Chloroprene-based polymer composition and dip-molded article

Abstract

To provide a chloroprene-based polymer composition enabling production of a dip-molded article that combines flexibility and tensile strength upon cutting, while offering high manufacturing efficiency, and a method for producing the chloroprene-based polymer composition, as well as a dip-molded article utilizing the chloroprene-based polymer composition.SOLUTION: A chloroprene-based polymer composition comprising a polymer component (S), wherein the polymer component (S) comprises a chloroprene-based polymer containing units derived from chloroprene, and in a molecular weight distribution obtained by gel permeation chromatography measurement of a tetrahydrofuran-soluble fraction of the polymer component (S), a low molecular weight peak (P1) having a peak top in the molecular weight range of 50,000 to 80,000 is detected, and a toluene swelling degree of a test dip-molded article is 12.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a chloroprene polymer composition and a dip-molded article. [Background technology]

[0002] Dip-molded articles of chloroprene polymer compositions containing chloroprene polymers have been widely used in applications such as gloves, balloons, boots, catheters, and the like. Among these applications, particularly in the application of medical rubber gloves, there is a demand for dip-molded products that have excellent flexibility and excellent tensile strength at break, similar to those obtained using natural rubber or polyisoprene.

[0003] Generally, when the tensile strength at break of a dip-molded product is increased, the flexibility tends to decrease, and therefore it is difficult to simultaneously improve the tensile strength at break and impart flexibility. In an effort to obtain a dip-molded product that combines flexibility and tensile strength at break, Patent Document 1 discloses a chloroprene polymer composition in which a high-molecular-weight chloroprene polymer is blended with a low-molecular-weight chloroprene polymer. Furthermore, in an effort to further improve the tensile strength at break, Patent Document 2 discloses a chloroprene polymer composition obtained by a production method in which a monomer such as chloroprene is polymerized in the presence of a low-molecular-weight chloroprene polymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023 / 190145 [Patent Document 2] International Publication No. 2023 / 188802 Summary of the Invention [Problem to be solved by the invention]

[0005] The chloroprene polymer composition of Patent Document 2 makes it possible to obtain a dip-molded product that has both flexibility and tensile strength at break. However, a new problem has arisen in that the polymer composition obtained in the first polymerization stage is sticky and sticks to the reactor after polymerization, resulting in a decrease in recovery rate.

[0006] In view of the above circumstances, an object of the present invention is to provide a chloroprene polymer composition that can give a dip-molded article that satisfies both flexibility and tensile strength at break, and that can be produced efficiently by suppressing stickiness of the polymer obtained in the first polymerization step, and a dip-molded article using the chloroprene polymer composition. [Means for solving the problem]

[0007] [1] A chloroprene polymer composition comprising a polymer component (S), the polymer component (S) comprising a chloroprene polymer containing a unit derived from chloroprene, In the molecular weight distribution obtained by measuring the tetrahydrofuran-soluble portion of the polymer component (S) by gel permeation chromatography, a low molecular weight peak (P1) having a peak top in the molecular weight range of 50,000 to 80,000 is detected, A chloroprene polymer composition characterized in that a test dip-molded product obtained by molding under the following molding conditions has a toluene swelling degree, as represented by the following formula (1), of 12.0 or less. Toluene swelling degree = 1 + (W2 / W1-1)(d1 / d2)(1 / r) Equation (1) (In formula (1), W1 represents the mass of the test dip-molded product before immersion in toluene, W2 represents the mass of the test dip-molded product after immersion in toluene, d1 represents the density of the polymer component (S) in the test dip-molded product at 23°C, d2 represents the density of toluene at 23°C, and r represents the mass fraction of the polymer component (S) of the chloroprene polymer composition in the test dip-molded product.) (Molding conditions) A 200 mm tip of a ceramic cylinder with an outer diameter of 50 mm was immersed for 1 second in a coagulation solution containing 62 parts by mass of water, 35 parts by mass of potassium nitrate tetrahydrate, and 3 parts by mass of calcium carbonate, then removed and dried for 3 minutes. The cylinder was then immersed for 2 minutes in the test composition described below, washed with running water at 45°C for 1 minute, and dried at 140°C for 1 hour to form a film on the circumferential surface of the cylinder. The formed film was then cut open along the length of the cylinder to form a rectangular dip-molded test specimen. (Test Composition) A test composition containing 100 parts by mass of the chloroprene polymer composition as a solid content, 2.0 parts by mass of zinc oxide, 2.0 parts by mass of a butylated reaction product of p-cresol and dicyclopentadiene, 1.0 part by mass of 2-mercaptobenzimidazole, 0.1 part by mass of a sodium salt of a β-naphthalenesulfonic acid formalin condensate, and water, the amount of water being adjusted so that the solid content concentration of the test composition would be 30% by mass. [2] The chloroprene polymer composition according to [1], wherein the solid content of the polymer component (S1) having a molecular weight in the range of [the molecular weight at the peak top of the low-molecular-weight peak (P1)+3.5 times the half-value width of the low-molecular-weight peak (P1)] and [the molecular weight at the peak top of the low-molecular-weight peak (P1)−0.6 times the half-value width of the low-molecular-weight peak (P1)] in the molecular weight distribution is 20 to 65 mass%, relative to 100 mass% of the total solid content of the polymer component (S). [3] The chloroprene polymer composition according to [2], wherein in the molecular weight distribution, the solid content of the polymer component (S2) having a molecular weight of 25,000 or less is 18 mass% or less relative to 100 mass% of the total solid content of the polymer component (S). [4] The chloroprene polymer composition according to any one of [1] to [3], wherein the toluene-insoluble content of the chloroprene polymer composition is 50 to 90 mass % relative to 100 mass % of the total solid content of the chloroprene polymer composition. [5] The polymer component (S) contains units derived from chloroprene and units derived from 2,3-dichloro-1,3-butadiene, The chloroprene polymer composition according to any one of [1] to [4], containing 8 to 20 mass% of the units derived from 2,3-dichloro-1,3-butadiene, relative to 100 mass% in total of the units derived from chloroprene and the units derived from 2,3-dichloro-1,3-butadiene. [6] The chloroprene polymer composition according to any one of [1] to [5], wherein the polymer component (S) is a latex dispersed in water. [7] A dip-molded product obtained by vulcanizing a composition for forming a dip-molded product, wherein the composition for forming a dip-molded product contains the chloroprene polymer composition according to [6]. [8] The dip-molded product according to [7], which is an industrial or general household glove, a medical glove, a balloon, a catheter, or a boot. [9] A method for producing a chloroprene-based polymer composition, comprising polymerizing a raw material monomer (A) containing chloroprene to obtain a precursor polymer (X), and then polymerizing a raw material monomer (B) containing chloroprene in the presence of the precursor polymer (X), A method for producing a chloroprene polymer composition, wherein a low molecular weight peak (P2) having a peak top in the molecular weight range of 45,000 to 75,000 is detected in the molecular weight distribution obtained by measuring the tetrahydrofuran-soluble portion of the precursor polymer (X) by gel permeation chromatography.

[10] Each of the raw material monomer (A) and the raw material monomer (B) contains chloroprene and 2,3-dichloro-1,3-butadiene, The method for producing a chloroprene polymer composition according to [9], wherein the 2,3-dichloro-1,3-butadiene is contained in an amount of 8 to 20% by mass relative to 100% by mass in total of the chloroprene and the 2,3-dichloro-1,3-butadiene.

[11] The method for producing a chloroprene polymer composition according to [9] or

[10] , wherein the raw material monomer (B) is polymerized in the presence of 5 to 60 parts by mass of the precursor polymer (X) relative to 100 parts by mass of the raw material monomer (B). [Effects of the Invention]

[0008] The chloroprene polymer composition of the present invention can be used to obtain a dip-molded product that has both flexibility and tensile strength at break, and can be produced with high production efficiency. Furthermore, the method for producing a chloroprene polymer composition of the present invention can provide a chloroprene polymer composition from which a dip-molded article having both flexibility and tensile strength at break can be obtained. In addition, since the stickiness of the polymer obtained in the first polymerization step is suppressed, the composition can be produced with high production efficiency. Furthermore, the dip-molded product of the present invention can achieve both flexibility and tensile strength at break, and can be produced efficiently. DETAILED DESCRIPTION OF THE INVENTION

[0009] The meanings and definitions of terms used in this specification are as follows: A numerical range expressed by "to" means that the numerical values before and after "to" are the lower and upper limits of the numerical range. The "unit" constituting a polymer means an atomic group formed directly by polymerization of a monomer.

[0010] <Chloroprene-based polymer composition> The chloroprene polymer composition of the present embodiment (hereinafter sometimes referred to as "the composition") contains a polymer component (S). The polymer component (S) is a component made of a chloroprene polymer containing units derived from chloroprene. The molecular weight distribution of the polymer component (S) is such that a low molecular weight peak (P1) is detected with a peak top in the molecular weight range of 50,000 to 80,000. Furthermore, by molding this composition under specific molding conditions, it is possible to obtain test immersion molded products having a low degree of swelling in toluene, i.e., sufficiently crosslinked products.

[0011] [Units constituting polymer component (S)] The polymer component (S) is a component made of a chloroprene polymer, which is a diene rubber having a double bond in the main chain. The chloroprene polymer contains at least units derived from chloroprene (2-chloro-1,3-butadiene).

[0012] The polymer component (S) preferably contains, in addition to chloroprene units, units derived from 2,3-dichloro-1,3-butadiene. Both chloroprene and 2,3-dichloro-1,3-butadiene are conjugated diene monomers having conjugated double bonds. By including units based on conjugated diene monomers, the polymer component (S) has double bonds in the main chain.

[0013] The polymer component (S) may contain, in addition to chloroprene units and 2,3-dichloro-1,3-butadiene units, units based on other monomers as long as the effects of the present invention are not impaired. Examples of other monomers include diene monomers other than chloroprene and 2,3-dichloro-1,3-butadiene, and monomers other than diene monomers that are copolymerizable with diene monomers.

[0014] The diene monomer other than chloroprene and 2,3-dichloro-1,3-butadiene is preferably a conjugated diene monomer from the viewpoint of flexibility of the dip-molded article obtained from the present composition. Furthermore, the number of carbon atoms of the diene monomer other than chloroprene and 2,3-dichloro-1,3-butadiene is preferably 4 to 6, more preferably 4 or 5, and particularly preferably 4. When the diene monomer has 4 or more carbon atoms, it can have a conjugated double bond.

[0015] The diene monomers other than chloroprene and 2,3-dichloro-1,3-butadiene preferably have a halogen atom as a substituent, particularly a chlorine atom, similar to chloroprene and 2,3-dichloro-1,3-butadiene. By having a halogen atom as a substituent, the oil resistance and weather resistance of the dip-molded article obtained from the composition are improved.

[0016] Examples of conjugated diene monomers having 4 to 6 carbon atoms other than chloroprene and 2,3-dichloro-1,3-butadiene include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1-chloro-1,3-butadiene. Examples of monomers other than diene-based monomers that can be copolymerized with diene-based monomers include styrene, methacrylic acid, acrylonitrile, and sulfur.

[0017] The polymer component (S) preferably contains 50 to 100 mass% of units based on a conjugated diene monomer having 4 to 6 carbon atoms, based on 100 mass% of all units constituting the polymer component (S), more preferably 70 to 100 mass%, and particularly preferably 100 mass%. By containing the units based on the conjugated diene monomer having 4 to 6 carbon atoms in an amount equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the present composition is improved.

[0018] Furthermore, polymer component (S) preferably contains 50 to 100 mass% of chloroprene units and 2,3-dichloro-1,3-butadiene units in total, based on 100 mass% of all units constituting polymer component (S), more preferably 70 to 100 mass%, and particularly preferably 100 mass%. By containing chloroprene units and 2,3-dichloro-1,3-butadiene units in total in an amount equal to or greater than the preferred lower limit, the tensile strength at break and flexibility of a dip-molded article obtained from the present composition are improved.

[0019] The polymer component (S) preferably contains 64 to 92 mass% of chloroprene units, more preferably 66.4 to 90 mass%, and even more preferably 69.6 to 89.5 mass%, relative to 100 mass% of all units constituting the polymer component (S). When the proportion of chloroprene units is equal to or greater than the preferred lower limit, the tensile strength at break of a dip-molded article obtained from the composition is improved, and when the proportion is equal to or less than the preferred upper limit, the flexibility of a dip-molded article obtained from the composition is improved.

[0020] The polymer component (S) preferably contains 6.4 to 20 mass% of 2,3-dichloro-1,3-butadiene units, more preferably 8 to 17 mass%, and even more preferably 8.4 to 13 mass%, relative to 100 mass% of all units constituting the polymer component (S). When the proportion of 2,3-dichloro-1,3-butadiene units is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0021] The polymer component (S) preferably contains 8 to 20 mass% of 2,3-dichloro-1,3-butadiene units, more preferably 10 to 17 mass%, and even more preferably 10.5 to 13 mass%, of chloroprene units and 2,3-dichloro-1,3-butadiene units constituting the polymer component (S) combined (100 mass%). When the proportion of 2,3-dichloro-1,3-butadiene units is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0022] The polymer component (S) is roughly classified into a mercaptan-modified type, a xanthogen-modified type, and a sulfur-modified type depending on the type of chain transfer agent used during polymerization. From the viewpoint of molecular weight controllability, the mercaptan-modified type is preferred.

[0023] [Molecular weight distribution of polymer component (S)] The polymer component (S) has a molecular weight distribution in which a low molecular weight peak (P1) having a peak top in the molecular weight range of 50,000 to 80,000 is detected in the polystyrene-equivalent molecular weight distribution obtained by measuring the tetrahydrofuran-soluble portion (23°C) by gel permeation chromatography. The specific method for determining the molecular weight distribution will be described in detail in the Examples.

[0024] The peak top of the low molecular weight peak (P1) is preferably in the molecular weight range of 50,000 to 75,000. By setting the molecular weight of the peak top of the low molecular weight peak (P1) to 50,000 or more, the stickiness of the polymer obtained in the first polymerization step is suppressed, and the tensile strength at break of the dip-molded article obtained from the composition is ensured.By setting the molecular weight of the peak top of the low molecular weight peak (P1) to 80,000 or less, the flexibility of the dip-molded article obtained from the composition is ensured.

[0025] In the molecular weight distribution of the polymer component (S), the solid content of the polymer component (S1) having a molecular weight in the range of [the molecular weight at the peak top of the low molecular weight peak (P1) + 3.5 times the half width of the low molecular weight peak (P1)] and [the molecular weight at the peak top of the low molecular weight peak (P1) - 0.6 times the half width of the low molecular weight peak (P1)] is preferably 20 to 65 mass%, and more preferably 30 to 65 mass%, relative to 100 mass% of the total solid content of the polymer component (S). Here, the proportion above the molecular weight of the peak top was set to 3.5 times the half-width, and the proportion below the molecular weight of the peak top was set to 0.6 times the half-width because the shape of the low-molecular-weight peak (P1) becomes broader above the molecular weight of the peak top.

[0026] When the ratio of the solid content of polymer component (S1) to the total solid content of polymer component (S) is at least the lower limit of the preferred range, the flexibility of the dip-molded article obtained from the composition is further improved, and when it is at most the upper limit of the preferred range, the tensile strength at break of the dip-molded article obtained from the composition is further improved.

[0027] In the molecular weight distribution of the polymer component (S), the solid content of the polymer component (S2) having a molecular weight of 25,000 or less is preferably 18% by mass or less relative to 100% by mass of the total solid content of the polymer component (S). When the ratio of the solid content of polymer component (S2) to the total amount of solid content of polymer component (S) is not more than the upper limit of the preferred range, the tensile strength at break of the dip-molded article obtained from the present composition is further improved.

[0028] In the molecular weight distribution of the polymer component (S), the solid content of the polymer component (S3) having a molecular weight of 3,000,000 or less is preferably 30 to 90 mass%, more preferably 30 to 85 mass%, relative to 100 mass% of the total solid content of the polymer component (S).

[0029] When the ratio of the solid content of polymer component (S3) to the total solid content of polymer component (S) is equal to or less than the upper limit of the preferred range, the proportion of high-molecular-weight components in polymer component (S) increases, and the tensile strength at break of the dip-molded article obtained from this composition is further improved. When the ratio is equal to or greater than the lower limit of the preferred range, the flexibility of the dip-molded article obtained from this composition is further improved.

[0030] The proportion of each of the polymer components (S1), (S2), and (S3) relative to the total amount of solids in the polymer component (S) can be determined by multiplying the proportion of tetrahydrofuran-soluble components relative to the total amount of solids in the polymer component (S) by the area proportion of each of the polymer components (S1), (S2), and (S3) in the gel permeation chromatogram.

[0031] The ratio of the solid content of polymer component (S4) having a molecular weight exceeding 3,000,000 to the total solid content of polymer component (S) (100% by mass) can be determined by subtracting the ratio of the solid content of polymer component (S3) to the total solid content of polymer component (S) (100% by mass) from 100% by mass. The molecular weight distribution of the polymer component (S) can be controlled by adjusting the breakdown of the units constituting the polymer component (S), the type and amount of the chain transfer agent, the polymerization temperature, the polymerization time, the polymerization rate, etc.

[0032] [Toluene swelling degree of test immersion molded product] This composition has a toluene swelling degree, as represented by the following formula (1), of 12.0 or less when a test dip-molded product is obtained by molding under the following molding conditions. Toluene swelling degree = 1 + (W2 / W1-1)(d1 / d2)(1 / r) Equation (1)

[0033] In formula (1), W1 represents the mass of the test dip-molded product before immersion in toluene, W2 represents the mass of the test dip-molded product after immersion in toluene, d1 represents the density of the polymer component (S) in the test dip-molded product at 23°C, d2 represents the density of toluene at 23°C, and r represents the mass fraction of the polymer component (S) of the chloroprene polymer composition in the test dip-molded product.

[0034] The d1 is the density of the polymer component (S) in the test dip-molded product at 23°C measured in accordance with JIS K6268, and the d2 is the density of toluene at 23°C measured using a DMA35 portable density meter manufactured by Anton Paar. The Anton Paar DMA35 portable density meter measures density by applying an electrical stimulus to a U-tube (a delicate glass tube) filled with a sample, causing it to vibrate, and obtaining the natural vibration frequency of the U-tube, which corresponds to the density. d2 can also be measured using other measurement methods as long as they produce the same value as the Anton Paar DMA35 portable density meter.

[0035] (Molding conditions) A 200 mm tip of a ceramic cylinder with an outer diameter of 50 mm was immersed for 1 second in a coagulation solution containing 62 parts by mass of water, 35 parts by mass of potassium nitrate tetrahydrate, and 3 parts by mass of calcium carbonate, then removed and dried for 3 minutes. The cylinder was then immersed for 2 minutes in the test composition described below, washed with running water at 45°C for 1 minute, and dried at 140°C for 1 hour to form a film on the circumferential surface of the cylinder. The formed film was then cut open along the length of the cylinder to form a rectangular dip-molded test specimen.

[0036] (Test Composition) A test composition containing 100 parts by mass of the chloroprene polymer composition as solid content, 2.0 parts by mass of zinc oxide, 2.0 parts by mass of a butylated reaction product of p-cresol and dicyclopentadiene, 1.0 part by mass of 2-mercaptobenzimidazole, 0.1 part by mass of a sodium salt of a β-naphthalenesulfonic acid formalin condensate, and water, the amount of water being adjusted so that the solid content concentration of the test composition would be 30% by mass.

[0037] The toluene swelling degree of the test immersion molded article is 12.0 or less, and preferably 10 or less. When the toluene swelling degree of the test dip-molded article is 12.0 or less, the dip-molded article obtained from the composition has sufficient tensile strength at break.When the toluene swelling degree of the test dip-molded article is equal to or greater than the preferred lower limit, the dip-molded article obtained from the composition has greater flexibility.

[0038] The degree of toluene swelling of the test dip-molded article indicates the degree of crosslinking of the test dip-molded article. The lower the degree of toluene swelling, the more advanced the crosslinking of the test dip-molded article. The degree of crosslinking of the test dip-molded specimen reflects the degree of crosslinking of the polymer component (S) in the composition. That is, the lower the degree of swelling in toluene, the more crosslinking of the polymer component (S) in the composition. The degree of swelling in toluene of the test immersion molded product can be controlled by adjusting the polymerization procedure of the polymer component (S), the type and amount of the chain transfer agent, the polymerization temperature, the polymerization time, the polymerization rate, and the like.

[0039] [Toluene insoluble matter in the present composition] The toluene-insoluble content of the composition is preferably 50 to 90 mass %, more preferably 60 to 85 mass %, relative to 100 mass % of the total solid content of the composition.

[0040] When the composition is a latex, it is freeze-dried to form a powder, and when the composition is a powder, it is immersed in toluene for 16 hours, and the proportion of the toluene insoluble matter can be calculated using the following formula (2). A specific method for calculating the toluene insoluble matter will be described in detail in the Examples. Toluene insolubles (gel fraction) = M2 / M1 × 100 (%) Equation (2) In formula (2), M1 represents the mass (dry solids) of the composition (or, in the case of latex, the freeze-dried product) before immersion in toluene, and M2 represents the mass (dry solids) of the gel fraction (insoluble fraction) separated after immersion in toluene.

[0041] When the toluene-insoluble content of the composition is equal to or greater than the preferred lower limit, the tensile strength at break of a dip-molded product obtained from the composition is increased.When the toluene-insoluble content of the composition is equal to or less than the preferred upper limit, the dip-molded product obtained from the composition is more flexible.

[0042] The proportion of the toluene-insoluble matter in the composition indicates the degree of crosslinking of the polymer component (S). The greater the proportion of the toluene-insoluble matter, the more advanced the crosslinking of the polymer component (S) in the composition. The proportion of the toluene-insoluble matter in the composition can be controlled by adjusting the polymerization procedure of the polymer component (S), the type and amount of the chain transfer agent, the polymerization temperature, the polymerization time, the polymerization rate, and the like.

[0043] [Emulsifier in test immersion molding] The present composition is obtained by extracting the same test immersion molding as the test immersion molding described above in the toluene swelling degree of the test immersion molding with an ethanol / toluene azeotropic mixture (ETA solution) specified in JIS K6229 and treating with hydrochloric acid, and analyzing the extract by gas chromatography. The ratio RB / RA of RA to RB is preferably 0.10 or more and 0.70 or less, more preferably 0.15 or more and 0.50 or less.

[0044] Here, RA is the peak area of the non-conjugated resin acid components obtained by the gas chromatography analysis, specifically the total peak area of dehydroabietic acid, pimaric acid, isopimaric acid, dihydroabietic acid, and their salts, and RB is the peak area of the conjugated resin acid components obtained by the gas chromatography analysis, specifically the total peak area of abietic acid, neoabietic acid, palustric acid, levopimaric acid, and their salts.

[0045] When RB / RA is at least the lower limit of the preferred range, the tensile strength at break of a dip-molded article obtained from the present composition is improved. RB / RA can be controlled by adjusting the type and amount of emulsifier (particularly rosin acid and its salts) used during emulsion polymerization of the polymer component (S).

[0046] [Changes in low-temperature hardness of test immersion molded products] The present composition preferably exhibits a low-temperature hardness change ΔH, expressed by the following formula (3), of 30 or less, more preferably 20 or less, when formed into the same test dip-molded product as the test dip-molded product described above in relation to the toluene swelling degree of the test dip-molded product. Low-temperature hardness change ΔH = HB - HA Equation (3)

[0047] In formula (3), HA represents the Shore hardness measured using a durometer type A at 23°C after heat-treating the test dip-molded specimens at 70°C for 30 minutes and then stacking the specimens to a thickness of 6.00±0.20 mm. HB represents the Shore hardness measured using a durometer type A at -10°C after the test dip-molded specimens were heated at 70°C for 30 minutes and then stored at -10°C for 168 hours and then stacked to a thickness of 6.00±0.20 mm.

[0048] In the HB measurement method, the heat treatment at 70°C for 30 minutes is carried out in order to melt the crystalline structure contained in the test immersion molded product before storing it at -10°C for 168 hours, and in the HA measurement method, the heat treatment at 70°C for 30 minutes is carried out in order to compare the conditions with those for HB measurement. The low-temperature hardness change ΔH can be controlled by adjusting the production conditions of the polymer component (S).

[0049] [Tensile strength at break of test specimens] The composition preferably has a tensile strength at break of 18.0 MPa or more, more preferably 19.0 MPa or more, and even more preferably 20.0 MPa or more, measured in accordance with JIS K6251 on the same test dip-molded product as the test dip-molded product described above in relation to the toluene swelling degree of the test dip-molded product. The specific method for measuring the tensile strength at break will be described in detail in the Examples.

[0050] [Modulus of test specimens at 100% elongation] The modulus of this composition at 100% elongation, measured in accordance with JIS K 6251 using the same test dip-molded product as described above in the toluene swelling degree of the test dip-molded product, is preferably 0.65 MPa or less, and more preferably 0.60 MPa or less. The specific method for measuring the modulus at 100% elongation will be described in detail in the Examples.

[0051] [latex] The present composition is preferably a latex in which the polymer component (S) is dispersed in water. When the present composition is a latex, the present composition may contain an emulsifier added during polymerization. Furthermore, any additives such as a freeze stabilizer, emulsion stabilizer, viscosity modifier, antioxidant, and preservative may be added after polymerization, provided that the effects of the present invention are not impaired.

[0052] When the present composition is a latex, the solid content of the polymer component (S) is preferably 20 to 70 mass %, and more preferably 45 to 65 mass %, relative to 100 mass % of the total amount of the present composition including water and optional additives.

[0053] <Method for producing chloroprene polymer composition> The method for producing a chloroprene polymer composition according to this embodiment (hereinafter sometimes referred to as "the present production method") is a method for producing a chloroprene polymer composition by polymerizing a raw material monomer (A) containing chloroprene to obtain a precursor polymer (X), and then polymerizing a raw material monomer (B) containing chloroprene in the presence of the precursor polymer (X). The present composition can be obtained by the present production method.

[0054] [Molecular weight distribution of precursor polymer (X)] The precursor polymer (X) preferably has a molecular weight distribution in which a low molecular weight peak (P2) having a peak top in the molecular weight range of 45,000 to 75,000 is detected in the molecular weight distribution obtained by measuring the tetrahydrofuran-soluble portion of the precursor polymer (X) by gel permeation chromatography.

[0055] By setting the molecular weight of the peak top of the low molecular weight peak (P2) within the preferred range, the polymer component (S) of the present composition can have a molecular weight distribution in which a low molecular weight peak (P1) with its peak top located in the molecular weight range of 50,000 to 80,000 can be detected.

[0056] The precursor polymer (X) can be obtained by polymerizing a raw material monomer (A) containing chloroprene. The precursor polymer (X) mainly becomes the polymer component (S3) in the polymer component (S).

[0057] [Raw material monomer (A)] The raw material monomer (A) contains at least chloroprene, and preferably contains 2,3-dichloro-1,3-butadiene in addition to chloroprene.

[0058] The raw material monomer (A) may contain, in addition to chloroprene and 2,3-dichloro-1,3-butadiene, other monomers within the range that does not impair the effects of the present invention. As the other monomers, similar to the other monomers mentioned in the description of the units based on other monomers constituting the polymer component (S), examples thereof include diene-based monomers other than chloroprene and 2,3-dichloro-1,3-butadiene, and monomers copolymerizable with diene-based monomers other than diene-based monomers, and preferred embodiments are also similar.

[0059] The raw material monomer (A) preferably contains 50 to 100 mass %, more preferably 70 to 100 mass %, and particularly preferably 100 mass % of a conjugated diene monomer having 4 to 6 carbon atoms relative to 100 mass % of the raw material monomer (A). By including the conjugated diene monomer having 4 to 6 carbon atoms in an amount equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the present composition is improved.

[0060] Furthermore, the raw material monomer (A) preferably contains 50 to 100 mass% of chloroprene and 2,3-dichloro-1,3-butadiene in total, based on 100 mass% of the raw material monomer (A), more preferably 70 to 100 mass%, and particularly preferably 100 mass%. By including chloroprene and 2,3-dichloro-1,3-butadiene in total in an amount equal to or greater than the preferred lower limit, the tensile strength at break and flexibility of a dip-molded product obtained from the present composition are improved.

[0061] The raw material monomer (A) preferably contains 64 to 92 mass % of chloroprene, more preferably 66.4 to 90 mass %, and even more preferably 69.6 to 89.5 mass %, based on 100 mass % of the raw material monomer (A). When the proportion of chloroprene is equal to or greater than the preferred lower limit, the tensile strength at break of the dip-molded article obtained from the composition is improved, and when the proportion is equal to or less than the preferred upper limit, the flexibility of the dip-molded article obtained from the composition is improved.

[0062] The raw material monomer (A) preferably contains 6.4 to 20 mass % of 2,3-dichloro-1,3-butadiene, more preferably 8 to 17 mass %, and even more preferably 8.4 to 13 mass %, based on 100 mass % of the raw material monomer (A). When the proportion of 2,3-dichloro-1,3-butadiene is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0063] The raw material monomer (A) preferably contains 8 to 20 mass% of 2,3-dichloro-1,3-butadiene, more preferably 10 to 17 mass%, and even more preferably 10.5 to 13 mass%, relative to 100 mass% in total of chloroprene and 2,3-dichloro-1,3-butadiene in the raw material monomer (A). When the proportion of 2,3-dichloro-1,3-butadiene is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0064] [Method for polymerizing raw material monomer (A)] Polymerization methods for the raw material monomer (A) containing chloroprene include emulsion 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.

[0065] In the case of emulsion polymerization, the raw material monomer (A) is charged into a polymerization vessel together with water, an emulsifier (dispersant), a reducing agent (e.g., sodium hydrogen sulfite, thiourea dioxide), a polymerization initiator, a chain transfer agent, an alkali (e.g., a metal hydroxide such as potassium hydroxide, sodium hydroxide), etc., and polymerized.

[0066] As the anionic emulsifier, it is preferable to use rosin acid and / or rosin acid salt. Examples of rosin acid salts include alkali metal salts such as sodium salts and potassium salts. The amount of rosin acid and / or rosin acid salt added is preferably 3.0 to 7.0 parts by mass per 100 parts by mass of the raw material monomer (A).

[0067] The rosin acid and / or rosin acid salt may contain a conjugated resin acid component and a non-conjugated resin acid component. Examples of the conjugated resin acid component include abietic acid, neoabietic acid, palustric acid, levopimaric acid, and salts thereof. Examples of the non-conjugated resin acid component include dehydroabietic acid, pimaric acid, isopimaric acid, dihydropimaric acid, dihydroabietic acid, and salts thereof.

[0068] The rosin acid and rosin acid salt used in the polymerization of the raw material monomer (A) preferably have a mass ratio of RA1 to RB1, RB1 / RA1, of 0.10 or more and 0.70 or less, more preferably 0.15 or more and 0.50 or less. Here, RA1 is the total mass of the non-conjugated resin acid components used in the polymerization of raw material monomer (A), namely, dehydroabietic acid, pimaric acid, isopimaric acid, dihydroabietic acid, and their salts, and RB1 is the total mass of the conjugated resin acid components used in the polymerization of raw material monomer (A), namely, abietic acid, neoabietic acid, palustric acid, levopimaric acid, and their salts. When RB1 / RA1 is equal to or greater than the lower limit of the preferred range, the tensile strength at break of a dip-molded article obtained from the composition is improved. When RB1 / RA1 is equal to or less than the upper limit of the preferred range, the flexibility of a dip-molded article obtained from the composition is improved.

[0069] As the emulsifier or dispersant, it is more preferable to use other anionic emulsifiers or dispersants in addition to rosin acid and / or rosin acid salts, and preferred anionic emulsifiers are sulfate-based or sulfonate-based emulsifiers. Specific examples include alkyl sulfonates having 8 to 20 carbon atoms, alkylaryl sulfates, condensates of sodium β-naphthalene sulfonate and formaldehyde, and sodium alkyl diphenyl ether disulfonate. The amount of the anionic emulsifier or dispersant added can be 0.05 to 5 parts by mass relative to 100 parts by mass of the raw material monomer (A), and more preferably 0.1 to 1.0 part by mass relative to 100 parts by mass of the raw material monomer (A).

[0070] The polymerization initiator is not particularly limited, and any known polymerization initiator generally used for polymerization of diene polymers can be used, including potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, and other organic peroxides.

[0071] The type of chain transfer agent is not particularly limited, and known chain transfer agents generally used in the polymerization of diene polymers 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.

[0072] By adjusting the type and amount of the chain transfer agent, it is possible to adjust the molecular weight distribution of the resulting precursor polymer (X). The amount of the chain transfer agent used is preferably 0.2 to 10 parts by mass, more preferably 0.4 to 5 parts by mass, per 100 parts by mass of the raw material monomer (A).

[0073] During emulsion polymerization, a polymerization terminator may be used as needed, such as diethylhydroxylamine, thiodiphenylamine, 4-tert-butylcatechol, or 2,2'-methylenebis-4-methyl-6-tert-butylphenol.

[0074] In the case of emulsion polymerization, the pH of the aqueous emulsion is preferably 10.5 to 13.5. The aqueous emulsion refers to a mixed solution of a chain transfer agent and a monomer 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. If 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. If the pH is 13.5 or lower, excessive viscosity increase during polymerization is suppressed, and the polymerization reaction can be controlled more stably.

[0075] The polymerization temperature is preferably within the range of 5 to 55° C. If it is 5° C. or higher, the emulsion will not freeze, and if it is 55° C. or lower, the raw material monomer (A) will not evaporate or boil. The polymerization rate is preferably in the range of 50 to 95%. The polymerization rate can be adjusted by adding a polymerization terminator to terminate the polymerization reaction or by stopping the addition of the polymerization initiator when the desired polymerization rate is reached. After the polymerization is completed, unreacted monomers can be removed by a conventional method such as vacuum distillation.

[0076] In the polymerization step of the raw material monomer (A), the polymerization can be started after all of the raw material monomers and chemicals to be used in the polymerization step are charged into a polymerization vessel before the start of polymerization, or at least a portion of the raw material monomers and / or chemicals to be used in the polymerization step can be charged into a polymerization vessel before the start of polymerization, and the remainder can be added in portions after the start of polymerization.

[0077] When at least a portion of the raw material monomers and chemicals are charged into a polymerization vessel before the start of polymerization, and the remaining raw material monomers and / or chemicals are added after the start of polymerization, the remaining raw material monomers and / or chemicals can be added in one or more divided portions, or can be added continuously at a constant flow rate.

[0078] The portionwise addition of the remaining raw material monomers and / or chemicals is preferably started when the polymerization rate of the raw material monomers charged before the start of polymerization reaches 50 to 95%. When the remainder of the raw material monomers is added after the initiation of polymerization, it is preferable to add 50 parts by mass or less of 100 parts by mass of all raw material monomers used in the polymerization step after the initiation of polymerization. When the remainder of the raw material monomers is added continuously after the initiation of polymerization, it is preferable to add the remaining raw material monomers over a period of 30 to 300 minutes.

[0079] [Raw material monomer (B)] The raw material monomer (B) contains at least chloroprene, and preferably contains 2,3-dichloro-1,3-butadiene in addition to chloroprene.

[0080] The raw material monomer (B) may contain, in addition to chloroprene and 2,3-dichloro-1,3-butadiene, other monomers within the range that does not impair the effects of the present invention. As the other monomers, similar to the other monomers mentioned in the description of the units based on other monomers constituting the polymer component (S), examples thereof include diene-based monomers other than chloroprene and 2,3-dichloro-1,3-butadiene, and monomers copolymerizable with diene-based monomers other than diene-based monomers, and preferred embodiments are also similar.

[0081] The raw material monomer (B) preferably contains 50 to 100 mass %, more preferably 70 to 100 mass %, and particularly preferably 100 mass % of a conjugated diene monomer having 4 to 6 carbon atoms relative to 100 mass % of the raw material monomer (B). By including the conjugated diene monomer having 4 to 6 carbon atoms in an amount equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the present composition is improved.

[0082] Furthermore, the raw material monomer (B) preferably contains 50 to 100 mass% of chloroprene and 2,3-dichloro-1,3-butadiene in total, based on 100 mass% of the raw material monomer (B), more preferably 70 to 100 mass%, and particularly preferably 100 mass%. By including chloroprene and 2,3-dichloro-1,3-butadiene in total in an amount equal to or greater than the preferred lower limit, the tensile strength at break and flexibility of a dip-molded product obtained from the present composition are improved.

[0083] The raw material monomer (B) preferably contains 64 to 92 mass % of chloroprene, more preferably 66.4 to 90 mass %, and even more preferably 69.6 to 89.5 mass %, based on 100 mass % of the raw material monomer (B). When the proportion of chloroprene is equal to or greater than the preferred lower limit, the tensile strength at break of the dip-molded article obtained from the composition is improved, and when the proportion is equal to or less than the preferred upper limit, the flexibility of the dip-molded article obtained from the composition is improved.

[0084] The raw material monomer (B) preferably contains 6.4 to 20 mass % of 2,3-dichloro-1,3-butadiene, more preferably 8 to 17 mass %, and even more preferably 8.4 to 13 mass %, based on 100 mass % of the raw material monomer (B). When the proportion of 2,3-dichloro-1,3-butadiene is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0085] The raw material monomer (B) preferably contains 8 to 20 mass% of 2,3-dichloro-1,3-butadiene, more preferably 10 to 17 mass%, and even more preferably 10.5 to 13 mass%, relative to 100 mass% in total of chloroprene and 2,3-dichloro-1,3-butadiene in the raw material monomer (B). When the proportion of 2,3-dichloro-1,3-butadiene is equal to or greater than the preferred lower limit, the flexibility of the dip-molded article obtained from the composition is improved. When the proportion is equal to or less than the preferred upper limit, the tensile strength at break of the dip-molded article obtained from the composition is improved.

[0086] [Method for polymerizing raw material monomer (B)] The polymerization of the raw material monomer (B) containing chloroprene is carried out in the presence of a precursor polymer (X) obtained by polymerizing the raw material monomer (A). Polymer component (S4) in polymer component (S) is mainly obtained by polymerizing raw material monomer (B) containing chloroprene.

[0087] The precursor polymer (X) may be added to the polymerization liquid in any form, and for example, the polymerization liquid obtained by polymerizing the raw material monomer (A) may be used as it is. When the precursor polymer (X) is obtained by emulsion polymerization of the raw material monomer (A), the latex-like composition precursor may be added to a polymerization liquid containing the raw material monomer (B) and the like.

[0088] Alternatively, the precursor polymer (X) may be separated from a polymerization solution obtained by polymerizing the raw material monomer (A), and the separated precursor polymer (X) may be added to a polymerization solution containing the raw material monomer (B) and the like. When a latex-like composition precursor is obtained by emulsion polymerization of the raw material monomer (A), the precursor polymer (X) can be separated by adding methanol to precipitate the precursor polymer (X) or by freeze-drying to obtain a powdery precursor polymer (X).

[0089] When polymerizing the raw material monomer (B), the precursor polymer (X) is preferably used in an amount of 5 to 60 parts by mass, more preferably 15 to 40 parts by mass, per 100 parts by mass of the raw material monomer (B). By using the precursor polymer (X) in an amount equal to or greater than the lower limit of the preferred range, the tensile strength at break of the dip-molded article obtained from the composition is improved, whereas by using the precursor polymer (X) in an amount equal to or less than the upper limit of the preferred range, the flexibility of the dip-molded article obtained from the composition is improved.

[0090] The polymerization method of the raw material monomer (B) includes emulsion 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.

[0091] In the case of emulsion polymerization, the raw material monomer (B) is charged into a polymerization vessel together with the precursor polymer (X), water, an emulsifier (dispersant), a reducing agent (e.g., sodium hydrogen sulfite), a polymerization initiator, a chain transfer agent, an alkali (e.g., a metal hydroxide such as potassium hydroxide or sodium hydroxide), and the like, and polymerized. As the polymerization initiator, those used in the polymerization of the raw material monomer (A) can be mentioned, and the preferred embodiments are also the same.

[0092] As the emulsifier, those used in the polymerization of the raw material monomer (A) can be mentioned, and the preferred embodiments are also almost the same. The rosin acid and rosin acid salt used in the polymerization of the raw material monomer (B) preferably have a mass ratio of RA2 to RB2, RB2 / RA2, of 0.10 or more and 0.70 or less, more preferably 0.15 or more and 0.50 or less. Here, RA2 is the total mass of the non-conjugated resin acid components used in the polymerization of raw material monomer (B), namely, dehydroabietic acid, pimaric acid, isopimaric acid, dihydroabietic acid, and their salts, and RB2 is the total mass of the conjugated resin acid components used in the polymerization of raw material monomer (B), namely, abietic acid, neoabietic acid, palustric acid, levopimaric acid, and their salts. When RB2 / RA2 is equal to or greater than the lower limit of the preferred range, the tensile strength at break of a dip-molded article obtained from the composition is improved. When RB2 / RA2 is equal to or less than the upper limit of the preferred range, the flexibility of a dip-molded article obtained from the composition is improved.

[0093] As the chain transfer agent, those used in the polymerization of the raw material monomer (A) can be mentioned, and the preferred embodiments are also almost the same. By adjusting the type and amount of the chain transfer agent, it is possible to adjust the molecular weight distribution of the resulting polymer component (S). The amount of the chain transfer agent used is preferably 0 to 0.4 parts by mass per 100 parts by mass of the raw material monomer (B).

[0094] In the emulsion polymerization, a polymerization terminator may be used as necessary. In the case of emulsion polymerization, the preferred pH of the aqueous emulsion, the preferred polymerization temperature and the preferred polymerization rate are the same as those in the case of polymerization of the raw material monomer (A). As in the case of polymerizing the raw material monomer (A), the polymerization can be started after all of the raw material monomers and chemicals to be used in the polymerization step are charged into a polymerization vessel before the start of polymerization, or at least a portion of the raw material monomers and / or chemicals to be used in the polymerization step can be charged into a polymerization vessel before the start of polymerization, and the remainder can be added in portions after the start of polymerization.

[0095] <Composition for forming immersion molded bodies> The composition for forming an immersion molded body of this embodiment includes the present composition of the above embodiment. The composition for forming an immersion molded body of this embodiment may contain one or more other polymer components in addition to the polymer component (S) of the present composition, as long as the effects of the present invention are not impaired.

[0096] Examples of other polymer components include natural rubber, isoprene-based polymers, butadiene-based polymers, styrene-butadiene-based polymers, chloroprene-based polymers, and acrylonitrile-butadiene-based polymers. The amount of polymer components other than the polymer component (S) in the composition for forming a dip-molded body is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the polymer component (S).

[0097] The composition for forming a dip-molded body of this embodiment preferably contains, in addition to the present composition, a vulcanizing agent, a vulcanization accelerator, a metal oxide, an emulsifier, and a dispersant. Note that it is not necessary to contain either or both of the vulcanizing agent and the vulcanization accelerator. In addition, the composition may contain, as necessary, an antioxidant, a heteroaromatic ring compound, and various additives such as a filler, a plasticizer, a pigment colorant, a wetting agent, and an antifoaming agent.

[0098] An example of the vulcanizing agent is sulfur. The amount of the vulcanizing agent added is preferably 0 to 10 parts by mass per 100 parts by mass of the solid content of the composition for forming a dip-molded body. The solid content of the composition includes not only the polymer component (S) but also the mass of the emulsifier and the like used during polymerization of the polymer component (S) (the same applies in the following explanations).

[0099] A vulcanization accelerator is an agent added during vulcanization of raw rubber to act with a vulcanizing agent to increase the vulcanization rate, thereby shortening the vulcanization time, lowering the vulcanization temperature, reducing the amount of vulcanizing agent, and improving the physical properties of the vulcanized rubber. Usually, this refers to an agent that accelerates the sulfur vulcanization reaction. Examples of vulcanization accelerators include, but are not limited to, thiuram-based, dithiocarbamate-based, thiourea-based, guanidine-based, xanthogenate-based, thiazole-based, etc. These may be used alone or in combination of two or more types as required.

[0100] Examples of thiuram vulcanization accelerators include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide.

[0101] 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.

[0102] Examples of the thiourea-based vulcanization accelerator include ethylene thiourea, N,N'-diethyl thiourea, trimethyl thiourea, and N,N'-diphenyl thiourea. 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.

[0103] Examples of xanthogenate-based vulcanization accelerators include zinc butylxanthogenate and zinc isopropylxanthogenate. 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.

[0104] The amount of vulcanization accelerator added is preferably 0 to 5.0 parts by mass, and more preferably 0 to 4.0 parts by mass, per 100 parts by mass of the solid content of the present composition contained in the composition for forming dip-molded bodies.

[0105] The composition for forming a dip-molded body of this embodiment contains a metal oxide together with a vulcanization accelerator, which promotes crosslinking of the polymer component and further improves the tensile strength at break. The metal oxide 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. Of these, zinc oxide is preferred. Zinc oxide is generally believed to function as a scavenger for chlorine atoms released from chloroprene polymers. The metal oxides may be used alone or in combination of two or more.

[0106] The amount of metal oxide added is preferably 0.5 to 15.0 parts by mass per 100 parts by mass of the solid content of the present composition contained in the composition for forming a dip molded body. When the amount of metal oxide added is equal to or greater than the preferred lower limit, the cross-linking effect between polymers is expected to improve the tensile strength at break.When the amount of metal oxide added is equal to or less than the preferred upper limit, a dip-molded product with excellent flexibility can be obtained. From the viewpoint of the balance of physical properties between the flexibility and tensile strength at break of the dip-molded product obtained, the amount of metal oxide added is more preferably 0.5 to 5.0 parts by mass.

[0107] In addition to the emulsifier derived from the present composition, the composition for forming a dip-molded body of this embodiment preferably contains an emulsifier or dispersant for dispersing the metal oxide. Examples of anionic emulsifiers and dispersants include sodium salt of β-naphthalenesulfonic acid formalin condensate.

[0108] The antioxidant is not particularly limited, and phenol-based antioxidants, amine-based antioxidants, heat-resistant oxidation (aging) inhibitors, ozone-resistant antioxidants, etc. can be used. When the dip-molded product is used as a medical glove, a phenolic antioxidant can be used from the viewpoint of the color tone, texture, and hygiene of the dip-molded product. In particular, a hindered phenolic antioxidant has a strong effect.

[0109] Examples of hindered phenol-based 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.

[0110] The amount of antioxidant added is preferably 0.5 to 10.0 parts by mass, and more preferably 0.5 to 5.0 parts by mass, per 100 parts by mass of the solid content of the composition contained in the composition for forming a dip-molded body. When the amount of antioxidant added is equal to or greater than the preferred lower limit, the effect of suppressing color change in the dip-molded body can be obtained. When the amount of antioxidant added is equal to or less than the preferred upper limit, the stability of the composition for forming a dip-molded body can be ensured.

[0111] The composition for forming a dip-molded body of the present embodiment may contain a heteroaromatic ring compound. Specifically, it is preferable to contain a heteroaromatic ring compound having a benzimidazole structure and represented by the following chemical formula (b1) (hereinafter, sometimes referred to as "compound (b1)"). The compound (b1) acts as a secondary antioxidant.

[0112] [ka]

[0113] In chemical formula (b1), X of the mercapto group represents a hydrogen atom or a metal atom. X may be a hydrogen atom, resulting in a thiol group. X may also be a metal atom, such as zinc, sodium, copper, nickel, or tellurium, with zinc being preferred. In the chemical formula (b1), R1 to R4 each represent a hydrogen atom, an alkyl group which may have a substituent, an ether group which may have a substituent, a nitro group, an amino group, or a carboxyl group. R1 to R4 may be the same or different.

[0114] Examples of compound (b1) include 2-mercaptobenzimidazole, 5-methyl-2-mercaptobenzimidazole, 4-methyl-2-mercaptobenzimidazole, 5-methoxy-2-mercaptobenzimidazole, 4-methoxy-2-mercaptobenzimidazole, 5-nitro-2-mercaptobenzimidazole, 5-amino-2-mercaptobenzimidazole, 5-carboxy-2-mercaptobenzimidazole, and zinc salts of 2-mercaptobenzimidazole.

[0115] Of these, 2-mercaptobenzimidazole, 5-methyl-2-mercaptobenzimidazole, 4-methyl-2-mercaptobenzimidazole, 5-methoxy-2-mercaptobenzimidazole, 4-methoxy-2-mercaptobenzimidazole, and zinc salts of 2-mercaptobenzimidazole are preferred. The compound (b1) may be used alone or in combination of two or more.

[0116] The amount of compound (b1) added is preferably 0.2 to 10.0 parts by mass, and more preferably 0.3 to 5.0 parts by mass, per 100 parts by mass of the solid content of the present composition contained in the composition for forming a dip molded body. When the amount of compound (b1) added is equal to or greater than the preferred lower limit, the breaking strength of the resulting dip-molded product is increased, whereas when the amount is equal to or less than the preferred upper limit, the stability of the composition for forming a dip-molded product is ensured.

[0117] The composition for forming a dip-molded body of this embodiment can be produced by mixing the above-mentioned metal oxide and the like with the present composition. Regarding the components to be added to the present composition, such as metal oxides, an aqueous dispersion containing these components may be prepared in advance, and this aqueous dispersion may be mixed with the present composition. The mixing can be carried out using a known mixing device such as a ball mill.

[0118] <Dip molded product> The dip-molded product of this embodiment is a dip-molded product obtained by vulcanizing the composition for forming a dip-molded product of the above embodiment, which contains the present composition. Examples of the dip molding method for obtaining a dip molded body include a dip solidification method, a simple dip method, a heat-sensitive dip method, an electrodeposition method, etc. From the viewpoints of ease of production and ease of obtaining a dip molded body with a uniform thickness, it is preferable to use the dip solidification method.

[0119] In the immersion coagulation method, a mold coated with a coagulation liquid containing a coagulant is immersed in the composition for forming an immersion molded body of the above embodiment, and the composition for forming an immersion molded body is coagulated on the surface. After drying for a short time, the mold is washed with warm water to remove water-soluble impurities by leaching, and then further dried. After that, the mold is heated and vulcanized to form a immersion molded film (rubber coating). The formed immersion molded film is demolded to obtain a film-like immersion molded body.

[0120] As the coagulant, an inorganic salt having a salting-out effect can be used, for example, a polyvalent metal salt such as a calcium salt. Examples of calcium salts include calcium carbonate and calcium nitrate. There are no particular limitations on the material of the mold, and a mold made of ceramics, etc. is usable. Since it is heated during vulcanization, a mold made of ceramics is preferred.

[0121] The heating temperature during vulcanization is preferably 120 to 180°C, more preferably 120 to 150°C. When the heating temperature is equal to or higher than the preferred lower limit, the tensile strength at break of the dip-molded article obtained from the composition is improved. When the heating temperature is equal to or lower than the preferred upper limit, the flexibility of the dip-molded article obtained from the composition is improved. The heating time is preferably 10 to 300 minutes. When the heating time is equal to or greater than the preferred lower limit, the tensile strength at break of the dip-molded product obtained from the composition is improved. When the heating time is equal to or less than the preferred upper limit, the flexibility of the dip-molded product obtained from the composition is improved.

[0122] The thickness of the dip-molded product can be adjusted appropriately within the range of 0.01 to 0.50 mm depending on the application. The thickness of the dip-molded product can be adjusted by the time for which the mold is immersed in the composition for forming a dip-molded product, the solids concentration of the composition for forming a dip-molded product, etc. To reduce the thickness of the dip-molded product, the immersion time can be shortened or the solids concentration of the composition for forming a dip-molded product can be reduced. [Example]

[0123] <Measurement method> The measurements and the like in the following description were obtained by the following methods.

[0124] [Polymerization rate] The polymerization rate in each synthesis example, example, and comparative example was measured as follows. 5 ml of the polymerization solution was mixed with a large amount of methanol to precipitate the rubber, which was then filtered and dried, and the weight of the dried rubber was measured. The polymerization rate was calculated from the measured weight.

[0125] [Recovery rate] The total amount of latex obtained in each synthesis example was extracted from the polymerization vessel, and the mass was measured, which was taken as the actual weight of the precursor polymer latex after polymerization. The recovery rate of the precursor polymer was calculated from the actual weight of the precursor polymer latex after polymerization and the theoretical weight of the precursor polymer latex according to the following formula (4): When the precursor polymer latex was extracted from the polymerization vessel, the stickier the precursor polymer latex was, the more the precursor polymer latex adhered to the wall of the polymerization vessel, and the less the amount recovered.

[0126] (Recovery rate of precursor polymer latex) = (actual weight of precursor polymer latex) / (theoretical weight of precursor polymer latex) Equation (4) The theoretical weight of the precursor polymer latex in formula (4) was calculated by subtracting the amounts of unreacted monomers and water removed from the system by vacuum distillation and concentration after polymerization from the charged amount. The theoretical weight of the precursor polymer latex corresponds to the amount of precursor polymer latex present in the polymerization vessel just before the recovery operation from the polymerization vessel.

[0127] [Molecular weight distribution] The molecular weight distribution of the precursor polymer obtained in each synthesis example and the polymer component obtained in each example and comparative example was determined from a chromatogram obtained as follows. First, a large amount of methanol was mixed with the latex obtained in each example to precipitate a rubber component (precursor polymer or polymer component), which was then filtered and dried to obtain a dried rubber component.

[0128] 20 mg of the dried rubber was dissolved in 20 ml of tetrahydrofuran to obtain a tetrahydrofuran-soluble fraction, which was used as a sample to obtain a chromatogram by gel permeation chromatography (GPC) under the measurement conditions described below. Narrow peaks in the chromatogram with a half-width molecular weight of 1000 or less were not considered to be peaks.

[0129] Device name: HLC-8320 (manufactured by Tosoh Corporation). Column: Three TSKgel GMHHR-H columns in series. Temperature: 40℃. Detection: Differential refractive index. Solvent: tetrahydrofuran. Calibration curve: Prepared using standard polystyrene (PS).

[0130] [Units that make up polymer components] The freeze-dried latex obtained in each Example and Comparative Example was freeze-dried, and the freeze-dried product was cut into a 0.05 mg test piece, which was measured by pyrolysis gas chromatography under the following conditions to determine the area ratio of the peak derived from chloroprene to the peak derived from 2,3-dichloro-1,3-butadiene. 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, the content (mass%) of 2,3-dichloro-1,3-butadiene unit relative to 100 mass% of the total of chloroprene unit and 2,3-dichloro-1,3-butadiene unit was determined.

[0131] Device name: HP5890-II (Agilent Technologies). 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

[0132] [Toluene insolubles] The latex obtained in each Example and Comparative Example was freeze-dried, and the freeze-dried product was cut into 2 mm squares to obtain test pieces. 20 test pieces and 80 g of toluene were placed in a conical beaker and immersed at 23°C for 16 hours. After centrifugation, the gel fraction (insoluble matter) was separated using a 200-mesh wire net. The gel fraction was then dried, and the mass of the dried product was measured.

[0133] The toluene insoluble content in the latex was calculated by the following formula (2), where M1 is the freeze-dried latex after freeze-drying, and M2 is the dried gel content (insoluble content) separated from the toluene-dissolved mixture. Toluene insolubles (gel fraction) = M2 / M1 × 100 (%) Equation (2)

[0134] [Thickness of test immersion molding] The dip-molded test specimens of each Example and Comparative Example were punched out into a flat dumbbell shape No. 3 as specified in JIS K 6251 to prepare test specimens for each Example. The thickness of three points on the parallel portion of each test piece was measured using a test piece thickness gauge (manufactured by Kobunshi Keiki Co., Ltd., trade name: ASKER SDA-12), and the smallest thickness was taken as the thickness of the dip-molded test piece.

[0135] [Tensile properties of test specimens] Using the test pieces of each example prepared in the measurement of the thickness of the dip-molded test pieces, the modulus at 100% elongation and the tensile strength at break were measured in accordance with JIS K 6251 at a tension speed of 500 mm / min.

[0136] [Toluene swelling degree] The dip-molded test specimens of each Example and Comparative Example were cut into 10 mm x 15 mm pieces to obtain test specimens. The mass W1 of the obtained test specimen before immersion was measured, and the test specimen was then immersed in toluene for 20 hours in an environment of 23°C. After immersion, the test specimen was removed from the toluene, and the toluene on the surface of the dip-molded test specimen was wiped off, after which the mass W2 of the test specimen after immersion was measured. The toluene swelling degree was calculated from the measured mass W1 before immersion and mass W2 after immersion using the following formula (1): Toluene swelling degree = 1 + (W2 / W1-1)(d1 / d2)(1 / r) Equation (1)

[0137] In formula (1), d1 is the density of the polymer component in the test immersion molded product at 23° C. Specifically, a large amount of methanol was mixed with the latex obtained in each example to precipitate the rubber component (polymer component), which was then filtered and dried, and the density of the dried rubber component was measured in accordance with JIS K6268.

[0138] In equation (1), d2 is the density of toluene at 23°C, and is the value (0.866 g / cm) measured using an Anton Paar DMA35 portable density meter. 3 ) In formula (1), r is the mass fraction of the polymer component (S) of the chloroprene polymer composition in the test dip-molded product, and is the value obtained by dividing the mass of the test composition excluding components other than the polymer component, such as zinc oxide and an emulsifier, by the mass of the test dip-molded product.

[0139] <Synthesis of precursor polymer (X)> [Synthesis example X-1] A 30 L polymerization vessel was charged with 64 parts by mass of chloroprene, 9 parts by mass of 2,3-dichloro-1,3-butadiene, 90 parts by mass of pure water, 4.5 parts by mass of conjugated resin acid-based rosin acid (trade name "Harthall R-WW", manufactured by Harima Chemicals Co., Ltd.), 0.8 parts by mass of n-dodecyl mercaptan, 1.6 parts by mass of potassium hydroxide, 0.5 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol N", manufactured by Kao Corporation), and 0.5 parts by mass of sodium hydrogen sulfite.

[0140] Polymerization was carried out at a polymerization temperature of 35°C under a nitrogen stream by continuously adding a 0.35 mass% aqueous potassium persulfate solution as a polymerization initiator. When the polymerization rate of the charged monomers reached 80%, 27 parts by mass of chloroprene was continuously added over 100 minutes. When the polymerization rate of the initially charged monomers and the continuously added monomers reached 91%, the addition of the aqueous potassium persulfate solution was stopped to terminate the polymerization, thereby obtaining a polymerization liquid. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of precursor polymer X-1 with a solid content of 60% by mass.

[0141] [Synthesis example X-2] Polymerization was carried out in the same manner as in Synthesis Example X-1, except that the amount of n-dodecyl mercaptan used in Synthesis Example X-1 was changed to 0.55 parts by mass. The resulting polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of precursor polymer X-2 with a solid content of 60% by mass.

[0142] [Synthesis example X-3] Polymerization was carried out in the same manner as in Synthesis Example X-1, except that the amount of n-dodecyl mercaptan used in Synthesis Example X-1 was changed to 0.44 parts by mass. The resulting polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of precursor polymer X-3 with a solid content of 60% by mass.

[0143] [Synthesis example X-4] Polymerization was carried out in the same manner as in Synthesis Example X-1, except that the amount of n-dodecyl mercaptan used in Synthesis Example X-1 was changed to 3.4 parts by mass. The resulting polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of precursor polymer X-4 with a solid content of 60% by mass.

[0144] [Synthesis example X-5] Polymerization was carried out in the same manner as in Synthesis Example X-1, except that the amount of n-dodecyl mercaptan used in Synthesis Example X-1 was changed to 1.5 parts by mass. The resulting polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of precursor polymer X-5 with a solid content of 60% by mass.

[0145] Table 1 shows the raw material composition used in each synthesis example, the polymerization temperature, the conversion at the time of polymerization termination, the peak-top molecular weight in the molecular weight distribution of the precursor polymer obtained in each synthesis example, and the recovery rate for each synthesis example.

[0146] [Table 1]

[0147] <Examples and Comparative Examples> [Example 1] A large amount of methanol was mixed with the latex of the precursor polymer X-1 obtained in Synthesis Example X-1 to precipitate a rubber component (precursor polymer X-1), which was then filtered and dried to obtain a dried precursor polymer X-1.

[0148] A 30 L polymerization vessel was charged with 21.3 parts by mass of the dried precursor polymer X-1, 91 parts by mass of chloroprene, 9 parts by mass of 2,3-dichloro-1,3-butadiene, 100 parts by mass of pure water, 5.5 parts by mass of conjugated resin acid-based rosin acid (trade name "Heartall R-WW", manufactured by Harima Chemicals Co., Ltd.), 2 parts by mass of potassium hydroxide, 0.5 part by mass of a sodium salt of a β-naphthalenesulfonic acid formalin condensate (trade name "Demol N", manufactured by Kao Corporation), 0.5 part by mass of sodium hydrogen sulfite, and 0.03 part by mass of thiourea dioxide.

[0149] Polymerization was carried out at a polymerization temperature of 13°C under a nitrogen stream by continuously adding a 0.35 mass% aqueous solution of potassium persulfate as a polymerization initiator. When the polymerization rate reached 85%, 0.1 mass parts of diethylhydroxylamine as a polymerization terminator was added to terminate the polymerization, obtaining a polymerization liquid. The obtained polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 1 containing a chloroprene polymer with a solid content of 60 mass%.

[0150] [Example 2] A polymerization liquid was obtained in the same manner as in Example 1, except that the latex of precursor polymer X-2 obtained in Synthesis Example X-2 was used instead of the latex of precursor polymer X-1 in Example 1. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 2 containing a chloroprene polymer at a solid content of 60% by mass.

[0151] [Example 3] A polymerization liquid was obtained in the same manner as in Example 1, except that the precursor polymer X-3 obtained in Synthesis Example X-3 was used instead of the latex of precursor polymer X-1 in Example 1. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 3 containing a chloroprene polymer at a solid content of 60% by mass.

[0152] [Example 4] A polymerization liquid was obtained in the same manner as in Example 2, except that the amount of precursor polymer X-2 in Example 2 was 45.8 parts by mass. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 4 containing a chloroprene polymer at a solid content of 60% by mass.

[0153] [Example 5] A polymerization liquid was obtained in the same manner as in Example 2, except that the amount of precursor polymer X-2 in Example 2 was 9.5 parts by mass. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 5 containing a chloroprene polymer at a solid content of 60% by mass.

[0154] [Example 6] A polymerization liquid was obtained in the same manner as in Example 2, except that the amount of chloroprene was 93 parts by mass and the amount of 2,3-dichloro-1,3-butadiene was 7 parts by mass. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Example 6 containing a chloroprene-based polymer with a solid content of 60% by mass.

[0155] [Comparative Example 1] A polymerization liquid was obtained in the same manner as in Example 1, except that precursor polymer X-4 was used instead of precursor polymer X-1 in Example 1. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Comparative Example 1 containing a chloroprene polymer at a solid content of 60% by mass.

[0156] Comparative Example 2 A polymerization liquid was obtained in the same manner as in Example 1, except that precursor polymer X-5 was used instead of precursor polymer X-1 in Example 1. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain a latex of Comparative Example 2 containing a chloroprene polymer at a solid content of 60% by mass.

[0157] Comparative Example 3 To a 30 L polymerization vessel were added 91 parts by mass of chloroprene, 9 parts by mass of 2,3-dichloro-1,3-butadiene, 100 parts by mass of pure water, 4.5 parts by mass of conjugated resin acid-based rosin acid (trade name "Harthall R-WW", manufactured by Harima Chemicals Co., Ltd.), 0.02 parts by mass of n-dodecyl mercaptan, 1.6 parts by mass of potassium hydroxide, 0.5 part by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol N", manufactured by Kao Corporation), 0.5 part by mass of sodium hydrogen sulfite, and 0.03 part by mass of thiourea dioxide.

[0158] Polymerization was carried out at a polymerization temperature of 13°C under a nitrogen stream by continuously adding a 0.35 mass% aqueous solution of potassium persulfate as a polymerization initiator. When the polymerization rate reached 85%, 0.1 mass parts of diethylhydroxylamine as a polymerization terminator was added to terminate the polymerization, obtaining a polymerization liquid. The polymerization liquid was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain latex Y1 containing a chloroprene polymer with a solid content of 60 mass%.

[0159] A polymerization solution was obtained in the same manner as in Synthesis Example X-1. The obtained polymerization solution was distilled under reduced pressure to remove unreacted monomers, and then concentrated to obtain Latex Y2 containing a chloroprene polymer with a solid content of 60% by mass. The latex Y1 and the latex Y2 were mixed in a mass ratio of Y1 / Y2=80 / 20 to obtain a latex of Comparative Example 3 containing a chloroprene polymer.

[0160] <Preparation of dip-molded product> Using the latex obtained in each Example and Comparative Example, i.e., a latex containing a chloroprene polymer, a test dip composition was prepared by the following method, which was then dip-molded to obtain a dip-molded body, and the dip-molded body was further subjected to a heat drying treatment to produce a test dip-molded body.

[0161] [Preparation of Test Composition] An aqueous dispersion was prepared by mixing 2 parts by mass of two types of zinc oxide, 2 parts by mass of a butylation reaction product of p-cresol and dicyclopentadiene (trade name "Nocrac PBK", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 1.0 part by mass of 2-mercaptobenzimidazole (trade name "Nocrac MB", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), which is a heteroaromatic ring compound, 0.1 part by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (trade name "Demol N", manufactured by Kao Corporation), and 10.7 parts by mass of water at 20°C for 16 hours using a ceramic ball mill.

[0162] A test composition for each example was prepared by adding 15.8 parts by mass of the aqueous dispersion and water to 100 parts by mass of the latex obtained in each example and comparative example in terms of solid content. The amount of water added to the latex together with the aqueous dispersion was set to an amount that would give a solids concentration of the test composition of 30% by mass (specifically, 101.2 parts).

[0163] [Dip molding] The tip 200 mm of a ceramic cylinder (manufactured by Shinko Co., Ltd.) with an outer diameter of 50 mm was immersed for 1 second in a coagulation solution containing 62 parts by mass of water, 35 parts by mass of potassium nitrate tetrahydrate, and 3 parts by mass of calcium carbonate, then removed and dried for 3 minutes. The cylinder was then immersed for 2 minutes in the test composition of each Example or Comparative Example, washed with running water at 45°C for 1 minute, and dried at 140°C for 1 hour to form a film on the circumferential surface of the cylinder. The formed film was cut open along the length of the cylinder to form a rectangular test piece for each Example.

[0164] Table 2 shows the raw material composition, polymerization temperature, and conversion at the time of polymerization termination used in each example and comparative example. Furthermore, Table 3 shows the molecular weight distribution, toluene insoluble matter and 2,3-dichloro-1,3-butadiene unit content of the latex (chloroprene polymer) obtained in each example and comparative example, as well as the evaluation results of the dip-molded test specimens prepared using the latex obtained in each example and comparative example.

[0165] [Table 2]

[0166] [Table 3]

[0167] As shown in Table 1, the precursor polymers X-1 to X-3 used in the examples (see Table 2) had higher recovery rates than the precursor polymers X-4 and X-5 used in the comparative examples (see Table 2). The recovery rates of precursor polymers X-4 and X-5 were low because the polymers were sticky and stuck to the polymerization vessel, making some of them unrecoverable. This is thought to be because the molecular weight distributions of precursor polymers X-4 and X-5 had peaks at lower molecular weights than precursor polymers X-1 to X-3.

[0168] Furthermore, as shown in Table 3, all of the dip-molded test articles of the Examples exhibited tensile properties equivalent to those of Comparative Examples 1 and 2. Moreover, in Comparative Example 3, which did not use a two-stage polymerization method as in Examples and Comparative Examples 1 and 2, but mixed latexes of polymers with different molecular weights, the tensile strength at break was low. Therefore, it was confirmed that the polymer composition of the present invention can provide a dip-molded product that is compatible with flexibility and tensile strength at break, and that the production efficiency is also excellent. [Industrial Applicability]

[0169] The dip-molded products obtained using the chloroprene polymer composition of the present invention can be suitably used as industrial and general household gloves, medical gloves, balloons, catheters, or boots.

Claims

1. A chloroprene polymer composition comprising a polymer component (S), the polymer component (S) being a chloroprene polymer containing a unit derived from chloroprene, In the molecular weight distribution obtained by measuring the tetrahydrofuran-soluble portion of the polymer component (S) by gel permeation chromatography, a low molecular weight peak (P1) having a peak top in the molecular weight range of 50,000 to 80,000 is detected, A chloroprene polymer composition characterized in that a test dip-molded product obtained by molding under the following molding conditions has a toluene swelling degree, as represented by the following formula (1), of 12.0 or less. Toluene swelling degree=1+(W2 / W1−1)(d1 / d2)(1 / r) Equation (1) (In formula (1), W1 represents the mass of the test dip-molded product before immersion in toluene, W2 represents the mass of the test dip-molded product after immersion in toluene, d1 represents the density of the polymer component (S) in the test dip-molded product at 23°C, d2 represents the density of toluene at 23°C, and r represents the mass fraction of the polymer component (S) of the chloroprene polymer composition in the test dip-molded product.) (Molding conditions) A 200 mm tip of a ceramic cylinder with an outer diameter of 50 mm was immersed for 1 second in a coagulation solution containing 62 parts by mass of water, 35 parts by mass of potassium nitrate tetrahydrate, and 3 parts by mass of calcium carbonate, then removed and dried for 3 minutes. The cylinder was then immersed for 2 minutes in the test composition described below, washed with running water at 45°C for 1 minute, and dried at 140°C for 1 hour to form a film on the circumferential surface of the cylinder. The formed film was then cut open along the length of the cylinder to obtain a rectangular dip-molded test specimen. (Test Composition) A test composition containing 100 parts by mass of the chloroprene polymer composition as a solid content, 2.0 parts by mass of zinc oxide, 2.0 parts by mass of a butylated reaction product of p-cresol and dicyclopentadiene, 1.0 part by mass of 2-mercaptobenzimidazole, 0.1 part by mass of a sodium salt of a β-naphthalenesulfonic acid formalin condensate, and water, the amount of water being adjusted so that the solid content concentration of the test composition would be 30% by mass.

2. 2. The chloroprene polymer composition according to claim 1, wherein in the molecular weight distribution, a solid content of the polymer component (S1) having a molecular weight in the range of [the molecular weight at the peak top of the low-molecular-weight peak (P1) + 3.5 times the half-value width of the low-molecular-weight peak (P1)] and [the molecular weight at the peak top of the low-molecular-weight peak (P1) - 0.6 times the half-value width of the low-molecular-weight peak (P1)] is 20 to 65% by mass, relative to 100% by mass of the total solid content of the polymer component (S).

3. 3. The chloroprene polymer composition according to claim 2, wherein, in the molecular weight distribution, a solid content of the polymer component (S2) having a molecular weight of 25,000 or less is 18% by mass or less, relative to 100% by mass of the total solid content of the polymer component (S).

4. 2. The chloroprene polymer composition according to claim 1, wherein the toluene-insoluble matter in the chloroprene polymer composition is 50 to 90% by mass, relative to 100% by mass of the total solid content of the chloroprene polymer composition.

5. the polymer component (S) contains units derived from chloroprene and units derived from 2,3-dichloro-1,3-butadiene, 2. The chloroprene polymer composition according to claim 1, wherein the chloroprene polymer composition contains 8 to 20% by mass of the units derived from 2,3-dichloro-1,3-butadiene, relative to 100% by mass in total of the units derived from chloroprene and the units derived from 2,3-dichloro-1,3-butadiene.

6. 6. The chloroprene polymer composition according to claim 1, wherein the polymer component (S) is a latex dispersed in water.

7. A dip-molded product obtained by vulcanizing a composition for forming a dip-molded product, wherein the composition for forming a dip-molded product comprises the chloroprene polymer composition according to claim 6.

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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