JPH08269248A - Rubber composition - Google Patents

Abstract

PURPOSE: To obtain a rubber compsn. from which a sponge rubber hardly creasing and having a desired cell structure is easily produced. CONSTITUTION: This compsn. is prepd. by compounding 100 pts.wt. rubber component with a chemical foaming agent pref. in an amt. of 0.5-15 pts.wt. and a thermally expansible microcapsules pref. in an amt. of 0.5-10 pts.wt. After thermally cured, the compsn. contains both cells formed by the chemical foaming agent and cells formed by the microcapsules, has a fine cell structure and a high closed cell content, and maintains the characteristics inherent in a sponge rubber such as softness and sealing properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition, and more particularly to a rubber composition from which a sponge rubber required to have flexibility and sealing properties can be obtained.

[0002]

2. Description of the Related Art Generally, sponge rubber is manufactured by vulcanization molding in which a chemical foaming agent and a foaming auxiliary agent are mixed in a rubber composition and heated. At the time of vulcanization molding, the chemical foaming agent is thermally decomposed to generate a gas such as nitrogen and generate bubbles in the rubber.

The foam structure of the sponge rubber needs to be appropriately adjusted according to the usage conditions. Currently, the types and amounts of the chemical foaming agents and chemical foaming aids, the vulcanization rate of the rubber composition, and the vulcanization are used. By changing the conditions such as the molding temperature, the bubble diameter of the sponge rubber, the mixing ratio of closed cells and open cells, and the like are changed to obtain a desired cell structure. However, these methods have limitations in making a large change in the bubble structure.

Further, as a foam using means for mixing only rubber and plastic with thermally expanded microcapsules,
Japanese Patent Laid-Open No. 59-138420 discloses a method of molding a foam having a stable expansion ratio using a mold. On the other hand, Japanese Unexamined Patent Publication No. 6-183305 discloses a microfoam weather strip that is made lighter by using microcapsules made of an acrylonitrile polymer for the purpose of weight saving.

[0005]

However, when the glass plate or the metal plate is pressed against the sponge rubber or the sponge rubber is bent, creases may be generated in the dent portion of the rubber. Depending on the location where the sponge rubber is folded and wrinkled, the sealability between the sponge rubber and the glass plate, the metal plate or the like may be deteriorated, and the appearance may be affected.

Further, in the case of molding sponge rubber, when high temperature vulcanization is carried out by using a chemical foaming agent, it is easy to have a cell structure having irregular cells and open cells with large bubbles, and when the rubber is deformed, a large breakage occurs. Wrinkles are likely to occur.

Therefore, in order to increase the strength against bending and dent, it is necessary to make the bubbles of the sponge rubber small. However, if it is attempted to greatly change the bubble structure by changing only the chemical foaming agent and the vulcanization conditions, the sponge rubber will be changed. Even the specific gravity of will change greatly.

Further, when the sponge rubber is formed only by the thermally expanded microcapsules, the size of the bubbles is small, but the hardness of the rubber itself is high, and the sponge rubber lacks flexibility and sealing property.

As described above, it is very difficult to obtain a desired cell structure without keeping the specific gravity of the sponge rubber substantially constant and without spoiling the characteristics of the sponge rubber.

The present invention has been made to solve the above problems in sponge rubber.
It is an object of the present invention to provide a sponge rubber composition in which a sponge rubber having a desired cell structure can be easily obtained, and the obtained sponge rubber is less likely to be creased.

[0011]

In order to solve the above-mentioned problems, the present invention comprises a chemical foaming agent and a thermal expansion microcapsule mixed in a rubber component. It is characterized in that bubbles generated by the chemical foaming agent and the microcapsules coexist.

Preferably, 0.5 to 15 parts by weight of the chemical foaming agent and 0.5 to 10 parts by weight of the thermal expansion microcapsules are mixed with 100 parts by weight of the rubber component.

In the above rubber composition, the bubbles of the rubber (sponge rubber) obtained after thermosetting become smaller and the closed cell structure becomes stronger.

Generally, a sponge rubber which is required to have flexibility and sealing properties has poor flexibility when its specific gravity is high, and its mechanical strength is poor when its specific gravity is low. Often molded.

Considering the specific gravity and flexibility of the sponge rubber, 0.5 to 15 parts by weight of the chemical foaming agent and 0.5 of the thermal expansion microcapsule are used with respect to 100 parts by weight of the rubber in the rubber composition.
It is possible to add 10 to 10 parts by weight, but more preferably 2 to 8 parts by weight of the chemical foaming agent and 1 to 6 parts by weight of the thermal expansion microcapsules.

The thermal expansion microcapsule used in the present invention is not particularly limited, but for example, an acryl nitrilo type copolymer or vinylidene chloride copolymer may be used as the outer shell part. The hydrocarbon contained in the outer shell is not particularly limited, but hydrocarbons such as isobutane, n-pentane, and n-hexane are used. Usually, there are various kinds such as 5 to 25 μm as the average particle diameter, but the average particle diameter may be appropriately selected according to the purpose of use of the rubber after curing, and there is no particular limitation.

When such a microcapsule is heated, the outer shell portion is softened, the hydrocarbon contained therein is vaporized and expanded, and the particle size of the capsule becomes large.

The chemical foaming agent is also not particularly limited, and includes, for example, azodicarponamide (ADCA), 4,
4'oxybisbenzenesulfonyl hydrazide (OB
SH), p-toluenesulfonyl hydrazide (TS
H), azobisisobutyronitrile (AIBN), dinitrosopentamethylenetetramine (DPT), sodium bicarbonate, ammonium bicarbonate and the like are used. Of course, two or more of these can also be used appropriately. In addition to these, a foaming aid may be used in order to carry out foaming at a low temperature.

When the rubber composition is heated to a predetermined molding temperature, the chemical foaming agent is thermally decomposed to generate nitrogen gas or the like.

The generated gas gradually agglomerates in the rubber to form bubbles, and as it is, it becomes irregular bubbles accompanied by large bubbles, and has a structure having continuous continuous bubbles.

Therefore, when the sponge rubber is deformed such as bent, air bubbles are easily crushed and large creases are generated, which deteriorates the sealing property.

Bubbles due to thermal expansion of the microcapsules are
The air bubbles are uniform and small, and have closed shells, and since there is no escape path for the gas, the repulsion against the deformation of the air bubbles becomes strong, and creases do not occur. However, in order to mold a sponge rubber having the same specific gravity as compared with a chemical foaming agent, it is necessary to mix a large amount of microcapsules into the rubber.
Further, since the cell structure is closed cells having an outer shell and the outer shell is inelastic and hard as compared with rubber, a sponge that is hard and rigid by blending in a large amount It becomes rubber, and its flexibility and sealability are impaired.

As described above, the rubber composition of the present invention contains the chemical foaming agent and the thermal expansion microcapsule in combination.

When this rubber composition is heated to a predetermined molding temperature, the microcapsules expand thermally in the rubber,
Generates closed cells having an outer shell.

At the same time, the chemical foaming agent is thermally decomposed to generate nitrogen gas and the like, and the generated gas is gradually aggregated in the rubber to form bubbles, but intervening of closed cells due to thermal expansion of the microcapsules. This prevents the generated gas from aggregating,
It becomes a sponge rubber with a small bubble diameter, and furthermore, it is difficult to connect bubbles and it has a closed cell structure.

As a result, even if the thermal expansion microcapsules are not blended in a large amount, by changing the blending amount and blending ratio of the chemical foaming agent and the thermal expansion microcapsules, the specific gravity of the sponge rubber can be kept the same. It is possible to control the size of the bubble diameter of the sponge rubber and the closed cell degree (keep the bubble of the sponge rubber small to some extent and increase the closed cell degree), and the characteristics of the sponge rubber (flexibility, flexibility,
(Sealability) can be maintained and the generation of creases can be significantly suppressed.

[0027]

Embodiments of the present invention will be described in detail below.
In this example, as shown in Table 1, common basic formulations (EPDM, zinc oxide, carbon black, stearic acid, calcium carbonate, process oil, moisture adsorbent (Ca
O), vulcanization accelerator A, vulcanization accelerator B, vulcanization accelerator C, vulcanization accelerator D, vulcanization accelerator E, sulfur), and a foaming agent (OBSH) and thermal expansion microcapsules. The sponge rubbers of Examples 1 to 5 and Comparative Examples 1 and 2 were manufactured by changing the compounding ratio of. At this time, the obtained sponge rubbers were compared so that the specific gravities of the obtained sponge rubbers were about the same, and the properties such as the average cell diameter and hardness were compared.

The sponge rubber was prepared by kneading the rubber compositions of Examples 1 to 5 and Comparative Examples 1 and 2 with a roll and using a known extruder at a temperature of 40 to 50 ° C. Preformed into a shape with a width of 25 mm and a thickness of 3 mm,
Then, it was obtained by performing vulcanization molding under the condition of 200 ° C. × 5 minutes in a gear oven.

[0029]

[Table 1]

Further, the compounding ratio of the foaming agent (OBSH) and the thermal expansion microcapsule in Examples 1 to 5 and Comparative Examples 1 and 2, the specific gravity of each of the obtained sponge rubbers, the average cell diameter (μm), and the closed cells. Degree (%), hardness (Asker C
Table 1 also shows the measurement results of each characteristic in the folded type and the folded state.

As shown in Table 1, the specific gravities of the sponge rubbers obtained from Examples 1 to 5 and Comparative Examples 1 and 2 are about 0.46, which are almost equal. It is confirmed.

The average cell diameter in each sponge rubber is obtained by enlarging the cut surface of the sponge rubber with a microscope and performing image analysis processing, and it is preferable that the sponge rubber has a small value. The values are small in the sponge rubbers containing thermal expansion microcapsules (Examples 1 to 5 and Comparative Example 2).

In particular, even if the amount of the thermally expanded microcapsules added is small, the average bubble diameter becomes small due to the influence.

For example, in Example 3, the compounding ratios of the foaming agent and the thermal expansion microcapsules are equal, and the average cell diameter is 81. Considering that the value in Comparative Example 2 containing only the thermal expansion microcapsules was 76 and the value in Comparative Example 1 containing only the foaming agent was 131, a value very close to that in Comparative Example 2 was obtained. You can see that

Further, although the addition ratio of the thermal expansion microcapsules in Example 1 is 1/10 of that of the foaming agent, the average cell diameter value is the average value of Comparative Example 1 and Comparative Example 2 (103 A value of 100, which is close to .5), is obtained. As described above, the average cell diameter is much smaller than the amount of the thermally expanded microcapsules added, which shows that the properties as sponge rubber are greatly improved.

The independent cell content is measured by compressing the sponge rubber molded article in water for a certain period of time, measuring the amount of water absorbed when the compression is released in water and returning it to the original state, and measuring the water content independent of the cell volume of the sponge rubber. The ratio of bubbles was converted.

When used as sponge rubber, it is preferable that the closed cell content is high. It is recognized that the degree of closed cells is increased by incorporating the thermally expanded microcapsules, and in particular, even if the addition amount of the thermally expanded microcapsules is small, the degree of closed cells is increased due to the influence.

For example, the value of the closed cell degree in Example 3 in which the compounding ratio of the foaming agent and the thermal expansion microcapsules is the same is 94. Considering that the value in Comparative Example 2 containing only the thermal expansion microcapsules is 99 and the value in Comparative Example 1 containing only the foaming agent is 77, a value very close to that of Comparative Example 2 is obtained. You can see that

Further, although the addition ratio of the thermal expansion microcapsules in Example 1 is 1/10 of that of the foaming agent, the value of the closed cell degree is the average value (88) of Comparative Example 1 and Comparative Example 2. The value of 85, which is close to that of (1), is obtained, and it is shown that the closed cell degree becomes extremely high by mixing the foaming agent and the thermal expansion microcapsule.

On the other hand, when used as sponge rubber, it is preferable that its hardness is small to some extent. The hardness of Comparative Example 2 in which only the thermally expandable microcapsules are blended is very high, which is not preferable as a sponge rubber.

As shown in this table, the hardness does not increase so much even if the ratio of the thermally expanded microcapsules increases. For example, the hardness of Example 5 having the highest compounding ratio of the thermal expansion microcapsules is 54, which is close to the average value (50) of Comparative Examples 1 and 2.

Further, the state of creases was measured. With the method of measuring the state of creases, a sponge rubber molded product is 20 m wide
m, length 40 mm, cut the rubber piece in two, clipped and left at room temperature for 24 hours. Then, the folded rubber piece was returned to the original state and left for 5 minutes, and the refracted portion was observed and evaluated.

In Comparative Example 1, creases were generated at several places,
Also, the wrinkles themselves were large.

In each of Examples 1 to 3, one creasing line was formed shallowly at the approximate center of the bent portion.

In Examples 4 and 5 and Comparative Example 2, the marks of the refraction portion were visible, not the creases.

The above results are also shown in Table 1. In addition,
The measurement results are shown according to the following evaluation criteria.

5: There is no crease.

4: It is not a crease, but the bent portion can be seen slightly.

3: A state in which the number of folds is shallow and there is about one.

2: A state in which there are few folds and there are several folds.

1: A state in which there are several deep creases.

As described above, by incorporating the thermal expansion microcapsules in addition to the foaming agent, the crease state was greatly improved. Particularly, in Examples 4 and 5, a comparative example using only the thermal expansion microcapsules. The same level of evaluation as 2 was obtained.

As described above, with respect to the preferable characteristics as the sponge rubber, even if the compounding ratio of the thermal expansion capsules is small, the characteristics largely appear in the molded product. Further, regarding properties that are not preferable as sponge rubber, even if the compounding ratio of the thermal expansion capsules increases, the properties do not appear much in the molded product. As described above, it was confirmed that by mixing the foaming agent and the thermal expansion microcapsules, an effect which cannot be predicted normally can be obtained. It is considered that this is due to the coexistence of bubbles due to the chemical foaming agent and bubbles due to the thermal expansion capsule in the cured rubber.

[0054]

As described in detail above, according to the present invention,
The size of the cells in the rubber obtained by thermosetting the rubber composition can be reduced, the closed cell degree can be increased, and the characteristics of the sponge rubber such as flexibility and sealability can be maintained. Occurrence of folds can also be suppressed.

Claims (2)

[Claims] 1. A rubber component containing a chemical foaming agent and a thermal expansion microcapsule, respectively, and the rubber after heat curing contains bubbles generated by the chemical foaming agent and the microcapsule, respectively. And a rubber composition. 2. The chemical foaming agent is added in an amount of 0.5 to 15 parts by weight, and the thermal expansion microcapsule is added in an amount of 0.5 to 10 parts by weight, based on 100 parts by weight of the rubber component. Rubber composition.