JPH10204376A - Polyester resin for powder coating material, and composition therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin that gives a powder coating material excellent in blocking resistance and capable of forming a coating film excellent in smoothness, and to provide a resin compsn. contg. the same. SOLUTION: This polyester resin is formed from an acid component mainly comprising an arom. dicarboxylic acid and an alcohol components mainly comprising an aliph. diol, of which 3-25mol% is 3-hydroxy-2,2-dimethylpropyl 3- hydroxy-2,2-dimethylpropanoate and has an intrinsic viscosity of 0.15-0.40 and a hydroxyl value of 15-80mgKOH/g. This resin is compounded with a blocked isophorone diisocyanate curing agent to give a resin compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin for powder coatings and a composition which gives a coating film having good smoothness.

[0002]

2. Description of the Related Art Compared to conventional solvent-based paints, powder paints are non-polluting paints, can be used immediately after painting, do not require multiple layers of coating, and are relatively inexpensive. In addition, advantages such as the ability to recover and use the surplus during painting are recognized, and in recent years the demand for paints for protection and decoration of members such as home appliances, building materials, and automobile parts has been rapidly expanding.

[0003] Epoxy resin, acrylic resin, and polyester resin-based powder coatings are mainly known. Among them, polyester resin-based powder coatings are coatings having a well-balanced coating film performance. Also known as

[0004] Paints have the main functions of protecting and decorating the base material, but recently, the beautiful finish of the paint finish on the surface has been demanded, and in particular, excellent smoothness of the paint surface has been demanded. I have. However, polyester resins used in powder coatings have relatively high molecular weights and high viscosities when melted, so they are not sufficient in terms of the smoothness of the coating film surface. At present, it is considerably inferior to solvent type paints.

Heretofore, as a method for improving the smoothness of the surface of a coating film of a powder coating material, a method has been adopted in which the molecular weight of a polyester resin which is a main component of the coating material is reduced to lower the viscosity at the time of melting. However, in this method, although the smoothness of the coating film is improved, the glass transition temperature of the polyester resin is also lowered, so that not only the storage stability (blocking resistance) of the paint is deteriorated, but also mechanical properties such as impact resistance are reduced. There is a problem that physical properties are deteriorated.

Further, a method of lowering the melt viscosity of a resin by copolymerizing a polyester resin with a general aliphatic diol or dicarboxylic acid component such as 1,6-hexanediol, diethylene glycol or adipic acid or dodecane diacid. However, even in this method, it is necessary to considerably increase the copolymerization amount in order to develop sufficient smoothness in the coating film, and the influence of this method can prevent a decrease in the glass transition temperature of the polyester resin. And the storage stability of the paint becomes poor. In addition, there is a problem that the other properties are greatly affected such as a decrease in weather resistance.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves such a problem and provides a powder coating having excellent smoothness without impairing the weather resistance and having good blocking resistance. To provide a polyester resin and a composition.

[0008]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that by using a polyester resin copolymerized with a specific diol component,
The inventors have found that this object is achieved, and have reached the present invention.

That is, the gist of the present invention is as follows. 1. An acid component mainly composed of an aromatic dicarboxylic acid and an aliphatic diol mainly composed of 3 to 25 mol% of the diol component
-Hydroxy-2,2-dimethylpropyl-3-hydroxy-2,2-dimethylpropanoate, having an intrinsic viscosity of 0.15 to 0.40 and a hydroxyl value of
A polyester resin for powder coatings, which is 15 to 80 mgKOH / g. 2. 2. A polyester resin composition for powder coatings, comprising: 71 to 94% by weight of the polyester resin according to claim 1 and 29 to 6% by weight of a blocked isophorone diisocyanate-based curing agent.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the polyester resin of the present invention, as the acid component, those mainly composed of aromatic dicarboxylic acids are used, and specifically, terephthalic acid and isophthalic acid are preferably used. Along with these, as long as the properties of the polyester resin are not impaired, if necessary, 5-sodium sulfoisophthalic acid, phthalic anhydride, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, adipic acid, sebacic acid, dodecane diacid, etc. A small amount of trivalent or higher carboxylic acid such as aliphatic dicarboxylic acid, trimellitic acid and pyromellitic acid may be used. Also, 4-hydroxybenzoic acid, ε
-A small amount of a hydroxycarboxylic acid such as caprolactone may be used in combination.

On the other hand, the alcohol component of the polyester resin is mainly composed of an aliphatic diol, and 3 to 25 mol% of the diol component is 3-hydroxy-2,2-dimethylpropyl-3-hydroxy-2,2-. Dimethyl propanoate (hereinafter referred to as HPPHP) is used.

HPHP is also called hydroxypivalyl hydroxypivalate and is a compound represented by the following formula.

[0014]

Embedded image

The proportion of HPHP is 3-25% of the diol component.
Mol%, preferably 5 to 15 mol%. When the proportion of HPHP is less than 3 mol%, the smoothness of the coating film cannot be made sufficient. On the other hand, HPH
If the proportion of P exceeds 25 mol%, not only the blocking resistance of the coating material will deteriorate, but also the mechanical properties of the coating film will decrease.

HPHP not only exhibits a remarkable effect of producing sufficient smoothness, which cannot be achieved by copolymerization of a small amount of a copolymer with a general aliphatic diol or dicarboxylic acid, but also has a comparative effect. Even if the copolymerization is carried out in an excessively large amount, the same amount of a general aliphatic diol does not cause a significant decrease in the weather resistance as in the case of copolymerizing the same amount, and the same amount of a general aliphatic dicarboxylic acid is copolymerized. This has a very specific effect of preventing the glass transition point from being greatly reduced as in the case of polymerization and the blocking resistance from being deteriorated accordingly.

HPHP is copolymerized in the polyester resin in a state where a part of the ester bond is transesterified during the polycondensation reaction, but the effect of improving the smoothness is sufficiently exhibited.

As the aliphatic diol used in combination with HPHP, neopentyl glycol and ethylene glycol are preferably used. If necessary, propylene glycol, 1,4-butanediol, 1,6-hexanediol,
Diethylene glycol or the like can be used in combination.

As long as the properties of the polyester resin are not impaired, 1,4-
Alicyclic diols such as cyclohexanedimethanol and 1,4-cyclohexanediol, diols having an aromatic group such as ethylene oxide adduct of bisphenol A and ethylene oxide adduct of bisphenol S, trimethylolpropane, pentaerythritol, glycerin, etc. May be used in a small amount.

Next, the polyester resin of the present invention needs to have an intrinsic viscosity in the range of 0.15 to 0.40, preferably 0.20 to 0.35. When the intrinsic viscosity is less than 0.15,
Since the molecular weight of the resin is low, the blocking resistance of the resin and the composition tends to decrease, and the mechanical strength of the coating film tends to decrease, which is not preferable. On the other hand, when the intrinsic viscosity exceeds 0.40, the pulverizability is deteriorated due to the high molecular weight of the resin, and the fluidity is reduced, so that the smoothness of the coating film is deteriorated.

The polyester resin has a hydroxyl value of 15
It should be in the range of 8080 mgKOH / g, preferably 20-60 mgKOH / g. If the hydroxyl value is less than 15 mgKOH / g, the molecular weight of the resin will be too high and the fluidity will decrease, resulting in large irregularities on the surface of the coating film and a tendency to decrease the smoothness, exceeding 80 mgKOH / g Then, the molecular weight of the resin becomes too low, and the mechanical strength of the coating film decreases.

Further, the polyester resin has a softening temperature.
Those in the range of 50 to 150 ° C are preferred. If the softening temperature is less than 50 ° C., the powdered resin is likely to coagulate and solidify,
On the other hand, when the temperature exceeds 150 ° C., it is necessary to increase the kneading temperature, and the curing reaction proceeds during the coating process, resulting in a decrease in the smoothness of the coating film.

The polyester resin which satisfies the above conditions is obtained by esterifying the carboxylic acid component and the diol component (including their ester-forming derivatives) at a temperature of 200 to 280 ° C. by a conventional method. Or after transesterification, under reduced pressure of 5 hPa or less, 200-300
The polyester can be prepared by performing a polycondensation reaction at a temperature of 230 ° C., preferably 230 to 290 ° C., to obtain a polyester having a high degree of polymerization, and then adding an alcohol to carry out a depolymerization reaction.

After an esterification or transesterification reaction is carried out by a conventional method, the mixture is subjected to a predetermined intrinsic viscosity at a temperature of 200 to 300 ° C., preferably 220 to 280 ° C. under normal pressure or a reduced pressure of about 50 to 100 hPa. It can also be prepared by a method in which a polycondensation reaction is performed to the extent possible.

In the esterification, transesterification and polycondensation, known reaction catalysts can be used.

When the polyester resin of the present invention is used as a powder coating material, a curing agent having a functional group that reacts with the hydroxyl group of the polyester resin is blended. In this respect, a blocked isophorone diisocyanate-based curing agent is used.

Specifically, a blocked isophorone diisocyanate blocked with a blocking agent such as ε-caprolactam and a uretdione-bonded isocyanate which is a self-blocking type are preferably used.

Commercial products of ε-caprolactam blocked isophorone diisocyanate include “Bestagon B 1530” manufactured by Huls and “Cleran U-type” manufactured by Bayer.
A commercially available uretdione-bonded isocyanate is "Bestagon BF 1540" manufactured by Huls.

The mixing ratio of the polyester resin and the curing agent in the resin composition of the present invention is as follows:
% By weight, and the curing agent should be 29 to 6% by weight. If the amount of the curing agent is too small, the curing reaction does not proceed sufficiently, so that the mechanical strength of the coating film decreases.If the amount of the curing agent is too large, the amount of the polyester resin becomes relatively small, so The mechanical strength of the film decreases.

It is appropriate that the amount of the curing agent is adjusted so that the amount of the functional group substantially corresponds to the hydroxyl value of the polyester resin (that is, 0.8 to 1.2 times equivalent) within the above range.

The resin composition for powder coating of the present invention is prepared by using a kneader or a roll together with the above-mentioned polyester resin, a curing agent and, if necessary, a known curing catalyst, a leveling agent, a pigment and other additives. It can be prepared by kneading at a temperature of 70 to 150 ° C.

The powder coating obtained by using the resin composition of the present invention is applied to an object to be coated, and usually baked at a temperature of 170 to 190 ° C. for 15 to 25 minutes to obtain a glossy and smooth surface. Gives a coating film with excellent properties.

[0033]

The reason why the polyester resin composition of the present invention gives a coating film having excellent smoothness without impairing the weather resistance has not been sufficiently elucidated, but it is known as HPHP having a structure excellent in weather resistance and reactivity. This is presumed to be based on a polyester resin obtained by copolymerizing a specific diol component in a well-balanced manner.

[0034]

Next, the present invention will be described in detail with reference to examples and comparative examples. The characteristic values and the like were measured and evaluated by the following methods. (a) Intrinsic viscosity The intrinsic viscosity was determined from the solution viscosity measured at 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (b) Copolymerization amount of HPHP component The polyester resin was dissolved in deuterated trifluoroacetic acid, and analyzed by using JMW-LA400 type NMR manufactured by JEOL Ltd. The total amount of the HPHP component and the hydroxypivalic acid component derived from the HPHP was defined as the copolymerization amount of the HPHP component. (c) Hydroxyl value 3 g of the resin was dissolved in 50 ml of pyridine, acetylated by adding 5 ml of an acetylated solution consisting of 6 ml of acetic anhydride and 44 ml of pyridine, and then titrated with a 0.5 N methanol solution of potassium hydroxide. . (d) Softening temperature The resin pulverized to a size of
Fill a glass tube with a length of 150 mm and a length of 150 mm to a height of 30 mm, immerse the resin-filled part in an oil bath, raise the temperature at a rate of 1 ° C./min, and visually determine the temperature at which liquefaction begins. The softening temperature was used. (e) Blocking resistance The obtained powder coating material is put into a bottomed glass tube having a diameter of 3 cm and a height of 7 cm up to a height of 4 cm, and left in a constant temperature bath at 40 ° C for one week. After one week, turn the glass tube upside down to remove the powder coating,
It was determined based on the state of the paint. ：: There is no lump in the paint. X: There is a large lump in which the coating material is agglomerated and solidified. (f) 60-degree specular gloss was determined according to JIS K 5400. (g) Smoothness The smoothness of the coating film was visually determined and evaluated in the following two steps. ：: The coating film has little unevenness and good smoothness. ×: The coating film has large unevenness and poor smoothness. (H) Impact resistance A shooting type with a spherical surface with a diameter of 1.27 cm according to JIS K 5400 and it A coated steel plate was sandwiched between the pedestal having a matching dent so that the coating film was in contact with the spherical surface, and a 1 kg weight was dropped vertically from above to determine the breaking height of the coating film.
(If the value is 50 cm or more, the test is acceptable.) (I) Eriksen JIS Z 2247 was found. (If this value is 9 mm or more, it is acceptable.) (J) Accelerated weathering resistance WEL-6XS-HC-B / Ec manufactured by Suga Test Machine Co., Ltd. according to JIS K 5400
The retention rate of the 60-degree specular gloss after 500 hours of irradiation was determined using a sunshine weather meter. (This value is 70
% Or more is a pass. )

Examples 1 to 6 and Comparative Examples 1 to 4 The starting compounds shown in Table 1 were used in the amounts (mol parts) shown in Table 1.
Into the esterification reactor at a pressure of 0.3 MPa and a temperature of 260 ° C
For 4 hours. After transferring the obtained esterified product to the polycondensation reaction tank, antimony trioxide was added to the reaction vessel for 2 hours.
X 10 ^-4 mol / acid component 1 mol was added, the pressure was reduced to 0.5 hPa, and a polycondensation reaction was carried out at a temperature of 280 ° C. for 3 hours to obtain a polyester having an intrinsic viscosity of 0.45. Then, the polyester was added to Table 1
The depolymerizing agent shown in Table 1 was added in the amount (mol parts) shown in Table 1, and a depolymerization reaction was carried out at 270 ° C. for 1 hour under normal pressure to obtain polyester resins A to I having the characteristic values shown in Table 1. Obtained.

[0036]

[Table 1]

To the polyester resins A to I in the amounts (parts by weight) shown in Table 2, a curing agent: "Vestagon B 153" manufactured by Huls Co.
0 "or" Bestagon BF 1540 ", dioctyltin maleate-based curing catalyst:" Stann OMF "manufactured by Sankyokisei Co., Ltd., butyl polyacrylate-based leveling agent:" Acronal 4F "manufactured by BASF, benzoin and rutile-type titanium dioxide pigment: After adding "CR-90" manufactured by Ishihara Sangyo Co., Ltd. in the amount (parts by weight) shown in Table 2 and dry blending with an FM 10B Henschel mixer (manufactured by Mitsui Miike Seisakusho), PR-46 type co-kneader (Buss Co., Ltd.) Was melt-kneaded at 110 ° C., cooled, pulverized, and classified with a 140-mesh wire net to obtain a powder coating.

The powder coatings obtained in the above Examples and Comparative Examples were electrostatically coated on a zinc phosphate-treated steel sheet so as to have a thickness of 50 to 60 μm, and baked at 180 ° C. for 20 minutes. Table 2 shows the results of evaluating the performance and the like of the coating film.

[0039]

[Table 2]

In Examples 1 to 6, the blocking resistance of the paint, the smoothness of the coating film, the mechanical strength, and the weather resistance were all good.

On the other hand, the comparative example had the following problems. In Comparative Example 1, the polyester resin HPHP was used.
Is small, the smoothness of the coating film is not sufficient, and in Comparative Example 2, the copolymerization ratio of HPHP is large.
The coating had poor blocking resistance. In Comparative Examples 3 and 4, since HPPHP was not copolymerized and 1,6-hexanediol or diethylene glycol was used instead, blocking resistance of the coating and weather resistance of the coating film were poor.

[0042]

According to the present invention, there is provided a polyester resin and a composition which provide a coating film having excellent smoothness without impairing the weather resistance and which is a powder coating having good blocking resistance. You.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08G 63/60 C08G 63/60

Claims (2)

[Claims] An acid component mainly composed of an aromatic dicarboxylic acid and an aliphatic diol mainly composed of 3 to 25 parts of a diol component.
Mol% is 3-hydroxy-2,2-dimethylpropyl-
An alcohol component which is 3-hydroxy-2,2-dimethylpropanoate, having an intrinsic viscosity of 0.15 to 0.40;
A polyester resin for powder coatings having a hydroxyl value of 15 to 80 mgKOH / g. 2. The polyester resin 71 to 94 according to claim 1.
1. A polyester resin composition for powder coatings, comprising: by weight, and 29 to 6% by weight of a blocked isophorone diisocyanate-based curing agent.