JPS5829822B2 - Composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a powder coating composition suitable for coating metal surfaces.

In recent years, the usefulness of powder coatings has attracted attention due to advances in electrostatic powder coating technology.

Powder coatings have the advantage of not using volatile solvents compared to solution-based coatings, and can also be applied thickly in one coat.
It has many advantages.

When the resin component of the powder coating is a thermoplastic resin & Main (a)
(o) The resin must have excellent adhesion to metals and flexibility; (o) The resin must be easily crushed and a fine powder can be easily obtained; and (2) The powder must be stable.

(The conditions that must be met include low power melt viscosity, (f) no deterioration during melting, and (f) melting at a relatively low temperature.

Conventionally, epoxy resin, vinyl chloride resin, nylon resin,
Powder coatings using polyethylene, cellulose acetate phthalate, etc. are known, but at present, a powder coating that has excellent properties as a top coat for metals has not yet been obtained.

In addition, attempts have been made to use thermoplastic polyester as powder coatings, but very few have been put into practical use, and the coating films of these are hard and clumpy.

■Poor weather resistance, ■poor adhesion to metal, ■requires high temperature for baking, or ■difficult to obtain a flat coating due to insufficient flow during melting. .

The present inventor focused on this point and as a result of intensive research, the acid component mainly consists of terephthalic acid and/or isophthalic acid, the glycol component mainly consists of ethylene glycol and neopentyl glycol, and the reduced specific viscosity is 0.
．． A composition comprising a polyester (1) having a specific viscosity of 5 to 2.5 and a polyester (2) having a specific reduced viscosity has excellent properties as a powder coating, that is,
It is a powder that is stable at room temperature and becomes fluidized by heating to form a uniform coating film that has excellent properties such as bending resistance, weather resistance, heat resistance, and adhesion to metals. They discovered this and arrived at the present invention.

That is, in the present invention, the main components of the acid are terephthalic acid and/or
or inphthalic acid, the main glycol components are ethylene glycol and neopentyl glycol,
Polyester mountain whose reduced specific viscosity is 0.5 to 2.5),
and a polyester (2) having a reduced specific viscosity of 0.05 to 0.5 and 0.1 or more lower than the reduced specific viscosity of the polyester (1), and which has a reduced specific viscosity of 200 Melt viscosity at °C is 10-1ooo
This is a powder coating composition characterized by being o-poise.

The composition of the present invention has the following characteristics.

(2) High molecular weight linear polyesters are difficult to be mechanically pulverized, but the composition of the present invention can easily be made into fine powder.

■ Powder coatings using high-molecular-weight linear polyester have a high softening point, require high temperatures for baking, and have high melt viscosity, making it difficult to obtain a smooth surface, but the powder of the composition of the present invention Since it can be baked at temperatures below 220'C and has a low melt viscosity, a smooth surface can be obtained.

(2) High molecular weight linear polyester powder coatings have poor adhesion to metals, but the composition of the present invention provides coatings with excellent adhesion.

(2) High molecular weight linear polyesters form coating films with poor flexibility due to their crystallinity, but flexible coating films can be obtained from the powder coating obtained from the composition of the present invention.

■ Provides a coating film with excellent weather resistance.

The polyester (1) used in the present invention has an acid component mainly consisting of terephthalic acid and/or isophthalic acid, a glycol component mainly consisting of ethylene glycol and neopentyl glycol, and a reduced specific viscosity of 0.5 to 2.
．． 5 polyester.

The polyester (1) has terephthalic acid and/or isophthalic acid as the main acid component, but may contain other third component, difunctional carboxylic acid, in an amount up to 30 mol% of the total acid component.

The third component difunctional carboxylic acids include diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethane dicarboxylic acid, and dibromo terephthalic acid 2.6.
- Aromatic difunctional carboxylic acids such as naphthalene dicarboxylic acid, ■.5-naphthalene dicarboxylic acid, phthalic acid, P-(β-hydroxyethoxy)benzoic acid, P-hydroxybenzoic acid, p-hydroxymethylbenzoic acid, etc.: Aliphatic difunctional carboxylic acids such as adipic acid, cepatic acid, decamethylene dicarboxylic acid, etc.Alicyclic difunctional carboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, etc. I can give an example.

Among these, it is preferable to use aliphatic dicarboxylic acids such as adipic acid and sepatic acid.

Although the mutual ratio of terephthalic acid and isophthalic acid is arbitrary, it is preferable that terephthalic acid is 50 mol % or more with respect to the total number of moles of terephthalic acid and isophthalic acid.

When the ratio of terephthalic acid and inphthalic acid to the total acid components is less than 70 mol %, undesirable phenomena such as a decrease in surface hardness of the resulting coating film and loss of flexibility occur.

The main glycol components are ethylene glycol and neopentyl glycol, but up to 30 mol% of the total glycol component may contain glycol as a third component.

Other glycols as third components include propylene glycol, 1.3-propanediol, 1.4-phthanediol, 1.5-bentanediol, 2-methyl-
1,4-butanediol, 1,6-hexanediol,
3-methyl-1,5-bentanediol, 2-methyl-
1,5-bentanediol, 3,3-dimethyl-1,5-bentanediol, 2,4-dimethyl-1,5-bentanediol, 2-methyl-dohexanediol, 3,4
- Aliphatic glycols such as dimethyl-1,6-hexanediol, 2,5-dimethyl-1,6-hexanediol, diethylene glycol, cyclopyrene glycol, triethylene glycol, tetraethylene glycol, etc., cyclohexane-1,4-dimetatool , alicyclic glycols such as cyclohexane-1,3-dimetatool, ■,4-xylylene glycol, 2,2-bis(4-
Examples include aromatic glycols such as (β-hydroxyethoxy)phenyl]propane.

If the other third component glycol exceeds 30 mol% of the total glycol components, the surface hardness of the resulting coating film may decrease,
Unfavorable phenomena such as poor weather resistance occur.

Although the mutual ratio of ethylene glycol and neopentyl glycol is arbitrary, it is preferable to use neopentyl glycol in a ratio of 40 to 90 mol % based on the sum of ethylene glycol and neopentyl glycol.

The polyester (1) used in the present invention needs to have a reduced specific viscosity of 0.5 to 2.5, and further has a reduced specific viscosity of 0.5 to 2.5.
It is preferable that it is 5-1.4.

If the reduced specific viscosity of polyester (2) is less than 0.5, the adhesion of the coating film to the metal will decrease and it will not be practical, and if it exceeds 2.5, the flow during baking will be poor. It is difficult to obtain a coating film with good smoothness.

The polyester (1) is composed of terephthalic acid and/or isophthalic acid and optionally other third component difunctional carboxylic acids or ester-forming derivatives thereof and ethylene glycol, neopentyl glycol and optionally other third component. It can be obtained by reacting component glycols or their ester-forming derivatives according to conventionally known polyester manufacturing methods.

Examples of the above-mentioned ester-forming derivatives of carboxylic acids include lower alkyl esters (for example, methyl esters), phenyl esters, anhydrides, and halides of carboxylic acids, with lower alkyl esters being particularly preferred.

Typical examples of these include dimethyl terephthalate and dimethyl adipic acid.

In addition, as the ester-forming derivatives of the above glycols,
Examples include lower fatty acid esters of glycols, carbonate esters, and alkylene oxides.

Examples of alkylene oxide include ethylene oxide.

The polyester (2) used as the second component in the present invention is hereinafter referred to as polyester (2).

The polyester (2) needs to have a reduced specific viscosity of 0.05 to 0.5, more preferably 0.05 to Q.3.

If it is less than 0.05, the compatibility with polyester resin becomes poor, crosstalk becomes difficult, and the sharpness of the coating film becomes poor.

If it exceeds 0.5, disadvantageous phenomena will occur, such as difficulty in pulverizing the composition and decreased fluidity of the coating film during baking, making it difficult to obtain a smooth coating film.

Matapolyester/L (2) needs to have a reduced specific viscosity that is 0.1 or more lower than the reduced specific viscosity of polyester (1), and preferably has a reduced specific viscosity that is 0.2 or more lower.

The reduced specific viscosity of polyester (2) is
) If the reduced specific viscosity is not lower than the reduced specific viscosity by 0.1 or more, the fluidity of the coating film during baking will decrease and it will be difficult to obtain a smooth coating film.

The polyester (2) can be produced by reacting a polyhydric carboxylic acid component and a polyhydric hydroxyalcohol component.

As the polycarboxylic acid component, ester-forming derivatives such as dicarboxylic acids, trivalent or higher polycarboxylic acids, or their lower alkyl esters and acid anhydrides can be used, but some of them may be monocarboxylic acids. It may be replaced with an acid or an ester-forming derivative thereof.

Such polyvalent carboxylic acids and ester-forming derivatives thereof include, for example, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, methylterephthalic acid, 4-methylisophthalic acid, adipic acid, cepatic acid, and anhydride. ...Dicarboxylic acids such as phosphoric acid, phthalic anhydride, dimethyl phthalate, dimethyl terephthalate, and dimethyl adipic acid; trivalent or higher valent acids such as trimellitic acid, pyromellitic acid, trimellitic anhydride, pyromellitic anhydride, etc. Polyhydric carboxylic acids and the like can be mentioned.

In addition, as the polyhydric hydroxy alcohol component, dihydroquine alcohol, trihydric or higher polyhydric alcohols, or ester-forming derivatives thereof can be used, but some of them may be replaced with monohydroquine alcohol or its ester-forming derivatives. It's okay.

Such polyhydric hydroxy alcohols and their forming derivatives include, for example, ethylene glycol, ethylene oxide, propylene glycol, 1.4-butanediol, neopentyl glycol, 1.5-bentanediol, 2.
・6-hexanediol, ■・7-hebutanediol,
■・4-Cyclohexane dimetatool, diethylene glycol, triethylene glycol, tetraethylene glycol, cyclopyrene glycol, ■・4-xylylene glycol, 2,2-bis(4-(β-hydroxyethoxy)phenyl)propane , glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, 1.2.6-hexanediol, nrubitol, tris-(2-hydroxyethyl)in cyanurate, and the like.

A hydroxyl group-containing carboxylic acid can also be used together with the polyhydric carboxylic acid component or polyhydric hydroxyalcohol component.

The reaction between the polyhydric carboxylic acid component and the polyhydric hydroxyalcohol component is carried out in one or more steps.

For example, dicarboxylic acid dimethyl ester and dihydroxy alcohol, dicarboxylic acid and dihydroxy alcohol, dicarboxylic acid and trihydroxy alcohol, dicarboxylic acid and dihydroxy alcohol do trihydroxy alcohol, dicarboxylic acid and dihydroxy alcohol and tricarboxylic acid, dihydroxy alcohol and tricarboxylic acid, etc.
A polyester is obtained by carrying out a step reaction or a multi-step reaction of two or more steps.

The reaction proceeds by distilling off water or lower alkyl alcohol at a temperature of 200 to 290°C, preferably in a stream of inert gas such as nitrogen.

The amount of the polyhydric hydroxy alcohol component to be used is preferably 0.8 to 13 mol per 1 mol of the polyhydric carboxylic acid component.

Esterification or transesterification catalysts may be used in the reaction.

Such catalysts include, for example, para-toluenesulfonic acid,
Organic acids such as metabenzenedisulfonic acid and citric acid; organic acid salts such as lead acetate and zinc octoate; and titanate esters such as tetrabutyl titanate and tetrapropyl titanate.

The amount of these catalysts is preferably 0.01 to 0.5% by weight based on the total amount of raw material components.

During the reaction, a small amount of an azeotropic solvent such as xylene can also be used to promote distillation of water.

The mixing ratio of polyester (1) and polyester (2) may be any ratio, but if polyester (1) is 60 to 9
5% by weight of polyester (2) and 40-5% by weight of polyester (2).

Examples of the method for mixing the two components include a method in which the two components are dissolved in a solvent and mixed, and then the solvent is removed, or a method in which the two components are melt-kneaded. However, the melt mixing method is preferable.

The melt-mixing temperature is preferably in the range of 120 to 280°C, taking into consideration the softening point of each polyester.

In the present invention, paint additives may be blended with the polyester (1) and polyester (2) as necessary.

Examples of such compounding agents include pigments, flow control agents, stabilizers, and the like.

Examples of the pigment include white pigments such as zinc white lithopone, zirconium oxide, and titanium oxide; carbon black;
Black pigments such as graphite; extender pigments such as pallite, chalk, clay, talc, silica white, alumina white, ceracola, bentonite, etc.; gray pigments such as zinc powder, zinc oxide, etc.;
Red pigments such as red red, red lead, vermilion, molybdenum red, antimony red, toluidine red, etc.; brown pigments such as amber, iron oxide, etc.; yellow pigments such as Hansa yellow, benzidine yellow, yellow lead 1 synthetic orca, etc.; copper- Green pigments such as phthalocyanine green, chrome green, chromium oxide green, zinc wire, etc.: copper-phthalocyanine blue, navy blue, gunpowder,
Blue pigments such as cobalt blue, manganese blue, etc. Purple pigments such as nioxazine violet, manganese purple, deep locobalt purple, Mars purple, etc. Metal powder pigments such as nialium powder, copper powder, gold powder, brass powder, etc. I can do it.

Examples of the flow control agent include silicone resin, acrylic resin, fine silicon oxide powder, polyvinyl butyral, organic bentonite, aluminum stearate, and zinc stearate.

Examples of the stabilizer include antioxidants and ultraviolet absorbers.

The blending ratio of such paint compounding agents can be selected arbitrarily depending on the type of paint, but the blending ratio that has been conventionally used is usually the best (
, for example, pigments in an amount of 0.5 to 50% by weight, preferably 1 to 40% by weight, based on the total composition, and flow control agents in an amount of 0.5 to 50% by weight, preferably 5 to 30% by weight, based on the total composition. %, and their total amount does not exceed 50% by weight.

The stabilizer is added in a proportion of not more than 5% by weight, preferably not more than 1% by weight, based on the total composition.

When adding the above-mentioned paint compounding agents, such as pigments, flow control agents, stabilizers, etc. to the polyester (1) and polyester (2), these are added to the polyester IAl) in advance.
Alternatively, it can be mixed with polyester (2), or added and mixed when polyester (1) and polyester (2) are mixed.

The mixing is preferably carried out by kneading using a mixer such as an extruder or kneader at a temperature equal to or higher than the softening point of polyester (1) or polyester (2).

The composition consisting of polyester (1) and polyester (2) has a melt viscosity of 0 to 1 ooo at 200°C.
o poise is required, preferably 100 to 5000 poise, and more preferably 200 to 2000 poise.

When the melt viscosity is less than 10 poise, the coating film becomes brittle and the adhesion to metal decreases.

If it exceeds 5000 poise, the fluidity of the coating film during baking will decrease, making it impossible to obtain a smooth coating film.

The polyester composition of the present invention is usually pulverized by mechanical methods.

In the case of mechanical methods, the first step is usually to coarsely grind the material using a grinder, and the second step is to produce a fine powder using a pulverizer.

When performing fine pulverization, it can also be performed at a low temperature of 0° C. or lower.

For example, a fine powder can be easily obtained by crushing while cooling with liquid nitrogen or the like.

The powder coating thus obtained is stable at room temperature,
No blocking phenomenon occurs.

Powder coatings are applied to pretreated metal surfaces using powder coating methods such as electrostatic spray coating, galvanic dipping, electrostatic dynamic dipping, and spraying.
Baking is carried out at a temperature of 0°C, preferably between 1.60 and 230°C.

Baking melts the resin and forms a uniform coating surface.

The present invention will be described in detail below with reference to Examples.

In addition, the reduced specific viscosity [ηSP/C) in the example is the following formula % formula % Solvent: orthochlorophenol, measurement temperature 35°c1η
SP: Specific viscosity).

The melt viscosity is the melt viscosity ηa of the glaze measured using a Koka type flow tester manufactured by Shimadzu Corporation, where ηa is Ha
gen-Poisill's law: pressure difference between two points of length L, R: inner diameter of the cylinder). The value was calculated from the formula CC/5ec), but if the value was 1000 poise or less using this measurement method, the value measured using a B-type viscometer was used.

The physical properties of the coating film were tested by the following method.

(1) Scratch test: Scratches are made with a record needle on the painted surface in a grid pattern at intervals of 1 space vertically and horizontally until the metal surface is reached. Expressed as the number of items.

(2) Erichsen test: A paint film is formed on a metal plate with a thickness of 1 myn, and a punch with a diameter of 20 mm is extruded from the inner side. It is expressed as the extrusion distance when cracks and peeling occur in the paint film (manufactured by Toyo Tester Kogyo Co., Ltd.) Erichsen test machine).

(3) DuPont impact test: JIS-ni-5400
According to 1970.

(4) Bending test (JIS-5400-1970 Paint General Test Method): After bending the test piece by 180° with a metal round bar of a specified diameter inserted, cracks are observed in the paint film on the bent surface. It is tested to see if it can be seen and expressed as the diameter of a round bar (bending tester manufactured by Toyo Tester Industries).

Example 1 In a three-bottle flask with a volume of 500 cc, 155.4 P (0.8 mol) of dimethyl terephthalate, 34.8 P (0.2 mol) of dimethyl adihinate, and 62.8 P (0.2 mol) of ethylene glycol were added. IP (1.0 mol), neopentyl glycol 104.29 (1.0 mol), and calcium arsenate A-J salt 0.176? (0,001-El) was charged, and the reaction was heated while methanol was distilled out of the system. When the distillation of methanol stopped, the transesterification reaction was completed.

The obtained reaction product was transferred to a stirrer-equipped polymerization flask purged with nitrogen, and further added with 0.0875P of antimony trioxide (0.
,00015 mol) and trimethyl phosphate 0.1
82P (0,0013 mol) was added, and reaction was carried out at 250° C. for 30 minutes under normal pressure, then under reduced pressure of about 201n111Hg for 15 minutes, and further under reduced pressure of 0.5 mmHg for a predetermined time.

The reduced specific viscosity of the obtained polyester was 0.752.

The acid component of this polyester is 82% terephthalic acid.
The amount of adipic acid was 18 mol%, and the glycol components were 31 mol% of ethylene glycol and 69 mol% of neopentyl glycol.

This polyester is referred to as polyester/L(A). Next, in a three-necked flask, add terephthalic acid dimethyl ester 389P (2 mol) and neopentyl glycol 208f.
(2 mol) and tetrabutyl titanate 0.1021 (
0,0003 mol) and heated while stirring to distill methanol out of the system.

When 1021 methanol has been distilled out, heating is continued at 220° C. for an additional 3 hours while flowing nitrogen gas into the system.

Next, the reaction was carried out at 250'C under a reduced pressure of about 20 mmHg for 15 minutes, and then for a predetermined time under a reduced pressure of about 0.5 mm Hg.

The reduced specific viscosity of the obtained polyester was 0.24.6.

This polyester is referred to as polyester (B).

Polyester (A) 35P and polyester (B) 15
and P were melt-mixed at 220°C for 10 minutes.

The melt viscosity of the resulting composition at 200°C was 710 poise.

This composition was crushed and attached to a steel plate with a thickness of 1 mvt.
It was baked by placing it in a heating oven at 0°C for 20 minutes.

The properties of the resulting coating film are shown in Table 1.

Example 2 In a 500 CC three-necked flask, dimethyl terephthalate 116.5S' (0.6 mol), dimethyl isophthalate 38.8f (0.2 mol), and dimethyl decamethylene dicarboxylate 51.71 (0, 2
mol), ethylene cre-1-ol 62. A polyester was prepared in the same manner as polyester (4) by adding IP (1.0 mol), 104.2 y (i, o mol) of neopentyl glycol, and 0.176 t of acetic acid hydrate.

The obtained polyester has a reduced specific viscosity of 0.820,
The composition of the acid component is 60 mol% of terephthalic acid, 22 mol% of isophthalic acid, and 18 mol% of decamethylene dicarboxylic acid, and the glycol component is 33 mol% of ethylene glycol.
The neopentyl glycol content was 67 mol%.

This polyester is referred to as polyester (C).

Polyester (C) 35P and polyester (B) 15F
A composition was prepared in the same manner as in Example 1.

The melt viscosity of this composition at 200°C was 600 poise.

A coating film was prepared from this composition in the same manner as in Example 1, and its properties are shown in Table 1.

Example 3 Terephthalic acid dimethyl ester 194.2? (1.0 mol), neopentyl glycol 104.2 + ☆☆P (1
, 0 mol), ethylene glycol 62.1? Polyester 0 was produced from (1.0 mol) in the same manner as in the production of polyester (A).

The reduced specific viscosity of this polyester was 0.989, and its composition consisted of glycol components: 33 mol% ethylene glycol and 67 mol% neopentyl glycol.

A composition was prepared from polyester 0 and polyester (B) in the same manner as in Example 1.

The melt viscosity of this composition at 200°C was 3500 poise.

A coating film was formed from this composition in the same manner as in Example 1.
Its properties are shown in Table 1.

Comparative Example 1 Example 1 from polyhexamethylene terephthalate 351 with a reduced specific viscosity of 1.03 and polyester (B) 1.5P
A composition was produced in the same manner as in the method of .

The melt viscosity of this composition at 200'C is 12,000
It was Poise.

A coating film was prepared from this composition in the same manner as in Example 1, and its properties are shown in Table 1.

Comparative Example 2 Polyester was produced from terephthalic acid dimethyl ester 389P (2 mol) and neopentyl glycol 208f (2.0 mol) in the same manner as polyester (B) (
However, the product was taken out when 1001 methanol was distilled out).

The obtained polyester had a reduced specific viscosity of 0.033.

This polyester is referred to as polyester 4).

A composition and a coating film were prepared from polyhexamethylene terephthalate 35P used in Comparative Example 1 and polyester (E) 15P in the same manner as in Example 1.

The melt viscosity of the composition at 200°C was 4500 poise.

The properties of the resulting coating film are shown in Table 1.

Example 4 Polyester L (A) 45f and polyester (B15P
A composition was produced in the same manner as in Example 1.

The melt viscosity and coating properties of this composition are shown in Table 2.

Example 5 ☆☆
Polyester (B) 60P and methyl type titanium oxide 50P
and were melt-kneaded at 140°C.

55 grams of this polyester composition and 7 grams of polyester (A)
A composition and a coating film were produced from 0P in the same manner as in Example 1.

The melt viscosity and coating properties of this composition are shown in Table 2.

Claims (1)

[Claims] 1 The main component of the acid is terephthalic acid and/or isophthalic acid, the main component of the glycol is ethylene glycol and neopentyl glycol, and the reduced specific viscosity is 0.
Polyester (1) having a reduced specific viscosity of 0.05 to 2.5, and polyester (1) having a reduced specific viscosity of 0.05 to 0.5.
A composition comprising polyester (2) having a reduced specific viscosity lower by 0.1 or more than the reduced specific viscosity of 20
A powder coating composition having a melt viscosity of 10 to 100 poise at 0°C.