JP2021024892A - Fluororubber composition, and rubber molded product and seal material using the same - Google Patents

Abstract

To provide a fluororubber composition in which the compression permanent set of the rubber molded product after cross-linking is suppressed to a low level as well as the processability is excellent as a result of incorporating magnesium oxide.SOLUTION: A fluororubber composition contains fluororubber, magnesium oxide, hydrotalcite, and barium sulfate. The contained amount of magnesium oxide is 1.3 pts.mass or more for 100 pts.mass of fluororubber. The mass ratio of the contained amount of hydrotalcite to the contained amount of magnesium oxide is 0.60 or more and 5.0 or less. The contained amount of barium sulfate is 5 pts.mass or more and 100 pts.mass or less for 100 pts.mass of fluororubber.SELECTED DRAWING: None

Description

The present invention relates to a fluororubber composition, a rubber molded product using the fluororubber composition, and a sealing material.

Fluororubber is excellent in heat resistance, chemical resistance, oil resistance, weather resistance, etc. Therefore, in a wide range of fields such as hydraulic equipment, pneumatic equipment, automobiles, aircraft, semiconductor-related equipment, food-related equipment, O-rings and It is used as a material for forming sealing materials such as packing. As a composition of such a fluororubber, for example, Patent Document 1 discloses a composition containing a fluororubber, magnesium oxide, and hydrotalcite.

Japanese Patent No. 5218048

When the fluororubber composition before cross-linking contains magnesium oxide, the compression set can be suppressed low by increasing the cross-linking density of the fluororubber in the rubber molded product after cross-linking.

On the other hand, if the fluororubber composition before crosslinking contains magnesium oxide, there is a problem that processability is impaired. Specifically, when the fluororubber composition is kneaded, brown stains may be generated on the roll surface of the open roll of the rubber kneader, and in that case, cleaning is required, so that the work efficiency is lowered. Further, when the rubber molded product is molded, the surface of the molding mold may be contaminated, and in that case, cleaning is required, so that the production efficiency is lowered. This cleaning requires a large number of man-hours as the size of the molding die becomes larger and the shape becomes more complicated. In addition, if the surface of the mold is dirty, the flow of the fluororubber composition is hindered, or the dirt adheres to the rubber, so that the appearance of the rubber molded product is poor, chipped, cracked, or the like.

An object of the present invention is to provide a fluororubber composition having excellent processability while suppressing the compression set of the rubber molded product after cross-linking to be low by blending magnesium oxide.

The present invention is a fluororubber composition containing fluororubber, magnesium oxide, hydrotalcite, and barium sulfate, wherein the content of magnesium oxide is 1. with respect to 100 parts by mass of the fluororubber. The mass ratio of the hydrotalcite content to the magnesium oxide content is 0.60 or more and 5.0 or less, and the barium sulfate content is 100 parts by mass of the fluorine rubber. It is 5 parts by mass or more and 100 parts by mass or less.

The present invention is a rubber molded product formed by cross-linking the fluororubber of the fluororubber composition of the present invention. Further, the present invention is a sealing material formed by cross-linking the fluororubber of the fluororubber composition of the present invention.

According to the present invention, by containing an appropriate amount of magnesium oxide, the compression set of the rubber molded product after cross-linking can be suppressed to a low level, and an appropriate amount of hydrotalcite and barium sulfate are contained. Therefore, excellent workability can be obtained.

Hereinafter, embodiments will be described in detail.

The fluororubber composition according to the embodiment contains fluororubber, magnesium oxide, hydrotalcite, and barium sulfate. The content of magnesium oxide in the fluororubber composition is 1.3 parts by mass or more with respect to 100 parts by mass of the fluororubber. The mass ratio of the content of hydrotalcite to the content of magnesium oxide is 0.60 or more and 5.0 or less. The content of barium sulfate in the fluororubber composition is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the fluororubber.

According to the fluororubber composition according to the above embodiment, an appropriate amount of magnesium oxide is contained as an antacid and the crosslink density of the fluororubber is increased, so that the compression set of the rubber molded product after cross-linking is suppressed to a low level. be able to. Further, by containing an appropriate amount of hydrotalcite and barium sulfate, excellent processability can be obtained. This is because the layered structure of hydrotalcite, which also functions as an acid receiver, takes in not only acid but also ions that cause stains, enhances mold releasability, and allows the fluororubber composition to flow with barium sulfate. Even in a molding mold with enhanced properties and a large size or a complicated shape, the fluororubber composition spreads throughout the molding mold regardless of whether the surface of the molding mold is dirty, so that a rubber kneader or molding can be used. This is because the burden of cleaning the mold is reduced.

Here, examples of the fluororubber include a copolymer (binary FKM) of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetra. Copolymer with fluoroethylene (TFE) (ternary FKM), copolymer with tetrafluoroethylene (TFE) and propylene (Pr) (FEP), vinylidene fluoride (VDF), propylene (Pr) and tetra Copolymer with fluoroethylene (TFE), copolymer with ethylene (E) and tetrafluoroethylene (TFE) (ETFE), ethylene (E), tetrafluoroethylene (TFE) and perfluoromethylvinyl ether (PMVE) Copolymer with vinylidene fluoride (VDF), tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE), tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) Examples thereof include a polymer (FFKM), a copolymer of vinylidene fluoride (VDF) and perfluoromethyl vinyl ether (PMVE), and the like. The fluororubber preferably contains one or more of these, and from the viewpoint of obtaining excellent processability, it is more preferable to contain a binary fluororubber, and further to include a binary FKM. preferable.

The powder of magnesium oxide is dispersed in fluororubber. The average particle size of magnesium oxide is preferably 0.3 μm or more and 40 μm or less, and more preferably 0.6 μm or more and 10 μm or less, from the viewpoint of suppressing the compression set of the rubber molded product to a low level. This average particle size is measured based on the air permeation method. The specific surface area of magnesium oxide, from the viewpoint of suppressing the compression set of the rubber molded article, preferably ^{40 m} 2 / g or more 200 meters ² / g or less, more preferably less 130m ² / g or more 160 m ² / g. This specific surface area is measured based on the BET method. The content of magnesium oxide in the fluororubber composition is 1.3 parts by mass or more with respect to 100 parts by mass of fluororubber, but preferably 1.5 parts by mass from the viewpoint of suppressing the compression set of the rubber molded product to a low level. It is 3 parts by mass or less, more preferably 1.8 parts by mass or more and 2.4 parts by mass or less.

What is "hydrotalcite" in this application?
[M (1) ²⁺ _1-x M (2) ³⁺ _x (OH) ₂ ] [An ^- _{x / n} · mH ₂ O]
M (1) ²⁺ : Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Li ²⁺ , Ni ²⁺ , Co ²⁺ , Cu ²⁺
M (2) ³⁺ : Al ³⁺ , Fe ³⁺ , Mn ³⁺
A ^n-: n-valent anion 0.20 ≦ x ≦ 0.33
Refers to a layered crystal structure represented by.

The powder of hydrotalcite is dispersed in fluororubber. The average particle size of hydrotalcite is preferably 0.2 μm or more and 100 μm or less, and more preferably 0.4 μm or more and 50 μm or less, from the viewpoint of obtaining excellent processability. This average particle size is the median diameter measured based on the laser diffraction / scattering method. The specific surface area of hydrotalcite is preferably 5 m ² / g or more and 20 m ² / g or less, and more preferably 8 m ² / g or more and 15 m ² / g or less. This specific surface area is measured based on the BET method.

From the viewpoint of obtaining excellent processability, the content of hydrotalcite in the fluororubber composition is preferably 1 part by mass or more and 5 parts by mass or less, and more preferably 2 parts by mass or more 4 with respect to 100 parts by mass of fluororubber. It is less than a part by mass. The mass ratio of the hydrotalcite content to the magnesium oxide content is 0.60 or more and 5.0 or less, but preferably 0.70 or more and 2.9 or less from the viewpoint of obtaining excellent processability. It is preferably 1.2 or more and 1.8 or less. The content of hydrotalcite in the fluororubber composition is preferably higher than the content of magnesium oxide from the viewpoint of obtaining excellent processability.

The sum of the contents of magnesium oxide and hydrotalcite in the fluororubber composition is preferable with respect to 100 parts by mass of the fluororubber from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. It is 3 parts by mass or more and 7 parts by mass or less, more preferably 4.5 parts by mass or more and 5.5 parts by mass or less.

The powder of barium sulfate is dispersed in fluororubber. The average particle size of barium sulfate is preferably 0.1 μm or more and 15 μm or less, and more preferably 0.3 μm or more and 2.0 μm or less, from the viewpoint of obtaining excellent processability. This average particle size is the median diameter measured based on the laser diffraction / scattering method. The specific gravity of barium sulfate is preferably 4.0 or more and 4.6 or less, and more preferably 4.4 or more and 4.6 or less.

The content of barium sulfate in the fluororubber composition is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the fluororubber, but from the viewpoint of obtaining excellent workability and excellent wear resistance of the rubber molded product. Therefore, it is preferably 10 parts by mass or more and 90 parts by mass or less, and more preferably 20 parts by mass or more and 40 parts by mass or less. The content of barium sulfate in the fluororubber composition is preferably higher than any of the magnesium oxide content, the hydrotalcite content, and the sum of these contents from the viewpoint of obtaining excellent processability.

The mass ratio of the barium sulfate content to the magnesium oxide content is preferably 4.5 or more and 50 or less, more preferably 10 from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. More than 20 or less.

The mass ratio of the barium sulfate content to the hydrotalcite content is preferably 3.0 or more and 35 or less, and more preferably 5 or more and 20 or less from the viewpoint of obtaining excellent processability.

The mass ratio of the content of barium sulfate to the sum of the contents of magnesium oxide and hydrotalcite is preferably 1.0 or more and 20 from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. Hereinafter, it is more preferably 5.0 or more and 8.0 or less.

The fluororubber composition according to the embodiment may contain calcium hydroxide. The content of calcium hydroxide in the fluororubber composition is preferably 4 parts by mass or more with respect to 100 parts by mass of the fluororubber from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. It is less than a part by mass. The content of calcium hydroxide in the fluororubber composition is preferably higher than the content of either magnesium oxide or hydrotalcite, and is preferably the same as or higher than the sum of the contents thereof.

The mass ratio of the calcium hydroxide content to the magnesium oxide content is preferably 2.0 or more and 7.5 or less from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. .. From the same viewpoint, the mass ratio of the calcium hydroxide content to the hydrotalcite content is preferably 1.0 or more and 5.0 or less. From the same viewpoint, the mass ratio of the calcium hydroxide content to the sum of the magnesium oxide and hydrotalcite contents is preferably 1.0 or more and 1.5 or less.

The fluororubber composition according to the embodiment may contain carbon black. Examples of the carbon black include furnace blacks such as HAF carbon black, MAF carbon black, FEF carbon black, SRF carbon black and GPF carbon black; and thermal blacks such as FT carbon black and MT carbon black. The carbon black preferably contains thermal black, and more preferably MT carbon black, from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability.

The content of carbon black in the fluororubber composition is preferably 15 parts by mass or more and 25 parts by mass with respect to 100 parts by mass of fluororubber from the viewpoint of suppressing the compression set of the rubber molded product to a low level and obtaining excellent processability. It is less than a part. From the same viewpoint, the content of carbon black in the fluororubber composition is preferably smaller than the content of barium sulfate. From the same viewpoint, the mass ratio of the carbon black content to the barium sulfate content is preferably 0.5 or more and 0.7 or less. From the same viewpoint, the sum of the contents of barium sulfate and carbon black in the fluororubber composition is preferably 40 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the fluororubber.

The fluororubber composition according to the embodiment may also contain a processing aid or the like.

The fluororubber composition according to the embodiment is obtained by kneading fluororubber with a rubber kneader such as an open roll, and adding a rubber compounding agent containing magnesium oxide, hydrotalcite, and barium sulfate to the kneading. Obtainable.

Then, the fluororubber composition according to the embodiment is filled in the cavity of the molding mold, held at a predetermined temperature for a predetermined time, and the fluororubber is crosslinked to form a rubber molded product. Examples of the fluororubber cross-linking system include a polyol cross-linking system, a peroxide cross-linking system, and a polyamine cross-linking system. Of these, the polyol cross-linking system is preferable as the fluororubber cross-linking system. As the obtained rubber molded product, for example, a sealing material such as an O-ring or packing is particularly suitable because the compression set is low.

The compression set of the crosslinked fluororubber composition forming the rubber molded product is preferably 16% or less, more preferably 13% or less. This compression set is measured based on JIS K6262: 2013 with a test temperature of 200 ° C. and a test time of 22 hours.

The rubber hardness measured using a type A durometer of the crosslinked fluororubber composition is preferably 60 or more and 90 or less. This rubber hardness is measured based on JIS K6253-3: 2012.

The tensile strength of the crosslinked fluororubber composition is preferably 8.0 MPa or more. The elongation at the time of cutting of the fluororubber composition after cross-linking is preferably 120% or more. These tensile strengths and elongation at break are measured based on JIS K6251: 2017.

(Fluororubber composition)
Fluororubber compositions of Examples 1 to 5 and Comparative Examples 1 to 5 were prepared. Each formulation is also shown in Table 1.

<Example 1>
Fluororubber (Daiel G-701 Daikin Co., Ltd., dual FKM) is kneaded with an open roll, and magnesium oxide (Kyowa Mag 150 Kyowa Kagaku Kogyo Co., Ltd., average particle size:) is kneaded there with respect to 100 parts by mass of fluororubber. 11.7, specific surface ^area: 144m 2 ^/g)2.5 parts by weight of hydrotalcite (DHT-4A manufactured by Kyowa chemical industry Co., Ltd., average particle diameter: 0.45 [mu] m, a specific surface area: 10.1m ² / g) 1 .5 parts by mass, barium sulfate (average particle size: 0.6 μm, specific surface area: 4.5) 30 parts by mass, calcium hydroxide (manufactured by Calbit Omi Chemical Industry Co., Ltd.) 6 parts by mass, MT carbon black (N990) 20 parts by mass And a fluororubber composition obtained by adding and kneading 1 part by mass of a processing aid (VPA No. 2 manufactured by Byton Co., Ltd.) as Example 1.

<Example 2>
The fluororubber composition obtained in the same manner as in Example 1 except that the blending amount of magnesium oxide and the blending amount of hydrotalcite were 2 parts by mass and 3 parts by mass, respectively, with respect to 100 parts by mass of the fluororubber. Was referred to as Example 2.

<Example 3>
It was obtained in the same manner as in Example 1 except that the blending amount of magnesium oxide and the blending amount of hydrotalcite were 1.5 parts by mass and 4.5 parts by mass, respectively, with respect to 100 parts by mass of fluororubber. The fluororubber composition was designated as Example 3.

<Example 4>
The amount of barium sulfate blended was 10 parts by mass with respect to 100 parts by mass of fluororubber, and the fluororubber composition obtained in the same manner as in Example 2 except that MT carbon black was not blended was referred to as Example 4. did.

<Example 5>
Example 5 was a fluororubber composition obtained in the same manner as in Example 4 except that the amount of barium sulfate blended was 90 parts by mass with respect to 100 parts by mass of fluororubber.

<Comparative example 1>
The fluororubber composition obtained in the same manner as in Example 1 except that magnesium oxide was not blended and the amount of hydrotalcite blended was 9 parts by mass with respect to 100 parts by mass of the fluororubber was compared with Comparative Example 1. did.

<Comparative example 2>
The fluororubber composition obtained in the same manner as in Example 1 except that the blending amount of magnesium oxide and the blending amount of hydrotalcite were 1 part by mass and 6 parts by mass, respectively, with respect to 100 parts by mass of the fluororubber. Was designated as Comparative Example 2.

<Comparative example 3>
The amount of magnesium oxide blended was 3 parts by mass with respect to 100 parts by mass of the fluororubber, and the fluororubber composition obtained in the same manner as in Example 1 except that hydrotalcite was not blended was compared with Comparative Example 3. did.

<Comparative example 4>
It was carried out without adding hydrotalcite and barium sulfate, except that the amount of calcium hydroxide and MT carbon black was 3 parts by mass and 45 parts by mass, respectively, with respect to 100 parts by mass of fluororubber. The fluororubber composition obtained in the same manner as in Example 2 was designated as Comparative Example 4.

<Comparative example 5>
The amount of magnesium oxide, the amount of hydrotalcite, and the amount of barium sulfate were 9 parts by mass, 5 parts by mass, and 5 parts by mass, respectively, with respect to 100 parts by mass of fluororubber. The fluororubber composition obtained in the same manner as in Example 1 was designated as Comparative Example 5.

(Test method)
<Physical characteristics>
The fluororubber compositions of Examples 1 to 5 and Comparative Examples 1 to 5 were subjected to primary cross-linking by press molding at 170 ° C. for 10 minutes using a sheet molding die, and then 230 ° C. using an oven. A sheet-shaped rubber molded product was produced by performing secondary cross-linking for 24 hours.

Using each sheet-shaped rubber molded product, the compression set was measured based on JIS K6262: 2013 with a test temperature of 200 ° C. and a test time of 22 hours. Further, the appearance of the compressed rubber molded product was visually confirmed, and those having no abnormality were evaluated as A and those with cracks were evaluated as B.

Further, the rubber hardness was measured using a type A durometer based on JIS K6253-3: 2012. In addition, tensile strength and elongation at break were measured based on JIS K6251: 2017.

<Workability>
For each of Examples 1 to 5 and Comparative Examples 1 to 5, the roll surface of the open roll after the fluororubber composition was kneaded and taken out was visually confirmed, and those without stains were evaluated as A and stains were recognized. The result was given a B rating.

For each of Examples 1 to 5 and Comparative Examples 1 to 5, the surface of the sheet molding die after taking out the press-molded rubber molded product was visually checked, and those with no stain were evaluated as A and stained. Was evaluated as B.

For each of Examples 1 to 5 and Comparative Examples 1 to 5, the press-molded rubber molded product on the sheet molding die was visually confirmed, and the one in which no appearance defect due to insufficient flow of the fluororubber composition was observed was A. The evaluation, the one in which a slight appearance defect was observed was evaluated as B, and the one in which a remarkable appearance defect was observed was evaluated as C evaluation.

(Test results)
The test results are shown in Table 2. According to Table 2, it can be seen that Examples 1 to 5 have low compression set and excellent workability of the rubber molded product. On the other hand, in Comparative Examples 1 and 2 in which the content of magnesium oxide is low, it can be seen that the compression set is large. Further, in Comparative Example 3 containing no hydrotalcite, stains on the roll surface of the open roll and the mold surface of the sheet molding die were observed, so that it can be seen that the processability is inferior. Similarly, in Comparative Example 4 which does not contain hydrotalcite, stains on the roll surface of the open roll were observed, indicating that the processability was inferior. Even in Comparative Example 5, which contains hydrotalcite but the ratio of the content to the magnesium oxide content is small, stains on the roll surface of the open roll and the mold surface of the sheet molding die were observed. It turns out that the sex is inferior. Further, in Comparative Example 4 which does not contain barium sulfate and Comparative Example 5 in which the content of barium sulfate is low, poor appearance of the rubber molded product was observed, and it can be seen that the processability is also inferior in this respect.

The present invention is useful for fluororubber compositions, rubber molded products and sealing materials using the same.

Claims (5)

A fluororubber composition containing fluororubber, magnesium oxide, hydrotalcite, and barium sulfate.
The content of magnesium oxide is 1.3 parts by mass or more with respect to 100 parts by mass of the fluororubber.
The mass ratio of the hydrotalcite content to the magnesium oxide content is 0.60 or more and 5.0 or less.
A fluororubber composition having a barium sulfate content of 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the fluororubber. In the fluororubber composition according to claim 1,
A fluororubber composition having an average particle size of magnesium oxide of 0.3 μm or more and 40 μm or less. In the fluororubber composition according to claim 1 or 2.
A fluororubber composition having a hydrotalcite content of 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the fluororubber. A rubber molded product formed by cross-linking the fluororubber of the fluororubber composition according to any one of claims 1 to 3. A sealing material formed by cross-linking the fluororubber of the fluororubber composition according to any one of claims 1 to 3.