Resin composition, steel sheet having resin composition, motor core obtained by laminating steel sheets, and method for producing resin composition

Abstract

A purpose of the present invention is to obtain: a resin composition having excellent storage stability; and a steel sheet that has the resin composition and that exhibits excellent corrosion resistance after being aged. Another purpose of the present invention is to provide a motor core obtained by laminating the steel sheets.　This resin composition comprises an epoxy resin (A), a phenoxy resin (B), and a curing agent (C). The resin composition is characterized in that the maximum peak in the range of 4.0-7.5 ppm in a 1H NMR spectrum thereof is present between 6.5 ppm and 7.0 ppm.

Description

A resin composition, a steel sheet having the resin composition, a motor core formed by laminating the steel sheets, and a method for manufacturing the resin composition.

[0001] The present invention relates to a resin composition, a steel sheet having the resin composition, a motor core formed by laminating steel sheets, and a method for producing the resin composition.

[0002] Traditionally, steel sheets have been used as components in automobiles, home appliances, and other products. While steel sheets undergo processing and heating before being used as components, they are stored in a humid environment during this time. Furthermore, even after becoming components, they are exposed to similar environments, and in some cases, rainwater or seawater, which can cause corrosion and the formation of red or black rust, potentially reducing their aesthetic appeal. Additionally, electrical steel sheets, which possess excellent magnetic properties, are widely used, but corrosion in electrical steel sheets can also reduce their magnetic properties. Therefore, appropriate surface treatment is required for steel sheets.

[0003] Patent Document 1 attempts to improve the corrosion resistance of steel plates using a UV-curing resin composition.

[0004] Patent Document 2 attempts to improve the corrosion resistance of steel plates by using a mixture of resins and crosslinking agents.

[0005] Japanese Patent Publication No. 2015-503022, Japanese Patent Publication No. 2012-131907

[0006] Generally, in the case of steel sheets to which a resin composition is applied, the resin composition is first applied to the surface of the steel sheet and dried, forming a steel sheet having the resin composition.

[0007] In the circumstances described above, the inventors evaluated the resin composition and found that its storage stability was insufficient, making it difficult to apply and dry on steel plates, and that the corrosion resistance of the steel plates with the resin composition after time had passed was also insufficient.

[0008] In other words, for resin compositions and steel sheets coated with resin compositions to continue exhibiting their inherent properties even under usage conditions that include moisture, the resin compositions must have high storage stability and high corrosion resistance even after a long period of time.

[0009] However, with conventional resin compositions, the bonding of inorganic compounds contained in the environment with the resin, or the reaction between the crosslinking agent and the resin, proceeds, making it extremely difficult to obtain a resin composition with excellent storage stability, and a steel sheet with excellent corrosion resistance over time after the resin composition has been applied and dried.

[0010] The following relationship typically exists between the storage stability of a resin composition and the corrosion resistance of a steel sheet coated with the resin composition: If the storage stability of the resin composition is low, the resin film formed on the surface of the coated steel sheet becomes uneven. As a result, when subjected to a salt spray test to evaluate corrosion resistance, areas with low barrier function against salt water and oxygen become the starting points for corrosion, and the corrosion resistance decreases as red rust progresses.

[0011] Therefore, the present invention aims to provide a resin composition with excellent storage stability and a steel sheet having a resin composition with excellent corrosion resistance. Furthermore, it aims to provide a motor core formed by laminating the steel sheets.

[0012] The present inventors have discovered that a resin composition containing an epoxy resin (A), a phenoxy resin (B), and a curing agent (C) can achieve a desired effect by having hydrogen atoms in a specific electronic state, and have arrived at the present invention.

[0013] (1) A resin composition containing epoxy resin (A), phenoxy resin (B), and a curing agent (C), １ A resin composition characterized in that the maximum peak in the 1H NMR spectrum, in the range of 4.0 ppm to 7.5 ppm, is between 6.5 ppm and 7.0 ppm.

[0014] (2) The resin composition according to (1), characterized in that the mass ratio of the epoxy resin (A) in the solid content is 85% by mass or less, the mass ratio of the phenoxy resin (B) in the solid content is 90% by mass or less, and the mass ratio of the curing agent (C) in the solid content is 30% by mass or less.

[0015] (3) The resin composition according to (1) or (2), characterized in that the epoxy resin (A) comprises an epoxy resin having an epoxy equivalent of 115 to 1050.

[0016] (4) The resin composition according to any one of (1) to (3), characterized in that the mass ratio of sulfur in the solid content is 0.3% by mass or more and 10.0% by mass or less.

[0017] (5) A steel sheet having the resin composition described in any one of (1) to (4) on its surface.

[0018] (6) The steel sheet according to (5), characterized in that the steel sheet is a non-oriented electrical steel sheet.

[0019] A motor core characterized by being formed by laminating the steel plates described in (7) and (6).

[0020] (8) A method for producing a resin composition according to any one of (1) to (4), wherein the raw epoxy resin (A) and curing agent (C) are mixed in a sealed container maintained at 30°C to 45°C using a stirrer at a rotation speed of 500 to 1000 rpm, and then phenoxy resin (B), maintained at 35°C to 50°C, is added and mixed for 10 to 60 minutes using a stirrer at a rotation speed of 500 to 800 rpm.

[0021] The resin composition of the present invention has excellent storage stability, and a steel sheet having the resin composition on its surface has excellent corrosion resistance. Furthermore, a motor core formed by laminating the steel sheets has excellent corrosion resistance.

[0022] The embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is just one example of an embodiment of the present invention, and the present invention is not limited to the following unless its essence is changed.

[0023] In this specification, when the expression "~" is used, it is used to mean an expression that includes the numbers before and after it.

[0024] Unless otherwise specified, the methods for producing each component described herein are not particularly limited. Examples include conventionally known methods.

[0025] In this specification, when the storage stability of the resin composition of the present invention is more excellent, it may be referred to as "the effect of the present invention is more excellent". The same applies to the steel plate of the present invention and the motor core formed by laminating the same when the corrosion resistance is more excellent.

[0026] The resin composition which is one embodiment of the present invention contains an epoxy resin (A), a phenoxy resin (B), and a curing agent (C). Hereinafter, each component will be described.

[0027] <Epoxy resin (A)> The resin composition which is one embodiment of the present invention contains an epoxy resin (A). By containing the phenoxy resin (A), the storage stability of the resin composition can be enhanced.

[0028] [Mass ratio of epoxy resin (A)] The epoxy resin (A) has the effect of enhancing the corrosion resistance of the steel plate, and generally, the higher the mass ratio, the more preferable. Therefore, for the epoxy resin (A), the mass ratio in the solid content of the resin composition may be 1% by mass or more, and may also be 3% by mass or more, 5% by mass or more, or 10% by mass or more. The upper limit of the mass ratio is not particularly limited, but since the mass ratio of other components (such as phenoxy resin (B)) in the resin composition may become too small, for the epoxy resin (A), the mass ratio in the solid content of the resin composition may be 85% by mass or less, and may also be 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0029] [Epoxy equivalent of epoxy resin (A)] The epoxy resin (A) preferably contains an epoxy resin having an epoxy equivalent of 115 to 1050. Alternatively, it is more preferable that the epoxy resin (A) is an epoxy resin having an epoxy equivalent of 115 to 1050. When the epoxy equivalent is less than 115, the reactivity with the curing agent (C) may become too high and the stability may be reduced. On the other hand, when the epoxy equivalent exceeds 1050, the solubility in the solvent decreases, which may reduce the storage stability. In addition, when the epoxy resin polymerizes a certain structure - (CH ２ -CH ２ -CH ２ ) ｎWhen it has a repeating unit represented by a formula such as, etc., the repeating unit may be regarded as one molecule.

[0030] The epoxy equivalent of the epoxy resin (A) is measured by a method conforming to JIS K7236:2009.

[0031] From the viewpoint that the effects of the present invention are more excellent, the epoxy equivalent of the epoxy resin (A) is more preferably 185 or more and 630 or less, and further preferably 204 to 320.

[0032] [Type of epoxy resin (A)] Although the type of the epoxy resin (A) is not limited, the following examples can be cited. Epoxy resins having an N,N-diglycidylamino group, bisphenol A type epoxy resins, cresol novolak type epoxy resins, phenol novolak type epoxy resins, etc.

[0033] The epoxy resin (A) may be at least one selected from the group consisting of nitrogen-containing epoxy resins, epoxy resins having an N,N-diglycidylamino group, bisphenol A type epoxy resins, cresol novolak type epoxy resins, phenol novolak type epoxy resins, bisphenol F type epoxy resins, phenol novolak type epoxy resins, bisphenol fluorene type epoxy resins, tert-butyl-catechol type epoxy resins, naphthalene type epoxy resins, glycidylamine type epoxy resins, cresol novolak type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexanedimethanol type epoxy resins, trimethylol type epoxy resins, and halogenated epoxy resins.

[0034] The epoxy resin (A) may be at least one selected from the group consisting of nitrogen-containing epoxy resins, epoxy resins having N,N-diglycidylamino groups, bisphenol A type epoxy resins, cresol novolac type epoxy resins, phenol novolac type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, bisphenol fluorene type epoxy resins, tert-butyl-catechol type epoxy resins, naphthalene type epoxy resins, glycidylamine type epoxy resins, cresol novolac type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, and alicyclic epoxy resins.

[0035] The epoxy resin (A) may be at least one selected from the group consisting of nitrogen-containing epoxy resins, epoxy resins having N,N-diglycidylamino groups, bisphenol A type epoxy resins, cresol novolac type epoxy resins, and phenol novolac type epoxy resins.

[0036] An epoxy resin having an N,N-diglycidylamino group may further have epoxy groups other than the N,N-diglycidylamino group (for example, epoxy groups such as glycidyl groups and glycidyloxy groups). In a nitrogen-containing epoxy resin, an epoxy group such as an N,N-diglycidylamino group can be bonded to a divalent or higher linking group. Examples include hydrocarbon groups, and hydrocarbon groups having aromatic hydrocarbon groups are preferred.

[0037] Cresol novolac epoxy resins are reaction products of common cresol novolac resins and epichlorohydrin.

[0038] Phenol novolac-type epoxy resins are reaction products of common phenol novolac resins and epichlorohydrin.

[0039] The epoxy resin (A) may have two or more epoxy groups in one molecule. In addition to monofunctional epoxy resins having one epoxy group in one molecule, examples include difunctional, trifunctional, tetrafunctional, pentafunctional, and hexafunctional epoxy resins (epoxy resins each having two to six epoxy groups in one molecule).

[0040] Examples of the bifunctional epoxy resins mentioned above include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, hydrogenated bisphenol A-type epoxy resin, bisphenol S-type epoxy resin, brominated bisphenol A-type epoxy resin, and bisphenol AF-type epoxy resin, as well as epoxy resins having bisphenyl groups, such as biphenyl-type epoxy resins.

[0041] When the composition of the present invention contains multiple types of epoxy resins, it is preferable that at least one of them be a bifunctional epoxy resin, and more preferably a bisphenol A type epoxy resin.

[0042] <Phenoxy resin (B)> One embodiment of the present invention is a resin composition containing phenoxy resin (B). By containing phenoxy resin (B), the storage stability of the resin composition can be improved.

[0043] The following reasons are possible: When the resin composition contains epoxy resin (A) and a curing agent (C), the reaction between the epoxy resin (A) and the curing agent (C) proceeds, which can increase the viscosity of the resin composition. When the resin composition further contains phenoxy resin (B), the phenoxy resin (B) prevents the reaction between the epoxy resin (A) and the curing agent (C). As a result, the increase in the viscosity of the resin composition is suppressed.

[0044] Phenoxy resin (B) has the effect of improving the storage stability of the resin composition, and a higher mass ratio of phenoxy resin (B) in the solid content of the resin composition is generally preferable. For this reason, the mass ratio of phenoxy resin (B) in the solid content of the resin composition may be 1% by mass or more, 2% by mass or more, 5% by mass or more, or 10% by mass or more. There is no particular upper limit to this mass ratio. However, because the molecular weight of phenoxy resin is relatively high, if the mass ratio of phenoxy resin (B) in the solid content is too high, the following problems may occur. For example, it may exceed the solubility of phenoxy resin in the resin composition. The viscosity of the resin composition may increase. The storage stability of the resin composition may decrease. For this reason, the mass ratio of phenoxy resin (B) in the solid content of the resin composition may be 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0045] In addition to improving storage stability, the above resin composition can enhance corrosion resistance when applied to steel plates. The reason for this is thought to be as follows: Because phenoxy resin is thermoplastic and has a relatively high molecular weight, it has the function of providing a barrier that prevents corrosive factors such as saltwater and oxygen from reaching the steel plate. As a result, the above resin composition can enhance corrosion resistance when applied to steel plates over time.

[0046] Furthermore, a resin obtained by increasing the molecular weight of a low molecular weight epoxy compound is called a phenoxy resin, and the above-mentioned phenoxy resin (B) does not contain the above-mentioned epoxy resin (A). The above-mentioned phenoxy resin (B) does not contain the additive (D) described later. In addition, phenoxy resin (B) is thermoplastic and does not undergo a reaction that increases its molecular weight through a chemical reaction with other components such as a curing agent, i.e., a crosslinking reaction. On the other hand, epoxy resin (A) is thermosetting and has the ability to undergo a crosslinking reaction with other components.

[0047] The phenoxy resin (B) may or may not have epoxy groups.

[0048] [Type of Phenoxy Resin (B)] The phenoxy resin (B) is not particularly limited, and examples thereof include a sulfur-containing phenoxy resin, a phenoxy resin having a naphthalene skeleton, a phenoxy resin having a biphenyl skeleton, a phosphorus-containing phenoxy resin, a fluorene-containing phenoxy resin, a phenoxy resin having a bisphenol skeleton, a phenoxy resin having a novolak skeleton, and the like.

[0049] The phenoxy resin (B) may be at least one selected from the group consisting of a sulfur-containing phenoxy resin, a phenoxy resin having a naphthalene skeleton, a phenoxy resin having a biphenyl skeleton, a phosphorus-containing phenoxy resin, a fluorene-containing phenoxy resin, a phenoxy resin having a bisphenol skeleton, a phenoxy resin having a novolak skeleton, a phenoxy resin containing a sulfone group, and a phenoxy resin containing a chloride.

[0050] The phenoxy resin (B) may be at least one selected from the group consisting of a sulfur-containing phenoxy resin, a phenoxy resin having a naphthalene skeleton, a phenoxy resin having a biphenyl skeleton, a phosphorus-containing phenoxy resin, a fluorene-containing phenoxy resin, a phenoxy resin having a bisphenol skeleton, a phenoxy resin containing a sulfone group, and a phenoxy resin containing a chloride.

[0051] The phenoxy resin (B) may be at least one selected from the group consisting of a sulfur-containing phenoxy resin, a phosphorus-containing phenoxy resin, a phenoxy resin having a bisphenol skeleton, a phenoxy resin containing a sulfone group, and a phenoxy resin containing a chloride.

[0052] The phenoxy resin (B) may be at least one selected from the group consisting of a phosphorus-containing phenoxy resin, a phenoxy resin having a bisphenol skeleton, and a phenoxy resin containing a sulfone group.

[0053] [Molecular Weight of Phenoxy Resin (B)] The molecular weight of the phenoxy resin (B) is not particularly limited, but -(CH ２ -CH ２ -CH ２ ) ｎIt is preferable that the molecular weight of the repeating unit represented by formulas such as - is between 100 and 400. Having a molecular weight between 100 and 400 increases the flexibility of the molecule. As a result, the steel plate to which the resin composition is applied has excellent corrosion resistance.

[0054] [Mass-average molecular weight of phenoxy resin (B)] From the viewpoint of achieving superior effects of the present invention, the mass-average molecular weight of phenoxy resin (B) is preferably 30,000 to 500,000, and more preferably 35,000 to 100,000. If the mass-average molecular weight of phenoxy resin (B) is less than 30,000, sufficient toughness cannot be obtained, and if it exceeds 100,000, the viscosity of the resin composition increases, which may make uniform application to the steel plate difficult.

[0055] In this invention, the mass-average molecular weight (Mw) of the phenoxy resin (B) is the standard polystyrene equivalent value measured by gel permeation chromatography (GPC) using tetrahydrofuran as the solvent. The mass-average molecular weight (Mw) of the phenoxy resin corresponds to the sum of the amounts obtained by multiplying the molecular weight of each component by their mass ratio, and is calculated by the method described in JIS K 7252-2:2016.

[0056] [Glass transition temperature of phenoxy resin (B)] In a resin composition according to one embodiment of the present invention, the glass transition temperature (Tg) of the phenoxy resin (B) in the uncured state, as determined by differential scanning calorimetry (DSC measurement), is preferably greater than 100°C. When the Tg of the phenoxy resin (B) contained in the resin composition exceeds 100°C, the cured resin product obtained from the composition of the present invention has excellent corrosion resistance.

[0057] <Curing Agent (C)> One embodiment of the present invention, a resin composition, contains a curing agent (C). The inclusion of curing agent (C) results in superior corrosion resistance of the steel plate to which the resin composition is applied. This is presumed to be due to the effect of the reaction between curing agent (C) and epoxy resin (A), which causes the molecules to chemically bond stably, thereby reducing the number of voids in the resin composition that serve as pathways for water and salt to permeate.

[0058] [Type of curing agent (C)] In the present invention, the type of curing agent (C) is not particularly limited. However, it is preferable that the curing agent (C) is a latent curing agent. Latent curing agents have extremely low reactivity from room temperature (25°C) to 60°C. Therefore, the resin composition has excellent stability. Furthermore, since the reaction with the epoxy resin proceeds when the temperature is raised by heating or the like, the cured product has excellent corrosion resistance.

[0059] As the latent curing agent, an amine-based latent curing agent is preferred. The amine-based latent curing agent has a nitrogen atom and can function as a curing agent for epoxy resin (A).

[0060] Examples of curing agents (C) include 4,4'-diaminodiphenylsulfone (DDS), modified polyamines, hydrazides, dicyandiamides, DCMU, ureas such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea, imidazole compounds such as 2-ethyl-4-methylimidazole, and melamine. These may be used individually or in combination of two or more.

[0061] From the viewpoint of achieving superior effects of the present invention, the curing agent (C) preferably contains at least one selected from the group consisting of ureas, 4,4'-diaminodiphenylsulfone, dicyandiamide, and imidazole compounds.

[0062] The curing agent (C) may be at least one selected from the group consisting of acid anhydrides such as phthalic anhydride, pyromellitic anhydride, and trimellitic anhydride; amines such as 4,4'-diaminodiphenylsulfone (DDS), metaphenylenediamine, diaminodiphenylmethane (DDM), modified polyamines, hydrazides, dicyandiamide, piperidine, and triethylenediamine; ureas such as DCMU and 3-(3,4-dichlorophenyl)-1,1-dimethylurea; imidazole compounds such as 2-methylimidazole, epoxy-imidazole adduct, and 2-ethyl-4-methylimidazole; polyamide resins; and melamine.

[0063] The curing agent (C) may be at least one selected from the group consisting of 4,4'-diaminodiphenylsulfone (DDS), modified polyamines, hydrazides, dicyandiamides, DCMU, ureas such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea, imidazole compounds such as 2-ethyl-4-methylimidazole, and melamine.

[0064] The curing agent (C) may be at least one selected from the group consisting of ureas, 4,4'-diaminodiphenylsulfone, dicyandiamide, and imidazole compounds.

[0065] The curing agent (C) may be at least one selected from the group consisting of 4,4'-diaminodiphenylsulfone and dicyandiamide.

[0066] [Mass ratio of curing agent (C)] The mass ratio of curing agent (C) (or the total mass ratio of the multiple types of curing agents (C) if curing agent (C) includes multiple types of curing agents (C)) is generally preferable as it is higher, from the viewpoint of achieving superior effects of the present invention such as corrosion resistance. For this reason, the mass ratio of curing agent (C) in the solid content of the resin composition may be 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more. There is no particular upper limit to this mass ratio, but if it exceeds 30% by mass, the volume ratio occupied by the curing agent in the resin composition becomes high, resulting in an excess relative to the resin that is the target of the curing reaction. In other words, there will be a large amount of curing agent that does not have a stable chemical bond with the resin. As a result, pathways for oxygen and water to enter in corrosive environments will be created, which may reduce corrosion resistance. Therefore, the mass ratio of the solid content in the resin composition may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less.

[0067] The mass ratio of the curing agent (C) is determined by dissolving the resin composition in methanol and measuring it by high-performance chromatography. The mass ratio can be determined using a calibration curve prepared in advance with reagents.

[0068] The latent curing agent (C) is preferably an amine-based curing agent having an amine equivalent of 15 to 70. If the amine equivalent of the amine-based curing agent is less than 15, the curing reaction may occur locally within the resin composition, which may reduce the corrosion resistance of the steel sheet coated with the resin composition. On the other hand, if the amine equivalent is greater than 70, there will be a large amount of curing agent that does not form a stable chemical bond with the resin, which can become a pathway for oxygen and water to penetrate in a corrosive environment, which may reduce the corrosion resistance of the steel sheet coated with the resin composition.

[0069] <Additive (D)> From the viewpoint of having superior toughness of the resulting cured resin product, it is preferable that the resin composition, which is one embodiment of the present invention, further contains additive (D).

[0070] Additive (D) refers to a compound that can further impart toughness to the resulting resin composition. Preferably, additive (D) is composed of a flexible polymer.

[0071] Examples of additives (D) include core-shell type additives, rubber-modified epoxy resins, and urethane-modified epoxy resins.

[0072] Additive (D) is not included in the epoxy resin (A), phenoxy resin (B), or curing agent (C). In other words, additive (D) may contain an epoxy resin different from epoxy resin (A).

[0073] Additive (D) may or may not react with the curing agent (C), epoxy resin (A), or phenoxy resin (B).

[0074] [Type of Additive (D)] From the viewpoint of superior toughness, it is preferable that additive (D) includes at least one selected from the group consisting of rubber-modified epoxy resin, core-shell type, and urethane-modified epoxy resin.

[0075] (Rubber-modified epoxy resin) Rubber-modified epoxy resin is an epoxy resin having two or more epoxy groups and a rubber backbone. Examples of rubbers that form the above backbone include polybutadiene and acrylonitrile butadiene rubber (NBR).

[0076] (Core-shell type additive) In one preferred embodiment, the core-shell type additive may be in particulate form. The core-shell type additive consists of a core layer and a shell layer. Examples of core-shell type additives include rubber particles with a two-layer structure in which the outer shell layer is a glassy polymer and the inner core layer is a rubbery polymer, and rubber particles with a three-layer structure in which the outer shell layer is a glassy polymer, the intermediate layer is a rubbery polymer, and the core layer is a glassy polymer. The glassy polymer is composed of, for example, a polymer of methyl (meth)acrylate and / or a polymer of styrene. The rubbery polymer layer is composed of, for example, a polymer of butyl acrylate (butyl rubber), silicone rubber, or polybutadiene.

[0077] (Urethane-modified epoxy resin) Urethane-modified epoxy resin is an epoxy resin having two or more epoxy groups and a polyurethane skeleton. The polyurethane forming the above skeleton is not particularly limited as long as it is a polymer having multiple urethane bonds and / or urea bonds.

[0078] [Mass Ratio of Additive (D)] When the resin composition, which is one embodiment of the present invention, further contains additive (D), the mass ratio of additive (D) is preferable for achieving better effects such as toughening. From this viewpoint, a higher mass ratio is generally preferable. For this reason, the mass ratio of additive (D) in the solid content of the resin composition may be 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more. The upper limit of this mass ratio is not particularly limited, but if it exceeds 40% by mass, the toughening effect and other effects may decrease. For this reason, the mass ratio in the solid content of the resin composition may be 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less. If additive (D) contains multiple types of additive (D), the total mass ratio of the above multiple types of additive (D) shall be considered the mass ratio of additive (D).

[0079] [Sulfur Mass Ratio] In a resin composition according to one embodiment of the present invention, the sulfur mass ratio in components other than the solvent (solid content of the resin composition) may be 0.3% by mass or more and 10.0% by mass or less. This further enhances the storage stability of the resin composition. The sulfur may be derived from phenoxy resin (B). When the sulfur mass ratio is within this range, electrical attractive forces such as hydrogen bonds and van der Waals forces are generated between the epoxy resin (A) and the sulfur, further stabilizing the resin composition. That is, it prevents the reaction between the epoxy resin (A) and the curing agent (C) from proceeding in the resin composition. If the sulfur mass ratio exceeds 10.0% by mass, the reaction between the sulfur and the curing agent will proceed, which may actually decrease the storage stability.

[0080] Furthermore, it is preferable to set the sulfur mass ratio within the above range because it improves the corrosion resistance of the steel sheet to which the resin composition is applied. This is presumed to be because when the sulfur mass ratio is 0.3% by mass or higher, the polarity of the resin composition when applied to the steel sheet increases, and the adhesion between the resin composition and the metal surface improves.

[0081] The mass ratio of sulfur can be measured using CHNS organic elemental analysis, as described in Japanese Industrial Standard M 8819:1997.

[0082] <Other Additives> A resin composition according to one embodiment of the present invention may further contain various additives (additives other than additive (D)) to the extent that the effects of the present invention are exhibited. Examples of additives include fillers, reaction retarders, antioxidants, pigments, dyes, plasticizers, silane coupling agents, thixotropy-imparting agents, adhesion-imparting agents, flame retardants, antistatic agents, ultraviolet absorbers, surfactants, dispersants, dehydrating agents, and solvents.

[0083] [Solvent] To improve the manufacturability of the resin composition, a solvent may be used. Examples of solvents include alcohol-based solvents such as ethanol and propanol, ketone-based solvents such as acetone, methyl ethyl ketone (MEK), and cyclohexanone, ester-based solvents such as ethyl acetate and butyl acetate, aliphatic solvents such as n-hexane, alicyclic solvents such as cyclohexane, and aromatic solvents such as toluene, xylene, and cellosolve acetate.

[0084] The amount of solvent is not particularly limited as a mass ratio to the solid content, but it is preferably between 20% by mass and 900% by mass. Below 20% by mass, the viscosity becomes high, making the resin composition difficult to handle and potentially reducing productivity. Above 900% by mass, the manufacturability during liquid production and application to the steel sheet is poor, potentially increasing costs.

[0085] The method for producing a resin composition according to one embodiment of the present invention is not particularly limited, but for example, an epoxy resin (A), a phenoxy resin (B), and a curing agent (C) may be used as needed. The resin composition may also have additives (D) (for example, epoxy compounds other than epoxy resin (A)), other additives, or solvents added. The resin composition can also be produced by mixing using stirring or the like.

[0086] <Resin composition １ H NMR spectrum > A resin composition, which is one embodiment of the present invention, when subjected to nuclear magnetic resonance spectroscopy (NMR) measurement, １ In the 1H NMR spectrum, the maximum peak in the range of 4.0 ppm to 7.5 ppm is located between 6.5 ppm and 7.0 ppm. This contributes to improved storage stability.

[0087] The mechanism by which resin compositions with peaks in the above range have increased storage stability is not clear, but the following is a possible explanation. １In the 1H NMR spectrum, peaks appear in the 4.0–7.5 ppm range for H atoms in various situations (bonding position in the molecule, partner atom (C, O, N, etc.)). The peak position depends on the bonding position and partner atom (i.e., polarity), and the peak intensity depends on the abundance ratio. H atoms with peaks in the 6.5–7.0 ppm range are located in an environment derived from hydrocarbon groups (aromatic, etc.) and have a less reactive electronic state. By having such a specific electronic state, the affinity between the epoxy group of the epoxy resin molecule and the curing agent (C) is moderately inhibited in the resin composition. In other words, it is thought to play a role in preventing the reaction between the epoxy resin and the curing agent from proceeding, which would increase the molecular weight and raise the viscosity of the entire resin composition, thus improving storage stability.

[0088] resin composition １ In the 1H NMR spectrum, the storage stability of the resin composition decreases when the maximum peak in the range of 4.0 ppm to 7.5 ppm is in the range of 4.0 ppm to less than 6.5 ppm or greater than 7.0 ppm and 7.5 ppm or less. The reason for this is unclear. However, when a peak is in the above range, the presence of relatively polar atoms or groups of atoms near the H atoms makes it less likely for the affinity between the epoxy groups of the epoxy resin molecule and the curing agent (C) to be inhibited. As a result, the reaction between the epoxy resin molecule and the curing agent (C) proceeds more easily, which may lead to a decrease in resin stability.

[0089] Furthermore, when the maximum peak is in the range of 6.6 ppm to 6.9 ppm, the storage stability of the resin composition is superior. The reason for this is not clear, but it is possible that the overall polarity of the resin composition makes it difficult for the reaction between the resin and the curing agent to proceed in liquid.

[0090] The sample preparation method and measurement conditions are shown below. １ The sample for 1H NMR spectroscopy is prepared as follows: Weigh out 1 g of the resin composition. If the resin composition contains a solvent, weigh out 1 × 10⁻¹⁶ g. －４Under vacuum conditions below Pa, the solvent is removed by standing at 40°C for 48 hours, and 1 g of the resin composition is weighed. The sample is dissolved in deuterated chromium form to a concentration of 1% by mass, and the resulting liquid is filtered using type 5C filter paper as specified in JIS P 3801:1995 filter paper (for chemical analysis). １ It will be used for 1H NMR measurement. １ The measurement parameters for the 1H NMR spectrum were set as follows: measurement sensitivity of 42, linebroadening factor (BF) of 0.25 Hz, number of data points (POINT) of 26214, OBFRQ of 600 MHz, FREEQ of 12019 Hz, number of scans of 32, and PD (pulsing delay) of 15 seconds. The peak (7.24 ppm) originating from deuterated chloroform was to be ignored. That is, １ In the 1H NMR spectrum, the largest peak, excluding the peak originating from the solvent (deuterated chloroform), is 6.5–7.0 ppm. For example, by measuring at Toray Research Center, Inc. １ A 1H NMR spectrum can be obtained.

[0091] The resin composition to be measured may be a resin composition applied to a steel plate (resin coating), or a slurry-like resin composition (for example, the resin composition before it is applied to the steel plate). Both resin compositions have excellent storage stability (i.e., the resin composition is uniform, and no components are localized). Therefore, the 1H NMR peak of the resin coating will be the same as the peak of the slurry-like resin composition within the range described above. In other words, it can be assumed that there is almost no change in the environment where hydrogen is present after the solvent has been removed from the slurry and after it has been heated to form a coating.

[0092] A resin composition according to one embodiment of the present invention exhibits excellent storage stability. Furthermore, by applying the resin composition to a steel plate, a steel plate with excellent corrosion resistance can be obtained. A motor core formed by laminating such steel plates can also have excellent corrosion resistance.

[0093] <Steel Plate> The steel plate used in one embodiment of the present invention is not particularly limited. The plate thickness is preferably 0.1 mm or more and 5 mm or less. The steel plate may be a non-directional electrical steel plate. A base layer may be provided between the steel plate and the resin composition in order to further improve the corrosion resistance of the steel plate and the adhesion of the resin composition.

[0094] The type of underlayer is not particularly limited, but examples include zinc plating layers, aluminum plating layers, zinc-aluminum alloy plating layers, zinc-aluminum-magnesium plating layers, zinc-aluminum-magnesium-silicon plating layers, and zinc-iron alloy plating layers. Methods for forming the plating include electroplating, hot-dip plating, and flux plating.

[0095] Furthermore, the underlayer may contain metal oxides or metal salts. Examples of metal oxides include zinc oxide, aluminum oxide, and silicon oxide, while examples of metal salts include zinc phosphate and aluminum phosphate. Organic materials may also be included. Examples of organic materials include resins composed of carbon, hydrogen, nitrogen, and oxygen, silane coupling agents, wax components, and pigments.

[0096] The above-mentioned underlayer may be provided between the steel plate and the resin composition, either alone or in combination.

[0097] One embodiment of the present invention, a steel sheet having a resin composition on its surface, can be obtained by applying the resin composition to the surface of the steel sheet and drying it. A typical manufacturing method is shown below, but is not limited thereto.

[0098] <Manufacturing Method> [Mixing Process] The mixing process is a process of mixing the raw materials of the resin composition to obtain a uniform resin composition. First, the raw materials epoxy resin (A) and curing agent (C) are mixed in a sealed container maintained at 30°C to 45°C using a stirrer at a rotation speed of 500 to 1000 rpm. The mixing time is 10 to 60 minutes. If the viscosity of the epoxy resin (A) is high and a solvent is used, the epoxy resin (A) is added to the solvent which has been maintained at 30°C to 50°C beforehand, and mixed for 30 to 60 minutes. Next, the phenoxy resin (B) maintained at 35°C to 50°C and any optional additives (D) are added. After addition, the mixture is mixed for 10 to 60 minutes using a stirrer at a rotation speed of 500 to 800 rpm. Normally, the epoxy resin and curing agent are not mixed first in order to prevent the curing reaction from progressing, but mixing in the order described above improves the uniformity of the resin composition. Furthermore, this resin composition also improves the corrosion resistance of steel plates having it on their surface.

[0099] [Coating Process] The coating process is the process of applying the resin composition to the steel plate. The method of applying the above resin composition to the steel plate is not particularly limited. Examples include the roll coater method, gravure coater method, air doctor coater method, plate coater method, knife coater method, rod coater method, kiss coater method, bead coater method, cast coater method, rotary screen method, slot orifice coater method, spray coating method, inkjet method, spin coating method, and electrodeposition coating method.

[0100] In the coating process, the resin composition may be applied to at least one surface of the steel plate.

[0101] [Drying process] After applying the resin composition, the drying temperature for removing the solvent from the resin composition is preferably 150 to 220°C, and more preferably 160 to 200°C. After the drying process (or after the application process if there is no drying process), a steel sheet coated with the resin composition according to one embodiment of the present invention can be obtained.

[0102] Examples of drying methods in the drying process include hot air drying, induction heating, and vacuum heating.

[0103] (Thickness of the resin composition after coating) After the coating process, the thickness of the resin composition after coating and drying is preferably 0.3 to 20 μm, more preferably 0.5 to 10 μm, and particularly preferably 1 to 5 μm, from the viewpoint of corrosion resistance and the like.

[0104] (Motor Core) A motor core is a core component of a motor. A motor core consists of a rotor core, which is fixed around the motor's rotation axis (output shaft), and a stator core, which is fixed to the motor case coaxially with the rotor core and generates rotational force on the rotor through the interaction of electromagnetic forces between the rotor's outer circumference and its own inner circumference when the motor is in use. However, both are sometimes collectively referred to as the motor core. A motor core can be manufactured by laminating many sheets of material punched into a predetermined shape from non-oriented electrical steel sheets and fixing them together by crimping, screwing, welding, etc. The steel sheets obtained as described above have excellent corrosion resistance. A motor core can also be obtained by laminating these steel sheets. This motor core also has excellent corrosion resistance. It is preferable that the steel sheets used for the motor core are non-oriented electrical steel sheets because they have excellent magnetic properties.

[0105] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0106] <Example 1> Resin composition A resin composition was prepared by mixing epoxy resin (A) and curing agent (C) under the solid content mass ratio (mass%) and temperature conditions shown in Table 1, and then adding and mixing phenoxy resin (B) and additive (D).

[0107]

[0108] Furthermore, the details of each component shown in Table 1 are as follows.

[0109] [Epoxy Resin (A)] ・(A)-1: Cresol novolac type epoxy resin: Product name YDCN-704A, manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(A)-2: Nitrogen-containing epoxy resin: Product name jER-604, manufactured by Mitsubishi Chemical Corporation. ・(A)-3: Nitrogen-containing epoxy resin: Epoxy equivalent weight 97. Product name EP-3950E, manufactured by ADEKA Corporation.

[0110] [Phenoxy Resins (B)] ・(B)-1: PKHH: Phenoxy resin having a bisphenol skeleton. Manufactured by Huntsman Corporation. ・(B)-2: PKHP-200: Phenoxy resin having a bisphenol skeleton. Manufactured by Huntsman Corporation. ・(B)-3: ERF-001M30: Phosphorus-containing phenoxy resin. Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-4: YP-50: Phenoxy resin having a bisphenol skeleton. Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-5: YPS-70: Phenoxy resin having a bisphenol skeleton. Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-6: YPS-007A30: Phenoxy resin containing sulfone groups. Manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0111] [Curing agent (C)] (Amine-based latent curing agent) ・(C)-1: 4,4'-diaminodiphenylsulfone, DDS manufactured by Wakayama Seika Kogyo Co., Ltd. ・(C)-2: Dicyandiamide, EH-3636AS manufactured by ADEKA Corporation

[0112] [Additives (D)] ・(D)-1: EPR-21 (rubber-modified epoxy): Rubber-modified epoxy resin. Product name EPR-21, manufactured by ADEKA Corporation. ・(D)-2: Kaneace MX-154 additive. Product name Kaneace MX-154, manufactured by Kaneka Corporation.

[0113] [Solvents] • (S)-1: Xylene • (S)-2: Toluene • (S)-3: Cyclohexanone • (S)-4: Ethanol

[0114] <Evaluation of Resin Composition> The resin composition was held at 40°C for 48 hours under vacuum. This removed the solvent contained in the resin composition. 1 g was recovered from the obtained sample, 1 to 10 g of deuterated chloroform was added, and the component dissolved at 25°C was filtered to obtain the liquid component, which was then recovered. １ Samples were prepared for 1H NMR spectroscopy. １ The 1H NMR spectrum was measured at Toray Research Center, Inc. １ The position of the maximum peak in the 4.0 ppm to 7.5 ppm range of the 1H NMR spectrum was identified.

[0115] Furthermore, the storage stability of the resin composition was evaluated as follows: ・A mixture of the resin composition diluted with a solvent was prepared. (100 g of the mixture was prepared by adding the solvent at 25°C so that the solid content concentration of the resin composition was 25%.) ・The mixture was sealed in a 50 mm diameter, 30 mL capacity polypropylene airtight container to a volume of 90% or more. ・The airtight container was stirred and mixed at a rotation speed of 100 rpm, and then stored under specified conditions. (The resin composition was stored in the airtight container at 30-40°C for 3-8 weeks.) ・During storage, the airtight container was sealed with a lid closed to isolate it from the outside air. ・The environment was atmospheric air with a relative humidity of 40% or less. ・After the storage period, the airtight container was stirred and mixed again, and the presence or absence of gel-like substances was visually checked.

[0116] These evaluation results are shown in Table 1.

[0117] [Evaluation Criteria] In this invention, the storage stability of the resin composition was evaluated according to the following criteria. After the above-mentioned storage period, the sealed container containing the resin composition was stirred at a rotation speed of 100 rpm for 5 minutes. After standing for 10 minutes, the presence or absence of gel-like substance was visually checked. If a lumpy substance was present at a position lower than half the height from the liquid surface to the bottom, it was determined that gel-like substance had formed. Score 5: No gel-like substance formed after 8 weeks of storage in a sealed container at 40°C. Score 4: No gel-like substance formed after 6 weeks of storage in a sealed container at 40°C. Score 3: No gel-like substance formed after 6 weeks of storage in a sealed container at 30°C. Score 2: No gel-like substance formed after 3 weeks of storage in a sealed container at 30°C. Score 1: Gel-like substance formed after 3 weeks of storage in a sealed container at 30°C. If multiple criteria (scores) are met, the higher score is used.

[0118] <Example 2> A resin composition was produced by mixing epoxy resin (A) and curing agent (C) under the solid content mass ratio (mass%) and temperature conditions shown in Table 2, and then adding phenoxy resin (B) and additive (D) and mixing them together.

[0119]

[0120] Furthermore, the details of each component shown in Table 2 are as follows.

[0121] [Epoxy Resin (A)] ・(A)-1: Nitrogen-containing epoxy resin: Epoxy equivalent 97. Product name EP-3950E, manufactured by ADEKA Corporation. ・(A)-2: Nitrogen-containing epoxy resin: Product name jER-604, manufactured by Mitsubishi Chemical Corporation. Epoxy equivalent 115 ・(A)-3: Bisphenol A type epoxy resin: Product name Adekarezin EP-4300E, manufactured by ADEKA Corporation. Epoxy equivalent 185. ・(A)-4: Cresol novolac type epoxy resin: Product name YDCN-704A, manufactured by Nippon Steel Chemical & Material Co., Ltd. Epoxy equivalent 204. ・(A)-5: Epoxy resin: Product name Sumiepoxy ELM-100H, manufactured by Sumitomo Chemical Co., Ltd. Epoxy equivalent 320. ・(A)-6: Epoxy resin: Product name Adekarezin EP-4000E, manufactured by ADEKA Corporation. Epoxy equivalent 320. ・(A)-7: Epoxy resin: Product name Adeka Resin EP-5100-75X, manufactured by ADEKA Corporation. Epoxy equivalent 630. ・(A)-8: Epoxy resin: Product name jER-1005F, manufactured by Mitsubishi Chemical Corporation. Epoxy equivalent 1050. ・(A)-9: Epoxy resin: Product name jER-1007FS, manufactured by Mitsubishi Chemical Corporation. Epoxy equivalent 1300.

[0122] [Phenoxy resin (B)] ・(B)-1: PKHH: Manufactured by Huntsman Corporation ・(B)-2: PKHP-200: Manufactured by Huntsman Corporation ・(B)-3: ERF-001M30: Phosphorus-containing phenoxy resin. Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-4: YP-50: Product name YP-50, manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-5: YPS-70: Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-6: YP-50EK35: Manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0123] [Curing agent (C)] (Amine-based latent curing agent) ・(C)-1: 4,4'-diaminodiphenylsulfone, DDS manufactured by Wakayama Seika Kogyo Co., Ltd. ・(C)-2: Dicyandiamide, EH-3636AS manufactured by ADEKA Corporation

[0124] [Additives (D)] ・(D)-1: Product name KaneAce MX-153, manufactured by Kaneka Corporation. ・(D)-2: Product name KaneAce MX-154, manufactured by Kaneka Corporation. ・(D)-3: Product name KaneAce MX-960, manufactured by Kaneka Corporation. ・(D)-4: Product name KaneAce MX-136, manufactured by Kaneka Corporation. ・(D)-5: Product name KaneAce MX-217, manufactured by Kaneka Corporation. ・(D)-6: Product name KaneAce MX-257, manufactured by Kaneka Corporation. ・(D)-7: Product name KaneAce MX-416, manufactured by Kaneka Corporation.

[0125] [Solvents] • (S)-1: Xylene • (S)-2: Toluene • (S)-3: Ethanol • (S)-4: Cyclohexanone

[0126] <Evaluation of Resin Composition> The resin composition was held at 40°C for 48 hours under vacuum to evaporate the solvent. After recovering 1 g of the solid residue, 1 to 10 g of deuterated chloroform was added, and the liquid component obtained by filtering the dissolved component at 25°C was recovered. １ Samples were prepared for 1H NMR spectroscopy. １ The 1H NMR spectrum was measured at Toray Research Center, Inc. １ The position of the maximum peak in the 4.0 ppm to 7.5 ppm range of the 1H NMR spectrum was identified.

[0127] Furthermore, the storage stability of the resin composition was evaluated. The evaluation criteria were the same as in Example 1.

[0128] These evaluation results are shown in Table 2.

[0129] <Example 3> A resin composition was produced by mixing epoxy resin (A) and curing agent (C) under the solid content mass ratio (mass%) and temperature conditions shown in Table 3, then adding phenoxy resin (B) and additive (D), and mixing them together.

[0130]

[0131] Furthermore, the details of each component shown in Table 3 are as follows.

[0132] [Epoxy resin (A)] ・(A)-1: Cresol novolac type epoxy resin: Product name YDCN-704A, manufactured by Nippon Steel Chemical & Material Co., Ltd. Epoxy equivalent 204. ・(A)-2: Nitrogen-containing epoxy resin: Product name jER-604, manufactured by Mitsubishi Chemical Corporation. Epoxy equivalent 115.

[0133] [Phenoxy resin (B)] ・(B)-1: PKHH: Manufactured by Huntsman Corporation ・(B)-2: PKHP-200: Manufactured by Huntsman Corporation ・(B)-3: ERF-001M30: Phosphorus-containing phenoxy resin. Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-4: YP-50: Product name YP-50, manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-5: YPS-70: Manufactured by Nippon Steel Chemical & Material Co., Ltd. ・(B)-6: YPS-007A30: Manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0134] [Curing agent (C)] (Amine-based latent curing agent) ・(C)-1: 4,4'-diaminodiphenylsulfone, DDS manufactured by Wakayama Seika Kogyo Co., Ltd. ・(C)-2: Dicyandiamide, EH-3636AS manufactured by ADEKA Corporation

[0135] [Additives (D)] ・(D)-1: EPR-21 (rubber-modified epoxy): Rubber-modified epoxy resin. Product name EPR-21, manufactured by ADEKA Corporation. ・(D)-2: Kaneace MX-154 additive, manufactured by Kaneka Corporation.

[0136] [Solvents] • (S)-1: Xylene • (S)-2: Toluene • (S)-3: Cyclohexanone • (S)-4: Ethanol

[0137] <Evaluation of Resin Composition> After holding the resin composition at 40°C for 48 hours under vacuum, 1 g was recovered, 1 to 10 g of deuterated chloroform was added, and the liquid component obtained by filtration after dissolving the component at 25°C was recovered. １ Samples were prepared for 1H NMR spectroscopy.

[0138] １ The 1H NMR spectrum was measured at Toray Research Center, Inc. １ The position of the maximum peak in the 4.0 ppm to 7.5 ppm range of the 1H NMR spectrum was identified.​

[0139] Furthermore, the storage stability of the resin composition was evaluated. The evaluation criteria were the same as in Example 1.

[0140] These evaluation results are shown in Table 3.

[0141] <Example 4> <Evaluation of Corrosion Resistance of Steel Sheet with Resin Composition> A resin composition was prepared with the composition (mass ratio) shown in Table 4. The resin composition was stored in a sealed container at 30°C. After three weeks, the resin composition was applied to a cold-rolled steel sheet with a thickness of 0.5 mm by the roll coater method, and the sheet was dried to a maximum plate temperature of 150°C in 30 seconds to produce a steel sheet with a resin composition thickness of 5 μm after drying. The steel sheet with the resin composition was cut to a size of 150 mm x 70 mm, the edges and back surface were sealed, and then subjected to a salt spray test (SST) as specified in Japanese Industrial Standard JIS Z 2371. The corrosion resistance was evaluated by the percentage of red rust generated after a predetermined time. The evaluation results are shown in Table 4. Score 5: Red rust area percentage less than 3% after 48 hours of SST Score 4: Red rust area percentage 3% or more but less than 10% after 48 hours of SST Score 3: Red rust area percentage 10% or more but less than 30% after 48 hours of SST Score 2: Red rust area percentage 30% or more but less than 50% after 48 hours of SST Score 1: Red rust area percentage 50% or more after 48 hours of SST

[0142] <Analysis and Evaluation of Resin Composition on Steel Plate> The resin composition was collected by peeling off only the film component (solid) from the steel plate using a cutter knife or similar tool (hereinafter referred to as the collected material). To confirm that the collected material did not contain Fe, a component of the original steel plate, it was measured in advance using ICP (Inductively Coupled Plasma). If it was confirmed that the element (Fe) was present in the collected material, a re-collection was performed to collect a sample containing only the film component (solid) excluding that element. Then, 1 g of the solid component was recovered, 1 to 10 g of deuterated chloroform was added, and the liquid component obtained by filtering the dissolved component at 25°C was recovered. １ Samples were prepared for 1H NMR spectroscopy. １ The 1H NMR spectrum was measured at Toray Research Center, Inc. １ The position of the maximum peak in the 4.0 ppm to 7.5 ppm range of the 1H NMR spectrum was identified.

[0143]

[0144] As shown in Table 1, in Comparative Examples a1 to a18, either epoxy resin or phenoxy resin is not included, or at least one of the following is outside the preferred temperature range: pre-mixing holding temperature of curing agent (C) (°C), pre-mixing holding temperature of phenoxy resin (B) (°C), pre-mixing holding temperature of additive (D) (°C), rotation speed after raw material mixing (rpm), stirring time after raw material mixing (minutes), and epoxy resin (A) temperature (°C). １ In the 1H NMR spectrum, the maximum peak position in the range of 4.0 ppm to 7.5 ppm was at 5.7 ppm or 7.3 ppm, resulting in a storage stability score of 1. On the other hand, inventive examples A1 to A13 contained epoxy resin, phenoxy resin, a curing agent, and additives, and the maximum peak positions were at 6.5 ppm, 6.6 ppm, 6.8 ppm, 6.7 ppm, or 7.0 ppm, demonstrating excellent storage stability (score of 2).

[0145] As shown in Table 2, Invention Examples B2-B4 and B6-B17, in which the epoxy equivalent of epoxy resin A was 115-1050 and the proportion of phenoxy resin in the solid content was 5% by mass or more and 80% by mass or less, showed superior storage stability (score 3).

[0146] As shown in Table 3, Invention Examples C2, C3, C4, C6, C7, C8, C9, C11, C12, and C13, in which the S ratio in the solid content was 0.3 to 10.0% by mass, exhibited even better storage stability.

[0147] Furthermore, the steel plates produced using the liquids used in Table 1 (No. A4), Table 2 (No. B2, B3), and Table 3 (No. C4, No. C5) exhibited excellent corrosion resistance, as shown in Table 4.

[0148] Based on these results, the resin composition of the present invention exhibited excellent storage stability. Furthermore, the steel plate treated with the resin composition showed excellent corrosion resistance.

Claims

1. A resin composition containing epoxy resin (A), phenoxy resin (B), and a curing agent (C), １ A resin composition characterized in that the maximum peak in the 1H NMR spectrum, in the range of 4.0 ppm to 7.5 ppm, is between 6.5 ppm and 7.0 ppm.

2. The resin composition according to claim 1, characterized in that the mass ratio of the epoxy resin (A) in the solid content is 85% by mass or less, the mass ratio of the phenoxy resin (B) in the solid content is 90% by mass or less, and the mass ratio of the curing agent (C) in the solid content is 30% by mass or less.

3. The resin composition according to claim 1, characterized in that the epoxy resin (A) comprises an epoxy resin having an epoxy equivalent of 115 to 1050.

4. The resin composition according to any one of claims 1 to 3, characterized in that the mass ratio of sulfur in the solid content is 0.3% by mass or more and 10.0% by mass or less.

5. A steel sheet having the resin composition according to any one of claims 1 to 3 on its surface.

6. The steel sheet according to claim 5, characterized in that it is a non-oriented electrical steel sheet.

7. A motor core characterized by being formed by laminating the steel plates described in claim 6.

8. A method for producing a resin composition, comprising mixing raw epoxy resin (A) and a curing agent (C) in a sealed container maintained at 30°C to 45°C using a stirrer at a rotation speed of 500 to 1000 rpm, then adding phenoxy resin (B) maintained at 35°C to 50°C, and mixing for 10 to 60 minutes using a stirrer at a rotation speed of 500 to 800 rpm.

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