JPS5840561B2 - Manufacturing method for rubber molded products - Google Patents

Description

Detailed Description of the Invention The present invention uses a latex of base cis-1,4-polyisoprene rubber (hereinafter abbreviated as IR), which has sufficient practical physical properties without applying a vulcanization operation. The present invention relates to a method of manufacturing a molded article.

Gloves from natural rubber latex, synthetic rubber latex,
It is well known that various rubber molded products such as soaked products such as sanitary products, foam rubber, rubber thread, and lock products are manufactured. stress, non-adhesiveness, etc.)
It is also well known that during the molding process of latex, it is essential to add a vulcanizing agent such as sulfur and a vulcanization accelerator to vulcanize the rubber.

In general, sulfur vulcanization requires sulfur, a vulcanization accelerator, and zinc oxide as vulcanizing agents for latex; other vulcanizing agents include various peroxides and quinone dioximes. However, in order to produce molded products from natural rubber latex or IR latex using these vulcanizing agents, many complicated steps must be performed as described below.

That is, first, a vulcanizing agent is made into an aqueous dispersion using a ball mill or the like using various stabilizers, and this is mixed with latex.

The resulting blended latex is then aged to facilitate the vulcanization reaction, and then cast, coated, or coagulated using a coagulant such as calcium nitrate.

After drying the obtained wet gel,
The molded product is heated to 0.degree. C. to carry out a vulcanization reaction, and after vulcanization, the molded product is washed with water to remove vulcanization residues and the like.

In this way, manufacturing vulcanized molded products from latex requires many steps, and in order to ensure good physical properties of the resulting molded products, the conditions for each manufacturing process must be set and controlled extremely strictly. must be done.

In addition, molded products made from latex made using sulfur, the most common vulcanizing agent, have problems that need to be improved in terms of physical properties such as low aging resistance and toxicity to the human body, as well as in terms of pollution. .

Natural rubber and IR are said to have poor heat aging resistance, weather resistance, etc., and one of the major factors contributing to this poor aging resistance is sulfur used in the vulcanization reaction.

It is well known that sulfur accelerates the deterioration of rubber.

In addition, toxicity is caused by various vulcanization accelerators used in sulfur vulcanization, such as diphenylguanidine and mercaptobenzothiazole, and for this reason, sulfur-cured rubber products are often not used for food sanitation purposes.

As mentioned above, natural rubber latic and IR latex give useful molded products by vulcanization, but there are major problems in terms of process and physical properties. It would be extremely convenient if a molded product of

However, with respect to natural rubber latex and IIIR latex, there is no known example of successfully obtaining a satisfactory molded product by omitting vulcanization.

Note that unvulcanized rubber latex is used in adhesive tapes, free albums, etc. that require viscosity.
This is a special case that does not fall within the scope of molded products that do not have viscosity and maintain a predetermined shape.

The present invention solves the above problems, and according to the present invention,
Synthetic cis-1.4 containing anionic surfactant as an emulsifier is added to a synthetic cis-1゜4-polyisoprene rubber with a content of 80% or more, with an average of 0 per 100 monomer units.
．． By introducing 4 to 10 carboxyl groups or their salts, the intrinsic viscosity at 30°C in toluene is 1.0 di/
By using an aqueous dispersion obtained by emulsifying a modified synthetic cis-1,4-polyisoprene rubber with a weight of more than Molded products with practical physical properties can be produced.

A modified IR having a carboxyl group is produced by reacting IR with maleic anhydride, and the modified IR is reacted with a divalent or tetravalent metal salt of a higher fatty acid or a corresponding higher fatty acid and a divalent or tetravalent metal in a solid state. It is well known that thermoplastic rubber having practical physical properties can be obtained by contacting it with a metal compound without vulcanization (Japanese Patent Publication No. 48-15
No. 450).

According to the present invention, as far as IR latex is concerned, by using a modified IR into which a specific amount of carboxyl groups has been introduced and using an anionic surfactant as an emulsifier, it is possible to achieve extremely It has been found that moldings with a high degree of strength properties and other physical properties can be obtained.

In the present invention, if the amount of carboxyl groups introduced into the IR is small, the physical properties such as tensile strength, tensile stress, and impact resilience of the molded product obtained from the latex will not be able to withstand use, and the adhesiveness will also be reduced. remain.

On the other hand, if the amount of carboxyl groups introduced is too large, the tensile stress of the molded product becomes too large, making the molded product hard and decreasing its tensile strength.

From these points, the number of carboxyl groups contained in the modified IR should be 0.4 to 10 per 100 isoprene monomer units constituting the main chain, preferably 0.6 to 10.
There are 4 pieces.

In the present invention, the modified IR containing a carboxyl group can be any of the following, as long as a carboxyl group (including salts of alkali metals such as lithium, sodium, potassium, etc. and ammonium salts) is introduced as a side group into the IR prepared in advance. It may be manufactured by such a method.

Furthermore, the carboxylating agent used for this purpose does not necessarily have to have free carboxyl groups itself.

That is, it only needs to have a group that forms a free carboxyl group through treatment such as hydrolysis after reaction with IR.

In the present invention, a modified IR reacted with such a carboxylating agent is also referred to as a modified IR containing a carboxyl group for convenience.

In the present invention, the following carboxylating agents can be used.

(1) α, β-, β-mono- or polycarboxylic acids and their esters, such as acrylic acid, methacrylic acid, maleic acid, monomethyl maleate, dimethyl maleate, fumaric acid, monomethyl fumarate, itaconic acid, Citraconic acid, maleic acid monoamide.

(2) α, β-, β-dicarboxylic acid anhydride and α,
β-unsaturated unsaturated dicarboxylic acid monoamide fish products such as maleic anhydride, dimethylmaleic anhydride, itaconic anhydride, citraconic anhydride, maleimide, N-methylmaleimide.

(3) α, β-, β-chlorides such as acrylic chloride, methacrylic chloride, maleic monochloride, maleic dichloride, itaconic chloride.

(4) Carboxyl group-containing allyl compounds such as allyl succinic acid and allyl succinic anhydride.

The process for producing a carboxyl group-containing modified IR by reacting IR with a carboxylating agent does not constitute a part of the present invention, but can be summarized as follows.

In the IR solution, 0.01 to 20 parts per 100 parts by weight of IR.
Parts by weight of carboxylating agent are added and heated to a temperature of 50-250°C under an inert gas atmosphere.

As the IR solvent, aliphatic hydrocarbons such as n-butane, impentane, and hexane, and aromatic hydrocarbons such as benzene, toluene, and xylene are used.

In the reaction in solution, benzoyl peroxide,
Radical generating catalysts such as azobisisobutylonitrile, diisopropylbenzene hydroperoxide, and di-t-butyl peroxide may also be included.

Another method is to contact the solid IR with the carboxylating agent while masticating it with a roll or a kneader such as a Banbury mixer.

Also in this method, a radical generating catalyst can be used.

If the IR-reacted carboxylating agent has groups that can be converted to carboxyl groups, such as anhydrides, esters or amides of carboxylic acids, such groups are removed during rubber emulsification and subsequent solvent removal. , undergoes hydrolysis and is converted into carboxyl groups in free or salt form.

Therefore, in the present invention, the carboxyl group content of the modified IR is defined as the amount of free carboxyl groups and salt-form carboxyl groups that the modified IR of the latex has.
Or it is expressed in terms of its amount.

The amount of carboxyl groups is measured by dissolving the rubber in benzene and titrating it using a methanol-benzene mixed solution (1:4 volume ratio) in a sodium hydroxide solution using promthymol blue or phenolphthalein as an indicator. be able to.

Modified IR containing carboxyl groups was prepared at 30% in toluene.
'The intrinsic viscosity at C must be 1.0 dl/fi or more.

The viscosity is 1. If it is lower than odll&, the tensile strength of the film obtained from the latex will be insufficient and it will also become sticky, making it difficult to use it as a general rubber molded product.

The IR preferably has a cis-1,4 content of 80% or more, especially 95% or more.

The aqueous dispersion (latex) of modified IR containing a carboxyl group is produced by the usual method of adding a solvent solution of the modified In to water containing an emulsifier, stirring and emulsifying it, and removing the solvent from the resulting emulsion. I can do something.

The emulsifier used here is an anionic surfactant containing an alkali metal such as potassium oleate or sodium dodecylbenzenesulfonate, so that the latex according to the present invention can give a molded article having a practical substance without being substantially vulcanized. Agents are particularly preferably used.

Although the use of small amounts of nonionic surfactants is acceptable, their use alone is inappropriate in the present invention.

By using a modified IR latex that satisfies the above requirements, molded products with sufficient practical physical properties, no stickiness and no harmful effects can be obtained without substantial vulcanization, and the vulcanization process can be eliminated. The method of the present invention is extremely useful because of the simplicity of the process in which the above-mentioned molded product can be produced by simply molding and drying.

Here, not performing substantial vulcanization means, most preferably, completely excluding the addition of a normal vulcanizing agent to carry out the vulcanization reaction, but this alone does not provide practical physical properties to the molded product. It also includes mild vulcanization to the extent that it does not result in vulcanization.

The rubber molded products obtained in this way are, for example, soaked products such as gloves and rubber balloons, rubberized cloth such as rubberized work gloves, rubber thread, foam rubber, lock products such as palm locks and hair locks, and seals for the crowns of bottles. Patsukin,
Suitable for a wide range of applications such as adhesives.

The latex can also be used as a fiber binder and for paper processing.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 High cis-1,4-polyisoprene (I
R) was used.

Ion IR was dissolved in toluene 11, and predetermined amounts of maleic anhydride (hereinafter abbreviated as MAn) and di-t-butyl peroxide (hereinafter abbreviated as t-BP) were added thereto, and the mixture was replaced with nitrogen at 150°C. It was heated for 2 hours.

Next, 500 cc of water in which potassium oleate was dissolved in the modified IR (8 phr: parts by weight per 100 parts by weight of rubber) was added to the solution of the modified IR, and the mixture was stirred at 900 revolutions/minute using a homomixer. Emulsified for minutes.

Toluene was removed from this emulsified dispersion under reduced pressure, and the mixture was centrifugally concentrated to obtain a latex with a comb content of 50%.

This latex was cast and dried at 70° C. for a day and night to prepare a single-layer comb film.

The physical properties of the obtained rubber film are shown in Table **1.

As seen in Table 1, IR has a carboxyl group of 0.4
contains 100 or more isoprene units/isoprene units, and has rubber [η
] is 1.0 or more, the cast film has a tensile strength of more than 100 w/ctd and is not sticky, and is a processed film prepared from so-called ordinary in-prene rubber latex. It shows physical properties similar to sulfur rubber and is suitable for use as general rubber moldings.

Example 2 A latex was produced in the same manner as in Example 1 by employing the unreacted experiment No. 4 and using sodium dodecylbenzenesulfonate in place of potassium oleate.

A film prepared by casting and drying the obtained latex exhibited physical properties of a tensile strength of 210 ky/ffl and a 300% elongation stress of 17 ky/i, and was an excellent rubber molded product with no stickiness.

Also, apply this latex to vinylon cloth and heat it at 80℃ for 1
By drying for a long time, it was possible to obtain a good rubberized cloth without stickiness.

Example 3 A glass plate to which a methanol solution of calcium nitrate (20%) was previously attached as a coagulant was immersed in the latex obtained in Example 2 for 1 minute, then pulled up and dried to a thickness of 0.3U. A rubber film was obtained.

The tensile strength of this film was 220-㎜, the 300% elongation stress was 17.5 kg/crl, and it had good properties without stickiness.

Claims (1)

[Claims] 1 Synthetic cis-1 containing 80% or more of cis-1,4
, 4-polyisoprene rubber is introduced with an average of 0.4 to 10 carboxyl groups or its salts per 100 units of inbrene monomer, and the intrinsic viscosity at 30°C in toluene is adjusted to 1. Modified synthesis cis 1 with Odll 9 or higher,
A method for producing a rubber molded article, which comprises molding an aqueous dispersion obtained by emulsifying a 4-polyisoprene rubber using an anionic surfactant as an emulsifier, without substantially vulcanizing it.