阅读说明：本技术 泡沫橡胶的制造方法 (Method for producing foamed rubber ) 是由 谷山友哉 羽根田英和 于 2018-07-10 设计创作，主要内容包括：本发明提供了一种泡沫橡胶的制造方法,其是通过使聚合物胶乳发泡来制造泡沫橡胶的方法,作为上述聚合物胶乳,使用：固体成分浓度为60.0重量％以上、体积基准的粒径分布中的体积累积粒径d10为超过140nm、所述聚合物胶乳中的消泡剂相对于100重量份聚合物的含有比例为0.001～1.0重量份的聚合物胶乳。(The present invention provides a method for producing a foamed rubber by foaming a polymer latex, wherein the polymer latex comprises: a polymer latex having a solid content of 60.0 wt% or more, a volume cumulative particle diameter d10 in a volume-based particle diameter distribution of more than 140nm, and a content ratio of an antifoaming agent to 100 parts by weight of a polymer in the polymer latex of 0.001 to 1.0 part by weight.)

1. A process for producing a foamed rubber by foaming a polymer latex,

as the polymer latex, the following polymer latexes were used: the solid content concentration is 60.0 wt% or more, the volume cumulative particle diameter d10 in the volume-based particle diameter distribution exceeds 140nm, and the content ratio of the antifoaming agent in the polymer latex is 0.001-1.0 part by weight relative to 100 parts by weight of the polymer.

2. The method for producing a foam rubber according to claim 1, wherein a volume cumulative particle diameter d50 in a volume-based particle diameter distribution of the polymer latex is 400nm or more.

3. The method for producing a foam rubber according to claim 1 or 2, wherein a volume cumulative particle diameter d90 in a volume-based particle diameter distribution of the polymer latex is 1000nm or more.

4. The method for producing a foam rubber according to any one of claims 1 to 3, wherein the polymer latex has 2 or more maxima in a volume-based particle size distribution.

5. The method for producing a foamed rubber according to claim 4, wherein the polymer latex has a 2 nd peak height h from a small diameter side in a volume-based particle size distribution_2ndPeak height h relative to the smallest diameter side in the particle diameter distribution_1stIs h_2nd/h_1stIs 1.8 or more.

6. The method for producing a foam rubber according to any one of claims 1 to 5, wherein the polymer constituting the polymer latex is a nitrile group-containing conjugated diene copolymer.

Technical Field

The present invention relates to a method for producing a foam rubber which can appropriately control foaming and is excellent in elasticity and durability.

Background

Foamed rubbers (rubber foams) produced using the polymer latex are used for various applications such as mattresses, puffs (cosmetic sponges), rollers, impact absorbers, and the like. In such applications of the foam rubber, particularly as the foam rubber for a puff, it is required to have a good foaming state, a uniform foamed structure, and an excellent balance between elasticity and texture.

For example, patent document 1 discloses a method for producing a puff using a copolymer latex in which the solid content concentration, gel content and mooney viscosity are controlled within specific ranges. However, the puff obtained by the technique of patent document 1 may have poor elasticity and durability against moisture in an aqueous cosmetic or the like.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a foamed rubber which can produce a foamed rubber having excellent elasticity and durability, in which foaming can be appropriately controlled.

Means for solving the problems

The present inventors have conducted intensive studies to achieve the above object and as a result, have found that the above object can be achieved by producing a foamed rubber using a polymer latex in which the solid content concentration, the volume cumulative particle diameter d10, and the content ratio of an antifoaming agent are controlled to specific ranges, and have completed the present invention.

That is, according to the present invention, there is provided a method for producing a foamed rubber by foaming a polymer latex, wherein the following polymer latex is used as the polymer latex: the solid content concentration is 60.0 wt% or more, the volume cumulative particle diameter d10 in the volume-based particle diameter distribution exceeds 140nm, and the content ratio of the antifoaming agent in the polymer latex is 0.001 to 1.0 part by weight relative to 100 parts by weight of the polymer.

In the method for producing a foamed rubber of the present invention, the polymer latex preferably has a volume cumulative particle diameter d50 of 400nm or more in a volume-based particle diameter distribution.

In the method for producing a foamed rubber of the present invention, the polymer latex preferably has a volume cumulative particle diameter d90 of 1000nm or more in a volume-based particle diameter distribution.

In the method for producing a foamed rubber of the present invention, the polymer latex preferably has 2 or more maximum values in a volume-based particle size distribution.

In the process for producing a foamed rubber of the present invention, it is preferable that the polymer latex has a 2 nd peak height h from a smaller diameter side in a volume-based particle size distribution_2ndPeak height h to the minimum diameter side in the particle size distribution_1stRatio of (h)_2nd/h_1st) Is 1.8 or more.

In the method for producing a foam rubber of the present invention, it is preferable that the polymer constituting the polymer latex is a nitrile group-containing conjugated diene copolymer.

Effects of the invention

According to the present invention, there can be provided a method for producing a foam rubber capable of producing a foam rubber which can be suitably controlled in foaming and is excellent in elasticity and durability.

Detailed Description

The method for producing the foam rubber of the present invention is a method for producing the foam rubber as follows: the polymer latex is used in a solid content concentration of 60.0 wt% or more, a volume cumulative particle diameter d10 in a volume-based particle diameter distribution of more than 140nm, and a content ratio of an antifoaming agent in the polymer latex is 0.001 to 1.0 part by weight relative to 100 parts by weight of the polymer, and the polymer latex is foamed to produce a foamed rubber.

< Polymer latex >

The polymer latex used in the present invention is a latex of the following polymers: the solid content concentration is 60.0 wt% or more, the volume cumulative particle diameter d10 in the volume-based particle diameter distribution exceeds 140nm, and the content ratio of the antifoaming agent in the polymer latex is 0.001 to 1.0 part by weight relative to 100 parts by weight of the polymer.

The polymer constituting such a polymer latex is not particularly limited, and examples thereof include: diene polymers, polyurethane polymers, acrylic polymers, fluorine polymers, silicone polymers, and the like. Among these, diene polymers are preferable, and a nitrile group-containing conjugated diene copolymer is particularly preferable, from the viewpoint that the resulting foam rubber can be more excellent in elasticity and durability. The polymer latex may be a latex containing 2 or more polymers, and for example, a latex containing a diene copolymer and a polyurethane polymer obtained by mixing a latex of a diene copolymer and a latex of a polyurethane polymer is preferably used. In this case, the latex of the diene copolymer mixed with the latex of the polyurethane polymer is preferably a latex of a nitrile group-containing conjugated diene copolymer.

The nitrile group-containing conjugated diene copolymer is a copolymer obtained by copolymerizing a conjugated diene monomer and an ethylenically unsaturated nitrile monomer, and may be a copolymer obtained by copolymerizing, in addition to these, another ethylenically unsaturated monomer copolymerizable with these monomers, which may be used as needed.

Examples of the conjugated diene monomer include: 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, 2-ethyl-1, 3-butadiene, 1, 3-pentadiene, chloroprene and the like. Of these, 1, 3-butadiene and isoprene are preferable. These conjugated diene monomers can be used alone or in combination of 2 or more. The content ratio of the conjugated diene monomer unit formed from the conjugated diene monomer in the nitrile group-containing conjugated diene copolymer is preferably 20 to 95% by weight, more preferably 30 to 85% by weight, and still more preferably 40 to 80% by weight. When the content ratio of the conjugated diene monomer unit is in the above range, the resultant foam rubber can be further excellent in touch and durability. In addition, from the viewpoint of enabling the balance between the hand and the durability of the resulting foam rubber to be more excellent, it is preferable to use both 1, 3-butadiene and isoprene, and it is preferable to set the ratio of the 1, 3-butadiene units and isoprene units in the nitrile group-containing conjugated diene copolymer to a range of 5/5 to 9/1 in terms of the ratio of 1, 3-butadiene units to isoprene units.

The ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an ethylenically unsaturated monomer containing a nitrile group, and examples thereof include acrylonitrile, methacrylonitrile, fumaronitrile, α -chloroacrylonitrile, α -cyanoethacrylonitrile, and the like, and among these, acrylonitrile and methacrylonitrile are preferable, acrylonitrile is more preferable, these ethylenically unsaturated nitrile monomers can be used alone or in combination of 2 or more, the content ratio of the ethylenically unsaturated nitrile monomer unit formed by the ethylenically unsaturated nitrile monomer in the nitrile group-containing conjugated diene copolymer is preferably 5 to 80% by weight, more preferably 15 to 70% by weight, and still more preferably 20 to 60% by weight, and the content ratio of the ethylenically unsaturated nitrile monomer unit is set in the above range, whereby the obtained foam rubber can be more excellent in touch and durability.

Examples of the other ethylenically unsaturated monomer copolymerizable with the conjugated diene monomer and the ethylenically unsaturated nitrile monomer include ethylenically unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid (anhydride), fumaric acid, itaconic acid, etc., (meth) acrylic acid methyl ester, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, monomethyl maleate, dimethyl maleate, monoethyl fumarate, diethyl fumarate, mono-N-butyl fumarate, di-N-butyl fumarate, mono-N-butyl itaconate, di-N-butyl itaconate, etc., monoalkyl esters or dialkyl esters of ethylenically unsaturated carboxylic acids such as methoxyacrylate, ethoxyacrylate, methoxyethoxyethyl acrylate, etc., (meth) acrylates having a hydroxyalkyl group such as 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc., (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, etc., and other ethylenically unsaturated monomers having a nitrile group such as acrylonitrile-butadiene, preferably, such as acrylonitrile, a copolymer containing no more preferably no less than 20% by weight of the above-styrene monomer, no less than 40% of the conjugated diene monomer, preferably no more preferably no less than 20% by weight of acrylonitrile, no less than 2-acrylonitrile, no more preferably no more than 20, no more preferably no more than 2-acrylonitrile, no more preferably no more than 40, no more than 2, no more preferably no more than 2, no more preferably no more than 40, no more preferably no more than.

The method for producing the polymer latex used in the present invention is not particularly limited as long as it is a method capable of obtaining a polymer latex having a solid content concentration of 60.0 wt% or more, a volume cumulative particle diameter d10 in a volume-based particle diameter distribution of more than 140nm, and a content ratio of the defoaming agent in the polymer latex of 0.001 to 1.0 part by weight relative to 100 parts by weight of the polymer, and the following methods are exemplified: monomers constituting a polymer contained in the polymer latex are copolymerized by an emulsion polymerization method, and the obtained emulsion is subjected to particle size enlargement treatment and concentration.

As the emulsion polymerization method, a conventionally known method can be employed. For example, when a monomer mixture containing the above-mentioned monomer is emulsion polymerized, a polymerization auxiliary material such as an emulsifier (surfactant), a polymerization initiator, a chelating agent, an oxygen scavenger, or a molecular weight regulator, which is generally used, can be used. The method of adding these polymerization auxiliary materials is not particularly limited, and any of an initial one-time addition method, a batch addition method, a continuous addition method, and the like may be used.

The emulsifier is not particularly limited, and examples thereof include: anionic emulsifiers, nonionic emulsifiers, and the like. Examples of the anionic emulsifier include: fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, potassium oleate, sodium oleate, etc.; resinates such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; alkyl benzene sulfonates such as sodium dodecylbenzenesulfonate, and the like. Examples of the nonionic emulsifier include: and pluronic emulsifiers such as polyethylene glycol ester type and block copolymers of ethylene oxide and propylene oxide. Among these, anionic emulsifiers are preferable, fatty acid salts are more preferable, and potassium oleate and sodium oleate are particularly preferable. Further, these emulsifiers can be used alone or in combination of 2 or more. The amount of the emulsifier used is preferably 0.5 to 5 parts by weight based on 100 parts by weight of the monomer mixture.

The polymerization initiator is not particularly limited, and examples thereof include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate and hydrogen peroxide, organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,3, 3-tetramethylbutyl hydroperoxide, 2, 5-dimethylhexane-2, 5-diperoxy hydride, di-t-butyl peroxide, di- α -cumene peroxide, acetyl peroxide, isobutyryl peroxide, benzoyl peroxide, octanoyl peroxide and 3,5, 5-trimethylhexanoyl peroxide, azo compounds such as azobisisobutyronitrile, azobis-2, 4-dimethylvaleronitrile and azobismethyl isobutyrate, and these polymerization initiators can be used alone or in combination of 2 or more, and the amount of the polymerization initiator is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 2 parts by weight, based on 100 parts by weight of the monomer mixture.

In addition, the peroxide initiator can be used as a redox-type polymerization initiator in combination with a reducing agent. The reducing agent is not particularly limited, and examples thereof include compounds containing a metal ion in a reduced state, such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds such as sodium methanesulfonate; amine compounds such as dimethylaniline; and the like. These reducing agents can be used alone or in combination of 2 or more. The amount of the reducing agent used is preferably 3 to 1000 parts by weight based on 100 parts by weight of the peroxide.

Examples of the molecular weight modifier include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and n-stearyl mercaptan, xanthate compounds such as dimethyl xanthogen disulfide and diisopropyl xanthogen disulfide, thiuram compounds such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide and tetramethyl thiuram monosulfide, phenol compounds such as 2, 6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as methylene chloride, methylene bromide and carbon tetrabromide, α -benzyloxy styrene, α -benzyloxy acrylonitrile, α -benzyloxy acrylamide, triphenyl ethane, pentaphenyl ethane, acrolein, methacrolein, thioglycolic acid, malic acid, 2-ethylhexyl thioglycolate, α -methyl styrene dimer and terpinolene, and the amount of the molecular weight modifier is preferably 0.3 to 2 parts by weight, more preferably 0.2 to 2.5 parts by weight, and more preferably 0.3 to 2.5 parts by weight, based on 100 parts by weight of the monomer mixture.

The amount of water used in the emulsion polymerization is preferably 80 to 600 parts by weight, and particularly preferably 100 to 200 parts by weight, based on 100 parts by weight of the total monomers used.

The emulsion polymerization reaction may be either a continuous type or a batch type, and the polymerization time and the like are not particularly limited. Examples of the method of adding the monomer include the following methods: a method of adding the monomers used to the reaction vessel at once; a method of continuously or intermittently adding the polymer as the polymerization proceeds; any method may be employed, for example, a method in which a part of the monomers is added to react to a specific conversion and then the remaining monomers are continuously or intermittently added to polymerize the monomers. In the case where the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be changed. The monomers may be added to the reaction vessel after previously mixing the various monomers to be used, or may be added separately to the reaction vessel. In the case of producing a latex containing a nitrile-based conjugated diene copolymer as a polymer latex, when a method of continuing polymerization by adding a part of the monomer to a reaction vessel after the start of the polymerization reaction is used, for example, the following methods are exemplified: the method comprises the steps of adding an ethylenically unsaturated nitrile monomer and a part of a conjugated diene monomer to a reaction vessel, adding the remaining part of the conjugated diene monomer to the reaction vessel at once or in portions while the polymerization reaction rate in the reaction vessel is 20 to 65% after the start of the polymerization reaction, and further continuing the polymerization reaction. In this case, the proportion of the conjugated diene monomer added after the start of the polymerization reaction is preferably 20 to 60% by weight of the total amount of the conjugated diene monomer used for polymerization.

Further, in the case of emulsion polymerization, polymerization auxiliary materials such as a chelating agent, a dispersant, a pH adjuster, a deoxidizer, and a particle size adjuster can be used as needed, and the kind and the amount of these are not particularly limited.

When the monomer mixture is emulsion polymerized to a predetermined polymerization conversion rate as described above, the polymerization system is cooled or a polymerization terminator is added to terminate the polymerization reaction. The polymerization conversion rate at the time of terminating the polymerization is not particularly limited, but is preferably 90% by weight or more, and more preferably 93% by weight or more. When the polymerization conversion is too low, productivity tends to be lowered. The polymerization temperature is not particularly limited, but is preferably 0 to 50 ℃ and more preferably 5 to 35 ℃.

The polymerization terminator is not particularly limited, and examples thereof include: and aromatic hydroxydithiocarboxylic acids such as hydroxylamine, hydroxylamine sulfate, diethylhydroxylamine, hydroxylamine sulfonic acid and alkali metal salts thereof, sodium dimethyldithiocarbamate, hydroquinone derivatives, catechol derivatives, and hydroxydimethylbenzithiocarboxylic acids, hydroxydiethylbenzenedithiocarboxylic acids, and hydroxydibutylbenzdithiocarboxylic acids, and alkali metal salts thereof. The amount of the polymerization terminator to be used is preferably 0.05 to 2 parts by weight based on 100 parts by weight of the monomer mixture.

The polymerization reaction was carried out as described above to obtain an emulsion. After the termination of the polymerization reaction to obtain an emulsion, the unreacted monomers may be removed from the emulsion as needed.

Further, in the production method of the present invention, the polymer latex can be obtained by subjecting the emulsion obtained after termination of the polymerization reaction to a particle size enlarging treatment for enlarging the polymer particles in the emulsion by merging the polymer particles with each other. By performing the particle size enlarging treatment, the particle size distribution of the obtained polymer latex can be controlled to a desired particle size distribution.

The method of the particle size increasing treatment is not particularly limited, and examples thereof include: (1) a method of adding a conjugated diene compound such as 1, 3-butadiene or the like and toluene or the like as a solvent to the emulsion after completion of the polymerization, and vigorously stirring the mixture, (2) a method of adding a particle size-enlarging agent such as a carboxyl group-containing polymer latex to the emulsion, and vigorously stirring the mixture, and the like.

When the particle size is increased by the method (1), the amount of the solvent to be added is preferably 30 to 300 parts by weight based on 100 parts by weight of the polymer in the emulsion. In the case of performing the particle size increasing treatment by the method (1), the conditions for stirring are not particularly limited, and examples thereof include a method in which a stirring device such as a paddle-type stirring blade is used, the rotation speed is preferably 50 to 2500rpm, and the stirring time is preferably 0.5 to 12.0 hours.

In addition, when the particle size increasing treatment is performed, it is preferable to add an antifoaming agent to the emulsion and perform the particle size increasing treatment in the presence of the antifoaming agent, from the viewpoint of suppressing foaming accompanied by stirring.

After the polymer latex is subjected to the particle size enlarging treatment to obtain the polymer latex, it is preferable to adjust the solid content concentration of the polymer latex by concentrating the polymer latex. The method of the concentration treatment is not particularly limited, and examples thereof include methods such as distillation under reduced pressure, distillation under atmospheric pressure, centrifugal separation, and membrane concentration, and among these, distillation under reduced pressure is preferred.

When the polymer latex is concentrated by distillation under reduced pressure, the concentration is preferably carried out under a pressure of 100 to 0kPa, more preferably 95 to 1.0kPa, and at a temperature of 30 to 100 ℃, more preferably 40 to 95 ℃.

From the viewpoint of suppressing foaming during concentration even when the concentration treatment is performed, it is preferable to add an antifoaming agent to the polymer latex and perform the concentration treatment in the presence of the antifoaming agent.

The defoaming agent used in the particle size increasing treatment and the concentration treatment is not particularly limited, and examples thereof include: examples of the defoaming agent include an oil-and-fat-based defoaming agent, a Mineral oil (Mineral oil) -based defoaming agent such as a modified hydrocarbon oil containing a Mineral oil as a base, a silicone-based defoaming agent such as silicone oil, and a polymer-based defoaming agent. These antifoaming agents can be used alone in 1 kind or in combination of 2 or more kinds. The defoaming agent may be added only when either one of the particle size enlarging treatment and the concentration treatment is performed, or the same defoaming agent or different defoaming agents may be added when both the treatments are performed, but adding the defoaming agent at least when the particle size enlarging treatment is performed is preferable because foaming can be suppressed by the defoaming agent not only in the concentration treatment performed after the particle size enlarging treatment in the particle size enlarging treatment.

The total amount of the antifoaming agent added during the particle size increasing treatment and the concentration treatment is preferably 0.001 to 1.0 part by weight, more preferably 0.001 to 1.00 part by weight, still more preferably 0.005 to 0.8 part by weight, particularly preferably 0.005 to 0.6 part by weight, and most preferably 0.01 to 0.6 part by weight, based on 100 parts by weight of the polymer in the obtained polymer latex. When the amount of the antifoaming agent added is less than 0.001 part by weight, foaming becomes vigorous when the particle size increasing treatment is performed, and the particle size cannot be increased appropriately, and a desired particle size distribution may not be obtained; when the concentration treatment is performed, foaming becomes vigorous, and the productivity of the polymer latex may be lowered. On the other hand, when the amount of the defoaming agent added exceeds 1.0 part by weight, the content of the defoaming agent in the finally obtained polymer latex becomes too large, and the appearance of the obtained foam rubber is deteriorated, and the young's modulus of the obtained foam rubber is too low, and the elasticity is deteriorated.

In the production method of the present invention, when the solid content concentration of the polymer latex is 60.0 wt% or more, the volume cumulative particle diameter d10 in the volume-based particle diameter distribution exceeds 140nm, and the content of the antifoaming agent in the polymer latex is 0.001 to 1.0 part by weight relative to 100 parts by weight of the polymer, the polymer latex can be more easily controlled for foaming and is excellent in handling properties, and further, the foam rubber obtained from the polymer latex can be made good in appearance, low in volume swelling ratio with water, excellent in durability, high in young's modulus, and excellent in elasticity.

The polymer latex used in the present invention has a solid content concentration of 60.0 wt% or more, preferably 62 wt% or more. When the solid content concentration is too low, the foaming rate of the polymer latex becomes too high, and it becomes difficult to control foaming, and the foamed rubber obtained by using the polymer latex has a non-uniform cell diameter and density, poor appearance, low Young's modulus, and poor elasticity. The upper limit of the solid content concentration is not particularly limited, but is preferably 70% by weight or less from the viewpoint of improving the handling properties of the polymer latex (enabling more appropriate transfer, blending of additives, and the like). The method of controlling the solid content concentration of the polymer latex within the above range is not particularly limited, and examples thereof include a method of concentrating the polymer latex by the above method to a desired solid content concentration.

The polymer latex used in the present invention has a volume cumulative particle diameter d10 (a particle diameter in which the cumulative volume calculated from the smaller diameter side in the volume-based particle diameter distribution is 10%) of more than 140nm, preferably 145nm or more, and more preferably 150nm or more. When the volume-cumulative particle diameter d10 is too small, the handling property of the polymer latex is poor, and the resulting foam rubber has a high volume swelling ratio with respect to water and poor durability with respect to moisture. The method of controlling the volume cumulative particle diameter d10 to fall within the above range is not particularly limited, and examples thereof include a method in which the treatment conditions in the particle diameter increasing treatment are set to fall within the above range.

Further, in the polymer latex used in the present invention, the content of the defoaming agent is 0.001 to 1.0 part by weight, preferably 0.001 to 1.00 part by weight, more preferably 0.005 to 0.8 part by weight, further preferably 0.005 to 0.6 part by weight, and particularly preferably 0.01 to 0.6 part by weight, based on 100 parts by weight of the polymer in the polymer latex. When the content of the defoaming agent is too small, the particle size cannot be increased properly in the particle size increasing treatment as described above, while when the content of the defoaming agent is too large, the appearance of the obtained foam rubber is poor, and the young's modulus of the obtained foam rubber is too low, resulting in poor elasticity. In addition, since the content of the defoaming agent in the polymer latex used in the present invention is almost the same as the amount of the defoaming agent used in the production process thereof, the content can be adjusted by adjusting the amount of the defoaming agent used in the production process.

According to the present invention, by using a polymer latex in which the solid content concentration, the volume cumulative particle diameter d10, and the content ratio of the defoaming agent are controlled to be in the above-mentioned ranges, the foaming rate of the polymer latex can be made appropriate, the foaming can be controlled more easily, and the polymer latex is excellent in handling properties.

The volume cumulative particle diameter d10 of the polymer latex used in the present invention is within the above range, and the volume cumulative particle diameter d50 (particle diameter having a cumulative volume of 50% in a volume-based particle diameter distribution) is preferably 400nm or more, more preferably 450nm or more, and still more preferably 500nm or more. By setting the volume-cumulative particle diameter d50 in the above range, the handling property of the polymer latex can be further improved, and the volume swelling ratio of the obtained foam rubber with respect to water can be made low, and the durability can be further improved. The upper limit of the volume-cumulative particle diameter d50 is not particularly limited, but is preferably 3000nm or less from the viewpoint of being able to control the viscosity of the polymer latex so as not to become too low and being able to form a foamed rubber more appropriately. The method of controlling the volume cumulative particle diameter d50 to fall within the above range is not particularly limited, and examples thereof include a method in which the treatment conditions in the particle diameter increasing treatment are set to fall within the above range.

Further, the polymer latex used in the present invention preferably has a volume cumulative particle diameter d90 (a particle diameter in which the cumulative volume in a volume-based particle diameter distribution is 90%) of 1000nm or more, more preferably 1200nm or more, and still more preferably 1500nm or more. By setting the volume-cumulative particle diameter d90 in the above range, the handling property of the polymer latex can be further improved, and the volume swelling ratio of the obtained foam rubber with respect to water can be made low, and the durability can be further improved. The upper limit of the volume-cumulative particle diameter d90 is not particularly limited, but is preferably 20000nm or less from the viewpoint of being able to control the viscosity of the polymer latex so as not to become too low and being able to form a foam rubber more appropriately. The method of controlling the volume cumulative particle diameter d90 to fall within the above range is not particularly limited, and examples thereof include a method in which the treatment conditions in the particle diameter increasing treatment are set to fall within the above range.

When the volume-based particle size distribution of the polymer latex used in the present invention is measured, the volume-based particle size distribution preferably has 2 or more local maxima, and particularly preferably has 2 local maxima (i.e., is bimodal). Further, when the volume-based particle size distribution has 2 or more maximum values, the height h of the 2 nd peak from the small diameter side in the volume-based particle size distribution_2ndHeight h of peak relative to the smallest diameter side_1stRatio of (h)_2nd/h_1st) Preferably 1.8 or more, more preferably 1.9 or more. In this case, when the volume-based particle size distribution has 2 maximum values (is bimodal), the peak height on the small diameter side is h_1stThe peak height on the major diameter side is h_2ndThese peak height ratios (h) are preferred_2nd/h_1st) The control is in the above range. By setting the volume-based particle size distribution to the above-mentioned distribution, the polymer latex obtained can be made more excellent in handling properties, and the foamed rubber obtained by using such a polymer latex can be made more excellent in durability against moisture by having a lower volume swelling ratio against water. The volume-based particle size distribution of the polymer latex is obtained by a method of providing the polymer latex with 2 or more maximum values and a method of adjusting the peak ratio (h)_2nd/h_1st) The method of controlling the particle size in the above range is not particularly limited, and examples thereof include a method in which the treatment conditions in the particle size increasing treatment are set to the above range.

Further, when the volume-based particle size distribution has 2 or more maximum values (maximum peaks), the particle size d of the peak on the minimum diameter side in the volume-based particle size distribution is_1stPreferably 50 to 700nm, more preferably 100 to 600nmMore preferably 150 to 500 nm. Further, the particle diameter d of the 2 nd peak from the small diameter side_2ndPreferably 900 to 5000nm, more preferably 900 to 4000nm, and further preferably 950 to 3000 nm. In this case, when the volume-based particle size distribution has 2 maximum values (is bimodal), the particle size of the small-diameter side peak is d_1stThe particle diameter of the peak on the major diameter side is d_2nd. By reducing the particle diameter d_1stAnd particle diameter d_2ndWithin the above range, the polymer latex can be further improved in handling properties, and the resulting foam rubber can be reduced in volume swelling ratio with water and can be further excellent in durability. As the particle diameter d_1stAnd particle diameter d_2ndThe method of controlling the particle size in the above range is not particularly limited, and examples thereof include a method in which the treatment conditions in the particle size increasing treatment are set to the above range.

As the polymer latex used in the present invention, as described above, a polymer latex containing 2 or more kinds of polymers may be used, and for example, a latex containing a diene copolymer such as a nitrile group-containing conjugated diene copolymer and a latex containing a polyurethane polymer obtained by mixing the diene copolymer and the polyurethane polymer may be used. In this case, the content ratio of the polyurethane polymer in the polymer latex is preferably 5 to 95 parts by weight, more preferably 15 to 70 parts by weight, and still more preferably 15 to 50 parts by weight, based on 100 parts by weight of the polymer (the total amount of the diene copolymer and the polyurethane polymer).

The latex of the polyurethane polymer is not particularly limited, and examples thereof include: a latex obtained by mixing an aqueous solution containing a neutralizing agent into an organic solvent solution or organic solvent dispersion of a polyurethane resin having a hydrophilic group obtained by reacting an active hydrogen-containing compound, a compound having a hydrophilic group, and a polyisocyanate. Alternatively, the latex of the polyurethane polymer may be the following latex: the polyurethane prepolymer having an isocyanate group at the end is obtained by mixing an aqueous solution containing a neutralizing agent and a polyamine with a polyurethane prepolymer having an isocyanate group at the end, which is obtained by reacting an active hydrogen-containing compound, a compound having a hydrophilic group and a polyisocyanate, and reacting the polyamine with the aqueous solution.

The active hydrogen-containing compound is not particularly limited, and examples thereof include: polyols such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyesteramide polyols, polythioether polyols, and polyolefin polyols such as polybutadiene polyols; polyhydric compounds such as ethylene glycol compounds, glycerin, trimethylolethane, trimethylolpropane, sorbitol, pentaerythritol, and the like, which are used as raw materials of polyester polyols; amine compounds such as ethylenediamine, 1, 6-hexamethylenediamine, piperazine, 2, 5-dimethylpiperazine, isophoronediamine, 4' -dicyclohexylmethanediamine, 3' -dimethyl-4, 4' -dicyclohexylmethanediamine, 1, 4-cyclohexanediamine, 1, 2-propanediamine, hydrazine, diethylenetriamine, and triethylenetetramine.

The compound having a hydrophilic group is not particularly limited, and examples thereof include: an ionic compound having 1 or more active hydrogen atoms in a molecule and containing at least one functional group selected from the group consisting of a carboxylate, a sulfonate, a phosphate, a quaternary ammonium salt, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a tertiary amine group, and a betaine group; and nonionic compounds having 1 or more active hydrogen atoms in the molecule and containing a group formed from a repeating unit of ethylene oxide or a group formed from a repeating unit of ethylene oxide and a repeating unit of another alkylene oxide.

The isocyanate is not particularly limited, and examples thereof include: 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4 '-diphenylmethane diisocyanate, 2' -diphenylmethane diisocyanate, 3 '-dimethyl-4, 4' -biphenyl diisocyanate, 3 '-dimethoxy-4, 4' -biphenyl diisocyanate, 3 '-dichloro-4, 4' -biphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 1, 5-tetrahydronaphthalene diisocyanate, tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimethylhexamethylene diisocyanate, dimethyl, 1, 3-cyclohexyl diisocyanate, 1, 4-cyclohexyl diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4' -dicyclohexylmethane diisocyanate, 3' -dimethyl-4, 4' -dicyclohexylmethane diisocyanate, and the like.

< Polymer latex composition >

As the polymer latex used in the present invention, a latex containing a compounding agent such as a crosslinking agent is preferably used. That is, it is preferably used as a polymer latex composition.

Examples of the crosslinking agent include sulfur such as sulfur powder, sublimed sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur; sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, N' -dithiobis (hexahydro-2H-aza)Sulfur-containing compounds such as-2-ketone), phosphorus-containing polysulfide, high-molecular polysulfide, and 2- (4' -morpholinodisulfide) benzothiazole. Among these, sulfur can be preferably used. The crosslinking agent can be used alone in 1 or in combination of 2 or more.

The content of the crosslinking agent is not particularly limited, and is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 3 parts by weight, based on 100 parts by weight of the polymer in the polymer latex. By setting the content of the crosslinking agent in the above range, the strength of the obtained foam rubber can be further improved.

The polymer latex used in the present invention preferably further contains a crosslinking accelerator.

As the crosslinking accelerator, crosslinking accelerators generally used in the production of foamed rubbers can be used, and examples thereof include: dithiocarbamic acids such as diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and zinc salts thereof; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2- (2, 4-dinitrophenylthio) benzothiazole, 2- (N, N-diethylthiocarbamoylthio) benzothiazole, 2- (2, 6-dimethyl-4-morpholinothio) benzothiazole, 2- (4' -morpholinodithio) benzothiazole, 4-morpholinyl-2-benzothiazyl disulfide, 1, 3-bis (2-benzothiazolylmethylmercapto) urea and the like, preferably zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate and zinc 2-mercaptobenzothiazole. The crosslinking accelerator can be used alone in 1 or in combination of 2 or more.

The content of the crosslinking accelerator is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, based on 100 parts by weight of the polymer in the polymer latex. By setting the content of the crosslinking accelerator within the above range, the strength of the obtained foam rubber can be further improved.

Further, the polymer latex used in the present invention preferably contains zinc oxide.

The content of zinc oxide is not particularly limited, but is preferably 0.5 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the polymer in the polymer latex. By setting the content of zinc oxide within the above range, the emulsion stability can be improved and the strength of the obtained foam rubber can be further improved.

The polymer latex used in the present invention may further contain, if necessary, an anti-aging agent, a coloring agent, a bubble stabilizer, and the like, as well as a dispersant (for example, NASF (sodium salt of naphthalene sulfonic acid formaldehyde condensate) or the like) for stably dispersing the above-mentioned various compounding agents in the latex, a thickener (for example, polyacrylic acid and its sodium salt, sodium alginate, polyvinyl alcohol, or the like), and a surfactant (for example, an aliphatic alkali soap such as potassium oleate, a sulfate of a higher alcohol such as sodium lauryl sulfate, or the like) as a foaming agent.

The method of mixing various compounding agents into the polymer latex is not particularly limited, and examples thereof include a method of obtaining a polymer latex as described above, and then mixing various compounding agents, which are compounded as necessary, into the polymer latex using a dispersing machine such as a ball mill, a kneader, or a disperser; a method of preparing an aqueous dispersion of compounding ingredients other than the polymer latex by using the above-mentioned dispersing machine and then mixing the aqueous dispersion with the polymer latex. The crosslinking agent may be added to the polymer latex before foaming the polymer latex, or may be added to the foamed polymer latex after foaming the polymer latex.

< foam rubber >

In the production method of the present invention, the foamed rubber can be obtained by foaming and coagulating the above polymer latex at a desired foaming ratio. Air is usually used for foaming, but carbonates such as ammonium carbonate and sodium bicarbonate; azo compounds such as azodicarboxylic acid amide and azobisisobutyronitrile; benzenesulfonyl hydrazide and the like. In the case of using air, the polymer latex can be foamed by stirring and entraining air. In this case, for example, an oxx (Oaks) foaming machine, an ultrasonic foaming machine, or the like can be used.

After foaming the polymer latex, the foamed polymer latex is coagulated in order to fix the foamed state. The coagulation method may be any method capable of gelling and solidifying the latex, and conventionally known methods may be used, and for example, the following methods may be used: dunlop method (ambient temperature coagulation method) in which an ambient temperature coagulant such as a fluorosilicic acid compound (e.g., sodium hexafluorosilicate, potassium hexafluorosilicate, or sodium titanium fluorosilicate) is added to a foamed polymer latex; a heat-sensitive coagulation method in which a heat-sensitive coagulant such as organopolysiloxane, polyvinyl methyl ether, zinc ammonium sulfate complex salt, or the like is added to the foamed polymer latex; freezing and solidifying method, etc. The amount of the coagulant such as a normal temperature coagulant or a heat-sensitive coagulant used is not particularly limited, but is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the polymer in the polymer latex.

The foamed polymer latex can be transferred to a mold having a desired shape after adding a coagulant and coagulated, thereby obtaining a foamed rubber. When a crosslinking agent is added to the polymer latex, it is preferable to crosslink the polymer latex by heating after coagulation. The crosslinking condition may be a condition in which the heat treatment is preferably performed at a temperature of 100 to 160 ℃ for 15 to 60 minutes.

The foamed rubber obtained is preferably washed after being taken out from the mold. The method of washing is not particularly limited, and examples thereof include a method of washing with water at about 20 to 70 ℃ for about 5 to 15 minutes by stirring using a washing machine or the like. Preferably, after the washing, the water is removed and the foam rubber is dried at a temperature of about 30 to 90 ℃ so as not to impair the hand feeling of the foam rubber. The foam rubber obtained in this way can be used as a puff (cosmetic sponge) or the like by, for example, cutting the foam rubber into a predetermined thickness and a predetermined shape, and then polishing the side surface by a rotary grinder or the like.

In the production method of the present invention, the foamed rubber can be obtained as described above. The foamed rubber obtained by the production method of the present invention is obtained by using the polymer latex of the present invention described above, and therefore, the foamed rubber is good in a foamed state and excellent in elasticity and durability, and thus can be suitably used for various applications such as a mattress, a puff (cosmetic sponge), a roller, an impact absorber, and the like. In particular, the foam rubber obtained by the production method of the present invention is excellent in durability against moisture, and therefore can be preferably used as a puff (cosmetic sponge) to be impregnated with an aqueous cosmetic or the like.