JP2880528B2 - Method for producing polyester resin and coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for producing a polyester resin used for a paint excellent in gloss, hardness, processability, stain resistance and weather resistance, and a polyester resin obtained. And a coating composition using the same.

(Prior art) Conventionally, home appliances were painted in a box shape after processing and forming a steel sheet.
In order to solve various problems such as improvement of productivity, prevention of pollution, and improvement of working environment, the pre-coating method, in which flat steel sheets are painted and then processed and formed, is being shifted. The pre-coated steel sheet used in this method is processed into a complicated shape after painting, so high workability is required. On the other hand, among household appliances, refrigerators, washing machines, and the like are required to be refined with high coating film hardness, stain resistance, and chemical resistance.

Conventionally, thermosetting acrylic resins have been mainly used for coating these home appliances. This is because the acrylic resin paint has excellent coating film hardness and stain resistance. However, acrylic resin paint has insufficient workability to be used for pre-coating, and it is necessary to soften the composition of acrylic resin in order to satisfy workability.
It is difficult to show coating film hardness and stain resistance that can withstand practical use.

Further, thermosetting polyester resins have been used for coil coating of colored tin and the like, but still have the disadvantage that workability, coating film hardness and stain resistance cannot be balanced. However, the high molecular weight polyester resin obtained by polycondensing the polyester resin under reduced pressure,
It has better processability than ordinary polyester resin, and has been put to practical use in painting home appliances such as refrigerators and washing machines.

Such an example is described in JP-A-59-8770.

(Problems to be Solved by the Invention) However, even with these high-molecular-weight polyester resins, the weather resistance is not sufficient as compared with conventionally used acrylic resins. The method disclosed in Japanese Patent Application Laid-Open No. 59-8770 has good weather resistance, but has problems in terms of balance between hardness and workability and stain resistance.

The present invention provides a method for producing a polyester resin having excellent weather resistance as well as hardness, workability, and stain resistance, and a coating composition using the obtained polyester resin.

(Means for Solving the Problems) The present invention relates to 3-methylpentanediol having good flexibility, weather resistance and hydrolysis resistance as an alcohol component of a polyester resin, and neopentyl glycol having good weather resistance and hydrolysis resistance. Is used as a main component to solve the above-mentioned problem.

That is, the present invention reacts an alcohol component mainly containing 3-methylpentanediol and neopentyl glycol with an acid component mainly containing dicarboxylic acid,
The present invention relates to a method for producing a polyester resin having a number average molecular weight of 5,000 or more, and a coating composition containing the obtained polyester resin and a solvent.

The 3-methylpentanediol used as an essential component in the present invention is preferably used in an amount of 20 mol% or more based on all alcohol components. If it is less than 20 mol%, the balance between hardness and workability and stain resistance tend to decrease. It is particularly preferable to use 90 mol% or less based on all alcohol components in view of the balance between hardness and workability.
In addition, neopentyl glycol is used as an essential alcohol component. Neopentyl glycol is preferably used in an amount of 10 to 60 mol% based on all alcohol components in view of the balance between hardness and workability and stain resistance. Other diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6
-Hexanediol, diethylene glycol, 1,4-cyclohexanedimethanol and the like, and these are preferably used in an amount of 20 mol% or less based on all alcohol components in view of a balance between hardness and workability.

Examples of the dicarboxylic acid used as the acid component in the present invention include aromatic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and the like, and lower alkyl esters and acid anhydrides thereof. Examples of the acid include adipic acid, azelaic acid, sebacic acid, succinic acid, fumaric acid, maleic acid, cyclohexanedicarboxylic acid, hymic acid and the like, and lower alkyl esters and acid anhydrides thereof.
More than one species can be used.

In the present invention, a trihydric or higher polyhydric alcohol and / or polybasic acid can be used in an amount of preferably 5% by weight or less, particularly preferably 3% by weight or less, based on the polyester resin. When these are contained, the solvent resistance is further improved. Here, when these contents exceed 5% by weight, workability tends to decrease. These include, of course, those containing both a hydroxyl group and a carboxyl group in one molecule. Examples thereof include glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, dimethylolpropionic acid, trimellitic acid, pyromellitic acid, trimesic acid and the like, and one or more of these can be used.

In the present invention, a polyester resin can be produced by blending the above-mentioned acid component and alcohol component and by a conventional method. For example, an acid component and an alcohol component are mixed at a ratio such that the carboxyl group of the acid component and the hydroxyl group of the alcohol component are almost equivalent to an excess of the hydroxyl group, and the ester is added at 150 to 300 ° C in the presence of a catalyst if necessary. A high-molecular-weight polyester resin can be obtained by removing the excess alcohol component by a transesterification reaction or a transesterification reaction, preferably under a reduced pressure of 1 mmHg or less.
The trihydric or higher polyhydric alcohol and / or polybasic acid may be added and reacted at normal pressure before or after the above-mentioned reduced pressure.

The polyester resin thus obtained must have a number average molecular weight of 5,000 or more, and is preferably
It is set to 30,000 or less, particularly preferably in the range of 7,000 to 25,000. If the number average molecular weight is less than 5,000, the processability decreases, and if the number average molecular weight is too large, the gloss tends to decrease.

In the present invention, the “number average molecular weight” is a value measured using gel permeation chromatography and using a calibration curve of standard polystyrene.

In order to make the polyester resin obtained according to the present invention into a resin composition, other known polyester resins may be used in combination with the above-mentioned polyester resin to such an extent that its properties are not impaired. The obtained polyester resin composition is diluted with a solvent such as an aromatic hydrocarbon, an aliphatic hydrocarbon, an ester, or a ketone, if necessary, and used for a paint, an adhesive and the like.

The polyester resin obtained by the present invention is an amino resin obtained by reacting an amino compound such as melamine, urea or benzoguanamine with formaldehyde, and an amino resin obtained by etherifying the amino resin with a lower alcohol such as methanol, ethanol, propanol or butanol. A thermosetting coating composition can be obtained in combination with an amino resin such as an etherified amino resin. In this case, the solid content ratio (weight ratio) of the polyester resin composition and the amino resin is 90/10 to 60/40, preferably 85/15 to 70/30.
Is appropriate.

The polyester resin obtained by the present invention can be used as a thermosetting coating composition by using polyisocyanate as a curing agent. Examples of the polyisocyanate include isophorone diisocyanate diphenyl methane diisocyanate, m-xylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, dicyclohexyl methane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, dodecane dicarbonyl diisocyanate, and the like. These were masked with a blocking agent, for example, alcohols such as methanol, ethanol and 2-butoxyethanol, phenols such as phenol and cresol, lactams such as caprolactam and butyrolactam, and oximes such as cyclohexane oxime and methyl ethyl ketone oxime. Block isocyanates can also be used. The compounding amount is usually such that the isocyanate value and the hydroxyl value of the polyester resin composition become approximately 1: 1.

Further, if necessary, a pigment, a plasticizer, a colorant and / or an acid catalyst such as p-toluenesulfonic acid and dodecylbenzenesulfonic acid can be appropriately added to obtain the coating composition of the present invention.

The coating composition thus obtained can be applied to the surface of iron, non-ferrous metal or the like by a known method such as spray coating or roll coating.

(Examples) Next, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example 1 (1) 377.6 parts by weight of 3-methylpentanediol (3.2
Mol), 728 parts by weight of neopentyl glycol (7.0 mol), 93 parts by weight of ethylene glycol (1.5 mol), 146 parts by weight of adipic acid (1.0 mol), 747 parts by weight of terephthalic acid (4.5 mol), 747 parts by weight of isophthalic acid ( 4.5 mol) and 0.5 parts by weight of dibutyltin dioxide and subjected to an esterification reaction at 250 ° C. in the presence of an inert gas.
The temperature was raised to 0 ° C., and a polycondensation reaction was performed under a reduced pressure of 106.7 Pa (0.8 mmHg) to obtain a polyester resin having the composition and resin characteristics shown in Table 1.

In the examples, the resin composition was determined by NMR, and the number average molecular weight was measured using a Hitachi 635 type high performance liquid chromatography analyzer (manufactured by Hitachi, Ltd.). Gelpack R440, R450 and R400M were used as columns. (Manufactured by Kogyo Co., Ltd., product name) were connected in series, a chromatogram was obtained using tetrahydrofuran as an eluent, and calculated based on standard polystyrene.

Examples 2 and 3 and Comparative Examples 1 to 3 A polyester resin having the resin composition and resin characteristics shown in Table 1 was obtained in the same manner as in Example 1 except that the charged components were changed. In Example 3 and Comparative Example 2, the trivalent component was subjected to an esterification reaction without being charged at the initial stage.
After reacting at 6.7 Pa (0.8 mmHg) for 2 hours, a trivalent component was added, and the mixture was kept warm for 30 minutes and cooled to obtain a polyester resin.

Manufacture and evaluation of coating composition The polyester resin obtained in each of Examples and Comparative Examples was
Solvetsso 150 (Etsuso Standard Oil Co., Ltd.)
(Trade name of organic solvent) / cyclohexanone / cellosolve acetate = 1/1/1 (weight ratio) to prepare a solution having a heating residue of 40% by weight. This polyester resin solution was formed into a paint by the following formulation.

Polyester resin solution of Example or Comparative Example 262.5 parts by weight Cymel 303 (methylated melamine, trade name of Mitsui Sinamide) 45 parts by weight Rutile type titanium white 150 parts by weight p-toluenesulfonic acid 1.5 parts by weight Solvesso 150 / cyclohexanone = 1 / 1 (weight ratio) 69 parts by weight The obtained coating composition was applied to Bonderite # 144 treated steel sheet (Nippon Test Panel Co., Ltd., 0.5 mm thick) with an applicator so as to have a dry film thickness of 20 μm, and then heated at 280 ° C. Bake for 65 seconds.

The properties of the obtained coating film were tested by the following test methods.
The results are shown in Table 2.

Test method Mitsuzawa Measured at an incident angle of 60 ° according to JIS K5400.

Pencil hardness According to JIS K 5400, the pencil hardness was measured using Mitsubishi Uni Pencil (Mitsubishi Pencil Co., Ltd.).

Workability 70 × 40 (mm) test specimen after painting from the center in the vertical direction
Bent and pressed 180 °.

Evaluation 5: No cracking 3: Cracking occurred on 1/3 1: Cracking occurred on the entire surface Stain resistance 24 hours after the black and red magic ink marks on the test piece were wiped off with ethanol, and visually judged.

Evaluation 5: No ink mark at all 4: Intermediate between 5 and 3 3: Slight ink mark remaining 2 ... Intermediate between 3 and 1 1: Ink mark clearly remained Weather resistance After irradiation for 800 hours using a Sanciain weatherometer The gloss (60 ° specular reflectance) was measured and expressed as a percentage of the initial gloss.

As seen from Examples 1 to 3, when the polyester resin composition of the present invention is used, a coating film having excellent gloss, hardness, workability, stain resistance and weather resistance can be obtained.

In Comparative Example 1, a polyester resin disclosed in JP-A-59-8770 was additionally tested, but the workability and stain resistance were reduced. Comparative Example 2 is a case where the molecular weight is small, but the workability and the stain resistance are reduced. Comparative Example 3 is an example in which ethylene glycol was used instead of 3-methylpentanediol, but the weather resistance was reduced.

(Effect of the Invention) The polyester resin obtained by the production method of the present invention is
A coating film excellent in gloss, hardness, workability, stain resistance and weather resistance can be provided, and is particularly effective as a coating composition.

Continuation of the front page (56) References JP-A-51-17921 (JP, A) JP-A-62-205117 (JP, A) JP-A-56-5682 (JP, A)

Claims (5)

(57) [Claims] An alcohol component containing 3-methylpentanediol and neopentyl glycol as a main component and an acid component containing a dicarboxylic acid as a main component are reacted to have a number average molecular weight of 5,000 or more. Manufacturing method of polyester resin. 2. The method for producing a polyester resin according to claim 1, wherein 3-methylpentanediol is contained in an amount of 20 mol% or more based on all alcohol components. 3. A polyhydric alcohol and / or polybasic acid having a valency of 3 or more as an alcohol component and / or an acid component.
The method for producing a polyester resin according to claim 1 or 2, wherein the amount is not more than 0% by weight (excluding 0). 4. A coating composition comprising a polyester resin obtained by the production method according to claim 1, 2 or 3, and a solvent. 5. The coating composition according to claim 4, further comprising an amino resin or a polyisocyanate as a curing agent component.