JPS6248783A - Polyurethane based adhesive with residual tackiness after curing prevented - Google Patents

Abstract

PURPOSE:The titled adhesive, consisting of an organic solvent, a polyisocyanate based derivative soluble in the above-mentioned organic solvent and specific polystyrene (PS), capable of transportation of stacked flexible printed circuit boards and having prevented residual tackiness after curing. CONSTITUTION:An adhesive consisting of (A) an organic solvent, e.g. toluene, and (B) an icocyanate derivative soluble in the above-mentioned organic solvent and (C) polystyrene (PS) having 5,000-20,000 average molecular weight.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a novel polyurethane adhesive that prevents tackiness remaining after adhesive curing.

(b) Problems to be Solved by the Prior Art and the Invention In recent years, polyurethane adhesives have been used to bond various articles due to their excellent performance. With the expansion of such application fields, residual tackiness after adhesive curing has become a problem, which was not considered a problem at all in the past. This residual tackiness is thought to be caused by the residual terminal NGO groups of the diisocyanate derivative, which is the main component of the polyurethane adhesive, and the NCO groups of the triisocyanate compound, which is the curing agent.

This problem is particularly important in the field of flexible printed wiring boards where the polyurethane adhesive is exposed after curing. In other words, a flexible printed wiring board is created by laminating a support such as a film and metal foil with a polyurethane adhesive, and then etching away the metal foil that becomes the non-wiring area, leaving the wiring area. However, the polyurethane adhesive after curing will be exposed in the non-wiring areas. Therefore, if there is residual tackiness in the polyurethane adhesive after curing, the wiring boards may stick to each other while the flexible printed wiring boards are stacked and transported. This adhesion reduces the commercial value of the flexible printed wiring board, and if the adhesion is significant, the wiring portion may peel off or the wiring board itself may be torn when it is removed.

Therefore, the present invention has been made with the aim of solving the drawbacks that have arisen with the expansion of the field of application of polyurethane adhesives, which did not exist in the past. The purpose is to prevent residual tackiness.

(c) Means and action for solving the problems, that is, the present invention provides a solution to the residual tackiness after curing, which is made of an organic solvent, a diisocyanate derivative soluble in the organic solvent, and polystyrene having an average molecular weight of 5,000 to 2,000 G. This relates to a polyurethane adhesive that prevents

The polyurethane adhesive according to the present invention is of a room temperature or heat curing type, and hardens as the organic solvent evaporates.

The organic solvent used in the present invention is toluene.

Desired substances such as benzene, xylene, carbon tetrachloride, ethyl methyl ketone, ethyl acetate, amyl acetate, etc. are used alone or in combination, and these dissolve both diisocyanate derivatives and polystyrene having an average molecular weight of 5,000 to 20,000. It has to be something. Therefore, depending on the type of diisocyanate derivative used, it is necessary to appropriately select or mix an organic solvent that dissolves it well.

Diisocyanate derivatives refer to relatively high-molecular-weight derivatives having the following structural units, which are mainly produced by the polyaddition reaction of diisocyanates and glycols.

(However, R, , R, and 4 are hydrocarbon groups.) However, the diisocyanate derivatives referred to in the present invention also include those with relatively high molecular weights having a urethane bond -eNHcOo÷ produced by other methods. .

Polystyrene having an average molecular weight of 5,000 to 20,000 functions to block the NGO groups remaining after the diisocyanate derivative is cured, thereby preventing its tackiness. If the average molecular weight is less than 5,000, the effect of preventing tackiness will be insufficient (unpreferable), and if the average molecular weight exceeds 20,000, the adhesive force of the polyurethane adhesive will become weak, which is not preferable. It was measured by permission chromatography method (GPC method).

The amount of polystyrene with an average molecular weight of 5,000 to 20,000 is 0 per 100 parts by weight of the diisocyanate derivative.
．． A small amount of about 5 to 3 parts by weight may be sufficient. This is because the amount of remaining NGO groups is small in the first place.

In the polyurethane adhesive of the present invention, a curing agent such as a diisocyanate compound or a triisocyanate compound is blended, as in conventional adhesives.

(d) Examples and Comparative Examples Polystyrene having the average molecular weight shown in Table 1 was added to an adhesive solution consisting of 70% by weight of polyurethane resin, 29.5% by weight of ethyl acetate, and 0.5% by weight of triisocyanate compound. Polyurethane adhesives were obtained (sample Nos. 3 to 7)
is an example, sample No. 2,8°9 is an example. )
. Peel test 1 using this polyurethane adhesive. II
I did it. The results are shown in Table 1.

In addition, in the peel test (■), a polyurethane adhesive was applied to the upper end of a rectangular polyester film of 5 cm X IQc + r, and after curing was completed, a 5 cm X IQ c + r strip of polyester film was applied onto the adhesive layer.
The lower end of another polyester film (m) was overlapped, and then a load of 2 kg/- was applied and left for 30 minutes.

Grip the non-adhesive parts of the two polyester films, which are separated into left and right sides around the adhesive part, and pull them left and right. In this way, the tensile load when the superimposed polyester films are peeled from the adhesive portion after curing is measured.

Peeling test (2): A polyurethane adhesive is applied to the upper edge of a 5cm x IQcm polyester film, and then the lower edge of a 5c+++XIQcm aluminum foil (thickness 10μ) is immediately placed over the coated area, and the polyurethane adhesive is cured. Grip the non-adhesive parts of the polyester film and aluminum foil, which are separated into left and right parts around the adhesive part, and pull them left and right.

As the tensile load was increased, the case where the aluminum foil broke before the adhesive part was evaluated as "good", and the case where the adhesive part broke first was evaluated as "unsatisfactory".

From the above results, the polyurethane adhesive containing polystyrene having an average molecular weight of 5,000 to 20,000 has a small residual tackiness after curing, and the strength of the bonded portion is high. On the other hand, the average molecular weight is 2000 or 4000
Polyurethane adhesives containing polystyrene have a large residual tackiness after curing.

Further, in the case of a polyurethane adhesive to which polystyrene having an average molecular weight of 123,000 or 25,000 is added, the strength of the bonded portion is low.

(e) Effects of the invention As is clear from the above explanation, if the polyurethane adhesive according to the present invention is used, the adhesive strength is equivalent to that of a polyurethane adhesive that does not contain polystyrene;
Moreover, it is possible to prevent the tackiness of the adhesive after hardening.

In particular, if the polyurethane adhesive according to the present invention is used to bond the film and metal foil of a flexible printed wiring board, the flexible printed wiring boards created by etching away the metal foil in the non-wiring areas can be immediately stacked and manufactured. This has the effect that it can be shipped as If this is a conventional polyurethane adhesive, it cannot be stacked immediately, so it is aged at high temperatures for more than 10 days before being stacked and shipped. As can be seen from this, the present invention is extremely useful from an industrial and economic perspective.

Claims (1)

[Claims] A polyurethane adhesive which prevents residual tackiness after curing and is composed of an organic solvent, a diisocyanate derivative soluble in the organic solvent, and polystyrene having an average molecular weight of 5,000 to 20,000.