JP2009235351A - Cationic electrodeposition coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic electrodeposition coating composition excellent in coating film smoothness and end face covering property of a cured electrodeposition coating film. <P>SOLUTION: The cationic electrodeposition coating composition includes a cationic epoxy resin, a block isocyanate curing agent, crosslinked resin particles, and an inorganic pigment of not more than 10 wt.% with respect to the coating material solid content in the cationic electrodeposition coating composition. The crosslinked resin particles have an average particle diameter of 1.0 to 3.0 μm. The block isocyanate curing agent includes a block isocyanate prepared by blocking polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating composition containing a specific cross-linked resin particle and a specific blocked isocyanate curing agent and excellent in coating film smoothness and end face coverage, and a coating electrode smoothing of a cured electrodeposition coating film using the same. The present invention relates to a method that achieves both compatibility and end face coverage.

  Electrodeposition coating is a coating method performed by immersing an object to be coated in an electrodeposition coating composition and applying a voltage. In this method, even an object to be coated having a complicated shape can be painted in detail, and can be painted automatically and continuously, so that it has a large and complicated shape, particularly for an automobile body. Widely used as an undercoating method for objects to be coated.

  Since electrodeposition coating is coating coating on an article, it is naturally desirable that the painted surface be smooth. On the other hand, end surfaces such as metal punched portions have acute end surfaces, and the anticorrosion performance deteriorates unless the coating film is sufficiently coated on these portions. Therefore, both coating surface smoothness and end face coverage are performances required in electrodeposition coating. The coating surface smoothness is obtained by fluidization by lowering the viscosity of the uncured coating during bake-curing, whereas the end surface coverage is achieved by preventing the viscosity of the uncured coating from decreasing. What is obtained, that is, end face coverage, is obtained by suppressing sagging of the coating film during curing of the coating film and leaving the coating film on an acute end face. That is, the coating film smoothness and the end face coverage are contradictory properties.

  Incidentally, in recent years, low ash differentiation has been promoted in electrodeposition coating compositions. Low ash differentiation is to reduce the amount of inorganic pigment that is a solid component having a high specific gravity. By low-ash differentiation of the electrodeposition coating composition, the content of inorganic pigments having a high specific gravity that tends to precipitate is reduced. Therefore, it is possible to reduce the occurrence of sedimentation during electrodeposition coating. Thus, by low ash differentiation in the electrodeposition coating composition, it is possible to reduce energy and labor that have been used to stir the electrodeposition bath to prevent sedimentation. Therefore, if the content of the inorganic pigment is decreased in order to meet the above-mentioned demand for low ash differentiation, the amount of resin in the paint will be relatively increased. And the relative increase in the amount of resin in the paint makes it impossible to increase the viscosity of the uncured deposited coating film obtained by electrodeposition coating to an appropriate range, resulting in sagging control at the end face portion. Can not be adjusted appropriately, and the end face coverage is reduced.

JP 2002-212488 (Patent Document 1) discloses emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture using an acrylic resin having an ammonium group as an emulsifier for the purpose of improving the rust prevention property of an edge portion. A cationic electrodeposition coating composition containing the crosslinked resin particles obtained by the above is disclosed. The resin particles obtained here have a small particle size of 0.05 to 0.3 μm. However, when the cross-linked resin particles having an average particle size of 1.0 μm or less described in Patent Document 1 are blended with the electrodeposition coating composition, sufficient smoothness is obtained when a high-grade appearance such as an automobile is required. It may not be possible.
JP 2002-212488 A

  In the present invention, as described above, for the purpose of low ash differentiation, a method for preventing sedimentation of the paint and achieving both conflicting performances of coating surface smoothness and end face coverage in a cationic electrodeposition coating composition, in particular, It is an object of the present invention to provide a method for further improving end face coverage.

  As a result of investigating a method for achieving both coating surface smoothness and end face coverage of a cationic electrodeposition coating composition aiming at low ash differentiation, the present inventors have an average particle diameter of 1.0 to 3.0 μm. By blending the crosslinked resin particles into the cationic electrodeposition coating composition and using a specific blocked isocyanate curing agent, the coating surface smoothness and the end face coverage are improved, especially the end face coverage is improved. As a result, the present invention has been completed.

That is, the present invention
A cationic electrodeposition coating composition comprising a cationic epoxy resin, a blocked isocyanate curing agent, crosslinked resin particles, and an inorganic pigment in an amount of 10% by weight or less based on the solid content of the cationic electrodeposition coating composition,
The crosslinked resin particles have an average particle diameter of 1.0 to 3.0 μm,
The blocked isocyanate curing agent comprises a blocked isocyanate obtained by blocking polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0.
A cationic electrodeposition coating composition is provided, whereby the above object is achieved.

A storage elastic modulus (G ′) at 140 ° C. of an uncured deposited coating film obtained by electrodeposition coating of the cationic electrodeposition coating composition is 80 to 500 dyn / cm ² , and a loss elastic modulus at 80 ° C. ( More preferably, G ″) is 10 to 150 dyn / cm ² .

  The content of the crosslinked resin particles is more preferably 3 to 15% by weight based on the resin solid content of the cationic electrodeposition coating composition.

  Furthermore, the heat softening temperature of the crosslinked resin particles is more preferably 120 to 180 ° C.

The present invention also provides
In the method of forming a cured electrodeposition coating film by immersing an object to be coated in a cationic electrodeposition coating composition, applying a voltage, and baking and curing, the cationic electrodeposition coating composition has an average particle diameter of 1.0 to 1.0. The cationic electrodeposition coating composition comprising a crosslinked resin particle having a size of 3.0 μm and a blocked isocyanate curing agent containing a blocked isocyanate obtained by blocking a polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0. There is also provided a method for achieving both coating film smoothness and end face coverage of a cured electrodeposition coating film, which is characterized in that it is.

The present invention also provides
In the method of forming a cured electrodeposition coating film by immersing an object to be coated in the cationic electrodeposition coating composition, forming an uncured deposited coating film by applying a voltage, and then baking and curing the coating film,
Coating film smoothness and end face of the deposited coating film having a storage elastic modulus (G ′) at 140 ° C. of 80 to 500 dyn / cm ² and a loss elastic modulus (G ″) at 80 ° C. of 10 to 150 dyn / cm ² Also provided is a method for forming a cured electrodeposition coating film with improved coverage.

  According to the present invention, a polyphenylene polymethylene having an isocyanate group content of 29.0 to 31.0 and containing crosslinked resin particles having an average particle size of 1.0 to 3.0 μm in the cationic electrodeposition coating composition. By using a blocked isocyanate curing agent containing a blocked isocyanate obtained by blocking polyisocyanate, it is possible to achieve both the smoothness of the coating film surface smoothness and the end face coverage, in particular, the improvement of the end face coverage. In an electrodeposition coating composition that is required to exhibit anticorrosion performance, end face coverage is an important property. In particular, in the case of a low ash type cationic electrodeposition coating composition, since it is impossible to obtain an increase in the viscosity of the coating film due to the inorganic pigment, it is expected that the end face coverage is deteriorated. On the other hand, in the present invention, by blending a specific crosslinked resin particle and a specific blocked isocyanate curing agent into the cationic electrodeposition coating composition, the coating film surface smoothness and the end face covering properties, which are contradictory properties, are obtained. Both are achieved, and in particular, the end face coverage is further improved. The present invention is particularly effective as a means for maintaining or improving coating film performance in a low ash type cationic electrodeposition coating composition.

Cationic electrodeposition coating composition The cationic electrodeposition coating composition of the present invention is a block isocyanate curing comprising a specific cross-linked resin particle, a blocked isocyanate blocked with a polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0. Agents, and cationic epoxy resins, neutralizing acids, organic solvents, and the like.

Crosslinked resin particles The average particle diameter of the crosslinked resin particles used in the present invention is 1.0 to 3.0 µm. Even in the prior art, proposals have been made for blending crosslinked resin particles into a cationic electrodeposition coating composition, but most of such crosslinked resin particles have an average particle size of less than 1.0 μm. In the prior art, since the crosslinked resin particles are blended simply to control the viscosity, the crosslinked resin particles having an average particle diameter of less than 1.0 μm are required. In contrast, in the present invention, crosslinked resin particles having an average particle size larger than that of the prior art are used in order to achieve both coating surface smoothness and end face coverage.

  The average particle diameter of the crosslinked resin particles used in the present invention is 1.0 to 3.0 μm as described above, and the lower limit thereof is preferably 1.2 μm, more preferably 1.5 μm. On the other hand, the upper limit is preferably 2.5 μm, more preferably 2.2 μm. As described above, when the particle diameter is smaller than 1.0 μm, the average particle diameter of the resin particles of the prior art is in the range, and the coating film surface smoothness is deteriorated. Crosslinked resin particles having an average particle diameter of more than 3.0 μm cause a decrease in coating film smoothness due to sedimentation without stirring of the electrodeposition coating composition and accumulation of particles on a horizontal surface during electrodeposition coating. The average particle size here can be measured by the following method.

  The average particle diameter of the crosslinked resin particles in the present invention can be measured by a granular particle transmission measurement method. As an apparatus which can be used for the measurement of the average particle diameter of a crosslinked resin particle, the Nikkiso Co., Ltd. make, MICROTRAC9340UPA etc. are mentioned, for example. The average particle size is measured by measuring the particle size distribution of the crosslinked resin particles using the refractive index of the solvent (water) 1.33 and the refractive index of the resin (depending on the type of resin. For example, 1.59 for acrylic resins). And it can measure by calculating the average particle diameter in cumulative relative frequency F (x) = 0.5 from the measured value.

  The crosslinked resin particles used in the present invention preferably have a heat softening temperature of 120 ° C. or higher, more preferably 120 to 180 ° C. The lower limit value of the thermal softening temperature is preferably 140 ° C, more preferably 160 ° C. When the heat softening temperature is lower than 120 ° C., the end face coverage cannot be secured. On the other hand, synthesis of a material in which the thermal softening temperature of the crosslinked resin particles exceeds 180 ° C. is substantially impossible with the current technology.

The thermal softening temperature is a temperature at which the crosslinked resin particles start to soften. That is, the storage elastic modulus G ′ at each temperature of the target crosslinked resin particle is obtained, and the temperature at which the change in the storage elastic modulus G ′ with respect to the temperature change changes abruptly. Here, the storage elastic modulus G ′ is a parameter indicating the elastic behavior of the material,
Storage elastic modulus G ′ (elastic term) G ′ = (σ ₀ / γ ₀ ) cos δ (dyn / cm ² )
It can be obtained more.

  The storage elastic modulus G ′ is a dynamic viscoelastic parameter. Dynamic viscoelasticity is an elastic modulus observed when a vibration (periodic) strain or force is applied to a linear viscoelastic body, and is related to frequency and temperature. The following descriptions of dynamic viscoelasticity include: lecture rheology (edited by the Japan Rheological Society), Chapter 2 Rheology of Polymer Liquids, p31-39, and Introduction to Polymer Chemistry (Seizo Okamura, Akio Nakajima, Shigeharu Onogi, Yasunori Nishijima, Higashimura Toshinobu and Norio Ise), Chapter 4 Performances of Polymeric Materials Viscoelasticity, p149-155.

The stress and strain at the angular velocity ω (2π × frequency f) are given by the following equations.
Strain γ (t) = γ ₀ e ^iωt (dyn / cm ² )
Stress σ (t) = σ ₀ e ^{i (ωt + δ)} (dyn / cm ² )
(Where γ (t) is the strain at time t, σ (t) is the stress at time t, γ ₀ is the strain at t = 0, σ ₀ is the stress at t = 0, and δ is the phase difference. )
The complex elastic modulus G ^{* at} this time is
G ^* = (σ ₀ / γ ₀ ) e ^iδ = (σ ₀ / γ ₀ ) (cos δ + i sin δ)
It is represented by The complex viscosity η ^* = G ^* / ω (Pa · s), which is generally used as a viscosity control factor for paints, is a quantification of viscoelasticity that has both properties of paint viscosity and elasticity. .

  The measurement of the heat softening temperature of the crosslinked resin particles used in the present invention can be performed as follows. A sample obtained by adjusting the solid content concentration of the crosslinked resin particles to 30% by weight was measured by temperature dependency measurement using a Rhesol-G3000 (manufactured by UBM Co., Ltd.) which is a rotary dynamic viscoelasticity measuring device. The storage elastic modulus G ′ is measured from 90 ° C. under the measurement conditions of 0.5 degree strain, 0.02 Hz frequency, and 4.0 ° C./min. A measurement result becomes like the graph of FIG. As apparent from FIG. 1, the storage elastic modulus G ′ of the crosslinked resin particles maintains a constant viscosity in the initial temperature range (near 90 to 140 ° C. in FIG. 1), but exceeds a certain temperature (140 ° C. in FIG. 1). The storage elastic modulus G ′ starts to decrease at the boundary of the temperature. The temperature of the intersection (inflection point) is defined as the thermal softening temperature by drawing the tangent of the region where the viscosity is changed and the tangent of the region where the viscosity is lowered.

  In order to increase the thermal softening temperature of the resin particles, it is necessary to increase the degree of crosslinking of the resin particles. And in order to ensure the heat softening temperature range in this invention, the resin particle needs to be a crosslinked resin particle. The glass transition temperature is also an index indicating the softening of the resin. However, when the glass transition temperature (Tg) is measured in the crosslinked resin particles, it reaches a level of several hundred degrees (° C.). It cannot measure its own softening properties. Therefore, in the present invention, the thermal softening temperature is used as an index indicating the degree of crosslinking of the crosslinked resin particles.

  The crosslinked resin particles are preferably produced by suspension polymerization considering that the average particle size is 1.0 to 3.0 μm. As a method for preparing the crosslinked resin particles, it can be produced by other methods such as emulsion polymerization, provided that the average particle diameter satisfies the above range. However, this is from the viewpoint of adjusting the average particle diameter to a desired range. Suspension polymerization is preferred.

  The cross-linked resin particles are not particularly limited. For example, resin particles made of a resin having a cross-linked structure obtained mainly from an ethylenically unsaturated monomer, resin particles made of internally cross-linked urethane resin, and internally cross-linked melamine resin. Crosslinked resin particles made of, for example, can be mentioned.

  The resin having a crosslinked structure obtained mainly from the ethylenically unsaturated monomer is not particularly limited. For example, a monomer composition containing an ethylenically unsaturated monomer containing a crosslinkable monomer as an essential component is used as an aqueous medium. Intra-crosslinked resin particles obtained by suspension polymerization in water to prepare an aqueous dispersion and solvent substitution of the obtained aqueous dispersion; low SP organic solvent such as aliphatic hydrocarbon or ester, ketone A monomer composition containing an ethylenically unsaturated monomer containing a crosslinkable monomer as an essential component in a non-aqueous organic solvent that dissolves a monomer but not a polymer like an organic solvent having a high SP such as alcohol Internally cross-linked resin particles obtained by copolymerization (NAD method); or internally cross-linked resin particles obtained by methods such as precipitation. Child; and the like.

  It does not specifically limit as said ethylenically unsaturated monomer, For example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, etc. Alkyl ester of acrylic acid or methacrylic acid; styrene, α-methyl styrene, vinyl toluene, t-butyl styrene, ethylene, propylene, vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, dimethylaminoethyl (meth) acrylate, etc. Can be mentioned. The ethylenically unsaturated monomers may be used in combination of two or more.

  The crosslinkable monomer is not particularly limited. For example, a monomer having two or more radically polymerizable ethylenically unsaturated bonds in the molecule and two kinds of ethylenically unsaturated groups each having a group capable of reacting with each other. The combination of a monomer containing can be mentioned.

  The monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule, which is a kind of a crosslinkable monomer that can be used for the production of the internally crosslinked resin particles, is not particularly limited. Glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate , Neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol Triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1,1-trishydroxymethylethanediacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethane dimethacrylate, 1,1,1-trishydroxymethylethane trimethacrylate, 1,1,1-trishydroxymethylpropanedi Polymerizable unsaturated monopolymers of polyhydric alcohols such as acrylates and 1,1,1-trishydroxymethylpropane dimethacrylate Bonic acid ester; polymerizable unsaturated alcohol ester of polybasic acid such as triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate; substituted with two or more vinyl groups such as divinylbenzene Aromatic compounds that have been prepared.

  There is no particular limitation on the combination of the functional groups that react with each other in the monomer having two types of ethylenically unsaturated groups, each having a group that can react with each other. For example, an epoxy group, a carboxyl group, and an amino group And combinations of carbonyl group, epoxy group and carboxylic acid anhydride group, amino group and carboxylic acid chloride group, alkyleneimino group and carbonyl group, organoalkoxysilane group and carboxyl group, hydroxyl group and isocyanate glycidyl acrylate group Can do. Of these, a combination of an epoxy group and a carboxyl group is more preferable.

  The resin particles comprising the internally cross-linked urethane resin side by side with a carboxylate formed by reacting a polyisocyanate component with a diol having a hydroxyl group at the end and a diol having a carboxyl group or an active hydrogen-containing component having a triol. Resin particles comprising a polyurethane polymer obtained by reacting an isocyanate end group-containing polyurethane prepolymer in the chain with an active hydrogen-containing chain extender.

  The polyisocyanate component used in the prepolymer is an aromatic diisocyanate such as diphenylmethane-4,4′-diisocyanate, tolylene diisocyanate or xylylene diisocyanate; an aliphatic such as hexamethylene diisocyanate or 2,2,4-trimethylhexane diisocyanate. Diisocyanates; 1-cyclohexane diisocyanate, 1-isocyanate-3-isocyanate methyl-3,5-trimethylcyclohexane (isophorone diisocyanate), 4,4′-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate, and the like; be able to. The polyisocyanate component is more preferably hexamethylene diisocyanate or isophorone diisocyanate.

  The diol having a hydroxyl group at the terminal is not particularly limited, and examples thereof include a polyether diol, a polyester diol, or a polycarbonate diol having a molecular weight of 100 to 5000. The diol having a hydroxyl group at the terminal is not particularly limited. For example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, polycaprolactone diol, poly-3-methyl Examples include valerolactone diol and polyhexamethylene carbonate.

  It does not specifically limit as said diol containing a carboxyl group, For example, dimethylol acetic acid, dimethylol propionic acid, dimethylol butyric acid etc. can be mentioned. Of these, dimethylolpropionic acid is preferable.

  The triol is not particularly limited, and examples thereof include trimethylolpropane, trimethylolethane, and glycerin polycaprolactone triol. By using triol, the inside of the urethane resin particles has a crosslinked structure.

  The crosslinked resin particles composed of the above internally crosslinked melamine resin are not particularly limited. For example, after the melamine resin and the polyol are dispersed in water in the presence of an emulsifier, the polyol and the melamine resin are dispersed in the particles formed by the dispersion. Examples thereof include internally cross-linked melamine resin particles obtained by performing a cross-linking reaction.

  The melamine resin is not particularly limited, and examples thereof include di-, tri-, tetra-, penta-, hexa-methylol melamine and alkyl etherified products thereof (alkyl is methyl, ethyl, propyl, isopropyl, butyl, isobutyl). And so on. Examples of the melamine resin that is commercially available include Cymel 303, Cymel 325, and Cymel 1156 manufactured by Mitsui Cytec.

  It does not specifically limit as said polyol, For example, the molecular weight 500-3000 triol, a tetrol, etc. can be mentioned. The polyol is more preferably polypropylene ether triol or polyethylene ether triol.

  The crosslinked resin particles are those obtained by isolating the internally crosslinked resin particles by a method such as filtration, spray drying, freeze drying, etc., and pulverizing them to an appropriate average particle size using a mill or the like and using them in a powder state. Even in such a case, the obtained aqueous dispersion may be used as it is or after replacing the medium by solvent replacement.

  The content of the crosslinked resin particles in the present invention is preferably 3 to 15% by weight with respect to the resin solid content in the cationic electrodeposition coating composition. The lower limit is preferably 4% by weight, more preferably 5% by weight. On the other hand, the upper limit is preferably 12% by weight, more preferably 10% by weight. When the content of the crosslinked resin particles is less than 3% by weight, it may be difficult to achieve both coating surface smoothness and end face coverage. If it exceeds 15% by weight, the coating film performance such as corrosion resistance may be deteriorated. In the present specification, the “resin solid content” means the solid weight of all resin components (including crosslinked resin particles) contained in the cationic electrodeposition coating composition.

Blocked isocyanate curing agent The cationic electrodeposition coating composition of the present invention comprises a blocked isocyanate curing agent in which an isocyanate group of a polyisocyanate having two or more isocyanate groups in one molecule is blocked. The cationic electrodeposition coating composition of the present invention is characterized by containing a blocked isocyanate obtained by blocking polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0 as a blocked isocyanate curing agent. Here, polyphenylene polymethylene polyisocyanate is generally referred to as “polymeric MDI”, and is a mixture of MDI oligomers that are more nucleated and functionalized than pure MDI (diphenylmethane diisocyanate) having two benzene rings in one molecule. It is.

  The polyphenylene polymethylene polyisocyanate used for the preparation of the blocked isocyanate curing agent in the present invention has an isocyanate group content of 29.0 to 31.0. The isocyanate group content is the weight part (average value) of the isocyanate group in 100 parts by weight of the isocyanate component. The isocyanate group content is preferably 29.5 to 30.5. With respect to the individual polyphenylene polymethylene polyisocyanates constituting the “polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0”, the structural formula can be used as follows. In addition, polyphenylene polymethylene polyisocyanate (polymeric MDI) is a mixture, and “n” in the following formula 1 is an integer. The average number of nuclei of the mixture having an isocyanate group content of 29.0 to 31.0 is 3.5. The average number of nuclei is the average number of isocyanate groups contained in one molecule of polyphenylene polymethylene polyisocyanate.

［式中、ｎは整数である。］

[Wherein n is an integer. ]

  Polymeric MDI (also referred to as crude MDI) that is generally used in electrodeposition coating compositions has an average number of nuclei of 2.8 (isocyanate group content 31.0-32.5). Thus, it can be said that the polyphenylene polymethylene polyisocyanate used in the present invention has a higher degree of polymerization as compared to the commonly used polymeric MDI.

  The degree of polymerization of polyphenylene polymethylene polyisocyanate used in the present invention is known to those skilled in the art in the polymerization reaction of aniline and formaldehyde in the preparation of diaminodiphenylmethane mixture, which is a raw material for polyphenylene polymethylene polyisocyanate and diphenylmethane diisocyanate. By adjusting by a method, it can be set as the polymerization degree of a specific range. In addition, when the isocyanate group content of polyphenylene polymethylene polyisocyanate exceeds 31.0, the polymerization degree of polyphenylene polymethylene polyisocyanate is low, and good end face coverage cannot be obtained. Further, when the isocyanate group content of the polyphenylene polymethylene polyisocyanate is less than 29.0, there is a disadvantage that the viscosity is increased as the isocyanate has a higher molecular weight, and the reactivity is further lowered.

  The blocking agent that blocks polyphenylene polymethylene polyisocyanate is added to the isocyanate group of the polyisocyanate and is stable at room temperature, but can regenerate free isocyanate groups when heated to a temperature higher than the dissociation temperature. As the blocking agent, commonly used alcohols, phenyls, ε-caprolactam, oximes, active methylene compounds and the like can be used, and in particular, ε-caprolactam and butyl cellosolve can be used. Blocking of the isocyanate group of the polyisocyanate can be carried out by a general method known to those skilled in the art. Adducts or prepolymers obtained by reacting polyphenylene polymethylene polyisocyanate with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, etc. at an NCO / OH ratio of 2 or more are also used for the preparation of block isocyanate curing agents. You can do it.

  In the present invention, a blocked isocyanate other than the blocked isocyanate obtained by blocking the polyphenylene polymethylene polyisocyanate may be included. Examples of such a blocked isocyanate include blocked isocyanates obtained by blocking polyisocyanates such as aliphatic, alicyclic, aromatic and aromatic-aliphatic other than polyphenylene polymethylene polyisocyanate. Examples of other polyisocyanates include aromatics such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI, but not including the above polyphenylene polymethylene polyisocyanate), p-phenylene diisocyanate, and naphthalene diisocyanate. Diisocyanates; C3-C12 aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI) ), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene Cyclohexyl-4,4′-diisocyanate and 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2. 1] Aliphatic diisocyanates having 5 to 18 carbon atoms such as heptane (also called norbornane diisocyanate); aromatic rings such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI) Aliphatic diisocyanates possessed; modified products of these diisocyanates (urethanes, carbodiimides, uretdiones, uretonimines, burettes and / or isocyanurates). These may be used alone or in combination of two or more. As these polyisocyanate blocking agents, those mentioned above can be used.

  The content of polyphenylene polymethylene polyisocyanate in the polyisocyanate used for preparing the blocked isocyanate curing agent is preferably 60 to 100% by weight, more preferably 70 to 100% by weight, and 80 to 100% by weight. More preferably.

  In the present invention, by blending the specific crosslinked resin particles and the specific blocked isocyanate curing agent in the cationic electrodeposition coating composition, it is difficult to achieve particularly in the low ash type cationic electrodeposition coating composition. The coating surface smoothness and the end face coverage, which are the performances to be achieved, are achieved, and in particular, the end face coverage is further improved. Here, the low ash type cationic electrodeposition coating composition means that the content of the inorganic pigment in the solid content of the cationic electrodeposition coating composition is 10% by weight or less.

In the present invention, by using the specific crosslinked resin particles and the specific blocked isocyanate curing agent, it is possible to achieve both contradictory performances of coating surface smoothness and end face coverage in a low ash type cationic electrodeposition coating composition. The reason for this is as follows.
The coating film (uncured electrodeposition coating film) deposited on the coating object by immersing the coating object in the cationic electrodeposition coating composition and applying a voltage is generally 10 to 30 at 120 to 260 ° C. It hardens | cures by baking for minutes and a cured electrodeposition coating film will be obtained. In this baking process, the deposited film on the object to be coated is gradually heated from the environmental temperature to the curing temperature.
By adding the above-mentioned specific crosslinked resin particles to the cationic electrodeposition coating composition, the present inventors cause a decrease in viscosity in a relatively low temperature range near 80 ° C. and a relatively high temperature range near 100 to 140 ° C. Viscoelastic behavior occurs, more specifically, the viscosity starts to decrease from 40 to 80 ° C., and the viscosity increases slightly between about 80 to 100 ° C., and when the temperature exceeds 100 ° C., the viscosity greatly decreases and flows, It has been experimentally found that after this flow, the curing reaction starts and the viscosity begins to rise again and gradually rises to around 150 ° C., and then the viscosity suddenly rises to complete the curing.
In the viscoelastic behavior of baking and hardening of this deposited coating film, a decrease in viscosity occurs in a relatively low temperature region around 80 ° C., so that a flow of a so-called coating film surface occurs, thereby improving coating film smoothness. . On the other hand, when a large viscosity drop occurs in a relatively high temperature range near 100 to 140 ° C., the coating film deposited on the article to be coated will flow down. This flow-down of the deposited coating film is particularly noticeable on the end face of the object to be coated, thereby reducing the end face coverage.

  This time, in addition to the addition of the specific cross-linked resin particles, the present inventors further reduce the viscosity in a relatively low temperature range near 80 ° C. by further using the specific block isocyanate curing agent, and It has been found by experiments that viscoelastic behavior that does not cause a large decrease in viscosity at a relatively high temperature range around 140 ° C. can be exhibited. Although it is not bound by theory, the reason why the contradictory performances of the coating film surface smoothness and the end face coverage are achieved by using the specific crosslinked resin particles and the specific blocked isocyanate curing agent is not limited by theory. It seems like.

  In the present invention, by using the specific crosslinked resin particles and the specific blocked isocyanate curing agent, the crosslinked resin particles, the blocked isocyanate curing agent, and the cationic epoxy resin are in a relatively high temperature range in baking curing. It is thought that an interaction occurs in This interaction is considered to hardly occur at a relatively low temperature range in the coating temperature and bake hardening. As a result, a viscoelastic behavior has been achieved in which a viscosity decrease occurs in a relatively low temperature region near 80 ° C., and a large viscosity decrease does not occur in a relatively high temperature region near 140 ° C. The compatibility of the contradictory performance of smoothness and end face coverage is achieved. In the present invention, the reason why such a limited interaction occurs according to the temperature is considered as follows. In the low temperature range, the crosslinked resin particles, the blocked isocyanate curing agent, and the cationic epoxy resin have a degree of freedom of molecular motion and do not increase in viscosity due to the solvent contained in the coating film. On the other hand, as the temperature shifts to a high temperature range, an increase in viscosity is caused by the volatilization of the solvent contained in the coating film. However, by using a specific blocked isocyanate curing agent, the entanglement between the molecules of the crosslinked resin particles and the cationic epoxy resin increases, and a high viscosity is developed because the molecular weight is increased in a pseudo manner.

  Of the resin components contained in the cationic electrodeposition coating composition, the blocked isocyanate curing agent generally has a lower viscosity than other resin components (such as cationic epoxy resins). Due to this difference in viscosity, the interaction between the blocked isocyanate curing agent and other resin components (cationic epoxy resin, etc.) in a relatively high temperature range around 140 ° C. does not generally occur, and the viscosity in this vicinity is low. There is. Further, as a polyisocyanate, a blocked isocyanate curing agent obtained by using other than MDI, for example, HDI, has a high polarity of HDI, and thus hardly interacts with the cationic epoxy resin and the crosslinked resin particles. On the other hand, the blocked isocyanate blocked with polyphenylene polymethylene polyisocyanate contained in the blocked isocyanate curing agent used in the present invention has an MDI skeleton that is more hydrophobic among the polyisocyanates, Compared with a typical block MDI, the degree of polymerization is higher and the molecular weight is higher. In the present invention, among polyisocyanates having an MDI skeleton having higher hydrophobicity, an isocyanate group content of 29.0 to 31.0 is used, and a polyphenylene polymethylene polyisocyanate having a higher degree of polymerization and a higher molecular weight is used. It is considered that the interaction between the crosslinked resin particles, the blocked isocyanate curing agent, and the cationic epoxy resin is developed in a high temperature range.

In the above cationic electrodeposition coating composition, the storage elastic modulus (G ′) at 140 ° C. of an uncured deposited coating obtained by electrodeposition coating of the cationic electrodeposition coating composition is 80 to 500 dyn / cm ² . More preferably, the loss elastic modulus (G ″) at 80 ° C. is 10 to 150 dyn / cm ^2. Here, the storage elastic modulus G ′ is a physical property parameter indicating the elastic behavior of the deposited coating, and the loss elastic modulus The rate G ″ is considered to be a physical property parameter indicating the viscous behavior of the deposited coating. When the loss elastic modulus G ″ at 80 ° C. and the storage elastic modulus G ′ at 140 ° C. are in the predetermined range, it is considered that better coexistence of the coating film surface smoothness and the cross-sectional coverage is achieved.

  In the case of a general paint containing a cationic electrodeposition coating composition, the uncured coating film is governed by the viscosity term at the initial stage of baking, and is greatly affected by the loss elastic modulus G ″. Or the pseudo-crosslinking, the gel point (apparently connected from end to end) is reached, and after that, the elastic term is governed and greatly influenced by the storage elastic modulus G '. The relationship between the loss elastic modulus G ″ (viscosity term) and the storage elastic modulus G ′ (elastic term) of the viscoelastic behavior is the temperature at which the loss elastic modulus G ″ <the storage elastic modulus G ′. The loss elastic modulus G ″ at a temperature below the gel point (80 ° C.) and the storage elastic modulus G ′ at a temperature above the gel point (140 ° C.) are within the above ranges. Better coating smoothness and edge coverage Both is to be achieved Do.

The loss elastic modulus G ″, which is a physical property parameter indicating the viscous behavior of the deposited coating film, can be obtained from the following equation.
Loss modulus (viscosity) G ″ = (σ ₀ / γ ₀ ) sin δ (dyn / cm ² )
Moreover, the storage elastic modulus G ′, which is a physical property parameter indicating the elastic behavior of the deposited coating film, can be obtained from the following formula.
Storage elastic modulus (elasticity) G ′ = (σ ₀ / γ ₀ ) cos δ (dyn / cm ² )
This storage elastic modulus (elasticity) G ′ is a force that tends to stay in place in the baking process, and is a parameter that is involved in ensuring end face coverage.

  If the storage elastic modulus G 'is below the desirable lower limit, the end face coverage of the resulting cured electrodeposition coating film may be deteriorated, and if it exceeds the desirable upper limit, the coating film smoothness may be degraded. If the loss elastic modulus G "is below the desired level, the smoothness of the coating film is improved, but the end face coverage of the resulting cured electrodeposition coating film may be deteriorated. If the upper limit is exceeded, the coating film smoothness is lowered. There is a fear.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. Cationic epoxy resins typically open all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, YD-7011R (manufactured by Toto Kasei Co., Ltd., epoxy equivalent 460 to 490), Epicoat 828 (manufactured by Yuka Shell Epoxy, epoxy equivalent 180 to 190), Epicoat 1001 (the same, epoxy equivalent 450) -500), Epicoat 1010 (the same, epoxy equivalent 3000-4000), etc., and the latter commercial product includes Epicoat 807 (the same, epoxy equivalent 170).

  The following formula described in JP-A-5-306327

[Wherein R represents a residue excluding the glycidyloxy group of the diglycidyl epoxy compound, R ′ represents a residue excluding the isocyanate group of the diisocyanate compound, and n represents a positive integer. An oxazolidone ring-containing epoxy resin represented by the above formula may be used as the cationic epoxy resin.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a blocked isocyanate curing agent blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and a by-product lower alcohol is formed in the system. It is obtained by further distilling off.

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of the oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known.

  These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. In addition, the epoxy resin can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds capable of introducing a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare a primary, secondary or / and tertiary amino group-containing epoxy resin, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of types of amines may be used in combination.

  The cationic epoxy tree used in the present invention preferably has a number average molecular weight of 1000 to 3000, and more preferably 1300 to 2500. If the number average molecular weight is less than 1000, the end face coverage is lowered, and if it is 3000 or more, the smoothness may be lowered. The number average molecular weight can be measured from the measurement result of gel permeation chromatography (GPC) using polystyrene as a standard.

Inorganic Pigment The cationic electrodeposition coating composition of the present invention may contain an inorganic pigment. However, the content of the inorganic pigment is required to be 10% by weight or less based on the solid content of the cationic electrodeposition coating composition. Thus, the cationic electrodeposition coating composition of the present invention is a low ash content type cationic electrodeposition coating composition having a small content of inorganic pigment. Examples of inorganic pigments include commonly used inorganic pigments, for example colored pigments such as titanium white and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; zinc phosphate; Iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, aluminum zinc phosphomolybdate, oxidized And rust preventive pigments such as bismuth, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate and bismuth sulfate.

  The content of the inorganic pigment is preferably 0.5 to 10% by weight, more preferably 0.5 to 7% by weight, based on the solid content of the cationic electrodeposition coating composition. More preferably, it is ˜5% by weight. The content of the inorganic pigment is also referred to as PWC (concentration (% by weight) of the inorganic pigment in the solid content of the cationic electrodeposition coating composition). If the content of the inorganic pigment exceeds 10% by weight, low ash differentiation cannot be achieved sufficiently, and the energy burden for preventing sedimentation increases.

  When a pigment is used as a component of an electrodeposition coating composition, generally the pigment is dispersed in an aqueous medium at a high concentration in advance to form a paste (pigment dispersion paste). This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

  The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous medium. As the pigment dispersion resin, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used.

  In general, the pigment dispersion resin is used in an amount of 20 to 100 parts by weight based on 100 parts by weight of the pigment. After mixing the pigment dispersion resin and the inorganic pigment, until the particle size of the inorganic pigment in the mixture reaches a predetermined uniform particle size, it is dispersed using a normal dispersing device such as a ball mill or a sand grind mill. A pigment dispersion paste is obtained.

  In addition to the above components, the cationic electrodeposition coating composition used in the present invention includes organic tin compounds such as dibutyltin laurate, dibutyltin oxide and dioctyltin oxide, amines such as N-methylmorpholine, strontium, cobalt, A metal salt such as copper may be included as a catalyst. These can act as a catalyst for the dissociation of the blocking agent of the curing agent. The concentration of the catalyst is preferably 0.1 to 6 parts by weight based on 100 parts by weight of the total of the cationic epoxy resin and the curing agent in the electrodeposition coating composition.

Preparation of cationic electrodeposition coating composition The cationic electrodeposition coating composition of the present invention comprises the above-mentioned crosslinked resin particles, cationic epoxy resin, blocked isocyanate curing agent, pigment dispersion paste, and catalyst as required, in an aqueous medium. It can be prepared by dispersing in. Usually, the aqueous medium contains a neutralizing acid in order to neutralize the cationic epoxy resin and improve the dispersibility. The neutralizing acid is inorganic acid or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid, sulfamic acid, acetylglycine. The aqueous medium in this specification is water or a mixture of water and an organic solvent. It is preferable to use ion exchange water as water. Examples of organic solvents that can be used include hydrocarbons (for example, xylene or toluene), alcohols (for example, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers (For example, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (for example, Methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoester) Ether acetate, ethylene glycol monobutyl ether acetate) or mixtures thereof.

  The method for adding the crosslinked resin particles contained in the cationic electrodeposition coating composition of the present invention can be added at any stage of the production stage of the electrodeposition coating composition. Especially, the method of adding directly to the manufactured cationic electrodeposition coating composition is preferable.

  The amount of blocked isocyanate curing agent must be sufficient to react with active hydrogen-containing functional groups such as primary, secondary amino groups, hydroxyl groups, etc. in the cationic epoxy resin during curing to give a good cured coating. In general, the content of the blocked isocyanate curing agent is preferably 10 to 50% by weight, more preferably 20 to 40% by weight, based on the total resin solid content. When the content is 10% by weight or less, curing may be insufficient and the coating film performance may be deteriorated. When it is 50% by weight or more, the viscoelasticity of the uncured coating film is lowered, and there is a possibility that sufficient end surface coverage is not obtained. The amount of neutralizing acid is that which is sufficient to neutralize at least 20%, preferably 30-60%, of the cationic groups of the cationic epoxy resin.

  Organic solvents are those brought in as those used as solvents when preparing resin components such as cationic epoxy resins and blocked isocyanate curing agents. This requires a cumbersome operation for complete removal during preparation. Moreover, when the organic solvent is contained in the cationic epoxy resin used as a binder resin component, the fluidity of the coating film during film formation is improved and the coating film smoothness of the coating film is improved.

  Examples of the organic solvent usually contained in the coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethyl hexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monophenyl ether, and methyl isobutyl ketone. Is mentioned.

  In addition to the above components, the cationic electrodeposition coating composition may contain commonly used coating additives such as a plasticizer, a surfactant, an antioxidant, and an ultraviolet absorber.

Method for applying cationic electrodeposition coating composition The above-mentioned cationic electrodeposition coating composition is electrodeposited on an object to form a cured electrodeposition coating film. The material to be coated is not particularly limited as long as it is electrically conductive, and examples thereof include iron plates, steel plates, aluminum plates, those obtained by surface treatment thereof, and molded products thereof.

  The electrodeposition coating of the cationic electrodeposition coating composition is usually performed by applying a voltage of 50 to 450 V between the object to be coated as a cathode and the anode. When the applied voltage is less than 50V, electrodeposition is insufficient, and when it exceeds 450V, the coating film is destroyed and an abnormal appearance is obtained. At the time of electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

  The electrodeposition coating process is composed of a process of immersing an object to be coated in a cationic electrodeposition paint composition, and a process of applying a voltage between the object to be coated as a cathode and an anode to deposit a film. . Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 4 minutes.

  The film thickness of the electrodeposition coating film can generally be formed in the range of 5 to 25 μm. If the film thickness is less than 5 μm, the rust prevention property may be insufficient. Moreover, when a film thickness exceeds 25 micrometers, it becomes a film thickness more than the film thickness required in order to obtain coating-film performance.

  The electrodeposition coating film obtained as described above is cured by baking at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition coating process, or after washing with water, A cured electrodeposition coating film is obtained.

  The cured electrodeposition coating film of the present invention has high coating film surface smoothness, and the Ra value used for evaluation of coating film surface smoothness is preferably 0.25 μm or less. The Ra value can be measured according to JIS-B0601, for example, using an evaluation type surface roughness measuring machine (manufactured by Mitutoyo Corporation, SURFTEST SJ-201P). The smaller the Ra value, the less the unevenness and the better the coating film appearance.

  In the present invention, in the method of forming a cured electrodeposition coating film by immersing an object to be coated in a cationic electrodeposition coating composition, applying a voltage and baking and curing, the cationic electrodeposition coating composition has an average Cationic battery containing crosslinked resin particles having a particle diameter of 1.0 to 3.0 μm and a blocked isocyanate curing agent containing a blocked isocyanate blocked with a polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0. Provided is a method for achieving both coating film smoothness and end face coverage of a cured electrodeposition coating film, which is a coating composition. In the present invention, even in the low ash type cationic electrodeposition coating composition, the aforementioned specific crosslinked resin particles and the specific blocked isocyanate curing agent are additively added to the cationic electrodeposition coating composition. As a result, the ability to prevent sedimentation of the solid content of the electrodeposition coating composition can be improved, and both coating surface smoothness and end face coverage can be achieved, and in particular, end face coverage is improved.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Production Example 1 Production of amine-modified epoxy resin In a flask equipped with a stirrer, cooler, nitrogen injection tube and dropping funnel, 71.34 parts of 2,4 / 2,6-tolylene diisocyanate (80/20 wt%) and methyl 111.98 parts of isobutyl ketone and 0.02 part of dibutyltin dilaurate were weighed and 14.24 parts of methanol was added dropwise from a dropping funnel over 30 minutes while stirring and nitrogen bubbling. The temperature was raised from room temperature to 60 ° C. due to heat generation. Thereafter, the reaction was continued for 30 minutes, and then 46.98 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from the dropping funnel over 30 minutes. The temperature was raised to 70 to 75 ° C. due to heat generation. After continuing the reaction for 30 minutes, 41.25 parts of bisphenol A propylene oxide (5 mol) adduct (BP-5P manufactured by Sanyo Chemical Industries, Ltd.) was added, the temperature was raised to 90 ° C., and the IR spectrum was measured. The reaction was continued until the NCO group disappeared.

  Subsequently, 475.0 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 475 (YD-7011R manufactured by Toto Kasei Co., Ltd.) was added and dissolved uniformly, then the temperature was raised from 130 ° C. to 142 ° C., and azeotrope with MIBK To remove water from the reaction system. After cooling to 125 ° C., 1.107 parts of benzyldimethylamine was added to carry out an oxazolidone ring formation reaction by a demethanol reaction. The reaction was continued until an epoxy equivalent of 1140.

  Thereafter, the mixture was cooled to 100 ° C., 24.56 parts of N-methylethanolamine, 11.46 parts of diethanolamine and 26.08 parts of aminoethylethanolamine ketimine (78.8% methyl isobutyl ketone solution) were added, and 110 ° C. for 2 hours. Reacted. Thereafter, 20.74 parts of ethylene glycol mono-2-ethylhexyl ether and 12.85 parts of methyl isobutyl ketone were added to dilute to adjust to 82% non-volatile matter. An amine-modified epoxy resin having a number average molecular weight (GPC method) of 1380 and an amine equivalent of 94.5 meq / 100 g was obtained.

Production Example 2 Production of Pigment Dispersion Resin A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel, and 382.20 parts of bisphenol A type epoxy resin (trade name DER-331J) having an epoxy equivalent of 188, 111.98 parts of bisphenol A was weighed, heated to 80 ° C. and dissolved uniformly, and then 1.53 parts of a 1% solution of 2-ethyl-4-methylimidazole was added and reacted at 170 ° C. for 2 hours. After cooling to 140 ° C., 196.50 parts of 2-ethylhexanol half-blocked isophorone diisocyanate (non-volatile content: 90%) was added thereto and reacted until the NCO group disappeared. To this was added 205.00 parts of dipropylene glycol monobutyl ether, followed by 408.00 parts of 1- (2-hydroxyethylthio) -2-propanol and 134.00 parts of dimethylolpropionic acid. 0.000 part was added and it was made to react at 70 degreeC. The reaction was continued until the acid value was 5 or less. The obtained pigment dispersion resin was diluted to 35% non-volatile content with 1150.50 parts of ion exchange.

Production Example 3 Production of pigment dispersion paste 120 parts of the pigment dispersion resin obtained in Production Example 3, 192.0 parts of titanium dioxide, 8.0 parts of dibutyltin oxide and 184 parts of ion-exchanged water were put into a sand grind mill, and the particle size was 10 μm or less. To give a pigment dispersion paste (solid content 48%).

Production Example 4 Production of blocked isocyanate curing agent (1) Polyphenylene polymethylene polyisocyanate (polymeric MDI, isocyanate group content (NCO content) 30.2) in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel ) 432.7 parts, 89 parts of methyl isobutyl ketone, and 0.30 part of dibutyltin dilaurate were weighed, and 367.3 parts of butyl cellosolve was added dropwise from the dropping funnel over 1 hour while stirring and bubbling nitrogen. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, 111.0 parts of methyl isobutyl ketone was added to obtain a non-volatile content of 80% to obtain a blocked isocyanate curing agent (1).

Production Example 5 Production of blocked isocyanate curing agent (2) Polyphenylene polymethylene polyisocyanate (polymeric MDI, isocyanate group content (NCO content) 29.8) in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel. ) 435.4 parts, 89 parts of methyl isobutyl ketone, and 0.30 part of dibutyltin dilaurate were weighed, and 364.6 parts of butyl cellosolve was dropped from the dropping funnel over 1 hour while stirring and bubbling nitrogen. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, 111.0 parts of methyl isobutyl ketone was added to obtain a non-volatile content of 80% to obtain a blocked isocyanate curing agent (2).

Comparative Production Example 1 Production of Blocked Isocyanate Curing Agent (3) Trimer of hexamethylene diisocyanate (Coronate HX: manufactured by Nippon Polyurethane Co., Ltd.) to a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel. Isocyanate group content (NCO content) 21) 199 parts, methyl isobutyl ketone 32 parts, and dibutyltin dilaurate 0.03 parts were weighed and stirred, and nitrogen was bubbled, and 87.0 parts of methyl ethyl ketoxime was added from the dropping funnel for 1 hour. It was dripped over. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, 0.74 parts of n-butanol and 39.93 parts of methyl isobutyl ketone were added to obtain a non-volatile content of 80% to obtain a blocked isocyanate curing agent (3).

Comparative Production Example 2 Production of Blocked Isocyanate Curing Agent (4) Polyphenylene polymethylene polyisocyanate (polymeric MDI, isocyanate group content (NCO content) 31) in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel. 3) 425.7 parts, 89 parts of methyl isobutyl ketone, and 0.30 part of dibutyltin dilaurate were weighed, and 374.3 parts of butyl cellosolve was dropped from the dropping funnel over 1 hour while stirring and bubbling nitrogen. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, 111.0 parts of methyl isobutyl ketone was added to obtain a nonvolatile content of 80% to obtain a blocked isocyanate curing agent (4).

Comparative Production Example 3 Production of Crosslinked Resin Particles for Comparative Example 120 parts of butyl cellosolve was placed in a reaction vessel and heated and stirred at 120 ° C. A solution prepared by mixing 2 parts of t-butylperoxy-2-ethylhexanoate and 10 parts of butyl cellosolve, 15 parts of glycidyl methacrylate, 50 parts of 2-ethylhexyl methacrylate, 20 parts of 2-hydroxyethyl methacrylate and n-butyl methacrylate A monomer mixture consisting of 15 parts was added dropwise over 3 hours. After aging for 30 minutes, a solution in which 0.5 part of t-butylperoxy-2-ethylhexanoate and 5 parts of butyl cellosolve were added dropwise in 30 minutes, and after aging for 2 hours, the mixture was cooled. . 7 parts of N, N-dimethylaminoethanol and 15 parts of 50% lactic acid aqueous solution were added thereto, and the mixture was heated and stirred at 80 ° C. When the acid value became 1 or less and the viscosity increase stopped, heating was stopped to obtain an acrylic resin having an ammonium group. The number of ammonium groups per molecule of the acrylic resin having ammonium groups was 6.0.

  To the reaction vessel, 120 parts of an acrylic resin having an ammonium group and 270 parts of deionized water were added and stirred with heating at 75 ° C. Thereto was added dropwise 1.5 parts of 2,2'-azobis (2- (2-imidazolin-2-yl) propane) 100% neutralized aqueous acetic acid solution over 5 minutes. After aging for 5 minutes, 30 parts of methyl methacrylate was added dropwise over 5 minutes. After further aging for 5 minutes, 170 parts of methyl methacrylate, 40 parts of styrene, 30 parts of n-butyl methacrylate, 5 parts of glycidyl methacrylate, and neopentyl were added to a solution obtained by mixing 170 parts of an acrylic resin having an ammonium group and 250 parts of deionized water. A pre-emulsion obtained by adding and stirring an ethylenically unsaturated monomer mixture consisting of 30 parts of glycol dimethacrylate was added dropwise over 40 minutes. After aging for 60 minutes, the mixture was cooled to obtain a dispersion of crosslinked resin particles 1. The resulting dispersion of the crosslinked resin particles had a non-volatile content of 35%, a pH of 5.0, and an average particle size of 0.1 μm. Here, the average particle diameter of the crosslinked resin particles was measured in the following manner.

  The average particle diameter of the resin particles was measured by a granular particle permeation measurement method using MICROTRAC 9340UPA manufactured by Nikkiso Co., Ltd. Further, in this measuring instrument, the particle size distribution of the crosslinked resin particles was measured, and the average particle diameter at the cumulative relative frequency F (x) = 0.5 was calculated from the measured value. In these measurements and calculations, a solvent (water) refractive index of 1.33 and a resin refractive index of 1.59 were used.

Example 1
A mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 and 155 parts of the blocked isocyanate curing agent (1) of Production Example 4 was weighed out slowly by weighing 310 parts of ion-exchanged water and 16 parts of acetic acid and heating to 70 ° C. And stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
818 parts of the emulsion thus obtained, 50 parts of crosslinked resin particles (crosslinked resin particles mainly composed of methyl methacrylate; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration 31% by weight) 34 parts of the pigment dispersion paste of Production Example 3 and 3761 parts of ion-exchanged water were mixed to form a cation having an inorganic pigment content (PWC) of 5% by weight, crosslinked resin particles of 5% by weight, and a solid content of 7.0% by weight. An electrodeposition coating composition was obtained.

Example 2
775 parts of emulsion prepared in Example 1, crosslinked resin particles (crosslinked resin particles containing methyl methacrylate as a main component; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration: 31% by weight) 100 parts, 34 parts of the pigment dispersion paste of Production Example 3 and 3754 parts of ion-exchanged water are mixed, the content of inorganic pigment (PWC) is 5% by weight, the cross-linked resin particles are 10% by weight, and the solid content is 7.0% by weight. A cationic electrodeposition coating composition was obtained.

Example 3
A mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 and 155 parts of the blocked isocyanate curing agent (2) of Production Example 5, which were weighed out by weighing 310 parts of ion-exchanged water and 16 parts of acetic acid and heated to 70 ° C., was gradually added dropwise. And stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
775 parts of the emulsion thus obtained, 100 parts of crosslinked resin particles (crosslinked resin particles mainly composed of methyl methacrylate; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration 31% by weight) 34 parts of the pigment dispersion paste of Production Example 3 and 3754 parts of ion-exchanged water were mixed to form a cation having an inorganic pigment content (PWC) of 5% by weight, crosslinked resin particles of 10% by weight, and a solid content of 7.0% by weight. An electrodeposition coating composition was obtained.

Comparative Example 1
A mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 and 155 parts of the blocked isocyanate curing agent (3) of Comparative Production Example 1 was weighed out and weighed 310 parts of ion exchange water and 16 parts of acetic acid and heated to 70 ° C. The solution was added dropwise and stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
818 parts of the emulsion thus obtained, 50 parts of crosslinked resin particles (crosslinked resin particles mainly composed of methyl methacrylate; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration 31% by weight) 34 parts of the pigment dispersion paste of Production Example 3 and 3761 parts of ion-exchanged water were mixed to form a cation having an inorganic pigment content (PWC) of 5% by weight, crosslinked resin particles of 5% by weight, and a solid content of 7.0% by weight. An electrodeposition coating composition was obtained.

Comparative Example 2
775 parts of emulsion prepared in Comparative Example 1, crosslinked resin particles (crosslinked resin particles containing methyl methacrylate as a main component; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration: 31% by weight) 100 parts, 34 parts of the pigment dispersion paste of Production Example 3 and 3754 parts of ion-exchanged water are mixed, the content of inorganic pigment (PWC) is 5% by weight, the cross-linked resin particles are 10% by weight, and the solid content is 7.0% by weight. A cationic electrodeposition coating composition was obtained.

Comparative Example 3
A mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 and 155 parts of the blocked isocyanate curing agent (4) of Production Example 2, which were weighed out by weighing 310 parts of ion-exchanged water and 16 parts of acetic acid and heated to 70 ° C, was gradually added dropwise. And stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
775 parts of the emulsion thus obtained, 100 parts of crosslinked resin particles (crosslinked resin particles mainly composed of methyl methacrylate; manufactured by Toyobo Co., Ltd., Tuftic ^{(registered trademark)} F-200, solid content concentration 31% by weight) 34 parts of the pigment dispersion paste of Production Example 3 and 3754 parts of ion-exchanged water were mixed to form a cation having an inorganic pigment content (PWC) of 5% by weight, crosslinked resin particles of 10% by weight, and a solid content of 7.0% by weight. An electrodeposition coating composition was obtained.

Comparative Example 4
A mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 and 155 parts of the blocked isocyanate curing agent (1) of Production Example 4 was weighed out slowly by weighing 310 parts of ion-exchanged water and 16 parts of acetic acid and heating to 70 ° C. And stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
775 parts of the emulsion thus obtained, 89 parts of the crosslinked resin particles for comparative example of Comparative Production Example 3, 34 parts of the pigment dispersion paste of Production Example 3 and 3765 parts of ion-exchanged water were mixed, and the inorganic pigment content (PWC) A cationic electrodeposition coating composition having 5% by weight, 10% by weight of crosslinked resin particles, and 7.0% by weight of solid content was obtained.

Comparative Example 5
Weighing 310 parts of ion-exchanged water and 16 parts of acetic acid, and gradually adding a mixture of 248 parts of the amine-modified epoxy resin of Production Example 1 heated to 70 ° C. and 155 parts of the blocked isocyanate curing agent (3) of Comparative Production Example 1 The solution was dropped into the solution and stirred to disperse it uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.
861 parts of the emulsion thus obtained, 192 parts of the pigment dispersion paste obtained in Production Example 4 and 958 parts of ion-exchanged water were mixed, and the content of inorganic pigment (PWC) was 23% by weight and the solid content was 20% by weight. A cationic electrodeposition coating composition was obtained.

  About the cationic electrodeposition coating composition obtained by the said Example and comparative example, evaluation, such as coating-film smoothness and end surface coverage, and the loss elastic modulus in 80 degreeC in dynamic viscoelasticity, and the storage elasticity in 140 degreeC The rate was measured by the following method.

Evaluation of Appearance (Coating Smoothness) of Electrodeposition Coating Film The appearance evaluation of the electrodeposition coating film was performed by measuring the arithmetic average roughness (Ra) of the roughness curve. The cold-rolled steel sheet treated with zinc phosphate is immersed in the cationic electrodeposition coating composition obtained in the production example and the comparative example in the vertical direction, and is applied at a coating voltage such that the film thickness after baking is 15 μm. The uncured electrodeposition coating film obtained by baking was baked at 160 ° C. for 10 minutes. Thereafter, the Ra value of the uncured electrodeposition coating film was measured using an evaluation type surface roughness measuring machine (manufactured by Mitutoyo Corporation, SURFTEST SJ-201P) in accordance with JIS-B0601. Measurement was performed 7 times using a sample with a 2.5 mm width cut-off (number of sections: 5), and an Ra value was obtained by an average of vertical erasure. The results are shown in Tables 1 and 2. It can be said that the smaller the Ra value, the less the unevenness and the better the coating film appearance. Specifically, it passes if the Ra value is 0.25 μm or less.

End surface coverage evaluation A coating material of a cutter knife (OLFA: LB-50K) subjected to zinc phosphate treatment was immersed in the cationic electrodeposition coating composition, and a voltage was applied between the coating material as a cathode and an anode. Apply to deposit film. The electrodeposition conditions were applied voltage and time adjusted so that the deposited film thickness was 15 μm on the cutter knife. The obtained electrodeposition coating film was washed with water and then baked at 160 ° C. for 10 minutes to obtain a cured electrodeposition coating film.

  The center of the cutter knife coated with the cured electrodeposition coating film is folded, and the film thickness of the cured electrodeposition coating film coated on the 30-micron region from the tip of the cutter knife (acute angle portion) is digital microscope (manufactured by Keyence Corporation: VH- 8000). FIG. 2 schematically shows a 30-micron region from the tip of the cutter knife. When this film thickness is 8 μm or more, it is acceptable.

Sedimentation evaluation (horizontal appearance)
Except that the cold-rolled steel sheet treated with zinc phosphate was immersed in the horizontal direction in the cationic electrodeposition coating compositions obtained in the production examples and comparative examples, The same operation was performed. Then, it evaluated on the same reference | standard as the said coating-film smoothness evaluation.

Measurement of Loss Modulus and Storage Modulus of Electrodeposition Coating Film A tin plate is immersed in the cationic electrodeposition coating composition obtained above, and is applied with a coating voltage such that the film thickness after baking is 15 μm. An adhesion coating film was formed and washed with water to remove excess electrodeposition coating composition. Next, after removing moisture, the uncured coating film piece was taken out immediately without drying to prepare a sample. The sample thus obtained was subjected to temperature-dependent measurement in dynamic viscoelasticity using a Rheosol-G3000 (manufactured by UBM Co., Ltd.), which is a rotary dynamic viscoelasticity measuring device, and setting conditions: strain 0.5 deg, frequency The storage elastic modulus (G ′) and loss elastic modulus (G ″) were measured at 0.02 Hz and a temperature increase rate of 2.0 ° C./min.

Measurement of average particle diameter of crosslinked resin particles The average particle diameter of the crosslinked resin particles used in the above Examples and Comparative Examples was measured as follows. The average particle diameter of the crosslinked resin particles was measured by a particulate particle permeation measurement method using MICROTRAC 9340UPA manufactured by Nikkiso Co., Ltd. Further, in this measuring instrument, the particle size distribution of the crosslinked resin particles was measured, and the average particle diameter at the cumulative relative frequency F (x) = 0.5 was calculated from the measured value. In these measurements and calculations, a solvent (water) refractive index of 1.33 and a resin refractive index of 1.59 were used.

The degree of cross-linking was expressed by thermal softening temperature based on thermal softening temperature measurement.
High degree of crosslinking: Thermal softening temperature 140 ° C or higher Crosslinking degree Medium: Thermal softening temperature 120 ° C or higher and lower than 140 ° C Low degree of crosslinking; Thermal softening temperature 120 ° C or lower

F-200: Toyobo F-200 (trade name)
Crosslinked resin particle # 2: Crosslinked resin particle for comparative example obtained in Comparative Production Example 3

As is clear from Examples 1 to 3 in the above table, the crosslinked resin particles having an average particle size of 1.0 to 3.0 μm are converted into a cationic electrodeposition coating material even in a low ash type cationic electrodeposition coating composition. Comparative example which is an example of a conventional paint by using a blocked isocyanate curing agent containing a blocked isocyanate which is included in the composition and which is blocked with polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0 As in 5, it was found that the coating film smoothness and end face coverage were excellent. Comparative Example 5 contains a conventional inorganic pigment that does not contain resin particles, and the coating film surface smoothness and end face coverage are good, but the amount of inorganic pigment (ash content) is high, so the sedimentation evaluation is poor.
Regarding Comparative Examples 1 to 4 which are low ash type cationic electrodeposition coating compositions, it was confirmed that Comparative Examples 1 and 2 in which the polyisocyanate used for the preparation of the blocked isocyanate was HDI were inferior in end face coverage.
Moreover, although polyisocyanate was polyphenylene polymethylene polyisocyanate (polymeric MDI), it was confirmed that Comparative Example 3 having an isocyanate group content of more than 31 also had poor end face coverage.
In Comparative Example 4 in which the average particle diameter of the crosslinked resin particles was 0.1 μm, it was confirmed that the coating film surface smoothness was inferior.

  According to the present invention, a polyphenylene polymethylene having an isocyanate group content of 29.0 to 31.0 and containing crosslinked resin particles having an average particle size of 1.0 to 3.0 μm in the cationic electrodeposition coating composition. By using a blocked isocyanate curing agent containing a blocked isocyanate blocked with a polyisocyanate, a low ash content cationic electrodeposition coating composition suitable for energy saving and shortening of the coating process can achieve both coating surface smoothness and end face coverage. It becomes possible. Thereby, the anti-corrosion property improvement and coating-film external appearance improvement in a low ash type cationic electrodeposition coating-material composition can be aimed at. INDUSTRIAL APPLICABILITY The present invention is effective as a means for maintaining or improving coating film performance in a low ash type cationic electrodeposition coating composition suitable for energy saving and coating process shortening.

It is a graph of the temperature and storage elastic modulus G 'for demonstrating a heat softening temperature. It is a figure which shows typically a 30 micron site | part from the front-end | tip of a cutter knife.

Claims (6)

A cationic electrodeposition coating composition comprising a cationic epoxy resin, a blocked isocyanate curing agent, crosslinked resin particles, and an inorganic pigment in an amount of 10% by weight or less based on the solid content of the cationic electrodeposition coating composition,
The crosslinked resin particles have an average particle size of 1.0 to 3.0 μm,
The blocked isocyanate curing agent comprises a blocked isocyanate obtained by blocking polyphenylene polymethylene polyisocyanate having an isocyanate group content of 29.0 to 31.0.
Cationic electrodeposition coating composition. A storage elastic modulus (G ′) at 140 ° C. of an uncured deposited coating obtained by electrodeposition coating of the cationic electrodeposition coating composition is 80 to 500 dyn / cm ² , and a loss elastic modulus at 80 ° C. ( The cationic electrodeposition coating composition according to claim 1, wherein G ″) is 10 to 150 dyn / cm ² .   3. The cationic electrodeposition coating composition according to claim 1, wherein the content of the crosslinked resin particles is 3 to 15% by weight based on the resin solid content of the cationic electrodeposition coating composition.   The cationic electrodeposition coating composition according to any one of claims 1 to 3, wherein a thermal softening temperature of the crosslinked resin particles is 120 to 180 ° C.   In the method of forming a cured electrodeposition coating film by immersing an object to be coated in a cationic electrodeposition coating composition, applying a voltage, and baking and curing, the cationic electrodeposition coating composition has an average particle size of 1.0. Any one of Claims 1-4 containing the crosslinked resin particle | grains which are -3.0 micrometers, and the block isocyanate hardening | curing agent containing the blocked isocyanate which blocked polyphenylene polymethylene polyisocyanate whose isocyanate group content is 29.0-31.0. A method for achieving both coating film smoothness and end face coverage of a cured electrodeposition coating film, which is the cationic electrodeposition coating composition described in 1. Curing electrodeposition by immersing an object to be coated in the cationic electrodeposition coating composition according to any one of claims 1 to 4, forming an uncured deposited coating film by applying a voltage, and then baking and curing the coating film. In the method of forming a coating film,
The deposited coating film has a storage elastic modulus (G ′) at 140 ° C. of 80 to 500 dyn / cm ² and a loss elastic modulus (G ″) at 80 ° C. of 10 to 150 dyn / cm ^2. A method for forming a cured electrodeposition coating film with improved end face coverage.

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