Coating method and coating system using ultraviolet ray curable coating material

Abstract

The present invention includes at least one of: a first step (ST 1 → ST 4 → ST 5) for forming a first cured coating film layer (261) having a porosity of 30-50% or a surface roughness Rz of 0.1-10 μm by applying an ultraviolet ray curable coating material onto a target coating surface (3) in order to separately coat a glossy surface and a non-glossy surface so as to be capable of thickening, and irradiating the result with ultraviolet rays; and a second step (ST 1 → ST 2 → ST 3) for forming a second cured coating film layer (262) having a porosity of 0-20% or a surface roughness Rz of less than 0.1 μm by applying the ultraviolet ray curable coating material onto the coating surface (3) and irradiating the result with ultraviolet rays.

Description

Coating method and coating system using ultraviolet curing paint

[0001] The present invention relates to a coating method and a coating system using ultraviolet curable paint.

[0002] In order to decorate the surface of a metal cap or metal container, which has a mixture of glossy and non-glossy surfaces, a method is known in which an ultraviolet-curable ink is uniformly applied to the surface of a metal substrate to form an ink coating layer of uniform thickness, the entire surface is irradiated with ultraviolet light for a predetermined period of time to cause partial curing, a mask is then placed in the position that should be the non-glossy surface, and the ultraviolet light irradiation is continued to form a printing ink precursor layer only in the area that should be the non-glossy surface and a printing ink layer in the other areas that should be the glossy surface, and finally an overcoating material is applied to the entire surface and finished and cured (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2008-200662

[0004] However, in the above-mentioned conventional technology, a non-glossy surface is realized by reflecting the surface irregularities of a printing ink precursor layer obtained by partially curing an ultraviolet-curable ink onto an overcoating layer, so the thickness of the printing ink precursor layer is set to 1 to 8 μm, and even if a thick film is made, the limit is said to be about 12 μm (see paragraph

[0064] and Table 1 of Patent Document 1). Therefore, the above-mentioned conventional technology has a problem in that it is not possible to make a film thick enough to be applied to painting the interior and exterior panels of automobile bodies and automobile parts.

[0005] The problem to be solved by the present invention is to provide a coating method and coating system that can coat glossy and non-glossy surfaces separately and produce thick films.

[0006] The present invention solves the above-mentioned problems by including at least one of a first step of applying an ultraviolet-curable paint to a target coating surface and irradiating it with ultraviolet light to form a first cured coating layer having a porosity of 30 to 50% or a surface roughness Rz of 0.1 to 10 μm, and a second step of applying an ultraviolet-curable paint to the coating surface and irradiating it with ultraviolet light to form a second cured coating layer having a porosity of 0 to 20% or a surface roughness Rz of less than 0.1 μm.

[0007] According to the present invention, the glossy surface and the non-glossy surface can be painted separately, allowing for thicker films.

[0008] FIG. 1 is a configuration diagram showing an example of an inkjet coating device used in a coating method using an ultraviolet-curable paint according to the present invention. FIG. 1 is a configuration diagram showing one embodiment of a coating system using an ultraviolet-curable paint according to the present invention. FIG. 2 is a cross-sectional view of a coating film for explaining the mechanism of generation of a first cured coating film layer (matte coating film) and a second cured coating film layer (gloss coating film) according to the present invention. FIG. 3 is a plan view of a coating film showing one embodiment of a coating method using an ultraviolet-curable paint according to the present invention, and its cross-sectional view (Part 1). FIG. 4 is a plan view of a coating film showing one embodiment of a coating method using an ultraviolet-curable paint according to the present invention, and its cross-sectional view (Part 4). FIG. 5 is a plan view of a coating film showing another embodiment of a coating method using an ultraviolet-curable paint according to the present invention, and its cross-sectional view (Part 1). FIG. 6 is a plan view of a coating film showing another embodiment of a coating method using an ultraviolet-curable paint according to the present invention, and its cross-sectional view (Part 2). FIG. 7 is a plan view of a coating film showing another embodiment of a coating method using an ultraviolet-curable paint according to the present invention, and its cross-sectional view (Part 3). 10A and 10B are a plan view and a cross-sectional view (part 4) of a coating film showing another embodiment of a coating method using an ultraviolet-curable coating material according to the present invention.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The coating method of this embodiment is a coating method using an ultraviolet-curable paint, and in particular, is a coating method that controls the gloss and unevenness of the dried coating film surface depending on the drying method of the wet coating film of the applied ultraviolet-curable paint. The coating method of this embodiment is not particularly limited, but can be applied to the coating process of automobile parts such as outer and inner panels of automobile bodies and bumpers.

[0010] <<Ultraviolet-Curable Coating of the Present Embodiment>> The ultraviolet-curable coating used in the coating method of the present embodiment can be a coating obtained by blending a known ultraviolet-curable resin composition with, as needed, a colorant and known coating additives (for example, an antifoaming agent such as silicone oil, a fluorine-based surfactant, a silicone-based surfactant, a leveling agent such as an acrylic copolymer, a thickener, a viscosity reducer, etc.). Ultraviolet-curable resin compositions are broadly classified into ultraviolet-radical-curable resin compositions and cation-curable resin compositions, and either type of ultraviolet-curable resin composition can be used in the coating method of the present embodiment.

[0011] The ultraviolet radical curable resin composition contains an ultraviolet curable monomer or prepolymer and a photoradical polymerization initiator. The ultraviolet curable monomer or prepolymer is a monomer or prepolymer having multiple ethylenically unsaturated groups in the molecule, or a mixture thereof, and typical examples thereof include epoxy acrylate resin, urethane acrylate resin, thermosetting acrylic resin, and thermosetting polyester resin.

[0012] Representative examples of photoradical polymerization initiators used in combination with ultraviolet-curable monomers or prepolymers include benzoin and its alkyl ethers, such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-hydroxycyclohexyl phenyl ketone. anthraquinones such as 2-methylanthraquinone and 2-amylanthraquinone; thioxanthone such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone and 2,4-diisopropylthioxanthone; ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzophenones or xanthones such as benzophenone; and the like.

[0013] Such a photoradical polymerization initiator is generally used in a proportion of 0.1 to 30 parts by weight, particularly 1 to 25 parts by weight, per 100 parts by weight of the above-mentioned ultraviolet-curable resin component. In addition, at least one of well-known and commonly used photopolymerization accelerators such as benzoic acid-based or tertiary amine-based accelerators may also be used together with the photoradical polymerization initiator.

[0014] In contrast, the cationically curable resin composition contains an ultraviolet-curable epoxy resin as a resin component and a cationic ultraviolet polymerization initiator as a photopolymerization initiator.

[0015] The ultraviolet-curable epoxy resin contains an epoxy resin component having an alicyclic group in the molecule and adjacent carbon atoms of the alicyclic group forming an oxirane ring, and for example, epoxy compounds having at least one epoxycycloalkane group in the molecule, such as an epoxycyclohexane ring or an epoxycyclopentane ring, are used alone or in combination. Suitable examples of the ultraviolet-curable epoxy resin include vinylcyclohexene diepoxide, vinylcyclohexene monoepoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-m-dioxane, bis(3,4-epoxycyclohexyl)adipate, limonene dioxide, etc.

[0016] The cationic ultraviolet polymerization initiator used in combination with the epoxy resin is decomposed by ultraviolet light to release a Lewis acid, which has the effect of polymerizing the epoxy group. Suitable examples thereof include aromatic iodonium salts, aromatic sulfonium salts, aromatic selenium salts, and aromatic diazonium salts.

[0017] <<Embodiment of Inkjet Coating Apparatus>> When applying the above-mentioned ultraviolet-curable paint to a target surface, an air atomization paint spray gun, a rotary atomization paint gun (a so-called bell-type paint gun), or the like can be used, or a so-called inkjet coater (a machine that prints by spraying minute droplets of ink from a thin nozzle onto paper) can also be used. Inkjet coaters produce significantly less paint dust than air atomization paint spray guns or rotary atomization paint guns, which has the advantage of significantly improving paint usage efficiency and significantly improving the working environment.

[0018] 1 is a structural diagram showing one embodiment of an inkjet coating apparatus 1 used in a coating method using an ultraviolet-curable paint according to the present invention. The inkjet coating apparatus 1 according to this embodiment is widely known as an "inkjet coating apparatus," and therefore the term "ink" will be used in this specification. However, since the objects to be coated according to the present invention are automobile parts such as the outer and inner panels of an automobile body and bumpers, this ink actually refers to "automotive coating paint" (the above-mentioned ultraviolet-curable paint).

[0019] The inkjet coating device 1 of this embodiment comprises a nozzle 11 having an inlet 111 for the paint 2, a paint chamber 112 and an outlet 113 for the paint 2, a needle 12 having at least a tip 121 arranged in the paint chamber 112 and capable of moving back and forth in the axial direction Y toward the outlet 113, an actuator 13 that moves the needle 12 back and forth in the axial direction Y so that the tip 121 approaches the outlet 113 when the needle 12 advances and moves away from the outlet 113 when the needle 12 retreats, a pressure sensor 14 that detects the pressure of the paint 2 in the paint chamber 112, and a control unit 15 that controls the actuator 13.

[0020] The nozzle 11 has a hollow housing 114 made of a metal, resin, or ceramic material, with an inlet 111 formed on one side and an outlet 113 at the tip, and a paint chamber 112 formed inside. Paint 2 is introduced from the inlet 111 into the paint chamber 112 and is ejected (dribbled) from the outlet 113 to the outside by being pushed by the needle 12. The interior of the housing 114 is partitioned liquid-tightly into the paint chamber 112 and an actuator chamber 115 by a seal member 123.

[0021] The needle 12 is a needle-shaped rod made of metal, resin, or ceramic material, with a tip end 121 disposed in the paint chamber 112 and a base end 122 disposed in the actuator chamber 115, with a seal member 123 provided therebetween. The actuator 13 is fixed to the base end 122 of the needle 12. The needle 12 is provided within the housing 114 so as to be movable back and forth in the axial direction Y.

[0022] The actuator 13 is, for example, a stack of multiple piezoelectric elements, and has the property of expanding and contracting in the axial direction Y in response to a voltage applied to the electrodes. The application of voltage to the actuator 13 is executed by the control unit 15, and by applying a voltage to the actuator 13 in response to a command signal from the control unit 15, the needle 12 can be moved back and forth in the axial direction Y. Note that the stroke start position of the needle 12 may also be controlled based on the pressure of the paint 2 in the paint chamber 112 detected by the pressure sensor 14.

[0023] The paint 2 in this embodiment is the ultraviolet curable paint described above, and is stored in a paint tank 21 in a state where it has been adjusted to an appropriate viscosity, and is supplied by a paint pump 23 via a paint pipe 22. Note that a paint pipe may be provided to return the paint 2 introduced into the paint chamber 112 of the nozzle 11 to the paint tank 21, so that the paint 2 is supplied while circulating.

[0024] Fig. 2 is a configuration diagram showing an example of a coating system S used in the coating method using an ultraviolet-curable paint according to the present invention. The coating system S of this embodiment comprises the inkjet coating device 1 described with reference to Fig. 1, an ultraviolet irradiator 4 that irradiates ultraviolet light onto a wet coating film 25 of ultraviolet-curable paint applied to a coating surface 3, a laser displacement meter 5 that measures the thickness of the wet coating film 25, a heater 6 that heats the wet coating film 25 applied to the coating surface 3, and a controller 7 that controls the ultraviolet irradiator 4, the laser displacement meter 5, and the heater 6.

[0025] The embodiment shown in FIG. 2 illustrates an example of an inkjet coating device 1 in which four nozzles 11 are provided for a target coating surface 3. In FIG. 2, if a plane parallel to the coating surface 3 is defined as the X-Y plane and an axis perpendicular to the X-Y plane is defined as the Z axis, the four nozzles 11 are arranged in a row along the Y axis. The four nozzles 11 drop droplets 24 of paint 2 onto the coating surface 3 while moving in a direction (X axis direction) perpendicular to the direction in which the nozzles 11 are arranged (Y axis direction), thereby forming four rows of a wet coating film 25 on the surface of the coating surface 3. The distance between two adjacent nozzles 11 is approximately equivalent to one droplet 24 of paint 2. As shown in FIG. 2, the droplets 24 of paint 2 dropped from the four nozzles 11 form a continuous wet coating film 25 on the coating surface 3. Note that, for the sake of simplicity, an inkjet coating device 1 including four nozzles 11 is exemplified in this specification; however, an appropriate number of nozzles 11 can be arranged in a row depending on the size of the coating surface 3.

[0026] In this specification, the paint 2, droplets 24 of paint 2, wet coating film 25, and cured coating film 26 are used as different technical terms. That is, the liquid material from the paint tank 21 until it adheres to the coating surface 3 is collectively referred to as paint 2, and the granular liquid material from the discharge portion 113 of the nozzle 11 until it adheres to the coating surface 3 is referred to as droplets 24 of paint 2. In contrast, the liquid or semi-cured film from the time when the droplets 24 of paint 2 adhere to the coating surface 3 until it is cured by ultraviolet irradiation is referred to as wet coating film 25, and the coating film obtained by curing the wet coating film is referred to as cured coating film 26.

[0027] The ultraviolet irradiator 4 is provided in a process subsequent to the application process of the ultraviolet-curable paint. For convenience, one ultraviolet irradiator 4 is shown in Fig. 2, but when the object to be coated has a large surface area 3, such as an automobile body or automobile part, multiple ultraviolet irradiators 4 may be provided inside a tunnel-type furnace, such as a coating and drying furnace for bake-curable paint, and ultraviolet light may be irradiated onto the automobile body or automobile part while it is being transported. The ultraviolet irradiator 4 controls the ultraviolet irradiation intensity, irradiation time, or the irradiation amount, which is the product of these, by control signals from a controller 7.

[0028] The laser displacement meter 5 irradiates the surface of the wet coating film 25 coated by the inkjet coating device 1 with laser light and detects the displacement from the state before coating, thereby measuring the film thickness of the wet coating film 25 in real time. The detected displacement of the wet coating film 25 is output to the controller 7, which then calculates the wet coating film 25. The controller 7 then outputs a control signal to the ultraviolet irradiator 4 according to the calculated film thickness of the wet coating film 25. For example, the controller 7 outputs a control signal to the ultraviolet irradiator 4 to increase the irradiation intensity of ultraviolet light or lengthen the irradiation time as the film thickness of the wet coating film 25 increases.

[0029] The heater 6 is a heating means for heating the wet coating film 25 applied to the coating surface 3, and is arranged on the back surface of the coating surface 3 as well as in the vicinity of the wet coating film 25 as shown in the figure. Alternatively, heat emitted from the ultraviolet irradiator 4 may be utilized. The heater 6 of this embodiment, or an alternative ultraviolet irradiator 4, is provided to evaporate a volatile solvent contained in the wet coating film 25 before curing the wet coating film 25 by irradiating it with ultraviolet light. Here, the technical significance of evaporating a volatile solvent contained in the wet coating film 25 of an ultraviolet-curable paint before curing the wet coating film 25 by ultraviolet light will be explained. Note that typical ultraviolet-curable paints contain a volatile solvent to improve the dispersibility of the resin component and the photopolymerization initiator, and this volatile solvent evaporates before and after curing by ultraviolet light.

[0030] 3 is a cross-sectional view of a coating film for explaining the mechanism of formation of the first cured coating film layer (matte coating film) and the second cured coating film layer (gloss coating film) according to the present invention. In FIG. 3, the cross-section of a coating film in which the volatile solvent contained in the wet coating film 25 of the ultraviolet-curable paint applied to the coating surface 3 is evaporated over time and then irradiated with ultraviolet light to form a cured coating film 26 is shown in steps ST1 → ST2 → ST3, and the cross-section of a coating film in which the volatile solvent contained in the wet coating film 25 of the ultraviolet-curable paint applied to the coating surface 3 is irradiated with ultraviolet light before evaporating is shown in steps ST1 → ST4 → ST5.

[0031] As shown in step ST1 of Figure 3, an ultraviolet-curable paint is applied to the coating surface 3 to form a wet coating film 25. Then, as shown in step ST2, the coating is left at room temperature or with heating for a sufficiently long time, causing the volatile solvent to slowly evaporate from inside the wet coating film 25 before the resin component is photocured. When ultraviolet light is irradiated onto the wet coating film 25 in a state where the volatile solvent has evaporated, the resin component is photocured without any stirring occurring inside the coating film, resulting in a cured coating film 26 with a smooth, glossy surface, as shown in step ST3. In this embodiment, the cured coating film 26 thus obtained is also referred to as a second cured coating film layer 262 or a glossy coating film.

[0032] In contrast, as shown in step ST1 of FIG. 3 , an ultraviolet-curable paint is applied to the coating surface 3 to form a wet coating film 25. Then, as shown in step ST4, ultraviolet light is irradiated and the wet coating film 25 is heated with a heater 6 before the volatile solvent evaporates. This causes the volatile solvent inside the wet coating film 25 to rapidly evaporate, resulting in an agitation phenomenon within the coating film. In this state, the resin component photocures as the volatile solvent evaporates, resulting in a cured coating film 26 with an uneven, non-glossy surface, as shown in step ST5. Even if the wet coating film 25 is cured with ultraviolet light while evaporating the volatile solvent with the heat of a UV irradiator 4 instead of the heater 6, an agitation phenomenon occurs within the wet coating film 25, resulting in a cured coating film 26 with an uneven, non-glossy surface, as shown in steps ST4 and ST5. In this embodiment, the cured coating film 26 with an uneven, non-glossy surface obtained in this manner is also referred to as a first cured coating film layer 261 or a matte coating film. A matte coating film is also called a matte coating film.

[0033] The coating method of this embodiment is characterized by utilizing the agitation phenomenon that occurs during the evaporation of the volatile solvent in the ultraviolet-curable paint to apply a second cured coating film layer 262 having a smooth and glossy surface as shown in steps ST2 to ST3 (where the agitation phenomenon is not generated) and a first cured coating film layer 261 having an uneven and non-glossy surface as shown in steps ST4 to ST5 (where the agitation phenomenon is generated). Then, by forming the cured coating film 26 with the uneven and non-glossy surface of the first cured coating film layer 261 and the smooth and glossy second cured coating film layer 262, either alone or in combination, it is possible to provide a coating film with the desired decorative properties.

[0034] In the coating method of this embodiment, the second cured coating layer 262 (glossy coating) having a smooth and glossy surface as shown in step ST3 refers to a cured coating film 26 having a surface roughness (ten-point average roughness Rz according to the Japanese Industrial Standards) of less than 0.1 μm, a porosity of 0 to 20%, and a gloss (20° specular gloss according to the Japanese Industrial Standards) of 90 or more.

[0035] The surface roughness Rz in this embodiment refers to the ten-point average roughness as defined in Japanese Industrial Standards (JIS) B 0601. A reference length is extracted from the roughness curve in the direction of the mean line, and the sum of the average absolute values ​​of the elevations (Yp) of the top five highest peaks and the average absolute values ​​of the elevations (Yv) of the bottom five lowest valleys is calculated from the average line in the longitudinal direction of the roughness curve. This sum is expressed in micrometers (μm). Furthermore, the porosity in this embodiment refers to the percentage of the area of ​​voids (e.g., voids) per unit area of ​​the cross section of the cured coating film 26. This porosity can be obtained by enlarging the cross section of the cured coating film 26 and measuring the area of ​​the voids visually or otherwise.

[0036] The glossiness in this embodiment is a numerical representation of the intensity ratio between incident light and specularly reflected light when an object is irradiated with light, and refers to the 20° specular glossiness measured in accordance with the Japanese Industrial Standards Specular Gloss Measurement Method (JIS Z8741-1997). The glossiness can be measured, for example, using a gloss measuring device (MICRO-GLOSS, manufactured by BYK Gardner).

[0037] In contrast, in the coating method of this embodiment, the first cured coating film layer 261 having an uneven, non-glossy surface as shown in step ST5 refers to a cured coating film 26 having a surface roughness (ten-point average roughness Rz according to the Japanese Industrial Standards) of 0.1 to 10 μm, a porosity of 30 to 50%, and a gloss (20° specular gloss according to the Japanese Industrial Standards) of 10 or less.

[0038] Next, a coating method of this embodiment will be described. In the coating method of this embodiment, an ultraviolet curing paint is applied to a target coating surface 3 to form a wet coating film 25, and ultraviolet light is irradiated onto the wet coating film 25 to increase the porosity to P １ % or surface roughness Rz is R １ a first step of forming a first cured coating layer 261 having a thickness of P μm; a step of applying an ultraviolet curable coating material to the coating surface 3 to form a wet coating film 25, and irradiating it with ultraviolet light to increase the porosity to P ２ % (where P ２ <P １ ) or the surface roughness Rz is R ２ μm (where R ２ <R １and a second step of forming a second cured coating layer 262 having a relatively large porosity or surface roughness Rz on the coating surface 3. That is, a first cured coating layer 261 having a relatively large porosity or surface roughness Rz is formed on the target surface, or a second cured coating layer 262 having a relatively small porosity or surface roughness Rz is formed on the target surface, or both the first cured coating layer 261 and the second cured coating layer 262 are formed.

[0039] A more specific example will be described. Figures 4A to 4D are plan and cross-sectional views of a coating film showing one embodiment of a coating method using an ultraviolet-curable coating material according to the present invention. In each of Figures 4A to 4D, the left side shows a plan view of the coating surface 3, and the right side shows a cross-sectional view of the coating film.

[0040] First, in step ST11 of Fig. 4A, an ultraviolet-curable paint is applied to the entire coating surface 3 to form a wet coating film 25 of a predetermined thickness. The predetermined thickness in this case is not particularly limited, but is, for example, 5 to 50 µm. Here, the thickness of the wet coating film 25 is measured using the laser displacement meter 5 shown in Fig. 2.

[0041] In the subsequent step ST12 of Fig. 4B , a light shielding plate 8 that shields ultraviolet radiation is set on the remaining portion of the wet coating film 25 so that a portion of the wet coating film 25 applied to the coating surface 3 becomes a non-glossy first cured coating film layer 261 (matte coating film) and the remaining portion becomes a glossy second cured coating film layer 262 (gloss coating film). In this example, the coating is divided so that two diagonally opposite corners of the four rectangles become the first cured coating film layer 261 and the other two rectangles become the second cured coating film layer 262. The light shielding plate 8 that shields ultraviolet radiation is the two rectangular portions at the upper left and lower right as shown in the left diagram of Fig. 4B , and is set between the wet coating film 25 and the ultraviolet irradiator 4 as shown in the right diagram.

[0042] With the light shielding plate 8 set in this manner, ultraviolet light is irradiated onto the entire coating surface 3. The amount of ultraviolet light irradiation may be controlled according to the film thickness of the wet coating film 25 measured by the laser displacement meter 5. As a result, the wet coating film 25, which is the two rectangular portions at the bottom left and top right of the left diagram in FIG. 4B and is not shielded by the light shielding plate 8, is irradiated with ultraviolet light in a state where the amount of evaporation of the volatile solvent contained in the wet coating film 25 is less than a predetermined value, in other words, the wet coating film 25 is in a state where the volatile solvent is sufficiently contained. Therefore, when the resin component of the wet coating film 25 is photo-cured by irradiation with infrared light, an agitation phenomenon occurs, resulting in a first cured coating film layer 261 (matte coating film) with an uneven surface, as shown in step ST13 in the following FIG. 4C. While step ST12 in FIG. 4B shows an example in which ultraviolet light is irradiated onto the wet coating film formed on the coating surface 3 without heat treatment, ultraviolet light may also be irradiated after a short heat treatment of less than the first predetermined time using the heater 6 shown in FIG. 2.

[0043] In the subsequent step ST13 of FIG. 4C , the light shielding plate 8 is removed, and the entire coating surface 3 is irradiated with ultraviolet light. Here, the amount of ultraviolet light irradiation may be controlled according to the film thickness of the wet coating film 25 measured by the laser displacement meter 5. The two rectangular areas at the bottom left and top right of the left diagram of FIG. 4C are irradiated with ultraviolet light in step ST12 of FIG. 4B to form the first cured coating film layer 261, while the two rectangular areas at the top left and bottom right of the left diagram are irradiated with ultraviolet light for the first time in step ST13 and photo-cured. These two rectangular areas at the top left and bottom right of the left diagram are not irradiated with ultraviolet light from step ST11 of FIG. 4A through step ST12 of FIG. 4B to step ST13 of FIG. 4C . Therefore, the volatile solvent contained in the wet coating film 25 slowly evaporates, and ultraviolet light is irradiated onto the wet coating film 25 in a state where it contains almost no volatile solvent. As a result, no stirring phenomenon occurs when the resin component of the wet coating film 25 is photo-cured by irradiation with infrared rays, and a second cured coating film layer 262 (glossy coating film) with a smooth surface is formed, as shown in the subsequent step ST14 in Figure 4D.

[0044] As a result of the above, a coating film is obtained in which, of the four squares shown in the left diagram of Figure 4D, the two squares at the bottom left and top right are made into a non-glossy first cured coating film layer 261 (matte coating film), and the other two squares are made into a glossy second cured coating film layer 262 (glossy coating film).

[0045] Another embodiment will now be described. Figures 5A to 5D are plan and cross-sectional views of a coating film showing another embodiment of a coating method using an ultraviolet-curable coating material according to the present invention. In each of Figures 5A to 5D, the left side shows a plan view of the coating surface 3, and the right side shows a cross-sectional view of the coating film.

[0046] First, in step ST21 of Fig. 5A, an ultraviolet-curable paint is applied to the entire coating surface 3 to form a wet coating film 25 of a predetermined thickness. The predetermined thickness in this case is not particularly limited, but is, for example, 5 to 50 µm. Here, the thickness of the wet coating film 25 is measured using the laser displacement meter 5 shown in Fig. 2.

[0047] In the subsequent step ST22 of FIG. 5B , the wet coating film 25 applied to the coating surface 3 is heated by a heater 6 installed below, forcibly evaporating the volatile solvent contained in the wet coating film 25. Here, the heating temperature by the heater 6 may be controlled according to the film thickness of the wet coating film 25 measured by the laser displacement meter 5. At this time, a heat insulating plate 9 that shields heat from the heater 6 is set on part of the wet coating film 25 so that part of the wet coating film 25 becomes a non-glossy first cured coating film layer 261 (matte coating film) and the remaining part becomes a glossy second cured coating film layer 262 (gloss coating film). In this example, the coating is divided so that two of the four diagonal rectangles are the first cured coating film layer 261 and the other two rectangles are the second cured coating film layer 262. The heat insulating plates 9 that block heat from the heater 6 are the two rectangular parts at the bottom left and top right as shown in the left diagram of Figure 5B, and are set between the wet coating film 25 and the heater 6 as shown in the right diagram.

[0048] With the heat insulating plate 9 set in this state, the wet coating film 25 is heated by the heater 6. As a result, the two rectangular portions of the wet coating film 25 at the top left and bottom right of the left diagram in Figure 5B, which are not shielded by the heat insulating plate 9, are heated by the heater 6, so that the amount of evaporation of the volatile solvent contained in the wet coating film 25 is equal to or greater than a predetermined value, in other words, the wet coating film 25 contains almost no volatile solvent. In contrast, the two rectangular portions of the wet coating film 25 at the bottom left and top right of the left diagram in Figure 5B, which are shielded by the heat insulating plate 9, are not heated by the heater 6, so that the amount of evaporation of the volatile solvent contained in the wet coating film 25 is less than a predetermined value, in other words, the wet coating film 25 contains a sufficient amount of volatile solvent. Heating by the heater 6 is then terminated.

[0049] In the subsequent step ST23 of Figure 5C, ultraviolet light is irradiated onto the entire coating surface 3. The two rectangular portions at the bottom left and top right of the left diagram of Figure 5C are wet coating film 25 that was not heated by heater 6 in step ST22 of Figure 5B and contains a sufficient amount of volatile solvent, so that a stirring phenomenon occurs when the resin component of wet coating film 25 is photocured, resulting in a first cured coating film layer 261 (matte coating film) with an uneven surface, as shown in the subsequent step ST24 of Figure 5D. In contrast, the two rectangular portions at the top left and bottom right of the left diagram are wet coating film 25 that was heated by heater 6 in step ST22 of Figure 5B and contains almost no volatile solvent, so that a stirring phenomenon does not occur when the resin component of wet coating film 25 is photocured, resulting in a second cured coating film layer 262 (glossy coating film) with a smooth surface, as shown in the subsequent step ST24 of Figure 5D.

[0050] As a result of the above, a coating film is obtained in which, of the four rectangles shown in the left diagram of Figure 5D, the two rectangles at the bottom left and top right are made into a non-glossy first cured coating film layer 261 (matte coating film), and the other two rectangles are made into a glossy second cured coating film layer 262 (glossy coating film).

[0051] As described above, the coating method and coating system S using ultraviolet-curable paint of this embodiment includes at least one of the following steps: a first step of applying ultraviolet-curable paint to a target coating surface and irradiating it with ultraviolet light to form a first cured coating layer having a porosity of 30 to 50% or a surface roughness Rz of 0.1 to 10 μm; and a second step of applying ultraviolet-curable paint to the coating surface and irradiating it with ultraviolet light to form a second cured coating layer having a porosity of 0 to 20% or a surface roughness Rz of less than 0.1 μm.Therefore, it is possible to coat the glossy surface, which is the second cured coating layer 262, and the non-glossy surface, which is the first cured coating layer 261, in a manner that allows for thicker films to be formed.

[0052] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, in the first step, ultraviolet rays are irradiated when the amount of evaporation of the solvent contained in the wet coating film 25 applied to the coating surface 3 is less than a predetermined value, and in the second step, ultraviolet rays are irradiated when the amount of evaporation of the solvent contained in the wet coating film applied to the coating surface 3 is equal to or greater than the predetermined value, so that the glossy surface which is the second cured coating film layer 262 and the non-glossy surface which is the first cured coating film layer 261 can be painted differently, allowing for thicker films to be formed.

[0053] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, in the first step, ultraviolet rays are irradiated to the wet coating film 25 without heat treatment, or ultraviolet rays are irradiated after heat treatment for less than a first predetermined time, so that the amount of evaporation of the solvent contained in the wet coating film 25 applied to the coating surface 3 is less than a predetermined value, thereby making it possible to generate the first cured coating film layer 261 more reliably.

[0054] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, in the second step, the wet coating film 25 is subjected to a heat treatment for a first predetermined time or more before being irradiated with ultraviolet light so that the amount of evaporation of the solvent contained in the wet coating film 25 applied to the surface of the first cured coating film layer 261 reaches a predetermined value or more, or ultraviolet light is irradiated after a time exceeding a second predetermined time has elapsed since the application of the ultraviolet-curable paint, thereby making it possible to generate the second cured coating film layer 262 even more reliably.

[0055] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, the amount of ultraviolet radiation is controlled according to the film thickness of the wet coating film 25 applied to the coating surface 3, so that it is possible to coat the glossy surface, which is the second cured coating film layer 262, and the non-glossy surface, which is the first cured coating film layer 261, with even greater thicknesses.

[0056] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, the heating temperature of the wet coating film 25 applied to the coating surface 3 is controlled according to the film thickness of the wet coating film 25, so that it is possible to coat the glossy surface, which is the second cured coating film layer 262, and the non-glossy surface, which is the first cured coating film layer 261, with even greater thicknesses.

[0057] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, a first cured coating film layer 261 is formed on a portion of the coating surface 3, and a second cured coating film layer 262 is formed on the remaining portion of the coating surface 3, so that the glossy surface which is the second cured coating film layer 262 and the non-glossy surface which is the first cured coating film layer 261 can be painted even thicker.

[0058] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, the ultraviolet-curable paint is applied to the entire coating surface 3, ultraviolet rays are irradiated onto a portion of the coating surface 3 while blocking ultraviolet irradiation to the remaining portion of the coating surface 3, forming a first cured coating layer 261 on that portion of the coating surface 3, and then ultraviolet rays are irradiated onto the remaining portion of the coating surface 3 to form a second cured coating layer 262.This makes it possible to coat the glossy surface, which is the second cured coating layer 262, and the non-glossy surface, which is the first cured coating layer 261, in a manner that allows for even thicker films to be formed.

[0059] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, the ultraviolet-curable paint is applied to the entire coating surface 3, a portion of the coating surface 3 is heated while the portion is insulated, and then ultraviolet rays are irradiated onto the entire coating surface 3, so that the glossy surface which is the second cured coating film layer 262 and the non-glossy surface which is the first cured coating film layer 261 can be painted even thicker.

[0060] Furthermore, according to the coating method and coating system S using the ultraviolet-curable paint of this embodiment, since the target coating surface 3 is an automobile body or an automobile part, the desired coating surface of the automobile body or automobile part can be painted separately into a glossy surface which is the second cured coating film layer 262 and a non-glossy surface which is the first cured coating film layer 261, allowing for a thick film to be formed.

[0061] REFERENCE SIGNS LIST 1... Inkjet coating device 11... Nozzle 111... Introduction section 112... Paint chamber 113... Discharge section 114... Housing 12... Needle 121... Tip section 122... Base section 123... Sealing member 13... Actuator 14... Pressure sensor 15... Control section 2... Paint 21... Paint tank 22... Paint piping 23... Paint pump 24... Droplet 25... Wet coating film 26... Cured coating film 261... First cured coating film layer (matte coating film) 262... Second cured coating film layer (glossy coating film) 3... Coating surface 4... Ultraviolet irradiator 5... Laser displacement meter 6... Heater 7... Controller 8... Light shielding plate 9... Heat insulating plate S... Coating system

Claims

1. a first step of applying an ultraviolet-curable coating material to a target coating surface and irradiating the coating surface with ultraviolet light to form a first cured coating layer having a porosity of 30 to 50% or a surface roughness Rz of 0.1 to 10 μm; a second step of applying an ultraviolet-curable paint to the coating surface and irradiating it with ultraviolet light to form a second cured coating film layer having a porosity of 0 to 20% or a surface roughness Rz of less than 0.1 μm.

2. In the first step, ultraviolet light is irradiated in a state where the amount of evaporation of the solvent contained in the wet coating film applied to the coating surface is less than a predetermined value, 2. A coating method using an ultraviolet-curable paint according to claim 1, wherein in the second step, ultraviolet light is irradiated when the amount of evaporation of the solvent contained in the wet coating film applied to the coating surface is equal to or greater than the predetermined value.

3. In the first step, Irradiating the wet coating film with ultraviolet light without heat treatment so that the amount of evaporation of the solvent contained in the wet coating film applied to the coating surface becomes less than the predetermined value, or 3. A coating method using an ultraviolet curable coating material according to claim 1, wherein the coating material is subjected to a heat treatment for a period of time shorter than the first predetermined time, followed by irradiation with ultraviolet light.

4. In the second step, or, after subjecting the wet coating film to heat treatment for the first predetermined time or more so that the amount of evaporation of the solvent contained in the wet coating film applied to the coating surface becomes equal to or greater than the predetermined value, irradiating the wet coating film with ultraviolet light; 4. The coating method using ultraviolet curable paint according to claim 3, wherein the ultraviolet ray is irradiated after a time exceeding a second predetermined time has elapsed since the application of the ultraviolet curable paint.

5. 3. A coating method using an ultraviolet-curable coating material according to claim 1, wherein the amount of ultraviolet radiation is controlled according to the thickness of the wet coating film applied to the coating surface.

6. 3. A coating method using an ultraviolet-curable coating material according to claim 1, wherein the heating temperature of the wet coating film is controlled in accordance with the thickness of the wet coating film applied to the coating surface.

7. 3. The coating method using an ultraviolet-curable coating material according to claim 1, wherein the first cured coating film layer is formed on a portion of the coating surface, and the second cured coating film layer is formed on the remaining portion of the coating surface.

8. The ultraviolet-curable coating material is applied to the entire coating surface, and ultraviolet light is irradiated onto a portion of the coating surface while blocking ultraviolet light irradiation onto the remaining portion of the coating surface, thereby forming the first cured coating film layer on that portion of the coating surface, and then The coating method using an ultraviolet-curable coating material according to claim 7, wherein the second cured coating layer is formed by irradiating the remaining part of the coating surface with ultraviolet light.

9. The ultraviolet curable paint is applied to the entire coating surface, and a portion of the coating surface is heated while the portion of the coating surface is insulated, and then 8. The coating method using an ultraviolet-curable coating material according to claim 7, wherein the entire coating surface is irradiated with ultraviolet light.

10. 3. A coating method using an ultraviolet-curable coating material according to claim 1, wherein the surface to be coated is an automobile body or an automobile part.

11. A coating device that applies ultraviolet curing paint to a target coating surface; a heater for heating the wet coating film applied to the coating surface; an ultraviolet irradiator that irradiates ultraviolet light onto the wet coating film applied to the coating surface; Applying an ultraviolet-curable coating material to the coating surface and irradiating it with ultraviolet light to form a first cured coating layer having a porosity of 30 to 50% or a surface roughness Rz of 0.1 to 10 μm; or a controller that controls the coating device, the heater, and the ultraviolet irradiator so as to coat the coating surface with an ultraviolet curable paint and irradiate it with ultraviolet light to form a second cured coating film layer having a porosity of 0 to 20% or a surface roughness Rz of less than 0.1 μm.