Coating composition for laminated steel sheet

Abstract

A coating composition for a laminated steel sheet, comprising (meth) acrylic resin particles A, a water-soluble (meth) acrylic resin B, and water, the (meth) acrylic resin particles A contain a constituent unit derived from a monomer having a carboxyl group in a proportion of 1% by mass or more but less than 20% by mass with respect to all constituent units, and a constituent unit derived from a monomer having a self-crosslinkable group in a proportion of 0.1% by mass to 7% by mass with respect to all constituent units; the glass transition temperature is 55 DEG C or higher, and the ratio of the content mass of the (meth) acrylic resin particles A to the content mass of the water-soluble (meth) acrylic resin B is 95 / 5-85 / 15.

Description

Technical Field

[0001] This disclosure relates to coating compositions for laminated steel sheets. Background Technology

[0002] For motors, high efficiency and miniaturization with high output are crucial, requiring high permeability and low iron loss in the motor core blank. However, core machining presents a problem of deterioration in core magnetic properties. Furthermore, from an environmental perspective, low noise and low vibration in motors are increasingly important, demanding high-precision positioning control. Motor cores typically use laminated steel plates composed of layers of electromagnetic steel sheets.

[0003] Traditionally, electromagnetic steel sheets were fixed together during the manufacturing of laminated steel sheets using methods such as welding, riveting, and bolting. However, these methods result in a deterioration of magnetic properties. Furthermore, the mechanical rigidity of laminated steel sheets manufactured using these methods is often insufficient, raising concerns about noise and vibration. Therefore, in recent years, a method has been adopted to manufacture laminated steel sheets using electromagnetic steel sheets with a pre-formed adhesive coating on their surface (also known as "electromagnetic steel sheets with adhesive coatings"). In this method, after laminating electromagnetic steel sheets with adhesive coatings that have undergone punching or shearing processes, they are fixed together by heating and pressurizing. Compared to laminated steel sheets made by fixing electromagnetic steel sheets together through welding or other means, laminated steel sheets made with adhesive films have less deterioration in magnetic properties due to the processing during fixing, and higher core rigidity. Therefore, they tend to be less prone to problems such as noise and vibration (see "Various Characteristics of Adhesive Electromagnetic Steel Sheet Cores" by Kaido Riki, Takeda Kazutoshi, Wakisaka Takeki, and Mizokami Masato, Theory of Electricity D, Vol. 119, No. 7, pp. 1010-1015, 2012).

[0004] As an example of an electromagnetic steel sheet with an adhesive coating, an adhesive-coated electromagnetic steel sheet is disclosed, characterized in that it is an electromagnetic steel sheet having an insulating coating on its surface that exhibits adhesive properties by heating and / or pressurizing, wherein the coating is a mixture of an epoxy resin or epoxy resin modifier having a glass transition temperature (Tg) of 80°C to 150°C, an epoxy resin curing agent, and a particulate polymer with a particle size of 0.01 μm to 0.5 μm (refer to International Publication No. 2004 / 070080). Summary of the Invention

[0005] When manufacturing laminated steel sheets using electromagnetic steel sheets with adhesive coatings, firstly, a coating agent for forming the adhesive coating (also called an "adhesive coating forming agent") is applied to the surface of the electromagnetic steel sheet, and then dried at high temperature to produce an electromagnetic steel sheet with an adhesive coating. Next, the laminated electromagnetic steel sheets with adhesive coatings are stacked and further heated and pressurized at high temperature to bond them together. Therefore, the adhesive coating forming agent is required to form a coating film that exhibits high adhesive strength under the high-temperature conditions used to bond the laminated electromagnetic steel sheets with adhesive coatings.

[0006] In addition to functioning as an adhesive for bonding stacked electromagnetic steel sheets, the adhesive film also needs to function as an insulating film formed on the surface of the electromagnetic steel sheets. Generally, the insulating film requires both insulation and corrosion resistance. Therefore, the coating agent used to form the adhesive film must be designed to prevent the formation of pinholes and cracks; in other words, excellent spreadability is required. If the coating agent has excellent spreadability, the uniformity of the formed adhesive film is improved, thus reducing the likelihood of damage to insulation and corrosion resistance, and also potentially leading to improved adhesion.

[0007] To improve the adhesion of an adhesive film, it is necessary to increase the cohesive strength of the resin used in the coating agent. However, increasing the cohesive strength of the resin will reduce the wettability required for the spreadability of the coating agent. Therefore, improving the adhesion of the adhesive film and improving the spreadability of the coating agent used to form the adhesive film are contradictory and difficult to achieve simultaneously.

[0008] One embodiment of this disclosure aims to solve the problem of providing a coating composition for laminated steel sheets, which is a composition for coating the surface of electromagnetic steel sheets used in the manufacture of laminated steel sheets, capable of forming a coating film that exhibits high adhesion under high temperature conditions when the electromagnetic steel sheets are fixed together, and has excellent spreadability.

[0009] The specific methods used to solve the problem include the following.

[0010] <1> A coating composition for laminated steel sheets, comprising (meth)acrylic resin particles A, water-soluble (meth)acrylic resin B, and water, wherein the (meth)acrylic resin particles A contain constituent units from monomers having carboxyl groups in a proportion of 1% to less than 20% by mass relative to all constituent units, and contain constituent units from monomers having self-crosslinking groups in a proportion of 0.1% to 7% by mass relative to all constituent units, and has a glass transition temperature of 55°C or higher.

[0011] The ratio of the mass content of the above-mentioned (meth)acrylic resin particles A to the mass content of the above-mentioned water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15.

[0012] <2> The coating composition for laminated steel sheets according to <1>, wherein the water-soluble (meth)acrylic resin B comprises constituent units from monomers having self-crosslinking groups.

[0013] <3> The coating composition for laminated steel sheets according to <1> or <2>, wherein the water-soluble (meth)acrylic resin B comprises a constituent unit derived from a monomer having a hydroxyl group.

[0014] <4> The coating composition for laminated steel sheets according to any one of <1> to <3>, wherein the average primary particle size of the (meth)acrylic resin particles A is 250 nm to 450 nm.

[0015] <5> The coating composition for laminated steel sheets according to any one of <1> to <4>, wherein the monomer having a self-crosslinking group in the (meth)acrylic resin particles A is selected from at least one of N-hydroxymethylacrylamide (NMAM), N-hydroxybutylacrylamide (NBMA), hydroxyethylacrylamide (HEAA) and glycidyl methacrylate (GMA).

[0016] <6> The coating composition for laminated steel sheets according to any one of <2> to <5>, wherein, relative to all the constituent units of the water-soluble (meth)acrylic resin B, the content of the constituent units derived from monomers having self-crosslinking groups in the water-soluble (meth)acrylic resin B is 0.1% to 10.0% by mass.

[0017] <7> The coating composition for laminated steel sheets according to any one of <3> to <6>, wherein, relative to all the constituent units of the water-soluble (meth)acrylic resin B, the content of the constituent units derived from monomers having hydroxyl groups in the water-soluble (meth)acrylic resin B is 5% to 30% by mass.

[0018] According to one embodiment of the present disclosure, a coating composition for laminated steel sheets is provided, which is a composition for coating the surface of an electromagnetic steel sheet used in the manufacture of laminated steel sheets. The composition is capable of forming a coating film that exhibits high adhesion under high temperature conditions when the electromagnetic steel sheets are fixed together, and has excellent spreadability. Detailed Implementation

[0019] The coating composition for laminated steel sheets of this disclosure will be described in detail below. The description of the elements described below is based on representative embodiments of this disclosure, but this disclosure is not limited to such embodiments and may be implemented with appropriate modifications within the scope of the purpose of this disclosure.

[0020] In this disclosure, the numerical range represented by “~” refers to the range that includes the values ​​recorded before and after “~” as the lower limit and upper limit, respectively.

[0021] In the numerical ranges described in this disclosure, the upper or lower limit of a certain numerical range can be replaced with the upper or lower limit of other numerical ranges described in different stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit of a certain numerical range can be replaced with the values ​​shown in the embodiments.

[0022] In this disclosure, a combination of two or more preferred methods is a more preferred method.

[0023] In this disclosure, when multiple substances corresponding to each component are present in the coating composition for laminated steel sheets, unless otherwise specified, the amount of each component in the coating composition for laminated steel sheets refers to the total amount of the multiple substances present in the coating composition for laminated steel sheets.

[0024] In this disclosure, "(meth)acrylic monomer" refers to a monomer having a (meth)acryloyl group.

[0025] In this disclosure, "(meth)acrylic resin" refers to a resin that contains constituent units derived from (meth)acrylic monomers and the proportion of constituent units derived from (meth)acrylic monomers is 50% or more by mass.

[0026] In this disclosure, "(meth)acrylic acid" is a term that includes both "acrylic acid" and "methacrylic acid", "(meth)acrylate" is a term that includes both "acrylate" and "methacrylate", "(meth)acryloyl" is a term that includes both "acryloyl" and "methacryloyl", and "(meth)acrylamide" is a term that includes both "acrylamide" and "methacrylamide".

[0027] In this disclosure, "n-" refers to positive, "i-" refers to negative, "s-" refers to middle, and "t-" refers to uncle.

[0028] In this disclosure, "mass%" and "weight%" have the same meaning, and "parts of mass" and "parts of weight" have the same meaning.

[0029] In this disclosure, the term "process" includes not only independent processes, but also processes that can be clearly distinguished from other processes, as long as they achieve the desired purpose of the process.

[0030] [Coating composition for laminated steel sheets]

[0031] The coating composition for laminated steel sheets disclosed herein (hereinafter also referred to as the "coating composition") comprises (meth)acrylic resin particles A, water-soluble (meth)acrylic resin B, and water. The (meth)acrylic resin particles A contain constituent units from monomers having carboxyl groups in a proportion of 1% to less than 20% by mass relative to all constituent units, and contain constituent units from monomers having self-crosslinking groups in a proportion of 0.1% to 7% by mass relative to all constituent units. The glass transition temperature is 55°C or higher, and the mass ratio of the (meth)acrylic resin particles A to the water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15.

[0032] The coating composition disclosed herein is a composition for coating the surface of an electromagnetic steel sheet used in the manufacture of coated laminated steel sheets, and exhibits high adhesion at a specific temperature.

[0033] Generally, if the cohesive strength of the resin contained in the coating agent is increased to improve the adhesion of the coating film, the wetting properties required for the spreadability of the coating agent will decrease. In contrast, by including (meth)acrylic resin particles A, which ensure cohesive strength, and water-soluble (meth)acrylic resin B, which ensures wetting properties, in a specific ratio in the coating composition of this disclosure, both high adhesion of the coating film and excellent spreadability of the coating composition can be achieved. Since the coating composition of this disclosure includes (meth)acrylic resin particles A with high cohesive strength and possessing carboxyl groups and self-crosslinking groups that are conducive to crosslinking in a specific ratio, a coating film exhibiting high adhesion can be formed. Furthermore, in the coating composition of this disclosure, since (meth)acrylic resin particles A have self-crosslinking groups that exhibit self-crosslinking properties above a specific temperature, the coating film can exhibit adhesion under high-temperature conditions when electromagnetic steel sheets are bonded together. Furthermore, the coating composition disclosed herein, by combining (meth)acrylic resin particles A and water-soluble (meth)acrylic resin B, exhibits better wettability on the electromagnetic steel sheet and increases the bonding area with the electromagnetic steel sheet compared to the case containing (meth)acrylic resin particles A alone, thereby improving the adhesion of the formed coating film.

[0034] Therefore, the coating composition disclosed herein can form a coating film that exhibits high adhesion under high temperature conditions when electromagnetic steel sheets are fixed together, and has excellent spreadability.

[0035] Furthermore, the coating composition of this disclosure does not require a curing agent to exhibit adhesive strength and also has the advantage of a long pot life. For example, the processing liquid (so-called coating agent) used in the manufacture of surface-coated electromagnetic steel sheets for bonding, as described in International Publication No. 2004 / 070080, requires a curing agent to exhibit adhesive strength because it uses epoxy resin. Coating agents containing curing agents tend to have a shorter pot life, but the coating composition of this disclosure is less prone to a decrease in pot life due to the addition of a curing agent.

[0036] In this disclosure, "(meth)acrylic resin particles A" that contain "constituents derived from monomers having carboxyl groups in a proportion of 1% or more and less than 20% by mass relative to all constituent units, and contain constituents derived from monomers having self-crosslinking groups in a proportion of 0.1% to 7% by mass relative to all constituent units, and have a glass transition temperature of 55°C or higher" are also referred to as "specific (meth)acrylic resin particles A".

[0037] [Specific (meth)acrylic resin particles A]

[0038] The coating composition disclosed herein comprises (meth)acrylic resin particles A, which contains constituent units from monomers having carboxyl groups in a proportion of 1% by mass or more and less than 20% by mass relative to all constituent units, and contains constituent units from monomers having self-crosslinking groups in a proportion of 0.1% by mass to 7% by mass relative to all constituent units, and has a glass transition temperature of 55°C or more.

[0039] The coating composition disclosed herein may contain only one specific (meth)acrylic resin particle A, or it may contain two or more.

[0040] In the coating composition disclosed herein, specific (meth)acrylic resin particles A are present in a state of dispersion in a water-containing medium.

[0041] <Building units from monomers containing carboxyl groups>

[0042] The specific (meth)acrylic resin particle A contains constituent units from monomers having carboxyl groups in a proportion of more than 1% by mass and less than 20% by mass relative to all constituent units.

[0043] In this disclosure, "constituent unit from a monomer having a carboxyl group" refers to a constituent unit formed by the addition polymerization of a monomer having a carboxyl group.

[0044] As a monomer having a carboxyl group, for example, a monomer having at least one carboxyl group and an olefinic unsaturated group in one molecule can be cited.

[0045] As an olefinic unsaturated group, there are no particular limitations; examples include vinyl, allyl, vinylphenyl, (meth)acrylamido, and (meth)acryloyl.

[0046] As an olefinic unsaturated group, (meth)acryloyl is preferred.

[0047] Specific examples of monomers having a carboxyl group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaric acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate (e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate) and succinic acid derivatives (e.g., 2-acryloyloxyethyl succinate).

[0048] The monomer having a carboxyl group preferably includes a (meth)acrylic acid monomer having a carboxyl group, more preferably a (meth)acrylic acid monomer having a carboxyl group. As a (meth)acrylic acid monomer having a carboxyl group, (meth)acrylic acid is preferred, and methacrylic acid is more preferred.

[0049] A specific (meth)acrylic resin particle A may contain only one type of constituent unit from a monomer with a carboxyl group, or it may contain two or more types.

[0050] The percentage of constituent units derived from monomers having carboxyl groups in specific (meth)acrylic resin particles A is more than 1% by mass and less than 20% by mass, relative to all constituent units of specific (meth)acrylic resin particles A.

[0051] If, relative to all the constituent units of a specific (meth)acrylic resin particle A, the content of constituent units derived from carboxyl-containing monomers in the specific (meth)acrylic resin particle A is 1% by mass or more, there is a tendency to form a coating film that exhibits high adhesion under high-temperature conditions when electromagnetic steel sheets are bonded together. From this perspective, the content of constituent units derived from carboxyl-containing monomers in the specific (meth)acrylic resin particle A is preferably 3% by mass or more, more preferably 5% by mass or more, further preferably 8% by mass or more, and particularly preferably 10% by mass or more, relative to all the constituent units of the specific (meth)acrylic resin particle A.

[0052] If, relative to all the constituent units of a specific (meth)acrylic resin particle A, the content of constituent units derived from carboxyl-containing monomers in A is less than 20% by mass, there is a tendency to form a coating film that exhibits high adhesion under high-temperature conditions when electromagnetic steel sheets are bonded together. From this perspective, the content of constituent units derived from carboxyl-containing monomers in A is preferably 18% by mass or less, more preferably 15% by mass or less, relative to all the constituent units of A.

[0053] In one manner, the content of constituent units from monomers having carboxyl groups in a specific (meth)acrylic resin particle A may be in the range of 5% by mass or more and less than 20% by mass, 8% by mass or more and less than 20% by mass, 10% by mass or more and less than 20% by mass, 8% by mass to 18% by mass, or 10% by mass to 15% by mass.

[0054] <Building units from monomers with self-crosslinking groups>

[0055] The specific (meth)acrylic resin particle A contains constituent units from monomers having self-crosslinking groups in a proportion of 0.1% to 7% by mass relative to all constituent units.

[0056] In this disclosure, "constituent unit from monomers having self-crosslinking groups" refers to a constituent unit formed by addition polymerization of monomers having self-crosslinking groups.

[0057] In this disclosure, "self-crosslinking" refers to the property of being able to crosslink even in the absence of a crosslinking agent.

[0058] The self-crosslinking groups in this disclosure can exhibit self-crosslinking properties by heating.

[0059] The temperature at which self-crosslinking groups exhibit self-crosslinking properties varies depending on the type of self-crosslinking group.

[0060] The temperature at which the self-crosslinking group exhibits self-crosslinking properties is not particularly limited, provided that the self-crosslinking group does not easily exhibit self-crosslinking properties at the temperature when the coating composition is applied to the surface of the electromagnetic steel sheet and dried, and exhibits self-crosslinking properties at the temperature when the electromagnetic steel sheets are fixed together.

[0061] Specific examples of self-crosslinking groups include N-hydroxymethyl, N-hydroxybutyl, glycidyl, and alkoxymethylamide.

[0062] As a self-crosslinking group, it is preferably selected from at least one of N-hydroxymethyl, N-hydroxybutyl and glycidyl groups.

[0063] Specific examples of monomers having self-crosslinking groups include N-hydroxyalkyl (meth)acrylamide, N,N-dihydroxyalkyl (meth)acrylamide, glycidyl (meth)acrylate, and N-alkoxymethyl (meth)acrylamide.

[0064] Examples of N-hydroxyalkyl (meth)acrylamides include, for example, N-hydroxymethylacrylamide (NMAM), N-hydroxybutylacrylamide (NBMA) and hydroxyethylacrylamide (HEAA).

[0065] Examples of N,N-dihydroxyalkyl (meth)acrylamides include, for instance, dihydroxymethyl (meth)acrylamide.

[0066] Examples of N-alkoxymethyl (meth)acrylamides include, for example, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide.

[0067] The monomer having a self-crosslinking group is preferably selected from at least one of N-hydroxymethylacrylamide (NMAM), N-hydroxybutylacrylamide (NBMA), hydroxyethylacrylamide (HEAA) and glycidyl methacrylate (GMA), more preferably containing hydroxyethylacrylamide (HEAA), and even more preferably hydroxyethylacrylamide (HEAA).

[0068] A specific (meth)acrylic resin particle A may contain only one type of constituent unit from a monomer with a self-crosslinking group, or it may contain two or more types.

[0069] The content of constituent units derived from monomers with self-crosslinking groups in specific (meth)acrylic resin particles A is 0.1% to 7% by mass relative to all constituent units of specific (meth)acrylic resin particles A.

[0070] A content of 0.1% by mass or more of the constituent units of a specific (meth)acrylic resin particle A from monomers having self-crosslinking groups, relative to all the constituent units of the specific (meth)acrylic resin particle A, means that the specific (meth)acrylic resin particle A actively contains constituent units from monomers having self-crosslinking groups.

[0071] Relative to all the constituent units of the specific (meth)acrylic resin particle A, the content of constituent units derived from monomers having self-crosslinking groups in the specific (meth)acrylic resin particle A is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more.

[0072] If, relative to all the constituent units of a specific (meth)acrylic resin particle A, the content of constituent units derived from monomers having self-crosslinking groups in the specific (meth)acrylic resin particle A is 7% by mass or less, there is a tendency to form a coating film that exhibits high adhesion under high-temperature conditions when electromagnetic steel sheets are bonded together. From this viewpoint, the content of constituent units derived from monomers having self-crosslinking groups in the specific (meth)acrylic resin particle A is preferably 6% by mass or less, more preferably 5% by mass or less, relative to all the constituent units of the specific (meth)acrylic resin particle A.

[0073] In one manner, the content of constituent units from monomers having self-crosslinking groups in a specific (meth)acrylic resin particle A can be in the range of 0.1% to 6% by mass, 0.1% to 5% by mass, 1% to 7% by mass, 1.5% to 6% by mass, or 1.9% to 5% by mass.

[0074] <Building units derived from (meth)acrylate alkyl ester monomers>

[0075] The specific (meth)acrylic resin particle A preferably contains a constituent unit derived from an alkyl (meth)acrylic ester monomer.

[0076] In this disclosure, "constituent unit from (meth)acrylate alkyl ester monomer" refers to a constituent unit formed by the addition polymerization of (meth)acrylate alkyl ester monomer. It should be noted that the "(meth)acrylate alkyl ester monomer" in a specific (meth)acrylate resin particle A does not include monomers that are monomers having carboxyl groups or monomers that are monomers having self-crosslinking groups.

[0077] There are no particular restrictions on the types of (meth)acrylate alkyl ester monomers.

[0078] (Meth)acrylate alkyl ester monomers can be either alkyl acrylate monomers or alkyl methacrylate monomers.

[0079] The alkyl group in the (meth)acrylate monomer may be unsubstituted or substituent (excluding carboxyl, self-crosslinking groups and hydroxyl groups), but is preferably unsubstituted.

[0080] The alkyl group in the (meth)acrylate monomer can be any one of linear, branched or cyclic.

[0081] The number of carbon atoms in the alkyl group of the (meth)acrylate monomer is preferably 1 to 18, more preferably 1 to 12, and even more preferably 1 to 8.

[0082] Specific examples of alkyl methacrylate monomers include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, n-nonyl methacrylate, isononyl methacrylate, n-decyl methacrylate, stearyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate.

[0083] The alkyl methacrylate monomer preferably comprises at least one selected from n-butyl acrylate, methyl methacrylate and 2-ethylhexyl acrylate, more preferably at least one selected from n-butyl acrylate, methyl methacrylate and 2-ethylhexyl acrylate.

[0084] When a specific (meth)acrylic resin particle A contains a constituent unit derived from an alkyl methacrylate monomer, it may contain only one constituent unit derived from an alkyl methacrylate monomer, or it may contain two or more constituent units.

[0085] When a specific (meth)acrylic resin particle A contains a constituent unit derived from an alkyl methacrylate monomer, the content of the constituent unit derived from the alkyl methacrylate monomer is not particularly limited. For example, it is preferably 50% to 98% by mass relative to all constituent units of the specific (meth)acrylic resin particle A, more preferably 50% to 85% by mass, and even more preferably 50% to 70% by mass.

[0086] Here, when the content of constituent units from alkyl methacrylate monomers in a specific (meth)acrylate resin particle A is 50% by mass or more, relative to all constituent units of the specific (meth)acrylate resin particle A, it means that constituent units from alkyl methacrylate monomers are included as the main components constituting the constituent units of the specific (meth)acrylate resin particle A.

[0087] <Constructing units from other monomers>

[0088] A specific (meth)acrylic resin particle A may contain constituent units from monomers that do not belong to any of the monomers having a carboxyl group, monomers having a self-crosslinking group, and (meth)acrylic alkyl ester monomers (so-called other monomers).

[0089] In this disclosure, "constituent units from other monomers" refers to constituent units formed by the addition polymerization of other monomers.

[0090] As a building block derived from other monomers, for example, a building block derived from styrene. If a specific (meth)acrylic resin particle A contains a building block derived from styrene, it is possible to impart gloss to the formed coating film.

[0091] In addition, as constituent units derived from other monomers, examples include constituent units derived from (meth)acrylates having aromatic rings, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; constituent units derived from (meth)acrylate alkoxyalkyl esters, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; constituent units derived from vinyl cyanides, such as acrylonitrile and methacrylonitrile; and constituent units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl tert-carbonate.

[0092] When a specific (meth)acrylic resin particle A contains constituent units from other monomers, it may contain only one type of constituent unit from other monomers, or it may contain two or more types.

[0093] When a specific (meth)acrylic resin particle A contains constituent units from other monomers, the content of the constituent units from other monomers can be appropriately set without impairing the effect of the coating composition disclosed herein.

[0094] <<Glass transition temperature of specific (meth)acrylic resin particle A>>

[0095] The glass transition temperature (also known as "Tg") of a specific (meth)acrylic resin particle A is above 55°C.

[0096] If the glass transition temperature of the specific (meth)acrylic resin particles A is 55°C or higher, there is a tendency to form a coating film that exhibits high adhesion under high-temperature conditions when the electromagnetic steel sheets are fixed together. From this point of view, the glass transition temperature of the specific (meth)acrylic resin particles A is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher.

[0097] There is no particular upper limit to the glass transition temperature of the specific (meth)acrylic resin particles A, but it is preferably below 80°C.

[0098] In one embodiment, the glass transition temperature of a specific (meth)acrylic resin particle A can be 55℃~80℃, 60℃~80℃, 65℃~80℃, or 70℃~80℃.

[0099] The glass transition temperature of a specific (meth)acrylic resin particle A was determined using a differential scanning calorimeter (DSC) by the method described below.

[0100] Aqueous dispersions of specific (meth)acrylic resin particles A were coated onto release paper using a 4 mil (101.6 μm) applicator. The coated aqueous dispersions of specific (meth)acrylic resin particles A were then dried (drying temperature: 105°C, drying time: 10 minutes) to obtain dried product of specific (meth)acrylic resin particles A. 10 mg of this dried product was placed in an aluminum sample container (e.g., Tzero Pan (trade name) manufactured by TA Instrument Co., Ltd.), sealed with an aluminum cap (e.g., Tzero Hermetic Lid (trade name) manufactured by TA Instrument Co., Ltd.), and the glass transition temperature was determined using a differential scanning calorimeter under the following conditions. It should be noted that in this determination, the temperature at which the straight line extending from the low-temperature side of the obtained DSC curve towards the high-temperature side intersects the tangent line drawn from the point where the slope of the curve in the step-like change portion of the glass transition is the largest is taken as the glass transition temperature.

[0101] As a differential scanning calorimeter, for example, a differential scanning calorimeter manufactured by TA Instruments Japan Co., Ltd. (trade name: Discovery DSC 2500) can be used. However, the differential scanning calorimeter is not limited to this.

[0102] -Determination Conditions-

[0103] Atmospheric conditions: Under the atmosphere

[0104] Measurement temperature range: -90℃~100℃

[0105] Heating rate: 10℃ / minute

[0106] Standard material: empty sample container

[0107] The glass transition temperature of a specific (meth)acrylic resin particle A can be appropriately adjusted, for example, by using two or more monomers with different glass transition temperatures when forming homopolymers.

[0108] <<Average primary particle size of specific (meth)acrylic resin particles A>>

[0109] The average primary particle size of the specific (meth)acrylic resin particles A is not particularly limited. For example, from the viewpoint of manufacturing stability of the specific (meth)acrylic resin particles A, it is preferably 200 nm to 450 nm, more preferably 230 nm to 450 nm, even more preferably 250 nm to 450 nm, and particularly preferably 280 nm to 400 nm.

[0110] The average primary particle size of a specific (meth)acrylic resin particle A can be controlled, for example, by adjusting the amount of surfactant used in the manufacture of the specific (meth)acrylic resin particle A. The particle size of the specific (meth)acrylic resin particle A tends to be smaller when the amount of surfactant used in the manufacture of the specific (meth)acrylic resin particle A is larger, and larger when the amount of surfactant used is smaller.

[0111] The average primary particle size of a specific (meth)acrylic resin particle A refers to its volume average primary particle size. The average primary particle size of the specific (meth)acrylic resin particle A is determined using a particle size distribution measuring apparatus via the dynamic light scattering method described in "New Experimental Chemistry Lectures 4: Basic Techniques 3: Light (II)" edited by the Chemical Society of Japan, pages 725-741 (published by Maruzen Co., Ltd. on July 20, 1951). The specific method is shown below.

[0112] Five mL of a dispersion of specific (meth)acrylic acid resin particles A was collected using a Pasteur pipette and placed in a 10 mm square glass cuvette, which was then set into a particle size distribution measuring apparatus. The attenuator was set to x8 (8 times), and the concentration of the dispersion of specific (meth)acrylic acid resin particles A was adjusted to a count rate of 150 kCps to 200 kCps. Using the adjusted concentration of the dispersion of specific (meth)acrylic acid resin particles A, the particle size distribution of specific (meth)acrylic acid resin particles A was measured at a measurement temperature of 25°C and a light scattering angle of 90°. The average primary particle size of specific (meth)acrylic acid resin particles A was calculated by computer processing of the measured results. Specifically, the particle size at the 50% (volume basis) cumulative value in the obtained particle size distribution was taken as the volume average primary particle size.

[0113] As a particle size distribution measuring device, for example, the "Zetasizer NanoZS-90" manufactured by Malvern can be appropriately used. However, the particle size distribution measuring device is not limited to this.

[0114] <<Content of Specific (Meth)acrylic Resin Particle A>>

[0115] The content of specific (meth)acrylic resin particles A in the coating composition disclosed herein is not particularly limited, but is preferably 85% to 95% by mass, more preferably 87% to 93% by mass, and even more preferably 89% to 91% by mass, relative to the total solid content in the coating composition.

[0116] In this disclosure, "total solids content in the coating composition" refers to the mass of the residue obtained after removing the solvent from the coating composition. In this disclosure, "solvent" refers to water and organic solvents.

[0117] [Method for manufacturing specific (meth)acrylic resin particles A]

[0118] The method for manufacturing specific (meth)acrylic resin particles A is not particularly limited as long as it can produce the aforementioned specific (meth)acrylic resin particles A.

[0119] Specific (meth)acrylic resin particles A can be manufactured, for example, by emulsion polymerization.

[0120] As an emulsion polymerization method for manufacturing specific (meth)acrylic resin particles A, the methods described below [1] to [3] can be cited, for example. In the following description, the monomer that forms the constituent unit of the specific (meth)acrylic resin particles A is also referred to as "monomer component A".

[0121] [1] A method of emulsion polymerization reaction is carried out by adding monomer component A, surfactant and water into a reactor equipped with a thermometer, stirrer, raw material inlet pipe, reflux cooler, nitrogen inlet pipe, etc., and stirring and heating under nitrogen flow. Then, appropriate polymerization initiators, reducing agents, etc. are added (the so-called one-time addition method).

[0122] [2] A method of emulsion polymerization reaction is carried out by adding at least surfactant and water into a reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux cooler, and a nitrogen inlet pipe, stirring and heating under a nitrogen flow, and then adding monomer component A dropwise, and appropriately adding polymerization initiator, reducing agent, etc. (so-called monomer dropwise addition method).

[0123] [3] In a separate container, monomer component A is pre-emulsified using at least a surfactant and water to prepare a pre-emulsion. A portion of the pre-emulsion and water are added to a reactor equipped with a thermometer, stirrer, feed inlet pipe, reflux cooler, and nitrogen inlet pipe. The mixture is heated while being stirred under a nitrogen flow. After the temperature in the reactor stabilizes, the remaining pre-emulsion is added dropwise to the reactor along with an appropriate amount of polymerization initiator and reducing agent to initiate the emulsion polymerization reaction (the so-called emulsified monomer dropwise addition method).

[0124] Of these, the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A is preferably the emulsion monomer dropwise addition method described above [3].

[0125] Monomer component A contains monomers with carboxyl groups.

[0126] Details of monomers containing carboxyl groups are as described above.

[0127] Monomer component A may contain only one type of monomer with a carboxyl group, or it may contain two or more types.

[0128] For example, relative to a total of 100 parts by mass of monomer component A, the amount of the monomer having a carboxyl group used is preferably in the range of 1 part by mass or more and less than 20 parts by mass.

[0129] Monomer component A contains monomers with self-crosslinking groups.

[0130] Details of monomers with self-crosslinking groups are as described above.

[0131] Monomer component A may contain only one type of monomer with a self-crosslinking group, or it may contain two or more types.

[0132] For example, the amount of monomer having self-crosslinking groups used is preferably in the range of 0.1 to 7 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0133] Monomer component A preferably contains an alkyl (meth)acrylate monomer.

[0134] Details of the (meth)acrylate alkyl ester monomers are as described above.

[0135] When monomer component A contains alkyl (meth)acrylate monomers, it may contain only one type of alkyl (meth)acrylate monomer or more than two types.

[0136] When using alkyl (meth)acrylate monomers, for example, the amount of alkyl (meth)acrylate monomers used is preferably in the range of 50 to 98 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0137] Monomer component A may contain other monomers such as styrene.

[0138] Details of styrene and other monomers are as described above.

[0139] When using styrene, for example, the amount of styrene used is preferably in the range of 10 to 48 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0140] There are no particular limitations on surfactants.

[0141] The surfactant can be any one of anionic surfactants, cationic surfactants, amphoteric surfactants, or nonionic surfactants, or a combination thereof. For example, from the viewpoint of manufacturing stability of a specific (meth)acrylic resin particle A, the surfactant is preferably anionic surfactant and / or nonionic surfactant, more preferably anionic surfactant and nonionic surfactant.

[0142] Examples of anionic surfactants include, for instance, polyoxyethylene polycyclic phenyl ether sulfates represented by polyoxyethylene styrene phenyl ether ammonium sulfate, polyoxyethylene polycyclic phenyl ether sulfates represented by polyoxyethylene styrene phenyl ether ammonium sulfate, polyoxyethylene alkyl phenyl ether sulfates represented by polyoxyethylene nonyl phenyl ether sodium sulfate, polyoxyethylene alkyl ether sulfates represented by polyoxyethylene lauryl ether sulfate, polyoxyethylene alkyl ether sulfates, and alkyl phosphates.

[0143] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, such as polyoxyethylene oil ethers and polyoxyethylene lauryl ethers, and polyoxyethylene styrene ethers, such as polyoxyethylene styrene ethers.

[0144] In the emulsion polymerization process used to manufacture specific (meth)acrylic resin particles A, only one surfactant may be used, or two or more surfactants may be used.

[0145] In the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A, the amount of surfactant used is not particularly limited, but for example, it is preferably 1.5 to 10.0 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0146] There are no particular limitations on the polymerization initiator, as long as it is a polymerization initiator that can be used in ordinary emulsion polymerization.

[0147] Examples of polymerization initiators include persulfates, organic peroxides, and azo compounds.

[0148] Specific examples of persulfates include ammonium persulfate (also known as "ammonium peroxydisulfate"), sodium persulfate, and potassium persulfate.

[0149] Specific examples of organic peroxides include tert-butyl hydroperoxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, diisopropyl peroxide dicarbonate, di-2-ethylhexyl peroxide dicarbonate, and tert-butyl peroxypentanoate.

[0150] Specific examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanitrile), 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile), 1,1'-azobis(cyclohexane-1-carboxylonitrile) and dimethyl 2,2'-azobis(isobutyric acid) ester.

[0151] In the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A, only one polymerization initiator can be used, or two or more can be used.

[0152] In the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A, the amount of polymerization initiator used is not particularly limited, but for example, it is preferably 0.2 to 1.0 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0153] In the emulsion polymerization process used to manufacture specific (meth)acrylic resin particles A, a reducing agent can be used in conjunction with the polymerization initiator.

[0154] Specific examples of reducing agents include sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium metabisulfite, sodium pyrophosphate, sodium hydroxymethyl sulfinate, mercaptoacetic acid, and sodium thiosulfate.

[0155] In the emulsion polymerization process used to manufacture specific (meth)acrylic resin particles A, when using a reducing agent, only one reducing agent may be used, or two or more reducing agents may be used.

[0156] In the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A, when a reducing agent is used, the amount of reducing agent used is not particularly limited, but for example, it is preferably 0.2 to 1.0 parts by mass relative to a total of 100 parts by mass of monomer component A.

[0157] In the emulsion polymerization method used to manufacture specific (meth)acrylic resin particles A, the polymerization temperature is, for example, 50°C to 80°C, preferably 60°C to 70°C. Furthermore, the polymerization time is, for example, 5 hours to 9 hours, preferably 6 hours to 8 hours.

[0158] [Water-soluble (meth)acrylic resin B]

[0159] The coating composition disclosed herein comprises a water-soluble (meth)acrylic resin B.

[0160] The coating composition disclosed herein may contain only one water-soluble (meth)acrylic resin B, or it may contain two or more.

[0161] In the coating composition disclosed herein, the water-soluble (meth)acrylic resin B exists in a state of being dissolved in a medium containing water.

[0162] In this disclosure, "water-soluble (meth)acrylic resin" refers to a (meth)acrylic resin whose haze value of the resin film is 3.0 or less as determined by the method described below.

[0163] The solids concentration of the (meth)acrylic resin was adjusted to 30% by mass using water as a sample solution. The sample solution was applied to one side of a substrate using a bar coater until the dried film thickness was 2 μm, forming a coated film. The coated film was then dried at 100°C for 1 minute to obtain a PET-coated resin film. The haze of the PET-coated resin film was measured using a haze meter. The haze value of the resin film was calculated by subtracting the haze value of the PET from the obtained haze value.

[0164] As the substrate, polyethylene terephthalate (PET) film is preferred. For example, "Lumirror 125T60" (haze value: 2.63) manufactured by TORAY Co., Ltd. can be used as the PET film. However, the substrate is not limited to this.

[0165] For example, a haze meter manufactured by Nippon Denshoku Kogyo Co., Ltd. (model: NDH5000SP) can be used. However, the haze meter is not limited to this.

[0166] <Building units from monomers with self-crosslinking groups>

[0167] Water-soluble (meth)acrylic resin B preferably contains constituent units derived from monomers having self-crosslinking groups.

[0168] If the water-soluble (meth)acrylic resin B contains constituent units from monomers having self-crosslinking groups, the resulting coated film tends to exhibit higher adhesive strength under high-temperature conditions when the electromagnetic steel sheets are bonded together.

[0169] Specific examples of self-crosslinking groups in water-soluble (meth)acrylic resin B are the same as specific examples of self-crosslinking groups in specific (meth)acrylic resin particles A.

[0170] As a self-crosslinking group, it is preferably selected from at least one of N-hydroxymethyl, N-hydroxybutyl and glycidyl groups.

[0171] Specific examples of monomers having self-crosslinking groups in water-soluble (meth)acrylic resin B are the same as specific examples of monomers having self-crosslinking groups in specific (meth)acrylic resin particles A.

[0172] The monomer having a self-crosslinking group preferably includes at least one selected from N-hydroxymethylacrylamide (NMAM) and hydroxyethylacrylamide (HEAA), more preferably at least one selected from N-hydroxymethylacrylamide (NMAM) and hydroxyethylacrylamide (HEAA).

[0173] When water-soluble (meth)acrylic resin B contains constituent units from monomers having self-crosslinking groups, it may contain only one type of constituent unit from monomers having self-crosslinking groups, or it may contain two or more types.

[0174] When the water-soluble (meth)acrylic resin B contains constituent units derived from monomers having self-crosslinking groups, the content of constituent units derived from monomers having self-crosslinking groups is not particularly limited. For example, it is preferably 0.1% to 10.0% by mass, more preferably 1.0% to 5.0% by mass, and even more preferably 1.5% to 2.0% by mass, relative to all constituent units of the water-soluble (meth)acrylic resin B.

[0175] If the content of constituent units from monomers having self-crosslinking groups in water-soluble (meth)acrylic resin B is within the above range relative to all constituent units of water-soluble (meth)acrylic resin B, the formed coating film tends to exhibit higher adhesive strength under high-temperature conditions when the electromagnetic steel sheets are fixed together.

[0176] <Building units from monomers containing hydroxyl groups>

[0177] Water-soluble (meth)acrylic resin B preferably contains constituent units derived from monomers having hydroxyl groups.

[0178] In this disclosure, "a constituent unit from a monomer having a hydroxyl group" refers to a constituent unit formed by the addition polymerization of a monomer having a hydroxyl group. It should be noted that, in this disclosure, the hydroxyl group constituting part of a self-crosslinking group is not included in the hydroxyl group of the monomer having a hydroxyl group.

[0179] As a monomer having a hydroxyl group, for example, a monomer having at least one hydroxyl group and an olefinic unsaturated group in one molecule can be cited.

[0180] As an olefinic unsaturated group, there are no particular limitations; examples include vinyl, allyl, vinylphenyl, (meth)acrylamido, and (meth)acryloyl.

[0181] As an olefinic unsaturated group, (meth)acryloyl is preferred.

[0182] Specific examples of monomers having hydroxyl groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylaurate (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, glyceryl mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate.

[0183] The monomer having a hydroxyl group preferably includes a hydroxyalkyl ester of (meth)acrylate, more preferably a hydroxyalkyl ester of (meth)acrylate. As a hydroxyalkyl ester of (meth)acrylate, a hydroxyalkyl ester of (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is preferred, 2-hydroxyethyl ester of (meth)acrylate is more preferred, and 2-hydroxyethyl ester of methacrylate is even more preferred.

[0184] When water-soluble (meth)acrylic resin B contains constituent units derived from monomers having hydroxyl groups, it may contain only one type of constituent unit derived from monomers having hydroxyl groups, or it may contain two or more types.

[0185] When the water-soluble (meth)acrylic resin B contains constituent units from monomers having hydroxyl groups, the content of constituent units from monomers having hydroxyl groups is not particularly limited. For example, it is preferably 5% to 30% by mass, more preferably 10% to 25% by mass, and even more preferably 15% to 25% by mass, relative to all constituent units of the water-soluble (meth)acrylic resin B.

[0186] If the content of constituent units from monomers having hydroxyl groups in water-soluble (meth)acrylic resin B is 5% by mass or more relative to all constituent units of water-soluble (meth)acrylic resin B, there is a tendency for the formed coating film to have higher adhesive properties.

[0187] If the content of constituent units from monomers having hydroxyl groups in water-soluble (meth)acrylic resin B is less than 30% by mass relative to all constituent units of water-soluble (meth)acrylic resin B, then water-soluble (meth)acrylic resin B tends to have better manufacturing stability.

[0188] <Building units derived from (meth)acrylate alkyl ester monomers>

[0189] Water-soluble (meth)acrylic resin B preferably contains constituent units derived from (meth)acrylic alkyl ester monomers.

[0190] It should be noted that the "(meth)acrylate alkyl ester monomer" in water-soluble (meth)acrylate resin B does not include monomers that are monomers with self-crosslinking groups or monomers that are monomers with hydroxyl groups.

[0191] There are no particular restrictions on the types of (meth)acrylate alkyl ester monomers.

[0192] (Meth)acrylate alkyl ester monomers can be either alkyl acrylate monomers or alkyl methacrylate monomers.

[0193] The alkyl group of the (meth)acrylate monomer may be unsubstituted or substituent (excluding carboxyl, self-crosslinking groups and hydroxyl groups), but is preferably unsubstituted.

[0194] The alkyl group in (meth)acrylate monomers can be any of the following: linear, branched, or cyclic.

[0195] The alkyl ester monomer of (meth)acrylate preferably has 1 to 12 carbon atoms in its alkyl group, more preferably 1 to 8, and even more preferably 1 to 4.

[0196] The specific examples of the (meth)acrylate alkyl ester monomers in water-soluble (meth)acrylate resin B are the same as the specific examples of the (meth)acrylate alkyl ester monomers in specific (meth)acrylate resin particles (A).

[0197] For example, from the viewpoint of water solubility, the (meth)acrylate alkyl ester monomer preferably contains at least one selected from n-butyl acrylate, methyl methacrylate and ethyl acrylate, more preferably contains at least one selected from methyl methacrylate and ethyl acrylate, and even more preferably contains methyl methacrylate.

[0198] When water-soluble (meth)acrylic resin B contains constituent units derived from (meth)acrylic alkyl ester monomers, it may contain only one type of constituent unit derived from (meth)acrylic alkyl ester monomers, or it may contain two or more types.

[0199] When the water-soluble (meth)acrylic resin B contains constituent units derived from alkyl methacrylate monomers, the content of constituent units derived from alkyl methacrylate monomers in the water-soluble (meth)acrylic resin B is not particularly limited. For example, it is preferably 40% to 90% by mass, more preferably 40% to 80% by mass, and even more preferably 40% to 70% by mass, relative to all constituent units of the water-soluble (meth)acrylic resin B.

[0200] <Constructing units from other monomers>

[0201] Water-soluble (meth)acrylic resin B may contain constituent units of monomers (so-called other monomers) that are not monomers with self-crosslinking groups, monomers with hydroxyl groups, and alkyl (meth)acrylic acid ester monomers.

[0202] Examples of constituent units derived from other monomers include (meth)acrylates having aromatic rings, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; (meth)acrylate alkoxyalkyl esters, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl cyanides, such as acrylonitrile and methacrylonitrile; and vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl tert-carbonate.

[0203] When water-soluble (meth)acrylic resin B contains constituent units from other monomers, it may contain only one type of constituent unit from other monomers, or it may contain two or more types.

[0204] When the water-soluble (meth)acrylic resin B contains constituent units from other monomers, the content of the constituent units from other monomers can be appropriately set without impairing the effect of the coating composition disclosed herein.

[0205] <<Glass Transition Temperature of Water-Soluble (Meth)Acrylic Resin B>>

[0206] The glass transition temperature of water-soluble (meth)acrylic resin B is not particularly limited, but is preferably below 100°C, more preferably below 90°C, and even more preferably below 80°C.

[0207] If the glass transition temperature of water-soluble (meth)acrylic resin B is below 100°C, it tends to have excellent film-forming properties.

[0208] The lower limit of the glass transition temperature of the water-soluble (meth)acrylic resin B is preferably -70°C or higher.

[0209] The glass transition temperature of water-soluble (meth)acrylic resin B was determined using the same method as that used for determining the glass transition temperature of the specific (meth)acrylic resin particle A described above.

[0210] The glass transition temperature of water-soluble (meth)acrylic resin B can be appropriately adjusted, for example, by using two or more monomers with different glass transition temperatures when making homopolymers.

[0211] <<Weight-average molecular weight of water-soluble (meth)acrylic resin B>>

[0212] The weight-average molecular weight (hereinafter also referred to as "Mw") of the water-soluble (meth)acrylic resin B is not particularly limited, but is preferably 0.1 million to 100,000, more preferably 0.5 million to 50,000, and even more preferably 0.8 million to 30,000.

[0213] If the weight-average molecular weight of water-soluble (meth)acrylic resin B is above 0.1 million, the resulting coating film tends to have better adhesive properties.

[0214] If the weight-average molecular weight of water-soluble (meth)acrylic resin B is less than 100,000, it tends to have better manufacturing stability and spreadability of the coating composition.

[0215] The weight-average molecular weight of water-soluble (meth)acrylic resin B was determined by the following method. Specifically, it was determined according to (1) to (3) below.

[0216] (1) Coat a solution of water-soluble (meth)acrylic resin B onto a release paper and dry it at 100°C for 1 minute to obtain a film-like water-soluble (meth)acrylic resin B.

[0217] (2) Using the film-like water-soluble (meth)acrylic resin B obtained in (1) above and tetrahydrofuran, a sample solution with a solid content concentration of 0.2% by mass was obtained. It should be noted that the "solid content concentration" mentioned here refers to the mass ratio of water-soluble (meth)acrylic resin B in the sample solution.

[0218] (3) The weight-average molecular weight of water-soluble (meth)acrylic resin B, converted to standard polystyrene, was determined by gel permeation chromatography (GPC) under the following conditions.

[0219] ~Conditions~

[0220] Measuring apparatus: High-speed GPC (Model: HLC-8220 GPC, manufactured by TOSOH Corporation)

[0221] Detector: Differential refractometer (RI) [assembled in HLC-8220, manufactured by TOSOH Corporation]

[0222] Columns: Use 4 TSKgel GMH XL [Made by TOSOH Co., Ltd.]

[0223] Column temperature: 40℃

[0224] Eluent: Tetrahydrofuran

[0225] Injection volume of sample solution: 100 μL

[0226] Flow rate: 0.8 mL / min

[0227] The weight-average molecular weight of water-soluble (meth)acrylic resin B can be adjusted to the desired value by changing the polymerization temperature, polymerization time, type and amount of polymerization initiator, and type and amount of chain transfer agent.

[0228] <<Content of water-soluble (meth)acrylic resin B>>

[0229] The content of water-soluble (meth)acrylic resin B in the coating composition disclosed herein is not particularly limited as long as the ratio of the mass of specific (meth)acrylic resin particles A to the mass of water-soluble (meth)acrylic resin B [mass of specific (meth)acrylic resin particles A / mass of water-soluble (meth)acrylic resin B] is 95 / 5 to 85 / 15.

[0230] If the mass ratio of the specific (meth)acrylic resin particles A to the water-soluble (meth)acrylic resin B in the coating composition of this disclosure is 95 / 5 to 85 / 15, it is possible to achieve both excellent coating on the surface of the electromagnetic steel sheet and the formation of a coating film exhibiting high adhesion under high-temperature conditions when the magnets are bonded together. For example, from the viewpoint of forming a coating film exhibiting even higher adhesion, the mass ratio of the specific (meth)acrylic resin particles A to the water-soluble (meth)acrylic resin B is preferably 95 / 5 to 90 / 10.

[0231] [Method for manufacturing water-soluble (meth)acrylic resin B]

[0232] The method for manufacturing water-soluble (meth)acrylic resin B is not particularly limited as long as it can produce the above-mentioned water-soluble (meth)acrylic resin B.

[0233] Water-soluble (meth)acrylic resin B can be manufactured, for example, by the following methods.

[0234] First, a dispersion containing carboxyl-containing (meth)acrylic resin particles as the dispersion medium is prepared by emulsion polymerization using a monomer component that contains at least a monomer with a carboxyl group. Next, an alkali is added to the prepared dispersion to neutralize the carboxyl groups of the (meth)acrylic resin particles. Through these steps, water-soluble (meth)acrylic resin B is obtained. It is believed that if the carboxyl groups of the (meth)acrylic resin particles are neutralized, it will promote the dissociation of the carboxyl groups, increasing the acidity, resulting in the destruction of micelles and the water solubility of the (meth)acrylic resin.

[0235] As an emulsion polymerization method for manufacturing water-soluble (meth)acrylic resin B, examples of the methods described below are [1] to [3]. In the following description, the monomer that forms the constituent unit of water-soluble (meth)acrylic resin B is also referred to as "monomer component B".

[0236] [1] Monomer component B, surfactant and water are added to a reactor equipped with a thermometer, stirrer, raw material inlet pipe, reflux cooler, nitrogen inlet pipe, etc., and the mixture is heated while being stirred under a nitrogen flow. Then, appropriate polymerization initiators, reducing agents, chain transfer agents, etc. are added to carry out emulsion polymerization reaction (the so-called one-time addition method).

[0237] [2] In a reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux cooler, a nitrogen inlet pipe, etc., at least surfactant and water are added. After stirring and heating under a nitrogen flow, monomer component B is added dropwise, and polymerization initiators, reducing agents, chain transfer agents, etc. are added appropriately to carry out emulsion polymerization (the so-called monomer dropwise addition method).

[0238] [3] In a separate container, monomer component B is pre-emulsified using at least a surfactant and water to prepare a pre-emulsion. A portion of the pre-emulsion and water are added to a reactor equipped with a thermometer, stirrer, feed inlet pipe, reflux cooler, and nitrogen inlet pipe. The mixture is heated while being stirred under a nitrogen flow. After the temperature in the reactor stabilizes, the remaining pre-emulsion is added dropwise while appropriately adding polymerization initiators, reducing agents, chain transfer agents, etc., to carry out the emulsion polymerization reaction (the so-called emulsified monomer dropwise addition method).

[0239] Of these, the emulsion polymerization method described above [3] is preferred as the emulsion monomer dropwise addition method for manufacturing water-soluble (meth)acrylic resin B.

[0240] Monomer component B contains monomers with carboxyl groups.

[0241] As a monomer having a carboxyl group, for example, a monomer having at least one carboxyl group and an olefinic unsaturated group in one molecule can be cited.

[0242] As an olefinic unsaturated group, there are no particular limitations; examples include vinyl, allyl, vinylphenyl, (meth)acrylamido, and (meth)acryloyl.

[0243] As an olefinic unsaturated group, (meth)acryloyl is preferred.

[0244] The specific examples of monomers containing carboxyl groups in monomer component B are the same as the specific examples of monomers containing carboxyl groups in specific (meth)acrylic resin particles A.

[0245] The monomer having a carboxyl group is preferably a (meth)acrylic acid monomer having a carboxyl group, more preferably (meth)acrylic acid, and even more preferably acrylic acid.

[0246] Monomer component B may contain only one type of monomer with a carboxyl group, or it may contain two or more types.

[0247] For example, the amount of the monomer having a carboxyl group used is preferably in the range of 10 to 30 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0248] Monomer component B preferably contains monomers with self-crosslinking groups.

[0249] Details of monomers with self-crosslinking groups are as described above.

[0250] When monomer component B contains monomers with self-crosslinking groups, it may contain only one type of monomer with self-crosslinking groups, or it may contain two or more types.

[0251] When using a monomer with self-crosslinking groups, for example, the amount of monomer with self-crosslinking groups used is preferably in the range of 1 to 5 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0252] Monomer component B preferably contains monomers having hydroxyl groups.

[0253] Details of monomers containing hydroxyl groups are as described above.

[0254] When monomer component B contains monomers with hydroxyl groups, it may contain only one type of monomer with hydroxyl groups, or it may contain two or more types.

[0255] When using monomers containing hydroxyl groups, for example, the amount of monomers containing hydroxyl groups used is preferably in the range of 10 to 30 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0256] Monomer component B preferably contains (meth)acrylate alkyl ester monomers.

[0257] Details of the (meth)acrylate alkyl ester monomers are as described above.

[0258] When monomer component B contains alkyl (meth)acrylate monomers, it may contain only one type of alkyl (meth)acrylate monomer or more than two types.

[0259] When using alkyl (meth)acrylate monomers, for example, the amount of alkyl (meth)acrylate monomers used is preferably in the range of 40 to 80 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0260] There are no particular restrictions on the types of surfactants.

[0261] The surfactant can be any one of anionic surfactants, cationic surfactants, amphoteric surfactants, or nonionic surfactants, or a combination thereof. For example, from the viewpoint of manufacturing stability of water-soluble (meth)acrylic resin B, the surfactant is preferably anionic surfactant and / or nonionic surfactant, and more preferably anionic surfactant.

[0262] Specific examples of anionic surfactants are the same as those used in emulsion polymerization for the manufacture of specific (meth)acrylic resin particles A.

[0263] Specific examples of nonionic surfactants are the same as those used in emulsion polymerization for the manufacture of specific (meth)acrylic resin particles A.

[0264] In the emulsion polymerization method used to manufacture water-soluble (meth)acrylic resin B, only one surfactant can be used, or two or more surfactants can be used.

[0265] In the emulsion polymerization method used to manufacture water-soluble (meth)acrylic resin B, the amount of surfactant used is not particularly limited, but for example, it is preferably 0.5 to 5.0 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0266] There are no particular limitations on the polymerization initiator, as long as it is a polymerization initiator that can be used in general emulsion polymerization.

[0267] Examples of polymerization initiators include persulfates, organic peroxides, and azo compounds.

[0268] The specific examples of persulfates, organic peroxides, and azo compounds are the same as those used in the emulsion polymerization process for manufacturing specific (meth)acrylic resin particles A.

[0269] In the emulsion polymerization method used to manufacture water-soluble (meth)acrylic resin B, only one polymerization initiator can be used, or two or more can be used.

[0270] In the emulsion polymerization method for manufacturing water-soluble (meth)acrylic resin B, the amount of polymerization initiator used is not particularly limited, but for example, it is preferably 0.5 to 3.0 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0271] In the emulsion polymerization process used to manufacture water-soluble (meth)acrylic resin B, a reducing agent can be used in conjunction with the polymerization initiator.

[0272] The specific examples of reducing agents are the same as those used in the emulsion polymerization process for manufacturing specific (meth)acrylic resin particles A.

[0273] In the emulsion polymerization process used to manufacture water-soluble (meth)acrylic resin B, when using a reducing agent, only one reducing agent may be used, or two or more reducing agents may be used.

[0274] In the emulsion polymerization method for manufacturing water-soluble (meth)acrylic resin B, when using a reducing agent, the amount of reducing agent used is not particularly limited, but for example, it is preferably 0.1 to 1.0 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0275] There are no particular restrictions on the types of chain transfer agents.

[0276] Specific examples of chain transfer agents include cyanoacetic acid, alkyl esters of cyanoacetic acid with 1 to 8 carbon atoms, bromoacetic acid, alkyl esters of bromoacetic acid with 1 to 8 carbon atoms, aromatic compounds represented by α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives represented by benzoquinone and 2,3,5,6-tetramethylp-benzoquinone, borane derivatives represented by tributylborane, and carbon tetrabromide. Halogenated hydrocarbons represented by carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene; aldehydes represented by trichloroacetaldehyde and furfural; aromatic thiols represented by alkyl thiols with 1 to 18 carbon atoms, thiophenol, and toluene thiol; mercaptoacetic acid, alkyl esters of mercaptoacetic acid with 1 to 10 carbon atoms, hydroxyalkyl thiols with 1 to 12 carbon atoms (e.g., 2-mercaptoethanol); and terpenes represented by pinene and terpinene.

[0277] In the emulsion polymerization process used to manufacture water-soluble (meth)acrylic resin B, when using chain transfer agents, only one type of chain transfer agent can be used, or two or more types can be used.

[0278] In the emulsion polymerization method for manufacturing water-soluble (meth)acrylic resin B, the amount of chain transfer agent used is not particularly limited, but for example, it is preferably 1 to 3 parts by mass relative to a total of 100 parts by mass of monomer component B.

[0279] In the emulsion polymerization method used to manufacture water-soluble (meth)acrylic resin B, the polymerization temperature is, for example, 58°C to 62°C, preferably 59°C to 61°C. Furthermore, the polymerization time is, for example, 3 hours to 6 hours, preferably 4 hours to 5 hours.

[0280] According to the emulsion polymerization method described above, a dispersion containing (meth)acrylic resin particles as a dispersion medium can be obtained. By adding an alkali to the obtained dispersion to neutralize the carboxyl groups of the (meth)acrylic resin particles, water-soluble (meth)acrylic resin B can be produced.

[0281] Specific examples of alkalis include ammonia (ammonium hydroxide aqueous solution) and sodium hydroxide aqueous solution.

[0282] As an alkali, ammonia is preferred, for example, from the viewpoint of the adhesive properties of the coated film.

[0283] 〔water〕

[0284] The coating composition disclosed herein contains water.

[0285] There are no specific restrictions on the type of water.

[0286] As for water, distilled water, deionized water (also known as "ion-exchanged water"), and pure water are preferred, for example, from the viewpoint of having fewer impurities.

[0287] The water content in the coating composition disclosed herein is not particularly limited, but is preferably 35% to 50% by mass, more preferably 40% to 45% by mass, relative to the total mass of the coating composition.

[0288] [Other ingredients]

[0289] The coating compositions disclosed herein may contain, as needed, other components (so-called other components) without impairing their effectiveness.

[0290] Other components include, for example, aqueous media other than water.

[0291] As an aqueous medium other than water, examples include water-mixable organic solvents.

[0292] Examples of organic solvents that are water-miscible include monohydric alcohols such as methanol and ethanol; polyhydric alcohols such as glycerol, ethylene glycol, and propylene glycol; and dihydric alcohol derivatives such as ethylene glycol monoethyl ether and propylene glycol monobutyl ether.

[0293] In addition, other components include, for example, various additives such as preservatives, wetting agents, and defoamers.

[0294] [Gel content of the coating composition]

[0295] For the coating compositions disclosed herein, for example, the gelation rate at a temperature higher than the temperature at which the crosslinking of the self-crosslinking groups contained in the specific (meth)acrylic resin particles A occurs is preferably greater than the gelation rate at a temperature lower than the temperature at which the crosslinking of the self-crosslinking groups contained in the specific (meth)acrylic resin particles A occurs.

[0296] If the gelation rate of the coating composition disclosed herein meets the requirements described above, the coating composition disclosed herein tends to achieve a balanced combination of excellent coating on the surface of the electromagnetic steel sheet and the formation of a coating film exhibiting high adhesion under high temperature conditions when the electromagnetic steel sheets are bonded together.

[0297] The gel ratio of the coating composition disclosed herein is the proportion of solvent-insoluble components determined using ethyl acetate as the extraction solvent. Specifically, the gel ratio of the coating composition disclosed herein is determined according to the steps shown in [1] to

[17] below.

[0298] [1] Ammonia was added to the coating composition of this disclosure to adjust the pH to 8.5 (liquid temperature 25°C). Next, the resulting liquid was coated onto a release film made of polyethylene terephthalate (PET) with a thickness of 100 μm to form a coated film. Then, the formed coated film was dried at 105°C for 2 minutes to obtain a resin film with a release film.

[0299] [2] The obtained resin membrane with release film was cut into 75mm×75mm pieces. The weight of the resin membrane in the cut resin membrane with release film was about 0.2g.

[0300] [3] Prepare a 250-mesh stainless steel wire mesh (wire diameter: 0.03 mm, aperture: 72 μm) and cut it into 100 mm × 100 mm pieces. It should be noted that loose wires at the ends of the wire mesh can cause measurement errors and should be removed beforehand.

[0301] [4] The cut metal mesh was degreased with ethyl acetate and then dried. The dried metal mesh was stored in a desiccator.

[0302] [5] Determine the mass of the metal mesh correctly. Set the measured mass of the metal mesh as A (unit: g).

[0303] [6] After attaching the resin film with a release film of the above [2] cut to a size of 75mm × 75mm to the center of the metal mesh, the release film is peeled off from the resin film to obtain a metal mesh with a resin film. It should be noted that the resin film is attached to the metal mesh in such a way that the resin film is placed in the face of the metal mesh after it has been folded through the processes [7] to [9] described later.

[0304] [7] Fold the metal mesh with the resin film on the inside. Specifically, fold the metal mesh with the resin film so that the back edge of the metal mesh with the resin film overlaps with the edge near the front edge.

[0305] [8] Fold one-third of the front side (the side where the two sides overlap) of the folded metal mesh with resin film to the back side, and then fold one-third of the back side to the front side. At this moment, the metal mesh with resin film becomes a state where it is folded to one-sixth of its original size (100 mm) in the longitudinal direction and is not folded in the transverse direction.

[0306] [9] Fold the left third of the long side of the folded metal mesh with resin film in [8] to the right, and then fold the right third to the left. Use this as sample X1. Sample X1 changes from its original size (100 mm) to a size that is folded to one-sixth in the longitudinal direction and one-third in the transverse direction.

[0307]

[10] The mass of sample X1 was accurately determined using a precision balance. This mass is set as B (unit: g).

[0308]

[11] Staple the fold of specimen X1 to prevent it from opening. Use it as specimen X2. Make two specimens X2 for each specimen.

[0309]

[12] The mass of sample X2 was accurately determined using a precision balance. This mass is set as C (unit: g).

[0310]

[13] Place sample X2 into a glass bottle containing 80g of ethyl acetate and seal it.

[0311]

[14] The glass bottle containing sample X2 was placed in an atmosphere of 23°C and 50%RH for 3 days.

[0312]

[15] Remove sample X2 from the glass bottle and wash it with a small amount of ethyl acetate.

[0313]

[16] Sample X2 was dried at a drying temperature of 100°C for 24 hours. The mass of the dried sample X2 was accurately determined using a precision balance. This mass is denoted as D (unit: g).

[0314]

[17] The gelation rate is calculated by the following formula, and the obtained values ​​are arithmetically averaged.

[0315] Gel yield [mass %] = (D - (A + (C - B))) / (B - A) × 100

[0316] [Uses of the coating composition]

[0317] The coating composition disclosed herein is used to coat the surface of an electromagnetic steel sheet used in the manufacture of laminated steel sheets. The coating composition of this disclosure is capable of forming a coating film exhibiting high adhesion under high-temperature conditions when the electromagnetic steel sheets are bonded together, and has excellent spreadability. Specific applications include fixing electromagnetic steel sheets together during the manufacture of laminated steel sheets. The coating composition of this disclosure is, for example, suitable for use as an adhesive film for forming an electromagnetic steel sheet with an adhesive coating used in the manufacture of laminated steel sheets.

[0318] [Electromagnetic steel sheet]

[0319] Electromagnetic steel sheet is the steel sheet to which the adhesive coating is to be formed; there are no particular limitations.

[0320] Electromagnetic steel sheets can be either non-directional or directional.

[0321] Specifically, as an electromagnetic steel sheet, for example, non-directional electromagnetic steel sheet of JIS C 2552:2014, directional electromagnetic steel sheet of JIS C 2553:2019, or non-directional thin electromagnetic steel sheet or directional thin electromagnetic steel sheet of JIS C 2558:2015 can be used.

[0322] [Method for manufacturing coating composition]

[0323] The method for manufacturing the coating composition disclosed herein is not particularly limited.

[0324] The coating composition disclosed herein can be manufactured, for example, by mixing a dispersion of specific (meth)acrylic resin particles A and an aqueous solution of water-soluble (meth)acrylic resin B in a mass ratio [A / B] of 95 / 5 to 85 / 15.

[0325] There are no particular restrictions on the mixing method.

[0326] As a mixing method, for example, mixing by stirring can be cited.

[0327] Stirring can be done using general stirring utensils or stirring devices.

[0328] There is no particular limitation on the stirring temperature; for example, it is preferably 20°C to 30°C.

[0329] Example

[0330] The coating compositions of this disclosure will be described in more detail below through examples. However, this disclosure is not limited to the following examples as long as it does not deviate from its spirit.

[0331] [Preparation of the coating composition]

[0332] [Example 1]

[0333] 1. Manufacturing of (meth)acrylic resin particles A

[0334] In a stainless steel container, 54.4 parts by mass of n-butyl acrylate (n-BA; alkyl acrylate monomer), 169.5 parts by mass of methyl methacrylate (MMA; alkyl methacrylate monomer), 128.4 parts by mass of styrene (St; other monomers), 40 parts by mass of methacrylic acid (MAA; monomer with carboxyl groups), and 7.8 parts by mass of hydroxyethyl acrylamide (HEAA; monomer with self-crosslinking groups) were added and mixed to prepare a monomer mixture.

[0335] Next, in a separate stainless steel container, add 172.0 parts by weight of deionized water, 2.7 parts by weight of nonionic surfactant NOIGEN (registered trademark) EA-197D (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), 4.1 parts by weight of EMULGEN (registered trademark) A-60 (manufactured by Kao Corporation), and 2.7 parts by weight of anionic surfactant NEOPELEX (registered trademark) G-65 (manufactured by Kao Corporation), and stir to dissolve them to prepare an aqueous surfactant solution.

[0336] Next, the monomer mixture prepared above was slowly added to the surfactant aqueous solution while stirring with a stirrer to emulsify it, thus preparing a pre-emulsion. This pre-emulsion was then used for polymerization.

[0337] Polymerization was carried out in a constant temperature bath in a 7L (liters; the same applies below) flask equipped with a reflux cooling tube, a stirring device, a nitrogen inlet tube, a pre-emulsion droplet pump (trade name: Hi-Cera Pump V-10, manufactured by IWAKI Co., Ltd.), and a polymerization initiator addition device (trade name: metering pump MP-2000, manufactured by Tokyo Riko Machinery Co., Ltd.). Specifically, polymerization was carried out as follows.

[0338] After adding 162.4 parts by weight of deionized water to the flask, add a portion (17.5 parts by weight) of the pre-emulsion prepared above. Purge nitrogen into the flask at a flow rate of 300 ml / min while stirring at an arbitrary rotation speed (standard condition: 240 rpm; the same applies below) to raise the internal temperature of the flask to an arbitrary reaction temperature (standard condition: 62°C). After the internal temperature stabilizes, add 2.3 parts by weight of 24% by weight ammonium persulfate aqueous solution (polymerization initiator) and 2.3 parts by weight of 20% by weight sodium bisulfite aqueous solution (reducing agent), adjusting the nitrogen flow rate to 50 ml / min. After confirming the temperature rise in the flask, add the remaining pre-emulsion (564 parts by weight) dropwise over 270 minutes, and then add 63.4 parts by weight of 2.4% by weight ammonium persulfate aqueous solution (polymerization initiator) and 63.4 parts by weight of 2.0% by weight sodium bisulfite aqueous solution (reducing agent) dropwise over 360 minutes. Thirty minutes after the addition of ammonium persulfate aqueous solution and sodium bisulfite, 6.4 parts by weight of 6.9% tert-butyl hydroperoxide aqueous solution (polymerization initiator) and 6.4 parts by weight of 4.4% sodium hydroxymethanesulfonate aqueous solution (reducing agent) were added dropwise over a period of 30 minutes. The polymerization reaction was terminated 150 minutes after the addition of the pre-emulsion and then cooled to 30°C.

[0339] An aqueous dispersion of (meth)acrylic resin particles A was obtained by adding 1.3 parts by weight of a preservative (trade name: Topside 350, manufactured by Permachem Asia Co., Ltd.) and a wetting agent (trade name: SURFYNOL (registered trademark) 440, manufactured by Nissin Chemical Industry Co., Ltd.) to an emulsion polymer obtained by polymerization.

[0340] 2. Manufacturing of water-soluble (meth)acrylic resin B

[0341] In a stainless steel container, 126.2 parts by weight of methyl methacrylate (MMA; alkyl methacrylate monomer), 48.0 parts by weight of ethyl acrylate (EA; alkyl methacrylate monomer), 60.0 parts by weight of acrylic acid (AA; a monomer with a carboxyl group), 60.0 parts by weight of 2-hydroxyethyl methacrylate (2HEMA; a monomer with a hydroxyl group), and 5.8 parts by weight of hydroxyethyl acrylamide (HEAA; a monomer with a self-crosslinking group) were added and mixed to prepare a monomer mixture.

[0342] Next, in another stainless steel container, add 121.0 parts by weight of deionized water and 4.5 parts by weight of anionic surfactant LATEMUL (registered trademark) E-118B (manufactured by Kao Corporation), and stir to dissolve, thus preparing an aqueous solution of surfactant.

[0343] Next, the monomer mixture prepared above was slowly added to the surfactant aqueous solution while stirring with a stirrer to emulsify it, thus preparing a pre-emulsion. This pre-emulsion was then used for polymerization.

[0344] Polymerization was carried out in a constant temperature bath in a 7L flask equipped with a reflux cooling tube, a stirring device, a nitrogen inlet tube, a pre-emulsion droplet pump (trade name: Hi-Cera Pump V-10, manufactured by IWAKI Co., Ltd.), and a polymerization initiator addition device (trade name: metering pump MP-2000, manufactured by Tokyo Riko Machinery Co., Ltd.). Specifically, polymerization was carried out as follows.

[0345] Add 415 parts by weight of deionized water and 7.0 parts by weight of the anionic surfactant LATEMUL (registered trademark) E-118B (manufactured by Kao Corporation) to a flask, followed by a portion (8.5 parts by weight) of the pre-emulsion prepared above. Purge nitrogen gas into the flask at a flow rate of 300 ml / min while stirring at an arbitrary speed (standard condition: 150 rpm) to raise the internal temperature of the flask to an arbitrary reaction temperature (standard condition: 60°C). Then add 1.0 part by weight of 69.0% by weight tert-butyl hydroperoxide aqueous solution (polymerization initiator) and 2.5 parts by weight of 10.0% by weight sodium hydroxymethanesulfonate aqueous solution (reducing agent). After the internal temperature stabilizes, adjust the nitrogen flow rate to 50 ml / min. After adjustment, the remaining pre-emulsion (456.6 parts by mass) was added dropwise over 180 minutes, followed by the addition of 24.5 parts by mass of 6.9% tert-butyl hydrogen peroxide aqueous solution (polymerization initiator), 24.5 parts by mass of 1.2% sodium hydroxymethanesulfonate aqueous solution (reducing agent), and 39.6 parts by mass of 14.7% 2-mercaptoethanol (chain transfer agent) over 180 minutes, resulting in an aqueous dispersion of (meth)acrylic acid resin particles. 58 parts by mass of 25.0% ammonia water (alkaline aqueous solution) were added to the obtained aqueous dispersion of (meth)acrylic acid resin particles to dissolve them in water, yielding a water-soluble aqueous solution of (meth)acrylic acid resin B.

[0346] 3. Preparation of the coating composition

[0347] After mixing 300.0 parts by weight (137.1 parts by weight of solids) of an aqueous dispersion of (meth)acrylic resin particles A and 48.1 parts by weight (15.2 parts by weight of solids) of an aqueous solution of water-soluble (meth)acrylic resin B, an appropriate amount of deionized water was added to obtain a coating composition with a solid content concentration of 43.5% by weight.

[0348] The "solids concentration" mentioned here refers to the total mass ratio of (meth)acrylic resin particles A and water-soluble (meth)acrylic resin B in the coating composition. The same applies to the coating compositions manufactured below.

[0349] [Examples 2-10]

[0350] The monomer components of (meth)acrylic resin particles A and water-soluble (meth)acrylic resin B are respectively the monomer components shown in Table 1, and the mass ratio of (meth)acrylic resin particles A to water-soluble (meth)acrylic resin B [A / B] is the mass ratio shown in Table 1. Otherwise, the same operation as in Example 1 is performed to obtain a coating composition with a solid component concentration of 43.5% by mass.

[0351] [Examples 11-21]

[0352] The monomer components of (meth)acrylic resin particles A and water-soluble (meth)acrylic resin B are respectively the monomer components shown in Table 2, and the mass ratio of (meth)acrylic resin particles A to water-soluble (meth)acrylic resin B [A / B] is the mass ratio shown in Table 2. Otherwise, the same operation as in Example 1 is performed to obtain a coating composition with a solid component concentration of 43.5% by mass.

[0353] [Comparative Examples 1-8]

[0354] The monomer components of (meth)acrylic resin particles A and water-soluble (meth)acrylic resin B are respectively the monomer components shown in Table 3, and the mass ratio of (meth)acrylic resin particles A to water-soluble (meth)acrylic resin B [A / B] is the mass ratio shown in Table 3. Otherwise, the same operation as in Example 1 is performed to obtain a coating composition with a solid component concentration of 43.5% by mass.

[0355] [Comparative Example 9]

[0356] Perform the same operation as in the method for manufacturing (meth)acrylic resin particles A in Example 6 to obtain an aqueous dispersion of (meth)acrylic resin particles A.

[0357] Next, in the method for manufacturing (meth)acrylic resin particles A in Example 6, the monomer composition of the (meth)acrylic resin particles is the same as that shown in Table 4. Otherwise, the same operation as the method for manufacturing (meth)acrylic resin particles A in Example 6 is performed to obtain an aqueous dispersion of other (meth)acrylic resin particles C.

[0358] Next, 300.0 parts by weight (137.1 parts by weight of solids) of aqueous dispersion of (meth)acrylic resin particles A and 48.1 parts by weight (15.2 parts by weight of solids) of aqueous dispersion of other (meth)acrylic resin particles C were mixed, and an appropriate amount of deionized water was added to obtain a coating composition with a solid content concentration of 43.5% by weight.

[0359] [Comparative Example 10]

[0360] Perform the same operation as in the method for manufacturing (meth)acrylic resin particles A in Example 6 to obtain an aqueous dispersion of (meth)acrylic resin particles A.

[0361] Next, in the method for manufacturing (meth)acrylic resin particles A in Example 6, the monomer composition of the (meth)acrylic resin particles is the same as that shown in Table 4. Otherwise, the same operation as the method for manufacturing (meth)acrylic resin particles A in Example 6 is performed to obtain an aqueous dispersion of other (meth)acrylic resin particles C.

[0362] Next, 300.0 parts by weight (137.1 parts by weight of solids) of aqueous dispersion of (meth)acrylic resin particles A and 105.0 parts by weight (34.3 parts by weight of solids) of aqueous dispersion of other (meth)acrylic resin particles C were mixed, and an appropriate amount of deionized water was added to obtain a coating composition with a solid content concentration of 43.5% by weight.

[0363] The monomer composition (unit: mass%), glass transition temperature (Tg) (unit: °C), and average primary particle size (unit: nm) of the (meth)acrylic resin particles A in Examples 1-21 and Comparative Examples 1-10 are shown in Tables 1-4.

[0364] The glass transition temperature of (meth)acrylic resin particle A was determined by the same method as the method described above for determining the glass transition temperature of specific (meth)acrylic resin particle A.

[0365] The average primary particle size of (meth)acrylic resin particles A was determined by the same method as the method described above for determining the average primary particle size of specific (meth)acrylic resin particles A.

[0366] The monomer composition [unit: mass %] and weight-average molecular weight (Mw) of the water-soluble (meth)acrylic resin B in Examples 1-21 and Comparative Examples 1-8 are shown in Tables 1-3.

[0367] The weight-average molecular weight of water-soluble (meth)acrylic resin B was determined by the same method as described above for determining the weight-average molecular weight of water-soluble (meth)acrylic resin B.

[0368] It should be noted that the haze values ​​of the water-soluble (meth)acrylic resin B in Examples 1-21 and Comparative Examples 1-8, measured by the above method, were all below 3.0, thus confirming that it was a water-soluble (meth)acrylic resin.

[0369] The monomer composition (in mass %), glass transition temperature (Tg) (in °C), and average primary particle size (in nm) of the other (meth)acrylic resin particles C in Comparative Examples 9 and 10 are shown in Table 4.

[0370] The glass transition temperature of other (meth)acrylic resin particles C was determined by the same method as that used for determining the glass transition temperature of the specific (meth)acrylic resin particles A described above.

[0371] The average primary particle size of the other (meth)acrylic resin particles C was determined by the same method as the method used to determine the average primary particle size of the specific (meth)acrylic resin particles A described above.

[0372] [Determination of gelation rate of coating composition]

[0373] The gel rate of the coating compositions of Examples 1-21 and Comparative Examples 1-10 was determined by the same method as the method for determining the gel rate of the coating compositions disclosed above. Specifically, the determination was performed as follows.

[0374] (1) Fabrication of resin membrane with release film

[0375] (1-1) Gel content of the coating composition at 170°C

[0376] The coating composition was applied to a 100 μm thick polyethylene terephthalate (PET) release film using a 4 mil (101.6 μm) applicator to form a coated film. The coated film was then dried at room temperature (25°C) for 24 hours, followed by further drying at 170°C for 90 seconds to obtain a resin film X with a release film.

[0377] (1-2) Gel content of the coating composition at 200℃

[0378] The coating composition was applied to a 100 μm thick polyethylene terephthalate (PET) release film using a 4 mil (101.6 μm) applicator to form a coated film. The coated film was then dried at room temperature (25°C) for 24 hours, followed by further drying at 170°C for 90 seconds, and then at 200°C for 60 seconds, thereby obtaining a resin film Y with a release film.

[0379] (2) Determination of gelation rate

[0380] Using the obtained resin film X with a release film and resin film Y with a release film, the following operations of the above-described method for determining the gel rate of the coating composition of this disclosure were performed [2]. The results of the determination are shown in Tables 1 to 4.

[0381] [evaluate]

[0382] The coating compositions of Examples 1-21 and Comparative Examples 1-10 were evaluated as follows.

[0383] 1. Spreadable

[0384] Prepare an electromagnetic steel sheet measuring 2cm x 10cm (product number: 30HX1600, manufactured by Nippon Steel Corporation). Apply a coating composition diluted to 32% by mass of solids to the surface of the prepared electromagnetic steel sheet with a wet film thickness of 6.25μm. Then, dry the coated composition by heating it to 170°C for 90 seconds using a hot air circulating dryer. Observe the dried film using an optical microscope to confirm the presence and extent of craters and cracks. Then, evaluate according to the evaluation criteria described below. The evaluation results are shown in Tables 1-4.

[0385] In the following evaluation criteria, “AA”, “A” and “B” represent usable levels, with “B” being preferred, “A” being more preferred, and “AA” being even more preferred.

[0386] -Evaluation Criteria-

[0387] AA: No shrinkage cavities or cracks were detected.

[0388] A: Although a very small number of shrinkage cavities were identified, no cracks were identified.

[0389] B: Although a small number of shrinkage cavities and cracks were identified, the level is sufficient for practical use.

[0390] C: Obvious shrinkage cavities and cracks have been identified, indicating a level that poses practical problems.

[0391] 2. High-temperature adhesion

[0392] Prepare two 2cm x 10cm electromagnetic steel sheets (product number: 30HX1600, manufactured by Nippon Steel Corporation). Apply a coating composition diluted to 32% by mass of solids to the surface of the two prepared electromagnetic steel sheets, with a dried film thickness of 2μm. Then, dry the coated composition by heating it at 170°C for 90 seconds using a hot air circulating dryer, thus preparing evaluation samples. Arrange the two evaluation samples with an overlap area of ​​2cm x 2cm and perform hot pressing (temperature: 200°C, time: 60 seconds, pressure: 3MPa). Perform a tensile shear bond strength test on the hot-pressed evaluation samples at 150°C. The tensile shear bond strength test was conducted based on JIS K 6852:1994. Evaluation was performed based on the measured bond strength (also known as "high-temperature bond strength") according to the following evaluation criteria. The measured values ​​and evaluation results are shown in Tables 1-4.

[0393] In the following evaluation criteria, “AA”, “A” and “B” represent usable levels, with “B” being preferred, “A” being more preferred, and “AA” being even more preferred.

[0394] -Evaluation Criteria-

[0395] AA: Shear strength of adhesive is above 0.60MPa.

[0396] A: The shear strength is above 0.40 MPa and below 0.60 MPa.

[0397] B: The shear strength is above 0.20MPa and less than 0.40MPa.

[0398] C: The range where the shear bond strength is less than 0.20 MPa.

[0399] 3. Applicable period

[0400] 300 ml of the freshly prepared coating composition was placed in a sealed plastic bottle (a polyethylene container) and allowed to stand for 2 days at an ambient temperature of 25°C. The viscosity of the coating composition at 25°C was measured using a BH type viscometer (model: BHII, manufactured by Toki Kogyo Co., Ltd.). The obtained value was compared with the previously measured viscosity of the freshly prepared coating composition, and the evaluation was conducted according to the evaluation criteria described below. The evaluation results are shown in Tables 1-4.

[0401] In the evaluation criteria below, "A" represents a usable level.

[0402] -Evaluation Criteria-

[0403] A: Even after 2 days, the viscosity of the coating composition did not change.

[0404] B: The viscosity of the coating composition changes within 2 days after manufacturing.

[0405]

[0406]

[0407]

[0408]

[0409] The details of each monomer recorded in Tables 1 to 4 are shown below.

[0410] <Monomers with self-crosslinking groups>

[0411] “NMAM”: N-hydroxymethylacrylamide

[0412] “NBMA”: N-hydroxybutylacrylamide

[0413] “GMA”: Glycidyl methacrylate

[0414] <Monomers with self-crosslinking groups and hydroxyl groups>

[0415] "HEAA": Hydroxyethylacrylamide

[0416] <Monomers with carboxyl groups>

[0417] “MAA”: Methacrylic acid

[0418] “AA”: Acrylic acid

[0419] <Monomers with hydroxyl groups>

[0420] “2HEMA”: 2-Hydroxyethyl methacrylate

[0421] <Alkyl (meth)acrylate monomers>

[0422] “n-BA”: n-Butyl acrylate

[0423] “MMA”: Methyl methacrylate

[0424] “2EHA”: 2-Ethylhexyl acrylate

[0425] “EA”: Ethyl acrylate

[0426] <Other monomers>

[0427] "St": Styrene

[0428] "HDDA": 1,6-Hexanediol diacrylate

[0429] "AAM": Acrylamide

[0430] In Tables 1-4, the “-” in the monomer composition column indicates that no monomer equivalent to that column was used.

[0431] In Tables 1-4, the values ​​recorded in the monomer composition column are all converted values ​​of solid composition.

[0432] As shown in Tables 1-4, the coating composition of this disclosure exhibits superior spreadability compared to the coating composition of the comparative examples. Furthermore, the coating composition of this disclosure is capable of forming a coating film exhibiting high adhesion at a high temperature of 200°C. Additionally, the coating composition of this disclosure demonstrates excellent pot life.

[0433] The disclosure of Japanese Patent Application No. 2023-163623, filed on September 26, 2023, is incorporated herein by reference in its entirety.

[0434] The inclusion of all documents, patent applications and technical standards described herein by reference is equivalent to the inclusion of each document, patent application and technical standard by reference, specifically and individually.

Claims

1. A coating composition for laminated steel sheets, comprising (meth)acrylic resin particles A, water-soluble (meth)acrylic resin B, and water. The (meth)acrylic acid resin particles A contain constituent units from monomers having carboxyl groups at a ratio of 1% to less than 20% by mass relative to all constituent units, and contain constituent units from monomers having self-crosslinking groups at a ratio of 0.1% to 7% by mass relative to all constituent units, and have a glass transition temperature of 55°C or higher. The mass ratio of the (meth)acrylic resin particles A to the mass ratio of the water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15.

2. The coating composition for laminated steel sheets according to claim 1, wherein, The water-soluble (meth)acrylic resin B comprises constituent units derived from monomers having self-crosslinking groups.

3. The coating composition for laminated steel sheets according to claim 1 or 2, wherein, The water-soluble (meth)acrylic resin B comprises constituent units derived from monomers having hydroxyl groups.

4. The coating composition for laminated steel sheets according to claim 1 or 2, wherein, The average primary particle size of the (meth)acrylic resin particles A is 250 nm to 450 nm.

5. The coating composition for laminated steel sheets according to claim 1 or 2, wherein, The monomer with self-crosslinking groups in the (meth)acrylic resin particles A is selected from at least one of N-hydroxymethylacrylamide (NMAM), N-hydroxybutylacrylamide (NBMA), hydroxyethylacrylamide (HEAA), and glycidyl methacrylate (GMA).

6. The coating composition for laminated steel sheets according to claim 1 or 2, wherein, The content of the constituent units derived from monomers having self-crosslinking groups in the water-soluble (meth)acrylic resin B is 0.1% to 10.0% by mass relative to all the constituent units of the water-soluble (meth)acrylic resin B.

7. The coating composition for laminated steel sheets according to claim 1 or 2, wherein, The content of the constituent units derived from monomers having hydroxyl groups in the water-soluble (meth)acrylic resin B is 5% to 30% by mass relative to all the constituent units of the water-soluble (meth)acrylic resin B.

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