Latex composition for foam rubber, and foam rubber

Abstract

Provided is a foam rubber latex composition containing: a copolymeric rubber latex containing 30-60 wt% of a cyano group-containing ethylenically unsaturated monomer unit and 40-70 wt% of an aliphatic conjugated diene-based monomer unit; a nitroxyl radical compound; and a thiazoline-based compound, wherein the solid content concentration is 55-75 wt%.

Description

[Technical Field]

[0001] The present invention relates to a latex composition for foam rubber and foam rubber, and more particularly to a latex composition for foam rubber that can provide foam rubber that has excellent oil resistance, a soft feel, and appropriately suppresses discoloration, deterioration, and odor generation during repeated use, and foam rubber obtained using such a latex composition for foam rubber. [Background technology]

[0002] Foam rubber (rubber foam) manufactured using polymer rubber latex is used in a variety of applications, including mattresses, cosmetic sponges (puffs), rolls, and shock absorbers. Among these applications, foam rubber is particularly required for puffs, which need to have good oil resistance to cosmetics and a soft feel.

[0003] From the viewpoint of providing good oil resistance to cosmetics, Patent Document 1 proposes a copolymer rubber latex for foam rubber as a material suitable for forming foam rubber for puffs as cosmetic sponges. This copolymer rubber latex is obtained by emulsion polymerization of a monomer mixture consisting of 45-60% by weight of a cyano group-containing ethylenically unsaturated monomer, 15-52% by weight of 1,3-butadiene, 3-40% by weight of isoprene, and 0-30% by weight of other ethylenically unsaturated monomers copolymerizable with these, characterized in that the gel content of the copolymer rubber is 65% by weight or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5186992 [Overview of the project] [Problems that the invention aims to solve]

[0005] According to the technology described in Patent Document 1, a foam rubber with excellent oil resistance and a soft feel can be obtained, but there were problems such as discoloration, deterioration, and odor generation when used repeatedly. This invention has been made in view of the above circumstances, and aims to provide a foam rubber latex composition that can provide a foam rubber that has excellent oil resistance, a soft feel, and in which discoloration, deterioration, and odor generation during repeated use are appropriately suppressed, and a foam rubber obtained using such a foam rubber latex composition. [Means for solving the problem]

[0006] The present inventors conducted intensive research to solve the above problems and found that a latex composition having a solid content within a predetermined range, comprising a copolymer rubber latex containing cyano group-containing ethylenically unsaturated monomer units and aliphatic conjugated diene monomer units in predetermined proportions, blended with a nitroxyl radical compound and a thiazoline compound, can solve the above problems. Based on this finding, the present invention was completed.

[0007] In other words, the present invention provides a latex composition for foam rubber containing a copolymer rubber latex containing 30 to 60% by weight of cyano group-containing ethylenically unsaturated monomer units and 40 to 70% by weight of aliphatic conjugated diene monomer units, a nitroxyl radical compound, and a thiazoline compound, with a solid content concentration of 55 to 75% by weight.

[0008] In the foam rubber latex composition of the present invention, the content of the nitroxyl radical compound is preferably 100 to 10,000 ppm by weight. In the foam rubber latex composition of the present invention, the content of the thiazoline compound is preferably 10 to 1,000 ppm by weight. In the foam rubber latex composition of the present invention, it is preferable that the nitroxyl radical compound is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). In the foam rubber latex composition of the present invention, the thiazoline compound is preferably 2-methyl-4-isothiazolin-3-one (MIT) or 1,2-benzoisothiazolin-3-one (BIT). The latex composition for foam rubber of the present invention preferably has a solid content concentration of 60 to 70% by weight. The latex composition for foam rubber of the present invention preferably has a solid content concentration of 63 to 69% by weight. The latex composition for foam rubber of the present invention preferably has a solid content concentration of 64.5 to 67.5% by weight.

[0009] Furthermore, the present invention provides a foam rubber obtained using the above-mentioned foam rubber latex composition. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a foam rubber latex composition that has excellent oil resistance, a soft feel, and appropriately suppresses discoloration, deterioration, and odor generation during repeated use, as well as foam rubber obtained using such a foam rubber latex composition. [Modes for carrying out the invention]

[0011] The foam rubber latex composition of the present invention contains a copolymer rubber latex containing 30 to 60% by weight of cyano group-containing ethylenically unsaturated monomer units and 40 to 70% by weight of aliphatic conjugated diene monomer units, a nitroxyl radical compound, and a thiazoline compound, with a solid content concentration of 55 to 75% by weight.

[0012] <Copolymer rubber latex> The copolymer rubber latex used in the present invention is a copolymer rubber latex containing 30 to 60% by weight of cyano group-containing ethylenically unsaturated monomer units and 40 to 70% by weight of aliphatic conjugated diene monomer units. More specifically, it is a dispersion in which particles of copolymer rubber having such a monomer composition are dispersed in water.

[0013] The copolymer rubber latex used in the present invention can be obtained, for example, by emulsion polymerization of a monomer mixture containing a cyano group-containing ethylenically unsaturated monomer, an aliphatic conjugated diene monomer, and other ethylenically unsaturated monomers copolymerizable with these, as needed.

[0014] Examples of cyano group-containing unsaturated monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate. These can be used individually or in combination of two or more. Among these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. The content of cyano group-containing unsaturated monomer units in the copolymer rubber constituting the copolymer rubber latex is 30 to 60% by weight of the total monomer units, preferably 35 to 55% by weight, and more preferably 40 to 50% by weight. If the content of cyano group-containing ethylenically unsaturated monomer units is too low, the oil resistance of the resulting foam rubber will be insufficient, while if it is too high, the texture of the resulting foam rubber will become hard and unpleasant to the touch.

[0015] Examples of the aliphatic 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. These can be used alone or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. The content of the aliphatic conjugated diene monomer unit in the copolymer rubber constituting the copolymer rubber latex is 40 to 70% by weight, preferably 45 to 65% by weight, and more preferably 50 to 60% by weight in all monomer units. If the content of the aliphatic conjugated diene monomer unit is too small, the resulting foam rubber becomes hard, while if it is too large, the oil resistance of the resulting foam rubber becomes insufficient.

[0016] In addition, as the aliphatic conjugated diene monomer, two or more can be used in combination. For example, 1,3-butadiene and isoprene may be used in combination. However, from the viewpoint of more appropriately suppressing discoloration, deterioration, and odor generation during repeated use of the resulting foam rubber, the content of the isoprene unit is preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 2 to 10% by weight in all monomer units. Also, the content ratio of the 1,3-butadiene unit to the isoprene unit is preferably 70:30 to 95:5, and more preferably 80:20 to 92:8 in terms of the weight ratio of 1,3-butadiene unit:isoprene unit.

[0017] In addition, the copolymer rubber constituting the copolymer rubber latex used in the present invention may contain units of other ethylenically unsaturated monomers copolymerizable with these monomers, in addition to the cyano group-containing ethylenically unsaturated monomer units and the aliphatic conjugated diene monomer units, if necessary.

[0018] Examples of other ethylenically unsaturated monomers that can be copolymerized include ethylenically unsaturated carboxylic acids such as (meth)acrylic acid, (anhydrous)maleic acid, fumaric acid, and itaconic acid; mono- or dialkyl esters of the ethylenically unsaturated carboxylic acids such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, maleic acid mono- or dimethyl, fumaric acid mono- or diethyl, fumaric acid mono- or di-n-butyl, itaconic acid mono- or di-n-butyl; alkoxyalkyl esters of the ethylenically unsaturated carboxylic acids such as methoxyacrylate, ethoxyacrylate, methoxyethoxyethyl acrylate; (meth)acrylates having a hydroxyalkyl group such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate; glycidyl (meth)acrylate; (meth)acrylamides and their derivatives such as (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide; acrylates having an amino group such as dimethylaminomethyl acrylate, diethylaminomethyl acrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene; α-olefins such as ethylene, propylene; non-conjugated diene monomers such as dicyclopentadiene, vinyl norbornene; etc. These monomers can be used alone or in combination of two or more.

[0019] In the copolymer rubber constituting the copolymer rubber latex, the content of units of other ethylenically unsaturated monomers is preferably 10% by weight or less, more preferably 5% by weight or less, based on all monomer units.

[0020] The gel content of the copolymer rubber constituting the copolymer rubber latex used in the present invention is not particularly limited, but is preferably 5 to 80% by weight, more preferably 10 to 75% by weight, and even more preferably 20 to 70% by weight, in order to further enhance the strength and flexibility of the resulting foam rubber. The gel content can be determined as the amount of methyl ethyl ketone-insoluble components by obtaining a film of copolymer rubber and immersing the film in methyl ethyl ketone for 48 hours in a constant temperature and humidity chamber at 23°C and 50% humidity. The gel content of the copolymer rubber can be adjusted by appropriately adjusting the emulsion polymerization conditions.

[0021] The copolymer rubber latex used in this invention can be produced by conventional emulsion polymerization methods.

[0022] The polymerization agents used in emulsion polymerization, such as emulsifiers (surfactants), polymerization initiators, chelating agents, oxygen scavengers, and molecular weight modifiers, can be conventionally known agents and are not particularly limited.

[0023] Typically, anionic and / or nonionic emulsifiers are used. Examples of anionic emulsifiers include fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, potassium oleate, and sodium oleate; resin salts such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate. Examples of nonionic emulsifiers include polyethylene glycol ester type, polyethylene glycol ester type, and Pluronic type such as block copolymers of ethylene oxide and propylene oxide. These can be used individually or in combination of two or more. The amount of emulsifier used is preferably 0.5 to 5 parts by weight per 100 parts by weight of the total monomer used in polymerization.

[0024] Examples of polymerization initiators include pyrolysis-type initiators such as persulfates like potassium persulfate and ammonium persulfate; organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, octanoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide; azo compounds such as azobisisobutyronitrile; and redox initiators consisting of these and reducing agents such as divalent iron ions. These can be used individually or in combination of two or more. Among these, redox initiators are preferred. The amount of polymerization initiator used is preferably 0.01 to 10 parts by weight per 100 parts by weight of the total monomers used for polymerization.

[0025] Examples of molecular weight modifiers include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; xanthogene compounds such as dimethyl xanthogene disulfide and diisopropyl xanthogene disulfide; thiram compounds such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram monosulfide; and 2,6-di-t-butyl-4 Examples include phenolic compounds such as methylphenol and styrene-phenol; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; and α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, α-methylstyrene dimer, and terpinolene. These can be used individually or in combination of two or more. The amount of molecular weight adjusting agent used is preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight, and particularly preferably 0.3 to 1.5 parts by weight, per 100 parts by weight of the total monomer used in polymerization.

[0026] The emulsion polymerization reaction may be continuous or batch-based, and the polymerization time is not particularly limited. The method of adding monomers is also not particularly limited; for example, a single-addition method or a divided-addition method can be used. However, from the viewpoint of further improving the balance between oil resistance and flexibility of the resulting foam rubber, it is preferable to add a portion of the aliphatic conjugated diene monomer used for polymerization to the reactor after the polymerization reaction has started and continue the polymerization. In this case, it is preferable to add a cyano group-containing ethylenically unsaturated monomer and a portion of the aliphatic conjugated diene monomer to the reactor to start the polymerization reaction, and then, when the polymerization reaction rate in the reactor is between 20% and 65%, add the remaining aliphatic conjugated diene monomer to the reactor all at once or in divided portions and continue the polymerization reaction.

[0027] The polymerization conversion rate at the time of stopping polymerization is not particularly limited, but is preferably 70 to 95% by weight, and more preferably 75 to 90% by weight. By setting the polymerization conversion rate within the above range, productivity can be improved while maintaining a suitable gel content. The polymerization temperature is not particularly limited, but is preferably 0 to 50°C, and more preferably 3 to 40°C.

[0028] After polymerization, it is preferable to remove unreacted monomers as needed and then perform a particle size enlargement treatment by a known method. This particle size enlargement treatment can increase the solid content concentration of the copolymer rubber latex to a range suitable for foam rubber.

[0029] Examples of particle size enlargement treatments include stopping the reaction during polymerization and vigorously stirring; adding an aliphatic conjugated diene monomer or toluene as a solvent after polymerization is complete and vigorously stirring; and adding a particle size enlargement agent such as a carboxyl group-containing polymer latex to the copolymer rubber latex and stirring.

[0030] After the particle size enlargement treatment, the solid content concentration is adjusted to an optimal range by a concentration operation. In the present invention, the solid content concentration of the copolymer rubber latex is preferably in the range of 55 to 75% by weight, and more preferably in the range of 60 to 70% by weight.

[0031] Furthermore, the viscosity of the copolymer rubber latex used in the present invention is preferably 1000 cps or less, more preferably 100 to 800 cps, and even more preferably 200 to 500 cps. By setting the viscosity of the copolymer rubber latex within the above range, a high balance between handling properties and foaming properties can be achieved. The viscosity of the copolymer rubber latex can be measured using a B-type viscometer under conditions of a temperature of 25°C and a rotation speed of 60 rpm. The copolymer rubber latex of the present invention may have a viscosity within the above range at 25°C at its solid content concentration (for example, the solid content concentration actually used), but it is preferable that the viscosity at 25°C be within the above range when the solid content concentration is 65% to 67% by weight. In this case, if the solid content concentration of the latex composition is less than 65% by weight, the solid content concentration can be adjusted by a concentration operation such as vacuum distillation, atmospheric distillation, centrifugation, or membrane concentration. If the solid content concentration of the latex composition exceeds 67% by weight, the solid content concentration can be adjusted by diluting with water before performing the viscosity measurement.

[0032] The volume-average particle size of copolymer rubber contained in copolymer rubber latex is not particularly limited, but is usually around 300 to 3000 nm, preferably 400 to 2000 nm. The volume-average particle size can be measured using a laser diffraction particle size analyzer. A specific example of a laser diffraction particle size analyzer is the laser diffraction particle size analyzer (model "LS-13320", manufactured by Beckman Coulter).

[0033] <Latex composition for foam rubber> The foam rubber latex composition of the present invention is obtained by blending the copolymer rubber latex described above with a nitroxyl radical compound and a thiazoline compound, and the solid content concentration is in the range of 55 to 75% by weight.

[0034] According to the present invention, by combining a nitroxyl radical compound and a thiazoline compound with the copolymer rubber latex described above, the resulting foam rubber can be made to have excellent oil resistance and a soft feel, while appropriately suppressing discoloration, deterioration, and odor generation during repeated use.

[0035] Nitroxyl radical compounds are compounds that act as stabilizers in the foam rubber latex composition of the present invention. Nitroxyl radical compounds are not particularly limited, as long as they have a nitroxyl radical structure, but examples include 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO), 2-azaadamantane-N-oxyl (AZADO), 1-methyl-2-azaadamantane-N-oxyl (1-Me-AZADO), or 9-azabicyclo[3.3.1]nonane-N-oxyl (ABNO). These can be used individually or in combination of two or more. Among these, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO) are preferred, and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) is more preferred.

[0036] The content of the nitroxyl radical compound in the foam rubber latex composition of the present invention is not particularly limited, but is preferably 100 to 10,000 ppm by weight, more preferably 300 to 7,000 ppm by weight, more preferably 500 to 5,000 ppm by weight, even more preferably 500 to 2,500 ppm by weight, even more preferably 500 to 2,000 ppm by weight, and particularly preferably 700 to 1,300 ppm by weight. By setting the content of the nitroxyl radical compound within the above range, discoloration, deterioration, and odor generation during repeated use of the resulting foam rubber can be more effectively suppressed.

[0037] As the thiazoline compound, any compound having a thiazoline structure may be used, and it is not particularly limited. For example, isothiazoline compounds represented by the following general formula (1), benzoisothiazoline compounds represented by the following general formula (2), etc. may be mentioned.

[0038]

Chemical formula

[0039]

Chemical formula

[0040] Specific examples of isothiazoline compounds represented by the above general formula (1) include 2-methyl-4-isothiazolin-3-one (MIT), 2-n-octyl-4-isothiazolin-3-one, 4-chloro-2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-n-octyl-4-isothiazolin-3-one, and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one. Specific examples of benzoisothiazoline compounds represented by the above general formula (2) include 1,2-benzoisothiazolin-3-one (BIT) and Nn-butyl-1,2-benzoisothiazolin-3-one. Among these, 2-methyl-4-isothiazolin-3-one (MIT) and 1,2-benzoisothiazolin-3-one (BIT) are preferred, and 1,2-benzoisothiazolin-3-one (BIT) is more preferred, from the viewpoint of further enhancing the effect of suppressing discoloration, deterioration, and odor generation during repeated use of the resulting foam rubber.

[0041] The content of the thiazoline compound in the foam rubber latex composition of the present invention is not particularly limited, but is preferably 10 to 1,000 ppm by weight, more preferably 10 to 500 ppm by weight, even more preferably 50 to 450 ppm by weight, even more preferably 80 to 400 ppm by weight, especially preferably 100 to 400 ppm by weight, particularly preferably 100 to 250 ppm by weight, and most preferably 100 to 150 ppm by weight. By setting the content of the thiazoline compound within the above range, discoloration, deterioration, and odor generation during repeated use of the resulting foam rubber can be more effectively suppressed.

[0042] The content of the nitroxyl radical compound and the thiazoline compound in the foam rubber latex composition of the present invention may be within the above range, but from the viewpoint of further enhancing the effect of suppressing discoloration, deterioration, and odor generation when the resulting foam rubber is repeatedly used, it is preferable that the content of these compounds be in the range of 1:1 to 30:1 by weight ratio of "nitroxyl radical compound:thiazoline compound", more preferably in the range of 5:1 to 20:1, and even more preferably in the range of 8:1 to 12:1.

[0043] Furthermore, the latex composition for foam rubber of the present invention may further contain a vulcanizing agent. Suitable vulcanizing agents include those commonly used in the manufacture of foam rubber, such as sulfur powder, sulfurous powder, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur; and sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, N,N'-dithio-bis(hexahydro-2H-azepinone-2), phosphorus-containing polysulfide, high-molecular-weight polysulfides, and 2-(4'-morpholinodithio)benzothiazole. Among these, sulfur is preferably used. The vulcanizing agent can be used alone or in combination of two or more.

[0044] The content of the vulcanizing agent in the foam rubber latex composition of the present invention is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 3 parts by weight, per 100 parts by weight of the rubber component in the foam rubber latex composition. By setting the amount of vulcanizing agent within the above range, the strength of the resulting foam rubber can be further increased.

[0045] The latex composition for foam rubber of the present invention may further contain a vulcanization accelerator. Suitable vulcanization accelerators include those commonly used in the manufacture of foam rubber, such as dithiocarbamates including diethyldithiocarbamic acid, dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, and their zinc salts; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole zinc, 2-mercaptobenzothiazole zinc Examples include captothiazoline, dibenzothiazil disulfide, 2-(2,4-dinitrophenylthio)benzothiazole, 2-(N,N-diethylthio / carbailthio)benzothiazole, 2-(2,6-dimethyl-4-morpholinothio)benzothiazole, 2-(4′-morpholino / dithio)benzothiazole, 4-morphonillyl-2-benzothiazil disulfide, and 1,3-bis(2-benzothiazil / mercaptomethyl)urea. The vulcanization accelerator can be used alone or in combination of two or more types.

[0046] The amount of vulcanization accelerator in the foam rubber latex composition of the present invention is not particularly limited, but is approximately 100 parts by weight of the rubber component in the foam rubber latex composition. The amount of the vulcanization accelerator is preferably 0.05 to 5 parts by weight, and more preferably 0.1 to 2 parts by weight. By setting the amount of the vulcanization accelerator within the above range, the strength of the resulting foam rubber can be further increased.

[0047] Furthermore, the foam rubber latex composition of the present invention may further contain zinc oxide. The amount of zinc oxide in the foam rubber latex composition of the present invention is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2 parts by weight, per 100 parts by weight of the rubber component in the foam rubber latex composition.

[0048] The method for preparing the foam rubber latex composition of the present invention is not particularly limited, but examples include mixing copolymer rubber latex with a nitroxyl radical compound, a thiazoline compound, and various compounding agents such as a vulcanizing agent, a vulcanization accelerator, and zinc oxide, which may be used as needed. On the other hand, since the nitroxyl radical compound acts as a stabilizer, it also acts as a polymerization inhibitor or polymerization stopper to stop the polymerization reaction. Therefore, some of the nitroxyl radical compound may be added as a polymerization stopper to stop the polymerization reaction when obtaining copolymer rubber latex by emulsion polymerization. In this case, some of the nitroxyl radical compound may be present bound to the stopping end of the copolymer rubber constituting the copolymer rubber latex. Furthermore, compounding agents other than copolymer rubber latex and nitroxyl radical compound may be added in the form of an aqueous dispersion or aqueous solution containing them.

[0049] Furthermore, the foam rubber latex composition of the present invention may contain, for example, an anti-aging agent; a coloring agent; a foam stabilizer; a dispersant such as NASF (sodium salt of naphthalene sulfonic acid formalin condensate); a thickener such as polyacrylic acid and its sodium salt, sodium alginate, or polyvinyl alcohol; a surfactant as a foaming agent such as an aliphatic alkaline soap such as potassium oleate or a sulfate of a higher alcohol such as sodium dodecyl sulfate; and the like.

[0050] The foam rubber latex composition of the present invention has a solid content concentration in the range of 55 to 75% by weight, preferably in the range of 60 to 70% by weight, more preferably in the range of 63 to 69% by weight, even more preferably in the range of 64.5 to 67.5% by weight, and particularly preferably in the range of 65 to 67% by weight. If the solid content concentration is too low, foam roughness occurs when obtaining foam rubber, resulting in a poor appearance of the resulting foam rubber. If the solid content concentration is increased above the above range, productivity decreases. The solid content concentration can be adjusted, for example, by adjusting the solid content concentration of the copolymer rubber latex used, the amount of compounding agents, etc.

[0051] <Foam Rubber> The foam rubber of the present invention is obtained using the foam rubber latex composition of the present invention described above. Specifically, the foam rubber of the present invention can be obtained by foaming, solidifying, and, if necessary, vulcanizing the above-described latex composition for foam rubber of the present invention.

[0052] Air is typically used to foam latex compositions for foam rubber, but carbonates such as ammonium carbonate and sodium bicarbonate; azo compounds such as azodicarboxylic acid amide and azobisisobutyronitrile; and gas-generating substances such as benzenesulfonyl hydrazide can also be used. When using air, the copolymer rubber latex is stirred to incorporate air and create foam. For example, an OAKS foaming machine or an ultrasonic foaming machine can be used for this purpose.

[0053] The foamed latex composition is foamed to a predetermined foaming ratio, and then solidified to fix the foamed state. The solidification method is not particularly limited as long as it can gel and solidify the foam rubber latex composition, and any conventionally known method can be used. For example, the Dunlop method (room temperature solidification method) is used, in which a silicon fluoride compound such as sodium hexafluorosilicate, potassium hexafluorosilicate (sodium silicafluoride, potassium silicafluoride), or titanium sodium silicafluoride is added as a solidifying agent to the foamed foam rubber latex composition; a heat-sensitive solidification method is used, in which a heat-sensitive solidifying agent such as organopolysiloxane, polyvinyl methyl ether, or zinc ammonium sulfate complex salt is added to the foamed foam rubber latex composition; and a cryo-solidification method is used. The amount of solidifying agent used is not particularly limited, but is usually about 0.5 to 10 parts by weight per 100 parts by weight of the foam rubber latex composition (solid content).

[0054] Then, the foamed latex composition for foam rubber, which has been foamed while still fluid after the addition of a coagulant, is transferred to a mold of a predetermined shape and solidified to obtain foam rubber. Alternatively, after solidification, heating may be performed for vulcanization. The vulcanization conditions can preferably be a heat treatment at a temperature of 100 to 160°C for 15 to 120 minutes.

[0055] The resulting foam rubber is preferably washed after being removed from the mold. The washing method is not particularly limited, but for example, it can be washed using a washing machine or the like, agitated in water at about 20 to 70°C for about 5 to 15 minutes. After washing, it is preferable to drain the water and dry the foam rubber at a temperature of about 30 to 90°C so as not to damage the texture of the foam rubber. The foam rubber thus obtained can be used as a puff (cosmetic sponge), for example, by slicing it to a predetermined thickness, cutting it into a predetermined shape, and then polishing the sides with a rotary grinding wheel or the like.

[0056] The foam rubber of the present invention is obtained using the foam rubber latex composition of the present invention described above, and therefore has excellent oil resistance, a soft feel, and appropriately suppresses discoloration, deterioration, and odor generation during repeated use, making it suitable as a puff (cosmetic sponge). In addition to puffs (cosmetic sponges), it can also be suitably used in various other applications such as mattresses, rolls, and shock absorbers. [Examples]

[0057] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the "parts" below refer to weight. Various physical properties were measured as follows.

[0058] <Solid content concentration of copolymer rubber latex and foam rubber latex composition> Two g of the sample was accurately weighed onto an aluminum dish (weight: X1) (weight: X2), and dried in a hot air dryer at 105°C for two hours. After cooling in a desiccator, the weight of the aluminum dish was measured (weight: X3), and the solid content concentration was calculated according to the following formula. Solid content concentration (wt%)=(X3-X1)×100 / X2

[0059] <Viscosity of copolymer rubber latex> The viscosity of the copolymer rubber latex was measured using a B-type viscometer at a rotation speed of 60 rpm under conditions of 25°C.

[0060] <Odor of copolymer rubber latex> 50 mL of copolymer rubber latex was placed in a 100 mL airtight container and left for 24 hours at 25°C. Afterward, five people checked for odor when opening and closing the container. The evaluation was conducted according to the following criteria. A: None of the five people detected any smell of decay. B: 1 to 4 out of 5 people can smell a putrid odor. C: All five people smelled a putrid odor.

[0061] <Oil resistance of foam rubber> A disc-shaped foam rubber with a thickness of 0.8 cm was punched out into a circle with a diameter of approximately 38 mm to obtain a test specimen. The obtained test specimen was immersed in toluene at 23°C for 24 hours, and the ratio of the diameter of the test specimen after immersion to the diameter of the test specimen before immersion (swelling rate (%) = (diameter of test specimen after immersion) / (diameter of test specimen before immersion) × 100) was calculated. A lower swelling rate indicates superior oil resistance.

[0062] <F-type hardness of foam rubber> The hardness of the foam rubber was measured using an Asker rubber hardness tester Type F (manufactured by Polymer Instruments Co., Ltd.). A lower value indicates that the foam rubber is softer and has a better feel.

[0063] <Discoloration, deterioration, and odor of foam rubber during repeated use> Test specimens were obtained by punching out a circular shape with a diameter of approximately 38 mm from a disc-shaped foam rubber with a thickness of 0.8 cm, and these specimens were subjected to repeated use procedures. For the repeated use procedure, the test specimens were first immersed in silicone oil (decamethylcyclopentasiloxane), then washed with water and a neutral dish soap, and air-dried at room temperature for 24 hours. This procedure was repeated 10 times, and then the specimens were left at 25°C for 10 days to obtain specimens after repeated use. Discoloration, deterioration, and odor during repeated use were evaluated using the specimens after repeated use. (Discoloration from repeated use) Regarding discoloration during repeated use, five people visually inspected the test pieces before and after repeated use, and judged them according to the following criteria by comparing them with the sample before repeated use. A: None of the five showed any obvious discoloration. B: 1 to 4 people noticed a change in color. C: All five of us clearly noticed a brownish discoloration. (Deterioration from repeated use) Deterioration during repeated use was confirmed through tactile evaluation by five people who actually touched the product, and the following criteria were used for the assessment. A: None of the five felt any noticeable change in texture. B: 1 to 4 people noticed a change in texture. C: All five of them were clearly hard and had a dry, crumbly texture. (Odor after repeated use) Regarding odor during repeated use, each test piece was placed in a 100 mL container, left at room temperature for 24 hours, and then the odor after standing was checked by five people and judged according to the following criteria. A: None of the five of us smelled anything at all. B: 1 to 4 people can detect a slight odor. C: All five of us clearly smell an odor.

[0064] <Example 1> (Preparation of copolymer rubber latex) In a pressure-resistant reaction vessel, 200 parts of deionized water, 1.5 parts of potassium oleate, 35 parts of acrylonitrile, 0.5 parts of t-dodecyl mercaptan, 0.03 parts of sodium formaldehyde sulfoxylate, 0.003 parts of ferrous sulfate, and 0.008 parts of ethylenediaminetetraacetic acid sodium were added. After thorough degassing, 45 parts of 1,3-butadiene were added. Next, 0.05 parts of cumene hydroperoxide as a polymerization initiator and an appropriate amount of reducing agent were added, and emulsion polymerization was started at a reaction temperature of 5°C. When the polymerization conversion rate reached 40%, 10 parts of 1,3-butadiene were added, and the polymerization reaction was continued. Furthermore, when the polymerization conversion rate reached 60%, another 10 parts of 1,3-butadiene were added, and the polymerization reaction was continued. When the polymerization conversion rate reached 80%, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was added in an aqueous dispersion to stop the polymerization reaction. The amount of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) used was such that the final foam rubber latex composition contained 2,000 ppm by weight. After removing the unreacted monomers, 80 parts of 1,3-butadiene were added, and the mixture was stirred at 1,000 rpm for 5 hours with a paddle-type stirring blade at a temperature of 15°C to enlarge the particle size. Subsequently, after removing the 1,3-butadiene, the mixture was concentrated to obtain a copolymer rubber latex with a solid content of 67% by weight. The pH of the obtained copolymer rubber latex was 11.3 and the viscosity (Type B viscosity) was 280 cps. Furthermore, the composition of monomer units contained in the copolymer rubber constituting the copolymer rubber latex was almost identical to that of the amount used (the same was true in Examples 2-5 and Comparative Examples 1-5, described later).

[0065] (Preparation of latex compositions for foam rubber) Then, to 100 parts of the solid content of the copolymer rubber latex obtained above, 4 parts of a vulcanizing aqueous dispersion (colloidal sulfur / dithiocarbamate-based vulcanization accelerator Noxellar EZ (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) / thiazole-based vulcanization accelerator Noxellar MZ (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) = 2 / 1 / 1 (weight ratio): solid content concentration 50% by weight), 3 parts of zinc oxide aqueous dispersion (solid content concentration 50% by weight), 1 part of a foam stabilizer (Trimenbase: manufactured by Crompton Corp.), and 1,2-benzoisothiazolin-3-one (BIT) were added and thoroughly dispersed to obtain a copolymer latex composition for foam rubber with a solid content concentration of 67% by weight. The amount of 1,2-benzoisothiazolin-3-one (BIT) added was such that the total amount in the copolymer latex composition for foam rubber was 100 ppm by weight.

[0066] (Manufacturing of foam rubber) The copolymer latex composition for foam rubber obtained above was stirred using a stand mixer (Electrolux ESM945) to foam up to approximately five times its original volume. Then, 1.5 parts of a sodium silicafluoride aqueous dispersion (solid content concentration 20% by weight) were added and stirred for another minute to obtain a foamed product. Next, the obtained foamed product was poured into a molding mold (7 cm in diameter, 8 cm in height), allowed to solidify, and then vulcanized at 110°C for 1 hour to obtain foam rubber. The foam rubber removed from the mold was washed with 40°C hot water for 10 minutes, dried in a 60°C oven for 4 hours, and then cut into discs with a thickness of 0.8 cm to obtain disc-shaped foam rubber. Oil resistance, F-type hardness, and discoloration, deterioration, and odor during repeated use were measured and evaluated according to the above method. The results are shown in Table 1.

[0067] <Example 2> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 1, except that the amount of acrylonitrile used was changed to 45 parts, the amount of 1,3-butadiene used at the start of polymerization was changed to 35 parts, and the amount of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) used was set to an amount that would result in 1,000 ppm by weight in the final foam rubber latex composition. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 65% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0068] <Example 3> A copolymer rubber latex with a solid content of 67% by weight was prepared in the same manner as in Example 2, except that the amount of 1,3-butadiene used at the start of polymerization was changed to 30 parts, and 5 parts of isoprene were added at the start of polymerization. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 67% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0069] <Example 4> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 2, except that the amount of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) used was such that the final foam rubber latex composition contained 500 ppm by weight. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 65% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0070] <Example 5> Using the copolymer rubber latex obtained in the same manner as in Example 2, the foam rubber latex composition (solid content concentration 65% by weight) was prepared and the foam rubber was manufactured in the same manner as in Example 2, except that the same amount of 2-methyl-4-isothiazolin-3-one (MIT) was used instead of 1,2-benzoisothiazolin-3-one (BIT). The results are shown in Table 1.

[0071] <Comparative Example 1> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 1, except that the amount of acrylonitrile used was changed to 47 parts, the amount of 1,3-butadiene used at the start of polymerization was changed to 18 parts, an additional 15 parts of isoprene were added at the start of polymerization, and an aqueous dispersion of diethylhydroxyamine (HAS) was used instead of an aqueous dispersion of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). The amount of diethylhydroxyamine (HAS) used was such that the final foam rubber latex composition contained 2,000 ppm by weight. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 65% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0072] <Comparative Example 2> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 2, except that an aqueous dispersion of diethylhydroxyamine (HAS) was used instead of an aqueous dispersion of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). The amount of diethylhydroxyamine (HAS) used was such that the final foam rubber latex composition contained 2,000 ppm by weight. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 65% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0073] <Comparative Example 3> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 2, except that 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was not used. In Comparative Example 3, no polymerization inhibitor was used for emulsion polymerization. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 66% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0074] <Comparative Example 4> Using the copolymer rubber latex obtained in the same manner as in Example 2, the foam rubber latex composition (solid content concentration 65% by weight) was prepared and the foam rubber was manufactured in the same manner as in Example 2, except that 1,2-benzoisothiazolin-3-one (BIT) was not used. The results are shown in Table 1.

[0075] <Comparative Example 5> A copolymer rubber latex with a solid content of 65% by weight was prepared in the same manner as in Example 3, except that the amount of acrylonitrile used was changed to 20 parts and the amount of 1,3-butadiene used at the start of polymerization was changed to 55 parts. The pH and viscosity (Type B viscosity) of the obtained copolymer rubber latex are shown in Table 1. Then, except that the copolymer rubber latex obtained above was used, a latex composition for foam rubber (solid content concentration 65% by weight) was prepared and foam rubber was manufactured in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 1.

[0076] [Table 1]

[0077] As shown in Table 1, foam rubber obtained using a foam rubber latex composition containing a copolymer rubber latex containing 30-60% by weight of cyano group-containing ethylenically unsaturated monomer units and 40-70% by weight of aliphatic conjugated diene monomer units, a nitroxyl radical compound, and a thiazoline compound, with a solid content concentration of 55-75% by weight, exhibited excellent oil resistance, a soft feel, and appropriately suppressed discoloration, deterioration, and odor generation during repeated use (Examples 1-5).

[0078] On the other hand, when diethylhydroxyamine (HAS) was used instead of the nitroxyl radical compound, the resulting foam rubber developed an odor upon repeated use, despite containing 1,2-benzoisothiazolin-3-one (BIT) as a thiazoline compound (Comparative Examples 1 and 2). When nitroxyl radical compounds were not used, the resulting foam rubber discolored and deteriorated with repeated use, and the effect of suppressing odor generation with repeated use was also insufficient (Comparative Example 3). Furthermore, when a nitroxyl radical compound was included but a thiazoline compound was not, the resulting foam rubber developed an odor upon repeated use (Comparative Example 4). Furthermore, when the composition of the copolymer rubber constituting the copolymer rubber latex was outside the range specified by the present invention, the resulting foam rubber had poor oil resistance, low F-type hardness, and a soft feel (Comparative Example 5).

Claims

1. A copolymer rubber latex containing 30-60% by weight of cyano group-containing ethylenically unsaturated monomer units and 40-70% by weight of aliphatic conjugated diene monomer units, Nitroxyl radical compounds and It contains thiazoline compounds, A latex composition for foam rubber having a solid content concentration of 55 to 75% by weight.

2. The foam rubber latex composition according to claim 1, wherein the content of the nitroxyl radical compound is 100 to 10,000 ppm by weight.

3. The foam rubber latex composition according to claim 1 or 2, wherein the content of the thiazoline compound is 10 to 1,000 ppm by weight.

4. The foam rubber latex composition according to any one of claims 1 to 3, wherein the nitroxyl radical compound is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).

5. The foam rubber latex composition according to any one of claims 1 to 4, wherein the thiazoline compound is 2-methyl-4-isothiazolin-3-one (MIT) or 1,2-benzoisothiazolin-3-one (BIT).

6. A latex composition for foam rubber according to any one of claims 1 to 5, wherein the solid content concentration is 60 to 70% by weight.

7. A latex composition for foam rubber according to any one of claims 1 to 6, wherein the solid content concentration is 63 to 69% by weight.

8. A latex composition for foam rubber according to any one of claims 1 to 7, wherein the solid content concentration is 64.5 to 67.5% by weight.

9. A foam rubber obtained using the foam rubber latex composition according to any one of claims 1 to 8.

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