JPH03185084A - Coating composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition having high extensibility and forming coated film having excellent weatherability and staining resistance containing an urethane-acrylic resin obtained by reaction of a specific acrylic resin and a polyfunctional isocyanate in a specific ratio. CONSTITUTION:(A) 100 pts.wt. acrylic resin having 5-50KOHmg/g hydroxyl value is reacted with (B) 0.05-0.5 pts.wt. polyfunctional isocyanate such as hexamethylene diisocyanate, isophorone diisocyanate or trimethylol propane adduct to afford the aimed coating composition containing an urethane-acrylic resin having 15000-50000 molecular weight and 25-50 deg.C glass transition point as a principal component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to paints & acids. Especially when used as a top coat material for multi-layer finish coatings in the architectural exterior field,
It is characterized by high extensibility even at low temperatures and forms a coating film with excellent weather resistance and stain resistance.

[Conventional technology]

Multi-layer finish coating materials are used as paints for exterior building materials.

Conventionally, acrylic lacquer with an acrylic resin as a binder has been used as the top coating material for multilayer finishing coating materials.

The top coat material used in the elongated multi-layer finish coat material is required to be highly flexible and stretchable even at low temperatures.

For this reason, in the case of resins used as topcoats, acrylic resins have traditionally been designed to have a low glass transition point and have the ability to stretch to follow the displacement of multilayer finishcoats even at low temperatures. This was needed to prevent cracks in the coating when paint was added.

However, in conventional acrylic lacquers, if the glass transition point of the resin is designed to be low, the elongation at low temperatures is improved to some extent, but the weather resistance and stain resistance are significantly reduced, and if the glass transition point is designed to be high, the weather resistance is Although the stain resistance was improved, the extensibility at low temperatures decreased, and it was not possible to meet all the performance requirements for top coat materials.

[Problem to be solved by the invention]

An object of the present invention is to provide a paint composition that has high extensibility even at low temperatures and forms a coating film with excellent weather resistance and stain resistance.

[Means for solving yA problem]

The present inventors have discovered that it is effective to introduce urethane bonds into an acrylic resin in order to increase its extensibility at low temperatures.

Furthermore, for weather resistance and stain resistance, specific ranges of molecular weight,
It was discovered that a urethane acrylic resin having a glass transition point is suitable, leading to the present invention.

That is, in the present invention, the hydroxyl value is 5 to 50 KOj
It is a resin obtained by reacting 100 parts by weight of an acrylic resin with i1g/g and 0.05 to 0.5 parts by weight of a polyvalent isocyanate, and has a molecular weight of 15,000 to 50,000.
This is a coating composition whose main component is a urethane acrylic resin having a glass transition point of 25 to 50°C.

The acrylic resin of the present invention is a copolymer of a monomer having a hydroxyl group, other acrylic monomers, and, if necessary, other copolymerizable monomers.

Monomers having hydroxyl groups include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, caprolactone ring-opening adducts thereof, and ethylene oxide or propylene oxide ring-opening adducts of acrylic acid and methacrylic acid. etc. were mentioned,
These can be used alone or in combination of two or more.

Other copolymerizable acrylic monomers include acrylic acid, methacrylic acid, esters of these consisting of long chain or branched aliphatic alcohols having 1 or more carbon atoms, dimethylaminoethyl acrylate, dimethylaminoethyl Examples include nitrogen-containing acrylates and methacrylate monomers such as methacrylate, diethylaminoethyl methacrylate, and diethylaminoethyl methacrylate. Further examples include epoxy group-containing acrylates and methacrylate monomers such as glycidyl methacrylate and glycidyl acrylate. These acrylic monomers have excellent weather resistance and are preferably used in an amount of 50% or more of the total monomers in the copolymer.

Other copolymerizable monomers include styrene, vinyltoluene, vinylacrylamide chloride, methacrylamide, vinyl acetate, vinylsilane, maleic acid, and half esters and diesters thereof.

The monomer having a hydroxyl group has a hydroxyl value of 5 in the acrylic resin.
Adjust the amount used so that it becomes ~50 OH/g. When the hydroxyl value is less than 5, extensibility at low temperatures is insufficient, and when it exceeds 50, gelation tends to occur during resin synthesis, which is not suitable.

The acrylic resin can be obtained by subjecting the monomer mixture described above to a polymerization reaction using a radical initiator such as azobisisobutyronitrile, benzoyl peroxide, or cumene hydroperoxide.

Furthermore, the zero-polymerization method in which a commonly used chain transfer agent can be used is carried out by a commonly used solution polymerization method, bulk polymerization method, suspension polymerization method, emulsion polymerization method, or the like.

Examples of polyvalent isocyanates include aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and lysine diisocyanate, and their water adducts, trimethylolpropane adducts,
Prepolymers such as isocyanurates are preferred from the viewpoint of weather resistance. Further examples include aromatic isocyanates such as toluene diisocyanate and xylene diisocyanate, and prepolymers thereof.

These polyvalent isocyanates can be used alone or in combination of two or more, and are 0 to 100 parts by weight of the acrylic resin.
．． 05 to 0.5 parts by weight to react. If it is less than 0.05 parts by weight, the extensibility at low temperatures will be insufficient, and if it exceeds 0.52 parts by weight, it will gel during resin production, which is not suitable.

The reaction between the hydroxyl group-containing acrylic resin and the polyvalent isocyanate is preferably carried out by dissolving the acrylic resin in an organic solvent and
This is carried out by heating to 120°C to 120°C, adding polyvalent isocyanate under stirring, and maintaining the temperature for about 1 to 10 hours. In this case, it is also possible to use commonly used urethanization catalysts such as tertiary amines, tin compounds, and titanium compounds.

The molecular weight of the urethane acrylic resin is defined by the number average molecular weight measured by gel permeation chromatography (GPC).The appropriate molecular weight is 15,000 to 50,000, and if it is less than 15,000, it will have poor weather resistance, adhesion, stain resistance, etc. The performance is poor, and if it exceeds 50,000, the pigment dispersibility decreases, resulting in a decrease in gloss, which is not suitable.

The glass transition point is a value measured by thermomechanical analysis (TMA). A suitable glass transition point is 25 to 50°C. Below 25°C, stain resistance and weather resistance will be poor.
If the temperature exceeds 50'C, the extensibility at low temperatures will be poor and it is not suitable.

In preparing the paint &Il or acid compound of the present invention, a resin solution is generally prepared by mixing urethane acrylic 4 & 4 resin and a solvent. In this case, the solvent is an aromatic solvent such as toluene and xylene, alcohols such as methanol and butanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, and commonly used organic solvents such as cellosolves. One fil or two or more solvents can be used. In this case, it is perfectly acceptable to use colorants such as pigments, additives such as ultraviolet absorbers and antioxidants, and other resins such as cell 91 acetate butyrate and nitrocellulose.Urethane acrylic resin and other ingredients may be used. The mixing can be carried out using a commonly used stirrer such as a dispersion sand mill or a bowl.

Painting can be done using equipment such as a brush, roll, or spray.

〔Example〕

The present invention will be explained in detail below using Examples. In the following, parts and percentages are based on weight unless otherwise specified.

The evaluation method was as follows.

Example 1 (Manufacture of paint) 100 parts of toluene was charged into a No. 51 four-bottle flask equipped with a stirrer and a condenser and heated to 100°C.
The monomer mixture and polymerization initiator shown in Table 1 were added dropwise over 5 hours. Further, the temperature was maintained at 100° C. for 5 hours to carry out a polymerization reaction. Thereafter, the mixture was cooled to 70°C, and polyvalent isocyanates shown in Table 1 were added thereto and reacted for 5 hours to obtain urethane acrylic resin solutions A-1 to A-11.

The number average molecular weight measured by GPC and the resin solution
Table 1 shows the glass transition point measured by TMA of the film obtained by drying at 0°C for 30 minutes.

Using 100 parts of urethane acrylic resin solution A-1-A-9 and 40 parts of titanium oxide as a pigment, both were mixed in a sand mill, diluted with a thinner consisting of toluene, methanol, and MIBK, and the viscosity was reduced to 20 seconds using a Ford cup 14. A test paint was obtained.

(Evaluation) The test paint was air-sprayed to a film thickness of 30 μm on a dry paint film with a film thickness of approximately 1 m created using MT Elastile (manufactured by Mitsui Toatsu Chemical Co., Ltd., acrylic emulsion-based elastic mastic paint). The coating was coated and dried at room temperature for 3 days, and then tested for gloss, adhesion, and stain resistance.

Further, an elongation test was conducted in accordance with JIS A-6910 (1984) 5.13.

In addition, a coating film was similarly prepared on a slate board and a weather resistance test was conducted.

Urethane acrylic resins A-10 and A-11 gelled,
Since it is unsuitable as a paint resin, no further tests were conducted. The test results are shown in Table-2.

Test conditions Adhesion: 100 squares were scored at IW intervals on the coating film using a knife, and cellophane tape was removed. For example, 100/100, which represents the number of cells in perfect contact with each other, means that all 100 squares are in perfect contact with each other.

Stain resistance: Make a 3% carbon aqueous dispersion, rub it lightly with cotton, leave it at room temperature for one day, wash it with water, and visually evaluate the traces.

For those that do not leave any marks, O1 leaves a small mark. Something that leaves a lot of marks Δ、Extremely visible marks are indicated by ×. did.

: Conducted in accordance with JIS 8-6910 (1984) 5.13.

The measurement temperature was -10°C.

Weather resistance: The 60' gloss retention rate was measured after conducting a 1000 hour acceleration test of Sunshine Weather.

〔Effect of the invention〕

The coating composition made of the urethane acrylic resin of the present invention is
It is possible to form a coating film with excellent elongation at low temperatures, stain resistance, and weather resistance.

It is particularly useful as an extensible multilayer finish coating material that requires extensibility at low temperatures.

Claims (1)

[Claims] 100 parts by weight of an acrylic resin with a hydroxyl value of 5 to 50 KOHmg/g and 0.05 parts by weight of a polyvalent isocyanate.
It is a resin obtained by reacting ~0.5 parts by weight, has a molecular weight of 15,000 to 50,000, and a glass transition point of 25 to 5.
A coating composition whose main component is a urethane acrylic resin that has a temperature of 0°C.