JP2012031440A - Electrodeposition film forming method, and double-layer coating film forming method using the same - Google Patents

Abstract

[PROBLEMS] To improve both crosslink density and layer separation in the formation of a two-layer separation type electrodeposition coating film, and to provide excellent corrosion resistance and weather resistance to the electrodeposition coating film in the coating of automobile bodies and the like. An electrodeposition coating film forming method capable of imparting light resistance, impact resistance, chipping resistance and appearance is provided.
Electrodeposition coating formation comprising a step of coating a coating composition onto an object to be coated, then separating the layers while heating and then curing to form a multilayer cured film consisting of at least two layers A method wherein the coating composition comprises a film-forming resin component (a) and (b), blocked polyisocyanate (c1) and (c2), and a pigment, and the film-forming resin component (a) And (b) are incompatible with each other, and the film-forming resin components (a) and (b) form emulsion particles A and B containing blocked polyisocyanates (c1) and (c2), The film-forming resin component (a) contains (meth) acrylamide as a copolymerization monomer.
[Selection figure] None

Description

  The present invention not only provides the electrodeposition coating film with functions such as excellent corrosion resistance, weather resistance, light resistance, impact resistance, and chipping resistance, but also provides an excellent coating appearance in the coating of automobile bodies and the like. In addition, the present invention also relates to a so-called intermediate coating-less multi-layer coating film forming method in which the intermediate coating process is omitted in the coating of automobile bodies and the like. The present invention relates to a method for forming a multilayer coating film capable of providing an excellent coating film appearance.

  In the field of painting such as automobile bodies, in general, an electrodeposition film is formed as an undercoat film on a coated object such as a steel plate for the purpose of improving rust prevention, and then an intermediate coating film is formed thereon. Further, a colored base coating film, a clear coating film, and the like are sequentially formed thereon as a top coating film to complete the coating.

However, in recent years, in the field of painting such as automobile bodies, there has been a demand for shortening and simplifying the painting process for the purpose of resource saving, energy saving, cost saving, and environmental load reduction (for example, low VOC and low CO ₂ ). Yes.

  In general, a three-coat one-bake (3C1B) method is well known as a simplified coating method. In the 3C1B method, intermediate coating, base coating, and clear coating are sequentially applied on the electrodeposition coating film by wet-on-wet, and these coating films are baked and cured simultaneously. By doing so, a multilayer coating film including these three layers in the order of an intermediate coating film, a base coating film, and a clear coating film can be easily formed on the electrodeposition coating film by one baking and curing. The 3C1B method is very advantageous from the viewpoints of energy saving and cost saving because a multilayer coating film can be formed by only one heat curing after the formation of the cured electrodeposition coating film. In addition, in the 3C1B method, generally, since the multilayer coating film to be formed includes an intermediate coating film, it has excellent base concealing properties, weather resistance, light resistance, impact resistance, chipping resistance, and smoothness. It can be applied to the coating film.

  In recent years, as a more simplified coating method, a method for forming a so-called intermediate coating-less multilayer coating film in which the intermediate coating step is omitted has been studied. In the case of omitting the intermediate coating film in a multilayer coating film applied to an automobile body or the like, generally, the electrodeposition coating film needs to play the role of the intermediate coating film. Therefore, the electrodeposition coating film has not only excellent anti-rust properties but also excellent weather resistance, light resistance, impact resistance, chipping resistance and other functions and excellent smoothness, i.e., excellent anti-rust properties. It must have a coated surface. In this case, even if the intermediate coating film is omitted, an excellent top coating film appearance equal to or higher than that of the coating film formed by the 3C1B method must be provided.

  For example, Japanese Patent Publication No. 2-333069 (Patent Document 1) discloses a two-layer coating film-forming thick film electrodeposition coating composition and an electrodeposition coating method. The electrodeposition coating composition disclosed in Patent Document 1 contains a hydrophobic cationic acrylic resin (A) containing 50% by weight or less of a monomer having a benzene nucleus in the composition and having a softening point of 80 ° C. or higher; It contains a hydrophilic cationic phenol type epoxy resin (B) having a softening point of 75 ° C. or less, and the weight ratio of (A) to (B) is 1 to 30: 1. In the electrodeposition coating composition disclosed in Patent Document 1, a lower layer composed of a hydrophilic cationic phenol type epoxy resin component excellent in rust prevention and an upper layer composed of a hydrophobic acrylic resin component excellent in weather resistance. An electrodeposition-cured coating film having a two-layer structure can be formed.

  Japanese Patent No. 4201923 (Patent Document 2) discloses an aqueous paint containing at least two types of resin components incompatible with each other (that is, a hydrophilic resin component and a hydrophobic resin component), a curing agent, and a pigment. A hydrophobic resin layer in direct contact with air in the process of electrodeposition coating the composition on a conductive substrate, then separating the layers while heating, and then curing to form a multilayer cured film comprising at least two layers The pigment distribution is controlled so that the pigment concentration (a) in the inside is relatively lower than the pigment concentration (b) in the hydrophilic resin layer in direct contact with the conductive substrate. A method for forming a multilayer electrodeposition coating film is disclosed.

  In both methods of forming a two-layer separation type electrodeposition coating film disclosed in Patent Documents 1 and 2, the electrodeposition coating composition contains a hydrophilic resin component and a hydrophobic resin component, and these are electrodeposited. By simultaneously heat-curing after coating, by utilizing the difference in solubility, a lower layer of a hydrophilic resin component excellent in rust prevention and an upper layer of a hydrophobic resin component excellent in weather resistance can be formed simultaneously. Yes.

  However, in these conventional electrodeposition coatings, when the intermediate coating film is omitted, the standard for the appearance of the top coating film required in the field of current automobile coating cannot be satisfied.

Japanese Examined Patent Publication No. 2-333069 Japanese Patent No. 4201923

  In general, in this field, when further coating is performed on an electrodeposition coating film, if the cross-linking density of the electrodeposition coating film is improved, the paint applied on the electrodeposition coating film and the solvent contained therein are electrodeposited. It has been known that since the coating film is difficult to absorb, swelling of the electrodeposition coating film and an increase in the viscosity of the coating film formed thereon can be suppressed, and a good top coating film appearance can be obtained. In general, as a method for improving the crosslinking density of the electrodeposition coating film, it has been known to improve the hydroxyl value (OHV) of the resin contained in the electrodeposition coating composition.

  However, in the conventional two-layer separation type electrodeposition coating film as described above, when the hydroxyl value (OHV) of the resin contained in the electrodeposition coating composition is increased for the purpose of improving the crosslinking density of the electrodeposition coating film, The resin contained in the electrodeposition coating composition, in particular, the hydrophobic resin (more specifically, acrylic resin) forming the outer layer becomes hydrophilic, and the hydrophilic resin (more specifically, the lower layer) It has been found for the first time by the present inventors that the layer separation does not proceed, that is, the layer separation is remarkably reduced to form a single layer. In such a case, only a single layer is formed without layer separation, or the layer separation is irregular and large island-shaped irregularities are formed on the surface of the electrodeposition coating film, and the electrodeposition coating is performed. The appearance of the film is significantly reduced. Furthermore, it has been found that when coating an automobile body or the like, omitting the intermediate coating film on such an electrodeposition coating film and further forming a top coating film, the appearance of the top coating film is significantly reduced. This is because, conventionally, the intermediate coating film has an effect of concealing the base and further smoothing.

  Therefore, in the present invention, in the formation of a two-layer separation type electrodeposition coating film, the purpose is to achieve both improvement of the crosslink density and layer separation, and in addition, the corrosion resistance excellent in the electrodeposition coating film in the coating of automobile bodies and the like. An object of the present invention is to provide an electrodeposition coating film forming method capable of providing not only functions such as weather resistance, light resistance, impact resistance and chipping resistance, but also an excellent coating film appearance. The present invention also provides a multilayer coating that can provide an excellent coating appearance even in a so-called intermediate coating-less multi-layer coating forming method in which an intermediate coating step is omitted in the coating of automobile bodies and the like. An object is to provide a film forming method.

  As a result of intensive studies, the present inventors can form a surface layer (uppermost layer) of a two-layer electrodeposition coating film in an electrodeposition coating composition capable of forming a two-layer separation type electrodeposition coating film. By blending (meth) acrylamide as a monomer component in the film-forming resin component at the time of copolymerization, the crosslink density of the electrodeposition coating film formed can be improved without degrading the layer separation. As a result, it has been found that the appearance of the electrodeposition coating film is dramatically improved, and the present invention has been completed. Accordingly, the present invention provides the following.

Electrodeposition coating formation comprising electrodeposition coating of electrodeposition coating composition on substrate, then separating layers while heating, and then curing to form a multilayer cured film consisting of at least two layers An electrodeposition coating composition comprising:
Film-forming resin components (a) and (b),
Blocked polyisocyanates (c1) and (c2), and pigments,
The film-forming resin components (a) and (b) are incompatible with each other;
The film-forming resin component (a) forms emulsion particles A containing blocked polyisocyanate (c1),
The film-forming resin component (b) forms emulsion particles B containing blocked polyisocyanate (c2),
The film-forming resin component (a) contains (meth) acrylamide as a copolymerization monomer,
The (meth) acrylamide is at least one selected from the group consisting of N-butoxymethyl (meth) acrylamide and N-isobutoxymethyl (meth) acrylamide;
The (meth) acrylamide is contained in an amount of 1 to 24 parts by weight with respect to 100 parts by weight of the resin solid content of the film-forming resin component (a).
Electrodeposition coating formation method.

In the electrodeposition coating film forming method of the present invention, preferably,
The film-forming resin component (a) is a cation-modified acrylic resin,
The film-forming resin component (b) is a cation-modified epoxy resin,
The solubility parameter (δa) of the coating film-forming resin component (a) and the solubility parameter (δb) of the coating film-forming resin component (b) satisfy the relationship {δb−δa} ≧ 0.5.

  In the electrodeposition coating film forming method of the present invention, the blending ratio ((a) / (b)) of the film-forming resin components (a) and (b) is preferably 50/50 to 50% by weight in terms of solid content. 40/60.

  In the electrodeposition coating film forming method of the present invention, preferably, the (meth) acrylamide is self-crosslinking.

  In the electrodeposition coating film forming method of the present invention, the (meth) acrylamide is preferably contained in an amount of 4 to 18 parts by weight with respect to 100 parts by weight of the resin solid content of the film-forming resin component (a).

In the electrodeposition coating film forming method of the present invention, preferably,
Blocked polyisocyanate (c1) is an aliphatic polyisocyanate blocked with a sealant,
The blocked polyisocyanate (c2) is obtained by blocking an alicyclic or aromatic polyisocyanate with a sealing agent.

Further, the present invention further comprises a step of applying an overcoating base coating composition on the electrodeposition coating film formed by the above electrodeposition coating film forming method to form an uncured topcoating base coating film,
A step of applying an overcoat clear coating composition on the uncured topcoat base coating to form an uncured topcoat clearcoat; and an uncured topcoat basecoat and an uncured topcoat clear coat A method for forming a multilayer coating film is provided, which comprises a step of simultaneously heating and curing.

  Conventionally, in the painting of automobile bodies, for the purpose of omitting the intermediate coating process, a two-layer separation type electrodeposition coating film is formed on an object to be coated such as steel, and the lowermost layer in contact with the object to be coated is formed. Rust resistance is imparted by hydrophilic resins such as cationic epoxy resins, and functions such as weather resistance, light resistance, impact resistance, and chipping resistance are imparted to the uppermost layer by hydrophobic resins such as acrylic resins. I was considering that. However, with the conventional two-layer separation type electrodeposition coating film, if the intermediate coating process is omitted, the standard for the appearance of the top coating film required in the current automotive coating field cannot be satisfied, and the intermediate coating-less process Realization was very difficult. In particular, in an electrodeposition coating composition capable of forming a conventional two-layer electrodeposition coating film, the hydrophobicity of an acrylic resin or the like contained therein is intended to improve the crosslinking density of the electrodeposition coating film. When the hydroxyl value (OHV) of the hydrophilic resin is improved, the hydrophobic resin as the upper layer becomes hydrophilic, so that mixing with the hydrophilic resin as the lower layer occurs, and the layer separation does not proceed well. Therefore, from the above, it has been very difficult to improve both the crosslink density and the layer separation. In addition, when the layer separation property is remarkably reduced, large island-like irregularities may be formed on the surface of the electrodeposition coating film, and the appearance of the electrodeposition coating film may be significantly reduced. In addition, in the field of automobile body coating, on such a conventional electrodeposition coating film, omitting the intermediate coating film that can impart base concealing properties and smoothness, and directly applying the top coating, Since the underlying concealability and smoothness cannot be obtained, the appearance of the top coat film (that is, the finish of the top coat) is significantly reduced. Furthermore, in the conventional electrodeposition coating film, if the intermediate coating process is omitted, the top coating material or the solvent contained therein penetrates into the electrodeposition coating film and the electrodeposition coating film swells. In addition, since the viscosity of the top coat film increases, the surface of the electrodeposition coat film and the top coat film may be greatly waved, and the appearance of the top coat film may be significantly reduced.

  However, in the present invention, a specified amount of (meth) acrylamide, desirably self-crosslinking and hydrophobic (meth) acrylamide, is added to the electrodeposition coating composition capable of forming a two-layer separation type electrodeposition coating film. As a monomer component, layer separation of a two-layer separation type electrodeposition coating film by blending into a film-forming resin component capable of forming the surface layer (uppermost layer) of a two-layer electrodeposition coating film during copolymerization To improve the crosslink density of the two-layer separation type electrodeposition coating film while maintaining the properties, that is, without significantly improving the hydroxyl value (OHV) of the hydrophobic resin contained in the electrodeposition coating composition Can do.

As a result, in the present invention, in the coating of automobile bodies, the electrodeposition coating film not only provides excellent functions such as corrosion resistance, weather resistance, light resistance, impact resistance, and chipping resistance, but also an excellent coating film. Appearance can also be imparted. Further, in the present invention, the electrodeposition coating film has excellent functions such as corrosion resistance, weather resistance, light resistance, impact resistance, chipping resistance, and excellent coating film appearance (that is, smoothness, etc.). In the painting of a vehicle body or the like, the intermediate coating process can be omitted, and resource saving, energy saving, cost saving, and reduction of environmental load (for example, low VOC and low CO ₂ ) can be achieved.

  Furthermore, in the present invention, since the electrodeposition coating film has an improved crosslink density, even when a top coating is applied wet-on-wet on the electrodeposition coating, the electrode of the paint or the solvent contained therein is applied. It is possible to suppress the penetration into the coating film and the swelling of the electrodeposition coating film, as well as the viscosity increase of the coating film formed on it, and it is possible to successfully reapply the paint and to form a multilayer coating formed. The film is not greatly undulated and the appearance is greatly improved.

  The present invention includes an electrodeposition coating process comprising electrodeposition coating an electrodeposition coating composition on an object to be coated, then separating the layers while heating and then curing to form a multilayer cured film comprising at least two layers. Regarding the method for forming a coating film, the electrodeposition coating composition that can be used in the present invention comprises at least two coating film-forming resin components (a) and (b) [i.e., hydrophobic A film-forming resin component (a) and a hydrophilic film-forming resin component (b)], at least two types of blocked polyisocyanates (c1) and (c2), and a pigment; (Meth) acrylamide is mix | blended as a monomer at the time of the copolymerization in the film-forming resin component (a) which can form the surface layer (uppermost layer) of a coating film. In the present invention, two layers are formed from such an electrodeposition coating composition in which the film-forming resin component (a) contains (meth) acrylamide, particularly preferably self-crosslinking and hydrophobic (meth) acrylamide, in a specified amount. By forming an electrodeposition-cured coating film, the electrodeposition coating film has not only excellent functions such as corrosion resistance, weather resistance, light resistance, impact resistance, and chipping resistance, but also an excellent coating appearance. It is possible to dispense with the intermediate coating process that has been conventionally required.

  As a coated object to which the method of the present invention can be applied, there is no particular limitation as long as it is a large and complicated shaped coated object such as an automobile body, and a conductive substrate that can constitute them. For example, metals (for example, iron, steel, copper, aluminum, magnesium, tin, zinc, etc. and alloys containing these metals), iron plates, steel plates, aluminum plates and surface treatments (for example, phosphates, Examples thereof include those subjected to chemical conversion treatment using chromate and the like, and molded products thereof.

(Meth) acrylamide In the present invention, the electrodeposition coating composition capable of forming a two-layer separation type electrodeposition coating film contains a specified amount of (meth) acrylamide, particularly preferably self-crosslinkable, and hydrophobic. By adding (meth) acrylamide, which is an adhesive, as a part of the coating film-forming resin component, that is, as a copolymerization monomer, the degree of crosslinking of the electrodeposition coating film after curing can be dramatically improved. In particular, when manufacturing the hydrophobic coating film-forming resin component (a) contained in the electrodeposition coating composition described in detail below, (meth) acrylamide is used as a copolymerization monomer in the specified amount described below. Then, in the formed film-forming resin component (a), the hydroxyl value (OHV) does not increase significantly, that is, the resin component does not become hydrophilic, and the hydrophilic film-forming resin component. There is no fear of forming a single layer by mixing with (b), and excellent layer separation can be provided.

  The (meth) acrylamide that can be used in the present invention is not particularly limited, but those having self-crosslinking properties are preferable, for example, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide. Etc.

  The (meth) acrylamide that can be used in the present invention is preferably self-condensed in the presence of heat and / or acid in the presence of a dealcoholization reaction.

  In addition, (meth) acrylamide that can be used in the present invention can also react with a functional group having reactivity such as an amino group and a hydroxyl group, so that the film-forming resin component (described in detail below) It can also react with a) and (b).

  Therefore, in the present invention, the (meth) acrylamide self-crosslinking proceeds during the heat curing of the electrodeposition coating film, and can react with both the film-forming resin components (a) and (b). The crosslink density of the electrodeposition coating is further improved dramatically.

  When the above (meth) acrylamide is used in the specified amount described in detail below, the hydroxyl value (OHV) of the hydrophobic film-forming resin component (a) is not significantly increased. The film-forming resin component (a) is not miscible with the hydrophilic film-forming resin component (b), and there is no possibility that layer separation is hindered. In addition, in the formation of the two-layer separation type electrodeposition coating film, when the hydroxyl number (OHV) of the hydrophobic coating film forming resin component (a) used increases, the coating film forming resin component (a) becomes hydrophilic. And may be mixed with the hydrophilic film-forming resin component (b), that is, a single layer may be formed without layer separation.

Therefore, in the present invention, by using (meth) acrylamide, the two-layer separation type electrodeposition coating film formed is 1.20 × 10 ⁻³ mol / cc or more, preferably 1.40 × 10 ^−3. It can have a crosslinking density of ˜1.69 × 10 ⁻³ mol / cc, more preferably 1.50 × 10 ^{−3 to} 1.65 × 10 ⁻³ mol / cc.

  In the present invention, the crosslink density of the electrodeposition coating film is determined by first baking an uncured electrodeposition coating film formed by applying the electrodeposition coating composition of the present invention onto a tin plate, and then using mercury. The coating film is peeled off and cut to prepare a measurement sample. Using a dynamic viscoelasticity measuring device “Reogel E4000 (manufactured by UBM)” or the like, the sample is heated at a rate of 2 ° C. per minute and 16 Hz. The dynamic viscoelastic modulus is measured by applying a synthetic wave vibration of the above, and the relationship between the minimum value of the dynamic viscoelasticity (ie, parallel elastic modulus) (E ′) and the absolute temperature (T) at that time From the formula: E ′ = 3 nRT (where n represents the crosslinking density and R represents the gas constant), the crosslinking density (mol / cc) of the sample can be calculated according to the theory of Flory.

If the cross-linking density of the two-layer separation type electrodeposition coating film formed by the method of the present invention is less than 1.20 × 10 ⁻³ mol / cc, the cross-linking density is insufficient. In such a case, the paint or the solvent contained therein may enter the electrodeposition coating film, causing the electrodeposition coating film to swell and increase the viscosity of the coating film formed thereon. When the electrodeposition coating film swells, the electrodeposition coating film itself or the coating film formed on the electrodeposition coating film may be greatly waved and the appearance of the coating film may be significantly reduced. Moreover, even if the viscosity of the coating film formed on the electrodeposition coating film increases, the coating film may be greatly waved and the coating film appearance may be remarkably reduced.

  If the (meth) acrylamide used is hydrophilic, the coating film-forming resin component (a) becomes hydrophilic and is mixed with the hydrophilic coating-film forming resin component (b) to form a single layer. (Ie, no layer separation). From such a viewpoint, the (meth) acrylamide that can be used in the present invention is at least one hydrophobic group selected from the group consisting of N-butoxymethyl (meth) acrylamide and N-isobutoxymethyl (meth) acrylamide. Sexual (meth) acrylamide is particularly preferred.

  In this invention, (meth) acrylamide is mix | blended in the film-forming resin component (a) demonstrated in detail below as a copolymerization monomer. (Meth) acrylamide is an amount of 1 to 24 parts by weight, preferably 4 to 18 parts by weight, more preferably 7 to 13 parts by weight with respect to 100 parts by weight of the resin solid content of the film-forming resin component (a). Included. When the amount of (meth) acrylamide is less than 1 part by weight, there is a possibility that the crosslinking density does not increase because there are few self-crosslinking components. When it exceeds 24 parts by weight, when hydrophobic (meth) acrylamide is used Even so, the film-forming resin component (a) may be hydrophilized, and may be mixed with the hydrophilic film-forming resin component (b) to form a single layer and not be separated. .

Film-forming resin component The electrodeposition coating composition that can be used in the method of the present invention contains at least two types of film-forming resin components (a) and (b). At least two types of emulsion particles are formed from the conductive resin components (a) and (b), and after application of the electrodeposition coating film, a two-layer electrodeposition curing coating film comprising at least two layers is formed by heat curing. In this specification, for convenience, the uppermost layer of the two-layer electrodeposition coating film, that is, the resin component contained in the coating film in contact with air is defined as the film-forming resin component (a), and the two-layer electrodeposition coating film The resin component contained in the lowermost layer, that is, the coating film that comes into contact with the object to be coated, is defined as a film-forming resin component (b).

  The film-forming resin components (a) and (b) that can be used in the present invention are incompatible with each other. In the present invention, the solubility parameter (δa) of the film-forming resin component (a) And the solubility parameter (δb) of the film-forming resin component (b) satisfy the relationship: {δb−δa} ≧ 0.5. The solubility parameter (δ) is generally called SP (solubility parameter), and is a measure indicating the degree of hydrophilicity and hydrophobicity of the resin component. Accordingly, relatively, the coating film-forming resin component (a) is a hydrophobic resin component, and the coating film-forming resin component (b) is a hydrophilic resin component. Further, the solubility parameter (δ) is an important measure for judging the compatibility between resin components. The solubility parameter (δ) is numerically quantified based on, for example, the following turbidity measurement method (reference document: kW Suh, DH Clarke J. Polymer). Sci., A-1, 5, 1671 (1967).).

  In general, if the difference in solubility parameter (δ) of a plurality of resin components contained in the electrodeposition coating composition is 0.5 or more, the compatibility is lost, and the formed coating film exhibits a two-layer separation structure. It is considered. In the present invention, the two types of resin components (a) and (b) can ensure sufficient incompatibility by satisfying the above formula relating to the above solubility parameter. A layered electrodeposition coating can be formed. In the present invention, the difference in solubility parameter between the resin components (a) and (b), that is, {δb−δa} is preferably 0.5 to 1.2, more preferably 0.8 to 1.0. .

  As described above, the solubility parameter (δa) of the resin component (a) and the solubility parameter (δb) of the resin component (b) satisfy the relationship {δb−δa} ≧ 0.5. It shows that the component (b) has a relatively high solubility parameter with respect to the resin component (a), and the resin component (b) has a relatively high polarity, that is, is hydrophilic. It shows that there is. Therefore, it shows that the resin component (b) has an excellent affinity for an object to be coated such as a conductive substrate having a high polarity, and the resin component (b) It is contained in the lowermost layer, and the resin component (a) is contained in the uppermost layer. Thus, the difference in the solubility parameter of the resin component is considered to be a driving force that causes layer separation when the two-layer electrodeposition coating film is formed.

  In the present invention, the structure of the two-layer electrodeposition coating film can be confirmed by observing the cross section of the electrodeposition coating film with a video microscope or with a scanning electron microscope (SEM). Moreover, identification of the resin component which comprises each resin layer can be performed by using a total reflection type Fourier-transform infrared spectrophotometer (FTIR-ATR), for example.

  The resin component (a) is particularly preferably a cation-modified acrylic resin containing the above (meth) acrylamide from the viewpoint of weather resistance, light resistance, impact resistance, chipping resistance, and the like.

  The cation-modified acrylic resin is not particularly limited, but can be synthesized by a ring-opening addition reaction between an acrylic copolymer containing a plurality of oxirane rings and a plurality of hydroxyl groups in the molecule and an amine. Such an acrylic copolymer includes a glycidyl (meth) acrylate and a hydroxyl group-containing acrylic monomer (for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or 2-hydroxyethyl (meth)). It can be obtained by copolymerizing a hydroxyl group-containing (meth) acrylic ester such as acrylate and an addition product of ε-caprolactone with other acrylic monomers and / or non-acrylic monomers.

  Examples of other acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, Examples include t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and isobornyl (meth) acrylate. Examples of non-acrylic monomers include styrene, vinyl toluene, α-methyl styrene, (meth) acrylonitrile, (meth) acrylamide and vinyl acetate other than those described above.

  An acrylic resin containing an oxirane ring based on the above glycidyl (meth) acrylate is a cation-modified acrylic resin which is opened by reaction with a primary amine, a secondary amine or a tertiary amine salt of the oxirane ring of the epoxy resin. It can be a resin.

  There is also a method of directly synthesizing a cation-modified acrylic resin by copolymerizing an acrylic monomer having an amino group with another monomer. In this method, an amino group-containing acrylic monomer such as N, N-dimethylaminoethyl (meth) acrylate or N, N-di-t-butylaminoethyl (meth) acrylate is used instead of the above glycidyl (meth) acrylate. Then, a cation-modified acrylic resin can be obtained by copolymerizing this with a hydroxyl group-containing acrylic monomer and other acrylic monomers and / or non-acrylic monomers.

  The cation-modified acrylic resin thus obtained is self-crosslinked cation-modified by introducing a blocked isocyanate group by addition reaction with a half-blocked diisocyanate compound as required, as described in JP-A-8-333528. An acrylic resin can also be used.

  The resin component (a) is preferably molecularly designed so that the hydroxyl value (OHV) is in the range of 50 to 150 (mgKOH / g). When the hydroxyl value is less than 50, the coating film is poorly cured. On the other hand, when it exceeds 150, excessive hydroxyl groups remain in the coated film after curing, and as a result, the water resistance of the cured coating film may be lowered. The number average molecular weight is preferably in the range of 1000 to 20000. If the number average molecule is less than 1000, the cured coating film has poor physical properties such as solvent resistance. On the other hand, if it exceeds 20000, it is difficult to handle the operation of the obtained resin, such as emulsification and dispersion, because the viscosity of the resin solution is high, and the appearance of the obtained electrodeposition coating film may be significantly reduced. is there. In addition, although only 1 type can also be used for the resin component (a), in order to balance the coating-film performance, 2 types or more types can also be used.

  As the resin component (a), the glass transition temperature (Tg (a)) is 0 to 50 ° C., preferably 5 to 40 ° C., and the number average molecular weight is more preferably 7000 to 12000, still more preferably 7000 to 700 ° C. A cation-modified acrylic resin of 10,000 is particularly preferred. The glass transition temperature (Tg (a)) of the resin component (a) can be measured by a differential scanning calorimeter, and the number average molecular weight can be measured by GPC (gel permeation chromatography).

  The resin component (b) needs to be a resin component that exhibits excellent rust prevention properties with respect to the conductive base material to be coated. As an example of such a resin component, a cation-modified epoxy resin is well known in the field of cationic electrodeposition coating, and can be suitably used in the present invention. Generally, the cation-modified epoxy resin is not particularly limited, but is produced by opening an epoxy ring in a starting material resin molecule by a reaction with an amine such as a primary amine, a secondary amine, or a tertiary amine acid salt. A typical example of the starting material resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, and epichlorohydrin. Examples of other starting material resins include oxazolidone ring-containing epoxy resins described in JP-A-5-306327. This epoxy resin is obtained by a reaction between a diisocyanate compound or a bisurethane compound obtained by blocking an NCO group of a diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

  The starting material resin can be used by extending the chain with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before the ring opening reaction of the epoxy ring with amines. In addition, prior to the ring-opening reaction of the epoxy ring with amines, for the purpose of adjusting the molecular weight or amine equivalent, adjusting the heat flow property, flexibility (softness), glass transition temperature, etc., some epoxy rings On the other hand, monohydroxy compounds such as 2-ethylhexanol, nonylphenol, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono n-butyl ether, propylene glycol mono-2-ethylhexyl ether, stearic acid, 2-ethylhexanoic acid, dimer It can also be used by adding an acid component such as an acid.

  Examples of amines that can be used for opening an epoxy ring and introducing an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine acid Mention may be made of primary, secondary or tertiary amineates such as salts, N, N-dimethylethanolamate. In addition, ketimine block primary amino group-containing secondary amines such as diethylenetriamine diketimine, aminoethylethanolamine ketimine, aminoethylethanolamine methylisobutyl ketimine can be used. These amines must be reacted at least in an equivalent amount with respect to the epoxy ring in order to open all the epoxy rings.

  The number average molecular weight of the cation-modified epoxy resin is preferably in the range of 1500 to 5000. If the number average molecular weight is less than 1500, the cured coating film may have poor physical properties such as solvent resistance and rust prevention. On the other hand, when it exceeds 5000, the viscosity of the resin solution is difficult to control and the synthesis is difficult, and handling such as emulsification and dispersion of the obtained resin may be difficult. Furthermore, because of its high viscosity, the flowability during heating and curing is poor, and the appearance of the coating film may be significantly impaired.

  The resin component (b) is preferably molecularly designed so that the hydroxyl value is in the range of 50 to 250 (mgKOH / g). When the hydroxyl number is less than 50, the coating film is poorly cured. On the other hand, when it exceeds 250, excessive hydroxyl groups remain in the coating film after curing, and as a result, the water resistance of the cured coating film may be lowered.

  The resin component (b) has a glass transition temperature (Tg (b)) of 20 to 35 ° C., preferably 28 to 33 ° C., and a number average molecular weight of 2000 to 200 ° C., from the viewpoint of rust prevention. Particularly preferred are cation-modified epoxy resins of 5000, more preferably 2500-3500. The glass transition temperature (Tg (b)) of the resin component (b) can be measured by a differential scanning calorimeter, and the number average molecular weight can be measured by GPC (gel permeation chromatography).

  The compounding ratio ((a) / (b)) of the resin components (a) and (b) in the electrodeposition coating composition is 50/50 to 40/60 in terms of solid content weight ratio. When the blending ratio is out of the range of 50/50 to 40/60, the cured coating after electrodeposition coating and baking does not have a two-layer structure, and the resin with the higher blending ratio forms a continuous phase, The resin with a lower blending ratio may have a sea-island structure (or microdomain structure) that forms a dispersed phase.

  Resin components (a) and (b) are either emulsified and dispersed in water as an emulsion as they are, or neutralized with an organic acid such as acetic acid, formic acid, lactic acid or the like that can neutralize the amino groups in each resin. The emulsion may be emulsified and dispersed in water. The curing agent may be of any type as long as each resin component can be cured at the time of heating. Among them, curing of a film-forming resin component of a general electrodeposition coating composition Blocked polyisocyanates suitable as agents are recommended.

  In a preferred embodiment, the emulsion particles A are formed using a cation-modified acrylic resin as the resin component (a), and the emulsion particles B are formed using a cation-modified epoxy resin as the resin component (b). Two-layer electrodeposition including an epoxy coating with excellent rust-preventing properties on the coating, and an acrylic coating with excellent weather resistance, light resistance, impact resistance, and chipping resistance. A cured coating film can be formed. By forming such an epoxy (lowermost layer) -acrylic (uppermost layer) -based multi-layer electrodeposition cured coating film, when applied to an automobile body, etc., excellent weather resistance due to the acrylic coating film on the outer plate part, Light resistance, impact resistance, and chipping resistance are obtained, and the inner plate part has excellent anti-corrosion properties due to the epoxy coating, and both the outer plate part and the inner plate part have an appropriate film thickness. A coating can be achieved and is very beneficial. Moreover, such an epoxy (lowermost layer) -acrylic (uppermost layer) type two-layer electrodeposition-cured coating film has excellent impact resistance and chipping resistance, etc., and is conventionally responsible for an intermediate coating film. It is particularly useful as an alternative to the intermediate coating film, and the intermediate coating film can be omitted. In addition, a film thickness of about 15 μm, preferably 14 to 15 μm, can be achieved in the outer plate portion of the automobile body, and a film thickness of about 10 μm, preferably 7 to 10 μm, can be achieved in the inner plate portion. It is very useful from the viewpoint of resource saving, energy saving, cost saving and environmental load reduction. Moreover, in this invention, the surface of an electrodeposition coating film can be smoothed and the outstanding coating-film external appearance can be obtained.

  For example, the smoothness of the surface of the electrodeposition coating film can be evaluated by measuring the surface roughness (that is, arithmetic average roughness (Ra)) in accordance with JIS-B0601, and the value of Ra is It shows that there are few unevenness | corrugations on the surface, and smoothness and a coating-film external appearance are excellent, so that it is small. In the present invention, the value of Ra is 0.34 μm or less, preferably 0.25 μm or less.

Curing Agent In the present invention, the electrodeposition coating composition contains blocked polyisocyanate as a curing agent.

  Examples of the polyisocyanate that is a raw material of the blocked polyisocyanate include aliphatic polyisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; isophorone diisocyanate, 4,4 ′ -Cycloaliphatic polyisocyanates such as methylene bis (cyclohexyl isocyanate); aromatic polyisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and the like. The blocked polyisocyanate can be obtained by blocking these with a suitable sealant.

  Examples of the sealant include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, methylphenyl carbinol, ethylene glycol mono Cellosolves such as hexyl ether, ethylene glycol mono 2-ethylhexyl ether, phenols such as phenol, para-t-butylphenol, cresol, dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, cyclohexanone oxime, etc. Oximes and lactams represented by ε-caprolactam and γ-butyrolactam are preferably used. In particular, sealants of oximes and lactams are suitable from the viewpoint of resin curability because they dissociate at a low temperature.

  The blending ratio of the blocked polyisocyanate to the resin components (a) and (b) varies depending on the degree of crosslinking required for the purpose of use of the cured coating film, but considering the coating film properties and topcoat coating compatibility A range of 15 to 40% by weight is preferred. If the blending ratio is less than 15% by weight, the coating film may be poorly cured. As a result, the physical properties of the coating film such as mechanical strength may be lowered, and the coating film may be damaged by the paint thinner at the time of top coating. There is a case. On the other hand, if it exceeds 40% by weight, it may be excessively cured, resulting in poor coating properties such as impact resistance. In addition, blocked polyisocyanate may be used in combination of a plurality of types for the convenience of coating film properties and adjustment of the degree of curing.

  The solubility parameter of the blocked polyisocyanate is important in securing the curability necessary for developing the coating performance of the upper layer and the lower layer after the separation of the two layers. That is, the solubility parameter (δc1) of the blocked polyisocyanate (c1) designed for the upper layer is designed to be about the same as or lower than the solubility parameter (δa) of the resin component (a) constituting the upper layer. More preferably, [(δa) − (1.0)] ≦ δc1 ≦ [(δa) + (0.2)]. Also, the solubility parameter (δc2) of the blocked polyisocyanate (c2) designed for the lower layer is designed to be about the same as or higher than the solubility parameter (δb) of the resin component (b) constituting the lower layer. More preferably, [(δb) − (0.2)] ≦ δc2 ≦ [(δb) + (1.0)].

  In the present invention, the electrodeposition coating composition preferably contains at least two types of blocked polyisocyanates (c1) and (c2). More preferably, the blocked polyisocyanate (c1) is obtained by blocking an aliphatic polyisocyanate with the above-mentioned sealing agent, and the blocked polyisocyanate (c2) is an alicyclic or aromatic type. Polyisocyanate is blocked with a sealing agent.

  The blocked polyisocyanate (c1) is preferably an aliphatic polyisocyanate blocked with the above-mentioned sealant, and in particular, a two-layer separation type electrodeposition coating that requires weather resistance, smoothness and chipping properties. It is effective for the upper part of the membrane.

  Further, the blocked polyisocyanate (c2) is preferably a alicyclic or aromatic polyisocyanate blocked with the above-mentioned sealing agent, and in particular, a two-layer separation type electric battery that requires rust prevention. It is effective for the lower layer portion of the coating film.

Modified epoxy resin having onium group (d)
In the present invention, the electrodeposition coating composition may further contain a modified epoxy resin (d) having an onium group.

  The onium group contained in the modified epoxy resin (d) having an onium group is selected from the group consisting of an ammonium group and a sulfonium group.

  Modified epoxy resin (d) having an onium group comprises resin components (a) and (b) of emulsion particles A and B and blocked polyisocyanates (c1) and (c2) [hereinafter, all resins of emulsion particles A and B It is contained in an amount of 1 to 10 parts by weight, preferably 3 to 5 parts by weight with respect to a total of 100 parts by weight of the solid content].

  In the electrodeposition coating composition that can be used in the present invention, the modified epoxy resin (d) having an onium group may form emulsion particles A together with the resin component (a) and the blocked polyisocyanate (c1). it can. The modified epoxy resin (d) having an onium group can form emulsion particles B together with the resin component (b) and the blocked polyisocyanate (c2).

  The modified epoxy resin (d) having an onium group is a resin that assists in emulsifying (emulsifying) the binder resin. In the case of the emulsion particles A, the binder resin here means the resin component (a) and the blocked polyisocyanate (c1), and in the case of the emulsion particles B, the resin component (b) and the blocked polyisocyanate (c2). is there.

  Examples of the modified epoxy resin (d) having an onium group include a modified epoxy resin having a quaternary ammonium group and a modified epoxy resin having a tertiary sulfonium group.

  The modified epoxy resin having a quaternary ammonium group is a resin obtained by reacting an epoxy resin with a tertiary amine.

  As the epoxy resin, polyepoxide is generally used. This epoxide has an average of 2 or more 1,2-epoxy groups in one molecule. These polyepoxides preferably have an epoxy equivalent of 180 to 1000, in particular an epoxy equivalent of 375 to 800. When the epoxy equivalent is less than 180, no film can be formed at the time of electrodeposition, and a coating film cannot be obtained. If it exceeds 1000, the amount of onium groups per molecule is insufficient, and sufficient water solubility cannot be obtained.

  Useful examples of such polyepoxides include epoxy resins that can be used in the production of the resin component (b). Furthermore, as the epoxy resin, an oxazolidone ring-containing epoxy resin described in JP-A-5-306327 can be used.

  In particular, an epoxy resin containing a hydroxyl group may be a urethane-modified epoxy resin in which a blocked isocyanate group is introduced by reacting a half-blocked isocyanate with the hydroxyl group.

  The half-blocked isocyanate used to react with the epoxy resin described above is prepared by partially blocking the organic polyisocyanate. The reaction between the organic polyisocyanate and the blocking agent is preferably performed by cooling to 40 to 50 ° C. while dropping the blocking agent with stirring in the presence of a tin-based catalyst as necessary.

  The polyisocyanate is not particularly limited as long as it has two or more isocyanate groups on average in one molecule. As a specific example, a polyisocyanate that can be used in the preparation of the above-mentioned blocked polyisocyanate curing agent can be used.

  Suitable blocking agents for preparing the above half-blocked isocyanate include lower aliphatic alkyl monoalcohols having 4 to 20 carbon atoms. Specific examples include butyl alcohol, amyl alcohol, hexyl alcohol, 2-ethylhexyl alcohol, heptyl alcohol and the like.

  The reaction between the epoxy resin and the half-blocked isocyanate is preferably carried out by maintaining at 140 ° C. for about 1 hour.

  As said tertiary amine, a C1-C6 thing is preferable and may have a hydroxyl group. Specific examples of the tertiary amine include dimethylethanolamine, trimethylamine, triethylamine, dimethylbenzylamine, diethylbenzylamine, N, N-dimethylcyclohexylamine, tri-n-, as well as the tertiary amine that can be used above. Butylamine, diphenethylmethylamine, dimethylaniline, N-methylmorpholine and the like can be used.

  Further, the neutralizing acid used by mixing with the tertiary amine is not particularly limited, and specifically, inorganic acids or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and lactic acid are used. The reaction between the neutralized salt of tertiary amine thus obtained and the epoxy resin can be carried out by a conventional method. For example, the epoxy resin is dissolved in a solvent such as ethylene glycol monobutyl ether, the resulting solution is heated to 60 to 100 ° C., and a neutralized acid salt of a tertiary amine is added dropwise to the acid value of 1. The reaction mixture is kept at 60-100 ° C. until

  A modified epoxy resin having a tertiary sulfonium group can be obtained by reacting in the same manner as above except that a sulfide is used instead of a tertiary amine. Examples of sulfides that can be used include aliphatic sulfides, mixed aliphatic-aromatic sulfides, aralkyl sulfides, and cyclic sulfides. Specifically, diethyl sulfide, dipropyl sulfide, dibutyl sulfide, diphenyl sulfide, dihexyl sulfide, ethyl phenyl sulfide, tetramethylene sulfide, pentamethylene sulfide, thiodiethanol, thiodipropanol, thiodibutanol, 1- (2-hydroxy And ethylthio) -2-propanol.

  The modified epoxy resin (d) having an onium group may be used alone or in combination of two or more.

  Due to the onium group of the modified epoxy resin (d) having an onium group, the emulsification performance is improved when the emulsion particles A and B are prepared.

Pigments The pigments that can be used in the method of the present invention can be used without particular limitation as long as they are usually used in paints. Examples include colored pigments such as carbon black, titanium dioxide, graphite, extender pigments such as kaolin, aluminum silicate (clay), and talc, aluminum phosphomolybdate, lead silicate, lead sulfate, zinc chromate, strontium chromate, Examples thereof include rust preventive pigments such as silicon dioxide. Among these, titanium dioxide, aluminum silicate (clay), and aluminum phosphomolybdate are particularly important as pigments having a dispersion concentration gradient in the two-layer cured film after electrodeposition coating. In particular, titanium dioxide is most suitable as an electrodeposition coating film because it has high concealability as a color pigment and is inexpensive. In addition, although the said pigment can also be used independently, it is common to use multiple according to the objective.

  In the two-layer cured film, the pigment is represented by a ratio P / V of the weight (V) of all vehicle components other than the pigment forming the multilayer cured film to the total pigment weight (P). A range of 1/3 is preferable. Here, the total vehicle component other than the pigment means all solid components (main resin components that are incompatible with each other, their respective curing agents, and other resin components, etc.) that constitute the paint other than the pigment. When the P / V is less than 1/10, the barrier property against corrosion factors such as light and moisture with respect to the coating film is excessively reduced due to insufficient pigment, and weather resistance and rust resistance at a practical level may not be exhibited. On the other hand, if P / V exceeds 1/3, an excessive pigment may cause an increase in viscosity at the time of curing, the flowability may be lowered, and the appearance of the coating film may be remarkably deteriorated. This ratio is substantially the same as the ratio of the weight of all vehicle components to the total pigment weight in the electrodeposition coating composition used in the present invention.

  As the pigment dispersion resin (e), it is generally preferable to use 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. The solubility parameter (δe) is preferably designed to be about the same as or higher than the solubility parameter (δb) of the resin component (b) constituting the lower layer, and more preferably, [(δb) − ( 0.2)] ≦ δe ≦ [(δb) + (1.0)]. Moreover, the suitable compounding quantity of the dispersion resin with respect to a pigment is 5-40 solid content weight% (vs. pigment weight). When the blending amount of the dispersion resin is less than 5, it is difficult to ensure the pigment dispersion stability, and when it exceeds 40, it may be difficult to control the curability of the coating film.

Preparation of electrodeposition coating composition The electrodeposition coating composition that can be used in the method of the present invention comprises at least two coating-forming resin components that are incompatible with each other (that is, hydrophobic coating formation). The resin-forming resin component (a) and the hydrophilic film-forming resin component (b)), a curing agent and a pigment are used. The electrodeposition coating composition only needs to contain acrylamide, and the electrodeposition coating composition is a curing agent suitable for each resin component, and other components such as a modified epoxy resin (d) having an onium group as necessary. At the same time, it can also be formed by emulsifying in an aqueous medium containing a neutralizing agent and then blending the emulsion so as to satisfy the above-mentioned blending ratio. Examples of the neutralizing agent include inorganic acids such as hydrochloric acid, nitric acid and phosphoric acid, and organic acids such as formic acid, acetic acid, lactic acid, sulfamic acid and acetylglycine acid. In addition, it is preferable to add a pigment separately as said pigment dispersion resin (e) as a pigment dispersion paste.

  In the electrodeposition coating composition that can be used in the present invention, the film-forming resin component (a) comprises a blocked polyisocyanate (c1) and, if necessary, a modified epoxy resin (d) having an onium group. Emulsion particles A containing a coating film-forming resin component (b) containing blocked polyisocyanate (c2) and, if necessary, a modified epoxy resin (d) having an onium group More preferably, the emulsion particles A and B are separately prepared in advance and are particularly preferably blended with the other components in the electrodeposition coating composition. In addition, in this invention, it is desirable to mix | blend (meth) acrylamide as a monomer in the film-forming resin component (a) from a viewpoint of a crosslinking density improvement.

  The electrodeposition coating composition that can be used in the present invention is preferably adjusted so that the solid content concentration is in the range of 15 to 25% by weight. The solid content is adjusted using an aqueous medium (water alone or a mixture of water and a hydrophilic organic solvent). A small amount of additives may be introduced into the coating composition. Examples of the additive include an ultraviolet absorber, an antioxidant, a surfactant, a coating film surface smoothing agent, a curing accelerator (such as an organic tin compound), and the like.

Formation of Double-Layer Electrodeposition Coating In the present invention, the two-layer electrodeposition coating film comprises a conductive substrate as a cathode as a cathode and a cathode (cathode electrode) terminal connected to the object to be coated. Generally, a coating film having an amount of a dry film thickness of 14 to 15 μm is applied by electrodeposition under conditions of a bath temperature of the coating composition of 15 to 35 ° C. and a load voltage of 100 to 400 V. Thereafter, baking is performed at 140 to 200 ° C., preferably 160 to 180 ° C. for 10 to 30 minutes. The emulsion particles A containing the resin component (a) and the blocked polyisocyanate (c1) contained in the electrodeposition coating composition coated by electrodeposition by heating for the purpose of baking, and the resin component (b) and It is preferable that the emulsion particles B containing the blocked polyisocyanate (c2) are oriented according to their inherent solubility parameters. When the coating film is cured to finish baking, the emulsion particles A form the uppermost layer in direct contact with air, and the emulsion particles B form the lowermost layer in direct contact with the object to be coated to form a two-layered electrodeposition cured film. Is done. In addition, the baking heating method includes a method of putting a coated material in a heating facility adjusted to a target temperature from the beginning and a method of raising the temperature after putting the coated material.

Formation of multilayer coating film A multilayer coating film excellent in weather resistance and appearance can be formed by further applying and baking a top coating on the two-layer electrodeposition cured coating film formed by the above method. . The top coat may be any of solvent type, aqueous type, and powder.

In the present invention, two types of top coats, that is, the top coat base paint composition and the top coat clear paint composition, can be used to obtain a more excellent coating appearance. In this case, the method for forming a multilayer coating film of the present invention is a so-called two-coat one-bake (2C1B) method including the following steps (1) to (3).
A step (1) of further applying an overcoating base coating composition on the two-layer electrodeposition-curing coating film formed by the above-mentioned electrodeposition coating film forming method to form an uncured topcoating base coating film;
A step (2) of forming an uncured top clear film by applying a top clear composition on the uncured top base film, and an uncured top base film and an uncured top coat Step of curing the clear coating film by heating simultaneously (3)

  The coating in the above step (1) or (2) is, for example, an air electrostatic spray commonly called “react gun”, commonly called “micro-microbell (μμbell)”, “microbell (μbell)”, “metallic”. It can be applied by spraying using a rotary atomizing electrostatic coating machine or the like called “bell”. The coating amount can be appropriately changed according to the type and application of the coating composition to be used.

  After the step (1) or (2), a time interval called an interval (or setting) may be performed, and the solvent contained in the coating film can be sufficiently volatilized by this interval. The appearance of the layer coating is improved. The interval is, for example, 10 seconds to 15 minutes.

  Moreover, you may perform drying operation called preheating within the time of an interval, and volatilization of the solvent contained in a coating film can be performed efficiently in a short time by this preheating. This drying operation does not actively cure the coating film. Therefore, as said drying conditions, it is 1 to 10 minutes at room temperature-100 degreeC, for example. Preheating can be performed using, for example, a warm air heater or an infrared heater.

  The heat curing step (3) can be performed using a conventional heat curing furnace (for example, a gas furnace, an electric furnace, an IR furnace, an induction heating furnace, or the like). The heat curing temperature can be appropriately set according to the coating composition to be used, and is, for example, 120 to 160 ° C., and the heat curing time is, for example, 10 to 30 minutes.

  The multilayer coating film formed according to the method of the present invention has an excellent appearance, that is, excellent finish finish. In the present invention, the appearance of the multi-layer coating film (finishing finish) is determined by using Wave scan-doi (BYK-Gardner), Wa of the top coating film (Mitsusawa on the coating surface), Wb ( It can be evaluated by measuring values of the sharpness of the coating surface, Wc (sharpness of the coating surface) and Wd (smoothness of the coating surface). In addition, values of Wa (Mitsusawa of the coating surface), Wb (Sharpness of the coating surface), Wc (Sharpness of the coating surface) and Wd (Smoothness of the coating surface) are all The smaller the value, the better the appearance of the coating film.

  In the present invention, the value of Wa is 25 or less, preferably 18 or less, more preferably 15 or less. In this case, an excellent coating film appearance is obtained in a short wavelength region of 100 to 300 μm.

  The value of Wb is 40 or less, preferably 35 or less, more preferably 30 or less. In this case, an excellent coating film appearance can be obtained in a medium wavelength region of 300 to 1000 μm.

  The value of Wc is 22 or less, preferably 18 or less, and more preferably 15 or less. In this case, an excellent coating film appearance is obtained in the medium wavelength region of 1000 to 3000 μm.

  The value of Wd is 22 or less, preferably 18 or less, and more preferably 15 or less. In this case, it is judged that an excellent coating film appearance was obtained in a long wavelength region of 3000 to 10000 μm.

  In the present invention, the values of Wa (Mitsusawa on the coating surface), Wb (Sharpness on the coating surface), Wc (Sharpness on the coating surface) and Wd (Smoothness on the coating surface) In this case, the multi-layer coating film has a very excellent finish of the top coat.

  Hereinafter, the present invention will be described in more detail with reference to production examples, examples and comparative examples. In each example, “part” represents “part by weight”, and “%” represents “% by weight”.

Production Example 1-1: Production of cation-modified acrylic resin (a-1) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen inlet tube, a thermometer, and a dropping funnel, methyl 50 parts of isobutyl ketone (hereinafter referred to as “MIBK”) was charged and heated to 115 ° C. in a nitrogen atmosphere. Furthermore, 6.5 parts of methyl methacrylate, 0.7 parts of stearyl methacrylate, 54.8 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then further t-butylperoxy 2-ethylhexanoic acid 0.5. The portion was added dropwise and held at 115 ° C. for 1.5 hours. The obtained cation-modified acrylic resin (a-1) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-2: Production of cation-modified acrylic resin (a-2) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 2.1 parts of stearyl methacrylate, 37.4 parts of ethylhexyl methacrylate, 33.0 parts of hydroxypropyl methacrylate, 11.5 parts of hydroxyethyl methacrylate, 16.0 parts of N, N-dimethylaminoethyl methacrylate, and A mixture of 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was added dropwise from a dropping funnel over 3 hours, and then 0.5 part of t-butylperoxy 2-ethylhexanoic acid was further added dropwise at 115 ° C. Hold for 1.5 hours. The obtained cation-modified acrylic resin (a-2) has a solid content of 65%, a solubility parameter (δa) of 11.2, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 180 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-3: Production of cation-modified acrylic resin (a-3) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 6.2 parts of methyl methacrylate, 1.0 part of stearyl methacrylate, 54.3 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate, 0.5 part of N-butoxymethylacrylamide, and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then further t-butyl. Peroxy 2-ethylhexanoic acid 0.5 part was dripped and it hold | maintained at 115 degreeC for 1.5 hours. The obtained cation-modified acrylic resin (a-3) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-4: Production of cation-modified acrylic resin (a-4) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 5.2 parts of methyl methacrylate, 1.9 parts of stearyl methacrylate, 52.9 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate, 2.0 parts of N-butoxymethylacrylamide, and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then further t-butyl. Peroxy 2-ethylhexanoic acid 0.5 part was dripped and it hold | maintained at 115 degreeC for 1.5 hours. The obtained cation-modified acrylic resin (a-4) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-5: Production of cation-modified acrylic resin (a-5) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Furthermore, 3.4 parts of methyl methacrylate, 4.5 parts of stearyl methacrylate, 49.1 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate, 5.0 parts of N-butoxymethylacrylamide, and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then further t-butyl. Peroxy 2-ethylhexanoic acid 0.5 part was dripped and it hold | maintained at 115 degreeC for 1.5 hours. The obtained cation-modified acrylic resin (a-5) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-6: Production of cation-modified acrylic resin (a-6) (coating film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 0.3 parts of methyl methacrylate, 8.2 parts of stearyl methacrylate, 43.5 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate, 10.0 parts of N-butoxymethylacrylamide, and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then further t-butyl. Peroxy 2-ethylhexanoic acid 0.5 part was dripped and it hold | maintained at 115 degreeC for 1.5 hours. The resulting cation-modified acrylic resin (a-6) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-7: Production of cation-modified acrylic resin (a-7) (coating film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Furthermore, 0.2 parts of methyl methacrylate, 6.3 parts of stearyl methacrylate, 45.5 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, N, N-dimethylamino A mixture of 16.0 parts of ethyl methacrylate, 10.0 parts of N-isobutoxymethylacrylamide, and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was dropped from the dropping funnel over 3 hours, and then t- Butyl peroxy 2-ethylhexanoic acid 0.5 part was dripped and it hold | maintained at 115 degreeC for 1.5 hours. The obtained cation-modified acrylic resin (a-7) has a solid content of 65%, a solubility parameter (δa) of 10.4, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-8: Production of cation-modified acrylic resin (a-8) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introduction tube, a thermometer, and a dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 11.4 parts of methyl methacrylate, 40.6 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, 16.0 parts of N, N-dimethylaminoethyl methacrylate, N A mixture of 10.0 parts of methoxymethyl acrylamide and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was added dropwise from the dropping funnel over 3 hours, and then further t-butylperoxy 2-ethylhexanoic acid 0. .5 parts was added dropwise and held at 115 ° C. for 1.5 hours. The obtained cation-modified acrylic resin (a-8) has a solid content of 65%, a solubility parameter (δa) of 10.9, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 1-9: Production of cation-modified acrylic resin (a-9) (film-forming resin component (a)) In a reaction vessel equipped with a stirrer, cooler, nitrogen introduction tube, thermometer and dropping funnel, MIBK 50 parts were charged and heated to 115 ° C. in a nitrogen atmosphere. Further, 5.3 parts of methyl methacrylate, 31.7 parts of ethylhexyl methacrylate, 11.6 parts of hydroxypropyl methacrylate, 10.4 parts of hydroxyethyl methacrylate, 16.0 parts of N, N-dimethylaminoethyl methacrylate, N -A mixture of 25.0 parts of butoxymethylacrylamide and 3.0 parts of t-butylperoxy 2-ethylhexanoic acid was added dropwise from the dropping funnel over 3 hours, and then further t-butylperoxy 2-ethylhexanoic acid 0. .5 parts was added dropwise and held at 115 ° C. for 1.5 hours. The obtained cation-modified acrylic resin (a-9) has a solid content of 65%, a solubility parameter (δa) of 11.0, a glass transition temperature (Tg) of 10 ° C., a hydroxyl value of 90 (mgKOH / g), and a number average molecular weight. 8000.

Production Example 2: Production of blocked polyisocyanate (c1) Into a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a condenser tube and a thermometer, 199 parts of a hexamethylene diisocyanate trimer was placed and diluted with 39 parts of MIBK. After adding 0.2 parts of butyltin laurate and raising the temperature to 50 ° C., 44 parts of methyl ethyl ketoxime and 87 parts of ethylene glycol mono 2-ethylhexyl ether were added so that the content temperature did not exceed 70 ° C. Then, the infrared absorption spectrum is maintained at 70 ° C. for 1 hour until the absorption of the isocyanate residue substantially disappears, and then diluted with 43 parts of n-butanol, thereby blocking 80% solid content of blocked polyisocyanate (c1) (dissolved) Sex parameter (δc1) 10.6).

Production Example 3: Production of modified epoxy resin (d) having sulfonium group Preparation of 2-ethylhexanol half-blocked IPDI (MIBK solution) Isophorone was added to a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe and a thermometer. After adding 222.0 parts of diisocyanate (hereinafter abbreviated as IPDI) and diluting with 39.1 parts of MIBK, 0.2 parts of dibutyltin dilaurate was added thereto. Then, after heating this to 50 degreeC, 131.5 parts of 2-ethylhexanol was dripped over 2 hours in dry nitrogen atmosphere, stirring. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI (MIBK solution) (resin solid content 90.0%) was obtained.
A suitable reaction vessel was charged with 382.2 parts of bisphenol A type epoxy resin (manufactured by Dow Chemical Company) having an epoxy equivalent of 188 and 117.8 parts of bisphenol A, and heated to 150 to 160 ° C. in a nitrogen atmosphere. The reaction mixture was reacted at 150-160 ° C. for about 1 hour, then cooled to 120 ° C., and 209.8 parts of 2-ethylhexanol half-blocked IPDI (MIBK solution) prepared above was added. After reacting at 140 to 150 ° C. for 1 hour, 205 parts of a polyalkylene oxide compound (trade name BPE-60, manufactured by Sanyo Chemical Co., Ltd.) was added and cooled to 60 to 65 ° C. Thereto, 408.0 parts of 1- (2-hydroxyethylthio) -2-propanol, 144.0 parts of deionized water and 134 parts of dimethylolpropionic acid were added, and the acid value was 65 to 75 ° C. until the acid value became 1. By reacting, a tertiary sulfonium group is introduced into the epoxy resin, and 1595.2 parts of deionized water is added to terminate the tertiaryization, thereby obtaining a varnish of a modified epoxy resin (d) containing a tertiary sulfonium group. (Solid content 30%).

Production Example 4-1: Production of cation-modified acrylic emulsion (A-1) 247.1 parts of the cation-modified acrylic resin (a-1) obtained in Production Example 1-1, and the blocked product obtained in Production Example 2 120.0 parts of polyisocyanate (c1) and 53.0 parts of the modified epoxy resin (d) having a sulfonium group obtained in Production Example 3 were added and stirred for 30 minutes. Thereafter, 5 parts of acetic acid was added and diluted with ion-exchanged water to a non-volatile content of 30%, and then concentrated under reduced pressure to a non-volatile content of 38% to obtain a cation-modified acrylic emulsion (A-1).
Production Example 4-2 to Production Example 4-9: Production of cation-modified acrylic emulsions (A-2) to (A-9) Cationic modification obtained in Production Example 1-1 in the same manner as Production Example 4-1. In place of the acrylic resin (a-1), the cation-modified acrylic resins (a-2) to (a-9) obtained in Production Examples 1-2 to 1-9 were used respectively. Emulsions (A-2) to (A-9) were prepared.

Production Example 5: Production of cation-modified epoxy resin (coating film-forming resin component (b)) A flask equipped with a stirrer, a cooler, a nitrogen injection tube and a dropping funnel was attached. : DER-331J, manufactured by Dow Chemical Co., Ltd.) 680.94 parts, bisphenol A 237.12 parts, stearic acid 105.27 parts, dimer acid (trade name: Tsunodim 216, manufactured by Tsukino Food Industries), 68.62 parts, After 115.54 parts of MIBK and 0.10 parts of dibutyltin dilaurate were added and dissolved uniformly, the temperature was raised from 130 ° C. to 142 ° C., and the reaction was continued until an epoxy equivalent of 1150 was reached.
Thereafter, 71.37 parts of MIBK was added and cooled to 100 ° C., 49.93 parts of N-methylethanolamine and 87.84 parts of diethylenetriamine diketimine (73% MIBK solution) were added and reacted at 110 ° C. for 2 hours. It was. The obtained cation-modified epoxy resin had a solid content of 85%, a solubility parameter (δb) of 11.3, and a glass transition temperature (Tg) of 26 ° C.

Production Example 6 Production of Blocked Polyisocyanate (c2) 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a condenser tube and a thermometer, diluted with 56 parts of MIBK, After 2 parts were added and the temperature was raised to 50 ° C., 17 parts of methyl ethyl ketoxime was added so that the content temperature did not exceed 70 ° C. Then, the infrared absorption spectrum is kept at 70 ° C. for 1 hour until the absorption of the isocyanate residue substantially disappears, and then diluted with 43 parts of n-butanol, whereby the blocked polyisocyanate (c2) (c2) (70% solid content) Solubility parameter (δc2) 11.8) was obtained.

Production Example 7: Production of cation-modified epoxy emulsion (B-1) 308.8 parts of the cation-modified epoxy resin obtained in Production Example 5, 112.5 parts of the blocked polyisocyanate (c2) obtained in Production Example 6, And 58.8 parts of the modified epoxy resin (d) having a sulfonium group obtained in Production Example 3 was added and stirred for 30 minutes. Thereafter, 6 parts of acetic acid was added, diluted with ion-exchanged water to a non-volatile content of 30%, and concentrated under reduced pressure to a non-volatile content of 38% to obtain a cation-modified epoxy emulsion (B-1).

Production Example 8: Production of pigment dispersion resin (e) Bisphenol A type epoxy resin having an epoxy equivalent of 198 in a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube, and a thermometer (trade name: Epon 829, manufactured by Shell Chemical Co., Ltd.) 710 parts and 289.6 parts of bisphenol A were charged and reacted at 150 to 160 ° C. for 1 hour under a nitrogen atmosphere. After cooling to 120 ° C., a MIBK solution of 2-ethylhexanolated half-blocked tolylene diisocyanate (solid content) 95%) 406.4 parts. After maintaining the reaction mixture at 110-120 ° C. for 1 hour, 1584.1 parts of ethylene glycol mono n-butyl ether was added. And it cooled to 85-95 degreeC and made it uniform.
In parallel with the production of the reaction product, another reaction vessel was prepared by adding 104.6 parts of dimethylethanolamine to 384 parts of MIBK solution (solid content 95%) of 2-ethylhexanolated half-blocked tolylene diisocyanate. Stir at 80 ° C. for 1 hour, then add 141.1 parts of 75% lactic acid water, mix 47.0 parts of ethylene glycol mono-n-butyl ether and stir for 30 minutes to add a quaternizing agent (solid content of 85%). It was manufactured. Then, 620.5 parts of this quaternizing agent was added to the above reaction product, and the mixture was kept at 85 to 95 ° C. until an acid value of 1 was reached. Pigment-dispersed resin (e) (resin solid content 56%, average molecular weight 2200) Solubility parameter (δe) 11.3) was obtained.

Production Example 9: Production of pigment dispersion paste 120 parts of the pigment dispersion resin of Production Example 8 in a sand grind mill, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, aluminum phosphomolybdate 18. 0 parts, 15 parts of silicon dioxide and 188.1 parts of ion-exchanged water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content 60%).

Production Example 10-1: Production of cationic electrodeposition coating composition ( 1) 211.6 parts of cation-modified acrylic emulsion (A-1) obtained in Production Example 4-1 and cation-modified epoxy obtained in Production Example 7 Cation electrodeposition paint by mixing 190.0 parts of emulsion (B-1), 75.5 parts of pigment dispersion paste obtained in Production Example 9, 3.5 parts of dibutyltin oxide, and 519.4 parts of ion-exchanged water A composition (1) was obtained. The solid content of this cationic electrodeposition coating composition (1) was 20%.

Production Example 10-2 to Production Example 10-9: Production of Cationic Electrodeposition Coating Compositions (2) to (9) Cationic modified acrylic emulsion obtained in Production Example 4-1 in the same manner as Production Example 10-1. In place of (A-1), the cation-modified acrylic emulsions (A-2) to (A-9) obtained in Production Example 4-2 to Production Example 4-9 were used, respectively. Products (2) to (9) were prepared (solid content: 20%).

Examples 1-4 and Comparative Examples 1-5
Using the cationic electrodeposition coating compositions (1) to (9) prepared in Production Example 10-1 to Production Example 10-9, respectively, a zinc phosphate-treated steel sheet (JIS G3141 SPCC-SD Electrodeposition coating was performed under the following electrodeposition coating conditions using Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.).
Electrode coating composition temperature: 28 ° C
Deposition conditions: 200 V, 180 seconds, coating film thickness: 15 μm
Heat curing conditions: 160 ° C., 20 minutes

  An aqueous base coating composition (“AQUAREX AR-3100 Base”, manufactured by Nippon Paint Co., Ltd., acrylic resin / melamine resin-based coating) is further dried by air spray coating on the electrodeposition coating as a top coating. The film was coated to a thickness of 12 μm and preheated at 80 ° C. for 3 minutes. Furthermore, a clear coating composition ("Polyure Excel O-3100 Clear", manufactured by Nippon Paint Co., Ltd., acrylic resin / isocyanate compound-based paint having a urethane crosslinking system) is applied to the coated plate by air spray coating to a dry film thickness of 35 μm. The two-layer coating film was heated at 140 ° C. for 30 minutes and simultaneously cured to form a multilayer coating film on the object to be coated.

  In Example 1, the electrodeposition coating composition (4) was used, in Example 2, the electrodeposition coating composition (5) was used, and in Example 3, the electrodeposition coating composition (6) was used. In No. 4, the electrodeposition coating composition (7) was used. In Comparative Example 1, the electrodeposition coating composition (1) was used, in Comparative Example 2, the electrodeposition coating composition (2) was used, and in Comparative Example 3, the electrodeposition coating composition (3) was used. In Comparative Example 4, the electrodeposition coating composition (8) was used, and in Comparative Example 5, the electrodeposition coating composition (9) was used.

  The layer separation property, surface roughness, and crosslinking density of the electrodeposition coating films formed in Examples and Comparative Examples were evaluated according to the following evaluation criteria. Furthermore, the coating film appearance (finishing finish property) of the multilayer coating film formed in Examples and Comparative Examples was evaluated according to the following evaluation criteria. The results are shown in the table below.

Layer separation property of electrodeposition coating film Using a video microscope (manufactured by Keyence Corporation), a cross section of the electrodeposition coating film was observed, and the layer separation property was evaluated according to the following evaluation criteria.

Evaluation criteria (circle): The cross section of the electrodeposition coating film has isolate | separated into at least 2 layer (namely, clear layer separation was confirmed).
Δ: The cross-section of the electrodeposition coating is partially separated into two layers (that is, the interface between the two layers is very rough, and a part of the lower layer appears on the surface of the electrodeposition coating, or a part of the upper layer) Is in contact with the steel plate surface).
X: The cross section of the electrodeposition coating film is a single layer (that is, layer separation could not be confirmed).
In addition, when the cross section of the electrodeposition coating is separated into at least two layers (that is, when the above evaluation is “◯”), a layer containing an acrylic resin and an epoxy resin are included by FTIR-ATR analysis. Each layer was confirmed separately.

Surface Roughness of Electrodeposition Coating Film The surface roughness ((arithmetic average roughness) (Ra) (μm)) of the electrodeposition coating film before top coating is measured in accordance with JIS-B0601, The surface was evaluated. The Ra value was measured using an evaluation type surface roughness measuring instrument (SURFTEST SJ-201P, manufactured by Mitsutoyo Corporation) seven times (2.5 mm width cut-off (number of sections: 5)), and the vertical erase average was used. Ra value (μm) was obtained).
In the present invention, when the value of Ra is 0.25 μm or less, it is judged that an electrodeposition coating film appearance excellent in smoothness is obtained.

Electrodeposition Coating Crosslink Density Electrodeposition Coating Compositions (1) to (9) were each electrodeposited and heat-cured on the tin plate under the same conditions as described above to form an electrodeposition coating. The electrodeposition coating film was peeled off using mercury and cut to prepare a measurement sample. Using a dynamic viscoelasticity measuring device Rhegel E4000 (manufactured by UBM), the dynamic viscoelasticity was measured by applying a temperature rising rate of 2 ° C. and vibration of a synthetic wave (16 Hz) per minute. From the relationship between the parallel elastic modulus (E ′) and the absolute temperature (T) at that time, the crosslinking density (mol / cc) of each sample was calculated according to Flory's theory.
In this invention, it is judged that the outstanding crosslinking density was obtained as the value of a crosslinking density is 1.20 * 10 < ^-3 > mol / cc or more.

Appearance of multi-layer coating film (finish finish)
The coating film appearance (finishing finish) of the multilayer coating film was evaluated by measuring the values of Wa, Wb, Wc and Wd of the top coating film using Wave scan-doi (BYK-Gardner). .

The value of the evaluation standard Wa indicates the mitsuzawa of the surface of the coating film. The smaller the value of Wa, the better the appearance of the coating film. When the value of Wa is 25 or less, the value is as short as 100 to 300 μm. It is judged that an excellent coating film appearance was obtained in the wavelength region.
The value of Wb indicates the sharpness of the coating surface, and the smaller the value of Wb, the better the appearance of the coating. When the value of Wb is 40 or less, the medium wavelength region of 300 to 1000 μm It was judged that an excellent coating film appearance was obtained.
The value of Wc indicates the sharpness of the coating surface, and the smaller the value of Wc, the better the appearance of the coating film. When the value of Wc is 22 or less, the medium wavelength region of 1000 to 3000 μm It was judged that an excellent coating film appearance was obtained.
The value of Wd indicates the smoothness of the coating film surface, and the smaller the value of Wd, the better the appearance of the coating film. When the value of Wd is 22 or less, in the long wavelength region of 3000 to 10000 μm It is judged that an excellent coating film appearance was obtained.

  * The blending amount (% by weight) of (meth) acrylamide is expressed as a percentage by weight of (meth) acrylamide relative to 100 parts by weight of resin solid content of the film-forming resin component (a). The (meth) acrylamide used was manufactured by Kasaoka Kosan Co., Ltd.

In Examples 1 to 4 of the present invention, N-butoxymethyl acrylamide or N-isobutoxymethyl acrylamide is blended as (meth) acrylamide in the acrylic resin that forms the surface layer after layer separation. It is sex. Moreover, these acrylamide is mix | blended in the range of 1-24 weight part with respect to 100 weight part (solid content) of acrylic resin. Thereby, in this invention, the hydroxyl value (OHV) of an acrylic resin becomes in the range of 50-150 (mgKOH / g). As a result, in Examples 1 to 4 of the present invention, the layer separation property is not significantly reduced. Moreover, in Examples 1-4 of this invention, the value of surface roughness (Ra) is set to 0.25 (micrometer) or less, and the very outstanding electrodeposition coating-film surface can be achieved.
Furthermore, in Examples 1 to 4 of the present invention, a crosslink density of 1.20 × 10 ⁻³ mol / cc or more can be achieved. As a result, even when a base coating film and a clear coating film are formed thereon, the electrodeposition coating film does not swell or wave, and an excellent multi-layer coating appearance (finishing finish) Property) (values of Wa, Wb, Wc and Wd). Therefore, in the present invention, the electrodeposition coating film can achieve both excellent crosslink density and excellent layer separation.

  On the other hand, in Comparative Example 1, a conventional two-layer separation type electrodeposition coating film containing no (meth) acrylamide was formed. In Comparative Example 1, excellent layer separability is obtained, but the crosslink density is remarkably reduced, and the appearance of the multilayer coating film (finishing finish) is remarkably reduced (values of Wa, Wb and Wc).

  Similarly, in Comparative Example 2, a conventional two-layer separation type electrodeposition coating film was formed without using any (meth) acrylamide. In Comparative Example 2, the solubility parameter (δa) of the acrylic resin (coating film forming resin component (a)) is 11.2, and the solubility of the epoxy resin (coating film forming resin component (b)) is There is no difference from the value (11.3) of the parameter (δb), and the relational expression defined in this specification: {δb−δa} ≧ 0.5 is not satisfied. As a result, the layer separation property is significantly reduced. Further, the surface roughness (Ra) value of the electrodeposition coating film is remarkably increased, and the appearance of the electrodeposition coating film is remarkably decreased. Further, in Comparative Example 2, the appearance of the multilayer coating film (finishing finish) is significantly reduced (values of Wa, Wb, Wc, and Wd).

  In Comparative Example 3, as in the present invention, hydrophobic N-butoxymethylacrylamide was used as (meth) acrylamide, but the amount used deviated from the lower limit specified in the present invention. Is not obtained, and the appearance of the multi-layer coating film (finishing finish) is reduced (values of Wa and Wb).

  In Comparative Example 4, since hydrophilic N-methoxymethylacrylamide was used as (meth) acrylamide, the solubility parameter (δa) of the acrylic resin (the film-forming resin component (a)) was 10.9. Therefore, there is no difference from the value (11.3) of the solubility parameter (δb) of the epoxy resin (the film-forming resin component (b)), and the relational expression defined in this specification: {δb− δa} ≧ 0.5 is not satisfied. As a result, the layer separation property decreases. Moreover, in the comparative example 4, the value of the surface roughness (Ra) of an electrodeposition coating film raises remarkably, and an electrodeposition coating film external appearance falls remarkably. Furthermore, in Comparative Example 4, the appearance of the multilayer coating film (finishing finish) is significantly reduced (values of Wa and Wb).

  Furthermore, surprisingly, in Comparative Example 5, hydrophobic N-butoxymethylacrylamide was used as (meth) acrylamide as in the present invention, but the amount used deviated from the upper limit prescribed in the present invention. Even in this case, the solubility parameter (δa) of the acrylic resin (film-forming resin component (a)) increases to 11.0, and the epoxy resin (film-forming resin component (b)) dissolves. The difference from the value (11.3) of the sex parameter (δb) becomes small, and the relational expression defined in this specification: {δb−δa} ≧ 0.5 is not satisfied. As a result, the layer separation property is significantly reduced. Moreover, in the comparative example 5, the value of the surface roughness (Ra) of an electrodeposition coating film also raises remarkably, and an electrodeposition coating film external appearance falls remarkably. Further, in Comparative Example 5, the appearance of the multilayer coating film (finishing finish) is remarkably reduced (values of Wa, Wb, Wc and Wd).

The present invention can impart not only excellent corrosion resistance, weather resistance, light resistance, impact resistance, chipping resistance, etc., but also excellent coating appearance to the electrodeposition coating film, such as an automobile body. This is very useful when coating an object having a large and complicated shape. In addition, according to the method of the present invention, it is possible to omit an intermediate coater that has been conventionally required, and to achieve resource saving, energy saving, cost saving, and reduction of environmental load (for example, low VOC and low CO ₂ ). Can do.
Moreover, when the method of the present invention is applied to the electrodeposition coating of automobile bodies, surprisingly, even when a top coating is applied directly on the electrodeposition coating, an excellent coating appearance is obtained. Since it can be provided also in a top coat film, it is very useful.

Claims (7)

Electrodeposition coating formation comprising electrodeposition coating of electrodeposition coating composition on substrate, then separating layers while heating, and then curing to form a multilayer cured film consisting of at least two layers An electrodeposition coating composition comprising:
Film-forming resin components (a) and (b),
Blocked polyisocyanates (c1) and (c2), and pigments,
The film-forming resin components (a) and (b) are incompatible with each other;
The film-forming resin component (a) forms emulsion particles A containing blocked polyisocyanate (c1),
The film-forming resin component (b) forms emulsion particles B containing blocked polyisocyanate (c2),
The film-forming resin component (a) contains (meth) acrylamide as a copolymerization monomer,
The (meth) acrylamide is at least one selected from the group consisting of N-butoxymethyl (meth) acrylamide and N-isobutoxymethyl (meth) acrylamide;
The (meth) acrylamide is contained in an amount of 1 to 24 parts by weight with respect to 100 parts by weight of the resin solid content of the film-forming resin component (a).
Electrodeposition coating formation method. The film-forming resin component (a) is a cation-modified acrylic resin,
The film-forming resin component (b) is a cation-modified epoxy resin,
The solubility parameter (δa) of the coating film-forming resin component (a) and the solubility parameter (δb) of the coating film-forming resin component (b) satisfy the relationship {δb−δa} ≧ 0.5.
The electrodeposition coating film forming method according to claim 1.   The blending ratio ((a) / (b)) of the film-forming resin components (a) and (b) is 50/50 to 40/60 in terms of solid content weight ratio. Electrodeposition coating formation method.   The electrodeposition coating film forming method according to claim 1, wherein the (meth) acrylamide is self-crosslinking.   The electrodeposition according to any one of claims 1 to 4, wherein the (meth) acrylamide is contained in an amount of 4 to 18 parts by weight with respect to 100 parts by weight of the resin solid content of the film-forming resin component (a). Coating film forming method. Blocked polyisocyanate (c1) is an aliphatic polyisocyanate blocked with a sealant,
The blocked polyisocyanate (c2) is obtained by blocking an alicyclic or aromatic polyisocyanate with a sealing agent.
The electrodeposition coating-film formation method of any one of Claims 1-5. An overcoating base coating composition is further applied on the electrodeposition coating film formed by the electrodeposition coating film forming method according to any one of claims 1 to 6, and an uncured top coating base coating film is applied. Forming a process,
A step of applying an overcoat clear coating composition on the uncured topcoat base coating to form an uncured topcoat clearcoat; and an uncured topcoat basecoat and an uncured topcoat clear coat A method for forming a multilayer coating film, comprising the step of simultaneously heating and curing.