JPH0649850B2 - Method for preventing foaming of adhesive layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvement of the performance of an adhesive film, and more particularly to a method of cleaning a base film for preventing foaming.

(Prior Art) In recent years, adhesive films have been used for optical materials, electronic materials,
It is used in various fields such as industrial materials.

In particular, many adhesive films used for optical materials and electronic device materials are required to have high performance.

One of the applications is a polarizing film used in a liquid crystal display device.

At present, a liquid crystal display device in which a polarizing film formed by forming a protective layer on at least one surface of a polarizing film is combined with a liquid crystal display cell is thin, lightweight, low voltage operation, low power consumption, etc. As it is attempted to be applied to applications that require durability under high temperature and low humidity conditions such as small items such as watches and calculators, large items such as automobile display panels, measuring instruments, terminal display devices, etc. The demand for liquid crystal display devices having excellent moisture resistance is increasing.

However, at present, in a reliability test, which is a measure of having excellent durability, foaming occurs at the interface between the adhesive layer and the polarizing film or the liquid crystal display cell, and the liquid crystal which is visually recognized by humans. As a display, there is a problem that the display function is deteriorated and the display cannot be used.

As a method for solving these problems, a method of providing a space between a liquid crystal display cell and a polarizing film has been conventionally used.
-91515), and a method of using a mixture of an adhesive composition and an organosilicon monomer having a functional group for adhesion to a liquid crystal display cell (JP-A-57-195208).

However, the method of providing the space is not preferable from the viewpoint of the problem of reduction in contrast and the thinness and lightness which are the features of the liquid crystal display device. The method of using a mixture of an adhesive composition and an organosilicon monomer, and the method of fundamentally preventing foaming are still insufficient. All of these prior arts have a problem of foaming of the substance itself constituting the pressure-sensitive adhesive layer, which is different from the present invention.

(Object of the invention) In view of the present circumstances as described above, an adhesive film used in the field of high precision including a polarizing film has excellent durability even in a reliability test under high temperature and low humidity conditions. The purpose is to provide a method for preventing foaming.

(Means for Solving the Problem) The inventors have conducted various studies on the cause of such foaming, and the foaming is caused by the gas generated from the base film of the adhesive film under high temperature or low humidity. I found out what to do. That is, the solvent remaining in the film formed by using a solvent having a low boiling point is vaporized under an environment such as high temperature and migrates to the pressure-sensitive adhesive layer to cause a foaming phenomenon.

Therefore, it was found that the occurrence of foaming can be prevented by ultrasonically cleaning the base film with water or alcohol-containing water in order to remove the vaporizable solvent that is the cause of foaming. Is. For the ultrasonic cleaning used in the present invention, a cleaning device having a high frequency output of 250 W and an oscillation frequency of 27 KW can be used. Further, as the pressure-sensitive adhesive layer, an acrylic pressure-sensitive adhesive that is used for general pressure-sensitive adhesive films is used.

As a typical example of the substrate film used for carrying out the present invention, a polarizing film having a protective layer made of a material having optical transparency on at least one surface of a polyvinyl alcohol-iodine polarizing film. Examples include films. The film used as a protective layer on the surface of the polarizing film is
There are cellulosic films such as cellulose diacetate, cellulose triacetate, but not necessarily limited thereto.

Examples of the present invention will be shown below.

(Example) Using a commercially available polarizing film obtained by laminating both surfaces of a polyvinyl alcohol-iodine type polarizing film with a cellulose triacetate film, ultrasonic cleaning treatment (high frequency output 250 W, high frequency output 250 W, in ethanol-containing water (ethanol content rate 10%)) was used. Oscillation frequency 27KHZ
Was used). After providing an acrylic pressure-sensitive adhesive layer on one surface of the polarizing film that has been subjected to such a treatment, it is attached to a glass plate, and under the predetermined conditions shown in Table 1, a heat resistance and moisture resistance reliability test is performed, and its foaming The presence or absence was visually confirmed. As a comparative example, Table 1 also shows the test results of the polarizing film not subjected to the cleaning treatment.

(Effect of the invention) As can be seen from the above results, by cleaning the base film with an aqueous cleaning solution, the vaporizable solvent that is the cause of foaming is removed. Foaming did not occur even in the reliability test under the conditions,
It showed excellent durability.

Claims (4)

[Claims] 1. A solvent-based film single layer, which is a plastic film formed by using a solvent, or a base film laminated with this film, and a pressure-sensitive adhesive layer provided on the surface of the solvent-based film. A method for preventing foaming of a pressure-sensitive adhesive layer, which comprises cleaning the surface of the solvent-based film in a pressure-sensitive adhesive film with a cleaning liquid composed of water or a water-based mixed liquid before providing the pressure-sensitive adhesive layer. 2. The method for preventing foaming of a pressure-sensitive adhesive layer according to claim 1, wherein the cleaning liquid is a mixed liquid of water / alcohol. 3. The method for preventing foaming of the pressure-sensitive adhesive layer according to claim 1, wherein the cleaning method is ultrasonic cleaning. 4. The method for preventing foaming of a pressure-sensitive adhesive layer according to claim 1, wherein the solvent-based film is a cellulose-based film.