JPH10195343A - Polyester resin composition for powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin compsn. which can be converted into a powder coating material excellent in external appearance, mechanical strengths, and weatherability. SOLUTION: This compsn. comprises 4.5-1wt.% melamine-based curative and 95.5-99wt.% polyester resin which is obtd. by reacting an acid component mainly comprising terephthalic acid and/or isophthalic acid and contg. 0.01-0.10mol% isophthalic acid having a metal sulfonate group with an alcohol component mainly comprising an aliph. diol and which has an intrinsic viscosity of 0.20-0.40 and a hydroxyl value of 12-40mgKOH/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin composition which can be used as a powder coating having excellent appearance, mechanical strength and weather resistance.

[0002]

2. Description of the Related Art Polyester resin-based powder coatings have advantages compared to conventional solvent-based coatings, such as low pollution, easy coating automation, and relatively low cost. The demand for paints for protection and decoration of products and building materials is rapidly increasing.

At present, for applications requiring weather resistance, a system in which a blocked isocyanate-based curing agent is blended with a polyester resin is mainly used, but there is a problem that the cost as a coating material is relatively high. .

[0004] On the other hand, a system in which a melamine-based curing agent is blended with a polyester resin is known to be a coating material having good weather resistance and being inexpensive. However, in this system, it is necessary to add a small amount of a sulfonic acid compound such as p-toluenesulfonic acid as a curing catalyst at the paint preparation stage in order to promote a crosslinking reaction. Such sulfonic acid compounds have a problem in that the catalytic effect is too strong and the smoothness of the coating film is reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a polyester resin composition capable of forming a powder coating having excellent appearance, mechanical strength and weather resistance. It is.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to solve the above-mentioned problems. The gist of the present invention is that terephthalic acid and / or isophthalic acid is the main component and the acid component is 0.01 to 0.1.
An acid component comprising 10 mol% of isophthalic acid having a metal salt sulfonate group and an alcohol component mainly composed of an aliphatic diol, having an intrinsic viscosity of 0.20 to 0.40 and a hydroxyl value of
95.5-99% by weight of polyester resin which is 12-40 mgKOH / g
And 4.5 to 1% by weight of a melamine-based curing agent.

[0007]

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

In the present invention, the acid component constituting the polyester resin is mainly terephthalic acid and / or isophthalic acid from the viewpoint of the mechanical strength of the cured coating film and the blocking resistance of the coating, and the acid component of 0.01%. What is used is that in which about 0.10 mol% is isophthalic acid having a metal salt sulfonate group.

As isophthalic acid having a metal salt sulfonate group (hereinafter abbreviated as SIP), 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid and 5-lithium sulfoisophthalic acid are preferably used, and dimethyl ester, diethylene glycol It may be used as an ester-forming derivative such as an ester.

[0010] The amount of SIP must be 0.01 to 0.10 mol% of the total acid component. If the amount is less than 0.01 mol%, the crosslinking reaction between the polyester resin and the melamine-based curing agent does not proceed sufficiently, and as a result, the mechanical strength of the coating film decreases. On the other hand, when this amount exceeds 0.10 mol%, the smoothness of the coating film tends to decrease.

On the other hand, the alcohol component is mainly composed of an aliphatic diol, and ethylene glycol and neopentyl glycol are preferably used.

The polyester resin may be, if necessary, an aliphatic dicarboxylic acid such as phthalic anhydride or naphthalenedicarboxylic acid, an aliphatic acid such as adipic acid, sebacic acid or dodecanedioic acid, as long as its properties are not impaired. A dicarboxylic acid component can be used in combination. In addition, a trivalent or higher carboxylic acid such as trimellitic acid or pyromellitic acid can be used together with the dicarboxylic acid component as long as the polyester resin is not gelled.

If necessary, diethylene glycol, propylene glycol, 1,4-butanediol,
Aliphatic alcohols such as 6-hexanediol, 1,4-cyclohexanedimethanol and stearyl alcohol, diols having an aromatic group such as an ethylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol S can be used in combination. . Further, a trivalent or higher alcohol such as trimethylolpropane, glycerin, and pentaerythritol can be used in combination as long as the polyester resin is not gelled.

Further, if necessary, a small amount of a hydroxycarboxylic acid such as p-hydroxybenzoic acid or ε-caprolactone may be used in combination.

Next, the polyester resin has an intrinsic viscosity of 0.1.
It must be between 20 and 0.40. Intrinsic viscosity is 0.
If it is less than 20, the mechanical strength of the coating tends to decrease, and if it exceeds 0.40, the pulverizability of the resin and the smoothness of the coating decrease.

The polyester resin has a hydroxyl value of 12
It must be の も の 40 mgKOH / g. If the hydroxyl value is less than 12 mgKOH / g, the mechanical strength of the coating film decreases because the number of crosslinking points between the polyester resin and the melamine-based curing agent decreases. On the other hand, if it exceeds 40 mgKOH / g, the number of crosslinking points between the polyester resin and the melamine-based curing agent becomes too large, and the smoothness of the coating film is reduced. The strength may decrease.

Further, the polyester resin has a softening temperature.
Preferably it is in the range of 50 to 150 ° C. If the softening temperature is less than 50 ° C., the powdered resin or the composition tends to aggregate and solidify, and the blocking resistance tends to be poor,
On the other hand, if the softening temperature exceeds 150 ° C, it is necessary to increase the kneading temperature during the production of the coating composition, and the reaction between the resin and the curing agent proceeds during kneading, resulting in the smoothness of the coating film and the mechanical properties. Strength tends to decrease.

The polyester resin which satisfies the above conditions can be esterified or prepared at a temperature of 200 to 280 ° C. by a conventional method using the above-mentioned acid component and alcohol component (including their ester-forming derivatives) as raw materials. After the transesterification reaction, under reduced pressure of 5 hPa or less, 200-300 ° C,
Preferably, it can be prepared by a method in which a polycondensation reaction is carried out at a temperature of 230 to 290 ° C to obtain a polyester having a high degree of polymerization, and then an alcohol is added 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 reactions, known reaction catalysts and the like can be used.

In the resin composition for powder coating of the present invention,
In order to satisfy all of the mechanical strength, appearance (smoothness), and weather resistance of the cured coating film, it is necessary to use a melamine-based curing agent as a curing agent for crosslinking the polyester resin.

As the melamine-based curing agent, there is an N-methylol ether compound represented by the following formula.

[0023]

Embedded image Here, R represents a hydrogen atom or a monovalent organic residue such as an alkyl group, an aryl group, or a cycloalkyl group.

Specific examples include hexamethoxymethyl melamine (commercially available from Sumitomo Chemical Co., Ltd. under the trade name of "Sumimar M-100C"), and hexabutoxymethyl melamine (commercial name of "Mycoat 506" from Psytech Co., Ltd.) Which are commercially available on the market). Among these, hexamethoxymethyl melamine is particularly preferable in terms of the mechanical strength of the coating film, the appearance of the coating film, and the like.

The mixing ratio of the polyester resin and the melamine-based curing agent must be 95.5 to 99% by weight of the polyester resin and 4.5 to 1% by weight of the melamine-based curing agent. When the proportion of the curing agent is less than 1% by weight, the mechanical strength of the coating film decreases because the number of crosslinking points between the polyester resin and the melamine-based curing agent decreases. On the other hand, if it exceeds 4.5% by weight,
There is a tendency that the blocking resistance of the coating material is reduced, and the number of crosslinking points between the polyester resin and the melamine-based curing agent is too large, so that the smoothness of the coating film is reduced.

It is appropriate that the amount of the curing agent is within the above range and the amount of the functional group substantially corresponding to the amount of the hydroxyl group of the polyester resin, preferably 0.8 to 1.2 times equivalent.

The resin composition for powder coatings of the present invention comprises the above-mentioned polyester resin, a melamine-based curing agent and, if necessary, known leveling agents, pigments, and other additives (excluding p-toluenesulfonic acid). ) Is kneaded at 70-130 ° C using a kneader or a roll.

[0028]

In the present invention, the use of SIP as a part of the acid component constituting the polyester resin allows the polyester resin itself to have a mild curing catalytic activity. When a body coating is used, it is not necessary to add a curing catalyst such as p-toluenesulfonic acid, and a cured coating having both good appearance (smoothness) and mechanical strength can be obtained.

[0029]

Next, the present invention will be described in detail with reference to examples. The characteristic values and the like in the examples were obtained by the following methods. (a) Copolymerization ratio of SIP component (SIP copolymerization amount) The amount of the SIP component in the resin was determined by a fluorescent X-ray method using a fluorescent X-ray analyzer system 3270 manufactured by Rigaku Co., Ltd. expressed. (b) Intrinsic viscosity The intrinsic viscosity was determined from a value measured at a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (c) Hydroxyl value To 3 g of polyester resin, 50 ml of pyridine and 0.6 ml of acetic anhydride
After heating and acetylation, titration was performed with a potassium hydroxide methanol solution. (d) Softening temperature Resin pulverized to a size of 60-100 mesh 2.5m in diameter
m, filled into a bottomed glass tube with a length of 150 mm to a height of 30 mm, immersed the resin-filled part in an oil bath, heated at a rate of 1 ° C./min, and visually determined the temperature at which liquefaction started, The softening temperature was used. (e) Blocking resistance The coating composition passed through a 140-mesh sieve was coated with a diameter of 3c.
m, filled into a 10 cm long test tube to a height of 5 cm, left in a 40 ° C. thermostat for 72 hours, then invert the test tube to discharge the coating composition, and visually check for the occurrence of blocking. did. (f) Smoothness The smoothness of the coating film was visually evaluated. (g) Impact resistance According to JIS K 5400, sandwich the coated steel plate so that the coating film comes in contact with the spherical surface between the shooting mold with a spherical surface with a diameter of 1.27 cm and a cradle with a depression matching it, and from above A weight of 500 g was dropped vertically from a height of 40 cm, and those which did not destroy the coating film were accepted, and those which did destroy the coating film were rejected. (h) 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 irradiation for 300 hours was determined using a sunshine weather meter. (This value is 60
% Or more is a pass. Note that the 60 ° specular gloss of the coating film was determined according to JIS K 5400.

REFERENCE EXAMPLE 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 200 to
The esterification reaction was performed at 260 ° C. for 6 hours. After transferring the obtained esterified product to a polycondensation reaction tank, 2 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of an acid component was added, the pressure was reduced to 0.4 hPa, and the polycondensation reaction was performed at 280 ° C. for 4 hours. A polyester having an intrinsic viscosity of 0.45 was obtained. To this polyester, a depolymerizing agent shown in Table 1 was added in an amount (mol part) shown in Table 1, and a depolymerization reaction was carried out under normal pressure at a temperature of 270 ° C. for 1 hour to obtain a polyester having characteristic values shown in Table 1. Resins A to I were obtained.

[0031]

[Table 1] In addition, the SIP copolymerization amount of the resin E and the resin I was below the detection limit.

Examples 1-4, Comparative Examples 1-5 A hexamethoxymethylmelamine-based curing agent: manufactured by Sumitomo Chemical Co., Ltd. was added to the polyester resins A to I obtained in the reference examples in the amounts (parts by weight) shown in Table 1. "Sumimar M-100C", butyl polyacrylate-based leveling agent: "Acronal 4F" manufactured by BASF, benzoin and rutile type titanium dioxide pigment: "CR-90" manufactured by Ishihara Sangyo Co., Ltd. The amount shown in Table 2 (parts by weight)
And dry-blended with a FM 10B Henschel mixer (Mitsui Miike Seisakusho), melt-kneaded at 110 ° C using a PR-46 type co-kneader (Buss), cooled, pulverized, To obtain a powder coating. In Comparative Example 5, p-toluenesulfonic acid was added as a curing catalyst in an amount (parts by weight) shown in Table 2.

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 film thickness of 50 to 60 μm, and baked at 190 ° C. for 20 minutes. Table 2 shows the results of evaluating the performance and the like of the coating film.

[0034]

[Table 2]

In Examples 1 to 4, all of the coatings exhibited good blocking resistance, appearance of the coating film, mechanical strength, and weather resistance.

On the other hand, the comparative example had the following problems. In Comparative Example 1, S in the polyester resin
Since the copolymerization ratio of IP was low, the mechanical strength of the coating film was not sufficient. In Comparative Example 2, the smoothness of the coating film was poor because the copolymerization ratio of SIP was high. In Comparative Example 3,
Since the intrinsic viscosity of the polyester resin is low, the mechanical strength of the coating film is not sufficient, and since the hydroxyl value is high, as a result, the blending ratio of the melamine-based curing agent is increased, and the smoothness of the coating film and the resistance of the coating are increased. The blocking property was also inferior. In Comparative Example 4, the intrinsic viscosity was high, and the smoothness of the coating film was inferior. In addition, since the hydroxyl value was low, the mechanical strength of the coating film was not sufficient. In Comparative Example 5, since the SIP was not copolymerized with the polyester resin and a curing catalyst was added at the time of coating, the smoothness of the coating film was insufficient.

[0037]

According to the present invention, there is provided a polyester resin composition which can be used as a powder coating having excellent appearance, mechanical strength and weather resistance.

Claims (1)

[Claims] 1. An acid component comprising terephthalic acid and / or isophthalic acid as a main component, wherein 0.01 to 0.10 mol% of an acid component is an isophthalic acid having a metal salt sulfonate group, and an alcohol component mainly comprising an aliphatic diol. 95.5-99% by weight of a polyester resin having an intrinsic viscosity of 0.20-0.40, a hydroxyl value of 12-40 mgKOH / g and a melamine-based curing agent 4.5
1% by weight of a polyester resin composition for powder coatings.