JP6496443B1 - Water-based paint for carbon dioxide painting, coating composition, and painting method - Google Patents

Abstract

An object of the present invention is to provide a water-based paint or the like that can reduce blockage of a coating apparatus in a carbon dioxide coating method.
An aqueous paint for carbon dioxide coating comprising a resin and an aqueous medium, wherein the aqueous paint is an emulsion having a pH of 7.0 or less.
[Selection] Figure 1

Description

  The present invention relates to a water-based paint for carbon dioxide coating and the like.

  As a kind of coating method, there is known a method (a carbon dioxide coating method) in which a coating composition is prepared by mixing carbon dioxide with a paint, and the obtained coating composition is sprayed on an object. Among the paints, water-based paints are considered promising because most of the contained solvent is water and the content of volatile organic compounds (VOC) that may adversely affect the environment is small. As an example of applying a carbon dioxide coating method to a water-based paint, there is a method described in Patent Document 1.

JP-T 09-502923

  In the carbon dioxide coating described in Patent Document 1, the resin contained in the water-based paint may gel and the coating apparatus may be blocked.

  This invention is made | formed in view of the said subject, and it aims at providing the water-based coating material for carbon dioxide coating etc. which can reduce the obstruction | occlusion of a coating device.

  As a result of intensive studies, the present inventors have found that water-based paints that stably form emulsions at a pH of 7.0 or lower can be used for precipitation and gelation of resins even when applied by a carbon dioxide coating method. Has been found to be reduced, and the present invention has been completed.

  The aqueous paint for carbon dioxide coating according to one embodiment of the present invention is an emulsion containing a resin and an aqueous medium and having a pH of 7.0 or less.

  The aqueous paint may be an emulsion having a pH of 6.0 or less.

  The coating composition which concerns on one form of this invention contains a water-based coating material and a carbon dioxide. The aqueous paint includes a resin and an aqueous medium, and the coating composition is an emulsion having a pH of less than 7.0.

  A coating method according to an aspect of the present invention includes a step of obtaining a coating composition by mixing an aqueous paint and carbon dioxide, and a step of spraying the coating composition onto an object. The aqueous paint is an emulsion containing a resin and an aqueous medium and having a pH of 7.0 or less.

  The coating composition can be an emulsion having a pH of less than 7.0.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based coating material for carbon dioxide coating etc. which can reduce the obstruction | occlusion of a coating device are provided.

It is a block diagram which shows one Embodiment of a coating device.

<Water-based paint>
The aqueous paint for carbon dioxide coating according to one embodiment of the present invention is an emulsion containing a resin and an aqueous medium and having a pH of 7.0 or less. In the present specification, an emulsion (also referred to as a dispersion) means a form in which a particulate resin is dispersed in an aqueous medium mainly composed of water. The diameter of the resin particles can be, for example, 0.01 μm or more, 0.05 μm or more, 0.05 to 5 μm, 0.05 to 0.5 μm, or 0.05 to 0.1 μm. The emulsion may be formed, for example, by emulsion polymerization. Alternatively, an emulsion can be formed by using an emulsifier (forced emulsification) or using a resin into which a hydrophilic group has been introduced (self-emulsification).

  The resin is a component that forms a polymer that functions as a binder or a matrix in a coating film formed after drying the water-based paint. Examples of the polymer include, for example, an acrylic resin, a polyurethane resin, an epoxy resin, a polyester resin, an alkyd resin, a polyol resin, a vinyl acetate resin, a fluororesin, a silicon resin, and a plurality of resins (including a prepolymer). Includes polymerized composite resin. Examples of the composite resin include acrylic-urethane resin, acrylic-styrene resin, vinyl acetate-acrylic resin, and acrylic-silicon resin. You may use resin individually or in combination of 2 or more types.

  The resin may be a compound that is already a polymer in the state of the water-based paint before painting, or it is not a polymer in the state of the water-based paint before painting, but the polymer is polymerized, crosslinked, etc. when dried after painting. It may be a mixture of a main agent (monomer or prepolymer) and a curing agent to be formed. In the latter case, the resin may be a one-pack type or a two-pack type. In this case, the main agent particles and the curing agent particles may be separately dispersed in the aqueous medium. Examples of the combination of the main agent and the curing agent include a combination of acrylic polyol and polyisocyanate. In this case, when the aqueous medium evaporates from the aqueous paint, an acrylic urethane resin is formed.

  The aqueous medium is a one-phase liquid medium mainly composed of water. The aqueous medium may be water or a mixed solvent containing a water-soluble solvent other than water.

  The amount of the resin in the aqueous paint may be, for example, 25 to 80% by mass, 30 to 75% by mass, 35 to 70% by mass, or 40 to 65% by mass based on the total amount of the resin and the aqueous medium. .

  The water-based paint may contain a solvent other than water, but most of the solvent contained in the water-based paint is water. The water content is, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, based on the total amount of the solvent in the water-based paint. It can be at least mass%, at least 95 mass%, at least 98 mass%, or at least 99 mass%. The water-based paint may not contain a solvent other than water.

  Examples of the solvent other than water include methyl ethyl ketone, propylene glycol monomethyl ether, ethylene glycol mono-n-butyl ether (butyl cellosolve), propylene glycol, ethanol, methanol, isopropyl alcohol, dimethylformamide, acetonitrile, dimethyl sulfoxide, ethylene glycol, diethylene glycol, Glycerol, 1-methoxy-2-propanol, diethylene glycol monobutyl ether (butyl carbitol), diethylene glycol monobutyl ether acetate (butyl carbitol acetate), propylene glycol monomethyl ether, 2,2,4-trimethyl 1,3-pentanediol monoiso Butyrate, 2-amino-2-methyl-1-propanol, etc. Number organic solvents are exemplified. Among solvents other than water, a water-soluble solvent can be dissolved in water to constitute the above-mentioned aqueous medium.

  The water-based paint may further contain an additive as necessary. For example, an aqueous medium is an emulsifier, a dispersant, a pH adjuster, an antifreezing agent (for example, propylene glycol), a film forming aid, an antifoaming agent, a pigment, a pigment dispersant, an antiseptic, an ultraviolet absorber, a light stabilizer. In addition, additives such as a leveling agent, an adhesion imparting agent, a rheology control agent and the like that are usually added to paints may be included.

  The pH of the water-based paint is 7.0 or less, less than 7.0, 6.5 or less, 6.0 or less, 5.5 or less, 5.0 or less, 4.7 or less, 4.6 or less, 4.6 or less. It can be 5 or less, 4.4 or less, or 4.0 or less. Water-based paints exist as emulsions at such pHs. That is, in the aqueous paint, the resin exists in a state dispersed in an aqueous medium. The additive may be dissolved in the aqueous medium or may be dispersed in the aqueous medium. In the present invention, it is important to select an aqueous paint in which an emulsion is stably formed in such a pH range.

<Coating method>
A coating method according to an aspect of the present invention includes a step of mixing the above-described aqueous paint and carbon dioxide to obtain a coating composition (mixing step), a step of spraying the coating composition onto an object (spraying step), Is provided.

(1. Mixing process)
In this step, a water-based paint and carbon dioxide are mixed to obtain a coating composition.

  The amount of carbon dioxide is not particularly limited, and is, for example, 0.5 parts by mass or more, 1.0 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 5 parts by mass with respect to 100 parts by mass of the water-based paint. Part or more, 6 parts by weight or more, or 10 parts by weight or more. When the amount of carbon dioxide is 0.5 parts by mass or more with respect to 100 parts by mass of the aqueous paint, fine mist can be formed. The amount of carbon dioxide is, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less with respect to 100 parts by mass of the water-based paint. Can do.

  The mixing temperature is not particularly limited, and can be, for example, 0 ° C to 60 ° C or 10 ° C to 30 ° C. When the water-based paint is a two-pack type, when the mixing temperature is 60 ° C. or less, the usable time (pot life) of the coating composition tends to be good.

  The mixing pressure is not particularly limited, and can be, for example, 2 MPa or more, 5 MPa or more, or 2 MPa to 25 MPa.

  The method of mixing is not particularly limited, and the mixing can be, for example, mixing by a line blend method using an in-line mixer.

  The coating composition obtained by mixing the water-based paint and carbon dioxide contains the water-based paint and carbon dioxide. As stated above, the water-based paint is an emulsion containing a resin and an aqueous medium and having a pH of 7.0 or less. The overall coating composition can be an emulsion having a pH of less than 7.0. In this case, carbon dioxide may be dissolved in an aqueous medium. The pH of the coating composition is, for example, less than 7.0, 6.5 or less, 6.0 or less, 5.5 or less, 5.0 or less, 4.7 or less, 4.6 or less, 4.6 or less, 4.5 or less, 4 .4 or less, or 4.0 or less.

  In the present embodiment, since the water-based paint stably forms an emulsion at a pH of 7.0 or lower, even if carbon dioxide is mixed and the pH is further inclined to the acidic side, the emulsion form is maintained and the resin is maintained. This may be because the deposition of the coating device can be reduced, and the blockage of the coating apparatus can be reduced.

(2. Spraying process)
In this step, the coating composition is sprayed. When the coating composition is sprayed, for example from a nozzle or orifice, the carbon dioxide in the coating composition released from the pressurized state is instantly vaporized and its volume expands significantly. Due to the energy generated by the expansion, the coating composition becomes a fine mist paint (mist).

  Although the temperature at the time of spraying is not specifically limited, For example, it can be 0-60 degreeC or 10 degreeC-30 degreeC. The temperature and pressure at the time of spraying may not be positively controlled, may be the same as the temperature and pressure at the time of mixing, or may be adjusted as appropriate. From the viewpoint of enabling spraying, the spray pressure is preferably 2 MPa or more or 5 MPa or more.

  The mist formed in the spraying process adheres to the object and forms a liquid film (water-based paint film) on the surface of the object. Thereafter, by drying the liquid film and removing the aqueous medium, the resin particles dispersed in the aqueous medium approach each other, and in some cases, a crosslinking reaction occurs, forming a coating film on the surface of the object. be able to.

<Coating equipment>
The coating by the above method can be performed using, for example, a coating apparatus shown in FIG. The coating apparatus includes a paint tank 1, a high-pressure pump 2, a heater 3, a carbon dioxide cylinder 4, a cooler 5, a high-pressure pump 6, a heater 7, a mixer 8, and a nozzle 9. The aqueous paint stored in the paint tank 1 is pressurized to a predetermined pressure by the high-pressure pump 2, heated to a predetermined temperature by the heater 3, and then supplied to the mixer 8. On the other hand, the carbon dioxide stored in the carbon dioxide cylinder 4 is cooled and liquefied by the cooler 5 and pressurized to a predetermined pressure by a high-pressure pump 6 (for example, a constant volume pump such as a plunger pump). The pressurized carbon dioxide is heated to a predetermined temperature by the heater 7 and then supplied to the mixer 8. A water-based paint and carbon dioxide are mixed in the mixer 8 to form a coating composition. As the mixer 8, for example, an in-line mixer can be used. The coating composition thus prepared is sprayed toward the object through the nozzle 9.

  The pressure in the mixer 8 can be adjusted by the discharge pressure of the high pressure pump 2 and the high pressure pump 6. Further, the temperature in the mixer 8 can be adjusted by the temperature of the water-based paint heated by the heater 3 and the temperature of carbon dioxide heated by the heater 7. The amount ratio of the water-based paint and carbon dioxide can also be adjusted by the discharge amount of each pump and a flow rate control valve (not shown).

  The coating apparatus is not limited to the apparatus shown in FIG. For example, in the apparatus shown in FIG. 1, the temperature during mixing is adjusted by the heaters 3 and 7 and the cooler 5, but these configurations are not essential. For example, instead of the heaters 3 and 7 and the cooler 5, a temperature adjusting unit such as a heat exchanger may be provided inside the mixer 8 to adjust the temperature during mixing. Moreover, in the apparatus shown in FIG. 1, although the pressure at the time of mixing is adjusted with the high pressure pumps 2 and 6, these structures are not essential. For example, instead of the high pressure pumps 2 and 6, the pressure during mixing may be adjusted by providing a pressure adjusting unit such as a pump or a pressure reducing valve in the mixer 8. Further, a temperature adjusting unit and / or a pressure adjusting unit may be provided on a line connecting the mixer 8 and the nozzle 9 to control the temperature and / or pressure during spraying.

  As described above, in the coating method according to the present embodiment, the water-based paint is an emulsion having a pH of 7.0 or less. When the water-based paint is an emulsion having a pH of 7.0 or less, blockage of the line in the carbon dioxide coating apparatus can be reduced. The present inventors presume this reason as follows.

When carbon dioxide dissolves in water, part of the dissolved carbon dioxide becomes carbonic acid, and part of the carbonic acid dissociates to release hydrogen ions. Therefore, when carbon dioxide and a water-based paint are mixed to form a coating composition, the pH of the aqueous medium in the coating composition is slightly inclined to the acidic side than the pH of the water-based paint before mixing.
In the emulsion, whether the aqueous medium is acidic or alkaline is considered to have a great influence on the dispersion stability of the emulsion. When an aqueous paint that stably forms an emulsion under alkaline conditions is mixed with carbon dioxide, the pH of the aqueous medium changes from alkaline to acidic due to a decrease in the pH of the aqueous medium in the coating composition as a result of mixing with carbon dioxide. It is considered that the emulsion cannot be stably formed. In this case, it is considered that the resins dispersed in the aqueous medium are deposited close to each other, and the deposited resin is a cause of blocking the line of the coating apparatus. On the other hand, according to one aspect of the present invention, since an aqueous paint that stably forms an emulsion at pH 7.0 or lower is used, even when the pH becomes more acidic by mixing carbon dioxide, It is considered that the emulsion can be stably maintained and the precipitation of the resin can be reduced because there is no significant change in the properties of the aqueous medium such that the pH of the aqueous medium changes from alkaline to acidic. As described above, according to the present invention, the precipitation of the resin is reduced, so that it is considered that the blocking of the coating apparatus can be reduced.

  EXAMPLES Hereinafter, although an invention is concretely demonstrated based on an Example, this invention is not limited to a following example.

  In the carbon dioxide coating apparatus as shown in FIG. 1, the paint components (resin, solvent, and pigment) shown in Table 1 are charged into the paint tank 1, and the mixing ratio of the aqueous paint and carbon dioxide in the mixer 8 is expressed. The flow rates of the high-pressure pumps 2 and 6 were set so that the mixing ratio (composition) shown in FIG. The temperature and pressure in the mixer 8 were adjusted to the temperatures and pressures shown in Table 1. In Table 1, the unit of the amount of each component is part by mass.

  The details of the paint components used are shown in Table 2. In Table 2, NV means the mass ratio of the non-volatile components (resin etc.) in the paint component. When NV is not 100%, a volatile solvent is contained in the paint component. Most of the solvent is water.

A painting test was performed and the object was painted with the coating composition for 5 minutes. The results are shown in Table 1. Regarding the evaluation of the “painting test”, ○ and × in Table 1 mean the following.
○: The object could be painted without blocking the line in the painting device.
X: The line in the coating apparatus was blocked.

  In Examples 1 to 6, in which the pH of the water-based paint before mixing with carbon dioxide was 7.0 or less, the object could be coated without blocking the line in the coating apparatus. In Comparative Examples 1 and 2 in which the pH of the paint before mixing with carbon dioxide was higher than 7.0, the line in the coating apparatus was blocked.

DESCRIPTION OF SYMBOLS 1 ... Paint tank, 2, 6 ... High pressure pump, 3, 7 ... Heater, 4 ... Carbon dioxide cylinder, 5 ... Cooler, 8 ... Mixer, 9 ... Nozzle.

Claims (4)

A water-based paint for carbon dioxide coating comprising a resin and an aqueous medium,
The water-based paint, which is an emulsion having a pH of 7.0 or less before being mixed with carbon dioxide . The water-based paint according to claim 1, which is an emulsion having a pH of 6.0 or less before mixing with carbon dioxide . Mixing a water-based paint and carbon dioxide to obtain a coating composition;
Spraying the coating composition onto an object, and
The coating method, wherein the aqueous paint is an emulsion containing a resin and an aqueous medium and having a pH of 7.0 or less. The coating method according to claim 3 , wherein the coating composition is an emulsion having a pH of less than 7.0.

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