JP2008095010A - Sash black paint composition and coating film forming method - Google Patents

Abstract

The present invention relates to a sash black paint that can be used for coating a sash part of an automobile, and that can provide a coating film that does not invert at the interface between coating films and has an excellent finished appearance. Providing a composition.
An oil-free polyester resin (a); an alkyd resin (b) in which the content of an oil and fat component in the resin is 12 to 50% by mass and a number average molecular weight is 1500 to 4000; and an imino group-containing melamine resin The mass ratio (a) :( b) of the oil-free polyester resin (a) to the alkyd resin (b) is 80:20 to 55:45, and the imino group-containing melamine resin (c) Is a mass ratio ((a) + (b)) :( c) to the oil-free polyester resin (a) and the alkyd resin (b), and is a sash black coating composition that is 70:30 to 50:50 object.
[Selection figure] None

Description

  The present invention relates to a sash black coating composition used for coating a sash portion of an automobile and a coating film forming method.

  In the painting of automobile bodies, the sash black paint composition is applied to the window frame (sash) part, pillar part, front grill part or rear hatch part or their peripheral parts in order to enhance the design, that is, to tighten the impression of the whole automobile. May be painted. This sash black paint composition is a black paint as the name suggests. When a sash black paint composition is used, the outer coating of the automobile body to be painted is usually formed by first forming an electrodeposition coating film and then applying an intermediate coating composition, and then obtaining the intermediate coating film obtained. Apply a sash black paint composition to the sash portion, etc. by a wet-on-wet method without curing the coating, heat cure, coat the top coating composition on portions other than the sash portion, and heat cure It is formed.

  The sash black paint composition is used for the purpose of forming a black paint film different from other parts when used for painting a car body outer plate of an automobile. Therefore, the sash black coating composition has technical problems peculiar to the sash black coating composition, such as lack of miscibility with the coating film formed in other portions and good masking property. On the other hand, the coating film formed on the outer body plate of the automobile is required to have good weather resistance and finished appearance (smoothness, gloss, etc. of the coating film). This requirement is no exception for the sash black coating composition targeted by the present invention.

  Japanese Patent Application Laid-Open No. 62-149765 (Patent Document 1) discloses an acrylic resin of 45 to 30% by mass for the purpose of improving the overall finish level of automobile coating by finishing the sash part to be equal to other parts. A wet-on-wet coating on a polyester resin as a main component, comprising 5 to 20% by mass of a melamine resin, 0.5 to 5% by mass of a pigment, and 49.5 to 45% by mass of a solvent. Acrylic / melamine resin coatings suitable for coating with are disclosed.

  In addition, in order to prevent the reversal of the coating film, the adjustment of the surface tension of the intermediate coating material and the sash top coating material, which was once required, is almost unnecessary, and the dust of the top coating material does not remain other than in the sash area. In order to develop a coating method that does not deteriorate the finished appearance even at a filling site such as a sealing agent, JP-A-5-7827 (Patent Document 2) describes a colored top coat on an uncured intermediate coating film surface. In a coating method in which a paint (sash black paint) is applied and then heated to cure both coating films, silica fine powder is added to the colored top coat to impart thixotropic properties. A coating method is disclosed. Here, “reversal” of the coating film means that when the sash black coating film is formed on the intermediate coating film, the previously applied intermediate coating film and the sash black coating film coated thereon In between, the ups and downs of the paint film partially or entirely (change of the paint film layer) occurs, and even from the surface of the paint film that is opaque, even in the part having a film thickness greater than the concealed film thickness, It means a phenomenon in which the color of the lower coating is visually recognized.

  For the purpose of preventing inversion that may occur at the boundary of both coatings on the sealer at the edge of the sash when a coating consisting of intermediate coating and sash black is laminated on the sash by wet-on-wet JP 2002-249709 (Patent Document 3) discloses a coating composition containing a polyester resin and a melamine resin, wherein the melamine resin has a number average molecular weight of 1500 to 5000 and the coating composition. The coating composition characterized by being 1-10 mass% with respect to the resin solid content of a thing is disclosed.

  Japanese Patent Application Laid-Open No. 2002-254024 (Patent Document 4) discloses a coating film forming method using an intermediate coating material that provides a specific dynamic elastic modulus as a coating film forming method in which no trace of a masking material remains on sash black. Is disclosed.

  Furthermore, Japanese Patent Laid-Open No. 10-314665 (Patent Document 5) discloses a two-tone metallic coating of a vehicle body composed of an upper color and a lower color as a coating method capable of obtaining a sash black coating that does not cause poor finish. A vehicle body coating method is disclosed, which uses a paint in which a bright pigment is blended with a sash black paint.

  As described above, inventions relating to paints or painting methods used for painting sash black have been disclosed. However, at present, no means has yet been found for clearing all the various problems in sash black painting.

Japanese Patent Laid-Open No. 62-149765 JP-A-5-7827 JP 2002-249709 A JP 2002-254024 A Japanese Patent Laid-Open No. 10-314665

  The present invention solves the above-mentioned conventional problems, the purpose of which is a coating composition used for coating the sash part of an automobile, without causing inversion at the interface between the coating layers, And it is providing the sash black coating composition which can obtain the coating film excellent in the finished external appearance.

The present invention
An oil-free polyester resin (a); an alkyd resin (b) having a content of oil and fat components in the resin of 12 to 50% by mass and a number average molecular weight of 1500 to 4000; and an imino group-containing melamine resin (c); Including
The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) is 80:20 to 55:45,
The amount of the imino group-containing melamine resin (c) is 70:30 to 50: as a mass ratio ((a) + (b)) :( c) with the oil-free polyester resin (a) and the alkyd resin (b). 50, a sash black coating composition, which achieves the above object.

  Moreover, it is preferable that the said alkyd resin (b) contains 20-40 mass% of tall oil.

The present invention also includes the following step: coating the intermediate coating composition on the object to be coated to form an uncured intermediate coating film,
Applying a sash black coating composition on the obtained uncured intermediate coating film to form an uncured sash black coating film, and heating the uncured intermediate coating film and sash black coating film Curing to obtain a laminated coating film,
A method of forming a coating film comprising:
This sash black coating composition comprises an oil-free polyester resin (a); an alkyd resin (b) having a content of oil and fat components in the resin of 12 to 50% by mass and a number average molecular weight of 1500 to 4000; and imino A group-containing melamine resin (c);
The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) is 80:20 to 55:45,
The amount of the imino group-containing melamine resin (c) is 70:30 to 50: as a mass ratio ((a) + (b)) :( c) with the oil-free polyester resin (a) and the alkyd resin (b). A method of forming a coating film, which is 50, is also provided.

  The present invention also provides an automobile body having a laminated coating film obtained by the coating film forming method.

  The sash black coating composition of the present invention can be applied to the intermediate coating film and the sash black coating even when the wet coating is applied on the uncured intermediate coating film formed on the substrate. It has an excellent advantage that there is no inconvenience such as inversion that may occur at the interface with the film. The coating film thus formed does not have other appearance defects such as rough skin, but has a good finished appearance. In the sash black coating composition of the present invention, the above-described excellent advantages are obtained by using a specific amount of the alkyd resin in which the content of the oil and fat component is in a specific range. The sash black coating composition of the present invention can form a coating film having excellent appearance, and is excellent in masking performance, weather resistance, scratch resistance, and top coat adhesion. It can be preferably used for coating the sash part.

Sash black coating composition The sash black coating composition of the present invention is a coating composition comprising an oil-free polyester resin (a), an alkyd resin (b) and an imino group-containing melamine resin (c). Hereinafter, various components contained in the sash black coating composition of the present invention will be described in detail.

Oil-free polyester resin (a)
The sash black coating composition of the present invention contains an oil-free polyester resin (a). It does not specifically limit as oil-free polyester resin (a), For example, what is normally used as a film-forming resin can be used.

  The oil-free polyester resin (a) preferably has a number average molecular weight of 1000 to 4000. If it is less than 1000, the coating performance such as water resistance is deteriorated, and there is a possibility that a mixed layer with the sash black coating may occur. If it exceeds 4000, the appearance (skin) of the resulting coating film may be deteriorated and the viscosity at the time of application may be too high. The number average molecular weight of the oil-free polyester resin (a) is preferably 1200 to 3200.

  In addition, the number average molecular weight (Mn) in this specification is a value measured by gel permeation chromatograph (GPC) and converted using polystyrene molecular weight as a standard.

  The oil-free polyester resin (a) preferably has an acid value of 4 to 15 mgKOH / g. If it is less than 4 mgKOH / g, the curability may be poor, and if it exceeds 15 mgKOH / g, the water resistance may be lowered. Preferably, it is 6-10 mgKOH / g. The oil-free polyester resin (a) preferably has a hydroxyl value of 50 to 250. If it is less than 50, the curability may be poor, and if it exceeds 250, the coating film becomes too hard and adhesion and chipping resistance may be deteriorated. Preferably, it is 80-220.

  The oil-free polyester resin (a) can be produced by polycondensation of polyvalent carboxylic acid and / or acid anhydride and polyhydric alcohol as essential components. The polyvalent carboxylic acid and / or acid anhydride is not particularly limited, and examples thereof include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, and methyltetrahydrophthalic acid. , Methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid And azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenyl succinic acid, dodecenyl succinic anhydride and the like.

  The polyhydric alcohol is not particularly limited. For example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 1 , 4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl -3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, tri Ji propane, trimethylol butane, hexanetriol, pentaerythritol, dipentaerythritol and the like.

  In the preparation of the oil-free polyester resin (a), a monocarboxylic acid, a hydroxycarboxylic acid or the like may be included as a reaction component other than the polyvalent carboxylic acid and / or acid anhydride and the polyhydric alcohol. However, since it is an oil-free polyester resin, it does not contain various fats and oils and fat components such as these fatty acids as a reaction component. Other reaction components that can be used for the preparation of the oil-free polyester resin (a) include monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co., Ltd.), lactones, and the like. The lactones can be subjected to ring-opening addition to polyvalent carboxylic acid and polyhydric alcohol polyesters to form a graft chain. For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ- Examples include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, and δ-caprolactone, among which ε-caprolactone is preferable. About the said polyhydric carboxylic acid and / or an acid anhydride, a polyhydric alcohol, other lactones, you may use individually, respectively, and may use 2 or more types together.

  The synthesis of the oil-free polyester resin (a) can be performed by heating and condensing the above reaction components in a nitrogen stream, for example, at 150 to 250 ° C. for 4 to 10 hours. In this case, known catalysts such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used. The reaction components may be added all at once, but may be added in several portions. The molar ratio of the reaction components and reaction conditions are such that the acid value, hydroxyl value, and number average molecular weight of the resulting oil-free polyester resin (a) are 4-15, hydroxyl value 50-250, and number average molecular weight 1000-4000. Adjustment is preferably made to reach the range. The oil-free polyester resin (a) may be used alone or in combination of two or more.

Alkyd resin (b)
In the sash black coating composition of the present invention, an alkyd resin (b) having an oil / fat component content of 12 to 50% by mass and a number average molecular weight of 1500 to 4000 is used.

  The alkyd resin (b) can be obtained by a three-component reaction of a polyvalent carboxylic acid and / or an acid anhydride, a polyhydric alcohol, and a fatty acid and / or a fatty acid triglyceride. The difference between the alkyd resin (b) and other polyester resins is that fatty acids and / or fatty acid triglycerides are bonded in the molecule. In the present specification, fatty acids and / or fatty acid triglycerides are collectively described as “oil / fat components”.

  The alkyd resin (b) in the present invention is characterized in that 12 to 50% by mass of the total mass of all reaction components is an oil and fat component. This amount is expressed as “content of fat and oil component in resin (mass%)”. This oil content is generally referred to as “oil length” in the paint field. The content of the oil and fat component in the alkyd resin (b) is preferably 20 to 40% by mass. When the content of the oil and fat component is less than 12% by mass, the coating may be reversed. Moreover, when content of an oil-fat component exceeds 50 mass%, there exists a possibility that a coating film may become soft and weak.

  Examples of the fat component constituting the alkyd resin (b) include castor oil, linseed oil, dehydrated castor oil, tung oil, safflower oil, soybean oil, tall oil, coconut oil, palm kernel oil, and fatty acids thereof. . It is preferable to use a semi-drying oil such as castor oil, soybean oil, safflower oil, tall oil or the fatty acid thereof as the fat component, and particularly preferably tall oil as the fat component.

  As the polyhydric carboxylic acid and / or acid anhydride and polyhydric alcohol used for the preparation of the alkyd resin (b), those used for the preparation of the oil-free polyester resin (a) can be used. The synthesis of the alkyd resin (b) is carried out by synthesizing three components of polyvalent carboxylic acid and / or acid anhydride, polyhydric alcohol, and fatty acid and / or fatty acid triglyceride in a nitrogen stream, for example, at 150 to 250 ° C. It can be performed by heating for 10 hours and condensing. As the catalyst, the catalysts listed in the preparation of the oil-free polyester resin (a) can be used. The reaction components may be added all at once, but may be added in several portions. The molar ratio of the reaction components and the reaction conditions are adjusted so that the acid value, hydroxyl value, and number average molecular weight of the alkyd resin (b) to be obtained reach the ranges of acid value 3-12 and hydroxyl value 100-150. preferable.

  The alkyd resin (b) used in the present invention is also characterized by a number average molecular weight of 1500 to 4000. If the number average molecular weight is less than 1500, inversion may occur during wet-on-wet coating with an intermediate coating film, whereas if the number average molecular weight exceeds 4000, the resulting coating film has poor smoothness. There is a risk of becoming.

  The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) contained in the sash black coating composition of the present invention is in the range of 80:20 to 55:45. When the amount of the oil-free polyester resin (a) exceeds this range, the smoothness of the resulting coating film may be inferior or inversion may occur. When the amount of the alkyd resin (b) exceeds this range, the smoothness of the resulting coating film may be inferior. In addition, mass ratio here means solid content mass ratio. The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) is more preferably 75:25 to 55:45.

Imino group-containing melamine resin (c)
The imino group-containing melamine resin preferably contains at least one hydrogen bonded to a nitrogen atom of a melamine resin having a melamine skeleton having the following chemical formula, that is, an imino group.

  Although there are six groups bonded to N of the triazine nucleus of the melamine resin, those having a large number of imino types are referred to as imino group-containing melamine resins (or imino type melamine resins). The remaining linking groups may have other groups.

  As described above, the imino group-containing melamine resin has an average of one or more imino groups in one molecule. If the lower limit is not reached, curability and adhesion may be reduced. However, those having too many imino groups, such as those having an average of 3.5 or more in one molecule, are not preferred because they tend to form a hard and brittle coating film, and the water resistance and impact resistance of the coating film are poor. .

  Examples of melamine resins containing one or more imino groups are Uban-125 (Mitsui Chemicals, trade name), Uban-225 (Mitsui Chemicals, trade name), Cymel 254, 325, 370, 327 (Mitsui Cytec). Industry, trade name), My Coat 508 (Mitsui Cytec Industry, trade name) and the like.

  The imino group-containing melamine resin (c) contained in the sash black coating composition of the present invention has a mass ratio ((a) + (b)) to the oil-free polyester resin (a) and the alkyd resin (b): ( c) is preferably included in an amount in the range of 70:30 to 50:50. The mass ratio ((a) + (b)) :( c) is more preferably 65:35 to 55:45. When the mass ratio of the imino group-containing melamine resin (c) is included in an amount that falls below the above range, the curability of the sash black coating composition may be lowered. On the other hand, when the mass ratio of the imino group-containing melamine resin (c) is included in an amount exceeding the above range, the curing reaction of the sash black coating composition proceeds too quickly, and the finished appearance may be deteriorated. In addition, mass ratio here means solid content mass ratio.

Pigment The sash black coating composition of the present invention is a black coating composition as the name suggests. The sash black coating composition of the present invention may be glossy black or matte black. The sash black paint composition further contains a pigment in addition to the above-described resins (a) to (c), and thereby has a glossy black or matte black.

  Conventionally known pigments can be used as the pigment. For example, carbon black can be used as the black pigment, and fine silica powder can be used as the matting agent. It is preferable that these pigments are 1-25 mass parts with respect to 100 mass parts of resin solid content of a sash black coating composition. If it is less than 1 part by mass, an appropriate black color or paint color (gloss) cannot be obtained as a sash black for automobiles. If it exceeds 25 parts by mass, the resulting coating film lacks smoothness and has poor appearance such as rough skin. It tends to happen. The amount of the pigment is more preferably 2 to 10 parts by mass.

  The sash black coating composition of the present invention may contain, if desired, colored pigments such as chromium oxide, phthalocyanine, iron oxide and quinacridone; other pigments such as extender pigments such as barium sulfate, talc, calcined kaolin, calcium carbonate and magnesium silicate. It can also be used.

Other components In addition to the above components, the sash black coating composition of the present invention includes crosslinked resin particles, organic bentonite, fatty acid polyamide, polyethylene wax, etc. as thickeners; aromatic hydrocarbons, aliphatic hydrocarbons as organic solvents System, ester system, alcohol solvent, etc .; other additives include acid catalyst, UV absorber, hindered amine light stabilizer, antioxidant, surface conditioner, leveling agent, pigment dispersant, plasticizer, antifoaming agent, etc. May be used.

  Moreover, the sash black coating composition of the present invention may contain other film-forming resins in addition to the oil-free polyester resin (a), alkyd resin (b) and (c) imino group-containing melamine resin. Examples of other coating film forming resins include acrylic resins, epoxy resins, and urethane resins.

Preparation of Sash Black Paint Composition As a method for producing the sash black paint composition of the present invention, it can be produced according to the paint form of the paint composition. For example, the oil-free polyester resin (a), alkyd resin (b ) And (c) an imino group-containing melamine resin, and a pigment, a solvent, and, if desired, a pigment dispersant and other coating-forming resin are mixed to obtain a pigment dispersion paste, Methods well known to those skilled in the art, such as mixing, can be used.

  Specific examples of the solvent used for the preparation and dilution of the sash black coating composition include aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone; diethyl ether and isopropyl Ether solvents such as ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, anisole, phenetole; ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol diacetate, etc. Ester solvents: dimethylformamide, diethylformamide, dimethyls Sulfoxide, N- amide solvents such as methyl pyrrolidone; methyl cellosolve, ethyl cellosolve, cellosolve solvents such as butyl cellosolve; and the like; methanol, ethanol, propanol alcohol solvents such as. These solvents may be used alone or in combination.

  The total solid content during coating of the sash black coating composition of the present invention is preferably 40 to 75% by mass. If it is less than 40% by mass, the viscosity is too low and appearance defects such as inversion and sagging may occur. On the other hand, when it exceeds 75 mass%, the viscosity is too high and the appearance of the coating film may be deteriorated. The total solid content during coating is preferably 50 to 70% by mass.

  The sash black coating composition of the present invention is a coating composition suitably used for a sash portion of an automobile outer plate. By using this coating composition for the coating of the sash portion, it is possible to effectively prevent abnormalities or inversions in the finished appearance. In addition to the sash portion, the sash black coating composition of the present invention can also be used for coating a rocker portion under the door, a vertical portion at the front, and the like.

Coating Film Forming Method The sash black coating composition of the present invention can be used in a coating film forming method including the following steps:
Applying an intermediate coating composition to an object to form an uncured intermediate coating film;
Applying a sash black coating composition on the obtained uncured intermediate coating film to form an uncured sash black coating film, and heating the uncured intermediate coating film and sash black coating film A step of curing to obtain a laminated coating film.

  A sash black coating film is formed as described above. In the coating of the outer plate of the automobile body, masking is applied to the portion of the sash black coating film formed on the sash portion, and then the top coat base coating composition is applied. By masking, the top-coating base coating composition is not applied to the sash black-coated portion, and the black color is maintained in appearance. The outer plate of the automobile body thus coated has a colored portion where the top coat base coating film is formed and a black portion where the sash black coating film is formed. As the topcoat base coating composition, a commonly used topcoat base coating composition of an aqueous type or a solvent type can be used.

  It does not specifically limit as a to-be-coated object, For example, a metal, a plastic, a foam etc. are mentioned. Of these objects to be coated, a metal substrate capable of cationic electrodeposition coating is particularly preferably used. The metal substrate is not particularly limited, and examples thereof include simple metals such as iron, copper, aluminum, tin, and zinc, and alloys and castings containing these simple metals. Specifically, passenger cars, trucks, etc. Automobile bodies such as motorcycles and buses, and parts.

  When these metal base materials are used as an object to be coated, it is particularly preferable that the metal base is previously subjected to chemical conversion treatment with phosphate, chromate or the like. And it is preferable that the electrodeposition coating film is formed on the metal base material which such chemical conversion treatment was made. As the electrodeposition coating composition, both a cation type and an anion type can be used, but it is preferable to use a cationic type electrodeposition coating composition because a coating film having better anticorrosion properties can be formed. . As the cationic electrodeposition coating composition, a commonly used coating composition can be used.

  In this way, the intermediate coating composition is formed by applying the intermediate coating composition to the article on which the chemical conversion film and the electrodeposition coating are formed as necessary. By forming the intermediate coating film, defects in the object to be coated and the electrodeposition coating film are concealed, thereby ensuring the surface smoothness after the sash black coating composition is applied. Furthermore, by forming an intermediate coating film, physical properties of the coating film such as impact resistance and chipping resistance can be improved.

  Although it does not specifically limit as an intermediate coating composition, The coating composition containing additives, such as a pigment, a film formation resin, a hardening | curing agent, and an antifoamer and a coating surface modifier as needed, is used preferably.

  Examples of the pigment that can be used in the intermediate coating composition include pigments that can be used in the sash black coating composition of the present invention. Examples of the pigment that can be used include a combination of carbon black and titanium dioxide. By using these, a gray-based intermediate coating composition can be prepared. In addition, the preparation method of the said electrodeposition coating composition and intermediate coating composition is not specifically limited, For example, it can prepare by a conventionally well-known method.

  The method for applying the intermediate coating composition is not particularly limited. For example, an air electrostatic spray commonly referred to as “react gun”; commonly referred to as “micro micro (μμ bell)”, “micro (μ) bell”, “ This can be done by using a rotary atomizing electrostatic coating machine or the like called “Metal Bell” or the like. The intermediate coating film is preferably coated so that the dry film thickness is 10 to 60 μm, and more preferably 20 to 50 μm. Exceeding the upper limit may cause problems such as cracking and sagging during painting. Below the lower limit, the unevenness of the base cannot be concealed, and the film may be cut or the coating film may be defective.

  After the intermediate coating film is formed, the process proceeds to the next step of forming the sash black coating film without heating and curing. Before forming the sash black coating film, the intermediate coating film obtained is allowed to stand at room temperature for a certain period of time, or is heated, for example, at 60 to less than 100 ° C. for 2 to 10 minutes, to form an intermediate coating film A preheating step for drying the membrane in advance can also be performed. In the present invention, “uncured” means a state in which the film is not completely cured, and includes a state of a coating film that has been preheated.

  On the uncured intermediate coating film thus obtained, the sash black coating composition is applied wet-on-wet to form a sash black coating film. The method for applying the sash black paint composition is not particularly limited, but usually, air spray, hand spray, REA gun coater, or the like is used. The film thickness of the sash black coating is preferably applied so that the dry film thickness is 10 to 30 μm, and more preferably 15 to 25 μm. If the upper limit is exceeded, the sharpness may be reduced, and problems such as unevenness and sagging may occur during painting. Below the lower limit, the hue of the intermediate coating film cannot be concealed, and the hue may be poor.

  By heating the thus obtained uncured intermediate coating film and sash black coating film, these two-layer coating films are cured by heating at a time. The heat curing can be performed under general baking conditions, for example, 120 to 160 ° C, preferably 130 to 150 ° C. Although the curing time varies depending on the curing temperature, 15 to 30 minutes is appropriate at 130 to 150 ° C. By baking in this way, a cured coating film having a high crosslinking density can be obtained. If the heat curing is less than 120 ° C, the curing is not sufficient, and if it exceeds 160 ° C, the coating film may be hard and brittle.

  As described above, the sash black coating composition of the present invention comprises an oil-free polyester resin (a); an alkyd resin in which the content of oil and fat components in the resin is 12 to 50% by mass and the number average molecular weight is 1500 to 4000. (B); and an imino group-containing melamine resin (c); and the mass ratio (a) :( b) of the oil-free polyester resin (a) to the alkyd resin (b) is 80:20 to 55:45 Therefore, even when applying wet-on-wet on the uncured intermediate coating film formed on the substrate, the interface between the intermediate coating film and the sash black coating film It has an excellent advantage that there is no inconvenience such as inversion that may occur. The coating film thus formed does not cause other appearance defects such as rough skin.

  In particular, the sash black coating composition of the present invention includes a specific alkyd resin in which the content of the oil and fat component in the resin is 12 to 50% by mass and the number average molecular weight is 1500 to 4000, thereby forming a hydrophobic part. It is possible to contain a specific amount of the introduced resin, thereby effectively suppressing inversion.

  As described above, the sash black coating composition of the present invention can form a coating film having excellent appearance, and is therefore preferably used for coating the outer plate of an automobile body. The sash black coating composition of the present invention can also be used for coating an inner plate of an automobile body.

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

Synthesis Example 1 Synthesis of oil-free polyester resin (a-1) Thermometer, stirrer, cooling pipe, nitrogen introduction pipe, water separator, and rectification tower 354 parts of isophthalic acid, 249 parts of sebacic acid, tri 84 parts of methylolpropane, 281 parts of neopentyl glycol, 42 parts of Cardura E (manufactured by Shell, Versatic acid glycidyl ester) and 2 parts of dibutyltin oxide were charged and heated to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. After cooling to 150 ° C., 105 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene were added to obtain a varnish having a nonvolatile content of 70% containing an oil-free polyester resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 100 mgKOH / g (solid content).

Synthesis Example 2 Synthesis Thermometer of Oil-Free Polyester Resin (a-2) , Stirrer, Cooling Tube, Nitrogen Introducing Tube, Water Separator and Reactor with 214 Parts of Isophthalic Acid, 328 Parts of Sebacic Acid, Tri 91 parts of methylolethane, 307 parts of neopentyl glycol, 45 parts of Cardura E (manufactured by Shell, Versatic acid glycidyl ester) and 2 parts of dibutyltin oxide were charged and heated to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. After cooling to 150 ° C., 114 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an oil-free polyester resin having a number average molecular weight of 1500, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 200 mgKOH / g (solid content).

Synthesis Example 3 Synthesis of alkyd resin (b-1) (content of oil and fat component in resin: 40%)
In a reaction vessel equipped with a thermometer, stirrer, cooling tube, nitrogen inlet tube, water separator and rectifying tower, 400 parts of tall oil (manufactured by Shiroishi Calcium Co., Ltd.), 230 parts of pentaerythritol, 70 parts of neopentyl glycol, anhydrous phthalate 380 parts of acid and 2 parts of dibutyltin oxide were charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. When the resin acid value reached 8.5 mg KOH / g (solid content), it was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Synthesis Example 4 Synthesis of alkyd resin (b-2) (content of fat and oil component in resin: 20%)
In a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen introduction pipe, water separator and rectifying tower, 200 parts of tall oil, 300 parts of pentaerythritol, 90 parts of neopentyl glycol, 490 parts of phthalic anhydride, dibutyltin 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Synthesis Example 5 Synthesis of alkyd resin (b-3) (content of fat and oil component in resin: 50%)
In a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen inlet pipe, water separator and rectifying tower, 500 parts of tall oil, 200 parts of pentaerythritol, 60 parts of neopentyl glycol, 320 parts of phthalic anhydride, dibutyltin 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Comparative Synthesis Example 1 Synthesis of alkyd resin (b-4) (content of oil and fat component in resin: 10%)
In a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen introduction pipe, water separator and rectifying tower, 100 parts of tall oil, 330 parts of pentaerythritol, 100 parts of neopentyl glycol, 550 parts of phthalic anhydride, dibutyltin 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Comparative Synthesis Example 2 Synthesis of alkyd resin (b-5) (content of oil and fat component in resin: 60%)
In a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen introduction pipe, water separator and rectifying tower, 600 parts of tall oil, 160 parts of pentaerythritol, 50 parts of neopentyl glycol, 270 parts of phthalic anhydride, dibutyltin 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 3000, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Comparative Synthesis Example 3 Synthesis of alkyd resin (b-6) (content of oil and fat component in resin: 40%)
400 parts tall oil, 245 parts pentaerythritol, 70 parts neopentyl glycol, 365 parts anhydrous phthalic anhydride, dibutyltin in a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen inlet pipe, water separator and rectifying tower 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene were added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 1200, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Comparative Synthesis Example 4 Synthesis of alkyd resin (b-7) (content of oil and fat component in resin: 40%)
In a reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen introduction pipe, water separator and rectifying tower, 400 parts of tall oil, 200 parts of pentaerythritol, 70 parts of neopentyl glycol, 410 parts of phthalic anhydride, dibutyltin 2 parts of oxide was charged and heated, and the temperature was raised to 210 ° C. However, from 160 ° C. to 210 ° C., the temperature was increased at a constant rate over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 210 ° C., the mixture was kept warm, and after 1 hour of warming, 30 parts of xylene as a refluxing solvent was gradually added to the reaction vessel, and the reaction was continued by switching to condensation in the presence of the solvent. The mixture was cooled to 150 ° C., 200 parts of ε-caprolactone was added, and the mixture was kept at 150 ° C. for 2 hours, and then cooled to 100 ° C. Further, 430 parts of xylene was added to obtain a varnish having a nonvolatile content of 70% containing an alkyd resin having a number average molecular weight of 4,500, an acid value of 8.5 mgKOH / g (solid content), and a hydroxyl value of 120 mgKOH / g (solid content).

Example 1
22.5 parts of polyester resin (a-1) obtained in the above synthesis example, 22.5 parts of polyester resin (a-2) and 15 parts of alkyd resin (b-1), 70 parts of xylene, sulfuric acid manufactured by Sakai Chemical Industry Co., Ltd. After 135 parts of barium BF-20 and 50 parts of carbon black MA-100 manufactured by Mitsubishi Chemical Corporation were added and premixed, the glass bead medium was added in a paint conditioner, and mixed and dispersed at room temperature for 1 hour. A pigment dispersion paste having a nonvolatile content of 71% was obtained. As shown in Table 1, 40 parts of an imino group-containing melamine resin is added to 100 parts of the pigment dispersion paste, and 0.1 part of Mitsui Chemicals Regix RL-4, and a matting agent Mizukacil NP8 made by Misawa Chemical Co., Ltd. 5 parts was added to obtain a sash black coating composition. As the melamine resin, an imino group-containing melamine “Uban 125” manufactured by Mitsui Chemicals, Inc. was used.

Examples 2-5 and Comparative Examples 1-6
A sash black coating composition was prepared in the same manner as in Example 1 except that the polyester resin and alkyd resin used were changed to the types and amounts shown in Table 1 or 2.

Formation of paint film Zinc phosphate treated 0.8cm, 20cm x 30cm SPCC-SD steel plate (Dal steel plate) and cationic electrodeposition coating composition ("Power Top U-50 (trade name) by Nippon Paint Co., Ltd.) )) Was applied to a dry film thickness of about 25 μm and baked at 170 ° C. for 30 minutes. Thereafter, a dry film obtained by diluting “Orga P-5-1 (trade name)” manufactured by Nippon Paint Co., Ltd. with a thinner (S-100 / Butyl acetate 50/50 manufactured by Exxon in mass ratio) as an intermediate coating composition. It was coated with an air spray gun so as to have a thickness of about 40 μm, and the sash black coating composition obtained by the above examples and comparative examples was thinner (by mass ratio: butyl acetate / Exxon S-100 = 50 / 50), and a dry film thickness was applied to about 25 μm with an air spray gun to form a sash black coating film. Next, after setting for 7 to 10 minutes, baking was performed at 140 ° C. for 30 minutes to obtain a cured coating film.

Coating Film Evaluation The obtained coating film was visually evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. In any of the following evaluations, it can be determined that 4 or more are acceptable.

Unevenness evaluation 5 on coating film surface : Unevenness is not confirmed at all, and it is very smooth.
4: Slight irregularities are confirmed.
3: Unevenness is confirmed.
2: Unevenness is somewhat remarkable.
1: Concavity and convexity are remarkable.

Evaluation of reversal between intermediate coating film and sash black coating film 5: The color of the intermediate coating film is completely obscured by the sash black coating film.
4: The color of the intermediate coating film is confirmed in less than 5% of the total area.
3: The color of the intermediate coating film is confirmed in 5% or more and less than 10% of the total area.
2: The color of the intermediate coating film is confirmed in 10% or more and less than 20 of the total area.
1: The color of the intermediate coating film is confirmed in 20% or more of the total area.

  As shown in Tables 1 and 2, the coating film formed using the sash black coating composition of the example was excellent in both the surface roughness evaluation and the inversion evaluation. On the other hand, all the coating films obtained by the comparative examples were inferior in surface unevenness. Moreover, the coating film obtained by Comparative Examples 1, 3, and 5 was inferior also in inversion evaluation.

  The sash black coating composition of the present invention can be applied to the intermediate coating film and the sash black coating even when the wet coating is applied on the uncured intermediate coating film formed on the substrate. It has an excellent advantage that there is no inconvenience such as inversion that may occur at the interface with the film. The coating film thus formed does not have other appearance defects such as rough skin, but has a good finished appearance. Since the sash black coating composition of the present invention can form a coating film having excellent appearance, it can be preferably used for coating the sash portion of the outer plate of an automobile body.

Claims (4)

An oil-free polyester resin (a); an alkyd resin (b) having a content of oil and fat components in the resin of 12 to 50% by mass and a number average molecular weight of 1500 to 4000; and an imino group-containing melamine resin (c); Including
The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) is 80:20 to 55:45,
The amount of the imino group-containing melamine resin (c) is 70:30 to 50: mass ratio ((a) + (b)) :( c) with the oil-free polyester resin (a) and the alkyd resin (b). : 50, the sash black coating composition.   The sash black coating composition according to claim 1, wherein the alkyd resin (b) contains 20 to 40% by mass of tall oil. Applying an intermediate coating composition to an object to form an uncured intermediate coating film;
Applying a sash black coating composition on the obtained uncured intermediate coating film to form an uncured sash black coating film, and heating the uncured intermediate coating film and sash black coating film Curing to obtain a laminated coating film,
A method of forming a coating film comprising:
The sash black coating composition comprises: an oil-free polyester resin (a); an alkyd resin (b) having a content of oil and fat components in the resin of 12 to 50% by mass and a number average molecular weight of 1500 to 4000; and imino A group-containing melamine resin (c);
The mass ratio (a) :( b) between the oil-free polyester resin (a) and the alkyd resin (b) is 80:20 to 55:45,
The amount of the imino group-containing melamine resin (c) is 70:30 to 50: mass ratio ((a) + (b)) :( c) with the oil-free polyester resin (a) and the alkyd resin (b). : 50,
Coating film forming method.   An automobile body having a laminated coating film obtained by the coating film forming method according to claim 3.