JPS63304063A - Clear coating composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition having excellent long-term weather resistance and corrosion resistance and suitable for the coating of a metallic substrate, by compounding an organotin compound to a polyol component consisting of a fluorine-containing copolymer having hydroxyl group and a curing agent component consisting of a polyvalent isocyanate, etc. CONSTITUTION:The objective coating composition can be produced by compounding (A) an organotin compound (e.g. dibutyltin dilaurate) to a coating composition composed mainly of (B) a polyol component comprising a fluorine- containing copolymer having hydroxyl group [preferably a copolymer composed of 30-70wt.% of a fluoroolefin, 5-60wt.% of cyclohexyl vinyl ether, 3-50wt.% of an alkyl vinyl ether, 3-25wt.% of a hydroxyalkyl vinyl ether and 0-40wt.% of other copolymers] and (C) a curing agent component composed of a polyvalent isocyanate compound (e.g. hexamethylene diisocyanate) or an aminoplast compound. The amount of the component A is preferably 0.1-5pts.wt. based on 100pts.wt. of the solid content of the components A+B.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a clear coating composition that is particularly suitable for metal substrates and has excellent long-term weather resistance and corrosion resistance.

<Prior Art> It has been widely practiced to coat metal substrates with colored paints in order to give them aesthetic appearance and corrosion resistance.

On the other hand, for metal substrates such as stainless steel, aluminum, copper, or true marks, it is common practice to use them without applying colored paint to take advantage of the metallic luster of the metal substrate itself. Metal substrates are also coated with clear paint to prevent dirt such as hand marks from adhering to them and to maintain their metallic luster.

However, when commonly used clear paints such as acrylic resin and polyester resin paints are applied, there is a problem that if left outdoors for several years, the paint film itself will develop chalking and its metallic luster will deteriorate.

Therefore, it has been considered to apply a fluororesin-based clear paint that has good long-term weather resistance.

(Problems to be Solved by the Invention) However, when a fluororesin-based clear paint is applied to a metal base material such as stainless steel, the metallic luster can be maintained for a long period of time, but when exposed outdoors, unexpectedly the paint is not maintained. Even though mackerel does not occur on metal substrates such as stainless steel, corrosion spots have appeared on the surface of the metal substrate under the fluororesin clear coating.

The reason for this is thought to be as follows. Namely, metal base materials such as stainless steel have a high reflectance of sunlight, including ultraviolet rays, while fluororesin-based clear coatings Compared to general acrylic resin-based, polyester-based, etc. clear coatings, it has a higher UV transmittance, so the coating film can be exposed to sunlight when outdoors (a) Transmitting and reflecting light)
The fluororesin partially decomposes, and its decomposition products, highly active low-molecular-weight compounds such as fluorides and chlorides, become corrosion factors and corrode the surface of the metal substrate.
This is thought to cause corrosion spots, etc.

As a result of intensive studies in view of the current situation, the inventors of the present invention have developed a method that maintains the metallic luster of the metal base material such as stainless steel for a long period of time, and takes advantage of the long-term weather resistance of the fluororesin clear coating. The inventors have also discovered a clear coating composition that can form a coating film that prevents the occurrence of rust, and have arrived at the present invention.

Means for Solving the Problems> That is, the present invention provides a coating composition whose main components are a polyol component made of a fluorine-containing copolymer having a hydroxyl group, and a curing agent component made of a polyvalent isocyanate compound or an aminoplast compound. The present invention relates to a clear coating composition containing an organic tin compound. The coating film obtained by applying the clear coating composition of the present invention to a metal substrate has good long-term weather resistance without causing paint film defects such as chalking for a long period of time, and therefore can maintain metallic luster for a long period of time. Furthermore, since an organic tin compound is added to the paint, it has become possible to prevent the occurrence of mackerel.

The present invention will be explained in detail below.

As the fluorine-containing copolymer having a hydroxyl group as a polyol component used in the present invention, any known fluorine-containing copolymer can be used without particular limitation as long as it is soluble in an organic solvent. In particular, JP-A No. 57-34107 which dissolves in ordinary organic solvents at room temperature, can form a coating film even by drying at room temperature or baking at a low temperature, and provides a coating film with excellent weather resistance, durability, and adhesion. Fluorine-containing copolymers described in publications are preferred. That is, the fluorine-containing copolymer contains fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether, and hydroxyalkyl vinyl ether as essential components, each containing 30 to 70% by weight,
It is a copolymer containing 5 to 60% by weight, 3 to 50% by weight, and 3 to 25% by weight and having a number average molecular weight of about 3,000 to 100,000.

Incidentally, if the fluoroolefin content is too low, the weather resistance will decrease, and if the fluoroolefin content is too high, it will be difficult to manufacture. Furthermore, if the cyclohexyl vinyl ether content is too low, the hardness of the coating film will decrease, and if the alkyl vinyl ether content is too low, the flexibility will decrease.

Furthermore, it is particularly important to contain hydroxyalkyl vinyl ether in a proportion within the above range from the viewpoint of improving curability without impairing various useful properties as a paint base. In other words, if the hydroxyalkyl vinyl ether content is too high, not only will the solubility of the copolymer in organic solvents decrease, but also the flexibility of the coating film will decrease, while if the hydroxyalkyl vinyl ether content is too low, the durability and , adhesion deteriorates.

In the fluorine-containing copolymer, perhaloolefins, particularly chlorotrifluoroethylene or tetrafluoroethylene, are preferred as the fluoroolefins.

In addition, as the alkyl vinyl ether, carbon number 2 to 8
Those containing a linear or branched alkyl group, particularly those in which the alkyl group has 2 to 4 carbon atoms, are preferred. Moreover, as the hydroxyalkyl vinyl ether, one containing a hydroxyalkyl group having 2 to 8 carbon atoms is suitable.

The fluorine-containing copolymer may contain comonomers other than the four essential components in an amount not exceeding 40% by weight. Typical examples of such comonomers include ethylene, propylene, isobutylene, vinyl chloride, vinylidene chloride, methyl methacrylate, and butyl acetate.

The fluorine-containing copolymer can be produced by causing a copolymerization reaction by allowing a polymerization initiator to act on a monomer mixture in a predetermined proportion in the presence of a polymerization medium. Examples of such fluorine-containing copolymers include Lumiflon LF100.
．． 200.210.300.400.502.504.
550.552.554.700.800.916 (all trade names manufactured by Asahi Glass Co., Ltd.), etc. are commercially available. Also,
A polyvalent isocyanate compound and/or an aminoplast compound are used as curing agent components in the present invention.

Examples of polyvalent isocyanate compounds include aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenyl diisocyanate, and hydrogenated xylylene diisocyanate; Typical examples include reaction products of excess amounts of these isocyanate compounds and low-molecular-weight polyols such as ethylene glycol, glycerin, trimethylolpropane, and pentaerythritol. By mixing these polyvalent isocyanate compounds in a predetermined ratio with the polyol component made of the fluorine-containing copolymer, a two-component coating material that can be cured even at room temperature is obtained.

Further, the polyvalent isocyanate compound may be phenols,
Blocked isocyanate compounds masked with masking agents such as alcohols, oximes, lactams, amines, amides, etc. can also be used, and in this case, a one-component paint that can be cured by baking by mixing with the polyol component in a predetermined ratio. becomes.

The mixing ratio of the polyol component and the polyvalent isocyanate compound curing agent component is determined by the equivalent ratio of the isocyanate group of the isocyanate compound to the hydroxyl group of the polyol component (NC○10H).
is (0.15 to 1.5/1"), particularly preferably (0.2 to 1.2/1), and it is possible to exhibit the original resin properties within this range. Become.

If the number of isocyanate groups is too large than the above range, the free isocyanate groups will react with moisture in the air, resulting in a decrease in weather resistance, while if it is too small, satisfactory curability will not be obtained and the crosslinking density will be low, resulting in poor durability. All of these are unfavorable because they reduce solvent resistance, stain resistance, chemical resistance, weather resistance, and the like.

Furthermore, as mentioned above, an aminoplast compound can also be used as a curing agent. The aminoplast compound is a condensation product of an amino compound such as melamine, urea, benzoguanamine, or acetoguanamine and an aldehyde compound, or a compound obtained by further etherifying the condensation product with an alcohol such as butanol. When an aminoplast compound is used, it becomes a one-component paint that can be cured by baking by mixing it with the polyol component in a predetermined ratio.

The mixing ratio (by weight) of the polyol component and the aminoplast compound curing agent component is (95:5 to 60:40), particularly preferably (90:10 to 70:30), and the original resin properties can be maintained within this range. It becomes possible to perform.

If the amount of the aminoplast compound is too much than the above range, reactions between the aminoblast compounds tend to occur, reducing the flexibility and chemical resistance of the coating film, and conversely, if the amount is too little, satisfactory curability may not be obtained and crosslinking may occur. Since the density is low, the dissolution resistance, stain resistance, etc. are deteriorated, and both are unfavorable.

In the present invention, an organic tin compound is added to a coating composition containing these polyol components and a curing agent component as main components in order to prevent the occurrence of rust.

The mechanism by which the formation of corrosion spots on the surface of the metal substrate under the coating film can be prevented by adding an organic tin compound is not clear, but the organic tin compound chemically bonds with the fluororesin, resulting in decomposition products of the fluororesin. This is thought to be because it suppresses the generation of corrosion factors such as chlorides and chlorides, and also causes some kind of reaction between the generated corrosion factors and the organic tin compound to inactivate the corrosion factors.

As the organic tin compound referred to in the present invention, for example, a compound represented by the following general formula can be suitably used.

That is, the general formula: % formula % (wherein R5, R3, R3, R4 are alkyl groups such as methyl, butyl, octyl and/or an alkyl group containing an ester bond and having 1 to 10 carbon atoms; Y
l, Y2 is an organic sulfur derivative represented by a fatty acid carboxyl group, an organic carboxyl group such as a maleic acid Hafester group, or a mercapto fatty acid residue such as mercaptoacetic acid or mercaptopropionic acid; Saturated carboxyl group; n is an integer of 0 to 10; when n is 0, monoalkyltin compounds in which R2 is the same substituent as Yl or Y2 are also included. ) is a compound represented by

Specifically, compounds represented by three systems, namely fatty acid salt systems such as dibutyltin dilaurate, dibutyltin distearate, dibutyltin simalate, and tribenzyltin laurate; dibutyltin simalate, dibutyltin laurate, methyl maleate, and dibutyltin Maleins such as dioleyl maleate, dibutyltin methoxymethyl maleate, dibutyltin dimethyl maleate, dibutyltin dioctyl maleate, monobutyltin trimethyl maleate, monobutyltin trioctyl maleate, tribenzyltin octyl maleate, tribenzyltin trimethyl maleate, etc. Acid salts: Representative examples include sulfur-containing organic tin compounds such as dibutyltin dioctyl thioglycolate, dibutyltin dilauryl mercaptide, dibutyltin mercaptopropanoate, and dibutyltin mercaptopropionate.

In addition to the compounds represented by the above general formula, organic tin compounds such as tetraphenyltin, tetraoctyltin, and tributyltin acetate may also be mentioned.

The appropriate amount of these organic tin compounds is about 0.1 to 5 parts by weight based on 100 parts by weight of the total solid content of the polyol component and curing agent component.

Note that if the amount of the organic tin compound is less than the above range, the rust prevention effect will not be sufficiently exhibited, and conversely, even if it is more than the above range,
The above range is desirable since the above effects are not significantly improved.

The clear coating composition of the present invention contains various organic solvents in addition to the above-described components as usual.

Examples of organic solvents include hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; methanol;
Typical examples include alcohol solvents such as ethanol and butanol.

The clear paint composition of the present invention may further contain various additives such as surface conditioners, ultraviolet absorbers, thickeners, etc., modifiers such as cellulose acetate butyrate, extender pigments, and other additives that do not inhibit metallic luster. It consists of a small amount of colored pigments, dyes, etc.

Next, a coating film forming method using the clear coating composition of the present invention will be explained.

The clear coating of the present invention is applied to the surface of a metal base material such as stainless steel, aluminum, copper, or true mark after roughening it by etching or treating it with a chelating agent, coupling agent, etc. in order to improve the adhesion as necessary. The coating composition is applied by air spraying, airless spraying, electrostatic spraying, shower coating, dip coating, roll coating, brush coating, etc. to a dry film thickness of about 10 to 100μ, and the curing agent, etc. After drying at room temperature, low-temperature baking at 130-170℃ for 10-30 minutes, 20
The above-mentioned excellent coating film can be formed by performing short-time baking at a high temperature of 0 to 230°C for 30 to 200 seconds.

<Effects of the Invention> By applying the clear coating composition of the present invention to a metal substrate, the coating film can be maintained for a long period of time without any coating defects such as chalking, and the metal base under the coating film can be maintained for a long period of time. The metal base material can maintain its metallic luster in good condition for a long period of time without causing corrosion spots on the material surface.

The present invention will be explained in more detail below. In the examples, "parts" and "%" are expressed on a weight basis.

[Fluorine-containing copolymer solution A]

52 parts of chlorotrifluoroethylene, 4-hydroxy-
Monomers consisting of 21 parts of n-butyl vinyl ether, 17 parts of cyclohexyl vinyl ether, and 10 parts of ethyl vinyl ether were converted into a fluorine-containing copolymer with a number average molecular weight of 6,800, according to the method described in JP-A-57-34107.
A 60% quijirole solution with a hydroxyl value of 100 was obtained. (Hereinafter referred to as fluorine-containing copolymer solution A) [Fluorine-containing copolymer solution B] 54 parts of chlorotrifluoroethylene, 4-hydroxy-
A fluorine-containing copolymer (number average molecular weight: 23,000
, a 60% quijirole solution with a hydroxyl value of 52) was obtained. (Hereinafter referred to as fluorine-containing copolymer solution B) [Fluorine-containing copolymer solution C] 30 parts of chlorotrifluoroethylene, 25 parts of tetrafluoroethylene, 101 parts of 4-hydroxy-n-butyl vinyl ether, 18 parts of cyclohexyl vinyl ether, ethyl A monomer consisting of 17 parts of vinyl ether was
According to the method described in Publication No. 34107, a fluorine-containing copolymer with a number average molecular weight of 45,000 and a hydroxyl value of 52) was prepared.
% cyclohexanone solution was obtained. (Hereinafter referred to as fluorine-containing copolymer solution C) [Acrylic resin solution] 30 parts of methyl methacrylate, 2 parts of butyl methacrylate
0 parts, 37 parts of 2-ethylhexyl acrylate, 1 part of methacrylic acid, 12 parts of 2-hydroxyethyl methacrylate
The monomer consisting of 1.5% was solution polymerized in a mixed solvent consisting of quidylole and butyl acetate to obtain an acrylic resin (number average molecular weight: 15,000, hydroxyl value: 50) solution (non-volatile content: 60%).

[Curing agent A]

55.5 parts of a polyisocyanate having a cyanurate ring, which is a trimer of hexamethylene diisocyanate, was dissolved in 20 parts of methyl ethyl ketone, and 24.5 parts of methyl ethyl ketone oxime was added thereto and reacted. minute 8
0%) was obtained.

(Hereinafter referred to as curing agent A) [Curing agent port] A polyisocyanate compound having cyanurate I, which is a trimer of hexamethylene diisocyanate (NC○ equivalent weight: 199, non-volatile content: 100%).

(hereinafter referred to as curing agent) [Curing agent C] A solution of butyl etherified melamine resin dissolved in a mixed solvent consisting of Kijirol and butanol (non-volatile content: 60±
2%). (Hereinafter referred to as curing agent c) Examples 1 to 10 and Comparative Examples 1 to 2 Each component shown in Table 1 was stirred and mixed to prepare a paint. In Example 2, a hardening agent (b) was mixed before coating to prepare a clear paint.

The clear paints obtained in Examples 1 to 10 and Comparative Examples 1 to 2 were applied as follows, and the resulting coated plates were subjected to an accelerated weather resistance test (Denny Cycle Weathermeter Test 500).
time) and an outdoor exposure test (2 years in Okinawa).

Test 1> The clear paints obtained in Example 1.4.5.6.9.10 and Comparative Example 1.2 were applied to degreased stainless steel plates (SUS304 hairline finish) each having a thickness of 0.5 mm. It was spray-painted and baked at 160°C for 20 minutes to obtain a cured coating (30μ thick), which was used for testing. The test results are second
It was as shown in the table.

Test 2> The clear paint obtained in Example 3.7 was applied in the same manner as Test 1, and baked at 160°C for 30 minutes to form a cured coating (2
0μ thickness) was obtained and used for testing. The test results are shown in Table 2.

Test 3> The clear paint obtained in Example 8 was applied to the stainless steel plate using a bar coater, and baked in a drying oven at 300°C for 1 minute to obtain a cured film (20 μm thick), which was used for testing. The test results are shown in Table 2.

<Test 4> The clear paint obtained in Example 2 was spray-painted on a chromate-treated aluminum plate with a thickness of 0.8 m, and dried at room temperature for 2 weeks to obtain a cured film (30μ thick), which was applied to the test. provided. The test results are shown in Table 3.

Table 3 As is clear from the test results in Tables 2 and 3, the clear paint of the present invention was confirmed to prevent the occurrence of rust in the weather resistance test, and was able to maintain metallic luster for a long period of time. Met.

On the other hand, the clear paint (Comparative Example 1) to which no organic tin compound was added was unable to prevent the occurrence of rust.

In addition, conventional acrylic resin clear paint (Comparative Example 2)
The paint film caused chalking and some peeling.

Claims (2)

[Claims] (1) A coating composition whose main components are a polyol component made of a fluorine-containing copolymer having a hydroxyl group and a curing agent component made of a polyvalent isocyanate compound or an aminoplast compound, in which an organic tin compound is blended. Clear paint composition. (2) The fluorine-containing copolymer is fluoroolefin 30
~70% by weight, cyclohexyl vinyl ether 5-60
Claim (1) characterized in that the copolymer is a copolymer consisting of 3 to 50% by weight of alkyl vinyl ether, 3 to 25% by weight of hydroxyalkyl vinyl ether, and 0 to 40% by weight of other copolymers. The clear paint composition described in .