JPS63305163A - Coating composition - Google Patents

Abstract

PURPOSE:To make it possible to markedly prolong the pot life of a coating composition, by adding a specified cellulose acetate butyrate to a two-pack paint comprising a specified polyol resin and a specified polyisocyanate compound. CONSTITUTION:A two-pack paint formed by mixing a polyol resin of a weight- average MW of about 5,000-40,000 and a glass transition temperature of about -20-100 deg.C with a polyisocyanate compound just before use, wherein cellulose acetate butyrate (CAB) of a weight-average MW of about 50,000-250,000 is added to at least either of said components. By the addition of CAB, the pot life of the composition can be markedly prolonged, for neither thickening nor gelation of the composition occurs immediately after the polyol resin is mixed with the polyisocyanate compound. The curability of the paint film is so excellent that, when heated to about 80-120 deg.C, it cures three-dimensionally into a cured paint film of a good appearance free of pinholes etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to coating compositions, and more particularly to two-component polyurethane coating compositions with extended pot life.

BACKGROUND ART AND PROBLEMS A two-component polyurethane paint consists of a polyol component having two or more hydroxyl groups in one molecule and a polyisocyanate compound having two or more isocyanate groups in one molecule. When these two components are mixed, they easily react and cure at room temperature, so it is necessary to mix these two components immediately before use (painting). The coating film made of this paint is rapidly cross-linked and cured three-dimensionally at room temperature or at a low temperature of 120°C or less, and therefore has excellent weather resistance, physical and chemical properties, etc., and as a result, 2. Liquid-type polyurethane paints are widely used for painting plastics that require low heat distortion temperature and dimensional stability (e.g. automobile exterior panels, bumpers, and other parts) and for repair painting of parts that are difficult to reheat. ing.

However, when the above-mentioned two-component polyurethane paints are mixed together, the curing reaction proceeds quickly and the viscosity increases.
Since it turns into a gel, it has a short pot life. Therefore, in industrial painting lines, the paint may thicken from the time the above components are mixed until it reaches the coating machine, which causes a decrease in the smoothness, sharpness, etc. of the resulting paint film. It becomes.

Methods for extending the pot life of two-component paints include, for example, ■ Adding a small amount of an acid component (negative catalyst) such as butyl phosphate, ■ Adding a ketone solvent (such as methyl ethyl ketone, methyl isobutyl ketone, etc.). , a method of suppressing the curing reaction of the same components by forming a coordinate bond between an isocyanate group and a carbonyl group has been studied. However, with the above method (■), it is difficult to extend the pot life to a practical level, and it may even increase the viscosity. The desired effect may not be achieved and the viscosity of the paint may therefore be lower than the optimum coating viscosity;
It has defects such as insufficient painting workability and finish quality for practical use.

Furthermore, the above-mentioned two-component polyurethane paint has the disadvantage that when the paint is applied to a porous plastic material, pinholes are generated due to air bubbles from inside the material, degrading the appearance of the paint film. .

Means for Solving the Problems As a result of repeated research in order to develop a two-component polyurethane paint composition free from such defects, the present inventors have found that the paint contains a specific cellulose acetate butyrate. It has been found that the intended purpose of the present invention can be achieved by this. The present invention was completed based on this knowledge.

That is, in the present invention, the weight average molecular weight is about 5,000 to about 40.
000 and a glass transition temperature of about -20°C to about 1
In a two-component paint in which a polyol resin and a polyisocyanate compound are mixed at 00°C immediately before use, one or both of the same components has a weight average molecular weight of about 50,000.
The present invention relates to a coating composition characterized in that it contains cellulose acetate butyrate of ~250,000%.

The polyol resin used in the present invention has two or more hydroxyl groups in one molecule and has a weight average molecular weight of about 500.
0 to about 40,000, preferably about 10,000 to about 300
00 and a glass transition temperature of about -20°C to about 100°C
C., preferably from about 5.degree. C. to about 80.degree. Examples of such resins include acrylic resin polyols obtained by copolymerizing hydroxyl group-containing vinyl monomers and acrylic monomers, polyester polyols obtained by condensing polybasic acids and polyhydric alcohols, and the like.

Examples of the hydroxyl group-containing vinyl monomer include monoesters of acrylic acid or methacrylic acid and glycols having 2 to 10 carbon atoms, specifically hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. etc. can be exemplified. Examples of acrylic monomers include alkyl (1 to 24 carbon atoms) esters of acrylic acid or methacrylic acid, and further include carboxyl group-containing vinyl monomers, amide vinyl monomers, glycidyl group-containing vinyl monomers, styrene and its derivatives, Acrylonitrile, vinyltoluene, vinyl chloride, vinyl acetate, etc. can also be used in combination. These are 1
The species can be used alone or in a mixture of two or more species. Polybasic acids are compounds containing two or more carboxyl groups in one molecule, and specifically include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, and het's acid. , maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid, and anhydrides thereof. Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, and specifically includes ethylene glycol, propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol,
Examples include triethylene glycol, glycerin, trimethylolpropane, pentaerythritol, dipentaerythritol, and the like. For the copolymerization reaction and condensation reaction using each of the above components, methods known per se may be employed.

If the weight average molecular weight of the polyol resin used in the present invention is less than 5,000, the flexibility of the resulting coating film tends to decrease, and conversely, if the weight average molecular weight of the polyol resin is greater than 40,000, the paint viscosity will be high. As a result, the appearance such as the smoothness of the finished coating film tends to deteriorate.
Neither is preferable. Furthermore, when the glass transition temperature of the polyol resin used in the present invention is lower than 120°C, the physical and chemical properties of the resulting coating film tend to deteriorate, while when the glass transition temperature is higher than 100°C, the paint Both are unfavorable as they tend to reduce the curability of the material.

In the present invention, it is particularly preferable to use a polyol resin having a hydroxyl value of about 35 to 150, and a hydroxyl value of about 80 to 1.
Most preferably, a polyol resin of about 20 is used.

As the polyisocyanate compound used in the present invention, any conventionally known polyisocyanate compound can be used as long as it is a compound having two or more isocyanate groups in one molecule. Specifically, tolylene diisocyanate, 4.4'-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate methyl ester, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated 4°4'
- diphenylmethane diisocyanate, an adduct of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane (for example Desmodur from Bayer), an adduct of 3 mol of hexamethylene diisocyanate and 1 mol of water, 3 mol of xylylene diisocyanate and Examples include adducts with 1 mol of trimethylolpropane. Among these, xylylene diisocyanate and hexamethylene diisocyanate are particularly preferred.

In the present invention, it is necessary to blend a specific cellulose acetate butyrate (hereinafter referred to as rCABJ) into both or either one of the polyol resin and polyisocyanate. CAB has a weight average molecular weight of approximately 500
00 to about 250,000, preferably about 100,000 to about 220,000, and is obtained by further converting a partially acetylated cellulose to butyl ester.

If the weight average molecular weight of the CAB used is less than 50,000, the pot life cannot be extended;
When the weight average molecular weight of B is greater than 250,000,
Both methods are unfavorable because they require a large amount of organic solvent to dissolve CAB, and as a result, the coating film formation efficiency tends to be poor.

Specific examples of CAB used in the present invention include, for example, C
AB381-1, CAB381-2, CAB381-0
5, CAB500-1, CAB551-02 [all manufactured by Eastman Kodak Company], and the like. The CAB used in the present invention preferably has an acetyl group content of 3 to 15% by weight and a butyl group content of 35 to 55% by weight.

The coating composition of the present invention contains the above polyol resin, polyisocyanate compound, and CAB as main components. The polyol resin and the polyisocyanate compound are selected so that the amount of isocyanate groups contained in the latter is usually about 0.6 to 1.4 mol, preferably about 0.6 to 1.0 mol, per 1 mol of hydroxyl group contained in the former. It is best to mix them in a suitable proportion. CAB is usually about 5 to 20 parts by weight, preferably 10 to 20 parts by weight, per 100 parts by weight of the above polyol resin.
It is preferable to mix it in a proportion of about 15 parts by weight.

In the present invention, pigments such as coloring pigments, extender pigments, metallic pigments, and organic tin compounds, etc., which are usually blended in this type of 2T& type polyurethane coating compositions, can also be blended.

The coating composition of the present invention is a two-component type, in which the polyol resin and the polyisocyanate compound are separated in advance,
It is mixed immediately before use (painting). In the present invention,
CAB may be blended into both the polyol resin and the polyisocyanate compound, or may be blended into only one of them.

There are no particular restrictions on the production of the coating composition of the present invention, and it can be produced in the same manner as conventional compositions.

The coating composition of the present invention is preferably stored at a solid content of about 20 to 30% by weight. Preferably, this is carried out using an organic solvent.

There are no particular restrictions on the use of the coating composition of the present invention, and it can be used in the same manner as conventional coating compositions.

Effects of the Invention Since the coating composition of the present invention contains CAB,
Even when a polyol resin and a polyisocyanate compound are mixed, they do not immediately thicken or gel, and the pot life can be significantly extended. Furthermore, the coating composition of the present invention has excellent curability, and is rapidly cured three-dimensionally by heating to about 80 to 120°C. Furthermore, the coating composition of the present invention has excellent coating workability and excellent finishing properties. Furthermore, the coating film formed from the coating composition of the present invention has excellent physical and chemical properties, weather resistance, smoothness, sharpness, etc., and when the composition is applied to a porous plastic material. Also, pinholes etc. may not occur (
The appearance of the coating film is also good.

EXAMPLES Examples and comparative examples are given below to further clarify the present invention.

Examples and Comparative Examples Based on the components and blending amounts (parts by weight) shown in Table 1 below, polyol resin, CAB, and pigment are first uniformly mixed and dispersed to form a base component, and then a curing agent is added to this base component. A coating composition was obtained by mixing the polyisocyanate compounds and adjusting the viscosity to be suitable for coating by adding a solvent. The solid content of each composition was 23 to 26% by weight.

Next, the performance of the coating composition itself (pot life, curability) and coating film performance were investigated. The coating film performance was determined by spraying the above coating composition onto RIM urethane to obtain a cured film thickness of 20 to 30 mm.
A coating film that was coated to give a thickness of μ and cured by heating at 80°C for 15 minutes was investigated. The results are also shown in Table 1.

Table 1 (Note 1) Polyol resin A: Copolymer consisting of styrene/n-butyl methacrylate/hydroxypropyl methacrylate/hydroxyethyl acrylate/acrylic acid = 15159/15/10/1 (weight ratio), hydroxyl value 107 , weight average molecular weight 30,000, glass transition temperature -3°C polyol resin B nitrimethylolpropane/1,6-hexanediol/hexahydrophthalic anhydride/adipic acid = 0.11
CAB I: CAB381-2 (weight average molecular weight approximately 200,000 , acetyl group content 13.5% by weight, butyl group content 3
7% by weight) II: CAB500-1 (weight average molecular weight approximately 11
(Note 3) The amount of pigment blended is the weight content (%) of each pigment in the cured coating film.

(Note 4) Polyisocyanate compound A: Hexamethylene diisocyanate: Xylylene diisocyanate Mixture of hexamethylene diisocyanate/xylylene diisocyanate = 1/1 (weight ratio) (Note 5) Kijirole/Ethyl acetate/Butyl acetate/Methyl ethyl ketone/Tsurupets =20/20/30/20/
Adjusted with a mixed thinner consisting of 10 (weight ratio) (Note 6) NGOloH is the hydroxyl group in the polyol resin.
Ratio of isocyanate groups in the polyisocyanate compound per mole (Note 7) Pot life Each coating composition (viscosity 15 seconds/2 in Ford cup #4
(adjusted to 0℃) into a 500cc glass bottle for about 7 minutes,
After sealing, the samples were stored at 20° C. and 35° C., and the time required for the viscosity (measured at each storage temperature) to rise to 20 seconds was determined.

(Note 8) Using a pendulum-type viscoelasticity measurement device for coating film curing, measure the logarithmic attenuation rate, which is a guideline for viscosity, in relation to temperature while increasing the temperature at a constant rate. Indicates the temperature at which the inflection point begins. The above measurement conditions are as follows.

■Angle θ between the blade surface of a stationary pendulum and the base surface = 60° ■Pulling of the pendulum M = 0.9g ■Length of the pendulum Q = 7.2cm ■Vibration period To = 0.65 seconds ■Temperature increase rate V = 20℃/min This measurement method is based on "Coloring Materials Association Magazine", Vol. 51, p. 403 (
(1978).

(Note 9) Adhesiveness Cut into the cured coating film with a knife to reach the surface to be coated to make 100 grids of 2 x 2 mm in size, stick adhesive cellophane tape on the surface, and The number of coatings remaining after rapid peeling was investigated.

(Note 10) Acid resistance: 0. An IN sulfuric acid aqueous solution was dropped onto the cured painted surface, and the degree and condition of the painted surface discoloration after 24 hours were examined.

◎: Color difference is 0.8NBS or less and no significant traces remain.

(Notice) The state of the coating film was examined after a 400-hour test using a weather-resistant Sunshine Weather-Ometer.

◎: Gloss retention rate is 70% or more, color difference is 3.0 NBS or less.

(that's all)

Claims (1)

[Claims] (1) A two-component paint in which a polyol resin having a weight average molecular weight of about 5,000 to about 40,000 and a glass transition temperature of about -20°C to about 100°C and a polyisocyanate compound are mixed immediately before use. Either or both of the components have a weight average molecular weight of about 50,000 to about 2,500.
A coating composition characterized in that it contains cellulose acetate butyrate No. 00.