JP3227001B2 - Powder coatings and polyester resins for powder coatings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powder coating and a polyester resin for powder coating. More specifically, the present invention relates to a powder paint capable of forming a coating film having excellent weather resistance and corrosion resistance that can withstand long-term outdoor use, and a polyester resin for powder paint.

[0002]

2. Description of the Related Art Thermosetting powder coatings are roughly classified into epoxy, acrylic and polyester.
Each has its strengths and weaknesses, but they are used differently depending on the purpose. In recent years, polyester-based resins have been receiving attention because of their well-balanced coating film performance and advantageous paint prices.

[0003] In particular, blocked isocyanate-cured polyester powder coatings have the advantage of being excellent in stain resistance, good in weather resistance, and capable of forming a well-balanced coating film with excellent flexibility. It has come to be used in large quantities in box products for PCM (a forming method in which a cut plate is coated and then bent).

[0004] On the other hand, in applications used outdoors,
Although a polyester resin composition and other devises are used to give a certain degree of weather resistance,
The weather resistance is still insufficient, and significant improvements are strongly desired. On the other hand, it is common practice to incorporate a small amount of epi, bis-type epoxy resin in order to maintain corrosion resistance, which further impairs weather resistance, so that it can withstand long-term outdoor use. Blocked isocyanate-curable polyester powder coatings capable of forming highly weather-resistant coating films and polyester resins for powder coatings that can be used therefor have not yet been realized.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a blocked isocyanate-curable polyester powder coating which has a high degree of weather resistance as described above, and which is sufficient without incorporating an epoxy resin. An object of the present invention is to provide a powder coating capable of forming a coating film capable of maintaining corrosion resistance, and a polyester resin for powder coating.

[0006]

The configuration of the present invention will be described in detail below. About the polyester resin component of the component (A) The polyester resin as the above-mentioned essential component is obtained by gel permeation chromatography (hereinafter abbreviated as GPC).
The number average molecular weight measured by 2000-7000,
Preferably 2500 to 6500, pyridine as a solvent,
The hydroxyl value measured by a method of acetylation while refluxing at the boiling point is 20 to 70 mg KOH / g, preferably 25 to 65 mg KOH / g, and the ring and ball method (JIS
K2207) is from 105 to 140.
C., preferably 110-135.degree. C., having a glass transition point of 40-75.degree. C., preferably 45-70.degree. C. as measured by differential scanning calorimetry (hereinafter abbreviated as DSC), and isophthalic acid in all monomer units. Acid unit is 18 to 52
Mol%, and 1,3 propanediol unit is 10 to 4
A branching agent having 0 mol% and having 3 or 4 functional groups has a monomer unit content of 0.5 to 8 mol%.

When the number average molecular weight is lower than 2,000, the mechanical properties of the coating become insufficient, and when it exceeds 7000, the smoothness of the coating becomes poor.

If the hydroxyl value is lower than 20 mg KOH / g, it is difficult to obtain sufficient mechanical properties of the coating film.
If the amount exceeds the range of 0 mg KOH / g, adding a corresponding amount of the blocked isocyanate curing agent will increase the cost significantly, and it cannot be expected that the coating performance will be correspondingly improved and the coating film will be improved. Has a high hardness and is inferior in flexibility. Further, if the amount of the blocked isocyanate curing agent is less than the amount corresponding to the hydroxyl value, it becomes difficult to obtain sufficient mechanical properties of the coating film.

As for the softening point and the glass transition point, when the softening point is lower than 105 ° C. and the glass transition point is lower than 40 ° C., the powder coating material has disadvantages such as easy blocking during storage. With a softening point of 14
When the temperature is higher than 0 ° C. and the glass transition point is higher than 75 ° C., the finished appearance of the coating film, particularly the smoothness, is extremely poor.

The proportion of isophthalic acid units in the total monomer units is preferably at least 18 mol%, more preferably at least 20 mol%, and if it is less than this, no sufficient effect can be expected. Regarding the upper limit of the content of the isophthalic acid unit, the entire amount of the acid component used for preparing the resin may be isophthalic acid. In this case, an alcohol component is used as the branching agent, but the upper limit of the isophthalic acid unit content varies depending on the number of functional groups and the amount used, but it cannot be specified unconditionally. It becomes 52 mol%.

Japanese Patent Application Laid-Open No. 2-284974 discloses a polyester resin mainly containing isophthalic acid for powder coatings. In this case, the polyester resin is mainly composed of a carboxylic acid terminal which is cured with an epoxy compound. , Different from the Polister resin of the present invention.

If the proportion of 1,3 propanediol units in the total monomer units is less than 10 mol%, the mechanical properties of the coating film are inferior, and if it exceeds 40 mol%, the softening point and the glass transition point are low. Thus, the powder coating prepared from this causes blocking during storage and becomes unusable.

When the content of the branching agent is more than 8 mol% in the total monomer units, an inappropriate resin partially gelled depending on the kind of the branching agent, and the hydroxyl value of the obtained resin is reduced. When the amount exceeds 70 mg KOH / g, the resulting coating film has high hardness and poor flexibility.

The method for synthesizing the polyester resin is not particularly limited, and a well-known and commonly used method can be applied. An aromatic dibasic acid or a derivative thereof is mainly used as the acid component, and an aliphatic glycol is mainly used as the alcohol component.

As the dibasic acid components other than isophthalic acid, terephthalic acid, phthalic anhydride, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid,
Examples thereof include cyclohexanedicarboxylic acid, fumaric acid, maleic anhydride, and tetrahydrophthalic anhydride.

Compounds suitable for glycol components other than 1,3 propanediol include ethylene glycol, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, and 1,6 hexanediol. , Etc. can be exemplified.

Examples of the tri- or tetrafunctional component serving as a branching agent include trimellitic anhydride, pyromellitic anhydride, trimethylolpropane, trimethylolethane, glycerin, and pentaerythritol.

Further, the method for producing a polyester resin may be either a transesterification method or a direct esterification method, and the reaction can be promoted by pressurizing or depressurizing operation or an inert gas.

Regarding the blocked isocyanate compound of the component (B) The blocked isocyanate compound as the essential component is an aromatic, aliphatic or alicyclic polymer such as tolylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate or dimethylcyclohexane diisocyanate. A typical example is a compound in which the isocyanate group at the molecular end of the isocyanate compound or its prepolymer is blocked by a known and commonly used blocking agent such as a lactam compound or an oxime compound.

The mixing ratio of the above two components is preferably such that the ratio of the isocyanate equivalent of the blocked isocyanate to the hydroxyl equivalent of the polyester resin is in the range of 0.8 to 1.2.

The powder coating composition of the present invention usually contains a pigment or other filler, a flow control agent such as an acrylate polymer,
A curing catalyst such as an organotin compound, a pinhole inhibitor such as benzoin, and the like are compounded, kneaded using a known and customary melt kneading apparatus, and then pulverized and classified to obtain a powder coating.

The powder coating thus obtained is applied and baked on the object by a known electrostatic coating method or a fluid immersion coating method.

[0023]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, in which the following parts are by weight.

Example 1 Preparation of polyester resin 1,3 propanediol (hereinafter abbreviated as 1,3PD) 26
7 parts, neopentyl glycol (hereinafter abbreviated as NPG) 7
54 parts and 86 parts of glycerin (hereinafter abbreviated as GL) were charged into a stainless steel reactor having a stirrer, a heating device, a thermometer, a fractionating device, and an inert gas inlet, and the temperature was raised to 160 ° C. while stirring. And the contents were melted. Then
913 parts of isophthalic acid (hereinafter abbreviated as IPA) and di-n
-Butyltin oxide (hereinafter abbreviated as DTO) is charged with 1 part, and the condensed water generated is gradually removed from the system by a nitrogen gas stream so that the temperature at the top of the fractionating apparatus does not exceed 100 ° C, and gradually to 230 ° C. The temperature was raised to carry out an esterification reaction. After the amount of condensed water produced reaches 90% or more of the theoretical amount and is once cooled to 180 ° C., isophthalic acid 913 is added.
The temperature was raised to 230 ° C. over 3 hours while the condensed water generated by the nitrogen gas stream was similarly removed from the system, and the reaction was continued at that temperature. A sample of the reaction product was appropriately collected during the reaction, and the acid value and the softening point were measured. The end point of the reaction was determined so that these values were within a predetermined range. In this case, a reaction time of 6 hours is required from 230 ° C., and a polyester resin having a number average molecular weight of 4,500, an acid value of 3.5, a hydroxyl value of 34.1, a softening point of 121 ° C., and a glass transition point of 60 ° C. is obtained. Was. The obtained resin was designated as polyester resin (A-1). The ratio of each monomer unit of the obtained resin was analyzed by a method in which the product after thermal decomposition with an amine was subjected to gas chromatography, and 15 mol% of 1,3 PD units, 32 mol% of NPG units, and 4 mol% of GL units were used. , 1
The PA unit was 49 mol%.

Coating, coating and baking operations 850 parts of polyester resin (A-1), 150 parts of blocked isocyanate B-1530 manufactured by Huls, 4 parts of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd.)
00 parts, benzoin 10 parts, flow control agent Polyflow S
(Kyoeisha Yushi Kagaku Kogyo Co., Ltd.) 6 parts, curing catalyst TK-
1 (manufactured by Takeda Pharmaceutical Co., Ltd.) was dry-blended with a Henschel mixer, then melt-kneaded at 50 ° C. screw temperature and 110 ° C. barrel temperature with a Buss kneader PR-46. The mesh passed through a sieve was used as a powder coating in the following coating.

This powder coating is applied to a zinc phosphate treated steel plate (SPCC-SB, PB3118M treated, 0.8 mm thick) using an electrostatic powder coating machine so that the film thickness becomes 40 to 60 microns. And baked at 180 ° C. for 20 minutes in a hot air heating furnace to obtain a cured coating film. Various properties of the coating film thus obtained were examined, and test results as shown in Table 1 were obtained.

Example 2 In the preparation of polyester, the charged amount in the first stage was 1,3P
D669 parts, NPG1331 parts, GL81 parts, IPA1
660 parts, DTO 1 part, IPA 166 in the second stage
A polyester resin (A-2) was obtained in the same manner as in Example 1 except that the amount was changed to 0 parts. Table 1 shows the characteristic values of the resin.
Further, instead of 850 parts of the resin (A-1) of Example 1, 130 parts of 870 parts of this resin and 150 parts of Blocked Isocyanate B-1530 manufactured by Huls Co. were used. After coating and baking, the test results of the cured coating film as shown in Table 1 were obtained.

Example 3 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D643, NPG1143, GL194, IPA
1660 parts, DTO 1 part, IPA 16
A polyester resin (A-3) was obtained in the same manner as in Example 1 except that the amount was changed to 60 parts. Table 1 shows the characteristic values of the resin. Further, instead of 850 parts of the resin (A-1) of Example 1, coating was carried out in the same manner as in Example 1 except that 800 parts of this resin and 200 parts of 150 parts of blocked isocyanate B-1530 manufactured by Huls were used. After coating and baking, the test results of the cured coating film as shown in Table 1 were obtained.

Example 4 The charged amount of 1,3PD in Example 1 was 355 parts,
A polyester resin was prepared in the same manner as in Example 1 except that the charge amount of PG was changed to 631 parts. This is (A-4)
And This resin was used in place of the resin (A-1) of Example 1, and a coating, coating and baking were performed in the same manner as in Example 1. Table 1 shows the characteristic values of the obtained resin and various properties of the cured coating film.

Example 5 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D903, NPG700, GL146, IPA1
494 copies, DTO 1 copy, IPA 149 in the second stage
A polyester resin (A-5) was obtained in the same manner as in Example 1 except that the amount was changed to 4 parts. Table 1 shows the characteristic values of the resin.
Further, this resin was used in place of the resin (A-1) of Example 1, and a coating was formed, painted, and baked in the same manner as in Example 1 to obtain a cured coating film test result as shown in Table 1.

Example 6 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D534 parts, NPG1142 parts, trimellitic anhydride (hereinafter abbreviated as TMA) 138 parts, IPA1434 parts, D
The same operation as in Example 1 was carried out except that TO1 part was used and IPA was 1434 parts in the second stage, and the polyester resin (A-
6) was obtained. Table 1 shows the characteristic values of the resin. Further, instead of 850 parts of the resin (A-1) in Example 1, this resin 87 was used.
0 parts, Huls Blocked Isocyanate B-15
Except that 30 and 150 parts were changed to 130 parts, coating, coating and baking were carried out in the same manner as in Example 1 to obtain test results of the cured coating film as shown in Table 1.

Example 7 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D385, NPG788, IPA913, DTO
A polyester resin (A-7) was obtained in the same manner as in Example 1 except that 1 part was used, and in the second stage, IPA 767 parts and TMA 169 parts were used. Table 1 shows the characteristic values of the resin. Further, this resin was used in place of the resin (A-1) of Example 1, and a coating, coating and baking were carried out in the same manner as in Example 1 to obtain a coating composition as shown in Table 1.
The test results of the cured coating film as shown in Table 2 were obtained.

Example 8 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D617, NPG1420, TMA346, IP
A1315 units, DTO1 unit, IPA 1 at the second stage
A polyester resin (A-8) was obtained in the same manner as in Example 1 except that the amount was changed to 315 parts. Table 1 shows the characteristic values of the resin. Further, instead of 850 parts of the resin (A-1) of Example 1, coating was carried out in the same manner as in Example 1 except that 800 parts of this resin and 200 parts of 150 parts of blocked isocyanate B-1530 manufactured by Huls were used. After coating and baking, the test results of the cured coating film as shown in Table 1 were obtained.

Example 9 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D268, NPG757, GL86, IPA54
8 parts, 548 parts of terephthalic acid (hereinafter abbreviated as TA), DT
The same operation as in Example 1 was carried out except that O1 part was used and IPA was 730 parts in the second stage, to obtain a polyester resin (A-9). Table 1 shows the characteristic values of the resin. Further, this resin was used in place of the resin (A-1) of Example 1, and a coating was formed, painted, and baked in the same manner as in Example 1 to obtain a cured coating film test result as shown in Table 1.

Example 10 In the preparation of polyester, the charged amount in the first stage was 1,3P
D538 parts, NPG 319 parts, 1,6 hexanediol (hereinafter abbreviated as 1,6HD) 83 parts, GL87 parts, TA5
A polyester resin (A-10) was obtained in the same manner as in Example 1 except that 48 parts, 548 parts of IPA and 1 part of DTO were used, and the second stage was changed to 730 parts of IPA. Table 1 shows the characteristic values of the resin. Further, this resin was used in place of the resin (A-1) of Example 1, and a coating was formed, painted, and baked in the same manner as in Example 1 to obtain a cured coating film test result as shown in Table 1.

COMPARATIVE EXAMPLE 1 In the polyester preparation, the charged amount was 1st stage, 1,3P
D841 copy, 1,6HD91 copy, GL95 copy, IPA1
195 copies, DTO 1 copy, IPA 797 in the second stage
A polyester resin (A-11) was obtained in the same manner as in Example 1 except that the above parts were used. Table 1 shows the characteristic values of the resin.
Further, using this resin, a paint was formed and painted in the same manner as in Example 1,
After baking, the test results of the cured coating film as shown in Table 1 were obtained.

Comparative Example 2 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D54, NPG1050, GL86, TA548
Unit, IPA 548 unit, DTO 1 unit, and IP in the second stage
A polyester resin (A-12) was obtained in the same manner as in Example 1 except that A was changed to 730 parts. Table 1 shows the characteristic values of the resin.
It was shown to. Using this resin, a coating was formed, painted, and baked in the same manner as in Example 1, and the test results of the cured coating film shown in Table 1 were obtained.

Comparative Example 3 In the preparation of polyester, the charged amount was 1st stage, 1,3P
D268 parts, NPG757 parts, GL86 parts, TA548
Unit, IPA 548 unit, DTO 1 unit, and the second stage is TA
730 parts, and the same procedure as in Example 1 was carried out except that the reaction temperature in the second step was 240 ° C., to obtain a polyester resin (A-13). Table 1 shows the characteristic values of the resin. Using this resin, a coating was formed, painted, and baked in the same manner as in Example 1, and the test results of the cured coating film shown in Table 1 were obtained.

Comparative Example 4 In the polyester preparation, the charged amount was 1st stage, NPG1
019 parts, 1,6 HD 78 parts, GL 51 parts, TA498
Section, IPA section 498, DTO section 1 and TA in the second stage.
Was changed to 664 parts and the reaction temperature in the second step was changed to 240 ° C., and the same operation as in Example 1 was carried out to obtain a polyester resin (A-14). Table 1 shows the characteristic values of the resin. Using this resin, a coating was formed, painted, and baked in the same manner as in Example 1, and the test results of the cured coating film shown in Table 1 were obtained.

[Table 1]

As shown in the examples in Table 1, the cured coating films obtained from the powder coatings obtained from the polyester resin for powder coatings of the present invention are all excellent in both weather resistance and corrosion resistance. It turns out that it has sufficient practicality in terms of mechanical properties and blocking resistance of the powder coating. On the other hand, in the case of the comparative example, one of the weather resistance, the corrosion resistance, the mechanical properties, and the blocking resistance of the powder coating was inferior, and it can be seen that the performances of all four cannot be satisfied.

[0041]

The powder coating using the polyester resin for powder coating of the present invention has good blocking resistance, excellent weather resistance and corrosion resistance, and is well-balanced in mechanical properties and other various properties. A membrane can be provided.

The polyester resin for powder coatings of the present invention has good blocking resistance, excellent weather resistance and corrosion resistance, and can provide an excellent coating film which is well balanced in mechanical properties and other various properties. Can be used as body paint.

Claims (2)

(57) [Claims] (A) a number average molecular weight of 2,000 to 700
0, a hydroxyl value of 20 to 70 mg KOH / g, a glass transition point of 40 to 75 ° C., a softening point of 105 to 140 ° C., and a dicarboxylic acid unit, a glycol unit, and a monomer unit as a branching agent having 3 or 4 functional groups. Is mainly
A ester resin, wherein the dicarboxylic acid unit comprises
The ratio of sophthalic acid units is 70 to 100% by mass;
34 to 52 mol% of isophthalic acid unit and glycol unit
15 to 40 mol position as 1,3 propanediol
%, And a polyester resin containing 0.5 to 8 mol% of a monomer unit as a branching agent having a functional group number of 3 or 4, (B) a powdered coating material containing a blocked isocyanate compound and a conventional additive . 2. Water having a number average molecular weight of 2,000 to 7000, water
An acid value of 20 to 70 mgKOH / g and a glass transition point of 4
0-75 ° C, softening point is 105-140 ° C,
Bonic acid unit, glycol unit and 3 or 4 functional groups
Mainly based on the number of monomer units as branching agentsPolyester
A resin, wherein the isophthalic acid in the dicarboxylic acid unit is
The unit ratio is 70 to 100% by mass, and
34-52 mol% of lactic acid units, as glycol units
1,3 propanediol units15-40 mol%, and
AndA monomer unit as a branching agent having 3 or 4 functional groups is added in an amount of 0.
Polyester tree for powder coating containing 5 to 8 mol%
Fat.