JP5568801B2 - Carbon dioxide coating method and apparatus - Google Patents

Description

  The present invention relates to a carbon dioxide coating method and an apparatus therefor, and more particularly, in a conventional spray coating with an organic solvent-based paint, a diluting solvent (VOC) used in a large amount is replaced with a very small amount of carbon dioxide. Thus, the present invention relates to a coating method and apparatus capable of greatly reducing the occurrence of VOC while ensuring coating finish quality such as coating film uniformity, smoothness, and sharpness equivalent to organic solvent-based coating. The present invention provides a new technology and a new product related to a new low-environmental load-type carbon dioxide coating that can significantly reduce the occurrence of VOC in the atmosphere.

  The generation of VOCs is a hazardous chemical substance that leads to global warming, and in 2010, a 30% reduction is required, including self-regulation. The coating industry uses a large amount of organic solvents as a viscosity reducing agent used in paints, and the coating industry has a VOC generation amount close to 60% of the VOC generation amount in Japan of about 1.5 million tons. It is the largest VOC generation industry that occupies, and VOC countermeasures are an urgent issue in the paint industry.

  In the coating industry, spray coating using this diluting solvent is the mainstream, and various measures are taken to reduce VOC. Specifically, technical developments such as conversion to water-based paints, paints with reduced organic solvents, that is, high solids, or recovery and decomposition treatment of exhausted organic solvents can be mentioned.

  However, among these countermeasure technologies, in particular, conversion to water-based paints requires ancillary equipment such as water treatment equipment and air-conditioning equipment. Water-based paints are compatible when the object to be painted is a metal material. However, the present situation is that it cannot respond to the coating of plastic parts and the like that require high paint finish quality.

  Therefore, in the coating industry, especially for small and medium-sized enterprises, dealing with the above-mentioned VOC countermeasures has problems such as requiring a large capital investment in the current technology. There was a strong demand for the development of new coating technologies that could replace organic solvent coating or water-based coating.

  On the other hand, in a patent application (Patent Document 1) filed by the United States Union Carbide Corporation, a technique using a supercritical fluid instead of an organic solvent as a viscosity reducing agent (diluent) is proposed. In this technology, the coating (the polymer and the true solvent that dissolves the polymer to make it fluid) dissolves the supercritical fluid, especially carbon dioxide, and reduces the viscosity to a sprayable level. It has been shown to be possible.

Since then, the company has applied for a dozen patents. For example, a spray width control method (Patent Document 2), a coating composition limitation (Patent Document 3), and a spray state improvement method (Patent Document 4). There are five patents registered as patents: a method for avoiding clogging (Patent Document 5) and a method for controlling the density of a paint / CO ₂ mixture (Patent Document 6).

  However, in these patents, only one flow is shown as the process flow, and there is a problem that the degree of completion is not sufficient for the construction of a practical process flow and a specific operation method. there were. As described above, the above-described prior art has not been disclosed practically at all for the instantaneous stop and the short-time stop operation that are essential in the painting operation in addition to the deficiencies in the steady operation, and cannot be practically implemented. there were. In other words, the spray coating technique using carbon dioxide as a viscosity reducing agent has not yet been established from the viewpoint of an industrial technology that can be put into practical use.

The process flow shown in the above patent is shown in FIG. In this flow, the paint and CO ₂ are pressurized by an air-operated piston pump, and the paint is heated and sent to the mixer for the purpose of viscosity reduction. The CO ₂ is not heated and is sent to the mixer in a liquid state. The supply amount of paint and CO ₂ at that time is supplied at a constant volume ratio by a mechanism that simultaneously controls the movements of the pistons of both pumps.

  The mixer is a fluid multi-stage static mixer, and after the mixture is heated, it passes through the filter, is mixed again by the static mixer, is decompressed as necessary, and is sent to the spray gun. It is done. In the spray gun, the flow rate is determined according to the pressure and sprayed. The surplus is pressurized in the circulation line and returned to the line after the first static mixer.

The above is a schematic process flow of the proposed conventional carbon dioxide coating. However, in order to make this flow practical, there is a problem that the paint / CO ₂ supply amount cannot be balanced with the spray amount. For example, there is a risk that the pump discharge pressure will increase. In this patent, when the pump discharge pressure exceeds a certain pressure, both the paint and CO ₂ are released to atmospheric pressure from the relief valve installed in the line. Is not preferable in terms of operation, and in the case of paint / CO ₂ , especially CO ₂ , it cannot be reused and is economically disadvantageous.

  In the process flow, a circulation line is provided, but this is not particularly necessary for operation. Furthermore, an electric heating method is used for heating the paint and the mixture. However, in this method, it is difficult to keep the temperature constant at the start of operation of the apparatus or when the flow rate is changed. Adoption of other heating methods is desired. Also, in actual painting work, when changing the painting surface or painting direction, or when changing the painting object itself, and further, for spraying check, painting worker's break / change, etc. Or it can often stop for a certain period of time. In such a case, in the above process flow, not only the temperature control is not good, but also the pressure fluctuation of the entire apparatus is assumed, and it is highly likely that it takes time to stabilize the state at the time of respraying, which is a problem. . As a matter of course, the sprayed surface cannot be sprayed until the sprayed state is stabilized, so that it becomes a so-called throwing-off, and the use efficiency (coating efficiency) of the paint is reduced.

  In such a case, problems such as an increase in system pressure are assumed in the proposed process flow, and considerable improvement is required to make the process flow practically operable. Furthermore, in the process flow, line cleaning at the time of stopping or at the end of coating, which is important in actual coating, is not considered at all. Thus, it is clear that the carbon dioxide coating shown in the above-mentioned series of patents is not necessarily a practical process flow configuration constructed at a level applicable as an actual coating technology. In the technical field, there has been a strong demand for the construction of a process flow that can be put into practical use.

Japanese Patent No. 1927328 Japanese Patent No. 2061845 Japanese Patent No. 2670904 Japanese Patent No. 2785099 Japanese Patent No. 2739548 Japanese Patent No. 2807927

Under such circumstances, the present inventors have solved the above-mentioned problems in carbon dioxide coating in view of the above prior art, and in particular, established a process flow that can be put into practical use and a stable operation method. As a result of intensive research with the goal of establishing a new process flow that employs a high-pressure micromixer and incorporates a stop operation into the flow configuration, and establishes a specific stable operation method. The present invention has been completed successfully. An object of the present invention is to provide a new coating method and apparatus suitable for low environmental load type low VOC coating using carbon dioxide as a viscosity reducing agent.

The present invention for solving the above-described problems comprises the following technical means.
(1) Diluting solvent (thinner) used in organic solvent-based spray coating, in carbon dioxide coating that replaces part or all with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer A spray gun for spraying the mixed paint / carbon dioxide pressurized mixture to the object to be coated under atmospheric pressure, and the paint / carbon dioxide pressurized mixture as a branch line from the mixer to the spray gun. A primary pressure adjustment valve that adjusts the pressure and discharges the excess to atmospheric pressure, and a close valve (V-2) upstream from the primary pressure adjustment valve from the junction of the branch line between the mixer and the spray gun. The downstream of the stop valve (V-3), and further of the downstream of the stop valve (V-3), a stop valve (V-4) for supplying high-pressure carbon dioxide and a carbon dioxide introduction pipe. The painting equipment using the characteristic carbon dioxide.
(2) Diluting solvent (thinner) used in organic solvent-based spray coating, carbon dioxide coating that replaces part or all with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer Secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture after mixing to a predetermined pressure, and the coating / carbon dioxide pressurized mixture after the secondary pressure regulating valve to be coated under atmospheric pressure There is a spray gun for spraying on the object, and the pressure of the paint / carbon dioxide pressurized mixture is adjusted as a branch line between the secondary pressure regulating valve and the spray gun, and the excess is discharged to atmospheric pressure. A primary pressure regulating valve and a closing valve (V-2) upstream thereof, and further, a closing valve (V-3) downstream from the junction of the branch line between the secondary pressure regulating valve and the spray gun. ) And high pressure dioxide downstream of the shut-off valve (V-3). Painting device using shut-off valve for supplying hydrogen and (V-4), providing the carbon dioxide inlet pipe, a carbon dioxide and said.
(3) Diluting solvent (thinner) used in organic solvent-based spray coating, in carbon dioxide coating that replaces part or all with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer Secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture after mixing to a predetermined pressure, and the coating / carbon dioxide pressurized mixture after the secondary pressure regulating valve to be coated under atmospheric pressure A spray gun for spraying on the object is provided, and the pressure of the paint / carbon dioxide pressurized mixture is adjusted as a branch line between the mixer and the secondary pressure regulating valve, and the excess is discharged to atmospheric pressure 1 A secondary pressure adjusting valve, a closing valve (V-2) upstream thereof, a closing valve (V-3) between the secondary pressure adjusting valve and the spray gun, and a further closing valve (V -3) downstream of the stop valve (V-4) for supplying high-pressure carbon dioxide; Providing the carbon dioxide introduction pipe coating apparatus using carbon dioxide, characterized in.
(4) The coating apparatus using carbon dioxide according to any one of (1) to (3), in which a plurality of lines are formed from the branch line merge point to the spray gun.
(5) The coating apparatus using carbon dioxide according to any one of (1) to (4), further including a paint heater that heats the pressurized paint to a predetermined temperature.
(6) Coating using carbon dioxide according to any one of (1) to (5) above, which has a cooler that cools excess carbon dioxide returned to the suction of the liquid carbon dioxide high-pressure pump to a predetermined temperature. apparatus.
(7) The coating apparatus using carbon dioxide according to any one of (1) to (6), including a carbon dioxide heater that heats pressurized liquid carbon dioxide to a predetermined temperature.
(8) The coating apparatus using carbon dioxide according to any one of (1) to (7), further including a mixture temperature controller for adjusting the paint / carbon dioxide pressure mixture after mixing to a predetermined temperature.
(9) The coating apparatus using carbon dioxide according to any one of (1) to (8), wherein the mixer is a micromixer capable of rapidly mixing a paint and carbon dioxide.
(10) The coating apparatus using carbon dioxide according to (9), wherein the micromixer is a T-shaped micromixer of 0.5 mm even if the flow path diameter is large.
(11) The micro-mixer is a center collision type micro-mixer that causes a fluid to collide with the center of a minute space, in which carbon dioxide is introduced from the upper part, and the paint is divided into a plurality of parts from a plurality of directions on the side surface in the central part. The coating apparatus using carbon dioxide according to (9) above, which is a mixer that flows in so as to collide.
(12) The carbon dioxide according to any one of (1) to (11) above, wherein the paint discharged from the primary pressure regulating valve provided downstream of the junction of the branch lines returns to the paint tank Painting equipment.
(13) The carbon dioxide according to any one of (1) to (12), wherein the stop valve (V-3) and the stop valve (V-4) are incorporated in a spray gun. The painting equipment used.
(14) The coating apparatus using carbon dioxide according to any one of (1) to (13), wherein the paint / carbon dioxide pressure mixture after the mixer is a one-phase mixture in which carbon dioxide is dissolved in the paint. .
(15) The coating apparatus using carbon dioxide according to any one of (1) to (14), wherein the paint is an ultraviolet curable paint, a one-part curable paint, or a two-part curable paint.
(16) A method of performing coating using carbon dioxide using the coating apparatus according to any one of (1) and (4) to (15), wherein a primary pressure regulating valve on a pump discharge side is provided. Carbon dioxide was used, characterized in that the primary pressure regulating valve provided downstream of the junction of the branch line was set to be equal to the spray pressure in the quantitative coating mode where the spray pressure was set higher than the total amount discharged from the pump. How to paint.
(17) A method of performing coating using carbon dioxide using the coating apparatus according to any one of (1) and (4) to (15), wherein the spray flow rate is set according to the spray pressure. The primary pressure regulating valve on the fluid discharge side, which is automatically variable, is set equal to or slightly higher than the spray pressure, and the primary pressure regulating valve on the fluid side that does not vary the flow rate is set on the variable fluid side. By setting it higher than the primary pressure regulating valve set value, the flow rate of the fluid that does not change the flow rate is made constant, and the spray flow rate of the fluid that changes the flow rate is made variable according to the flow rate characteristics of the orifice of the spray nozzle, A coating method using carbon dioxide, characterized in that, in a constant pressure coating mode in which the surplus is returned to the pump suction, a primary pressure regulating valve provided downstream of the junction of the branch lines is set to be equal to the spray pressure.
(18) A method of performing coating using carbon dioxide using the coating apparatus according to any one of (2) and (4) to (15), which is determined by a set value of a secondary pressure regulating valve The primary pressure regulating valve on the fluid discharge side that automatically varies the spray flow rate according to the spray pressure to be set is set higher than the spray pressure, and the primary pressure regulating valve on the fluid side that does not vary the flow rate is set. By setting the variable fluid side higher than the set value of the primary pressure adjustment valve on the variable fluid side, the flow rate of the fluid that does not vary the flow rate is made constant, and the spray flow rate of the fluid that varies the flow rate depends on the flow rate characteristics of the orifice of the spray nozzle A coating method using carbon dioxide, wherein the primary pressure regulating valve provided downstream of the junction of the branch lines is set lower than the spray pressure in the constant pressure coating mode in which the surplus is returned to the pump suction as a variable.
(19) A method of performing coating using carbon dioxide using the coating apparatus according to any one of (3) and (4) to (15), which is determined by a set value of a secondary pressure regulating valve. The primary pressure regulating valve on the fluid discharge side that automatically varies the spray flow rate according to the spray pressure to be set is set higher than the spray pressure, and the primary pressure regulating valve on the fluid side that does not vary the flow rate is set. By setting it higher than the set value of the primary pressure adjustment valve on the variable fluid side, the flow rate of the fluid that does not change the flow rate is made constant, and the spray flow rate of the fluid that changes the flow rate depends on the flow rate characteristics of the orifice of the spray nozzle In a constant pressure coating mode in which the surplus is returned to the pump suction as a variable, a coating method using carbon dioxide, characterized in that the primary pressure regulating valve provided downstream of the junction of the branch lines is set higher than the spray pressure.
(20) Measure the mass flow rate of paint and carbon dioxide flowing into the mixer, and control the flow rate so that the pump discharge rate on the fluid side without variable flow rate is a constant ratio to the mass flow rate on the variable flow rate side. The coating method using carbon dioxide according to any one of (17) to (19), wherein:
(21) The coating method according to any one of (17) to (20), wherein the fluid for changing the flow rate is a paint.
(22) The painting operation is divided into a painting mode in which painting is actually performed, an instantaneous stop mode in which painting is stopped for several seconds, a short-time stop mode in which tens of seconds are stopped, and a long-time stop mode in which the paint is stopped for several minutes. In V-1 open, V-2 close, V-3 open, V-4 close, and instantaneous stop mode, V-1 open, V-2 close, V-3 close, V-4 close, short stop In the mode, V-1 open, V-2 open, V-3 close, V-4 open → close, and in the long stop mode, V-1 open, V-2 close, V-3 close, V- 4. The coating method according to the above (16) or (18), wherein 4 is open → closed.
(23) The painting operation is divided into a painting mode in which painting is actually performed, an instantaneous stop mode in which painting is stopped for a few seconds, a short-time stop mode in which the paint is stopped for several tens of seconds, and a long-time stop mode in which the paint is stopped for several minutes. In V-1 open, V-2 close, V-3 open, V-4 close, and instantaneous stop mode, V-1 open, V-2 close, V-3 close, V-4 close, short stop In the mode, V-1 closed, V-2 opened, V-3 closed, V-4 opened → closed, and in the long stop mode, V-1 opened, V-2 closed, V-3 closed, V- 4. The coating method according to the above (17) or (19), wherein 4 is open → closed.

Next, the present invention will be described in more detail.
In the spray coating with a conventional organic solvent-based paint, the present invention replaces a diluting solvent (VOC) used in a large amount with a very small amount of carbon dioxide, thereby achieving a paint finish quality equivalent to that of an organic solvent-based paint, that is, It is characterized by providing a new low-environmental load-type carbon dioxide coating method and apparatus capable of greatly reducing the occurrence of VOC while ensuring film uniformity, smoothness, sharpness, etc. is there.

  The present invention provides a tank for storing paint as a paint supply line in a carbon dioxide coating in which part or all of the diluent solvent (thinner) used in organic solvent-based spray coating is replaced by carbon dioxide. Paint high-pressure pump that pressurizes the paint to be applied to a predetermined pressure, a paint primary pressure adjusting valve that adjusts the discharge pressure of the paint high-pressure pump and returns excess to the paint tank, and a close valve (V- 1) as a carbon dioxide supply line, a tank for storing liquid carbon dioxide, a cooler for cooling the liquid carbon dioxide to a predetermined temperature, and pressurizing the liquid carbon dioxide supplied from the cooler to a predetermined pressure A liquid carbon dioxide high pressure pump, a liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high pressure pump and returns the excess to the suction of the pump; And a mixer for mixing the pressurized paint supplied from the paint supply line and the pressurized carbon dioxide supplied from the carbon dioxide supply line as the paint / carbon dioxide mixture line, and the mixer It has a spray gun that sprays the mixed paint / carbon dioxide pressurized mixture supplied from the above to the object to be coated under atmospheric pressure, and the paint / carbon dioxide pressurized as a branch line from the mixer to the spray gun The primary pressure regulating valve that adjusts the pressure of the mixture and discharges the surplus to atmospheric pressure, and the close valve (V-2) upstream from it, and further joins the branch line between the mixer and the spray gun. It has a shut-off valve (V-3) downstream from the point, and further a shut-off valve (V-4) for supplying high-pressure carbon dioxide and a carbon dioxide introduction pipe downstream of the shut-off valve (V-3). Coating equipment using carbon dioxide, A.

The present invention is a method of performing coating using carbon dioxide using the above-described coating apparatus,
The primary pressure adjustment valve on the pump discharge side is set higher than the spray pressure, and the primary pressure adjustment valve provided downstream of the branch line merging point is equivalent to the spray pressure in the quantitative coating mode in which the entire pump discharge amount is sprayed. A coating method using carbon dioxide consisting of:

  Further, the present invention is a method of performing coating using carbon dioxide using the above-described coating apparatus, and the fluid discharge pump 1 that automatically varies the spray flow rate according to the spray pressure. Set the primary pressure adjustment valve to be equal to or slightly higher than the spray pressure, and set the primary pressure adjustment valve on the fluid side, which does not change the flow rate, higher than the primary pressure adjustment valve setting value on the variable fluid side. In constant pressure coating mode, the flow rate of the fluid that does not change the flow rate is made constant, the spray flow rate of the fluid that changes the flow rate is made variable according to the flow rate characteristics of the orifice of the spray nozzle, and the surplus is returned to the pump suction. It is the coating method using the carbon dioxide which consists of setting the primary pressure regulating valve provided downstream of the line confluence to be equal to the spray pressure.

  The present invention provides a tank for storing paint as a paint supply line in a carbon dioxide coating in which part or all of the diluent solvent (thinner) used in organic solvent-based spray coating is replaced by carbon dioxide. Paint high-pressure pump that pressurizes the paint to be applied to a predetermined pressure, a paint primary pressure adjusting valve that adjusts the discharge pressure of the paint high-pressure pump and returns excess to the paint tank, and a close valve (V- 1) as a carbon dioxide supply line, a tank for storing liquid carbon dioxide, a cooler for cooling the liquid carbon dioxide to a predetermined temperature, and pressurizing the liquid carbon dioxide supplied from the cooler to a predetermined pressure A liquid carbon dioxide high pressure pump, a liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high pressure pump and returns the excess to the suction of the pump; And a mixer for mixing the pressurized paint supplied from the paint supply line and the pressurized carbon dioxide supplied from the carbon dioxide supply line as the paint / carbon dioxide mixture line, and the mixer A secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture supplied from the pressure to a predetermined pressure, and the paint / carbon dioxide pressurized mixture after the secondary pressure regulating valve under atmospheric pressure. It has a spray gun that sprays on the object to be painted, adjusts the pressure of the paint / carbon dioxide pressurized mixture as a branch line between the secondary pressure regulating valve and the spray gun, and discharges the excess to atmospheric pressure A primary pressure adjusting valve and a closing valve (V-2) upstream thereof, and further, a closing valve (V-3) downstream from the branch line junction between the secondary pressure adjusting valve and the spray gun. And high pressure carbon dioxide downstream of the shut-off valve (V-3). A shut-off valve to supply the (V-4), it has a carbon dioxide inlet pipe, coating apparatus using carbon dioxide consisting of a.

  The present invention is a method of performing coating using carbon dioxide using the above-described coating apparatus, and automatically controls the spray flow rate according to the spray pressure determined by the set value of the secondary pressure regulating valve. The variable primary pressure regulating valve on the fluid discharge side of the pump is set higher than the spray pressure, and the primary pressure regulating valve on the fluid side that does not change the flow rate is set from the primary pressure regulating valve setting value on the variable fluid side. By setting it higher, the flow rate of the fluid that does not change the flow rate is constant, the spray flow rate of the fluid that changes the flow rate is variable according to the flow rate characteristics of the orifice of the spray nozzle, and the excess pressure is returned to the pump suction In the painting mode, a primary pressure regulating valve provided downstream of the branch line merging point is set to be lower than the spray pressure. This is a painting method using carbon dioxide.

  Furthermore, the present invention relates to a tank for storing paint as a paint supply line in carbon dioxide coating in which a diluent solvent (thinner) used in organic solvent-based spray coating is partially or entirely replaced with carbon dioxide, A paint high pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, a paint primary pressure adjusting valve that adjusts the discharge pressure of the paint high pressure pump and returns the excess to the paint tank, and is closed upstream A tank for storing liquid carbon dioxide, a cooler for cooling the liquid carbon dioxide to a predetermined temperature, and a predetermined amount of liquid carbon dioxide supplied from the cooler. Liquid carbon dioxide high-pressure pump that pressurizes to the pressure, liquid carbon primary pressure that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump A mixing valve that mixes pressurized paint supplied from the paint supply line and pressurized carbon dioxide supplied from the carbon dioxide supply line as a paint / carbon dioxide mixture line A secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture supplied from the mixer to a predetermined pressure, and a paint / carbon dioxide pressurized mixture after the secondary pressure regulating valve Has a spray gun that sprays on the object to be coated under atmospheric pressure, and adjusts the pressure of the paint / carbon dioxide pressurized mixture as a branch line between the mixer and the secondary pressure regulating valve to increase the surplus. A primary pressure regulating valve that discharges to atmospheric pressure, a closing valve (V-2) upstream thereof, and a closing valve (V-3) between the secondary pressure regulating valve and the spray gun, Closed to supply high-pressure carbon dioxide downstream of the stop valve (V-3) A valve (V-4), it has a carbon dioxide inlet pipe, coating apparatus using carbon dioxide consisting of a.

The present invention is a method of performing coating using carbon dioxide using the above-described coating apparatus,
The primary pressure regulating valve on the fluid discharge side that automatically varies the spray flow rate according to the spray pressure determined by the set value of the secondary pressure regulating valve is set higher than the spray pressure, and the flow rate is variable. By setting the primary pressure regulating valve on the fluid side that does not perform the flow higher than the primary pressure regulating valve set value on the variable fluid side, the flow rate of the fluid that does not vary the flow is kept constant, In the constant pressure coating mode in which the spray flow rate is variable according to the flow rate characteristics of the orifice of the spray nozzle and the surplus is returned to the pump suction, the primary pressure adjustment valve provided downstream of the branch line merge point is set higher than the spray pressure. A coating method using carbon dioxide.

  In the present invention, as a configuration of the coating apparatus, a plurality of lines from the junction of the branch line to the spray gun are configured, a paint heater for heating the pressurized paint to a predetermined temperature, liquid carbon dioxide high pressure Having a cooler that cools excess carbon dioxide returned to the pump suction to a predetermined temperature, a carbon dioxide heater that heats pressurized liquid carbon dioxide to a predetermined temperature, and a paint / It has a mixture temperature controller that adjusts the carbon dioxide pressurized mixture to a predetermined temperature, the mixer is a micro mixer that can rapidly mix paint and carbon dioxide, and 1 provided downstream of the junction of the branch line The paint discharged from the secondary pressure adjusting valve returns to the paint tank, the closing valve (V-3) and the closing valve (V-4) are incorporated in the spray gun, the paint after the mixer Preferably, the carbon dioxide pressure mixture is a one-phase mixture in which carbon dioxide is dissolved in the paint, and the paint is an ultraviolet curable paint, a one-part curable paint, or a two-part curable paint. It is an aspect.

  Further, in the present invention, as a painting method, the painting operation is performed in a painting mode in which painting is actually performed, an instantaneous stop mode in which painting is stopped for a few seconds, a short-time stop mode in which the paint is stopped for several tens of seconds, and a long time in which the paint operation is stopped for several minutes. It is divided into the time stop mode. In the paint mode, V-1 open, V-2 close, V-3 open, V-4 close, and in the instantaneous stop mode, V-1 open, V-2 close, V-3 close, In V-4 closed and short stop mode, V-1 open or closed, V-2 open, V-3 closed, V-4 open → closed, and in long stop mode, V-1 open, V- 2 close, V-3 close, and V-4 open → close are preferred embodiments.

  In general, in organic solvent-based coatings, on a weight basis, a paint, that is, a polymer and a dilute solvent of 50 to 150% of a true solvent that dissolves the polymer and has fluidity, such as toluene and xylene, are added, It is necessary to reduce the viscosity to enable spraying. The low-viscosity paint / dilution solvent mixture is sprayed as fine droplets by an air spray method using air as an atomizing medium or a high-pressure spray method that does not use atomized air. Applied.

  The present invention provides a coating method in which the diluent solvent used in the organic solvent-based coating is partially or entirely replaced with carbon dioxide. The paints targeted in the present invention are roughly classified into three types: ultraviolet curable paints, one-part curable paints, and two-part curable paints. UV curable paint is a paint that cures with ultraviolet rays and forms a film, and is excellent in high hardness, abrasion resistance, scratch resistance, chemical resistance, solvent resistance, etc., for example, as a hard coat for mobile phones, etc. Used.

  The coating material is a coating material that forms a coating film by radical polymerization of an acrylic oligomer or monomer compound using ultraviolet rays (UV) as energy. In addition, the one-component curable paint is a paint that is used undiluted or by blending only a diluent (viscosity modifier) such as thinner, and is mainly used for home appliances such as TV cabinets and automobile parts. Used for industrial parts.

  The above-mentioned paint is a paint that has an acrylic resin as a main component and that forms a coating film without using a curing agent. By blending nitrocellulose, it is quick-drying, high in hardness, and excellent in wear resistance. The applicable material is used for a wide range of applications such as polystyrene resin, ABS resin, AS resin, Noryl resin, hard vinyl chloride resin, polycarbonate resin and the like.

  On the other hand, a two-component curable paint is a paint that is mixed with a curing agent before use, cured by chemical reaction, and dried. It is excellent in alcohol resistance and abrasion resistance, mainly in automobile interiors and precision equipment. Used in optical equipment. This paint is a two-component reaction-curing acrylic urethane paint containing an acrylic resin as a main component and a polyisocyanate compound as a curing agent.

  In the present invention, carbon dioxide is mixed and dissolved in the paint. The conditions are a temperature of 30 to 70 ° C., preferably 35 to 45 ° C., and a pressure of 5 to 20 MPa, preferably 7 to 10 MPa. Accordingly, it is necessary to pressurize the paint, but the paint generally has a high viscosity of 50 to 500 cp, and a piston pump, a diaphragm pump, or the like is used as the paint high-pressure pump.

  If the paint viscosity is sufficiently high, a gear pump can be used. When explosion-proof measures are required, air can be adopted as a pump drive source, or the pump can be installed in an explosion-proof box and an inert gas can be circulated therein. On the other hand, as a high-pressure carbon dioxide pump, a plunger pump can be adopted in addition to a piston pump and a diaphragm pump. However, in pressurization of carbon dioxide, pressurization with liquid carbon dioxide is advantageous, and in this case, cooling at the front stage of the pump is required.

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

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

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

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

  In addition, in these micro mixers, the paint and carbon dioxide are sufficiently mixed to form a stable one-phase mixture. However, even if the paint and carbon dioxide are completely mixed, A certain holding time is required until carbon dioxide completely dissolves, and depending on the conditions, a two-phase system of paint and carbon dioxide may be formed between the mixer and the spray gun. In this case, since the viscosities of the two fluids differ greatly, there is a risk that the spray is not stable and a clean application cannot be realized. The solubility of carbon dioxide in the paint varies greatly depending on the kind of paint, temperature and pressure, but is greatly influenced by the mixer and the configuration after the mixer.

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

  For example, when the spray flow rate is about 100 g / min and the pressure at that time is 5 to 10 MPa, 0.1 to 0.2 mm is selected as the equivalent diameter of the orifice. The shape of the orifice varies depending on the required spray pattern, but if it is a flat spray, it has an elliptical orifice shape. In addition, if the orifice shape is circular, it becomes a full cone spray, but it is also possible to change the full cone spray to a flat spray by blowing air or the like immediately after jetting and controlling the spray pattern.

  Actually, there are two methods (modes) for painting, and one method is a constant spray mode that sprays the entire amount of paint and carbon dioxide at the set pump flow rate. In this case, the flow rate and viscosity The pressure is determined by the physical properties of the mixture and the characteristics of the nozzle orifice. The greater the flow rate and the greater the viscosity, the greater the spray pressure. The other method is a constant pressure spray mode in which the spray pressure is constant, in which the flow rate of one of the paint or carbon dioxide is constant and the spray flow rate of the other is variable according to the pressure. Naturally, the discharge amount of the pump on the variable fluid side is set to be larger than the assumed spray amount, and the surplus is returned to the pump suction from the primary pressure regulating valve provided on the pump discharge side.

  Usually, a paint is often selected as the variable fluid. In terms of configuration, carbon dioxide can be used as a variable fluid. In this case, the flow rate of the paint / carbon dioxide mixture increases and the spray pressure tends to increase as the amount of carbon dioxide increases. The spray pressure can become unstable due to both of the low flow viscosity of the paint / carbon dioxide mixture and the tendency to lower the spray pressure. Therefore, normally, a paint is selected as the variable fluid.

  The pressure control in the constant pressure spray mode is performed by a primary pressure regulating valve provided on the pump discharge side on the variable fluid side or by a secondary pressure regulating valve provided after mixing of the paint / carbon dioxide. Is possible. Also in the latter case, the surplus is returned to the pump suction from the primary pressure regulating valve provided on the pump discharge side on the variable fluid side.

  In an actual painting operation, various levels of spray stop operations are performed. For example, when changing the painting surface or painting direction, spraying stops (instantaneous stopping) for several seconds are frequently performed, and when changing the painting object itself (when the object is changed to the painting booth), it is several tens of seconds. The spray stop (stop for a short time) is repeated at regular intervals. Furthermore, spraying is stopped for a few minutes (long-time stop) when checking the state of painting or taking a break or changing a painter.

  If the pump is stopped every time these various spray stop operations are performed, not only does the temperature control fail, but it is also assumed that pressure fluctuations occur in the entire device, and it takes time for the state to stabilize during respraying. Most likely a problem. As a matter of course, the sprayed surface cannot be sprayed until the sprayed state is stabilized, so that it becomes a so-called throwing-off, and the use efficiency (coating efficiency) of the paint is reduced. Therefore, it is extremely important to establish operations corresponding to various spray stop operations in actual painting work.

Next, embodiments of the present invention will be specifically described with reference to the accompanying drawings. The apparatus shown in FIGS. 2-5 is an example of suitable embodiment of the carbon dioxide coating apparatus which concerns on this invention. The reference numerals in the figure indicate the following means. That is, 1: paint tank, 2: (paint) filter, 3: paint high pressure pump, 4: (paint) primary pressure regulating valve, 5: mass flow meter, 6: paint heater, 7: CO ₂ cylinder, 8 : (CO ₂ ) filter, 9: (CO ₂ ) cooler, 10: (CO ₂ ) high pressure pump, 11: mass flow rate / control meter, 12: CO ₂ heater, 13: (CO ₂ ) primary pressure adjustment Valve, 14: (CO ₂ ) cooler 2, 15: paint check valve, 16: CO ₂ check valve, 17: mixer, 18: mixture temperature regulator, 19: secondary pressure regulator, 20: spray Gun, 40: (mixture) primary pressure regulating valve, V-1, 2, 3, 4: Shown as a closing valve.

  The above apparatus and its operation (constant pressure operation mode) will be described in detail. The paint is filled in the paint tank 1 and, if necessary, pressurized (several atmospheres) with nitrogen gas or the like and passes through the filter 2. And supplied to the suction of the paint high-pressure pump 3. Usually, the aperture of the filter 2 may be several tens of μm if it is a clear paint, but it is preferably several hundreds of μm because it contains a solid pigment in the case of a colored paint.

  The paint high-pressure pump 3 is a positive displacement pump, and it is sufficient that the discharge pressure is about 20 MPa. Generally, a diaphragm pump, preferably a double diaphragm pump is selected as a countermeasure against pulsation. Depending on the paint, a plunger pump is also possible, but it is not usually selected because there is a risk that the plunger seal portion will be stuck with the paint. As a countermeasure, the plunger seal portion can be appropriately immersed in a solvent.

  The pump drive source is appropriately selected from the air-operated type and the electric type depending on the installation location of the apparatus. The paint is normally pressurized to around 7.5 MPa by the paint high-pressure pump 3, and the spray amount of the spray gun 20 corresponding to the set value of the secondary pressure adjusting valve 19, usually 7 MPa, is measured by the mass flow meter 5. Is done. The spray flow rate in the spray gun is determined by the set value of the secondary pressure adjusting valve and the diameter of the nozzle orifice installed at the tip of the gun. Here, the discharge amount of the paint high-pressure pump 3 is set in advance larger than the flow rate of the spray gun, and the surplus is circulated to the paint tank 1 via the paint primary pressure regulating valve 4. Thereafter, if necessary, the paint heater 6 is heated to around 40 ° C. and sent to the mixer 17.

On the other hand, CO ₂ sucks the liquid portion of the cylinder 7, passes through the filter 8, is cooled to a temperature equal to or lower than the saturation temperature by the cooler 9, and is supplied to the suction of the CO ₂ high-pressure pump 10. The liquid CO ₂ is pressurized by the CO ₂ high-pressure pump 10, further, in a CO ₂ heater 12, the critical temperature (31 ° C.) or higher, usually, is heated to supercritical CO ₂ of 40 ° C., the mixer 17 Sent to.

Here, as the CO ₂ high pressure pump, a diaphragm pump, a plunger pump, or the like is usually selected. However, as in the case of the paint, it is desirable to employ a double pump to prevent pulsation. Also, the required amount of CO ₂ supply is usually a small amount of 30% or less of the paint. Therefore, when the spray flow rate is small, a plunger pump is employed. The discharge amount of the CO ₂ high-pressure pump 10 is such that the signal from the mass flow rate / control meter 11 is CO _{2 so that} the discharge rate of the paint flow rate measured by the mass flow meter 5 is a constant ratio, usually 20-30%. _{(2) It} is sent to the drive system of the high-pressure pump 10 and controlled by adjusting the stroke, controlling the frequency of the motor, or controlling the air amount for operation.

The pressurized and heated paint and CO ₂ are instantaneously mixed in the mixer 17 to become a paint / CO ₂ mixture. As the structure of the mixer, it is desirable to adopt a micro mixer in consideration of quick mixing and complete mixing. For example, a T-shaped mixer having a flow path diameter of 0.5 mm or less, a swirl type micro mixer using a swirling flow, a center collision type micro mixer that enables a fluid to collide at the center of a minute space, and A double-tube micromixer having an inner diameter of 0.5 mm or less is preferably used.

The structure of the center collision type micromixer is shown in FIG. In the figure, CO ₂ is introduced from the upper inlet and flows downward through an annular portion around the needle that adjusts the mixing state. On the other hand, the paint is introduced from the lower inlet, and is divided into a plurality of flows (usually divided into two or four), and CO ₂ and the paint collide with each other in the minute space at the tip of the needle to instantaneously To be mixed. The paint / CO ₂ mixture is adjusted to a predetermined temperature by the mixture temperature regulator 18 as necessary, and is introduced into the secondary pressure regulating valve 19.

  As described above, since the spray amount in the spray gun 20 is determined by the set value of the secondary pressure adjusting valve, the relationship between the spray amount and the nozzle orifice and secondary pressure set value set in advance at the tip of the spray gun is obtained. Then, it is sprayed toward the object to be painted with the required amount of coating. The number of spray guns from the secondary pressure regulating valve can be changed from one to the desired number, and the pressure setting value is changed for each series and coating is performed with different spray amounts. Is also possible. Although not shown, it is also possible to install a plurality of secondary pressure regulating valves and spray guns downstream of the secondary pressure regulating valve. It is possible to build.

Paint / CO ₂ mixture, CO ₂ is disengaged immediately after the spraying, the coating material of the fine particles. The particle diameter of the paint particles depends on temperature, pressure, and the structure of the spray gun, typically the nozzle orifice diameter, but is usually in the range of 10 to 50 μm. When the object to be painted has a three-dimensional shape, a spray gun is mounted on the three-dimensional robot to perform painting. The above state is the painting mode in which painting is actually performed, and the open / close states of the shut-off valve are V-1 open, V-2 closed, V-3 open, and V-4 closed. When changing the painting surface or painting direction, spray stop for several seconds (instantaneous stop) is frequently performed. At this time, the open / close state of the closing valve is V-1 open, V-2 closed, V-3 closed, V -4 closed.

  In this case, V-3 is closed and the paint / carbon dioxide mixture is momentarily closed, but only the paint returning from the primary pressure regulating valve 4 to the pump suction is increased, and the paint supply system remains as it is. It is kept at 7.5 MPa. On the other hand, in the carbon dioxide supply system, the pressure tends to slightly increase toward the set value 8 MPa of the primary pressure regulating valve 13, but the stop time is several seconds and the spray mode (V-1 open, V -2 closed, V-3 open, V-4 closed), so that there is no significant fluctuation and a stable coating state is immediately obtained.

  On the other hand, when changing the coating object itself (that is, when switching the object to the painting booth), the spray stop (short-time stop) for several tens of seconds is repeated at regular intervals. The states are V-1 closed, V-2 open, V-3 closed, V-4 open → closed. In this case, the primary pressure regulating valve on the discharge side of the paint pump does not return because the upstream closing valve V-1 is closed, and instead the closing valve V-2 is opened. It is discharged through the regulating valve 40. At this time, since the set pressure of the primary pressure adjusting valve 40 is 7.5 MPa, which is the same as the set pressure of the primary pressure adjusting valve 4, the paint supply system hardly fluctuates. Moreover, there is no change in the carbon dioxide supply system.

  Therefore, even if it becomes spray mode again (V-1 opening, V-2 closing, V-3 opening, V-4 closing), there is no big change and it can return to a stable paint state immediately. . During this short-time stop mode, the paint / carbon dioxide mixture is discharged, but since the carbon dioxide is depressurized and gasified, it almost returns to the original paint, so the primary pressure regulating valve 40 is discharged. By using the paint tank 1 as the tip, the discharged paint can be reused. In this case, it is also possible to connect directly to the upstream line of the primary pressure regulating valve 4 from the closing valve V-2, and the short time stop mode is realized without installing the primary pressure regulating valve 40. can do.

  Furthermore, when the paint state is checked or when the painter takes a break or shift, the spraying is stopped for several minutes (stop for a long time). At this time, the open / close state of the stop valve is V-1 open, V- 2 closed, V-3 closed, V-4 open → closed. Also in this case, basically, there is not much difference from the instantaneous stop mode, the paint supply system is maintained at 7.5 MPa as it is, and the carbon dioxide supply system is maintained at 8 MPa. The difference from the instantaneous stop mode is that only the operation of blowing the tip of the spray gun with carbon dioxide, V-4 open → close, and the spray mode (V-1 open, V-2 close, V-3 again). Even if it is open and V-4 closed), there is no large fluctuation, and a stable coating state is immediately obtained.

The present invention has the following effects.
(1) It is possible to provide a new low environmental load type coating apparatus capable of greatly reducing the occurrence of VOC and a coating method therefor.
(2) In spray coating with a conventional organic solvent-based paint, it is possible to replace a diluting solvent (VOC) used in large quantities with a very small amount of carbon dioxide.
(3) It is possible to provide a new coating technique that prevents the dilution solvent (VOC) from being discharged into the atmosphere.
(4) It is possible to provide a practical coating technique that can surely suppress the problem of blockage of the apparatus due to the high viscosity of the paint.
(5) Stop spraying instantaneously or for a certain period of time when changing the painting surface or direction, or when changing the painting object itself, or for checking the painting condition or taking a break or change of the painting worker. Although it is carried out on a daily basis, it is possible to minimize temperature fluctuations, pressure fluctuations, and flow rate fluctuations until respraying, and it is possible to stabilize the spraying state in a very short time during respraying. As a result, it is possible to achieve coating with high quality coating and good paint utilization efficiency (coating efficiency).

The process flow of the coating apparatus shown by the prior patent is shown. An example (quantitative operation mode) of an embodiment of a carbon dioxide painting device concerning the present invention is shown. An example (constant pressure operation mode I) of an embodiment of a carbon dioxide painting device concerning the present invention is shown. An example (constant pressure operation mode II-1) of the embodiment of the carbon dioxide painting device concerning the present invention is shown. An example (constant pressure operation mode II-2) of the embodiment of the carbon dioxide painting device concerning the present invention is shown. An example (constant pressure operation mode II-3) of the embodiment of the carbon dioxide painting device concerning the present invention is shown. 1 shows an example of an embodiment of a carbon dioxide coating apparatus according to the present invention [Overview of laterally moving spray (constant spray stop at both ends of a coated product) in constant pressure operation mode II-3]. The fluctuation | variation of the pressure and the flow rate in the lateral movement spray in the constant pressure operation mode II-3 is shown. A sectional view of the center collision type micromixer (left side figure) and a three-dimensional configuration diagram of the center collision type micromixer (right side figure) are shown.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.

(Coating experiment 1)
A coating experiment was conducted on a commercially available UV curable clear paint (without adding thinner) as a paint. A typical coating composition is a resin component 49%, a true solvent 47%, and an additive 4%. The resin component contains a polyfunctional acrylate as a main component, and a thermoplastic acrylate and a urethane acrylate, respectively. True solvent consists of toluene, butyl acetate, n-butyl alcohol, xylene, and ethylbenzene in descending order of content. Additives include trace amounts of UV absorbers and surface conditioners in addition to photopolymerization initiators. It is.

The coating apparatus was configured as shown in FIG. However, the mass flow rate / control meter 11 that measures and controls the CO ₂ flow rate is a function of only the mass flow rate meter in this experimental system, and cascade control with the coating flow rate is not performed. Since this experimental system has two spray guns (20, 22), in order to measure each spray amount, a mass flow meter is added to the line of the spray gun 22, and the spray amount of the spray gun 20 is reduced as a whole. The spray amount of the spray gun 22 was subtracted from the spray amount.

As the paint high pressure pump 3, a double diaphragm pump is used, and as the CO ₂ high pressure pump 10, a double plunger pump is used. Controlled to ° C. Here, the paint heater 6, the CO ₂ heater 12, and the mixture temperature adjuster 18 employ a coil / shell type heat exchanger that circulates hot water as a heat medium. On the other hand, the coolers 9 and 14 for reliably maintaining the liquid phase state employ a double tube heat exchanger, supply the refrigerant to the outer tube, and control the amount of the refrigerant so that it becomes 5 ° C. or less. did. As the mixer 17, a 1/16 inch T-shaped joint having a flow path diameter after mixing of 0.3 mm (loaded volume T-shaped joint, abbreviated as LDV-T) was used.

The pressure of each part was set to 8 MPa for the primary pressure adjustment valve 4, 11 MPa for the primary pressure adjustment valve 13, and 6 MPa for the secondary pressure adjustment valves 19 and 21, respectively. The stroke was adjusted from the flow rate / pump stroke relationship obtained in advance so that the discharge amount of the paint high-pressure pump was 100 g / min. The scale was adjusted from the flow rate / pump scale relationship determined in advance so that the discharge amount of the CO ₂ high-pressure pump was 18 g / min. An elliptical high-pressure nozzle having an orifice equivalent diameter of 0.15 mm was attached to the tip of the spray guns 20 and 22.

The operation of the paint high-pressure pump 3 and the CO ₂ high-pressure pump 10 was started with the stop valves V-3-1 and V-3-2, V-4-1 and V-4-2 being closed. After the operation is started, the pressure from the discharge part of the paint high-pressure pump 3 to the inlet of the primary pressure adjusting valve 4 and the check valve 15 is pressurized to 8 MPa, and the paint is passed through the primary pressure adjusting valve 4 to the paint tank. The total amount was recycled to 1. On the other hand, from the discharge part of the CO ₂ high pressure pump 10 to the primary pressure regulating valve 13, the secondary pressure regulating valves 19 and 21, and further to the inlets of the stop valves V-4-1 and V-4-2, the pressure is increased to 11 MPa. The total amount of CO ₂ was circulated to the pump suction via the primary pressure regulating valve 13. Moreover, from the outlet part of the secondary pressure regulating valves 19 and 21 to the inlet part of the stop valves V-3-1 and V-3-2, the pressure became 6 MPa, which was stable.

When the stop valves V-3-1 and V-3-2 are opened from the above state, the paint and CO ₂ begin to flow toward the spray gun, and the primary pressure regulating valve 4 and 13, up to the inlet of the secondary pressure regulating valves 19 and 21 was stabilized at about 8 MPa in a few seconds, and the spray guns 20 and 22 were stabilized at 6 MPa. The numerical value of the paint mass flow meter 5 after stabilization was almost constant at 90 g / min. At this time, the numerical value of the mass flow meter installed in the line of the spray gun 22 was about 45 g / min, and it was confirmed that the paint was sprayed evenly with the two spray guns. Since the discharge amount of the paint high-pressure pump 3 was set to 100 g / min, the remaining 10 g / min was circulated to the paint tank 1 via the primary pressure regulating valve 4.

At this time, the CO ₂ mass flow meter 11 showed 18 g / min, and became 20% with respect to the paint flow rate. After a certain time of painting operation, the stop valves V-3-1 and V-3-2 were closed for several tens of seconds in order to replace the painting object. At that time, in order to prevent the spray gun nozzle from being blocked, the stop valves V-4-1 and V-4-2 were opened for several seconds and then closed. Hereinafter, changes with time in pressure and flow rate when these series of operations are repeated are shown in FIG. 8 (1).

As is apparent from the figure, the spray guns 20 and 22 spray almost the same amount, but it takes time until the spray amount of the paint is stabilized at the start of spraying. These results from the fact that when the spraying is stopped, the pressure in the mixing section increases and it takes time to stabilize at the time of respraying. Moreover, it became clear that the CO ₂ flow rate also slightly fluctuated with the pressure fluctuation. Subsequently, the spray gun was attached to a two-dimensional painting robot, and two plastic plates were painted simultaneously. The coated plastic plate is held at room temperature for 5 minutes, then dried in a dryer at 50 ° C. for 10 minutes, and then the coating film surface is cured with an ultraviolet irradiator. Was evaluated.

  As a result, both the plastic plates have an average film thickness of 20 μm and an average roughness of 0.4 μm, which is equivalent to an organic solvent air spray performed by adding the same amount of thinner as the paint, and is a practical level coating film. It was evaluated. This result was exactly the same as the result of painting performed with one spray gun. As a result of applying the same ultraviolet curable clear paint by air spraying without adding thinner, the film thickness was 20 μm, the average roughness was 0.9 μm, and it was confirmed that the roughness was twice or more. This shows the result of demonstrating the superiority of carbon dioxide coating. In this example, spraying on the object to be coated was performed after the state of each part was stabilized, so it did not affect the state of the coating film. Therefore, in the actual operation, it may be improved from the viewpoint of paint utilization efficiency (coating efficiency).

(Painting experiment 2-with instantaneous stop)
Coating was performed using the same paint and the same apparatus as in Example 1. However, in this embodiment, the object to be painted is a single horizontally long plastic plate, and while painting with two spray guns, the two-dimensional painting robot moves sideways and stops instantaneously at both ends of the object. The range of painting is expanded to the depth (vertically) while reversing the painting direction. The spray outline (instantaneous stop timing) is shown in FIG. One side of the two spray guns stops instantaneously. At this time, as shown in FIG. 6, V-1 is open, V-2 is closed, V-3 is closed, and V-4 is closed.

The pressure of each part was set to 8 MPa for the primary pressure adjustment valve 4, 11 MPa for the primary pressure adjustment valve 13, and 6 MPa for the secondary pressure adjustment valves 19 and 21, respectively. The stroke was adjusted from the flow rate / pump stroke relationship obtained in advance so that the discharge amount of the paint high-pressure pump was 100 g / min. The scale was adjusted from the flow rate / pump scale relationship determined in advance so that the discharge amount of the CO ₂ high-pressure pump was 15 g / min. An elliptical high-pressure nozzle having an orifice equivalent diameter of 0.13 mm was attached to the tip of the spray guns 20 and 22. The change with time in the pressure and flow rate in this example is shown in FIG.

The numerical value of the paint mass flow meter 5 was 75 g / min immediately after the start of spraying, and gradually decreased to 60 to 65 g / min. At this time, the numerical value of the mass flow meter installed in the line of the spray gun 22 was about 30 to 35 g / min, and the increase and decrease were repeated. However, even if the instantaneous stop is performed at both ends of the coating object, two spray guns Thus, it was confirmed that the paint was sprayed evenly (the instantaneous stop operation was confirmed to be effective). Since the discharge amount of the paint high-pressure pump 3 was set to 100 g / min, the remaining less than 40 g / min was circulated to the paint tank 1 via the primary pressure regulating valve 4. At this time, the CO ₂ mass flow meter 11 showed 10 to 15 g / min, which was 15 to 20% with respect to the paint flow rate.

After a certain time of painting operation, the stop valves V-3-1 and V-3-2 were closed for several tens of seconds in order to replace the painting object. At that time, in order to prevent the spray gun nozzle from being blocked, the stop valves V-4-1 and V-4-2 were opened for several seconds and then closed. In the present embodiment as well, as in the first embodiment, it takes time until the spray amount of the paint is stabilized at the start of spraying. These results from the fact that when the spraying is stopped, the pressure in the mixing section increases and it takes time to stabilize at the time of respraying. Moreover, it became clear that the CO ₂ flow rate also slightly fluctuated with the pressure fluctuation. Thereafter, the same operation as in Example 1 was performed, and the coating film was evaluated. However, since spraying on the object to be coated was performed after the state of each part was stabilized, the coating film state of the plastic plate was a practical level. It was evaluated.

(Painting experiment 3-with instantaneous stop and short stop)
Coating was performed using the same paint, the same apparatus, and the same coating object as in Example 2. In this example, in addition to the instantaneous stop, a short stop operation was performed when replacing the coating object. At this time, the open / close state of the stop valve is V-1 closed, V-2 open, V-3 closed, V-4 open → closed. The pressure setting for each part is as follows: the primary pressure adjusting valve 4 is set to 9.3 MPa, the primary pressure adjusting valve 13 is set to 10 MPa, and the secondary pressure adjusting valves 19 and 21 are set to 6 MPa, respectively. The primary pressure regulating valve 40 is 9.3 MPa.

The stroke was adjusted based on the flow rate / pump stroke relationship obtained in advance so that the discharge amount of the paint high-pressure pump was 70 g / min. The scale was adjusted from the flow rate / pump scale relationship determined in advance so that the discharge amount of the CO ₂ high-pressure pump was 10 g / min. An elliptical high-pressure nozzle having an orifice equivalent diameter of 0.13 mm was attached to the tip of the spray guns 20 and 22. The change with time in the pressure and flow rate in this example is shown in FIG.

  The numerical value of the paint mass flow meter 5 is almost constant immediately after the start of spraying. The numerical value of the mass flow meter installed in the line of the spray gun 22 is about 30 to 35 g / min. It was confirmed that the paint was sprayed evenly with the two spray guns even if the instantaneous stop was performed at both ends of the object to be coated (the instantaneous stop operation was confirmed to be effective).

Since the discharge amount of the paint high-pressure pump 3 was set to 70 g / min, the remaining less than 5 g / min was circulated to the paint tank 1 via the primary pressure regulating valve 4. At this time, the CO ₂ mass flowmeter 11 also showed almost no fluctuation, indicating 10 g / min, and 15% with respect to the paint flow rate. After a certain period of painting operation, a short stop operation was performed for several tens of seconds in order to replace the object to be painted. That is, stop valve-1 and V-3-2 were closed, and V-1 was closed and V-2 was opened at the same time. At that time, in order to prevent the spray gun nozzle from being blocked, the stop valves V-4-1 and V-4-2 were opened for several seconds and then closed. As is clear from the figure, it was confirmed that there was no large fluctuation in all pressures and flow rates during a short stop, and it was stable, and even after respraying, it reached a stable state in a short time. Confirmed to be valid).

  Then, operation similar to Example 1, 2 was performed, and the coating film was evaluated. In this example, although the spray onto the object to be coated was performed immediately after the start of spraying, the coating state of the plastic plate was evaluated as a practical level. Unlike the first and second embodiments, the present embodiment does not perform abandonment when resuming spraying, and has a very important meaning from the viewpoint of paint utilization efficiency (coating efficiency).

  In addition to UV-curing clear paint, carbon dioxide coating is applied to the two-part curable acrylic urethane clear paint and one-part curable acrylic clear paint using the same equipment and method as in the above examples. did. Although it was necessary to slightly change the true solvent composition depending on the paint, it was confirmed that the coating operation could basically be performed without any problem and a coating film having no practical problem was formed.

  As described above in detail, the present invention relates to a carbon dioxide coating method and a coating apparatus thereof, and according to the present invention, a new low-environmental load-type carbon dioxide coating capable of greatly reducing VOC generation. An apparatus and a coating method thereof can be provided. In the present invention, it becomes possible to replace a diluting solvent (VOC) used in a large amount with a very small amount of carbon dioxide in spray coating with a conventional organic solvent-based paint. It is possible to provide a new painting technology that prevents emission in the atmosphere. According to the present invention, it is possible to obtain a particularly effective effect that a carbon dioxide coating technique that can be practically used and that can surely suppress the problem of the device blockage due to the high viscosity of the paint can be provided. INDUSTRIAL APPLICABILITY The present invention is useful because it makes it possible to provide a new low-environmental load type carbon dioxide coating method and coating apparatus for preventing VOC emission into the atmosphere.

Claims (23)

In carbon dioxide coating, where the diluent solvent (thinner) used in organic solvent-based spray coating replaces part or all of it with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer A spray gun for spraying the mixed paint / carbon dioxide pressurized mixture to the object to be coated under atmospheric pressure, and the paint / carbon dioxide pressurized mixture as a branch line from the mixer to the spray gun. A primary pressure adjustment valve that adjusts the pressure and discharges the excess to atmospheric pressure, and a close valve (V-2) upstream from the primary pressure adjustment valve from the junction of the branch line between the mixer and the spray gun. The downstream of the stop valve (V-3), and further of the downstream of the stop valve (V-3), a stop valve (V-4) for supplying high-pressure carbon dioxide and a carbon dioxide introduction pipe. The painting equipment using the characteristic carbon dioxide. In carbon dioxide coating, where the diluent solvent (thinner) used in organic solvent-based spray coating replaces part or all of it with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer Secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture after mixing to a predetermined pressure, and the coating / carbon dioxide pressurized mixture after the secondary pressure regulating valve to be coated under atmospheric pressure There is a spray gun for spraying on the object, and the pressure of the paint / carbon dioxide pressurized mixture is adjusted as a branch line between the secondary pressure regulating valve and the spray gun, and the excess is discharged to atmospheric pressure. A primary pressure regulating valve and a closing valve (V-2) upstream thereof, and further, a closing valve (V-3) downstream from the junction of the branch line between the secondary pressure regulating valve and the spray gun. ) And high pressure dioxide downstream of the shut-off valve (V-3). Painting device using shut-off valve for supplying hydrogen and (V-4), providing the carbon dioxide inlet pipe, a carbon dioxide and said. In carbon dioxide coating, where the diluent solvent (thinner) used in organic solvent-based spray coating replaces part or all of it with carbon dioxide,
As a paint supply line, a tank that stores paint, a paint high-pressure pump that pressurizes the paint supplied from the tank to a predetermined pressure, and a paint 1 that adjusts the discharge pressure of the paint high-pressure pump and returns the excess to the paint tank. A secondary pressure regulating valve and a closing valve (V-1) upstream thereof,
As a carbon dioxide supply line, a tank that stores liquid carbon dioxide, a cooler that cools the liquid carbon dioxide to a predetermined temperature, a liquid carbon dioxide high-pressure pump that pressurizes the liquid carbon dioxide supplied from the cooler to a predetermined pressure, A liquid carbon dioxide primary pressure regulating valve that adjusts the discharge pressure of the liquid carbon dioxide high-pressure pump and returns the surplus to the suction of the pump;
As a paint / carbon dioxide mixture line, a mixer for mixing pressurized paint supplied from the paint supply line with pressurized carbon dioxide supplied from the carbon dioxide supply line, supplied from the mixer Secondary pressure regulating valve for reducing the mixed paint / carbon dioxide pressurized mixture after mixing to a predetermined pressure, and the coating / carbon dioxide pressurized mixture after the secondary pressure regulating valve to be coated under atmospheric pressure A spray gun for spraying on the object is provided, and the pressure of the paint / carbon dioxide pressurized mixture is adjusted as a branch line between the mixer and the secondary pressure regulating valve, and the excess is discharged to atmospheric pressure 1 A secondary pressure adjusting valve, a closing valve (V-2) upstream thereof, a closing valve (V-3) between the secondary pressure adjusting valve and the spray gun, and a further closing valve (V -3) downstream of the stop valve (V-4) for supplying high-pressure carbon dioxide; Providing the carbon dioxide introduction pipe coating apparatus using carbon dioxide, characterized in.   The coating apparatus using carbon dioxide according to any one of claims 1 to 3, wherein a part from the branch line merging point to the spray gun is configured in a plurality of series.   The coating apparatus using carbon dioxide according to any one of claims 1 to 4, further comprising a paint heater for heating the pressurized paint to a predetermined temperature.   The coating apparatus using carbon dioxide according to any one of claims 1 to 5, further comprising a cooler that cools surplus carbon dioxide returned to the suction of the liquid carbon dioxide high-pressure pump to a predetermined temperature.   The coating apparatus using the carbon dioxide in any one of Claim 1 to 6 which has a carbon dioxide heater which heats pressurized liquid carbon dioxide to predetermined temperature.   The coating apparatus using carbon dioxide according to any one of claims 1 to 7, further comprising a mixture temperature controller that adjusts the paint / carbon dioxide pressure mixture after mixing to a predetermined temperature.   The coating apparatus using carbon dioxide according to any one of claims 1 to 8, wherein the mixer is a micromixer capable of rapidly mixing paint and carbon dioxide.   The coating apparatus using carbon dioxide according to claim 9, wherein the micro mixer is a T-shaped micro mixer having a large channel diameter of 0.5 mm.   The micro-mixer is a center collision type micro-mixer that makes fluid collide at the center of a minute space. Carbon dioxide is allowed to flow in from the top, and the paint is divided into multiple parts so that they collide at the center from multiple directions on the side. The coating apparatus using the carbon dioxide of Claim 9 which is a mixer made to flow in.   The coating apparatus using carbon dioxide according to any one of claims 1 to 11, wherein the paint discharged from a primary pressure adjusting valve provided downstream of the branch line merging point returns to the paint tank.   The coating apparatus using carbon dioxide according to any one of claims 1 to 12, wherein the closing valve (V-3) and the closing valve (V-4) are incorporated in a spray gun.   The coating apparatus using carbon dioxide according to any one of claims 1 to 13, wherein the paint / carbon dioxide pressure mixture after the mixer is a one-phase mixture in which carbon dioxide is dissolved in the paint.   The coating apparatus using carbon dioxide according to any one of claims 1 to 14, wherein the paint is an ultraviolet curable paint, a one-part curable paint, or a two-part curable paint.   A method for performing coating using carbon dioxide using the coating apparatus according to any one of claims 1 and 4, wherein a primary pressure regulating valve on a pump discharge side is set higher than a spray pressure, and the pump A coating method using carbon dioxide, characterized in that, in a quantitative coating mode in which the entire discharge amount is sprayed, a primary pressure adjustment valve provided downstream of the junction of the branch lines is set to be equal to the spray pressure.   A method for performing coating using carbon dioxide using the coating apparatus according to any one of claims 1 and 4, wherein the flow rate of the fluid is automatically varied according to the spray pressure. The primary pressure adjustment valve on the pump discharge side is set to be equal to or slightly higher than the spray pressure, and the primary pressure adjustment valve on the fluid side that does not change the flow rate is set from the primary pressure adjustment valve setting value on the variable fluid side. By setting it higher, the flow rate of the fluid that does not change the flow rate is constant, the spray flow rate of the fluid that changes the flow rate is variable according to the flow rate characteristics of the orifice of the spray nozzle, and the excess pressure is returned to the pump suction A coating method using carbon dioxide, characterized in that, in the painting mode, a primary pressure adjusting valve provided downstream of the junction of the branch lines is set to be equal to the spray pressure.   A method for performing coating using carbon dioxide using the coating apparatus according to any one of claims 2 and 4 to 15, according to a spray pressure determined by a set value of a secondary pressure regulating valve. The primary pressure adjustment valve on the fluid discharge side that automatically changes the spray flow rate is set higher than the spray pressure, and the primary pressure adjustment valve on the fluid side that does not change the flow rate is adjusted on the primary pressure on the variable fluid side. By setting the flow rate higher than the valve setting value, the flow rate of the fluid that does not change the flow rate is made constant, the spray flow rate of the fluid that changes the flow rate is made variable according to the flow rate characteristics of the orifice of the spray nozzle, and the excess is pump suction A coating method using carbon dioxide, characterized in that, in the constant-pressure coating mode to return to, the primary pressure regulating valve provided downstream of the junction of the branch lines is set lower than the spray pressure.   A method of performing coating using carbon dioxide using the coating apparatus according to any one of claims 3 and 4 to 15 according to a spray pressure determined by a set value of a secondary pressure regulating valve. The primary pressure adjustment valve on the fluid discharge side that automatically changes the spray flow rate is set higher than the spray pressure, and the primary pressure adjustment valve on the fluid side that does not change the flow rate is adjusted on the primary pressure on the variable fluid side. By setting the flow rate higher than the valve setting value, the flow rate of the fluid without variable flow is made constant, the spray flow rate of the fluid with variable flow rate is made variable according to the flow rate characteristics of the orifice of the spray nozzle, and the excess is pumped A coating method using carbon dioxide, characterized in that, in a constant pressure coating mode for returning to suction, a primary pressure regulating valve provided downstream of a branch line merging point is set higher than a spray pressure.   Measure the mass flow rate of paint and carbon dioxide flowing into the mixer, and control the flow rate so that the pump discharge rate on the fluid side, which does not change the flow rate, is a constant ratio to the mass flow rate on the flow rate variable side. The coating method using the carbon dioxide according to any one of claims 17 to 19, characterized by the above.   21. The coating method according to claim 17, wherein the fluid for changing the flow rate is a paint.   The painting operation is divided into the painting mode in which painting is actually performed, the instantaneous stop mode in which painting is stopped for a few seconds, the short stop mode in which the paint is stopped for several tens of seconds, and the long-time stop mode in which the paint is stopped for several minutes. -1 open, V-2 closed, V-3 open, V-4 closed, in instantaneous stop mode, V-1 open, V-2 closed, V-3 closed, V-4 closed, in short stop mode, V-1 open, V-2 open, V-3 closed, V-4 open → closed, and in the long stop mode, V-1 open, V-2 closed, V-3 closed, V-4 open → The coating method according to claim 16 or 18, wherein the coating method is closed.   The painting operation is divided into the painting mode in which painting is actually performed, the instantaneous stop mode in which painting is stopped for a few seconds, the short stop mode in which the paint is stopped for several tens of seconds, and the long-time stop mode in which the paint is stopped for several minutes. -1 open, V-2 closed, V-3 open, V-4 closed, in instantaneous stop mode, V-1 open, V-2 closed, V-3 closed, V-4 closed, in short stop mode, V-1 closed, V-2 open, V-3 closed, V-4 open → closed, and in the long stop mode, V-1 open, V-2 closed, V-3 closed, V-4 open → The coating method according to claim 17 or 19, wherein the coating method is closed.