speed, whereas in Examples 2-6, in which 1 part by mass or more of the morpholine vulcanizing agent is blended, There is no problem.

  Further, for example, as can be seen from the comparison between Examples 3 and 7 to 9 and Comparative Examples 10 to 13, in Comparative Examples 10 to 13 having a large diene content, the diene content is 5 while the elongation in the atmosphere at 150 ° C. is small. In Example 3 and 7-9 which are -6.9 mass%, elongation in 150 degreeC atmosphere is large.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the meaning of invention, it can change suitably and can be actualized.

It is a front view which shows the outline of a door weather strip. It is a perspective view explaining the coating-film discoloration property by the door weather strip attached to the door. It is a perspective view explaining the cracking property of the door weather strip. It is a chemical formula which shows the action mechanism of this invention.

Explanation of symbols

10 Door weather strip 11 Extrusion product 12 Mold forming part

Claims (6)

  A foamed rubber composition in which 5-14 parts by mass of OBSH as a foaming agent and 1-7 parts by mass of a sulfur-donating vulcanizing agent are blended with an EPDM rubber component having a diene content of 5-6.9% by mass. .   The foamed rubber composition according to claim 1, wherein sulfur as a vulcanizing agent is blended together with the sulfur donating vulcanizing agent, and the sulfur donating vulcanizing agent / sulfur = 0.5 to 3 (weight ratio).   The foamed rubber composition according to claim 1 or 2, wherein the sulfur-donating vulcanizing agent is a morpholine vulcanizing agent.   A foamed rubber composition in which 5 to 14 parts by mass of OBSH as a foaming agent is blended with an EPDM rubber component, and the foamed rubber molded body after foam molding has an elongation at 150 ° C. of 100% or more.   A foamed rubber molded article foam-molded with the foamed rubber composition according to any one of claims 1 to 4.   6. The foamed rubber molded product according to claim 5, wherein the foamed rubber molded product is a molded part of a weather strip for automobiles.

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