JP2023004820A - Composition for hydrophilic coating and structure comprising hydrophilic coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a composition for a hydrophilic coating that is easily formed on an underlayer coating film without deteriorating the function of the underlayer coating film; and a structure comprising such a hydrophilic coating.

SOLUTION: The composition for a hydrophilic coating comprises colloidal silica and a thickening agent, where when a 10 μm-thick coating is formed on a white substrate, the color difference ΔE^* before and after coating the white substrate is 0.50 or less, and the viscosity measured according to JIS K5600-2-2 using a Stormer viscometer is in the range of 40-120 KU. The structure comprises a base, an underlayer coating film, and a coating with the composition for a hydrophilic coating, where the underlayer coating film is a thermally insulating coating film.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to hydrophilic coating compositions. The present invention also relates to structures containing hydrophilic coatings.

It is known to form a photocatalytic coating with titanium oxide in order to impart antifouling properties to buildings and the like. Although such a photocatalyst coating can impart high antifouling properties, there is a problem that coating unevenness is likely to occur and application is difficult.

Hydrophilic coatings using colloidal silica are known as other antifouling coatings. The surface on which the hydrophilic coating is formed can be easily washed off with rain or the like even if dirt adheres to it.

US Pat. No. 5,300,001 discloses a hydrophilic coating composition comprising a swellable layered silicate, colloidal silica, and a cross-linking agent. The paint described in Patent Document 1 improves the hydrophilicity of the coating and improves stain resistance, weather resistance and hot water resistance by containing a specific amount of swelling layered silicate.

JP 2014-070138 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydrophilic coating composition which does not impair the function of an undercoat and can be easily formed on the undercoat. Another object of the present invention is to provide a structure comprising such a hydrophilic coating.

The inventors have found that the above problems can be solved by the present invention having the following aspects.
<<Aspect 1>>
A hydrophilic coating composition comprising colloidal silica and a thickening agent,
When a coating with a thickness of 10 μm is formed on a white substrate, the color difference ΔE ^* before and after coating the white substrate is 0.50 or less, and a Stormer viscometer is used to conform to JIS K5600-2-2. is in the range of 40 to 120 KU,
Compositions for hydrophilic coatings.
<<Aspect 2>>
The hydrophilic coating composition according to aspect 1, wherein the thickener is a swellable layered silicate or a water-soluble polymer.
<<Aspect 3>>
A hydrophilic coating composition according to aspect 2, wherein the thickening agent is a synthetic smectite.
<<Aspect 4>>
A hydrophilic coating composition according to aspect 2, wherein the thickening agent is hydroxyethylcellulose.
<<Aspect 5>>
5. The hydrophilic coating composition according to any one of aspects 1 to 4, wherein the colloidal silica is contained in a solid concentration of 2 to 10% by mass.
<<Aspect 6>>
A hydrophilic coating composition according to any one of aspects 1 to 5, further comprising a water-soluble dye.
<<Aspect 7>>
A structure comprising a substrate, an undercoat, and a coating with the hydrophilic coating composition according to any one of aspects 1 to 6, wherein the undercoat is a heat barrier coating. body.

ADVANTAGE OF THE INVENTION According to this invention, the hydrophilic coating composition which does not deteriorate the function of an undercoat and can be easily formed on an undercoat can be provided. Also according to the present invention, a structure comprising such a hydrophilic coating can be provided.

FIG. 1 shows the results of coating tests using the hydrophilic coating compositions of Example 1 and Reference Example. FIG. 2 shows the results of exposure testing of coatings with the hydrophilic coating composition of Example 1. FIG.

<<Hydrophilic coating composition>>
The hydrophilic coating composition contains colloidal silica and a thickening agent, is highly transparent, and is relatively viscous. The hydrophilic coating composition has a color difference ΔE ^* of 0.50 or less before and after coating of the white substrate when a coating with a thickness of 10 μm is formed on the white substrate, and a Stormer viscometer The viscosity measured according to JIS K5600-2-2 is in the range of 40 to 100 KU.

Conventionally, a heat-shielding coating film used for a roof of a building or the like has improved heat-shielding properties by being used on the outermost surface. However, as a result of investigations by the present inventors, it has been found that dirt adhering to the heat-shielding coating film has a non-negligible effect on the heat-shielding performance of the coating film. Therefore, as a result of further studies by the present inventors, it was found that the use of the above-described hydrophilic coating composition does not affect the function of the heat-shielding coating film even when a coating is formed on the heat-shielding coating film. It has been found that the coating can be formed even on the thermal coating film with little coating unevenness, dirt does not adhere easily, and even if dirt adheres, it can be easily washed away by rain or the like. On the other hand, in the hydrophilic coating composition described in Patent Document 1, the coating is partially cloudy as described in the examples, so light irradiation of the heat-shielding coating film etc. is important. It has not been found to be effective in forming a coating over a basecoat.

The hydrophilic coating composition has a color difference ΔE ^* of 0.50 or less, 0.40 or less, or 0.30 or less before and after coating of the white substrate when a coating having a thickness of 10 μm is formed on the white substrate. , 0.25 or less, 0.20 or less, 0.15 or less, or 0.10 or less. Here, as the white substrate, a white coating film having a dry film thickness of 50 μm formed on a coating hiding rate test paper (Miracool Farm, Miracool Co., Ltd.) is used. The color difference ΔE ^* can be obtained by measuring the L ^* a ^* b ^* values before and after forming the hydrophilic coating using a color difference meter CR-410 manufactured by Konica Minolta, Inc. and calculating from those values. can. When the hydrophilic coating composition contains a water-soluble dye, the color difference ΔE ^* is measured in a state where there is no coloring effect of the dye, for example, after the dye is faded after forming the coating. .

A coating with a hydrophilic coating composition may have a haze of 50% or less, 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less. Haze is measured by coating a hydrophilic coating composition on a glass substrate and drying at a temperature of 0 to 80° C. for 60 minutes to 10 days to form a coating. etc. can be measured.

The hydrophilic coating composition has a viscosity in the range of 40 KU to 120 KU as measured at 25° C. using a Stormer viscometer according to JIS K5600-2-2. As a Stormer viscometer, specifically, a Brookfield Digital Stormer viscometer KU-3 available from Eiko Seiki Co., Ltd. is used, a Krebs standard rotor KU-1030 is used, and the rotor is 100 in about 30 seconds. Viscosity can be measured as it rotates. The viscosity may be 40 KU or greater, 42 KU or greater, 45 KU or greater, 49 KU or greater, 50 KU or greater, 55 KU or greater, or 60 KU or greater; It may be 60 KU or less. The viscosity may be, for example, 42 KU to 100 KU, 45 KU to 70 KU, or 49 KU to 60 KU. A viscosity within this range facilitates the formation of a thin and uniform coating on the base coat. If the viscosity is too high, the coating will tend to be thick, which may result in reduced transparency, longer drying times, and economic problems. In this specification, when the measured value tends to vary, the measurement may be performed 10 times or more, and the average value thereof may be used as the measured value.

Also, the hydrophilic coating composition was measured at 25° C. using a Brookfield B-type viscometer RV/DVE available from Eiko Seiki Co., Ltd., using a spindle No. 5 (RV-5) measured at 6 rpm may have a viscosity of 500 mPa s or more, 1000 mPa s or more, 2000 mPa s or more, 3000 mPa s or more, or 30000 mPa s or less and 20000 mPa s or less. , 10000 mPa·s or less, 8000 mPa·s or less, or 5000 mPa·s or less. This viscosity may be, for example, from 500 mPa·s to 30000 mPa·s, or from 2000 mPa·s to 10000 mPa·s. In addition, the viscosity measured at 60 rpm may be 300 mPa s or more, 500 mPa s or more, or 1000 mPa s or more, and may be 8000 mPa s or less, 5000 mPa s or less, 3000 mPa s or less, and 2000 mPa s. or less, or 1000 mPa·s or less. This viscosity may be, for example, from 300 mPa·s to 8000 mPa·s, or from 300 mPa·s to 2000 mPa·s.

For example, when the thickener of the hydrophilic coating composition is an inorganic thickener, the viscosity measured under the above conditions at 6 rpm is 2000 mPa s or more, 2500 mPa s or more, or 3000 mPa s or more. 20000 mPa·s or less, 15000 mPa·s or less, 10000 mPa·s or less, 8000 mPa·s or less, or 5000 mPa·s or less. This viscosity may be, for example, from 2000 mPa·s to 20000 mPa·s, or from 3000 mPa·s to 10000 mPa·s. In that case, the viscosity measured under the above conditions at 60 rpm may be 300 mPa s or more, 400 mPa s or more, or 500 mPa s or more, 3000 mPa s or less, 2000 mPa s or less, or 1500 mPa s. or less, or 1000 mPa·s or less. The viscosity may be, for example, from 300 mPa·s to 3000 mPa·s, or from 300 mPa·s to 1000 mPa·s.

For example, when the thickener of the hydrophilic coating composition is an organic thickener, the viscosity measured under the above conditions at 6 rpm is 500 mPa·s or more, 1000 mPa·s or more, or 2000 mPa·s or more. 30000 mPa·s or less, 20000 mPa·s or less, 10000 mPa·s or less, 8000 mPa·s or less, or 5000 mPa·s or less. This viscosity may be, for example, from 500 mPa·s to 30000 mPa·s, or from 500 mPa·s to 10000 mPa·s. In that case, the viscosity measured under the above conditions at 60 rpm may be 300 mPa s or more, 500 mPa s or more, or 1000 mPa s or more, and may be 8000 mPa s or less, 5000 mPa s or less, or 3000 mPa s. Below, it may be 2000 mPa·s or less, or 1000 mPa·s or less. This viscosity may be, for example, from 300 mPa·s to 10000 mPa·s, or from 300 mPa·s to 5000 mPa·s.

The hydrophilic coating composition can have thixotropic properties, thereby facilitating formation of a coating formation on the underlying coating. The thixotropy can be evaluated from the ratio (TI value) of the viscosity measured at 6 rpm to the viscosity measured at 60 rpm using the viscosity measured under the above measurement conditions. The TI value (viscosity measured at 6 rpm/viscosity measured at 60 rpm) of the hydrophilic coating composition may be 1.0 or more, 3.0 or more, 5.0 or more, or 8.0 or more, It may be 12.0 or less, 10.0 or less, 8.0 or less, 5.0 or less, or 3.0 or less. This TI value may be, for example, 1.0 to 12.0, or 3.0 to 10.0.

For example, when the thickener of the hydrophilic coating composition is an inorganic thickener, the thixotropy may be 5.0 or more, 7.0 or more, or 8.0 or more, and 12.0 11.0 or less, or 10.0 or less. This thixotropy may be, for example, 5.0 to 12.0, or 7.0 to 11.0.

For example, when the thickener of the hydrophilic coating composition is an organic thickener, the thixotropy may be 1.0 or more, 1.5 or more, 2.0 or more, or 3.0 or more. It may well be 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less. This thixotropy may be, for example, from 1.0 to 5.0, or from 1.5 to 3.0.

The hydrophilic coating composition coating may have a static contact angle with pure water of 50° or less, 30° or less, 25° or less, 22° or less, 20° or less, or 15° or less. This makes it possible to have a very high hydrophilicity and give the coating a high antifouling property. The static contact angle is measured by, for example, coating a hydrophilic coating composition on a glass substrate, drying at a temperature of 0 to 80° C. for 60 minutes to 10 days to form a coating, and using a contact angle meter DMo for this coating. -501 (manufactured by Kyowa Interface Science Co., Ltd.) or the like.

The hydrophilic coating composition does not need to contain an emulsion-based resin binder, such as an acrylic emulsion-based binder, and even if it does, it is 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less. can do.

<Colloidal silica>
Since the hydrophilic coating composition contains colloidal silica, a hydrophilic layer is formed on the coating surface by hydroxyl groups when the coating is formed, thereby making the coating antifouling.

Colloidal silica is preferably water-dispersed colloidal silica from the environmental point of view. Water-dispersed colloidal silica is silica particles dispersed in an aqueous medium. There are various types of colloidal silica, and although not particularly limited, approximately spherical silica particles having an average particle size of 5 to 100 nm as measured by observation with an electron microscope are dispersed in the medium. Type, type in which silica particles agglomerated in a chain shape with a thickness of 5 to 50 nm and a length of about 40 to 400 nm are dispersed in a medium, spherical silica particles with an average particle size of 10 to 50 nm and a pearl necklace shape with a length of 50 to 400 nm Examples include a pearl necklace-like type in which a continuous chain of particles is dispersed in a medium, and an annular type in which silica particles having an average particle size of 5 to 50 nm are annularly aggregated and dispersed in a medium. From the viewpoint of antifouling properties, colloidal silica of a type in which spherical silica particles are dispersed in a medium can be used. Also, the silica particles in the colloidal silica preferably have an average particle size of 5 to 100 nm or 8 to 20 nm. Within this range, antifouling properties, stability and the like tend to be good.

Examples of colloidal silica of a type in which substantially spherical or spherical silica particles are dispersed in water include Snowtex-20, Snowtex-O, Snowtex-C, and Snowtex-S manufactured by Nissan Chemical Industries, Ltd.; Adelite AT-20, AT-20N, AT-20A and AT-300 manufactured by ADEKA can be mentioned. Examples of chain type colloidal silica in which silica particles aggregated in a chain form are dispersed in water include SNOWTEX-UP and SNOWTEX-OUP manufactured by Nissan Chemical Industries, Ltd., and the like. Examples of pearl necklace type colloidal silica in which spherical silica particles linked in a pearl necklace shape are dispersed in a medium include Snowtex-PS-S, Snowtex-PS-M, and Snowtex-PS-S manufactured by Nissan Chemical Industries, Ltd. PS-SO, Snowtex-PS-MO and the like.

In the hydrophilic coating composition, the solid content of colloidal silica in the total solid content may be 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more. , 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, or 75% by mass or less. For example, the solid content of colloidal silica in the total solid content may be 60% by mass or more and 95% by mass or less, or 65% by mass or more and 90% by mass or less.

In the hydrophilic coating composition, the solid content of colloidal silica may be 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, 15% by mass or less, 10% by mass or more. % by mass or less, 8% by mass or less, or 6% by mass or less. For example, the solid content of colloidal silica may be 1% by mass or more and 15% by mass or less, or 2% by mass or more and 10% by mass or less.

<Thickener>
Hydrophilic coating compositions include thickeners and are relatively viscous as described above. The present inventors have found that when a colloidal silica-based coating composition contains a thickener and has sufficient viscosity, a coating can be formed relatively uniformly even on a resin-based coating. I found In the case of not containing a thickener, it was not possible to form a uniform coating particularly on a resin-based coating film of a silicone-based resin.

The type of the thickening agent is not particularly limited, and may be an inorganic thickening agent or an organic thickening agent. Examples of inorganic thickeners include inorganic thickeners that swell in water to increase viscosity, such as swelling clay, particularly swelling layered silicate. Examples of organic thickeners include organic thickeners that dissolve in water to increase viscosity, such as water-soluble polymers.

Examples of swelling layered silicates include smectite clay minerals such as montmorillonite, saponite, hectorite, beidellite, stevensite, and nontronite, vermiculite, halloysite, and swelling mica (mica). Among these, mention may be made in particular of synthetic, rather than natural, swelling layered silicates, such as synthetic smectites. Synthetic swellable layered silicates are preferred because they are low in impurities and can result in increased coating transparency.

When using an inorganic thickener, the content thereof may be 1.0% by mass or more, 1.5% by mass or more, or 2.0% by mass or more, and 5.0% by mass or less. It may be 0% by mass or less, 2.5% by mass or less, or 2.0% by mass or less. For example, the content of the inorganic thickener may be 1.0% by mass or more and 5.0% by mass or less, or 1.5% by mass or more and 3.0% by mass or less.

Water-soluble polymers include gum arabic, succinoglycan, welan gum, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, caseink santhan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid. Sodium, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, sodium polyacrylate, carboxyvinyl polymer, polyethylene oxide, copolymer of vinyl acetate and polyvinylpyrrolidone, crosslinked acrylic acid polymer, styrene acrylic acid copolymer Polymer salts and the like can be mentioned.

When using an organic thickener, the content thereof may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, and 2.0% by mass or less. It may be 5% by mass or less, 1.0% by mass or less, or 0.8% by mass or less. For example, the content of the organic thickener may be 0.1% by mass or more and 2.0% by mass or less, or 0.3% by mass or more and 1.0% by mass or less.

<Water-soluble dye>
The hydrophilic coating composition may further contain a water-soluble dye. Also, in another embodiment, the hydrophilic coating composition comprises colloidal silica and a water-soluble dye.

When a coating is formed using a composition that does not contain a water-soluble dye, the coating is transparent, so it is very difficult to determine whether the coating has been formed uniformly without coating unevenness. However, when the water-soluble dye is contained, it is possible to see at a glance whether or not the coating is uneven, so it is advantageous to contain the water-soluble dye in the hydrophilic coating composition. It was also found that when colloidal silica contains a water-soluble dye, only the water-soluble dye can be easily washed out with water after forming the coating. Therefore, after forming a colored coating containing a water-soluble dye, a clear and colorless coating can be obtained by washing the water-soluble dye out of the coating with water or rain.

The water-soluble dye is not particularly limited as long as it can be easily washed out with water from the coating, but known dyes such as direct dyes, acid dyes, and basic dyes can be used. Dyes for various applications can be used. Among these, food dyes are particularly safe and can be faded by ultraviolet light. Therefore, it is possible to fade the coloring with sunlight without washing off the coating with water, which is preferable. Moreover, even if it is washed with water, it is preferable because the environmental load is low. Among food dyes, blue food dyes such as Blue No. 1 are particularly preferable because they can provide a clean appearance to the hydrophilic coating composition. In this specification, the term "food dye" refers to dyes that can also be used in foods. For example, Blue No. 1 is known to be used in foods, but it is also used in pharmaceuticals, cosmetics, and the like.

The color of the dye is not limited to blue as described above, and may be any color that can be visually recognized when the coating is formed. For example, blue, green, yellow, orange, red, purple, etc. can be mentioned, and specifically, known as food dyes, Blue No. 1, Blue No. 2, Green No. 3, Yellow No. 4, Yellow Red No. 5, Red No. 2, Red No. 3, Red No. 40, Red No. 102, Red No. 104, Red No. 105, Red No. 106, etc., or combinations thereof can be used.

The content of the water-soluble dye is not particularly limited as long as the above functions can be exhibited, but it may be 0.005% by mass or more, 0.01% by mass or more, or 0.02% by mass or more, It may be 0.3% by mass or less, 0.2% by mass or less, 0.1% by mass or less, or 0.05% by mass or less. For example, the content of the water-soluble dye may be 0.005% by mass or more and 0.3% by mass or less, or 0.01% by mass or more and 0.1% by mass or less.

<Other ingredients>
The hydrophilic coating composition can further contain other components. For example, the hydrophilic coating composition includes deionized water, solvents, antifoaming agents, plasticizers, antifreeze agents, drying accelerators, ultraviolet absorbers, surfactants, curing agents, cross-linking agents, and the like. are not limited to these. However, they do not have to be substantially contained.

《Hydrophilic coating》
A hydrophilic coating can be formed by applying the hydrophilic coating composition described above. This coating can have anti-fouling properties and can be washed away with water from the surface.

"Structure"
The construction comprises, in that order, a substrate, a basecoat, and a coating with the hydrophilic coating composition described above. The structure is preferably a building, but is not limited to this, and may be a vehicle body or the like.

In order to form the undercoating film on the substrate, the undercoating may be applied onto the substrate by a brush, roller, spray, or the like. Similarly, brushes, rollers, sprays, etc. can be used to form the coating on the basecoat.

<Substrate>
The base of the structure is, for example, buildings such as buildings, houses, fences, etc.; soundproof walls of highways; bridges, various structures made of iron, concrete, etc. installed in parks; The outer wall surface can be exemplified. Common exterior wall materials can be mentioned as materials that constitute the exterior wall surface. For example, inorganic exterior materials such as ceramic siding boards, mortar, concrete, and slate; Exterior material: Wooden exterior materials such as natural wood and plywood can be mentioned.

<Undercoat>
The base coat is not particularly limited as long as it can exhibit its function as a base coat while being protected by a transparent coating, but particularly includes a heat-shielding coating formed by a heat-shielding paint.

Heat-shielding paint is a paint that suppresses temperature rise by reflecting sunlight. can be used. Here, weak solvent-based paints are those that use mineral spirits called weak solvents, aliphatic hydrocarbons, etc. as the main solvent, form a coating film at room temperature, and have adhesion to a wide range of substrates. There is such a feature. Examples of binder resins for paints include one or more paints composed of acrylic resins, urethane resins, silicone-based resins, fluorine-based resins, and the like.

Among these, it has been found that the above hydrophilic coating composition is particularly advantageous because it can form a uniform coating without coating unevenness even for a heat-shielding coating containing a silicone resin as a binder. . As used herein, the silicone-based resin is not particularly limited as long as it is a silicone-based resin used in the field of paint, and includes not only silicone resins but also other resins modified with silicone. Other silicone-modified resins include silicone-modified acrylic resins, silicone-modified polyurethane resins, silicone-modified polyester resins, silicone-modified alkyd resins, and silicone-modified epoxy resins. Moreover, organic resin-modified silicone resins can also be mentioned, and examples thereof include epoxy-modified silicone resins, polyester-modified silicone resins, alkyd resin-modified silicone resins, and the like. Such silicone-based resins generally have water repellency, and it is generally difficult to form a uniform coating without coating unevenness with a hydrophilic coating composition. Specific examples of such a heat-shielding paint include Miracool Farm, which is a water-based paint, and Miracool S100, which is a weak solvent-based paint.

As the heat-shielding material contained in the heat-shielding paint, heat-shielding materials conventionally used in heat-shielding paints can be used, for example, heat-shielding pigments and/or hollow particles can be used.

The heat-shielding pigment that can be used as the heat-shielding material of the heat-shielding paint is not particularly limited, whether it is an inorganic pigment or an organic pigment, as long as it can reflect at least near-infrared rays. For example, white pigments include titanium oxide and zinc oxide pigments, black pigments include manganese yttrium black pigments, and yellow pigments include azo pigments and benzimidazolone pigments. Examples of red pigments include quinacridone pigments, and examples of blue pigments include copper phthalocyanine blue pigments. The heat-shielding paint can contain one or more pigments selected from these pigments.

Hollow particles that can be used as a heat-shielding material for the heat-shielding paint include transparent or translucent ceramic hollow particles. Examples of such ceramic hollow particles include hollow particles of zirconia-titania composites, silicon boride-based ceramics, shirasu balloons, glass balloons, and the like. The particle diameter of the hollow particles can be in the range of 5 μm to 150 μm or 30 μm to 100 μm, and the inside of the hollow may be air, a gas other than air, or a vacuum. It is more effective from points etc.

The content of the heat insulating material contained in the heat insulating paint is, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 30% by mass. 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 15% by mass or less. For example, the content of the heat insulating material contained in the heat insulating paint may be 1% by mass or more and 50% by mass or less, or 10% by mass or more and 30% by mass or less.

<Other layers>
The construction may have other layers besides those mentioned above, such as a primer layer between the substrate and the basecoat, as is well known in the art.

The present invention will be described in more detail with the following examples, but the invention is not limited thereto.

《Manufacturing example》
25 parts by mass of colloidal silica (Snowtex C: water-dispersed colloidal silica, average particle size 10 to 20 nm, Nissan Chemical Co., Ltd.) is added to a container containing 59.10 parts by mass of ion-exchanged water and stirred, and an organic system is added. Hydroxyethyl cellulose (SP-900, Daicel Miraise Co., Ltd.) as a thickener was gradually added and further mixed. Thereafter, 0.015 parts by mass of Blue No. 1 as a coloring agent was added and further mixed to obtain a hydrophilic coating composition of Example 1.

The hydrophilic coating composition of Example 2 was prepared in the same manner as in Example 1, except that a synthetic smectite (Smecton SA, Kunimine Industries Co., Ltd.), which is an inorganic thickener, was used instead of the organic thickener. got

A hydrophilic coating composition of Reference Example was obtained in the same manner, except that no thickening agent was added.

《Physical property measurement》
<Transparency: ΔE ^* measurement>
A white paint was applied to a dry film thickness of about 50 μm over the white and black portions of the coating hiding rate test paper. Using a color difference meter CR-410 manufactured by Konica Minolta, Inc., the L ^* a ^* b ^* values of the coating film of the white paint were measured. Thereafter, the compositions of the above examples were used to form coatings of about 5-20 μm, and the L ^* a ^* b ^* values were also measured on the coatings. After forming the coating, the coloring agent was washed off before the measurement.

The results are shown in Table 1.

As can be seen from the results, all coatings have low ΔE ^* values before and after coating formation and are very transparent.

<Transparency: transmittance measurement>
A coating thickness of about 5-20 μm was formed on 2 mm float glass to measure total light transmittance (T.T), parallel line transmittance (P.T), haze, and diffuse transmittance (DIF). , haze meter NDH7000II (manufactured by Nippon Denshoku Industries Co., Ltd.) and the like. For reference, the transmittance of only the float glass was also measured.

The results are shown in Table 2.

<viscosity>
The viscosity of the hydrophilic coating composition was measured at 25° C. using a Stormer viscometer according to JIS K5600-2-2. As a Stormer viscometer, the viscosity was measured using a Brookfield digital viscometer KU-3 available from Eiko Seiki Co., Ltd. Spindle NO. 5 (RV-5) was measured for viscosity at 6 rpm and 60 rpm, and the TI value was also calculated.

The results are shown in Table 3.

<Static contact angle>
The static contact angle with water of the coating formed on the silicone rubber was measured using DMo-501 (manufactured by Kyowa Interface Science Co., Ltd.) or the like.

Table 4 shows the results of the average value when the measurement was performed three times.

《Coating test》
Example 1 in which a coating film is formed on a substrate with a weak solvent-based heat-shielding paint (Miracool S100, Miracool Co., Ltd.) containing a silicone resin as a binder, and 0.5 parts by mass of a thickener is further added. of the hydrophilic coating composition was used to form a coating. Similarly, a coating is formed using the hydrophilic coating composition of Example 2 containing 2.0 parts by mass of a thickener, and similarly, a coating is formed using the hydrophilic coating composition of Reference Example. bottom.

FIG. 1 shows photographs of the state of Example 1 and Reference Example immediately after coating formation and before coating decolorization. As shown in FIG. 1, the coating according to Example 1 was able to be formed relatively uniformly on the coating film, whereas the coating according to Reference Example caused large coating unevenness. In addition, the coating of Example 2 could be formed relatively uniformly on the coating film in the same manner as in Example 1.

《Exposure test》
A coating film is formed on the substrate with a weak solvent-based heat-shielding paint containing a silicone resin as a binder (Miracool S100, Miracool Co., Ltd.), and only half of the area contains 0.5 parts by mass of a thickener. The hydrophilic coating composition of Example 1 was used to form a coating. Then, the specimen was left outdoors for a certain period of time to observe the condition.

The results are shown in FIG. The area where the coating was formed was very clean because the dirt was washed out by the rain while it was left standing, while the area where the coating was not formed was dirty because the dirt was not washed out. is found to remain.

Claims (6)

A hydrophilic coating composition comprising colloidal silica and a water-soluble dye. A hydrophilic coating composition according to claim 1, wherein the water-soluble dye is a food dye. The food dyes are Blue No. 1, Blue No. 2, Green No. 3, Yellow No. 4, Yellow No. 5, Red No. 2, Red No. 3, Red No. 40, Red No. 102, Red No. 104, Red No. 105, Red 106, or a combination thereof. 4. The hydrophilic coating composition according to any one of claims 1 to 3, wherein the emulsion resin binder is 10% by mass or less. The hydrophilic coating composition according to any one of claims 1 to 4, comprising 2 to 10% by mass of the colloidal silica in terms of solid content. The hydrophilic coating composition according to any one of claims 1 to 5, wherein the solid content of colloidal silica in the total solid content is 60% by mass or more and 95% by mass or less.

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