Coating method with excellent coating efficiency

Abstract

The present invention addresses the problem of providing a non-electrostatic air atomization coating method using an automatic coating gun, in which coating efficiency is 80% or more, reproducibility of the coating efficiency is good, excellent coating film appearance can be obtained, and noise during coating is reduced. As a solution, the present invention provides a non-electrostatic air atomization coating method using an automatic coating gun, wherein the coating method satisfies the following requirements: (1) the coating efficiency is 80% or more; and (2) the gun distance is 20-90 mm. The coating method further satisfies the following requirements: (3a) the atomization air pressure is 0.013-0.070 MPa∙s and the pattern air pressure is 0.020-0.100 MPa∙s; and / or (3b) the atomization air flow rate is 5-25 L / min and the pattern air flow rate is 2-35 L / min.

Description

Coating method excellent in coating efficiency

[0001] The present invention relates to a coating method excellent in coating efficiency. Specifically, the present invention relates to a coating method having a coating efficiency of 80% or more, preferably 85% or more.

[0002] Coating can dramatically extend the service life (life cycle) of products by preventing product deterioration caused by rust and ultraviolet rays, and further can impart added value to products by improving design properties, functions and the like. In industrial coating, for example, at coating sites for plastic products, spray coating, in which liquid coating material is atomized and applied, is employed from the viewpoints of finished quality of the coating film and workability. On the other hand, coating materials used for coating are mainly petrochemical products, and CO from production to disposal ２ emission has become a major social problem. In coating, CO ２ As a solution for reducing and suppressing [[x]], improving coating efficiency is an extremely important approach. If coating efficiency can be improved and the amount of coating material wasted without being deposited can be reduced, the generation of coating (material) waste such as booth sludge and VOC (volatile organic compounds) can be suppressed, along with CO ２ emissions can also be suppressed, which is advantageous from an environmental perspective. Furthermore, it also enables reduction of raw material costs. However, conventional spray coating has a coating efficiency of only about 60% at most, and improvement of coating efficiency has been an issue.

[0003] As prior art related to improvement of coating efficiency, for example, the following Patent Documents 1 to 3 can be mentioned. Patent Document 1 describes a coating method excellent in coating efficiency, wherein when coating a substrate having irregularities on the surface, after coating using a sponge roll wrapped with cloth, air is blown to the recesses of the substrate to scatter the coating material accumulated in the recesses.

[0004] Patent Document 2 discloses a liquid spraying method that can be applied to an object with high coating efficiency, comprising the steps of: discharging at least one liquid from a liquid discharge port; ejecting a first compressed gas from a first compressed gas outlet provided around the liquid discharge port to atomize the liquid discharged from the liquid discharge port and create a particle ejection flow; and ejecting a second compressed gas from a plurality of second compressed gas outlets toward the liquid particle ejection flow, causing at least a portion of the second compressed gas to collide with the liquid particle ejection flow, thereby causing the liquid particle ejection flow to swirl and atomize it into fine particles.

[0005] Patent Document 3 discloses a method for applying metallic paint in an automobile topcoat base coating process, which involves using a bell-type coating apparatus and supplying shaping air to the bell-type coating apparatus at an air pressure of 196 to 294 kPa and an air flow rate of 500 to 700 NL / min to form a coating film that provides substrate concealment and a metallic feel, and has high coating efficiency.

[0006] Japanese Patent Publication No. 2005-111314, Japanese Patent Publication No. 2004-089976, Japanese Patent Publication No. Hei 11-300239

[0007] The coating method described in Patent Document 1 is a roll coating method, making it difficult to form a coating film with a high visual evaluation, and therefore cannot be applied to coating methods other than roll coating. The coating method described in Patent Document 2 is complex in terms of its apparatus and control. The coating method described in Patent Document 3 is a technology specific to bell-type coating apparatuses and cannot be applied to coating methods that do not use bell-type coating apparatuses.

[0008] In industrial painting, CO ２ To reduce and control emissions, it is necessary to significantly increase coating efficiency. Therefore, it is necessary to establish advanced coating technologies that offer superior coating efficiency, such as "electrostatic atomization" or "hydraulic spraying," or to establish coating technologies that solve the problem of splashing in "air atomization" while maintaining appearance quality. However, electrostatic atomization cannot be applied to non-conductive substrates, and hydraulic spraying is difficult to apply to large-area coatings.

[0009] In industrial painting, particularly in the painting of plastic parts, spray painting, which atomizes liquid paint for application, is widely adopted from the standpoint of paint finish quality and workability. Among the atomization methods for liquid paint, the most common conventional method is air atomization, which atomizes the liquid paint by discharging high-pressure compressed air along with the paint from the tip of the nozzle, thereby forming a homogeneous paint film with a high level of appearance evaluation. While air atomization can form a high-quality paint film and offers good workability, it has low coating efficiency, high paint loss, a large environmental impact, and noise problems, so improvements have been desired.

[0010] The problem that this invention aims to solve is to provide a non-electrostatic air atomization coating method using an automatic paint gun that has a coating efficiency of 80% or more, good reproducibility of coating efficiency, can produce a superior coating film appearance, and reduces noise during coating.

[0011] The inventors of this invention conducted diligent research to solve the above problems. They found that the above problems could be solved by adopting specific coating conditions. Specifically, these conditions are as follows.

[0012] [Item 1] A non-electrostatic air atomization coating method using an automatic paint gun, wherein the following requirements (1) and (2): (1) a coating efficiency of 80% or more, (2) a gun distance of 20 mm to 90 mm, and further satisfying the following requirements (3a) and / or (3b): (3a) an atomizing air pressure of 0.013 MPa·s to 0.070 MPa·s and a pattern air pressure of 0.020 MPa·s to 0.100 MPa·s, and (3b) an atomizing air flow rate of 5 L / min to 25 L / min and a pattern air flow rate of 2 L / min to 35 L / min, the coating method. [Item 2] The painting method described in Item 1, further satisfying one or more of the following requirements (4) to (7): (4) The paint supply amount is 7 mL / min to 55 mL / min; (5) The viscosity of the paint used for painting, measured by the Iwata Cup method, is 5 seconds to 13 seconds; (6) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, wherein the evaporation rate is 140 to 1100 when the value of butyl acetate is set to 100; (7) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, wherein the boiling point at a pressure of 0.1 MPa is 150°C or higher. [Item 3] The painting method described in Item 1 or 2, wherein multiple coats are applied. [Item 4] The painting method described in any one of Items 1 to 3, wherein multiple coats are applied so that the center positions of the coatings are different.

[0013] The present invention provides a non-electrostatic air atomization coating method using an automatic paint gun, which has a coating efficiency of 80% or more, good reproducibility of coating efficiency, can produce a superior coating film appearance, and reduces noise during coating.

[0014] A schematic diagram of one embodiment of the coating system used in the coating method of the present invention. A schematic diagram of one embodiment of the coating system used in the coating method of the present invention. A schematic diagram of the air cap type M attached to the automatic coating gun of the present invention. A schematic diagram of the round air cap type 1 attached to the automatic coating gun of the present invention. A diagram showing the film thickness distribution of a coated object obtained by the coating method of Example D1 of the present invention.

[0015] The present invention relates to a non-electrostatic air atomization coating method using an automatic coating gun, which satisfies the following requirements (1) and (2): (1) a coating efficiency of 80% or more, and (2) a gun distance of 20 mm to 90 mm, and further satisfies the following requirements (3a) and / or (3b): (3a) an atomizing air pressure of 0.013 MPa·s to 0.070 MPa·s and a pattern air pressure of 0.020 MPa·s to 0.100 MPa·s, and (3b) an atomizing air flow rate of 5 L / min to 25 L / min and a pattern air flow rate of 2 L / min to 35 L / min.

[0016] The coating method of the present invention may further satisfy one or more of the following requirements (4) to (7): (4) The paint supply amount is 7 mL / min to 55 mL / min; (5) The viscosity of the paint used for coating by the Iwata Cup method is 5 seconds to 13 seconds; (6) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, and the evaporation rate value is 140 to 1100 when the value of butyl acetate is set to 100; (7) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, and the boiling point at a pressure of 0.1 MPa is 150°C or higher.

[0017] The painting method of the present invention may involve applying multiple coats. The painting method of the present invention may also involve applying multiple coats so that the center position of the paint is different from that of the previous coat.

[0018] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and examples, and can be implemented with appropriate modifications.

[0019] [(1) Coating Efficiency] In the coating method of the present invention, coating efficiency is a value expressed as a percentage (%) of the ratio of the amount of solid matter in the paint used for coating to the amount of solid matter in the paint applied to the product. Coating efficiency is given by the following formula (I), where E (%) is the coating efficiency, W (g) is the mass of the applied dry coating film, F (g) is the amount of paint sprayed, and NV (%) is the solid content of the paint: It is calculated by the following method.

[0020] In equation (I), the mass W (g) of the applied dry coating can be calculated by subtracting the mass (g) of the substrate before coating from the mass (g) of the substrate on which the dry coating was formed.

[0021] In equation (I), the paint spray volume F(g) can be calculated by, for example, using a flow meter installed in the paint flow path, first determining a conversion factor using the integrated value of the instantaneous paint flow rate measured by the flow meter and the actually measured paint flow rate, then multiplying the integrated value of the instantaneous flow rate during painting by the conversion factor to calculate the flow rate, and then using the specific gravity of the paint to calculate the paint spray volume F(g). Alternatively, in equation (I), the paint spray volume F(g) can also be calculated by determining the total amount W1(g) of paint in the paint tank before painting, the total amount W2(g) of paint in the paint tank after painting, and the total amount W3(g) of paint remaining in the painting system (in the paint gun) after painting, and then using the specific gravity of the paint to calculate the paint spray volume F(g).

[0022] The solid content NV (%) of the paint can be determined using the paint's catalog value, or it can be calculated from the difference between the mass (g) of the test board immediately after applying a specified amount (ml) of paint and the mass (g) of the test board after drying and forming the paint film.

[0023] In the coating method of the present invention, the coating efficiency is 80% or more. Preferably, it is 82% or more, and more preferably 85% or more. The upper limit of the coating efficiency is theoretically 100%, and usually 97% or less.

[0024] [(2) Gun Distance] In the painting method of the present invention, (B) gun distance is the distance from the paint discharge port of the automatic painting gun to the object to be painted. In the painting method of the present invention, the gun distance is 20 mm to 90 mm. The lower limit of the gun distance can be 20 mm or more, preferably 25 mm or more, more preferably 30 mm or more, and even more preferably 40 mm or more, and the upper limit of the gun distance can be 90 mm or less, preferably 80 mm or less, more preferably 75 mm or less, and even more preferably 70 mm or less.

[0025] By setting the gun distance to 20 mm to 90 mm or less, the paint can be reliably applied to the object to be painted, splashing from the object can be prevented, and the painting efficiency can be improved. Until now, in painting using automatic paint guns, the gun distance has been set to 100 mm or more (see, for example, the website of Meiji Machine Works Co., Ltd. https: / / www.meijiair.co.jp / product / gun / detail / 73). The painting method of the present invention enables improvement in painting efficiency from a completely different technical perspective than before.

[0026] [(3a) Atomizing air pressure and pattern air pressure] In the painting method of the present invention, the atomizing air pressure in the automatic painting gun can be set to 0.013 MPa·s to 0.070 MPa·s, and the pattern air pressure in the automatic painting gun can be set to 0.020 MPa·s to 0.100 MPa·s.

[0027] If the atomizing air pressure in an automatic paint gun is less than 0.013 MPa·s, the paint workability may decrease, and it may become impossible to properly spray the paint. If the atomizing air pressure in an automatic paint gun exceeds 0.070 MPa·s, the sprayed paint may bounce back, reducing the coating efficiency, and it may become impossible to properly spray the paint.

[0028] If the pattern air pressure in an automatic paint gun is less than 0.020 MPa·s, it may become difficult to achieve an appropriate spray shape for the paint ejected from the automatic paint gun, potentially resulting in improper paint ejection. If the pattern air pressure in an automatic paint gun exceeds 0.070 MPa·s, it may become difficult to achieve an appropriate spray shape for the paint ejected from the automatic paint gun, potentially causing the ejected paint to bounce back and reducing the coating efficiency, potentially resulting in improper paint ejection.

[0029] The lower limit of the atomizing air pressure in an automatic paint gun is preferably 0.010 MPa or higher, more preferably 0.011 MPa or higher, and even more preferably 0.012 MPa or higher. The upper limit of the atomizing air pressure in an automatic paint gun is preferably 0.065 MPa or lower, more preferably 0.060 MPa or lower, and even more preferably 0.055 MPa or lower.

[0030] The lower limit of the pattern air pressure in an automatic paint gun is preferably 0.022 MPa or higher, more preferably 0.025 MPa or higher, and the upper limit of the pattern air pressure in an automatic paint gun is preferably 0.095 MPa or lower, more preferably 0.090 MPa or lower.

[0031] In the painting method of the present invention, both the atomizing air pressure and the pattern air pressure are pressures in the automatic paint gun. The atomizing air pressure and pattern air pressure in the automatic paint gun can be confirmed by installing pressure gauges near the automatic paint gun in the atomizing air piping and pattern air piping. Specifically, pressure gauges can be installed in a position that is not affected by pressure loss in the atomizing air piping and pattern air piping. Alternatively, the atomizing air pressure and pattern air pressure in the automatic paint gun may be calculated by obtaining in advance the relationship of pressure loss occurring between the pressure adjustment mechanism and the automatic paint gun. If the atomizing air piping and pattern air piping become long, and the distance between the automatic paint gun and the automatic paint gun controller becomes long, the effects of pressure loss may cause errors between the atomizing air pressure and pattern air pressure in the automatic paint gun controller and the atomizing air pressure and pattern air pressure in the automatic paint gun, which may prevent accurate control of the painting process.

[0032] [(3b) Atomizing air flow rate and pattern air flow rate] In the painting method of the present invention, the atomizing air flow rate supplied to the automatic painting gun can be set to 5 L / min to 25 L / min, and the pattern air flow rate supplied to the automatic painting gun can be set to 2 L / min to 35 L / min.

[0033] If the atomizing air flow rate supplied to the automatic paint gun is less than 5 L / min, painting workability may decrease, and it may become impossible to properly spray the paint. If the atomizing air flow rate supplied to the automatic paint gun exceeds 25 L / min, the sprayed paint may bounce back, reducing the coating efficiency, and it may become impossible to properly spray the paint.

[0034] If the pattern air flow rate supplied to the automatic paint gun is less than 5 L / min, it may become difficult to achieve an appropriate spray shape for the paint ejected from the automatic paint gun, potentially resulting in improper paint ejection. If the pattern air flow rate supplied to the automatic paint gun exceeds 35 L / min, it may become difficult to achieve an appropriate spray shape for the paint ejected from the automatic paint gun, potentially causing the ejected paint to bounce back and reducing the coating efficiency, potentially resulting in improper paint ejection.

[0035] The lower limit of the atomizing air flow rate is preferably 7 L / min or more, more preferably 10 L / min or more, and even more preferably 12 L / min or more. The upper limit of the atomizing air pressure in the automatic painting gun is preferably 22 L / min or less, more preferably 20 L / min or less, and even more preferably 18 L / min or less.

[0036] The lower limit of the pattern air flow rate can preferably be 3 L / min or more, more preferably 4 L / min or more, and even more preferably 5 L / min or more, and the upper limit of the atomizing air pressure in the automatic painting gun can preferably be 32 L / min or less, more preferably 30 L / min or less, and even more preferably 28 L / min or less.

[0037] In the painting method of the present invention, the atomizing air flow rate and pattern air flow rate supplied to the automatic paint gun can be confirmed by installing flow meters in the atomizing air piping and pattern air piping. Even if the atomizing air piping and pattern air piping are long, the atomizing air flow rate and pattern air flow rate at any point in the piping will remain constant. Therefore, when controlling the automatic paint gun using the atomizing air flow rate and pattern air flow rate, painting can be accurately controlled without considering the effects of pressure loss.

[0038] [(4) Paint supply amount] In the painting method of the present invention, the amount of paint supplied to the automatic paint gun can be 7 mL / min to 55 mL / min.

[0039] If the paint supply rate to the automatic paint gun is less than 7 mL / min, the painting workability may decrease, and it may become impossible to spray the paint properly. If the paint supply rate to the automatic paint gun exceeds 55 mL / min, it may become difficult to maintain an appropriate spray shape for the paint sprayed from the automatic paint gun, the sprayed paint may bounce back, reducing the coating efficiency, and it may become impossible to spray the paint properly.

[0040] The lower limit of the paint supply amount can preferably be 8 mL / min or more, more preferably 10 mL / min or more, and even more preferably 12 mL / min or more, and the upper limit of the paint supply amount can preferably be 45 mL / min or less, more preferably 42 mL / min or less, and even more preferably 40 mL / min or less.

[0041] [(5) Viscosity of paint] In the painting method of the present invention, the paint used for painting is a paint whose viscosity by the Iwata Cup method is 5 seconds to 13 seconds. In the painting method of the present invention, the viscosity of the paint used for painting is the viscosity at the time the paint is prepared to be used for painting, and is measured using the Iwata Cup.

[0042] If the viscosity of the coating material used for coating measured by the Iwata cup method is less than 5 seconds, pinholes and sagging may occur in the dried coating film, which may reduce coating workability. If the viscosity of the coating material used for coating measured by the Iwata cup method exceeds 13 seconds, orange peel texture and poor appearance may occur in the dried coating film.

[0043] In the coating method of the present invention, the viscosity measured by the Iwata cup method is a viscosity measured using a viscosity cup NK-2 manufactured by Anest Iwata Corporation, and is the viscosity at the temperature and pressure of the coating environment. The viscosity measurement is performed by: after submerging the viscosity cup in the coating material, pulling the viscosity cup up from the coating material, and measuring the time (in seconds) from pulling up the viscosity cup until the outflow of the coating material in the viscosity cup is interrupted. For reactive coating materials, the measurement is performed within 5 minutes after the coating material is prepared.

[0044] [(6) Evaporation rate of organic solvent contained in coating material] In the coating method of the present invention, the coating material used for coating may contain one or more organic solvents selected from the group consisting of ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, wherein the evaporation rate of the organic solvent is 140 or more and 1100 or less when the evaporation rate of butyl acetate is defined as 100.

[0045] When the coating material used for coating contains one or more organic solvents selected from the group consisting of ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, it is less likely to adversely affect the environment and the health of workers, and is advantageous in terms of safety and other aspects. When the coating material used for coating contains an organic solvent whose evaporation rate is 140 or more and 1100 or less when the evaporation rate of butyl acetate is defined as 100, the drying speed of the coating film can be made appropriate, and a coating film with excellent appearance can be formed.

[0046] It is preferable that the coating material used for coating contains one or more selected from the group consisting of ketone-based organic solvents and ester-based organic solvents.

[0047] The lower limit of the evaporation rate, when the value of butyl acetate in the organic solvent contained in the paint used for painting is set to 100, is preferably 150 or more, more preferably 200 or more, and even more preferably 350 or more. The upper limit of the evaporation rate, when the value of butyl acetate in the organic solvent contained in the paint used for painting is set to 100, is preferably 1000 or less, more preferably 900 or less, and even more preferably 800 or less.

[0048] One or more organic solvents, including ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, whose evaporation rate is 140 to 1100 when the value of butyl acetate is set to 100, include, for example, acetone (evaporation rate 720), methyl ethyl ketone (evaporation rate 465), methyl isobutyl ketone (evaporation rate 165), methyl alcohol (evaporation rate 370), ethyl alcohol (203), isopropyl alcohol (205), methyl acetate (evaporation rate 1040), ethyl acetate (evaporation rate 525), isobutyl acetate (evaporation rate 145), ethyl tert-butyl ether (evaporation rate 717), diisopropyl ether (evaporation rate 662), methyl tert-butyl ether (evaporation rate 1167), 2-methylfuran (evaporation rate 488), methylcyclohexane (evaporation rate 320), and ethylcyclohexane (evaporation rate 145).

[0049] [(7) Boiling point of organic solvent contained in the paint] In the painting method of the present invention, the paint used for painting may contain one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, the organic solvent having a boiling point of 150°C or higher at a pressure of 0.1 MPa.

[0050] When the paint used for coating contains one or more organic solvents, such as ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, and has a boiling point of 150°C or higher at a pressure of 0.1 MPa, the orientation of pigments in the paint, such as flake-shaped pigments, can be adjusted, the drying speed of the coating film can be made appropriate, and a coating film with an excellent appearance can be formed.

[0051] The paint used for coating preferably contains one or more ether-based organic solvents and ester-based organic solvents.

[0052] One or more organic solvents, including ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents, and aliphatic hydrocarbon-based organic solvents, having a boiling point of 150°C or higher at a pressure of 0.1 MPa, include, for example, ketone-based organic solvents such as diisobutyl ketone, cyclohexanone, diacetone alcohol, and γ-butyrolactone; and 1-octanol, 2-ethylhexanol, 1-nonanol, 1-decanol, 1-undecanol, ethylene glycol, 1,2-propylene glycol, and 1,3-butylene glycol. Alcohol-based organic solvents such as 2,4-pentanediol, 2-methyl-2,4-pentanediol, 2,5-hexanediol, 2,4-heptanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, glycerin; monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monoethyl ether Ether-based organic solvents such as diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol monomethyl ether, triethylene glycol n-butyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-n-butyl ether, tripropylene glycol dimethyl ether, tripropylene glycol mono-n-propyl ether, tripropylene glycol mono-n-butyl ether, etc.Examples of ester-based organic solvents include ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, triacetin, propylene glycol diacetate, dipropylene glycol methyl-n-propyl ether, dipropylene glycol methyl ether acetate, 1,4-butanediol diacetate, 1,3-butylene glycol diacetate, 1,6-hexanediol diacetate, triethylene glycol diacetate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, dihexyl malonate, diethyl succinate, dipropyl succinate, dibutyl succinate, dihexyl succinate, dimethyl adipate, diethyl adipate, dibutyl adipate, ethyl lactate, nonyl acetate, and other similar ester-based organic solvents; and one or more such solvents.

[0053] [Overcoating] In the painting method of the present invention, overcoating may be performed. Overcoating can be done by painting the object to be painted two or more times. When overcoating by painting two or more times, a drying step may be provided in between, or it may be done wet on wet without a drying step in between, or a combination of these may be performed. In the painting method of the present invention, overcoating may be performed so that the center position of the paint is different from that of the previous painting, or so that the center position of the paint is the same as that of the previous painting, or a combination of these may be performed. In the painting method of the present invention, it is preferable to perform overcoating in order to improve uniform film thickness and finish. When overcoating, by performing overcoating so that the center position of the paint is different from that of the previous painting, the paint ejection pattern width from the automatic paint gun can be overlapped to some extent, and a paint film with a uniform film thickness can be formed. When overcoating, it is preferable to prevent paint particles that have been oversprayed from adhering to the previously painted surface and causing roughness.

[0054] [Paint] The paint used in the painting method of the present invention is not particularly limited. Commercially available paints may be used, or newly formulated paints may be used. The paint used in the painting method of the present invention contains at least a resin component, and may optionally contain a hardening agent component, pigment, solvent, or other additive components. The paint used in the painting method of the invention may be any of the following: solvent-based paint, emulsion (dispersion) type paint, solvent-free paint, one-component paint, or two-component paint.

[0055] The resin component is a component that functions as a coating film-forming element. Conventional resin components known as paint components can be used as the resin component. Examples of resin components include one or more acrylic resins, polyester resins, alkyd resins, fluororesins, epoxy resins, polyurethane resins, polyether resins, olefin resins, epoxy resins, vinyl chloride resins, silicone resins, and alkoxysilane condensates.

[0056] Examples of curing agent components include curing agent components that react with the reactive groups in the resin component. The curing agent component can be selected according to the reactive groups in the resin component. For example, one or more of the following can be selected: polyisocyanate compounds, amino resins, polyamine compounds, polycarboxylic acid compounds, polyol compounds, melamine compounds, epoxy compounds, aldehyde compounds, aziridine compounds, carbodiimide compounds, hydrazine compounds, etc., which may be blocked by a blocking agent.

[0057] Examples of pigments include coloring pigments for coloring paints and filler pigments. Examples of coloring pigments include one or more inorganic pigments such as titanium dioxide, red iron oxide, and carbon black, organic pigments such as phthalocyanine blue, dyes, and fluorescent pigments. Examples of filler pigments include one or more extender pigments such as calcium carbonate, talc, mica, and silica, and rust-preventive pigments.

[0058] As a solvent, conventionally known solvents that constitute paints can be used. As a solvent, for example, those listed as solvents that satisfy requirement (6) or requirement (7) above can be used. Specifically, alcohol-based organic solvents such as methanol, ethanol, 2-propanol, 1-butanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, pentamethylene glycol, 1,3-octylene glycol; ester-based organic solvents such as ethyl acetate, butyl acetate, isobutyl acetate, ethyl propionate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate; diethyl ether, propylene glycol monomethyl ether, ethylene glycol Examples of organic solvents include ether-based organic solvents such as chloroform monoethyl ether, dioxane, and tetrahydrofuran (THF); amide-based organic solvents such as formamide, N-methylformamide, dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP); ketone-based organic solvents such as acetone, methyl ethyl ketone (MEK), methyl propyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aliphatic hydrocarbons such as mineral spirits and kerosene; aromatic hydrocarbons such as toluene, xylene, mesitylene, and dodecylbenzene; and halogenated organic solvents such as chloroform and dichloromethylene.

[0059] In addition to resin components, hardening agents, pigments, and solvents, paints may contain one or more of the following components: dispersants, film-forming aids, antifreezes, crosslinking accelerators, hardening agents, leveling agents, surface modifiers, defoamers, plasticizers, preservatives, fungicides, and UV stabilizers.

[0060] [Substrate] In the coating method of the present invention, the material constituting the substrate to which the paint is applied is not particularly limited. Examples include various plastics, metals such as iron and aluminum, glass, ceramics, concrete, paper, wood, etc., and may also be composite materials such as laminates or compositions composed of one or more of these. The coating method of the present invention can be suitably used for coating plastics, metals, glass, wood, and composite materials composed of one or more of these.

[0061] In the painting method of the present invention, the shape of the object to be painted is not particularly limited. Examples include plates, films, rods, and various molded products. Examples include vehicle parts, building interior materials, household goods, and electrical equipment parts.

[0062] If the surface of the object to be coated is contaminated with oil or other contaminants, it can be degreased and cleaned with alcohol or the like. Furthermore, the object to be coated may undergo surface treatments such as roughening, plasma treatment, flame treatment, or primer treatment to improve the adhesion of the coating and the corrosion resistance of the painted object.

[0063] [Painting System] Figures 1 and 2 are schematic diagrams of a painting system suitable for carrying out the painting method of the present invention. Hereinafter, embodiments of a painting system suitable for carrying out the painting method of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. Furthermore, it is possible to make appropriate modifications without departing from the scope in which the effects of the present invention are achieved. Note that the use of the same reference numeral in different drawings indicates similar or identical items or features.

[0064] Figure 1 is a schematic diagram showing one embodiment of a painting system suitable for implementing the painting method of the present invention using a general automatic paint gun. In Figure 1, G1 is an automatic paint gun, and S is a paint pattern sprayed from the automatic paint gun. The automatic paint gun G1 is connected to a needle valve operating air pipe 12, an atomizing air pipe 13, and a pattern air pipe 14, which are supplied with air from a compressor 11. The automatic paint gun G1 is also connected to a paint pipe 25 that supplies paint 21 from a paint tank 22. Furthermore, although not shown, a controller is provided to control the air in each air pipe and the paint in the paint pipe, and a three-way valve or the like is provided as needed.

[0065] The atomizing air piping 13 is equipped with an atomizing air pressure adjustment mechanism 15a, a first atomizing air flow rate / pressure sensor 16a located near the automatic paint gun G1 side of the atomizing air pressure adjustment mechanism 15a, and a second atomizing air flow rate / pressure sensor 17a located near the automatic paint gun G1. The pressure of the air from the compressor 11 is adjusted by the atomizing air pressure adjustment mechanism 15a, and the operation of the atomizing air pressure adjustment mechanism 15a is controlled by the measurement value of the first atomizing air flow rate / pressure sensor 16a. In addition, the pressure and / or flow rate of the atomizing air supplied to the automatic paint gun G is measured by the second atomizing air flow rate / pressure sensor 17a. Note that the atomizing air pressure adjustment mechanism 15a may be part of the control mechanism of the painting device (automatic paint gun).

[0066] The atomizing air pressure adjustment mechanism 15a can be controlled by a computer or the like, if necessary. Furthermore, the operating data and measured values ​​of the atomizing air pressure adjustment mechanism 15a, the first atomizing air flow rate / pressure sensor 16a, and the second atomizing air flow rate / pressure sensor 17a may be sent to a controller or storage means (not shown) for controlling the atomizing air pressure / flow rate, pattern air pressure / flow rate, paint flow rate, etc., as needed, for control and recording.

[0067] The pattern air piping 14 is equipped with a pattern air pressure adjustment mechanism 15b, a first pattern air flow rate / pressure sensor 16b located near the automatic paint gun G side of the pattern air pressure adjustment mechanism 15b, and a second pattern air flow rate / pressure sensor 17b located near the automatic paint gun G. The pressure of the air from the compressor 11 is adjusted by the pattern air pressure adjustment mechanism 15b, and the operation of the pattern air pressure adjustment mechanism 15b is controlled by the measurement value of the first pattern air flow rate / pressure sensor 16b. In addition, the pressure and / or flow rate of the pattern air supplied to the automatic paint gun G1 is measured by the second pattern air flow rate / pressure sensor 17a. The pattern air pressure adjustment mechanism 15b may be part of the control mechanism of the painting device (automatic paint gun).

[0068] The pattern air pressure adjustment mechanism 15b can be controlled by a computer or the like, if necessary. Furthermore, the operating data and measured values ​​of the pattern air pressure adjustment mechanism 15b, the first pattern air flow rate / pressure sensor 16b, and the second pattern air flow rate / pressure sensor 17a can be recorded by transmitting them via wired or wireless means to a recording device or control means (not shown). The pattern air-related data measured by the first pattern air flow rate / pressure sensor 16b and the second pattern air flow rate / pressure sensor 17a may be sent, if necessary, to a controller or storage means (neither shown) that controls atomizing air pressure / flow rate, pattern air pressure / flow rate, paint flow rate, etc., for control or recording.

[0069] The paint piping 25 is equipped with a pump 24 and a valve 26. The paint 21 in the paint tank 22, which is sucked in by the pump 24 and enters the paint piping, is controlled by the valve 26 to be supplied to the automatic paint gun g when painting is in progress and returned to the paint tank 22 when not painting. A paint flow sensor 27 is provided between the valve 26 and the automatic paint gun G1 to measure the flow rate of the paint supplied to the automatic paint gun G1. The paint flow data measured by the paint flow sensor 27 may be sent, if necessary, to a controller or storage means (not shown) that controls atomizing air pressure and flow rate, pattern air pressure and flow rate, paint flow rate, etc., for control and recording.

[0070] Figure 2 is a schematic diagram showing one embodiment of a painting system suitable for implementing the painting method of the present invention using an automatic paint gun with improved needle valve responsiveness. The painting system shown in Figure 2 is provided with an internal switching valve operating air piping 18 for the automatic paint gun body that controls a switching valve that switches the communication between the needle valve control air chamber and the exhaust port, which are located inside the automatic paint gun G2, ON (connected: when not painting) or OFF (not connected: when painting). By providing a switching valve inside the automatic paint gun G, the responsiveness (paint shutdown performance) when switching from painting to non-painting can be improved.

[0071] [Automatic Paint Gun] The automatic paint gun used in the painting method of the present invention is not particularly limited, as long as it is an automatic paint gun capable of atomizing paint into fine particles with atomizing air and forming a pattern with pattern air. In the painting method of the present invention, an automatic paint gun is preferred in which the nozzle tip is tapered and the flow velocity in the atomization region is increased so that the atomizing air contacts the paint at supersonic speed and atomizes the paint. For example, the A110 series, A210 series, FA110 series, FA210 series, SA110 series, JA110 series, A55 series, AJ-P series, AJ55-P series, AJ55-PR series, A110L series, etc. manufactured by Meiji Machine Works Co., Ltd. can be used. As the air cap attached to the automatic paint gun, for example, the M-type air cap shown in Figure 3 or the round 1-type air cap shown in Figure 4 can be used. The painting method of the present invention can reproducibly achieve a coating efficiency of 80% or more even when using a general-purpose automatic paint gun.

[0072] [Other Painting Conditions, etc.] <Paint Gun Speed> In the painting method of the present invention, the scanning speed of the automatic paint gun during painting is not particularly limited. For example, it can be 10 mm / s or more, preferably 50 mm / s or more, more preferably 100 mm / s or more, and for example, 1000 mm / s or less, preferably 700 mm / s or less, more preferably 500 mm / s or less. If the paint gun speed is slow, painting workability may decrease, the paint film thickness may become uneven, and the appearance of the paint film may deteriorate. If the paint gun speed is fast, the paint film thickness may become thin, and the appearance of the paint film may deteriorate.

[0073] <Film Thickness of the Coating Film> The thickness of the coating film (dry film thickness) formed by the coating method of the present invention is not particularly limited and can be adjusted as appropriate according to the application, etc. For example, the dry film thickness can be 0.1 μm or more, preferably 1 μm or more, and can be, for example, 1000 μm or less, preferably 300 μm or less.

[0074] <Conditions for Forming a Coating Film> In the coating method of the present invention, the spraying angle of the paint from the automatic spray gun is not particularly limited. For example, it can be 90° (the painted surface of the object to be coated is perpendicular to the discharge direction). In the coating method of the present invention, the orientation of the painted surface of the object to be coated is also not particularly limited. For example, it can be a horizontal plane (perpendicular to the direction of gravity). In the coating method of the present invention, after applying the paint to the object to be coated, the coating film may be dried and hardened at room temperature or by heating to form a coated object. When heating, the temperature can be raised above room temperature, for example, 50°C or higher, by heating with a heating furnace or by blowing hot air. The heating time is not particularly limited. Also, when using an active energy ray curing type paint, hardening can be performed by energy rays such as ultraviolet rays or heat. From the viewpoint of finish quality, the object may be set (left to stand) at room temperature beforehand before drying or hardening.

[0075] <Noise> In the painting method of the present invention, it is preferable that the noise level during painting with an automatic paint gun is 75 dB or less. Compared to conventional painting methods using automatic paint guns, the painting method of the present invention has lower atomizing air pressure and pattern air pressure, and the gun distance, which is the distance from the paint discharge port of the automatic paint gun to the object to be painted, is shorter, so the noise level during painting can be suppressed to 75 dB or less.

[0076] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0077] [Paints] The paints used in the examples and comparative examples are as follows. The following paints were used. All are two-component acrylic urethane paints. The diluents all contain a ketone-based organic solvent with an evaporation rate of 140 to 1100 when the value of butyl acetate is set to 100, and an ester-based organic solvent with an evaporation rate of 140 to 1100 when the value of butyl acetate is set to 100. Paint 1: Main component (Musashi Paint Co., Ltd. "EC-P79- Eco High-Urex P MATT BLACK GT") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-800") + Thinner (Musashi Paint Co., Ltd. "Z-EC-K775") Paint 2: Main component (Musashi Paint Co., Ltd. "EC-P79- Eco High-Urex P MATT BLACK GT") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-800") + Thinner (Musashi Paint Co., Ltd. "Z-EC-K781") Paint 3: Main component (Musashi Paint Co., Ltd. "EC-P79- Eco High-Urex P MATT BLACK GT") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-800") + Thinner (Musashi Paint Co., Ltd. "Z-EC-K060") Paint 4: Main component (Musashi Paint Co., Ltd. "EC-P79- Eco High Urex P Matt Black GT") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-800") + Diluent (Musashi Paint Co., Ltd. "Z-EC-K060" and a high-boiling point organic solvent containing diethylene glycol mono-n-butyl ether) Paint 5: Main component (Musashi Paint Co., Ltd. "EC-MH62- Eco Sunshine Super MH Piano Black") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-760") + Diluent (Musashi Paint Co., Ltd. "Z-EC-K657") Paint 6: Musashi Paint Co., Ltd. "EC-GPX79- Eco High Urex P Grande Bonheur Metallic Silver") + Hardener (Musashi Paint Co., Ltd. "Z-EC-H-250") + Diluent (Musashi Paint Co., Ltd. "Z-EC-K775")

[0078] [Automatic Paint Guns] The automatic paint guns and air caps used in the examples and comparative examples are as follows: Paint Gun 1: Meiji Machine Works Co., Ltd. "AJ-P55-P-GO" (Air Cap M) Paint Gun 2: Meiji Machine Works Co., Ltd. "AJ-P55-P-GO" (Air Cap Round 1) Paint Gun 3: Meiji Machine Works Co., Ltd. "AJ-P55-P-GO-1" (Air Cap M) Paint Gun 4: Meiji Machine Works Co., Ltd. "AJ-P55-P-GO-1" (Air Cap Round 1) Paint Gun 5: Meiji Machine Works Co., Ltd. "AJ-P13P"

[0079] [Measurement Method] In the examples and comparative examples, the methods for measuring viscosity, paint supply amount, atomizing air pressure, pattern air pressure, atomizing air flow rate, and pattern air flow rate are as follows.

[0080] <Viscosity> Viscosity was measured using an NK-2 viscosity cup manufactured by Anest Iwata Corporation under the temperature and pressure conditions of the painting environment.

[0081] <Paint supply amount> Measured using a flow meter installed in the paint supply piping.

[0082] <Atomizing Air Pressure> The pressure value of the pressure adjustment mechanism in the control device was defined as atomizing air pressure 1. The pressure measured by a pressure gauge installed near the automatic paint gun, more than 10 m away from the pressure adjustment mechanism, was defined as atomizing air pressure 2.

[0083] <Pattern Air Pressure> The pressure value of the pressure adjustment mechanism in the control device was defined as pattern air pressure 1. The pressure measured by a pressure gauge installed near the automatic paint gun, more than 10 m away from the pressure adjustment mechanism, was defined as pattern air pressure 2.

[0084] <Atomizing Air Flow Rate> Measured using a flow meter installed in the atomizing air supply piping.

[0085] <Pattern Air Flow Rate> Measured using a flow meter installed in the pattern air supply piping.

[0086] [Calculation and Evaluation] In the examples and comparative examples, the calculation of coating efficiency, evaluation of the appearance of the coating film, and evaluation of noise were performed as follows.

[0087] <Coating Efficiency> This was calculated using the method described in [(1) Coating Efficiency] above. The paint spray volume F(g) used in formula (I) was calculated by first determining a conversion factor using the integrated value of the instantaneous paint flow rate measured in advance with a flow meter installed in the paint flow path and the measured paint flow rate, and then multiplying the integrated value of the instantaneous paint flow rate during painting by the conversion factor to calculate the flow rate, and then using the specific gravity of the paint to calculate the paint spray volume F(g).

[0088] <Appearance of the coating film> The appearance of the coated objects obtained in the examples and comparative examples was observed visually and evaluated according to the following criteria. A rating of 5 or 4 is considered passing, and a rating of 3 or lower is considered failing. Rating 5: No defects in the appearance of the coating film, such as pooling or unevenness, are observed with the naked eye. Rating 4: Minor defects in the appearance of the coating film, such as fine pooling or fine unevenness, are observed upon close inspection. Rating 3: Defects in appearance, such as pooling or unevenness, are observed with the naked eye. Rating 2: Defects in appearance, such as pooling or unevenness, are clearly observed with the naked eye. Rating 1: No coating film was formed. Note that "pooling" refers to a situation in which paint pools are formed due to problems with the flow of the paint during paint application and coating film formation, and these are observed in the coating film.

[0089] <Noise Evaluation> A noise meter was placed 5 meters away from the automatic paint gun, and noise levels were measured.

[0090] [Examples A1-A77, Comparative Examples A1-A5] Painting conditions were set as shown in Tables 1 and 2, and painting was performed on an aluminum plate on a horizontal surface using an automatic spray gun. The spraying angle was 90° (the painted surface of the object to be painted was perpendicular to the discharge direction). The results are shown in Tables 1 and 2. In Tables 1 and 2, the numbers in the recoating column represent the number of coats.

[0091]

[0092]

[0093] [Examples B1-B35, Comparative Examples B1-B5] Painting conditions were set as shown in Tables 3 and 4, and painting was performed on an aluminum plate on a horizontal surface using an automatic spray gun. The spraying angle was 90° (the painted surface of the object to be painted was perpendicular to the discharge direction). The results are shown in Tables 3 and 4. In Tables 3 and 4, the numbers in the recoating column represent the number of coats.

[0094]

[0095]

[0096] [Examples C1-C8, Comparative Examples C1-C2] Painting conditions were set as shown in Table 5, and painting was performed on a plastic plate on a horizontal surface using an automatic spray gun. The spraying angle was 90° (the painted surface of the object to be painted was perpendicular to the discharge direction). The appearance of the paint film on the obtained painted objects was also evaluated. The results are shown in Table 5. In Table 5, the number in the recoating column represents the number of coats.

[0097]

[0098] [Example D1] A paint gun 4 was used as an automatic spray gun to paint 2 on a horizontal surface plastic film and plastic plate. The paint gun speed was 200 mm / s, the spray gun distance was 50 mm, the paint supply amount was 11 mL / min, the atomizing air pressure 1 was 0.040 MPa, the atomizing air pressure 2 was 0.034 MPa, the pattern air pressure 1 was 0.090 MPa, and the atomizing air pressure 2 was 0.068 MPa. Ten coats were applied to obtain painted objects. The ten coats were performed by shifting the painting center by 20 mm each time, making 2.5 back-and-forth movements for five coats, and then applying another five coats along the same trajectory. The spray angle was 90° (the painted surface of the object to be painted was perpendicular to the discharge direction). After drying, the appearance of the painted film on the plastic plate was evaluated and it received a rating of 5. After drying, the film thickness of the painted film on the plastic film was measured using a digital micrometer (manufactured by Shinwa Sokutei Co., Ltd.). The results are shown in Figure 5. The coating obtained in Example D1 was a uniform coating with a thickness of 18 μm over an effective pattern of 60 mm.

[0099] [Noise Measurement] The noise level during painting in Example C3 was measured to be 73 dB. On the other hand, when paint 2 was applied to an aluminum plate using paint gun 5 as an automatic spray gun under the standard painting conditions of paint gun 5 (atomizing air pressure 0.25 MPa, pattern air pressure 0.25 MPa, gun distance (spraying distance) 200 mm, paint supply amount (paint discharge amount) 310 mL / min), the noise level was measured to be 90 dB.

[0100] Although the present invention has been described in detail above, various modifications can be made to the above configuration without departing from the scope of the invention. Therefore, all matters included in the above description or shown in the accompanying drawings should be construed as illustrative.

[0101] G: Automatic paint gun S: Atomized paint 11: Compressor 12: Needle valve operating air piping 13: Atomizing air piping 14: Pattern air piping 15a: Atomizing air pressure adjustment mechanism 15b: Pattern air pressure adjustment mechanism 16a: First atomizing air flow rate / pressure sensor 16b: Second pattern air flow rate / pressure sensor 17a: Second atomizing air flow rate / pressure sensor 17b: Second pattern air flow rate / pressure sensor 18: Automatic paint gun body internal switching valve operating air piping 21: Paint 22: Paint tank 23: Weight measuring device 24: Pump 25: Paint piping 26: Valve 27: Paint flow rate sensor

Claims

1. A non-electrostatic air atomization coating method using an automatic paint gun, wherein the following requirements (1) and (2): (1) a coating efficiency of 80% or more, (2) a gun distance of 20 mm to 90 mm, and further satisfying the following requirements (3a) and / or (3b): (3a) an atomizing air pressure of 0.013 MPa·s to 0.070 MPa·s and a pattern air pressure of 0.020 MPa·s to 0.100 MPa·s, and (3b) an atomizing air flow rate of 5 L / min to 25 L / min and a pattern air flow rate of 2 L / min to 35 L / min, the coating method.

2. Furthermore, the painting method according to claim 1 satisfies one or more of the following requirements (4) to (7): (4) The paint supply amount is 7 mL / min to 55 mL / min; (5) The viscosity of the paint used for painting by the Iwata Cup method is 5 seconds to 13 seconds; (6) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, and the evaporation rate value is 140 to 1100 when the value of butyl acetate is set to 100; (7) The paint contains one or more organic solvents from among ketone-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, ether-based organic solvents and aliphatic hydrocarbon-based organic solvents, and the boiling point at a pressure of 0.1 MPa is 150°C or higher.

3. The painting method according to claim 1 or 2, wherein multiple coats are applied.

4. The painting method according to claim 1 or 2, wherein the painting is carried out in layers so that the center positions of the paint are different.

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