JP2000226430A - Preparation of epoxy resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation process of epoxy resins which excludes hand operations for handling novolak resins, generates no dust, stabilizes the quality of epoxy resins and is easily applied to preparations of various epoxy resins having different physical properties. SOLUTION: In a preparation process, a phenol is allowed to react with an aldehyde to obtain a novolak resin which is then stored at a melt state under an inert gas atmosphere. Subsequently, the novolak resin and epihalohydrin are subjected to an epoxidation reaction. Here, multiple novolak resins having different softening points are separately stored at melt states and are mixed when required to react with epihalohydrin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a novolak type epoxy resin used as a sealing material in the electric and electronic industries.

[0002]

2. Description of the Related Art In the production of an ordinary o-cresol novolak type epoxy resin, first, o-cresol novolak resin as an intermediate raw material is produced by reacting o-cresol with formalin, and then the o-cresol novolak resin is converted to epichlorohydrin. The epoxidation reaction tank is charged with a solvent together with a solvent if necessary.
A major factor that determines the physical properties or quality of the epoxy resin thus produced is the molecular structure (particularly, skeleton structure) of the novolak resin.

[0003] Whether or not a novolak resin has a desired molecular structure is usually controlled by measuring a softening point.
That is, by performing an epoxidation reaction using a novolak resin having a specific softening point, an epoxy resin having a target molecular structure or physical properties (softening point or the like) can be produced. Therefore, in order to produce an epoxy resin suitable for the intended use, it is necessary to prepare a novolak resin having a predetermined softening point.

[0004]

In the conventional novolak resin production process, the novolak resin produced in the reaction tank may be deteriorated in quality, so that the novolak resin is once cooled and solidified to form a flake-like solid. This was put in an appropriate container and stored, and a predetermined amount thereof was put into a reaction tank during the production of the epoxy resin.

However, since the work of putting the novolak resin into a container or taking out a predetermined amount from the container and putting it into the reaction tank is almost a manual operation relying on humans, the dust of the novolak resin generated in those operations is reduced. There was a possibility that the working environment was deteriorated.

Further, there is another problem that the epoxy resin is colored and the hue of the epoxy resin is difficult to stabilize. Especially when storing novolak resin under high temperature conditions such as in the summer,
Oxidation degradation occurs, and the coloring of the epoxy resin becomes remarkable. In addition, quality deterioration such as an increase in epoxy equivalent and a change in softening point is caused.

The inventors of the present invention have conducted intensive studies to solve such problems, and as a result, by storing the obtained novolak resin in a molten state under an inert gas atmosphere, the quality of the novolak resin does not deteriorate. The inventor has found that the workability and the work environment can be improved because the work can be handled in-line, and the present invention has been completed.

[0008] That is, a main object of the present invention is to provide a method for producing an epoxy resin in which no manual operation is required when handling a novolak resin, dust is not generated, and the quality of the epoxy resin is stable. Another object of the present invention is to provide a method for producing an epoxy resin which can easily produce an epoxy resin having desired physical properties.

[0009]

In order to solve the above-mentioned problems, a method for producing an epoxy resin according to the present invention comprises reacting a phenol with an aldehyde to obtain a novolak resin, and converting the obtained novolak resin into an inert gas. It is stored in a molten state under an atmosphere, and then the stored novolak resin is introduced into an epoxidation reaction tank and reacted with epihalohydrin.

According to the present invention, the novolak resin, which is an intermediate material, is stored in a molten state without being taken out to the outside as a flaky solid as in the prior art. It becomes possible to supply. This eliminates the need for manual operations such as transportation and introduction of the novolak resin, and eliminates the generation of dust, and also suppresses the deterioration of the epoxy resin quality due to the exposure of the novolak resin to air at high temperatures.

In the present invention, a plurality of novolak resins having different softening points are preferably stored separately in a molten state. This makes it possible to easily cope with the case where various epoxy resins having different physical properties such as softening points are produced. Further, in the present invention, a plurality of novolak resins which are stored in a molten state and have different softening points may be mixed to cause an epoxidation reaction with epihalohydrin.

The reason why the novolak resin is divided by the softening point is that the softening point serves as an index indicating the molecular structure of the novolak resin, such as the molecular weight and the molecular weight distribution, as described above. Therefore, instead of the softening point, a viscosity or a melting point which is an index similar to the softening point may be used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production method of the present invention mainly comprises a novolak production step, a novolak storage step and an epoxidation reaction step. In the novolak production process, a phenol and an acid catalyst are charged into a reaction vessel, and an aldehyde is dropped while heating and stirring at a predetermined temperature to cause a polymerization reaction. After completion of the reaction, a treatment such as neutralization is performed, and the mixture is further heated under normal pressure or reduced pressure to remove water and unreacted substances.
Obtain novolak resin.

Examples of phenols include phenol, o-cresol, m-cresol, p-cresol, resorcinol, brominated phenol, brominated cresol, brominated resorcinol, naphthol and the like. Examples of the acid catalyst include p-toluenesulfonic acid,
Oxalic acid, sulfuric acid, hydrochloric acid and the like. Examples of the aldehydes include formaldehyde, acetaldehyde,
Butyraldehyde, benzaldehyde and the like.

The novolak resin obtained usually has a degree of polymerization of 2
~ 20. The molecular structure [skeleton structure such as average molecular weight (degree of polycondensation), molecular weight distribution, bond form, etc.] of the produced novolak resin includes the molar ratio of aldehydes / phenols charged, the dropping rate of aldehydes, reaction time, and reaction temperature. It can be controlled by adjusting the reaction conditions such as the amount of the catalyst and the amount of the catalyst. The charged molar ratio of aldehydes / phenols is usually selected from the range of 0.4 to 0.9.

As an index indicating the molecular structure of the novolak resin, a softening point is generally used, and various novolak resins having a softening point usually in the range of room temperature to 200 ° C. can be obtained by adjusting the above production conditions. Can be manufactured. The obtained novolak resin may be stored in a molten state as it is in the reaction tank in which the novolak resin is manufactured, or may be stored in a molten state in another storage tank. When various novolak resins having different softening points are produced, each novolak resin is separately stored in a different storage tank depending on the softening point.

In the present invention, the novolak resin is deteriorated in quality when it comes into contact with oxygen, and the storage of the molten novolak resin is performed in an inert gas atmosphere. The inert gas is not particularly limited as long as it is inert to the molten novolak resin, and examples include nitrogen gas, helium gas, and hydrogen gas, but from the viewpoint of economy and ease of handling, Usually, nitrogen gas is used. The oxygen concentration in the inert gas is usually about 1000 ppm or less, preferably about 500 ppm or less, more preferably about 250 ppm or less.

When nitrogen gas is used, it is not particularly purified but general industrial nitrogen can be used.
Usually, the oxygen concentration in this nitrogen gas is about 1000 ppm or less. To store the molten novolak resin, the inside of the tank is replaced with an inert gas, and then the molten novolak resin is charged. Prevent and store.

The storage tank is provided with a suitable heating means for storing the novolak resin in a molten state. At that time, if the heating temperature is too low, it becomes difficult to maintain an appropriate fluidized state. On the other hand, if stored at an unnecessarily high temperature, there is a possibility that quality degradation may occur due to cleavage or rearrangement of chemical bonds of the novolak resin. Therefore, it is preferable to store at the lowest temperature that gives a suitable flow state, and usually about 2 to less than the softening point of the novolak resin.
Suitably the temperature is 0-60 ° C, preferably about 20-40 ° C higher. The pH of the novolak resin during storage
Is also related to quality degradation, so in general, p
Preferably, H is adjusted to be in the range of 6 to 9 and stored.

Further, each storage tank is preferably provided with a stirrer or a circulator for circulating in the tank to keep the novolak resin in a fluidized state. The circulation device is, for example, a device that extracts contents from the bottom of a storage tank, sends the contents to the top of the tank by a circulation pump, and returns the contents to the inside of the tank again.

It is preferable that the storage period of the novolak resin is short, and it is generally preferable that the storage period be within one week. For example, an o-cresol novolak resin having a softening point of about 90 ° C.
When stored at 20 ° C., no significant change in physical properties is observed in about one week. In order to carry out the epoxidation reaction in the next step, a novolak resin having a desired softening point is extracted from each storage tank and dissolved in an organic solvent together with epihalohydrin.

Examples of the epihalohydrin include, for example, epichlorohydrin, epibromohydrin and the like. Epihalohydrin is used in a range of 2 to 15 moles per mole of the phenolic hydroxyl group of the novolak resin. Also,
Examples of the organic solvent include ketones such as methyl ethyl ketone and methyl isobutyl ketone, hydrocarbons such as toluene and xylene, alcohols such as methanol and ethanol, cellosolves such as methyl cellosolve and ethyl cellosolve, dioxane, and diethoxyethane. Ethers,
Dimethyl sulfoxide, dimethylformamide and the like can be mentioned.

The epoxidation reaction is carried out according to a conventional method using the solution mixed and dissolved as described above. That is, it is 0.1 to the phenolic hydroxyl group of the novolak resin.
A reaction is carried out by gradually adding 9 to 1.1 equivalents of an aqueous caustic solution at a temperature of 30 to 100 ° C. under normal pressure or reduced pressure. At that time, it is preferable to carry out azeotropic dehydration for the purpose of controlling water in the system.

Examples of the caustic alkali include potassium hydroxide, sodium hydroxide and the like.
It is added in the form of an aqueous solution of 0 to 55% by weight. The epoxidation reaction described above may be performed in one stage, or may be performed in two stages. After completion of the reaction, excess epihalohydrin and the solvent are recovered, and the generated salts and the like are removed to obtain an epoxy resin.

In order to produce an epoxy resin having a desired softening point, viscosity, molecular weight distribution, etc., a novolak resin having a predetermined softening point is used as an intermediate raw material.
At that time, if a plurality of novolak resins having different softening points are stored in a molten state as described above, two or more of them may be mixed to prepare a novolak resin having a desired softening point. it can. For example a mixing weight ratio of novolak resin A having a softening point T _A and is W, and W parts by weight of the novolak resin A, was mixed with (1-W) parts by weight of the novolac resin B having a softening point T _B Softening point T _C
When 1 part by weight of the novolak resin C having the following formula is obtained, the relationship represented by the following formula is established. Therefore, the mixing amount W of the novolak resin A can be determined from this equation, and the mixing amount (1-W) of the novolak resin B can also be determined from this formula.

[0026]

(Equation 1) Usually, the difference in softening point between the plurality of novolak resins to be mixed is preferably about 30 ° C. or less. That is, if the softening point difference is about 30 ° C. or less, even if they are mixed and used as an intermediate material for producing an epoxy resin, the obtained epoxy resin uses a single novolak resin having the same softening point as the mixture. There is no significant difference in the softening point, viscosity, molecular weight distribution and other physical properties as compared with the case of the above.

As a criterion for mixing a plurality of novolak resins having different softening points, a blend coefficient represented by the following formula is suitably adopted. In order to obtain a novolak resin having a desired softening point, a blend coefficient of 10 or less is required. Preferably it is. The following formula shows a general formula when i pieces of novolak resins are mixed.

[0028]

(Equation 2) S _n: the softening point of the n-th novolak resin S _x: average softening point of the novolak resin (the same as the softening point T _C of the mixed novolac resin) V _n: the n-th novolac resin weight V _t: Total amount of novolak resin

The novolak resins to be mixed may have the same chemical structure (that is, the phenols and / or aldehydes used) or may have different chemical structures. .

[0030]

EXAMPLES Hereinafter, the method for producing the epoxy resin of the present invention will be described in detail with reference to Examples and Reference Examples.

Example 1 (Production and storage of novolak resin) o-cresol 1
67.6 parts by weight of 37% formalin was added to 00 parts by weight, and a reaction was carried out at 103 ° C. for 6 hours using 1.2 parts by weight of p-toluenesulfonic acid as a catalyst. After neutralization with sodium hydroxide, 49.2 parts by weight of water was charged, water-soluble impurities were removed by liquid separation, and the mixture was further concentrated under reduced pressure at 155 ° C.
The softening point of the obtained o-cresol novolak resin is 12
5.6 ° C. Hereinafter, the o-cresol novolak resin is referred to as Sample A. Sample A was placed in a storage tank equipped with a stirrer and a bottoming circulation pump, and stored in a molten state at 160 ° C. under a nitrogen gas (industrial, the same applies hereinafter) atmosphere.

Example 2 (Production and storage of novolak resin) o-cresol 1
61.5 parts by weight of 37% formalin was added to 00 parts by weight, and the mixture was reacted at 103 ° C. for 5 hours using 1.2 parts by weight of p-toluenesulfonic acid as a catalyst. After neutralization with sodium hydroxide, 49 parts by weight of water was charged, water-soluble impurities were removed by liquid separation, and the mixture was further concentrated under reduced pressure at 160 ° C. The softening point of the obtained o-cresol novolak resin is 104.
5 ° C. Hereinafter, the o-cresol novolak resin is referred to as Sample B. Sample B was placed in a storage tank equipped with a stirrer and a bottoming circulation pump, and stored in a molten state at 140 ° C. under a nitrogen gas atmosphere.

Example 3 (Production and storage of novolak resin) o-cresol 1
56.9 parts by weight of 37% formalin was added to 00 parts by weight, and the mixture was reacted at 103 ° C. for 4 hours using 0.7 parts by weight of p-toluenesulfonic acid as a catalyst. After neutralization with sodium hydroxide, 46.8 parts by weight of water was charged, water-soluble impurities were removed by liquid separation, and the mixture was further concentrated under reduced pressure at 160 ° C.
The resulting o-cresol novolak resin has a softening point of 8
9.3 ° C. Hereinafter, the o-cresol novolak resin is referred to as Sample C. Sample C was placed in a storage tank equipped with a stirrer and a bottoming circulation pump, and stored in a molten state at 130 ° C. under a nitrogen gas atmosphere.

Reference Example 1 (Production and storage of novolak resin) o-cresol 1
62 parts by weight of 37% formalin were charged with respect to 00 parts by weight, and reacted at 103 ° C. for 5 hours using 1.2 parts by weight of p-toluenesulfonic acid as a catalyst. After neutralization with sodium hydroxide, 49.0 parts by weight of water was charged, water-soluble impurities were removed by liquid separation, and the mixture was further concentrated under reduced pressure at 160 ° C. The softening point of the obtained o-cresol novolak resin was 109.
7 ° C. Hereinafter, the o-cresol novolak resin is referred to as sample REF1. Sample REF1 was rolled, cooled and stored in containers in flake form.

Reference Example 2 (Production and storage of novolak resin) o-cresol 1
60.5 parts by weight of 37% formalin was charged with respect to 00 parts by weight, and reacted at 103 ° C. for 5 hours using 1.2 parts by weight of p-toluenesulfonic acid as a catalyst. After neutralization with sodium hydroxide, 49.0 parts by weight of water was charged, water-soluble impurities were removed by liquid separation, and the mixture was further concentrated under reduced pressure at 160 ° C.
The softening point of the obtained o-cresol novolak resin is 9
9.3 ° C. Hereinafter, the o-cresol novolak resin is referred to as sample REF2. Sample REF2 was rolled and cooled and stored in flake form in a container.

Reference Examples 3 and 4 (Storage test of molten novolak resin) The molten novolak resin obtained in the same manner as in Example 2 was stirred in a molten state at 125 ° C. for 7 days under a nitrogen gas atmosphere and an air atmosphere. Stored. As a result, the molten novolak resin stored under an air atmosphere was markedly colored. Hue is Gardner No. Were 1 (stored in a nitrogen gas atmosphere) and 7 (stored in an air atmosphere), respectively.

Example 4 (Production of epoxy resin) Softening point after mixing is 109.7 ° C.
The weight ratio of the samples A and B is set to 0.24.
6: 0.754 (the aforementioned blend coefficient was 7.14). Epichlorohydrin 5 was added to 100 parts by weight of o-cresol novolak resin obtained by mixing them.
39.6 parts by weight and 188.8 parts by weight of 1,4-dioxane were charged, and 19.4 parts by weight of a 48% aqueous potassium hydroxide solution was added dropwise at 60 ° C. under reduced pressure at 39 ° C. over 1 hour. For 3.5 hours. During this time, the distillate was subjected to removal of the aqueous phase in a separating pot, and the oil phase was returned to the system.
Then, the inside of the system was adjusted to 150 torr and 60 ° C., and 53.5 parts by weight of 48% sodium hydroxide was added dropwise over 3.5 hours. During this time, the distilled water was removed.

After completion of the reaction, excess epichlorohydrin,
1,4-Dioxane was distilled off, methyl isobutyl ketone was added to the residue, and by-product sodium chloride was removed by washing with water and filtration. Finally, methyl isobutyl ketone was distilled off to obtain an o-cresol novolak resin type epoxy resin.

Example 5 (Production of epoxy resin) The above samples B and C were mixed in a weight ratio of 0.658 so that the softening point after mixing was 99.3 ° C.
An o-cresol novolak type epoxy resin was obtained in the same manner as in Example 4, except that 100 parts by weight of the o-cresol novolak resin mixed at a ratio of 0.342 was used. The blend coefficient between Samples B and C is 6.89.

Comparative Example 1 (Production of epoxy resin) 539.6 parts by weight of epichlorohydrin and 188.8 parts by weight of 1,4-dioxane per 100 parts by weight of sample REF1 having a softening point of 109.7 ° C.
19.4 parts by weight of a 48% aqueous potassium hydroxide solution was added dropwise at 39 ° C. over 1 hour under reduced pressure of 60 torr, and the mixture was aged for 3.5 hours under the same conditions. During this time, the distillate was subjected to removal of the aqueous phase in a separating pot, and the oil phase was returned to the system.
Then, the system was adjusted to 150 torr and 60 ° C., and 53.5 parts by weight of 48% sodium hydroxide was added dropwise over 3.5 hours. During this time, the distilled water was removed.

After completion of the reaction, excess epichlorohydrin,
1,4-Dioxane was distilled off, methyl isobutyl ketone was added to the residue, and by-product sodium chloride was removed by washing with water and filtration. Finally, methyl isobutyl ketone was distilled off to obtain an o-cresol novolak type epoxy resin.

Comparative Example 2 (Production of Epoxy Resin) An o-cresol novolac type was prepared in the same manner as in Comparative Example 1 except that 100 parts by weight of sample REF2 having a softening point of 99.3 ° C. was used instead of sample REF1. An epoxy resin was obtained. The softening point, kinematic viscosity and gel permeation chromatography dispersion ratio (hereinafter referred to as GPC dispersion ratio) of each epoxy resin obtained in Examples 4 and 5 and Comparative Examples 1 and 2 were measured. Table 1 shows the results.

The softening point, kinematic viscosity and GPC dispersion ratio of the epoxy resin were measured by the following methods. (1) Softening point Automatic softening point measuring device (EX-8 manufactured by ELEC Kagaku Co., Ltd.)
20) was measured by the ball and ring method.

(2) Kinematic Viscosity A 1,4-dioxane solution containing 50% by weight of a sample was prepared and a Cannon-Fenske viscometer (No. 200, 300) was prepared.
Was used to measure the viscosity at 25 ° C. (3) GPC Dispersion Ratio The sample was dissolved in tetrahydrofuran, and the GPC dispersion ratio was determined using tetrahydrofuran as a carrier liquid and Plegel-MIXED-E (trade name, manufactured by Polymer Laboratory) as a column (two).

[0045]

[Table 1]

From Table 1, it can be seen that, in Example 4, in which Samples A and B were mixed so as to have the same softening point as Sample REF1 used as a starting material in Comparative Example 1, the softening point and dynamic Comparative example 1 having almost the same viscosity and GPC dispersion ratio
Are found to be the same as those values. The same applies to Example 5 and Comparative Example 2.

Accordingly, it can be understood that a desired epoxy resin can be easily produced by mixing a plurality of novolak resins having different softening points in a molten state as described above and using them as a raw material for producing an epoxy resin.

Example 6 (Production of epoxy resin) Example 3 was repeated except that the amount of 37% formalin was changed to 58.7 parts by weight.
To produce o-cresol novolak resin in the same manner as
A novolak resin having a pH of 6.7 and a softening point of 96.7 ° C. was obtained. A part of the obtained novolak resin was put in a container controlled at 120 ° C. under a nitrogen gas atmosphere, melted and stored under stirring for 18 days, and then an epoxy resin was produced in the same manner as in Example 4.

The pH of the novolak resin was measured as follows. <Method for measuring pH of novolak resin> A resin sample (2 g) was dissolved in chloroform (40 g), pure water (40 g) was added, and the mixture was sufficiently mixed. The mixture was allowed to stand and separated, and the pH of the aqueous layer was measured with a pH meter.

Comparative Example 3 (Production of Epoxy Resin) The remainder of the novolak resin obtained in Example 6 was poured into a vat and solidified by cooling. Then, after being stored in a cold and dark place having an average temperature of 15 ° C. for 18 days in the same manner as in Example 6 under contact with the atmosphere, an epoxy resin was produced in the same manner as in Example 4.

Comparative Example 4 (Production of Epoxy Resin) The procedure of Comparative Example 3 was repeated except that the cooled and solidified novolak resin was stored for 14 days in an air-circulating thermostat set at a temperature of 50 ° C. To produce an epoxy resin.

The epoxy equivalents, softening points and hues of the epoxy resins obtained in Example 6 and Comparative Examples 3 and 4 were measured. The epoxy equivalent was measured as follows. <Measurement method of epoxy equivalent> A dioxane solution of 0.1N-hydrochloric acid was added to the sample, and the mixture was reacted with stirring for 15 minutes. This was subjected to potentiometric titration with a methanol solution of 0.1 N sodium hydroxide, the equivalent of the epoxy group reacted with hydrochloric acid was determined from the difference from the titer of the blank, and the value obtained by dividing the sample amount by this was used as the epoxy equivalent (g). / Eq).

The softening point was measured in the same manner as described above. Hue is Gardner No. Was evaluated. Table 2 shows the test results.

[Table 2]

From Table 2, it can be seen that the novolak resin stored in the solid state has an increased epoxy equivalent when stored under contact with air and under conditions where the storage temperature may rise, such as in summer (Comparative Example 4). It can be seen that oxidation deterioration such as lowering of the softening point and coloring of the epoxy resin is caused to significantly lower the quality of the epoxy resin. On the other hand, it can be seen that Example 6 in which the sample was melted and stored at 120 ° C. hardly caused the above-described deterioration.

Examples 7 and 8 In Example 3, except that the pH of the novolak resin was adjusted to 8 by neutralization with sodium hydroxide,
An o-cresol novolak resin was produced in the same manner as in Example 3. This novolak resin was placed in a nitrogen gas atmosphere,
The mixture was melted and stored at a temperature of 20 ° C. or 150 ° C. with stirring, and the change with time was examined on the 10th and 20th days. Table 3 shows the results.

[0056]

[Table 3]

As is clear from Table 3, the novolak resin stored under any of the temperature conditions of 120 ° C. and 150 ° C. has an abnormal softening point as compared with that immediately after production (storage period 0 days). Was not found.

Next, an epoxy resin was produced in the same manner as in Example 4 using each of the novolak resins stored at the above-mentioned temperatures of 120 ° C. and 150 ° C. for 10 days and 20 days. Further, as a blank, an epoxy resin was manufactured using a novolak resin immediately after the manufacture. About each obtained epoxy resin, the epoxy equivalent and the softening point were measured similarly to the above. Table 4 shows the results.

[0059]

[Table 4]

From Tables 3 and 4, it can be seen that the pH of the novolak resin to be stored is adjusted to about 6 to 9 in order to increase the thermal stability during storage of the novolak resin and to produce an epoxy resin of almost the same quality as the blank. The storage temperature is about 20 to 60 ° C, preferably about 20 to 40 ° C, from the softening point of the novolak resin.
It can be seen that a higher temperature is suitable.

[0061]

According to the present invention, the novolak resin, which is an intermediate material, is stored in a molten state, not in a solid state as in the prior art, and can be supplied to the epoxidation reaction in-line. In addition to improving the working environment, the production efficiency is improved and the production cost is reduced, and quality deterioration such as coloring of the epoxy resin caused by exposure of the solid novolak resin to air at high temperatures is also eliminated. There is an effect that it can be suppressed.

When a plurality of novolak resins having different softening points are separately stored in a molten state, it is possible to easily cope with the production of various epoxy resins having different physical properties by mixing them. it can.

Claims (8)

[Claims] A phenol and an aldehyde are reacted to obtain a novolak resin, the obtained novolak resin is stored in a molten state under an inert gas atmosphere, and the stored novolak resin is introduced into an epoxidation reaction tank. And reacting with an epihalohydrin. 2. The method according to claim 1, wherein the novolak resin is stored in a storage tank. 3. The method according to claim 1, wherein a plurality of novolak resins having different softening points are separately stored in a molten state. 4. The method for producing an epoxy resin according to claim 1, wherein a plurality of novolak resins having different softening points stored in a molten state are mixed and reacted with epihalohydrin. 5. An oxygen concentration in an inert gas atmosphere of about 100.
The method for producing an epoxy resin according to any one of claims 1 to 4, wherein the amount is 0 ppm or less. 6. The method for producing an epoxy resin according to claim 1, wherein the novolak resin is adjusted to pH 6 to 9 and stored. 7. The method for producing an epoxy resin according to claim 1, wherein the novolak resin is stored at a temperature 20 to 60 ° C. higher than the softening point of the novolak resin. 8. The method according to claim 1, wherein the phenol is o-cresol and the aldehyde is formaldehyde.