Method for producing chloroprene latex

Abstract

Provided is a method which is for producing a chloroprene-based latex and by which it is possible to obtain a chloroprene-based latex that achieves an excellent balance in average particle size, standard deviation and variance of the particle size distribution, viscosity, molecular weights of the gel fraction and the sol fraction, and the amounts of 1,2-isomers in a chloroprene-based polymer.　The present invention provides a method that is for producing a chloroprene-based latex and that comprises a polymerization step for polymerizing material monomers including a chloroprene monomer. In the polymerization step, an emulsifier and a pH adjustor are added. The polymerization temperature in the polymerization step is 30°C or lower. In the polymerization step, 0.0001-0.0150 parts by mass of the polymerization inhibitor is added to 100 parts by mass of the material monomers before the start of polymerization and / or at the initial stage of the polymerization. The polymerization inhibitor is soluble to chloroprene but is insoluble to water.

Description

[Technical Field]

[0001] This invention relates to a method for producing chloroprene latex. [Background technology]

[0002] Materials derived from chloroprene latex and rubber exhibit excellent heat resistance, weather resistance, ozone resistance, chemical resistance, flame retardancy, and mechanical properties. These properties are utilized in a wide range of applications, including automotive parts, adhesives, and various industrial rubber components.

[0003] For example, Patent Document 1 discloses a chloroprene latex characterized in that the particle size (median diameter) of the latex is within a range expressed by a specific formula, and the weight fraction of the emulsifier contained in the latex is within a range shown by a specific formula. Furthermore, Patent Document 2 discloses a method for producing a chloroprene polymer, characterized by radical polymerization of 2-chloro-1,3-butadiene alone or a monomer mixture containing 2-chloro-1,3-butadiene in the presence of 0.1 parts by mass or more but less than 10 parts by mass of alcohols per 100 parts by mass of the total monomers. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-155535 [Patent Document 2] Japanese Patent Publication No. 2003-055409 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, attempts have been made to control the particle size of chloroprene latex, but conventional techniques have not been able to highly control the average particle size of chloroprene latex, as well as the standard deviation and dispersion of the particle size distribution. Furthermore, it has been difficult to simultaneously control the viscosity, gel content, sol content molecular weight, and the amount of 1,2-isomers in the chloroprene polymer of chloroprene latex.

[0006] The present invention has been made in view of these circumstances, and provides a method for producing chloroprene latex that can be obtained in which the average particle size, the standard deviation and dispersion of the particle size distribution, viscosity, the molecular weight of the gel and sol components, and the balance of the amount of 1,2-isomers in the chloroprene polymer are excellent. [Means for solving the problem]

[0007] According to the present invention, a method for producing chloroprene latex is provided, wherein the production method includes a polymerization step of polymerizing a raw material monomer containing a chloroprene monomer, an emulsifier and a pH adjuster are added in the polymerization step, the polymerization temperature in the polymerization step is 30°C or lower, and in the polymerization step, before the start of polymerization and / or during the initial stages of polymerization, 0.0001 to 0.0150 parts by mass of a polymerization inhibitor are added per 100 parts by mass of the raw material monomer, the polymerization inhibitor is soluble in chloroprene and insoluble in water.

[0008] Through diligent research, the inventors have discovered that by adjusting the type and amount of agents added to the polymerization process, as well as the polymerization temperature, in a polymerization process for polymerizing a raw material monomer containing a chloroprene monomer, and particularly by adding a specific amount of a specific type of polymerization inhibitor before the start of polymerization and / or in the early stages of polymerization, it is possible to obtain a chloroprene-based latex with an excellent balance of average particle size, standard deviation and dispersion of particle size distribution, viscosity, molecular weight of gel and sol components, and the amount of 1,2-isomers in the chloroprene-based polymer. This has led to the completion of the present invention.

[0009] The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other. It is Noh. [1] A method for producing chloroprene latex, wherein the method comprises a polymerization step of polymerizing a raw material monomer containing a chloroprene monomer, wherein an emulsifier and a pH adjuster are added in the polymerization step, the polymerization temperature in the polymerization step is 30°C or lower, and in the polymerization step, before the start of polymerization and / or in the initial stages of polymerization, 0.0001 to 0.0150 parts by mass of a polymerization inhibitor is added per 100 parts by mass of the raw material monomer, wherein the polymerization inhibitor is soluble in chloroprene and insoluble in water. [2] The method for producing a chloroprene-based latex according to [1], wherein the raw material monomer containing chloroprene further comprises a monomer other than chloroprene that can be copolymerized with chloroprene. [3] The method for producing chloroprene latex according to [1] or [2], wherein the chloroprene latex contains 1 to 40% by mass of gel and the weight-average molecular weight of the sol is 400,000 or more. [4] The average particle size obtained by the cumulant analysis method of the chloroprene latex is 80 to 150 nm, and the dispersion of the particle size distribution is 3000 nm. 2 A method for producing chloroprene latex as described in any one of the following items [1] to [3]. [5] The chloroprene polymer contained in the chloroprene latex is measured in deuterated chloroform solvent. 1 A method for producing chloroprene-based latex according to any one of [1] to [4], wherein the ratio A / B of the peak area A at 5.80 to 6.00 ppm to the peak area B at 4.05 to 6.20 ppm in the 1H-NMR spectrum is 0 / 100 to 1.5 / 100. [6] A method for producing chloroprene latex according to any one of [1] to [5], wherein the viscosity of the chloroprene latex is 30 mPa·s or more. [7] A method for producing a chloroprene latex according to any one of [1] to [6], wherein the chloroprene latex is for use as a water-based adhesive. [Effects of the Invention]

[0010] According to the method for producing a chloroprene-based latex according to the present invention, a chloroprene-based latex excellent in the balance of the average particle diameter, the standard deviation of the particle diameter distribution and dispersion, viscosity, gel content, molecular weight of the sol content, and the amount of 1,2-isomer in the chloroprene-based polymer can be obtained. Furthermore, the obtained chloroprene-based latex can be used for various applications by taking advantage of its characteristics. The chloroprene-based latex according to the present invention can be, for example, a chloroprene-based latex for adhesives, and particularly, a chloroprene-based latex for water-based adhesives.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail by exemplifying embodiments of the present invention. The present invention is not limited in any way by these descriptions. Each feature of the embodiments of the present invention shown below can be combined with each other. Also, the invention can be established independently for each feature.

[0012] 1. Method for Producing Chloroprene-Based Latex The method for producing a chloroprene-based latex according to the present invention includes a polymerization step of polymerizing a raw material monomer containing a chloroprene monomer.

[0013] 1.1 Polymerization Step In the polymerization step according to the present invention, an emulsifier and a pH adjuster are added, and the polymerization temperature in the polymerization step is 30°C or lower. Also, in the polymerization step, before the start of polymerization and / or in the initial stage of polymerization, 0.0001 to 0.0150 parts by mass of a polymerization inhibitor is added to 100 parts by mass of the raw material monomer, and the polymerization inhibitor is soluble in chloroprene and insoluble in water.

[0014] According to the method for producing a chloroprene-based latex according to the present invention, a chloroprene-based latex containing a chloroprene-based polymer can be obtained. In the present invention, the chloroprene-based polymer refers to a polymer containing monomer units derived from 2-chloro-1,3-butadiene (hereinafter referred to as chloroprene).

[0015] <Raw material monomer> In the polymerization step according to the present invention, a raw material monomer containing a chloroprene monomer is polymerized. The raw material monomer according to the present invention contains a chloroprene monomer. Further, the raw material monomer containing chloroprene according to the present invention can further contain monomers other than chloroprene that are copolymerizable with chloroprene.

[0016] Note that commercially available chloroprene may contain a small amount of 1-chloro-1,3-butadiene as an impurity. Such 2-chloro-1,3-butadiene containing a small amount of 1-chloro-1,3-butadiene can also be used as the chloroprene monomer in this embodiment.

[0017] Examples of monomers other than chloroprene that are copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, styrene, ethylene, unsaturated nitriles (acrylonitrile, methacrylonitrile, ethacrylonitrile, phenylacrylonitrile, etc.), acrylic acid or its esters, methacrylic acid or its esters, sulfur, and the like. These can be used alone or in combination of two or more.

[0018] While not particularly limited, a raw material monomer containing chloroprene monomers may contain 60 to 100% chloroprene monomers when the total mass of the raw material monomers is considered to be 100%. The chloroprene monomer content in the raw material monomers may be, for example, 60, 65, 70, 75, 80, 85, 90, 95, 99, or 100% by mass, and may be within the range of any two of the values ​​exemplified here. By setting the chloroprene monomer content in the raw material monomers within the above numerical range, the resulting chloroprene-based latex can exhibit the effects of copolymerizing monomers other than chloroprene without impairing the properties derived from chloroprene.

[0019] In a polymerization process according to one embodiment of the present invention, at least a portion of the raw material monomers to be used in the polymerization process can be loaded into the polymerization vessel before polymerization begins. In a polymerization process according to one embodiment of the present invention, all of the raw material monomers to be used in the polymerization process can be loaded into the polymerization vessel before polymerization begins.

[0020] Furthermore, in the polymerization process according to one embodiment of the present invention, a portion of the raw material monomers to be used in the polymerization process can be placed in the polymerization container before the start of polymerization, and at least a portion of the raw material monomers can be added after the start of polymerization (after the start of polymerization). When adding at least a portion of the raw material monomers after polymerization has started, the remaining monomers can be added in one or more installments, or continuously at a constant flow rate. When adding at least a portion of the raw material monomer after polymerization has started, up to 60 parts by mass of the 100 parts by mass of raw material monomer used in the polymerization process can be added after polymerization has started. In this case, the amount of raw material monomer added after polymerization has started can be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 parts by mass, and may be within the range of any two of the values ​​exemplified here.

[0021] In the polymerization process according to the present invention, an emulsifier and a pH adjuster are added.

[0022] <Emulsifier> The emulsifier is not particularly limited, and known anionic, nonionic, or cationic emulsifiers used in the polymerization process of chloroprene latex can be used. Anionic emulsifiers include carboxylic acid type, sulfonic acid type, and sulfate ester type, and examples include higher fatty acid salts, alkenyl succinates, alkali metal salts of rosinic acid, alkyl sulfonates with 8 to 20 carbon atoms, alkylaryl sulfates, and condensates of sodium naphthalene sulfonate and formaldehyde. Examples of nonionic emulsifiers include polyvinyl alcohol or its copolymers (e.g., copolymers with acrylamide), polyvinyl ether or its copolymers (e.g., copolymers with maleic acid), polyvinylpyrrolidone or its copolymers (e.g., copolymers with vinyl acetate), or chemically modified versions of these (co)polymers, or cellulose derivatives (hydroxyethylcellulose), etc. Cationic emulsifiers include aliphatic amine salts and aliphatic quaternary ammonium salts, such as octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, and dilauryldimethylammonium chloride. Among these, the emulsifier preferably contains rosin acid or an alkali metal salt of rosin acid. These may be used alone or in combination of two or more.

[0023] The amount of total emulsifier used in the polymerization process can be 1.0 to 6.0 parts by mass per 100 parts by mass of total monomers used in the polymerization process. The amount of total emulsifier used in the polymerization process can be, for example, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, or 6.0 parts by mass per 100 parts by mass of total monomers used in the polymerization process, and may be within the range of any two of the values ​​exemplified here.

[0024] In the polymerization process according to one embodiment of the present invention, all of the emulsifiers to be used in the polymerization process can be placed in the polymerization vessel before the polymerization starts. In addition, in the polymerization step according to an embodiment of the present invention, at least a part of the emulsifier used in the polymerization step can be added separately after the start of polymerization.

[0025] <pH adjuster> Examples of the pH adjuster include potassium pyrosulfite, potassium sulfite, potassium bisulfite, potassium phosphate, dipotassium hydrogen phosphate, sodium pyrosulfite, sodium sulfite, sodium bisulfite, sodium phosphate, disodium hydrogen phosphate, potassium hydroxide, sodium hydroxide, and the like. Among these pH adjusters, the use of potassium hydroxide or sodium hydroxide is preferable because it has a high effect of increasing the pH value. The pH adjuster may be used alone or in combination of two or more thereof.

[0026] The amount of the pH adjuster used in the polymerization step can be 0.01 to 2.0 parts by mass with respect to 100 parts by mass of all the monomers used in the polymerization step. The amount of the pH adjuster used in the polymerization step is, for example, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 parts by mass with respect to 100 parts by mass of all the monomers used in the polymerization step, and may be within the range between any two of the numerical values exemplified here.

[0027] In the polymerization step according to an embodiment of the present invention, all of the pH adjuster used in the polymerization step can be charged into the polymerization vessel before the start of polymerization. In addition, in the polymerization step according to an embodiment of the present invention, at least a part of the pH adjuster used in the polymerization step can be added separately after the start of polymerization.

[0028] By setting the types and amounts of the raw material monomers, and the types and amounts of the emulsifier and the pH adjuster as described above, a chloroprene-based latex excellent in the balance of the average particle diameter, the standard deviation of the particle diameter distribution and dispersion, viscosity, gel content, sol content molecular weight, and the amount of 1,2-isomer in the chloroprene-based polymer can be obtained.

[0029] <Polymerization temperature> In the polymerization process according to the present invention, the polymerization temperature is 30°C or lower. The polymerization temperature may be, for example, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30°C, and may be within the range of any two of the values ​​exemplified here. By setting the polymerization temperature below the above upper limit, the polymerization reaction can be carried out more smoothly and safely, and the chloroprene polymer contained in the resulting chloroprene latex can contain a more appropriate amount of 1,2-isomers in the chloroprene polymer.

[0030] <Polymerization inhibitors> In the polymerization process according to the present invention, before the start of polymerization and / or in the early stages of polymerization, 0.0001 to 0.0150 parts by mass of polymerization inhibitor are added per 100 parts by mass of raw material monomer. The polymerization inhibitor is a compound that has a polymerization-inhibiting effect, is soluble in chloroprene, and is insoluble in water, but is not particularly limited. The polymerization inhibitor according to one embodiment of the present invention is soluble in chloroprene, and preferably dissolves at 25°C in an amount of 0.1 g or more per 100 g of chloroprene, and can dissolve in amounts of 0.2, 0.5, 1.0, or 1.5 g or more. The polymerization inhibitor according to one embodiment of the present invention is insoluble in water, and preferably does not dissolve in amounts of 1 g or more per 100 g of water at 25°C (when 1 g of the polymerization inhibitor is added to 100 g of water, undissolved residue remains), and preferably does not dissolve in amounts of 0.5, 0.2, or 0.1 g or more.

[0031] Examples of polymerization inhibitors include amine compounds such as phenothiazines, and phenolic compounds such as t-butylcatechol, 1,3,5-trihydroxybenzene, 2,6-di-t-butyl-4-methylphenol, 2,2-methylenebis(6-t-4-methylphenol), and 4,4-butylenebis(6-t-butyl-3-methylphenol). Furthermore, polymerization inhibitors may include ethylenebis(oxyethylene)bis[3-(5-t-butyl-4-hydroxy-m-tolyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], etc. The polymerization inhibitors preferably include amine compounds and phenolic compounds, and more preferably include phenothiazine and t-butylcatechol, and more preferably include phenothiazine. These may be used alone or in combination of two or more. The polymerization inhibitor may be one that does not contain 2,4-dinitrochlorobenzene. 2,4-dinitrochlorobenzene is known to induce type IV allergies.

[0032] In the polymerization process of the present invention, before the start of polymerization and / or in the early stages of polymerization, 0.0001 to 0.0150 parts by mass of a polymerization inhibitor is added to 100 parts by mass of the raw material monomer. In the present invention, "before polymerization initiation" means before the raw material monomer containing chloroprene monomer and the polymerization initiator are added to the reaction system, and "polymerization initiation" means when the raw material monomer containing chloroprene monomer and the polymerization initiator are added to the reaction system. The raw material monomer may contain a polymerization inhibitor to suppress polymerization during storage. The polymerization inhibitor added "before polymerization initiation" includes the polymerization inhibitor contained in the raw material monomer at the time of addition to the reaction system. Furthermore, in the present invention, "initial polymerization phase" can be defined as the period from the start of polymerization until 20% by mass of the total monomers used in the polymerization process are converted into polymers. In the polymerization process of the present invention, by adding a specific polymerization inhibitor before the start of polymerization and / or in the early stages of polymerization, the growth of monomer droplets and polymerization within micelle particles are suppressed. As a result, compared to conventional emulsion polymerization, the number of particles formed increases, the average particle size of the formed particles decreases, and the width of the particle size distribution narrows.

[0033] In the polymerization process of the present invention, before polymerization begins and / or in the early stages of polymerization, a polymerization inhibitor can be added in an amount of 0.0001 to 0.0150 parts by mass per 100 parts by mass of the raw material monomer, preferably 0.0005 to 0.0100 parts by mass, and more preferably 0.0005 parts by mass or more and less than 0.0100 parts by mass. The amount of polymerization inhibitor added before polymerization begins and / or in the early stages of polymerization is, for example, 0.0001, 0.0002, 0.0005, 0.0010, 0.0020, 0.0050, 0.0100 parts by mass, less than 0.0100 parts by mass, 0.0120, 0.0130, 0.0140, and 0.0150 parts by mass per 100 parts by mass of the raw material monomer, and may be within the range of any two of the values ​​exemplified here. By keeping the amount of polymerization inhibitor added before the start of polymerization and / or in the early stages of polymerization within the above numerical range, the polymerization reaction can proceed while appropriately adjusting the particle size of the resulting latex, making it possible to obtain a chloroprene-based latex with an excellent balance of average particle size, standard deviation of particle size distribution and dispersion, viscosity, gel content and sol content molecular weight.

[0034] In the polymerization process according to one embodiment of the present invention, a polymerization inhibitor can also be added after the initial stage of polymerization, that is, after more than 20% by mass of the total monomers used in the polymerization process have been converted into polymers, but before the polymerization is stopped. The total amount of polymerization inhibitor added before and during the polymerization process is preferably less than 0.0200 parts by mass per 100 parts by mass of the total monomers used in the polymerization process. The total amount of polymerization inhibitor added before and during the polymerization process can be, for example, less than 0.0001, 0.0002, 0.0005, 0.0010, 0.0020, 0.0050, 0.0100, 0.0120, 0.0130, 0.0140, 0.0150 parts by mass, or 0.0200 parts by mass per 100 parts by mass of the total monomers used in the polymerization process, and may be within the range of any two of the values ​​exemplified here. Note that the "total amount of polymerization inhibitors added in the polymerization process" does not include the amount of polymerization inhibitors added at the end of the polymerization process to stop the polymerization.

[0035] Furthermore, in the polymerization process according to one embodiment of the present invention, when the total amount of polymerization inhibitors added before and during the polymerization process is set to 100% by mass, it is preferable to add 50% by mass or more of polymerization inhibitors before the start of polymerization and in the early stages of polymerization. When the total amount of polymerization inhibitors added before and during the polymerization process is set to 100% by mass, the amount of polymerization inhibitors added before the start of polymerization and in the early stages of polymerization can be, for example, 60, 70, 80, 90, or 100% by mass, and may be within the range of any two of the values ​​exemplified here.

[0036] <Polymerization initiator> In the polymerization step according to one embodiment of the present invention, a polymerization initiator can be used. Examples of polymerization initiators that can be used include potassium persulfate, benzoyl peroxide, ammonium persulfate, and hydrogen peroxide, which are commonly used in radical polymerization. These may be used individually or in combination of two or more. The polymerization initiator can be added continuously, depending on the polymerization rate.

[0037] <Chain movement agent> In the polymerization step according to one embodiment of the present invention, a chain transfer agent can be used. The chain transfer agent is not particularly limited as long as it is commonly used in the production of chloroprene latex, and for example, known chain transfer agents such as long-chain alkyl mercaptans such as n-dodecyl mercaptan, tert-dodecyl mercaptan, and n-octyl mercaptan, dialkyl xanthogen disulfides such as diisopropyl xanthogen disulfide and diethyl xanthogen disulfide, and iodoform can be used. These may be used alone or in combination of two or more. The amount of chain transfer agent added can be 0.001 to 10 parts by mass per 100 parts by mass of the total monomers used in the polymerization process.

[0038] 1.2 Polymerization completion process A method for producing chloroprene latex according to one embodiment of the present invention may include a polymerization termination step. In the polymerization termination step, polymerization is stopped by adding a polymerization inhibitor in addition to the polymerization inhibitors added before and during the polymerization step, thereby obtaining a polymerization solution in which the reaction has been completed.

[0039] As polymerization inhibitors, those listed as polymerization inhibitors to be added in the polymerization process can be used. Furthermore, as polymerization inhibitors to be added at the end of the polymerization process, polymerization inhibitors other than those listed as polymerization inhibitors to be added in the polymerization process can be used; specifically, water-soluble polymerization inhibitors such as diethylhydroxylamine can be used. The amount added can be 0.02 to 0.1 parts by mass per 100 parts by mass of the total monomers used in the polymerization process.

[0040] 1.3 Removal of unreacted monomers A method for producing chloroprene latex according to one embodiment of the present invention may include a step for removing unreacted monomers. In the step for removing unreacted monomers, unreacted monomers remaining after polymerization are removed from the polymerization solution after polymerization is completed by conventional methods such as steam stripping or reduced-pressure heating evaporation, thereby obtaining chloroprene latex.

[0041] The solid content concentration of chloroprene latex in the polymerization solution at the end of polymerization can be 60% by mass or less. The solid content concentration can be, for example, 20, 25, 30, 35, 40, 45, 50, 55, or 60% by mass, and may be within the range of any two of the values ​​exemplified here.

[0042] 1.4 Concentration process A method for producing chloroprene latex according to one embodiment of the present invention may optionally include a concentration step to remove water by a vacuum heating evaporation method or the like and adjust the solid content concentration. In the concentration step, the solid content concentration can be adjusted to 45 to 65% by mass. The solid content concentration can be, for example, 45, 50, 55, 60, or 65% by mass, and may be within the range of any two of the values ​​exemplified here.

[0043] 2. Chloroprene-based latex The chloroprene-based latex according to the present invention includes a chloroprene-based polymer. The chloroprene-based polymer according to the present invention can be a homopolymer of chloroprene, or a copolymer of chloroprene and another monomer copolymerizable with chloroprene.

[0044] Other monomers copolymerizable with chloroprene include those listed as starting monomers.

[0045] In one embodiment of the present invention, the chloroprene polymer preferably contains 60 to 100% by mass of chloroprene monomer units when the chloroprene polymer is considered to be 100% by mass. The content of chloroprene monomer units in the chloroprene polymer may be, for example, 60, 65, 70, 75, 80, 85, 90, 95, 99, or 100% by mass, and may be within the range of any two of the values ​​exemplified here. By setting the content of chloroprene monomer units within the above numerical range, it is possible to exhibit the effects of copolymerizing monomers other than chloroprene without impairing the properties derived from chloroprene.

[0046] The chloroprene polymer according to the present invention may be a sulfur-modified chloroprene polymer, a mercaptan-modified chloroprene polymer, a xanthogene-modified chloroprene polymer, a dithiocarbonate-based chloroprene polymer, a trithiocarbonate-based chloroprene polymer, a carbamate-based chloroprene polymer, and the like.

[0047] The chloroprene-based latex according to one embodiment of the present invention preferably contains 1 to 40% by mass of gel content. The gel content may be, for example, 0, 5, 10, 15, 20, 25, 30, 35, or 40% by mass, and may be within the range of any two of the values ​​exemplified herein. In the present invention, the gel content in chloroprene latex refers to the toluene-insoluble content of chloroprene latex after freeze-drying, and can be specifically measured by the method described in the examples. The gel content in chloroprene latex can be adjusted by controlling the polymerization conditions of chloroprene latex, specifically the types and amounts of raw materials and additives used during polymerization, as well as the polymerization conditions themselves.

[0048] In one embodiment of the present invention, the chloroprene latex preferably has a sol weight-average molecular weight of 400,000 or more. The sol weight-average molecular weight may be, for example, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000, and may be within the range of any two of the values ​​exemplified herein. The sol content refers to the toluene-soluble content of the chloroprene latex after freeze-drying. The molecular weight of the sol content is a polystyrene-converted value measured by gel permeation chromatography (GPC), and can be specifically measured by the method described in the examples. The weight-average molecular weight of the sol in chloroprene latex can be adjusted by controlling the polymerization conditions of chloroprene latex, specifically the types and amounts of raw materials and additives used during polymerization, as well as the polymerization conditions themselves.

[0049] In the chloroprene latex according to one embodiment of the present invention, the molecular weights of the gel and sol components are appropriately adjusted, specifically within the above numerical range. For example, when the chloroprene latex is blended with a water-based adhesive, the resulting water-based adhesive becomes more entangled with molecules, resulting in improved adhesive strength.

[0050] The chloroprene-based latex according to one embodiment of the present invention preferably has an average particle diameter of 80 to 150 nm obtained by cumulant analysis. The average particle diameter may be, for example, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, or 150 nm, and may be within the range of any two of the values ​​exemplified here. The chloroprene-based latex according to one embodiment of the present invention has a particle size distribution dispersion of 3000 nm 2 The following is preferable: The dispersion is, for example, 500 nm. 2 , 1000nm 2, 1500 nm 2 , 2000 nm 2 , 2500 nm 2 , 3000 nm 2 and may be within the range between any two of the numerical values exemplified herein. The chloroprene-based latex according to an embodiment of the present invention preferably has a standard deviation of the particle size distribution of 50 nm or less. The standard deviation is, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, and may be within the range between any two of the numerical values exemplified herein.

[0051] The average particle size, the standard deviation of the particle size distribution, and the dispersion of the chloroprene-based latex can be calculated using the scattering intensity distribution obtained by the dynamic light scattering method by diluting and adjusting the chloroprene-based latex immediately after the polymerization reaction with distilled water so that the solid content concentration becomes 0.05% by mass, and specifically, can be measured by the method described in the examples. The average particle size, the standard deviation of the particle size distribution, and the dispersion of the sol in the chloroprene-based latex can be adjusted by controlling the polymerization conditions of the chloroprene-based latex, specifically, the types and amounts of the raw materials and additives during polymerization, and the polymerization conditions, particularly the type, addition amount, and addition timing of the polymerization inhibitor. According to the present invention, by appropriately controlling these, the average particle size, the standard deviation of the particle size distribution, and the dispersion can be preferably controlled, and at the same time, a chloroprene-based latex excellent in the balance of viscosity, gel content, molecular weight of the sol fraction, and the amount of 1,2-isomers in the chloroprene-based polymer can be obtained.

[0052] The chloroprene-based latex according to an embodiment of the present invention is measured in a heavy chloroform solvent of the chloroprene-based polymer contained in the latex 1In the 1H-NMR spectrum, the ratio A / B of the peak area A (5.80-6.00 ppm) to the peak area B (4.05-6.20 ppm) is preferably 0 / 100 to 1.5 / 100. A / B may be, for example, 0, 0.3, 0.6, 0.9, 1.2, or 1.5 / 100, and may be within the range of any two of the values ​​exemplified here.

[0053] Chloroprene polymers contained in chloroprene latex 1 The H-NMR spectrum was obtained by purifying chloroprene latex with benzene and methanol, freeze-drying it, dissolving it in a 5% deuterated chloroform solution, and then performing nuclear magnetic resonance analysis. 1 H-NMR spectrum It can be measured by measuring, and specifically, it can be measured by the method described in the examples.

[0054] Chloroprene polymers 1 In the 1H-NMR spectrum, peaks with peak tops of 5.80–6.00 ppm (e.g., peak groups) are peaks originating from vinyl hydrogen in the 1,2-isomers of chloroprene monomer units in chloroprene polymers. 1 In the 1H-NMR spectrum, peaks with peak tops between 4.05 and 6.20 ppm (e.g., peak groups) are peaks originating from vinyl hydrogen in the chloroprene monomer units of chloroprene polymers. In other words, the peak area ratio A / B between peak area A (5.80–6.00 ppm) and peak area B (4.05–6.20 ppm) indicates the relative abundance of 1,2-isomers in the chloroprene monomer units of chloroprene polymers. In the chloroprene latex according to one embodiment of the present invention, the peak area ratio A / B is within the above numerical range, that is, the abundance ratio of 1,2-isomers is below the above upper limit, thereby reducing the branching of the chloroprene polymer, increasing the abundance ratio of linear chloroprene polymers, and improving crystallinity. Therefore, when the chloroprene latex is blended with an aqueous adhesive, the adhesive strength and bonding speed of the aqueous adhesive are further improved.

[0055] In one embodiment of the present invention, the chloroprene-based latex preferably has a viscosity of 30 mPa·s or more. The viscosity may be, for example, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200 mPa·s, and may be within the range of any two of the values ​​exemplified herein. Viscosity can be defined as the viscosity measured at 25°C. Viscosity can be measured using a rotational viscometer, and a single-cylinder viscometer (Type B viscometer) can be used. Specifically, it can be measured using the method described in the examples. The viscosity of chloroprene latex can be adjusted by controlling the type and amount of raw materials and additives used during polymerization, as well as the polymerization conditions, particularly the type, amount, and timing of polymerization inhibitors, thereby suitably controlling the average particle size, the standard deviation of the particle size distribution, and the dispersion.

[0056] A chloroprene-based latex according to one embodiment of the present invention can be used as an adhesive, and in particular, as a water-based adhesive. The chloroprene-based latex according to the present invention has an excellent balance of average particle size, standard deviation and dispersion of particle size distribution, viscosity, molecular weight of gel and sol components, and the amount of 1,2-isomers in the chloroprene polymer. As a result, the molecular entanglement and crystallinity of the chloroprene polymer are improved, and an adhesive with improved adhesive strength and bonding speed can be obtained.

[0057] 3. Chloroprene-based latex compositions A chloroprene-based latex composition according to one embodiment of the present invention contains the above-mentioned chloroprene-based latex. The chloroprene-based latex composition according to one embodiment of the present invention can also be an adhesive composition, and in particular, it can be an aqueous adhesive composition.

[0058] The aqueous adhesive composition according to one embodiment of the present invention may, in addition to the chloroprene latex described above, appropriately contain pH adjusters, plasticizers, fillers, antioxidants, tackifiers, pigments, colorants, wetting agents, defoamers, thickeners, and other resin emulsions (latex).

[0059] Examples of pH adjusters include weak acids and buffers. Specifically, examples include hydroxy acids such as citric acid and glycolic acid, and at least one compound selected from boric acid and amino acids, with amino acids being preferred. Specific examples of amino acids include glycine, alanine, threonine, and proline.

[0060] The amount of pH adjuster to be added is not particularly limited, but it is preferable to use an amount that can adjust the pH of the water-based adhesive to a range of 7 to 10. More preferably, it is desirable to add an amount that can adjust the pH to a range of 8 to 10.

[0061] As for plasticizers, those with good compatibility with chloroprene polymers are preferred and are not particularly limited, but examples include dibutyl sebacate, dibutyl phthalate, dioctyl adipate, dioctyl azelate, dioctyl sebacate, dioctyl phthalate, tricresyl phosphate, cresyl diphenyl phosphate, etc.

[0062] The amount of plasticizer added is not particularly limited, but is 0.1 to 30 parts by mass, preferably 1 to 20 parts by mass, and more preferably 2 to 15 parts by mass, per 100 parts by mass of solid content of chloroprene latex.

[0063] The water-based adhesive according to one embodiment of the present invention can be a one-component water-based adhesive. Suitable adherends for the water-based adhesive according to one embodiment of the present invention are foams made of materials such as polyurethane, ethylene-vinyl acetate copolymer, and polyethylene, or absorbent adherends such as wood, cloth, and textiles. The chloroprene-based latex according to one embodiment of the present invention can be suitably used not only as an adhesive but also as an immersion molded article or film. A particularly suitable adherend for the water-based adhesive according to one embodiment of the present invention is polyurethane foam. [Examples]

[0064] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0065] (Example 1) Using a 10 L reactor, 100 parts by mass of chloroprene monomer, 0.1 parts by mass of n-dodecyl mercaptan, 0.0100 parts by mass of phenothiazine, 3.5 parts by mass of potassium salt of rosinic acid (Harima Chemical Industries, Ltd., disproportionated gum rosin potassium salt), 0.3 parts by mass of sodium salt of β-naphthalene sulfonic acid formalin condensate (Kao Corporation, product name: Demol N), 0.45 parts by mass of potassium hydroxide, 30.3 parts by mass of NaHSO4, and 90 parts by mass of pure water were added under a nitrogen atmosphere. Potassium persulfate was used as a polymerization initiator and thiourea dioxide as a reducing agent, and polymerization was carried out at a polymerization temperature of 10°C while continuously adding these substances. When the polymerization rate reached 83%, an emulsion of 0.02 parts by mass of phenothiazine and 0.02 parts by mass of t-butylcatechol was added to stop the polymerization. Chloroprene-based latex was obtained by removing unreacted monomers under reduced pressure. Furthermore, the water was evaporated under reduced pressure to concentrate the mixture, and the solid content was adjusted to 55% by mass.

[0066] (Examples 2, 3, Comparative Examples 1-4) Chloroprene-based latex was obtained in the same manner as in the examples, except that the polymerization formulation and polymerization conditions were as shown in Table 1. In Comparative Examples 3 and 4, too much polymerization inhibitor was added during the polymerization process, and polymerization did not proceed even with the addition of an excess initiator, failing to reach the target polymerization rate.

[0067] <Latex Evaluation> (Average particle size, standard deviation of particle size distribution, variance) Chloroprene-based latex, after adjusting the solid content concentration, was diluted with distilled water to a solid content concentration of 0.05% by mass. The particle size distribution was measured using an ELSZ Series (manufactured by Otsuka Electronics Co., Ltd.), and the average particle size, as well as the standard deviation and variance of the particle scattering intensity distribution, were determined. Here, the average particle size of the latex was obtained by applying the cumulant analysis method to the scattering intensity distribution obtained by dynamic light scattering. The results are shown in Table 1.

[0068] (viscosity) The polymerization reaction was completed, and the residual monomer was removed. The solid content of the chloroprene latex was adjusted to 55% by mass, and its viscosity was measured at 25°C. The results are shown in Table 1. A TV-25 viscometer (manufactured by Toki Sangyo Co., Ltd.) was used for the measurement. The measurement conditions were rotor No. 2 and rotation speed of 30 rpm.

[0069] (Gel content) The obtained chloroprene latex was freeze-dried and accurately weighed. The mass of the freeze-dried chloroprene latex was denoted as X g. The freeze-dried chloroprene latex was dissolved in toluene at 23°C for 20 hours (adjusted so that the latex was 0.6% by mass relative to the total mass of latex and toluene, which was 100% by mass). The gel component was separated from the mixture of chloroprene latex and toluene using a centrifuge and then a 200-mesh wire mesh. The obtained gel component was air-dried, then dried at 110°C for 1 hour and accurately weighed. The mass of the dried gel component was denoted as Y g. The gel component was calculated according to the following formula. The results are shown in Table 1. Gel content = Y / X × 100 (%)

[0070] (Weight-average molecular weight (Mw) in the sol portion) In the preparation of the gel component described above, the weight-average molecular weight (Mw) of the sol component, obtained by removing the gel component from the mixture of chloroprene latex and toluene, was measured by gel permeation chromatography (GPC). The weight-average molecular weight (Mw) is a polystyrene-converted value measured by gel permeation chromatography (GPC), and was measured under the measurement conditions described below. The results are shown in Table 1. 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).

[0071] <Nuclear magnetic resonance analysis ( 1 Peak area ratio A / B in H-NMR spectrum Chloroprene latex is purified with benzene and methanol, freeze-dried, dissolved in a 5% deuterated chloroform solution, and then processed using a JEOL Ltd. JNM-ECX-400 (400MHz, FT type). 1 The 1H-NMR spectrum was measured. 1 In the 1H-NMR spectrum, the peak area A from 5.80–6.00 ppm and the peak area B from 4.05–6.10 ppm were measured, with the chloroform peak in deuterated chloroform (7.24 ppm) as the reference point, and the ratio A / B was calculated. The results are shown in Table 1.

[0072] The measurement conditions for nuclear magnetic resonance analysis (1H-NMR) are as follows. • Measurement mode: Non-decoupling • Flip angle: 45 degrees Waiting time: 4.3 seconds • Sample rotation speed: 0~12Hz • Windowing: Exponential function • Number of cumulative measurements: 128 • Measurement temperature: 30℃

[0073] Table 1

Claims

1. A method for producing chloroprene latex, The chloroprene-based latex contains 1 to 40% by mass of gel, and the weight-average molecular weight of the sol is 400,000 or more and 1,000,000 or less. The above manufacturing method includes a polymerization step of polymerizing a raw material monomer containing a chloroprene monomer, In the polymerization step, an emulsifier, a pH adjuster, and a polymerization initiator are added. The emulsifier comprises rosin acid or an alkali metal salt of rosin acid. The polymerization initiator is at least one of potassium persulfate, benzoyl peroxide, ammonium persulfate, and hydrogen peroxide. The polymerization temperature in the polymerization step is 30°C or lower. In the polymerization process, before the start of polymerization and / or in the early stages of polymerization, 0.0001 to 0.0150 parts by mass of polymerization inhibitor are added to 100 parts by mass of the raw material monomer. The polymerization inhibitor is soluble in chloroprene and insoluble in water. A method for producing chloroprene latex, wherein the polymerization inhibitor is at least one selected from phenothiazine, t-butylcatechol, and 1,3,5-trihydroxybenzene.

2. The method for producing a chloroprene-based latex according to claim 1, wherein the raw material monomer containing chloroprene further comprises monomers other than chloroprene that can copolymerize with chloroprene.

3. The chloroprene-based latex obtained by cumulant analysis has an average particle diameter of 80 to 150 nm, and the dispersion of the particle size distribution is 3000 nm. ２ The method for producing chloroprene-based latex according to claim 1 or claim 2, which is as follows:

4. A method for producing a chloroprene latex according to claim 1 or claim 2, wherein the ¹H-NMR spectrum of the chloroprene polymer contained in the chloroprene latex, measured in a deuterated chloroform solvent, has a ratio A / B of peak area A at 5.80 to 6.00 ppm to peak area B at 4.05 to 6.20 ppm, which is 0 / 100 to 1.5 / 100.

5. A method for producing a chloroprene-based latex according to claim 1 or claim 2, wherein the viscosity of the chloroprene-based latex is 30 mPa·s or more.

6. The method for producing a chloroprene-based latex according to claim 1 or claim 2, wherein the chloroprene-based latex is for use in a water-based adhesive.

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