JPH0553839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to adhesive compositions. Conventionally, polyvinyl acetal, especially polyvinyl butyral, has good adhesive properties and excellent physical strength, so it has been widely used as an interlayer film for safety laminated glass.However, on the other hand, it is soluble in many organic solvents, and Because it has excellent adhesion and adhesion to metals, it is widely used in metal paints such as wash primers and metal adhesives. When polyvinyl acetal is used as an adhesive and adhesive strength at high temperatures is required,
Generally, a thermosetting resin such as a phenolic resin or an epoxy resin is added to polyvinyl acetal and dissolved in an organic solvent to be used as an adhesive. However, even in the above adhesives made of polyvinyl acetal and thermosetting resin, the adhesive strength, especially at high temperatures, is insufficient, and there is a need to further improve the adhesive strength. The present invention was made with the aim of solving the above-mentioned drawbacks and providing an adhesive with even better adhesive strength at high temperatures. A mixed polyvinyl acetal mixed with acetaldehyde, the total degree of acetalization being X (mol%),
When the half-width of hydroxyl group absorption in an infrared absorption spectrum where the vertical axis is the transmittance and the horizontal axis is the wave number is Y (cm ^-1 ), the transmittance of the peak of the hydroxyl group absorption spectrum is about 50%. The adhesive composition comprises a mixed polyvinyl acetal whose half-width Y satisfies formula (1) when the film thickness is adjusted, and a thermosetting resin. (1) Y≧−5X+550 In the present invention, the half width of hydroxyl group absorption in an infrared absorption spectrum is defined as follows. First, in the infrared absorption spectrum of mixed polyvinyl acetal, where the vertical axis is the transmittance (%) and the horizontal axis is the wave number (cm ^-1 ), as shown in Figure 1, there is no infrared absorption at wave numbers 3900 cm ^-1 and 2300 cm ^-1. Connect the positions showing the transmittance at ¹ and use this as the reference line. Next, let the distance from the horizontal axis (transmittance 0%) to the reference line passing through the peak P of the absorption spectrum of the hydroxyl group between wave numbers 3900 cm ^-1 and 2300 cm ^-1 be I ₀ , and the peak P of the absorption spectrum of the hydroxyl group If the distance to I ₁ is the transmittance that gives the half-width, that is, the distance I _A from the horizontal axis, I ₀ and I ₁
It is determined as the geometric mean of I _A = √ ₀ × ₁ . Next, consider a point _Q whose distance from the horizontal axis is IA, which is the same distance from the vertical axis as the peak P of the hydroxyl group spectrum. The line segment Y obtained by passing through Q and drawn parallel to the horizontal axis as shown in FIG. 1 intersects the spectrum of the hydroxyl group is the half width (cm ^-1 ). Further, the total degree of acetalization is defined as follows. That is, when the general formula of mixed polyvinyl acetal is expressed by the following formula, The total acetalization degree X (mol %) is expressed by the following formula. X=2a+2b/2a+2b+c-d×100 (mol%) Here, a, b, c, and d can be calculated by an appropriate method, and an example of a specific procedure will be shown below. First of all,
The proportions (wt%) of the vinyl alcohol part and the vinyl acetate part are determined by the JIS method (JIS K 6728), and the total amount is calculated as 100% by weight.Then, using an infrared spectrophotometer, the butyl acetal part and the acetate part are determined. Find the weight ratio of the acetal part, a, b,
The values expressed in weight corresponding to c and d are converted into mole representation to calculate a, b, c, and d. The present inventors have discovered that even if polyvinyl acetals have the same degree of acetalization, the absorption bands of hydroxyl groups in their infrared absorption spectra are slightly different. That is, the half-width of polyvinyl acetal, which provides an adhesive with improved adhesive strength at high temperatures, is always larger than that of polyvinyl acetal used in conventional adhesives, even if the degree of acetalization is the same. The reason for this is still not fully clear, but
Polyvinyl acetal, in which hydroxyl groups are arranged in a chain, tends to have stronger association through hydrogen bonds than polyvinyl acetal in which hydroxyl groups are arranged irregularly, resulting in increased rigidity and adhesive strength even at high temperatures. It is believed that a composition is obtained,
The hydroxyl group absorption band in the infrared absorption spectrum of polyvinyl acetal is swelled toward the lower energy side, that is, the lower wavenumber side, because there is a part where the association by hydrogen bonding is stronger than that of polyvinyl acetal, where the arrangement of hydroxyl groups is irregular. It is thought that the half width of hydroxyl group absorption becomes large. The present invention was completed based on this knowledge. Mixed polyvinyl acetal satisfying the above formula (1) can be obtained, for example, by a precipitation method, in which butyraldehyde and acetaldehyde are added to an aqueous polyvinyl alcohol solution in the presence of an acid catalyst to obtain a precipitate at a relatively low temperature, and then the reaction system It is obtained by raising the temperature and aging for a long time under high conditions, followed by neutralization, washing with water, and drying using conventional methods. Note that acetaldehyde includes various acetaldehydes that can be converted into these. or,
The amount of aldehyde used is preferably within a range such that the total degree of acetalization of the mixed polyvinyl acetal obtained by the acetalization reaction is 50 to 80 mol%. Further, the average degree of polymerization of the polyvinyl alcohol used as a raw material for the mixed polyvinyl acetal in the present invention is 100 to 2,500, preferably 300 to 2,500, and the saponification degree is usually 85 mol% or more. The above mixed polyvinyl acetal is mixed with a thermosetting resin to form the adhesive composition of the present invention, and examples of the thermosetting resin include phenol resin, epoxy resin, urea resin, melamine resin, etc. Phenol resin is particularly preferably used as a printed circuit adhesive for bonding metal to a base material made of paper impregnated with phenol resin. The mixing ratio of the mixed polyvinyl acetal to the thermosetting resin is preferably 1:4 to 4:1, particularly 2:3 to 3:2, by weight. Alternatively, in order to mix the above mixed polyvinyl acetal and thermosetting resin to form a composition, it is best to add and dissolve both in an appropriate organic solvent to make a uniform mixed solution. The solvent may be appropriately selected from solvents used in solvent-based adhesives such as alcohols, ethers, ketones, and aromatics.
Also, a mixture of these solvents may be used. Since the adhesive composition of the present invention has the above-mentioned structure, it has excellent adhesive strength, particularly adhesiveness at high temperatures, and excellent heat resistance.
For example, it can be used in applications requiring heat resistance, such as adhesives for metals, particularly adhesives for printed circuits, adhesives for brake shoes, etc., and can exhibit excellent performance. Next, examples of the present invention will be described. Example 1 Production of resin A 225 g of polyvinyl alcohol with a degree of polymerization of 2000 and a degree of saponification of 98.5 mol% was added to 3000 g of water and heated at 90°C for 2 hours.
After standing for a while to dissolve the polyvinyl alcohol, the solution was cooled to 50°C and diluted with 200% hydrochloric acid at a concentration of 35%.
g and cooled to 30℃. Next, add 58g of paraacetaldehyde (99% purity) and heat to 30-25℃.
It was kept at a temperature of 3 hours and then cooled to 15°C. Next, 78 g of n-butyraldehyde was added to the reaction system at 15°C.
When this was added, a fine white powdery resin precipitated out.
The temperature of this reaction system was raised and the temperature was maintained at 60° C. for 5 hours, and then the temperature was lowered and the mixture was neutralized, washed with water, and then dried. 1 g of the mixed polyvinyl acetal resin A thus obtained was mixed with 10 c.c. of toluene and 10 c.c. of ethanol.
After dissolving in a mixed solvent of cc and casting on a mirror surface,
The mixture was dried in a vacuum dryer at 60°C for 3 hours to obtain a mixed polyvinyl acetal film. The infrared absorption spectrum of this film was measured using an EPI-G ₃ diffraction grating infrared spectrophotometer manufactured by Hitachi, Ltd., and the half-width of the hydroxyl groups was determined based on FIG. 1 in accordance with the definition of half-width in the present invention. The half width Y was 236 cm ^-1 and the total degree of acetalization was 67.3 mol %, that is, the value of -5X+550 was 214, so the above formula (1) was satisfied. These relationships are shown in Table 1. Preparation of Adhesive The above resin A and phenol resin (trade name: Plyophene 5010, manufactured by Dainippon Ink Co., Ltd.) are dissolved in a 1:1 mixed solvent of ethanol/toluene at the composition ratio shown in Table 1. Resin content: 15% by weight
An adhesive was prepared as a solution of Using the above adhesive, the adhesive surface was polished with sandpaper and then cleaned with Triclean.The wall thickness is 2 mm and the width is
Two iron plates 25mm long and 110mm long with an adhesive surface of 25mm x
Glue together to make 20mm, 20Kg/cm ² at 180℃.
A test piece for measuring adhesive strength was prepared by leaving the sample under pressure for 30 minutes. The adhesive strength of the sample piece was measured using a tensile tester at a tensile rate of 10 mm/min and a temperature of 150° C. The results are shown in Table 1. Example 2 An adhesive was obtained in the same manner as in Example 1, except that the composition ratio of resin A obtained in Example 1 and phenolic resin was changed as shown in Table 1, and adhesiveness was measured under the same conditions. The strength is shown in Table 1. Example 3 Resin B was obtained in the same manner as in Example 1, except that the aging temperature was changed to 80° C., and an adhesive was also obtained. Table 1 shows the half width of the hydroxyl group in the infrared absorption spectrum of Resin B, the adhesive strength of the adhesive, etc. Comparative Examples 1 and 2 Para-acetaldehyde and n-butyraldehyde were added to the same polyvinyl alcohol aqueous solution used in Example 1 containing a hydrochloric acid catalyst, and a precipitate was obtained in the same manner as in Example 1. The mixture was kept at ~40°C for about 5 hours, and then neutralized, washed with water, and dried according to conventional methods to obtain polyvinyl acetal resin E.
Using this resin E, an adhesive with the same composition ratio as in Example 1 (Comparative Example 1) and polyvinyl acetal 40
An adhesive (Comparative Example 2) containing 60 parts by weight of phenol and 60 parts by weight of phenol was prepared. Each characteristic value is shown in Table 1. Comparative Example 3 342g of polyvinyl acetal used in Example 1
0.675 g of sodium dodecylbenzenesulfonate and 26.4 g of hydrochloric acid having a density of 1.18 were added to an aqueous solution at a temperature of 10°C in which 2,950 g of water was dissolved and mixed. This mixture was kept at a temperature of 10°C and the butyraldehyde was added at 170 °C.
When g was added, a slight temperature rise was observed, and a fine white powdery resin was precipitated. Next, this reaction system was stored at 13°C for 60 minutes, then gradually raised to 70°C over 150 minutes, and then kept at 70°C for 30 minutes.
After holding for a minute, 13 g of sodium hydroxide was added to neutralize the solution to a pH of 9 to 11. The reaction system was maintained at 60°C or higher for about 57 minutes. Thereafter, the resin was kept at 70° C. for 120 minutes, washed with water, and dried to obtain resin F. The half width of hydroxyl group absorption in the infrared absorption spectrum of Resin F thus obtained was 220 cm ^-1 . An adhesive was prepared in the same manner as in Example 1 except that Resin F was used. Each characteristic value was as shown in Table 1. 【table】

[Brief explanation of drawings]

FIG. 1 is a chart showing an example of the infrared absorption spectrum of the mixed polyvinyl acetal used in the composition of the present invention. P...Peak of absorption spectrum of hydroxyl group.

Claims (1)

[Scope of Claims] 1. A mixed polyvinyl acetal in which polyvinyl alcohol with a degree of polymerization of 2500 or less is mixed and acetalized with butyraldehyde and acetaldehyde, where the total degree of acetalization is defined as X (mol %),
When the half-width of hydroxyl group absorption in an infrared absorption spectrum where the vertical axis is the transmittance and the horizontal axis is the wave number is Y (cm ^-1 ), the transmittance of the peak of the hydroxyl group absorption spectrum is about 50%. An adhesive composition comprising a mixed polyvinyl acetal whose half width Y satisfies formula (1) when the film thickness is adjusted, and a thermosetting resin. (1) Y≧−5X+550 2. The adhesive composition according to claim 1, wherein the thermosetting resin is a phenol resin. 3. The adhesive composition according to claim 1 or 2, wherein the weight ratio of mixed polyvinyl acetal to thermosetting resin is 1:4 to 4:1.