KR820000991B1 - Electrical insulating resin comprising a polyester resin - Google Patents

Abstract

Title compn., useful for coating material, was prepd. by reacting more than trivalent of alcohol, more than trivalent of polyacid, divalent alcohol, dibasic acid, monovalent acid contg. aromatic ring, and monovalent alcohol contg. aromatic ring. Thus, a mixt. contg. ethyleneglycol 102 g, glycerol 67 g. 3-phenyl propionic acid 67 g, and di-n-Bu tin oxide 2g was reacted at 175-190≰C for 3 hr, cooled to 140≰C and then terephthalic acid 220 g, isophthalic acid 20 g, and trimellitic anhydride 20 g were added. The reaction mixt. was esterified at 175-225≰C for 7 hr and the polyester compn. was mixed with TBT 18 g and Zn naphthenate 4 g to give polyester enamel varnish.

Description

Electrical Insulation Resin Composition

The present invention relates to an electrically insulating resin composition comprising a polyester resin or an ester-imide resin having low viscosity, low softening point and high solubility.

The recent release of solvents in paints and varnishes into the air has serious problems to be solved in terms of pollution, raw material savings, and the like.

The same problems arise with electrically insulating varnishes such as enamel varnishes.

General purpose polyester enamel varnishes currently use solvents with strong polarity, such as cresols, due to the solubility of the resin. In addition, since the viscosity of varnish requires less than 100 poss at a normal temperature, in particular less than 70 to 80 poss at 30 ° C., a large amount of solvent in the varnish, such as 50% or more, in order to satisfy the conditions suitable for coating workability and coated film properties. Is used.

On the other hand, the so-called melt coating method is actually used in a very limited field in recent years, in which the amount of solvent for the resin is considerably reduced in comparison with the conventional coating composition, which is coated by preheating before the coating composition is used for coating. The viscosity of the coating composition is reduced to suit the task.

However, the method cannot be used in practice because there are many problems to be solved, such as heating devices, thermal stability of varnishes and the like. Therefore, although solvent type varnishes having a low viscosity are usually used at normal temperatures, an unnecessary amount of solvent for forming a coating film must naturally be reduced as described above. Various methods have been proposed to reduce the molecular weight of the resin used to increase the resin content and to reduce the amount of solvent used in the varnish, but this significantly reduces the physical properties of the synthetic hardened film, such as heat resistance and mechanical strength. It has been known for a long time that a new method other than reducing the molecular weight of the resin is required.

It is an object of the present invention to provide a high solid electrically insulating resin composition comprising an increased resin content with the same or better physical properties compared to the conventional one which does not reduce the molecular weight of the resin used.

The present invention relates to (a) one or more tri- or higher polyhydric alcohols and / or tri- or higher poly basic acids.

(b) one or more dihydric alcohols

(c) one or more dibasic acids

(d) one or more mono-basic acids comprising one or more aromatic rings in the molecule

(e) An electrically insulating resin composition comprising, as a main component, a resin obtained by reacting one or more monohydric alcohols containing one or more aromatic rings in a molecule.

Compounds of the invention also include organic solvents.

One embodiment of the invention

(a) one or more tri- or higher polyhydric alcohols and tri- or higher polybasic acids

(b) one or more dihydric alcohols

(c) one or more divalent basic acids

(d) one or more mono-basic acids containing one or more rings in the molecule

(e) An electrically insulating resin composition comprising, as a main component, a saturated polyester resin having a low softening point and a high solubility obtained by reacting one or more monohydric alcohols containing one or more aromatic rings in a molecule.

The varnish according to the present invention may include the saturated polyester resin described above at 10 to 20% by weight or more than conventional general-use polyester enamel varnish without degrading the physical properties of the produced film. Examples of tri- or higher polyhydric alcohols are tri methylol propane, glycerin, tris (2-hydroxyethyl) isocyanurate and the like.

Examples of the dihydric alcohols are ethylene glycol, propylene glycol, neopentyl glycol and the like.

Examples of tri- or higher polyacids or esters thereof, that is, alkyl esters are anhydrides, pyromellitic anhydrides, and trimethyl esters of trimellitic acid.

The term “acid” in the present invention includes the acid itself, acid anhydrides and esters thereof.

Examples of the dibasic acid and these esters, i.e., alkyl esters, are terephthalic acid, isophthalic acid, phthalic anhydride and the like, dimethyl terephthalate and dimethyl isophthalate.

Monobasic acids and their esters, i.e., alkyl esters, containing one or more aromatic rings in the molecule, for example benzoic acid 2,3-dimethoxybenzoic acid, P-toluic acid, phenoxy acetic acid, 2-phenoxypropionic acid phenyl acetic acid , Alkyl esters of the aforementioned acids such as phenylpropionic acid, P-turruyl-0-benzoic acid, α-naphthyl acetic acid, β-naphthoxy acetic acid and methylbenzoate.

In the present invention, one or more dibasic acids, monobasic and tri or higher polybasic acids containing one or more aromatic rings in the molecule are reacted as esters such as alkyl esters or all acids are reacted in acid form.

Examples of monohydric alcohols containing one or more aromatic rings in the molecule include benzyl alcohol, phenylethane alcohol and the like.

The reason for using tri- or higher polyhydric alcohols and tri- or higher polybasic acids in the present invention lies in the preparation of non-linear saturated polyester resins.

Linear saturated polyester resins are not suitable for the physical properties of the coating film.

In the case of producing saturated polyester resins from the raw materials of (a), (b), (c) and (d), total alcohols such as (b) dihydric alcohols and (a) tri- or higher polyhydric alcohols Based on total carboxylic acids or esters thereof such as (c) diacids, (a) tri- or more polyacids, and (d) monobasic acids or esters thereof comprising one or more aromatic rings in the molecule It is recommended to use 80 or less equivalent percentage as a surplus percentage of the hydroxyl group.

Total carboxylic acids such as one or more in the molecule, based on (d) monobasic acids comprising one or more aromatic rings in the molecule, (c) diacids and (a) tri- or more polyorganes or esters thereof It is preferable to use 8 to 20 equivalent percent monovalent acid containing an aromatic ring.

When preparing saturated polyester resins from the raw materials of (a), (b), (c) and (e), for example (b) dihydric alcohols, (a) tri- or higher polyhydric alcohols and (e) molecules Total alcohols of monohydric alcohols containing one or more aromatic rings in the hydroxide are based on, for example, (c) diacids and (a) tri- or higher polyhydric acids or their total carboxylic acids or esters thereof. It is appropriate to use 50 or less equivalent percentages as a surplus percentage of the group.

(e) monoalcohols containing one or more aromatic rings in the molecule, (b) 5-30 equivalent percent one in the molecule, based on the hydroxyl group of the total alcohols of dihydric and tri- or higher polyhydric alcohols. Or monohydric alcohols containing more aromatic rings are suitable.

The same effect can be obtained by combining monobasic acids containing one or more aromatic rings in the molecule with monohydric alcohols containing one or more aromatic rings in the molecule.

When preparing a saturated polyester resin from (a), (b), (c) and (d), the following methods can be used as a method for charging raw materials into the reaction system.

(1) Monovalent and dihydric alcohols containing one or more aromatic rings in the molecule are reacted first with tri- or higher polyhydric alcohols as necessary, followed by diacids, and tri- or higher as necessary The reaction is carried out by addition with the polyacid.

(2) A monohydric acid comprising a dihydric alcohol, a diacid, and one or more aromatic rings in the molecule is added and reacted simultaneously with tri- or higher polyalcohols and tri- or higher polyacids as necessary.

(3) dihydric alcohols and diacids are first reacted with tri- or higher polyacids and tri- or higher polyhydric alcohols as necessary and reacted, one or more in the molecule, especially with a percent reactant of 50 or less during the reaction. The reaction is carried out by addition of a monovalent acid containing an aromatic ring.

(4) Mixing method of the above-mentioned methods (1), (2) and (3)

When producing a saturated polyester resin from (a), (b), (c) and (e), the following methods are used as a method for charging the raw material into the reaction system.

(1) Monohydric alcohols containing one or more aromatic rings in the molecule and diacids are first reacted with tri- or higher polyacids as necessary, followed by reaction of the dihydric alcohols with tri- or higher polyhydric alcohols as necessary. It is added together with the reaction.

(2) Simultaneously add and react with monoalcohols, diacids and tri- or higher polyacids containing one or more aromatic rings in the molecule.

(3) dihydric alcohols, diacids and tri- or higher polyhydric alcohols are first reacted with tri- or higher polyhydric acids as necessary and reacted, with one or more aromatic rings in the molecule at a reactant percentage of not more than 50 during the reaction. The reaction is carried out by addition of a monohydric alcohol having.

(4) Mixing method of the above-mentioned methods (1), (2) and (3)

The reaction is carried out by charging the raw materials in the above-mentioned ratios and in the above-described order until the average molecular weight of the resulting resin reaches 800-2000, especially 1200-1700, when the acid value or viscosity is actually measured by GPC analysis. Di-n-butyl tin oxide, lead vinegar, and the like are used as a catalyst to remove water or alcohol generated from the reaction system during the condensation reaction at a temperature of 150 to 240 ° C.

The saturated polyester resins obtained as above have a significantly lower softening point than conventional polyester resins used for electrical insulation, especially when using phenyl acetic acid or phenyl propionic acid as monobasic acids containing one or more aromatic rings in the molecule or benzyl The softening point is below 50 ° C. when the alcohol is used as a monohydric alcohol containing one or more aromatic rings in the molecule.

In view of this, the melt coating can be carried out at a relatively lower temperature than the conventional method when the composition of the present invention is used, for example, as an electrical insulation varnish for wire coating, and because of its high solubility when used as a solvent type varnish. The amount of solvent can be reduced. For example, to obtain a viscosity of 70 poise at 30 ° C., the resin content is raised to 70-75% when using Cervsolve Acetate as a solvent.

In the present invention, a saturated polyester resin may be added to conventional additives such as solvents, curing agents, and surfactants.

As the solvent, cresol, serosolve acetate, glycol ether, alcohol derivative and the like can be used.

When the saturated polyester resin is dissolved in the glycol ether represented by the following general formula (I) and the alcohol derivative of the following general formula (II), a varnish having a higher content of nonvolatile substance than a conventional varnish at the same viscosity is obtained.

R ₁ O (CHR ₂ CH ₂ O) n H (I)

R ₄ O (CHR ₂ CH ₂ O) nCOR ₃ (II)

In the above formula

R ₁ is lower alkyl group, R ₂ is hydrogen or methyl group, R ₃ and R ₄ are independently lower alkyl, aryl or arylalkyl group and n is an integer of 1-3.

The aforementioned glycol ethers and alcohol derivatives may be used together. Examples of glycol ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono isopropyl ether, diethylene glycol monobutyl ether dipropylene glycol monomethyl ether, and the like. have. Examples of alcohol derivatives include ethylene glycol monomethyl ether acetate (cerosolve acetate), ethylene glycol monoethyl ether acetate, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether Acetates and the like.

When the saturated polyester resin used in the present invention is used as an enamel varnish, a small amount of hardener such as tetrabutyl titanate (hereinafter referred to as “TBT”), surfactants such as solvent, zinc naphthenate, zinc octoate are added.

The high solid polyester varnishes prepared are cured in a short time at high temperature to obtain a crosslinked polyester resin or coating film having excellent heat resistance, flexibility, mechanical strength and the like.

The following examples are provided to illustrate the present invention. In Examples below, Comparative Examples 1 and 2 show a process for preparing a conventional polyester resin varnish and a process for preparing a polyester resin varnish having a lower molecular weight of the polyester resin in order to increase the resin content in the varnish. will be.

Table 2 shows the varnishes of Examples 1-7 and the physical properties of the cured films obtained from Comparative Examples 1 and 2 for comparison.

Comparative Example 1

In a flask equipped with a stirrer, thermometer and cooling tube for fractional distillation, 137 g of ethylene glycol, 90 g of glycerin, 500 g of terephthalic acid and 3 g of di-n-butyltin oxide are stirred and distilled in a mantle heater. It heats to 185-240 degreeC with a mantle heater for 8 hours, removing the water produced | generated during reaction by this.

When the acid value reaches 20 or less, the reaction is stopped and the reaction system is cooled.

The polyester produced has an average molecular weight of 1650. To the resin was added 760 g of m-cresol, 25 g of TBT and 8 g of zinc naphthenate to produce a varnish whose viscosity was 70 poise at 30 ° C.

The resin content in the varnish was 39.5% by weight when the weight ratio before and after the heat treatment of the varnish was measured at 200 ° C for 2 hours.

Comparative Example 2

The reaction of Comparative Example 1 was repeated except for using 154 g of ethylene glycol, 125 g of glycerin, 500 g of terephthalic acid, and 4 g of di-n-butyltin oxide, and the reaction was stopped when the acid value reached 40 or less. Cool the system. The polyester produced has an average molecular weight of 700. A varnish is prepared by adding 330 g of Cervsolve Acetate, 27 g of TBT and 9 g of zinc naphthenate to the resin.

The varnish point was 70 poses at 30 ° C. and the resin content in the varnish was 62% when the weight ratio of the varnish was measured before and after the heat treatment at 200 ° C. for 2 hours.

EXAMPLES 1-5

In a flask equipped with a stirrer, a thermometer and a cooling tube for fractional distillation, all raw materials listed in Table 1 are placed and heated with a mantle heater. The reactant in the flask reacts with the ester at 175-225 ° C. for 8 hours while distilling off the water produced from the reaction system during the reaction and the reaction continues to 225 ° C.

When the acid number reaches the values listed in Table 1, the reaction is stopped and the reaction system is cooled.

The average molecular weight and softening point of the prepared polyesters are listed in Table 1. To the polyester resin, varnishes listed in Table 1 were prepared by adding longitudinal sol acetate as a solvent, TBT as a curing agent, and zinc naphthenate as a surfactant, and the viscosity of the varnish was adjusted to longitudinal sol acetate so that the viscosity of the varnish was 70 poise at 30 ° C. .

TABLE 1

Example 6

Into a flask equipped with a stirrer, a thermometer and a cooler by fractional distillation, 102 g of ethylene glycol, 67 g of glycerin, 67 g of 3-phenyl propionic acid and 2 g of di-n-butyl-tinoxide are slowly heated with a mantle heater.

The mixture in the flask is reacted for 3 hours at 175 ° C.-190 ° C. while removing water from the reaction system by distillation.

When the acid value was 2 or less, the reaction system was cooled to 140 ° C. and 220 g of terephthalic acid, 21 g of isophthalic acid and 20 g of trimellitic anhydride were added to the flask, followed by distillation to remove the water generated from the reaction system. The esterification reaction is carried out at 캜 to 225 캜 for 7 hours.

The reaction is continued at 225 ° C. until the acid number is 4 or less, then the reaction is stopped and the reaction system is cooled.

The average molecular weight of the resulting polyester is 1200 and the softening point is 49 ° C.

The varnish is prepared by dissolving the resin in 140 g of Cervsolve Acetate and adding 18 g of TBT and 4 g of zinc naphate. The resin content in the varnish was 60% by weight when measuring the weight ratio before and after the varnish was heat treated at 200 ° C. for 2 hours.

Example 7

Into a flask equipped with a stirrer, a thermometer and a cooling tube for fractional distillation, 85 g of ethylene glycol, 84 g of glycerin, 220 parts of terephthalic acid, 21 g of isophthalic acid, 20 g of trimellitic anhydride and 3 g of di-n-butyltin oxide were placed. The flask is slowly heated with a mantle heater.

The reaction in the flask is reacted at 175 ° C to 195 ° C for 4 hours while removing the water produced from the reaction system by distillation. When the distilled water reaches 33 ml, the reaction system is cooled to 140 ° C., 60 g of phenylacetic acid is added, and the esterification reaction is carried out at 185 to 225 ° C. for 5 hours while removing the water produced by distillation.

The reaction is continued until the acid value is 4 or less, then the reaction is stopped and the reaction system is cooled.

The polyester produced has an average molecular weight of 1300 and a softening point of 52 ° C.

The varnish is prepared by dissolving the resin in 157 g of Cervsolve Acetate and adding 20 g of TBT and 5 g of zinc naphthenate. The resin content in the varnish was 64% by weight when the weight ratio before and after the varnish was heated at 200 ° C. for 2 hours.

Example 8

The reaction of Example 7 was repeated and the reaction was stopped when the acid value was 10 or less. The varnish is prepared by dissolving the resin in 300 g of diethylene glycol monoisopropyl ether and adding 20 g of TBT and 5 g of zinc naphthenate.

The resin content in the varnish was 56% when the weight ratio before and after the varnish was heat treated at 200 ° C. for 2 hours.

[Physical Properties of Cured Film]

The varnishes obtained from Examples 1 to 7 and Comparative Examples 1 and 2 are coated on a 50 [mu] m uniform copper plate and heated at 200 [deg.] C. for 30 minutes. The results of measuring the physical properties of the cured film are shown in Table 2.

TABLE 2

As apparent from Table 2, when using varnishes with reduced average molecular weight of the resin to increase the resin content in the varnish (Comparative Example 2), all physical properties of the cured film were worse than those of Comparative Example 1.

On the other hand, the physical properties of the cured film when using a varnish with an increase in the resin content in the varnish without reducing the average molecular weight of the resin according to the present invention, for example, the strength, alkali resistance, adhesion and weight loss starting temperature of the film The gelation time of the varnishes of Examples 1 to 7 was the same as that of Comparative Example 1, but slightly later than that of Comparative Example 1, but this is not a problem.

[Examples 9-11]

Into a flask equipped with a stirrer, thermometer and fractional distillation tube, all raw materials listed in Table 3 are heated with a mantle heater. Evaporation is performed for 8 hours at 175-225 ° C. while distilling off the water produced during the reaction, and the reaction is continued at 225 ° C. until the acid value reaches the value listed in Table 3. The reaction is then stopped and the reaction system Cool.

The average molecular weight and softening point of the prepared polyesters are listed in Table 3. Thus obtained polyester resin was added as vertical solvent acetate as a solvent, TBT as a curing agent, and zinc naphthenate as a surfactant to make varnishes as shown in Table 3, and the viscosity of the varnish was adjusted to 70 poise at 30 ° C. as the vertical solve acetate. do.

TABLE 3

Example 12

286 g of terephthalic acid, 75 g of benzyl alcohol and 2 g of di-n-butyltin oxide are placed in a flask equipped with a stirrer, a thermometer and a cooling tube for fractional distillation, and heated slowly with a mantle heater.

Water generated from the reaction system is removed by distillation while reacting the reaction product in the flask at 180 ° C to 210 ° C for 3 hours. When the distilled water reaches 10 ml or more, the reaction system is cooled to 140 ° C., 61 g of ethylene glycol and 60 g of glycerin are added, and the resulting water is further removed by distillation while reacting at 180 to 225 ° C. for 6 hours.

The reaction is continued at 225 ° C. until the acid number is less than 7 and then the reaction is stopped and the reaction system is cooled.

The polyester produced had an average molecular weight of 1400 and a softening point of 58 ° C.

The resin was dissolved in 161 g of Cervsolve Acetate to add 16 g of TBT and 4 g of zinc naphthenate to make a varnish.

The resin content in the varnish was 65% when the weight ratio was measured before and after heating the varnish at 200 ° C for 2 hours.

Example 13

The reaction of Example 9 was repeated and the resulting resin was dissolved in 210 g of diethylene glycol monoisopropyl ether to prepare a varnish by adding 18 g of TBT and 6 g of zinc naphthenate. The resin content in the varnish was 58% as measured by the weight ratio before and after the varnish was heat treated at 200 ° C. for 2 hours.

[Physical Properties of Cured Film]

The varnishes obtained in Examples 9-12 were coated on a uniform copper plate having a thickness of 50 mu and heated at 200 캜 for 30 minutes.

The physical properties of the cured film were measured, as shown in Table 4.

For reference, the results of Comparative Examples 1 and 2 are also listed in Table 4.

Note: ^* 1 to ^* 5 refer to the note in Table 2

As can be clearly seen from Table 4, all the physical properties of the cured film are worse than Comparative Example 1 when using varnishes having lowered average molecular weight of the resin to increase the resin content in the varnish.

TABLE 4

On the other hand, when using varnishes with increased resin content in the varnish without lowering the average molecular weight of the resin according to the present invention all the physical properties of the cured film, such as the strength, alkali resistance, adhesion and weight loss starting temperature of the film The gelation time of the varnishes of Examples 9 to 12 is the same as that of Comparative Example 1, but slightly later than Comparative Example 1, but this is not a problem.

Another realization of the present invention

(a) one or more tri- or higher polyhydric alcohols and tri- or higher polyacids

(b) one or more dihydric alcohols

(c) one or more diacids

(d) one or more monovalent additions comprising one or more aromatic rings in the molecule

(e) An electrically insulating resin composition comprising as a main component a resin (ester-imide resin) having a low viscosity and excellent solubility obtained by reacting one or more monohydric alcohols containing one or more aromatic rings in a molecule.

According to the present invention, the varnish may include 10 to 20% more resin by weight than the content of the enamel varnish resin in the conventional ester-imide form without degrading the physical properties of the produced film. When preparing saturated polyester resins, tri- or higher polyhydric alcohols, tri- or higher polyacids, dihydric alcohols, dibasic acids, monohydric alcohols containing one or more aromatic rings in the molecule and one or more in the molecule As monovalent acid containing more aromatic rings, those mentioned above can be used.

The reason for using tri- or higher polyhydric alcohols and tri- or higher polyacids in the present invention is to prepare non-linear saturated polyester-imide resins. Linear saturated polyester-imide resins do not have adequate physical properties of the coating film.

Excellent heat resistance can be obtained when using tris (2-hydroxyethyl) isocyanurate as the tri- or higher polyhydric alcohol. It is suitable to use at least 35 equivalent percent of tri- or higher polyhydric alcohols based on total alcohol in view of the physical properties of the films formed and their solubility in solvents.

If the amount of tri- or higher polyhydric alcohol is less than 35 equivalent percent based on total alcohol, the solubility of the ester already resin is reduced and the stability of the varnish is unsuitable.

The amount of monobasic acid containing one or more aromatic rings in the molecule is suitably 8 to 20 equivalent percent based on total carboxylic acid in terms of heat resistance and solubility in solvents.

Preference is given to using monohydric alcohols having one or more aromatic rings in the molecule of 5 to 30 equivalent percent based on the total alcohol.

If the monohydric alcohol is less than 5 equivalent percent, the properties of low viscosity and high solubility cannot be manifested, whereas if it is more than 30 equivalent percent, the crosslink density decreases and heat resistance is reduced.

The same effect can be obtained from the combined use of monohydric acids containing one or more aromatic rings in the molecule and monohydric alcohols containing one or more aromatic rings in the molecule.

The ester imide resins used in the present invention may be prepared without the use of solvents or in the presence of about 10% solvents such as cresol, phenol, n-methyl-pyrrolidone, and the like (a), (b), (c), It is obtained by reacting (d) and (e), and the reaction temperature is suitably 150 to 240 캜.

When the prepared ester imide resin is dissolved in a conventional solvent such as phenol, cresol, or xylene, a conventional ester image having the same molecular weight but not containing a monohydric alcohol having one or more aromatic rings in the molecule at the same viscosity Varnishes having a nonvolatile material that is about 10% by weight higher than conventional varnishes, including resin, can be obtained.

In addition, the ester imide resin used in the present invention is R ₁ , R ₂ and n in the formula (I) R ₁ O (CHR ₂ CH ₂ O) _n H as described above or in the glycol ether of formula R ₂ , Non-volatile substances of higher content than those of the former at the same viscosity when R ₃ , R ₄ and n are dissolved in the alcohol derivative of the general formula (II) R ₄ O (CHR ₂ CH ₂ O) _n COR ₃ as described above You can get varnish with

When the ester imide resin used in the present invention is actually used as an enamel varnish, a solvent, a small amount of a curing agent such as TBT, a surfactant such as zinc naphthenate, zinc octoate, and the like are added.

The high solid content of the ester imide varnish prepared above may be cured at high temperature for a short time to obtain a crosslinked ester imide resin or coating film having excellent heat resistance flexible mechanical strength and the like.

The following examples are given to illustrate the present invention. Comparative Examples 3 and 4 in the following Examples are a process for preparing conventional ester imide resin varnishes and the preparation of conventional ester imide resin varnishes having lowered the molecular weight of the ester imide resin to increase the resin content in the varnish. The process is shown.

Comparative Example 3

83.7 g of ethylene glycol 156.6 g of tris (2-hydroxyethyl) isocyanurate, 199.2 g of terephthalic acid, 57.6 g of trimellitic anhydride, 29.7 in a flask equipped with a stirrer, thermometer and cooling tube for fractional distillation Negative diamino diphenylmethane, 24.9 g isophthalic acid, 66.7 g meta-cresol and 0.6 g TBT as catalyst were added and heated with a mantle heater.

The reaction in the flask is heated with stirring for 8 hours at 185-230 ° C. while removing water produced from the reaction system by distillation. When the acid value reaches 20 or less, the reaction is stopped and the reaction system is cooled.

The prepared ester imide resin has an average molecular weight of 2000. A varnish is prepared by adding 730 g of meta-cresol, 16.5 g of TBT, and 5.5 g of zinc naphtanate to this resin.

The viscosity of the prepared varnish was 65 poses at 30 ° C. and the resin content in the varnish was 35.7% by weight as measured by the weight ratio before and after the varnish was heat treated at 200 ° C. for 2 hours.

Comparative Example 4

The reaction of Comparative Example 3 was repeated, the reaction was stopped when the acid value was 40 or less, and the reaction system was cooled.

The produced ester imide resin has an average molecular weight of 900.

A varnish was prepared by adding 480 g of meta-cresol, 16.5 g of TBT, and 5.5 g of zinc naphthenate to this resin.

The viscosity of the prepared varnish was 62 poses at 30 ° C. and the resin content in the varnish was 47.2% by weight when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

On the other hand, a varnish according to the present invention is used in which a monovalent alcohol containing one or more aromatic rings in a molecule or a monohydric alcohol containing one or more aromatic rings in a molecule is used and the resin content in the varnish is increased without lowering the molecular weight of the resin. When used, cutting and abrasion resistance through temperature are the same as those in Comparative Example 3.

Claims (1)

One or more comprising at least one or more tri- or higher polyhydric alcohols and tri- or higher polyacids, one or more dihydric alcohols, one or more dibasic acids, and one or more aromatic rings in the molecule An electrically insulating resin composition comprising a resin obtained by reacting at least one of the above monovalent acids and one or more monohydric alcohols containing one or more aromatic rings in the molecule.