Chloroprene latex composition

Abstract

Provided is a chloroprene latex composition that has good mechanical properties due to smoothing a film surface during dip molding.　This chloroprene latex composition includes a chloroprene polymer and an emulsifying agent, wherein when X% is the percentage originating from 2,3-dichloro-1,3-butadiene in a peak originating from chloroprene and a peak originating from 2,3-dichloro-1,3-butadiene in a 1H-MAS-NMR spectrum of a sample obtained by drying a latex, said percentage being calculated using expression (I), and Y is the sodium content (ppm) of the latex, the range indicated by expression (II) is satisfied, the potassium content is 3000 ppm or less, and the toluene-insoluble matter is in the range 89-95 wt%.

Description

Chloroprene latex composition

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

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

[0003] Above all, chloroprene rubber has a good balance of mechanical strength, weather resistance, oil resistance, heat resistance, flame retardancy, adhesion and the like, and further various physical properties such as film flexibility and texture are close to those of natural rubber, so substitution for natural rubber gloves is being promoted.

[0004] In the production of rubber gloves, a so-called dip molding method is widely used, in which a coagulating liquid is adhered to a former, dried, and then immersed in a composition obtained by mixing a latex with a compound such as a vulcanization accelerator to form a rubber film and obtain a product. It is known that the compounded vulcanization accelerator also causes allergies, and attempts have been made to produce gloves without using it. However, since unvulcanized rubber generally has inferior mechanical properties, it has been necessary to obtain good film properties without using a vulcanization accelerator.

[0005] Further, for a film obtained by dip molding, if there is thickness unevenness or flow marks (poor processability with residual dripping traces) on the film surface, there is a problem that the film physical properties deteriorate, and good surface smoothness is required to improve the physical properties.

[0006] Japanese Unexamined Patent Publication No. 2017-214593

[0007] The present invention has been made in view of this problem, and an object thereof is to provide a chloroprene latex composition for obtaining a film product by dip molding, which improves the surface smoothness of the film, has excellent mechanical properties such as breaking strength in a formulation that does not use a vulcanization accelerator, and is suitable for producing dip-molded products such as gloves, and a rubber composition.

[0008] Under these circumstances, the inventors diligently investigated the problem and found that, in the ¹H-MAS-NMR spectrum of a sample obtained by drying latex, when the ratio of the peak derived from 2,3-dichloro-1,3-butadiene to the peak derived from chloroprene, calculated using the following formula (I), is X%, and the sodium content of the latex (ppm) is Y, the composition falls within the range shown by the following formula (II), and the potassium content is 3000 ppm or less, and the toluene-insoluble portion is in the range of 89 to 95% by weight, the surface smoothness of the immersion molded body is excellent and the tensile strength is good, even in a formulation without the use of a vulcanization accelerator.

[0009] In other words, the embodiments of the present invention are as follows: [1] to [6].

[0010] [1] A chloroprene latex composition comprising a chloroprene polymer and an emulsifier, wherein, in the ¹H-MAS-NMR spectrum of a sample obtained by drying the latex, the ratio of the peak derived from 2,3-dichloro-1,3-butadiene to the peak derived from chloroprene, calculated using the following formula (I), is within the range shown by the following formula (II), where X is the ratio of the peak derived from 2,3-dichloro-1,3-butadiene to the peak derived from chloroprene, and Y is the sodium content (ppm) of the latex, and the potassium content is 3000 ppm or less, and the toluene-insoluble portion is in the range of 89 to 95% by weight.

[0011] [Formula I] Formula for calculating X when the areas of each peak in the 1H-MAS-NMR spectrum are (A) to (E): X (%) = (2A - B - 8C + 14D + 9E) × 100 / (2A + 3B + 6D + 5E) (A): Peak area of ​​2.0 to 3.3 ppm (B): Peak area of ​​5.0 to 5.3 ppm (C): Peak area of ​​5.3 to 5.7 ppm (D): Peak area of ​​5.7 to 5.8 ppm (E): Peak area of ​​5.8 to 6.0 ppm [Formula II] Y ≥ -100X + 2550 (where the ranges of X and Y are 7 ≤ X ≤ 20 and Y ≤ 3000.) [2] The chloroprene latex composition described in [1], wherein the pH is 11.0 to 13.5.

[0012] [3] A chloroprene latex composition according to [1] or [2], which does not contain a vulcanization accelerator. [4] A chloroprene latex composition according to any one of [1] to [3], which further contains zinc oxide.

[0013] [5] A chloroprene latex composition for immersion molding, characterized by comprising the chloroprene latex composition described in any of [1] to [4].

[0014] [6] A rubber composition comprising the chloroprene latex composition for immersion molding described in [5].

[0015] The chloroprene latex composition of the present invention reduces the amount of precipitate in the compounding solution, and the immersion molded product produced using a formulation without a vulcanization accelerator has good mechanical properties.

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

[0017] One embodiment of the present invention is a chloroprene latex composition comprising a chloroprene polymer, an alkali metal salt of a carboxylic acid as an emulsifier, and a nonionic emulsifier.

[0018] The chloroprene polymer may be a polymer of chloroprene, which is 2-chloro-1,3-butadiene, or a copolymer obtained by polymerizing a monomer of chloroprene with one or more monomers copolymerizable with chloroprene.

[0019] 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. These can be used, for example, in amounts of 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 one that has a lipophilic group and a hydrophilic group, with the hydrophilic group being 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 rosinic acid, alkali metal salts of fatty acids, alkali metal salts of alkenyl succinic acid, and polymer compounds of alkali metal salts of polycarboxylic acids. Examples of alkali metal salts include lithium, sodium, potassium, and cesium. These may be present individually or in combination of two or more. From the viewpoint of polymerization stability and adhesive performance, an alkali metal salt of rosinic acid is preferred, and a potassium salt of rosinic acid is more preferred. The content of this emulsifier is not particularly limited, but from the perspective of stability in latex formulation and balance with adhesive properties, it is preferably 3.0 to 6.0 parts by weight per 100 parts by weight of chloroprene polymer.

[0021] Nonionic emulsifiers have an HLB (Hydrophilic Balance) index indicating the balance between lipophilicity and hydrophilicity. This is calculated by dividing the molecular weight of the hydrophilic portion by the molecular weight of the emulsifier and multiplying by 20. If the HLB is 18.0 or less, the surface smoothness of the immersion-molded film of the resulting chloroprene latex composition is poor.

[0022] Nonionic emulsifiers include ester-type and ether-type, and are not particularly limited, but ether-type is preferred, and more preferably an ether-type nonionic emulsifier represented by the following general formula (1) is preferred.

[0023] R-O(CH ２ CXHO) ｎH (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 in which the HLB of the nonionic emulsifier is 18.1 to 20.0.) The content of the nonionic emulsifier is preferably 0.15 parts by weight or more and 0.9 parts by weight or less per 100 parts by weight of chloroprene polymer, and more preferably 0.2 parts by weight or more and 0.7 parts by weight or less, in order to balance the surface smoothness and physical properties of the immersed film.

[0024] ¹H-MAS-NMR spectroscopy is a common method for structural analysis of organic compounds. This method allows for the analysis of the microstructure of polymers, and the molar ratio of each microstructure corresponds to the peak area in the ¹H-MAS-NMR spectrum. The microstructure of chloroprene polymer consists of 1,4-bonds, 1,2-bonds, and 3,4-bonds, while the microstructure of 2,3-dichloro-1,3-butadiene polymer consists of 1,4-bonds and 1,2-bonds. In the ¹H-MAS-NMR spectrum of a sample obtained by drying a chloroprene latex composition, the ratio X% of the peaks derived from 2,3-dichloro-1,3-butadiene compared to the peaks derived from chloroprene is shown by the following formula (I). [Formula I] X (%) = (2A - B - 8C + 14D + 9E) × 100 / (2A + 3B + 6D + 5E) (A): Peak area from 2.0 to 3.3 ppm (B): Peak area from 5.0 to 5.3 ppm (C): Peak area from 5.3 to 5.7 ppm (D): Peak area from 5.7 to 5.8 ppm (E): Peak area from 5.8 to 6.0 ppm The peak area from 2.0 to 3.3 ppm in (A) includes signals originating from the hydrogen of -CH2- in the 1,4-bond in chloroprene polymer, signals from the hydrogen of -CH- in the 3,4-bond, signals originating from the hydrogen of -CH2- in the 1,4-bond in 2,3-dichloro-1,3-butadiene polymer, and signals originating from one of the two hydrogens of -CH2- in the 1,2-bond.

[0025] The peak area of ​​5.0–5.3 ppm in (B) includes signals originating from one of the two hydrogen atoms of =CH2 in the 1,2-bond in the chloroprene polymer and signals originating from the hydrogen of =CH2 in the 3,4-bond.

[0026] The peak area of ​​5.3–5.7 ppm in (C) includes signals originating from the hydrogen of =CH- in the 1,4-bond in chloroprene polymer, signals originating from one of the two hydrogens of =CH2 in the 1,2-bond, and signals originating from one of the two hydrogens of =CH2 in the 1,2-bond in 2,3-dichloro-1,3-butadiene polymer.

[0027] The peak area of ​​5.7–5.8 ppm in (D) contains a signal originating from one of the two hydrogen atoms in the =CH2 bond at the 1,2-bond in the 2,3-dichloro-1,3-butadiene polymer.

[0028] The peak area of ​​(E) between 5.8 and 6.0 ppm contains signals originating from the hydrogen atoms in the -CH= 1,2-bond in the chloroprene polymer.

[0029] In other words, by performing C-E-D, the 1,2-bonded component in the 2,3-dichloro-1,3-butadiene polymer contained in C is eliminated by D, and the 1,2-bonded component in the chloroprene polymer is eliminated by E, which is also derived from 1,2-bonds and present in the same amount. Therefore, the relative amount of 1,4-bonds in the chloroprene polymer can be represented.

[0030] Furthermore, E can represent the relative amount of 1,2-bonds in the chloroprene polymer.

[0031] Furthermore, by performing (B - E) / 2, the 1,2-bonded components in the chloroprene polymer contained in B can be eliminated by E, which is also derived from 1,2-bonded structures and is present in the same amount. Therefore, the relative amount of 3,4-bonded structures in the chloroprene polymer can be expressed.

[0032] Therefore, the relative amount of chloroprene polymer can be expressed as (B + 2C - 2D - E) / 2, which is the sum of the relative amounts of each microstructure.

[0033] Similarly, the relative amount of 1,4-bonds in the 2,3-dichloro-1,3-butadiene polymer can be expressed by (A - (C - E - D) × 4 - (B - E) / 2 - D) / 4.

[0034] Furthermore, D can represent the relative amount of 1,2-bonds in the 2,3-dichloro-1,3-butadiene polymer.

[0035] Therefore, the relative amount of 2,3-dichloro-1,3-butadiene polymer can be expressed as (2A-B-8C+14D+9E) / 8, which is the sum of each microstructure.

[0036] From the above, the proportion X% derived from 2,3-dichloro-1,3-butadiene in the sample obtained by drying the chloroprene latex composition is calculated by (relative amount of 2,3-dichloro-1,3-butadiene polymer) × 100 / (relative amount of chloroprene polymer and 2,3-dichloro-1,3-butadiene polymer), and is shown by formula (I).

[0037] Regarding the relationship between the content ratio of 2,3-dichloro-1,3-butadiene in the chloroprene polymer and the amount of sodium in the chloroprene latex composition, in the 1H-MAS-NMR spectrum of a sample obtained by drying the latex, if the ratio of the peak derived from 2,3-dichloro-1,3-butadiene to the peak derived from chloroprene calculated by formula (I) is X%, and the sodium content of the latex (ppm) is Y, then when X and Y are within the range shown by formula (II), and the potassium content is 3000 ppm or less, the immersion molded body exhibits a stable rate of film deposition, and a film with good surface smoothness can be obtained. By adjusting the 2,3-dichloro-1,3-butadiene ratio, an immersion molded body with good tensile strength can be obtained while maintaining elongation and modulus.

[0038] The toluene-insoluble portion of the chloroprene latex composition is in the range of 89 to 95% by weight. If it is less than 89% by weight, the tensile strength of the immersion-molded film is poor due to insufficient crosslinking of molecular chains, and if it is more than 95% by weight, the tensile properties are poor due to excessive crosslinking of molecular chains.

[0039] The pH of the chloroprene latex composition is preferably 11.0 to 13.5. This improves the immersion moldability. Within this pH range, the liquid has good stability, and rubber does not precipitate during storage or use. For pH adjustment, any common acid or alkali can be used, and there are no particular limitations, but it is common to add hydrochloric acid, sodium hydroxide, potassium hydroxide, etc., diluted with water to prevent rubber precipitation.

[0040] The chloroprene latex composition preferably contains zinc oxide. The inclusion of zinc oxide improves the storage stability of the chloroprene latex composition and also improves the mechanical properties of the rubber composition, which is a dipping-molded film. The amount of zinc oxide used is not limited, but it is preferably 1.0 part by weight to 10.0 parts by weight, and more preferably 2 to 7 parts by weight, per 100 parts by weight of chloroprene polymer.

[0041] Furthermore, if necessary, fillers, reinforcing agents, antioxidants, plasticizers, lubricants, vulcanization accelerators, sulfur, etc., or dispersions thereof in water, may be added to the chloroprene latex composition and immersion molding may be performed. The chloroprene latex composition can be synthesized using a monomer of chloroprene or a monomer copolymerizable with a monomer of chloroprene and chloroprene, an emulsifier having an alkali metal salt of a carboxylic acid, and a nonionic emulsifier with an HLB of 18.1 to 20.0. The nonionic emulsifier with an HLB of 18.1 to 20.0 may be added during or after polymerization. In addition, two or more types of latex can be mixed to form a chloroprene latex composition.

[0042] For example, a method for synthesizing chloroprene latex involves using the monomers and emulsifiers containing alkali metal salts of carboxylic acids as described above, along with polymerization initiators, chain transfer agents, and other stabilizers, to carry out polymerization at a predetermined temperature, and then adding a polymerization termination agent at a predetermined polymerization conversion rate to stop the polymerization.

[0043] As the polymerization initiator, known free radical substances can be used, for example, peroxides such as potassium persulfate and ammonium persulfate, and inorganic or organic peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide. In addition, these may be used alone or in a redox system used in combination with reducing substances such as thiosulfate, hydrosulfite, organic amines, etc.

[0044] Examples of the chain transfer agent include molecular weight regulators such as alkyl mercaptans, halogenated hydrocarbons, alkyl xanthogen disulfides, and sulfur. Among these, n-dodecyl mercaptan is preferable from the viewpoints of odor and workability.

[0045] The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 40°C, and more preferably in the range of 15 to 35°C.

[0046] The timing of terminating polymerization is not particularly limited, but from the viewpoint of productivity, it is preferable to carry out polymerization until the monomer conversion rate is 70% or more, more preferably 85% or more.

[0047] The polymerization terminator is not particularly limited as long as it is a commonly used terminator, and for example, phenothiazine, 2,6-di-tert-butyl-4-methylphenol, hydroxylamine, etc. can be used.

[0048] The chloroprene latex composition is mixed with anti-aging agents, pigments for coloring, and other general fillers such as calcium carbonate as necessary, and is used for dip molding. A rubber composition containing the chloroprene latex composition for dip molding is suitably used for rubber gloves.

[0049] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to only these examples. pH and surface smoothness were measured by the following methods.

[0050] <1H-MAS-NMR Measurement> As preparation before measurement, 5 g of chloroprene polymer latex is weighed onto a petri dish, air-dried in a fume hood for one day, and then dried under reduced pressure at 50°C for 2 hours. 2 g of the dried sample is placed in a beaker containing 50 mL of ethanol and left to stand for 48 hours. After that, the sample is removed, washed with ethanol, and then dried under reduced pressure at 50°C for 48 hours to complete the preparation before measurement. The prepared sample is punched out in a circular shape and packed into the sample tube to be used for measurement. For the spectrum after measurement, the peak top in the 2.0–3.3 ppm region of the chloroprene polymer is set to 2.4 ppm, and the peak area in the regions (A) to (E) in equation (I) is analyzed.

[0051] <Measurement conditions for 1H-MAS-NMR measurement> 1H-MAS-NMR was performed under the following measurement conditions.

[0052] • Measurement frequency: 700 MHz • Measured nuclide: 1H • Pulse width: 3.0 μs • Number of integrations: 1024 • Rotation frequency: 24 kHz <Potassium and sodium amounts> The sample was wet-decomposed with sulfuric acid and nitric acid, and then quantified by ICP-AES.

[0053] <pH> Measured using a pH meter (manufactured by Horiba, Ltd.).

[0054] <Toluene-Insoluble Portion> The amount of toluene-insoluble portion in the chloroprene polymer was calculated by adjusting the pH of the chloroprene polymer latex to 6.0 with acetic acid, freeze-drying it, removing water-soluble components such as emulsifiers by washing with water, and then heat-drying the resulting polymer. The polymer was weighed, stirred and immersed in toluene for more than 20 hours to a concentration of 1%, and the insoluble portion filtered through a 200-mesh wire mesh was weighed and the amount was calculated from the ratio.

[0055] <Surface Smoothness> A ceramic former was preheated at 70°C for 30 minutes, immersed in a coagulation solution (30% calcium nitrate aqueous solution) for 10 seconds, and then dried at 70°C for 10 minutes. After that, the dried former was immersed in a chloroprene latex composition for immersion molding for 20 seconds, removed, and air-dried at room temperature for 30 minutes or more, and the surface was visually observed.

[0056] ○: The surface is smooth.

[0057] ×: Dripping or uneven surface <Immersion molding> A ceramic former was preheated at 70°C for 30 minutes, immersed in a coagulation solution (30% calcium nitrate aqueous solution) for 10 seconds, and then dried at 70°C for 10 minutes. After that, the dried former was immersed in a chloroprene latex composition for immersion molding for 20 seconds, removed and air-dried at room temperature for 30 minutes or more, and then heated at 130°C for 40 minutes to produce a coating.

[0058] <Physical Properties under Normal Conditions> The coating obtained by the immersion molding operation was peeled off the former to form a sheet, and a dumbbell-shaped C-type test specimen was prepared in accordance with ASTM D-412. The tensile strength at fracture was measured under conditions of a tensile speed of 500 mm / min and 23°C.

[0059] Example 1 Chloroprene latex was prepared by polymerizing 4.6 kg of chloroprene monomer and 0.4 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 20°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.4 parts by weight of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), 0.2 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. Polymerization was stopped at a polymerization conversion rate of 90% by adding 0.05 wt parts of 2,6-tert-butyl-4-methylphenol as a polymerization stopper. This was designated as latex A. Subsequently, 0.3 wt parts of sodium hydroxide, 1 wt part of potassium rosinate, 0.7 wt parts of a condensate of sodium naphthalene sulfonate and formaldehyde, and 0.5 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The pH was 12.8, and the toluene-insoluble portion was 89 wt%. Furthermore, a zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Industries Co., Ltd.) was mixed with 100 parts by weight of chloroprene polymer so that the zinc oxide content was 5 parts by weight on a pure content basis, thereby obtaining a chloroprene latex composition for immersion molding. An immersion molded body was prepared using this composition, and its surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. From the results in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0060]

[0061] Example 2 Chloroprene latex was prepared by polymerizing 4.4 kg of chloroprene monomer and 0.6 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 5 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.3 parts by weight of a copolymer of sodium styrenesulfonate and methacrylic acid, 0.5 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. When the polymerization conversion rate reached 90%, 0.05 wt parts of 2,6-tert-butyl-4-methylphenol were added as a polymerization stopper to halt the polymerization. Subsequently, 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The pH was 12.8, and the toluene-insoluble portion was 89 wt%. In addition, zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100 wt parts of chloroprene polymer so that the zinc oxide content was 5 wt parts on a pure content basis to obtain a chloroprene latex composition for immersion molding. Immersion molded bodies were prepared using this composition, and the surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. As shown in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0062] In Example 3, the surface smoothness and normal physical properties were evaluated in the same manner as in Example 2, except that n-dodecyl mercaptan was changed to 0.02 parts by weight. The results are shown in Table 1. From the results in Table 1, the surface smoothness was good and the normal physical properties were also good.

[0063] Example 4 Chloroprene latex was prepared by polymerizing 4.1 kg of chloroprene monomer and 0.9 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 5 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.3 parts by weight of a copolymer of sodium styrenesulfonate and methacrylic acid, 0.5 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. When the polymerization conversion rate reached 90%, 0.05 wt parts of 2,6-tert-butyl-4-methylphenol were added as a polymerization stopper to halt the polymerization. Subsequently, 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The toluene-insoluble portion was 89 wt%. In addition, zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100 wt parts of chloroprene polymer so that the zinc oxide content was 5 wt parts on a pure basis to obtain a chloroprene latex composition for immersion molding. Immersion molded bodies were prepared using this composition, and the surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. As shown in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0064] Example 5 Chloroprene latex was prepared by polymerizing 4.4 kg of chloroprene monomer and 0.6 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of chloroprene monomer and 2,3-dichloro-1,3-butadiene total, using 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.4 parts by weight of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), 0.2 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. When the polymerization conversion rate reached 90%, 0.05 wt parts of 2,6-tert-butyl-4-methylphenol were added as a polymerization stopper to halt the polymerization. Subsequently, 0.3 wt parts of sodium hydroxide, 1 wt part of potassium rosinate, 0.7 wt parts of a condensate of sodium naphthalene sulfonate and formaldehyde, and 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The pH was 12.8, and the toluene-insoluble portion was 89 wt. Furthermore, a zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Industries Co., Ltd.) was mixed with 100 parts by weight of chloroprene polymer so that the zinc oxide content was 5 parts by weight on a pure content basis, thereby obtaining a chloroprene latex composition for immersion molding. An immersion molded body was prepared using this composition, and its surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. From the results in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0065] Example 6 Chloroprene latex was prepared by polymerizing 4.1 kg of chloroprene monomer and 0.9 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.4 parts by weight of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), 0.2 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. When the polymerization conversion rate reached 90%, 0.05 wt parts of 2,6-tert-butyl-4-methylphenol were added as a polymerization stopper to halt the polymerization. Subsequently, 0.3 wt parts of sodium hydroxide, 1 wt part of potassium rosinate, 0.7 wt parts of a condensate of sodium naphthalene sulfonate and formaldehyde, and 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The pH was 12.8, and the toluene-insoluble portion was 89 wt. Furthermore, a zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Industries Co., Ltd.) was mixed with 100 parts by weight of chloroprene polymer so that the zinc oxide content was 5 parts by weight on a pure content basis, thereby obtaining a chloroprene latex composition for immersion molding. An immersion molded body was prepared using this composition, and its surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. From the results in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0066] Example 7 Chloroprene latex was prepared by polymerizing 3.9 kg of chloroprene monomer and 1.1 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.4 parts by weight of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), 0.2 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. Polymerization was stopped at a polymerization conversion rate of 90% by adding 0.05 wt parts of 2,6-tert-butyl-4-methylphenol as a polymerization stopper. Subsequently, 1 wt part of potassium rosinate, 0.7 wt parts of a condensate of sodium naphthalene sulfonate and formaldehyde, and 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The toluene-insoluble portion was 89 wt%. In addition, zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100 wt parts of chloroprene polymer so that the zinc oxide content was 5 wt parts on a pure basis to obtain a chloroprene latex composition for immersion molding. Using this, immersion-molded bodies were produced, and their surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. From the results in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0067] Example 8 Chloroprene latex was prepared by polymerizing 3.9 kg of chloroprene monomer and 1.1 kg of 2,3-dichloro-1,3-butadiene in a 10 L autoclave with a stirrer at 25°C with 100 parts by weight of the total of chloroprene monomer and 2,3-dichloro-1,3-butadiene, using 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.3 parts by weight of a copolymer of sodium styrenesulfonate and methacrylic acid, 0.5 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. When the polymerization conversion rate reached 90%, 0.05 wt parts of 2,6-tert-butyl-4-methylphenol were added as a polymerization stopper to halt the polymerization. Subsequently, 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The toluene-insoluble portion was 89 wt%. In addition, zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100 wt parts of chloroprene polymer so that the zinc oxide content was 5 wt parts on a pure basis to obtain a chloroprene latex composition for immersion molding. Immersion molded bodies were prepared using this composition, and the surface smoothness and normal physical properties were evaluated. The results are shown in Table 1. As shown in Table 1, the surface smoothness was good, and the normal physical properties were also good.

[0068] Comparative Example 1 The surface smoothness and normal physical properties were evaluated in the same manner as in Example 1, except that the amount of sodium hydroxide added to latex A described in Example 1 was changed to 0 parts by weight. The results are shown in Table 2. From the results in Table 2, the surface smoothness was inferior and the tensile strength of the film was low.

[0069]

[0070] Comparative Example 2 The surface smoothness and normal physical properties were evaluated in the same manner as in Example 1, except that the amount of sodium hydroxide added to latex A described in Example 1 was changed to 0.1 parts by weight. The results are shown in Table 2. From the results in Table 2, the surface smoothness was inferior and the tensile strength of the film was low.

[0071] Comparative Example 3 The surface smoothness and normal physical properties were evaluated in the same manner as in Example 1, except that the amount of sodium hydroxide added to latex A described in Example 1 was changed to 0.2 parts by weight. The results are shown in Table 2. From the results in Table 2, the tensile strength of the film was good, but the surface smoothness was poor.

[0072] Comparative Example 4: 4.6 kg of chloroprene monomer and 0.4 kg of 2,3-dichloro-1,3-butadiene were used. To a total of 100 parts by weight of chloroprene monomer and 2,3-dichloro-1,3-butadiene, 0.04 parts by weight of n-dodecyl mercaptan, 5 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.3 parts by weight of a copolymer of sodium styrenesulfonate and methacrylic acid, 0.5 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water were used to polymerize the mixture in a 10 L autoclave with a stirrer at 25°C to produce chloroprene latex. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. Polymerization was stopped at a polymerization conversion rate of 90% by adding 0.05 wt parts of 2,6-tert-butyl-4-methylphenol as a polymerization stopper. Subsequently, 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name Neugen XL-400D: manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The toluene-insoluble portion was 89 wt%. In addition, zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Kogyo Co., Ltd.) was mixed with 100 wt parts of chloroprene polymer so that the zinc oxide content was 5 wt parts on a pure basis to obtain a chloroprene latex composition for immersion molding. Immersion molded bodies were prepared using this composition, and the surface smoothness and normal physical properties were evaluated. The results are shown in Table 2. As shown in Table 2, the surface smoothness was good, but the normal physical properties were poor.

[0073] Comparative Example 5: 4.1 kg of chloroprene monomer and 0.9 kg of 2,3-dichloro-1,3-butadiene were used. To a total of 100 parts by weight of chloroprene monomer and 2,3-dichloro-1,3-butadiene, 0.04 parts by weight of n-dodecyl mercaptan, 4 parts by weight of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.4 parts by weight of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), 0.2 parts by weight of sodium hydroxide, 0.01 parts by weight of sodium hydrosulfite, and 80 parts by weight of pure water were used to polymerize the mixture at 25°C in a 10 L autoclave with a stirrer to produce chloroprene latex. Polymerization was carried out by continuously adding a 0.35 wt% aqueous potassium persulfate solution dropwise under a nitrogen atmosphere. Polymerization was stopped when the polymerization conversion rate reached 90% by adding 0.05 wt parts of 2,6-tert-butyl-4-methylphenol as a polymerization stopper. Subsequently, 1 wt part of potassium rosinate (trade name: Rondis® K-25, Arakawa Chemical Industries, Ltd.), 0.7 wt parts of a condensate of sodium naphthalene sulfonate and formaldehyde (trade name: Demol® N, Kao Corporation), and 0.4 wt parts of a nonionic emulsifier (polyoxyethylene decyl ether; product name: Neugen XL-400D, manufactured by Daiichi Kogyo Seiyaku) were added, and the solid content of the latex was adjusted to 50 wt% by removing unreacted monomers and water under reduced pressure. The toluene-insoluble portion was 89 wt%. Furthermore, a zinc oxide emulsion (product name AZ-SW, manufactured by Osaki Industries Co., Ltd.) was mixed with 100 parts by weight of chloroprene polymer so that the zinc oxide content was 5 parts by weight on a pure content basis, to obtain a chloroprene latex composition for immersion molding. An immersion molded body was prepared using this composition, and its surface smoothness and normal physical properties were evaluated. The results are shown in Table 2. From the results in Table 2, the normal physical properties were good, but the surface smoothness was poor.

[0074] Comparative Example 6: Surface smoothness and normal physical properties were evaluated in the same manner as in Example 1, except that n-dodecyl mercaptan was changed to 0.07 parts by weight. The results are shown in Table 2. From the results in Table 2, the surface smoothness was good, but the normal physical properties were poor.

[0075] Although 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 essence and scope of the invention.

[0076] Furthermore, the entire contents of the specifications, claims, and abstracts of Japanese Patent Application No. 2025-031992, filed on February 28, 2025, and Japanese Patent Application No. 2025-181122, filed on October 27, 2025, are incorporated herein by reference as disclosures of the present invention.

[0077] The chloroprene latex composition of the present invention is used in dipping molded products and is widely used in the rubber products field.

Claims

1. A chloroprene latex composition comprising a chloroprene polymer and an emulsifier, wherein, in the 1H-MAS-NMR spectrum of a sample obtained by drying the latex, the ratio of the peak derived from 2,3-dichloro-1,3-butadiene to the peak derived from chloroprene, calculated using the following formula (I), is X%, and the sodium content of the latex (ppm) is Y, such that X and Y are within the range shown by the following formula (II), the potassium content is 3000 ppm or less, and the toluene-insoluble portion is in the range of 89 to 95% by weight. [Formula I] Formula for finding X when the area of ​​each peak in the 1H-MAS-NMR spectrum is (A) to (E): X (%) = (2A - B - 8C + 14D + 9E) × 100 / (2A + 3B + 6D + 5E) (A): Peak area from 2.0 to 3.3 ppm (B): Peak area from 5.0 to 5.3 ppm (C): Peak area from 5.3 to 5.7 ppm (D): Peak area from 5.7 to 5.8 ppm (E): Peak area from 5.8 to 6.0 ppm [Formula II] Y ≥ -100X + 2550 (However, the ranges of X and Y are 7 ≤ X ≤ 20 and Y ≤ 3000.) 2. The chloroprene latex composition according to claim 1, wherein the pH is 11.0 to 13.

5.

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

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

5. A chloroprene latex composition for immersion molding, characterized by comprising the chloroprene latex composition described in any one of claims 1 to 4.

6. A rubber composition comprising the chloroprene latex composition for immersion molding described in claim 5.

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