JPS5826377B2 - Powder coating composition with good pigment dispersibility - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention significantly improves pigment dispersibility, which is a defect of glycidyl group-containing acrylic powder coatings, and as a result provides a powder coating that provides a smooth and glossy pigmented coating appearance. composition for use.

Thermosetting acrylic powder coatings made of glycidyl group-containing acrylic copolymers and polyvalent carboxylic acid compounds are widely used in practical applications because of their excellent weather resistance, stain resistance, chemical resistance, and flexibility. I am forced to do so.

However, with conventional thermosetting acrylic powder paints, if the pigment preparation is too high or the conditions for mixing the pigments are insufficient, the smoothness and gloss of the formed coating will decrease, which is one of the reasons for this. One reason was thought to be due to poor pigment dispersibility.

An object of the present invention is to provide a powder coating composition that significantly improves the disadvantages of pigment dispersibility while maintaining the advantages of conventional thermosetting acrylic powder coatings. , where R is hydrogen or a methyl group, R1 and R2 are hydrogen, an alkyl group, or an alkenyl group, and at least R , I R
(a-1) and (a-2) and a monomer copolymerizable with (a-1) and (a-2).
-1) and (a-2) as the remaining monomers (total copolymerized monomers are 100% by weight); and (B) the polyhydric carboxylic acid compound in the above copolymer. This is a powder coating composition with good pigment dispersibility, characterized in that it is blended as a crosslinking agent.

The monomers having the structure (a-1) (in the formula, R is hydrogen or methyl group), which are the constituent components of the copolymer in (4) above, include glycidyl acrylate, glycidyl methacrylate, and β-acrylate. -Methylglycidyl, methacrylic acid β-
There is methylglycidyl, and one or more of these monomers are added in an amount of 5 to 40 weight φ of the total copolymerized monomers, preferably 1
It is appropriate to use a 5 to 35 weight φ copolymer, and if it is less than 5 weight %, the crosslinking reaction in the baking process after powder coating will be insufficient, resulting in poor flexibility and solvent resistance. If it exceeds this, the melt viscosity increases rapidly during the baking process, resulting in poor coating surface smoothness, which is unsuitable.

(a-2), which is a constituent component of the copolymer in (4) above, or a methyl group, R□, R2 is hydrogen, an alkyl group, or an alkenyl group, and at least one of Rlt R2 is an alkyl group or an alkenyl group) As monomers having the structure, ψ1j is N-dimethylacrylamide, N-dimethylmethacrylamide, N-dibutylacrylamide1
N-dibutyl methacrylamide, N-dioctyl acrylamide, N-dioctyl acrylamide, N-dilauryl acrylamide, N-dilauryl methacrylamide, N-distearylacrylamide, N-distearyl methacrylamide, N-dioleylacrylamide, N
-Dioleyl methacrylamide, N-monobutylacrylamide, N-monoctylacrylamide, N-monolauryl acrylamide, N-monostearyl methacrylamide, N-monooleyl acrylamide, etc., especially at least R, R2 in the general formula Preferably, one is an alkyl group or an alkenyl group.

Pigment dispersibility is significantly improved by copolymerizing one or more of these (a-2) monomers at 0.05% by weight of the total copolymerized monomers. In the case of upwind copolymerization, yellowing of the coating film occurs during baking, which is not preferable.

The amount of monomer (a-2) to be used is preferably 0.2 to 2 by weight.

Monomers copolymerizable with the above (a-1) and (a-2) include acrylic acid alkyl esters, methacrylic acid alkyl esters, acrylic acid alkoxyalkyl esters, methacrylic acid Alkoxyalkyl esters, hydroxyalkyl acrylic esters, hydroxyalkyl nuccrylic esters, dialkyl esters of unsaturated dibasic acids, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, etc. Commonly used.

The copolymer (4) of the present invention can be produced by common polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization, and usually has a number average molecular weight of 3.0.
It is preferably in the range of 00 to 15,000, and
It is preferable that the glass transition point is 20°C or higher, particularly 30 to 60°C (measured by diradometric method).

The above copolymer (4) forms a tough coating film only after a crosslinking reaction occurs during the baking process during the practical use of powder coatings, so it is necessary to use a crosslinking agent. The polyhydric carboxylic acid compound (B) is used.

Examples of polyhydric carboxylic acid compounds include aliphatic dibasic acids such as adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, hexadecanedioic acid, icosanedioic acid, and tetraeicosanedioic acid, such as isophthalic acid, trimellitic acid, etc. Examples include aromatic polycarboxylic acids such as alicyclic dibasic acids such as hexahydrophthalic acid and tetrahydrophthalic acid, carboxyl-terminated polyesters, carboxyl-terminated polyamides, carboxyl-terminated polyurethanes, carboxyl group-containing acrylic resins, etc. In particular, polycarboxylic acid compounds having a melting point or softening point of 40° C. or more and 200° C. or less and a number of carboxyl groups per molecule of 2.0 to 3.0 are particularly preferred.

In addition, the amount of polycarboxylic acid compound used is usually the same as (4) above.
0.7 to 1.0% per glycidyl group in the copolymer.
A polyhydric carboxylic acid compound is blended in an amount that provides two carboxyl groups.

When producing a thermosetting acrylic powder coating comprising the copolymer (4) of the present invention and the polyhydric carboxylic acid compound (B), pigments, coating surface conditioners, etc. are usually used as necessary. ,
Furthermore, it is also possible to mix and use other components such as epoxy resins, polyester resins, blocked isocyanate resins, cellulose derivatives, melamine formaldehyde resins, N-acyllactam resins, etc. within a range that does not impair the object of the present invention.

As a method for producing the thermosetting acrylic powder coating of the present invention, a melt-kneading method using an extruder, roll mill, Banbury mixer, etc. is used, but the degree of dispersion of the pigment into the resin component in this melt-mixing step Since this affects the smoothness and gloss of the coated film, it is important to select melt-kneading conditions that allow sufficient pigment dispersion. Coalescing and crosslinking agents are required, and the powder coating composition of the present invention can simplify the melt mixing process by shortening the melt kneading time and making it compatible with various melt mixing machines. It is what makes it happen.

Generally, when the blending ratio of pigments such as titanium oxide and iron oxide increases, sufficient pigment dispersion becomes difficult and the smoothness and gloss of the formed coating film decreases. Defects can also be improved.

The mixture melted and kneaded as described above is cooled to room temperature and then ground to a size of 100 μm or less using a grinder to obtain a powder coating.

The powder coating produced in this way is usually applied to the object to be coated using an electrostatic powder coating machine, and is usually applied at a temperature of 150 to 220°C.
Baking is performed for 5 to 30 minutes to form a coating film.

Details will be explained below using examples.

Example 1 A mixture of 230 g of glycidyl methacrylate, 20 g of N-dioctyl acrylamide, 250 g of ethyl acrylate, 250 g of methyl methacrylate, 400 g of styrene and 40 g of azobisisobutyronitrile as a polymerization initiator was heated at 100 °C in a 31 flask. toluene heated to
The mixture was continuously added dropwise over a period of 10 hours during the 10 hour period, while stirring to maintain the temperature of the contents at 90°C.

At the end of the dropwise addition, 10 g of azobisisobutyronitrile was further added and the mixture was heated and stirred at 100°C for 3 hours to complete the polymerization.

Next, toluene was completely distilled off under reduced pressure to obtain a solid copolymer (I).

The copolymer (1) had a glass transition point of 488 C1 determined by diradometric method and a number average molecular weight of 4,800 determined by GPC (Köl permeation chromatography) method.

Example 2 100 g of glycidyl acrylate, 191 g of β-methylglycidyl methacrylate. N-monostearyl acrylamide 5g1 ethyl methacrylate 50F11 hydroxyethyl methacrylate 100g1 vinyltoluene 100g and abbisisobutyronyl l-IJ 45 as a polymerization initiator
The mixture of g was polymerized in the same manner as in Example 1, and toluene was distilled off to obtain a solid copolymer (If).

The glass transition point of copolymer (I) by diradometric method is 44°C.The number average molecular weight by GPC method is 3900.
Met.

Example 3 150 g of glycidyl methacrylate, 35 g of β-methylglycidyl acrylate, 10 g of N-monooleyl acrylamide and 5 g of N-dilauryl methacrylamide, 600 g of methyl methacrylate, 150 g of lauryl methacrylate.
A mixture of 50 g of dimethyl itaconate and 50 g of azobisisobutyronitrile as a polymerization initiator was polymerized in the same manner as in Example 1, and toluene was distilled off to obtain a solid copolymer (2). .

The glass transition point of the copolymer (In) determined by diradometric method is 43°C, and the number average molecular weight by GPC method is 670.
It was 0.

Example 4 300 g of glycidyl methacrylate, 50 g of N-dimethylacrylamide, 150 g of methyl methacrylate, 300.91 g of isobutyl methacrylate, 200 g of styrene, and 50 g of azobisisobutyroni I-IJ as a polymerization initiator.
The mixture of Example 9 was polymerized in the same manner as in Example 1, and toluene was distilled off to obtain a solid copolymer body.

The copolymer (1) has a glass transition point of 45°C by the dilatome l-IJ method, and a number average molecular weight of 4 by the GPC method.
It was 000.

Comparative Example 1 230 g of glycidyl methacrylate, 250 g of methyl methacrylate, 110 g of ethyl acrylate, 41 g of styrene
Polymerization was carried out in the same manner as in Example 1 using a mixture of 0 g and 40 g of azobisisobutyronitrile as a polymerization initiator, and toluene was distilled off to obtain a solid copolymer (■).

The copolymer (■) had a glass transition point of 47° C. as determined by diradometric method, and a number average molecular weight as determined by GPC method of 4,800.

Comparative Example 2 100 g of glycidyl acrylate, 190 g of β-methylglycidyl methacrylate, 510 g of ethyl methacrylate
A mixture of 100 g of hydroxyethyl methacrylate, 100 g of vinyltoluene, and 45 g of azobisisobutyronitrile as a polymerization initiator was polymerized in the same manner as in Example 1, and the toluene was distilled off to obtain a solid copolymer (vI). I got it.

The copolymer (Vl) has a glass transition point of 44°C by diradometric method and a number average molecular weight of 3.90 by GPC method.
It was 0.

[Preparation of powder coating]

Copolymers (I) obtained in Examples 1 to 4 and Comparative Examples 1 to 2
) to (VI) were premixed with a crosslinking agent, pigment, and coating surface conditioner in the proportions shown in Table 1, and then heated using a twin-screw extruder (PCM-30, Ikegai) under heating at 100°C. After cooling, the powder was crushed using a pulverizer and passed through a 200-mesh sieve.
Powder coatings (I) to (Vl) were prepared, respectively.

[Preparation and evaluation of painted board]

The above powder coatings (I) to ■ were applied to a polished steel plate with an electrostatic powder coating machine to a coating thickness of 60μ, and baked in a hot air dryer at 180°C (ambient temperature) for 20 minutes. I went there and created each painted board.

The coating film performance was evaluated for each coated board, and the results shown in 2 were obtained.

The coating film performance test in Table 2 was conducted by the following method.

60° specular reflectance: Measured using a gloss meter Smoothness: Visual judgment Sharpness Two-eye judgment Heat yellowing: The coating film was baked at 180°C for 120 minutes for two more times.
Baking was performed for 20°0120 minutes, and the degree of yellowing was visually determined.

Impact resistance: DuPont impact tester, 500!9, l/2
Inch Diameter Stain Resistance: After applying the oil-based marker ink, it was left at 30°C for one day, and the traces after wiping with ethanol were visually evaluated.

Chemical resistance: The condition of the coated surface was visually judged after being immersed in a 5% NaOH aqueous solution at 30° C. for one week.

Weather resistance: Gloss retention after 1 year of outdoor exposure.

Claims (1)

[Scope of Claims] 5 to 40 parts by weight of monomers having the structure (wherein R is hydrogen or a methyl group), (wherein R is hydrogen or a methyl group, R,, R2Lt hydrogen,
an alkyl group or an alkenyl group, at least R,,R
(a-1) and (a-2) are copolymerizable with (a-1) and (a-2). A copolymer pressed as the remaining monomers of 1) and (a-2) (all copolymerized monomers are 100% by weight), and (B) a polyhydric carboxylic acid compound. A powder coating composition characterized by: