JPS6329691B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new method for producing a polyester resin having a carboxyl group at the end of the molecule. More specifically, the present invention relates to a method for producing a polyester resin in which a carboxyl group is introduced at the end of the molecule by using a terephthalic acid mono-lower alkyl ester as a carboxylic acid component. Polyester resins having a carboxyl group at the end of the molecule can be used in a wide range of applications such as solution-type paints, powder paints, and adhesives when combined with compounds that react with carboxyl groups, such as polyepoxy compounds and polyoxazoline compounds. Conventionally, the method for manufacturing such polyester resins involves adjusting the ratio of the carboxylic acid component to the alcohol component so that the alcohol component is in excess, and then proceeding with the reaction to produce a polyester resin in which the functional group at the end of the molecule is a hydroxyl group. After that, a common method was to add an aromatic acid anhydride such as phthalic anhydride, trimellitic anhydride, or pyromellitic anhydride to convert the functional group at the end of the molecule from a hydroxyl group to a carboxyl group. However, the polyester resin produced by this method can only be obtained with the terminal carboxyl group bonded to an asymmetric position of the benzene ring, so solution-based paints and powder paints using this polyester resin have a curing reactivity. However, the mechanical properties of the cured film were not fully satisfactory. It is known that terephthalic acid, which has superior structural symmetry, has much better mechanical properties than phthalic acid, isophthalic acid, trimellitic acid, etc. in terms of composition. Another manufacturing method is to adjust the ratio of carboxylic acid component to alcohol component so that the carboxylic acid component is in excess and incorporate a carboxyl group at the molecular end, but terephthalic acid does not melt under normal manufacturing conditions and the reaction is delayed. It was difficult to introduce the terephthalic acid component at the end because it remained in the resin as an unreacted product even if the reaction proceeded. The present invention solves these problems. That is, in the present invention, a hydroxyl group-containing polyester resin and a mono-lower alkyl terephthalate are reacted to produce a polyester resin having an acid value of 10 to 200, and at least 60% of the carboxyl groups of the polyester resin are The present invention relates to a method for producing a polyester resin having a carboxyl group, which is characterized by subjecting the mono-lower alkyl terephthalic acid ester to a transesterification reaction so that the carboxyl group is the same. The carboxylic acid component which is a component of the hydroxyl group-containing polyester resin of the present invention is not particularly limited, and known raw materials can be used. Specific examples include malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dimer acid, phthalic acid, isophthalic acid, isophthalic acid dimethyl ester, terephthalic acid, terephthalic acid dibutyl ester, terephthalic acid dimethyl ester, tetrahydro Phthalic acid, methyltetrahydrophthalic acid,
Hexahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, endomethylenehexahydrophthalic acid, naphthalene dicarboxylic acid, diphenolic acid, trimellitic acid, pyromellitic acid, trimesic acid, cyclopentanedicarboxylic acid, 3,3', 4,4'-benzophenonetetracarboxylic acid, 1,2,3,4-butanetetracarboxylic acid, 2,2'-bis-(4-carboxyphenyl)propane, trimellitic anhydride and 4,4' -diimidocarboxylic acid obtained from diaminophenylmethane, tris-(β-carboxyethyl)isocyanurate, isocyanurate ring-containing polyisocyanurate obtained from isocyanurate ring-containing polyisocyanurate and trimellitic anhydride, such as tolylene diimide An isocyanurate ring-containing polyimide polycarboxylic acid obtained from a trimerization reactant of isocyanate, xylylene diisocyanate or isophorone diisocyanate and trimellitic anhydride, and one or more of these may be used. Specific examples of alcohol components include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, isopentyl glycol, hydrogenated bisphenol A, 1,3
-butanediol, 1,4-butanediol,
1,6-hexanediol, neopentyl glycol, xylylene glycol, 1,4-cyclohexanedimethanol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, bis-(β-hydroxyethyl) terephthalate, tris-(β -hydroxyethyl) isocyanurate, 2,2,4-trimethylpentane-1,3-diol, and an oxycarboxylic acid component can be added. Examples include p-oxybenzoic acid, vanillic acid, dimethylolpropionic acid, malic acid, tartaric acid, and 5-hydroxyisophthalic acid. Furthermore, the hydroxyl group-containing polyester resin is
Performances such as pigment dispersibility, flowability, and solubility in solvents can be improved by adding a monohydric carboxylic acid or a monohydric alcohol to some of the constituent components. Such compounds include phenylacetic acid, O-toluic acid, cyclohexanecarboxylic acid, caprylic acid, lauric acid, myristic acid, palmitic acid,
Monovalent carboxylic acids such as stearic acid, benzoic acid, p-tertiary butylbenzoic acid, stearyl alcohol, lauryl alcohol, ethyl cellosolve, butyl cellosolve, methyl carbitol, butyl carbitol, benzyl alcohol, etc.
There is alcohol. Note that for all of the above raw materials, ester-forming derivatives thereof can be used. The terephthalic acid mono-lower alkyl ester may not be used as the acid component of the hydroxyl group-containing polyester resin, or may be a part or all of the acid component. The above raw materials are OH group/COOH group (equivalent ratio,
Note that here, the ester-forming groups derived from the OH group and the COOH group are regarded as the OH group and the COOH group, respectively. ) is reacted at a ratio of 1/1 or more. This hydroxyl group-containing polyester resin has a carboxyl value of 10 to 200 (KOHmg/g), preferably 20 to 200.
100 (KOHmg/g) and a softening point of 50 to 200°C, preferably 90 to 150°C.
Preferably, the above raw materials are mixed and reacted so that the equivalent ratio of OH group/COOH group is 1.03/1 or more. Further, the number average molecular weight of the hydroxyl group-containing polyester resin is preferably 1000 to 5000. If it is less than 1,000, the blocking resistance of the final powder coating tends to be poor, and if it exceeds 5,000, the leveling property tends to be poor. This hydroxyl group-containing polyester resin is
Can be transesterified with terephthalic acid mono-lower alkyl ester. Here, the terephthalic acid mono-lower alkyl ester includes terephthalic acid monomethyl ester, terephthalic acid monoethyl ester, terephthalic acid monobutyl ester, etc., and terephthalic acid monomethyl ester is particularly preferred. The reaction between the hydroxyl group-containing polyester resin and terephthalic acid mono-lower alkyl ester is such that the resulting polyester resin having carboxyl groups has an acid value of 10 to 200 (KOHmg/g), preferably 20 to 100 (KOHmg/g). It is preferable to adjust it as follows. If the carboxyl value is less than 10, when combined with a polyepoxy compound or polyoxazoline compound, the crosslinking density is insufficient and the material becomes brittle, while if it exceeds 200, flexibility decreases. Furthermore, at least among the carboxyl groups of the polyester resin having carboxyl groups,
Preferably, 60% of the terephthalic acid mono-lower alkyl ester is reacted with carboxyl groups. If it is less than 60%, the effect of improving mechanical properties tends to be insufficient. When the polyester resin having a carboxyl group obtained by the present invention is desired to be obtained as a powderable resin, the softening point is 50 to 200°C, preferably 90 to 150°C.
It is necessary to select the composition of the polyester resin so that the temperature is ℃. Therefore, aromatic carboxylic acid components (including aromatic oxycarboxylic acids) are at least
Preferably it is 70 mol%. If the softening point of the obtained resin is less than 50°C, the powdered resin will easily re-agglomerate and solidify, and if it exceeds 200°C, the resin will be too hard and difficult to powder. In order to impart toughness to the cured product, as a component of the polyester resin, 1 to 15% by mass of raw materials having three or more carboxyl groups and/or hydroxyl groups in the molecule based on the total amount of raw materials charged.
It is preferable to use Preferred examples include trimesic acid, tris-(β-carboxyethyl) isocyanurate, trimethylolpropane, tris-(β-hydroxyethyl)isocyanurate, dimethylolpropionic acid, and the like. Furthermore, when the above-mentioned monohydric carboxylic acid or monohydric alcohol is included as a modifier for pigment dispersibility, flowability, etc. in the constituent components of the polyester resin, the amount of these additions is 0.1 to 10.0 with respect to the total amount of raw materials charged.
It is desirable that the content be % by weight, preferably 0.5-5.0% by weight. If it is less than 0.1% by mass, no modification effect can be expected, and if it is more than 10.0% by mass, the chemical resistance and stain resistance will be significantly reduced, and in the case of producing resins that can be powdered, it will not be possible to obtain solids at room temperature. The negative effects of this occur. According to the present invention, a polyester resin having a carboxyl group at the end of the molecule is produced, for example, by the following method. In the composition system consisting of the above-mentioned carboxylic acid component, alcohol component, optionally an oxycarboxylic acid component, and monomethyl terephthalate according to the present invention, (1) When the carboxylic acid component is a free carboxylic acid compound that does not contain an ester group. In this method, a carboxylic acid compound is placed in a reaction vessel along with other components.
While blowing an inert gas such as nitrogen gas,
Start the reaction at a temperature of 170°C to 190°C. Condensation water produced as a by-product is continuously removed from the reaction system. After several hours from the start of the reaction, increase the temperature to 210°C to 250°C.
to promote the reaction. To further accelerate the reaction, add 0.1 to 1 mass of a common esterification catalyst, such as an oxide such as zinc oxide, antimony oxide, dibutyltin oxide, or a metal alkoxide such as tetrabutyl titanate, to the total amount of raw materials charged. It is effective to use %. After producing the hydroxyl group-containing polyester resin in this way, terephthalic acid mono-lower alkyl ester and a transesterification catalyst such as zinc acetate,
Metal acetates and metal alkoxides such as calcium acetate, lead acetate, and magnesium acetate are preferably added at a rate of 0.005 to 0.05 based on the total amount of raw materials charged.
% by mass is added to proceed with the reaction, and a carboxyl group is introduced at the end of the molecule. (2) If the carboxylic acid component is a lower alkyl ester, the same method as (1) can be used, but all components are charged into a reaction vessel together with a transesterification catalyst,
Start the reaction at a temperature of 150°C to 170°C. The lower alcohol produced as a by-product is continuously removed from the reaction system. Then, gradually increase the reaction temperature to 210℃~
After proceeding with the reaction at 240°C to produce a hydroxyl group-containing polyester resin, a transesterification reaction is carried out with mono-lower alkyl terephthalic acid ester in the same manner as in method (1) above to introduce carboxyl groups. (3) When the carboxylic acid component is a carboxylic acid compound and a lower alkyl ester, the method (1) can be applied. That is, after proceeding with the esterification reaction with components excluding the lower alkyl ester (including mono-lower alkyl terephthalic acid ester), the reaction is proceeded with the addition of the lower alkyl ester and a transesterification catalyst to produce a hydroxyl group-containing polyester resin. Terephthalic acid mono-lower alkyl ester is added and a transesterification reaction is carried out to introduce a carboxyl group. In the above method, after producing the hydroxyl group-containing polyester resin, other carboxylic acid components (excluding terephthalic acid) may be used together with the terephthalic acid mono-lower alkyl ester. but,
It is preferable to blend the polyester resin so that at least 60% of the carboxyl groups in the finally obtained polyester resin are carboxyl groups of mono-lower alkyl terephthalic acid ester. As described above, by reacting hydroxyl group-containing polyester resin with mono-lower alkyl terephthalate, the transesterification reaction proceeds faster than a normal esterification reaction, so unreacted mono-lower alkyl terephthalate remains. Aromatic carboxylic acids with a symmetrical structure can be introduced into the molecular terminals of polyester resins without any problems. Therefore, it does not have the conventional drawbacks. The present invention is particularly characterized by such points. The carboxyl group-containing polyester resin produced according to the present invention can be combined with a polyepoxy compound and used as a thermosetting resin composition in solution-type paints, powder paints, adhesives, and the like. A polyepoxy compound is a compound having two or more epoxy groups in its molecule, and when used in powder coatings, it preferably has a softening point of 50 to 130°C. However, even if the softening point is less than 50°C, if the epoxy equivalent is 500 or less, the amount of polyepoxy compound blended can be reduced, so it can be used for powder coatings. Examples of the above-mentioned polyepoxy compounds include bisphenol type epoxy resins obtained by reacting bisphenol A such as bisphenol A with epichlorohydrin, and bisphenol type epoxy resins obtained by reacting hydrogenated bisphenols such as hydrogenated bisphenol A with epichlorohydrin. The obtained hydrogenated bisphenol A type epoxy resin, terephthalic acid diglycidyl ester,
Polyglycidyl ester type epoxy resins such as isophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, endomethylenetetrahydrophthalic acid diglycidyl ester, glycidyl esters such as p-oxybenzoic acid glycidyl ester ether, etc. Ether type epoxy resin, tris-(2-epoxypropyl) isocyanurate, glycidyl acrylate or glycidyl methacrylate and other copolymerizable unsaturated monomers, preferably with a molecular weight of 3000 to
There are acrylic resins with 30,000 oxirane groups. Among these, the use of bisphenol type epoxy resin and tris-(2-epoxypropyl) isocyanurate is particularly effective. The ratio of polyester resin (A) and polyepoxy compound (B) obtained by the present invention is (A)/(B) from 40/60 to
It is desirable to mix them so that the ratio is 95/5 (mass ratio). If it exceeds 95/5, the curing property is not sufficient and it becomes 40/
When the molecular weight is less than 60, unfavorable effects such as a significant decrease in weather resistance in the case of bisphenol type epoxy resin and a decrease in flexibility in the case of tris-(2-epoxypropyl) isocyanurate appear. This resin composition may contain known colorants, pigments, fillers, fluidity regulators, and curing accelerators as appropriate. When it is desired to take out the polyester resin according to the present invention as a solution, commonly used solvents such as toluene, xylene, ethyl cellosolve, butyl cellosolve, butyl carbitol, cellosolve acetate, ethyl acetate, butyl acetate, methyl isobutyl ketone, cyclohexanone, cresol, dimethyl acetamide, dimethyl formamide,
Dissolved or suspended in N-methylpyrrolidone, etc. Examples of the present invention are shown below. Example 1

[Table] Of the above components, terephthalic acid, neopentyl glycol, trimethylolpropane, and dibutyltin oxide were placed in a reaction vessel and kept at 190°C for 8 hours. Condensation water was continuously removed from the reaction system.
After raising the reaction temperature to 230°C and proceeding with the reaction, terephthalic acid monomethyl ester and lead acetate were added and kept warm for 2 hours to give a carboxyl value of 83 (KOHmg/g) and a softening point (ring and ball method) of 110°C. A transparent polyester resin with an acid value of 85% was obtained. Of the carboxyl groups in this polyester resin, 85% were carboxyl groups of the terephthalic acid monomethyl ester component. Example 2

[Table] The above components were placed in a reaction container and kept at 170°C for 2 hours, and then the temperature was raised to 220°C over about 5 hours to proceed with the reaction. Methanol produced as a by-product was continuously removed from the reaction system. The obtained polyester resin is transparent, has a carboxyl value of 80 (KOHmg/g), and a softening point.
It was 115℃. All the carboxyl groups of this polyester resin are carboxyl groups of the terephthalic acid monomethyl ester component. Example 3

[Table] Among the above ingredients, isophthalic acid, adipic acid, ethylene glycol, neopentyl glycol,
1,6-Hexanedioltrimethylolpropane was placed in a reaction vessel and heated at 180°C for 3 hours, then at 210°C for 6 hours.
After allowing the reaction to proceed for several hours, dimethyl terephthalate, monomethyl terephthalate, and zinc acetate were added and reacted at 220°C for 10 hours to increase the carboxyl value.
48 (KOHmg/g) and a softening point of 93°C. A transparent polyester resin was obtained. 98% of the carboxyl groups in this resin are those of the terephthalic acid monomethyl ester component. Comparative example 1

[Table] The above ingredients were placed in a reaction container and heated to 190℃ for 8 hours, then the temperature was raised to 230℃ to proceed with the reaction, but the resulting resin was opaque due to residual unreacted terephthalic acid. It was not suitable as a resin. Comparative example 2

[Table] The above components except trimellitic anhydride were placed in a reaction vessel and kept at 190°C for 8 hours, then the temperature was raised to 230°C to proceed with the reaction. Then, the temperature was lowered to 180°C, trimellitic anhydride was added, and the mixture was reacted for 3 hours to obtain a polyester resin whose end groups were trimellitic acid components and had a carboxyl value of 82 (KOH mg/g) and a softening point of 111°C. Application examples 1-2 and reference column 1

[Table] After dry-blending the above ingredients in a super mixer at 500 rpm for 20 minutes, the Co-kneader PR manufactured by Busu Co., Ltd.
- Melt-kneaded at 46°C. After the kneaded mixture is quickly cooled,
It was crushed and classified to obtain a white powder coating of 80 μm or less. Apply this paint to a thickness of 60±10 μm on a zinc phosphate treated plate.
Perform electrostatic spray painting at 180℃ so that
Baked for 20 minutes. Table 1 shows the properties of the cured film. Application example 3 Paint components Composition ratio (parts by mass) Polyester resin obtained in Example 3 60.0 Epikote 1004 40.0 Modaflow 0.7 Benzoin 0.5 Rutile titanium white 45.0 A powder coating was obtained in the same manner as Application Examples 1 and 2 with the above composition. . This paint was also baked in the same manner as in Application Examples 1-2. Table 1 shows the properties of the cured film.

[Table] The polyester resins of Comparative Examples 1 and 2 are those of Example 1.
The molecular design values (molecular weight, carboxyl value, etc.) are exactly the same, except that the terephthalic acid monomethyl ester in the above was changed to terephthalic acid and trimellitic anhydride. However, in the resin obtained in Comparative Example 1, unreacted terephthalic acid remained and the desired product could not be obtained, and in Comparative Example 2, the mechanical properties (Erichsen, Impact) of the cured film were insufficient. .
On the other hand, in Examples 1 to 3, there were no problems in the production of the polyester resin or in the properties of the cured film, demonstrating the effectiveness of using monomethyl terephthalate. As is clear from the above, according to the present invention, a polyester resin having carboxyl groups with excellent mechanical properties can be obtained.

Claims (1)

[Claims] 1. Reacting a hydroxyl group-containing polyester resin and a mono-lower alkyl terephthalic acid ester,
A polyester resin having an acid value of 10 to 200 is produced, and a transesterification reaction is carried out so that at least 60% of the carboxyl groups of the polyester resin are carboxyl groups of the mono-lower alkyl terephthalic acid ester. A method for producing a polyester resin having a carboxyl group. 2. The hydroxyl group-containing polyester resin contains at least one compound selected from the group consisting of polycarboxylic acid components, polyhydric alcohol components, oxycarboxylic acids, and ester-forming derivatives thereof, with OH groups/COOH groups (equivalent ratio, In addition, here OH
and ester-forming groups derived from the COOH group are considered to be the OH group and the COOH group, respectively. 2. The method for producing a polyester resin having a carboxyl group according to claim 1, which is a polyester resin obtained by reacting the polyester resin at a ratio such that the ratio of the polyester resin is 1/1 or more. 3. The method for producing a polyester resin having a carboxyl group according to claim 2, wherein the OH group/COOH group (equivalent ratio) is 1.03/1 or more.