Method for the production of a chloroprene graft copolymer latex

Abstract

A process for producing a chloroprene graft copolymer latex, the process comprising: a chloroprene polymerization step in which at least chloroprene (A-1) is subjected to an emulsion radical polymerization of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1) to form a chloroprene polymer and a chloroprene polymer latex is obtained in which particles of the chloroprene polymer are dispersed in water; and a graft copolymerization step in which a (meth)acrylate (B) of the general formula CH2=CR-CO-OR' (in the general formula R is a methyl group or a hydrogen atom; and R' is an alkyl group with a carbon number of 4 or more and 12 or less) is added to the chloroprene polymer latex, an organic peroxide (C) with an octanol / water partition coefficient of -2.0 or more and 3.0 or less is added as a polymerization initiator to subject the chloroprene polymer to a graft copolymerization with the (meth)acrylate (B) at a temperature of 10°C or more and 35°C or less to form a chloroprene graft copolymer, and a chloroprene graft copolymer latex is obtained in which particles of the chloroprene graft copolymer are dispersed in water and wherein a content of insoluble tetrahydrofuran materials is not less than 6 mass % and less than 70 mass % of the chloroprene graft copolymer.

Description

Technical area

[0001] The present invention relates to a process for producing a chloroprene graft copolymer latex. State of the art

[0002] Homopolymers of chloroprene and copolymers of chloroprene with other monomers (hereinafter also collectively referred to as "chloroprene polymer") offer high bond strength under low pressure for various types of bonding surfaces and are therefore suitably used in adhesives, including organic solvent-type contact adhesives and organic solvent-type graft adhesives. To meet the controls on volatile organic chemicals (VOCs) or organic solvents, while considering environmental pollution or human health, aqueous adhesives without organic solvents have been developed, and aqueous adhesives containing a chloroprene polymer latex have been disclosed.

[0003] For example, PLT 1 discloses an aqueous adhesive containing a latex of a copolymer of chloroprene, an α,β-unsaturated carboxylic acid, and 2,3-dichloro-1,3-butadiene. Copolymerization with the α,β-unsaturated carboxylic acid improves the high-temperature bond strength (heat resistance). However, the aqueous adhesive disclosed in PLT 1 exhibits lower bond strength than conventional chloroprene polymer-containing organic solvent-type adhesives and chloroprene graft copolymer-containing organic solvent-type adhesives. Therefore, the aqueous adhesive is unlikely to provide high bond strength to soft polyvinyl chloride, to which a chloroprene polymer barely adheres.

[0004] Such a copolymer of chloroprene with other monomers, as disclosed in PLT 1, can exhibit higher adhesive strength than a homopolymer of chloroprene due to modification by copolymerization. However, chloroprene has low copolymerizability with other monomers and is copolymerizable with few monomers. Modification by copolymerization is thus limited. Furthermore, even when using a copolymerizable monomer (e.g., an α,β-unsaturated carboxylic acid), a copolymer with a high copolymerization ratio is difficult to prepare due to the low copolymerizability, and thus, significant modification has been difficult.

[0005] Graft copolymerization with another monomer is known as a method for modifying a chloroprene polymer, and graft copolymerization is intended to improve the bond strength. For example, PLTs 2 to 5 disclose organic solvent-type adhesives containing a chloroprene graft copolymer prepared by graft copolymerizing a chloroprene polymer with an alkyl methacrylate. However, each adhesive disclosed in PLTs 2 to 5 contains an organic solvent and therefore has difficulty meeting the requirements regarding volatile organic chemicals or organic solvents.

[0006] DE 20 16 935 B2 and DE 23 10 778 B2 disclose a process for producing a chloroprene graft copolymer latex, wherein a (meth)acrylate is grafted onto a water-dispersed chloroprene polymer latex in an emulsion polymerization to obtain a water-dispersed chloroprene graft copolymer latex. JP 861-181 880 A discloses a radically initiated emulsion graft polymerization of a methacrylate onto a chloroprene polymer latex prepared by emulsion polymerization at a temperature below 30°C. JP H01-284 544 A discloses an aqueous emulsion polymerization of an acrylate onto a chloroprene polymer latex which itself was prepared in an aqueous emulsion polymerization reaction.DE 694 17 061 T2 discloses a grafting of a (meth)acrylate onto a chloroprene copolymer latex (chloroprene copolymerized with a (meth)acrylate), whereby both the preparation of the chloroprene copolymer latex and the subsequent grafting of (meth)acrylate onto it take place in an aqueous emulsion polymerization. JP 861-275 315 A discloses an aqueous polymerization of an acrylate onto a chloroprene polymer latex. Citation listPatent literature PTL 1: JP 2007-191710 A PTL 2: JP 01-28454444 A PTL 3: JP 01-123882 A PTL 4: JP 02-286771 A PTL 5: JP 2000-7833 A Summary of the inventionTechnical problem

[0007] The present invention is therefore intended to solve such problems of the prior art as described above and to provide a process for producing a chloroprene graft copolymer latex which contains no organic solvent and has high adhesive strength even to soft polyvinyl chloride. Solution to the problem

[0008] The present invention is defined in the appended claims. Advantageous effects of the invention

[0009] According to the present invention, a process for producing a chloroprene graft copolymer latex which contains no organic solvent and has high adhesive strength even to soft polyvinyl chloride can be provided. Description of the embodiments

[0010] Conventional organic solvent-type adhesives containing an organic solvent and a chloroprene graft copolymer are in a homogeneous system in which the chloroprene graft copolymer is homogeneously present in the organic solvent. In contrast, aqueous adhesives containing no organic solvent but water and a chloroprene graft copolymer are prepared by emulsion radical polymerization and are in an inhomogeneous system in which the chloroprene graft copolymer is inhomogeneously present in water.

[0011] Therefore, during the graft copolymerization of a chloroprene polymer, graft-copolymerized portions of emulsified particles of the chloroprene polymer influence the physical properties. For this reason, aqueous graft copolymerization in emulsified particles is also required for aqueous adhesives, so that the graft polymers are uniformly distributed on a chloroprene polymer as the base polymer, as in organic solvent-type adhesives. In particular, aqueous graft copolymerization is required while generating radicals homogeneously on the surface and in the emulsified particles.

[0012] The inventors of the present invention have conducted extensive studies and found that by graft copolymerizing a (meth)acrylate to a chloroprene polymer with a certain polymerization initiator under a certain temperature condition, radicals are homogeneously generated on the surface and in emulsified particles to enable graft copolymerization in emulsified particles so that graft polymers are uniformly arranged on the chloroprene polymer, and have completed the present invention.

[0013] In other words, a process for producing a chloroprene graft copolymer latex of the present invention includes a chloroprene polymerization step for providing a chloroprene polymer latex in which particles of a chloroprene polymer are dispersed in water, and a graft copolymerization step for providing a chloroprene graft copolymer latex in which particles of a chloroprene graft copolymer are dispersed in water.

[0014] The chloroprene polymerization step is a step in which at least chloroprene (A-1) of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1) is subjected to emulsion radical polymerization to obtain a chloroprene polymer, and a chloroprene polymer latex is formed.

[0015] The graft copolymerization step is a step in which a (meth)acrylate (B) represented by the general formula CH2=CR-CO-OR' is added to the chloroprene polymer latex, an organic peroxide (C) having an octanol / water partition coefficient of -2.0 or more and 3.0 or less is added as a polymerization initiator, and the chloroprene polymer undergoes graft copolymerization with the (meth)acrylate (B) at a temperature of 10°C or more and 35°C or less to form a chloroprene graft copolymer, and a chloroprene graft copolymer latex is obtained. In the general formula, R is a methyl group or a hydrogen atom, and R' is an alkyl group having a carbon number of 4 or more and 12 or less.

[0016] The chloroprene graft copolymer latex prepared as above is a chloroprene graft copolymer latex in which particles of a chloroprene graft copolymer are dispersed in water as a graft copolymer of a chloroprene polymer and a (meth)acrylate (B). The chloroprene polymer is a homopolymer of chloroprene (A-1) or a copolymer of a monomer (A-2) copolymerizable with chloroprene (A-1) and chloroprene (A-1). The grafting efficiency of the (meth)acrylate (B) to the chloroprene polymer is preferably 60% or more and 100% or less.

[0017] The chloroprene graft copolymer latex contains no organic solvent and exhibits high bond strength even with soft polyvinyl chloride. In other words, even if at least one of two bonding surfaces is made of soft polyvinyl chloride, which is a material with poor adhesion, the chloroprene graft copolymer latex exhibits high bond strength, for example, 2.0 kN / m or more, enabling the two bonding surfaces to adhere. Thus, the chloroprene graft copolymer latex can be used in a binder or adhesive. The bonding surface can have any shape, and the binder or adhesive can be used for bonding foams, sheets, films, and the like. Soft polyvinyl chloride is polyvinyl chloride that is softened by adding a plasticizer.

[0018] A chloroprene graft copolymer latex, a process for producing the latex according to the present invention, a binder, and an adhesive will now be described in detail. The present embodiment is only one example of the present invention. [1] Chloroprene (A-1)

[0019] Chloroprene, which is a main monomer of a chloroprene graft copolymer as a component of a chloroprene graft copolymer latex of the embodiment, is a compound also called 2-chloro-1,3-butadiene or 2-chlorobutadiene. [2] Monomer (A-2) copolymerizable with chloroprene (A-1) and chloroprene polymer

[0020] A chloroprene polymer formed in a production process of a chloroprene graft copolymer latex in the embodiment (chloroprene polymerization step) is a polymer produced by emulsion radical polymerization of at least chloroprene (A-1) selected from the group consisting of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1). In other words, the chloroprene polymer may be a homopolymer of chloroprene (A-1) or a copolymer of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1).

[0021] The monomer (A-2) can be any type that can be copolymerized with chloroprene (A-1), and examples include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, styrene, methacrylic acid, acrylic acid, itaconic acid, 2-ethylmethacrylic acid, and 2-butylacrylic acid. These monomers (A-2) can be used singly or in combination with two or more of them. The copolymerization ratio between the chloroprene (A-1) and the monomer (A-2) is not limited to any specific values. [3] Chloroprene polymer latex

[0022] In a typical latex, a lipophilic substance is emulsified with an emulsifier and dispersed as particles in water. In the chloroprene polymer latex in the embodiment, particles of a chloroprene polymer are dispersed in water, and the chloroprene polymer latex can be prepared by emulsion radical polymerization of at least chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1). 4] Chloroprene polymerization step

[0023] The chloroprene polymerization step is, as described above, a step in which, of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1), at least chloroprene (A-1) is subjected to emulsion radical polymerization to obtain a chloroprene polymer, thereby producing a chloroprene polymer latex in which particles of the chloroprene polymer are dispersed in water.

[0024] In the chloroprene polymerization step, an emulsifier is used to conduct the aqueous emulsion radical polymerization. The emulsifier can be any type. However, the (meth)acrylate (B) added in the subsequent step has a hydrolyzable ester structure, so the pH of the reaction system is preferably neither acidic nor basic. Therefore, an emulsifier with emulsifying ability even at a neutral pH is preferably used.

[0025] Examples of the anionic emulsifier are alkali metal salts of disproportionated resin acid, dodecylbenzenesulfonates (such as sodium dodecylbenzenesulfonate and triethanolamine dodecylbenzenesulfonate), diphenyl ethersulfonates (such as sodium diphenyl ethersulfonate and ammonium diphenyl ethersulfonate), naphthalenesulfonates (such as a sodium salt of naphthalenesulfonic acid-formaldehyde condensate) and fatty acid alkali metal salts (such as potassium laurate).

[0026] Examples of the non-ionic emulsifier are partially saponified polyvinyl alcohol, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether and polyoxyethylene lauryl ether.

[0027] These emulsifiers can be used individually or in combination with two or more of them.

[0028] In the chloroprene polymerization step, the polymerization temperature can be 10°C or more and 50°C or less, and is preferably 15°C or more and 45°C or less. At a polymerization temperature within this range, aggregates are unlikely to form, and a resulting chloroprene graft copolymer latex has sufficiently high adhesive strength. At a polymerization temperature within this range, polymerization proceeds rapidly, so the chloroprene polymer latex can be produced efficiently.

[0029] The polymerization initiator used in the chloroprene polymerization step is not limited to specific initiators, and common radical polymerization initiators can be used. Examples include organic or inorganic peroxides such as benzoyl peroxide, potassium persulfate, ammonium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide, as well as azo compounds such as azobisisobutyronitrile. These polymerization initiators can be used individually or in combination with two or more of them.

[0030] In the chloroprene polymerization step, a catalytic promoter can be used in combination with the polymerization initiator. In the chloroprene polymerization step, the usable catalytic promoter in combination with the polymerization initiator is not limited to specific catalytic promoters, and common catalytic promoters can be used. Examples include anthraquinone sulfonates, potassium sulfite, sodium disulfite, sodium sulfite, tetraethylenepentamine, and N,N-dimethyl-p-toluidine. These catalytic promoters can be used individually or in combination with two or more of them.

[0031] In the chloroprene polymerization step, the total conversion rate of chloroprene (A-1) and the chloroprene-copolymerizable monomer (A-2) can be 60% or more and 100% or less, respectively. When the conversion rate is within the range, the chloroprene polymer latex has a sufficient solid concentration, and the possibility of generating odors due to unreacted chloroprene (A-1) or unreacted monomer (A-2) or reducing the adhesive strength or adhesion of a chloroprene graft copolymer latex is eliminated. Furthermore, the possibility of unreacted chloroprene (A-1) or unreacted monomer (A-2) reacting to rapidly generate heat in the subsequent graft copolymerization step is eliminated.In addition, no process for removing unreacted volatile components is required after the chloroprene polymerization step, or even if the removal process is carried out, a lightly loaded treatment can be carried out.

[0032] After completion of the chloroprene polymerization step, a polymerization terminal may be added to stop the polymerization reaction when the reaction reaches a predetermined polymerization rate, to stop further polymerization, and to obtain a chloroprene polymer with a desired molecular weight distribution. The polymerization terminal may be any type, and specific examples include phenothiazine, para-t-butylcatechol, hydroquinone, hydroquinone monomethyl ether, diethylhydroxylamine, and a free radical of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl. These polymerization terminals may be used individually or in combination with two or more of them. 5] (Meth)acrylate (B)

[0033] The (meth)acrylate (B) is a compound of the general formula CH2=CR-CO-OR', has a reactive double bond in the molecule, and can undergo graft copolymerization with the chloroprene polymer. In the general formula, R is a methyl group or a hydrogen atom, and R' is an alkyl group having a carbon number of 4 or more and 12 or less. In this specification, "(meth)acrylate" means methacrylate and / or acrylate, and "(meth)acrylic" means methacrylic and / or acrylic.

[0034] When R' in the general formula is an alkyl group with a carbon number of 4 or more, the ester portion in such (meth)acrylate (B) is unlikely to be hydrolyzed. When R' in the general formula is an alkyl group with a carbon number of 12 or less, such (meth)acrylate (B) has a low viscosity and thus an advantage in emulsification or mixing. R' in the general formula is preferably an alkyl group with a carbon number of 4 or more and 6 or less from the perspective of stability during graft polymerization.

[0035] Examples of (meth)acrylate (B) are butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate. These (meth)acrylates (B) can be used individually or in combination with two or more of them. 6] Chloroprene graft copolymer

[0036] A chloroprene graft copolymer formed in a production process of a chloroprene graft copolymer latex in the embodiment (graft copolymerization step) is a polymer produced by graft copolymerizing the chloroprene polymer with a (meth)acrylate (B). Carbon-carbon double bonds of the chloroprene polymer are reacted with the carbon-carbon double bond of a (meth)acrylate (B) to effect graft copolymerization. 7] Chloroprene graft copolymer latex

[0037] In a chloroprene graft copolymer latex of the embodiment, particles of a chloroprene graft copolymer as a graft copolymer of the chloroprene polymer and a (meth)acrylate (B) are dispersed in water, and the chloroprene graft copolymer latex can be prepared by graft copolymerizing the chloroprene polymer with a (meth)acrylate (B).

[0038] The chloroprene graft copolymer latex may have a solid concentration of 35 mass% or more and 65 mass% or less, preferably 45 mass% or more and 65 mass% or less, and more preferably 53 mass% or more and 65 mass% or less. When the solid concentration is within this range, the drying time of a chloroprene graft copolymer latex can be shortened and the load on a drying device can be reduced. When the solid concentration is within this range, such a chloroprene graft copolymer latex can more easily maintain colloidal stability, and the formation of aggregates can be minimized.

[0039] The solids concentration of a chloroprene polymer latex or a chloroprene graft copolymer latex can be determined, for example, by the following method. A chloroprene polymer latex or a chloroprene graft copolymer latex is dried by heat treatment (e.g., heating to 141°C for 30 minutes) to obtain only solid components, and the solids concentration is calculated from the mass before drying and the mass after drying.

[0040] The chloroprene graft copolymer latex may appropriately contain stabilizers such as an acid acceptor and an antioxidant so as not to be adversely affected. The amount of the acid acceptor may be 0.01 parts by mass or more and 5 parts by mass or less, and preferably 0.05 parts by mass or more and 1 part by mass or less, based on 100 parts by mass of the chloroprene graft copolymer. The amount of the antioxidant may be 0.1 parts by mass or more and 3 parts by mass or less, and preferably 0.5 parts by mass or more and 2.5 parts by mass or less, based on 100 parts by mass of the chloroprene graft copolymer.

[0041] When the stabilizer is added within the range, an adhesive layer formed by drying such a chloroprene graft copolymer latex can exhibit higher temporal stability in flexibility. When the amount of the acid acceptor is within the range, the hydrochloric acid eliminated from the chloroprene graft copolymer over time is sufficiently neutralized, and excellent adhesive strength or bonding strength is achieved. In addition, the chloroprene graft copolymer latex has satisfactory colloidal stability and is unlikely to cause problems including sedimentation. When the amount of the antioxidant is within the range, a sufficient antioxidant effect is achieved, and excellent adhesive strength or bonding strength is achieved.

[0042] When a stabilizer is insoluble in water or is a compound that destabilizes the colloidal state of a chloroprene graft copolymer latex, the stabilizer may be previously dispersed in water to prepare a dispersion, and the dispersion may be added to a chloroprene graft copolymer latex.

[0043] The acid acceptor can be any type, and examples include zinc oxide and hydrotalcite (e.g., trade name: DHT-4A, DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.). These acid acceptors can be used individually or in combination with two or more of them.

[0044] The antioxidant can be any type, and diphenylamine antioxidants such as octylated diphenylamine, p-(p-toluenesulfonylamide)diphenylamine, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are preferred due to lower stain resistance.

[0045] To improve ozone resistance, N,N'-diphenyl-p-phenylenediamine (DPPD) or N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD) can be used. If discoloration of the glueline or hygiene is a concern, a hindered phenol antioxidant is preferred.

[0046] The chloroprene graft copolymer latex in the embodiment may, if necessary, appropriately contain, in addition to the above-mentioned stabilizers (such as an acid acceptor and an antioxidant), a filler, a tackifier, a pigment, a colorant, a wetting agent, an antifoaming agent, a thickener, or the like to an extent that it is not impaired.

[0047] The chloroprene graft copolymer latex may have a pH of 7.0 or more and 10.0 or less. The pH of the chloroprene graft copolymer latex can be adjusted within this range by using a base or the like. Examples of the base include amines such as diethanolamine and triethanolamine, metal hydroxides such as potassium hydroxide and sodium hydroxide or aqueous solutions thereof, and amino acids such as glycine.

[0048] If the pH is within the range, the chloroprene graft copolymer latex is unlikely to cause aggregation. Furthermore, the chloroprene graft copolymer latex is unlikely to cause solidification due to hydrolysis of an ester moiety. Depending on the type of adhesion promoter for which the chloroprene graft copolymer latex is used, hydrolysis (e.g., hydrolysis of polyurethane) or corrosion (e.g., dissolution of aluminum) may damage an adhesive surface. If the pH is within the range, it is unlikely to cause such deterioration of an adhesive surface.

[0049] Such a chloroprene graft copolymer latex of the present invention exhibits high adhesive strength, exhibiting a high adhesive strength of, for example, 2.0 kN / m or more, even for soft polyvinyl chloride, which is a difficult-to-adhere material, and enabling adhesion. The method for measuring the adhesive strength is described in more detail in the examples. [8] Graft copolymerization step

[0050] The graft copolymerization step is, as described above, a step in which the chloroprene polymer is subjected to graft copolymerization with a (meth)acrylate (B) to obtain a chloroprene graft copolymer, thereby forming a chloroprene graft copolymer latex in which particles of the chloroprene graft copolymer are dispersed in water.

[0051] In the graft copolymerization step, a (meth)acrylate (B) and an organic peroxide (C) as a polymerization initiator are added to the chloroprene polymer latex prepared in the chloroprene polymerization step, and the reaction is carried out at a temperature of 10°C or more and 35°C or less. Accordingly, the chloroprene polymer is graft copolymerized with the (meth)acrylate (B) to form a chloroprene graft copolymer latex.

[0052] The polymerization temperature, as described above, must be 10°C or more and 35°C or less, and is preferably 15°C or more and 30°C or less. When the polymerization temperature is within this range, the grafting efficiency of the (meth)acrylate (B) to the chloroprene polymer is 60% or more and 100% or less. Consequently, when the conversion rate of the (meth)acrylate (B) is 90% or more and 100% or less, the grafting rate is 0.5% or more and 90% or less, and the chloroprene graft copolymer latex has sufficiently high adhesive strength. When the polymerization temperature is within this range, graft copolymerization proceeds rapidly, and thus the chloroprene graft copolymer latex can be produced efficiently.

[0053] In the graft copolymerization, an organic peroxide (C) with an octanol / water partition coefficient of -2.0 or more and 3.0 or less is used. When the octanol / water partition coefficient is within the range, a sufficient number of radicals are generated in the emulsified particles (chloroprene polymer) of the chloroprene polymer matrix, so that radicals are generated homogeneously on the surface of and within the emulsified particles. Therefore, graft polymers are not unevenly arranged on the surface or within the emulsified particles, and graft copolymerization occurs on the surface and within the emulsified particles, so that graft polymers are uniformly arranged for the chloroprene polymer. As a result, the grafting efficiency of the (meth)acrylate (B) to the chloroprene polymer is 60% or more and 100% or less.In addition, when the conversion rate of the (meth)acrylate (B) is 90% or more and 100% or less, a chloroprene graft copolymer having a grafting rate of 0.5% or more and 90% or less can be prepared.

[0054] Examples of the organic peroxide (C) with an octanol / water partition coefficient of -2.0 or more and 3.0 or less are t-butyl hydroperoxide and cumene hydroperoxide. A liquid organic peroxide (C) can be added without treatment, and a solid liquid organic peroxide (C) can be added as a solution into the (meth)acrylate (B).

[0055] A catalytic promoter can be used in combination with the polymerization initiator if necessary. The catalytic promoter can be any type that supports the function of the polymerization initiator, and specific examples include anthraquinone sulfonates, potassium sulfite, sodium disulfite, sodium sulfite, sodium sulfite, tetraethylenepentamine, and N,N-dimethyl-p-toluidine.

[0056] The octanol / water partition coefficient, also expressed as LogPow, is an index that represents the hydrophobicity (lipid solubility) of a chemical substance. The method for measuring the octanol / water partition coefficient generally corresponds to OECD Test Guideline (C (81) 30 appendix 1), determined by the OECD Directorate) 107 or Japanese Industrial Standard Z7260-107 (2000), "Determination of the Partition Coefficient (1-Octanol / Water) - Shake Flask Method."

[0057] The grafting efficiency of a (meth)acrylate (B) onto a chloroprene polymer can be determined, for example, by the following method. A chloroprene graft copolymer latex is added dropwise to methanol, and the resulting precipitate is collected by filtration. The collected precipitate is dried on a pour plate at 50°C for 24 hours or more, and then the mass of the dried product is determined (referred to as "mass before extraction"). The dried product is finely cut with scissors or the like, and 4 g of the finely cut pieces are subjected to Soxhlet extraction with a mixed solvent of methyl ethyl ketone and methanol (in terms of a mixing ratio of methyl ethyl ketone:methanol = 2:1) for 48 hours. By Soxhlet extraction, homopolymers of a (meth)acrylate (B) and the like are extracted.The residue is dried at 50°C for 24 hours and then the mass of the dried product is determined (referred to as “mass after extraction”).

[0058] The grafting efficiency is calculated from the mass change before and after Soxhlet extraction using the following formula. Grafting efficiency (%) = 100 × (X − Y) / X

[0059] In the formula, X is [mass before extraction (g)] × [amount of (meth)acrylate (B) in the graft copolymerization step (g)] × [conversion rate of (meth)acrylate (B) in the graft copolymerization step (%)] / ([total amount of chloroprene (A-1) and monomer (A-2) in the chloroprene polymerization step (g)] × [total conversion rate of chloroprene (A-1) and monomer (A-2) in the chloroprene polymerization step (%)] + [amount of (meth)acrylate (B) in the graft copolymerization step (g)] × [conversion rate of (meth)acrylate (B) in the graft copolymerization step (%)]).

[0060] Y is [mass before extraction (g)] - [mass after extraction (g)].

[0061] The total conversion rate of chloroprene (A-1) and a chloroprene-copolymerizable monomer (A-2) in the chloroprene polymerization step or the conversion rate of a (meth)acrylate (B) in the graft copolymerization step can be determined, for example, by the following method.

[0062] The solid concentration of a chloroprene polymer latex or a chloroprene graft copolymer latex is determined as described above, and the measured value of the solid concentration is regarded as S. Separately, the solid concentration (theoretical value) when the polymerization reaction proceeds to 100% is theoretically calculated, and the theoretical value is regarded as T 100The solid concentration (theoretical value) when the polymerization reaction proceeds at 0% is calculated theoretically, and the theoretical value is considered T0. The conversion rate (unit: %) is calculated using the following formula. Conversion rate=(S−T0) / (T100−T0)×100

[0063] In the graft copolymerization step, the amount of the (meth)acrylate (B) may be 1 part by mass or more and 90 parts by mass or less relative to 100 parts by mass of the chloroprene polymer. In such a state, the graft copolymerization step yields a chloroprene graft copolymer as a graft copolymer of 100 parts by mass of the chloroprene polymer and 1 part by mass or more and 90 parts by mass or less of the (meth)acrylate (B).

[0064] When the amount of (meth)acrylate (B) is within the range, the cohesive force of the chloroprene polymer is improved by graft copolymerization, and thus an adhesive layer formed by drying such a chloroprene graft copolymer latex has high strength and excellent contact adhesive strength. The amount of (meth)acrylate (B) may, as described above, be 1 part by mass or more and 90 parts by mass or less, based on 100 parts by mass of the chloroprene polymer, preferably 10 parts by mass or more and 85 parts by mass or less, and more preferably 20 parts by mass or more and 55 parts by mass or less. In the graft copolymerization step, the grafting rate of (meth)acrylate (B) is defined as follows: [(Grafting rate of meth)acrylate (B) (%)]=[Amount of (meth)acrylate (B) based on 100 parts by mass of chloroprene polymer (parts by mass)]×[Conversion rate of (meth)acrylate (B)]×[Grafting efficiency of (meth)acrylate (B)].

[0065] The grafting rate of the (meth)acrylate (B) is preferably 0.5% or more and 90% or less, and more preferably 10% or more and 55% or less from the viewpoint of adhesiveness.

[0066] In the chloroprene graft copolymer latex, the content of tetrahydrofuran-insoluble materials must be no less than 6 mass% and less than 70 mass% of the chloroprene graft copolymer, more preferably no less than 15 mass% and less than 50 mass%, and even more preferably no less than 17 mass% and less than 45 mass% to maintain high bond strength. The tetrahydrofuran-insoluble material is a gel mass that is not dissolved in tetrahydrofuran and is a hard component with no elastic properties.

[0067] When the content of tetrahydrofuran-insoluble substances is less than 70 mass%, an adhesive layer formed by drying such a chloroprene graft copolymer latex exhibits excellent rubber properties, including extensibility, flexibility, and elasticity. When the content of tetrahydrofuran-insoluble substances is not less than 10 mass%, an adhesive layer formed by drying such a chloroprene graft copolymer latex exhibits excellent strength. Accordingly, such a chloroprene graft copolymer latex has excellent adhesive strength for soft polyvinyl chloride and can exhibit a high adhesive strength of, for example, 2.0 kN / m or more.

[0068] The content of tetrahydrofuran in insolubles can be determined, for example, by the following method. First, 0.5 g of a chloroprene graft copolymer latex (containing 40 mass% or more and 65 mass% or less of water) is added dropwise to 100 mL of tetrahydrofuran. The mixture is then shaken overnight and separated with a centrifugal separator to obtain a dissolved phase as the supernatant liquid. The obtained dissolved phase is heated to 100°C to evaporate the tetrahydrofuran for 1 hour to a dried product, and the mass of the dissolved content in the dissolved phase is determined. The mass of the dissolved content is subtracted from the mass of the chloroprene graft copolymer in the chloroprene graft copolymer latex to obtain the tetrahydrofuran insolubles.

[0069] The content of tetrahydrofuran-insoluble substances can be controlled by the type of emulsifier, chain transfer agent, polymerization initiator, or polymerization terminator used in the graft copolymerization step, the polymerization temperature in the graft copolymerization, the conversion rate of the (meth)acrylate (B), or the like. By appropriately adjusting these conditions, a chloroprene graft copolymer latex with a desired content of tetrahydrofuran-insoluble substances can be prepared.

[0070] The chain-transfer agent usable in the graft copolymerization step can be any agent, and it can be a xanthogen disulfide or an alkyl mercaptan. Specific examples of the xanthogen disulfide are diisopropyl xanthogen disulfide, diethyl xanthogen disulfide, dicyclohexyl xanthogen disulfide, dilauryl xanthogen disulfide, and dibenzyl xanthogen disulfide. Specific examples of the alkyl mercaptan are n-dodecyl mercaptan, n-decyl mercaptan, and octyl mercaptan. These chain-transfer agents can be used individually or in combination with two or more of them.

[0071] In the graft copolymerization step, the conversion rate of the (meth)acrylate (B) can be 90% or more and 100% or less. When the conversion rate of the (meth)acrylate (B) is within this range, such a chloroprene graft copolymer latex has a sufficient solid concentration, and possibilities of odor generation due to an unreacted (meth)acrylate (B) or a reduction in the adhesive strength or adhesion of a chloroprene graft copolymer latex are eliminated. Furthermore, after the graft copolymerization step, no process for removing unreacted volatile components is required, or even if the removal process is performed, a lightly loaded treatment can be performed.

[0072] In the graft copolymerization step, aqueous emulsion radical polymerization can also be carried out with an emulsifier. The emulsifier can be any type, and similar anionic emulsifiers and nonionic emulsifiers to those used in the chloroprene polymerization step can be used. The resulting chloroprene graft copolymer latex therefore contains an emulsifier, for example, an anionic emulsifier and a nonionic emulsifier.

[0073] In the graft copolymerization step, the amount of the emulsifier is not limited to any specific values, and is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 3 parts by mass or more and 8.5 parts by mass or less, based on 100 parts by mass of the (meth)acrylate (B). When the amount of the emulsifier is within this range, it is unlikely to cause insufficient emulsification or viscosity increase, thus preventing problems such as poor control of polymerization heat generation, the generation of aggregates, and poor product appearance.If the amount of emulsifier is within the range, the emulsifier is unlikely to remain, so problems such as deterioration of water resistance of a chloroprene graft copolymer, reduction of adhesive strength or bonding force, foaming during drying, and deterioration of color tone of a product are unlikely to be caused.

[0074] In the graft copolymerization step, the chloroprene polymer is graft copolymerized with the (meth)acrylate (B) to form a chloroprene graft copolymer, and the chloroprene polymer may be graft copolymerized with an additional monomer copolymerizable with the (meth)acrylate (B) together with the (meth)acrylate (B). The amount of the additional monomer copolymerizable with the (meth)acrylate (B) is not limited to any specific values ​​and may be 0.1 parts by mass or more and 10 parts by mass or less based on 100 parts by mass of the chloroprene polymer. When the amount of the additional monomer copolymerizable with the (meth)acrylate (B) is within the range, a resulting chloroprene graft copolymer latex has excellent adhesive strength or adhesion.

[0075] The additional monomer can be any type copolymerizable with the (meth)acrylate (B), and examples include 1-chloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, butadiene, isoprene, styrene, acrylonitrile, vinyl acetate, acrylic acid, and methacrylic acid. These additional monomers can be used individually or in combination with two or more of them.

[0076] After completion of the graft copolymerization step, a polymerization terminator may be added to stop the polymerization reaction when the reaction reaches a predetermined polymerization rate, to stop further polymerization reaction, and to obtain a chloroprene graft copolymer with a desired molecular weight distribution. The polymerization terminator may be of any type, and a polymerization terminator similar to the one used after completion of the chloroprene polymerization step may be used.

[0077] The method for producing a chloroprene graft copolymer latex of the embodiment includes, as described above, the chloroprene polymerization step and the graft copolymerization step, and may include an additional step in addition to these steps. For example, a step for removing unreacted volatile components may be provided between the chloroprene polymerization step and the graft copolymerization step or after the graft copolymerization step. A cooling step, a polymerization reaction aging step, or a heating step may be provided after and / or before at least one of the chloroprene polymerization steps and the graft copolymerization step. [9] Adhesion promoter, adhesive

[0078] The chloroprene graft copolymer latex of the above-prepared embodiment can be used in a binder or an adhesive. The chloroprene graft copolymer latex of the embodiment can be used alone as a binder or adhesive without treatment, or it can be blended with a tackifier to improve adhesion strength and used as a binder or adhesive with high adhesion strength.

[0079] The tackifier can be of any type, and phenolic resins, terpene resins, rosin-derived resins, petroleum hydrocarbons, and the like can be used. Specific examples include a hydrogenated rosin, a pentaerythritol ester of a hydrogenated rosin, a polymerized rosin, a resin-modified resin containing mainly rosin, an alkylphenol resin, a resin-modified phenolic resin, a terpene-modified phenolic resin, and a natural terpene resin. These tackifiers can be used individually or in combination with two or more of them.

[0080] The amount of the tackifier may be 10 parts by mass or more and 60 parts by mass or less, and preferably 20 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the solid content in the chloroprene graft copolymer latex. When the amount of the tackifier is within this range, sufficient tackiness is achieved and the adhesive strength can be sufficiently improved. The method for adding the tackifier can be any method, and an emulsion prepared by emulsifying and dispersing the tackifier can be added to the chloroprene graft copolymer latex.

[0081] By adding the tackifier to the chloroprene graft copolymer latex of the embodiment and appropriately adding an acid acceptor, an antioxidant, a filler, a pigment, a colorant, a wetting agent, a defoaming agent, a thickener or the like, a binder or an adhesive can be prepared as needed.

[0082] The binder or adhesive containing the chloroprene graft copolymer latex of the embodiment has a high adhesive strength, shows a high adhesive strength of, for example, 2.0 kN / m or more even for soft polyvinyl chloride, and enables adhesion. [Examples]

[0083] The present invention is described in more detail below using examples and comparative examples. [Example 1](1) Preparation of chloroprene polymer latex

[0084] In a reactor with an internal volume of 5 L, 1,600 g of chloroprene, 69 g of disproportionated rosin, 1,367 g of pure water, 20 g of potassium hydroxide and 0.57 g of n-dodecyl mercaptan (molecular weight modifier) ​​were added and emulsified.

[0085] Sodium sulfite was added to the emulsion, then potassium persulfate was added as a polymerization initiator, and the polymerization was carried out under a nitrogen atmosphere at 40°C. Immediately after the reaction reached the desired polymerization rate, a phenothiazine emulsion was added to stop the polymerization. The obtained reaction product had a solid concentration of 49 mass%, and the chloroprene conversion rate was 88%. Subsequently, unreacted chloroprene was removed by steam stripping, and a chloroprene polymer latex was prepared. The measurement methods for the solid concentration and conversion rate were the same as those described in "[7] Chloroprene Graft Copolymer Latex" and "[8] Graft Copolymerization Step." (2) Preparation of chloroprene graft copolymer latex

[0086] In a reactor with an internal volume of 5 L, 200 g of the chloroprene polymer latex obtained in the above preparation (1) was added to 22.0 g of butyl methacrylate, 0.22 g of tetraethylenepentamine, 17.6 g of pure water, 0.88 g of potassium laurate and 28 mg of n-dodecyl mercaptan (molecular weight modifier) ​​and emulsified.

[0087] Cumene hydroperoxide (with an octanol / water partition coefficient of 2.16) was added to the emulsion as a polymerization initiator, and the aqueous graft copolymerization was carried out under a nitrogen atmosphere at 30°C. Immediately after the reaction reached a desired polymerization rate, an aqueous free radical solution of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl was added to stop the polymerization, and a chloroprene graft copolymer latex was prepared. At this time, the conversion rate of butyl methacrylate was 100%. The amounts of the compounds used in the preparation of the chloroprene graft copolymer latex and the polymerization temperature are shown in Table 1. In Table 1, the amount of a chloroprene polymer latex represents the amount of chloroprene polymer contained in the chloroprene polymer latex. [Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Conditions for the graft copolymerization step Chloroprene polymer (mass parts) 100 100 100 100 100 100 100 100 100 (Meth)acrylate monomer (parts by mass) Butyl methacrylate 20 40 40 60 - 40 40 20 85 Methyl methacrylate - - - - - - - - - 2-Ethylhexyl methacrylate - - - - 40 - - - - Polymerizable monomer (parts by mass) Methacrylic acid - - - - - - - - - Polymerization initiator (parts by mass) Cumene hydroperoxide 0.34 0.45 0.45 0.34 0.45 - 0.34 0.34 0.34 t-butyl hydroperoxide - - - - - 0.27 - - - Benzoyl peroxide - - - - - - - - - Molecular weight modifier (parts by mass) n-Dodecylmercaptan 0.05 - - - - - - 0.05 - Emulsifier (parts by mass) Potassium laurate 0.8 1.6 1.6 2.4 1.6 1.6 1.6 0.8 3.4 Polymerization temperature (°C) 30 30 25 30 30 30 30 40 30 Conversion rate of (meth)acrylate monomer (%) 100 100 100 100 100 100 100 100 100 Grafting efficiency (%) 95 91 96 88 90 93 91 63 77 Grafting rate (%) 19 36 38 53 36 37 36 13 65 Evaluation Substances insoluble in tetrahydrofuran (mass%) 37.1 35.2 17.7 16.1 14.8 43.4 63.8 6.6 9.5 Adhesive strength (kN / m) 2.5 2.3 2.8 2.1 2.1 2.4 2.0 2.1 2.0 [Table 1] (continued) See Example 1 See Example 2 See Example 3 See Example 4 See Example 5 See Example 6 Conditions for the graft copolymerization step Chloroprene polymer (mass parts) 100 100 100 100 100 - (Meth)acrylate monomer (parts by mass) Butyl methacrylate - 40 40 - - - Methyl methacrylate 40 - - - - - 2-Ethylhexyl methacrylate - - - - - - Polymerizable monomer (parts by mass) Methacrylic acid - - - - 20 - Polymerization initiator (parts by mass) Cumene hydroperoxide 0.34 - 0.34 - 0.34 - t-butyl hydroperoxide - - - - - - Benzoyl peroxide - 0.51 - - - - Molecular weight modifier (parts by mass) n-Dodecylmercaptan - - - - - - Emulsifier (parts by mass) Potassium laurate 0.8 1.6 1.6 - 0.8 - Polymerization temperature (°C) 30 30 45 - 30 - Conversion rate of (meth)acrylate monomer (%) 80 100 100 - * - Grafting efficiency (%) * 91 62 - * - Grafting rate (%) * 36 25 - * - Evaluation Substances insoluble in tetrahydrofuran (mass%) * 31.4 7.7 0 * - Adhesive strength (kN / m) 0.3 1.9 1.9 1.8 * 1.2 * Not measurable [Examples 2 to 9 and Comparative Examples 1 to 5](1) Preparation of chloroprene polymer latex

[0088] A similar operation as in Example 1 was performed to prepare a chloroprene polymer latex. (2) Preparation of chloroprene graft copolymer latex

[0089] A similar procedure to Example 1 was performed except that the type and amount of a (meth)acrylate monomer to be graft-copolymerized to the chloroprene polymer, the type and amount of a polymerization initiator, the amount of n-dodecyl mercaptan, the amount of an emulsifier, the conversion rate of a (meth)acrylate monomer, and the polymerization temperature were changed as shown in Table 1, thereby obtaining chloroprene graft copolymer latexes of Examples 2 to 9 and Comparative Examples 1 to 5. The octanol / water partition coefficient of each polymerization initiator is as follows: t-butyl hydroperoxide has an octanol / water partition coefficient of -1.3, while benzoyl peroxide has an octanol / water partition coefficient of 3.43. [Evaluation of chloroprene graft copolymer latex]

[0090] The tetrahydrofuran insoluble content, grafting efficiency, grafting rates, and bond strengths of the chloroprene graft copolymer latexes of Examples 1 to 9 and Comparative Examples 1 to 5 prepared as described above were evaluated. The evaluation methods are described below. <Messverfahren für den Gehalt an Tetrahydrofuran unlöslichen Stoffen>

[0091] The method for measuring the content of substances insoluble in tetrahydrofuran is the same as the method described in “[8] Graft copolymerization step”. <Messmethoden der Transplantationseffizienz und der Transplantationsrate>

[0092] The measurement methods for grafting efficiency and grafting rate are the same as those described in “[8] Graft copolymerization step”. <Messmethode der Haftfestigkeit>

[0093] To each of the chloroprene graft copolymer latexes of Examples 1 to 9 and Comparative Examples 1 to 5, a terpene phenol tackifier (a tackifier manufactured by Arakawa Chemical Industries, Ltd., trade name: Tamanol E-100) and a thickener (a thickener manufactured by San Nopco Limited, trade name: SN Thickener 612) were added to prepare an adhesive. The terpene phenol tackifier was added in an amount of 30 parts by mass per 100 parts by mass of the chloroprene graft copolymer in a chloroprene graft copolymer latex. The thickener was added as a 15% by mass aqueous solution in an amount of 2 parts by mass per 100 parts by mass of the chloroprene graft copolymer.

[0094] In Comparative Example 6, an organic solvent type adhesive containing a chloroprene graft copolymer (trade name: Showa Denko Chloroprene WHV, manufactured by Showa Denko KK) was used without adding other components.

[0095] In addition to a soft polyvinyl chloride film with a length of 25 mm, a width of 200 mm, and a thickness of 2 mm (trade name: Toughnyl Top D blue, manufactured by Japan Wavelock Co., Ltd.), each adhesive of Examples 1 to 9 and Comparative Examples 1 to 6 was applied with a brush. The coating amount of each adhesive was 200 g / m 2 The coating was heated and dried for 6 minutes at 60°C. Two films were prepared as above, and the adhesive surfaces were bonded together and pressed with a hand roller. The composite films were cured for 7 days at 23°C and a relative humidity of 60% RH to form a test specimen for the adhesion test. The adhesion strength (peel strength) was measured using the T-peel test according to JIS K6854-3.

[0096] The evaluation results of tetrahydrofuran insolubility content, transplantation efficiency, transplantation rate, and adhesion strength are shown in Table 1.

[0097] As can be seen from Table 1, Examples 1 to 9 had higher adhesion strength than Comparative Examples 1 to 6. Satisfactory adhesion was observed in a tetrahydrofuran-insoluble matter content range of 15 mass% or more and 50 mass% or less, and more satisfactory adhesion was observed in a tetrahydrofuran-insoluble matter content range of 17 mass% or more and 45 mass% or less. Higher grafting efficiency likely resulted in higher adhesion strength, and high adhesion strength was observed at a graft copolymerization temperature of 30°C or less.

[0098] In contrast, in Comparative Example 1, in which methyl methacrylate was used for graft copolymerization instead of butyl methacrylate, the ester moiety at a graft portion was likely to be hydrolyzed, thus allowing hydrolysis to occur easily. Therefore, the chloroprene graft copolymer latex was unstable, and the chloroprene graft copolymer latex solidified during the curing of the test specimen (on day 3). Furthermore, the cohesive strength of the (meth)acrylate polymer was lost due to hydrolysis of the ester portion, resulting in a reduction in the bond strength.

[0099] In Comparative Example 2, in which benzoyl peroxide with an octanol / water partition coefficient of more than 3.0 was used as the polymerization initiator, it was assumed that polymerization occurred mainly in the emulsified particles due to the high lipophilicity of the polymerization initiator, and graft polymers were unevenly distributed within the emulsified particles. As a result, the adhesive strength was estimated to be low.

[0100] Comparative Example 3 was an example in which the polymerization temperature in the graft copolymerization step was more than 40°C, and it was considered that the grafting efficiency deteriorated due to the high polymerization temperature and a butyl methacrylate homopolymer prevented adhesion.

[0101] Comparative Example 4 was an adhesive prepared using a chloroprene polymer latex obtained in the chloroprene polymerization step, which had low adhesive strength due to lack of graft copolymerization.

[0102] In Comparative Example 5, where methacrylic acid was used instead of (meth)acrylate, an increase in viscosity impaired the stable graft copolymerization.

[0103] In Comparative Example 6, in which an organic solvent type adhesive was used instead of an aqueous adhesive, the bonding strength to soft polyvinyl chloride was lower than that of the chloroprene graft copolymer latexes of Examples 1 to 9.

Claims

[1] A process for producing a chloroprene graft copolymer latex, the process comprising: a chloroprene polymerization step in which at least chloroprene (A-1) of chloroprene (A-1) and a monomer (A-2) copolymerizable with chloroprene (A-1) is subjected to emulsion radical polymerization to form a chloroprene polymer, and a chloroprene polymer latex in which particles of the chloroprene polymer are dispersed in water is obtained; and a graft copolymerization step in which a (meth)acrylate (B) of the general formula CH2=CR-CO-OR' (in the general formula, R is a methyl group or a hydrogen atom; and R' is an alkyl group having a carbon number of 4 or more and 12 or less) is added to the chloroprene polymer latex, an organic peroxide (C) having an octanol / water partition coefficient of -2.0 or more and 3.0 or less is added as a polymerization initiator to subject the chloroprene polymer to graft copolymerization with the (meth)acrylate (B) at a temperature of 10°C or more and 35°C or less to form a chloroprene graft copolymer, and a chloroprene graft copolymer latex is obtained in which particles of the chloroprene graft copolymer are dispersed in water and wherein a content of insoluble tetrahydrofuran materials is not less than 6 mass% and less than 70 mass% of the chloroprene graft copolymer. [2] A process for producing a chloroprene graft copolymer latex according to claim 1, wherein in the graft copolymerization step, the (meth)acrylate (B) is added in an amount of 1 part by mass or more and 90 parts by mass or less with respect to 100 parts by mass of the chloroprene polymer. [3] A process for producing a chloroprene graft copolymer latex according to claim 1 or 2, wherein in the step of chloroprene polymerization, at least one emulsifier selected from an anionic emulsifier and a nonionic emulsifier is used to conduct the emulsion radical polymerization.