Cationic electrodeposition coating composition

Abstract

The present invention provides a cationic electrodeposition coating composition, which makes the adhesion and barrier properties of the coating obtained from the cationic electrodeposition coating composition further improved compared with the conventional coating, and improves the rust resistance. The present invention provides a cationic electrodeposition coating composition, which is a cationic electrodeposition coating composition containing an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein the aminated epoxy resin is an aminated epoxy resin obtained by reacting an amine compound with an epoxy resin, and the molecular weight distribution of the aminated epoxy resin is 2.7 or less, and the cationic electrodeposition coating composition is applied to a steel plate so that the cured film thickness is 20 μm, and the elongation of the electrodeposition coating after baking at 160° C. for 15 minutes is 0.1 to 4.5%.

Description

Technical Field

[0001] The present invention relates to a cationic electrodeposition coating composition, in particular to a cationic electrodeposition coating composition having high corrosion resistance. Background Art

[0002] Cationic electrodeposition coatings are often used as primer coatings to impart corrosion resistance to industrial products such as automobiles, and contain aminated epoxy resins and blocked polyisocyanate curing agents. Cationic electrodeposition coatings are required to have high adhesion and high hydrophobicity (barrier properties) in addition to high rust resistance.

[0003] The adhesion and hydrophobicity (barrier property) of cationic electrodeposition coatings are important properties that contribute to rust prevention, and are always required to be improved. For example, Japanese Patent Publication No. 2000-501448 (Patent Document 1) discloses a cationic electrodeposition coating composition, which uses a product obtained by reacting a diamine compound having primary and tertiary amino groups with an epoxy resin, but further improvements are required in adhesion or barrier property.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2000-501448. Summary of the invention

[0007] Problems to be solved by the invention

[0008] The present invention provides a cationic electrodeposition coating composition which can further improve the adhesion and barrier properties of a coating film obtained from the cationic electrodeposition coating composition compared with conventional coating films and can also improve the rust prevention properties.

[0009] Means for solving problems

[0010] That is, the present invention provides the following solutions:

[0011] A cationic electrodeposition coating composition, which is a cationic electrodeposition coating composition containing an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein:

[0012] The aminated epoxy resin is obtained by reacting an amine compound with an epoxy resin.

[0013] The molecular weight distribution of the aminated epoxy resin is below 2.7,

[0014] The cationic electrodeposition coating composition was applied to a steel plate to a cured film thickness of 20 μm and the electrodeposition coating film was baked at 160° C. for 15 minutes. The elongation of the electrodeposition coating film was 0.1 to 4.5%.

[0015] [1] The cationic electrodeposition coating composition, wherein the amine compound is a combination of a primary amine and a secondary amine,

[0016] Primary amines have the formula (1):

[0017] NH2-(CH2)n-NR 1 R 2 (1)

[0018] (In formula (1), R 1 and R 2 are the same or different, and represent an alkyl group having 1 to 6 carbon atoms which may have a hydroxyl group at the end, and n represents an integer of 2 to 4. )

[0019] Secondary amines have the formula (2):

[0020] R 3 R 4 NH (2)

[0021] (In formula (2), R 3 and R 4 It represents an alkyl group having 1 to 4 carbon atoms and having a hydroxyl group at the end.

[0022] The cationic electrodeposition coating composition according to [1] or [2], wherein the tertiary amination ratio of the amine compound when the aminated epoxy resin is obtained is 85% or more.

[0023] A cationic electrodeposition coating film obtained by coating using the cationic electrodeposition coating composition described in any one of [1] to [3].

[0024] Effects of the Invention

[0025] The cationic electrodeposition coating composition of the present invention is characterized in that it contains an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein the aminated epoxy resin has a molecular weight distribution of 2.7 or less, and the elongation of the electrodeposition coating film after the cationic electrodeposition coating composition is applied to a steel plate to a cured film thickness of 20 μm and baked at 160° C. for 15 minutes is 0.1 to 4.5%. The molecular weight distribution of the aminated epoxy resin is narrowed to 2.7 or less, which reduces the side reaction of the reaction between the epoxy resin and the amine compound, and obtains an aminated epoxy resin of a desired structure, which can exert its performance (specifically, corrosion resistance, etc.). In addition, the elongation of the electrodeposition coating film is 0.1 to 4.5%, which is within the range of elongation required for exerting the performance of the electrodeposition coating film, so that corrosion resistance, adhesion and barrier properties can be exerted. DETAILED DESCRIPTION

[0026] The cationic electrodeposition coating composition of the present invention contains an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein the aminated epoxy resin is obtained by reacting an amine compound with an epoxy resin, wherein the molecular weight distribution of the aminated epoxy resin is 2.7 or less, and the cationic electrodeposition coating composition is applied to a steel plate to a cured film thickness of 20 μm and the elongation of the electrodeposition coating film after baking at 160° C. for 15 minutes is 0.1 to 4.5%. It should be noted that in this specification, when a numerical range is expressed as “a to b” (a and b both represent numerical values), it means a or more and b or less.

[0027] <Aminated epoxy resin>

[0028] The aminated epoxy resin is a coating film forming resin constituting the electrodeposition coating film. The aminated epoxy resin is obtained by modifying the oxirane ring (also referred to as "epoxy group") of the epoxy resin with an amine compound, that is, amination.

[0029] The epoxy resin of the starting material is a reaction product of polycyclic phenol compounds such as bisphenol A, bisphenol F, bisphenol S, phenol novolac, cresol novolac and epichlorohydrin, that is, a polyphenol polyglycidyl ether type epoxy resin. In this specification, "polyphenol polyglycidyl ether type epoxy resin" includes the state after the polyphenol polyglycidyl ether type epoxy resin and the polycyclic phenol compound react (chain extension reaction). In this amine modification process, it is preferred to use an epoxy resin obtained by reacting a polyphenol polyglycidyl ether type epoxy resin and a polycyclic phenol compound (chain extension reaction). The reaction conditions for the chain extension reaction of the polyphenol polyglycidyl ether type epoxy resin and the polycyclic phenol compound can be appropriately selected according to the stirring device used and the reaction scale. As the reaction conditions, for example, the reaction at 85 to 180°C for 0.1 to 8 hours, more preferably at 100 to 150°C for 2 to 8 hours, etc. As the stirring device used, a stirring device commonly used in the coating field can be used.

[0030] Examples of other starting material resins include oxazolidinone ring-containing epoxy resins described in Japanese Patent Application Laid-Open No. 5-306327. These epoxy resins can be prepared by reacting a diisocyanate compound or a bisurethane compound obtained by blocking the isocyanate group of a diisocyanate compound with a lower alcohol such as methanol or ethanol with epichlorohydrin.

[0031] Before amination, a portion of the epoxy resin may be subjected to a chain extension reaction by a bifunctional polyester polyol, a polyether polyol (e.g., a polyol having a polyethylene oxide group, a polyol having a polypropylene oxide group, etc.), a dicarboxylic acid, etc. For example, when a polyol having a polypropylene oxide group is used for a chain extension reaction, a polypropylene oxide group-containing epoxy resin is obtained. As an example of this scheme, there can be cited: a state after a polyphenol polyglycidyl ether type epoxy resin, a polycyclic phenol compound, and a polypropylene oxide group-containing epoxy resin react (chain extension reaction). In the case where the epoxy resin reacted with the amine compound in the amine modification step contains a polypropylene oxide group-containing epoxy resin, the content of the polypropylene oxide group-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 the epoxy resin.

[0032] In general, the aminated epoxy resin is obtained by reacting the oxirane ring of the above-mentioned epoxy resin with an amine compound. As the amine compound, an amine compound commonly used in the manufacture of the aminated epoxy resin 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 above-mentioned primary amine can form a ketone imine group using a ketone compound, and the reaction is controlled by so-called end-capping. The amine compounds having a ketone imine group or a diketone imine group that can be used include: ketone imine of aminoethylethanolamine, diketone imine of diethylenetriamine, etc. Examples of ketone compounds that generate ketimino groups include methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), methyl isobutyl ketone (MIBK), diethyl ketone (DEK), ethyl butyl ketone (EBK), ethyl propyl ketone (EPK), dipropyl ketone (DPK), butanone (MEK), etc., and methyl isobutyl ketone (MIBK) is preferably used. As the amine compound, a tertiary amine can be used, and specific examples thereof include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine. These amines may be used alone or in combination of two or more.

[0033] In the present invention, the molecular weight distribution of the aminated epoxy resin needs to be controlled to be below 2.7. If the above-mentioned amine compound is selected as a specific amine compound in order to control the molecular weight distribution, it is easy to control. Specifically, the amine compound is a combination of two kinds of primary amines and secondary amines, and the following amine compounds are suitable for use, wherein:

[0034] Primary amines have the formula (1):

[0035] NH2-(CH2)n-NR 1 R 2 (1)

[0036] (In formula (1), R 1and R 2 are the same or different, and represent an alkyl group having 1 to 6 carbon atoms which may have a hydroxyl group at the end, and n represents an integer of 2 to 4. )

[0037] Secondary amines have the formula (2):

[0038] R 3 R 4 NH (2)

[0039] (In formula (2), R 3 and R 4 It represents an alkyl group having 1 to 4 carbon atoms and having a hydroxyl group at the end.). When these amine compounds are used, it is believed that the primary amino group of the primary amine reacts with the epoxy resin first and is consumed, and the remaining amino group is only the secondary amino group, which reacts with the epoxy group of the epoxy resin. Therefore, there is no superiority or inferiority in reactivity, and the reaction proceeds uniformly, and the molecular weight distribution can be controlled. It is believed that the tertiary amino group present in the primary amine or the tertiary amino group generated in the reaction of the secondary amino group also reacts with the epoxy group to become a quaternary ammonium group, but it is believed that the reaction is rare.

[0040] The primary amine is an amine having the above formula (1), specifically, R 1 and R 2 is a methyl group, an ethyl group, a propyl group or a butyl group, and may have a hydroxyl group at the end. In addition, n is 2 to 4, preferably 3. Specific examples of primary amines include aminopropyldiethanolamine, dimethylaminopropylenediamine, diethylaminopropylenediamine, dibutylaminopropylenediamine, etc. The secondary amine is a secondary amine having the above formula (2), wherein R is bonded to the nitrogen atom. 3 and R 4 , R 3 and R 4 All of them are alkyl groups having 1 to 4 carbon atoms and having a hydroxyl group. Specifically, examples of the secondary amine include dimethanolamine and diethanolamine.

[0041] In the amine modification step, the amount of the amine compound reacting with the epoxy resin is preferably used in an amount of 0.9 to 1.2 equivalents relative to 1 equivalent of epoxy group possessed by the epoxy resin. As described above, when the amine compound uses a primary amine and a secondary amine, the amount of the primary amine is 30 to 80% by weight of the entire amine compound, and more preferably 40 to 70% by weight. If the amount of the primary amine exceeds 80% by weight of the entire amine compound, the viscosity of the resin increases and it is difficult to stir. If it is less than 30% by weight, there is a disadvantage that the stability of the emulsion decreases.

[0042] The reaction conditions for amine modification by reacting the epoxy resin with the amine compound can be appropriately selected according to the reaction scale, etc. Examples of the reaction conditions include reaction at 80 to 150° C. for 0.1 to 5 hours, and more preferably reaction at 120 to 150° C. for 0.5 to 3 hours.

[0043] The number average molecular weight of the aminated epoxy resin is preferably in the range of 1,000 to 7,000. By setting the number average molecular weight to be 1,000 or more, the physical properties of the obtained cured electrodeposition coating film, such as solvent resistance and corrosion resistance, become good. On the other hand, by setting the number average molecular weight to be 7,000 or less, the viscosity of the aminated epoxy resin is easily adjusted, and the synthesis can be smoothly performed. In addition, the operation of emulsification and dispersion of the obtained aminated epoxy resin becomes easy. The number average molecular weight of the aminated epoxy resin is more preferably in the range of 1,500 to 4,000.

[0044] In the present invention, the molecular weight distribution of the aminated epoxy resin is required to be 2.7 or less, preferably 2.5 or less. The molecular weight distribution refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw / Mn. The average molecular weight and molecular weight distribution refer to the polystyrene-converted weight average molecular weight measured by gel permeation chromatography. If the molecular weight distribution of the aminated epoxy resin exceeds 2.7, many side reactions occur in the reaction between the epoxy resin and the amino compound, and sometimes the performance of the aminated epoxy resin as the target cannot be exerted.

[0045] In order to control the molecular weight distribution of the aminated epoxy resin to be less than 2.7, as described above, it is suitable to use a combination of a primary amine and a secondary amine as the amine compound, and it can also be carried out by controlling the reaction temperature or reaction time, etc. For example, if the reaction temperature is lower than 120°C or exceeds 180°C, the molecular weight distribution tends to be higher.

[0046] In the amine compound of the aminated epoxy resin, the primary amino group reacts to become the secondary amino group and further to become the tertiary amino group, but at this time, the tertiary amination rate needs to be 85% or more. It should be noted that the tertiary amination rate is calculated by tertiary amine value / total amine value×100 and expressed in %. The tertiary amine value refers to the number of mg of potassium hydroxide equivalent to perchloric acid required to neutralize the tertiary amine contained in 1g of the sample. According to ASTM D2073, it is measured by the following method.

[0047] Test method for tertiary amine value

[0048] (1) Weigh the sample into a 100 ml beaker.

[0049] (2) Add 0.5 g of pure water.

[0050] (3) The above sample was dissolved in 50 g of THF (tetrahydrofuran).

[0051] (4) Stir for 5 minutes.

[0052] (5) Next, 7.5 ml of acetic anhydride and 2.5 ml of acetic acid were added, and the mixture was stirred at about 40°C for 5 minutes.

[0053] (6) Use an automatic potentiometric titrator to titrate with 0.1 N perchloric acid-acetic acid solution.

[0054] (7) Next, the tertiary amine value is measured.

[0055] Tertiary amine value = (titration mL × factor × 10) / (sample amount g × solid content)

[0056] Total amine value test method

[0057] (1) Accurately weigh 500 mg of sample into a 200 ml Erlenmeyer flask.

[0058] (2) Add about 50 ml of glacial acetic acid and dissolve evenly.

[0059] (3) Add 5 to 6 drops of indicator methyl violet solution to make it uniform.

[0060] (4) When titrating with 0.1 N perchloric acid-acetic acid solution, the point at which the solution turns bright green is regarded as the end point.

[0061] (The above (3) and (4) can also be subjected to potentiometric titration).

[0062] The amine value of the aminated epoxy resin (same as the total amine value described above) is preferably in the range of 20 to 100 mgKOH / g. By making the amine value of the aminated epoxy resin 20 mgKOH / g or more, the emulsified dispersion stability of the aminated epoxy resin in the electrodeposition coating composition becomes good. On the other hand, by making the amine value 100 mgKOH / g or less, the amount of amino groups in the cured electrodeposition coating film is appropriate, and the water resistance of the coating film is unlikely to be reduced. The amine value of the aminated epoxy resin is more preferably in the range of 20 to 80 mgKOH / g.

[0063] The tertiary amine ratio of the aminated epoxy resin is also related to the conductivity of the electrodeposition coating composition. If the tertiary amine ratio decreases, the conductivity increases and the gas entrapment property deteriorates. The conductivity of the electrodeposition coating composition is preferably 1500 to 2000 μS / cm 2 If the conductivity is less than 1500, the covering property will decrease, and if it exceeds 2000, the gas blocking property will deteriorate and the appearance of the coating surface will deteriorate. The conductivity can be measured using a commercially available conductivity meter.

[0064] The hydroxyl value of the aminated epoxy resin is preferably in the range of 150 to 650 mgKOH / g. By making the hydroxyl value above 150 mgKOH / g, curing becomes good in the cured electrodeposition coating, and the coating appearance is also improved. On the other hand, by making the hydroxyl value below 650 mgKOH / g, the amount of hydroxyl groups remaining in the cured electrodeposition coating becomes appropriate, and the water resistance of the coating will not be reduced. The hydroxyl value of the aminated epoxy resin is more preferably in the range of 150 to 400 mgKOH / g.

[0065] In the electrodeposition coating composition of the present invention, by using an aminated epoxy resin having a number average molecular weight in the range of 1,000 to 7,000, an amine value of 20 to 100 mgKOH / g, and a hydroxyl value of 150 to 650 mgKOH / g, more preferably 150 to 400 mgKOH / g, there is an advantage that excellent corrosion resistance can be imparted to the coated object.

[0066] It should be noted that as the aminated epoxy resin, an aminated epoxy resin with different amine values ​​and / or hydroxyl values ​​can be used in combination as needed. In the case of using two or more aminated epoxy resins with different amine values ​​and hydroxyl values, it is preferred that the average amine value and the average hydroxyl value calculated according to the mass ratio of the aminated epoxy resins used are in the above-mentioned numerical range. In addition, as the aminated epoxy resin used in combination, it is preferred to use an aminated epoxy resin with an amine value of 20 to 50 mgKOH / g and a hydroxyl value of 50 to 300 mgKOH / g and an aminated epoxy resin with an amine value of 50 to 200 mgKOH / g and a hydroxyl value of 200 to 500 mgKOH / g. If such a combination is used, the core of the emulsion becomes more hydrophobic and the shell becomes hydrophilic, so it has the advantage of being able to impart excellent corrosion resistance.

[0067] In addition, the aminated epoxy resin may contain an amino group-containing acrylic resin, an amino group-containing polyester resin, etc. as necessary.

[0068] <Blocked polyisocyanate curing agent>

[0069] The blocked polyisocyanate curing agent (hereinafter, sometimes simply referred to as "curing agent") is a coating film forming resin constituting the electrodeposition coating film. The blocked polyisocyanate curing agent can be prepared by blocking polyisocyanate with a blocking agent.

[0070] Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimers), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate); and aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, and xylylene diisocyanate.

[0071] As examples of end-capping agents, preferably used are: monoalkyl (or aromatic) alcohols such as n-butanol, n-hexanol, 2-ethylhexanol, lauryl alcohol, phenol methanol, methyl phenyl methanol, etc.; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type two-terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol phenol; polyester-type two-terminal polyols obtained from diols such as ethylene glycol, propylene glycol, 1,4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as p-tert-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam.

[0072] The blocking ratio of the blocked polyisocyanate curing agent is preferably 100%, which has the advantage that the storage stability of the electrodeposition coating composition becomes good.

[0073] As the blocked polyisocyanate curing agent, it is preferable to use in combination a curing agent prepared by blocking an aliphatic diisocyanate with a blocking agent and a curing agent prepared by blocking an aromatic diisocyanate with a blocking agent.

[0074] The blocked polyisocyanate curing agent preferentially reacts with the primary amine of the aminated epoxy resin and then reacts with the hydroxyl group to cure. As the curing agent, at least one curing agent selected from organic curing agents such as melamine resin or phenolic resin, silane coupling agent, and metal curing agent can be used together with the blocked isocyanate curing agent.

[0075] Preparation of resin emulsion

[0076] The resin emulsion can be prepared by dissolving the aminated epoxy resin and the blocked polyisocyanate curing agent in an organic solvent to prepare a solution, mixing these solutions, and then neutralizing with a neutralizing acid. Examples of the neutralizing acid include organic acids such as methanesulfonic acid, aminosulfonic acid, lactic acid, dimethylolpropionic acid, formic acid, and acetic acid. In the present invention, it is more preferred to neutralize the resin emulsion containing the aminated epoxy resin and the curing agent with one or more acids selected from formic acid, acetic acid, and lactic acid.

[0077] The content of the blocked polyisocyanate curing agent needs to be an amount sufficient to react with the primary amino group, secondary amino group or hydroxyl group containing active hydrogen in the aminated epoxy resin during curing to give a good cured coating film. The preferred content of the curing agent is expressed as a solid content mass ratio of the aminated epoxy resin to the curing agent (aminated epoxy resin / curing agent) in the range of 90 / 10 to 50 / 50, more preferably 80 / 20 to 65 / 35. By adjusting the solid content mass ratio of the aminated epoxy resin to the blocked polyisocyanate curing agent, the fluidity and curing speed of the coating film (precipitated film) during film formation are improved, and the coating appearance is improved.

[0078] Generally, the solid content of the resin emulsion is preferably 25 to 50% by mass, particularly 35 to 45% by mass, relative to the total amount of the resin emulsion. Here, the "solid content of the resin emulsion" refers to the components contained in the resin emulsion, and refers to the total mass of the components that will become solids and remain after removing the solvent. Specifically, it refers to the total mass of the aminated epoxy resin, curing agent, and other solid components added as needed contained in the resin emulsion.

[0079] The neutralizing acid is more preferably used in an amount of 10 to 100%, and further preferably in an amount of 20 to 70%, based on the equivalent ratio of the neutralizing acid to the amino equivalents possessed by the aminated epoxy resin. In this specification, the equivalent ratio of the neutralizing acid to the amino equivalents possessed by the aminated epoxy resin is referred to as the neutralization rate. By setting the neutralization rate to 10% or more, affinity to water is ensured, and water dispersibility becomes good.

[0080] <Pigment dispersion paste>

[0081] The cationic electrodeposition coating composition of the present invention may contain a pigment dispersion paste as required. The pigment dispersion paste is a component arbitrarily (optionally) contained in the electrodeposition coating composition, and generally contains a pigment dispersion resin and a pigment.

[0082] Pigment dispersion resin

[0083] The pigment dispersing resin is a resin for dispersing pigments and is used after being dispersed in an aqueous medium. As the pigment dispersing resin, a pigment dispersing resin having a cationic group such as a modified epoxy resin having at least one or more selected from a quaternary ammonium group, a tertiary sulfonium group and a primary amino group can be used. Specific examples of the pigment dispersing resin include, for example, epoxy resins containing quaternary ammonium groups, epoxy resins containing tertiary sulfonium groups, and the like. As the aqueous solvent, water containing ion exchange water or a small amount of alcohols can be used.

[0084] pigment

[0085] The pigment is a pigment commonly used in the electrodeposition coating composition. Examples of the pigment include commonly used inorganic pigments and organic pigments, coloring pigments such as titanium white (titanium dioxide), carbon black, and red iron oxide; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay; and anti-rust pigments such as iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate.

[0086] Production of pigment dispersion paste

[0087] The pigment dispersion paste is prepared by mixing a pigment dispersion resin and a pigment. The content of the pigment dispersion resin in the pigment dispersion paste is not particularly limited, and for example, 20 to 100 parts by mass of the pigment can be used in terms of resin solid content ratio relative to 100 parts by mass of the pigment.

[0088] Usually, the solid content of the pigment dispersion paste is preferably 40 to 70% by mass, particularly preferably 50 to 60% by mass, based on the total amount of the pigment dispersion paste.

[0089] In this specification, the "solid content of the pigment dispersion paste" refers to the components contained in the pigment dispersion paste, and refers to the total mass of the components that remain after the solvent is removed and becomes solid. Specifically, it refers to the total mass of the pigment dispersion resin and pigment contained in the pigment dispersion paste, and other solid components added as needed.

[0090] <Other ingredients, etc.>

[0091] The cationic electrodeposition coating composition of the present invention may further contain a metal nitrite in addition to the above-mentioned components. As the metal nitrite, an alkali metal nitrite or an alkaline earth metal nitrite is preferred, and an alkaline earth metal nitrite is more preferred. Examples of the metal nitrite include calcium nitrite, sodium nitrite, potassium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, zinc nitrite, and the like.

[0092] The cationic electrodeposition coating composition has the advantage of improved corrosion resistance, especially improved edge corrosion resistance (edge ​​rust resistance) by including a metal nitrite. When the cationic electrodeposition coating composition includes a metal nitrite, the metal nitrite is preferably included in an amount of 0.001 to 0.2% by mass in terms of the metal element of the metal component relative to the total mass of the coating film forming resin.

[0093] The above-mentioned metal nitrite can be added to the cationic electrodeposition coating composition by any method. For example, there can be mentioned a method such as preparing an aqueous solution of the metal nitrite in advance and adding it to the cationic electrodeposition coating composition. In addition, the metal nitrite can also be mixed with a pigment in advance and dispersed in the same manner as the pigment.

[0094] <Production of cationic electrodeposition coating composition>

[0095] The cationic electrodeposition coating composition of the present invention can be prepared by mixing a resin emulsion containing an aminated epoxy resin and a blocked polyisocyanate curing agent, a pigment dispersion paste, additives, and the like by a commonly used method.

[0096] In this specification, "solid content of the electrodeposition coating composition" refers to the components contained in the electrodeposition coating composition, and refers to the total mass of the components that become solid after the solvent is removed. Specifically, it refers to the total mass of the solid content of the aminated epoxy resin, the blocked polyisocyanate curing agent, and the pigment dispersion resin, pigment, and other solid components contained in the electrodeposition coating composition as required.

[0097] The solid content of the cationic electrodeposition coating composition of the present invention is preferably 1 to 30% by mass relative to the total amount of the electrodeposition coating composition. When the solid content of the cationic electrodeposition coating composition is less than 1% by mass, the amount of electrodeposition coating film precipitation is reduced, and it is likely to be difficult to ensure sufficient corrosion resistance. In addition, when the solid content of the cationic electrodeposition coating composition exceeds 30% by mass, the coverage or coating appearance may deteriorate.

[0098] The cationic electrodeposition coating composition of the present invention preferably has a pH of 4.5 to 7. When the pH of the cationic electrodeposition coating composition is less than 4.5, the amount of acid present in the cationic electrodeposition coating composition becomes an excess amount, and the coating appearance or coating workability may deteriorate. On the other hand, when the pH exceeds 7, the filterability of the cationic electrodeposition coating composition decreases, and the horizontal appearance of the cured electrodeposition coating film sometimes decreases. The pH of the cationic electrodeposition coating composition can be set to the above range by adjusting the amount of neutralizing acid used, the amount of free acid added, etc. The above pH is more preferably 5 to 7.

[0099] The pH of the cationic electrodeposition coating composition can be measured using a commercially available pH meter having a temperature compensation function.

[0100] The milliequivalent amount (MEQ(A)) of the acid relative to 100 g of the solid content of the cationic electrodeposition coating composition is preferably 10 to 50. The milliequivalent amount (MEQ(A)) of the acid relative to 100 g of the resin solid content of the cationic electrodeposition coating composition can be adjusted by the amount of neutralized acid and the amount of free acid.

[0101] Here, MEQ(A) is the abbreviation of milliequivalent (acid), which refers to the total mg equivalent of all acids per 100 g of solid content of the coating. The MEQ(A) can be measured by accurately weighing about 10 g of the solid content of the electrodeposition coating composition, dissolving it in about 50 ml of a solvent (THF: tetrahydrofuran), and then performing potentiometric titration using a 1 / 10N NaOH solution to quantify the amount of acid contained in the cationic electrodeposition coating composition.

[0102] The cationic electrodeposition coating composition of the present invention may contain additives commonly used in the coating field as required, such as organic solvents such as ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monophenyl ether, etc., surfactants such as anti-drying agents and defoamers, viscosity modifiers such as acrylic resin particles, anti-sag agents, vanadium salts, copper, iron, manganese, magnesium, calcium salts and other inorganic rust inhibitors, etc. In addition to these, known auxiliary complexing agents, buffers, smoothing agents, stress relaxation agents, glossing agents, semi-glossing agents, antioxidants and ultraviolet absorbers, etc. may also be blended according to the purpose. These additives may be added when the resin emulsion is manufactured, may be added when the pigment dispersion paste is manufactured, or may be added when the resin emulsion and the pigment dispersion paste are mixed or added after mixing.

[0103] The cationic electrodeposition coating composition of the present invention may further include other film-forming resin components in addition to the above-mentioned aminated epoxy resin. Examples of other film-forming resin components include acrylic resins, polyester resins, urethane resins, butadiene resins, phenolic resins, and xylene resins. Examples of other film-forming resin components that may be included in the electrodeposition coating composition include phenolic resins and xylene resins. Examples of phenolic resins and xylene resins include xylene resins having 2 or more and 10 or less aromatic rings.

[0104] The cationic electrodeposition coating composition of the present invention also uses the solubility parameter (SP) of the mixture obtained by mixing the aminated epoxy resin and the above-mentioned blocked polyisocyanate curing agent as an indicator of the performance of the electrodeposition coating. In the present invention, the solubility parameter (SP) of the mixture obtained by mixing the aminated epoxy resin and the above-mentioned blocked polyisocyanate curing agent needs to be 9.9 to 11.3, preferably 9.9 to 11.2, and more preferably 9.9 to 11.1. If the solubility parameter (SP) of the mixture obtained by mixing the aminated epoxy resin and the above-mentioned blocked polyisocyanate curing agent is less than 9.9, the adhesion decreases, and conversely, if it is greater than 11.3, the hydrophilicity increases and the barrier property of the coating film decreases.

[0105] The cationic electrodeposition coating composition of the present invention is preferably applied to a steel plate so that the dry film thickness is 15 μm and the number of residual close-fitting functional groups after baking at 170° C. for 20 minutes is 78.6 to 134.7 mgKOH / g. This is to define the performance of the coating film after obtaining the coating composition. The number of residual close-fitting functional groups is a theoretical value and can be calculated by subtracting the amount of isocyanate groups (mgKOH / g) of the blocked polyisocyanate curing agent from the total amount of functional groups of the aminated epoxy resin, specifically the amount of hydroxyl groups (mgKOH / g) and the amount of primary amines (mgKOH / g). The number of residual close-fitting functional groups is preferably 89.8 to 123.4 mgKOH / g, and more preferably 95.4 to 117.8 mgKOH / g. If the number of residual adhesive functional groups in the coating film coated under this condition is less than 78.6 mgKOH / g, sufficient adhesive performance cannot be imparted to the coating film, while if it exceeds 134.7 mgKOH / g, the hydrophilicity of the coating film increases, which has the disadvantage of reducing the barrier property of the coating film.

[0106] <Electrodeposition coating and electrodeposition coating film formation>

[0107] By using the cationic electrodeposition coating composition of the present invention to perform electrodeposition coating on the object to be coated, an electrodeposition coating film can be formed. In the electrodeposition coating using the cationic electrodeposition coating composition of the present invention, the object to be coated is used as a cathode, and a voltage is applied between the cathode and an anode. Thus, an electrodeposition coating film is precipitated on the object to be coated.

[0108] As the coating material to be coated with the cationic electrodeposition coating composition of the present invention, various coating materials that can be electrified can be used. Examples of the coating materials that can be used include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy steel sheets, zinc-iron alloy steel sheets, zinc-magnesium alloy steel sheets, zinc-aluminum-magnesium alloy steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy steel sheets, tin-plated steel sheets, etc.

[0109] In the electrodeposition coating process, the object to be coated is immersed in the electrodeposition coating composition, and then a voltage of 50 to 450 V is applied to perform electrodeposition coating. If the applied voltage is less than 50 V, the electrodeposition may be insufficient, and if it exceeds 450 V, the appearance of the coating film may deteriorate. During electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45°C.

[0110] The time for applying the voltage varies depending on the electrodeposition conditions, but can generally be set to 2 to 5 minutes.

[0111] In the electrodeposition coating using the cationic electrodeposition coating composition of the present invention, the film thickness of the electrodeposition coating film precipitated is preferably such that the film thickness of the electrodeposition coating film finally obtained by heat curing is preferably 5 to 60 μm, more preferably 10 to 25 μm. If the film thickness of the electrodeposition coating film is less than 5 μm, the rust resistance may be insufficient.

[0112] The electrodeposition coating film deposited as described above is washed with water as necessary, and then cured by heating at 120 to 260° C., preferably 140 to 220° C. for 10 to 30 minutes, for example. Thus, a cured electrodeposition coating film is formed.

[0113] In the present invention, the elongation of the cured coating is controlled. The elongation is obtained by coating a cationic electrodeposition coating composition on a steel plate so that the cured film thickness is 20 μm, and measuring the elongation of the electrodeposition coating after baking at 160° C. for 15 minutes. Specifically, the elongation is calculated by calculating the ratio (%) of the length elongated before the coating breaks to the length of the coating before the measurement. The elongation based on the measurement is 0.1 to 4.5%, preferably 2.0 to 4.5%. If the elongation is less than 0.1%, there is a disadvantage of decreased impact resistance test, and if it exceeds 4.5%, there is a disadvantage of increased expansion of the coating during the corrosion resistance test.

[0114] The cationic electrodeposition coating composition of the present invention has the following advantages: even when a cured electrodeposition coating film is provided on a coated object having an edge portion, a cured electrodeposition coating film having excellent rust resistance at the edge portion can be provided. The cationic electrodeposition coating composition of the present invention has a function of retaining the precipitated electrodeposition coating film, and therefore can be suitably used in the case of providing a cured electrodeposition coating film on a coated object having an edge portion.

[0115] In this specification, the corrosion resistance of the cured electrodeposition coating formed on the coated object with an edge portion is evaluated by a salt spray test (35°C x 72 hours) in accordance with JIS Z 2371 (2000). For example, when a high-thickness cured electrodeposition coating with a film thickness of 25 to 50 μm is subjected to a salt spray test, the number of rust on the edge coating portion of the cured electrodeposition coating formed on the coated object with an edge portion is 1 cm 2 For example, the edge portion is less than 3 / cm 2 In the case of , it can be said that the coating film has excellent corrosion resistance (rust resistance) at the edge, and the number of rusts per 1cm 2 Less than 1 / cm at the edge 2 In this case, it can be said that the coating film has very excellent edge corrosion resistance.

[0116] Example

[0117] The present invention is further specifically described by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass standards unless otherwise specified.

[0118] Preparation Example 1-A Preparation of aminated epoxy resin (resin A)

[0119] 12 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 600 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 110 parts of diethanolamine (DETA) and 80 parts of aminopropyldiethanolamine (APDEA) was added, and the mixture was reacted at 140° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin A).

[0120] Preparation Example 1-B Preparation of aminated epoxy resin (resin B)

[0121] 12 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 620 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 110 parts of diethanolamine (DETA) and 70 parts of diethylaminopropylenediamine (DEAPA) was added, and the mixture was reacted at 140° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin B).

[0122] Preparation Example 1-C Preparation of aminated epoxy resin (resin C)

[0123] 12 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 620 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 110 parts of diethanolamine (DETA) and 100 parts of dibutylaminopropylenediamine (DBAPA) was added, and the mixture was reacted at 140° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin C).

[0124] Preparation Example 1-D Preparation of Aminated Epoxy Resin (Resin D)

[0125] 12 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 23 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 650 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 50 parts of dimethylaminopropylamine (DMAPA) and 100 parts of diethanolamine (DETA) was added, and the mixture was reacted at 160° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin D).

[0126] Preparation Example 1-E Preparation of aminated epoxy resin (resin E)

[0127] 25 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 380 parts of bisphenol A, 58 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 1100 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. 110 parts of diethanolamine (DETA) and 10 parts of N-methylethanolamine (MMA) were added, and the reaction was carried out at 140° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin E).

[0128] Preparation Example 1-F Preparation of aminated epoxy resin (resin F)

[0129] 26 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 380 parts of bisphenol A, 58 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 1100 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. 60 parts of diethanolamine (DETA), 20 parts of N-methylethanolamine (MMA), and 85 parts of diethylenetriamine diketimine (diketimine: a methyl isobutyl ketone solution having a solid content of 73%) were added, and the reaction was carried out at 140° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin F).

[0130] Preparation Example 1-G Preparation of Aminated Epoxy Resin (Resin G)

[0131] 12 parts of butyl cellosolve, 940 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 620 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 110 parts of diethanolamine (DETA) and 70 parts of diethylaminopropylenediamine (DEAPA) was added, and the mixture was reacted at 90° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin G).

[0132] Preparation Example 1-H Preparation of Aminated Epoxy Resin (Resin H)

[0133] 12 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical), 325 parts of bisphenol A, 4.2 parts of phenol, and 2 parts of dimethylbenzylamine were added, and the temperature in the reaction container was kept at 120° C. to allow the reaction to proceed until the epoxy equivalent reached 600 g / eq, and then the reaction container was cooled until the temperature in the reaction container reached 110° C. Then, a mixture of 110 parts of diethanolamine (DETA) and 80 parts of aminopropyldiethanolamine (APDEA) was added, and the mixture was reacted at 220° C. for 1 hour to obtain an aminated epoxy resin (cationically modified epoxy resin: resin H).

[0134] The type and amount of the amine compound of the aminated epoxy resin obtained in the above production example, the amination temperature (° C.), the molecular weight distribution and the tertiary amination ratio of the amine compound are shown in Table 1. The molecular weight distribution and the tertiary amination ratio were measured as follows.

[0135] The molecular weight distribution is measured by gel permeation chromatography. Specifically, the number average molecular weight is measured under the following GPC system measurement conditions.

[0136] Device: alliance2695 separation module;

[0137] Column: Tosoh TSKgel ALPHA-M;

[0138] Flow rate: 0.05 ml / min;

[0139] Detector: alliance2414 refractive index detector;

[0140] Mobile layer: N,N'-dimethylformamide;

[0141] Standard samples: TSK STANDARD POLYSTYRENE (manufactured by Tosoh), A-500, A-2500, F-1, F-4, F-20, F-80, F-700, 1-phenylhexane (manufactured by Aldrich Corporation).

[0142] Tertiary amination rate

[0143] Tertiary amination rate (%) = tertiary amine value / total amine value

[0144] Test method for tertiary amine value

[0145] (1) Weigh the sample into a 100 ml beaker.

[0146] (2) Add 0.5 g of pure water.

[0147] (3) The above sample was dissolved in 50 g of THF (tetrahydrofuran).

[0148] (4) Stir for 5 minutes.

[0149] (5) Next, 7.5 ml of acetic anhydride and 2.5 ml of acetic acid were added, and the mixture was stirred at about 40°C for 5 minutes.

[0150] (6) Use an automatic potentiometric titrator to titrate with 0.1 N perchloric acid-acetic acid solution.

[0151] (7) The tertiary amine value is determined according to the following formula.

[0152] Tertiary amine value = (titration amount mL x factor x 10) / (sample amount g x solid content).

[0153] Total amine value test method

[0154] (1) Accurately weigh 500 mg of sample into a 200 ml Erlenmeyer flask.

[0155] (2) Add about 50 ml of glacial acetic acid and dissolve evenly.

[0156] (3) Add 5 to 6 drops of indicator methyl violet solution to make it uniform.

[0157] (4) Titrate with 0.1 N perchloric acid-acetic acid solution and take the point where the solution turns bright green as the endpoint.

[0158] (The above (3) and (4) can also be subjected to potentiometric titration).

[0159] [Table 1]

[0160]

[0161] Preparation Example 2 Preparation of blocked polyisocyanate curing agent (1)

[0162] 1370 parts of polymethylene polyphenyl polyisocyanate (MDI) and 732 parts of MIBK were placed in a reaction container and heated to 60° C. 300 parts of butyl glycol ether and butyl cellosolve 1330 were added dropwise at 60° C. over 2 hours. The mixture was further heated at 75° C. for 4 hours, after which the absorption due to the isocyanate group disappeared in IR spectrum measurement. After cooling, 27 parts of MIBK were added to obtain a blocked polyisocyanate curing agent (1).

[0163] Preparation Example 3 Preparation of Pigment Dispersing Resin

[0164] 2220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were placed in a reaction vessel equipped with a stirring device, a condenser, a nitrogen introduction tube and a thermometer, and the temperature was raised. 2.2 parts of dibutyltin dilaurate were added at 50°C, and 878.7 parts of butanone oxime were added at 60°C. After that, the temperature was kept at 60°C for 1 hour, and the NCO equivalent was confirmed to be 348, and 890 parts of dimethylethanolamine were added. After keeping the temperature at 60°C for 1 hour and confirming that the NCO peak disappeared in IR, 1872.6 parts of 50% lactic acid and 495 parts of deionized water were added while cooling in a manner not exceeding 60°C, and a quaternizing agent was obtained. Then, 870 parts of toluene diisocyanate and 49.5 parts of methyl isobutyl ketone were placed in different reaction vessels, and 667.2 parts of 2-ethylhexanol were added dropwise over 2.5 hours in a manner not to reach above 50°C. After the dropwise addition, 35.5 parts of methyl isobutyl ketone was added and the mixture was kept warm for 30 minutes. Thereafter, the NCO equivalent was confirmed to be 330 to 370, and a semi-blocked polyisocyanate was obtained.

[0165] In a reaction vessel equipped with a stirring device, a condenser, a nitrogen inlet tube and a thermometer, 940.0 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by Dow Chemical) were diluted with 38.5 parts of methanol, and 0.1 parts of dibutyltin dilaurate were added thereto. After the temperature was raised to 50°C, 87.1 parts of toluene diisocyanate were added and the temperature was further raised. 1.4 parts of N,N-dimethylbenzylamine were added at 100°C and the temperature was kept at 130°C for 2 hours. At this time, methanol was fractionated using a fractionating tube. It was cooled to 115°C, methyl isobutyl ketone was added until the solid content concentration was 90%, and then 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added. After heating and stirring at 125°C for 2 hours, 516.4 parts of the above-mentioned semi-blocked polyisocyanate were added dropwise over 30 minutes, and then heated and stirred for 30 minutes. 1506 parts of polyoxyethylene bisphenol A ether was slowly added to dissolve it. After cooling to 90°C, the above-mentioned quaternizing agent was added and the temperature was kept at 70-80°C. The acid value was confirmed to be 2 or less, and a pigment dispersion resin (resin solid content 30%) was obtained.

[0166] Preparation Example 4 Preparation of Pigment Dispersion Paste

[0167] In a sand mill, 106.9 parts of the pigment dispersion resin obtained in Preparation Example 3, 1.6 parts of carbon black, 40 parts of kaolin, 55.4 parts of titanium dioxide, 3 parts of aluminum phosphomolybdate, and 13 parts of deionized water were placed and dispersed to a particle size of less than 10 μm to obtain a pigment dispersion paste (solid content: 60%).

[0168] Preparation Example 5-A Preparation of Electrodeposition Coating Resin Emulsion (EmA)

[0169] 400 g of the resin (resin A) obtained in Production Example 1-A (solid content) and 160 g of the blocked polyisocyanate curing agent (1) obtained in Production Example 2 (solid content) were mixed, and ethylene glycol mono-2-ethylhexyl ether was added so as to be 3% (15 g) relative to the solid content. Next, formic acid was added for neutralization so as to make the neutralization ratio 40%, and ion exchange water was added for gradual dilution to obtain an electrodeposition coating resin emulsion (EmA).

[0170] Preparation Example 5-B~H Preparation of Electrodeposition Coating Resin Emulsions (EmB~H)

[0171] Regarding the aminated epoxy resins (resins B to H) obtained in Production Examples 1-B to 1-H, electrodeposition coating resin emulsions (EmB to EmH) were obtained in the same manner as in Production Example 5-A.

[0172] Example 1

[0173] 1394 g of ion exchange water, 560 g of the resin emulsion (EmA) and 41 g of the pigment dispersion paste obtained in Production Example 4 were added to a stainless steel container, followed by aging at 40° C. for 16 hours to form an electrodeposition coating composition.

[0174] Examples 2 to 4 and Comparative Examples 1 to 4

[0175] In Examples 2, 3, and 4 (EmB, EmC, and EmD) and Comparative Examples 1, 2, 3, and 4 (EmE, EmF, EmG, and EmH), the electrodeposition coating compositions were obtained in the same manner as in Example 1.

[0176] <Electrical conductivity>

[0177] In the electrodeposition bath containing 200 ml of the cationic electrodeposition coating composition obtained in the examples and comparative examples, the conductivity was measured at 25°C using a conductivity meter (CM-305 manufactured by Toa Denpa Kogyo Co., Ltd.). The measured conductivity is recorded in Table 2. The unit is μS / cm 2 .

[0178] Electrodeposition coating

[0179] Cold rolled steel sheets (JIS G3141, SPCC-SD) were immersed in Surf Cleaner EC90 (manufactured by Japan PaintSurf Chemicals Co., Ltd.) at 50°C for 2 minutes for degreasing treatment. Then, they were immersed in a zirconization treatment solution containing 0.005% ZrF and adjusted to pH 4 using NaOH at 40°C for 90 seconds for zirconization treatment. Then, a required amount of 2-ethylhexyl glycol was added to cure the electrodeposition coating composition obtained in the example or comparative example so that the film thickness of the electrodeposition coating film was 20 μm, and then the steel sheet was immersed, and a voltage was applied under the condition of increasing the voltage for 30 seconds to reach 180 V and then maintaining it for 150 seconds, so that an uncured electrodeposition coating film was precipitated on the coated object.

[0180] The uncured electrodeposition coating obtained in this way was cured by baking at 160°C for 15 minutes to obtain an electrodeposition coated plate with a cured electrodeposition coating. The cured electrodeposition coating obtained was evaluated as follows. The results are shown in Table 2. Table 2 also records the characteristics of each electrodeposition coating composition (curability (friction), elongation, cyclic corrosion test (CCT), edge rust prevention, coating workability and coating stability). The respective evaluation methods and evaluation criteria are recorded.

[0181] The following evaluation tests were carried out using the electrodeposition coating compositions and coated plates obtained by the above examples.

[0182] Curing properties (friction)

[0183] The coating film was rubbed 50 times with gauze soaked in methyl isobutyl ketone (MIBK), and the curability was evaluated based on the surface state of the coating film. The evaluation criteria are as follows.

[0184] ○: There is no change in the coating film.

[0185] △: The coating film has streaks.

[0186] ×: The gauze is colored.

[0187] Elongation(%)

[0188] A stress-strain curve of the coating film was prepared, and the ratio (%) of the elongated length before the sample broke to the initial sample length was calculated.

[0189] Cycle Corrosion Test (CCT)

[0190] On the coating film of the cured electrodeposition coated plate using a cold rolled steel sheet, a crosscut scratch was made with a knife until it reached the substrate, and 100 cycles of JASOM609-91 "Automotive Material Corrosion Test Method" were performed. Afterwards, the rust or bulging phenomenon from the crosscut was observed to evaluate the corrosion resistance in accordance with the actual corrosive environment. The evaluation criteria are as follows.

[0191] Evaluation Criteria

[0192] ◎: The maximum width of rust or bulge is less than 5mm from the cutting part (on both sides);

[0193] ○: The maximum width of rust or bulge is 5 mm or more and less than 7.5 mm (on both sides) from the cut part; there is no blistering outside the cut part;

[0194] ○△: The maximum width of rust or bulge is 5 mm or more and less than 7.5 mm (on both sides) from the cut part, and there are also bubbles outside the cut part;

[0195] △: The maximum width of rust or bulge is 7.5 mm or more and less than 10 mm (on both sides) from the cut part;

[0196] △×: The maximum width of rust or bulge is 10 mm or more and less than 12.5 mm (on both sides) from the cut part;

[0197] ×: The maximum width of rust or swelling is 12.5 mm or more from the cut portion (both sides).

[0198] The passing score is ○△ or above.

[0199] Edge rust prevention (edge ​​corrosion test)

[0200] In the evaluation of this test, the following steel plates were used instead of the above-mentioned cold-rolled steel plates: L-shaped special blades (replacement blades) (LB10K: manufactured by Olfa Co., Ltd.) were degreased by immersing them in Surf Cleaner EC90 (manufactured by Japan Paint Surf Chemicals Co., Ltd.) at 50°C for 2 minutes, surface-conditioned by Surf Fine GL-1 (manufactured by Japan Paint Surf Chemicals Co., Ltd.), and then zinc phosphate treated by immersing them in Surf Dyne SD-5000 (manufactured by Japan Paint Surf Chemicals Co., Ltd., zinc phosphate treatment solution) at 40°C for 2 minutes. The coatings of Examples 1 to 4 and Comparative Examples 1 to 4 were electrodeposited on the steel plates under the same conditions as the above-mentioned electrodeposition coating to form a cured electrodeposition coating film, and then the number of rusts on the front end of the L-shaped special blades after the salt spray test at 35°C × 168 hours was examined.

[0201] Evaluation Criteria

[0202] ◎: less than 10;

[0203] ○: more than 10 to less than 20;

[0204] ○△: more than 20 to less than 50;

[0205] △: more than 50 to less than 100;

[0206] ×: More than 100.

[0207] The passing score is ○△ or above.

[0208] Coating workability (GP: grinding unevenness)

[0209] The appearance of the ground portion of the steel plate ground with a grindstone during electrodeposition coating was visually determined to be rough.

[0210] ○: has uniform coating appearance;

[0211] ○△: Although there are some parts that appear slightly uneven, the coating film has a generally uniform appearance as a whole;

[0212] △: Unevenness is seen;

[0213] ×: The coating film appearance is obviously uneven.

[0214] Stability of electrodeposition coating compositions (coating stability)

[0215] The coating stability was evaluated by visually judging the state of the coating composition while the electrodeposition coating composition was left standing or stirred. The evaluation criteria were as follows. Stability here means that the pigment did not precipitate within 15 minutes after the stirring stopped.

[0216] Evaluation Criteria

[0217] ○: Stable in a state where the electrodeposition coating composition is left standing;

[0218] ○△: Although the electrodeposition coating composition is unstable when left standing, it becomes stable immediately after stirring again;

[0219] △: Stable under the condition of continuous stirring of the electrodeposition coating composition;

[0220] ×: The electrodeposition coating composition is not stable even when it is continuously stirred.

[0221] [Table 2]

[0222]

[0223] As shown in Table 2, when the molecular weight distribution of the aminated epoxy resin is 2.7 or less and the elongation is in the range of 0.1 to 4.5%, good results are obtained in corrosion resistance (cyclic corrosion test and edge rust prevention), and other properties (coating workability or coating stability) are also excellent. On the other hand, in the comparative examples, when the molecular weight distribution of the aminated epoxy resin and the elongation of the electrodeposition coating film are out of these ranges, the results of corrosion resistance are insufficient and the results of coating workability are also insufficient.

Claims

1. A cationic electrodeposition coating composition, which is a cationic electrodeposition coating composition containing an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein: The aminated epoxy resin is obtained by reacting an amine compound with an epoxy resin. The molecular weight distribution of the aminated epoxy resin is below 2.7, The cationic electrodeposition coating composition is applied to a steel plate so that the cured film thickness is 20 μm, and the electrodeposition coating film after baking at 160° C. for 15 minutes has an elongation of 0.1 to 4.5%. The above amine compound is a combination of two kinds of primary amine and secondary amine, Primary amines have the formula (1): NH2-(CH2)n-NR 1 R 2 (1) In formula (1), R 1 and R 2 are the same or different, and represent an alkyl group having 1 to 6 carbon atoms which may have a hydroxyl group at the end, and n represents an integer of 2 to 4, Secondary amines have the formula (2): R 3 R 4 NH(2) In formula (2), R 3 and R 4 It represents an alkyl group having 1 to 4 carbon atoms and having a hydroxyl group at the terminal.

2. The cationic electrodeposition coating composition according to claim 1, wherein When the aminated epoxy resin is obtained, the tertiary amination rate of the amine compound is 85% or more.

3. A cationic electrodeposition coating film obtained by coating with the cationic electrodeposition coating composition according to claim 1 or 2.

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