JP2000080307A - Polyester resin and composition for powder coating, and powder coating using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable baking at low temperatures, improve curing properties and storage stability, and enable forming a coating with a good appearance by specifying an acid component, an alcohol component and physical properties. SOLUTION: This polyester resin comprises an acid component including an aromatic dicarboxylic acid as a main component and a glycol component mainly comprising an aliphatic glycol, and has a limiting viscosity of 0.10-0.30 dl/g, an acid value of 30-85 mgKOH/g and a melt viscosity at 150 deg.C of 100-800 dPa.s. Furthermore, the resin contains, as copolymerization components, (A) an aliphatic dicarboxylic acid, (B) an aromatic glycol and (C) a carboxylic acid having a functionality of 3 or more and the blending ratio is such that the ratio of component A to the total acid components is 5-25 mol%, the ratio of component B to the total glycol components is 10-45 mol% and that of component C to the total acid components is 1-10 mol%. Based on 100 pts.wt. the total of the polyester resin and an epoxy resin-based curing agent, 0.4-1.0 pts.wt. of an imidazole-based curing accelerator is blended to obtain the objective resin composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can provide a powder coating having good blocking resistance and low-temperature curability, and forms a coating film having good appearance (particularly, surface smoothness) and mechanical strength. The present invention relates to a polyester resin and a composition for a powder coating which can be used, and a powder coating using the same.

[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 recent years, there have been recognized advantages such as the fact that they can be recovered and used, and the demand for protective decorative coatings for members such as home electric appliances, building materials and automobile parts has been rapidly expanding in recent years.

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

[0004] Incidentally, polyester resin-based powder coatings generally require a higher baking temperature than solvent-based coatings. However, by lowering the baking temperature, coating equipment for a solvent coating line is required. Since it can be diverted as it is and the amount of generated heat is reduced, there is an advantage that not only the workability and the work environment are improved but also the running cost is reduced by energy saving. In addition, since the baking temperature is lowered, the heat resistance is not sufficient, and it is possible to apply to a material that could not be applied by the conventional powder coating. From such a point, in the polyester resin-based powder coating,
There is a strong demand for a lower baking temperature.

[0005] In addition, paint has a main function of protecting and decorating members, but recently, a beautiful finish of the surface paint finish is required, and in particular, the paint surface has excellent smoothness. Is required.

However, the conventional polyester resin powder coating has a problem that, when baked at a low temperature, the curing reactivity is lowered and the curing is not sufficiently performed. To increase the curing reactivity, a large amount of a curing accelerator is used. , There is a problem that the smoothness of the coating film is remarkably deteriorated.

Therefore, in order to bring the smoothness of the coating film to a practical level, a method has been adopted in which the molecular weight of the polyester resin which is the main component of the coating material is reduced to lower the viscosity at the time of melting. However, according to this method, the smoothness of the obtained coating film is improved, but the glass transition temperature of the polyester resin is lowered, so that not only the storage stability (blocking resistance) of the paint is deteriorated, but also the impact resistance is reduced. However, there is a problem that the mechanical strength decreases.

Further, a method has been proposed in which an aliphatic diol component such as 1,6-hexanediol, diethylene glycol, adipic acid and dodecanedicarboxylic acid or a dicarboxylic acid component is copolymerized with a polyester resin to lower the melt viscosity of the resin. (JP-A-10-46056). However, even in this method, in order to develop the smoothness and sufficient mechanical strength of the coating film, it is necessary to considerably increase the copolymerization amount of the above components, and the glass transition temperature of the polyester resin is lowered. In addition, there is a problem that the storage stability (blocking resistance) of the paint is deteriorated.

Furthermore, in order to raise the glass transition temperature of the polyester resin, a method of copolymerizing a condensed polycyclic hydrocarbon compound has also been proposed. However, in this method, the melt viscosity of the resin increases and the coating film and In this case, there is a problem that not only the smoothness is lowered but also the cost is increased.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves such a problem and can form a coating film which can be baked at a low temperature, has excellent curability and storage stability, and has a good appearance. An object of the present invention is to provide a polyester resin and a composition for a powder coating, and a powder coating using the same.

[0011]

Means for Solving the Problems The present inventors have conducted studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the gist of the present invention is as follows. (1) Consisting of an acid component mainly composed of an aromatic dicarboxylic acid and a glycol component mainly composed of an aliphatic glycol, having an intrinsic viscosity of 0.10 to 0.30 dl / g, an acid value of 30 to 85 mgKOH / g, and 150 ° C.
Is a polyester resin having a melt viscosity of 100 to 800 dPa · s, wherein the polyester resin contains an aliphatic dicarboxylic acid A, an aromatic glycol B, and a carboxylic acid C having three or more functional groups as a copolymer component. The ratio to the acid component is 5 to 25 mol%, the ratio of B to the total glycol component is 10 to 45 mol%, and the ratio of C to the total acid component is 1 to 1 mol%.
A polyester resin for powder coatings, which is 10 mol%. (2) A resin composition in which 0.4 to 1.0 part by weight of an imidazole-based curing accelerator is blended with respect to a total of 100 parts by weight of the polyester resin for powder coating and the epoxy resin-based curing agent according to the above (1), A polyester resin composition for powder coating, wherein the gel time of the resin composition at 150 ° C. is 8 to 13 minutes. (3) A powder coating using the polyester resin composition for powder coating according to (2).

[0012]

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

The polyester resin of the present invention comprises an acid component mainly composed of an aromatic dicarboxylic acid and a glycol component mainly composed of an aliphatic glycol.

As the aromatic dicarboxylic acid, terephthalic acid and isophthalic acid are mainly used for reasons such as required resin properties and cost performance. Also,
As the aliphatic glycol, ethylene glycol and neopentyl glycol are mainly used for reasons such as required resin properties and cost performance.

The above polyester resin has an intrinsic viscosity of 0.1.
It is in the range of 10 to 0.30 dl / g, preferably 0.10 to 0.20 dl / g. When the intrinsic viscosity is less than 0.10 dl / g, the blocking resistance of the powder coating material is reduced and the mechanical strength of the coating film is reduced due to the low molecular weight of the resin. On the other hand, when the intrinsic viscosity exceeds 0.30 dl / g, the resin has a high molecular weight, so that the pulverizability becomes poor or the fluidity is lowered, so that the smoothness of the coating film becomes poor.

The above polyester resin has an acid value of
It is in the range of 30-85 mgKOH / g, preferably 40-80 mgKOH / g. When the acid value is less than 30 mgKOH / g, the molecular weight of the resin becomes too high and the fluidity is reduced, so that large irregularities are generated on the surface of the coating film and the smoothness is reduced. On the other hand, when the acid value exceeds 85 mgKOH / g, the molecular weight of the resin becomes too low, and the mechanical strength of the coating film decreases.

Further, the above polyester resin has a
Melt viscosity at 100 ° C is 100 to 800 dPa · s, preferably 150 to
It is in the range of 500 dPa · s. This melt viscosity is 100dPa
If it is less than s, the fluidity is too large when baked as a paint and sagging occurs at the edge of the coating film. On the other hand, when the melt viscosity exceeds 800 dPa · s, the fluidity decreases and the smoothness of the coating film deteriorates. The melt viscosity of the conventional polyester resin for powder coatings is about 1500 to 3000 dPa · s, and in the present invention, it is necessary to use a resin having a significantly lower melt viscosity than the conventional one.

Conventionally, when an aliphatic dicarboxylic acid is copolymerized with a polyester resin comprising an aromatic dicarboxylic acid component and an aliphatic glycol component, the glass transition temperature of the polyester resin decreases as the amount of copolymerization increases. It is known that when an aromatic glycol is copolymerized with a polyester resin comprising an aromatic dicarboxylic acid component and an aliphatic glycol component, the glass transition temperature of the polyester resin slightly increases, but there is no significant change.
However, only when a specific amount of an aliphatic dicarboxylic acid and an aromatic glycol is copolymerized with a polyester resin comprising an aromatic dicarboxylic acid component and an aliphatic glycol component, a decrease in the glass transition temperature of the polyester resin can be suppressed. I found an effect.

That is, in the polyester resin of the present invention, in addition to the above-mentioned aromatic dicarboxylic acid component and aliphatic glycol component, an aliphatic dicarboxylic acid A, an aromatic glycol B and a tri- or higher functional carboxylic acid C are copolymerized. It is necessary to include it as a component.

Examples of the aliphatic dicarboxylic acid A include succinic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and the like. From the viewpoints of cost and smoothness and mechanical strength of the coating film, adipic acid, sebacic acid and Acids are preferred.
As the aromatic glycol B, bisphenol A
Ethylene oxide adducts of bisphenol S, ethylene oxide adducts of bisphenol F, etc., and in terms of smoothness and mechanical strength of the coating film, ethylene oxide adducts of bisphenol A and bisphenol S Ethylene oxide adducts are preferred. Further, examples of the carboxylic acid C having three or more functional groups include trimellitic anhydride, trimellitic acid, and pyromellitic acid. Acids and trimellitic acid are preferred.

The ratio of the aliphatic dicarboxylic acid A to the total acid component is 5 to 25 mol%, the ratio of the aromatic glycol B to the total glycol component is 10 to 45 mol%, and the total acid of the trifunctional or higher carboxylic acid C is It is necessary that the ratio to the components is 1 to 10 mol%, the ratio of A to the total acid components is 8 to 20 mol%, and the ratio of B to the total glycol components is
It is preferable that the ratio of C to 10 to 30 mol% and the total acid component be 1 to 5 mol%.

When the ratio of the aliphatic dicarboxylic acid A to the total acid components is less than 5 mol%, the melt viscosity of the resin does not decrease,
It becomes inferior in smoothness when made into a coating film, and this ratio is
If it exceeds 25 mol%, the glass transition temperature of the polyester resin is lowered, and the coating has poor blocking resistance. If the ratio of the aromatic glycol B to the total glycol component is less than 10 mol%, the glass transition temperature of the polyester resin is lowered, and the coating has poor blocking resistance. The melt viscosity is increased, and the coating film is not only poor in smoothness but also expensive. Further, when the ratio of the trifunctional or higher carboxylic acid C to the total acid components is less than 1 mol%, the curing reactivity at low temperature is reduced and the mechanical strength is deteriorated.
If it exceeds mol%, the speed of the curing reaction becomes too high, and the smoothness of the coating film decreases.

Further, in addition to the above-mentioned components, aromatic dicarboxylic acids such as 5-sodium sulfoisophthalic acid, phthalic anhydride, and naphthalenedicarboxylic acid may be added to the polyester resin as long as the effects of the present invention are not impaired. Acid, 4-hydroxybenzoic acid, oxycarboxylic acid such as ε-caprolactone, aliphatic glycol such as diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1 A small amount of an alicyclic glycol such as 1,4-cyclohexanediol, or a tri- or higher-valent alcohol such as trimethylolpropane, pentaerythritol, or glycerin may be copolymerized.

The polyester resin preferably has a glass transition temperature in the range of 45 to 75 ° C. If the glass transition temperature is lower than 45 ° C., the powdered resin tends to aggregate and form a lump, and the blocking resistance decreases. On the other hand, if the glass transition temperature exceeds 75 ° C., it is necessary to increase the kneading temperature, and the curing reaction proceeds during the formation of the coating, and as a result, the smoothness of the coating film decreases.

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

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

In the polyester resin composition of the present invention, it is necessary to mix an epoxy resin-based curing agent and an imidazole-based curing accelerator with the above-mentioned polyester resin.

As the epoxy resin-based curing agent, an epi-bis type epoxy resin derived from bisphenol A and epichlorohydrin is preferable. Specifically, “Epototo YD-014” manufactured by Toto Kasei Co., Ltd. Epicoat
1003 ”and“ Araldite AER 600 ”manufactured by Ciba Geigy.
3 ".

The amount of the epoxy resin-based curing agent is suitably 0.8 to 1.2 times, preferably 1.0 times the equivalent of the acid value of the polyester resin.

Examples of the imidazole curing accelerator include 2-
Undecyl imidazole, 2 is preferable, heptadecylimidazole, specifically, and the like manufactured by Shikoku Chemicals Corporation of "Curezol C ₁₁ Z""Curezol C ₁₇ Z".

It is necessary that the amount of the imidazole-based curing accelerator is 0.4 to 1.0 part by weight based on 100 parts by weight of the total of the polyester resin and the epoxy resin-based curing agent. And both low-temperature curability and smoothness can be achieved.

The resin composition of the present invention must be prepared so that the gelation time at 150 ° C. is in the range of 8 to 13 minutes, preferably 9 to 12 minutes. If the gelation time of the resin composition is less than 8 minutes, the curing reaction becomes too fast, so that the smoothness of the coating film is significantly deteriorated. If the gelation time exceeds 13 minutes, the curing reactivity decreases, so And the mechanical strength of the coating decreases.

The powder coating composition of the present invention is prepared by adding a mixture of a leveling agent and other additives, for example, pigments such as titanium dioxide and carbon black, to the above-mentioned polyester resin composition, if necessary, using a kneader or a roll. And melt-kneading at 70 to 120 ° C.

The obtained powder coating is applied to an object to be coated and baked at a relatively low temperature of 140 to 160 ° C. for 15 to 25 minutes to obtain a coating having excellent smoothness and gloss. Give the membrane.

[0035]

The reason that the polyester resin of the present invention can be baked at a low temperature, and the blocking resistance and the smoothness of the coating film when coated are improved is because aliphatic dicarboxylic acid having a flexible molecular chain. By using an acid as a copolymer component,
By lowering the melt viscosity of the resin and simultaneously lowering the glass transition temperature of the resin, the aromatic glycol is used as a copolymer component to control the copolymerization amount of trifunctional or higher carboxylic acid. It is presumed that it was expressed by performing

[0036]

Next, the present invention will be described specifically with reference to examples and comparative examples. In the examples and comparative examples, the characteristic values of the polyester resin and the resin composition, and the evaluation of the powder coating and the coating film performance were measured by the following methods. (a) Proportion of Copolymerization Component The polyester resin was dissolved in deuterated trifluoroacetic acid and determined by ¹ H-NMR (JNM-LA400, manufactured by JEOL Ltd.). (b) Intrinsic viscosity Measured at 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (c) Acid value 0.5 g of polyester resin was added to dioxane / distilled water = 10/1.
(Weight ratio) in 50 ml of mixed solvent
It was determined by titration with a specified potassium hydroxide methanol solution. (d) Melt viscosity The melt viscosity was measured with a Brookfield melt viscometer (VISCO METER DV-1 manufactured by Brookfield) at a sample weight of 15 g and a temperature of 150 ° C. (e) Glass transition temperature Differential scanning calorimeter (DSC-220 manufactured by Seiko Instruments Inc.)
Using a mold) at a heating rate of 10 ° C./min. (f) Gelation time Total 100 of polyester resin and epoxy resin-based curing agent
A mixture of a given part by weight of an imidazole-based curing accelerator and 50 parts by weight of a titanium dioxide pigment is mixed with a 100 parts by weight sample at a temperature of 150 ° C., using a Brabender Plasticorder (Brabender, PLV). -340) was used to determine the curing curve, and the time from the start of the measurement until the torque value reached 250 mg · g was defined as the gel time. (g) Blocking resistance In a bottomed glass tube with a diameter of 3 cm and a height of 7 cm, put the powder coating material to a height of 4 cm, leave it in a constant temperature bath at 40 ° C for one week, and turn the glass tube upside down to powder. The paint was taken out and evaluated in the following two stages according to the condition of the paint. ：: There is no lump in the paint, or the lump is too small to be lifted by hand. ×: There is a large lump solidified by aggregation of the paint, and the lump can be lifted. (h) Smoothness The smoothness of the coating film was visually evaluated in the following two stages. ：: The coating film has little unevenness and good smoothness. X: The coating film has large unevenness and poor smoothness. (i) Specular glossiness at 60 degrees Calculated according to JIS K 5400. (j) Impact resistance According to JIS K 5400, a coated steel plate is sandwiched between a shooting platform having a spherical surface with a diameter of 1.27 cm and a receiving platform with a depression matching it so that the coating film contacts the spherical surface. Was dropped vertically to determine the breaking height of the coating film.
(If this value is 20cm or more, it passes.)

Examples 1, 2, 5 to 7 and Comparative Examples 1 to 3,
5, 6 The raw material compounds shown in Tables 1 and 2 were charged into the esterification reaction tank in the amounts (mol parts) shown in Tables 1 and 2, and the pressure was increased.
The esterification reaction was performed at 0.3 MPaG and a temperature of 260 ° C. for 3.5 hours. After transferring the obtained esterified product to a polycondensation reaction tank, 2.5 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of an acid component was added, the pressure was reduced to 0.5 hPa, and the polycondensation reaction was performed at 280 ° C. for 3 hours. Polyester was obtained. Next, the depolymerizing agents shown in Tables 1 and 2 were added to the polyester in the amounts (mol parts) shown in Tables 1 and 2 and depolymerized at 250 ° C. for 2 hours under normal pressure. 1 and polyester resins having the characteristic values shown in Table 2 were obtained. An epi-bis epoxy resin curing agent having an epoxy equivalent of 760 g / eq (“Araldite AER 6003” manufactured by Ciba-Geigy, an imidazole-based curing accelerator [Curesol C manufactured by Shikoku Chemicals Co., Ltd.) is added to the obtained polyester resin.
₁₁ Z "(2-undecylimidazole)], a butyl polyacrylate-based leveling agent (" Acronal 4F "manufactured by BSF Inc.), a benzoin and rutile type titanium dioxide pigment (" Taipe "CR" manufactured by Ishihara Sangyo Co., Ltd.) −9
0 ") was added in the amounts (parts by weight) shown in Tables 1 and 2, and dry-blended with a Henschel mixer (Mitsui Miike Seisakusho, Model FM 10B), followed by Ko Kneader (Buss, PR-46).
Melt and knead at 100 ° C using a
The powder was classified using a mesh (106 μm) wire mesh to obtain a powder coating. The obtained powder coating was electrostatically coated on a zinc phosphate-treated steel sheet so as to have a thickness of 50 to 60 μm, and baked at 150 ° C. for 20 minutes. The results of evaluating the performance of the coating film are shown in Tables 1 and 2.

Example 3 and Comparative Example 4 The paint was baked under the conditions shown in Table 1 at 140 ° C. for 20 minutes.

Example 4 An epi-bis type epoxy resin having an epoxy equivalent of 950
The procedure was performed in the same manner as in Example 1, except that g / eq “Epototo YD-014” manufactured by Toto Kasei Co., Ltd. was used.

Comparative Example 7 A phosphorus-based curing accelerator ("Triphenylphosphine PP-360" manufactured by Ihara Chemical Industry Co., Ltd.) was used as a curing accelerator, and the procedure was the same as in Example 1 except that benzoin was not used. went.

The results of Examples 1 to 7 and Comparative Examples 1 to 7 are summarized in Tables 1 and 2.

[0042]

[Table 1]

[0043]

[Table 2]

Each of the powder coatings obtained in Examples 1 to 7 gave a good coating film having satisfactory strength and smoothness, and also had good blocking resistance.

On the other hand, the comparative example has the following problem. In Comparative Example 1, since the copolymerization amount of the aliphatic dicarboxylic acid was small, the melt viscosity of the polyester resin was high, and the smoothness of the coating film was insufficient. In Comparative Example 2, since the copolymerization amount of the aliphatic dicarboxylic acid was large, the glass transition temperature of the polyester resin was too low, and the coating had poor blocking resistance. In Comparative Example 3, since the copolymerization amount of the aromatic glycol was small, the glass transition temperature of the polyester resin was low, the blocking resistance of the paint was poor, and the gelation time of the resin composition was small because the amount of the curing accelerator was small. And the strength of the coating film was insufficient. In Comparative Example 4, since the copolymerization amount of the aromatic glycol was large, the melt viscosity of the polyester resin was high, and
Since the amount of the curing accelerator was large, the gelation time of the resin composition was short, and the smoothness of the coating film was insufficient. Comparative Example 5
In this case, the copolymerization amount of the carboxylic acid having three or more functional groups was large and the intrinsic viscosity of the polyester resin was low, so that the mechanical strength of the coating film was insufficient. In Comparative Example 6, since the copolymerization amount of the trifunctional or higher carboxylic acid was small, the acid value of the polyester resin was too small, so that the gelation time of the resin composition was prolonged and the strength of the coating film was insufficient. Was. In Comparative Example 7, since the type of the curing accelerator was inappropriate, the gelation time of the resin composition was shortened, and the smoothness of the coating film was insufficient.

[0046]

According to the present invention, a powder coating which can be baked at a low temperature, has excellent curability and storage stability, and can form a coating film having sufficient smoothness and mechanical strength. The present invention provides a polyester resin and composition for use, and a powder coating using the same.

Claims (3)

[Claims] An acid component mainly composed of an aromatic dicarboxylic acid and a glycol component mainly composed of an aliphatic glycol having an intrinsic viscosity of 0.10 to 0.30 dl / g and an acid value of 30 to 85 mgKOH /
g, a polyester resin having a melt viscosity at 150 ° C. of 100 to 800 dPa · s, wherein the polyester resin contains an aliphatic dicarboxylic acid A, an aromatic glycol B, and a tri- or more functional carboxylic acid C as a copolymer component. , A has a ratio of 5 to 25 mol% to the total acid component, B has a ratio of 10 to 45 mol% to the total glycol component, and C has a ratio of 1 to 10 mol% to the total acid component. Polyester resin for body paint. 2. A resin composition comprising 0.4 to 1.0 parts by weight of an imidazole-based curing accelerator, based on 100 parts by weight of the polyester resin for powder coating and the epoxy resin-based curing agent according to claim 1 in total. A polyester resin composition for powder coatings, wherein the gel time of the resin composition at 150 ° C. is 8 to 13 minutes. 3. A powder coating using the polyester resin composition for powder coating according to claim 2.