JPH0533251B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a method for producing a novel bisphenol A novolak resin useful as a curing agent for epoxy resins. (Prior art) Novolac resins obtained by dehydrating and condensing a phenol compound and formaldehyde in the presence of an acidic catalyst are well known, and novolac resins obtained using bisphenol A as the phenol compound are It is known as phenol A novolak resin. This is mainly mixed with an epoxy resin as a curing agent for the epoxy resin and used for manufacturing prepregs and circuit-forming laminates. On the other hand, in the production of laminates using epoxy resins, dicyandiamide is the predominant epoxy resin curing agent. Generally, a laminate is manufactured by dissolving an epoxy resin and a curing agent in a solvent such as methyl ethyl ketone, and then adding a curing accelerator to form a resin varnish. Next, after impregnating the glass cloth with this resin varnish,
The solvent is evaporated in a dryer to form a prepreg. This prepreg is laminated in an appropriate amount, or copper foil is further laminated and heated and cured under press pressure. The thus obtained laminate is subjected to processing such as etching and drilling to form a circuit. In addition, in the field of laminates, resin hardenability,
Required items include heat resistance of the cured resin, drillability of the laminate, moisture resistance, electrical properties and hue stability, and stability of the resin varnish. (Problems to be Solved by the Invention) When dicyandiamide is used as a curing agent for epoxy resins, the curing properties of the resin (requires high temperature heating), the heat resistance of the cured resin, the hue stability of the laminate, and the drill workability are affected. Since there are some disadvantages, it is expected to improve these drawbacks by using bisphenol A novolak resin, which has excellent curability. The present inventors conducted various studies on the conventionally known bisphenol A novolak resins and found the following. That is, the conventionally known bisphenol A
The epoxy resin composition prepared using the novolac resin had no particular problems with respect to the drillability of the laminate, hue stability, and electrical properties, but (1)
The curing properties of the resin are insufficient (it can be cured at a lower temperature than dicyandiamide, but it will not cure sufficiently unless it is relatively high temperature), (2) the heat resistance of the cured resin is poor, (3) the storage stability of the resin varnish is poor. (4) The compatibility between the epoxy resin and the bisphenol A novolak resin is poor, resulting in whitening of the prepreg and insufficient curing. Therefore, we further investigated the bisphenol A novolak in detail and found the following. That is, when the ratio of formaldehyde to bisphenol A was varied, for example, the amount of formaldehyde was varied from 0.4 to 1.0 mol to 1 mol of bisphenol A, and when the amount of formaldehyde was 1.0 mol, In this case, gelation occurred during the reaction and the target substance could not be obtained, and when the amount of formaldehyde charged was 0.9 mol, the obtained novolak resin contained about 18% by weight of unreacted bisphenol A monomer. When the amount of formaldehyde charged is less than 0.9 mol, more unreacted bisphenol A monomer is contained. Therefore, the present inventors focused on this point and decided to study the relationship between the amount of remaining unreacted bisphenol A monomer and the above-mentioned drawback. As a result, a new method for producing bisphenol A novolak resin without the above-mentioned drawbacks was developed. The object of the present invention is to provide this manufacturing method. (Means for Solving the Problems) The present invention involves blending 0.4 to 0.8 mol of formaldehyde with respect to 1 mol of bisphenol A, and heating and reacting the mixture in the presence of an acidic catalyst. Heating in the presence of ~400% by weight toluene and separating it into two layers, a light liquid (upper layer) and a heavy liquid (lower layer) at a temperature of 80°C or higher, separating the heavy liquid and removing toluene from it. The present invention relates to a method for producing a bisphenol A novolak resin. The target substance of the present invention is particularly preferably one having the following characteristics. However, it is not limited to this. That is, in the target substance bisphenol A novolac, bound formaldehyde is 0.7 to 0.9 mol per 1 mol of phenol component (including residual unreacted monomer) and the phenol monomer content is 10% by weight or less. It is a certain thing. If the number of moles of bound formaldehyde per mole of phenol component is too small, the content of residual unreacted monomers will increase or the number average molecular weight will decrease, resulting in decreased curability and heat resistance; if it is too large, the molecular weight will decrease. becomes too high, and the compatibility with the epoxy resin tends to decrease. Here, the number of moles of bound formaldehyde per mole of the phenol (bisphenol A) component is the 1.5 ppm peak based on the methyl group in the bisphenol A component of the nuclear magnetic resonance spectrum of the bisphenol A novolak resin and the bisphenol A component.
It was determined from the area intensity ratio of the peak at 3.75 ppm, which is based on the methylene group formed by addition and condensation of formaldehyde. The solvent used in this measurement is dimethyl sulfoxide (however, all hydrogens in the methyl groups are diuterium, DMSO
−d ₆ ). The bisphenol A novolak resin which is the object substance of the present invention preferably has a phenol monomer content of 10% by weight or less. If this content exceeds 10% by weight, the curability and heat resistance of the cured resin tend to decrease. In addition, phenol (bisphenol A) component 1
If the number of moles of bound formaldehyde and the phenol (bisphenol A) monomer content are not within the above ranges, the storage stability of the resin varnish tends to be poor. The bisphenol A novolac resin according to the present invention preferably has a number average molecular weight of 600 to 2,000. When the number average molecular weight is less than 600, the heat resistance of the cured resin tends to decrease, and when it exceeds 2000, the compatibility with the epoxy resin tends to deteriorate. Further, the bisphenol A novolak resin in the present invention preferably has a dispersity of 2.2 or less. When the degree of dispersion is within this range, it is effective to prevent a part of the curing reaction from proceeding during drying of the prepreg and to prevent discoloration of the laminate by lowering the curing temperature. Here, the degree of dispersion is the ratio of weight average molecular weight/number average molecular weight. In the present invention, the weight average molecular weight and number average molecular weight are determined by gel permeation chromatography. The calibration curve is based on bisphenol monomer (molecular weight 228), a compound having 2 to 7 bisphenol A components in the reaction product obtained by reacting 1 mol of bisphenol A with 0.4 to 0.8 mol of formaldehyde under an acidic catalyst. Use what you have created. The eluent is tetrahydrofuran, the flow rate is 1.7 ml per minute, the temperature is 38° C., and the pressure is 48 Kg/cm ² . The bisphenol A novolak resin, which is the object substance of the present invention, can be produced as follows. Preferably, 0.4 to 0.8 mol of formaldehyde is reacted with respect to 1 mol of bisphenol A in an aromatic solvent such as benzene, xylene, or toluene in the presence of an acidic catalyst (first step). Then, 25% of the obtained resin and the charged bisphenol A were added.
Mix ~400% by weight toluene, preferably
After stirring at a temperature of 80°C or higher and lower than the boiling point of toluene, preferably for 0.5 hour or longer, if left to stand at that temperature, it will separate into two layers, so the lower layer (a viscous or slightly thick layer containing toluene and bisphenol A novolac resin) The viscous liquid substance) is separated and toluene is removed from it (second step). Each step will be explained in more detail. In the first step, formaldehyde is used in an amount of 0.4 to 0.8 mol per mol of bisphenol A.
If it is less than 0.4 mol, unreacted bisphenol A will increase and it will be difficult to increase the amount of bound formaldehyde to 0.7 mol or more per mol of bisphenol A component in the final resin.
In addition, if it exceeds 0.8 mol%, there is a risk of gelation during the reaction, and the generation of molecular species with a molecular weight of more than 20,000 increases, which tends to reduce the compatibility of the final resin with the epoxy resin, and may cause This increases the number average molecular weight and dispersity. Formaldehyde can be used in the form of paraformaldehyde, formalin aqueous solution, α-polyoxymethylene, and the like. The aromatic solvent is preferably one that forms an azeotropic composition with water. The amount used is 20 to 100% by weight based on the amount of bisphenol A used.
is preferred. Furthermore, it is preferable to use toluene as the aromatic solvent since the second step can be carried out following the first step. As the acidic catalyst, those normally used in the production of phenol novolac resins, such as mineral acids such as sulfuric acid and hydrochloric acid, and organic acids such as para-toluenesulfonic acid and oxalic acid, can be used. It is preferably 0.1 to 2% by weight based on phenol A.
The reaction temperature was 70 to 90°C for 1.5 to 4 hours.
It is preferable to carry out the addition reaction of formaldehyde mainly to bisphenol A, and then raise the temperature to 100°C or higher and lower than the reflux temperature to carry out the reaction, and to carry out a dehydration condensation reaction. In this case, the process is carried out while removing condensed water,
It is preferable to carry out the reaction until no condensed water is produced. This time is usually 3 to 5 hours. After this, it is preferable to add an alkali to the reaction solution in an amount equivalent to that of the acidic catalyst in order to neutralize the acidic catalyst. Examples of the alkali include lithium hydroxide, sodium hydroxide, potassium hydroxide, triethanolamine, and morpholine. The first step reaction solution thus obtained is subjected to the second step after the solvent is removed by distillation or the like (when toluene is used as the solvent, the reaction solution may be used as it is). In the second step, the amount of toluene in the first step is 25 to 400% by weight based on the charged bisphenol A.
The resin obtained in the process and toluene are mixed or toluene is added to the reaction solution. The resin solution thus obtained is then heated and stirred, preferably at a temperature of 80° C. or above and below the boiling point of toluene, preferably for 0.5 hours or more. Thereafter, the resin solution is separated into two layers, upper and lower, at a temperature of 80°C or higher, preferably lower than the boiling point of toluene. At this time, the lower layer consists of a viscous or slightly viscous liquid containing toluene and bisphenol A novolak resin, and the upper layer has two bisphenol A monomers and a small amount of bisphenol A component in the molecule. This is a toluene solution in which formaldehyde reactants are dissolved. This separation is preferably carried out while standing still, or can be forcibly separated using a centrifugal separator. This separation
If the temperature is lower than 80°C, the bisphenol A monomer will precipitate from the toluene solvent in the upper layer and mix with the lower layer, which is not preferable. After separating and collecting the lower layer, toluene is distilled off to obtain the bisphenol A novolac resin according to the present invention. In the second step, if toluene is less than 25% by weight of the charged bisphenol A, toluene becomes a viscous substance absorbed in bisphenol A novolac resin, and if it exceeds 400% by weight, bisphenol A novolac resin becomes a viscous substance. Relatively low molecular weight molecular species of the resin dissolve in the upper layer of toluene, reducing the yield, and when there is a large excess, the mixture does not separate into two layers and becomes a homogeneous solution of toluene. If the second step is performed once, the bisphenol A novolak resin according to the present invention can usually be obtained.
It may be repeated two or more times depending on the case. In this case, the amount of toluene mentioned above is based on the amount of resin. In the second step, the number average molecular weight and dispersity of the resulting bisphenol A novolak can be adjusted by adjusting the treatment conditions. The bisphenol A novolak resin thus obtained can be used as it is without removing the neutralized salts contained therein, or after removing the neutralized salts by hot water treatment etc.
Can be put to use. The solvent used in the second step is toluene, but other solvents such as benzene and xylene cannot achieve the purpose. The bisphenol A novolak resin of the present invention may contain phenols other than bisphenol A as its constituent components within a range that meets the purpose of the present invention. Examples of such phenols include cresol and phenol, which are used together with bisphenol A during the above production. (Example) Next, an example of the present invention will be shown. Example 1 228 g (1.0 mol) of bisphenol A and 22.5 g (formaldehyde equivalent) of 80% paraformaldehyde were placed in a four-neck glass flask equipped with a Dean Stark oil-water separator, a thermometer, and a stirrer.
0.6 mol) and 171 g of toluene were charged, and the temperature was raised while stirring. When the temperature inside the flask reached 80℃, add 1.5g of oxalic acid dihydrate as a catalyst and heat to 80℃.
Stirring was continued for 3 hours. Thereafter, the temperature inside the flask was raised to 105°C, toluene was refluxed, and the water that azeotropically flowed out was removed from the system. Toluene reflux was continued until there was no more water flowing out. The temperature inside the flask at this time was 113°C, and the total amount of water removed was 15.7ml. This amount corresponds to the total amount of water contained in 80% paraformaldehyde, the amount of water in oxalic acid dihydrate, and the amount of condensation water to be generated. The reaction solution at this time was a homogeneous solution. Then, after neutralizing by adding triethanolamine, 228 g of toluene was added and the temperature was raised to a temperature at which toluene refluxed. At this time, when stirring is stopped, the liquid separates into two layers: a light liquid (upper layer) and a heavy liquid (lower layer).
After raising the temperature and stirring for 30 minutes, stirring was stopped and the reaction solution was separated into two layers, a light liquid and a heavy liquid. The light liquid was removed by decantation to obtain a heavy liquid. 400 g of toluene was added to this heavy liquid, and after stirring for 30 minutes under toluene reflux, stirring was stopped and the mixture was separated into two layers again, and the heavy liquid (lower layer) was separated and collected. This was a slightly viscous liquid. Toluene was removed from this using an evaporator to obtain 132 g of pale yellow resin [A]. The softening point of the obtained resin was determined using the ring and ball equation. The residual bisphenol A monomer and molecular weight contained in the resin were measured using gel permeation chromatography (GPC). The separation columns used at this time were GELPACK-R420,
R430 and R440 (both are Hitachi Chemical Co., Ltd. product names,
Porous styrene-divinylbenzene copolymer particles were used as the column packing material) were connected in series one by one, tetrahydrofuran was used as the eluent, a differential refractometer was used as the detector, and the flow rate was 1.75ml/
It was a minute. The chromatogram obtained at this time is shown in FIG. Further, the calibration curve used for calculating the molecular weight is shown below. The number f of formaldehyde bound to 1 mole of bisphenol A component in the resin was determined from the nuclear magnetic resonance (NMR) spectrum of the resin. This spectrum is shown in FIG. That is, from the integrated intensity A of the peak based on the methyl group of the bisphenol A component appearing at 1.5 ppm and the integrated intensity F of the peak based on the methylene group of bound formaldehyde appearing at 3.75 ppm, the formula f = (F / 2) / (A/6). The above results are shown in Table 1. Example 2 In Example 1, the amount of 80% paraformaldehyde used was 30g (0.8 mol in terms of formaldehyde).
The reaction was carried out in the same manner as in Example 1, except that the amount of toluene used was 115 g, and the light liquid was removed to obtain a heavy liquid. 200 g of toluene was added to this heavy liquid, and after stirring for 30 minutes under toluene reflux, stirring was stopped and the mixture was separated into a light liquid and a heavy liquid, and the light liquid was removed by decantation to obtain a heavy liquid. This operation was then repeated once again. Toluene was removed from the thus obtained heavy liquid using an evaporator to obtain 178 g of pale yellow resin [B]. Table 1 shows the physical properties of this resin [B] measured in the same manner as in Example 1. Example 3 The reaction proceeded according to Example 1 to obtain a heavy liquid. Next, 200 g of toluene was added to the heavy liquid, and after stirring for 30 minutes under toluene reflux, the stirring was stopped, the light liquid and the heavy liquid were separated, and the light liquid was removed by decantation to obtain the heavy liquid. was repeated four times. Toluene was removed from the thus obtained heavy liquid using an evaporator to obtain 74 g of pale yellow resin [C]. Table 1 shows the physical properties of this resin [C] measured in the same manner as in Example 1. Comparative Example 1 In Example 1, toluene was removed using an evaporator from the toluene solution neutralized by adding triethanolamine, and a pale yellow resin [D] was obtained.
Obtained 231g. Table 1 shows the physical properties of this resin [D] measured in the same manner as in Example 1. Also, resin [D]
The GPC chromatogram is shown in Figure 3. Comparative Example 2 The reaction proceeded in the same manner as in Example 1, except that 33.8 g (0.90 mol of formaldehyde equivalent) of 80% paraformaldehyde was used, and triethanolamine was added to neutralize. . Toluene was removed from this reaction solution using an evaporator to obtain 235 g of pale yellow resin [E]. Table 1 shows the physical properties of this resin [E] measured in the same manner as in Example 1. [Preparation of calibration curve] A calibration curve for determining molecular weight by GPC was prepared as follows. That is, the resin [C] obtained in Example 3
GPC measurement was performed and a chromatogram was obtained.
This chromatogram is shown as graph 1 in FIG. In this chromatogram, peaks 2 to 8
are, respectively, in the following general formula [I], where n is 0 to
6, and when n is 0, it is a bisphenol A monomer. (However, in the formula, B represents two hydrogens in the ortho position to one hydroxyl group of the bisphenol A monomer, or one hydrogen in the ortho position to both hydroxyl groups, for a total of two hydrogens. (n is 0 or an integer of 1 to 6) Here, the molecular weight of each compound where n corresponds to 0 to 6 is as follows. When n is 0, 228 When n is 1, 469 When n is 2, 709 When n is 3, 949 When n is 4, 1190 When n is 5, 1430 When it is 6, it is 1670. Next, the elution time (minutes) of each compound is plotted on the horizontal axis.
The molecular weight was plotted on a logarithmic scale on the vertical axis, and based on this, a calibration curve 9 was determined as shown in FIG. As is clear from FIG. 4, the calibration curve 9 shows clear linearity. Comparative Example 3 100 g of the resin [D] obtained in Comparative Example 1 was dissolved in xylene (a mixture of meta and para forms) and heated at 135°C for 30
After heating and stirring for a minute, stirring was stopped and the reaction solution was separated into a heavy liquid and a light liquid. The light liquid was removed by decantation to obtain a heavy liquid. Xylene was removed from this heavy liquid using an evaporator to obtain a pale yellow resin [F]. Table 1 shows the physical properties of this resin [F] measured in the same manner as in Example 1.

[Table] Reference examples 1 to 5 Epicote 828 (trade name of Ciel Chemical Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent: 190)
After thoroughly mixing 100 parts by weight of the curing agent obtained in Examples 1 to 3 and Comparative Examples 1 to 2 at 130°C, 0.5 part by weight of 2-ethyl-4methylimidazole was added to form an epoxy resin composition. created something. Immediately after creation, it was cured by heating at 170°C for 2 hours. A heat resistance test was conducted on the obtained cured product. The results are shown in Table 2. Heat resistance tests include glass transition temperature and
The heat distortion temperature was measured based on JISK 7207 (1983). The glass transition point was defined as the temperature that indicates the inflection point of the thermal expansion coefficient when measured using a thermomechanical testing machine.

[Table] Reference Examples 6-7 100 parts by weight of an epoxy resin (epoxy equivalent: 410) obtained by reacting 100 parts by weight of Epicote 828 and 63 parts by weight of tetrabromobisphenol A in the presence of 0.1 part by weight of tetramethylammonium chloride, An epoxy resin composition varnish was prepared by dissolving 31 parts by weight of resin [A] or resin [D] as a curing agent and 0.7 parts by weight of 1-cyanoethyl-2-phenylimidazole in 120 parts by weight of methyl ethyl ketone. The gel time of this varnish was measured. Gel time was measured by measuring the time (seconds) until the varnish gelled on a hot plate at 150°C, either immediately after the varnish was prepared or after being stored for one month at 23°C. In addition, after creating the above varnish, a glass cloth (glass cloth of glass fiber whose surface was treated with epoxy silane, thickness 0.18 mm, manufactured by Nitto Boseki Co., Ltd. G-9020-
A prepreg was prepared by impregnating 100 parts by weight of BZG) with 52 parts by weight of varnish as a solid content. This prepreg was dried for 10 minutes in a drying oven at 70-110°C. The appearance of this dried prepreg was visually observed. Further, the dried prepreg was cured by heating at 170° C. for 2 hours, and the change in hue of the prepreg at this time was visually examined. Further, when the dried prepreg was heated to a temperature of 150° C. using a differential scanning calorimeter, the time from the start to the end of heat generation of the dried prepreg was measured. Furthermore, 15 sheets of the above dried prepreg and 6 sheets of 35 μm copper foil were laminated for every 3 sheets of prepreg (however, 2 sheets were on the front and back sides), and
Then, press molding was performed at 150° C. for 15 minutes at a pressure of 40 kg/cm ² to obtain a laminate. This laminate was left standing in a steam atmosphere at 121° C. and a pressure of 2 kg/cm ² for 6 hours, and the weight increase was measured to examine the hygroscopicity of the laminate. On the other hand, 10,000 holes were drilled in the laminate plate obtained above using a 1 mmφ drill, and 200 holes were selected to examine the smear occurrence rate and determine the drillability. The above results are shown in Table 3. Reference Example 8 A dried prepreg was prepared in the same manner as Reference Example 6 using resin [D] as a curing agent, and its appearance was visually observed. The results are shown in Table 3.

[Table] From the results in Table 3, it is clear that the gel time of the varnish immediately after preparation and after storage for one month is different when resin [A] is used as a hardener (Example 1), and when resin [D] is used as a hardener. Compared to the case (comparative example 1),
Changes are small and storage stability is excellent. The fact that the prepreg has a semi-transparent appearance and no whitening parts means that
This shows that the epoxy resin and curing agent have excellent compatibility. In addition, a short time until the end of heat generation means that curing is completed in a short time, and in this respect, when resin [A] is used as a curing agent (Example 1)
It can be seen that this is superior to the case where resin [D] is used as a curing agent (Comparative Example 1). Further, from the volume resistivity values, it can be seen that the laminate obtained using resin [A] as a curing agent has better electrical insulation than the laminate obtained using resin [D] as a curing agent. When resin [E] was used as a curing agent (Comparative Example 2), the prepreg turned white. This is resin [E]
As can be seen from the fact that although it contains 18.2% by weight of residual bisphenol A monomer, its weight average molecular weight is comparable to that of resin [B].
This is because there are relatively many molecular species with a molecular weight of over 20,000, which results in poor compatibility with the epoxy resin. (Effects of the Invention) According to the present invention, a novel bisphenol A novolak resin is obtained, and this bisphenol A novolak resin is useful as a curing agent for epoxy resin. An epoxy resin varnish that exhibits excellent heat resistance and contains the resin as a curing agent has excellent storage stability, and a prepreg obtained using this varnish has excellent curability and hue stability.
In addition, the laminate obtained from this prepreg exhibits good volume resistance, moisture absorption resistance, and drilling workability.

[Brief explanation of drawings]

Figure 1 shows the resin [A] obtained in Example 1.
GPC chromatogram, Figure 2 is the nuclear magnetic resonance spectrum of resin [A], Figure 3 is the GPC chromatogram of resin [D] obtained in Comparative Example 1, and Figure 4 is the nuclear magnetic resonance spectrum of resin [A].
The figure shows the GPC chromatogram and calibration curve of resin [C] obtained in Example 3. Explanation of symbols, 1 ...GPC chromatogram of resin C, 9 ...calibration curve.

Claims (1)

[Claims] 1 Blend 0.4 to 0.8 mole of formaldehyde to 1 mole of bisphenol A, heat the reaction in the presence of an acidic catalyst, and then heat in the presence of 25 to 400% by weight toluene based on the bisphenol A,
Light liquid (upper layer) and heavy liquid (lower layer) at a temperature of 80℃ or higher
A method for producing bisphenol A novolak resin, which comprises separating into two layers, separating a heavy liquid, and removing toluene from it.