JPS585943B2 - Netsukokasei Polyester Materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermosetting polyester powder coating composition that is particularly excellent in corrosion resistance, beautiful appearance of a coating film, blocking resistance, and also has good weather resistance.

In recent years, from the perspective of reducing the release of paint solvents into the atmosphere, powder paints that do not use any solvents have been attracting attention as so-called pollution-free paints, and various synthetic polymer materials have been used as raw material resins for such powder paints. However, with the advancement of the Seiden powder coating method, which is currently generally regarded as the most economical coating method, epoxy resin powder coating has come into widespread use.

However, such epoxy resin powder coatings have extremely poor weather resistance, and the application of acrylic resins or polyester resins, which have good weather resistance, to powder coatings has been actively studied.
The acrylic resin powder coatings and polyester powder coatings that have been developed so far have achieved their intended purpose in terms of weather resistance, but they do not necessarily have the same level of corrosion resistance, beautiful appearance of the paint film, and blocking resistance. I can't say I'm satisfied.

As a result of intensive research, the present inventors found that (A) polyester resin containing 0.2 to 4.0 equivalents of hydroxyl groups per 1000 g of resin and having a glass transition point of 20°C or higher, (B) polyvalent oxazolone By discovering a thermosetting polyester powder coating composition that is characterized by containing compounds, it has not only excellent weather resistance but also corrosion resistance.
The present invention has been achieved which greatly improves the quality of conventional polyester powder coatings, with excellent coating film appearance and anti-blocking properties.

The above-mentioned polyester resin (A) is usually produced by a condensation reaction between a polybasic acid and/or an alkyl ester of a polybasic acid and a polyhydric alcohol.

Examples of the polybasic acids include terephthalic acid, isophthalic acid, phthalic anhydride, tetrahydrofucric anhydride, hexahydrophthalic anhydride, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, and maleic anhydride. , fumaric acid, itaconic acid, trimellitic anhydride, pyromellitic anhydride, etc., and examples of alkyl esters of the above-mentioned polybasic acids include dimethyl terephthalate, dinotyl isophthalate, and the like.

In addition, examples of the polyhydric alcohol include ethylene glycol, propylene glycol, butylene glycol,
Hexison glycol, neopentyl glycol, trimethylpentanediol, 1,4 dihydroxymethylcyclohexane, hydrogenated hisphenol A, bishydroxybutyl terephthalate, bishydroxyethyl isophthalate, glycerin, trinotylolethane, trimethylolpropane, penquerythritol , trishydroxyethyl cyanurate, etc., but also bisphenol type epoxy resin Epicoat 1 as a polyhydric alcohol.
An epoxy resin such as 001 (trade name manufactured by Shell Chemical Co., Ltd.) may also be used.

In addition, when producing a polyester resin using the above-mentioned polybasic acid and/or polybasic acid alkyl ester and polyhydric alcohol, monocarboxylic acids such as lauric acid, palmitic acid, stearic acid, benzoic acid, etc. Each of the above may be used in combination as a small amount of raw material.

When synthesizing the polyester resin (A) mentioned above, the temperature is usually 160 to 250°C at a ratio such that the number of equivalents of polyhydric alcohol is in excess of the equivalent of polybasic acid.
The synthesis is preferably carried out by polymerization while removing water or alcohol such as methanol produced by the condensation reaction from the reaction system by heating to The polyester resin (A) may be produced by carrying out the condensation reaction using a known catalyst for esterification or ester conversion reactions such as organometallic compounds such as butyl orthotitanate.

When the coating composition of the present invention is put to practical use as a powder coating, the polyester resin (A) mentioned above and the polyvalent oxazolone compound (B) mentioned above, which constitute the composition, are usually mixed at a concentration of 150 to 250%. In the polyester resin (A) used in the present invention, 0.2 to 4.0 equivalents per 1000 g of the resin are added as reactive groups so as to react at a baking temperature such as °C to obtain a tough reticulated coating film. Preferably 0.
Although 5 to 2.5 equivalents of hydroxyl groups are contained, if the amount of hydroxyl groups is less than 0.2 equivalents per 1000 g of resin, it is unsuitable in practical use because network formation by crosslinking reaction is insufficient and good corrosion resistance cannot be obtained. Also, the hydroxyl group is 4.0
If the amount exceeds the equivalent amount, the beautiful appearance of the coating film will be impaired and it is inappropriate.

In addition, in the present invention, it is necessary for the polyester resin (A) described above to have a glass transition point of 20° C. or higher in order to obtain a powder coating with good blocking resistance.
It is desirable that the glass transition point of the polyester resin is 40°C or higher.

In addition, the glass transition point shown in this application is a value defined by the temperature of the inflection point of measuring the temperature dependence of specific volume with a teiratometer, and obtains a polyester resin with a glass transition point of 20 ° C. or higher. In order to achieve this, it is preferable to appropriately select the types and proportions of the raw materials for the polybasic acid and polyhydric alcohol described above.

In addition, as for the average molecular weight of the polyester resin (A) mentioned above, it is desirable to adjust the number average molecular weight between 2,000 and 10,000.

Next, the above-described polyvalent oxazolone compound (B) is particularly preferably one represented by the following general formula, namely, the general formula (wherein R1 and R2 are hydrogen or an alkyl group, R is a benzene nucleus, a cyclohexyl nucleus, or a residue consisting of a hydrocarbon such as an alkylene group having 2 or more carbon atoms, where n is an integer of 1 or 2).

Particularly desirable polyvalent oxazolone compounds for use in the present invention include, for example, 2,2'-p-5. Nylenebis[(4H)oxazolone-5],2,2'-m-phenylenebis[(4H)oxazolone-5],2,2'
-P-phenylenebis[4-methyl(4H)oxazolone-5], 2,2'-m-phenylenebis[4-methyl(4H)oxazolone-5), 1,2,4tris.2[
4-Methyl(4H)5-oxazolonyl]benzene, 1
,4bis・2[4-methyl(4H)5-oxazolonyl]cyclohexane,1,2bis・2[4-methyl(4H)
)-5oxazolonyl]cyclohexane, 2,2'-tetramethylenebis[(4H)-oxazolone-5),2
．． 2'-tetramethylenebis[4,4-dimethyl-(4
H) Oxazolone-5],2,2'-dimethelene bis.
(4,4 dimethyl(4H)-oxazolone-5) and the like.

In the coating composition of the present invention, the polyvalent oxazolone compound (B) combines the hydroxyl group contained in the polyester resin (A) with the hydroxyl group contained in the polyester resin (A), and is usually heated to a temperature of 120° C. to A ring-opening reaction occurs specifically at a temperature such as 250° C., forming a reticulated resin film that is excellent in corrosion resistance, beautiful appearance, blocking resistance, and weather resistance.

In the coating composition of the present invention, the above-mentioned polyvalent oxazolone compound (B) undergoes a crosslinking reaction with the hydroxyl group of the above-mentioned polyester resin (A) in the baking step to form a cured film, thereby solving this problem. For example, when the above compound is a polyvalent oxazolone compound represented by the above general formula, the crosslinking reaction (wherein R1- and R2 are hydrogen or an alkyl group, R is a benzene nucleus, a cyclohexyl nucleus, or a carbon number of 2 or more) It provides a so-called polyester polyamide structure, such as a structure represented by a hydrocarbon residue such as an alkylene group, and provides excellent corrosion resistance and weather resistance.

Furthermore, when the coating composition according to the present invention is used, the crosslinking reaction proceeds as a ring-opening addition reaction, so that no volatile substances are generated during the baking process, and a beautiful coating film appearance can be obtained in practical use.

The polyvalent oxazolone compound (B) described above is preferably blended in a proportion that is usually 0.7 to 1.2 times equivalent to the hydroxyl group of the polyester resin (A) described above.

The composition for powder coating in the present invention usually includes, for example, metal oxides such as titanium oxide and iron oxide, carbon blank,
Various pigments such as phthalocyanine blue, phthalocyanine green, syncasia red, toluidine red, etc., various additives such as silicone oil polyacrylic acid ester, fatty acid metal salt, fatty acid amide, higher aliphatic alcohol, and so-called surface conditioner such as wax. It is preferable to mix them appropriately, knead them using a kneader such as a roll or an extruder under a temperature condition of usually 70 to 120°C, cool them, and then pulverize them for practical use as a powder coating.

In addition to the above-mentioned additives, the coating composition of the present invention also contains an epoxy resin in order to achieve more sufficient adhesion to the coating substrate, which is the object to be coated. It may be put to practical use as a powder coating.

The powder coating produced as described above is applied to the above-mentioned object by a method such as electrostatic powder spraying, and is usually applied at a coating temperature of 120 to 2.
Baking is carried out at a temperature of 50° C. to obtain a reticulated resin film with excellent weather resistance and corrosion resistance and a beautiful appearance of the coating film.As a reaction accelerator during the baking process, for example,
Tertiary amines such as dimethylbenzylamine and trimethylbenzylammonium chloride, quaternary ammonium salts, or organometallic compounds such as dibutyltin oxide and zinc naphthenate may be blended in advance in the coating composition of the present invention.

Examples will be described below.

Example (1) Production of polyester resin: Polyester resin was produced for each experiment number shown in Table 1 by the method shown below.

A flask equipped with a stirrer, a thermometer, and a distillation condenser tube is equipped with a tea cup for the amount of raw materials for producing polyester shown in Table 1, and the flask is heated from the outside with a mantle heater to dissolve the raw materials in the form of a slurry. The temperature of the contents is 20
The temperature was raised to 0°C, and the esterification reaction was carried out for the reaction time shown in Table 1. At the same time, the distillate consisting of water or alcohol in the amount shown in Table 1 produced by this reaction was distilled out of the reaction system. The above reaction was continued at ~230°C to obtain each solid polyester resin of Experiment Nos. 1 to 4 having the properties shown in Table 1.

(2) Synthesis of polyvalent oxazolone: (2-1) 100 g of DL-alanine and 50 g of magnesium oxide were dissolved in 700 CC of water in a flask equipped with a stirrer, and 500 g of a 20% dioxane solution of terephthalic acid dichloride was dissolved in 2 The mixture was added dropwise over a period of time, and the contents were stirred while cooling the flask while keeping the internal temperature at 20°C.

Next, hydrochloric acid was added to adjust the pH of the contents to 1.5, and the precipitated solids were separated, washed with water, and dried in vacuum to obtain an intermediate product.

100 g of this intermediate product was heated to 50°C.
ml of acetic anhydride, dissolved and kept at 50°C for 1 hour with stirring, and after removing excess acetic anhydride under reduced pressure,
℃, the precipitated crystals were washed separately with water, dried in vacuo, and recrystallized again with diether ether to give 2,2'
-p'-phenylenebis(4-methyl(4H)oxazolone-5) was obtained.

The melting point of this compound was 180°C.

(2-2) In the same manner as in (2-1) above, using DL-alanine and terephthalic acid dichloride in the above (2-1), but using glycine and isophthalic acid dichloride instead, 2, 2'-m-phenylenebis [(4H)
Oxazolone-5] was synthesized.

The melting point of this compound was 192°C.

(2-3) Although DL-alanine and terephthalic acid dichloride were used in (2-1) above, DL-α aminoisobutyric acid and adipic acid dichloride were used instead.
-1) in the same manner as 2,2'tetramethylenebis[4
, 4-dimethyl-(4H)oxazolone-5] was synthesized.

The melting point of this compound was 107°C. (3) Preparation of powder coating: Polyvalent oxazolone compounds, pigments and surface conditioners shown in Table 2, or epoxy resins were added to each of the solid polyester resins of Experiment Nos. 1 to 4 produced by the method described above. They were added and mixed, melted and kneaded for 10 minutes under heating conditions of 100°C with a hot roll, and after cooling, they were pulverized with a pulverizer and passed through a 150-mesh sieve.
4 powder coatings were obtained.

(Example of the invention).

As a comparative example for the example of the present invention, as shown in Table 2, the polyester resin of Experiment No. 1 according to the example of the present invention was added with Cymel #300 (A.C.C. Co., Ltd. Product name) Powder coatings or epoxy resins containing pigments and surface conditioners, dicyanamide as a curing agent, powder coatings containing pigments and surface conditioners, respectively, were prepared in the same manner as in the experiment according to the present invention described above. The powder coatings of Experiment Nos. 5 and 6 were prepared using the following methods.

(4) Evaluation test of powder coating: (a). 50g of each of the powder coatings of experiment numbers 1 to 6 prepared by the above method were placed in stoppered bottles with a radius of 50mm, and each was left separately in a constant temperature bath at 30°C and 45°C for one week to test the blocking resistance. was tested.

The test results are shown in Table 3.

(B). In addition, each powder coating obtained in the above experiment was applied to a 0.8 mm thick zinc phosphate treated steel plate using an electrostatic powder spray gun, and baked at 200°C for 30 minutes in a hot air dryer. Each test plate having the film thickness shown in Table 3 was obtained.

The evaluation results of the formation, weather resistance, corrosion resistance, and aesthetic appearance of the coating film on the test plates prepared using the powder coatings of Experiment Nos. 1 to 6 are also listed in Table 3.

Claims (1)

[Claims] 1 (A) A polyester resin containing 0.2 to 4.0 equivalents of hydroxyl groups per 1000 g of resin and having a glass transition point of 20°C or higher, and (B) a polyvalent oxazolone compound. A thermosetting polyester powder coating composition characterized by: