JP2023124013A - rubber foam - Google Patents

Abstract

To provide a chloroprene rubber foam that has excellent hardness, strength, and elongation, and has small anisotropy.SOLUTION: A foam is composed of a vulcanized rubber composition comprising 0.01-0.90 pt.wt. of cellulose nanofiber with an average fiber diameter of 40 nm or less relative to 100 pts.wt. of chloroprene rubber.SELECTED DRAWING: None

Description

The present invention relates to rubber foams containing chloroprene rubber.

Among various synthetic rubbers, chloroprene rubber has a good balance of physical properties and is used in a wide range of applications, such as belts, hoses, boots, air springs, stretch fabrics, anti-vibration rubber, gloves, adhesives, etc. It is used. In addition, the foam has excellent characteristics such as toughness, heat insulation, non-water absorption, flame retardancy, and weather resistance, so it can be used in various applications such as wet suits, shoe soles, packing, anti-vibration materials, sealing materials, and cushioning materials. used for purposes.

A significant feature of the foamed material is that it is lighter than the unfoamed material with the same volume. The specific gravity of non-foamed chloroprene rubber is about 1.2 when no reinforcing material is added, but it can be reduced to less than 1.0 by foaming. It can be adjusted to any specific gravity by changing. However, there is a problem that the mechanical properties are deteriorated due to the inclusion of air bubbles in the rubber by foaming, and there is a demand for a foam that is lightweight, has high mechanical properties, and is inexpensive.

In order to improve the mechanical properties of such foams, attempts to utilize cellulose nanofibers as reinforcing materials are being investigated. However, since cellulose nanofibers are hydrophilic, they have poor dispersibility in hydrophobic rubber, and cellulose aggregates in rubber, making it difficult to exhibit a reinforcing effect.

For example, Patent Document 1 reports that mechanical properties such as shape stability and wear resistance are improved by adding unmodified cellulose nanofibers to diene rubber. However, improvement in tensile strength was insufficient. Also, in Patent Document 2, by adding unmodified cellulose nanofibers to natural rubber and various synthetic rubbers, when a load is applied for a long time to deform, the deformation is maintained even after the load is removed, and the bulk is reduced. reported the improvement of the phenomenon. However, the tensile strength is not improved here either. On the other hand, Patent Document 3 proposes a foam containing microfibrillated plant fibers esterified with an alkyl or alkenyl succinic anhydride, and a foam having excellent bending strength can be obtained. However, the addition of the step of modifying the cellulose nanofibers increases the price, and the vertical and horizontal dimensions of the resulting foam are the same. As the value of the horizontal side of time increases, there is a problem that large anisotropy occurs in the mechanical properties.

JP 2016-191007 A JP 2018-188514 A JP 2013-185085 A

The present invention has been made in view of this problem, and its object is to provide a chloroprene rubber foam which has excellent mechanical properties, is inexpensive, and has small anisotropy.

In view of this background, the present inventors have made intensive studies to solve the above problems, and found that a foam obtained by vulcanizing and foaming a rubber composition containing chloroprene rubber and cellulose nanofibers has excellent mechanical properties. We have found that it has physical properties, is inexpensive, and exhibits small anisotropy. That is, each aspect of the present invention is [1] to [5] shown below.
[1] A foam comprising a vulcanizate of a rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers having an average fiber diameter of 40 nm or less per 100 parts by weight of chloroprene rubber.
[2] The foam according to [1] above, wherein the cellulose nanofibers are unmodified and fibrillated only by mechanical treatment.
[3] The foam according to [1] or [2] above, wherein the chloroprene rubber contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid.
[4] The above [1] to [3], wherein the value of the horizontal side is within 1 ± 0.02 when the vertical side of the foam vulcanized and foamed in a mold with equal vertical and horizontal dimensions is 1. ] The foam according to any one of above.

According to the present invention, a rubber foam having excellent mechanical properties and low anisotropy can be obtained at low cost.

The present invention will be described in detail below.

A rubber foam that is one aspect of the present invention is a vulcanized product of a rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers having an average fiber diameter of 40 nm or less per 100 parts by weight of chloroprene rubber. foam.

Chloroprene rubber is rubber obtained by polymerizing chloroprene or chloroprene and a monomer copolymerizable therewith. Chloroprene rubber includes mercaptan-modified chloroprene rubber, sulfur-modified chloroprene rubber with excellent dynamic properties, and xanthogen-modified chloroprene rubber with excellent mechanical properties. Sulfur-modified chloroprene rubber is characterized by excellent flex crack resistance, but mercaptan-modified rubber is superior in tensile fatigue. In the present invention, similar effects can be expected with any modified species.

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, and one or more of them can be used in combination, and are appropriately used according to 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 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, so as to obtain a good balance between heat resistance and physical properties.

The chloroprene rubber preferably contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid. A content of 3% by weight or more provides excellent emulsion stability during chloroprene polymerization, and a content of 7% by weight or less provides excellent processability and a stable quality rubber product.

In the emulsion polymerization of chloroprene rubber, for example, the above monomers are mixed with an emulsifier, water, a polymerization initiator, a chain transfer agent, other stabilizers, etc., polymerized at a predetermined temperature, and polymerized at a predetermined polymerization conversion rate. A method of terminating the polymerization by adding a terminator can be used.

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 rubber 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 contained in an amount of 3 to 8 parts by weight, more preferably 5 to 7 parts by weight.

In order to maintain the stability 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 the pH adjuster include basic compounds such as sodium hydroxide, potassium hydroxide, sodium phosphate, potassium phosphate, triethylamine, diethylamine, triethanolamine, diethanolamine, ethanolamine, and ammonia. The above can be used alone or in combination.

As the emulsion polymerization initiator, known free-radical substances such as peroxides such as potassium persulfate and ammonium persulfate, inorganic or organic peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide, etc. are used. be able to. Further, these may be used alone or in combination with reducing substances such as thiosulfate, thiosulfite, hydrosulfite, organic amine, etc., in a redox system.

Examples of chain transfer agents include molecular weight modifiers such as alkylmercaptans, halogenated hydrocarbons, alkylxanthogen disulfides, alkylxanthogen polysulfides, and sulfur. is preferred. The amount of the chain transfer agent is not particularly limited as long as it is an amount used in general radical polymerization for adjusting the molecular weight. For the flexibility and good mechanical properties of the vulcanized rubber obtained by molding, it is preferably 0.01 to 1.0% by weight with respect to 100% by weight of the monomer mixture other than the chain transfer agent.

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

The timing of completion of the polymerization is not particularly limited, but a monomer conversion rate of 60% or more can ensure production volume, and a conversion rate of 95% or less prevents the polymerization time from becoming too long. , 60 to 95% is preferable in terms of productivity.

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.

Cellulose nanofibers are obtained by defibrating cellulose fibers contained in wood to an average fiber diameter of several nanometers to several tens of nanometers. In the present invention, cellulose nanofibers having an average fiber diameter of 40 nm or less, preferably 32 nm or less are used. By setting the average fiber diameter to 40 nm or less, the longitudinal side of the foam obtained by vulcanizing the rubber composition obtained by vulcanization and foaming in a mold having the same vertical and horizontal dimensions was set to 1. The value of the horizontal side of time can be within 1±0.02, which is the same level as a foam made of a vulcanized rubber composition to which cellulose nanofibers are not added.

In addition, unmodified cellulose nanofibers are preferred because chemically modified cellulose nanofibers are much more expensive than unmodified ones. Furthermore, if the hydroxymethyl groups of cellulose are modified with carboxylic acid and carboxylate by chemical treatment, the dispersion state of cellulose nanofibers in the rubber deteriorates. Preferably not.

In the present invention, in order to improve the state of dispersion of cellulose nanofibers in rubber, cellulose nanofibers that are defibrated only by mechanical treatment without chemical treatment are preferred.

Furthermore, it is preferable to use cellulose nanofibers having a surface tension of 60 mN/m or less in a 1% by weight aqueous dispersion of cellulose nanofibers. Such cellulose nanofibers include amphipathic cellulose nanofibers. Amphiphilicity means that cellulose nanofibers have both a hydrophilic portion with a high affinity for water and a hydrophobic portion with a low affinity for water, and is described in Japanese Patent No. 5419120 etc. can be obtained by subjecting water-suspended samples to high-speed opposing collisions. Having amphiphilicity increases the affinity between the hydrophobic rubber and cellulose, and a smaller mixing amount provides a significant improvement in mechanical properties. Pure water generally has a surface tension of about 72 mN/m, but the surface tension decreases as the hydrophobicity increases. If the aqueous dispersion of cellulose nanofibers has a concentration of 1% by weight and a surface tension of 60 mN/m or less, it has amphipathic properties and high affinity with rubber.

Lignin is contained in wood or the like, which is the raw material of cellulose nanofibers, but since cellulose nanofibers containing a large amount of lignin may impair the stability of chloroprene latex, 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. The fibrillation treatment of cellulose is mainly performed by mechanical treatment, and by adding various functional groups by chemical treatment and using mechanical treatment together, it is performed to a finer single nano level.

The rubber composition contains 0.01 to 0.90 parts by weight, preferably 0.01 to 0.40 parts by weight of cellulose nanofibers per 100 parts by weight of chloroprene rubber. If the content of cellulose nanofibers is less than 0.01 parts by weight, there is no effect of improving the mechanical properties of the resulting vulcanized foam, and if it exceeds 0.90 parts by weight, the vertical When the side is taken as 1, the value of the horizontal side becomes large, resulting in large anisotropy in the mechanical properties.

The rubber composition can be obtained by mixing chloroprene latex with an aqueous dispersion of cellulose nanofibers to prepare a cellulose nanofiber-dispersed rubber latex mixture, and removing water from the cellulose nanofiber-dispersed rubber latex mixture. .

The chloroprene latex is not particularly limited as long as the chloroprene rubber is emulsified and dispersed in water with an emulsifier, and may be an emulsion obtained by emulsion polymerization of a chloroprene monomer and an unsaturated monomer copolymerizable, or a chloroprene rubber. is dissolved in an organic solvent such as toluene and then emulsified by mixing with water and an emulsifier.

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.).

Methods for removing water (drying method) from the cellulose nanofiber-dispersed rubber latex mixture include drying by heating, coagulation with acid or salt, and freeze-drying. Therefore, the method of precipitating (freezing and solidifying) the rubber by freezing, washing away the excess emulsifier and the like with water, and then drying with hot air is the most efficient and easy drying method, and is therefore preferable. Furthermore, it is more preferable to freeze-dry the cellulose nanofiber-dispersed rubber latex mixture at a pH of 10 or less so that the rubber can easily precipitate.

In the method of freeze-coagulating and drying the cellulose nanofiber-dispersed rubber latex mixture, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1000 mPa·s or less, more preferably 600 mPa or less. If the viscosity exceeds 1000 mPa·s, compatibility with current production facilities is significantly reduced, making it difficult to obtain a rubber composition.

In addition, by making the solid content of the cellulose nanofiber-dispersed rubber latex mixture liquid 20% by weight or more, the strength of the rubber is increased, the handling in continuous production is improved, and from the balance with the viscosity, 20% by weight to 40% by weight. 25% by weight or more and 35% by weight or less is preferable.

The rubber foam, which is one aspect of the present invention, is produced by kneading a foaming agent in addition to various compounding agents similar to those of ordinary chloroprene rubber, and the resulting rubber composition is cured at an appropriate vulcanization temperature. , is obtained by heat molding and vulcanization foaming for a vulcanization time. The obtained rubber foam exhibits excellent mechanical properties as compared to a chloroprene rubber foam containing no cellulose nanofibers with the same formulation. In addition, it exhibits the same mechanical properties as a chloroprene rubber foam containing cellulose nanofibers with an average fiber diameter of 40 nm or more in the same formulation, and is vulcanized and foamed in a mold with equal vertical and horizontal dimensions. It is possible to reduce the value of the horizontal side when the vertical side of the foam is 1. That is, since it exhibits excellent mechanical properties and has the same anisotropy as a chloroprene rubber foam that does not contain cellulose nanofibers, it can be used as a lightweight rubber foam with a higher expansion ratio than the conventional formulation. The rubber foam can be suitably used for various purposes such as wet suits, shoe soles, packings, anti-vibration materials, sealing materials, cushioning materials, and the like.

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

<Creation of chloroprene 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, An emulsified aqueous solution containing 0.05 parts by weight of sodium hydroxide, 1.0 parts by weight of sodium orthophosphate, and 100 parts by weight of water was mixed and stirred to emulsify. A polymerization catalyst consisting of 0.01 parts by weight of sodium and 30 parts by weight of water was added at a constant rate by a pump to carry out polymerization. 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 Subsequently, a toluene solution of 2 parts by weight of tetraethylthiuram disulfide emulsified with potassium rosinate and 0.3 parts by weight of sodium dibutyldithiocarbamate were added thereto, and deflocculated at 40° C. until the Mooney viscosity reached 60. After that, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure to obtain a chloroprene rubber latex.

<Measurement of cellulose nanofiber average fiber diameter>
After diluting the cellulose nanofiber with pure water to a concentration of 0.1 wt %, filtration and drying were carried out. After that, an osmium coat was applied, and SEM observation at a magnification of 20,000 times was performed with FE-SEM JSM-7100F manufactured by JEOL Ltd. 100 fibers were randomly selected from the observation image obtained, the fiber diameter was measured, and the average value was defined as the average fiber diameter.

<Preparation of chloroprene rubber containing cellulose nanofibers>
A predetermined amount of an aqueous dispersion of cellulose nanofibers is added to the sulfur-modified chloroprene rubber latex, mixed for 10 minutes at 2,000 rpm in an auto homomixer (PRIMIX), and then freeze-coagulated to precipitate the polymer. , dried.

<Production of rubber composition>
100.2 parts by weight of sulfur-modified chloroprene rubber containing cellulose nanofibers, or 3 parts by weight of magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.) shown in Table 1 for 100 parts by weight of sulfur-modified chloroprene rubber, stearic acid (manufactured by Shin Nihon Rika Co., Ltd.) 1 part by weight, Suntite S (manufactured by Seiko Kagaku Co., Ltd., Microcrystalline wax) 2 parts by weight, Nocrac AD-F (manufactured by Ouchi Shinko Kagaku Co., Ltd., anti-aging agent) 0. 5 parts by weight, Nocrack 6C (manufactured by Ouchi Shinko Kagaku Co., Ltd., anti-aging agent) 0.5 parts by weight, Seast S (manufactured by Tokai Carbon Co., Ltd., carbon black), Shiroenka CC (manufactured by Shiraishi Kogyo Co., Ltd., Calcium carbonate) 15 parts by weight, Neo N (manufactured by Tenma Sub Kako Co., Ltd., Neofatix) 18 parts by weight, JSO aroma 790 (manufactured by Nippon Sun Oil Co., Ltd., aroma oil) 25 parts by weight, Sansen 415 (Japan Sun Oil Co., Ltd. ), naphthenic oil), and 5 parts by weight of zinc oxide (manufactured by Sakai Chemical Co., Ltd.) were mixed in an open roll kneader. After cooling them, sulfur (manufactured by Hosoi Chemical Industry Co., Ltd.) 1.0 parts by weight, Noccellar TS (manufactured by Ouchi Shinko Kagaku Co., Ltd., vulcanization accelerator) 1 part by weight, Noccellar D (Ouchi Shinko Kagaku Co., Ltd.) ), vulcanization accelerator) and 6 parts by weight of Cellmic S (manufactured by Sankyo Kasei Co., Ltd., foaming agent) were mixed in an open-roll kneader to obtain a rubber composition.

<Production of foam>
The resulting rubber composition is vulcanized and foamed under press conditions of 140° C. for 13 minutes using a square trapezoidal mold having equal vertical and horizontal dimensions and a height of 3 mm to produce a foam. did.
<Measurement of hardness of foam>
The hardness of the resulting foam was evaluated according to JIS K7312 (1996). Type C was selected for the durometer.

<Measurement of tensile strength and elongation of foam>
The tensile strength and elongation of the resulting foam were evaluated according to JIS K7312 (1996). A No. 3 dumbbell-shaped test piece was selected and evaluated under the conditions of a tensile speed of 500 mm/min and a temperature of 23°C. The strength and elongation when the test piece was cut were recorded.

<Measurement of specific gravity of foam>
The density of the obtained foam was evaluated according to JIS K6268 (1998), and the specific gravity was obtained by dividing the obtained density by the density of water.

<Measurement of dimensions of foam>
Using a square trapezoidal mold with a top surface of 87 mm × 87 mm, a bottom surface of 76 mm × 76 mm, and a height of 7 mm, the vertical and horizontal dimensions of the top surface and the bottom surface were measured 1 day and 7 days after the completion of vulcanization and foaming. . Next, by dividing the measured horizontal dimension by the vertical dimension, the value of the horizontal dimension when the vertical dimension is set to 1 was obtained.

Example 1
An aqueous dispersion of cellulose nanofibers produced by mechanical fibrillation means (manufactured by Chuetsu Pulp Co., Ltd., grade: C, solid content concentration: 3% by weight, average fiber diameter : about 32 nm, lignin content of 1% or less, unmodified, amphipathic) were mixed and stirred for 10 minutes by the above method to obtain a cellulose nanofiber-dispersed rubber latex mixture. The cellulose nanofiber was mixed in an amount such that the cellulose content was 0.2 parts by weight with respect to 100 parts by weight of the solid rubber component.

The cellulose nanofiber-containing chloroprene rubber is used to obtain a cellulose nanofiber-containing sulfur-modified chloroprene rubber composition, a vulcanized foam, and a vulcanized foam for dimensional measurement according to the above method, and the hardness, tensile strength, elongation, specific gravity, Dimensional measurements were performed. Table 1 shows the results. From Table 1, the hardness was 22, the tensile strength was 2.8 MPa, and the elongation was 680%, which were improved compared to Comparative Example 1 containing no cellulose nanofibers described later, showing good results. In addition, when the vertical side of the obtained foam vulcanized and foamed in a mold having the same vertical and horizontal dimensions is 1, the value of the horizontal side is within 1 ± 0.02, which is a comparative example. there was no big difference.

Comparative example 1
A sulfur-modified chloroprene rubber composition, a vulcanized foam, and a vulcanized foam for dimension measurement were obtained in the same manner as in Example 1, except that the cellulose nanofiber was not mixed. , and tensile strength, elongation, specific gravity, and dimensional measurements were carried out. Table 1 shows the results. The hardness is 18, the tensile strength is 2.2 MPa, and the elongation is 600%. was within 1±0.02.

Comparative example 2
An aqueous dispersion of cellulose nanofibers produced by mechanical fibrillation means (manufactured by Chuetsu Pulp Co., Ltd., grade: S1, solid content concentration: 3% by weight, average fiber diameter : about 50 nm, lignin content of 1% or less, unmodified, amphiphilic) were mixed and stirred for 10 minutes by the above method to obtain a cellulose nanofiber-dispersed rubber latex mixture. The cellulose nanofiber was mixed in an amount such that the cellulose content was 0.2 parts by weight with respect to 100 parts by weight of the solid rubber component.

The cellulose nanofiber-containing chloroprene rubber is used to obtain a cellulose nanofiber-containing sulfur-modified chloroprene rubber composition, a vulcanized foam, and a vulcanized foam for dimensional measurement according to the above method, and the hardness, tensile strength, elongation, specific gravity, Dimensional measurements were performed. Table 1 shows the results. From Table 1, the hardness was 21, the tensile strength was 2.9 MPa, and the elongation was 690%, which were improved compared to Comparative Example 1, showing good results. However, when the vertical side of the foam vulcanized and foamed with a mold having the same vertical and horizontal dimensions of the obtained foam is 1, the value of the horizontal side exceeds 1 ± 0.02. From Example 1 and Comparative Example 1, laterally stretched samples were obtained.

Claims (4)

A foam comprising a vulcanizate of a rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers having an average fiber diameter of 40 nm or less per 100 parts by weight of chloroprene rubber. 2. The foam of claim 1, wherein the cellulose nanofibers are unmodified and defibrated only by mechanical treatment. 3. The foam according to claim 1, wherein the chloroprene rubber contains 3 to 7% by weight of carboxylic acid or alkali metal salt of carboxylic acid. 4. The method according to any one of claims 1 to 3, wherein the value of the horizontal side of the foam obtained by vulcanization and foaming in a mold having equal vertical and horizontal dimensions is within 1±0.02 when the vertical side is 1. foam.