JP2005187592A - Water-based intermediate coating composition, method for forming coating film and coated product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based intermediate coating composition capable of giving a coating film having excellent chipping resistance. <P>SOLUTION: The water-based intermediate coating composition comprises a polyester resin having a hydroxyl value of 100 to 200 mg KOH/g, a curing agent and a color pigment, wherein activation energy of the coating film obtained from the water-based intermediate coating composition is 200 KJ/mol or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous intermediate coating composition, a method for forming a coating film, and a coated product obtained by this method.

  It is known that the coating film coated on the outer panel of automobiles encounters a so-called chipping phenomenon in which pebbles, gravel, etc. collide with each other during driving, resulting in cracks and peeling of the coating film. ing. When such chipping occurs, moisture enters from this portion and rust is generated on the surface of the outer plate of the vehicle body. Especially in cold regions, a large amount of rock salt and sand is sprayed on the road surface to melt snow in the winter, so pebbles, gravel, etc. easily collide with the paint on the car skin. Is desired.

  Usually, an intermediate coating film is formed on a coating film to be applied to an automobile in order to impart chipping resistance to the coating film. Although melamine resin is used, in order to impart chipping resistance, trifunctional or higher polyfunctional isocyanate compounds are often used by replacing all or part of melamine resin (see Patent Documents 1 and 2). .

  The intermediate coating materials described in Patent Document 1 and Patent Document 2 use a water-soluble organic solvent as a solvent from the viewpoint of paint stability and coating workability, and therefore consider the problem of reducing environmental impact (VOC, etc.) Then, it is not preferable.

In addition, it has been studied to control the mechanical properties of the coating film, including tensile properties, and to use a polyfunctional isocyanate compound having a functionality of 3 or more as a curing agent. It could not be completely suppressed (see Patent Documents 3 and 4).
JP-A-8-209066 JP 2001-139879 A JP 2003-268314 A JP 2001-64589 A

  According to the present inventors, it was found that the chipping resistance of the coating film is affected by the cross-linked structure in the coating. A paint having a dense and uniform cross-linked structure is superior in chipping resistance. However, in consideration of the uniformity of the crosslinked structure of the coating, an aqueous intermediate coating that can impart sufficient chipping resistance has not been obtained.

  In view of the above problems, an object of the present invention is to provide an aqueous intermediate coating composition that can obtain a coating film having excellent chipping resistance.

  The present invention is an aqueous intermediate coating composition comprising a coating film-forming resin, a curing agent, and a color pigment, characterized by controlling the crosslinking structure of the coating film obtained from the aqueous intermediate coating composition. It is an aqueous intermediate coating composition.

  (1) An aqueous intermediate coating composition comprising a polyester resin having a hydroxyl value of 100 mgKOH / g to 200 mgKOH / g, a curing agent and a color pigment, and activating a coating film obtained from the aqueous intermediate coating composition An aqueous intermediate coating composition characterized by having an energy of 200 KJ / mol or more.

  According to the present invention, it has been experimentally proved that a multilayer coating film having excellent chipping resistance can be obtained by setting the activation energy of the coating film to 200 KJ / mol or more.

Here, the “activation energy of the coating film” refers to a scale indicating the uniformity and density of the crosslinking points in the coating film. Specifically, the dynamic viscoelasticity measurement of the coating film was performed using the FT-RM method capable of measuring several frequencies at the same time, and the obtained relaxation spectrum was in α dispersion, β dispersion and γ dispersion. The maximum value of the ratio of the storage elastic modulus and the loss elastic modulus (hereinafter referred to as tan δ) in at least two dispersion regions, and the temperature and frequency at this time are Arrhenius plots (f = f ₀ exp (−Ea / RT The value of Ea obtained by)) is called activation energy.

  Since the main resin must have appropriate reactivity with the isocyanate used as the curing agent, it is preferably a polyester resin having a hydroxyl group or a polymer blend containing a polyester resin.

  (2) The aqueous intermediate coating composition according to (1), wherein the curing agent is a polyisocyanate compound having 2 or 3 isocyanate groups and / or block isocyanate groups in one molecule.

  According to the present invention, a coating film having an activation energy of 200 KJ / mol or more can be obtained by using an isocyanate compound as a curing agent. In conventional intermediate coating compositions, when an isocyanate compound is used as a curing agent, a trifunctional or higher functional isocyanate compound has been used. However, in this case, since the three-dimensional crosslinking proceeds in a complicated manner, the crosslinking density of the intermediate coating film increases with a low activation energy, and a coating film having sufficient chipping resistance cannot be obtained. Moreover, also when using only a melamine resin as a hardening | curing agent, since it is difficult to obtain the intermediate coating film with high activation energy, there exists a possibility that it may be inferior to chipping property similarly. On the other hand, in the present invention, by using a bifunctional and / or trifunctional isocyanate compound as the curing agent, an intermediate coating film satisfying the above relational expression can be obtained, and as a result, a compound having excellent chipping resistance is obtained. A layer coating can be obtained.

  (3) The ratio (A ÷ B × 100) of the number of hydroxyl groups (A) of the polyester resin and the total number of isocyanate groups and / or block isocyanate groups (B) is 60% to 150 % Of the water-based intermediate coating composition according to (1) or (2).

  According to the present invention, the ratio (A ÷ B × 100) of the number of hydroxyl groups (A) in the polyester resin and the total number (B) of isocyanate groups and / or block isocyanate groups is 60 to 150. By setting it as%, it becomes possible to obtain a coating film having an activation energy of 200 KJ / mol or more. When the ratio of (A) and (B) is 60% or less, not only curing failure occurs, but also the crosslinking density of the coating film is too high, and the activation energy cannot be increased to 200 KJ / mol or more. Moreover, when the ratio of (A) and (B) is 150% or more, as a result of excess hydroxyl groups remaining in the coating film after curing, the water resistance is poor.

  (4) A method of forming a coating film, comprising a step of coating the article to be coated with the aqueous intermediate coating composition according to any one of (1) to (3).

  (5) A coated product comprising an intermediate coating film obtained from the intermediate coating film composition according to any one of (1) to (3).

  As described above, the present invention is an aqueous intermediate coating composition comprising a polyester resin having a hydroxyl value of 100 to 200 mg KOH / g, a curing agent, and a color pigment, and can increase the activation energy of the coating film. A possible aqueous intermediate coating composition. As a result, the crosslinked structure of the coating film can be controlled, and a coating film having excellent chipping resistance can be provided.

  Hereinafter, embodiments of the present invention will be described.

  In the present invention, it was proved that a multilayer coating film having excellent chipping resistance can be obtained by using an aqueous intermediate coating composition that satisfies the activation energy of the coating film of 200 KJ / mol or more.

  In the present invention, the polyester resin used as the main resin is “polyester resin having a hydroxyl value of 100 mgKOH / g to 200 mgKOH / g”. That is, it is not particularly limited as long as it has an ester bond in the main chain and is a polycondensate of a polyhydric alcohol and a polybasic acid. If the hydroxyl value is less than 100 mgKOH / g, curing failure may occur. If it exceeds 200 mgKOH / g, excessive hydroxyl groups may remain in the coated film after curing, resulting in poor water resistance.

  Further, this polyester resin preferably has a number average molecular weight obtained by gel permeation chromatography (GPC) of 1000 to 30000. If it is less than 1000, physical properties such as solvent resistance of the cured coating film may be inferior, and if it exceeds 30000, the viscosity of the resin solution is high, so that it is difficult to handle in operation due to emulsification dispersion of the obtained resin, In addition, the appearance of the resulting coating film may be significantly reduced.

  Moreover, it is preferable that the hardening | curing agent in this invention is a diisocyanate compound. The said diisocyanate compound can suppress that the crosslinking density of the intermediate coating film obtained from the number of functional groups in one molecule being 2 becomes high. That is, in the case where a curing agent comprising an isocyanate compound is used in the intermediate coating, a polyfunctional isocyanate compound that is usually trifunctional or higher is used as the isocyanate compound, but since the number of functional groups in one molecule is three or more. Although the three-dimensional crosslinking proceeds in a complicated manner, the crosslinking density of the resulting intermediate coating film becomes high. In the present invention, a curing agent made of a diisocyanate compound is used, and the number of functional groups in one molecule is 2. It is possible to prevent the cross-linking density of the intermediate coating film obtained as a result from becoming high because the three-dimensional cross-linking does not proceed beyond a certain level because of the individual. Thereby, the chipping resistance of the multilayer coating film obtained by applying the aqueous intermediate coating composition of the present invention can be improved.

  The diisocyanate compound is not particularly limited. For example, trimethylene diisocyanate, tetramethylene diisocyanate (TMDI), pentamethylene diisocyanate, hexamethylene diisocyanate (HMDI), 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2, Aliphatic compounds such as 3-butylene diisocyanate, 1,3-butylene diisocyanate, ethylidene diisocyanate, butylidene diisocyanate; isophorone diisocyanate (IPDI), 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane Aliphatic cyclic compounds such as diisocyanate; m-phenylene diisocyanate, p-phenylene diisocyanate (PD ), 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate and other aromatic compounds; 4,4'-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-tri Diisocyanate (TDI) or mixtures thereof, aliphatic-aromatic compounds such as 4,4'-toluidine diisocyanate, xylylene diisocyanate (XDI); hydrogenated MDI, hydrogenated TDI (HTDI), hydrogenated XDI; dimer acid Examples include diisocyanate (DDI); nuclear-substituted aromatic compounds such as dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and chlorodiphenyl diisocyanate. These diisocyanate compounds may be used as they are or as polyisocyanates reacted with diols, diamines and the like. Of these, aliphatic diisocyanates are preferred and isophorone diisocyanate is more preferred from the viewpoint of improving chipping resistance. These diisocyanate compounds may be used independently and may use 2 or more types together.

  The diisocyanate compound may be a block diisocyanate compound. Examples of the blocking agent that can be used when the diisocyanate compound is a blocked diisocyanate compound include oximes such as methyl ethyl ketoxime, methyl isobutyl ketoxime, acetone oxime, and cyclohexane oxime; 1-chloro-2-propanol, ethylene Halogenated hydrocarbons such as chlorohydrin; aliphatic or heterocyclic alcohols such as n-propanol, furfuryl alcohol, alkyl-substituted furfuryl alcohol; phenol, m-cresol, p-nitrophenol, p-chlorophenol And phenols such as nonylphenol; active methylene compounds such as acetylacetone, ethyl acetoacetate and ethyl malonate; and caprolactam. Of these, methyl ethyl ketoxime is preferable from the viewpoint of the dissociation temperature of the blocked isocyanate compound. These blocking agents may be used alone or in combination of two or more.

  Examples of the dissociation catalyst for the blocking agent include organic tin compounds such as dibutyltin laurate, dibutyltin oxide and dioctyltin, amines such as N-methylmorpholine, and metal salts such as lead acetate. The dissociation catalyst is preferably 0 to 5 parts by mass with respect to 100 parts by mass of the solid content of the curing agent in the curing agent composition.

  Furthermore, as a hardening | curing agent in this invention, you may contain another hardening | curing agent besides the said diisocyanate compound. As said other hardening | curing agent, a trifunctional isocyanate compound, a melamine resin, etc. can be mentioned, for example.

  Examples of the trifunctional isocyanate compound include triphenylmethane-4,4′4 ″ -triisocyanate, 1,3,5-triisocyanatebenzene, 2,4,6-triisocyanate toluene, hexamethylene diisocyanate, and the like. Examples include triisocyanate compounds such as trimers (isocyanurates), etc. Polyisocyanates obtained by reacting diisocyanate compounds with polyols having three or more hydroxyl groups per molecule may also be used. However, hexamethylene diisocyanate trimers are preferable from the viewpoint of improving chipping resistance, and these may be used alone or in combination of two or more. A blocked isocyanate compound may also be used.

Examples of the melamine resin include a complete alkyl type in which the reactive group is N— (CH ₂ OR) ₂ , a methylol type in which N— (CH ₂ OR) CH ₂ OH is present, and an imino in which N— (CH ₂ OR) H is present. 4 types of imino / methylol type in which N— (CH ₂ OR) H and N— (CH ₂ OR) CH ₂ OH are mixed can be exemplified, but from the standpoint of concealing property, it is a completely alkyl type. Preferably there is.

  As what is marketed by the said melamine resin, Cymel 235, Cymel 236, Cymel 267, Cymel 350 (all are Mitsui Cytec Co., Ltd.) etc. can be mentioned, for example. These melamine resins may be used alone or in combination of two or more.

  In addition to the diisocyanate compound, the curing agent in the present invention can be used in combination with a trifunctional isocyanate compound as necessary, but it is more preferable that the curing agent is composed only of the diisocyanate compound. When the curing agent is only a diisocyanate compound, it is possible to further suppress the crosslinking density in the formed intermediate coating film from becoming too high, thereby further improving the chipping resistance of the resulting multilayer coating film. Can be made.

  In the curing agent in the present invention, when a diisocyanate compound and a curing agent other than the diisocyanate compound are used in combination as a curing agent, the diisocyanate compound has a lower limit of 10% by mass with respect to 100% by mass of the curing agent solid content. The upper limit is preferably 100% by mass. Thereby, it can suppress that the crosslinking density of the intermediate coating film formed becomes high, and the chipping resistance of a coating film can be improved. More preferably, the lower limit is 30% by mass and the upper limit is 100% by mass.

  The diisocyanate compound is preferably 10% by mass or more with respect to 100% by mass of the solid content of the aqueous intermediate coating composition. Thereby, it can suppress that the crosslinking density of an intermediate coating film becomes high, and can improve the chipping resistance of the multilayer coating film obtained. More preferably, it is 30 mass% or more.

  The method for producing the coating film-forming resin is not particularly limited, and can be appropriately selected according to the type and properties of the target coating film-forming resin. For example, a melt polymerization method, a transesterification method, Conventionally known production methods such as an interfacial polymerization method and a solution polymerization method can be used.

  The solid content mass ratio of the coating film-forming resin and the curing agent in the aqueous intermediate coating composition of the present invention is preferably 85/15 to 50/50. When the ratio exceeds 85/15, the curability may be lowered, and when it is less than 50/50, various performances of the obtained coating film may be lowered.

  The color pigment is not particularly limited as long as it improves weather resistance and ensures concealment, but titanium dioxide is more preferable because it is excellent in white color concealment and is inexpensive.

  Examples of the pigments other than titanium dioxide include, for example, azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindo. Examples thereof include organic color pigments such as linone pigments and metal complex pigments; inorganic color pigments such as yellow lead, yellow iron oxide, bengara and carbon black. In the present invention, extender pigments such as calcium carbonate, barium sulfate, clay and talc may also be used as the pigment.

  As the coloring pigment, a standard gray-based intermediate coating material having carbon black and titanium dioxide as main pigments can be used, or a so-called combination of a top coating material and a set gray or various coloring pigments combined with lightness or hue. A color intermediate coating can also be used. These pigments may be used alone or in combination of two or more.

  The pigment (the colored pigment and the extender pigment) is a pigment and a resin solid content (colored pigment, extender pigment, resin solid content in the film-forming resin and resin solid content in the curing agent) in the aqueous intermediate coating. The ratio of the mass of the pigment to the total mass (PWC) of the total mass) is preferably 10 to 60% by mass. If it is less than 10% by mass, the concealability may be lowered due to insufficient pigment. If it exceeds 60% by mass, the viscosity during curing is increased due to an excessive amount of pigment, the flowability is lowered, and the appearance of the coating film may be lowered.

  In addition to the above components, the aqueous intermediate coating composition of the present invention further comprises an organic solvent, a curing catalyst, a surface conditioner, an antifoaming agent, a plasticizer, a film-forming aid, an ultraviolet absorber, and an antioxidant, as necessary. Etc. can be contained. These are not particularly limited, and those known by those skilled in the art can be used.

  The method for obtaining the aqueous intermediate coating composition of the present invention is not particularly limited, and a composition such as the above-mentioned film-forming resin, the above-mentioned curing agent and the above-mentioned pigment is kneaded using a kneader, a roll, etc., and a sand grind mill. Any method known to those skilled in the art such as dispersion using a disperser or the like can be used.

  The intermediate coating film forming method of the present invention comprises a step of coating the above-mentioned aqueous intermediate coating composition on an object to be coated. As a preferable form as the intermediate coating film forming method, for example, a water-based intermediate coating material is applied on an object on which an electrodeposition coating film is formed, and then heated and cured to form an intermediate coating film ( 1) The step (2) of forming an uncured top coat film by applying a top coat on the intermediate coat film obtained in the above step (1), the uncoated product obtained by the above step (2) A method for forming a multilayer coating film comprising the step (3) of obtaining a multilayer coating film by heating and curing the cured top coating film, wherein the aqueous intermediate coating composition is the above-described aqueous intermediate coating composition. Can be mentioned.

  It does not specifically limit as an electrodeposition coating material which forms the said electrodeposition coating film, Although any of a cation type and an anion type may be sufficient, it is preferable that it is a cation type from a viewpoint of corrosion resistance and rust prevention property.

  The material to be coated is not particularly limited, and examples thereof include iron, steel, aluminum, tin, zinc, and the like, and alloys and castings containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are preferably subjected to surface treatment in advance before electrodeposition coating is performed.

  The first step in the method for forming a multi-layer coating film is a process of forming an intermediate coating film by applying a water-based intermediate coating composition on an object to be coated on which an electrodeposition coating film has been formed, followed by heat curing (1) The aqueous intermediate coating composition is the above-described aqueous intermediate coating composition.

The water-based intermediate coating is usually applied so that the dry film thickness is 10 to 60 μm. If the thickness is less than 10 μm, there is a risk that the underlying layer may be insufficiently concealed. If the thickness exceeds 60 μm, sagging occurs during coating, heating occurs during heating and curing, and the appearance of the resulting intermediate coating film is degraded. There is a fear.

  It does not specifically limit as the coating method of the said water-based intermediate coating material, A spray coating method, an electrostatic coating method, etc. can be mentioned. Industrially, for example, an air electrostatic spray coating machine called “react gun” or a rotary atomizing electrostatic coating machine called “micro micro bell”, “micro bell”, “metallic bell” or the like is used. A method can be mentioned. A method using a rotary atomizing electrostatic coating machine is preferable.

  After the aqueous intermediate coating is applied, an intermediate coating film can be obtained by heat-curing at a predetermined temperature. The conditions for the heat curing are not particularly limited, and are appropriately determined according to the type of the water-based intermediate coating composition. As conditions for the heat curing, for example, the heating temperature is a lower limit of 110 ° C. and an upper limit of 200 ° C., more preferably, the lower limit is 120 ° C. and the upper limit is 180 ° C., and the heating time is a lower limit of 10 minutes and an upper limit of 60 minutes.

  The second step in the multilayer coating film forming method is a step of obtaining an uncured top coating film by applying a top coating composition on the intermediate coating film obtained in the step (1). The above-mentioned top coat paint gives beauty and protection to an object to be coated.

  The top coating composition is not particularly limited, and examples thereof include coating film-forming resins, curing agents, bright pigments, pigments such as coloring pigments and extender pigments, and various additives. Examples of the coating film-forming resin, curing agent, color pigment, and various additives include those described in the previous aqueous intermediate coating composition. From the viewpoint of pigment dispersibility and workability, a combination of acrylic resin and / or polyester resin and melamine resin is preferred. Moreover, the method illustrated in the said water-based intermediate coating material can also be mentioned also about the preparation method of top coating material.

  The glitter pigment is not particularly limited. For example, an uncolored or colored metallic glitter material such as a metal or an alloy and a mixture thereof, interference mica powder, colored mica powder, white mica powder, graphite or colorless or colored. A flat pigment etc. can be mentioned. Since it is excellent in dispersibility and can form a highly transparent coating film, non-colored or colored metallic glitter materials such as metals or alloys and mixtures thereof are preferred. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, tin and the like.

  The shape of the glitter pigment is not particularly limited and may be further colored. For example, the average particle diameter (D50) is a lower limit of 2 μm and an upper limit of 50 μm, and the thickness is a lower limit of 0.1 μm and an upper limit of 5 μm. The scaly thing which is is preferable. The average particle diameter is more preferably a lower limit of 10 μm and an upper limit of 35 μm because it is excellent in glitter.

The said pigment can use 1 type (s) or 2 or more types, and it uses it combining 1 type (s) or 2 or more types from a color pigment, an extender pigment, and a flat pigment and a luster pigment as needed. Can do.

  The concentration of all pigments (PWC) contained in the top coating is generally a lower limit of 0.1% by mass and an upper limit of 50% by mass, more preferably a lower limit of 0.5% by mass and an upper limit of 40% by mass. More preferably, the lower limit is 1% by mass and the upper limit is 30% by mass. When the pigment concentration is less than 0.1% by mass, the effect of the pigment cannot be obtained, and when it exceeds 50% by mass, the appearance of the resulting coating film may be deteriorated.

  The form of the top coating is not particularly limited, and may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), and non-water-dispersed type. The top coat is usually applied so that the dry film thickness is 15 to 70 μm. If the dry film thickness is less than 15 μm, the background may not be sufficiently concealed or color unevenness may occur. If it exceeds 70 μm, sagging may occur during coating or heat generation may occur during heat curing. There is.

  Examples of the method for applying the top coating material include the methods exemplified in the application of the water-based intermediate coating material. When the top coating is applied to an automobile body or the like, in order to improve the design, multi-stage coating by the air electrostatic spray coating, preferably two stages are applied, or the air electrostatic coating is performed. It is preferable to carry out by a coating method in which spray coating and the above-mentioned rotary atomizing electrostatic coating are combined.

The uncured topcoat film may be composed of a base film and an uncured clear film. In this case, the step (2) is, for example, a step of obtaining a base coating film by applying a base coating, and further applying a clear coating to obtain an uncured clear coating. Examples of the base paint include the top coat paint.

  The base paint is usually applied so as to have a dry film thickness of 5 to 35 μm. If the dry film thickness is less than 5 μm, the masking of the base may be insufficient or color unevenness may occur, and if it exceeds 35 μm, sagging may occur during coating, and cracking may occur during heat curing. There is a risk. Examples of the method for applying the base paint include the same method as the method for applying the top coat.

  The clear coating obtained from the above-mentioned clear coating smoothes the unevenness and flickering of the base coating caused by the glittering pigment when the metallic base coating containing the glittering pigment is used as the base coating. It is formed to protect the film. The clear coating is not particularly limited, and examples thereof include those composed of a film-forming resin, a curing agent, and other additives.

  The film-forming resin is not particularly limited, and examples thereof include acrylic resins, polyester resins, epoxy resins, urethane resins, and the like. These are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. . From the viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.

  As the clear paint, since the base paint described above is applied in an uncured state, it is preferable to contain a viscosity control agent as an additive in order to prevent familiarity, reversal or sagging between layers. . The amount of the viscosity control agent added is lower limit 0.01 parts by mass and upper limit 10 parts by mass, preferably 0.02 parts by mass and upper limit 8 parts by mass with respect to 100 parts by mass of the resin solid content of the clear paint. More preferably, the lower limit is 0.03 parts by mass and the upper limit is 6 parts by mass. When it exceeds 10 parts by mass, the appearance is deteriorated, and when it is less than 0.1 parts by mass, the viscosity control effect cannot be obtained, which causes problems such as sagging.

  The clear coating composition may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-aqueous dispersion type, and powder type. If necessary, a curing catalyst, a surface conditioner, etc. Can be used.

  The clear coating material can be prepared and applied according to conventional methods. Although the dry film thickness of the said clear coating film changes with uses, it is 10-70 micrometers. If the dry film thickness exceeds the upper limit, the sharpness may be deteriorated, and defects such as unevenness and flow may occur during coating. If the dry film thickness is less than the lower limit, the appearance may be deteriorated.

  The base coating film may be an uncured base coating film or a cured base coating film. The uncured base coating film is a concept including a state after the preheating treatment is performed. As said preheating process, it is a heat processing for 1 to 10 minutes at room temperature-about 100 degreeC, for example. Further, the cured coating film is obtained by heating and curing the uncured base coating film. It does not specifically limit as said heat-hardening conditions, Although it can set suitably according to the kind of used base coating material, For example, it is 10 to 60 minutes at 110-180 degreeC. From the viewpoint of energy saving and process shortening, the base coating film is preferably not an uncured base coating film but a cured base coating film. Such a method is called wet-on-wet coating.

  The 3rd process in the said multilayer coating-film formation method heat-hardens the uncured top coat film obtained by the said process (2), and obtains a multilayer coating film. In the case where the uncured top coat film is composed of the uncured base film and the uncured clear film, the third step includes the uncured base film and the uncured base film. The clear coating film is cured by heating at the same time.

  The temperature for the heat curing is preferably a lower limit of 110 ° C. and an upper limit of 180 ° C., more preferably a lower limit of 120 ° C. and an upper limit of 160 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. When the temperature is less than 110 ° C., curing is insufficient, and when it exceeds 180 ° C., the obtained coating film may be hard and brittle. The time for heat-curing can be appropriately set according to the temperature, but when the temperature is 120 ° C. to 160 ° C., for example, 10 to 60 minutes.

  The film thickness of the multilayer coating film obtained by the steps (1), (2) and (3) is usually preferably a lower limit of 30 μm and an upper limit of 300 μm, more preferably a lower limit of 50 μm and an upper limit of 250 μm. If it is less than 30 μm, the film strength of the resulting multilayer coating film may be reduced, and if it exceeds 300 μm, film physical properties may be deteriorated or coating film performance may be impaired.

  Since the coated product having the intermediate coating film obtained by the intermediate coating film forming method is obtained by using the aqueous intermediate coating composition, it has excellent chipping resistance. Such a painted product is also one aspect of the present invention.

  Examples The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

<Production Example 1 Production of water-based polyester resin>
176 parts of phthalic anhydride, 197 parts of isophthalic acid, 87 parts of adipic acid, 102 parts of trimethylolpropane, 272 parts of neopentyl glycol in a reaction vessel equipped with a nitrogen introduction tube, a stirring device, a temperature controller, a cooling tube and a decanter 0.8 part of dibutyltin oxide and 17 parts of xylene were charged, and the temperature was raised to 200 ° C. over about 2 hours after the reflux of xylene started. Meanwhile, water produced by the reaction was removed by azeotropy with xylene. When the acid value of carponic acid reached 8, cooled to 150 ° C, added 49 parts of trimellitic anhydride, further cooled to 60 ° C, mixed with 46 parts of dimethylethanolamine 1137 parts of ion-exchanged water was added thereto to obtain an aqueous polyester resin having a number average molecular weight of 2,000, a solid content of 40%, a solid content acid value of 40, and a hydroxyl value of 105 as determined by gel-permeation chromatography.

<Production Example 2 Production of Block Diisocyanate Compound>
After adding and stirring and diluting 222 parts of isophorone diisocyanate and 99 parts of methyl isobutyl ketone to a reaction vessel equipped with a nitrogen introduction tube, a stirring device, a temperature controller, a cooling tube and a decanter, 0.2 parts of butyltin laurate And the temperature was raised to 50 ° C, and then 174 parts of methyl ethyl ketoxime was added so that the content temperature did not exceed 70 ° C. The mixture was kept at 70 ° C. for 1 hour until the absorption of the isocyanate residue substantially disappeared by the infrared absorption spectrum to obtain a block diisocyanate compound having a solid content of 80%.

<Production Example 3 Preparation of pigment paste for intermediate coating>
50 parts of the aqueous polyester resin obtained in Production Example 1, 24.5 parts of CR-97 (titanium dioxide manufactured by Ishihara Sangyo Co., Ltd.), 12 parts of B-34 (precipitated barium sulfate manufactured by Sakai Chemical Co., Ltd.), MA-100 (Carbon black manufactured by Mitsubishi Chemical Co., Ltd.) 0.5 parts, 3 parts LMR-100 (talc manufactured by Fuji Talc Co., Ltd.) and 10 parts ion-exchanged water were premixed, and glass bead medium was added in a paint conditioner at room temperature. Mixing and dispersing for a time, a pigment paste 1 for an intermediate coating material having a particle size of 5 μm or less was obtained.

<Examples 1-5, Comparative Examples 1-4>
The molar ratio (BI) of blocked isocyanate (BI) and hydroxyl group (OH) between the aqueous polyester resin having a hydroxyl value of 105 mgKOH / g obtained in Production Example 1 and the blocked diisocyanate compound obtained in Production Example 2 / OH) was 65. Furthermore, to the 100 parts of the blended polyester resin component, the amount of the pigment component contained in the intermediate coating paint paste obtained in Production Example 3 is 100 parts, and the intermediate coating pigment paste is added. And mixed. Further, 0.5 part of Surfynol 104E (Surface Conditioner manufactured by Air Products Japan Co.) was mixed with 100 parts of the resin component in the mixture to obtain the aqueous intermediate coating material of Example 1.

  Moreover, about Examples 2-5 and Comparative Examples 1-4, the hydroxyl value 70, 90, 150, 190 and 220 mgKOH / g aqueous | water-based are changed by changing the compounding quantity of the acid component and alcohol component as described in manufacture example 1. Examples 2-5 and Comparative Example 1 were prepared in the same manner as in Example 1 except that each type polyester resin was produced and the block diisocyanate compound obtained in Production Example 2 was blended so as to have the molar ratio (BI / OH) shown in Table 1. The aqueous intermediate coating materials of Examples 1 to 4 were obtained.

<Formation method of coating film>
Cathodic electrodeposition paint (Power Top U-50, manufactured by Nippon Paint Co., Ltd.) is electrodeposited onto a dull steel sheet with a thickness of 0.8 mm, length 30 cm, width 40 cm treated with zinc phosphate so that the dry film thickness is 20 μm. Then, the pre-diluted intermediate coating A is applied to the coated plate baked at 160 ° C. for 30 minutes for 25 seconds (measured at 20 ° C. using a No. 4 Ford cup) so that the dry film thickness becomes 35 μm. Two-stage coating was performed by spraying, and heating was performed at 140 ° C. for 30 minutes.

  After cooling, an aqueous base paint (for example, AR-2000 (manufactured by Nippon Paint)) is applied on the intermediate coating film to form a dry film thickness of 15 μm at room temperature of 25 ° C. and humidity of 75%. Two-stage coating was performed with a machine (μμ Bell COPES-IV type, manufactured by ABB Industry). An interval setting of 1 minute was performed between the two coatings. After the second application, setting was performed with an interval of 2 minutes. Thereafter, preheating was performed at 80 ° C. for 3 minutes. After preheating, the coated plate is allowed to cool to room temperature, and clear paint (Mac Flow O-1810 (manufactured by Nippon Paint)) is micro-microbell (ABB Landsberg Co., Ltd.) so that the dry film thickness is 35μ. 1-stage coating with a static electrostatic coating machine) and set for 7 minutes. Furthermore, the obtained coated plate was baked in a drying furnace at 140 ° C. for 30 minutes to form a multilayer coating film on the dull steel plate.

<Measurement method of activation energy>
The paint obtained by each production method (Examples 1 to 5 and Comparative Examples 1 to 4) was applied to a polypropylene test plate by spray coating, and this was baked at 140 ° C. for 30 minutes in a drying furnace to obtain a coating film. It was. This coating film was peeled off from the test plate to obtain a free film. The dynamic viscoelasticity of the obtained free film was measured with a dynamic viscoelasticity measuring device, Rheogel E4000. The activation energy Ea was calculated from the obtained measurement result using the Arrhenius equation “f = f ₀ exp (−Ea / RTg)”. The results are shown in Table 1.

<Testing method for chipping resistance>
Evaluation of chipping resistance of the resulting coated plate was performed by cooling a No. 7 crushed stone 50 g from a distance of 35 cm to air pressure of 4.0 kg / cm ² to −20 ° C. using a gravel tester (manufactured by Suga Test Instruments Co., Ltd.). The coated film was made to collide at an angle of 90 degrees, the degree of peeling was observed visually, and evaluated according to the following criteria. The results are shown in Table 1.

5 No peeling at all.
4 Small peel area and low frequency.
3 The peeling area is small, but the frequency is slightly high.
2 The peeled area is large, but the frequency is low.
1 Large peel area and high frequency.

<Implementation method of water resistance test>
After immersing the coating film in a constant temperature water bath adjusted to 40 ° C. for 10 days, it is visually examined for discoloration, itching, and coating film adhesion by a cross-cut test, and evaluated comprehensively as the best and the lowest as x. evaluated. The results are shown in Table 1.

  From the results shown in Table 1, the sample is a water-based intermediate coating composition comprising a polyester resin having a hydroxyl value of 100 to 200 mgKOH / g, a curing agent and a color pigment, and the activation energy of the coating film is 200 KJ / mol or more. It was shown to be excellent in chipping resistance and water resistance.

Claims (5)

An aqueous intermediate coating composition comprising a polyester resin having a hydroxyl value of 100 mgKOH / g to 200 mgKOH / g, a curing agent and a color pigment,
An aqueous intermediate coating composition, wherein the activation energy of a coating film obtained from the aqueous intermediate coating composition is 200 KJ / mol or more.   The aqueous intermediate coating composition according to claim 1, wherein the curing agent is a polyisocyanate compound having 2 or 3 isocyanate groups and / or block isocyanate groups in one molecule.   The ratio (A ÷ B × 100) of the number of hydroxyl groups (A) of the polyester resin and the total number of isocyanate groups and / or block isocyanate groups (B) is 60% to 150%. The aqueous intermediate coating composition according to claim 1 or 2.   A method for forming a coating film, comprising a step of coating the article to be coated with the aqueous intermediate coating composition according to any one of claims 1 to 3.   A coated article comprising an intermediate coating film obtained from the intermediate coating film composition according to claim 1.