Chloroprene latex, rubber asphalt emulsion, asphalt layer, and asphalt mixture

Abstract

The purpose of the present invention is to provide a rubber asphalt emulsion with which it is possible to exhibit a higher aggregate holding property when combined with an aggregate and to provide a chloroprene latex with which it is possible to yield such a rubber asphalt emulsion. Provided is a chloroprene latex containing a polymer that contains a structural unit derived from a chloroprene monomer and a structural unit derived from a second monomer other than the chloroprene monomer. The gel amount in the chloroprene latex is 70% or more, the second monomer has a crystallization temperature, a glass transition temperature, or a melting point of 80°C or higher when homopolymerized, the content of the structural unit derived from the second monomer in the polymer is 3-10 mass parts per 100 mass parts of the total structural units constituting the polymer, and the z average particle size of the polymer is 150 nm or less.

Description

Chloroprene latex, rubber asphalt emulsion, asphalt layer and asphalt mixture

[0001] The present invention relates to a chloroprene latex, a rubber asphalt emulsion, an asphalt layer, and an asphalt mixture.

[0002] Asphalt is widely used in the fields of civil engineering and construction, for example, as a waterproofing agent for road paving and residential roofs. In road paving, asphalt is used in combination with aggregates such as crushed stone and sand, and functions as an adhesive that bonds the aggregates together. To effectively mix the asphalt and aggregate, asphalt is often used in the form of an asphalt emulsion that does not contain aggregate. Aggregate-free asphalt emulsions are also used in applications such as fog seals and thin-layer surface treatment methods.

[0003] However, simply combining asphalt with aggregate does not provide the durability and adhesion required for road pavement, and there is a problem in that the paved road is prone to damage such as flow, rutting, and cracking. Therefore, various attempts have been made to modify asphalt by adding rubber to form a rubber-asphalt emulsion, thereby improving durability when combined with aggregate. For example, various rubbers such as natural rubber, SBR (styrene-butadiene polymer), CR (polychloroprene), SBS (styrene-butadiene block copolymer), EVA (ethylene-vinyl acetate copolymer), and polyurethane have been used as asphalt modifiers (Non-Patent Document 1).

[0004] Published by the Japan Asphalt Association, Asphalt No. 161, 1989, pp. 3-18

[0005] Even when asphalt containing polychloroprene latex is combined with aggregate and used for road paving, sufficient aggregate gripping ability may not always be achieved. Poor aggregate gripping ability means that the aggregate is easily removed from the asphalt-aggregate mixture, which means that the durability required for road paving is insufficient. Therefore, there is still a demand for rubber asphalt emulsions that can demonstrate higher durability when combined with aggregate.

[0006] An object of the present invention is to provide a rubber asphalt emulsion that can exhibit higher aggregate gripping ability when combined with aggregate, and a chloroprene latex that can provide such a rubber asphalt emulsion.

[0007] As a result of extensive research into solving the above problems, the present inventors have found that by using a chloroprene latex containing a polymer of chloroprene and a specific monomer, a rubber asphalt emulsion obtained by blending this chloroprene latex with asphalt can exhibit sufficient aggregate-holding ability.

[0008] That is, the present invention relates to the following chloroprene latex, rubber asphalt emulsion, asphalt layer, and asphalt mixture: [1] A chloroprene latex comprising a polymer containing structural units derived from chloroprene monomers and structural units derived from a second monomer other than chloroprene monomers, the polymer having a gel content of 70% or more, the second monomer being a monomer that, when homopolymerized, has a crystallization temperature, glass transition temperature, or melting point of 80°C or higher, the content of the structural units derived from the second monomer in the polymer is 3 to 10 parts by mass per 100 parts by mass of all structural units constituting the polymer, and the z-average particle size of the polymer is 150 nm or less.

[0009] [2] The chloroprene latex according to [1], wherein the second monomer is 2,3-dichloro-1,3-butadiene.

[0010] [3] The chloroprene latex according to [1] or [2], wherein the polymer has a z-average particle size of 10 nm or more.

[0011] [4] The chloroprene latex according to any one of [1] to [3], wherein the gel content is 99% or less.

[0012] [5] A rubber asphalt emulsion obtained by mixing the chloroprene latex according to any one of [1] to [4] with asphalt.

[0013] [6] An asphalt layer obtained by applying and drying the rubber asphalt emulsion described in [5].

[0014] [7] An asphalt mixture obtained by mixing the rubber asphalt emulsion according to [5] with aggregate.

[0015] The chloroprene latex of the present invention can provide a rubber asphalt emulsion that is suitable for forming an asphalt layer and can exhibit high aggregate gripping ability.

[0016] Hereinafter, embodiments of the present invention will be described in detail. [Polymer] The polymer used in the present invention contains structural units derived from chloroprene monomers and structural units derived from a second monomer other than chloroprene monomers. Here, the second monomer is a monomer whose crystallization temperature, glass transition temperature, or melting point is 80°C or higher when homopolymerized. In the present invention, this polymer is contained in the chloroprene latex and rubber asphalt emulsion described below, and constitutes the rubber component in the chloroprene latex and rubber asphalt emulsion. In addition, this polymer also functions as an asphalt modifier, and is contained in the asphalt layer and asphalt mixture described below.

[0017] <Chloroprene Monomer> The chloroprene monomer is the first monomer that gives the polymer. The structural unit derived from the chloroprene monomer constitutes the basic skeleton of the polymer.

[0018] The term "chloroprene monomer" refers to a monomer of chloroprene (2-chloro-1,3-butadiene), and the term "structural unit derived from chloroprene monomer" refers to a structural unit corresponding to 2-chloro-1,3-butadiene, that is, a structural unit represented by the following formulas (1a), (1b), and (1c): *—CH ２ -CCl(-CH=CH ２ )-*...(1a) *-CH(-CCl=CH ２ )-CH ２ -*...(1b) *-CH ２ It refers to a structural unit having any structure selected from the group consisting of: -CCl(-CH(-*)-CH(-*))-* ... (1c) (where "-*" and "*-" represent a bond bonding to another structural unit). Here, the "other structural unit" may be a structural unit that falls under the category of a "structural unit derived from a chloroprene monomer", or may be a structural unit that does not fall under the category of a "structural unit derived from a chloroprene monomer", such as a "structural unit derived from a second monomer" described below.

[0019] <Second Monomer> The "second monomer" used in the present invention is a monomer other than a chloroprene monomer that, when homopolymerized, has a crystallization temperature, glass transition temperature, or melting point of 80°C or higher. That is, a monomer other than a chloroprene monomer that, when homopolymerized, gives a homopolymer having a crystallization temperature, glass transition temperature, or melting point of 80°C or higher. Here, the crystallization temperature, glass transition temperature, or melting point of the "homopolymer" may be affected by the degree of polymerization (or molecular weight) of the "homopolymer." On the other hand, it is believed that when the degree of polymerization (or molecular weight) of the "homopolymer" is equal to or higher than a certain level, the influence of the degree of polymerization (or molecular weight) on the crystallization temperature, glass transition temperature, or melting point becomes sufficiently small. In consideration of these factors, the "homopolymer" to be evaluated for its crystallization temperature, glass transition temperature, or melting point preferably has a relatively large molecular weight, for example, a weight-average molecular weight Mw of 30,000 or higher.

[0020] The polymer used in the present invention contains structural units derived from the "second monomer," and can impart higher aggregate gripping ability to asphalt compared to polymers that do not contain structural units derived from the "second monomer." In this specification, the second monomer may also be referred to as a "high cohesive strength monomer."

[0021] In the present invention, the second monomer is usually a monomer that has a crystallization temperature, glass transition temperature or melting point of 80° C. or higher when homopolymerized and is copolymerizable with chloroprene.

[0022] Here, the monomer copolymerizable with chloroprene is not particularly limited as long as it does not impair the object of the present invention, and examples thereof include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, styrene, acrylonitrile, acrylic acid and its esters, and methacrylic acid and its esters. In the present invention, among "monomers copolymerizable with chloroprene," those that have a crystallization temperature, glass transition temperature, or melting point of 80°C or higher when homopolymerized can be used as the second monomer.

[0023] In one preferred embodiment of the present invention, the "second monomer" is a monomer that, when homopolymerized, has a crystallization temperature or glass transition temperature of 80°C or higher. Examples of monomers that, when homopolymerized, have a glass transition temperature of 80°C or higher include styrene, vinyl chloride, acrylonitrile, polymethyl methacrylate, polyethyl methacrylate, and polyacrylic acid. Table 1 below shows the glass transition temperatures of the homopolymers obtained from 2,3-dichloro-1,3-butadiene, styrene, vinyl chloride, acrylonitrile, polymethyl methacrylate, polyethyl methacrylate, polyacrylic acid, dicyclopentanyl acrylate, and dicyclopentanyl methacrylate.

[0024] In another preferred embodiment of the present invention, the "second monomer" is a monomer that has a melting point of 80° C. or higher when homopolymerized. An example of a monomer that has a melting point of 80° C. or higher when homopolymerized is 2,3-dichloro-1,3-butadiene (melting point: 133° C.).

[0025]

[0026] In the present invention, the second monomer is preferably 2,3-dichloro-1,3-butadiene or 1-chloro-1,3-butadiene, and particularly preferably 2,3-dichloro-1,3-butadiene.

[0027] The second monomer may be a single type or a combination of two or more types. The "structural unit derived from the second monomer" refers to a structural unit corresponding to the second monomer. For example, the structural unit derived from 2,3-dichloro-1,3-butadiene is a structural unit corresponding to 2,3-dichloro-1,3-butadiene, that is, a structural unit represented by the following formulas (2a), (2b), and (2c): *-CH ２ -CCl(-CCl=CH ２ )-*...(2a) *-CCl(-CCl=CH ２ )-CH ２ -*...(2b) *-CH ２ -CCl(-CCl(-*)-CH(-*))-* ... (2c) (where "-*" and "*-" represent a bond bonding to another structural unit). ａ X ｂ =CX ｃ X ｄ (X ａ , X ｂ , X ｃ and X ｄ are each independently a hydrogen atom or a suitable substituent. In the case where the structural unit derived from the second monomer has a structure represented by ａ X ｂ -CX ｃ X ｄA structural unit having a structure represented by -* ("-*" and "*-" represent bonds bonding to other structural units). In either case, the "other structural unit" may be a structural unit corresponding to the "structural unit derived from the second monomer", or may be a structural unit not corresponding to the "structural unit derived from the second monomer", such as the "structural unit derived from a chloroprene monomer".

[0028] <Third Monomer> As described above, the polymer used in the present invention contains structural units derived from chloroprene monomers and structural units derived from the second monomer. In a preferred and exemplary aspect of the present invention, the polymer consists only of structural units derived from chloroprene monomers and structural units derived from the second monomer. However, the polymer may further contain structural units derived from a third monomer (hereinafter referred to as "third monomer") that do not fall under the category of structural units derived from chloroprene monomers or structural units derived from the second monomer, as long as the object of the present invention is not impaired.

[0029] The third monomer may be any of the monomers described above as the "monomer copolymerizable with chloroprene" that do not fall under the category of the second monomer. The third monomer may be used alone or in combination of two or more.

[0030] Furthermore, the term "structural unit derived from a third monomer" refers to a structural unit corresponding to the third monomer. For example, the third monomer may be a structural unit represented by the formula: ｅ X ｆ =CX ｇ X ｈ (X ｅ , X ｆ , X ｇ and X ｈ are each independently a hydrogen atom or a suitable substituent. In the case where the structural unit derived from the third monomer has a structure represented by ｅ X ｆ -CX ｇ X ｈ It is a structural unit having a structure represented by -* ("-*" and "*-" represent bonds that bond to other structural units).

[0031] <Polymer Structure> The polymer used in the present invention contains structural units derived from the chloroprene monomer and structural units derived from the second monomer.

[0032] As described above, by including the "structural units derived from the second monomer," the polymer can impart higher aggregate gripping ability to asphalt compared to polymers that do not include the "structural units derived from the second monomer." This aggregate gripping ability tends to be particularly favorable when the amount of the "structural units derived from the second monomer" in the polymer is within a specific range. Specifically, the content of the structural units derived from the second monomer in the polymer used in the present invention is 3 to 10 parts by mass per 100 parts by mass of all structural units constituting the polymer. Looking at the upper limit of the content, it is preferably 9.5 parts by mass or less, and more preferably 9.0 parts by mass or less. On the other hand, looking at the lower limit, it is preferably 3.5 parts by mass or more, and more preferably 4.0 parts by mass or more. Here, when two or more types of second monomers are included in the polymer, the total content of the structural units corresponding to the "structural units derived from the second monomer" is the content.

[0033] Furthermore, when the polymer contains the above-mentioned "structural unit derived from a third monomer," the content of the structural unit derived from the third monomer in the polymer is not particularly limited as long as it does not impair the object of the present invention, but is, for example, 10 parts by mass or less per 100 parts by mass of all structural units constituting the polymer. Here, when there are two or more types of third monomers that can constitute the polymer, the total content of structural units corresponding to the "structural unit derived from a third monomer" is the content.

[0034] The polymer can typically be obtained by polymerizing a chloroprene monomer and the second monomer, as described later in "Method for producing a chloroprene latex." When it is difficult to directly measure the content of the structural unit derived from the second monomer in the polymer, the content of the structural unit derived from the second monomer in the polymer may be estimated as the ratio of the amount of the second monomer to the amount of all monomers used in the step of polymerizing a chloroprene monomer and the second monomer in the "Method for producing a chloroprene latex" described later (i.e., the total amount of the amount of the chloroprene monomer, the amount of the second monomer, and the amount of the optional third monomer).

[0035] The presence of the structural units derived from the chloroprene monomer and the structural units derived from the second monomer in the polymer is not particularly limited as long as it does not impair the object of the present invention. The polymer may be, for example, a copolymer containing structural units derived from the chloroprene monomer and structural units derived from the second monomer, a mixture of a first homopolymer consisting only of structural units derived from the chloroprene monomer and a second homopolymer consisting only of structural units derived from the second monomer, or a mixture of a copolymer containing structural units derived from the chloroprene monomer and structural units derived from the second monomer with one or more members selected from the group consisting of a first homopolymer consisting only of structural units derived from the chloroprene monomer and a second homopolymer consisting only of structural units derived from the second monomer. However, since a monomer copolymerizable with chloroprene is usually used as the second monomer, the inventors presume that the polymer is a copolymer containing structural units derived from a chloroprene monomer and structural units derived from the second monomer, or a mixture of a copolymer containing structural units derived from a chloroprene monomer and structural units derived from the second monomer and one or more homopolymers selected from the group consisting of a first homopolymer consisting only of structural units derived from a chloroprene monomer and a second homopolymer consisting only of structural units derived from the second monomer. Here, when the polymer contains the above-mentioned "structural units derived from a third monomer," the polymer may include a copolymer containing structural units derived from a chloroprene monomer and at least one of the structural units derived from the second monomer and structural units derived from the third monomer, or may include a third homopolymer consisting only of structural units derived from the third monomer.

[0036] In the present invention, the polymer is contained in the chloroprene latex described below, and when combined with asphalt, becomes a constituent component of the rubber-asphalt emulsion, asphalt layer, and asphalt mixture. From this, it is presumed that the polymer can fully function as an asphalt modifier and has a particle size that allows the particles to maintain a relatively stable emulsion state without coagulation when formed into a rubber-asphalt emulsion. Specifically, the z-average particle size of the polymer is 150 nm or less. The lower limit of the z-average particle size is preferably 10 nm or more. The z-average particle size can be measured using a dynamic light scattering photometer with a chloroprene latex containing the polymer as a sample. Even when the z-average particle size of the polymer exceeds 150 nm, for example, when the z-average particle size of the polymer is greater than 150 nm and less than 200 nm, or greater than 150 nm and less than 180 nm, sufficiently high aggregate gripping ability may be obtained. However, when the z-average particle diameter of the polymer exceeds 150 nm, aggregate grasping ability tends to be relatively low compared to when the z-average particle diameter of the polymer is 150 nm or less. Therefore, when attempting to obtain sufficiently high aggregate grasping ability using a polymer with a z-average particle diameter exceeding 150 nm, the preferred range for the content of the structural unit derived from the second monomer in the polymer may also be narrower than the above-mentioned range (for example, 7.0 to 10 parts by mass, or 8.0 to 9.0 parts by mass, per 100 parts by mass of all structural units constituting the polymer). Considering the above points, from the viewpoint of obtaining sufficiently high aggregate grasping ability, it tends to be more advantageous for the z-average particle diameter of the polymer to be 150 nm or less.

[0037] [Chloroprene Latex] The chloroprene latex according to the present invention contains the polymer described above in the "Polymer" section. In a typical embodiment of the present invention, the chloroprene latex according to the present invention contains the polymer and a solvent such as water. The chloroprene latex may further contain an emulsifier or surfactant, a polymerization initiator, a molecular weight modifier (chain transfer agent), a polymerization terminator, and the like, which may be introduced during the manufacturing process. However, unlike the rubber asphalt emulsion described below, the chloroprene latex does not contain asphalt.

[0038] The solid content in the chloroprene latex (i.e., the ratio by mass of components (solid content) obtained by excluding water and other volatilizable components from the chloroprene latex to the total mass of the chloroprene latex) is often 40 to 65 mass%, and the content of the polymer in the chloroprene latex is often 35 to 63 mass%. Here, examples of the solid content in the chloroprene latex include the "polymer", reagents that can be used in the production process of the "polymer" (for example, emulsifiers, polymerization initiators, cocatalysts, molecular weight modifiers (chain transfer agents), and polymerization terminators, which will be described later in the section "Production method of chloroprene latex" below), and non-volatilizable monomers among the chloroprene monomer, the second monomer, and the third monomer.

[0039] In the present invention, the gel content in the chloroprene latex is 70% or more, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. When the gel content in the chloroprene latex is a certain amount or more, sufficiently high aggregate gripping ability tends to be obtained when the chloroprene latex is combined with asphalt to form an asphalt layer. While the upper limit of the gel content is not particularly limited, it is often 99% or less, preferably 98% or less, and more preferably 95% or less. In the present invention, the gel content can be determined as the amount of THF (tetrahydrofuran)-insoluble matter in the chloroprene latex. Specifically, when 1 g of chloroprene latex is added to 100 mL of THF, the gel content can be determined as the ratio of the mass of the tetrahydrofuran-insoluble matter in the polymer to the mass of the solids in the chloroprene latex. Therefore, the "%" for the gel content is % by mass.

[0040] As described above, the gel amount can be determined as the amount of THF (tetrahydrofuran) insoluble matter in the chloroprene latex. However, in many cases, the actually obtained chloroprene latex may contain, in addition to the "polymer," reagents that can be used in the production process of the "polymer." However, the amount of reagents that can be used in the production process of the "polymer" tends to be sufficiently small compared to the amount of the "polymer." In consideration of this, the gel amount can be substantially estimated as a parameter related to the ratio of the amount of THF insoluble matter in the "polymer" to the total amount of the "polymer," i.e., the ratio of the amount of components in the "polymer" whose degree of polymerization is higher than a certain level.

[0041] For a specific method for measuring the gel amount, see the description in the Examples below. <Method for producing chloroprene latex> In the present invention, the method for producing the chloroprene latex is not particularly limited as long as it does not impede the object of the present invention. However, in a typical aspect of the present invention, the production method includes a step of polymerizing a chloroprene monomer and the second monomer (polymerization step). The polymer is formed by this polymerization step. Here, when a polymer containing a structural unit derived from the third monomer is formed as the polymer, the polymerization step is carried out as a step of polymerizing a chloroprene monomer, the second monomer, and the third monomer.

[0042] In the polymerization step, the method for polymerizing the chloroprene monomer, the second monomer, and the optional third monomer is not particularly limited, but emulsion polymerization is preferred, and industrially, aqueous emulsion polymerization is particularly preferred. Here, when emulsion polymerization is performed in the polymerization step, the polymerization step is often performed as a step of adding a polymerization initiator to a mixture containing monomers such as the chloroprene monomer and the second monomer, an emulsifier, and a solvent such as water, and polymerizing the monomers.

[0043] The emulsifier for emulsion polymerization is preferably an anionic surfactant, a nonionic surfactant, or a compound that acts as a protective colloid, such as polyvinyl alcohol. Specific examples of anionic surfactants include rosin acid soap, sodium salt of naphthalenesulfonic acid condensate, sodium salt of dodecylbenzenesulfonic acid, and sodium salt of dodecyl sulfate.

[0044] Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0045] When a rosin acid soap is used as an emulsifier, the amount of the rosin acid soap used is preferably 3 to 8 parts by mass, more preferably 3 to 5 parts by mass, in terms of rosin acid, per 100 parts by mass of the total of all monomers (i.e., the total of the chloroprene monomer, the second monomer, and the optional third monomer).

[0046] When the amount of rosin acid soap used is 3 parts by mass or more, good emulsification can be achieved, good control of polymerization heat generation can be obtained, and the formation of aggregates can be suppressed, resulting in good product appearance. When the amount of rosin acid soap used is 8 parts by mass or less, product costs can be reduced, which is preferable. The particle size of the resulting chloroprene latex can be adjusted by adjusting the amount of the emulsifier used. For example, when rosin acid soap is used as the emulsifier, the particle size of the resulting chloroprene latex can be increased by reducing the amount of rosin acid soap used.

[0047] The sodium salt of a naphthalenesulfonic acid condensate is, for example, a sodium salt of a naphthalenesulfonic acid formaldehyde condensate. Addition of a dispersant for a sodium salt of a naphthalenesulfonic acid condensate can suppress problems such as the formation of aggregates, even in a system emulsified with 3 parts by mass or less of a rosin acid soap. The emulsifier used in emulsion polymerization may be a single type or a combination of two or more types.

[0048] When a rosin acid soap is used as the emulsifier, the emulsifier may consist solely of the rosin acid soap, or may be a combination of the rosin acid soap and an emulsifier other than the rosin acid soap. The emulsifier may be a combination of the rosin acid soap and an anionic surfactant other than the rosin acid soap, for example, a combination of the rosin acid soap and any surfactant selected from the group consisting of the sodium salt of a naphthalenesulfonic acid condensate, the sodium salt of dodecylbenzenesulfonic acid, and the sodium salt of dodecyl sulfate. In one preferred exemplary embodiment of the present invention, the emulsifier is a combination of the rosin acid soap and the sodium salt of a naphthalenesulfonic acid condensate. In this case, the amount of the sodium salt of the naphthalenesulfonic acid condensate used in combination with the rosin acid soap is, for example, 0.1 to 0.5 parts by mass per 100 parts by mass of the total of all monomers.

[0049] As the polymerization initiator, a conventional radical polymerization initiator can be used. For example, in the case of emulsion polymerization, conventional organic or inorganic peroxides such as benzoyl peroxide, potassium persulfate, ammonium persulfate, etc., and azo compounds such as azobisisobutyronitrile, etc., can be used. In addition, a co-catalyst such as anthraquinone sulfonate, potassium sulfite, sodium sulfite, etc. can be used as appropriate. The amount of the initiator can be set appropriately.

[0050] Generally, in the production of chloroprene latex, a molecular weight modifier (chain transfer agent) may be used during polymerization in order to obtain a copolymer having a desired molecular weight and distribution. The chain transfer agent is not particularly limited, and examples thereof include alkyl xanthogen disulfides such as dithiobis(thioformate)O,O-diisopropyl, and alkyl mercaptans such as dodecyl mercaptan.

[0051] The chain transfer agent may be used alone or in combination of two or more. Here, the amount of chain transfer agent used during polymerization can be set appropriately, but the greater the amount of chain transfer agent, the less gel there is in the resulting polymer and the less aggregate gripping there is in the asphalt layer obtained by combining this polymer with asphalt. In such cases, it is preferable to carry out the polymerization in the absence of a chain transfer agent or in the presence of the minimum necessary amount of chain transfer agent.

[0052] In general, in the production of chloroprene latex, a polymerization terminator is added to terminate the reaction when a predetermined polymerization rate is reached in order to obtain a polymer having a desired molecular weight and distribution. The polymerization terminator is not particularly limited, and commonly used terminators such as phenothiazine, para-tert-butylcatechol, hydroquinone, hydroquinone monomethyl ether, and diethylhydroxylamine can be used.

[0053] The production method may further include a step of removing unreacted monomers after the termination of the polymerization reaction. The step of removing unreacted monomers can be carried out by a known method, for example, steam distillation.

[0054] [Rubber Asphalt Emulsion] The rubber asphalt emulsion according to the present invention contains the polymer described above in the "Polymer" section and asphalt. In a typical embodiment of the present invention, the rubber asphalt emulsion according to the present invention is obtained by mixing the chloroprene latex with asphalt. The rubber asphalt emulsion contains the polymer, asphalt, and water, and may further contain a surfactant.

[0055] <Polymer> The polymer constituting the rubber asphalt emulsion according to the present invention is the polymer described above in the section "Polymer." In a typical embodiment of the present invention, the polymer is combined with asphalt in the form of the "chloroprene latex."

[0056] The blending ratio of chloroprene latex to asphalt is preferably 0.5 to 40.0 parts by mass, more preferably 1.0 to 30.0 parts by mass, and even more preferably 2.0 to 20.0 parts by mass, in terms of solid content of chloroprene latex, per 100 parts by mass of asphalt.

[0057] The chloroprene latex may be used alone or in combination of two or more types. The amount of solids of the chloroprene latex in the rubber asphalt emulsion is preferably 0.5 to 20 parts by mass, more preferably 1.0 to 10 parts by mass, and even more preferably 2.0 to 5.0 parts by mass, per 100 parts by mass of the solids of the rubber asphalt emulsion. Here, the solids in the rubber asphalt emulsion refer to the components remaining after excluding water and other volatile components from the rubber asphalt emulsion, and examples thereof include the solids in the chloroprene latex (i.e., the "polymer," reagents that may be used in the production process of the "polymer," and non-volatile monomers among the chloroprene monomer, the second monomer, and the third monomer), asphalt, a surfactant, as described below, and other components as described below in the "Other Components" section.

[0058] Here, with regard to the "compounding ratio of chloroprene latex to asphalt" and the "amount of solids of chloroprene latex in the rubber asphalt emulsion," the amount of the "polymer" in the rubber asphalt emulsion is the amount of solids of chloroprene latex minus the amount of solids other than polymer contained in the chloroprene latex. The inventors assume that in many cases, the amount of solids other than polymer contained in the chloroprene latex is sufficiently small compared to the amount of solids of the chloroprene latex. Therefore, the inventors believe that in many cases, there will be no substantial problem even if the "compounding ratio of chloroprene latex to asphalt" and the "amount of solids of chloroprene latex in the rubber asphalt emulsion" are considered to be the ratio of the "polymer" to asphalt and the amount of the "polymer" in the rubber asphalt emulsion, respectively. One type of chloroprene latex may be used alone, or two or more types may be used in combination.

[0059] <Asphalt> The asphalt constituting the rubber asphalt emulsion according to the present invention is not particularly limited, and any known and commonly used asphalt can be used. Examples of asphalt include straight asphalt, blown asphalt, semi-blown asphalt, natural asphalt, modified asphalt, solvent deasphalted asphalt, bitumen such as tar and pitch, heavy oil A, heavy oil B, and heavy oil C, etc.

[0060] The asphalt content is preferably 50 to 99.9% by mass, more preferably 83 to 99% by mass, and even more preferably 89 to 99% by mass, based on 100% by mass of the solid content of the rubber asphalt emulsion.

[0061] The content of asphalt is preferably 30 to 74% by mass, more preferably 35 to 72% by mass, and even more preferably 40 to 70% by mass, based on 100% by mass of the rubber asphalt emulsion. One type of asphalt may be used alone, or two or more types may be used in combination.

[0062] The asphalt preferably has the form of particles (asphalt particles). The shape of the asphalt particles is not particularly limited and may be spherical or elliptical. Of these, the shape of the asphalt particles is preferably spherical.

[0063] The z-average particle size of the asphalt is preferably 0.5 to 20.0 μm, more preferably 1.0 to 10.0 μm, and even more preferably 2.0 to 8.0 μm. The z-average particle size is determined using a dynamic light scattering photometer.

[0064] <Surfactant> The rubber asphalt emulsion of the present invention preferably further contains a surfactant. The surfactant is not particularly limited, and examples thereof include anionic surfactants, cationic surfactants, and nonionic surfactants.

[0065] Examples of anionic surfactants include neutralized products of tall oil with sodium hydroxide or potassium hydroxide. Examples of cationic surfactants include alkylamide polyamines, alkylimidazopolyamines, N-alkylpolypropylene diamines, and other amine hydrochlorides and phosphates. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0066] Among these, the surfactant is preferably a nonionic surfactant, more preferably a polyoxyethylene alkyl ether. Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene myristyl ether, polyoxyethylene octyldodecyl ether, polyoxyalkylene alkyl ether, polyoxyphenylenedistyrenated phenyl ether, polyoxyethylene tribenzyl phenyl ether, polyoxyalkylene alkenyl ether, and polyoxyethylene nonyl phenyl ether. The surfactant may be synthesized or may be a commercially available product.

[0067] Commercially available products include, for example, Emulgen 103, 104P, 106, 108, 109P, 120, 123P, 130K, 147, 150, 210P, 220, 306P, 320P, 350, 404, 408, 409PV, 420, 430, 705, 707, 709, 1108, 1118S-70, 1135S-70, 1150S-60, 2020G-HA, 2025G, LS-106, LS-110, LS-114, MS-110, A-60, A-90, B-66, PP-290, Latemul PD-420, PD-430, PD-430S, PD450, Super SP-L10, AS-10V, Examples of such amines include AO-10V, AO-15V, TW-L120, TW-L106, TW-P120, TW-S120V, TW-S320V, TW-O120V, TW-O106V, TW-IS399C, Super TW-L120, 430V, 440V, 460V, MS-50, MS-60, MO-60, MS-165V, Emanon 1112, 3199V, 3299V, 3299RV, 4110, CH-25, CH-40, CH-60(K), Amit 102, 105, 105A, 302, 320, Aminone PK-02S, L-02, and Homogenol L-95 (all manufactured by Kao Corporation).

[0068] The content of the surfactant is preferably 0.1 to 10.0 parts by mass, more preferably 0.2 to 7.0 parts by mass, and even more preferably 0.3 to 6.0 parts by mass, per 100 parts by mass of the solid content of the rubber asphalt emulsion. The surfactant may be used alone or in combination of two or more types.

[0069] <Water> The water is not particularly limited, and examples thereof include industrial water, tap water, etc. The amount of water is preferably 25 to 400 parts by mass, more preferably 35 to 230 parts by mass, and even more preferably 40 to 150 parts by mass, per 100 parts by mass of the solid content of the rubber asphalt emulsion.

[0070] <Other Components> The rubber asphalt emulsion according to the present invention may further contain components other than the above-mentioned polymer, asphalt, surfactant, and water (hereinafter also referred to as "other components"). Examples of other components include salts such as calcium chloride for emulsion stabilization, film-forming agents, thickening stabilizers, and retarders.

[0071] <Physical Properties of Rubber Asphalt Emulsions> The multiple stress creep recovery (MSCR) of a rubber asphalt emulsion also depends on the mass percentage of chloroprene latex solids in the asphalt composition obtained by drying the rubber asphalt emulsion. From the viewpoint of excellent aggregate gripping ability, the %R value obtained by measuring the MSCR of the asphalt composition obtained by drying the rubber asphalt emulsion in accordance with AASHITO T350-14 is preferably 20 to 95%, more preferably 21 to 80%, even more preferably 23 to 50%, and particularly preferably 25 to 40%. The %R value of the MSCR of a rubber asphalt emulsion can be determined by the method described in the Examples below.

[0072] <Method for Producing Rubber Asphalt Emulsion> The method for producing a rubber asphalt emulsion preferably includes a step of adding asphalt, a surfactant, and water to the chloroprene latex (hereinafter also referred to as a "rubber asphalt emulsion formation step"). In the rubber asphalt emulsion formation step, the order in which the asphalt, surfactant, and water are added to the chloroprene latex is not particularly limited as long as a rubber asphalt emulsion is formed, and these may be added separately or simultaneously.

[0073] However, it is preferable that the "rubber asphalt emulsion formation step" includes a step of preparing a mixture containing asphalt, a surfactant, and water to form an asphalt emulsion (asphalt emulsion formation step). In a preferred and exemplary aspect of the present invention, the "rubber asphalt emulsion formation step" may be performed as a step including: Step GS1 of preparing a mixture containing asphalt, a surfactant, and water to form an asphalt emulsion; Step GS2 of preparing a mixture containing chloroprene latex and a surfactant; and Step GS3 of mixing the mixture obtained in Step GS2 with the asphalt emulsion obtained in Step GS1.

[0074] In addition, in step GS1, the order in which asphalt, surfactant, and water are added is not particularly limited as long as an asphalt emulsion is formed, and they may be added separately or simultaneously. For example, step GS1 (asphalt emulsion formation step) may be performed as step GS1A in which a surfactant is added to asphalt and then mixed with water to form an asphalt emulsion, or as step GS1B in which asphalt is added to a mixture of surfactant and water.

[0075] Alternatively, asphalt may be mixed in the step GS2. In this case, the step GS2 is carried out as a step GS2' for preparing a mixture containing chloroprene latex, a surfactant, and asphalt.

[0076] The method for mixing the chloroprene latex with the asphalt, surfactant, and water is not particularly limited, and includes various known methods, such as mixing with a defoaming kneader, a dry ball mill, a dry bead mill, a planetary motion blade mixer, a rotating container planetary motion mixer, a crusher, a mortar, a homogenizer, a colloid mill, etc. Among these, the mixing method is preferably emulsification with a homogenizer or a colloid mill.

[0077] The method for producing a rubber asphalt emulsion may include a step of adding the other components described above as necessary. Also, for example, it may include a step of adjusting the pH of the chloroprene latex before mixing the chloroprene latex with asphalt (for example, when the "rubber asphalt emulsion formation step" includes steps GS1, GS2, and GS3, the pH may be adjusted in step GS2 by adding a pH adjuster such as hydrochloric acid to the chloroprene latex and surfactant).

[0078] The pH of the chloroprene latex after the pH adjustment step is preferably 1.0 to 4.5, more preferably 1.5 to 3.5. There are no particular restrictions on the pH adjuster used in the pH adjustment step, and any known pH adjuster can be used.

[0079] The rubber asphalt emulsion according to the present invention is preferably a rubber asphalt emulsion produced by the above-mentioned rubber asphalt emulsion production method, and it is more preferable that the rubber asphalt emulsion produced by the above-mentioned rubber asphalt emulsion production method forms a sea-island structure when dried.

[0080] It is presumed that the composition obtained by the method for producing a rubber asphalt emulsion according to the present invention, that is, by mixing chloroprene latex and asphalt, has an island-sea structure in which chloroprene forms the sea portion.

[0081] [Uses of Rubber Asphalt Emulsion] The rubber asphalt emulsion according to the present invention can be suitably used as a material for forming an asphalt layer and an asphalt mixture.

[0082] Here, the asphalt layer is obtained by applying and drying the rubber asphalt emulsion, more specifically, by applying the rubber asphalt emulsion to a suitable flat surface (substrate or ground) and then drying it. In other words, the asphalt layer can be considered to contain the polymer described above under "polymer" and asphalt.

[0083] An asphalt mixture can be obtained by mixing the rubber asphalt emulsion with aggregate. In other words, the asphalt mixture can be considered to contain the polymer described above under "polymer," asphalt, and aggregate. The aggregate may be crushed stone, sand, or other aggregate commonly used in asphalt pavement, and its particle size can be appropriately set depending on the application.

[0084] The rubber asphalt emulsion according to the present invention preferably forms an island-sea structure when dried. In particular, a rubber asphalt emulsion obtained by mixing the chloroprene latex with the asphalt emulsion described above (for example, a rubber asphalt emulsion obtained by a production method including steps GS1, GS2, and GS3) tends to form an island-sea structure when dried. The layered structure obtained by drying the rubber asphalt emulsion has asphalt regions (island regions) present in regions containing the polymer (sea regions), resulting in excellent aggregate gripping ability.

[0085] The drying conditions for forming the sea-island structure are preferably a drying time of 1 minute to 168 hours and a drying temperature of 10° C. to 95° C. From the viewpoint of facilitating the formation of the sea-island structure, the drying time is more preferably 30 minutes to 96 hours, and even more preferably 18 to 36 hours, and the drying temperature is more preferably 20° C. to 85° C., still more preferably 30 to 75° C., and even more preferably 50 to 75° C.

[0086] The drying method is not particularly limited, and known methods can be used, for example, drying methods using warm air, hot air, or low-humidity air.When the rubber asphalt emulsion is obtained by mixing the chloroprene latex with the asphalt emulsion described above, the solids content of the chloroprene latex is preferably 0.5 to 20 parts by mass, more preferably 1.0 to 10 parts by mass, and even more preferably 2.0 to 5.0 parts by mass, per 100 parts by mass of the solids content of the asphalt emulsion.

[0087] The chloroprene latex may be used alone or in combination of two or more types.The rubber asphalt emulsion according to the present invention is suitable for road paving because of its excellent aggregate grip.As a road paving method, for example, the chip seal method can be mentioned, in which the rubber asphalt emulsion and aggregate are layered in this order on the surface side of the road, and then compacted.

[0088] In the chip seal method, a single layer (seal coat) of rubber asphalt emulsion and a layer of aggregate may be formed, or a multi-layer (armor coat) of these single layers may be stacked.

[0089] From the viewpoint of excellent aggregate gripping ability, the above-mentioned rubber asphalt emulsion can be applied to not only chip seal methods but also scrub seals, tack coats, roadbed binders (including roadbed regeneration and cold in-place recycling), fog seals, thin layer surface treatment methods, etc.

[0090] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0091] Example 1 Preparation of Chloroprene Latex A 60-liter reactor was charged with 18.3 kg of 2-chloro-1,3-butadiene (chloroprene) (91.5 parts by mass (91.5 phm) when the total amount of monomers is 100 parts by mass), 1.7 kg of 2,3-dichloro-1,3-butadiene (8.5 parts by mass (8.5 phm) when the total amount of monomers is 100 parts by mass), 18 kg of purified water, 860 g of disproportionated rosin acid (R-600, manufactured by Arakawa Chemical Industries, Ltd.), 230 g of potassium hydroxide, 50 g of sodium hydroxide, and 43 g of sodium salt of β-naphthalenesulfonic acid-formalin condensate. The mixture was emulsified to convert the disproportionated rosin acid to the corresponding rosin soap. Potassium persulfate was then added as a polymerization initiator to the resulting mixture, and polymerization was carried out at 40°C under a nitrogen atmosphere. When the polymerization conversion rate reached 88%, an emulsion of phenothiazine was immediately added to the reaction mixture to terminate the polymerization. Subsequently, unreacted monomers were removed from the resulting mixture by steam distillation to obtain a polymer latex of a chloroprene polymer (hereinafter referred to as "chloroprene latex"). The solid content of the obtained chloroprene latex was 49.7% by mass. The physical properties of the obtained chloroprene latex are shown in Table 2-1 below.

[0092] <Production of asphalt emulsion> 3.50 kg of pure water heated to 80 ° C. was placed in a 5-liter container, and 24 g of dimethyl hardened tallow amine (manufactured by NOF Corporation, product name: Nissan Amine (registered trademark) ABT) as a surfactant was added. 19 g of 35% by mass hydrochloric acid (manufactured by Kanto Chemical Co., Ltd.) and 14 g of calcium chloride (manufactured by Kanto Chemical Co., Ltd.) were charged and stirred to prepare an aqueous surfactant solution. This aqueous surfactant solution and 3.50 kg of straight asphalt (Showa Rekisei Kogyo Co., Ltd., product name: SA120-150) heated and melted at 140 ° C. were emulsified using a colloid mill (IKA Japan Co., Ltd., product name: MagicLAB (registered trademark) XP) so that the asphalt emulsion production rate was 0.5 L / min, and an asphalt emulsion with a solids content of 50% by mass was obtained.

[0093] <Production of Rubber Asphalt Emulsion> To 100 g of the chloroprene latex obtained in the above "Preparation of Chloroprene Latex", polyoxyethylene alkyl ether (Emulgen 1118S-70, manufactured by Kao Corporation) was added as a nonionic surfactant so as to make the concentration 3 mass %, and 0.5 g of 35 mass % hydrochloric acid (manufactured by Kanto Chemical Co., Inc.) was further added to adjust the pH to 2.0, thereby preparing a chloroprene latex containing polyoxyethylene alkyl ether.

[0094] 40 g of the asphalt emulsion (solid content 50% by mass) prepared in the above "Production of asphalt emulsion" was heated at 60° C. 1.25 g of the polyoxyethylene alkyl ether-containing chloroprene latex was added to this heated asphalt emulsion to obtain a rubber asphalt emulsion.

[0095] The amount of chloroprene latex added to the resulting rubber asphalt emulsion was determined so that the solid content of the chloroprene latex was 3 parts by mass when the solid content of the asphalt emulsion was taken as 100 parts by mass. Specifically, the amount of chloroprene latex added was calculated based on the following formula.

[0096] Amount of chloroprene latex added = Amount of asphalt emulsion (40 g) × (Solid content of asphalt emulsion) × (3 parts by mass / 100 parts by mass) / (Solid content of chloroprene latex) Although hydrochloric acid may be used for the purpose of adjusting the pH after preparing the chloroprene latex, hydrochloric acid does not affect the solid content because it volatilizes under the conditions for measuring the solid content.

[0097] <Preparation of Sample for MSCR (Multiple Stress Creep Recovery) Measurement> 40 g of the rubber asphalt emulsion prepared in the above "Production of Rubber Asphalt Emulsion" was poured into a silicone batt with a base area of ​​216 mm x 175 mm and a depth of 40 mm, and allowed to spread throughout the batt. The batt was then dried at 23°C for 24 hours, and then dried in a 60°C oven for 24 hours to obtain a sample for multiple stress creep recovery (MSCR) measurement (corresponding to the asphalt layer). The obtained measurement sample was used in the MSCR measurement described below in the section "Multiple Stress Creep Recovery (MSCR) %R". The results are shown in Table 2-1 below.

[0098] [Various Evaluation Methods] <Gel Amount (Tetrahydrofuran Insoluble Content)> 1 g of the chloroprene latex to be measured was dropped into 100 mL of THF (tetrahydrofuran) solvent and shaken overnight. The resulting mixture was centrifuged to separate into a supernatant (dissolved phase) and a precipitate. The solvent contained in the supernatant and the solvent contained in the precipitate were evaporated to dryness at 100°C under normal pressure for 1 hour for the separated supernatant (dissolved phase) and the precipitate, respectively. The mass of the residue obtained from the precipitate by the evaporation and dryness was measured, and this mass was defined as the mass of the tetrahydrofuran insoluble content. Meanwhile, 1 g of the chloroprene latex to be measured was evaporated to dryness at 141°C under normal pressure for 30 minutes. The mass of the residue obtained from the precipitate by the evaporation and dryness was measured, and this mass was defined as the mass of the solid content of the chloroprene latex.

[0099] Using these amounts, the gel amount (amount of tetrahydrofuran insoluble matter) was calculated and evaluated according to the following formula: Gel amount (%) = mass of tetrahydrofuran insoluble matter / (mass of solid matter of chloroprene latex) × 100

[0100] <Polymerization Conversion Rate> The chloroprene latex obtained after polymerization was collected and dried at 100° C. under normal pressure for 2 hours, and the polymerization conversion rate was calculated from the amount of solid content obtained.

[0101] The solid content and polymerization conversion rate in the chloroprene latex were calculated by the following formulas: Solid content [mass %] = [(mass of solid content obtained after drying the chloroprene latex at 100°C under normal pressure for 2 hours) / (mass of the chloroprene latex before drying)] × 100 Polymerization conversion rate [%] = [(amount of polymer produced / charged amount of monomer)] × 100 Here, the amount of polymer produced was calculated by subtracting the amount of solid content other than polymer contained in the chloroprene latex from the amount of solid content contained in the chloroprene latex obtained after polymerization.

[0102] <z-average particle size> The z-average particle size of latex particles (polymer particles) in chloroprene latex was measured as follows: Chloroprene latex was diluted with pure water to 0.01 to 0.1% by mass, and the z-average particle size of the obtained solution was measured using a dynamic light scattering photometer (ZETASIZER (registered trademark) Nano-S manufactured by Malvern Panalytical Ltd).

[0103] <Multiple Stress Creep Recovery (MSCR) %R> The aggregate gripping ability of the asphalt composition obtained by drying the rubber asphalt emulsion was evaluated by measuring the multiple stress creep recovery (MSCR) in accordance with AASHTO (American Association of State Highway and Transportation Officials) T350-14, and the MSCR was evaluated as an index of aggregate gripping ability.

[0104] Specifically, a rheometer (MCR301 manufactured by Anton Paar) was used for the measurement, and the measurement jig used was a parallel plate with a diameter of 25 mm specified in JIS K 7244-10:2005.

[0105] After the device was set to 64°C and the temperature was adjusted sufficiently, approximately 1.0 g of the measurement sample was set, and then the excess sample was removed and the measurement was carried out. The measurement was carried out in the following steps: (1) The deformation amount (A) before applying stress was recorded. (2) A stress of 3.2 kPa was applied for 1 second, and the deformation amount (B) at that time was recorded. (3) After stopping the application of stress, a wait of 9 seconds was held (during which time the sample attempts to return to its original shape due to rubber elasticity), and the deformation amount (C) after 9 seconds had passed was recorded. The above steps (1) to (3) were repeated 10 times.

[0106] In each cycle, the recovery percentage (%R) from deformation due to stress was calculated using the following formula: %R = (deformation (B) - deformation (C)) ÷ (deformation (B) - deformation (A)) x 100 The above formula was used for 10 cycles, and the average was calculated as the multiple stress creep recovery. It can be said that the higher the %R value of multiple stress creep recovery (MSCR), the better the aggregate gripping ability. Note that MSCR %R values ​​of over 25% can be said to have sufficient aggregate gripping ability even in actual pavements.

[0107] Examples 2 and 3, Comparative Examples 1 to 8, and Reference Example R1 were performed in the same manner as in Example 1, except that in the "Preparation of chloroprene latex" described above, the amount of 2,3-dichloro-1,3-butadiene in all monomers, the amount of optional n-dodecyl mercaptan (chain transfer agent) relative to the amount of all monomers, and the polymerization addition rate were changed to the values ​​shown in Tables 2-1 to 2-3. In Comparative Examples 7 and 8 and Reference Example R1, the amount of disproportionated rosin acid charged was also changed to 340 g.

[0108] The physical properties of the obtained chloroprene latex and the results of the multiple stress creep recovery measurement are shown in the following Tables 2-1 to 2-3.

[0109]

[0110]

[0111]

[0112] The rubber asphalt emulsions of the examples have an MSCR %R value of more than 25%, and can be said to have sufficient aggregate gripping ability even in actual paving.

Claims

1. A chloroprene latex comprising a polymer containing a structural unit derived from a chloroprene monomer and a structural unit derived from a second monomer other than the chloroprene monomer, having a gel content of 70% or more, wherein the second monomer is a monomer that, when homopolymerized, has a crystallization temperature, a glass transition temperature, or a melting point of 80°C or higher, and the content of the structural unit derived from the second monomer in the polymer is 3 to 10 parts by mass based on 100 parts by mass of the total amount of structural units constituting the polymer, and the z-average particle diameter of the polymer is 150 nm or less.

2. The chloroprene latex according to claim 1, wherein the second monomer is 2,3-dichloro-1,3-butadiene.

3. The chloroprene latex according to claim 1, wherein the z-average particle diameter of the polymer is 10 nm or more.

4. The chloroprene latex according to claim 1, wherein the gel content is 99% or less.

5. A rubber asphalt emulsion obtained by mixing the chloroprene latex according to any one of claims 1 to 4 with asphalt.

6. An asphalt layer obtained by applying and drying the rubber asphalt emulsion according to claim 5.

7. An asphalt mixture obtained by mixing the rubber asphalt emulsion according to claim 5 with an aggregate.

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