JP2002080787A - Coating composition for determining film thickness and method for producing multilayer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film thickness-determining coating composition, capable of obtaining a prescribed film thickness, not causing lifting, etc., to old coating film and having adaptability to old coating film when already coated coating film is deteriorated with time and repair coating of old coating film is required and a method for forming a bilayer coating film by using the above coating composition. SOLUTION: This film thickness-determining coating composition comprises a top coat formed on old coating film and applied to an undercoating film having <=70 color value V of Munsel color system. A wet coating film obtained by applying the above top coat to the undercoating film so as to provide >=50 μm target dried film thickness satisfies the following items: (a) >=20 color difference between the above wet coating film and the above undercoating film, (b)>2 color difference between the above wet coating film and wet coating film having a film thickness which becomes less than (the above target dried film thickness -50 μm) by drying and (c) <1 color difference between the above wet coating film and wet coating film having a film thickness of 1.2 times based on the above wet coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for repairing a coating film on an old coating film when the coating film coated on various substrates is deteriorated with time and needs to be repaired. The present invention relates to a coating composition for judging a film thickness capable of obtaining a target dry film thickness almost accurately and a method for forming a multilayer coating film using the coating material.

[0002]

2. Description of the Related Art Large structures composed of metal base materials, such as ships, marine structures, bridges, tanks, plant facilities, etc., and large civil engineering structures composed of inorganic base materials, For example, a concrete bridge, a concrete pier, a railing, a dam site, a harbor facility, a building, and the like are required to be provided with a coating film having a predetermined thickness capable of withstanding long-term exposure. . However, since the coating film deteriorates with time, repair painting is required to protect the base material. In this repair coating, since the coating environment is severer than when newly installed, it is more difficult to maintain a predetermined target dry film thickness.

[0003] For measuring the film thickness, an electromagnetic film thickness meter is used for steel structures. On the other hand, in the case of the inorganic base material, the thickness is controlled by a wet gauge at the time of coating, or a cut surface is inserted into a part of the coating film after drying, and the thickness of the coating film cross section is measured. For structures and the like, it was practically impossible to check all over the coating film using these methods.

[0004] In addition, in areas where it is determined that the predetermined target dry film thickness is not reached, additional coating is required. This additional coating requires the installation of a scaffold, which leads to delays in the overall process and hinders on-site process management.

[0005] Such a method of controlling the film thickness is disclosed in Japanese Patent Application Laid-Open No. 10-2166 as an approach from the viewpoint of paint.
No. 21 discloses a paint film for judging film thickness containing a specific pigment composition. However, this paint is intended for spray painting at the time of new construction and could not be used as it is for painting the old paint film at the time of repair.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coating film having a predetermined thickness when deterioration of an existing coating film with time progresses and repair coating of an old coating film is required. An object of the present invention is to provide a coating composition for judging the thickness of an old coating film which does not cause lifting or the like with respect to the old coating film, and a method for forming a multilayer coating film using the coating composition.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above problems, and have reached the present invention. 1. Munsell color system lightness V formed on old coating film is 7
A wet coating film obtained by applying this coating material to the undercoat film so as to obtain a target dry film thickness of 50 μm or more, which is a coating film applied to the undercoat film of 0 or less, A) a color difference between the wet coating film and the undercoating film of 20 or more, and (b) a color difference between the wet coating film and a wet coating film which is dried to have a film thickness of less than (the target dry film thickness−50 μm). And (c) a difference in color difference between the wet coating film and a wet coating film having a thickness twice as large as that of the wet coating film is less than 1. 2. The above coating composition for judging film thickness, wherein a color difference between the wet coating film and a dried coating film obtained by drying the wet coating film is 0. 3. The coating composition for judging thickness described above, wherein the stretchability of the obtained coating film is 1% or more. 4. The above-mentioned coating composition for judging film thickness, wherein the paint for forming the undercoat coating film has an elongation followability of 1% or more and a color difference from the old coating film of 20 or more.

[0008] 5. In a coating film forming method in which a paint is applied to an old coating film formed on a substrate to obtain a coating film having a predetermined dry film thickness, first, an undercoat coating film having a Munsell color system lightness V of 70 or less is formed. After the formation, a target dry film thickness is set for the predetermined dry film thickness, and the coating is performed using the above-described film thickness determination paint as a paint suitable for the target dry film thickness. A method for forming a multilayer coating film in which the color of the film is observed and it is determined whether or not the target dried film thickness has been reached. 6. When the hue of the wet film obtained by the above coating is 0 on the Munsell 100 hue circle, the undercoating is 0, the counterclockwise is 0 to +50, and the clockwise is 0 to -50,
The method for forming a multilayer coating film according to the above, which is 20 to +50 or -50 to -20. 7. The hue of the wet film is +40 in the display.
To +50 or -40 to -50. 8. The above-described method for forming a multilayer coating film, wherein the base material is a steel plate. 9. The above-described method for forming a multilayer coating film, wherein the steel sheet has a connection portion by welding or joining. 10. In a coating film forming method for applying a coating material on the coating film obtained by the above-described multilayer coating film forming method to obtain a coating film having a predetermined dry film thickness, the target is determined with respect to the predetermined dry film thickness. The dry film thickness is set, and as a paint suitable for the above-mentioned target dry film thickness, the paint is applied so that a target dry film thickness of 50 μm or more is obtained on the coating film obtained by the first multilayer coating film forming method. The wet coating obtained by coating is (a) a color difference of 20 or more between the wet coating and the coating obtained by the multilayer coating forming method, and (b) the wet coating is dried. (C) a color difference of 2 or more from the coating film obtained by the method for forming a multilayer coating film having a film thickness of less than (the target dry film thickness-50 µm); Use a paint that satisfies the condition that the color difference from a wet coating film having a double film thickness is less than 1. A coating film forming method for observing the color of the wet film obtained by the coating and judging whether or not the target dry film thickness has been reached.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The paint composition for judging film thickness of the present invention is a top coat paint which is applied to an undercoat film having a Munsell color system lightness V of 70 or less formed on an old paint film. Wherein a wet coating film obtained by coating so as to obtain a target dry film thickness of 50 μm or more satisfies the following three conditions (a) to (c). The target dry film thickness is set with respect to a required predetermined dry film thickness.
It is set to 120%. The target dry film thickness is 50 μm
As described above, for example, when the predetermined dry film thickness is 50 μm, the thickness can be set to 50 to 60 μm. (A) The color difference between the wet coating film and the undercoating film is 2
0 or more; (b) a difference in color between the wet coating film dried and a film thickness of less than (the target dried film thickness—50 μm) of 2 or more; (c) the wet coating film; A color difference of less than 1 from a wet coating film having a film thickness 1.2 times that of the wet coating film. If the color difference under condition (a) is less than 20, the color difference changes as the thickness of the wet coating film increases. Is difficult to confirm visually. In order to make it easier to visually confirm the change in color difference, it is preferable that the color difference between the coating composition for judging film thickness itself and the undercoat film be 35 or more.

On the other hand, the color difference under the condition (b) is based on the lack of 50 μm or more with respect to the target dry film thickness. I can't check if I did it. However, if the color difference at that time is too large, the coating of the undercoating film becomes insufficient even with a coating film having a target dry film thickness, and color unevenness may be remarkable. Therefore, the upper limit of this color difference is 10
Is more preferable, and a more preferable upper limit value is 5.

Further, the color difference under the third condition (c) is for the target dry film thickness or more. Since this color difference is a condition indicating the completion of coating, the color difference must be as small as possible with respect to the color tone of the coating film having the target dry film thickness at that time. The dried coating film obtained from the coating composition for judging the film thickness of the present invention needs to have a predetermined film thickness or more. That is, it is not a problem that the obtained dry film thickness is slightly larger than the target dry film thickness, but it may be preferable in some cases. The wet coating and 1.2 of the wet coating
The color difference from a wet coating film having twice the film thickness is less than 1, and the preferred color difference is less than 0.5. By defining the wet film thickness up to 1.2 times the wet film thickness at which the target dry film thickness can be obtained, it is possible to easily perform coating to a predetermined film thickness or more.

The color difference can be determined, for example, by measuring using a colorimeter such as an SM color computer (model SM-7CH, manufactured by Suga Test Instruments Co., Ltd.).

In the above-mentioned coating composition for judging film thickness, the color difference between the above-mentioned wet coating film and a dried coating film obtained by drying the same is preferably as close to 0 as possible, more preferably 0.

[0015] Further, as the paint for forming the undercoat film, the obtained film has a stretchability of 1% or more and a color difference from the old film of 20 or more. A coating composition can be used.

Examples of the binder resin contained in the coating composition for judging film thickness include (1) an epoxy resin,
(2) epoxy resin modified with coal tar, pitch or petroleum resin, (3) acrylic resin, (4) polyester resin, (5) alkyd resin, (6) vinyl chloride resin, (7) chlorinated olefin resin, At least one kind of binder resin selected from the group consisting of (8) chlorinated rubbers, (9) vinyl acetate resin, and (10) urethane resin can be used.

The epoxy resin (1) may be a conventionally used solid or liquid epoxy resin. For example, bisphenol type epoxy resins (bisphenol compounds such as bisphenol A, bisphenol F, bisphenol B or halogen-substituted products thereof) may be used. Resin mainly composed of a condensation unit with epihalohydrin). Particularly preferred are diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, phenol novolak epoxy resin, and alkylene oxide adducts of bisphenol compounds. Also, JP-A-63-3056
No. 9, carboxylic acid-modified epoxy resin,
An amine-modified epoxy resin described in JP-A-30568, a phosphoric acid-modified epoxy resin described in JP-A-61-91217, and the like can also be used. Further, an epoxy polyol resin can be used.

Examples of the modified epoxy resin (2) include those obtained by modifying an epoxy resin with coal tar, pitch, or petroleum resin.

The coal tar or pitch used for the above modification preferably contains a large amount of a polycyclic aromatic polymer substance soluble in an organic solvent in addition to free carbon. The softening point of coal tar or pitch is 50 to 150
C is preferred. If the softening point is less than 50 ° C, the coating film becomes tacky, and if it exceeds 150 ° C, the modified epoxy resin solidifies. Examples of those satisfying such conditions include α-bitumen, β-bitumen, and γ-bitumen.

[0020] As the petroleum resin, diolefin-produced in petroleum cracking, a monoolefin which was polymerized without isolation, can be mentioned C ₅ petroleum resins and C ₉ petroleum resins and the like.

In the case of the epoxy resin, in the case of an epoxy resin, a method of mixing the epoxy resin with coal tar, pitch, acrylic resin, urethane resin or petroleum resin at room temperature, or reacting them at 80 to 150 ° C. It can be carried out by a method of partially opening a group. The amount of coal tar, pitch, acrylic resin, urethane resin or petroleum resin in the modified epoxy resin is generally 10 to 50 based on the solid content based on 100 parts by weight of the epoxy resin.
It may be 0 parts by weight.

Examples of the acrylic resin (3) include resins made of a copolymer of an acrylic monomer and another ethylenically unsaturated monomer. Acrylic monomers that can be used in the above copolymerization include acrylic acid or methacrylic acid methyl, ethyl, propyl, n-butyl,
i-butyl, t-butyl, 2-ethylhexyl, lauryl, phenyl, benzyl, 2-hydroxyethyl, 2-
Esters such as hydroxypropyl, Praxel FM-
1 (an adduct of 2-hydroxyethyl methacrylate and polycaprolactone, manufactured by Daicel Chemical Industries, Ltd.), acrylamide, N-methylolacrylamide, and the like. Other ethylenically unsaturated monomers copolymerizable therewith include: Examples include styrene, α-methylstyrene, itaconic acid, maleic acid, and vinyl acetate.

The polyester resin (4) includes a saturated polyester resin and an unsaturated polyester resin, and examples thereof include a condensate obtained by heating and condensing a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include saturated polybasic acids and unsaturated polybasic acids.Examples of the saturated polybasic acids include phthalic anhydride, terephthalic acid, and succinic acid. For example, maleic acid, maleic anhydride, fumaric acid and the like can be mentioned.
Examples of polyhydric alcohols include dihydric alcohols and trihydric alcohols.
Examples include ethylene glycol and diethylene glycol, and examples of the trihydric alcohol include glycerin and trimethylolpropane.

As the alkyd resin (5), in addition to the above polybasic acids and polyhydric alcohols, modifiers such as fats and oils and fatty acids (soy oil, linseed oil, stearic acid, etc.) and natural resins (rosin, succinic acid, etc.) And a resin obtained by denaturation.

The above (6) vinyl chloride resin contains vinyl chloride as a main component, and further comprises vinyl acetate, if necessary.
Resins obtained by (co) polymerizing maleic acid, (meth) acrylic acid, acrylic esters, hydroxyl group-containing monomers, carboxyl group-containing monomers, styrene, acrylonitrile, and the like.

Examples of the chlorinated olefin resin (7) include resins obtained by chlorinating polyolefins such as polyethylene and polypropylene. Among them, polypropylene having a chlorine content of 20 to 40% is preferable. If the chlorine content is less than 20%, the compatibility with other resins becomes poor, and if it exceeds 40%, the adhesiveness is reduced.

The above (8) chlorinated rubbers include resins obtained by chlorinating rubber latex such as natural rubber latex or synthetic polyisoprene rubber latex in an aqueous medium.

Further, as the above (9) vinyl acetate resin, ethylene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, vinyl acetate-vinyl versatate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer Polymers.

Further, as the urethane resin (10), those obtained by combining various polyols with the following polyisocyanate compound-based crosslinking agents are exemplified.

The coating composition for determining the film thickness contains the following crosslinking agent. Examples of the crosslinking agent include amine-based, polyamide-based, polyisocyanate-based compounds, and amino resin-based ones. As the crosslinking agent for the epoxy resin or the modified epoxy resin, an amine-based, polyamide-based, or polyisocyanate compound-based crosslinking agent is preferable.
These crosslinking agents can be used in combination of two or more.

Examples of the amine-based crosslinking agent include linear aliphatic polyamines such as diethylenetriamine, triethylenetetramine, and ethylaminopropylamine, cyclic aliphatic polyamines, aliphatic polyamine adducts, ketimines, modified aliphatic polyamines, polyamideamines, and aromatic amines. Amines,
Examples thereof include aromatic modified amines, aromatic polyamines such as diaminodiphenylmethane, and aromatic modified polyamines.

Examples of the polyamide crosslinking agent include an aliphatic polyamide obtained by polycondensation of a polycarboxylic acid and a polyamine, an aromatic polyamide having an aromatic ring introduced therein, an aliphatic polyamide adduct, an aromatic polyamide adduct, and the like. Is mentioned.

As the polyisocyanate compound-based crosslinking agent, hexamethylene diisocyanate (HMDI)
Polyisocyanate such as aliphatic polyfunctional isocyanate such as isophorone diisocyanate (IPDI), polyisocyanate compound such as diphenylmethane-4,4'-diisocyanate (MDI) and hydrogenated MDI, or these polyisocyanate compounds Wherein the functional group is partially or completely blocked.

The amino resin-based cross-linking agent includes melamine resin, guanamine resin, urea resin and the like, and the melamine resin includes alkoxyalkylated melamine resin. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-butoxy group, and an isobutoxy group.
Examples of the alkyl group include a methyl group, an ethyl group, and a butyl group.

The ratio of the binder resin to the cross-linking agent in the coating composition for judging the film thickness of the present invention is 100
It is preferred that the crosslinking agent is used in an amount of 5 to 200 parts by weight per solid part by weight. If the blending ratio of the crosslinking agent is less than 5 parts by weight, the resulting coating film has a low crosslinking density, so that the hardness, weather resistance, corrosion resistance, heat resistance, water resistance, etc. of the coating film are insufficient. On the other hand, if it exceeds 200 parts by weight, the coating film becomes brittle. Preferred weight ratio of crosslinking agent / binder resin is 20/100 to 60/1.
00.

When the above-mentioned coating composition for judging film thickness is applied to an inorganic base material in which cracks may occur, the occurrence of cracks is smaller than that of an inorganic base material.
Cracks occur even on metal base materials depending on the conditions,
To follow the cracks in the base material and to re-apply the old paint film with cracks or reduced adhesion to repair, if the stretchability of the repainted paint film is low, the old paint film May undergo lifting, and the stretchability of a coating film obtained from the coating composition for judging film thickness is 1
% Is preferable. More preferably 1 to 10
0%, even more preferably 5-30%. If the stretchability is less than 1%, there is a concern that cracks and lifting may occur in the coating film, and if it exceeds 100%, there is a concern that the tensile strength of the coating film will decrease and there will be a risk of causing early defects in the coating film. Is a dry film thickness of 200 dried at 20 ° C. for 7 days.
It can be measured according to JIS A 6910 in μm. The stretch compliance in the present invention is measured at a measurement temperature of 23 ° C.

As the material, it is particularly important to select a resin. For example, a modified epoxy resin obtained by modifying an epoxy resin with a petroleum resin, urethane or dimer acid, an epoxy resin obtained by mixing a petroleum resin or the like with an epoxy resin, a monomer By selecting an acrylic resin, a polyester resin or a polymerized curing agent or the like having a lowered glass transition temperature by selecting the above, a flexible coating film can be obtained, and the elongation of the coating film can be set in the above range. .

The above-mentioned coating composition for judging film thickness contains a pigment. Examples of the pigment include a coloring pigment, an extender pigment, and a rust preventive pigment. As described above, the coating composition for judging film thickness of the present invention is used for judging whether or not a predetermined film thickness is obtained based on a color difference, that is, a difference between hue, saturation and lightness. Hue, saturation and lightness are mainly determined by the color pigments in the paint, but extender pigments and rust preventive pigments may also affect them, in order to develop a desired color difference,
It is necessary to determine the composition including the coloring pigment, the extender pigment and the rust preventive pigment.

Examples of the coloring pigment include carbon black, titanium dioxide, lead white, graphite, zinc sulfide, zinc oxide,
Chromium oxide, yellow nickel titanium, yellow chromium titanium,
Examples include yellow iron oxide, red iron oxide, black iron oxide, phthalocyanine blue, phthalocyanine green, ultramarine blue, quinacridones, and azo red / yellow pigments. Titanium dioxide has a large effect on the hue and lightness of the coating composition for judging the film thickness and makes the coating film pale, so it is preferable to use titanium dioxide alone or in combination with other coloring pigments.

The extender pigments include talc, clay,
Examples include calcium carbonate, magnesium carbonate, barium sulfate, silicic acid, silicate, aluminum oxide hydrate, calcium sulfate, and the like. Of these, talc is preferred.

The rust preventive pigment is considered to be unnecessary when the base material is an inorganic base material because rust preventive property is not required. However, in the case of a painted object adjacent to an inorganic base material and a base material such as a steel material requiring rust prevention is arranged, when the metal base material and the inorganic base material are used in common, the rust prevention If a pigment is blended, a common paint can be used, which is preferable from the viewpoint of coating workability. Examples of rust preventive pigments include zinc phosphate, lead tetroxide, basic lead sulfate, lead oxide, cyanamide lead, cyanamide calcium zinc, zinc molybdate, aluminum molybdate, basic lead chromate, zinc chromate, and chromium. Compounds such as strontium acid and barium chromate are exemplified.

Since the coating composition for judging the film thickness needs to have a relatively small base concealing property, the amount of the coloring pigment to be added therein is reduced. Specifically, the amount of the coloring pigment to be added is preferably 0.01 to 3% by volume based on the solid content of the paint. If the addition amount of the coloring pigment is less than 0.01% by volume, the underlying layer concealing power is too small, and even if the film thickness is about 50 μm, there is almost no color difference from the substrate, and the film thickness may not be determined. . In addition, the addition amount of the coloring pigment is 3% by volume.
If it exceeds, the color difference of the coating film may be lost before the target film thickness is reached due to too large a base hiding power. However, when using titanium dioxide alone or in combination with other color pigments as the color pigment, the content of the color pigment is 0.1 to
It is preferred to be 3% by volume.

The extender pigment is used in an amount of 0 to 5 with respect to the solid content of the paint.
It is preferably set to 9.99% by volume. Extender is 59.
If the content exceeds 99% by volume, the film-forming property is reduced.

The rust preventive pigment is used in an amount of 0 to 1 with respect to the solid content of the paint.
It is preferably 0% by volume. Even if the content of the rust-preventive pigment exceeds 10% by volume, it does not affect the rust-preventive power, the content of the extender pigment is reduced, and the paint cost is unnecessarily increased. When the extender pigment and / or the rust-preventive pigment are added, the ratio of the color pigment is 0.1% per 100% by volume of the total pigment.
It is preferred to be 3 to 7% by volume.

The total pigment content of the coating composition for judging film thickness is such that the total amount of the coloring pigment, extender pigment and rust-preventive pigment is in the range of 10 to 60% by volume based on the solid content of the coating material. preferable. A more preferred pigment content is 15
~ 45% by volume. Since the binder resin also has a slight color depending on the type, in such a case, the pigment content may be adjusted according to the color of the binder resin.

The above-mentioned coating composition for determining the film thickness contains, in addition to a binder resin, a crosslinking agent and a pigment, the following organic solvent:
It may contain additives and the like.

As the organic solvent, an organic solvent widely used in paints or a mixture thereof can be used. Preferred examples include aromatic hydrocarbons such as toluene or xylene, aliphatic hydrocarbons such as n-hexane and heptane, and petroleum fractions of various boiling ranges consisting mainly of aliphatic hydrocarbons and having some aromatic hydrocarbons. And esters such as butyl acetate, acetylene glycol diacetate, and 2-ethoxyethyl acetate; ketones such as methyl isobutyl ketone; alcohols such as butyl alcohol; and ethers such as ethylene glycol monobutyl ether.

Examples of the above-mentioned additives include common ultraviolet absorbers, surface modifiers, viscosity modifiers, leveling agents, pigment dispersants, plasticizers, defoamers and the like.

Method for Forming a Multi-Layer Coating Film The method for forming a multi-layer coating film of the present invention is a coating film in which a paint is applied to an old coating film formed on a substrate to obtain a coating film having a predetermined dry film thickness. In the forming method, first, the Munsell color system lightness V
After forming an undercoat film having a thickness of 70 or less, a target dry film thickness is set for the predetermined dry film thickness, and the above-mentioned film thickness determination paint composition is applied as a paint suitable for the target dry film thickness. And observing the color of the wet film obtained by coating, and judging whether or not the target dry film thickness has been reached.

As the above-mentioned base material, as a metal base material, an iron plate, a plated steel plate, a steel plate such as a stainless steel plate, various alloy materials, an aluminum plate, a zinc plate, etc., and as an inorganic base material, concrete, stone, Ceramics and the like can be mentioned. The metal substrate is preferably a steel plate from the viewpoint of workability, and a steel plate having a non-smooth surface having a connecting portion by welding or joining is more preferable from the viewpoint of strength. These base materials are, for example, ships, marine structures, bridges, tanks, plant facilities, etc. made of metal, and concrete bridges, concrete piers, railing, dam sites, port facilities, buildings, etc. as inorganic materials. What constitutes a structure, such as, is suitable. In addition, it can be particularly suitably used for a substrate of a large structure where it is difficult to secure a scaffold or the like. In addition, the old coating film which passed with time from the time of coating is formed in the base material.

In the method for forming a multilayer coating film of the present invention, the Munsell color system lightness V is first applied to the old coating film formed on the base material.
Is characterized by forming an undercoating film of 70 or less. When the Munsell color system lightness V exceeds 70, the hiding properties become insufficient depending on the hue of the old coating film, and it is necessary to increase the film thickness for hiding. By setting the Munsell color system lightness V of the undercoating film to 70 or less, it becomes easy to determine whether or not the target film thickness has been reached by using the film thickness determination coating composition. Preferred Munsell color system lightness V
Is 40 to 65. As the undercoat film, a binder function of a substrate and a film formed using the film thickness determination coating composition is performed, and a color difference between the undercoat film and the undercoat film is formed using a clear hue. Can be. Such an undercoat paint can be obtained by, for example, blending a binder resin, a crosslinking agent, a pigment, an organic solvent, an additive, and the like used in the above-mentioned paint composition for judging film thickness.

Further, the coating film formed by the undercoat paint has an elongation followability of 1% or more and a color difference from the old coating film of 20%.
It is preferable that it is above. The method for having the stretch-following property is the same as that of the coating composition for judging film thickness.

The above-mentioned undercoat is applied on the above-mentioned old coating using a generally well-known coating device such as a roller, a brush or a spray. After the coating, an undercoating film can be obtained by air drying. The coating thickness of the undercoat film is preferably 30 to 150 μm as a dry film thickness.

In the method for forming a multilayer coating film of the present invention, a coating film of the above-mentioned coating composition for judging film thickness is formed on the above-mentioned undercoat coating film. In the method for forming a multilayer coating film of the present invention, first, a target dry film thickness is set for the predetermined dry film thickness. As described in the description of the coating composition for judging film thickness, the target dry film thickness is usually one of the required predetermined film thickness.
The thickness is set to 00 to 120%. For example, when the predetermined dry film thickness is 50 μm, the thickness can be set to 50 to 60 μm.

After setting the target dry film thickness in this way, a paint suitable for the target dry film thickness is prepared. This paint is the above paint composition for judging film thickness, and can be selected according to the target dry film thickness and the coating specifications at that time.

Here, the hue range of the coating composition for judging film thickness is as follows:
Since the color difference is more likely to occur as the hue with the undercoat film is closer to the complementary color, the hue of the undercoat film is set to 0 on the Munsell 100 hue circle, and the counterclockwise is 0 to +50 and the clockwise is When displayed as 0 to -50, -20 to -50 or +50 to +20 is preferable. More preferably,-
40 to -50 or +50 to +40.

The above-prepared coating composition for judging film thickness is applied onto the above-mentioned undercoating film using a generally well-known coating device such as a roller, a brush, a spray, or the like. Since the film thickness determination coating composition has a relatively small underlying concealing property, the color changes with an increase in the thickness of the wet coating film, and the wet film and the undercoating film to obtain the target dry film thickness Since the color difference is 20 or more, it is easy to confirm the color change visually or using a color difference meter.

The above-mentioned coating composition for judging film thickness is prepared by mixing a wet coating film having a target dry film thickness with a target dry film thickness of −50 μm.
Since the color difference from the wet coating film at a film thickness of less than 2 is 2 or more, if the film thickness is larger than the target dry film thickness and the film thickness is insufficient, the color difference can be visually confirmed. Therefore, when the coating is performed using a spray, if the color difference does not change, the target dry film thickness has been reached. On the other hand, when coating is performed using a roller or a brush, it is preferable that a color of a wet coating film that can obtain a target dry film thickness is used in advance as a reference sample plate. By comparing this standard with the color of the wet coating film, it can be determined whether or not the target dry film thickness has been reached. Here, if the film thickness is insufficient, overcoating is performed, and it is determined again whether or not the target dry film thickness has been reached. The wet film thus formed can be dried under predetermined conditions to obtain a coating film.

The thickness of the dried film thickness is measured by observing the thickness of the fractured surface of the coating film in the case of an inorganic base material or a non-magnetic metal base material, for example, PAINT BOER ERIC.
The measurement can be performed with a film thickness meter manufactured by HSEN, or in the case of a magnetic metal substrate such as a steel material with an electromagnetic film thickness meter.

In the method for forming a multilayer coating film of the present invention, a paint is applied on the coating film obtained by the above-described method for forming a multilayer coating film to obtain a coating film having a predetermined dry film thickness. In the coating film forming method, a target dry film thickness is set for the predetermined dry film thickness, and as a coating material suitable for the target dry film thickness, the coating film obtained by the method for forming a multilayer coating film is used. To 5
A wet coating film obtained by coating so as to obtain a target dry film thickness of 0 μm or more has (a) a color difference between the wet coating film and the coating film obtained by the multilayer coating film forming method of 20 or more, (B) the color difference between the wet coating film and the coating film obtained by drying to a film thickness less than (the target dry film thickness—50 μm) is 2 or more; A wet paint film is coated with a paint that satisfies the condition that the color difference between the wet paint film and the wet paint film having a thickness twice as large as that of the wet paint film is less than 1, and the color of the wet film obtained by the above-mentioned painting is applied. And determining whether or not the target dry film thickness has been reached.

At this time, the color of the coating film for judging the film thickness used in the method of forming the multilayer coating film and the color of the coating film for judging the film thickness used in the method of forming the coating film are different. This coating film forming method can be performed with reference to the above-described multilayer coating film forming method. This coating film forming method is applicable to two or more coating films.

An overcoat may be further applied on the coating film obtained by the method for forming a multilayer coating film and the method for forming a coating film of the present invention. Topcoat paints include epoxy resin paints, chlorinated rubber resin paints, vinyl chloride resin paints, alkyd resin paints, silicone alkyd resin paints, acrylic resin paints, and urethane resins that are highly resistant to weathering and stretchability. Paints such as paints based on fluororesins, paints based on fluororesins, paints based on polyester resins, and paints based on epoxy acrylic resins can be used. The dry film thickness per coat of the top coat is preferably from 20 to 50 μm, and depending on the purpose, it may be applied a plurality of times.

[0063]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Preparation of paint composition for judging film thickness Coating compositions 1 to 11 having the compositions shown in Table 1 were prepared. Paints 1 to 7 are for the examples, paints 8 to 11 are for the comparative examples, and paints 5 to 7 are paints for forming an undercoat film.

Elongation followability: A coating composition for determining film thickness is applied to a thickness of 0.2 mm in accordance with JIS A 6910,
After drying for 7 days at 80 ° C. and drying for 4 days at 80 ° C., a dumbbell-shaped No. 2 shape was used as a test piece, and a test temperature of 2
It was measured at a test speed of 5 ± 1 mm per minute at 3 ° C. Table 1 shows the measurement results.

Concealment ratio: The concealment ratio at a dry film thickness of 60 and 120 μm was determined according to JIS K 5400 7.2 (7.
2) The measurement was performed using the opacity test paper specified in f in accordance with the same specification.

Munsell lightness: Munsell lightness (V) is expressed by S
It was measured with an M color computer (type SM-7CH, manufactured by Suga Test Instruments Co., Ltd.).

Old film suitability: The suitability for the old coating film was determined by using a cutter knife to cross-cut the old coating film to determine the lifting status of the old coating film by forming an undercoat film. The occurrence of lifting was evaluated as "poor".

[0069]

[Table 1]

Notes to Table 1: (1) Zinc molybdate, (2) Color pigment,% by volume based on total paint, (3) 20% solids, expressed as volume% including solvent, (4) 99% solids %, Expressed as volume% containing solvent, (5) Varnish of bisphenol A type epoxy resin (solid content 70%, expressed as volume% containing solvent), (6) Varnish of urethane-modified epoxy resin (solid content 70) %, Expressed as volume% containing solvent), (7) Varnish of dimer acid epoxy resin (solid content 70%, expressed as volume% containing solvent), (8) Polyamine resin varnish crosslinking agent (solid content 70%) , Expressed as volume% containing solvent), (9) aromatic hydrocarbon solvent and ketone solvent (weight ratio 1/1).

Examples 1-16, Comparative Examples 1-4 Panel Types Panels 1-4 (steel plate thickness: 0.1 cm, 30 cm × 15
cm): Two kinds of JIS K5622 as undercoat paints with a dry film thickness of 35 μm, and JIS K5516 as intermediate coats
JIS as two topcoat paints
K 55162 type overcoat (panel 1 is white, panel 2 is blue, panel 3 is green, panel 4 is red)
A steel plate formed 5 μm and exposed in Okinawa for 2 years. Panel 5:
2. Japan Highway Public Corporation “Maintenance and Repair Procedures (Bridges)” Part 3 “Concrete Structures” II “Trails and Earthquakes” "Repair method"
Painted according to the standards of Japan, and the hue exposed in Okinawa for 2 years is red.

Method for Forming Multi-Layer Coating Film The coating materials 1 to 11 obtained above were applied to the above panels under the specifications shown in Tables 2 and 3 and the target dry film thickness was set to 120 μm. In, brush painting,
It was left at room temperature for 24 hours. The wet film thickness / dry film thickness of each coating composition for judging film thickness was 95/60 μm, 190/12
0 μm and 290/180 μm. In all cases, the wet film thickness was about 1.5 times the dry film thickness. For each of the obtained coating films, the color difference from the old coating film was measured by the above color difference meter, and the film thickness judgment was visually observed from the state of the coating film (wet and dried). The results are shown in Tables 2 and 3.

[0073]

[Table 2]

[0074]

[Table 3]

Notes on Tables 2 and 3: (1) Munsell symbol (hue / lightness / saturation) display, (2)
The color difference between the old coating film and the film thickness determination coating film, (3) concealment judgment (confirmed with both the wet coating film and the dried coating film),…: Examples 17 to 24 concealing and Comparative Example 5 panel 1 Using the coating composition for judging film thickness obtained in the above Examples and Comparative Examples, using a combination of different hues according to the specifications shown in Table 3, and setting the target dry film thickness to 125 μm,
The first layer thickness determination paint and the second layer thickness determination paint were applied by a brush coating method, and allowed to stand at room temperature for 24 hours.
The dry thickness of the first layer thickness determination paint is 120 μm,
The wet film thickness / dry film thickness at the end of application of the second layer thickness determination paint is 80/50 μm, 120/75 μm,
160/100 μm, 200/125 μm, 240/1
There were six patterns: 50 μm and 280/175 μm.
For each of the obtained coating films, the color difference from the first layer thickness determination coating film, and the color difference ΔE from the second layer thickness determination coating film were measured by the color difference meter, and the coating film state was visually observed. Observed. Table 4 shows the results.

[0076]

[Table 4]

Notes on Table 4: (1) Munsell symbol (hue / lightness / saturation) display, (2)
Color difference between undercoat and overcoat, (3) film thickness determination criteria: same as the visual determination criteria in Table 2.

As is clear from the results of Tables 1 to 3, Examples 1 to 24 were obtained by forming a coating film layer by the method of forming a multilayer coating film of the present invention. In the wet coating film, the target film thickness could be obtained, and no lifting was caused on the old coating film.

On the other hand, in Comparative Examples 1 to 5, the target film thickness could not be obtained or the old coating film was lifted because it was out of the range of the present invention.

[0080]

According to the coating composition for judging film thickness and the method for forming a multilayer coating film of the present invention, a base material on which an old coating film having a non-uniform film thickness and, in some cases, an uneven hue, is formed. When performing coating, the coating operator can visually determine whether or not the coating has reached the target film thickness during coating, and without lifting the old coating. A coating film having a target dry film thickness can be reliably and easily obtained.

Further, since the visual judgment can be made when the coating film is wet, a quick judgment can be made at the site where the old coating film is repair-painted, which contributes to the efficiency of the repair painting work.
According to the method for forming a multilayer coating film of the present invention, it is not necessary to perform complicated film thickness measurement, so that the number of steps in the repair coating process can be significantly reduced, and deterioration of the base material due to insufficient film thickness and excessive film thickness. Paint waste can be prevented.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Yasui 4-1-1, Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. F-term (reference) 4D075 AE03 BB92Z CA02 CA03 CA18 CA32 CA33 CA38 CA48 DA06 DA23 DA27 DA33 DB02 DB04 DB05 DB07 DB12 DB14 DC05 DC06 DC08 EA07 EB08 EB09 EB13 EB15 EB19 EB22 EB32 EB33 EB35 EB36 EB38 EB39 EB45 EC11 EC13 4J038 NA01 PA07 PB06 PB12

Claims (10)

[Claims] 1. An overcoat paint applied to an undercoat film having a Munsell color system lightness V of 70 or less formed on an old paint film, wherein the paint is applied to the undercoat film with a thickness of 50 μm or more. A wet coating film obtained by coating so as to obtain a target dry film thickness is obtained by drying (a) the color difference between the wet coating film and the undercoating film is 20 or more, and (b) the wet coating film. (C) a wet coating having a color difference of 2 or more from a wet coating having a thickness of less than (the target dry film thickness—50 μm); and (c) a wet coating having a thickness 1.2 times the wet coating. A coating composition for judging film thickness that satisfies the condition that the color difference from the film is less than 1. 2. The coating composition for judging film thickness according to claim 1, wherein the color difference between the wet coating film and a dried coating film obtained by drying the wet coating film is 0. 3. The coating composition for judging film thickness according to claim 1, wherein the stretchability of the obtained coating film is 1% or more. 4. The film thickness determination according to claim 1, wherein the paint for forming the undercoating film has an elongation followability of 1% or more and a color difference from the old coating film of 20 or more. Paint composition. 5. A coating film forming method for obtaining a coating film having a predetermined dry film thickness by applying a paint to an old coating film formed on a base material, wherein the Munsell color system lightness V is 70 or less. After forming an undercoat film, a target dry film thickness is set for the predetermined dry film thickness, and the paint according to any one of claims 1 to 4 is used as a paint suitable for the target dry film thickness. A multi-layer coating film forming method in which the coating is performed, and the color of the wet film obtained by the coating is observed, and it is determined whether or not the target dry film thickness has been reached. 6. The hue of a wet film obtained by said coating,
The undercoating film is defined as 0 on the Munsell's 100 hue circle, and when the counterclockwise direction is displayed as 0 to +50 and the clockwise direction is displayed as 0 to -50, it is +20 to +50 or -50 to -20. A method for forming a multilayer coating film. 7. The display according to claim 5, wherein the hue of said wet film is +40 to +50 or -40 to -50 in said display.
Or the method for forming a multilayer coating film according to 6. 8. The method according to claim 5, wherein the base material is a steel plate.
The method for forming a multilayer coating film according to claim 1. 9. The method according to claim 8, wherein the steel sheet has a connection portion by welding or joining. 10. A coating film obtained by applying a coating material on a coating film obtained by the method for forming a multilayer coating film according to claim 5 to obtain a coating film having a predetermined dry film thickness. In the forming method, a target dry film thickness is set with respect to the predetermined dry film thickness, and as a paint suitable for the target dry film thickness, the paint is applied to the coating film obtained by the multilayer coating film forming method by 50 μm.
m, a wet coating film obtained by coating so as to obtain a target dry film thickness of not less than (a) has a color difference of 20 or more between the wet coating film and the coating film obtained by the multilayer coating film forming method,
(B) the color difference between the wet coating film and the coating film obtained by the method for forming a multilayer coating film having a thickness of less than (the target dry film thickness—50 μm) is 2 or more; A wet paint film and a wet paint film having a film thickness 1.2 times the wet paint film are coated with a paint that satisfies the condition that the color difference is less than 1, and the color of the wet film obtained by the above paint is applied. To determine whether the target dry film thickness has been reached or not.