JP2722674B2 - Method for producing water-swellable rubber composition - Google Patents

Description

The present invention relates to a method for producing a water-swellable rubber composition. More specifically, the present invention relates to a method for producing a water-swellable rubber composition that gives a vulcanizate having stable water absorption performance without a decrease in mechanical strength.

[Conventional technology]

Many proposals have been made on water-swellable rubbers in the past, most of which are methods of compounding a rubber with a water-absorbing substance (for example, JP-A-54-7463 and JP-A-54-20066).
JP-A-57-158279, JP-A-60-197784,
No. 61-26661). However, these methods simply knead the rubber and the water-absorbing substance, and have poor compatibility because only the rubber component is involved in the crosslinking reaction, resulting in inconveniences such as falling off of the components and insufficient mechanical strength.

To improve such a method, it has been proposed to use a urethane-based substance as a water-swellable substance (Japanese Patent Laid-Open No. 57-23618). In this case, MOCA is used as a curing agent.
(4,4'-diamino-3,3'-dichlorodiphenylmethane) and the like are usually used. However, these curing agents are toxic and cause contamination such as use environment. Therefore, it is desirable to use water or an alcohol-based curing agent without using an amine-based curing agent, but there is a problem that the mechanical strength of the vulcanized molded product is low.

[Problem to be Solved by the Invention] Japanese Patent Publication No. 62-44032 describes a caulking material composition in which a natural rubber is added with a swellable urethane substance which is a reactant of a polyether polyol, a polyisocyanate and a curing agent. However, even when a water-swellable rubber composition is prepared by adding a polyalkylene oxide diisocyanate adduct to a synthetic rubber based on this proposal, a decrease in the mechanical strength of a vulcanized molded product cannot be avoided.

An object of the present invention is to provide the water-swellable rubber composition,
An object of the present invention is to provide a method for producing a water-swellable rubber composition which gives a vulcanizate having stable water absorption performance without a decrease in mechanical strength.

[Means for solving the problem]

The object of the present invention is achieved by adding a carboxyl group-containing acrylic rubber latex to a mixture of a synthetic rubber compound and a polyalkylene oxide diisocyanate adduct and reacting the mixture to produce a water-swellable rubber composition.

Synthetic rubber compounds include various synthetic rubbers such as styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene rubber, isoprene rubber, chloroprene rubber, and, depending on the type of rubber, carbon black, silica, and clay. , Such as talc, fillers, zinc oxide, stearic acid and other auxiliaries, antioxidants, stabilizers, plasticizers and other necessary additives. It is desirable to add it after the production of the composition so as not to cause a vulcanization reaction during the production of the water-swellable rubber composition.

As polyalkylene oxide diisocyanate adducts, ethylene glycol, propylene glycol,
A polymer obtained by homopolymerizing or copolymerizing an alkylene oxide such as ethylene oxide or propylene oxide in the presence or absence of a polyol such as glycerin, and having diol groups at both ends thereof, tolylene diisocyanate or diphenylmethane diisocyanate. ,
diisocyanates such as m-xylene diisocyanate, hexamethylene diisocyanate, etc .;
It is obtained by performing an addition reaction at an O / -OH equivalent ratio of 1.
These adducts have a viscosity (25 ° C.) of about 1,000 to 10,000 centipoise, preferably about 3,000 to 7000 centipoise.

The mixing of the synthetic rubber compound and the polyalkylene oxide diisocyanate adduct is performed by first kneading the synthetic rubber compound well in an internal mixer such as a kneader, and then sufficiently plasticizing the mixture. About 10 per 100 parts by weight
This is done by slowly adding the adduct in an amount of up to 250 parts by weight, preferably about 50 to 200 parts by weight, and thoroughly mixing and stirring to form a low viscosity mixture there.

While stirring this mixture as it is, it is cooled to a temperature of about 50 ° C. or less, generally around room temperature, and a carboxyl group-containing acrylic rubber latex is gradually added while suppressing the generation of water vapor due to reaction heat at the time of adding the latex. The isocyanate group of the adduct reacts with the carboxyl group and water in the acrylic rubber, and the viscosity gradually increases, so if it is ready to be taken out as a rubber material, take it out from a closed mixer such as a kneader. ,
Dispense using an open roll.

The carboxyl group-containing acrylic rubber is an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, and the like, or those having 2 to 2 carbon atoms. 8
A mixture of an alkoxyalkyl acrylate having an alkoxyalkyl group of, for example, methoxyethyl acrylate, ethoxymethyl acrylate, butoxyethyl acrylate, and the like, is copolymerized with about 0.5 to 15 mol% of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, and the like. Copolymers having a solids content of about 5 to 80% by weight, preferably about 20 to 50% by weight, in the form of a latex in an amount of about 5 to 200% by weight per 100 parts by weight of the synthetic rubber compound. It is used in an amount of latex of about 50 parts by weight, preferably about 50 to 150 parts by weight.

The water-swellable rubber composition as a reactant described above is added with a vulcanizing agent and a vulcanization accelerator, and vulcanized by a steam vulcanization method or the like.

〔The invention's effect〕

According to the method of the present invention, a liquid obtained by first dispersing and mixing a liquid hydrophilic polyalkylene oxide diisocyanate adduct into a synthetic rubber compound and then reacting isocyanate groups with a carboxyl group-containing acrylic rubber latex to increase the molecular weight. Since the swellable rubber composition has its reactant stably present in the synthetic rubber, it is possible to give a vulcanizate having stable water absorbing performance without any decrease in mechanical strength. it can.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 SER (Nippon Zeon SBR1507) 100 parts by weight FEF carbon black 20 hard clay 20 precipitated silica 10 zinc oxide 5 stearic acid 1 trimethyl-dihydroquinoline polymer 2 wax 2 wax After kneading and plasticizing sufficiently, a polyalkylene oxide diisocyanate adduct (viscosity: 3,000 centipoise) in which one molecule of tolylene diisocyanate is bonded to both terminal hydroxyl groups of the ethylene oxide-propylene oxide copolymer is subjected to SB.
140 parts by weight per 100 parts by weight of the R formulation is gradually added and mixed and stirred.

Thereafter, the kneader was cooled to around room temperature (about 30 ° C.), and 100 parts by weight of a latex (solid content: 30% by weight) of an ethyl acrylate-acrylic acid (molar ratio: 99: 1) copolymer was gradually added. After reacting for several minutes, 1 part by weight of sulfur as a flowing agent and 4 parts by weight of N-cyclohexyl-2-benzothiazylsulfonamine as a vulcanization accelerator were added.

The extrudability of the obtained vulcanizable SBR composition is good, 5 × 25 m
Extruded into a strip with a cross section of m and steam vulcanized at 130 ° C for 2 hours. The following physical properties (measured with a dumbbell of 5mm thickness)
A vulcanized molded product having a water swelling ratio (measured on a sample of 5 × 25 × 25 mm) was obtained.

Hardness (JIS-A) 55 Tensile strength 52 kgf / cm ² Elongation 300% Water swelling rate (70 hours immersion) 150% Example 2 In Example 1, tolylene diisocyanate was added to polyethylene oxide as the polyalkylene oxide diisocyanate compound. Product (viscosity: 6000 centipoise) at a ratio of 100 parts by weight per 100 parts by weight of the SBR compound, and as a latex, a latex having a solid content concentration of ethyl acrylate-methacrylic acid (molar ratio: 95: 5) copolymer of 30% by weight 70 parts by weight were used.

The extrudability of the obtained vulcanizable SBR composition was good, and the steam vulcanizate had the following physical properties.

Hardness (JIS-A) 55 Tensile strength 47kgf / cm ² Elongation 350% Water swelling rate (70hrs immersion) 100% Example 3 In Example 1, the same amount of NBR (Nippon Synthetic Rubber N230SV) was used instead of SBR. Using), a vulcanized molded product having the following physical properties and water swelling ratio was obtained.

Hardness (JIS-A) 60 Tensile strength 47 kgf / cm ² Elongation 270% Water swelling rate (70 hrs immersion) 110% Comparative Example In Example 1, water was used instead of latex.
After steam vulcanization at 130 ° C. for 2 hours, the obtained vulcanized molded product had the following physical properties.

Hardness (JIS-A) 50 Tensile strength 38kgf / cm ² Elongation 280% Water swelling rate (70hrs immersion) 120%

Claims (1)

(57) [Claims] 1. A process for producing a water-swellable rubber composition, comprising adding a carboxyl group-containing acrylic rubber latex to a mixture of a synthetic rubber compound and a polyalkylene oxide diisocyanate adduct and reacting the mixture.