KR820000990B1 - Electrical insulating resin comprisisng a polyester resin - Google Patents

Abstract

Title compn., useful for coating material, was prepd. by reacting more than trivalent of alcohol and polybasic acid, divalent alcohol, dibasic acid, monovalent alcohol contg. aromatic ring, and 5 membered imide ring compd. Thus, a mixt. contg. ethylene glycol 207.0 g, tris-(2-hydroxyethyl) isocyanurate 470.0 g, terephthalic acid 597.6 g, trimellitic anhydride 172.8 g, diaminodiphenyl methane 89.1 g, isophthalic acid 154.4 g, benzyl alcohol 154.4 g, amd meta-cresol 202.0 g was reacted at 185-230≰C for 8 hr. the obtained esterimide resin 600g was mixed with meta-cresol 444 g, TBT 15.7 g and Zn naphthenate 5.3 g to give 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 a low viscosity, a low softening point and a 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, especially 70 to 80 poss at 30 ° C., a large amount of solvent in the varnish, for example, 50% or more in order to satisfy suitable conditions 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 can be used in practice because there are many problems to be solved, such as heating devices, varnish thermal stability. 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 cured 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 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) one or more monohydric alcohols containing one or more aromatic rings in the molecule, and

(f) An electrically insulating resin composition comprising, as a main component, a resin obtained by reacting one or more compounds that may include or form one or more 5-member imide rings.

One embodiment of the present 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 trimethylol propane, glycerin, tris (2-hydroxy ethyl) isocyanurate and the like. Examples of the dihydric alcohols are ethylene glycol, propylene glycol, neopentyl glycol and the like.

Examples of the tri- or higher polyacids or esters thereof, i.e., alkyl esters, are anhydrides, pyromellitic anhydrides and trimellitic esters of trimellitic acid.

In the present invention, the term “acid” 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-dimethoxy benzoic acid, p-toluic acid, phenoxy acetic acid, 2-phenoxypropionic acid phenyl Acetic acid, phenylpropionic acid, p-tolyl-0-benzoic acid, d-naphthyl acetic acid, β-naphthoxy acetic acid and alkyl esters of the aforementioned acids such as methyl benzoate.

In the present invention one or more dibasic acids, monobasic and tri- or higher polyvalent basic 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, phenylethyl 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) monohydric alcohols containing one or more aromatic rings in the molecule,

(b) using monohydric alcohols comprising one or more aromatic rings in the molecule of 5 to 30 equivalent percent, based on the hydroxyl group of the total alcohols of the dihydric and tri- or higher polyhydric alcohols. It is 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, it is possible to perform melt coating at a relatively lower temperature than the conventional method when using the composition of the present invention as an electrically insulating varnish for wire coating, for example, 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 poises 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 OC (CHR ₂ CH ₂ O) n H (I)

R ₄ O (CHR ₂ CH ₂ O) nCOR ₃ (II)

Where

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 resins used in the present invention are used as enamel varnishes, small amounts of hardeners such as tetrabutyl titanate (hereinafter referred to as “TBT”), surfactants such as solvents, zinc naphthenates, zinc octoates 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 viscosity of the varnish 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.

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) one or more monohydric alcohols comprising one or more aromatic rings in the molecule and

(f) containing, as a main component, a resin having low viscosity and good solubility (ester-imide resin) obtained by reacting one or more compounds containing or forming one or more 5-membered imide rings; Electrically insulating resin composition.

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.

Examples of the compound which may include or form a 5-membered imide ring include polyacid anhydrides such as trimellitic anhydride and pyromellitic anhydride such as primary diamines such as diamino diphenyl methane and meta-phenylenediamine, and ethanol amines. Those having one or more 5-membered imide rings obtained by reaction with amino carboxylic acids such as aminoalcohols, amide acetic acid, aminohexinoic acid, and the like can be used. In addition, mixtures of the above-mentioned polyacid anhydrides with primary diamines, amino alcohols, amino carboxylic acids which can be mixed with other raw materials can be used.

For example, 1 mole of primary diamine per 2 moles of triacid anhydride, about 1 mole of amino alcohol per mole of triacid anhydride, about 1 mole of 2 moles of amino carboxylic acid tetracarboxylic dianhydride per mole of triacid anhydride 2 moles of amino carboxylic acid per mole of primary diamine, tetraacid dianhydride can be used.

Compounds which may comprise or form one or more 5-membered imide rings in the preparation of ester imide resins may be a compound comprising a previously formed 5-membered imide ring or mixed with other raw materials It is used as a compound capable of reacting to form a 5-membered imide ring to form one or more 5-membered imide rings.

Therefore, in the actual reaction for producing the ester imide resin, a 5-membered imide ring may be first formed and then other raw materials may be added thereto or all the raw materials may be reacted at the same time.

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 the total alcohol in view of the physical properties of the film formed and 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 clearly expressed, whereas if it is more than 30 equivalent percent, the crosslink density decreases and heat resistance is reduced.

The same effect can be obtained in the combination 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 making (d) and (e) and (f) react, and the reaction temperature is suitable from 150 to 240 ° C.

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 can be cured in a short time at high temperature 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 parts in a flask equipped with a stirrer, a thermometer and a cooling tube for fractional distillation. Diamidino phenylmethane, 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 to stop the reaction when the acid value reached 40 or less, and then cooled the reaction system.

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.

Example 1

207.0 g of ethylene glycol, 470.0 g of tris (2-hydroxyethyl) isocyanurate, 597.6 g of terephthalic acid, 172.8 g of trimellitic anhydride, 89.1 g of diamino diphenylmethane, 74.7 g of isophthalic acid The reaction is carried out in the same manner as described in Comparative Example 3, except that 154.4 g benzyl alcohol and 202.0 g meta-cresol are used.

The reaction is stopped when the acid number reaches 8.

Take 600 g of the resin prepared and add varnish to this resin by adding 444 g of meta-cresol, 15.7 g of TBT and 5.3 g of zinc naphthenate.

The viscosity of the prepared varnish was 57 poses at 30 ° C. and the resin content in the varnish was 47.7% by weight when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

The average molecular weight of the produced resin was 1800.

Example 2

A varnish was prepared by adding 248 g of diethylene glycol monoisopropyl ether, 15.7 g of TBT and 5.3 g of zinc naphthenate to 600 g of the resin prepared in Example 1.

The viscosity of the prepared varnish was 59 poses at 30 ° C. and the resin content in the varnish was 57.6% when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

On the other hand, the resin obtained in Comparative Example 3 did not dissolve in diethylene glycol monoisopropyl ether and formed white cloud-like precipitates.

Example 3

A varnish was prepared by adding 107 g of diethylene glycol monoisopropyl ether, 107 g of cersolved acetate, 15.7 g of TBT and 5.3 g of zinc naphthenate to 600 g of the resin prepared in Example 1.

The viscosity of the prepared varnish was 64 poses at 30 ° C. and the resin content in the varnish was 62.5 wt% when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

Example 4

75 g of ethylene glycol, 74 g of glycerin, 211 g of terephthalic acid, 23 g of isophthalic acid, 28 g of diaminodiphenylmethane, 77 g of trimethite anhydride, 28 g of benzyl alcohol and 2 g of di-n-butyl tin oxide as a catalyst The reaction is carried out in the same manner as described in Comparative Example 3 except for using.

The reaction was stopped when the acid value reached 10 and the produced ester imide resin had an average molecular weight of 1900.

To the obtained resin, 110 g of Cervsolve Acetate, 18 g of TBT and 6 g of zinc naphthenate were added to prepare a varnish.

The viscosity of the prepared varnish was 72 poses at 30 ° C. and the resin content in the varnish was 64.1 wt% when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

Example 5

59 g ethylene glycol, 57 g glycerin, 212 g terephthalic acid, 22 g isophthalic acid, 30 g diaminodiphenylmethane, 82 g trimellitic anhydride, 80 g phenylethyl alcohol and 2 g di-n-butyltin as catalyst The reaction was carried out in the same manner as described in Comparative Example 3 except for using oxide. The reaction was stopped when the acid value reached 8 and the produced ester imide resin had an average molecular weight of 2000.

A varnish is prepared by adding 180 g of Cervsolve Acetate, 20 g of TBT, and 7 g of zinc naphthenate to this resin.

The viscosity of the prepared varnish was 69 poses at 30 ° C. and the resin content in the varnish was 60.0 wt% when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

Example 6

29.7 g of diaminodiphenyl methane, 57.6 g of trimellitic anhydride and 67.3 g of meta-cresol were added to a flask equipped with a stirring paper, a thermometer and a cooling tube for fractional distillation, and 0.6 g of TBT was added as a catalyst. The flask is heated to 200 ° C. while removing the water produced by stirring in the mantle heater.

After 2 hours at 200 ° C., 199.2 g of terephthalic acid, 24.9 g of isophthalic acid, 51.5 g of benzyl alcohol, 69.0 g of ethylene glycol and 156.7 g of tris (2-hydroxyl ethyl) isocyanurate were added. The temperature is raised to 185 ° C to 230 ° C and reacted for 6 hours while distilling off water generated from the reaction system during the reaction. The reaction was continued until the acid value reached 12 and then stopped, and the resin composition thus prepared had an average molecular weight of 1900.

140 g of meta-cresol, 15.0 g of TBT and 5.1 g of zinc naphthenate are added to this resin to prepare a varnish.

The viscosity of the varnish was 72 poses at 30 ° C. and the resin content in the varnish was 48.1 wt% when the weight ratio was measured before and after the varnish was heat treated at 200 ° C. for 2 hours.

The varnishes obtained in Examples 1 to 6 were coated on a copper plate to obtain a rigid film when heated at 200 ° C. for 2 hours.

The varnishes obtained in Example 1 and Comparative Examples 3 and 4 were coated on copper wire having a diameter of 1 mm to prepare enameled wires after heat treatment.

Physical properties of the enameled wire are shown in Table 1.

TABLE 1

As is apparent from Table 1, when the varnish having reduced average molecular weight of the resin was used to increase the water content in the varnish (Comparative Example 4), the physical properties of the enameled wire were compared with those of Comparative Example 3 in the heat cutting and abrasion resistance. Worse than that.

On the other hand, the varnish according to the present invention using a thermal addition including one or more aromatic rings in the molecule or a monohydric alcohol containing one or more aromatic rings in the molecule 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 of Comparative Example 3.

Claims (1)

One or more monohydric alcohols comprising at least one or more tri- or higher polyhydric alcohols and tri- or higher polybasic acids, one or more dihydric alcohols, one or more aromatic rings in one or more dibasic acid molecules, And an electrically insulating resin composition comprising a resin obtained by reacting one or more compounds capable of containing or forming one or more 5-membered imide rings.