Chloroprene polymer latex and dip-molded products

Abstract

The present invention provides a chloroprene polymer latex which enables the achievement of a dip-molded article of a chloroprene polymer, the dip-molded article having a sufficient tensile strength at break and excellent texture. The present invention provides a chloroprene polymer latex which contains a chloroprene polymer, wherein: the apparent hardness of a dip-molded article film, which contains the chloroprene polymer latex and has a thickness of 0.60 ± 0.10 mm, is 25.0 IRHD to 40.0 IRHD as measured at 23°C using a Wallace automatic microhardness meter; the dip-molded article film that has a thickness of 0.60 ± 0.10 mm is obtained by stacking a plurality of dip-molded article films that have a thickness of 0.15 mm to 0.25 mm; the dip-molded article films that have a thickness of 0.15 mm to 0.25 mm are obtained by subjecting dip-molded films, which are obtained by dipping ceramic molds to which a calcium-based coagulating solution has been adhered into a chloroprene polymer latex composition that contains the chloroprene polymer latex by means of a dipping coagulation method, to a heat drying process at 150°C for 60 minutes.

Description

[Technical Field]

[0001] The present invention relates to a chloroprene polymer latex and a dip-molded article, more particularly to a chloroprene polymer latex containing a chloroprene polymer and a dip-molded article obtained using a chloroprene polymer latex composition. [Background technology]

[0002] Chloroprene polymers are known as materials for dip-molded products such as medical surgical gloves, medical examination gloves, industrial gloves, balloons, catheters, and rubber boots.

[0003] Various techniques have been proposed for improving the flexibility of chloroprene polymers by using chloroprene polymer latexes for dip-molded products and for dip-molded products of chloroprene polymers. Patent Document 1 describes a polychloroprene latex with a pH of 7 to 14 for use in dip-molded products, which contains 100 parts by mass of modified polychloroprene obtained by copolymerizing chloroprene and methacrylic acid, 90 to 150 parts by mass of water, 1 to 5 parts by mass of an emulsifier, and 0.5 to 2.5 parts by mass of potassium ions. Patent Document 2 describes a mercaptan-modified polychloroprene latex for use in dip-molded products, obtained by copolymerizing chloroprene and 2,3-dichloro-1,3-butadiene, such that in the C-solid-state NMR spectrum of the polychloroprene, the peak areas (A) at 126.2 to 127.6 ppm, (B) at 122.0 to 126.2 ppm, and (C) at 129.9 to 130.3 ppm are within the ranges shown by the following general formula (I). Patent Document 3 describes a chloroprene polymer latex for use in dip-molded products, which contains both high-molecular-weight and low-molecular-weight components, thereby achieving excellent flexibility and mechanical properties in the vulcanized rubber produced by dip molding. Patent Document 4 describes a chloroprene polymer latex that exhibits excellent flexibility and mechanical properties even under mild vulcanization conditions, obtained by copolymerizing chloroprene monomer with isoprene monomer, a raw material for isoprene rubber.

[0004]

number

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-114342 [Patent Document 2] International Publication No. 2019 / 009038 [Patent Document 3] Japanese Patent Application Publication No. 2019-143002 [Patent Document 4] International Publication No. 2021-132460 Summary of the Invention [Problem to be solved by the invention]

[0006] Chloroprene polymer latex has been used as a rubber latex raw material for coatings of dip-molded products such as gloves, balloons, boots, catheters, etc. In particular, in the application to medical rubber gloves, high flexibility similar to that of dip-molded products obtained using natural rubber or polyisoprene tends to be required, and there has been a demand for the development of a chloroprene polymer latex that can give a dip-molded product having excellent texture when made into a dip-molded film.

[0007] Therefore, a main object of the present invention is to provide a chloroprene polymer latex that can give a dip-molded product of a chloroprene polymer having sufficient tensile strength at break and excellent texture. [Means for solving the problem]

[0008] According to the present invention, there is provided a chloroprene polymer latex containing a chloroprene polymer, wherein the apparent hardness of a dip-molded film containing the chloroprene polymer latex and having a thickness of 0.60±0.10 mm, as measured at 23°C using a Wallace micro automatic hardness tester, is 25.0 IRHD or more and 40.0 IRHD or less, The dip-molded film having a thickness of 0.60±0.10 mm is obtained by stacking a plurality of dip-molded films having a thickness of 0.15 to 0.25 mm, The dip-molded film having a thickness of 0.15 to 0.25 mm is obtained by a dip-coagulation method in which a ceramic mold having a calcium-based coagulation liquid attached thereto is immersed in a chloroprene polymer latex composition containing the chloroprene polymer latex to form a dip-molded film, and then the dip-molded film is subjected to a heat drying treatment at 150°C for 60 minutes. A chloroprene-based polymer latex is provided.

[0009] Various embodiments of the present invention will be described below as examples, and the embodiments described below can be combined with each other. Preferably, the above-described chloroprene polymer latex has at least a peak corresponding to a weight average molecular weight of 3,000 to 80,000 detected when the chloroprene polymer latex is freeze-dried, dissolved in tetrahydrofuran, and the soluble matter is subjected to gel permeation chromatography. Preferably, the above-described chloroprene polymer latex contains 2,3-dichloro-1,3-butadiene monomer units. Preferably, the above-described chloroprene polymer latex contains 1 to 25 mass% of 2,3-dichloro-1,3-butadiene monomer units relative to 100 mass% in total of chloroprene monomer units and 2,3-dichloro-1,3-butadiene monomer units. Preferably, the chloroprene polymer latex described above has a toluene-insoluble content of 45 to 85% by mass of the solid content obtained by freeze-drying the chloroprene polymer latex.

[0010] According to another aspect of the present invention, there is provided a dip-molded product using the above-described chloroprene polymer latex. Preferably, the dip moldings described above contain a metal oxide and an antioxidant. Preferably, the dip-molded article is an industrial or general household glove, a medical glove, a balloon, a catheter or a boot.

[0011] In the present invention, "JIS" means Japanese Industrial Standards. [Effects of the Invention]

[0012] According to the present invention, there is provided a chloroprene polymer latex from which a dip-molded product of a chloroprene polymer having sufficient tensile strength at break and excellent softness and texture can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments. However, the present invention is not limited to the preferred embodiments described below.

[0014] 1. Chloroprene polymer latex First, a chloroprene polymer latex according to one embodiment of the present invention will be described.

[0015] 1.1 Chloroprene polymers The chloroprene polymer described in this embodiment is a polymer containing monomer units derived from 2-chloro-1,3-butadiene (hereinafter also referred to as chloroprene). Furthermore, the chloroprene polymer according to one embodiment of the present invention may be a copolymer of chloroprene and another monomer copolymerizable with chloroprene. Examples of the other monomer include 1-chloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, isoprene, styrene, methacrylic acid, acrylonitrile, and sulfur. Two or more of these may be used in combination. The chloroprene polymer according to one embodiment of the present invention preferably contains monomer units derived from 2,3-dichloro-1,3-butadiene. The chloroprene polymer according to one embodiment of the present invention may be sulfur-free, or the chloroprene polymer according to one embodiment of the present invention may be free of an -SS- structure due to sulfur in the main chain.

[0016] The chloroprene polymer according to one embodiment of the present invention may be obtained by blending two or more different chloroprene polymers. The chloroprene polymer contains at least one selected from the group consisting of a homopolymer of chloroprene (2-chloro-1,3-butadiene), a copolymer of chloroprene and 1-chloro-1,3-butadiene, a copolymer of chloroprene and 2,3-dichloro-1,3-butadiene, and a copolymer of chloroprene, 1-chloro-1,3-butadiene, and 2,3-dichloro-1,3-butadiene, and more preferably contains at least one of a homopolymer of chloroprene and a copolymer of chloroprene and 2,3-dichloro-1,3-butadiene.

[0017] A chloroprene polymer according to one embodiment of the present invention may contain 50 to 100 mass% of chloroprene-derived monomer units, preferably 70 to 100 mass%, of chloroprene-derived monomer units, based on 100 mass% of the chloroprene polymer contained in the chloroprene polymer latex composition. The content of the chloroprene-derived monomer units may be, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 mass%, or may be within a range between any two of the values ​​exemplified here.

[0018] A chloroprene polymer according to one embodiment of the present invention may contain 1 to 25 mass% of monomer units derived from 2,3-dichloro-1,3-butadiene, where the total of chloroprene monomer units and 2,3-dichloro-1,3-butadiene monomer units in the chloroprene polymer contained in the chloroprene polymer latex composition is 100 mass%. The content of the monomer units derived from 2,3-dichloro-1,3-butadiene is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 mass%, and may be within a range between any two of the values ​​exemplified here.

[0019] A chloroprene-based polymer according to one embodiment of the present invention may contain monomer units derived from chloroprene and monomer units derived from 2,3-dichloro-1,3-butadiene, or may consist of monomer units derived from chloroprene and monomer units derived from 2,3-dichloro-1,3-butadiene.

[0020] When the chloroprene polymer is a mixture of two or more different chloroprene polymers, the content of each monomer unit means the total amount of each monomer unit in all chloroprene polymers contained in the chloroprene polymer latex.

[0021] 1.2 Chloroprene polymer latex The chloroprene polymer latex according to one embodiment of the present invention may be a chloroprene polymer dispersed in water, and may be at least one selected from the group consisting of a chloroprene homopolymer, a copolymer of chloroprene and 1-chloro-1,3-butadiene, a copolymer of chloroprene and 2,3-dichloro-1,3-butadiene, and a copolymer of chloroprene, 1-chloro-1,3-butadiene, and 2,3-dichloro-1,3-butadiene dispersed in water, or may be a chloroprene homopolymer or a copolymer of chloroprene and 2,3-dichloro-1,3-butadiene dispersed in water.

[0022] 1.2.1 Apparent Hardness of Dip-molded Films Containing Chloroprene Polymer Latex The chloroprene polymer latex according to the present invention has a dip-molded film containing the chloroprene polymer latex and having a thickness of 0.60±0.10 mm, and has an apparent hardness of 25 to 40 IRHD, as measured at 23° C. using a Wallace micro automatic hardness tester. The apparent hardness of the dip-molded film containing the chloroprene polymer latex is, for example, 25.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0, 36.0, 37.0, 38.0, 39.0, or 40.0 IRHD, and may be within a range between any two of the values ​​exemplified here.

[0023] Here, the 0.60±0.10 mm thick dip-molded film is a stack of multiple dip-molded films with thicknesses of 0.15 to 0.25 mm. The 0.15 to 0.25 mm thick dip-molded film can be formed by the immersion coagulation method, which involves immersing a ceramic mold coated with a calcium-based coagulation liquid in a chloroprene polymer latex composition containing a chloroprene polymer latex. The dip-molded film is then thermally dried at 150°C for 60 minutes. In this measurement, samples of the above shape were used, and the International Rubber Hardness (IRHD) measured in accordance with JIS K 6253-2 was used as the apparent hardness. The hardness measured by the above method based on JIS K 6253-1 was referred to as the "apparent hardness." The manufacturing method of the dip-molded product and the method for measuring the "apparent hardness" (International Rubber Hardness IRHD) can be specifically as described in the Examples.

[0024] The apparent hardness of the dip-molded film containing the chloroprene polymer latex can be controlled by adjusting the types and amounts of raw materials blended and polymerization conditions in producing the chloroprene polymer latex, and by adjusting the type (weight average molecular weight, type and content of monomer units contained, etc.) and amount of the chloroprene polymer contained in the chloroprene polymer latex.

[0025] 1.2.2 Weight-average molecular weight of chloroprene polymer latex When the chloroprene polymer latex according to one embodiment of the present invention is freeze-dried, dissolved in tetrahydrofuran, and the soluble matter is subjected to gel permeation chromatography, a peak having a weight-average molecular weight of preferably 3,000 to 80,000 is detected, and more preferably a peak having a weight-average molecular weight of 5,000 to 50,000 is detected. That is, the chloroprene polymer latex according to one embodiment of the present invention preferably contains a low-molecular-weight chloroprene polymer having a weight-average molecular weight of 3,000 to 80,000, and more preferably contains a low-molecular-weight chloroprene polymer having a weight-average molecular weight of 5,000 to 50,000.

[0026] When the weight-average molecular weight of the low-molecular-weight chloroprene polymer is at least the above-mentioned lower limit, a dip-molded article having better tensile strength at break can be obtained. From the viewpoint of more easily obtaining a dip-molded article, the weight-average molecular weight of the low-molecular-weight chloroprene polymer may be at least 10,000 or at least 15,000.

[0027] When the weight-average molecular weight of the low-molecular-weight chloroprene polymer is not more than the above upper limit, a dip-molded product having lower apparent hardness can be obtained. From the viewpoint of easily achieving even better flexibility, the weight-average molecular weight of the low-molecular-weight chloroprene polymer may be not more than 80,000, not more than 70,000, not more than 50,000, or not more than 30,000.

[0028] The peaks detected in the weight average molecular weight range of 3,000 to 80,000 are, for example, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000, 19, 000, 20,000, 21,000, 22,000, 23,000, 24,000, 25,000, 26,000, 27,000, 28,000, 29,000, 30,000, 35,000, 40,000, 50,000, 60,000, 70,000, 80,000, and may be within a range between any two of the numerical values ​​exemplified here.

[0029] The chloroprene polymer latex according to one embodiment of the present invention has the above molecular weight distribution, and therefore the apparent hardness of the dip-molded film can be appropriately adjusted.

[0030] The chloroprene polymer latex according to one embodiment of the present invention preferably further has a peak of weight average molecular weight of 500,000 to 1,500,000 detected when the chloroprene polymer latex is freeze-dried, dissolved in tetrahydrofuran, and the soluble matter is subjected to gel permeation chromatography. That is, the chloroprene polymer latex according to one embodiment of the present invention preferably contains a high molecular weight chloroprene polymer having a weight average molecular weight of 500,000 to 1,500,000. The weight-average molecular weight of the peak detected in the weight-average molecular weight range of 500,000 to 1,500,000 is, for example, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,200,000, 1,300,000, 1,400,000, or 1,500,000, and may be within a range between any two of the values ​​exemplified here.

[0031] The weight-average molecular weight of a chloroprene polymer can be controlled by adjusting the type and amount of a chain transfer agent, the polymerization temperature, the polymerization time, the polymerization conversion rate, etc., during polymerization of each chloroprene polymer. In addition, the apparent hardness of a dip-molded product containing a chloroprene polymer latex can be adjusted by adjusting the weight-average molecular weight of the chloroprene polymer or the blending ratio of chloroprene polymers having different weight-average molecular weights.

[0032] The molecular weight distribution of the tetrahydrofuran-soluble sol fraction in the chloroprene polymer latex can be obtained by measuring the weight-average molecular weight by gel permeation chromatography. Specifically, the chloroprene polymer latex is freeze-dried and dissolved in tetrahydrofuran, and the eluted fraction (sol fraction) is analyzed by gel permeation chromatography (GPC). The GPC measurement conditions can be as described in the Examples.

[0043] Note that, when the analysis target is a chloroprene polymer latex composition, the chloroprene polymer latex composition is freeze-dried, dissolved in tetrahydrofuran, and analyzed in the same manner, the molecular weight distribution of the tetrahydrofuran-soluble sol component in the chloroprene polymer latex contained in the chloroprene polymer latex composition can also be determined. Furthermore, when the analysis target is a dip-molded product, the dip-molded product is dissolved in tetrahydrofuran, and analyzed in the same manner, the molecular weight distribution of the tetrahydrofuran-soluble sol component in the chloroprene polymer latex contained in the dip-molded product can also be determined.

[0033] The chloroprene polymer latex according to the present invention can be obtained by mixing two or more chloroprene polymer latexes having different weight-average molecular weights. By mixing two or more chloroprene polymer latexes having different weight-average molecular weights, a chloroprene polymer latex having a weight-average molecular weight peak detected in the above range in the molecular weight distribution may be obtained. When two or more chloroprene polymer latexes are mixed, the weight-average molecular weight of each chloroprene polymer latex can be controlled by adjusting the type and amount of chain transfer agent, polymerization temperature, polymerization time, polymerization conversion rate, etc., during polymerization of each chloroprene polymer latex. When two or more chloroprene polymer latexes are used, the chloroprene polymer latex may be obtained by stirring and mixing the two or more chloroprene polymer latexes using a paddle blade at 100 rpm for 2 minutes.

[0034] The chloroprene polymer latex according to one embodiment of the present invention is preferably such that a peak having a weight-average molecular weight of 3,000 to 80,000 and a peak having a weight-average molecular weight of 500,000 to 1,500,000 are detected in the molecular weight distribution obtained by freeze-drying the chloroprene polymer latex, dissolving it in tetrahydrofuran, and measuring the soluble portion by gel permeation chromatography. That is, the chloroprene polymer latex according to one embodiment of the present invention preferably contains a chloroprene polymer having a weight-average molecular weight of 3,000 to 80,000 and a chloroprene polymer having a weight-average molecular weight of 500,000 to 1,500,000.

[0035] The chloroprene polymer latex according to one embodiment of the present invention preferably contains 5 to 40% by mass of a chloroprene polymer having a weight-average molecular weight of 3,000 to 80,000, based on 100% by mass of the chloroprene polymer contained in the chloroprene polymer latex. The chloroprene polymer latex according to one embodiment of the present invention may contain, for example, 5, 10, 15, 20, 25, 30, 35, or 40% by mass of a chloroprene polymer having a weight-average molecular weight of 5,000 to 50,000, based on 100% by mass of the chloroprene polymer contained in the chloroprene polymer latex, and may be within a range between any two of the numerical values ​​exemplified here.

[0036] The chloroprene polymer latex according to one embodiment of the present invention preferably contains 60 to 95 mass% of a chloroprene polymer having a weight-average molecular weight of 500,000 to 1,500,000, when the total mass of the chloroprene polymer contained in the chloroprene polymer latex is taken as 100 mass%. The chloroprene polymer latex according to one embodiment of the present invention may contain, for example, 60, 65, 70, 75, 80, 85, 90, or 95 mass% of a chloroprene polymer having a weight-average molecular weight of 500,000 to 1,500,000, when the total mass of the chloroprene polymer contained in the chloroprene polymer latex is taken as 100 mass%, and may be within a range between any two of the numerical values ​​exemplified here.

[0037] By adjusting the contents of the chloroprene polymers having different weight-average molecular weights to fall within the above range, the apparent hardness can be adjusted more appropriately.

[0038] 1.2.3 Amount of 2,3-dichloro-1,3-butadiene copolymerized with chloroprene polymer contained in chloroprene polymer latex The copolymerization amount of 2,3-dichloro-1,3-butadiene in the chloroprene polymer contained in the chloroprene polymer latex according to one embodiment of the present invention is preferably 1 to 25 mass%, more preferably 5 to 25 mass%, when the total of the chloroprene-derived monomer units and the 2,3-dichloro-1,3-butadiene-derived monomer units contained in the chloroprene polymer is taken as 100 mass%. The copolymerization amount of this component is, for example, 1, 2, 5, 8, 9, 10, 12, 15, 20, or 25 mass%, and may be within a range between any two of the values ​​exemplified here.

[0039] By adjusting the copolymerization amount of 2,3-dichloro-1,3-butadiene in the chloroprene polymer contained in the chloroprene polymer latex according to one embodiment of the present invention to fall within the above numerical range, the apparent hardness of a dip-molded film obtained using the chloroprene polymer latex can be more appropriately adjusted, and a dip-molded product having sufficient tensile strength at break and superior texture can be easily obtained. The copolymerization amount of 2,3-dichloro-1,3-butadiene may be adjusted by preparing two or more chloroprene polymer latexes each having a different copolymerization amount of the component and adjusting the mixing ratio of these. The copolymerization amount of 2,3-dichloro-1,3-butadiene in each chloroprene polymer latex can be adjusted by controlling the type and amount of raw materials used in polymerization of each chloroprene polymer latex, as well as the polymerization conditions.

[0040] The "amount of 2,3-dichloro-1,3-butadiene copolymerized" can be determined by analyzing a chloroprene polymer latex or a chloroprene polymer latex composition, freezing the chloroprene polymer latex or the chloroprene polymer latex composition, drying the resulting material, cutting the material, and measuring the amount of 2,3-dichloro-1,3-butadiene copolymerized in the chloroprene polymer latex (contained in the chloroprene polymer latex composition) by pyrolysis gas chromatography. Alternatively, a dip-molded product can be analyzed.

[0041] 1.2.4 Toluene-insoluble matter in chloroprene polymer latex The toluene-insoluble content (gel content) of the chloroprene polymer latex according to one embodiment of the present invention can be 45 to 85% by mass, more preferably 60 to 80% by mass, based on the solid content obtained by freeze-drying the chloroprene polymer latex. The toluene-insoluble content may be, for example, 45, 50, 55, 60, 65, 70, 75, 80, or 85% by mass, or may be within a range between any two of the values ​​exemplified here. By controlling the toluene-insoluble content within the above range, superior tensile strength at break is achieved. This range can be adjusted by preparing two or more chloroprene polymer latexes with different toluene-insoluble content and adjusting the mixing ratio between them. The toluene-insoluble content in each chloroprene polymer latex can be adjusted by controlling the type and amount of raw materials used in polymerization of each chloroprene polymer latex, as well as the polymerization conditions.

[0042] The "toluene insoluble content" can be calculated by cutting 1 g of chloroprene polymer rubber obtained by freeze-drying chloroprene polymer latex into 2 mm cubes, dissolving it in toluene for 16 hours, centrifuging it, separating the insoluble content using a 200 mesh wire net, and measuring the dried weight. The toluene insoluble content can be calculated using the following formula. (Mass of the solid obtained by separating and drying the gel fraction) / (Mass of the solid obtained by freeze-drying the latex containing a chloroprene polymer)×100 In addition, when the analysis object is a chloroprene polymer latex composition and a dried product obtained by freezing the chloroprene polymer latex composition is analyzed in the same manner, the toluene-insoluble content in the chloroprene polymer latex contained in the chloroprene polymer latex composition can also be determined. In addition, when the analysis object is a dip-molded product and the dip-molded product is analyzed in the same manner, the toluene-insoluble content in the chloroprene polymer latex contained in the dip-molded product can also be determined.

[0043] 1.2.5 Tensile strength at break of dip-molded films containing chloroprene polymer latex The chloroprene polymer latex according to one embodiment of the present invention can produce a dip-molded film containing the chloroprene polymer latex with a tensile strength at break of 16.0 MPa or more, preferably 17.0 MPa or more. The tensile strength at break is, for example, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, or 30.0 MPa, and may be within a range between any two of the values ​​exemplified here. The chloroprene polymer latex according to one embodiment of the present invention can be dip-molded to have sufficient tensile strength at break and excellent texture by adjusting the type and amount of the chloroprene polymer contained in the chloroprene polymer latex (weight-average molecular weight, type and content of the monomer units contained, etc.) so that the apparent hardness falls within the above-mentioned range.

[0044] 1.2.6 Manufacturing method of chloroprene polymer latex Next, the method for producing the chloroprene polymer latex according to the present invention will be described.

[0045] The method for producing a chloroprene polymer latex may include a polymerization step of polymerizing a chloroprene-containing monomer to obtain a chloroprene polymer latex, and may further include a mixing step of mixing two or more chloroprene polymer latexes having different weight-average molecular weights.

[0046] In the polymerization process, the monomer includes chloroprene and may also include other monomers copolymerizable with chloroprene, such as 1-chloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, isoprene, styrene, methacrylic acid, acrylonitrile, and sulfur. The monomer may also include chloroprene and 2,3-dichloro-1,3-butadiene.

[0047] The type and amount of each monomer are preferably adjusted so that the content of each monomer unit in the resulting chloroprene polymer falls within the above-mentioned range. For example, the copolymerization amount of 2,3-dichloro-1,3-butadiene in the chloroprene polymer contained in the chloroprene polymer latex can be set to a range of 1 to 25 mass% relative to 100 mass% of the total of the chloroprene monomer and 2,3-dichloro-1,3-butadiene contained in the chloroprene polymer. In this case, the amount of 2,3-dichloro-1,3-butadiene charged before the start of emulsion polymerization is preferably set to a range of 1 to 25 parts by mass relative to 100 parts by mass of the total of the chloroprene monomer and 2,3-dichloro-1,3-butadiene monomer. From the viewpoint of controlling the polymerization, it is more preferable to set the amount of 2,3-dichloro-1,3-butadiene charged to 5 to 25 parts by mass per 100 parts by mass of the total of the chloroprene monomer and the 2,3-dichloro-1,3-butadiene monomer.

[0048] When producing a chloroprene polymer, raw material monomers are polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, bulk polymerization, etc. Among these polymerization methods, emulsion polymerization is preferred because it has various advantages such as ease of control, ease of extracting the polymer from the polymerization-finished liquid, and a relatively fast polymerization rate.

[0049] Emulsion polymerization is a type of radical polymerization in which raw material monomers are polymerized by being introduced into a reaction vessel together with a chain transfer agent, water, an alkali (e.g., a metal hydroxide such as potassium hydroxide or sodium hydroxide), an emulsifier (dispersant), a reducing agent (e.g., sodium hydrogen sulfite), a polymerization initiator, etc.

[0050] The type of chain transfer agent used in emulsion polymerization is not particularly limited, and known chain transfer agents generally used in emulsion polymerization of chloroprene can be used, such as long-chain alkyl mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, dialkyl xanthogen disulfides such as diisopropyl xanthogen disulfide and diethyl xanthogen disulfide, iodoform, etc. As the chain transfer agent, long-chain alkyl mercaptans are preferred, and n-dodecyl mercaptan is more preferred.

[0051] By adjusting the type and amount of the chain transfer agent, the weight average molecular weight of the resulting chloroprene polymer latex can be adjusted.

[0052] For example, to obtain a latex containing a chloroprene polymer having a weight-average molecular weight of 500,000 or more, i.e., to obtain a chloroprene polymer latex having a peak indicating a weight-average molecular weight of 500,000 or more in its molecular weight distribution, the amount of chain transfer agent added before the start of emulsion polymerization is preferably 0.01 part by mass or more per 100 parts by mass of monomer (e.g., 100 parts by mass of chloroprene and 2,3-dichloro-1,3-butadiene in total). From the viewpoint of obtaining a chloroprene polymer latex having a peak indicating a weight-average molecular weight of 500,000 or more, the amount of chain transfer agent added is more preferably 0.02 to 0.05 part by mass, and may be, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 part by mass, or less than 0.10 part by mass, and may be within a range between any two of the values ​​exemplified herein. When the amount of the chain transfer agent, particularly long-chain alkyl mercaptans, added is 0.01 part by mass or more, the storage stability of the latex is further improved. When the amount is less than 0.10 part by mass, particularly less than 0.05 part by mass, the toluene-insoluble matter increases, and the tensile strength at break of the obtained dip-molded product containing the chloroprene polymer latex is further increased.

[0053] To obtain a latex containing a chloroprene polymer having a weight-average molecular weight of 3,000 to 80,000, i.e., to obtain a chloroprene polymer latex having a peak of a weight-average molecular weight of 3,000 to 80,000 in its molecular weight distribution, the amount of chain transfer agent added before the start of emulsion polymerization is preferably 0.5 or 1.0 to 10.0 parts by mass per 100 parts by mass of monomer. In this case, the amount is, for example, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0 parts by mass, and may be within a range between any two of the values ​​exemplified here.

[0054] Examples of emulsifiers include anionic emulsifiers and nonionic emulsifiers. 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 acid salts such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; and sodium salts of β-naphthalene sulfonic acid formalin condensates. Examples of nonionic emulsifiers include polyethylene glycol ester-type emulsifiers and polyvinyl alcohol. Among these, anionic emulsifiers are preferred, resin acid salts are preferred, and rosin acids such as rosin acid and rosin acid salts are preferred, with at least one selected from the group consisting of potassium rosinate and sodium rosinate being more preferred. These emulsifiers can be used alone or in combination. The amount of emulsifier used is preferably 1.0 to 6.5 parts by mass per 100 parts by mass of the monomer.

[0055] In particular, the emulsifier used in emulsion polymerization preferably contains an anionic emulsifier, and more preferably contains a resin acid salt, particularly a rosin acid. The use of a rosin acid can prevent aggregation of rubber solids and pH fluctuations when blended with a base chloroprene polymer latex. Rosin acids include disproportionated rosin acid, conjugated resin acid, alkali metal salts of disproportionated rosin acid, alkali metal salts of conjugated resin acid, etc.

[0056] In the method for producing a chloroprene polymer latex according to one embodiment of the present invention, in addition to the rosin acids, other commonly used emulsifiers or fatty acids can also be used in combination. Examples of the other emulsifiers include, for example, an anionic emulsifier, such as the above-mentioned anionic emulsifiers, as well as metal salts of aromatic sulfinic acid-formalin condensates, sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, sodium alkyldiphenylethersulfonate, potassium alkyldiphenylethersulfonate, sodium polyoxyethylene alkylethersulfonate, sodium polyoxypropylene alkylethersulfonate, potassium polyoxyethylene alkylethersulfonate, and potassium polyoxypropylene alkyletherethersulfonate.

[0057] The content of the anionic emulsifier excluding rosin acid is preferably 0.2 to 1.0% by mass relative to 100% by mass of the chloroprene polymer contained in the chloroprene polymer latex. Therefore, the amount of the anionic emulsifier excluding rosin acid added before the start of emulsion polymerization is preferably set within the range of 0.2 to 0.9 parts by mass relative to 100 parts by mass of the monomer (for example, the total of chloroprene and 2,3-dichloro-1,3-butadiene).

[0058] The pH of the aqueous emulsion at the start of emulsion polymerization is preferably 10.5 to 13.5. The aqueous emulsion refers to a mixed solution of a chain transfer agent and a monomer (chloroprene, 2,3-dichloro-1,3-butadiene, etc.) immediately before the start of emulsion polymerization, but also includes cases where the composition changes due to the subsequent addition or divided addition of each component. When the pH of the aqueous emulsion at the start of emulsion polymerization is 10.5 or higher, the polymerization reaction can be controlled more stably. When the pH is 13.5 or lower, excessive viscosity increase during polymerization is suppressed, and the polymerization reaction can be controlled more stably.

[0059] The polymerization temperature for emulsion polymerization is preferably within the range of 5 to 55° C. A temperature of 5° C. or higher is preferred because the emulsion does not freeze, and a temperature of 55° C. or lower is preferred because the chloroprene monomer does not evaporate or boil.

[0060] As the polymerization initiator, potassium persulfate, benzoyl peroxide, ammonium persulfate, hydrogen peroxide, etc., which are used in ordinary radical polymerization, can be used.

[0061] The polymerization conversion rate is preferably in the range of 50 to 95%. The polymerization reaction is terminated by adding a polymerization terminator. If the polymerization conversion rate is 50% or more, the toluene insoluble content tends to increase, and the strength of the resulting dip-molded coating tends to increase. This is also advantageous from the viewpoint of production costs. If the polymerization conversion rate is less than 95%, it is possible to avoid a decrease in polymerization reactivity due to a decrease in unreacted monomer, and thus a decrease in productivity.

[0062] Examples of the polymerization terminator include diethylhydroxyamine, thiodiphenylamine, 4-tert-butylcatechol, 2,2'-methylenebis-4-methyl-6-tert-butylphenol, etc. After the emulsion polymerization is completed, unreacted monomers can be removed by a conventional method such as vacuum distillation.

[0063] Furthermore, to the chloroprene polymer latex obtained by the production method according to one embodiment of the present invention, after polymerization, any additive such as a freeze stabilizer, an emulsion stabilizer, a viscosity modifier, an antioxidant, or a preservative may be added, as long as the effects of the present invention are not impaired.

[0064] The method for producing a chloroprene polymer latex according to one embodiment of the present invention may further include a mixing step of mixing two or more chloroprene polymer latexes having different weight-average molecular weights after the polymerization step. In the mixing step, the two or more chloroprene polymer latexes may be mixed by a known method. In the mixing step, the chloroprene polymer latex may be obtained by stirring and mixing using a paddle blade at 30 to 300 rpm for 20 seconds to 3 minutes, e.g., at 100 rpm for 2 minutes.

[0065] 2. Chloroprene polymer latex composition A chloroprene polymer latex composition according to one embodiment of the present invention includes a chloroprene polymer latex containing the chloroprene polymer according to the present invention. The chloroprene polymer latex composition according to one embodiment of the present invention may contain a metal oxide, an antioxidant, and other necessary chemicals in addition to the chloroprene polymer latex. The types and amounts of the metal oxide, antioxidant, and other necessary chemicals that may be contained in the chloroprene polymer latex composition will be described below as components that may be contained in the dip-molded product.

[0066] 3. Method for producing chloroprene polymer latex composition The method for producing the chloroprene polymer latex composition may include a raw material mixing step of mixing raw materials including the chloroprene polymer latex, a metal oxide, an antioxidant, and other necessary chemicals. In the mixing step, an aqueous dispersion containing a metal oxide, an antioxidant, and other necessary chemicals may be prepared in advance, and the chloroprene polymer latex and the aqueous dispersion may be mixed. The mixing step can be carried out using a known mixing device such as a ball mill.

[0067] 4. Dip-molded products (dip-molded coatings and films) A dip-molded article according to one embodiment of the present invention is obtained using a chloroprene polymer latex composition containing the above-described chloroprene polymer latex. The dip-molded article of this embodiment can be obtained by dip-molding the above-described chloroprene polymer latex composition, either alone or in a blend with other chloroprene polymer latex compositions, and then dip-molding the chloroprene polymer latex composition by a dip coagulation method, followed by heat drying at 150°C for 60 minutes. The dip-molded article according to the present invention has sufficient tensile strength at break and excellent texture. The dip-molded article can be suitably used for industrial and general household gloves, medical gloves, balloons, catheters, and boots.

[0068] The dip-molded product according to the present invention may contain components contained in the chloroprene polymer latex. The dip-molded product may contain a chloroprene polymer as a base polymer, and may contain 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more of the chloroprene polymer, based on 100% by mass of the dip-molded product. The content of the chloroprene polymer in the dip-molded product based on 100% by mass of the dip-molded product may be, for example, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or 100% by mass, or may be within a range between any two of the values ​​exemplified here.

[0069] The dip-molded product according to the present invention may contain a metal oxide and an antioxidant. The dip-molded product according to the present invention has sufficient tensile strength at break and excellent texture, regardless of whether a vulcanizing agent and a vulcanization accelerator are added. In addition, the chloroprene polymer latex composition according to one embodiment of the present invention may be free of a vulcanizing agent and a vulcanization accelerator, and may not contain sulfur or a vulcanization accelerator such as a thiuram-based, dithiocarbamate-based, thiourea-based, guanidine-based, xanthogenate-based, or thiazole-based vulcanization accelerator. Components that the dip-molded product according to the present invention may contain will be described in detail below.

[0070] 4.1 Metal oxides The dip-molded product of the chloroprene polymer according to the present invention may contain a metal oxide. The metal oxide contained in the chloroprene polymer latex composition used to obtain the dip-molded product is not particularly limited, and examples thereof include zinc oxide, lead oxide, trilead tetroxide, magnesium oxide, aluminum oxide, iron oxide, beryllium oxide, and titanium oxide. The metal oxide preferably contains zinc oxide. Zinc oxide is generally believed to function as a scavenger for dechlorinated atoms in chloroprene polymers. These metal oxides may be used alone or in combination of two or more.

[0071] The amount of metal oxide added is preferably 0.5 to 15.0 parts by mass per 100 parts by mass of the solids content of the chloroprene polymer latex contained in the chloroprene polymer latex composition used to obtain the dip-molded product. When the amount of metal oxide added is 0.5 parts by mass or more, an improvement in tensile strength at break is expected due to the crosslinking effect between polymers. When the amount of metal oxide added is 15.0 parts by mass or less, a dip-molded product with excellent flexibility can be obtained. Furthermore, from the viewpoint of the balance of physical properties between flexibility and tensile strength at break of the obtained dip-molded product, the amount of metal oxide added is more preferably 0.5 to 5.0 parts by mass. The dip-molded product according to the present invention may also be free of metal oxide.

[0072] 4.2 Antioxidants The dip-molded product of the chloroprene polymer according to the present invention may also contain an antioxidant. The antioxidant is not particularly limited, and examples thereof include phenolic antioxidants, amine-based antioxidants, heat-resistant oxidation (aging) inhibitors, and ozone-resistant antioxidants. When the resulting dip-molded product is used as a medical glove, phenolic antioxidants can be used from the viewpoints of color, texture, and hygiene of the dip-molded product. Hindered phenolic antioxidants are particularly effective. Examples of hindered phenolic antioxidants include 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-butylidene(3-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), butylated reaction products of p-cresol and dicyclopentadiene, 2,5'-di-t-butylhydroquinone, and 2,5'-di-t-amylhydroquinone. Among these, the butylated reaction product of p-cresol and dicyclopentadiene is desirable from the viewpoint of general dispersibility in aqueous materials. These compounds may be used alone or in combination of two or more.

[0073] The amount of antioxidant added is preferably 0.5 to 10.0 parts by mass per 100 parts by mass of the solids content of the chloroprene polymer latex contained in the chloroprene polymer latex composition used to obtain the dip-molded product. The amount of antioxidant added is, for example, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0 parts by mass, and may be within a range between any two of the values ​​exemplified herein. When the amount of antioxidant added is 0.5 parts by mass or more, the effect of suppressing color change in the dip-molded product can be obtained. When the amount of antioxidant added is 10.0 parts by mass or less, the stability of the chloroprene polymer latex composition can be ensured. Furthermore, from the viewpoint of the balance of physical properties between flexibility and tensile strength at break of the obtained dip-molded product, the amount of antioxidant added is more preferably 0.5 to 5.0 parts by mass. The dip-molded product of the present invention may also be antioxidant-free.

[0074] 4.3 Vulcanizing agents and vulcanization accelerators The dip-molded product of a chloroprene polymer according to one embodiment of the present invention may contain a vulcanizing agent and / or a vulcanization accelerator. The chloroprene polymer latex composition used to obtain the dip-molded product may not contain sulfur or the aforementioned vulcanization accelerators such as thiuram, dithiocarbamate, thiourea, guanidine, xanthogenate, and thiazole. That is, the dip-molded product of a chloroprene polymer latex composition includes those containing a vulcanizing agent but not a vulcanization accelerator, those containing a vulcanization accelerator but not a vulcanizing agent, those containing a vulcanization accelerator and a vulcanization accelerator, and those containing neither a vulcanizing agent nor a vulcanization accelerator. Whether or not a vulcanizing agent and a vulcanization accelerator are added may be determined depending on the desired dip-molded product.

[0075] Examples of vulcanizing agents include, but are not limited to, sulfur. The amount of vulcanizing agent added can be 0 to 10.0 parts by mass per 100 parts by mass of the solid content of the chloroprene polymer latex contained in the chloroprene polymer latex composition. The amount of vulcanizing agent added is, for example, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0 parts by mass, and may be within a range between any two of the values ​​exemplified here.

[0076] A vulcanization accelerator is a chemical added during the vulcanization of raw rubber to act with the vulcanizing agent to increase the vulcanization speed, thereby shortening the vulcanization time, lowering the vulcanization temperature, reducing the amount of vulcanizing agent, and improving the physical properties of the vulcanized rubber. It usually refers to a chemical that accelerates the sulfur vulcanization reaction.

[0077] Examples of vulcanization accelerators generally used in the vulcanization of chloroprene polymer latex include, but are not limited to, thiuram-based, dithiocarbamate-based, thiourea-based, guanidine-based, xanthogenate-based, thiazole-based, etc. These accelerators may be used singly or in combination of two or more types as required.

[0078] Examples of thiuram vulcanization accelerators include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide.

[0079] Examples of dithiocarbamate vulcanization accelerators include sodium dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, copper dimethyldithiocarbamate, ferric dimethyldithiocarbamate, and tellurium diethyldithiocarbamate, with zinc dibutyldithiocarbamate being particularly preferred.

[0080] Examples of the thiourea-based vulcanization accelerator include ethylene thiourea, N,N'-diethyl thiourea, trimethyl thiourea, and N,N'-diphenyl thiourea.

[0081] Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and di-o-tolylguanidine salts of dicatechol borate.

[0082] Examples of xanthogenate-based vulcanization accelerators include zinc butylxanthogenate and zinc isopropylxanthogenate.

[0083] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-mercaptobenzothiazole zinc salt, cyclohexylamine salt of 2-mercaptobenzothiazole, and 2-(4'-morpholinodithio)benzothiazole.

[0084] The amount of the vulcanization accelerator added can be 0 to 5.0 parts by mass relative to 100 parts by mass of the solid content of the chloroprene polymer latex contained in the chloroprene polymer latex composition, and may be, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0, or may be within a range between any two of the numerical values ​​exemplified here.

[0085] 4.4 Shape of dip-molded product The thickness of the dip-molded product (e.g., the minimum thickness) may be 0.01 to 0.50 mm. The thickness of the dip-molded product may be, for example, 0.01, 0.05, 0.10, 0.20, 0.30, 0.40, or 0.50 mm, or may be within a range between any two of the values ​​exemplified here. The thickness of the dip-molded product can be adjusted by the time the mold is immersed in the polymer latex composition, the solids concentration of the chloroprene polymer latex composition, etc. To reduce the thickness of the dip-molded product, the immersion time may be shortened or the solids concentration of the chloroprene polymer latex composition may be reduced.

[0086] 4.5 Apparent hardness of dip-molded product In one embodiment of the present invention, the dip-molded product preferably has an apparent hardness of 25.0 IRHD or more and 40.0 IRHD or less for a 0.60±0.10 mm thick dip-molded film measured at 23°C using a Wallace micro automatic hardness tester. Here, the 0.60±0.10 mm thick dip-molded film can be obtained by stacking multiple dip-molded films each having a thickness of 0.15 to 0.25 mm. The apparent hardness of the dip-molded film is more preferably 37.0 IRHD or less. A hardness of 40.0 IRHD or less means that the dip-molded film has excellent texture and feel and sufficient tensile strength at break. The apparent hardness of the dip-molded product according to one embodiment of the present invention is, for example, 25.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0, 36.0, 37.0, 38.0, 39.0, or 40.0 IRHD, and may be within a range between any two of the values ​​exemplified here. The apparent hardness of the dip-molded product can be controlled by adjusting the types and amounts of raw materials blended and polymerization conditions during production of the chloroprene polymer latex, and by adjusting the type and amount of the chloroprene polymer contained in the chloroprene polymer latex (weight-average molecular weight, type and content of monomer units contained, etc.).

[0087] In this measurement, samples of the above-mentioned shape were used, and the apparent hardness was determined as the International Rubber Hardness IRHD measured in accordance with JIS K 6253-2. Based on JIS K 6253-1, the hardness measured by the above method was referred to as "apparent hardness." The manufacturing method of the dip-molded product and the method for measuring the "apparent hardness" of the International Rubber Hardness IRHD can be as described in the Examples.

[0088] 4.6 Tensile strength at break of immersion molded product The dip-molded product according to one embodiment of the present invention may have a tensile strength at break of 16.0 MPa or more, preferably 17.0 MPa or more. The tensile strength at break may be, for example, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, or 30.0 MPa, or may be within a range between any two of the values ​​exemplified here. The tensile strength at break of the dip-molded product is the tensile strength at break measured in accordance with JIS K 6251:2017.

[0089] As described above, the dip-molded product according to one embodiment of the present invention has an excellent texture and can have sufficient tensile strength at break regardless of whether a vulcanizing agent, vulcanization accelerator, or crosslinking agent is added. Conventional latex containing chloroprene rubber has been used as a rubber latex raw material for the coating of dip-molded products such as gloves, balloons, boots, catheters, etc. However, particularly in the application of medical rubber gloves, there is a tendency for high flexibility to be required similar to that of dip-molded products obtained using natural rubber or polyisoprene, and there is a demand for dip-molded products of chloroprene polymers with improved texture of dip-molded products (films).

[0090] As described above, the dip-molded product according to one embodiment of the present invention has flexibility, sufficient tensile strength at break even without containing sulfur or a vulcanization accelerator that raises concerns about hygiene, and can have a sufficiently excellent texture.

[0091] The dip-molded product obtained from the chloroprene polymer latex of the present embodiment may contain sulfur or a vulcanization accelerator. However, even if the dip-molded product does not contain sulfur or a vulcanization accelerator, the dip-molded product has a texture that is equal to or better than that of vulcanized dip-molded products obtained from conventional chloroprene polymer latexes. Therefore, the chloroprene polymer latex of the present embodiment is suitably used as a raw material for dip-molded products (dip-molded product coatings).

[0092] 5. Manufacturing method of dip-molded products The method for producing a dip-molded product containing a chloroprene polymer according to the present invention comprises the steps of: a molding step of molding the chloroprene polymer latex composition containing the chloroprene polymer by a dip coagulation method using a calcium-based coagulation liquid to obtain a dip-molded product; and A drying step in which the obtained dip-molded body is subjected to a heat drying treatment to obtain a dip-molded product. may include:

[0093] The molding method for producing the immersion molded article of one embodiment of the present invention is not particularly limited, and may be performed according to a conventional method. Examples of molding methods include immersion coagulation, simple immersion, thermal immersion, and electrodeposition. The immersion coagulation method can be used from the viewpoints of ease of production and the ease of obtaining immersion molded articles of a uniform thickness. Specifically, a ceramic mold coated with a calcium-based coagulation liquid is immersed in a chloroprene polymer latex composition to coagulate the chloroprene polymer latex composition. After removing water-soluble impurities by leaching, the composition is dried, and then heated and vulcanized to form a immersion molded article coating (rubber coating), which is then released from the mold. This produces a film-like immersion molded article.

[0094] Furthermore, a method for producing a dip-molded product according to one embodiment of the present invention may include a step of subjecting the obtained dip-molded product to a heat drying treatment to vulcanize the unvulcanized dip-molded product. The heat drying temperature may be appropriately set depending on the composition of the chloroprene polymer latex composition, and may be 100 to 220°C or 120 to 150°C. The heat drying temperature may be, for example, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, or 220°C, or may be within a range between any two of the values ​​exemplified here. The heat drying time may be appropriately set depending on the composition of the chloroprene polymer latex composition, the shape of the unvulcanized molded product, and the like, and may be 10 to 300 minutes. The heat drying time may be, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 minutes, or may be within a range between any two of the values ​​exemplified here. As an example, a dip-molded product according to one embodiment of the present invention may be subjected to heat drying treatment at 150°C for 60 minutes. [Example]

[0095] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples relating to the synthesis of a chloroprene polymer latex, unless otherwise specified, "parts by mass" refers to the amount relative to 100 parts by mass of the total of the chloroprene monomer and 2,3-dichloro-1,3-butadiene monomer before the start of emulsion polymerization. Furthermore, "% by mass" refers to the amount relative to 100% by mass of the chloroprene polymer contained in the chloroprene polymer latex.

[0096] [Synthesis Example A1] <Preparation of chloroprene polymer latex> A 40-liter polymerization vessel was charged with 91 parts by mass of chloroprene monomer, 9 parts by mass of 2,3-dichloro-1,3-butadiene monomer, 0.02 parts by mass of n-dodecyl mercaptan, 76.5 parts by mass of purified water, 18 parts by mass of gum rosin-based disproportionated potassium rosinate (aqueous solution, solids content 25%) (manufactured by Arakawa Chemical Industries, Ltd., product name: Longis K-25), 0.80 parts by mass of potassium hydroxide, and 0.50 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (product name: Demol N, manufactured by Kao Corporation). The pH of the aqueous emulsion before polymerization was 13.2. 0.1 parts by mass of potassium persulfate was added as a polymerization initiator, and polymerization was carried out at a polymerization temperature of 15°C under a nitrogen gas flow. When the polymerization conversion rate reached 83%, 0.01 parts by mass of diethylhydroxyamine as a polymerization terminator was added to terminate the polymerization, yielding a latex.

[0097] The latex was distilled under reduced pressure to remove unreacted monomers and a portion of water, thereby obtaining a chloroprene polymer latex with a solid content of 60%.

[0098] [Synthesis examples A2-A5] Chloroprene polymer latex samples of Synthesis Examples A2 to A5 were prepared in the same manner as in Synthesis Example A1, except that the amounts of 2,3-dichloro-1,3-butadiene and n-dodecyl mercaptan as a chain transfer agent, the polymerization temperature, and the polymerization conversion rate were set as shown in Table 1 below.

[0099] [Synthesis Example B1] <Preparation of chloroprene polymer latex> A 40-liter polymerization vessel was charged with 91 parts by mass of chloroprene monomer, 9 parts by mass of 2,3-dichloro-1,3-butadiene monomer, 3.0 parts by mass of n-dodecyl mercaptan, 76.5 parts by mass of purified water, 18 parts by mass of gum rosin-based disproportionated potassium rosinate (aqueous solution, solids content 25%) (manufactured by Arakawa Chemical Industries, Ltd., product name: Longis K-25), 0.80 parts by mass of potassium hydroxide, and 0.50 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (product name: Demol N, manufactured by Kao Corporation). The pH of the aqueous emulsion before polymerization was 13.1. 0.1 parts by mass of potassium persulfate was added as a polymerization initiator, and polymerization was carried out at a polymerization temperature of 30°C under a nitrogen gas flow. When the polymerization conversion rate reached 83%, 0.01 parts by mass of diethylhydroxyamine as a polymerization terminator was added to terminate the polymerization, yielding a latex.

[0100] The latex was distilled under reduced pressure to remove unreacted monomers, thereby obtaining a chloroprene polymer latex with a solid content of 60%.

[0101] [Synthesis examples B2 to B8] Chloroprene polymer latex samples of Synthesis Examples B2 to B8 were prepared in the same manner as in Synthesis Example B1, except that the amounts of 2,3-dichloro-1,3-butadiene and n-dodecyl mercaptan as a chain transfer agent, the polymerization temperature, and the polymerization conversion rate were set as shown in Table 1 below.

[0102] The latex was distilled under reduced pressure to remove unreacted monomers, thereby obtaining a chloroprene polymer latex with a solid content of 60%.

[0103] The obtained chloroprene polymer latex was subjected to the following analyses, the results of which are shown in Table 1. <Measurement of weight average molecular weight of each chloroprene polymer latex> The obtained chloroprene polymer latex was freeze-dried and dissolved in THF (tetrahydrofuran), and the weight-average molecular weight of the eluted fraction (sol fraction) was measured by gel permeation chromatography (GPC). The detected peak can be obtained as the weight-average molecular weight in terms of polystyrene, and was measured under the conditions described below.

[0104] <Weight-average molecular weight measurement by gel permeation chromatography> GPC measurement was carried out under the following conditions. The weight average molecular weight was calculated in terms of polystyrene. Gel permeation chromatography (GPC) measurement equipment: Tosoh gel permeation chromatograph (HLC-8320) Column: Tosoh TSKgel ALPHA-M Eluent: Tetrahydrofuran (Kanto Chemical) ·Eluent flow rate: 1.0ml / min Column temperature: 40℃ Detection method: Differential refractive index (RI) meter Calibration curve: Created using standard polystyrene

[0105] <Measurement of the amount of copolymerization of 2,3-dichloro-1,3-butadiene> The resulting chloroprene polymer latex was freeze-dried to obtain a rubber sample of the chloroprene polymer, which was cut into 0.05 mg test pieces and analyzed by pyrolysis gas chromatography to determine the area ratio of the peak derived from chloroprene to the peak derived from 2,3-dichloro-1,3-butadiene. The content (mass%) of 2,3-dichloro-1,3-butadiene monomer units in the chloroprene polymer was determined using a calibration curve of the area ratio of the peak derived from chloroprene to the peak derived from 2,3-dichloro-1,3-butadiene and the 2,3-dichloro-1,3-butadiene content.

[0106] <Measurement by pyrolysis gas chromatography> The measurement conditions for the pyrolysis gas chromatograph are shown below. Device name: HP5890-II Column: DB-5 0.25 mm diameter x 30 m (film thickness 1.0 μm) Column temperature: 50°C (5 min) → 10°C / min → 150°C → 25°C / min → 300°C Inlet temperature: 250℃ Detector temperature: 280℃ Detector: FID

[0107] <Measurement of toluene insoluble matter in chloroprene polymer latex> The resulting chloroprene polymer latex was freeze-dried to obtain a solid (chloroprene polymer rubber), which was then cut into 2 mm square pieces (1 g), placed in a conical beaker, and dissolved in toluene for 16 hours. The mixture was then centrifuged, and the gel fraction was separated using a 200-mesh wire netting, and the dried mass was measured. The toluene-insoluble fraction was calculated using the following formula: (Mass of the solid obtained by separating and drying the gel fraction) / (Mass of the solid obtained by freeze-drying the chloroprene polymer latex)×100

[0108] [Table 1]

[0109] [Example 1] When the total amount of the chloroprene polymer latex of Synthesis Example A1 and the chloroprene polymer latex of Synthesis Example B1 was 100 parts by mass, 80 parts by mass of the sample of Synthesis Example A1 and 20 parts by mass of the sample of Synthesis Example B1 were mixed and stirred using a paddle blade at 100 rpm for 2 minutes to obtain the chloroprene polymer latex of Example 1.

[0110] <Measurement of weight average molecular weight of chloroprene polymer latex> The chloroprene polymer latex obtained by mixing was freeze-dried and dissolved in tetrahydrofuran, and the soluble matter was subjected to gel permeation chromatography (GPC) measurement, whereby a peak corresponding to a weight average molecular weight (Mw) of 22,715 was confirmed. The GPC measurement conditions were the same as those for measuring the weight average molecular weight in each of the above synthesis examples.

[0111] <Amount of 2,3-dichloro-1,3-butadiene copolymerized in chloroprene polymer contained in chloroprene polymer latex> The 2,3-dichloro-1,3-butadiene copolymerization amount (content of 2,3-dichloro-1,3-butadiene monomer units) of the chloroprene polymer rubber obtained by freeze-drying the mixed chloroprene polymer latex was measured and found to be 9.5% by mass. From this analytical value, it was confirmed that the 2,3-dichloro-1,3-butadiene copolymerization amount in the chloroprene polymer in the mixed latex generally agreed with the calculated value calculated from the 2,3-dichloro-1,3-butadiene copolymerization amount (analytical value) in each latex and the mixing ratio of each chloroprene polymer latex in the mixed latex. Furthermore, it was confirmed that there was a general correlation between the charged amount of 2,3-dichloro-1,3-butadiene in each latex and the calculated value calculated from the mixing ratio of each chloroprene polymer latex in the mixed latex. The measurement conditions were the same as those for the pyrolysis gas chromatography measurement in each synthesis example described above.

[0112] <Measurement of toluene insoluble matter in chloroprene polymer latex> The toluene insoluble content of the solid content (chloroprene polymer rubber) obtained by freeze-drying the mixed chloroprene polymer latex was measured and found to be 67 mass%. From this analytical value, it was confirmed that the toluene insoluble content of the chloroprene polymer latex roughly correlates with the calculated value calculated from the toluene insoluble content of each chloroprene polymer latex to be mixed and the mixing ratio.

[0113] <Preparation of Dip-molded Product (Dip-molded Product Film Sample)> (Preparation of Chloroprene Polymer Latex Composition) A chloroprene polymer latex composition was prepared by mixing 100 parts by weight of a chloroprene polymer latex solids solution with an aqueous dispersion, and then adding water to adjust the total solids concentration of the blend to 30% by weight. The aqueous dispersion was prepared by mixing 2 parts by weight of zinc oxide (type 2), 2 parts by weight of a butylated reaction product of p-cresol and dicyclopentadiene (trade name "Nocrac PBK" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 2 parts by weight of dibutyldithiocarbamic acid (trade name "Noccela BZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 1 part by weight of sulfur, 0.1 part by weight of a sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol N" manufactured by Kao Corporation), and 10.7 parts by weight of water in a ceramic ball mill at 20°C for 16 hours. The obtained chloroprene polymer latex composition contains, relative to 100 parts by mass of the solid content of the chloroprene polymer latex, 2 parts by mass of two types of zinc oxide, 2 parts by mass of a butylated reaction product of p-cresol and dicyclopentadiene (trade name "Nocrac PBK", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 2 parts by mass of dibutyldithiocarbamic acid (trade name "Noccela BZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 1 part by mass of sulfur, 0.1 part by mass of a sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol N", manufactured by Kao Corporation), and water.

[0114] (Preparation of dip-molded film) A ceramic cylinder (manufactured by Shinko Corporation) with an outer diameter of 50 mm and a length of 300 mm was immersed for 1 second in a coagulation solution containing 62 parts by mass of water, 35 parts by mass of calcium nitrate tetrahydrate, and 3 parts by mass of calcium carbonate, and then removed. After drying for 3 minutes, the cylinder was immersed for 2 minutes in the sulfur- and vulcanization accelerator-free chloroprene polymer latex composition prepared by the procedure described above. The cylinder was then washed with running water at 45°C for 1 minute and dried at 150°C for 60 minutes to prepare a dip-molded product (dip-molded product coating) for evaluation.

[0115] <Evaluation of dip-molded products> (film thickness) The thickness (film thickness) of the evaluation film was measured at three points in the center using a test piece thickness measuring instrument (manufactured by Kobunshi Keiki Co., Ltd., product name: ASKER SDA-12), and the smallest thickness was taken as the thickness of the evaluation film.

[0116] (International Rubber Hardness IRHD measurement) Three dip-molded films of this chloroprene polymer, each 0.20 mm thick, were stacked to a thickness of 0.60 mm, and the IRHD hardness was measured at 23°C using a Wallace micro automatic hardness tester, resulting in a result of 31.6 IRHD. The number of films stacked during measurement may be varied depending on the thickness of the resulting dip-molded product, as long as the total thickness was 0.60±0.10 mm. The thickness of the dip-molded film can be adjusted to 0.15 to 0.25 mm. Alternatively, three to four dip-molded films having the above thicknesses can be stacked to obtain a dip-molded film with a total thickness of 0.60±0.10 mm, which can then be used for measurement. The results are shown in Tables 2 and 3.

[0117] <Evaluation of texture of immersion molded products> The obtained dip-molded products were touched by five subjects, who evaluated the surface condition, stretched, and bent them to assess their texture. The evaluation was based on the following criteria, and the average of each subject's evaluation was rounded off to the nearest whole number.

[0118] (Texture evaluation criteria) 3: Extremely soft and pleasant to the touch, with an excellent texture 2: It was soft, had no practical problems with the feel, and had a good texture. 1: It didn't feel very soft, it felt a little hard to the touch, and the texture was not good.

[0119] (tensile strength at break) The tensile strength at break of the dip-molded film was measured in accordance with JIS K 6251. The results are shown in Tables 2 and 3.

[0120] [Examples 2 to 12, Comparative Examples 1 to 5] Dip-molded products were prepared in the same manner as in Example 1, except that the formulation of the chloroprene polymer latex composition was set under the conditions shown in Tables 2 and 3 below, and dip-molded film samples were produced and evaluated. In Examples 2, 3, 4, 5 and 8, 9, and 10 and Comparative Examples 2, 3, and 4, chloroprene polymer latexes having different detected weight-average molecular weight peaks and / or different amounts of 2,3-dichloro-1,3-butadiene copolymerized were used. In Examples 6 and 7 and Comparative Examples 1 and 5, the mixing ratio of each chloroprene polymer latex was changed. In Example 11, the metal oxide zinc oxide and antioxidant were omitted from the chloroprene polymer latex composition used to obtain the dip-molded product of the chloroprene polymer latex. In Example 12, dibutyldithiocarbamic acid as a vulcanization accelerator and sulfur as a vulcanizing agent were added to the chloroprene polymer latex composition used to obtain the dip-molded product of the chloroprene polymer latex.

[0121] [Table 2]

[0122] [Table 3]

[0123] As is clear from Tables 1 to 3 above, the dip-molded products (dip-molded film) obtained using the chloroprene polymer latex composition of the present invention in Examples 1 to 12 had low apparent hardness values ​​in the International Rubber Hardness Scale, and when made into dip-molded products (dip-molded films), they had excellent texture and sufficient tensile strength at break.

[0124] In Comparative Example 1, the chloroprene polymer latex did not contain a chloroprene polymer with a low weight-average molecular weight and had a large amount of toluene-insoluble matter, i.e., a very large amount of gel content, and a high apparent hardness, resulting in a poor texture of the obtained dip-molded product.

[0125] In Comparative Example 2, since 2,3-dichloro-1,3-butadiene was not copolymerized in the chloroprene polymer latex, the crystallinity had a strong effect, which is thought to have resulted in a high apparent hardness, and as a result, the texture of the obtained dip-molded product was deteriorated.

[0126] In Comparative Example 3, the chloroprene polymer latex did not contain a chloroprene polymer with a low weight-average molecular weight, and the apparent hardness was high, resulting in a deterioration in feel.

[0127] In Comparative Example 4, the chloroprene polymer latex did not contain a chloroprene polymer with a low weight-average molecular weight and did not contain a copolymerized amount of 2,3-dichloro-1,3-butadiene, which is thought to have caused the crystallinity to have a strong effect, resulting in a high apparent hardness and a poor feel.

[0128] In Comparative Example 5, since only low-molecular-weight chloroprene polymers were present in the chloroprene polymer latex, the product was very sticky during molding and a dip-molded product could not be obtained.

[0129] Example 12 shows that, when a chloroprene polymer latex is used, the apparent hardness of a dip-molded film containing the chloroprene polymer latex is a specific value or less, a dip-molded product having sufficient tensile strength at break and excellent texture can be obtained, even if a vulcanization accelerator or sulfur is contained. That is, the chloroprene polymer latex composition and dip-molded product according to one embodiment of the present invention may contain sulfur or a vulcanization accelerator.

[0130] Furthermore, from Examples 2, 3 and 8, 9 using Synthesis Examples B2, B3, B5, and B6, it was found that the weight-average molecular weight in the low molecular weight region affects the apparent hardness, and the larger the weight-average molecular weight, the higher the hardness tends to be. From the above, it was confirmed that the apparent hardness of a dip-molded film containing the chloroprene polymer latex according to the present invention can be controlled by appropriately adjusting the weight-average molecular weight of each chloroprene polymer contained in the chloroprene polymer latex, the type and amount of monomer units contained in the chloroprene polymer, and the blending ratio of each chloroprene polymer contained in the chloroprene polymer latex, and that a dip-molded film excellent in texture can be obtained by adjusting the apparent hardness of the dip-molded film containing the chloroprene polymer latex.

Claims

1. a chloroprene polymer latex containing a chloroprene polymer, the apparent hardness of a dip-molded film containing the chloroprene polymer latex and having a thickness of 0.60±0.10 mm, as measured at 23°C using a Wallace micro automatic hardness tester, is 25.0 IRHD or more and 40.0 IRHD or less; The dip-molded film having a thickness of 0.60±0.10 mm is obtained by stacking a plurality of dip-molded films having a thickness of 0.15 to 0.25 mm, The dip-molded film having a thickness of 0.15 to 0.25 mm is obtained by a dip-coagulation method in which a ceramic mold having a calcium-based coagulation liquid attached thereto is immersed in a chloroprene polymer latex composition containing the chloroprene polymer latex, and then the dip-molded film is subjected to a heat drying treatment at 150°C for 60 minutes. Chloroprene polymer latex.

2. 2. The chloroprene polymer latex according to claim 1, wherein when the chloroprene polymer latex is freeze-dried, dissolved in tetrahydrofuran, and the soluble matter is subjected to gel permeation chromatography, at least a peak corresponding to a weight average molecular weight of 3,000 to 80,000 is detected.

3. 2. The chloroprene polymer latex according to claim 1, wherein the chloroprene polymer contains 2,3-dichloro-1,3-butadiene monomer units.

4. 4. The chloroprene polymer latex according to claim 3, wherein the chloroprene polymer contains 1 to 25 mass% of 2,3-dichloro-1,3-butadiene monomer units relative to 100 mass% in total of the chloroprene monomer units and the 2,3-dichloro-1,3-butadiene monomer units.

5. 2. The chloroprene polymer latex according to claim 1, wherein the toluene-insoluble content of the solid fraction obtained by freeze-drying the chloroprene polymer latex is 45 to 85% by mass.

6. A dip-molded product using the chloroprene polymer latex according to any one of claims 1 to 5.

7. The dip-molded article of claim 6, comprising a metal oxide and an antioxidant.

8. The dip-molded article according to claim 7, which is an industrial or general household glove, a medical glove, a balloon, a catheter, or a boot.

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