JP7182055B2 - Coating film forming method and water-based coating composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coating film forming method and a water-based coating composition.

A plurality of panels may be juxtaposed on the wall surface of a building. In wall surfaces where a plurality of panels are juxtaposed, a sealing material is often cast at the joints of the panels in order to provide waterproofness and the like. On a wall where a plurality of panels are juxtaposed, the interval between adjacent panels may change due to an earthquake, temperature difference, or the like. A flexible resin material is used as the sealing material so as to follow such changes in the interval between the panels.

After the sealing material is placed in the joint, the entire wall surface including the joint is painted to form a coating film in order to protect the joint and hide the joint.
The coating film formed at this time is required to adhere to both the sealing material placed in the joint portion and the panel.
Further, when the interval between the panels changes, the sealing material follows the panels on both sides and is displaced. Therefore, the coating film is also required to follow the displacement of the sealing material.

Patent Document 1 describes a coating composition capable of forming a coating film that follows the displacement of a sealing material, comprising an isocyanate group-containing urethane prepolymer and an acrylic acid ester and/or a methacrylic acid ester having a polyoxyethylene chain in the molecule. A sealant topcoat composition containing

JP 2006-241259 A

However, the coating film of the coating composition of Patent Document 1 is too hydrophilic and has a problem of water resistance.
In order to improve the water resistance of the coating film, it is conceivable to lower the hydroxyl value of the resin in the coating composition. However, according to the study of the present inventors, simply lowering the hydroxyl value of the resin reduces the adhesion to the urethane-based sealant, causing the paint film to peel off from the surface of the sealant when the urethane-based sealant is displaced. In some cases, the coating film cracks and rolls up from the cracked part.

An object of the present invention is to provide a coating film-forming method and a water-based coating composition capable of forming a coating film having excellent adhesion to urethane-based sealing materials and water resistance.

The present invention has the following aspects.
[1] A method of applying a water-based coating composition to the surface of a urethane-based sealing material on which isocyanate remains and drying to form a coating film,
The water-based coating composition comprises an aqueous medium, a hydroxyl-free acrylic resin dispersed in the aqueous medium, and a hydroxyl-containing resin dissolved or dispersed in the aqueous medium,
the total hydroxyl value of the acrylic resin and the hydroxyl-containing resin is 13 to 65 mgKOH/g;
A method for forming a coating film, wherein the mass ratio represented by the acrylic resin/the hydroxyl group-containing resin is 20/80 to 80/20.
[2] A water-based coating composition to be applied to the surface of a urethane-based sealing material on which isocyanate remains,
An aqueous medium, an acrylic resin having no hydroxyl group dispersed in the aqueous medium, and a hydroxyl group-containing resin dissolved or dispersed in the aqueous medium,
the total hydroxyl value of the acrylic resin and the hydroxyl-containing resin is 13 to 65 mgKOH/g;
A water-based coating composition, wherein the acrylic resin/hydroxyl-containing resin has a mass ratio of 20/80 to 80/20.

ADVANTAGE OF THE INVENTION According to this invention, the coating-film formation method and water-based coating composition which can form the coating film which is excellent in the adhesiveness to a urethane-type sealing material, and water resistance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining one Embodiment of the coating-film formation method of this invention.

The coating film forming method of the present invention is a method of applying a water-based coating composition to the surface of a urethane-based sealing material on which isocyanate remains and drying to form a coating film,
The water-based coating composition comprises an aqueous medium, a hydroxyl-free acrylic resin dispersed in the aqueous medium, and a hydroxyl-containing resin dissolved or dispersed in the aqueous medium,
The mass ratio represented by the acrylic resin/the hydroxyl group-containing resin is 20/80 to 80/20,
The acrylic resin and the hydroxyl group-containing resin as a whole have a hydroxyl value of 13 to 65 mgKOH/g.

<Urethane sealant>
In the present invention, the “urethane-based sealing material” is a sealing material that contains isocyanate and that is hardened by the reaction (crosslinking reaction) of the isocyanate to generate urethane bonds.
Examples of urethane-based sealing materials include those of a type that contains isocyanate and polyol and that are cured by reaction between the NCO groups of the isocyanate and the hydroxyl groups of the polyol; A type that cures upon reaction (moisture-curing type) is exemplified.

As the isocyanate, polyisocyanate is generally used, and specific examples include hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and the like.
A hydroxyl-containing resin is generally used as the polyol. Examples of hydroxyl group-containing resins include acrylic polyols and polyester polyols.

The urethane-based sealing material may further contain a plasticizer. When the urethane-based sealing material contains a plasticizer, it is less likely to crack after curing.
Conventionally, when a urethane-based sealing material contains a plasticizer, bleeding of the plasticizer tends to reduce adhesion of a coating film formed thereon. However, according to the present invention, even when the urethane-based sealing material contains a plasticizer, it is possible to form a coating film with good adhesion to the urethane-based sealing material.
The plasticizer is not particularly limited, and examples thereof include phthalates such as dioctyl phthalate (DOP), dibutyl phthalate (DBP), and diisononyl phthalate (DINP).

<Water-based paint composition>
The water-based coating composition contains an aqueous medium, an acrylic resin having no hydroxyl group (hereinafter also referred to as "acrylic resin (A)"), and a hydroxyl-containing resin. Acrylic resin (A) is dispersed in an aqueous medium. The hydroxyl group-containing resin is dissolved or dispersed in the aqueous medium.
If necessary, the water-based coating composition may further contain components other than the water-based medium, the acrylic resin (A), and the hydroxyl group-containing resin within a range that does not impair the effects of the present invention. Each component will be described in detail later.

In the aqueous coating composition, the total hydroxyl value of the acrylic resin (A) and the hydroxyl-containing resin is 13-65 mgKOH/g, preferably 20-60 mgKOH/g, more preferably 30-50 mgKOH/g. When hydroxyl groups are present in the coating film of the water-based coating composition, the hydroxyl groups react with the isocyanate of the urethane-based sealing material at the interface with the urethane-based sealing material to improve adhesion, while the hydrophilicity of the coating increases and the water resistance. diminished sexuality. When the hydroxyl value is 13 mgKOH/g or more, the adhesion of the coating film to the urethane sealant is excellent. When the hydroxyl value is 65 mgKOH/g or less, the coating film has excellent water resistance.
The hydroxyl value of the acrylic resin (A) and the hydroxyl group-containing resin as a whole is the hydroxyl value (mgKOH/g) of each of the acrylic resin (A) and the hydroxyl group-containing resin, and the mass ratio of the acrylic resin (A) and the hydroxyl group-containing resin. calculated from

The mass ratio represented by acrylic resin (A)/hydroxyl-containing resin is 20/80 to 80/20, preferably 30/70 to 70/30, more preferably 40/60 to 65/35, and 51/ 49 to 60/40 is more preferred. If the mass ratio is 20/80 or more, the coating film of the water-based coating composition is excellent in water resistance, and if it is 80/20 or less, the coating film of the water-based coating composition has good adhesion to the urethane-based sealant. Excellent.

The solid content of the water-based coating composition is preferably 30-80% by mass, more preferably 40-70% by mass, relative to the total mass of the water-based coating composition.
The solid content means non-volatile components contained in the coating material remaining after drying at 125° C. for 1 hour, and is measured by the method of JIS K 5601-1-2.

(aqueous medium)
The aqueous medium is a medium containing only water or a medium obtained by adding a water-compatible solvent to water. The proportion of water in the aqueous medium is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.
As water, ion-exchanged water, tap water, or the like can be used.
Solvents compatible with water include alcohols such as ethanol and isopropyl alcohol, and ethylene glycol.

(Acrylic resin (A))
The acrylic resin (A) does not have a hydroxyl group and should be dispersible in an aqueous medium.
Acrylic resin (A) is typically at least one monomer selected from the group consisting of hydroxyl-free (meth)acrylic esters and (meth)acrylic acid (hereinafter also referred to as "acrylic monomer" ) (hereinafter also referred to as “acrylic polymer”). Here, "(meth)acrylic acid ester" means at least one of acrylic acid ester and methacrylic acid ester. "(Meth)acrylic acid" means at least one of acrylic acid and methacrylic acid.
Hereinafter, structural units based on monomers are also referred to as "monomer units".

(Meth)acrylic acid esters having no hydroxyl group include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, (meth)acryl alkyl (meth)acrylates such as isobutyl acid, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate; benzyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate and the like.

The acrylic polymer may have units of monomers other than acrylic monomers (hereinafter also referred to as “non-acrylic monomers”). Examples of non-acrylic monomers include styrene and vinyl acetate.
The ratio of acrylic monomer units to the total mass of all structural units constituting the acrylic polymer is preferably 70% by mass or more, more preferably 80% by mass or more, and may be 100% by mass.

At least part of the acrylic monomer units are preferably hydroxyl-free (meth)acrylic acid ester units. The (meth)acrylic acid ester unit having no hydroxyl group is preferably an alkyl (meth)acrylate unit.
The ratio of (meth)acrylic acid ester units having no hydroxyl group to the total mass of all structural units constituting the acrylic polymer is preferably 70% by mass or more, more preferably 80% by mass or more, and 100% by mass. may

Examples of the acrylic resin (A) include acrylic resins composed only of acrylic polymers, acrylic silicone resins, acrylic urethane resins, acrylic styrene resins, vinyl acetate-acrylic resins, and acrylic-fluororesins. These may be used individually by 1 type, and may use 2 or more types together. Among these resins, acrylic resins and acrylic silicone resins are preferable because they can form coating films with excellent weather resistance and water resistance.

The hydroxyl value of acrylic resin (A) is 0 mgKOH/g.

The glass transition temperature (hereinafter also referred to as “Tg”) of the acrylic resin (A) is preferably 30° C. or lower, more preferably 10° C. or lower. If the Tg of the acrylic resin (A) is equal to or less than the above upper limit, the adhesion of the coating film will be more excellent. The lower limit of the Tg of the acrylic resin (A) is not particularly limited, but is -20°C, for example.

Tg is a value obtained from the FOX formula shown in formula (i) below.
1/(Tg _P +273.15)=Σ[W _i /(Tg _i +273.15)] (i)
In formula (i), Tg _P is the Tg (°C) of the polymer, _Wm is the mass fraction of the monomer constituting the polymer, and _Tgm is the Tg (°C) of the homopolymer of the monomer.
The _Tgm is widely known as a characteristic value of a homopolymer, and for example, the value described in "POLYMER HANDBOOK, THIRD EDITION" or the manufacturer's catalog value may be used.

The average particle size of the acrylic resin (A) is, for example, 40-1000 nm.

(Resin containing hydroxyl group)
The hydroxyl-containing resin may be a resin (water-soluble resin or water-dispersible resin) that has hydroxyl groups and is soluble or dispersible in an aqueous medium. A water-dispersible resin is preferable in terms of durability.

Examples of hydroxyl-containing resins include hydroxyl-containing polyester resins, hydroxyl-containing silicone-modified polyester resins, hydroxyl-containing acrylic resins, hydroxyl-containing silicone-modified acrylic resins, hydroxyl-containing epoxy resins, hydroxyl-containing vinyl resins, and hydroxyl-containing fluorine resins. . These resins may be used singly or in combination of two or more.
Among them, hydroxyl group-containing acrylic resins and hydroxyl group-containing silicone-modified acrylic resins are preferable from the viewpoint of excellent water resistance and durability.

A hydroxyl group-containing acrylic resin typically includes a polymer having a hydroxyl group-containing (meth)acrylic acid ester unit (hereinafter also referred to as "hydroxyl group-containing acrylic polymer").
Examples of hydroxyl group-containing (meth)acrylic acid esters include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate.

The hydroxyl-containing acrylic polymer may further have a (meth)acrylic acid ester unit, a (meth)acrylic acid unit, a non-acrylic monomer unit, or the like, which does not have a hydroxyl group. Examples of the (meth)acrylic acid ester having no hydroxyl group and the non-acrylic monomer are the same as those described above.
The hydroxyl-containing acrylic polymer preferably has a (meth)acrylic acid ester unit having no hydroxyl group. The (meth)acrylic acid ester unit having no hydroxyl group is preferably an alkyl (meth)acrylate unit.

The ratio of the hydroxyl group-containing (meth)acrylic acid ester unit to the total mass of all structural units constituting the hydroxyl group-containing acrylic polymer is preferably 3 to 50% by mass, more preferably 5 to 40% by mass.

The hydroxyl value of the hydroxyl-containing resin is preferably from 20 to 120 mgKOH/g, more preferably from 30 to 100 mgKOH/g, even more preferably from 40 to 90 mgKOH/g. If the hydroxyl value of the hydroxyl-containing resin is within the above range, the hydroxyl value of the acrylic resin (A) and the hydroxyl-containing resin as a whole can easily be within the above range.

The hydroxyl value of the hydroxyl-containing resin is calculated from the monomer composition forming the hydroxyl-containing resin by the following formula.
Hydroxyl value (mgKOH/g) = (mass (parts) of hydroxyl-containing monomer + mass (parts) of monomer other than hydroxyl-containing monomer)/molecular weight of hydroxyl-containing monomer x 56.1 x 1000

The Tg of the hydroxyl group-containing resin is preferably 30°C or lower, more preferably 10°C or lower. If the Tg of the hydroxyl group-containing resin is equal to or less than the above upper limit, the adhesion of the coating film will be more excellent. The lower limit of the Tg of the hydroxyl group-containing resin is not particularly limited, but is -20°C, for example.

When the hydroxyl-containing resin is a water-dispersible resin, the average particle size of the hydroxyl-containing resin is, for example, 40 to 1000 nm.

(other ingredients)
The water-based coating composition may contain known additives as necessary. Known additives include antifoaming agents, viscosity modifiers, film-forming aids, antifreeze agents, dispersants, wetting agents, water-soluble resins, penetration aids, preservatives, surface modifiers, matting agents, gels agents, UV absorbers, antioxidants, heat shields, pH adjusters, and the like.
The water-based coating composition may contain a design material as necessary. Examples of design agents include coloring pigments, extender pigments, brightness pigments, cold water stones, colored stones, colored beads, delustered beads, and colored resin chips.

(Method for producing a water-based coating composition)
The water-based coating composition can be produced, for example, by mixing an emulsion in which an acrylic resin (A) is dispersed in an aqueous medium (hereinafter also referred to as "acrylic emulsion (A)") and a hydroxyl group-containing resin. At this time, if necessary, other components and further aqueous media may be mixed. The hydroxyl-containing resin may be mixed with the acrylic emulsion (A) in the form of a solution in which the hydroxyl-containing resin is dissolved in an aqueous medium or an emulsion in which the hydroxyl-containing resin is dispersed in an aqueous medium.

The acrylic emulsion (A) may contain components (emulsifier, pH adjuster, etc.) other than the acrylic resin (A) and the aqueous medium.
The solid content of acrylic emulsion (A) is, for example, 30 to 60% by mass relative to the total mass of acrylic emulsion (A).
As the acrylic emulsion (A), a commercially available one may be used, or one produced by a known production method may be used. For example, the acrylic emulsion (A) can be produced by polymerizing a monomer mixture containing acrylic monomers in the presence of an aqueous medium and a radical polymerization initiator. A chain transfer agent may be used during the polymerization. Examples of the polymerization method include an emulsion polymerization method and a suspension polymerization method, and the emulsion polymerization method is preferred.

The hydroxyl-containing resin solution or emulsion may contain components (emulsifier, pH adjuster, etc.) other than the hydroxyl-containing resin and the aqueous medium.
The solid content of the hydroxyl-containing resin solution or emulsion is, for example, 10 to 60% by mass based on the total mass of the hydroxyl-containing resin solution or emulsion.
The hydroxyl group-containing resin, solution or emulsion thereof may be commercially available or may be produced by a known production method. For example, a hydroxyl group-containing acrylic resin emulsion can be produced in the same manner as the above acrylic emulsion (A), except that the monomer mixture contains a hydroxyl group-containing (meth)acrylic acid ester.

<Method of Forming a Coating Film>
One embodiment of the coating film forming method of the present invention will be described in detail below with reference to the accompanying drawings. Note that the dimensional ratios in FIG. 1 are different from the actual ones for convenience of explanation.

As shown in FIG. 1, in the coating film forming method of the present embodiment, first, a urethane-based sealing material 12 is placed at the seam C between adjacent panels 10 on a wall surface on which a plurality of panels 10 are arranged ( step (a)). Next, while the isocyanate remains in the placed urethane sealing material 12, a water-based coating composition is applied to the surfaces of the urethane sealing material 12 and the panels 10 on both sides thereof, and dried (step (b)). ). Thereby, the coating film 1 is formed.

The panel 10 is not particularly limited, and can be applied to panels of various materials such as lightweight cellular concrete (ALC), siding boards, slate boards, and the like.

A commercially available product can be used as the urethane-based sealing material 12 .
The urethane-based sealing material 12 can be applied by a conventional method.
In the cast urethane-based sealing material 12, isocyanate reacts and hardens, and the amount of isocyanate decreases over time. The period during which isocyanate remains on the surface of the urethane-based sealing material 12 varies depending on the temperature, humidity, etc., but is generally about two weeks after placement.

There are no particular restrictions on the method of applying the water-based coating composition, and it can be applied by a known method such as a brush, trowel, roller, or spray.
The coating amount of the water-based coating composition is appropriately set according to the thickness of the coating film 1 to be formed.
The thickness of the coating film 1 (after drying) is, for example, 100 to 500 μm.
Drying may be performed by removing the aqueous medium, and drying at room temperature or drying by heating may be used. The drying temperature is, for example, 5-50°C. The drying time varies depending on the drying temperature, but is, for example, 30 minutes to 12 hours.

In addition, the coating film forming method of the present invention is not limited to the embodiment described above. Each configuration and combination thereof in the above-described embodiment are examples, and addition, omission, replacement, and other modifications of the configuration are possible without departing from the scope of the present invention.
For example, in the above embodiment, the urethane-based sealing material 12 is placed and the water-based coating composition is applied, but the water-based coating composition may be applied to the existing urethane-based sealing material.
Although the surface of the urethane-based sealing material 12 and the panels 10 on both sides thereof were coated with the water-based coating composition, the water-based coating composition may be applied only to the surface of the urethane-based sealing material 12 .
Another coating film may be formed by applying a known coating material on the coating film 1 by a known coating method.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the following, "parts" means "mass parts".

<Measurement method>
(Glass transition temperature (Tg))
The glass transition temperature (Tg) was calculated from the FOX formula.

(Hydroxyl value (OHV))
The hydroxyl value (OHV) was calculated by the following formula from the monomer composition used during polymerization.
Hydroxyl value (mgKOH/g) = (mass (parts) of hydroxyl-containing monomer + mass (parts) of monomer other than hydroxyl-containing monomer)/molecular weight of hydroxyl-containing monomer) x 56.1 x 1000

<Production Example 1>
60 parts of deionized water and 6.7 mass of Sunol NP-2030 (anionic emulsifier manufactured by Lion Corporation, 30% active ingredient) are placed in a polymerization apparatus equipped with a stirrer, cooler, and thermometer capable of heating and cooling. Nitrogen was bubbled under the liquid surface at a rate of 40 mL/min for 15 minutes, and then the internal temperature was raised to 80° C. while stirring.
In another container, 18 parts of methyl methacrylate, 27 parts of ethyl methacrylate, and 55 parts of n-butyl acrylate are mixed, and then 10 parts of Sunol NP-2030 and Leocol TD-300 (a nonionic emulsifier manufactured by Lion Corporation) are mixed. , active ingredient 100%) and 35 parts of deionized water are added, put in a Waring blender (DYNAMIC CORPORATION OFAMERICA, model LB10S) and stirred at 5000 rpm for 10 minutes to form a uniformly emulsified pre-emulsion (hereinafter referred to as "PE abbreviated as "liquid") was prepared, and nitrogen bubbling was performed for 15 minutes.
5 parts of the resulting PE solution was placed in a polymerization vessel, heated to 80° C., and when the internal temperature was stabilized, a solution of 0.2 parts of sodium persulfate dissolved in 1 part of deionized water was polymerized. It was put into a container and left for 1 hour while being stirred.
After 1 hour had passed, the rest of the PE liquid and a solution of 2 parts of sodium persulfate dissolved in 10 parts by mass of deionized water were stirred for 3 hours while maintaining the internal temperature of the polymerization vessel at 80°C. and dropped into the polymerization vessel. After the dropwise addition was completed, the internal temperature was maintained at 80° C. for 2 hours to complete the reaction.
After the reaction is completed, the temperature is cooled to 30° C., dimethylethanolamine is added so that the pH of the emulsion becomes 8.5, and deionized water is added so that the solid content becomes 40% by mass to form an acrylic resin emulsion (E -1) was obtained. Table 1 shows the monomer composition and the properties (Tg, OHV) of the acrylic resin.

<Production Examples 3 to 5>
Acrylic resin emulsions (E- 3 ) to (E-5) were obtained in the same manner as in Production Example 1, except that the monomer composition was changed as shown in Table 1. Table 1 shows the properties of the acrylic resin.

Abbreviations in Table 1 indicate the following.
MMA: methyl methacrylate.
EMA: ethyl methacrylate.
HEMA: 2-hydroxyethyl methacrylate.
BA: n-butyl acrylate.
2-EHA: 2-ethylhexyl acrylate.
NP-2030: an anionic emulsifier manufactured by Lion Corporation, active ingredient 30%.
TD-300: Nonionic emulsifier manufactured by Lion Corporation, 100% active ingredient.
The acrylic resin of the acrylic resin emulsion (E-1) corresponds to the acrylic resin (A), and the acrylic resins of the acrylic resin emulsions (E- 3 ) to (E-5) correspond to the hydroxyl group-containing resins.

[Examples 1 , 3, 4, 8 to 11, Comparative Examples 1 , 3 to 5]
(Manufacture of water-based coating composition)
Each material was placed in a container according to the formulations shown in Tables 2 and 3 and dispersed with a dissolver to prepare a water-based coating composition.
Tables 2 and 3 show the ratio (mass%) of the resin content to the total mass of the water-based coating composition, the hydroxyl value of the entire resin content, the mass of the acrylic resin (Ac) having no hydroxyl group and the hydroxyl-containing resin (AcOH) The ratio (Ac/AcOH ratio) is shown. Here, the "resin content" means the entire acrylic resin having no hydroxyl group and the hydroxyl group-containing resin.
In Tables 2 and 3, the unit of the blending amount of each material is parts. Materials used other than the acrylic resin emulsion are as follows.
Calcium carbonate: "Heavy calcium carbonate" manufactured by Maruo Calcium.
TiO ₂ : "Tipaque CR95" manufactured by Ishihara Sangyo Co., Ltd.
Formulation water: deionized water.
HEC: Hydroxyethyl cellulose, "QP52000H" manufactured by Dow Chemical Company.
Associative agent: "Coapur 6050" manufactured by Arkema.
Surface conditioner: "BYK-346" manufactured by BYK-Chemie.
Film-forming auxiliary: "Texanol" manufactured by EASTMAN CHEMICAL.

(Production of evaluation plate)
A urethane-based sealing material (Auto Sealer 101R, manufactured by Auto Kagaku Kogyo Co., Ltd.) was placed on the entire surface of a 7 cm x 15 cm slate plate to a thickness of 3 mm, and left at room temperature for 72 hours. Thereafter, the water-based coating composition was applied onto the placed urethane-based sealing material so that the thickness after drying was 150 μm, and dried at room temperature for 2 weeks to form a coating film. As a result, an evaluation plate was obtained in which the urethane-based sealing material and the coating film were laminated.

(Evaluation of curling up (adhesion evaluation))
The coating film of the produced evaluation plate was cut into strips of 1 cm long×5 cm wide together with the urethane-based sealing material, and the strips were peeled off from the slate plate to obtain test pieces. Holding both ends of the test piece in the longitudinal direction, the test piece was pulled to a length of 15 cm to generate cracks in the coating film. After that, the hand was released from the test piece, and the state of the coating film was visually observed and evaluated according to the following criteria. The results are shown in Tables 2-3. The higher the evaluation score, the better the adhesion of the coating film to the urethane sealant.
5: No change in the appearance of the coating film (no splitting is observed in the cracked portion).
4: A small hangnail (length of 3 mm or less) is observed in the cracked portion, but the end of the hangnail is not pinched by hand.
3: A hangnail was observed in the portion where the crack occurred, and the end of the hangnail was pinched by hand. If you pinch the edge of the hangnail and pull it, it will be torn off, and the coating will not come off on the part other than the hangnail.
2: A hangnail was observed in the portion where the crack occurred, and the end of the hangnail was pinched by hand. If you pick up the edge of the hangnail and pull it, the paint film on the part other than the hangnail also peels off, but the paint film breaks during the peeling, and it does not come off until the end.
1: A hangnail was observed in the portion where the crack occurred, and the end of the hangnail was pinched by hand. If you pick up the edge of the hangnail and pull it, the paint film on the part other than the hangnail also peels off, and the paint film does not break during peeling, and it can be peeled off to the end.

(Cold temperature cycle test (water resistance evaluation))
The prepared evaluation plate was subjected to 10 cycles, one cycle being "immersed in water at 23°C for 18 hours, then left in an atmosphere of -20°C for 3 hours, and then left in an atmosphere of 50°C for 3 hours." did. After that, the appearance of the coating film on the evaluation plate was visually observed and evaluated according to the following criteria. The results are shown in Tables 2-3.
○: No change.
Δ: Fine blisters are observed.
x: Blisters are observed on the entire surface.

The coating films formed in Examples 1 , 3, 4, 8 to 11 were excellent in adhesion to urethane sealants and water resistance.
On the other hand, the coating film formed in Comparative Example 1 had an OHV of less than 13 mgKOH/g of the entire resin content, and thus had poor adhesion to the urethane-based sealing material .
The coating film formed in Comparative Example 3 had an Ac/AcOH ratio of more than 80/20 and a small amount of the hydroxyl group-containing resin, and therefore had poor adhesion to the urethane-based sealing material.
The coating film formed in Comparative Example 4 had an Ac/AcOH ratio of less than 20/80 and a large amount of the hydroxyl group-containing resin, and thus was inferior in water resistance.
The coating film formed in Comparative Example 5 had an OHV of 13 to 65 mgKOH/g for the entire resin content, but was inferior in water resistance because it did not contain an acrylic resin having no hydroxyl group.

1 coating film C seam 10 panel 12 urethane-based sealing material

Claims (2)

A method of applying a water-based coating composition to the surface of a urethane-based sealing material on which isocyanate remains and drying to form a coating film,
The water-based coating composition comprises an aqueous medium, a hydroxyl-free acrylic resin dispersed in the aqueous medium, and a hydroxyl-containing resin dissolved or dispersed in the aqueous medium,
the total hydroxyl value of the acrylic resin and the hydroxyl-containing resin is 13 to 65 mgKOH/g;
A method for forming a coating film, wherein the mass ratio represented by the acrylic resin/the hydroxyl group-containing resin is 20/80 to 80/20. A water-based coating composition to be applied to the surface of a urethane-based sealing material on which isocyanate remains,
An aqueous medium, an acrylic resin having no hydroxyl group dispersed in the aqueous medium, and a hydroxyl group-containing resin dissolved or dispersed in the aqueous medium,
the total hydroxyl value of the acrylic resin and the hydroxyl-containing resin is 13 to 65 mgKOH/g;
A water-based coating composition, wherein the acrylic resin/hydroxyl-containing resin has a mass ratio of 20/80 to 80/20.

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