JPH04236233A - Production of epoxy resin - Google Patents

Abstract

PURPOSE:To obtain the title resin having excellent heat resistance, fluidity and curing characteristics and useful as a molding material by subjecting phenols to aminomethylation, recovering unreacted phenol and epoxidating the reaction product containing a salt of aminomethylated phenols. CONSTITUTION:Phenols such as phenol are reacted with aldehydes such as formaldehyde and ammonium salt such as ammonium chloride to aminomethylate phenols and unreacted phenols are recovered without carrying out neutralization treatment and the reaction product containing a salt of aminomethylated phenols is epoxidated with epichlorohydrin, etc., to provide the objective resin.

Description

Description: FIELD OF INDUSTRIAL APPLICATION This invention relates to a method for producing epoxy resins and their uses. The epoxy resin according to the present invention generally exhibits a low viscosity liquid state at room temperature, and provides a cured product with excellent heat resistance, water resistance, and mechanical properties. It has a wide range of uses including matrix resins, adhesives, and coating materials. [Prior Art] In the FW method (filament winding method), a reinforcing fiber base material such as glass fiber or carbon fiber is impregnated with a thermosetting resin and wound around a mandrill, and after the resin is cured, the mandrel is This is a method of manufacturing FRP (fiber reinforced plastic), which is a composite material product, by extracting it. According to the FW method, properties such as strength and rigidity can be imparted by arranging fibers in any direction, so this method is particularly suitable for manufacturing high-strength FRP. Typical thermosetting resins used in the FW method include phenol resins and epoxy resins. When manufacturing high-strength FRP, a low-viscosity liquid resin is used that can be well impregnated into the fiber base material. [0003] There are the following problems in the production of FRP using resol and using phenolic resin as the matrix resin. That is, when the resol is cured, the cured product tends to foam, and the work efficiency is poor in preventing this, and methods using expensive catalysts have drawbacks in terms of cost and quality of the cured product. Furthermore, in low-viscosity resols, a large amount of unreacted phenol remains, resulting in poor curing properties. When reducing the viscosity of a high-viscosity resol by heating or using a solvent, there are problems such as shortened pot life and removal of the solvent. As described above, there has been no phenolic resin that can satisfy both the fluidity and curing properties required for the FW method. On the other hand, epoxy resins have excellent curing properties such as short curing time, and are widely used in various fields. Among epoxy resins, glycidyl ether of bisphenol A is particularly frequently used in the FW method. However, since the resulting cured product has a low glass transition temperature, it cannot be used in fields where heat resistance is required. [0005] In fields where heat resistance is required, polyfunctional epoxy resins made from phenol novolac, cresol novolac, etc., ie, epoxy novolac resins, are used, but they are viscous liquids at room temperature. or solid. In addition, epoxy resin compounds are produced by reacting single resol compounds, namely p-cresol dialcohol, o-cresol dialcohol, and cresol dinuclear dialcohol, with epichlorohydrin to epoxidize the phenolic hydroxyl groups. However, all of these are crystals or viscous liquids at room temperature, and are not suitable for manufacturing FRP. Further, the glass transition temperature of the cured product measured by the vibron method is 160° C. at most, and the heat resistance is not sufficient. Furthermore, simple aromatic amine compounds such as metaxylylene diamine, diaminenodiphenylmethane, and 5-amino-1-naphthol were reacted with epichlorohydrin to epoxidize the active hydrogen of the amino group. Epoxy resins are also well known, and these are liquids with low viscosity at room temperature, making them suitable for manufacturing FRP (Japanese Patent Publication No. 5
4-65798 and 59-78177)
. However, these epoxy resins are currently expensive because they are made from special amino compounds, and are not suitable for large-scale use. [0007] The present inventors have developed a method for producing epoxy resins using aminomethylated phenols as raw materials in order to solve the above-mentioned problems of epoxy resins and phenolic resins. I suggested it earlier. Epoxy resins using aminomethylated phenols are excellent in that they can simultaneously improve heat resistance, fluidity, and curing properties, and can be produced at relatively low cost. Furthermore, as a method for producing aminomethylated phenols, a method in which phenols, aldehydes, and ammonium salts are reacted is effective in suppressing side reactions such as polymerization, and is a method for producing low-viscosity epoxy resin raw materials. It was also proposed that it would be useful as a In this method, when phenol is selected as the phenol, formaldehyde is selected as the aldehyde, and ammonium chloride is selected as the ammonium salt, aminomethylated phenol is synthesized as follows. [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 2] By producing an acid addition salt of aminomethylated phenol as shown in formula (1) above, condensation of the addition products can be suppressed and polymerization can be achieved. It has the advantage of suppressing Next, when producing an epoxy resin using the aminomethylated phenol obtained by neutralization as a raw material as shown in formula (2),
Although the mixture in which unreacted phenols and the like remain can be used as is, in order to obtain an epoxy resin with excellent heat resistance, it is desirable to separate unreacted phenols. However, when unreacted phenols are recovered by means such as distillation after the neutralization reaction, the following condensation or deammonization reaction between aminomethylphenols occurs depending on the distillation conditions. [0012] Condensation reaction [Chemical formula 3] [Chemical formula 4] [0014] When these reactions occur, the viscosity of the resin after epoxidation increases, the crosslinking density decreases, and the heat resistance decreases. The downside was that it happened. The present invention solves the above-mentioned drawbacks in a method for producing an epoxy resin by aminomethylating phenols with aldehydes and ammonium salts, and then epoxidizing the resulting product, which has excellent heat resistance, fluidity, and curing properties. The aim is to obtain a relatively inexpensive epoxy resin. [Means for Solving the Problems] As a result of studies to achieve the above object, the present inventors found that when phenols are aminomethylated with aldehydes and ammonium salts, neutralization after aminomethylation is performed. The inventors have discovered that the above-mentioned condensation reactions and deammoniation reactions can be suppressed by recovering unreacted phenols without performing any treatment, and have completed the present invention. The gist of the present invention is: (1) a step of aminomethylating phenols in which phenols, aldehydes, and ammonium salts are reacted, (2) a step of recovering unreacted phenols without performing a neutralization treatment, and (2) A method for producing an epoxy resin, comprising the step of epoxidizing a reaction product containing a salt of an aminomethylated phenol. The present invention also provides a molding material using the epoxy resin obtained by the above method and a method for manufacturing FRP by the FW method. The present invention will be explained in detail below. According to the method of the present invention, epoxy resin is produced by reacting phenols, aldehydes, and ammonium salts to obtain salts of aminomethylated phenols, and then recovering unreacted phenols without neutralization. It can be obtained by converting Raw material phenols include phenol, cresol, xylenol, ethylphenol, phenylphenol, catechol, resorcinol, hydroquinone,
Compounds having at least one phenolic hydroxyl group such as naphthol and methylnaphthol can be used alone or in combination of two or more. In the following, phenol will be used as a representative of phenols. [0018] Examples of aldehydes include formaldehyde,
Aliphatic or aromatic aldehydes such as acetaldehyde and benzaldehyde, or aldehyde generating substances such as trioxane and paraformaldehyde can be used alone or in combination of two or more. In the following, formaldehyde will be used as a representative example of aldehydes. As formaldehyde, formalin, which is an aqueous solution thereof, can also be used. As the ammonium salt, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate, etc. are used. Alternatively, ammonia and an inorganic acid may be added during the reaction so that these ammonium salts are generated during the reaction. Hereinafter, ammonium chloride will be explained as a representative ammonium salt. The aminomethylation reaction in this method proceeds as shown in formula (1) above. By producing a salt of aminomethylated phenol in this way, it is possible to suppress condensation of addition products with each other and to suppress polymerization, compared to the case of aminomethylated phenol. The reaction conditions for aminomethylation are not particularly limited and are appropriately determined depending on the properties of the desired aminomethylated product. Typical reaction conditions will be explained below. The molar ratio of phenol and formaldehyde is preferably within the range of 0.5 to 5.0. If this molar ratio is less than 0.5, the reaction efficiency tends to decrease, and although a low viscosity resin can be obtained, the cured product may have a low glass transition temperature and insufficient heat resistance. be. On the other hand, if this molar ratio exceeds 5.0, the yield of the obtained liquid resin tends to decrease. The amount of ammonium salt used is preferably in the range of 1 to 10 (molar ratio) to formaldehyde. If the ammonium salt/formaldehyde molar ratio is less than 1, the resin viscosity tends to increase due to undesirable side reactions, while if it exceeds 10, the reaction efficiency decreases. Preferably, the ammonium salt is added as such. When added as an aqueous solution, the reaction efficiency decreases. The aminomethylation reaction is preferably carried out at a reaction temperature of 20 to 130°C and a reaction time of 0.1 to 10 hours. Although the reaction pressure is not particularly limited, it is usually carried out at normal pressure. If the reaction temperature is less than 20° C., the aminomethylation reaction will not proceed sufficiently, requiring a long reaction time, and the reaction efficiency will tend to decrease. On the other hand, 13
If the temperature exceeds 0°C, undesirable side reactions will proceed. The reaction time is preferably in the range of 0.1 to 10 hours. If the time is less than 0.1 hour, the aminomethylation reaction will not proceed sufficiently, and the reaction efficiency will tend to decrease. On the other hand, if the reaction time exceeds 10 hours, undesirable side reactions will proceed. The aminomethylation reaction produces acid addition salts of aminomethylated phenols as shown in the above chemical formula. For ammonium salts other than ammonium chloride, acid addition salts of aminomethylated phenols corresponding to the respective ammonium salts are produced by a similar reaction. Furthermore, when an aldehyde other than formaldehyde is used, a phenol containing an aminomethyl group having a substituent depending on the type of aldehyde can be obtained. [0022] An aqueous solvent is used as a reaction solvent during the aminomethylation reaction. The aqueous solvent may contain alcohol. When formalin is used as the aldehyde, there is no need to add it separately as long as the water contained therein is sufficient as a solvent. After the aminomethylation reaction is completed, it is desirable to add alcohol to the reaction product and leave it for a certain period of time. Addition of alcohol prevents undesirable side reactions. There are no particular restrictions on the type of alcohol to be added, but methanol, which can be easily separated from water by distillation, is preferred. Although the amount used is not limited, it is desirable that the entire amount of unreacted raw materials other than the reaction product and ammonium salt be dissolved. If alcohol is added, the alcohol is removed from the reaction product by distillation or the like after it is left for a certain period of time. Removal of alcohol prevents the condensation reaction from proceeding.
It is preferable to carry out by distillation under reduced pressure. There is no particular restriction on the degree of pressure reduction, but in order to prevent side reactions, it is preferable to keep the pressure as low as possible and the distillation temperature. After distilling off the alcohol from the reaction product, a mixture containing unreacted phenol and a salt of aminomethylated phenol is obtained. Unreacted phenol is recovered from this mixture by distillation or the like. Although distillation conditions are not particularly limited, it is preferable to carry out the distillation under reduced pressure in order to prevent undesirable side reactions. The recovered unreacted phenols can be recycled and used again in the aminomethylation step. In the production of this salt of aminomethylated phenol, it is desirable to omit washing the oil phase with water. This suppresses the loss of the aminomethylated phenol salt due to elution into the aqueous phase, and furthermore, the decomposition of the aminomethyl group is suppressed by leaving the ammonium salt in the system. [0024] When the aminomethyl group decomposes, the crosslinking density of the resulting resin after epoxidation decreases, resulting in a disadvantage that the heat resistance decreases. Using the salt of aminomethylated phenol obtained as described above after recovering unreacted phenol as a starting material, this was reacted with epihalohydrin in the presence of an alkali metal hydroxide by a conventional method to obtain aminomethylated phenol. Part or all of the phenolic hydroxyl group and N-aminomethyl group are epoxidized to obtain a low-viscosity liquid epoxy resin. Epoxidation proceeds via addition of epihalohydrin and dehydrohalogenation with an alkali metal hydroxide. This epoxidation proceeds without any problem even if the aminomethylated phenol is in the form of a salt. As the epihalohydrin, epichlorohydrin, epibromohydrin, β-methylepichlorohydrin, etc. can be used. The amount of epihalohydrin used is the weight ratio to the raw material aminomethylated product.2.
It is 0 to 30 times, preferably 3.0 to 25 times. As the alkali metal hydroxide, sodium hydroxide, potassium hydroxide, etc. can be used. The amount of alkali metal hydroxide used is 0.5 in weight ratio to the raw material aminomethylated product.
A range of 3.0 times to 3.0 times, preferably 0.8 to 2.5 times, particularly preferably approximately equimolar amounts is suitable. The alkali metal hydroxide is preferably added to the reaction system as a concentrated aqueous solution or in the form of granules, which are added little by little. If a large amount is added at once, addition polymerization reaction tends to occur locally. This epoxidation reaction can be carried out in one step, but it can also be carried out in two steps: an addition reaction and a dehydrohalogenation reaction (ring-closing reaction). In the case of a two-step reaction, the addition reaction of epihalohydrin to hydroxyl and amino groups is carried out at 40 to 150 °C in the presence of a phase transfer catalyst.
, preferably at a temperature range of 50 to 120°C for 1 to 50 hours. The dehydrohalogenation reaction from the addition reaction product is carried out at a temperature of 40 to 150°C, preferably 50 to 150°C.
It is preferable to conduct the treatment at a temperature range of 100° C. for 2 to 50 hours. It is preferable to carry out the reaction while removing water by-product from the reaction from the reaction system by azeotroping with the epihalohydrin. Also, in order to prevent polymerization, the reaction is carried out under reduced pressure to lower the azeotropic temperature. It is preferable to lower it. After completion of the epoxidation reaction, the epoxy resin product is recovered from the reaction mixture. The resin can be recovered, for example, by recovering epihalohydrin from the resin solution by distillation, and then by solvent extraction to separate the solvent-soluble epoxy resin of the present invention from the alkali metal salt and the solvent-insoluble resin. The solvent used for this solvent extraction is preferably an aromatic hydrocarbon solvent such as benzene, toluene, or xylene, or a ketone solvent such as acetone, methyl ethyl ketone, or methyl isobutyl ketone. The amount of solvent used is not particularly limited as long as it is sufficient to extract the low viscosity liquid epoxy resin. The target low-viscosity liquid epoxy resin can be isolated by separating the solvent from the obtained extract by distillation. The low-viscosity liquid epoxy resin of the present invention obtained by the above-mentioned method contains an N-glycidylaminoalkyl group in addition to a glycidyl ether group on the benzene ring, and a part of the resin contains a dialkyleneamino group or a trialkyleneamino group. It has a structure crosslinked by groups. For example, when formaldehyde and ammonium chloride are used for aminomethylation of phenol, the resulting epoxy resin contains N-diglycidylaminomethyl, dimethyleneglycidylamino, and trimethyleneamino groups in addition to glycidyl ether groups. It is believed to consist of a mixture of various mononuclear or polynuclear epoxy compounds having at least one amino-containing group, such as a radical. Examples of epoxy compounds with such structures are shown below. ##STR5## While the conventional epoxy resins derived from single resol compounds described above were solid or viscous liquid at room temperature, the epoxy resin of the present invention has a low viscosity at room temperature. It is obtained as a liquid resin. This is presumably because the epoxy resin of the present invention is a mixture of various components and has a low proportion of crosslinked structures. In particular, in the method of the present invention, since condensation of aminomethylated phenols is prevented during the recovery stage of unreacted phenol, an epoxy resin with less crosslinked structure and low viscosity can be obtained even after epoxidation. Moreover, since it does not contain epoxidized products of unreacted phenol, the resin has excellent heat resistance. The low-viscosity liquid epoxy resin of the present invention can be cured using conventionally used epoxy curing agents. Specific examples of usable curing agents include amine curing agents, polyaminoamide curing agents, acid and acid anhydride curing agents, and the like. Among these curing agents, aromatic amine curing agents are particularly preferred because the resulting cured product has a high glass transition temperature and provides a cured product with excellent heat resistance. The amount of curing agent used may be the same as for conventional epoxy resins based on the epoxy equivalent weight of the epoxy resin. It is believed that the curing of the epoxy resin of the present invention proceeds with the involvement of ring-opening polymerization of epoxy groups. In the curing of conventional resols, as mentioned above, there was a problem of foaming due to evaporation of water added to reduce viscosity and condensed water, but no foaming was observed in the cured product of the epoxy resin of the present invention. This is because the resin of the present invention does not contain water, and because the amount of free methylol groups is small due to the formation of aminomethyl groups, almost no condensation reaction occurs, and the amount of condensed water produced is also very small. It is assumed that this is the case. Since the epoxy resin of the present invention is in the form of a liquid with low viscosity, it has excellent moldability. Furthermore, the cured product of the epoxy resin of the present invention has excellent heat resistance, water resistance, and mechanical properties. This epoxy resin can be used alone for coating, adhesion, various molding applications, or as an encapsulation or substrate material for electronic components. In addition, by taking advantage of its low viscosity liquid property, it can be advantageously used as a matrix resin for composite materials, and is suitable, for example, for manufacturing FRP by blending reinforcing fibers. It is particularly suitable as a matrix resin when manufacturing FRP by the FW method. Other epoxy resins may be mixed and used within a range that does not impair the useful properties of the epoxy resin of the present invention. [Examples] Examples according to the present invention will be shown below to specifically illustrate the present invention. [Example 1] (Aminomethylation of phenol) 470 g of phenol and 535 g of ammonium chloride were placed in a 2 liter 5-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, thermometer, dropping funnel and reflux tube. The mixture was heated to 50°C under stirring, and 203 g of a 37% formalin aqueous solution was gradually added dropwise. After the dropwise addition was completed, the temperature was raised to 80°C and the reaction was allowed to proceed for 1 hour. The formaldehyde/phenol molar ratio in this reaction system is 1.0
The ammonium chloride/formaldehyde molar ratio was 2. After adding 1.5 liters of methanol to the obtained reaction solution and stirring for 1 hour, solid-liquid separation was carried out by standing overnight, and aminomethylation was carried out by completely distilling off the methanol in the liquid phase using an evaporator. 660 g of a mixture containing phenol salt as a main component was obtained. The content of unreacted phenol contained in this mixture was about 16% by weight, and no unreacted formaldehyde was detected. (Recovery of unreacted phenol) Mixture 660 containing the above aminomethylated phenol salt as a main component
The unreacted phenol was recovered from g by distillation. The distillation conditions were 5 mmHg and a temperature of 180°C. The weight of the aminomethylated phenol salt mixture after distillation was 341 g, and the content of unreacted phenol was 1% or less. (Epoxidation of aminomethylated phenol salt) A stirring device, a thermometer, a nitrogen inlet tube, a dropping funnel, and a condensation separation of an azeotrope of epichlorohydrin and water to form a lower layer of epichlorohydrin. 70 g of the aminomethylated product obtained in Example 1, 509 g of epichlorohydrin, and 29 g of a 50% aqueous tetramethylammonium chloride solution were placed in a 1 liter 5-necked flask equipped with a separator for returning the layer to the reactor. After charging, the temperature was started to increase while stirring, and the mixture was heated at 60° C. for 1 hour to perform an addition reaction of epichlorohydrin. Next, after raising the temperature of the reaction solution to 85°C, about 3.0 g of sodium hydroxide was added to the flask.
The addition took 5 hours to complete the ring-closing reaction by dehydrochlorination. Further, the above reaction conditions were maintained for about 30 minutes to completely remove water from the reaction system, and then epichlorohydrin was distilled off using an evaporator. Approximately 1 part of toluene is added to the remaining reaction product.
．． Add 5 liters and dissolve the resin component at room temperature.
Filtered. Toluene was removed from the filtrate using an evaporator to obtain about 124 g of a solvent-soluble low viscosity liquid epoxy resin product of the present invention. The viscosity of this epoxy resin is 20
℃, and the number average molecular weight was 406. The epoxy equivalent of this epoxy resin was measured by the hydrochloric acid-dioxane method and was found to be about 142 g/mol. (Curing of epoxy resin) Ancamine, a commercially available aromatic amine curing agent, was mixed in an amount of 26% phr with the liquid epoxy resin obtained above, and the mixture was placed in a mold and heated for 7
It was cured at 0°C for 1 hour and at 190°C for 3 hours. As a result, a cured product with high strength was obtained. 15 of the obtained cured product
The bending strength at 0°C was 6 kgf/mm2. [Comparative Example] Ancamine 23% phr was mixed with DER330 (manufactured by Dow Chemical Company), which is a commercially available bisphenol A glycidyl ether type epoxy resin, and cured under the same curing conditions as in the above example. The bending strength of the obtained cured product at 150°C is 4 kgf/mm.
It was 2. Effects of the Invention: Although the epoxy resin of the present invention is a liquid resin with low viscosity at room temperature, it can be cured in the same curing time as conventional epoxy resins, thereby improving heat resistance. An excellent cured product can be formed. Also,
The water resistance and mechanical properties of the cured product are also good. Therefore,
The epoxy resin of the present invention has excellent moldability, can be cured in a shorter time than conventional resols, does not cause foaming problems, and has a long pot life, so it has outstanding workability. . Furthermore, the cured product of this epoxy resin is
It has superior strength at high temperatures compared to conventional epoxy resins, and exhibits high heat resistance comparable to resol. Due to these characteristics, the low viscosity liquid epoxy resin of the present invention has
It can be used for a wide range of applications such as various molding materials, encapsulating materials and substrates for electronic parts, matrix resins for composite materials, as well as adhesives and coating materials, and is particularly suitable for manufacturing FRP, especially FRP using the FW method. be.

Claims (3)

[Claims] Claim 1: ■ An aminomethylation process for phenols in which phenols, aldehydes, and ammonium salts are reacted, ■ A process for recovering unreacted phenols without performing a neutralization treatment, and ■ Aminomethylated phenol. A method for producing an epoxy resin, comprising the step of epoxidizing a reaction product containing a salt of the same type. 2. A molding material containing an epoxy resin obtained by the method according to claim 1 and reinforcing fibers. 3. A method for producing fiber-reinforced plastic products by a filament winding method using the epoxy resin obtained by the method according to claim 1.