JPH093428A - Polyvinyl acetal resin for adhesive and adhesive composition - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a polyvinyl acetal resin for adhesives and an adhesive composition that have excellent heat resistance and peel strength at high temperature and are less likely to generate bubbles when precoated on a metal foil. A polyvinyl acetal resin containing free acid in a range of 0.01 to 0.1% by weight, and an adhesive composition containing the polyvinyl acetal resin, a thermosetting resin and a solvent. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyvinyl acetal resin for adhesives and an adhesive composition using the polyvinyl acetal resin, for example, heat resistance suitable for use in a printed circuit board, a conductor such as copper foil. To a polyvinyl acetal resin and an adhesive composition having excellent peeling strength and processability when applying an adhesive to a conductor.

[0002]

2. Description of the Related Art A printed circuit board is usually constructed by bonding a metal foil such as copper foil to a base material such as phenol-impregnated paper using an adhesive. Conventionally, as the adhesive, a polyvinyl acetal resin typified by polyvinyl butyral resin and an adhesive composition containing a phenol resin, a thermosetting resin typified by an epoxy resin or a melamine resin as main components have been widely used. There is.

In manufacturing the above-mentioned printed circuit board,
First, a metal foil such as a copper foil is attached to a substrate using the above adhesive to obtain a laminated plate. Next, the metal foil is etched to form a desired printed circuit made of the metal foil.

In recent years, along with the weight reduction and miniaturization of various electronic / electrical devices, miniaturization of printed circuit boards and high density of printed circuits have been advanced. With the increase in density, the solder bath immersion time for mounting a large number of electronic components on a printed circuit board is becoming longer. As a result, as an adhesive for forming the above-mentioned printed circuit board, an adhesive showing more excellent characteristics than before has been required.
Specifically, it is strongly desired to improve the bonding strength of the metal foil at high temperature, that is, the peeling strength, and the adhesive itself is required to exhibit excellent heat resistance.

To meet the above demands, various polyvinyl acetal resin adhesive compositions have been proposed. JP-A-55-27342 discloses that the degree of polymerization is 2
There has been proposed a polyvinyl acetal resin obtained by reacting a polyvinyl alcohol having a molecular weight of more than 500 and 3,000 or less with an aldehyde. In addition, JP
Japanese Patent Laid-Open No. 3802/1982 proposes a method in which a polyvinyl acetal resin is mixed into an acetal to thereby increase the heat resistance of the polyvinyl acetal resin itself. Further, in JP-A-63-301208, a polyvinyl acetal resin having improved heat resistance is obtained by using about 85 to 100% by weight of the total acetalized portion as an acetalized portion by acetaldehyde having a high glass transition point. Is disclosed.

[0006]

However, the solder bath immersion time for mounting components on a printed circuit board has been further extended, and when the polyvinyl acetal resin described in each of the above prior arts is used. However, it has not been possible to sufficiently meet the above-mentioned demand.

In actual production of a printed circuit board, an adhesive layer is usually applied to a copper foil to prepare a copper foil with an adhesive layer, while a prepreg is separately produced.
Then, finally, a copper foil with an adhesive layer is laminated on a base material, that is, a prepreg, and heat-pressed to obtain a printed circuit board. Therefore, when obtaining a copper foil with an adhesive layer, the coating workability of the adhesive becomes a problem, and therefore an adhesive composition having a low viscosity is used. However, when a low-viscosity adhesive composition is used, bubbles are generated on the adhesive layer surface during the production of the adhesive-coated copper foil, or foaming occurs during the above-mentioned thermocompression bonding, and the defective rate of the printed circuit board is reduced. It could be high.

The object of the present invention is to solve the above-mentioned problems of the prior art and to have excellent heat resistance, and particularly to have excellent solder heat resistance and peeling strength of an adherend under high temperature, that is, a metal foil. Moreover, it is an object of the present invention to provide a polyvinyl acetal resin for an adhesive in which bubbles are unlikely to be generated when producing a metal foil with an adhesive layer, and an adhesive composition using the polyvinyl acetal resin.

[0009]

The present invention has been made to achieve the above object, and the invention according to claim 1 provides free acid in the range of 0.01 to 0.1% by weight. It is a polyvinyl acetal resin for adhesives that is contained. The free acid is not particularly limited, but as described in claim 2, an inorganic acid or an organic acid can be used as the free acid. Examples of the inorganic acid include, but are not particularly limited to, hydrochloric acid, nitric acid, sulfuric acid, sulfonic acid, phosphoric acid and the like, and examples of the organic acid include, but are not particularly limited to, formic acid. , Acetic acid, valeric acid, butyric acid, oxalic acid, paratoluenesulfonic acid and the like.

The content of the above-mentioned free acid needs to be in the range of 0.01 to 0.1% by weight based on the whole polyvinyl acetal resin. If it is less than 0.01% by weight, the desired solder heat resistance cannot be obtained, and bubbles may be generated on the surface of the adhesive layer during the production of the adhesive-attached metal foil. When the content of the free acid exceeds 0.1% by weight, the viscosity stability of the adhesive composition decreases, and the heat resistance of the structure obtained by adhering with the polyvinyl acetal resin is high. That is, not only the heat resistance of the adhesive layer is lowered, but when it is present in a much larger amount than 0.1% by weight, the metal foil may be corroded when used for bonding the metal foil.

The method for incorporating the free acid into the polyvinyl acetal resin is not particularly limited, and it may be added in the production process of the polyvinyl acetal resin, or the free acid may be added after the polyvinyl acetal resin is produced. You may mix.

In order to add the free acid during the production of the polyvinyl acetal resin and adjust the content thereof, the acid catalyst used in the production of the polyvinyl acetal resin may be utilized. That is, conventionally, when synthesizing a polyvinyl acetal resin, for example, an acid catalyst is added to an aqueous solution of polyvinyl alcohol, an aldehyde compound is added, an acetalization reaction is carried out to obtain a polyvinyl acetal, and the acid catalyst is then washed or neutralized. However, the initial addition amount of the acid catalyst, the washing conditions and the conditions of the neutralization treatment may be adjusted so that the free acid in the specific range described above is present after the treatment such as washing and neutralization. . By setting the content of the free acid in the polyvinyl acetal resin finally obtained by using this method within the range of the present invention, the free acid can be contained without performing an additional step.

As the type of polyvinyl acetal resin used in the present invention, generally, any polyvinyl acetal used as an adhesive component in the production of printed circuit boards can be used, butyral resin, acetoacetal resin, Examples thereof include formal resin and various coacetal resins, or modified products of these polyvinyl acetal resins may be used.

The degree of polymerization of the polyvinyl acetal resin is not particularly limited, but it is usually in the range used as an adhesive for printed circuit boards, for example, 100.
The thing of about 0-3000 is used.

Regarding the content of vinyl acetal group,
The same content is selected as in the case of the polyvinyl acetal resin which is usually used for constituting a printed circuit board. That is, the ratio of all acetal groups is about 60 to 80 mol%, more preferably 65 to 78 mol%, as in the case of the polyvinyl acetal resin used as an adhesive for ordinary printed circuit boards. To be done. When the proportion of all acetal groups is less than 60 mol%, the solubility in a solvent and the compatibility with a thermosetting resin used in combination with an adhesive for printed circuit boards, such as phenol resin, epoxy resin, melamine resin, etc. Deteriorates, which adversely affects the coatability of the adhesive, the peeling strength of the metal foil, and the heat resistance of the adhesive layer. On the other hand, if it exceeds 80 mol%, the heat resistance and peeling strength of the adhesive layer will be insufficient, and satisfactory quality may not be obtained.

In the present invention, the amount of residual acetyl groups in the polyvinyl acetal resin is the same as that of the acetal resin usually used as an adhesive for printed circuit boards. That is, the amount of residual acetyl groups is usually 10 mol% or less, preferably 5 mol% or less. When the content of residual acetyl groups exceeds 10 mol%,
The heat resistance of the acetal resin is reduced, and the solder heat resistance of the produced printed circuit board is reduced.

As a method for synthesizing the polyvinyl acetal resin, an acetalization reaction which has been widely used in the past can be used. For example, an acid catalyst is added to an aqueous solution of polyvinyl alcohol, an aldehyde compound is added, a polyvinyl acetal is generated by an acetalization reaction, and a precipitation method in which polyvinyl acetal is precipitated, polyvinyl alcohol is dispersed in an organic solvent, and an acid catalyst and an aldehyde compound are mixed. The polyvinyl acetal solution obtained by adding and reacting may be dispersed in a poor solvent, or a poor solvent may be added to the polyvinyl acetal solution to obtain a resin powder. For example, a dissolution method may be used.

Examples of the acid catalyst include hydrochloric acid, nitric acid, sulfuric acid,
An inorganic acid such as phosphoric acid or an organic acid such as acetic acid or organic sulfonic acid can be used. An example of using the above precipitation method will be specifically described. Usually, polyvinyl alcohol is dispersed in water and dissolved by heating, and then the obtained polyvinyl alcohol aqueous solution is cooled at a predetermined temperature. Next, an acid catalyst and an aldehyde compound are appropriately added to the polyvinyl alcohol aqueous solution. After adding the acid catalyst and the aldehyde compound, the polyvinyl acetal compound is deposited by keeping the temperature at a constant temperature for about 30 minutes or longer. Furthermore, after completing the reaction by adding a catalyst and heating, etc., according to a conventional method,
It is neutralized and produced to obtain the desired polyvinyl acetal resin.

As the neutralizing agent used for neutralization, any basic reagent can be used, and generally sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate, sodium carbonate, ammonia or the like can be used. .

Next, the thermosetting resin used together with the polyvinyl acetal resin for adhesives of the present invention will be explained. That is, as in the invention described in claim 3, in the adhesive composition of the present invention, the polyvinyl acetal resin described in claim 1, the thermosetting resin, and the solvent are blended.

As the above-mentioned thermosetting resin, any one may be used as long as it is commonly used in adhesives for printed circuit boards. Generally, phenol resin,
Epoxy resin, urea resin, melamine resin, butylated melamine resin, urethane resin and the like are preferably used. Further, when the blending ratio of the polyvinyl acetal resin is small, the flexibility of the adhesive layer is reduced and the peel adhesive force is reduced, and when it is too large, the curing degree of the adhesive layer is reduced and the solder heat resistance is reduced. Therefore, the weight ratio of the polyvinyl acetal resin to the thermosetting resin is usually 1: 4 to 4: 1, and preferably in the range of 2: 3 to 3: 2.

As the solvent, ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol and butanol, and aromatic hydrocarbons such as toluene and xylene can be used.

In the adhesive composition according to the third aspect of the present invention, in order to improve the heat resistance of the adhesive, if necessary, an appropriate antioxidant and an antioxidant which are commonly used in printed circuit board adhesives are used. You may mix | blend a foaming agent, an additive, etc. suitably.

[0024]

In the polyvinyl acetal resin of the invention described in claim 1, the free acid is blended in the range of 0.01 to 0.1% by weight as described above. Therefore, the free acid acts as a catalyst to promote the curing reaction of the thermosetting resin itself, and further the thermosetting resin and the butyral resin, and it is considered that the heat resistance of the polyvinyl acetal resin is enhanced. . Moreover, since the content ratio of the free acid is in the above specific range, the viscosity stability of the adhesive composition is maintained, it is possible to suppress the generation of bubbles when applied to a copper foil, and the metal. Foil corrosion is also unlikely to occur.

Further, in the invention described in claim 3, since the polyvinyl acetal resin containing the free acid, the thermosetting resin, and the solvent are contained, the same as in the invention described in claim 1, , An adhesive layer with excellent heat resistance is formed,
Moreover, since the content ratio of the free acid is in the above specific range, the viscosity stability of the adhesive composition is maintained, it is possible to suppress the generation of bubbles when applied to a copper foil, and the metal. Foil corrosion is also unlikely to occur.

[0026]

EXAMPLES The present invention will be made clear by describing non-limiting examples and comparative examples of the present invention.

(Example 1) Preparation of polyvinyl acetal resin 3600 g of pure water was placed in a 5 liter separable flask, and 176 g of polyvinyl alcohol having a degree of polymerization of 1700 (saponification degree of 98.4 mol%) was added thereto to complete the addition. Dissolved in. The solution is then cooled to 50 ° C., 35% by weight
230 g of hydrochloric acid was added. After that, the liquid temperature was lowered to 35 ° C., and 60 g of paraaldehyde was put into the flask to make it 3
A temperature of 0-25 ° C was maintained for 3 hours. Then, adjust the liquid temperature to 1
When the temperature was lowered to 5 ° C and 79 g of n-butyraldehyde was added, a white powdery resin was precipitated. The resin dispersion thus obtained was kept at a temperature of 30 ° C. for 4 hours and then washed with water. The separated resin is dispersed again in water, and the p
It was neutralized with sodium hydroxide so that H became 6 to 7, washed with 200 times the pure water of the slurry, filtered, and the obtained resin was dried. The free acid content in the obtained resin was measured by the following measuring method, and was found to be 0.01% by weight. Table 1 shows the degree of polymerization, the degree of acetalization, and the viscosity of the polyvinyl acetal resin obtained as described above when dissolved in ethanol / toluene, together with the adhesive viscosity.

Measurement of Free Acid 1 g of the resin was precisely weighed in an Erlenmeyer flask, 40 ml of a mixed solvent of ethanol / water (9: 1 by volume) was added and shaken to dissolve. After the dissolution, a 1% by weight aqueous solution of phenolphthalein was used as an indicator to titrate with a 0.02 mol / liter KOH alcohol solution using a micro burette to the point where the deep red color was maintained for 30 seconds or more. Separately, a blank test was performed, and the free acid content was calculated by the following formula.

[0029]

[Equation 1]

Preparation and Application of Adhesive 40 g of the above polyvinyl acetal resin, 62 g of butylated melamine resin and 4 g of epoxy resin (trade name: Epicoat 828, manufactured by Yuka Shell Epoxy Co., Ltd.) were mixed with methanol /
An adhesive composition was prepared by dissolving it in 258 g of a mixed solvent of methyl ethyl ketone / toluene (weight ratio 2: 2: 1). The obtained adhesive composition was applied to a copper foil for a printed circuit board so that the thickness as a solid content was 33 μm, and dried at 140 ° C. for 4 minutes to obtain an adhesive layer-attached copper foil. 1 of the above-mentioned copper foil with an adhesive layer and phenol-impregnated paper
A copper foil laminate was prepared by pressure bonding at 50 ° C. for 30 minutes at a pressure of 120 kg / cm ² .

Evaluation The presence or absence of foaming in the adhesive when obtaining the copper foil with the adhesive layer was observed. Further, the "solder heat resistance" and the "peeling strength" of the copper foil laminate obtained as described above were measured according to JIS C-6485. In addition,
The test temperature was 260 ° C. for “solder heat resistance” and 20 ° C. and 150 ° C. for “peeling strength”.
Table 2 shows the evaluation results.

(Examples 2 to 11) Polyvinyl acetal resins shown in Table 1 below were obtained in the same manner as in Example 1. However, in the method of Example 1, the polyvinyl acetal resin was neutralized so that the pH of the resin dispersion became 7 to 8 when neutralized, washed with 1000 times of pure water, and dried. Next, the acid shown in Table 1 was added to the dried resin using a blender, and mixed sufficiently to contain the free acid. Using the polyvinyl acetal resin to which the acid was added as described above, an adhesive composition and a copper foil laminate were obtained in the same manner as in Example 1 and evaluated in the same manner.
Table 2 shows the results.

(Comparative Examples 1, 3 and 5) The polyvinyl acetal resins shown in Table 1 below were prepared in the same manner as in Example 1, except that the pH of the resin dispersion liquid when the polyvinyl acetal resin was neutralized was 7 to 8. To obtain a resin by washing with 1000 times pure water and drying. The free acid content of the obtained polyvinyl acetal resin is 0.005% by weight.
Met. Moreover, it carried out similarly to Example 1, the adhesive composition and the copper foil laminated board were obtained, and it evaluated by the same method. Table 2 shows the results.

(Comparative Examples 2, 4, 6) The polyvinyl acetal resins shown in Table 1 were prepared in the same manner as in Examples 2-11 and evaluated in the same manner. Table 2 shows the evaluation results.

[0035]

[Table 1]

In Table 1, the viscosity of ethanol / toluene is a value measured by a B-type rotational viscometer at 20 ° C. with a resin concentration of 5% by weight. Moreover, PTS shows paratoluenesulfonic acid.

[0037]

[Table 2]

As is clear from Table 2, in the polyvinyl acetal resin having a free acid content of 0.01% by weight or less (Comparative Examples 1, 3, 5), the solder heat resistance is 20 to 28 seconds,
Peel strength is 1.6-1.9kg at 20 ° C
/ Cm ² , 0.24 to 0.28 kg even at 150 ° C
/ Cm ² . On the other hand, the free acid content is 0.01
Weight% or more of polyvinyl acetal resin (Examples 1 to 1)
In 2), heat resistance is 28 seconds or more, peel strength is 20
2.0 kg / cm ² or more at ℃, 0.30kg / cm ² or more and performance has been improved at 0.99 ° C.. In addition, in Examples 1 to 12, it was confirmed that foaming did not occur after drying even when producing the copper foil with an adhesive.

When the free acid content exceeds 0.1% by weight (Comparative Examples 2 and 4), heat resistance and peeling strength are improved, and foaming hardly occurs, but corrosion of the copper foil surface does not occur. It was confirmed that it occurred and was lacking in practicality.

[0040]

As described above, according to the invention of claim 1, the polyvinyl acetal resin contains 0.01 to 0.
Since the free acid is contained in the range of 1% by weight, when the polyvinyl acetal resin of the present invention is used as an adhesive, heat resistance and peel strength under high temperature can be effectively enhanced. Therefore, by using the polyvinyl acetal resin for adhesives of the invention according to claim 1 as an adhesive for forming a printed circuit board, excellent solder heat resistance,
In addition, it is possible to provide a printed circuit board having an adhesive layer that is excellent in peel strength under high temperature.
Moreover, when the adhesive is applied to the metal foil, bubbles are unlikely to be generated in the adhesive, so that it is possible to reduce the defective product rate in manufacturing the printed circuit board.

Similarly, according to the invention of claim 3,
Since the polyvinyl acetal resin containing the free acid in the specific ratio, the thermosetting resin, and the solvent are contained, the heat resistance and the peel strength under high temperature are similar to the invention according to claim 1. An excellent adhesive layer can be formed. Therefore, when used as an adhesive for forming a printed circuit board, it is possible to provide a printed circuit board having an adhesive layer which has excellent solder heat resistance and excellent peel strength at high temperatures, and which is bonded to a metal foil in advance. No bubbles are generated when the agent is applied.

Therefore, according to the present invention as set forth in claims 1 to 3, the reliability of the printed circuit board is improved even when the size and density of the printed circuit board are increased and the solder bath immersion time is further extended. It is possible to provide a high-quality printed circuit board having excellent properties and excellent bonding strength of the metal foil.

Claims (3)

[Claims] 1. 0.01 to 0.1% by weight of the total amount of free acid
A polyvinyl acetal resin for adhesives, which is contained in the range of. 2. The polyvinyl acetal resin for adhesives according to claim 1, wherein the free acid is an inorganic acid or an organic acid. 3. An adhesive composition comprising the polyvinyl acetal resin according to claim 1 or 2, a thermosetting resin, and a solvent.