JPH0292980A - Polyvinyl acetal resin for adhesive - Google Patents

Abstract

PURPOSE:To obtain the subject resin containing more than a specific amount of a totally acetalized fraction, having excellent heat-resistance and soldering resistance as well as peel strength and suitable as an adhesive for a laminated board of printed circuit by condensing acetaldehyde, furfural and PVA. CONSTITUTION:The objective polyvinyl acetal resin for adhesive can be produced by condensing PVA with at least two kinds of aldehydes consisting of acetaldehyde and furfural. The ratio of the totally acetalized component in the resin is >=65wt.%, preferably 70wt.%. The ratio of component acetalized with acetaldehyde and furfural is >=85wt.% based on the whole acetalized component and the ratio of the component acetalized with furfural is preferably 0.2-2wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polyvinyl acetal resin for adhesives which has excellent heat resistance and is suitably used, for example, as an adhesive for laminated boards of printed circuits.

(Prior art) Adhesive compositions whose main components are polyvinyl acetal resins such as polyvinyl butyral resins and thermosetting resins such as phenol resins and epoxy resins have been conventionally used as adhesives for laminates. more widely used.

Laminates are usually formed by laminating copper foil on the top surface of phenolic resin-impregnated paper via an adhesive, then heating and pressurizing this. Printing is done by etching the copper foil on the surface of this copper-clad laminate. A board is created.

In recent years, as various electrical appliances have become lighter and smaller, printed circuit boards like this have been immersed in solder baths for longer periods of time (
There is also a tendency for circuit density to become higher. Therefore, as an adhesive used for the above laminate,
Even better heat resistance than before is now required, especially the "peel strength" of copper foil at high temperatures.
Improvements are desired.

For this reason, in JP-A-57-3802, by adjusting the ratio of the acetalized part by acetaldehyde and the acetalized part by butyraldehyde,
It has been proposed to improve the heat resistance of the polyvinyl acetal resin itself, and Japanese Patent Publication No. 47-47574 proposes an adhesive composition containing a polyvinyl acetal resin, a phenol formaldehyde resin, and an organic phosphorus compound.

(Problem to be Solved by the Invention) However, the current situation is that none of the adhesive compositions described above is sufficient to meet the above-mentioned demand for a high degree of heat resistance improvement. be.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to provide a polyvinyl acetal resin for adhesives that has excellent heat resistance, particularly "soldering heat resistance" and "peel strength". It's about doing.

(Means for Solving the Problems) The polyvinyl acetal resin for adhesives of the present invention is a polyvinyl acetal resin for adhesives obtained by condensing at least two types of aldehydes, acetaldehyde and furfural, and polyvinyl alcohol. , the proportion of the total acetalized portion in the resin is 65% by weight or more,
In addition, the proportion of the acetalized portion by acetaldehyde and furfural is 85% by weight or more of the total acetalized portion, thereby achieving the above object.

The polyvinyl alcohol used in the present invention preferably has a degree of polymerization of 1,000 to 3,000, more preferably 1,500 to 2,500. If polyvinyl alcohol with a degree of polymerization exceeding 3000 is used, the viscosity of the adhesive produced as described below will be too high to be practical. Furthermore, when polyvinyl alcohol having a degree of polymerization of less than 1000 is used, the adhesive properties of the adhesive at high temperatures tend to decrease.

In the present invention, at least two types of aldehyde, furfural and acetaldehyde, are used. In addition to the two types of aldehydes, furfural and acetaldehyde, other aldehydes may be used in small amounts. As other aldehydes, commonly known aldehydes used in the production of conventionally known polyvinyl acetal resins are used. Preferred examples thereof include formaldehyde, propionaldehyde, butyraldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, and the like having 1 to 1 carbon atoms.
Examples include alkyl aldehyde No. 8, cyclohexyl aldehyde, glyoxal, glutaraldehyde, benzaldehyde, and phenylaldehyde.

The proportion of the total acetalized portion acetalized by each of the above-mentioned aldehydes is 65% by weight or more, preferably 70% by weight, based on the total amount of the polyvinyl acetal resin. If the proportion of the total acetalized portion is less than 65% by weight, the heat resistance, particularly the peel strength between the obtained adhesive and the above-mentioned copper foil, will be insufficient. Therefore, the proportion of the total acetalized portion in the resin is 65% by weight or more, preferably 70% by weight.

In addition, the proportion of the acetalized part by furfural and acetaldehyde is 85% by weight of the total acetalized part.
This is considered to be the above. If this proportion is less than 85% by weight of the total acetalized portion, the above-mentioned furfural and other aldehydes other than acetaldehyde will be used in an amount exceeding 15% by weight of the total amount of the acetalized portion, and the furfural ring will be This may cause problems such as the crosslinking reaction being inhibited or the furfural acetalization reaction itself being difficult to proceed.

Further, the proportion of the acetalized portion by furfural is preferably 0.1 to 4% by weight, more preferably 0.2% by weight.
~2% by weight. If the proportion of the acetalized moiety due to furfural is less than this range, the self-crosslinking reaction due to furfural will be difficult to occur, which will tend to cause a decrease in soldering heat resistance.

Moreover, if the proportion of the acetalized portion by furfural is higher than the above range, the self-crosslinking reaction by furfural will proceed excessively, which will tend to impair flexibility and cause a decrease in the peel strength of the copper foil.

Polyvinyl acetal resin for adhesives can be obtained by condensing polyvinyl alcohol and aldehyde through a conventionally employed acetalization reaction. For example, after adding an acid catalyst to a polyvinyl alcohol aqueous solution,
A precipitation method in which furfural and an aldehyde such as acetaldehyde are added and reacted to precipitate the resulting polyvinyl acetal resin, and a dissolution method in which polyvinyl alcohol is dispersed in an organic solvent and an acid catalyst and an aldehyde compound are added and reacted. can be adopted.

As the catalyst, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and hydrosulfuric acid, and organic acids such as organic sulfonic acids can be used.

To further explain the precipitation method for obtaining the polyvinyl acetal resin of the present invention, generally polyvinyl alcohol is dissolved in hot water and then cooled, and after reaching a predetermined temperature, an acid catalyst and an aldehyde such as furfural and acetaldehyde are added as appropriate. throw into. The order in which each aldehyde is added is not limited. For example, furfural may be first added to the above solution to carry out the acetalization reaction, and then acetaldehyde and other aldehydes may be added as necessary, or acetaldehyde and other aldehydes may be added first as necessary. Furfural may be added to the solution after the acetalization reaction is performed, or furfural and each aldehyde such as acetaldehyde may be added to the solution at the same time to perform the acetalization reaction.

In particular, it is preferable to add furfural first in terms of resin particle control. This acetalization reaction precipitates an acetalized product. Next, the reaction system is maintained at a relatively high temperature for a predetermined period of time to mature, and then the acid catalyst is neutralized and washed with water to remove the catalyst and unreacted aldehyde, and then purified and dried by a conventional method. A polyvinyl acetal resin for adhesives is obtained.

To prepare adhesives for laminates using the polyvinyl acetal resin for adhesives obtained in this way, the resin may be used alone, or other thermoplastic resins or thermoplastic resins may be used. It may be used in combination with a curable resin. Thermosetting resins include phenolic resin, epoxy resin, urea resin,
Melamine resins, urethane resins, etc. are preferably used, and these may be used alone or in combination. The blending ratio of polyvinyl acetal resin and thermosetting resin is 1:4 to 1:4 by weight.
A range of 4:1 is preferred, particularly 2:3 to 3:2.

In addition, the adhesive for laminates contains a solvent that can dissolve the above resin, and additives such as antioxidants and antifoaming agents are appropriately blended as needed to improve heat resistance and for other reasons. may be done. As the solvent, those generally used for adhesives can be used, and suitable examples include ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol and butanol, and aromatic hydrocarbons such as toluene and xylene. used.

Therefore, as mentioned above, polyvinyl acetal resin obtained by condensing furfural and acetaldehyde, which are aldehydes with self-crosslinking properties, with polyvinyl alcohol, increases the bonding strength between the resins by crosslinking them with each other by heating, It is possible to improve "soldering heat resistance" and "peel strength". This crosslinking using furfural rings does not cause a decrease in electrical properties as seen with the addition of carboxylic acid, and it is possible to obtain favorable results when the resulting polyvinyl acetal resin is blended into an adhesive for laminates. Furthermore, since the crosslinking reaction using the furfural ring is an addition reaction rather than a condensation reaction, volatile substances such as water are not generated during the reaction, unlike in condensation reactions, and a good adhesive layer can be obtained. be able to.

(Example) The present invention will be explained in detail below based on examples.

Example 11U - Preparation of Polyvinyl Acetal Resin 2570 g of pure water was placed in the separable flask of 52, and 220 g of polyvinyl alcohol (degree of polymerization 2400, residual acetyl group 2.7% by weight) was added thereto and completely dissolved. After maintaining the temperature of this solution at 25°C and adding 580 g of 35% by weight hydrochloric acid, furfural 10
g was added, the liquid temperature was lowered to lOoC, and 154 g of acetaldehyde was appropriately added to precipitate a colorless powder.

Next, the reaction system was heated to 45° C., maintained at this temperature for 5 hours, neutralized and washed with water to remove the catalyst and unreacted aldehyde, and then dried to obtain a polyvinyl acetal resin.

Preparation of adhesive for laminates: 50 g of the polyvinyl acetal resin obtained above, 55 g of phenol resin (PL-2205 manufactured by Gunei Chemical Co., Ltd.),
and epoxy resin (Epicoat 82B manufactured by Shell Chemical Co., Ltd.)
7g of mixed solvent (acetone/MEK/) toluene = 1
/1/1) was dissolved in 340 g to prepare a laminate adhesive.

Next, this adhesive for laminates was applied as a solid content to a copper foil for a printed circuit board (thickness: 35 μm) to a thickness of 33 μm, and dried at 140° C. for 4 minutes to obtain an adhesive-coated copper foil. This copper foil and phenol resin-impregnated paper were pressure-molded at 150° C. for 40 minutes at 120 kg/cd to create a copper-clad laminate.

The "solder heat resistance" and "peel strength" of the obtained copper-clad laminate were measured in accordance with JIS C-6481.

The test temperature for "soldering heat resistance" is 260℃.
20°C and 15°C for "peel strength"
Each test was carried out at 0°C. Further, the degree of acetalization was measured according to the hydroxylamine hydrochloride method.

2-5 and 1-4 As shown in Table t-1, adhesives for laminates were obtained in the same manner as in Example 1, except that the amounts and types of acetaldehyde, furfural, and other aldehydes were changed. A copper-clad laminate was created using the following methods. The "soldering heat resistance" and "peel strength" of each copper-clad laminate were tested in the same manner as in Example 16.The degree of acetalization of the mixed polyvinyl acetal resin was calculated based on data from an infrared spectrophotometer. This was done using

The results are summarized in Tables 1-1 and 1-2.

Table 1-2 From the results in the table above, we can see that when the ratio of furfural is increased as in Comparative Example 1, when furfural is not used as in Comparative Example 2, and when acetaldehyde and aldehyde other than furfural (as in Comparative Example 3) In this case, when acetalization is performed using a large amount of butyraldehyde,
And as in Comparative Example 4, the ratio of the total acetalized portion is 65
When the amount is less than % by weight, the test results of the laminates showed that the solder heat resistance was poor and the peel strength of the copper foil was also low. On the other hand, in the laminates using the laminate adhesives of Examples 1 to 5, satisfactory results were obtained in both solder heat resistance and peel strength.

(Effects of the Invention) As described above, the present invention provides a resin in which the proportion of the total acetalized part is 65% by weight or more, and the proportion of the acetalized part by acetaldehyde and furfural is 85% by weight or more of the total acetalized part. Therefore, it is possible to improve the soldering heat resistance and the peeling strength of the copper foil, and it is possible to obtain an adhesive for a laminate that is excellent in both soldering heat resistance and peeling strength.

Claims (1)

[Claims] 1. A polyvinyl acetal resin for adhesives obtained by condensing at least two aldehydes, acetaldehyde and furfural, with polyvinyl alcohol, in which the proportion of the total acetalized portion in the resin is 65% by weight or more, In addition, the proportion of acetalized parts by acetaldehyde and furfural is 8% of the total acetalized parts.
A polyvinyl acetal resin for adhesives, characterized in that the content is 5% by weight or more.