Cationic electrodeposition coating composition and method for producing a cationic electrodeposition coating composition

Abstract

This invention provides a cationic electrodeposition coating composition that maintains coating properties such as corrosion resistance while exhibiting good low-temperature curing properties. A cationic electrodeposition coating composition comprises an amination epoxy resin (A) and a polyisocyanate curing agent (B), wherein the polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) selected from polyisocyanates selected from 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers.

Description

Technical Field

[0001] This invention relates to cationic electrodeposition coating compositions and methods for manufacturing cationic electrodeposition coating compositions. Background Technology

[0002] Cationic electrodeposition coating compositions are widely used as primers to impart corrosion resistance to industrial products such as automobiles. These compositions are typically water-based, containing amino-based epoxy resins and polyisocyanate curing agents. Due to their water-based nature, they offer the advantage of low environmental impact.

[0003] In recent years, with increasing awareness of environmental issues, low-temperature curing properties are required even in water-based coating compositions. For example, WO2019 / 039467 (Patent Document 1) describes how low-temperature curing properties can be improved by using emulsion particles containing Michael addition reaction donor components and emulsion particles containing Michael addition reaction acceptor components in cationic electrodeposition coating compositions.

[0004] Existing technical documents Patent documents Patent document 1: WO2019 / 039467. Summary of the Invention

[0005] The problem that the invention aims to solve The purpose of this invention is to provide a cationic electrodeposition coating composition that has good low-temperature curing properties while maintaining coating properties such as corrosion resistance.

[0006] Methods for solving problems To address the aforementioned issues, the present invention provides the following solution.

[0007] [1] A cationic electrodeposition coating composition comprising an amination epoxy resin (A) and a polyisocyanate curing agent (B), The polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) selected from polyisocyanate compounds in 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers. The equivalence ratio of the hydroxyl equivalent of the amination epoxy resin (A) to the isocyanate equivalent of the polyisocyanate curing agent (B), NCO / OH, is greater than 0.5 and less than 3.1.

[0008] [2] According to the cationic electrodeposition coating composition of [1], wherein the blocking agent used in the preparation of the blocked polyisocyanate compound (B1) comprises one or more selected from oxime compounds, pyrazole compounds, imidazole compounds and triazole compounds.

[0009] [3] According to the cationic electrodeposition coating composition of [1] or [2], wherein the Tg of the coating film cured by dynamic viscoelasticity determination of the mixture of the amination epoxy resin (A) and the polyisocyanate curing agent (B) at 135°C for 25 minutes is 65°C or higher and 95°C or lower.

[0010] [4] A method for manufacturing a cationic electrodeposition coating composition, comprising the following steps: The process of preparing the blocked polyisocyanate compound (B1); and The process of mixing a polyisocyanate curing agent (B) containing the blocked polyisocyanate compound (B1) with an amination epoxy resin (A) to prepare an amination epoxy resin emulsion. The blocked polyisocyanate compound (B1) is formulated by blocking a polyisocyanate compound selected from 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers with a blocking agent. The blocking agent comprises one or more selected from oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds.

[0011] Invention Effects In this invention, the polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) selected from polyisocyanate compounds in 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers, and the equivalence ratio (NCO / OH) of the hydroxyl equivalent of the amination epoxy resin (A) and the isocyanate group equivalent of the polyisocyanate curing agent (B) is 0.5 or more and less than 3.1, thereby having the following advantages: ensuring coating properties such as corrosion resistance, while exhibiting good low-temperature curing properties. Detailed Implementation

[0012] The cationic electrodeposition coating composition disclosed herein comprises an amination epoxy resin (A) and a polyisocyanate curing agent (B). The polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) selected from 1,5-pentamethylene diisocyanate and its polymers, and the equivalence ratio (NCO / OH) of the amination epoxy resin (A) to the polyisocyanate curing agent (B) is 0.5 or more and less than 3.1. The specific requirements will be described below.

[0013] Amine epoxy resin (A) Amination epoxy resin (A) is a film-forming resin. In amination epoxy resin (A), at least one ethylene oxide ring (also referred to as "epoxy group") of the epoxy resin is amination. Amination epoxy resin (A) is preferably contained in the electrodeposition coating composition in the form of a resin emulsion together with a polyisocyanate curing agent (B).

[0014] The number average molecular weight of the amination epoxy resin (A) is, for example, 1,000 or more and 7,000 or less. If the number average molecular weight is 1,000 or more, the rust resistance and solvent resistance of the resulting cured electrodeposited coating are easily improved. If the number average molecular weight is 7,000 or less, the viscosity of the amination epoxy resin (A) becomes easier to adjust, allowing for smooth synthesis, and the emulsification and dispersion of the resulting amination epoxy resin (A) becomes easier. The number average molecular weight of the amination epoxy resin (A) can be 1,500 or more and 4,000 or less.

[0015] The number-average molecular weight of the amination epoxy resin (A) is the converted value of styrene homopolymer obtained by gel permeation chromatography.

[0016] The amine value of the amination epoxy resin (A) is, for example, 20 mg KOH / g or higher and 100 mg KOH / g or lower. If the amine value of the amination epoxy resin (A) is 20 mg KOH / g or higher, the stability of the emulsification and dispersion of the amination epoxy resin (A) in the coating composition becomes good. If the amine value is 100 mg KOH / g or lower, the amount of amino groups in the cured electrodeposited coating film is appropriate, and the decrease in the water resistance of the coating film is suppressed. The amine value of the amination epoxy resin (A) can be 20 mg KOH / g or higher and 80 mg KOH / g or lower.

[0017] The amine value can be determined according to ASTM D2073 using the following method. (1) Accurately weigh 500mg of amination epoxy resin into a 200ml Erlenmeyer flask. (2) Add about 50ml of glacial acetic acid and dissolve evenly. (3) Add 5-6 drops of indicator (methyl violet solution) and stir well. (4) Titrate with 0.1N perchloric acid acetic acid solution until the spot turns bright green, which is the endpoint. The above (3) and (4) can be replaced by potentiometric titration.

[0018] The amination epoxy resin (A) may have hydroxyl groups, and the hydroxyl value of the amination epoxy resin (A) is, for example, 150 mg KOH / g or more and 650 mg KOH / g or less. If the hydroxyl value is 150 mg KOH / g or more, the curability of the coating composition is improved, and the appearance of the coating film is also improved. If the hydroxyl value is 650 mg KOH / g or less, the amount of residual hydroxyl groups in the cured electrodeposited coating film is appropriate, and the water resistance of the coating film is easily improved. In one embodiment, the hydroxyl value of the amination epoxy resin (A) is 150 mg KOH / g or more, 180 mg KOH / g or more, 200 mg KOH / g or more, 250 mg KOH / g or more, 300 mg KOH / g or more, 350 mg KOH / g or more, 400 mg KOH / g or more, 450 mg KOH / g or more, 500 mg KOH / g or more, 550 mg KOH / g or more, or 600 mg KOH / g or more. In another embodiment, the hydroxyl value of the amination epoxy resin (A) component is 650 mg KOH / g or less, 600 mg KOH / g or less, 550 mg KOH / g or less, 500 mg KOH / g or less, 450 mg KOH / g or less, 400 mg KOH / g or less, 350 mg KOH / g or less, 300 mg KOH / g or less, 250 mg KOH / g or less, or 200 mg KOH / g or less. In yet another embodiment, the hydroxyl value of component (A) is 180 to 300 mg KOH / g.

[0019] The hydroxyl value can be obtained by neutralization titration using an aqueous solution of potassium hydroxide as described in JIS K 0070.

[0020] In particular, when the number average molecular weight of the amination epoxy resin (A) is in the range of 1,000 to 7,000, the amine value is 20 to 100 mg KOH / g, and the hydroxyl value is 150 to 650 mg KOH / g (preferably 150 to 400 mg KOH / g), the rust resistance of the coated object can be further improved.

[0021] The coating composition may contain multiple aminated epoxy resins (A) with different amine values ​​and / or hydroxyl values. In this case, the average amine value and average hydroxyl value calculated based on the mass ratio of the multiple aminated epoxy resins (A) are preferably within the aforementioned ranges. Preferably, the multiple aminated epoxy resins (A) include aminated epoxy resins with an amine value of 20-50 mg KOH / g and a hydroxyl value of 50-300 mg KOH / g, and aminated epoxy resins with an amine value of 50-200 mg KOH / g and a hydroxyl value of 200-500 mg KOH / g. This makes the core of the emulsion more hydrophobic and the shell more hydrophilic, thus easily further improving the rust resistance of the coated object.

[0022] Amination of epoxy resin (A) can be obtained by reacting the epoxy groups of the above-mentioned epoxy resin with an amine compound.

[0023] (Epoxy resin) The epoxy resin used as the starting material for the amination epoxy resin (A) is, for example, the reaction product of a polycyclic phenolic compound and epichlorohydrin, namely, a polyphenolic polyglycidyl ether type epoxy resin. Examples of such polycyclic phenolic compounds include bisphenol A, bisphenol F, bisphenol S, phenolic varnish, and cresol varnish. In this specification, the term "polyphenolic polyglycidyl ether type epoxy resin" includes the state in which the polyphenolic polyglycidyl ether type epoxy resin undergoes alternating and continuous chain extension reactions with a polycyclic phenolic compound.

[0024] As the aforementioned epoxy resin, a product obtained by chain extension reaction of a portion of the epoxy resin before modification with an amine compound can be used. In the chain extension reaction, for example, difunctional polyester polyols, polyether polyols, dicarboxylic acids, etc., can be used. Examples of the aforementioned polyether polyols include polyols containing polyethylene oxide and polypropylene oxide. Thus, for example, when using a polypropylene oxide-containing polyol for the chain extension reaction, a polypropylene oxide-containing epoxy resin is formed. The content of the polypropylene oxide-containing epoxy resin is preferably 1 to 40 parts by mass, more preferably 15 to 25 parts by mass, relative to 100 parts by mass of epoxy resin. Examples of epoxy resins with the same form as the polypropylene oxide-containing epoxy resin include epoxy resins obtained by chain extension reaction of polyphenolic polyglycidyl ether type epoxy resin, polycyclic phenolic compounds, and polypropylene oxide-containing epoxy resin.

[0025] Amination-modified epoxy resin (A) is obtained by reacting the epoxy groups of the aforementioned epoxy resin with an amine compound. The epoxy groups of the aforementioned epoxy resin are completely consumed through the reaction with the aforementioned amine compound, leaving substantially no residue in the molecule of the amination-modified epoxy resin (A).

[0026] (amine compounds) As the amine compound, the amine compound commonly used in the manufacture of amination-modified epoxy resins is used. Examples of commonly used amine compounds include: primary amines such as butylamine, octylamine, and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine, and N-methylethanolamine; and complex amines such as diethylenetriamine. The aforementioned primary amines can be controlled by forming a ketone imine group using ketone compounds, through a process known as blocking. Examples of amine compounds that have a ketone imine group or a diketone imine group include: ketone imine of aminoethylethanolamine, diketone imine of diethylenetriamine, etc. Examples of ketone compounds that generate a ketone imine group include: methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), diethyl ketone (DEK), ethylbutyl ketone (EBK), ethylpropyl ketone (EPK), dipropyl ketone (DPK), methyl ethyl ketone (MEK), etc., with methyl isobutyl ketone (MIBK) being preferred. Tertiary amines can also be used as amine compounds. Specific examples include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine. These amines can be used alone or in combination with two or more.

[0027] During amination, the amine compound is preferably used in an amount of 0.9 equivalents or more and 1.2 equivalents or less relative to the 1 equivalent of epoxy groups present in the raw epoxy resin. The amination reaction conditions can be appropriately selected according to the reaction scale, etc. For example, the reaction can be carried out at 80°C or higher and 150°C or lower for 0.1 hours or more and 5 hours or less, or at 120°C or higher and 150°C or lower for 0.5 hours or more and 3 hours or less.

[0028] In one aspect of the present invention, the following approach may be cited: as an amine compound for modifying the ethylene oxide ring (also called "epoxy group") of an epoxy resin, an amine compound having at least one of a primary amino group, a secondary amino group, and a tertiary amino group other than a ketoimine (including a diketoimine).

[0029] When it is necessary to control the molecular weight distribution of ammoniated epoxy resin to a narrow range, especially when it is necessary to control the molecular weight distribution below 2.7, selecting a specific type of amine compound has advantages such as ease of control. Specifically, for example, the following scheme can be adopted: the amine compound is a combination of a first amine and a second amine, and the first amine has the formula: NH2-(CH2)n-NR 11 R 12 (1) (In equation (1), R) 11 and R 12 Same or different, indicating alkyl groups with 1 to 6 carbon atoms that may have a hydroxyl group at the end, where n represents an integer from 2 to 4; The second amine has the formula: R 13 R 14 NH (2) (In equation (2), R) 13 and R 14 This refers to an alkyl group with 1 to 4 carbon atoms and a terminal hydroxyl group. It is believed that if these amine compounds are used, the primary amino group of the first amine will first react with the epoxy resin and be consumed, leaving only the secondary amino group. This secondary amino group reacts with the epoxy group of the epoxy resin, so there is no preference in reactivity, and the reaction proceeds uniformly, thus allowing control over the molecular weight distribution. It is also believed that the tertiary amino group present in the first amine or the tertiary amino group generated in the reaction of the secondary amino group will also react with the epoxy group to form a quaternary ammonium group, but this reaction is considered to be less frequent.

[0030] The first amine described above has the above formula (1), wherein R 11 and R 12 Specifically, it is methyl, ethyl, propyl, or butyl, and may have a hydroxyl group at the end. Furthermore, n is 2 to 4, preferably 3. Specific examples of the first amine include: aminopropyl diethanolamine, dimethylaminopropyl diamine, diethylaminopropyl diamine, dibutylaminopropyl diamine, etc. The above-mentioned second amine is a secondary amine having the above formula (2), which has R bonded to the nitrogen atom. 13 and R 14 The compound, wherein R 13 and R 14 All of them have an alkyl group with 1 to 4 carbon atoms containing a hydroxyl group. Specifically, examples of second amines include diethanolamine or diethanolamine.

[0031] In another aspect of the invention, the amine compound used for amination may comprise an amine compound having a ketimine group or a diketimine group.

[0032] The coating composition may, as needed, contain aminated resins other than aminated epoxy resin (A), such as aminated acrylic resins, aminated polyester resins, etc. The coating composition may also contain other film-forming resins besides the aforementioned aminated resins. Examples of other film-forming resins include: hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, polyurethane resins, butadiene-based resins, phenolic resins, and xylene resins. Of the film-forming resins in the coating composition that react with the curing agent to form a film, 80% by mass or more, further 90% by mass or more, and particularly 100% by mass, may be composed of aminated epoxy resin.

[0033] In one approach, the combined use of aminated epoxy resin and aminated acrylic resin offers advantages such as improved weather resistance of the electrodeposited coating. Aminated acrylic resin (B) can be formulated through copolymerization of amino-containing acrylic monomers, hydroxyl-containing acrylic monomers, and other olefinically unsaturated monomers. Alternatively, it can be formulated by replacing amino-containing acrylic monomers with epoxy-containing acrylic monomers in copolymerization with hydroxyl-containing acrylic monomers and other olefinically unsaturated monomers, and then ring-opening the epoxy groups of the resulting copolymer using amines.

[0034] Polyisocyanate curing agent (B) The polyisocyanate curing agent (B) (hereinafter, sometimes simply referred to as curing agent (B)) is a component that preferentially reacts with the amino group of the aminated epoxy resin (A) and then with the hydroxyl group to cure the aminated epoxy resin (A) and form an electrodeposited coating. The polyisocyanate curing agent (B) disclosed herein comprises a blocked polyisocyanate compound (B1) selected from polyisocyanate compounds of 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers. Using the above configuration, it has the advantages of ensuring good coating properties of the electrodeposited coating with corrosion resistance, while also obtaining good low-temperature curing properties.

[0035] The use of blocked polyisocyanates, such as hexamethylene diisocyanate and / or its polymers, in polyisocyanate curing agents (B) has been a long-standing research area. For example, blocked polyisocyanates, such as hexamethylene diisocyanate and / or its polymers, can impart flexibility to electrodeposited coatings and improve properties such as crack resistance. However, while blocked polyisocyanates, such as hexamethylene diisocyanate and / or its polymers, can impart flexibility, their corrosion resistance, a contradictory property, can sometimes be compromised. In this invention, experiments have shown that by using 1,5-pentamethylene diisocyanate and / or its polymers, the balance between flexibility and other properties such as corrosion resistance can be achieved, and low-temperature curing properties are also improved, thus completing this invention.

[0036] In addition to the advantages mentioned above, the use of 1,5-pentamethylene diisocyanate and / or its polymers also has the advantage of achieving environmental load reduction effects from biomass-derived feedstocks (non-fossil feedstocks).

[0037] Examples of polymers of the aforementioned 1,5-pentamethylene diisocyanate include: isocyanurate forms, adducts, biuret forms, uretdione forms, ureocarbamate forms, and prepolymers containing isocyanate residues. Examples of prepolymers of 1,5-pentamethylene diisocyanate include: prepolymers (adducts) obtained by reacting 1,5-pentamethylene diisocyanate with polyols such as ethylene glycol, propylene glycol, trimethylolpropane, and glycerol under conditions where the NCO / OH ratio is 2 or higher.

[0038] The aforementioned blocked polyisocyanate compound (B1) can be formulated by blocking a polyisocyanate compound selected from 1,5-pentamethylene diisocyanate and its polymers using a blocking agent. Examples of blocking agents include: Monoalkyl (or aromatic) alcohols such as n-butanol, n-hexanol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylmethanol; Cellulose-solerating compounds such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; Polyether-type diol compounds such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether diol phenol; Polyester-type two-terminal polyol compounds obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, octanoic acid, and sebacic acid; Phenolic compounds such as tert-butylphenol and cresol; Oxidime compounds such as dimethyl ketone oxime, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, methyl pentyl ketone oxime, and cyclohexanone oxime; 3,5-Dimethylpyrazole and other pyrazole compounds; Imidazole compounds such as 2-ethyl-4-methylimidazolium; and Lactam compounds, such as ε-caprolactam and γ-butyrolactam.

[0039] As the blocking agent used in the preparation of the above-mentioned blocked polyisocyanate compound (B1), it is preferable to use a blocking agent containing one or more of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds, and more preferably a blocking agent containing oxime compounds. By using these blocking agents in the preparation of the blocked polyisocyanate compound (B1), it is advantageous to ensure good low-temperature curing properties and to suitably maintain a balance of properties in the resulting electrodeposited coating.

[0040] The polyisocyanate curing agent (B) disclosed herein may contain other blocked polyisocyanate compounds in addition to the aforementioned blocked polyisocyanate compound (B1). These other blocked polyisocyanate compounds can be formulated by blocking polyisocyanate compounds other than 1,5-pentamethylene diisocyanate and its polymers with a blocking agent. The aforementioned blocking agent can be used as the blocking agent.

[0041] Examples of polyisocyanate compounds other than 1,5-pentamethylene diisocyanate and its polymers include: Hexamethylene diisocyanate (including trimer), 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate, and other aliphatic polyisocyanate compounds with 3 to 12 carbon atoms; Alicyclic polyisocyanate compounds such as 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis(isocyanomethyl)-bicyclo[2.2.1]heptane (also known as norbornane diisocyanate); Aromatic polyisocyanate compounds such as toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), polymethylene polyphenyl polyisocyanate (MDI polymer, polymeric MDI), terephthalic diisocyanate, and naphthalene diisocyanate. Aliphatic polyisocyanate compounds with aromatic rings, such as phenyl dimethyl diisocyanate (XDI) and tetramethyl phenyl dimethyl diisocyanate (TMXDI); These are modified diisocyanates (carbamates, carbodiimides, urea diketones, urea ketone imides, biuret, isocyanurate modified products, etc.).

[0042] The polyisocyanate curing agent (B) disclosed herein may contain other blocked polyisocyanate compounds in addition to the aforementioned blocked polyisocyanate compound (B1). In one embodiment, the polyisocyanate curing agent (B) comprises the aforementioned blocked polyisocyanate compound (B1) and a blocked polyisocyanate compound of an aromatic polyisocyanate compound. In the above embodiment, the mass ratio of the blocked polyisocyanate compound (B1) to the blocked polyisocyanate compound of the aromatic polyisocyanate compound, i.e., the mass ratio of (B1) / other blocked polyisocyanate compounds, may be 5 / 95 to 95 / 5, 20 / 80 to 80 / 20, or 30 / 70 to 70 / 30.

[0043] The content of the polyisocyanate curing agent (B) in the cationic electrodeposition coating composition disclosed herein is set taking into account the structure of the curable resin (specifically, an amination epoxy resin (A) and other curable resins as needed). Specifically, a sufficient amount of curing agent is used for reaction with the functional groups containing active hydrogen, such as primary amines, secondary amines, and hydroxyl groups, present in the curable resin (represented by an amination epoxy resin (A)). The curing agent is blended, for example, in a solids mass ratio (expressed as curable resin / curing agent) of 90 / 10 to 50 / 50, more preferably 80 / 20 to 65 / 35. The flowability and curing speed of the electrodeposition coating composition are controlled by the solids mass ratio of the curable resin to the curing agent.

[0044] The ratio of the hydroxyl equivalent of the aforementioned aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B), NCO / OH, is preferably 0.5 or more and less than 3.1. The aforementioned isocyanate group equivalent refers to the equivalent of free isocyanate groups generated and cured due to the dissociation of the sealing agent during heat curing, while the aforementioned hydroxyl equivalent of the aforementioned aminated epoxy resin (A) is the equivalent of hydroxyl groups that react with the aforementioned isocyanate groups. The lower limit of the aforementioned equivalent ratio is more preferably 0.6 or more, and the upper limit is more preferably 2.8 or less. By keeping the equivalent ratio NCO / OH within the aforementioned range, it has the advantage of further improving the corrosion resistance and isoelectric deposition coating properties.

[0045] The coating composition may contain curing agents other than polyisocyanate curing agent (B) as needed. Other curing agents include, for example, organic curing agents such as melamine resin or phenolic resin, silane coupling agents, and metal curing agents. Of all the curing agents contained in the coating composition, 80% by mass or more, further 90% by mass or more, and particularly 100% by mass, may be polyisocyanate curing agent (B).

[0046] A mixture (resin emulsion) of amination-modified epoxy resin (A) and polyisocyanate curing agent (B). A preferred feature of the cationic electrodeposition coating composition of the present invention is that: the amination epoxy resin (A) and the polyisocyanate curing agent (B) are mixed to form an amination epoxy resin emulsion, which is then cured (heated and cured at 135°C for 25 minutes) to form a cured coating film with a Tg of 65°C or higher and 95°C or lower by dynamic viscoelasticity measurement. Dynamic Tg refers to the stress and strain resulting from applying a strain or stress that varies with time (vibration) to a sample, which differs from ordinary Tg (glass transition temperature: also known as static glass transition temperature), i.e., it differs from applying a constant strain or stress that does not change with time and measuring the resulting stress and strain. The values ​​of dynamic glass transition temperature (dynamic Tg) and static glass transition temperature (static Tg) are not significantly different, but the difference lies in the application of a strain or stress that varies with time. The preferred range of dynamic Tg is 70°C to 90°C, and a more preferred range is 75°C to 85°C. When the dynamic Tg of the coating film formed by the amination epoxy resin emulsion is below 65°C, the coating film will be too soft; on the other hand, when the dynamic Tg exceeds 95°C, the coating film will become hard and brittle.

[0047] The dynamic Tg described in this specification can be obtained from the test sample using the same method as the Tg measurement method based on conventional dynamic viscoelasticity. A specific measurement method usable in this invention is as follows: a cured electrodeposited coating formed on a substrate is peeled off with mercury and cut, and the dynamic viscoelasticity of the test sample prepared therefrom is measured. In this method, the prepared test sample is vibrated at a heating rate of 2°C / min and a frequency of 11Hz within a temperature range of room temperature to 200°C, and its viscoelasticity is measured. The ratio (tanδ) of the loss modulus (E'') to the storage modulus (E') obtained in this operation is measured, and the dynamic Tg is measured in the form of the temperature at which the tanδ peaks under this condition by plotting the tanδ against temperature. Examples of apparatus for performing the above dynamic viscoelasticity measurement include: a dynamic viscoelasticity measuring apparatus (Rheogel-E4000: manufactured by UBM Corporation).

[0048] Other ingredients The cationic electrodeposition coating composition disclosed herein may, as needed, contain components other than those described above. Other components include, for example, pigments, curing catalysts, additives, etc.

[0049] Pigments Pigments are commonly used in coating compositions. Examples of pigments include: coloring pigments such as titanium dioxide, carbon black, and iron oxide red; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay; and rust-inhibiting pigments such as iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and zinc aluminum phosphomolybdate. From the perspective of further improving edge rust resistance, coating compositions may include extender pigments.

[0050] The solid components of a coating composition refer to all components that would remain as solids even after the solvent is removed. Specifically, the solid components of a coating composition include the amination epoxy resin (A), the polyisocyanate curing agent (B), and, if necessary, pigments, pigment dispersion resins, additives, and other solid components.

[0051] Pigments are typically added to coating compositions in the form of a pigment dispersion paste containing a pigment dispersion resin and the pigment.

[0052] (Pigment dispersion resin) Pigment dispersion resin is a resin used for dispersing pigments. Examples of pigment dispersion resins include modified epoxy resins having cationic groups, such as those containing at least one quaternary ammonium group, tertiary sulfonium group, and primary amino group. Specific examples of pigment dispersion resins include quaternary ammonium group-containing epoxy resins and tertiary sulfonium group-containing epoxy resins. Examples of aqueous solvents include ion-exchanged water and ion-exchanged water containing a small amount of alcohol.

[0053] (Catalyst solidification) The coating composition may contain a curing catalyst. There are no particular limitations on the curing catalyst; substances known in the coating industry can be used. Examples of curing catalysts include organotin compounds and bismuth compounds. Examples of organotin compounds include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, bismuth subsalicylate, and bismuth subnitrate. In a preferred embodiment of the cationic electrodeposition coating composition disclosed herein, a curing catalyst containing a bismuth compound may be used.

[0054] From an environmental impact perspective, the content of curing catalysts (especially organotin compounds) can be less than 0.5% by mass or less than 0.25% by mass of the solid components of the coating composition.

[0055] (Metal nitrite salts) The coating composition may further contain a metal nitrite salt. The metal nitrite salt can further improve the rust resistance of the edges. Preferably, the metal nitrite salt is an alkali metal nitrite or an alkaline earth metal nitrite, more preferably an alkaline earth metal nitrite. Examples of metal nitrite salts include: calcium nitrite, sodium nitrite, potassium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, and zinc nitrite.

[0056] For example, relative to the total mass of the coating-forming resin and the curing agent, the content of nitrite metal salts, calculated as metal elements of the metal component, is 0.001% by mass or more and 0.2% by mass or less.

[0057] (Additives, etc.) The coating composition may include, as needed, additives commonly used in the coating industry, such as organic solvents, anti-drying agents, surfactants such as defoamers, viscosity modifiers such as acrylic resin microparticles, anti-cracking agents, and inorganic rust inhibitors. Examples of organic solvents include: ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Examples of inorganic rust inhibitors include: vanadium salts, copper, iron, manganese, magnesium, and calcium salts.

[0058] In addition to the above, depending on the purpose, it may also include known auxiliary complexing agents, buffers, smoothers, stress relievers, gloss agents, semi-gloss agents, antioxidants, and ultraviolet absorbers.

[0059] <Preparation of Cationic Electrodeposition Coating Compositions> First, a blocked polyisocyanate compound (B1) is prepared as described above. Then, a resin emulsion containing a film-forming resin (representatively an amination epoxy resin (A)) and a curing agent (representatively a polyisocyanate curing agent (B)) is mixed using a conventional method, along with a pigment dispersion paste containing pigments and additives as needed, to prepare the resin emulsion, thereby obtaining a coating composition.

[0060] (Preparation of resin emulsion) As one method for preparing resin emulsions, aminated epoxy resin (A) and other coating-forming resins as needed, as well as polyisocyanate curing agent (B) and other curing agents as needed, are dissolved in organic solvents to prepare solutions. These solutions are then mixed and neutralized with a neutralizing acid, thereby preparing the emulsion.

[0061] Examples of neutralizing acids include: methanesulfonic acid, aminosulfonic acid, lactic acid, dimethylolpropionic acid, formic acid, acetic acid, and other organic acids. The neutralizing acid can be one or more selected from formic acid, acetic acid, and lactic acid.

[0062] For example, relative to the total amount of resin emulsion, the solid content of the resin emulsion is 25% by mass or more and 50% by mass or less, or 35% by mass or more and 45% by mass or less. The solid content of the resin emulsion refers to all components contained in the resin emulsion that would remain as solids even after the solvent is removed. Specifically, the solid content of the resin emulsion includes the amination epoxy resin (A), the blocked polyisocyanate curing agent (B), and other solid components added as needed.

[0063] The amount of neutralizing acid used, expressed as the ratio of the neutralizing acid equivalent to the amino equivalent of the aminated epoxy resin, can be 10% or more and less than 100%, or 20% or more and less than 70%. Hereinafter, the ratio of the neutralizing acid equivalent to the amino equivalent of the aminated epoxy resin is referred to as the neutralization rate. A neutralization rate of 10% or more ensures good affinity for water and good water dispersibility.

[0064] (Method for preparing pigment dispersion paste) Pigment dispersion paste is prepared by mixing pigment dispersion resin and pigment. There is no particular limitation on the mass of the solid component of pigment dispersion resin in pigment dispersion paste; for example, it can be more than 20 parts by mass and less than 100 parts by mass relative to 100 parts by mass of pigment.

[0065] The solid content of the pigment dispersion paste is, for example, 40% or more and 70% or less by mass, or 50% or more and 60% or less by mass.

[0066] The solid component of a pigment dispersion paste refers to all the components that remain as solids even after the solvent is removed. Specifically, the solid component of a pigment dispersion paste includes the pigment dispersion resin, the pigment, and any other solid components added as needed.

[0067] [Manufacturing method of electrodeposited coatings] An electrodeposited coating film is formed by electrodepositing an object using a coating composition.

[0068] The electrodeposited coating having an electrodeposited film is manufactured by a method comprising the following steps: immersing the object to be coated in the cationic electrodeposited coating composition according to this embodiment, and then applying a voltage between the object to be coated and the counter electrode to form an uncured electrodeposited coating on the object; and heating the coating at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposited coating.

[0069] As described above, the cationic electrodeposition coating composition comprises an amination epoxy resin (A), a polyisocyanate curing agent (B), pigments, additives, etc., as needed.

[0070] (1) Formation of uncured electrodeposited coating The substrate is immersed in a cationic electrodeposition coating composition, and then a voltage is applied between the substrate as the cathode and the counter electrode (anode). As a result, an uncured electrodeposition coating is deposited on the substrate.

[0071] (Applying conditions) The voltage is, for example, 50V or higher and 450V or lower. The bath temperature is, for example, 10°C or higher and 45°C or lower. There is no particular limitation on the duration of voltage application, for example, 2 minutes or higher and 5 minutes or lower.

[0072] (Object to be painted) There are no particular limitations on the material of the object to be coated, as long as it is electrically conductive. There are also no particular limitations on the shape of the object; it can be flat or have a complex three-dimensional shape. Examples of objects to be coated include: cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electro-galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy coated steel sheets, zinc-iron alloy coated steel sheets, zinc-magnesium alloy coated steel sheets, zinc-aluminum-magnesium alloy coated steel sheets, aluminum-based coated steel sheets, aluminum-silicon alloy coated steel sheets, tin-based coated steel sheets, and steel sheets that have undergone chemical forming treatment (e.g., surface treatment using phosphates, zirconium salts, etc.). In the case of chemical forming treatment with phosphates, zinc-based, titanium-based, or manganese-based surface modifiers can be used to condition the surface of the object before the chemical forming treatment. This results in a denser crystal structure in the zinc phosphate film.

[0073] (2) Curing of electrodeposited coating The uncured electrodeposited coating is washed with water as needed, and then heated at a temperature above 75°C and below 200°C. This causes a curing reaction, resulting in a cured electrodeposited coating.

[0074] (Curing conditions) The curing temperature can be above 100℃ or above 110℃. Alternatively, the curing temperature can be below 180℃ or below 150℃. There is no specific limitation on the heating time; for example, it can be 10 to 30 minutes.

[0075] (Electrodeposited coating) The electrodeposited coating has a substrate and a cured electrodeposited coating film formed on the substrate by the above-described cationic electrodeposited coating composition.

[0076] From a rust prevention perspective, the thickness of the cured electrodeposited coating can be greater than 5 μm and less than 60 μm. The film thickness of the cured electrodeposited coating can be greater than 10 μm. The film thickness of the cured electrodeposited coating can be less than 25 μm.

[0077] The cationic electrodeposition coating composition disclosed herein has the advantage of achieving low-temperature curing while ensuring coating properties such as corrosion resistance by using a curing agent containing a blocked polyisocyanate compound (B1) selected from 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers as the polyisocyanate curing agent (B). The cationic electrodeposition coating composition disclosed herein is suitable for coating schemes where the formation of intermediate and / or topcoat films, which are typically formed on electrodeposited coatings, is omitted, such as coating specific parts or components of an automotive body. Example

[0078] The invention is further illustrated by the following examples, but is not limited thereto. In the examples, unless otherwise stated, "parts" and "%" are based on a mass basis.

[0079] Manufacturing Example 1: Manufacturing of Amine Epoxy Resin (A) 92 parts of methyl isobutyl ketone, 940 parts of bisphenol A type epoxy resin (trade name: DER-331J, manufactured by Dow Chemical), 382 parts of bisphenol A, 63 parts of octanoic acid, and 2 parts of dimethylbenzylamine were added. The temperature inside the reaction vessel was maintained at 140°C, and the reaction was carried out until the epoxy equivalent reached 1145 g / eq. The reaction vessel was then cooled to 120°C. A mixture of 78 parts of diethylenetriaminedioneimine (73% solids methyl isobutyl ketone solution) and 92 parts of diethanolamine was then added, and the mixture was reacted at 120°C for 1 hour to obtain amination epoxy resin (A) (cationically modified epoxy resin). The resin has a number average molecular weight of 2,560, an amine value of 56 mg KOH / g, and a hydroxyl value of 186 mg KOH / g.

[0080] Manufacturing Example 2-1: Manufacturing of a Blocked Polyisocyanate Curing Agent (Curning Agent B1-1) 1540 parts of 1,5-pentamethylene diisocyanate (PDI) and 732 parts of MIBK were placed in a reaction vessel and heated to 60°C. At 60°C, a solution obtained by dissolving 346 parts of trimethylolpropane in 1067 parts of MEK oxime was added dropwise over 2 hours. After heating at 75°C for another 4 hours, the disappearance of isocyanate-based absorption was confirmed by IR spectroscopy. After cooling, 101 parts of MIBK were added to obtain a blocked polyisocyanate curing agent (B1-1) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 148.

[0081] Manufacturing Example 2-2: Manufacturing of a Blocked Polyisocyanate Curing Agent (Curning Agent B1-2) 143.3 parts of 1,5-pentamethylene diisocyanate isocyanurate and 24 parts of MIBK were placed in a reaction vessel and heated to 60°C. 75 parts of methyl ethyl ketone oxime (MEK oxime) were added dropwise over 2 hours. After heating at 70°C for another 2 hours, the disappearance of absorption based on the isocyanate groups was confirmed by IR spectroscopy. Subsequently, 36 parts of butyl cellosolve were added to obtain a blocked polyisocyanate curing agent (B1-2) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 256.

[0082] Manufacturing Example 2-3: Manufacturing of Blocked Polyisocyanate Curing Agent (Curning Agent B1-3) 1340 parts of 4,4'-diphenylmethane diisocyanate and 277 parts of MIBK were placed in a reaction vessel and heated to 80°C. Then, a solution obtained by dissolving 226 parts of ε-caprolactam in 944 parts of butyl cellosolve was added dropwise over 2 hours at 80°C. After heating at 100°C for another 4 hours, the disappearance of absorption based on isocyanate groups was confirmed by IR spectroscopy. After cooling, 349 parts of MIBK were added to obtain the blocked polyisocyanate curing agent (B1-3) (80% solids). The NCO equivalent of this blocked polyisocyanate curing agent was 251.

[0083] Manufacturing Example 2-4: Manufacturing of Blocked Polyisocyanate Curing Agent (Curning Agent B1-4) 1680 parts hexamethylene diisocyanate (HDI) and 732 parts MIBK were placed in a reaction vessel and heated to 60°C. A solution obtained by dissolving 346 parts trimethylolpropane in 1067 parts MEK oxime was added dropwise over 2 hours at 60°C. After heating at 75°C for another 4 hours, the disappearance of isocyanate-based absorption was confirmed by IR spectroscopy. After cooling, 140 parts MIBK were added to obtain a blocked isocyanate curing agent (B1-4) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 155.

[0084] Manufacturing Example 2-5: Manufacturing of Blocked Polyisocyanate Curing Agent (Curning Agent B1-5) 165 parts of hexamethylene diisocyanate isocyanurate (trade name Sumidur N3300, manufactured by SumikaBayer Urethane Co., Ltd.) and 24 parts of MIBK were placed in a reaction vessel and heated to 60°C. 75 parts of methyl ethyl ketone oxime (MEK oxime) were added dropwise over 2 hours. After heating at 70°C for another 2 hours, the disappearance of isocyanate-based absorption was confirmed by IR spectroscopy. Subsequently, 44 parts of butyl cellosolve were added to obtain a blocked polyisocyanate curing agent (B1-5) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 281.

[0085] Manufacturing Examples 2-6: Manufacturing of Blocked Polyisocyanate Curing Agent (Curning Agent B1-6) 1540 parts of 1,5-pentamethylene diisocyanate (PDI) were placed in a reaction vessel and heated to 60°C. At 60°C, a solution obtained by dissolving 346 parts of trimethylolpropane in 732 parts of MIBK was added dropwise over 2 hours. Then, 1178 parts of 3,5-dimethylpyrazole were slowly added at 60–70°C. After heating at 70°C for another 2 hours, the disappearance of isocyanate-based absorption was confirmed by IR spectroscopy. After cooling, 132 parts of MIBK were added to obtain a blocked polyisocyanate curing agent (B1-6) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 153.

[0086] Manufacturing Example 2-7: Manufacturing of Blocked Polyisocyanate Curing Agent (Curning Agent B1-7) 143.3 parts of 1,5-pentamethylene diisocyanate isocyanurate and 24 parts of MIBK were placed in a reaction vessel and heated to 60°C. At 60–70°C, 83 parts of 3,5-dimethylpyrazole were slowly added. After heating at 70°C for another 2 hours, the disappearance of absorption based on the isocyanate groups was confirmed by IR spectroscopy. Subsequently, 40 parts of butyl cellosolve were added to obtain a blocked polyisocyanate curing agent (curing agent B1-7) with a solid content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 265.

[0087] Manufacturing Example 3: Preparation of Pigment Dispersion Resin In a reaction vessel equipped with a stirrer, cooling pipe, nitrogen inlet pipe, and thermometer, 2220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were charged. The temperature was raised to 50°C, and then 2.2 parts of dibutyltin laurylate were added. The temperature was raised to 60°C, and then 878.7 parts of methyl ethyl ketone oxime were added. The mixture was then held at 60°C for 1 hour, and the NCO equivalent was confirmed to have reached 348. Then, 890 parts of dimethylethanolamine were added. The mixture was held at 60°C for another hour, and the NCO peak disappeared as confirmed by IR spectroscopy. Next, while cooling to ensure the temperature did not exceed 60°C, 1872.6 parts of 50% lactic acid and 495 parts of deionized water were added to obtain the quaternizing agent.

[0088] 870 parts of toluene diisocyanate and 49.5 parts of methyl isobutyl ketone were placed in different reaction vessels. While cooling to a temperature below 50°C, 667.2 parts of 2-ethylhexanol were added dropwise over 2.5 hours. After the addition was complete, 35.5 parts of methyl isobutyl ketone were added, and the mixture was kept at this temperature for 30 minutes. The NCO equivalent was then confirmed to be 330–370, yielding a semi-closed polyisocyanate.

[0089] In a reaction vessel equipped with a stirrer, cooling pipe, nitrogen inlet pipe, and thermometer, 940.0 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical) and 38.5 parts of methanol were added, followed by 0.1 parts of dibutyltin dilaurate. The mixture was heated to 50°C, and then 87.1 parts of toluene diisocyanate were added. The temperature was then raised to 100°C, and 1.4 parts of N,N-dimethylbenzylamine were added. The mixture was then kept at 130°C for 2 hours. During this time, the methanol was fractionated off using a distillation tube. The mixture was cooled to 115°C, and methyl isobutyl ketone was added until the solid content concentration reached 90%. Then, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added, and the mixture was heated and stirred at 125°C for 2 hours. Next, 516.4 parts of the above semi-closed polyisocyanate were added dropwise over 30 minutes, followed by heating and stirring for another 30 minutes. Then, slowly add 1506 parts of polyoxyethylene bisphenol A ether to dissolve it. After cooling to 90°C, add the above-mentioned quaternizing agent and maintain the temperature at 70-80°C. After confirming that the acid value has reached below 2, add deionized water to obtain the pigment dispersion resin (resin solids content is 30%).

[0090] Example 4: Preparation of Pigment Dispersion Paste 1,200 parts of the pigment dispersion resin obtained in Manufacturing Example 3, 3 parts of carbon black, 620 parts of kaolin, 500 parts of titanium dioxide, 70 parts of bismuth oxide, and 713 parts of deionized water were added to a sand mill and dispersed until the particle size was less than 10 μm to obtain a pigment dispersion paste (50% solid content).

[0091] [Example 1] Preparation of cationic electrodeposition coating composition (Preparation of Amine Epoxy Resin Emulsion) 400 parts (solid component) of the aminated epoxy resin (A) obtained in Manufacturing Example 1 and 600 parts (solid component) of the blocked polyisocyanate curing agent (B1-1) obtained in Manufacturing Example 2-1 were mixed, and ethylene glycol mono-2-ethylhexyl ether was added to make it 3% relative to the solid component. Next, formic acid was added to neutralize it to make the neutralization rate reach 40%, and deionized water was added to slowly dilute it to obtain an aminated epoxy resin emulsion.

[0092] (Preparation of cationic electrodeposition coating composition) 1666 parts of deionized water, 1172 parts of the prepared amination epoxy resin emulsion, and 330 parts of the pigment dispersion paste obtained in Manufacturing Example 4 were added to a stainless steel container. The mixture was then aged at 40°C for 16 hours to obtain a cationic electrodeposition coating composition.

[0093] Examples 2 through 6 and Comparative Examples 1 through 6 Except for changing the type and amount of the blocking polyisocyanate curing agent as described in Table 1 below, the cationic electrodeposition coating composition was manufactured according to the same procedure as in Example 1.

[0094] Using the obtained cationic electrodeposition coating composition, electrodeposited coatings (single-layer coatings) were prepared according to the same procedure as in Example 1.

[0095] The following evaluations were conducted using the cationic electrodeposition coating compositions prepared in the Examples and Comparative Examples. The evaluation results are shown in the table below.

[0096] Preparation of electrodeposited coatings Prepare a cold-rolled steel sheet (JIS G3141, SPCC-SD) as the coating material. The steel sheet was degreased by immersing it in SURFCLEANER EC90 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at 50°C for 2 minutes. Then, it was immersed in SURFDINE EC3200 (manufactured by Nippon Paint Surf Chemicals Co., Ltd., a zirconification treatment agent) at 35°C for 90 seconds. Afterwards, it was rinsed with deionized water.

[0097] To adjust the viscosity, a necessary amount of 2-ethylhexyl glycol was added to the cationic electrodeposition coating composition obtained above, so that the cured electrodeposition coating film thickness reached 20 μm. The steel plate was completely immersed in the obtained cationic electrodeposition coating composition, and then a voltage was immediately applied. The voltage was applied under the condition of boosting to 180V for 30 seconds and holding for 150 seconds. As a result, an uncured electrodeposition coating film was deposited on the substrate. The obtained uncured electrodeposition coating film was heated and cured at 135°C for 25 minutes to obtain an electrodeposition coating with a cured electrodeposition coating film thickness of 20 μm. The gel fraction (low-temperature curability evaluation), solvent polishing properties, and corrosion resistance of the obtained electrodeposition coating were evaluated as follows, and the results are recorded in Table 1. It should also be noted that Table 1 also records the equivalent ratio NCO / OH of the hydroxyl equivalent of the amination epoxy resin (A) and the isocyanate group equivalent of the polyisocyanate curing agent (B).

[0098] Evaluation of low-temperature curability (determination of gel fraction) The electrodeposited coating formed according to the above procedure is placed in a Soxhlet extractor and extracted for 6 hours under acetone reflux. The gel fraction of the coating is calculated according to the following formula. Gel fraction (%) = [mass after extraction (g) / mass before extraction (g)] × 100 The calculated gel fraction was evaluated according to the following criteria. ◎: Gel fraction is over 95%; ○: The gel fraction is above 90% and less than 95%; ×: Gel fraction is less than 90%.

[0099] Solvent resistance evaluation (solvent polishability) For the cured electrodeposited coating, a rubbing test was conducted using a cloth containing MIBK solvent under a 500g load to observe the surface condition of the coating. The following criteria will be used for evaluation. ○: After 30 rounds of polishing, the coating surface will not lose its gloss; △: After 20 rounds of polishing, the coating surface loses its gloss; ×: After 10 rounds of polishing, the coating surface loses its gloss.

[0100] Corrosion resistance (Salt solution immersion test (SDT)) On the coating of a cured electrodeposited coated board made of cold-rolled steel sheet, scratches were made with a knife down to the substrate. The coated board was then immersed in 5% saline solution at 55°C for 240 hours, followed by tape peeling, and the peel width on both sides was measured. The measured peel width was evaluated according to the following criteria. Evaluation criteria ○: Peeling width is less than 12mm; △: The peeling width is 12mm or more but less than 14mm; ×: The peeling width is 14mm or more.

[0101] Determination of dynamic Tg of cured coating film of ammoniated epoxy resin emulsion The amination of epoxy resin emulsion prepared according to the examples and comparative examples was electrodeposited onto a galvanized iron plate for dynamic viscoelasticity testing and cured at 135°C for 25 minutes to obtain a cured electrodeposited coating. The obtained coating was peeled off and sheared with mercury to prepare a sample for testing. Using a dynamic viscoelasticity testing device (Rheogel-E4000: manufactured by UBM Corporation), the sample was viscoelasticity was measured by applying vibration at a heating rate of 2°C / min from room temperature to 200°C and at a frequency of 11Hz. The ratio of loss modulus (E”) to storage modulus (E’) (tanδ) was calculated, the temperature at which the peak value was obtained was determined, and the dynamic Tg was calculated.

[0102] [Table 1] As can be seen from the results in Table 1 above, cationic electrodeposition coating compositions (Examples 1 and 3) using 1,5-pentamethylene diisocyanate as a blocking agent (Manufacturing Example 2-1) or ureate form of 1,5-pentamethylene diisocyanate as a blocking agent (Manufacturing Example 2-2), and combinations thereof with other blocking polyisocyanate compounds (4,4'-diphenylmethane diisocyanate as a blocking agent in Manufacturing Example 2-3) (Examples 2 and 4) exhibited excellent gel fraction, solvent polishing properties, and corrosion resistance. In Examples 5 and 6, when a pyrazole compound (specifically 3,5-dimethylpyrazole) was used as the blocking agent for the polyisocyanate, the performance remained unchanged despite the change in the blocking agent. On the other hand, Comparative Example 1, which used a hexamethylene diisocyanate blocking agent as a curing agent, exhibited very poor gel fraction and corrosion resistance. In Comparative Example 2, a combination of 4,4'-diphenylmethane diisocyanate and hexamethylene diisocyanate blocking agents was used, resulting in very poor gel content and solvent polishability. Comparative Example 3 used a hexamethylene diisocyanate isocyanurate blocking agent as a curing agent, exhibiting very poor gel content and corrosion resistance. Comparative Example 4 used a combination of 4,4'-diphenylmethane diisocyanate and hexamethylene diisocyanate isocyanurate blocking agents as a curing agent, resulting in very poor gel content and solvent polishability. Comparative Examples 5 and 6 had poor performance in all aspects because the NCO / OH ratio was not within the appropriate range. The dynamic Tg range of the cured coating of the amination epoxy resin emulsion was too high in Comparative Example 5 and too low in Comparative Example 6.

[0103] Industrial applicability The cationic electrodeposition coating composition disclosed herein has the advantage of maintaining coating properties such as corrosion resistance while exhibiting good low-temperature curing properties. Furthermore, the cationic electrodeposition coating composition disclosed herein has the advantage of achieving environmental reduction effects due to biomass-derived raw materials (non-fossil raw materials).

Claims

1. A cationic electrodeposition coating composition comprising an amination epoxy resin (A) and a polyisocyanate curing agent (B), in, The polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) selected from polyisocyanates and 1,5-pentamethylene diisocyanate polymers. The equivalence ratio of the hydroxyl equivalent of the amination epoxy resin (A) to the isocyanate equivalent of the polyisocyanate curing agent (B), NCO / OH, is greater than 0.5 and less than 3.

1.

2. The cationic electrodeposition coating composition according to claim 1, wherein, The blocking agent used in the formulation of the blocked polyisocyanate compound (B1) comprises one or more selected from oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds.

3. The cationic electrodeposition coating composition according to claim 1 or 2, wherein, The cured coating of the amination epoxy resin emulsion, which is a mixture of the amination epoxy resin (A) and the polyisocyanate curing agent (B), at 135°C for 25 minutes, has a Tg of 65°C or higher and 95°C or lower as determined by dynamic viscoelasticity measurement.

4. A method for manufacturing a cationic electrodeposition coating composition, comprising the following steps: The process of preparing the blocked polyisocyanate compound (B1); and The process of mixing a polyisocyanate curing agent (B) containing the blocked polyisocyanate compound (B1) with an amination epoxy resin (A) to prepare an amination epoxy resin emulsion. The blocked polyisocyanate compound (B1) is formulated by blocking a polyisocyanate compound selected from 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers with a blocking agent. The blocking agent comprises one or more selected from oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds.

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