Chloroprene latex composition

Abstract

The present invention provides a chloroprene latex composition, a coating film of which has good surface smoothness during immersion molding.　The present invention uses a chloroprene latex composition which contains a chloroprene polymer and an emulsifying agent. The emulsifying agent is composed of an alkali metal carboxylate and a nonionic emulsifying agent having an HLB of 18.1 to 20.0. The chloroprene latex composition contains 3.0 to 6.0 parts by weight of the alkali metal carboxylate and 0.15 to 0.9 part by weight of the nonionic emulsifying agent relative to 100 parts by weight of the chloroprene polymer.

Description

Chloroprene latex composition

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

[0002] In glove applications, conventionally used natural rubber latex has become a problem due to allergies caused by proteins contained in the latex among medical professionals and patients, 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, and adhesiveness, and furthermore, various physical properties such as flexibility and texture of the coating are close to those of natural rubber, so it is being used as a replacement for natural rubber gloves.

[0004] In the production of rubber gloves, a so-called dip molding method is often used, in which a coagulating liquid is applied to a former, which is then dried, and then the former is immersed in a latex composition to form a rubber coating, thereby obtaining a product. However, when the immersed former is pulled out from the latex composition, there is a problem that the smoothness of the surface is impaired due to dripping or the like.

[0005] Since impairing the surface smoothness can lead to holes, cracks, breaks, etc. in the coating, various methods for improving this have been proposed (see, for example, Patent Documents 2 and 3). However, these methods are limited in the type and glass transition temperature of the polymers that can be used.

[0006] Japanese Patent Publication No. 2017-214593 Japanese Patent Publication No. 2021-116389 Japanese Patent Publication No. 2016-055542

[0007] 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 are suitable for producing dipped products such as gloves by improving the surface smoothness of a dip-molded coating film formed from a chloroprene latex composition used to obtain coated products by dip molding, thereby preventing holes and cracks and maintaining excellent mechanical properties such as breaking strength.

[0008] Under such circumstances, the present inventors have conducted extensive research to solve the above-mentioned problems, and have found that the surface smoothness of a dip-molded coating can be improved by using a chloroprene latex composition containing an alkali metal carboxylate and a nonionic emulsifier having an HLB of 18.1 to 20.0 as an emulsifier.

[0009] That is, the respective aspects of the present invention are the following [1] to [6].

[0010] [1] A chloroprene latex composition containing a chloroprene polymer and an emulsifier, wherein the emulsifier is an alkali metal carboxylate and a nonionic emulsifier having an HLB of 18.1 to 20.0, and the chloroprene latex composition contains 3.0 to 6.0 parts by weight of the alkali metal carboxylate and 0.15 to 0.9 parts by weight of the nonionic emulsifier per 100 parts by weight of the chloroprene polymer.

[0011] [2] The chloroprene latex composition according to [1], wherein the nonionic emulsifier is a nonionic emulsifier represented by the following general formula (1):

[0012] R-O(CH ２ CXHO) ｎ H (1) (wherein 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 within a range that results in an HLB of 18.1 to 20.0 of the nonionic emulsifier.) [3] The chloroprene latex composition according to [1] or [2], which has a pH of 11.0 to 13.5.

[0013] [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].

[0014] [6] A rubber composition comprising the chloroprene latex composition for dip molding according to [5].

[0015] The chloroprene latex composition of the present invention improves the surface smoothness of dip-cast coatings.

[0016] The present invention will be described in detail below.

[0017] A chloroprene latex composition according to one embodiment of the present invention comprises a chloroprene polymer and, as an emulsifier, an alkali metal salt of a carboxylic acid and a nonionic emulsifier having an HLB of 18.1 to 20.0.

[0018] 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 and one or more types of monomers copolymerizable with chloroprene.

[0019] Examples of the monomer 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 the monomer copolymerizable with chloroprene include those obtained by using these in an amount of, for example, 20 parts by weight or less per 100 parts by weight of chloroprene monomer.

[0020] An emulsifier having an alkali metal salt of a carboxylic acid is an emulsifier having a lipophilic group and a hydrophilic group, wherein 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 3.0 to 6.0 parts by weight per 100 parts by weight of the chloroprene polymer in terms of stability in latex blending and balance of adhesive properties.

[0021] The chloroprene latex of the present invention contains a nonionic emulsifier having an HLB of 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 18.0 or less, the surface smoothness of the dip-molded coating of the obtained chloroprene latex composition is poor.

[0022] 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).

[0023] 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 within the range in which the HLB of the nonionic emulsifier is 18.1 to 20.0.) The amount of the nonionic emulsifier used is 0.15 to 0.9 parts by weight, and preferably 0.2 to 0.7 parts by weight, per 100 parts by weight of the chloroprene polymer, in order to balance the surface smoothness and physical properties of the dip coating.

[0024] The pH of the chloroprene latex composition of the present invention is preferably 11.0 to 13.5. This improves dip-moldability. A pH within this range ensures good liquid stability and prevents rubber precipitation during storage or use. A common acid or alkali can be used to adjust the pH, and although there are no particular limitations, hydrochloric acid, sodium hydroxide, potassium hydroxide, etc. are typically diluted with water and added to prevent rubber precipitation.

[0025] The chloroprene latex composition of the present invention preferably contains zinc oxide. By containing zinc oxide, the storage stability of the chloroprene latex composition is improved, and the mechanical properties of the rubber composition, which is a dip-molded coating, are also improved. The amount of zinc oxide used is not limited, but is preferably 1.0 part by weight or more and 10.0 parts by weight or less per 100 parts by weight of the chloroprene polymer.

[0026] If necessary, fillers, reinforcing agents, antioxidants, plasticizers, lubricants, vulcanization accelerators, sulfur, etc., or a dispersion of any of these in water, may be added to the chloroprene latex composition and dip molding may be performed. 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 18.1 to 20.0. The nonionic emulsifier having an HLB of 18.1 to 20.0 may be added during or after the polymerization. The chloroprene latex composition may also be prepared by mixing two or more types of latex.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 50°C.

[0031] There is no particular limitation on the time when the polymerization is to be 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.

[0032] 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.

[0033] The chloroprene latex composition of the present invention is mixed with an antioxidant, a pigment for coloring, and other general fillers such as calcium carbonate, if necessary, and is used for dip molding. A rubber composition containing the chloroprene latex composition for dip molding is suitably used for rubber gloves.

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The pH and surface smoothness were measured by the following methods.

[0035] <pH> Measured using a pH meter (manufactured by Horiba, Ltd.).

[0036] <Surface Smoothness> A ceramic former was preheated at 70°C for 30 minutes, immersed in a coagulating liquid (a 25% aqueous solution of calcium nitrate) for 10 seconds, and then dried at 70°C for 10 minutes. The dried former was then immersed in a chloroprene latex composition for 10 seconds, pulled out, and air-dried at room temperature for 30 minutes or more, and the surface was visually observed.

[0037] ○: The surface is smooth.

[0038] ×: Dripping or unevenness on the surface Example 1 A chloroprene latex was prepared by polymerizing 5 kg of chloroprene monomer, 0.07 part by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Longis K-25, Arakawa Chemical Industries, Ltd.) (4.2 parts by weight per 100 parts by weight of chloroprene polymer), 0.3 part by weight of a condensate of sodium naphthalenesulfonate and formaldehyde (trade name: Demol 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 in a 10 L autoclave equipped with a stirrer at 40°C. The polymerization was carried out under a nitrogen atmosphere by continuously adding dropwise a 0.35 wt% aqueous solution of potassium persulfate, and when the polymerization conversion reached 95%, 0.05 parts by weight of 2,6-tert-butyl-4-methylphenol was added as a polymerization terminator to terminate the polymerization. Thereafter, the solid content of the latex was adjusted to 50% by removing unreacted monomers and water under reduced pressure, thereby obtaining chloroprene latex A.

[0039] To the synthesized chloroprene latex A, 0.5 parts by weight of nonionic emulsifier A (polyoxyethylene decyl ether; product name Noigen XL-400D, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) having an HLB of 18.4 was added per 100 parts by weight of the chloroprene polymer to obtain a chloroprene latex composition. The pH was 12.5. Using this, surface smoothness was evaluated. The results are shown in Table 1. The results in Table 1 indicate that the surface smoothness was good.

[0040]

[0041] Example 2 A chloroprene latex composition was obtained in the same manner as in Example 1, except that the amount of nonionic emulsifier A mixed with latex A was changed to 0.4 parts by weight per 100 parts by weight of the chloroprene polymer, and the surface smoothness was evaluated using this. The results are shown in Table 1. The results in Table 1 showed that the surface smoothness was good.

[0042] Example 3 A chloroprene latex composition was obtained in the same manner as in Example 1, except that the amount of nonionic emulsifier A mixed with latex A was changed to 0.3 parts by weight per 100 parts by weight of the chloroprene polymer, and the surface smoothness was evaluated using this. The results are shown in Table 1. The results in Table 1 showed that the surface smoothness was good.

[0043] Example 4 Chloroprene latex B was obtained in the same manner as in Example 1, except that the monomers used were 4.5 kg of chloroprene monomer and 0.5 kg of 2,3-dichloro-1,3-butadiene, and other additives were weighed out based on a total of 100 parts by weight of the chloroprene monomer and 2,3-dichloro-1,3-butadiene. Then, 0.5 parts by weight of nonionic emulsifier A was added to chloroprene latex B based on 100 parts by weight of the chloroprene copolymer, and a chloroprene latex composition was obtained in the same manner as in Example 1, and the surface smoothness was evaluated using this. The results are shown in Table 1. The results in Table 1 showed that the surface smoothness was good.

[0044] Comparative Example 1 A chloroprene latex composition was obtained in the same manner as in Example 1 except that nonionic emulsifier A was not used, and surface smoothness was evaluated using this composition. The results are shown in Table 1. The results in Table 1 show that the surface smoothness was poor.

[0045] Comparative Example 2 A chloroprene latex composition was obtained in the same manner as in Example 1, except that the amount of nonionic emulsifier A used was changed to 0.1 parts by weight per 100 parts by weight of the chloroprene polymer, and the surface smoothness was evaluated using this composition. The results are shown in Table 1. As can be seen from the results in Table 1, the surface smoothness was poor.

[0046] Comparative Example 3 A chloroprene latex composition was obtained in the same manner as in Example 1, except that the amount of nonionic emulsifier A used was changed to 1.0 part by weight per 100 parts by weight of the chloroprene polymer, and the surface smoothness was evaluated using this composition. The results are shown in Table 1. As can be seen from the results in Table 1, the surface smoothness was poor.

[0047] Comparative Example 4 A chloroprene latex composition was obtained in the same manner as in Example 1, except that nonionic emulsifier B (Noigen XL-140, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used instead of nonionic emulsifier A, and surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. As can be seen from the results in Table 1, the surface smoothness was poor.

[0048] Comparative Example 5 A chloroprene latex composition was obtained in the same manner as in Example 1, except that nonionic emulsifier C (Noigen XL-80, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used instead of nonionic emulsifier A, and surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. As can be seen from the results in Table 1, the surface smoothness was poor.

[0049] Comparative Example 6 A chloroprene latex composition was obtained in the same manner as in Example 1, except that nonionic emulsifier D (Noigen TDS-100, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used instead of nonionic emulsifier A, and surface smoothness was evaluated using the obtained composition. The results are shown in Table 1. As can be seen from the results in Table 1, the surface smoothness was poor.

[0050] The chloroprene latex composition of the present invention is used for dip-molded products and is widely used in the field of rubber products.

[0051] While the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0052] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-192746 filed on November 13, 2023 are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. A chloroprene latex composition comprising a chloroprene polymer and an emulsifier, the emulsifier being an alkali metal carboxylate and a nonionic emulsifier having an HLB of 18.1 to 20.0, the chloroprene latex composition comprising 3.0 to 6.0 parts by weight of the alkali metal carboxylate and 0.15 to 0.9 parts by weight of the nonionic emulsifier per 100 parts by weight of the chloroprene polymer.

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 C.X.H.O. ｎ H (1) (wherein 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 HLB of the nonionic emulsifier 18.1 to 20.0.) 3. The chloroprene latex composition according to claim 1, having a pH of 11.0 to 13.

5.

4. The chloroprene latex composition according to claim 1, further comprising zinc oxide.

5. A chloroprene latex composition for dip molding, comprising the chloroprene latex composition according to claim 1 or 2.

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

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