JP2023075367A - Rubber foam, production method of the same, and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber foam having excellent hardness and composed of chloroprene rubber composition.

SOLUTION: There is used a foam composed of a vulcanized product of a rubber composition including: a chloroprene rubber; and a cellulose nanofiber having an average fiber diameter of 10-300 nm, an average fiber length of 0.5-200 μm, and a lignin content of 20 wt.% or less where a hydroxymethyl group of cellulose is not modified with a carboxylic acid or a carboxylic acid salt, where the amount of the cellulose nanofiber is 1-7 pts.wt. to 100 pts.wt. of the chloroprene rubber.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a foam comprising a vulcanized product of a lighter and harder rubber composition and a method for producing the same.

Among various synthetic rubbers, chloroprene rubber has well-balanced physical properties and is used in a wide range of applications, such as belts, hoses, air springs, and adhesives.
They are also widely used as foams, such as cushioning materials, sound insulation materials, heat insulating materials, and door packings.

One of the major features of foam is weight reduction by foaming. While unfoamed vulcanized rubber has a specific gravity of approximately 1.0 to 1.3, vulcanized rubber foam can have a specific gravity of less than 1.0,
The specific gravity can be arbitrarily adjusted by increasing the amount of the foaming material to be added or by changing the vulcanization conditions. However, weight reduction by increasing the amount of foamed material increases the ratio of air bubbles, so changing the vulcanization conditions ends vulcanization in an insufficient state. There are limits to transformation. Other weight reduction methods include reducing the amount of reinforcing agents (carbon black, silica, etc.) and inorganic fillers (talc, clay, etc.) having a specific gravity greater than that of the rubber composition. However, reducing the amount of reinforcing agents lowers the strength of the rubber composition, and reducing the amount of inorganic fillers increases compounding costs, making significant weight reduction difficult.

Therefore, a method has been proposed in which a supercritical fluid is introduced into unvulcanized rubber to foam it, thereby reducing the weight without lowering the strength (Patent Document 1). However, the supercritical method is difficult to industrialize,
The cost is also very high, so it is not practical. Further, a method for reducing weight by microdispersing a polyolefin resin in a molten state has been proposed (Patent Documents 2 and 3). However,
Since it contains a polyolefin resin, it is inferior in setting property and is not suitable for use as a foam.

On the other hand, as a new material, cellulose nanofiber, which is made by miniaturizing wood pulp, has been developed, and various fields are searching for its industrial use. One of them is compounding into rubber. For example, a rubber composition is disclosed in which cellulose nanofibers are modified to enhance durability (Patent Document 4
). Also, a tire with low energy loss is proposed in which cellulose nanofibers are modified (Patent Document 5). Also, a rubber composition has been proposed in which a silane coupling agent is added to cellulose nanofibers to enhance compatibility with the polymer (Patent Document 6). A vulcanized rubber foam for shoe soles containing cellulose nanofibers has also been proposed (Patent Document 7).

Japanese Patent Application Laid-Open No. 2002-322308 Japanese Unexamined Patent Application Publication No. 2011-16978 JP 2008-111137 A JP 2017-554109 A JP 2015-056788 A JP 2009-191198 A JP 2015-072833 A

However, Patent Documents 4 to 6 do not target rubber vulcanized foams with high foaming and low specific gravity, and do not solve the problem of achieving both weight reduction and high strength. Although Patent Document 7 is directed to vulcanized rubber foams, the rubber components are natural rubber, SBR, EPDM, and EVA for use in shoe soles.
Not suitable for chloroprene rubber.

The present invention has been made in view of this problem, and its object is to provide a foam made of a chloroprene rubber composition that is lightweight and exhibits high hardness.

In view of this background, the present inventors have made intensive studies to solve the above problems. It was found that hardness can be compatible with each other. That is, each aspect of the present invention is [1] to [8] shown below.
[1] With respect to 100 parts by weight of chloroprene rubber, the average fiber diameter is 10 to 300 nm, the average fiber length is 0.5 to 200 μm, the lignin content is 20% by weight or less, and the hydroxymethyl group of cellulose is carboxylic. A foam comprising a vulcanizate of a rubber composition containing 1 to 7 parts by weight of cellulose nanofibers not modified with acid or carboxylate.
[2] The foam according to [1] above, wherein the chloroprene rubber contains 3 to 7 parts by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid per 100 parts by weight of the chloroprene rubber.
[3] The relationship between the hardness (Hs) described in JIS-K-6253 and the density (ρ) described in JIS-K-6268 is 100ρ (1. 2-ρ
) The foam according to any one of [1] or [2] above, which satisfies +14≦Hs.
[4] A method for producing a foam according to any one of [1] to [3] above, which includes steps 1 to 3 below.

Step 1: Chloroprene latex with a pH of 10 to 14 and an average fiber diameter of 10 to 300 n
m, the average fiber length is 0.5 to 200 μm, and the lignin content is 20% by weight or less,
An aqueous dispersion of cellulose nanofibers in which the hydroxymethyl group of cellulose is not modified with carboxylic acid or carboxylate is mixed to prepare a cellulose nanofiber-dispersed rubber latex mixture, and water is removed from the cellulose nanofiber-dispersed rubber latex mixture. Step 2: 2 to 15 parts by weight of a foaming agent with respect to 100 parts by weight of the rubber composition produced in Step 1. Step of preparing a compound by blending and kneading Step 3: The compound prepared in step 2 is heat-molded at 120 to 180 ° C. for 5 to 90 minutes to vulcanize and expand [5] In step 1, freeze solidification The method for producing a foam according to [4] above, wherein water is removed.
[6] The viscosity of the cellulose nanofiber-dispersed rubber latex mixture in step 1 is 1500
The method for producing a foam according to [5] above, wherein the viscosity is mPa·s or less.
[7] The method for producing a foam according to any one of [4] to [6] above, wherein the cellulose nanofiber-dispersed rubber latex mixture in step 1 has a solid content of 20% by weight or more.
[8] A sponge rubber made of the foam according to any one of [1] to [3] above.

The present invention will be described in detail below.

The foam of the present invention has an average fiber diameter of 10 to 300 per 100 parts by weight of chloroprene rubber.
1 to 7 weight of cellulose nanofibers in which the hydroxymethyl groups of cellulose are not modified with carboxylic acid or carboxylate, and the average fiber length is 0.5 to 200 μm, the lignin content is 20% by weight or less, and the cellulose nanofibers are not modified with carboxylic acid or carboxylate. It consists of a vulcanizate of a rubber composition containing parts.

Chloroprene rubber can be obtained by emulsion polymerization of chloroprene or chloroprene and a monomer copolymerizable therewith.

Examples of monomers copolymerizable with chloroprene include sulfur, 2,3-dichloro-1,
3-butadiene, 2-cyano-1,3-butadiene, 1-chloro-1,3-butadiene,
1,3-butadiene, styrene, acrylonitrile, methyl methacrylate, methacrylic acid, acrylic acid and the like can be mentioned, and one or more of them can be used in combination. Although it is possible to improve mechanical properties such as modulus, heat resistance is lowered, so it is not always necessary and is used as appropriate depending on the required physical properties. Although the amount of the copolymerizable monomer is not particularly limited, it is generally used in an amount of 30 parts by weight or less per 100 parts by weight of the chloroprene rubber as long as the properties of the chloroprene polymer are not impaired. In particular, sulfur lowers the heat resistance, so it is preferably 3 parts by weight or less, more preferably 1 part by weight or less per 100 parts by weight of the chloroprene monomer.

The chloroprene rubber preferably contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid. When it is 3% by weight or more, the emulsification stability during chloroprene polymerization is excellent, and when it is 7% by weight or less, poor freezing does not occur in the rubber deposition step due to freezing, and stable production of rubber products becomes possible.

In the emulsion polymerization of chloroprene rubber, for example, the above monomers are combined with an emulsifier, water, a polymerization initiator,
A method of mixing a chain transfer agent, other stabilizers, etc., performing polymerization at a predetermined temperature, and adding a polymerization terminator at a predetermined polymerization conversion rate to terminate the polymerization can be mentioned.

Examples of emulsifiers include alkali metal salts of carboxylic acids and alkali metal salts of sulfonic acids. Examples include alkali metal salts, alkali metal salts of polycarboxylic acids, nonionic emulsifiers such as polyoxyethylene alkyl ethers, and water-soluble polymer compounds. Alkali metal salts include, for example, lithium, sodium, potassium, cesium and the like. These may be one type or two or more types, but from the viewpoint of polymerization stability, cohesiveness during drying, and rubber performance, it is preferable to contain an alkali metal salt of a carboxylic acid. It preferably contains an alkali metal salt of rosin acid, more preferably a potassium salt of rosin acid.

The amount of the emulsifier is not particularly limited, but considering the stability of the chloroprene latex obtained after polymerization, it is preferably 3 to 10 parts by weight per 100 parts by weight of the chloroprene rubber. Among them, the alkali metal salt of carboxylic acid is preferably 3 to 8 parts by weight, more preferably 5 to 7 parts by weight.
It is preferable to include parts by weight.

In order to adjust the pH of the polymerization liquid, it is preferable to adjust the pH to 11 or higher with a pH adjuster. Below this, the alkali metal salt of the carboxylic acid is acidified and the stability of the latex is lowered. Examples of pH adjusters include basic compounds such as sodium hydroxide, potassium hydroxide, sodium phosphate, potassium phosphate, triethylamine, diethylamine, triethanolamine, diethanolamine, ethanolamine, and ammonia.
More than one type is used alone or in combination.

Emulsion polymerization initiators include known free-radical substances such as potassium persulfate,
Peroxides such as ammonium persulfate, inorganic or organic peroxides such as hydrogen peroxide, tertiary butyl hydroperoxide, and the like can be used. Further, these may be used alone or in combination with reducing substances such as thiosulfate, thiosulfite, hydrosulfite, organic amine, etc., in a redox system.

Although the polymerization temperature is not particularly limited, it is preferably in the range of 10 to 50°C.

The timing of completion of polymerization is not particularly limited.
% to 95%. If it is less than 60%, the production amount is small and the solid content of the latex becomes low. On the other hand, if it is 95% or more, the polymerization time becomes very long.

The polymerization terminator is not particularly limited as long as it is a commonly used terminator. For example, phenothiazine, 2,6-t-butyl-4-methylphenol, hydroxylamine and the like can be used.

In the case of sulfur-modified chloroprene copolymerized with sulfur, a deflocculating agent and a deflocculating aid can be added to the latex whose polymerization has been terminated, and peptization can be carried out until an appropriate Mooney viscosity is achieved.
Peptizing agents include thiuram compounds such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetraoctylthiuram disulfide, etc., and can be added in an emulsified state using the above emulsifier or the like. Examples of peptization reaction initiators include thiocarbamic acid compounds such as sodium dibutyldithiocarbamate and ammonium dimethyldithiocarbamate.

Peptization temperature can be in the range of 5 to 60°C, preferably in the range of 20 to 50°C. Generally, the higher the peptization temperature, the faster the peptization reaction.

The Mooney viscosity for completing the deflocculation reaction is not particularly limited as long as it satisfies the high elastic stress of the present invention.

Cellulose nanofibers are obtained by defibrating cellulose fibers contained in wood to an average fiber diameter of several nanometers to several tens of nanometers. Although lignin is contained in wood or the like, which is the raw material of cellulose nanofibers, cellulose nanofibers containing a large amount of lignin impair the stability of chloroprene latex, so the amount of lignin contained is preferably 20% by weight or less. It is preferably 10% by weight or less, more preferably 5% by weight or less. There are two types of fibrillation treatment, one is mainly mechanical treatment, and the other is chemical treatment to give various functional groups and mechanical treatment is used together to achieve finer single nano level. Cellulose nanofibers obtained by the treatment have an average fiber diameter of 10 to 300 nm, an average fiber length of 0.5 to 200 μm, and the hydroxymethyl groups of cellulose are not modified with carboxylic acid or carboxylate. Cellulose nanofibers having an average fiber diameter of less than 10 nm increase the viscosity of the cellulose nanofiber-dispersed rubber latex, causing problems in the rubber deposition step by freezing. Cellulose nanofibers having an average fiber diameter of more than 300 nm increase the viscosity of the chloroprene rubber composition containing cellulose nanofibers, and have problems in moldability of the foam. It is preferably 10 to 100 nm. On the other hand, cellulose nanofibers having an average fiber length of less than 0.5 μm reduce the hardness of foams made of rubber vulcanizates containing cellulose nanofibers. If the average fiber length exceeds 200 μm, the viscosity of the cellulose nanofiber-containing rubber composition increases, and the moldability of the foam deteriorates. It is preferably 0.5 to 100 μm. In addition, if the cellulose nanofibers contain a carboxylate or a carboxylic acid, the state of dispersion of the cellulose nanofibers in the rubber deteriorates, so that the obtained foam made of the vulcanized rubber has a low hardness and is difficult to handle. Therefore, cellulose that has not been modified with carboxylate and carboxylic acid is used.

In the present invention, the content of cellulose nanofiber is 1 to 7 parts by weight with respect to 100 parts by weight of chloroprene rubber. When the cellulose nanofiber content is less than 1 part by weight, the hardness of the foam is lowered. If the cellulose nanofiber content exceeds 7 parts by weight, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture increases, causing problems in the rubber precipitation step due to freezing, and from the viewpoint of economic superiority. not appropriate. It is preferably 1 to 5 parts by weight, more preferably 1 to 3 parts by weight.

The foam of the present invention is a vulcanizate of the above rubber composition.

The foam of the present invention is produced by the following steps 1-3.

Step 1: Chloroprene latex with a pH of 10 to 14 and an average fiber diameter of 10 to 300 n
m, the average fiber length is 0.5 to 200 μm, and the lignin content is 20% by weight or less,
An aqueous dispersion of cellulose nanofibers in which the hydroxymethyl group of cellulose is not modified with carboxylic acid or carboxylate is mixed to prepare a cellulose nanofiber-dispersed rubber latex mixture, and water is removed from the cellulose nanofiber-dispersed rubber latex mixture. Step 2: 2 to 15 parts by weight of a foaming agent with respect to 100 parts by weight of the rubber composition produced in Step 1. A step of preparing a compound by blending and kneading Step 3: A step of heating and molding the compound prepared in step 2 at 120 to 180 ° C. for 5 to 90 minutes to vulcanize and foam The foam of the present invention is also produced. The rubber composition for is obtained by mixing an aqueous dispersion of cellulose nanofibers with chloroprene latex to prepare a cellulose nanofiber-dispersed rubber latex mixture, and removing water from the cellulose nanofiber-dispersed rubber latex mixture. can be done.

In step 1, the chloroprene latex contains a chloroprene monomer and an unsaturated monomer copolymerizable with the chloroprene monomer, and is not particularly limited as long as it is produced by an emulsion polymerization method. From the viewpoint of emulsion stability, the pH is preferably 10-14.

The aqueous dispersion of cellulose nanofibers is obtained by dispersing cellulose nanofibers with a lignin content of 20% by weight or less, which are fibrillated to an average fiber diameter of 10 to 300 nm and an average fiber length of 0.5 to 200 μm, in water. is.

The method for mixing the chloroprene rubber latex and the aqueous dispersion of cellulose nanofibers is not particularly limited, and a propeller-type stirring device, homomixer, high-pressure homogenizer, etc. is used to mix the aqueous dispersion of chloroprene latex and cellulose nanofibers. It can be obtained by mixing until it becomes uniform in appearance (no lumps, etc.).

Method for removing water from cellulose nanofiber-dispersed rubber latex mixture (drying method)
There are heat drying, coagulation by acid or salt, and freeze-drying, but when coagulation is performed, the emulsifier, coagulating liquid, and moisture remain inside the rubber, so the rubber is precipitated by freezing (freezing coagulation).
The method of drying with hot air after removing the excess emulsifier and the like by washing with water is the most efficient and easy drying method, which is preferable. In that case, the method of freezing and solidifying the cellulose nanofiber-dispersed rubber latex mixed solution at a pH of 10 or less is more preferable since the rubber is easily precipitated by freezing.

The obtained rubber composition is dried by hot air drying to evaporate water. Specifically, a sheet-like rubber that has been frozen and solidified is placed on a belt conveyor, and air heated to 100° C. or higher is fed into the sheet to evaporate the moisture to obtain a dried rubber composition.

Specifically, a sheet-like rubber that has been frozen and solidified is placed on a belt conveyor, and air heated to 100° C. or higher is fed into the sheet to evaporate moisture to obtain dried rubber.

In the freeze-coagulation drying method, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1500 mPa·s or less, more preferably 1000 mPa·s or less and 30 mPa·s or more. The solid content of the cellulose nanofiber-dispersed rubber latex mixture is preferably 20% by weight or more, and more preferably 25% by weight or more and 35% by weight or less. When the viscosity is 1500 mPa·s or less, freeze-coagulation is good and preferable. Further, when the solid content is 20% by weight or more, the frozen rubber film is less likely to crack and the strength of the rubber film increases when thawed, which is suitable and preferable for continuous production of rubber products.

In step 2, 2 to 15 parts of a foaming agent is added to 100 parts by weight of the rubber composition prepared in step 1.
A compound is prepared by blending and kneading parts by weight, and in step 3, the compound prepared in step 2 is heat molded at 120 to 180° C. for 5 to 90 minutes to be vulcanized and foamed.

In step 2, the rubber composition prepared in step 1 is compounded and kneaded with various compounding agents in the same manner as for ordinary chloroprene rubber. In step 2, the blowing agent is not particularly limited, but from the viewpoint of workability and production efficiency, for example, OBSH (4,4'-oxybis(benzenesulfonylhydrazide)) and the like can be used. The number of parts of the foaming agent to be blended is
2 to 15 parts by weight is preferred, 2 to 10 parts by weight is more preferred, and 2 to 8 parts by weight is most preferred.

In step 3, the compound containing the foaming agent prepared in step 2 is heated using a rubber mold at 120 to 180° C. for 5 to 90 minutes, preferably at 130 to 170° C. for 10 to 60 minutes. A gas is generated from the foaming agent, vulcanization and foaming proceed simultaneously, and a rubber foam (hereinafter sometimes referred to as a vulcanized rubber foam) composed of the vulcanizate is obtained.

The foam of the present invention preferably has a density of 0.6 kg/cm ³ or less, more preferably 0.5 kg/cm ³ or less, and 0.45 kg/cm ³ or less in terms of weight reduction. is particularly preferred.

The obtained vulcanized rubber foam is lightweight and has a high hardness, so that it can be used for various purposes, and is particularly preferably applied to wet suits and cushion materials.

In general, the hardness (Hs) of a vulcanized rubber foam decreases as the foam density (ρ) decreases.

For example, a vulcanized rubber foam obtained by vulcanizing and foaming a rubber compound containing 10 parts by weight of OBSH as a foaming agent had a density (ρ) of 0.21 and a hardness (Hs) of 32. In addition, OB
The density of the vulcanized rubber foam (
ρ) is 0.3 and the hardness (Hs) is 38. The vulcanized rubber foam obtained by vulcanizing and foaming a rubber compound containing 5 parts by weight has a density (ρ) of 0.39 and a hardness (Hs) of 43. , 2.1 parts by weight of a rubber compound compounded by vulcanization and foaming. The density (ρ) of the vulcanized rubber foam is 0.5 and the hardness (Hs)
was 47. From these experimental results, the 4-point approximate curve is 100ρ(1.2-ρ) +
11=Hs. On the other hand, vulcanized rubber foams containing cellulose nanofibers exhibit lower densities at the same hardness. This makes it possible and desirable to reduce the weight of products that require hardness. Difficult to achieve. For example, a chloroprene rubber composition having a cellulose content of 1 part by weight per 100 parts by weight of a rubber component and a foaming agent OBSH
The density (ρ) of the vulcanized rubber foam obtained by vulcanizing and foaming a rubber compound containing 5 parts by weight of
. 37, the hardness (Hs) is 45, satisfying 100ρ(1.2−ρ)+14≦Hs. Furthermore, a vulcanized rubber foam obtained by vulcanizing and foaming a rubber compound obtained by blending 5 parts by weight of OBSH as a foaming agent into a chloroprene rubber composition having a cellulose content of 2.5 parts by weight with respect to 100 parts by weight of a rubber component. has a density (ρ) of 0.35 and a hardness (Hs) of 46.
2−ρ)+16≦Hs. In addition, the density of a vulcanized rubber foam obtained by vulcanizing and foaming a rubber compound obtained by blending 5 parts by weight of OBSH, a foaming agent, with a chloroprene rubber composition having a cellulose content of 5 parts by weight with respect to 100 parts by weight of a rubber component ( ρ) is 0.33 and the hardness (Hs) is 4
9 and satisfies 100ρ(1.2−ρ)+18≦Hs. Therefore, in the density range of 0.2 to 0.6, which is useful as a vulcanized rubber foam, it is preferable that 100ρ(1.2−ρ)+14≦Hs, and further 100ρ(1.2−ρ)+16 It is more preferable that ≦Hs, and most preferably 100ρ(1.2−ρ)+18≦Hs.

By using the foam made of the cellulose nanofiber-containing chloroprene rubber composition of the present invention, it is possible to obtain a vulcanized rubber foam that is lightweight and has high hardness.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited only to these examples.

<Production of chloroprene rubber latex>
As a monomer mixture, 0.3 parts by weight of sulfur is added to 100 parts by weight of chloroprene, 4.0 parts by weight of potassium salt of rosin acid, 0.5 parts by weight of sodium salt of condensate of naphthalenesulfonic acid and formaldehyde, 0.05 parts by weight of sodium hydroxide and sodium orthophosphate1.
0 part by weight, mixed with an emulsified aqueous solution containing 100 parts by weight of water, stirred and emulsified, and then polymerized with 1.0 part by weight of potassium persulfate, 0.01 part by weight of sodium anthraquinone-β-sulfonate, and 30 parts by weight of water. Polymerization was carried out by adding the catalyst at a constant rate by means of a pump. Polymerization was carried out by adding a polymerization catalyst until the polymerization conversion rate reached 70%. A polymerization terminator consisting of 0.05 parts by weight of butylphenol, 0.1 parts by weight of diethylhydroxylamine, 0.05 parts by weight of sodium lauryl sulfate, 5.0 parts by weight of chloroprene and 1.0 parts by weight of water was added to terminate the polymerization. let me This was followed by tetraethylthiuram disulfide 2
A product emulsified by weight parts of a toluene solution with potassium rosinate and 0.3 parts by weight of sodium dibutyldithiocarbamate were added, deflocculated at 40° C. until the Mooney viscosity reached 60, and steam-stoved under reduced pressure. Unreacted chloroprene was removed and recovered by ripping to obtain a chloroprene rubber latex. The pH of the obtained chloroprene rubber latex was 11.
. was 3.

<Production of chloroprene rubber composition containing cellulose nanofibers>
A predetermined amount of an aqueous dispersion of cellulose nanofibers was added to chloroprene rubber latex, and the mixture was mixed at 2,000 rpm with an auto homomixer (PRIMIX: PRIMIX).
Mix for 0 minutes.

Thereafter, the pH was adjusted to 6.5 using 15% by weight of dilute acetic acid, and then the rubber composition was precipitated by freezing and coagulation, washed with water, and dried with hot air.

<Viscosity, solid content, pH>
Viscosity was measured with a Vismetron viscometer (manufactured by Shibaura Semtech Co., Ltd.: VD2).

About 3 g of the liquid was weighed, dried on an aluminum evaporating dish at 170° C. for 15 minutes to remove moisture, and the solid content was calculated from the weight before and after removal.

The pH was determined by a pH meter (manufactured by Horiba, Ltd.) at 23°C.
was measured.

<Concentration of Carboxylic Acid or Alkali Metal Salt of Carboxylic Acid>
Concentration per solid content was calculated from the amount used.

<Production of compound>
Chloroprene rubber component 1 in chloroprene rubber composition containing cellulose nanofibers
00 parts by weight, magnesium oxide (Kyowa Mag 150 manufactured by Kyowa Chemical Industry Co., Ltd.) 4
parts by weight, stearic acid (manufactured by NOF Corporation) 0.5 parts by weight, zinc oxide (manufactured by Sakai Chemical Co., Ltd.) 5 parts by weight, SRF carbon black (manufactured by Tokai Carbon Co., Ltd. SEAST S) 30 parts by weight, Ethylene thiourea (Suncellar 22-C manufactured by Sanshin Chemical Industry Co., Ltd.) 0.35 parts by weight, OBS
5 parts by weight of H (Celogen OT manufactured by Uniroyal Chemical Co., Ltd.) was added using an open-roll kneader to obtain a cellulose nanofiber-containing chloroprene rubber compound.

<Production of vulcanized rubber foam>
The obtained cellulose nanofiber-containing chloroprene rubber compound was heated at 150°C for 1
Press vulcanization was carried out for 5 minutes to produce a vulcanized foam sheet.

<Measurement of mechanical properties of vulcanizate>
The hardness (Hs) of the obtained vulcanized foamed sheet was evaluated with a type C durometer according to JIS-K-6253. Furthermore, the density (ρ) was evaluated under the conditions of Method A according to JIS-K-6268.

Example 1
An aqueous dispersion of cellulose nanofibers produced by mechanical fibrillation means in chloroprene rubber latex (solid content: 36.5%) (manufactured by Mori Machinery, grade: C-100
Fiber diameter: 30 to 200 nm, average fiber length: 100 μm, solid content concentration: 3% by weight, lignin content: less than 1% by weight) are mixed and stirred for 10 minutes by the above method, and the cellulose nanofiber dispersed rubber latex mixture is mixed. got In addition, the mixed amount of cellulose nanofiber is
The content of cellulose was adjusted to 2.5 parts by weight with respect to 100 parts by weight of the solid rubber component. Table 1 shows the viscosity and solid content of the obtained cellulose nanofiber-dispersed rubber latex mixture. The viscosity of the cellulose nanofiber-dispersed rubber latex mixture is 520 mPa s,
The solid content was 28.7%, and a chloroprene rubber composition containing cellulose nanofibers was obtained without any problems during the freezing and drying steps.

A chloroprene rubber compound containing cellulose nanofibers and a vulcanized foamed sheet were obtained from the chloroprene rubber composition containing cellulose nanofibers according to the above method, and hardness and density were measured. Table 1 shows the test results. From Table 1, the hardness is 46 and the density is 0.3
5, high hardness and low density.

Example 2
A cellulose nanofiber-containing chloroprene rubber compound and a cellulose nanofiber-containing chloroprene rubber compound and A vulcanized foam sheet was obtained and measured for hardness and density. Table 1 shows the test results. From Table 1, the cellulose nanofiber-dispersed rubber latex mixture has a viscosity of 1200 mPa s and a solid content of 23.8%.
There were no problems with the drying process. The hardness was 49 and the density was 0.32, indicating high hardness and low density.

Example 3
A cellulose nanofiber-containing chloroprene rubber compound and a cellulose nanofiber-containing chloroprene rubber compound and A vulcanized foam sheet was obtained and measured for hardness and density. Table 1 shows the test results. From Table 1, the cellulose nanofiber-dispersed rubber latex mixture had a viscosity of 110 mPa·s and a solid content of 32.9%, and there was no problem in the freezing and drying steps. The hardness was 45 and the density was 0.37, indicating high hardness and low density.

Comparative example 1
A cellulose nanofiber-dispersed rubber latex mixed solution was prepared in the same manner as in Example 1, except that the cellulose nanofiber content was adjusted to 10 parts by weight with respect to 100 parts by weight of the solid rubber component. got The obtained cellulose nanofiber-dispersed rubber latex mixture has a viscosity of 3020 mPa s and a solid content of 18.1%.
There were problems with film smoothness and strength after freezing, and a chloroprene rubber composition containing cellulose nanofibers could not be obtained.

Comparative example 2
Cellulose nanofiber-containing chloroprene rubber was prepared in the same manner as in Example 1, except that the cellulose nanofiber content was adjusted to 0.5 parts by weight with respect to 100 parts by weight of the solid rubber component. Compounds and vulcanized foam sheets were obtained and measured for hardness and density. Table 1 shows the test results. From Table 1, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture was 50 mPa s, and the solid content was 34.6%.
There were no problems with the drying process. The hardness was 44 and the density was 0.38, indicating that both high hardness and low density could not be achieved.

Comparative example 3
A chloroprene rubber compound and a vulcanized foamed sheet were obtained in the same manner as in Example 1, except that the cellulose nanofiber was not mixed, and hardness and density were measured. Table 1 shows the test results
shown in The hardness was 43 and the density was 0.39, indicating that both high hardness and low density could not be achieved.

Comparative example 4
A chloroprene rubber compound and a vulcanized foam sheet were obtained in the same manner as in Comparative Example 3 except that the amount of OBSH mixed was changed to 2 parts by weight, and hardness and density were measured. Table 1 shows the test results
shown in The hardness was 48 and the density was 0.52, indicating that both high hardness and low density could not be achieved.

Comparative example 5
A chloroprene rubber compound and a vulcanized foam sheet were obtained in the same manner as in Comparative Example 3 except that the amount of OBSH mixed was 8 parts by weight, and hardness and density were measured. Table 1 shows the test results
shown in The hardness was 33 and the density was 0.23, and both high hardness and low density could not be achieved.

Comparative example 6
Cellulose nanofibers are lignin-containing lignocellulose nanofibers (manufactured by Mori Machinery, grade: L-45, fiber diameter: 50 to 300 nm, average fiber length: 45 μm
A cellulose nanofiber-dispersed rubber latex mixture was prepared in the same manner as in Example 1 except that solid content concentration: 3% by weight, lignin content: about 30% by weight), but rubber precipitated during the preparation process. , a chloroprene rubber containing cellulose nanofibers was not obtained.

Claims (3)

With respect to 100 parts by weight of chloroprene rubber, the average fiber diameter is 10 to 300 nm, the average fiber length is 0.5 to 200 μm, the lignin content is 20% by weight or less, and the hydroxymethyl group of cellulose is carboxylic acid or carboxylic acid. It consists of a vulcanizate of a rubber composition containing 1 to 7 parts by weight of cellulose nanofibers not modified with an acid salt, and has a hardness (Hs) according to JIS-K-6253 and a density according to JIS-K-6268. (ρ) relationship is 100ρ(1.2-ρ)+14 in the range of density 0.2 or more to 0.6 or less
A foam characterized by satisfying ≦Hs. 2. The foam according to claim 1, wherein the chloroprene rubber contains 3 to 7 parts by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid per 100 parts by weight of the chloroprene rubber. A sponge rubber comprising the foam according to claim 1 or 2.