JPH03103417A - Production of self-curing phenolic resin - Google Patents

Abstract

PURPOSE:To obtain the subject resin, excellent in metallic mold releasability and blocking resistance and suitable as a binder with hardly any unreacted substances without causing clouding of metallic molds in molding by reacting a phenol novolak resin with aldehydes in the presence of a basic catalyst. CONSTITUTION:The objective resin obtained by reacting a phenol novolak resin (preferably with <=10wt.% content of unreacted phenols) with aldehydes (e.g. formaldehyde) in the presence of a basic catalyst [e.g. oxide, hydroxide or carbonate of an alkali (earth) metal, ammonia or amines].

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a self-curing phenolic resin, and more particularly to a method for producing a phenolic resin used as a material for metal insert molded products in the field of electrical parts. The present invention relates to a method for producing a solid self-curing phenolic resin suitable as a binder for shaped materials.

[Conventional technology]

In general, phenolic resin molding materials contain a novolak type phenolic resin and hexamethylenetetramine (hereinafter abbreviated as hexamine) as a curing agent, a curing aid, a filler,
It is manufactured by roll-kneading it with colorants, mold release agents, etc., and then granulating or crushing it.

However, when such phenolic resin molding materials that use hexamine as a curing agent are molded in a mold heated to a high temperature such as 180-170°C, ammonia gas is generated due to the decomposition of hexamine, resulting in the production of ammonia gas. Part of it remains in the molded product along with undecomposed hexamine. This ammonia gas causes corrosion of metals inserted into the molded product or metals used adjacently, making it impossible to use the molded product for a long period of time. In particular, if the shaped part is of a closed type or is used under harsh conditions such as high temperature and high humidity, the corrosion caused by the ammonia gas described above becomes even more severe.

In order to solve these problems, we developed a self-curing solid pengylic ether type phenolic resin (hereinafter referred to as BE).
A phenolic resin molding material, which is mainly composed of phenolic resin (abbreviated as "resin") and uses a phenolic resin as a binder, has been developed and is now widely used.

The BE resins disclosed in these publications contain phenols and formaldehyde in a molar ratio of 1:1.5 to 2.0 or 1:1.0 to 3.0 in the presence of a divalent metal salt.
It reacts at a rate of

[Problem to be solved by the invention]

In electrical parts molded with metal inserts using a phenolic resin molding material with BE resin having the above structure as a binder, the conventional problem of corrosion of the metal inserts due to ammonia gas has been solved, but these BE resins Resins and phenolic resin molding materials using them have the following problems.

1. Mold fogging is likely to occur during continuous molding, and no ammonia-free material using conventional BE resin has yet completely solved this mold fogging problem.

2. Due to the high content of methylol groups and dimethylol groups in the bonding structure, the releasability of the material when rolls are mixed together and the mold releasability of hollow-shaped products during molding are poor, and improvements in this point are desired. .

3. It has a lower melting point than general novolac-type phenolic resins, and is difficult to handle because it easily blocks, especially in the summer.

The present invention was made in view of the problems of the prior art described above, and its purpose is to provide a method for producing a self-curing phenolic resin that can solve all of these problems.

[Means to solve the problem]

As a result of various studies in view of the problems of the prior art described above, the present inventors have discovered that a self-curing phenol resin obtained by reacting aldehydes with a phenol novolac resin in the presence of a basic catalyst solves all of the above problems. Find out what you can do,
This led to the present invention.

First, it has become clear that the degree of mold fogging is most influenced by gaseous components, especially phenols and formaldehyde, generated during heat molding from molding materials.If the generated phenols and formaldehyde are reduced,
It was found that the occurrence of mold fogging was significantly improved.

In order to reduce the amount of these generated, unreacted phenols and unreacted formaldehyde contained in the phenol resin can be reduced. In addition, it has become clear that the curability of molding materials is greatly influenced by unreacted phenols in the phenolic resin and can be significantly improved by reducing this. The present invention relates to a method for producing a self-curing phenol resin that has improved the above-mentioned drawbacks and contains less unreacted phenols and unreacted formaldehyde.

The present invention will be explained in more detail below.

As is well known, the phenol novolak resin used in the present invention contains phenols and formaldehyde for 1 mole of phenols and 1 mol of formaldehyde.
It is a brittle resin with a softening point of 60 to 150°C obtained by reaction and dehydration in an acidic environment with a pH of 4 or less.

The content of unreacted phenols in the phenol novolak resin is preferably 10% by weight or less.

If it is present in an amount greater than 10% by weight, the physical properties will also deteriorate, which is not preferable.

Examples of the phenols used include phenol, o-, m-, p-cresol, or mixtures thereof;
Examples include xylenols, -bisphenol A1-substituted alkylphenol, resorcinol, and mixtures thereof.

Catalysts include sulfuric acid, hydrochloric acid, para-toluenesulfonic acid, phosphoric acid,
An acidic catalyst such as oxalic acid is used.

Examples of aldehydes used in the present invention include formaldehyde and paraformaldehyde, of which formaldehyde is representative (formaldehyde will be described below as a representative example).

The reaction ratio of the phenol novolak resin and formaldehyde of the present invention is 100ffi of the phenol novolak resin.
3 to 100 as formaldehyde to ffl part
It is necessary to set the amount in parts by weight, preferably 5 to 50 parts by weight.

If the amount of formaldehyde is less than 3 parts by weight, the curing speed of the resulting resin will be slow, and the strength and heat resistance of the molded product will be reduced.

On the other hand, if the amount of formaldehyde exceeds 100 parts by weight, the amount of gas generated during curing increases, which is undesirable.

Next, as the basic catalyst used in the present invention, alkali and alkaline earth oxides, hydroxides, carbonates, ammonia, amines, hexamine, divalent metal salts, etc. are used.

The reaction between phenol novolac and formaldehyde is
A temperature of 50 to 110°C is desirable; if the reaction temperature is below 50°C, the viscosity within the system will be high, and if it is above 110°C, the reaction will be rapid and it will be difficult to produce a stable product.

The reaction time varies depending on the amount of formaldehyde and the type and amount of the catalyst used, but is usually 30 minutes to 5 hours.

After the condensation reaction is completed, the reaction product is dehydrated under reduced pressure at a temperature of 120°C or lower, and when the resulting resin reaches the desired hot plate gel time at a measurement temperature of 150°C, the reduced pressure dehydration is completed and the resulting resin is taken out from the reaction vessel. A desired resin can be obtained by cooling.

According to the method of the present invention, the content of unreacted phenols and formaldehyde in the self-curing phenolic resin can be reduced to 0.10% by weight or less, and almost zero if suitable conditions are selected. It is effective in preventing mold fogging.

〔Example〕

Examples of the present invention will be described below, but it goes without saying that the technical scope of the present invention is not limited to these examples.

Example 1 l. Synthesis of Phenol Novolak 1000 g of phenol, 890 g of 37% formalin, and 10 g of oxalic acid are added to a 3 g Sevarapuru flask equipped with a stirrer, a reflux condenser, and a thermometer, and the temperature is gradually raised.

After refluxing for 4 hours, the distillate was distilled off by heating at room temperature to 150°C.
rr until there was no distillate left.

A phenol novolak resin (A) having a softening point of 90° C. and 2.1% by weight of unreacted phenol was obtained.

2. A mixture of self-curing phenolic resins or phenolic novolak resin (A) is cooled to 95°C,
Add 270g of 37% formalin and stir to mix evenly.
After further cooling to 65°C, 2g of magnesium oxide was added and reacted at 65°C for 2 hours. Then heated to 60 Tor
The mixture was dehydrated under reduced pressure to obtain a solid resin.

The hot plate gel time of the thus obtained resin at 150°C was 85 seconds, and the amount of unreacted phenol was 0. I
O weight%, unreacted formaldehyde 0.06% by weight
Met.

Example 2 The same procedure as in Example 1 was carried out except that 400 g of 37% formalin was used and the reaction was carried out at 65° C. for 3 hours.

The hot plate gel time of the thus obtained resin at 150°C was 38 seconds, and the amount of unreacted phenol was 0.0
The amount of unreacted formaldehyde was 0.43% by weight.

Example 3 The same procedure as in Example 1 was carried out, except that at the end of the phenol novolak resin synthesis, water vapor was blown into the resin to obtain a phenol novolak resin (B) containing 0.05% by weight of unreacted phenol.

The hot plate gel time of the thus obtained resin at 150'c was 83 seconds, there was no unreacted phenol amount, and the unreacted formaldehyde amount was 0.07%.

Examples 4 to 6 Synthesis of self-curing phenolic resin was carried out in the same manner as in Example 1 except that the reaction time, type and amount of catalyst were as shown in Table 1.

The evaluation results of the obtained resin are shown in Table 1.

Table 1 a 25% caustic soda, b barium hydroxide C
Calcium hydroxide comparative example 1 Into the same apparatus as in Example 1, 1000 g of phenol was added. 37
% formalin 1032. , 0.4 g of zinc acetate was added, and the reaction was carried out at reflux temperature for 6 hours. Then under reduced pressure 100
Dehydration was performed at Torr and a temperature of 100°C to obtain a solid resin.

The hot plate gel time of the thus obtained resin at 150°C was 94 seconds, and the amount of unreacted phenol was 4.2 seconds.
The amount of unreacted formaldehyde was 1.2% by weight.

〔Effect of the invention〕

As explained above, the self-curing phenolic resin obtained by the production method of the present invention has a lower amount of unreacted phenols and formaldehyde than conventionally known self-curing phenolic resins, so it has the following effects. is obtained.

1. Mold fogging does not occur during continuous molding.

2. Good mold releasability of molded products.

3. Excellent roll workability in the kneading process in molding material production.

4. Since it does not easily absorb moisture, it has excellent block resistance and good workability.

It goes without saying that the self-curing phenolic resin obtained by the method of the present invention can also be suitably used as a binder in various fields other than phenolic resin molding materials.

Claims (1)

[Claims] 1. A method for producing a self-curing phenol resin, which comprises reacting a phenol novolac resin with an aldehyde in the presence of a basic catalyst. 2. The method for producing a self-curing phenol resin according to claim 1, wherein the amount of unreacted phenols in the phenol novolac resin is 10% by weight or less.