JP2014223599A - Coating method of low viscosity coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method which is a low environmental load coating method and where the strength of coating films on coating objects having coarse surfaces such as a building material, paper, a fiber-reinforced plate, cloth and the like is enhanced.SOLUTION: In a coating method of a low viscosity coating material comprising: a step to coat the surface of a coating object having surface roughness Rz of 0.8 μm or more by injecting the coating material whose viscosity is reduced because carbon dioxide is dissolved; and a step to harden the coated coating material, the coating object is selected from among a building material, paper, a fiber-reinforced plate and cloth and the push-in strength regulated by the calculation method of the surface of the coating object after coating is increased by 40% or more in comparison with the surface of the coating object before coating.

Description

  The present invention relates to a coating method for a paint in which carbon dioxide is dissolved and its viscosity is lowered.

  Conventionally, for porous materials, paints with various functionalities have been applied to the surface of the material in order to provide design and functionality on the surface. The permeability on the surface of the material was high, and it was difficult to improve the added value by painting.

  For example, in the case of painting that places emphasis on designability and productivity, the use of a large amount of surfactant components and diluents is used to increase the resin permeability from the surface in order to adjust the penetrating power with the paint composition. There are also methods for coating by core-sealing with cores and strengthening the base material, but there are adverse effects such as solvent removal after repeated coating of the paint several times, surface hardening of the surfactant used, and surface bleeding. In addition, a large amount of energy is required in the heat drying process for drying a large amount of thinner used.

In addition, when a porous building material is coated, a concavo-convex pattern is formed on the surface, and since it is porous, a large number of fine irregularities due to pores may be generated on the surface.
When there are such large and small irregularities, unevenness and defects are caused in the coating film, and it is difficult to obtain a sufficiently satisfactory coating film such as coating film forming property, waterproof property or freeze-thaw resistance.

  For example, when strengthening the coating on the surface of a substrate such as a particle board defined in JIS A 5908-1994 or a volcanic glassy multilayer board (for example, Daiken Kogyo Co., Ltd .: trade name Dylite) The surface has remarkably high permeability of the paint, so it is necessary to apply the paint several times, and in order to dry the thinner used in large quantities, it can be done at a high temperature dryer of 60 ° C to 150 ° C for several tens of seconds. It was necessary to dry several tens of minutes with hot air. For this reason, it has been difficult to take measures such as prevention of global warming, regulation of harmful chemical substances, and reduction of VOC (Volatile Organic Compounds) with conventional coating methods.

  In addition, when trying to enhance the functional characteristics of the surface of a porous wood structure such as softwood plywood or lauan wood, the resin is injected into the base material using an impregnation device such as reduced pressure-pressurization. In the past, surface modification of the substrate such as hardness, corrosion resistance, and weather resistance has been performed, but a large-scale device for maintaining and controlling the injection pressure is required, and batch processing is also required. Therefore, there is a problem that the productivity is limited and the cost is increased.

  On the other hand, in order to impart functionality such as weather resistance to the surface of the porous elastic paved road, paint such as acrylic is applied by roller brush application or spraying, but the durability of the porous elastic paved road is In order to improve the durability, long-term weather resistance, rubber elastic body, and aggregate against wear caused by heavy loads such as trucks are applied by applying acrylic paint with sufficient permeability. Etc. can be retained.

For example, Patent Document 1 describes a carbon dioxide coating method and an apparatus thereof, in which a part or all of a diluent solvent used in organic solvent-based spray coating is replaced with carbon dioxide. According to this method, since a diluting solvent that has been used in the past can be replaced with an extremely small amount of carbon dioxide, it is possible to greatly reduce the occurrence of VOCs, and a new low-environmental load type coating apparatus and coating method are provided. It is stated that it can be done.
Also, in general, it is possible to increase the ratio of oligomer components by diluting with carbon dioxide without using organic solvents or reactive diluent monomers that are likely to reduce the physical properties of the coating film. It is easy to improve the film properties.

  In Patent Document 2, a mixture having at least one of a precursor of a polymer compound or a polymer compound dissolved in at least one subcritical or supercritical fluid is sprayed from a nozzle or an orifice. The film is applied to the surface of a planar or three-dimensional object to form a film, and the film is cured by at least one of natural standing, heating, or active energy ray irradiation to obtain a thickness. A step of forming a high-quality film having a surface roughness Rz of 0.8 μm or less, which is a thin film of 20 μm or less and the surface shape curve measured with a contact-type surface roughness meter, with swell removal at a cutoff value of 8 mm. The method for forming a film by high-pressure carbon dioxide coating is described. According to this method, it is described that it is possible to coat with a thin film thickness [20 μm or less] while ensuring a very good surface appearance [surface roughness Rz value is 0.8 μm or less].

  In general, the higher the penetrability of the base material to be coated with the active energy ray-curable coating material, the more remarkable is the decrease in the energy reached by UV inside the base material, making it difficult to cure the penetrated portion. It becomes. For this reason, harmful effects such as residual odor after curing and hardness reduction due to poor curing are likely to occur, and expensive, highly reactive initiators and two-component mixed type hybrid curing type paints combined with isocyanate are used. Therefore, phenomena such as odor after curing and blocking such that substrates after coating stick to each other are likely to occur.

JP 2010-234348 A JP 2012-086175 A

In the prior art, it is known that a low environmental impact coating method can be provided and a thin film coating is possible when carbon dioxide is replaced without using an organic solvent diluent. At present, there is no known coating method that enhances the strength of the coating film of an object to be coated having a rough surface such as a building material, paper, fiber reinforced board, or cloth.
Therefore, in the present invention, it is an object to provide a coating method that is a low environmental load coating method and that enhances the strength of a coating film of a rough surface to be coated such as building materials, paper, fiber reinforced boards, or cloth. To do.

In the present invention, a step of coating the surface of an object having a surface roughness Rz of 0.8 μm or more by spraying a paint in which carbon dioxide is dissolved and a viscosity is lowered, and a step of curing the coated paint A coating method comprising:
The object to be coated is any one selected from building materials, paper, fiber reinforced boards, or cloth,
Also provided is a coating method characterized in that the indentation strength of the surface of the object to be coated after coating specified in the following calculation method is improved by 40% or more compared to the indentation strength of the surface of the object to be coated before painting. This solves the above problem.

  ADVANTAGE OF THE INVENTION According to this invention, while being a low environmental impact coating method, the coating method which reinforce | strengthened the intensity | strength of the coating film | membrane of rough coated objects, such as building materials, paper, a fiber reinforced board, or cloth, can be provided.

It is drawing which shows the relationship between the force of Example 1 and an indentation depth. It is drawing which shows the result of Example 1 and Comparative Examples 1-4.

The present invention will be described in more detail.
That is, the present invention includes the following items.
1. A coating method having a step of coating the surface of an object to be coated having a surface roughness Rz of 0.8 μm or more by spraying a coating material in which carbon dioxide is dissolved and a viscosity is lowered, and a step of curing the coated coating material. There,
The object to be coated is any one selected from building materials, paper, fiber reinforced boards, or cloth,
And, the coating method characterized in that the indentation strength of the surface of the coated object after painting specified in the following calculation method is improved by 40% or more compared to the indentation strength of the surface of the painted object before coating,
(1) Using a tensile tester equipped with a stainless steel spherical jig having a diameter of 1/4 inch, the surface of an object to be coated before painting the jig at a speed of 0.1 mm / second at 25 ° C., and painting Indentation depth (mm) and force (kg) when the depth of indentation is pushed from 85% to 80% of the initial thickness of the object to be painted before and after painting. ).
(2) Create a graph plotting the relationship between the indentation depth and force, and determine the slope (kg / mm) when the graph is regarded as a straight line as the surface of the object to be coated before coating and the coating after coating. Calculate the surface of the paint.
(3) Each of the calculated inclinations is defined as the indentation strength of the surface of the object to be coated before painting, and the indentation strength of the surface of the object to be painted after painting.
2. 1. The paint is an active energy ray curable paint The painting method described in
3. The active energy ray-curable coating material contains an acrylic resin. Or 2. The coating method as described in 4.

(paint)
In general, in organic solvent-based coating, a true solvent is used for the purpose of reducing the viscosity of the paint by dilution, and a poor solvent that controls the behavior after coating such as surface smoothness, permeability, and solvent removal, for example, Toluene, xylene, cellosolve solvent which is a slow-drying solvent, etc. are added to reduce the viscosity to enable spraying. The low-viscosity paint / dilution solvent mixture is sprayed as fine droplets by an air spray method using air as an atomizing medium or a high-pressure spray method that does not use atomized air. Applied.

The present invention provides a coating method in which the diluent solvent used in the organic solvent-based coating is partially or entirely replaced with carbon dioxide. A preferable coating material used in the present invention is an active energy ray-curable coating material. An active energy ray-curable coating is a coating that is cured by UV or electron beam to form a film, and is excellent in high hardness, abrasion resistance, scratch resistance, chemical resistance, solvent resistance, etc. Used as a hard coat for telephones.
The coating material is a coating material that forms a coating film by radical polymerization of an acrylic oligomer or monomer compound using ultraviolet rays (UV) or electron beams (EB) as energy. The one-component curable paint is a paint that is used undiluted or by blending only a diluent (viscosity modifier) such as thinner.

  The above-mentioned paint is a paint that has an acrylic resin as a main component and can form a coating film without using a reactive curing agent such as isocyanate. By blending the fiber-based resin, quick drying, high smoothness, and film-forming property can be improved.

  In the present invention, carbon dioxide is mixed and dissolved in the paint. The conditions are a temperature of 30 to 70 ° C., preferably 35 to 45 ° C., and a pressure of 5 to 20 MPa, preferably 7 to 10 MPa.

(Coating object)
The object to be coated used in the present invention is characterized in that the surface roughness Rz is 0.8 μm or more. In the present invention, the surface of the object to be coated is coated with a surface having a surface strength higher than that before coating. Is characterized by improvement.
Such an object to be coated is not particularly limited as long as the surface roughness Rz is 0.8 μm or more, and examples thereof include building materials, paper, fiber reinforced boards, and cloth. In the present invention, the surface of the object to be coated is characterized in that the rougher one can exhibit the surface strength enhancement that is the effect of the present invention. For example, when Rz is 5 μm or more, the effect of the present invention is easily exhibited. . However, furniture wood is excluded as the object to be coated of the present invention.

(Apparatus and painting method)
The coating apparatus used in the present invention is not particularly limited as long as it can inject a paint in which carbon dioxide is dissolved and its viscosity is lowered. For example, an apparatus described in Patent Document 1 can be given.

  That is, the present invention relates to a tank for storing paint as a paint supply line in carbon dioxide painting in which a diluent solvent (thinner) used in organic solvent-based spray painting is partially or entirely replaced with carbon dioxide, and the tank A high-pressure paint pump that pressurizes the paint supplied to a predetermined pressure, a paint primary pressure adjusting valve that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank, and serves as a carbon dioxide supply line A tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes liquid carbon dioxide supplied from the cooler to a predetermined pressure, and the liquid carbon dioxide high pressure It has a liquid carbon dioxide primary pressure regulating valve that adjusts the pump discharge pressure and returns the surplus to the suction of the pump. In, a pressurized paint supplied from the paint supply line, a mixer for mixing the pressurized carbon dioxide supplied from the carbon dioxide supply line, and a mixed material supplied from the mixer A coating apparatus using carbon dioxide consisting of having a spray gun for spraying a paint / carbon dioxide pressurized mixture onto a coating object under atmospheric pressure can be used.

In the coating method of the present invention, the primary pressure regulating valve on the discharge side of the paint high pressure pump or CO ₂ high pressure pump that performs spray control is set to the spray pressure, and the paint high pressure pump or CO ₂ high pressure pump that does not perform spray pressure control. By operating the discharge side primary pressure regulating valve at a pressure higher than the spray pressure, the flow rate of the fluid for which the spray pressure control is not performed is made constant, and the flow rate of the fluid for which the spray pressure control is performed is set to the orifice of the spray nozzle. It is possible to use a method comprising returning the surplus to the pump suction as being variable according to the flow rate characteristics.

  Further, the coating method in the present invention is a method of performing coating using carbon dioxide using the above-described coating apparatus, and sprays the primary pressure regulating valve on the discharge side of the paint high-pressure pump and the carbon dioxide high-pressure pump. It is possible to use a method using carbon dioxide consisting of setting the pressure higher than the pressure, spraying the whole amount of fluid discharged from both pumps, and adjusting the spray pressure depending on the flow rate characteristics of the nozzle orifice of the spray gun .

  In the present invention, having a paint heater for heating the pressurized paint to a predetermined temperature, having a cooler for cooling the surplus carbon dioxide returned to the suction of the liquid carbon dioxide high-pressure pump to a predetermined temperature, A carbon dioxide heater that heats the liquid carbon dioxide that has been mixed to a predetermined temperature, a mixture heater that heats the mixed paint / carbon dioxide pressurized mixture to a predetermined temperature, and the mixer includes a paint and carbon dioxide It is a preferred embodiment that it is a micromixer capable of rapidly mixing the above.

  In the present invention, the fluid for controlling the spray pressure is paint, and the primary pressure regulating valve on the discharge side of the paint high-pressure pump and the carbon dioxide high-pressure pump is set higher than the spray pressure and discharged from both pumps. By spraying the entire amount of fluid, adjusting the spray pressure depending on the flow characteristics of the nozzle orifice of the spray gun, and setting the residence time from the mixer to the spray gun to at least 15 seconds. A preferred embodiment is a one-phase mixture.

  In general, active energy ray curable paints dislike the generation of radicals due to mechanical stress, so the use of gear pumps can be avoided, but if the paint viscosity is sufficiently high, mono pumps, large-diameter dies and fram pumps are often used. Is done.

  On the other hand, as a high-pressure carbon dioxide pump, a plunger pump can be adopted in addition to a piston pump and a diaphragm pump. However, in pressurization of carbon dioxide, pressurization with liquid carbon dioxide is advantageous, and in this case, cooling at the front stage of the pump is required.

  In the present invention, the type of the heater is not particularly limited. However, when the apparatus is started or when the flow rate is changed, the temperature is controlled to be constant as soon as possible, or the spray is temporarily changed by switching the painted surface. When the operation is stopped and spraying is started again, it is required that the temperature of each fluid does not change greatly. Therefore, a tank / coil type heat exchange in which a high-pressure pipe through which a fluid passes is immersed in a tank filled with a heating medium (usually water) rather than a commonly used electric heater. A vessel is preferably used.

  In the present invention, it is necessary to efficiently mix the paint and carbon dioxide and dissolve the carbon dioxide in the paint. Conventionally, static mixers (static mixers) applying the fluid multistage division principle, which is an inline mixer, have been used for this purpose, but sufficient mixing and dissolution cannot always be realized. In the present invention, a high-pressure micromixer using the principle of micromixing is used.

  The type of the high-pressure micromixer is not particularly limited. However, in consideration of the high viscosity of the paint and the blocking property, an interdigital channel structure that mixes two fluids with an extremely short diffusion distance, for example, A micro mixer utilizing the turbulent mixing effect of a fluid is preferable to a laminar flow type micro Kimisa provided by IMM, Germany.

  As these mixers, for example, a T-shaped mixer having a flow path diameter of 0.5 mm or less, a swirl type micro mixer using a swirling flow, and a center collision type micro mixer that causes a fluid to collide at the center of a minute space And a double-tube micromixer having an inner diameter of 0.5 mm or less.

  In addition, by connecting a conventionally used static mixer to the subsequent stage of these micromixers, it is possible to achieve sufficient dissolution of carbon dioxide in the paint and to form a stable one-phase mixture. Become. Depending on the conditions, between the mixer and the spray gun, there may be a two-phase form of paint and carbon dioxide. In that case, the viscosity of the two fluids differ greatly, so the spray is not stable and a clean application is realized. There is a danger that cannot be done. The solubility of carbon dioxide in paint greatly varies depending on the kind of paint, temperature, and pressure, but is greatly influenced by the configuration of the mixer.

  The spray gun used in the present invention may be an airless high-pressure spray gun, but the final control of the spray flow rate, spray pressure, and spray pattern is controlled by the opening diameter of the high-pressure nozzle orifice mounted on the spray gun. Since it depends on (equivalent diameter) and its shape, it is extremely important. The spray flow rate differs greatly depending on how much the coating amount per unit time is set, but generally, a range of 50 to 500 g / min is selected as the flow rate of the paint.

(Strength evaluation)
The present invention is characterized in that the strength defined by the following calculation method is improved by 40% or more after coating than before coating.
That is, in this invention, it evaluates with the following calculation method.
(1) Using a tensile tester equipped with a stainless steel spherical jig having a diameter of 1/4 inch, the surface of an object to be coated before painting the jig at a speed of 0.1 mm / second at 25 ° C., and painting Indentation depth (mm) and force (kg) when the depth of indentation is pushed from 85% to 80% of the initial thickness of the object to be painted before and after painting. ).
(2) Create a graph plotting the relationship between the indentation depth and force, and determine the slope (kg / mm) when the graph is regarded as a straight line as the surface of the object to be coated before coating and the coating after coating. Calculate the surface of the paint.
(3) Each of the calculated inclinations is defined as the indentation strength of the surface of the object to be coated before painting and the indentation strength of the surface of the object to be coated after painting.
Moreover, according to the coating method of the present invention, a coated product with reduced odor after coating can be obtained.
More specific evaluation methods are described in the examples.

The examples illustrate the invention in more detail.
Example 1
Cracks, cracks, holes, joints, spears, etc. inherent in dry veneer from a board cut from 3mm x 6mm thick with a rotary slicer that is slightly thicker than 3mm thick with a rotary slicer. A plate having a 20 cm square was cut out so as to have uniform properties.
In order to eliminate irregularities in thickness and fiber on the surface of the wood, prepare 5 pieces of wood boards that have a uniform surface by polishing the surface using water-resistant sanding paper (# 240 and # 320). A material was used.

  Next, as a supercritical paint composed of a UV curable paint, superpreparation “preparation paint A” mainly containing the paint shown in Table 1 and “preparation paint B” used for viscosity adjustment were prepared.

Unidic V4007S: UV curable resin (manufactured by DIC Corporation)
ACMO: acryloylmorpholine (manufactured by Kojin Co., Ltd.)
Ilgar Cure 184: UV initiator (1-hydroxy-cyclohexyl-phenyl-ketone (manufactured by BASF),
DYNOL 604: Wetting agent (manufactured by Nissin Chemical Industry Co., Ltd.)
BYK-A501: Antifoaming agent (by Big Chemie Japan)

After removing fine dust and dust from the surface of the coating substrate in advance by air blow, adjust the paint flow rate of supercritical CO ₂ to 55 g / min and the addition amount to 20% using an automatic spray gun. Spray painting was performed.
After wet spraying once in the vertical direction with a wet film thickness of 35 μm, setting at room temperature for 30 seconds, wetting the inside of the base material and defoaming residual CO ₂ , rotate the base material 90 degrees, Further, spray coating with a wet film thickness of 35 μm was performed in the lateral direction.
Similarly, after setting in a room temperature space for 2 minutes for the purpose of wetting and defoaming the substrate, the paint is applied with ultraviolet light with an integrated light quantity of 300 mJ / cm ² (peak intensity 100 mW / cm ² , high pressure Hg lamp) by a UV irradiation device. A target sample for surface strength measurement (sample A) was obtained by curing.

(Comparative Example 1); unpainted (Sample B)
The base material whose surface was sanded and adjusted as shown in Example 1 was used as a base material before coating (sample B) without coating.
(Comparative Example 2); When no solvent is added (Sample C)
When “Formulation paint A” is applied using an air spray gun of Wider W-101 (manufactured by Anest Iwata Co., Ltd.), the upper limit of the appropriate viscosity is exceeded, and the atomization state is deteriorated. Therefore, in order to lower the viscosity of the paint, the paint and the spray gun were previously heated to 40 ° C. and sprayed. The conditions were the same as in Example 1, after applying the same coating amount in the vertical direction and the horizontal direction by air spray coating, and then using a UV irradiation device, integrated light quantity 300 mJ / cm ² (peak intensity 100 mW / cm ² , high pressure Hg lamp) The desired coating agent was obtained by curing the paint with ultraviolet rays.

(Comparative Example 3); In case of monomer dilution (Sample D)
A paint prepared by mixing “preparation paint B” at a ratio of 100: 30 parts to “preparation paint A” was used.
As in Example 1, the substrate shown in Example 1 was wet sprayed in the vertical direction once with a wet film thickness of 35 μm, set at room temperature for 30 seconds, and then rotated by 90 degrees in the horizontal direction. Further, ordinary air spray coating was performed using a Wet film thickness of 35 μm and Weider W-101 (manufactured by Anest Iwata Co., Ltd.).

Similarly, after setting in a room temperature space for 2 minutes for the purpose of wetting and defoaming the substrate, the paint is applied with ultraviolet light with an integrated light quantity of 300 mJ / cm ² (peak intensity 100 mW / cm ² , high pressure Hg lamp) by a UV irradiation device. Cured to obtain the target solvent-free spray coating sample.

(Comparative Example 4); When diluted with a solvent (Sample E)
Using a paint in which “ethyl acetate” is mixed at a ratio of 100: 30 parts to “preparation paint A”, the base material shown in Example 1 has a wet film thickness of 35 μm once in the same manner as in Example 1. After spray coating in the direction and setting at room temperature for 30 seconds, rotate the substrate 90 degrees, and further use a Wet film thickness of 35 μm and Weider W-101 (Anest Iwata Co., Ltd.) Air spray painting was performed.
Similarly, after setting in a room temperature space for 2 minutes for the purpose of wetting and defoaming the substrate, the paint is applied with ultraviolet light with an integrated light quantity of 300 mJ / cm ² (peak intensity 100 mW / cm ² , high pressure Hg lamp) by a UV irradiation device. Cured to obtain the target solvent-free spray coating sample.
The results of Example 1 and Comparative Examples 1 to 4 are shown in FIG.

(Evaluation method)
In the examples and comparative examples, the strength of the surface of the object to be coated before and after coating was evaluated as follows.
-Paint penetration The five-step sensory evaluation ((circle), (circle) (triangle | delta), (triangle | delta), (triangle | delta) *, *) was performed visually about the ease of the penetration of the paint in the wet state immediately after coating.
-Residual odor immediately after coating In the state where the coating film was cured immediately after UV irradiation, the odor on the surface was sniffed, and similarly judged by 5-step sensory evaluation. The results are shown in Table 2.

・ Physical properties The surface strength after coating and curing was measured using a small tensile / compression tester "Texture Analyzer TA.XT plus" (manufactured by Stable Micro Systems) with a 1/4 inch stainless steel sphere of 0.1 mm / sec. It was pushed in at a speed until the indentation depth reached 80% of the substrate thickness before the test. Of the relationship between the obtained displacement and force, the inclination (kg / mm ⁻¹ ) when a portion where the indentation depth is from 85% to 80% of the base material thickness before the test is approximated by a straight line is tested. The indentation strength of the substrate was evaluated. The results are shown in FIG.

(Summary of results)
As a result of measuring the surface hardness characteristics using a texture analyzer, it was confirmed that a high surface hardness can be obtained.
With reference to the base material of the uncoated, surface condition after coating, odor, results of evaluating the physical properties, in the coating method of the present invention, with respect to the surface of a porous wood substrate, CO ₂ characteristics with supercritical The permeability of the paint due to the above was confirmed.
Furthermore, since CO ₂ remains in the paint, it was confirmed that the smoothness was maintained by the effect of preventing radical deactivation by oxygen, and the residual odor immediately after UV curing was drastically reduced.

  The coating method according to the present invention can be used as a coating method in which the surface strength of an object to be coated selected from building materials, paper, fiber reinforced boards, or cloth is enhanced.

A: Line showing relationship between force and indentation depth B: Line showing relationship between ratio from initial thickness and indentation depth C: Relationship between force and indentation depth when ratio from initial thickness is 85 to 80% Straight line

Claims (3)

A coating method having a step of coating the surface of an object to be coated having a surface roughness Rz of 0.8 μm or more by spraying a coating material in which carbon dioxide is dissolved and a viscosity is lowered, and a step of curing the coated coating material. There,
The object to be coated is any one selected from building materials, paper, fiber reinforced boards, or cloth,
In addition, the coating method is characterized in that the indentation strength of the surface of the object to be coated as defined in the following calculation method is improved by 40% or more compared to the indentation strength of the surface of the object to be coated before painting.
(1) Using a tensile tester equipped with a stainless steel spherical jig having a diameter of 1/4 inch, the surface of an object to be coated before painting the jig at a speed of 0.1 mm / second at 25 ° C., and painting Indentation depth (mm) and force (kg) when the depth of indentation is pushed from 85% to 80% of the initial thickness of the object to be painted before and after painting. ).
(2) Create a graph plotting the relationship between the indentation depth and force, and determine the slope (kg / mm) when the graph is regarded as a straight line as the surface of the object to be coated before coating and the coating after coating. Calculate the surface of the paint.
(3) Each of the calculated inclinations is defined as the indentation strength of the surface of the object to be coated before painting and the indentation strength of the surface of the object to be coated after painting. The coating method according to claim 1, wherein the paint is an active energy ray-curable paint. The coating method according to claim 1 or 2, wherein the active energy ray-curable coating material contains an acrylic resin.

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