JPS5829819B2 - Polyester materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel polyester resin composition having particularly favorable properties as a paste resin for powder coatings.

Compared to conventional solvent-based paints, powder coatings have the following advantages: - It is easier to prevent pollution, ■ It is possible to apply thick coats with a thickness of 100μ or more, and the paint can be collected and reused. It has many advantages and has shown remarkable growth in recent years.

Generally, in order to use a resin as a paste resin for a powder coating, it is desirable that the following requirements be satisfied.

(1) Can be ground into micro powder at room temperature.

(2) The pulverized powder does not flora during transportation or storage.

(3) Pigmentation is easy at relatively low temperatures.

(4) Scales that form a strong and beautiful paint film by baking the paint.

(5) The coating film has excellent various properties such as weather resistance, heat resistance, and corrosion resistance.

Until now, a large number of materials have been provided as a pace range for powder coatings, but there is still no ideal material that can satisfy all of the requirements.

In addition, coating agents and paints made of polyester copolymerized with cyclohexanedimethanol as an alcohol component and hexaalkoxymethylmelamine were developed in
Although it is known from Japanese Patent Publication No. 9-20611 and Japanese Patent Publication No. 49-20735, these inventions relate to solvent-based paints and do not relate to powder paints.

In order to develop an ideal material as a pace resin for powder coatings, the present inventors aimed to ideally improve the crushability, blocking resistance, workability of coating, coating film performance, etc. of polyester resin compositions. In order to achieve a balance, the composition of the polyester resin, average degree of polymerization, secondary rearrangement point, acid value, and the number of equivalents of hydroxyl groups possessed by the polyester resin and the number of equivalents of alkoxy groups possessed by hexaalkoxymethylmelamine or its condensate used as a curing agent. The present invention was arrived at as a result of intensive research into the ratio.

That is, the present invention uses aromatic dicarboxylic acid or/and aromatic oxyacid as the main acid component, 98 to 50 mol% of ethylene glycol, and 2 to 30 mol% of cyclohexanedimethanol as the main alcohol component, in an amount that does not cause gelation. A polyester resin having an average degree of polymerization of 11 to 50, a secondary rearrangement point of 40 to 70°C, and an acid value of 4 to 12 is copolymerized with trivalent or higher polyhydric carboxylic acid or/and polyhydric alcohol, and has the following structural formula. The amount of hexaalkoxymethylmelamine or its condensate shown below that satisfies the formula 0.5≦-≦20 (M is the number of equivalents of the alkoxy group possessed by the hexaalkoxymethylmelamine, H is the number of equivalents of the hydroxyl group possessed by the polyester resin) This is a polyester resin composition for powder coating obtained by mixing.

(In the formula, R is an alkyl group having 6 or less carbon atoms, such as a methyl group or an ethyl group.) The polyester resin composition of the present invention is prepared, for example, by the following method.

That is, an esterification reaction or transesterification reaction is carried out between aromatic dicarboxylic acids and/or aromatic oxyacids or their alkyl esters as raw materials, and ethylene glycol and cyclohexane dimetatool in the presence of a catalyst if necessary. followed by a polycondensation reaction under reduced pressure to obtain the intrinsic viscosity (measured at 20°C in a mixed solvent of phenol/tetrachloroethane-1/1 (weight ratio)).
A polyester with a high degree of polymerization of 0.4 or more, preferably 0.6 or more is prepared, and the high degree of polymerization polyester is mixed with a substantially non-volatile polyhydric alcohol or/and a small amount of alcohol in one molecule. A depolymerization reaction is carried out using an ester having a functional hydroxyl group to prepare a polyester resin having an arbitrarily controlled average degree of polymerization within the range of 11 to 50.

Then, after controlling the acid value of the obtained polyester resin to an arbitrary value within the range of 4 to 12, hexaalkoxymethylmelamine is added to the mixture, if necessary, a pigment and further a regulator, preferably at 150°C or lower. A polyester resin composition is prepared by melt-mixing at a temperature of 120° C. or lower.

However, the polyester resin composition of the present invention is not limited to the polyester resin composition prepared by the above method.

The aromatic dicarboxylic acid component and aromatic oxyacid component constituting the polyester resin included in the present invention include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, P-oxybenzoic acid, P-oxyethoxybenzoic acid, Lower alkyl esters thereof are used.

In addition, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can also be used in an amount of 10 mol % or less of the total acid component.

As the alcohol component, neopentyl glycol propanediol, butanediol, hexanediol, etc. can be used in an amount of 50 mol% or less, mainly consisting of ethylene glycol and cyclohexane dimetatool.

Examples of trivalent or higher polyhydric carboxylic acids or polyhydric alcohol components include trimellitic acid, pyromellitic acid, their anhydrides, trimethylolethane, trimethylolpropane, pentaerythritol, glycerin, etc. Depending on the number of functional groups in the alcohol and the average degree of polymerization of the polyester resin, it is used in an amount that does not cause gelling.

Substantially non-volatile alcohols or esters used in depolymerization reactions to control the average degree of polymerization include:
Bis-β-hydroxyethyl terephthalate obtained by reacting the above-mentioned polyhydric alcohol, the above-mentioned aromatic dicarboxylic acid, aromatic oxyacid or polyhydric carboxylic acid, or a lower alkyl ester thereof with the above-mentioned dihydric alcohol; Bis-β-hydroxyethyl isophthalate, bis-β-hydroxyethyl phthalate, P-oxyethoxy (β-hydroxyethyl) benzoate, tris-
Examples include β-hydroxyethyl trimellitate, tetra-β-hydroxyethylpyromellitate, and copolymerized low polymers thereof, which can be used alone or in combination of two or more.

The acid value of polyester resin is controlled by mixing or reacting dicarboxylic acids, polycarboxylic acids with 3 or more valences, or their anhydrides, but it is important to have carboxyl groups uniformly present on a microscopic scale to obtain a beautiful coating film. desirable for formation.

The mixture of hexaalkoxymethylmelamine is ★★15
0'C: Below, it is particularly preferable to carry out the reaction at 120°C or lower u-9 Next, the present invention will be specifically explained with reference to Examples and Reference Examples.

Example 1 Dimethyl terephthalate (hereinafter abbreviated as DMT) was prepared in the amounts shown in Table 1.

) dimethyl isophthalate (hereinafter abbreviated as DMI).

), methyl P-oxyethoxybenzoate (hereinafter OEBM
It is abbreviated as

), ethylene glycol (hereinafter referred to as EG).

), cyclohexane dimetatool (hereinafter abbreviated as CHDM).

), neopentyl glycol (hereinafter abbreviated as NPC).

) was placed in a stainless steel reaction vessel, and zinc acetate was added as a catalyst.
, oi moles were added, and a transesterification reaction was carried out at 150°C to 250°C under normal pressure to remove the theoretical amount of methanol from the reaction system, followed by 0.02 mol of trimethyl phosphate and 0.02 mol of antimony trioxide. under reduced pressure.
A polycondensation reaction was carried out at 270° C. to prepare a highly polymerized polyester, followed by trimethylolpropane (hereinafter abbreviated as TP) in the amount shown in Table 1.

) or/and pentaerythritol (hereinafter abbreviated as PE).

) was added to conduct a depolymerization reaction at 270°C. Subsequently, to each polyester resin shown in Table 2, trimellitic anhydride was added and allowed to react in a closed system at 200°C for 60 minutes to form A1-
The polyester resin of No. 6 has an acid value of 6.0 (carboxyl group equivalent: 107.0 geq/l), and the polyester resin of No. 7.8 has an acid value of 5.5 (carboxyl group equivalent: 98.1).
geq/l).

Table 3 shows the average degree of polymerization, secondary transition point, hydroxyl group equivalent, and alcohol component of the polyester resin whose acid value was adjusted in this way.

Then, using three rolls, the mixture was kneaded at 100° C. for 5 minutes to prepare a polyester resin having the composition shown in Table 4.

The obtained polyester resin composition was pulverized using a Micron Victory Mill VP-1 type pulverizer, and then 100×20
A beautiful coating film was obtained by electrostatically coating a 0X0.8 (unit: %) steel plate to a film thickness of 80μ and baking it at 190°C for 30 minutes.The coating film performance was evaluated using the method shown below. The results shown in Table 5 were obtained.

(1) Eriksen test: Based on JIS Z 2247.

★★(2) Impact resistance test: DuPont type %'-500S'.

(3) Boiling water resistance test: Erichsen test 2 hours after flood treatment (4) Acetone resistance test: JIS K 6911
In accordance with

(5) 60 degree specular reflectance: Based on JIS Z 8741.

(6) Weather resistance test: Sunshine Weather Off-Ter 5
Gloss retention after 00 hours exposure.

Table 6 shows the measurement of the secondary rearrangement point of each polyester resin composition.
The results shown are obtained.

Furthermore, none of the polyester resin compositions caused freonking even when left at 40° C. for one week.

Example 2 A polyester resin having the same composition as Tsuta 1 of Example 1 was prepared, and the acid value was adjusted to 8.0 (carboxyl group equivalent: 1.42.6 geq/t) in the same manner as in Example 1, and then the following was performed. A polyester resin composition was prepared by kneading the following mixture using a three-roll machine (-100°C for 5 minutes).

In addition, the polyester resin whose acid value was adjusted to 80 has an average degree of polymerization of 25 and a secondary transition point of 55°C1 hydroxyl group equivalent of 581.0.
geq/t, EG amount 62 mol%, CHDM amount 4
It was mol%.

Polyester resin 100 parts Rutile titanium oxide 5 Q // Hexabutoxymethylmelamine 7 Leveling agent
111 The obtained polyester resin was crushed and electrostatically coated in the same manner as in Example 1, and then baked at 170°C for 30 minutes to perform the Erichsen test>
9%, impact resistance of 40%, boiling water resistance of 9%, good acetone resistance, 60% specular reflectance of 93%, and weather resistance of 90%.

The secondary rearrangement point of the polyester resin composition is 43°C and 40°C.
No blocking occurred even after being left at ℃ for one week.

Reference Example 1 To synthesize polyester A described in Japanese Patent Publication No. 4-9-20611, page 7, 0.4 mol of phthalic anhydride, 0.3 mol of adipic acid, and 0.0 mol of cyclohexane dimetatool were used.
7 mol of ethylene glycol and 0.1 mol of ethylene glycol were placed in a glass Mitsuro flask, and an esterification reaction was carried out at 180°C to synthesize a resin having an average molecular weight of 2200 (average degree of polymerization -8.06).

The polyester resin exhibited remarkable L-blocking properties at room temperature below the glass transition point of 40° C., and could not be used to form a powder coating.

Reference Example 2 A polyester resin having an average degree of polymerization of 5 was prepared in the same manner as AI in Example 1, except that 20 mol of TP was added in place of 3.8 mol of TP and 0.2 mol of PE, and a depolymerization reaction was carried out.

The polyester resin has a secondary dislocation point of 32°C and a softening point of 70°C.
℃, and a polyester resin composition prepared by blending 100 parts of polyester resin, 50 parts of rutile titanium oxide, 20 parts of HMM, and 2 parts of a leveling agent could not be pulverized by the same method as in Example 1.

Reference Example 3 A polyester resin having an average degree of polymerization of 67 was prepared in the same manner as AI in Example 1, except that 5 mol of TPl was added in place of 3.8 mol of TP and 0.2 mol of PE.

The polyester resin is tough and could be pulverized by the same method as in the examples, and it was difficult to make it into a paint.

Reference Example 4 In the same manner as Tsuta 1 of Example 1, a polyester resin was prepared, and then 5 parts of HMMl (M/H=0.
4o) or HMM 15 parts (M/)l=3.9
Polyester resin compositions were prepared using each of 8).

The obtained polyester resin composition was painted and baked in the same manner as in Example 1, and an Erichsen test was performed.
When 15 parts of MM was used, it was 0.8%, and when 15 parts was used, it was i, o%, and a tough coating film was not obtained.

Reference Example 5 In the same manner as in Example 1, polyester resins without acid value adjustment (acid value 36) and polyester resins adjusted to acid value 20 were made into paints, pulverized, painted and baked.

The coating film using a polyester resin with an acid value of 36 has an Efsentest value of 2.0%, indicating insufficient curing during baking, while the coating film using a polyester resin with an acid value of 2o It lacked beauty due to its pronounced "boiling".

Reference Example 6 A polyester resin was prepared in the same manner as in Example 10 Tsuta 2, except that EG and NPC were not used and 200 moles of CHDM were used.

The polyester resin has a secondary rearrangement point of 85°C and a softening point of 28°C.
The temperature was 0°C, and it was L. which could not be turned into a powder coating.

As is clear from a comparison between Examples and Reference Examples, the polyester resin composition according to the present invention is an extremely excellent material for powder coatings.

That is, the secondary rearrangement point of the polyester resin of the present invention is 40
By maintaining the temperature between .degree. C. and 70.degree. C., it is possible to maintain desirable crushability and anti-blocking properties, which are the minimum characteristics required for a powder coating, and it is also possible to form a coating at a low temperature of 150.degree. C. or lower.

In addition, if the average degree of polymerization of the polyester resin is 10 or less, the crushability and blocking resistance will be poor regardless of the composition, and if the average degree of polymerization is 50 or more, the melt viscosity will be high when used as a paint. This not only makes it difficult to form into a paint at low temperatures where gelation is less likely to occur, but also makes it difficult to pulverize it by ordinary mechanical grinding due to its toughness.

On the other hand, if the amount of curing agent is outside the range of 0.5≦-≦2.0, curing during baking will be insufficient, making polyester the ideal material for powder coatings that can provide a tough coating film. It cannot be a resin composition.

The acid value of polyester resin is derived from the carboxyl group that acts as a catalyst for the crosslinking reaction between the hydroxyl group in the polyester resin and hexaalkoxymethylmelamine, and if the acid value is low, the speed of the crosslinking reaction will be lower. On the other hand, if the acid value is high, the rate of crosslinking reaction is too fast, making it impossible to obtain a smooth coating film.

Therefore, in the polyester resin composition of the present invention, it is necessary to control the acid value of the polyester resin within the range of 4 to 12.

Claims (1)

[Scope of Claims] 1 Main acid component is aromatic dicarboxylic acid or/and aromatic oxyacid, 98 to 50 mol% of ethylene glycol and 2 to 30 mol% of cyclohexane dimetatool
as the main alcohol component, and an amount of 3 that does not cause gelation.
Average degree of polymerization of copolymerized polyhydric carboxylic acid or/and polyhydric alcohol of 11 to 50. Secondary dislocation point 40~
0.5≦-≦20 (M is the number of equivalents of alkoxy groups in hexaalkoxymethylmelamine , H is the equivalent number of hydroxyl groups possessed by the polyester resin). (In the formula, R is an alkyl group having 6 or less carbon atoms, such as a methyl group or an ethyl group).