Chloroprene latex composition

Abstract

To provide a chloroprene latex composition capable of achieving favorable film properties during dip molding without use of a vulcanization accelerator.SOLUTION: A chloroprene latex composition comprises a chloroprene polymer and an emulsifier, wherein the composition includes a chloroprene polymer having a toluene-insoluble fraction of 89 to 95 wt.% and, as the emulsifier, includes an alkali metal salt of a carboxylic acid and a nonionic emulsifier having an HLB of 16.2 to 20.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a chloroprene latex composition. [Background technology]

[0002] In glove applications, the proteins contained in the natural rubber latex that has been used conventionally have become a problem for medical workers and patients, causing allergies, and replacement with synthetic rubber gloves is being promoted (see, for example, Patent Document 1).

[0003] Among them, chloroprene rubber has a good balance of mechanical strength, weather resistance, oil resistance, heat resistance, flame retardancy, adhesiveness, etc., and furthermore, various physical properties such as flexibility and texture of the coating are similar to those of natural rubber, so it is being used as a replacement for natural rubber gloves (see, for example, Patent Document 2). In the manufacture of rubber gloves, the so-called dip molding method is often used, in which a coagulating liquid is applied to a former, which is dried, and then the former is immersed in a composition made by mixing latex with compounds such as vulcanization accelerators to form a rubber coating, thereby obtaining a product.However, it is known that the vulcanization accelerators that are compounded can also cause allergies, and attempts have been made to manufacture gloves without using them.However, since unvulcanized rubber generally has poor mechanical properties, it was necessary to obtain good coating properties without using vulcanization accelerators. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-214593 [Patent Document 2] Japanese Patent Application Publication No. 2019-143002 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a chloroprene latex composition and a rubber composition which, regarding a chloroprene latex composition for obtaining a coated product by dip molding, maintain the film formability of the dip-molded coating, excellent mechanical properties such as breaking strength, and good heat aging resistance without using a vulcanization accelerator, and are suitable for producing an allergen-free dip-molded product. [Means for solving the problem]

[0006] Under these circumstances, the present inventors have conducted extensive research to solve the above-mentioned problems, and have found that the surface smoothness of the dip-molded coating can be improved by using a chloroprene latex composition containing a chloroprene polymer having a toluene-insoluble portion of 89 to 95% by weight, and containing, as an emulsifier, an alkali metal carboxylate and a nonionic emulsifier having an HLB of 16.2 to 20.0.

[0007] That is, the respective aspects of the present invention are the following [1] to [6].

[0008] [1] A chloroprene latex composition containing a chloroprene polymer and an emulsifier, wherein the toluene-insoluble portion of the chloroprene polymer is 89 to 95% by weight, the emulsifier is an alkali metal carboxylate and a nonionic emulsifier having an HLB of 16.2 to 20.0, and the chloroprene latex composition contains 4.0 to 7.0 parts by weight of the alkali metal carboxylate and 0.2 to 0.8 parts by weight of the nonionic emulsifier per 100 parts by weight of the chloroprene polymer.

[0009] [2] The chloroprene latex composition according to [1], wherein the nonionic emulsifier is a nonionic emulsifier represented by the following general formula (1):

[0010] RO(CH2CXHO) n H (1) (In the formula, R represents a lipophilic group consisting of an alkyl chain having 9 to 16 carbon atoms, X represents hydrogen or an alkyl chain having 1 to 2 carbon atoms, and n represents an integer in the range that gives the nonionic emulsifier an HLB of 16.2 to 20.0.) [3] The chloroprene latex composition according to any one of [1] to [2], which does not contain a vulcanization accelerator.

[0011] [4] The chloroprene latex composition according to any one of [1] to [3], further containing zinc oxide. [5] A chloroprene latex composition for dip molding, comprising the chloroprene latex composition according to any one of [1] to [4].

[0012] [6] A rubber composition comprising the chloroprene latex composition for dip molding according to [5]. [Effects of the Invention]

[0013] The chloroprene latex composition of the present invention produces a dip-molded coating that maintains film-forming properties, excellent mechanical properties such as breaking strength, and good heat aging resistance, even without the addition of a vulcanization accelerator. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] A chloroprene latex composition according to one embodiment of the present invention contains a chloroprene polymer having a toluene-insoluble portion of 89 to 95% by weight, and an alkali metal salt of a carboxylic acid and a nonionic emulsifier having an HLB of 16.2 to 20.0 as emulsifiers.

[0016] The chloroprene polymer may be a polymer of chloroprene, which is 2-chloro-1,3-butadiene, or a copolymer obtained by polymerizing a chloroprene monomer with one or more types of monomers copolymerizable with chloroprene.

[0017] Examples of monomers copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, butadiene, isoprene, styrene, acrylonitrile, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, and methyl methacrylate. Examples of monomers copolymerizable with chloroprene include those obtained by using 20 parts by weight or less of these monomers per 100 parts by weight of chloroprene monomer.

[0018] The toluene-insoluble portion of the chloroprene polymer or chloroprene copolymer is 89 to 95% by weight. By making it 89% by weight or more, mechanical properties can be improved without adding a vulcanization accelerator, while if it exceeds 95% by weight, the reaction takes a long time, productivity is reduced, and the film has poor breaking strength and flexibility. In the present invention, the toluene-insoluble portion refers to an insoluble portion obtained by adjusting the pH of a chloroprene polymer latex to 6.0 with acetic acid, freeze-drying it, washing it with water to remove water-soluble components such as emulsifiers, and then heating and drying it, weighing the resulting polymer, immersing it in toluene with stirring for 20 hours or more to make the concentration 1%, and filtering it through a 200-mesh wire screen.

[0019] An emulsifier having an alkali metal salt of a carboxylic acid has a lipophilic group and a hydrophilic group, and the hydrophilic group is an alkali metal salt of a carboxylic acid. Examples of emulsifiers having an alkali metal salt of a carboxylic acid include alkali metal salts of rosin acid, alkali metal salts of fatty acids, alkali metal salts of alkenyl succinic acids, and polymeric compounds of alkali metal salts of polycarboxylic acids. Examples of alkali metal salts include lithium, sodium, potassium, and cesium. These may be used alone or in combination with two or more. From the viewpoints of polymerization stability and adhesive performance, alkali metal salts of rosin acid are preferred, and potassium salts of rosin acid are even more preferred. The content of this emulsifier is not particularly limited, but is 4.0 to 7.0 parts by weight per 100 parts by weight of the chloroprene polymer in terms of the balance between stability in latex compounding and mechanical properties.

[0020] The chloroprene latex of the present invention contains a nonionic emulsifier having an HLB of 16.2 to 20.0, preferably 18.1 to 20.0. HLB indicates the balance between lipophilicity and hydrophilicity, and is calculated by dividing the molecular weight of the hydrophilic moiety by the molecular weight of the emulsifier and multiplying the result by 20. If the HLB is less than 16.2, the surface smoothness of the dip-molded coating of the obtained chloroprene latex composition will be poor.

[0021] Nonionic emulsifiers include ester-type and ether-type emulsifiers, and are not particularly limited. However, ether-type emulsifiers are preferred, and more preferred are ether-type nonionic emulsifiers represented by the following general formula (1).

[0022] RO(CH2CXHO) n H (1) (In the formula, R represents a lipophilic group consisting of an alkyl chain having 9 to 16 carbon atoms, X represents hydrogen or an alkyl chain having 1 to 2 carbon atoms, and n represents an integer in the range that gives the nonionic emulsifier an HLB of 16.2 to 20.0.) The amount of nonionic emulsifier used is 0.2 to 0.8 parts by weight, preferably 0.3 to 0.7 parts by weight, per 100 parts by weight of chloroprene polymer, in view of the balance between the surface smoothness and physical properties of the dip coating. The chloroprene latex composition of the present invention can be synthesized using a chloroprene monomer or a chloroprene monomer and a monomer copolymerizable with chloroprene, an emulsifier having an alkali metal salt of a carboxylic acid, and a nonionic emulsifier having an HLB of 16.2 to 20.0. The nonionic emulsifier having an HLB of 16.2 to 20.0 may be added during or after the polymerization. The chloroprene latex composition can also be prepared by mixing two or more types of latex.

[0023] As a method for synthesizing the chloroprene latex, for example, polymerization may be carried out at a predetermined temperature using the above-mentioned monomer, an emulsifier containing an alkali metal salt of carboxylic acid, a polymerization initiator, a chain transfer agent, other stabilizers, etc., and then adding a polymerization terminator at a predetermined polymerization conversion rate to terminate the polymerization.

[0024] As the polymerization initiator, known free radical substances can be used, for example, peroxides such as potassium persulfate and ammonium persulfate, hydrogen peroxide, inorganic or organic peroxides such as tertiary butyl hydroperoxide, etc. These can be used alone or in combination with reducing substances such as thiosulfates, thiosulfites, hydrosulfites, organic amines, etc. in a redox system. The amount of the toluene insoluble portion of the chloroprene copolymer is adjusted by the amount of the chain transfer agent and the polymerization temperature.

[0025] Examples of the chain transfer agent include alkyl mercaptans, halogenated hydrocarbons, alkyl xanthogen disulfides, molecular weight regulators such as sulfur, and of these, n-dodecyl mercaptan is preferred from the standpoint of odor and workability.

[0026] The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 40°C, more preferably 15 to 35°C.

[0027] There is no particular limitation on the time when the polymerization is completed, but from the viewpoint of productivity, it is preferable to carry out the polymerization until the conversion rate of the monomer reaches 70% or more, more preferably 85% or more.

[0028] The polymerization terminator is not particularly limited as long as it is a commonly used terminator, and examples thereof include phenothiazine, 2,6-t-butyl-4-methylphenol, and hydroxylamine.

[0029] Generally, a dip-molded product using a chloroprene latex is produced using a vulcanization accelerator, but the chloroprene latex composition of the present invention can be used without a vulcanization accelerator. Typical vulcanization accelerators include thiourea compounds such as diphenylthiourea, ethylenethiourea, and diethylthiourea, guanidine compounds such as diphenylguanidine and di-o-tolylguanidine, thiazole compounds such as 2-mercaptobenzothiazole and zinc salt of 2-mercaptobenzothiazole, thiuram compounds such as tetramethylthiuram disulfide and tetraethylthiuram disulfide, and carbamic acid compounds such as zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate.

[0030] The chloroprene latex composition of the present invention preferably contains zinc oxide. By including zinc oxide, the storage stability of the chloroprene latex composition is improved. The amount of zinc oxide used is not limited, but is preferably 1 part by weight or more and 10 parts by weight or less, and more preferably 2 to 7 parts by weight, per 100 parts by weight of the chloroprene polymer.

[0031] If necessary, an antioxidant, a plasticizer, a lubricant, a pigment for coloring, or other general fillers such as calcium carbonate, or a dispersion thereof dispersed in water may be added to the chloroprene latex composition and then dip-molded. Thus, the chloroprene latex composition can be suitably used for dip-molded rubber products such as rubber gloves. [Example]

[0032] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Physical properties for evaluation were measured by the following methods.

[0033] <Toluene insolubles> The amount of toluene-insoluble matter in the chloroprene polymer was calculated from the ratio of the amount of the polymer obtained by adjusting the pH of the chloroprene polymer latex to 6.0 with acetic acid, freeze-drying the polymer, washing with water to remove water-soluble components such as emulsifiers, and then heating and drying the polymer to a weighed amount, immersing the polymer in toluene with stirring for 20 hours or more to a concentration of 1%, and filtering the insoluble matter through a 200-mesh wire screen to a weighed amount.

[0034] <Dip molding> A ceramic former was preheated at 70°C for 30 minutes, immersed in a coagulating solution (25% aqueous calcium nitrate solution) for 10 seconds, and then dried at 70°C for 10 minutes. The dried former was then immersed in a chloroprene latex composition for dip molding for 10 seconds, pulled out, and air-dried at room temperature for 30 minutes or more, and then heated at 130°C for 40 minutes to produce a coating.

[0035] <Surface smoothness> After dip molding, the coating surface on the former was visually inspected after air drying at room temperature for 30 minutes or more.

[0036] ○: The surface is smooth.

[0037] ×: Dripping or uneven surface <Normal physical properties> The coating obtained by the dip molding operation was peeled off from the former to form a sheet, and dumbbell-shaped C-type test pieces were prepared in accordance with ASTM D-412. The tensile strength at break, elongation at break, and 500% tensile stress were measured at a pulling rate of 500 mm / min at 23°C.

[0038] <Heat aging properties> The resulting dumbbell-shaped C-type test piece was subjected to accelerated aging at 70°C for 7 days in accordance with ASTM D-412, and then 500% tensile stress was measured to determine the rate of change in state physical properties.

[0039] Example 1 A chloroprene latex was prepared by polymerization at 30°C in a 10-L autoclave equipped with a stirrer using 4.75 kg of chloroprene monomer and 0.25 kg of 2,3-dichloro-1,3-butadiene, with 0.03 part by weight of n-dodecyl mercaptan, 5 parts by weight of potassium rosinate (trade name: Longis (registered trademark) K-25, Arakawa Chemical Industries, Ltd.), 0.35 parts by weight of a condensate of sodium naphthalenesulfonate and formaldehyde (trade name: Demol (registered trademark) N, Kao Corporation), 0.4 part by weight of sodium hydroxide, 0.01 part by weight of sodium hydrosulfite, and 90 parts by weight of pure water, relative to 100 parts by weight of the total monomers. Polymerization was carried out under a nitrogen atmosphere by continuously adding dropwise a 0.35 wt% aqueous solution of potassium persulfate. When the polymerization conversion reached 90%, 0.05 parts by weight of 2,6-tert-butyl-4-methylphenol was added as a polymerization terminator to terminate the polymerization. Subsequently, unreacted monomers and water were removed under reduced pressure to adjust the solid content of the latex to 50%, yielding chloroprene latex A. The toluene insoluble content was 91 wt%.

[0040] A nonionic emulsifier A (polyoxyethylene decyl ether; product name Noigen (registered trademark) XL-400D: manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) having an HLB of 18.4 was added to chloroprene latex A in an amount of 0.4 part by weight relative to 100 parts by weight of the chloroprene polymer in terms of pure content, and further a zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed therewith so that the zinc oxide content was 5% by weight relative to 100% by weight of the chloroprene polymer, thereby obtaining a chloroprene latex composition for dip molding.

[0041] This was used to carry out dip molding and evaluation, and the results are shown in Table 1. The results in Table 1 show that the surface smoothness, tensile strength, and heat aging resistance were good.

[0042] [Table 1]

[0043] Example 2 A chloroprene latex composition was obtained and evaluated in the same manner as in Example 1, except that the amount of nonionic emulsifier A mixed with latex A was changed to 0.5 parts by weight per 100 parts by weight of the chloroprene polymer. The results are shown in Table 1. As can be seen from the results in Table 1, each physical property was good.

[0044] Example 3 Chloroprene latex B was obtained in the same manner as in Example 1, except that the monomers used were 4.15 kg of chloroprene monomer and 0.35 kg of 2,3-dichloro-1,3-butadiene, 0.02 parts by weight of n-dodecyl mercaptan per 100 parts by weight of the total monomers, and the polymerization temperature was 20°C. The toluene insoluble portion was 94% by weight. A chloroprene latex composition was obtained in the same manner as in Example 1, except that 1 part by weight of anionic emulsifier A (a condensate of sodium naphthalenesulfonate and formaldehyde (trade name: Demol (registered trademark) N, Kao Corporation)) and 0.5 parts by weight of nonionic emulsifier A per 100 parts by weight of chloroprene copolymer were added to chloroprene latex B, and the composition was evaluated. The results are shown in Table 1. As can be seen from the results in Table 1, the physical properties were good.

[0045] Comparative Example 1 A chloroprene latex composition was obtained in the same manner as in Example 1 except that the anionic emulsifier A and the nonionic emulsifier A were not used, and the surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. The results in Table 1 showed that the surface smoothness was poor and the change in physical properties after heat aging was also large.

[0046] Comparative Example 2 A chloroprene latex composition was obtained in the same manner as in Example 3 except that nonionic emulsifier A was not used, and surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. The results in Table 1 show that the change in physical properties after heat aging was large.

[0047] Comparative Example 3 A chloroprene latex composition was obtained in the same manner as in Example 1, except that nonionic emulsifier B (polyoxyethylene decyl ether; product name Noigen (registered trademark) XL-100, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) having an HLB of 14.7 was used instead of nonionic emulsifier A, and the surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. The results in Table 1 show that the surface smoothness was poor, the tensile strength at break was low, and the change in physical properties after heat aging was significant.

[0048] Comparative Example 4 Chloroprene latex C was obtained in the same manner as in Example 1, except that 0.06 parts by weight of n-dodecyl mercaptan was used relative to 100 parts by weight of the total monomers. The toluene insoluble portion was 87% by weight. Zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100% by weight of the chloroprene polymer of chloroprene latex C so that the zinc oxide content was 5% by weight in terms of pure content, to obtain a chloroprene latex composition for dip molding, which was then evaluated. The results are shown in Table 1. The results in Table 1 showed poor surface smoothness, low tensile strength at break, and significant changes in physical properties after heat aging. [Industrial Applicability]

[0049] The chloroprene latex composition of the present invention is used for dip-molded products and is widely used in the field of rubber products.

Claims

1. A chloroprene latex composition containing a chloroprene polymer and an emulsifier, wherein the toluene-insoluble portion of the chloroprene polymer is 89 to 95% by weight, and the emulsifier is an alkali metal carboxylate and a nonionic emulsifier having an HLB of 16.2 to 20.0, and the chloroprene latex composition contains 4.0 to 7.0 parts by weight of the alkali metal carboxylate and 0.2 to 0.8 parts by weight of the nonionic emulsifier per 100 parts by weight of the chloroprene polymer.

2. 2. The chloroprene latex composition according to claim 1, wherein the nonionic emulsifier is a nonionic emulsifier represented by the following general formula (1): R-O(CH ２ CXHO) ｎ H (1) (In the formula, R represents a lipophilic group consisting of an alkyl chain having 9 to 16 carbon atoms, X represents hydrogen or an alkyl chain having 1 to 2 carbon atoms, and n represents an integer in the range that results in an HLB of the nonionic emulsifier of 16.2 to 20.0.)

3. 2. The chloroprene latex composition according to claim 1, which does not contain a vulcanization accelerator.

4. 10. The chloroprene latex composition of claim 1, further comprising zinc oxide.

5. A chloroprene latex composition for dip molding, comprising the chloroprene latex composition according to any one of claims 1 to 4.

6. A rubber composition comprising the chloroprene latex composition for dip molding according to claim 5 .

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