JPS6250646A - Flaw detection of triacetyl cellulose film for polarizing plate - Google Patents

Abstract

PURPOSE:To develop flaws which are hardly observable with naked eyes without damaging the material of a polarizing plate by bringing a prescribed solvent into contact with the surface of a triacetyl cellulose film for the polarizing plate subjected to an alkali hydrolysis treatment so that the flaws on the treated surface are developed. CONSTITUTION:The triacetyl cellulose film for the polarizing plate is immersed for about one minute into a heated (60 deg.C) aq. alkali soln. of 3N sodium hydroxide, etc. by which the film is subjected to the hydrolysis treatment. The treated film is immersed for about 10 seconds in a solvent selected from a methyl ethyl ketone, ethyl acetate, acetone and tetrahydrofuran and is then air-dried. As a result, the damaged part of the film is whitened and is made distinctively observable by naked eyes.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for inspecting the presence or absence of scratches on the hydrolyzed surface of a triacetyl cellulose film for polarizing plates.

``Conventional technology'' Polarizing plates that are currently widely used are composed of a polyvinyl alcohol film that adsorbs and orients iodine, etc. as the original side light film, and an acetyl cellulose film that serves as a protective film that is adhered to both the front and back sides of the polyvinyl alcohol film. There is.

The reason why an acetylcellulose film is used as a protective film for a polarizing plate is that it has excellent optical transparency and does not impair polarization properties.

However, although cellulose acetate film has the above-mentioned advantages, it has insufficient adhesion with polyvinyl alcohol film, and when manufacturing polarizing plates, the adhesive surface of cellulose acetate film must be pretreated with alkaline hydration. It is considered appropriate to decompose the acetyl cellulose film and adhere the polyvinyl alcohol film to the polyvinyl alcohol film using various adhesives.
9-51911).

By the way, although cellulose acetate film has excellent optical transparency as mentioned above, the light transmittance of cellulose acetate film used for polarizing plates is
It is said that the light transmittance is 92% or more, and this light transmittance is so strict that even a slight decrease (around 0.5%) will cause the film to lose its suitability as a polarizing plate.

It is naturally expected that an acetylcellulose film, which requires high optical transparency, will be partially damaged during various operation steps, including alkaline hydrolysis treatment, and become unsuitable as a polarizing plate material. Therefore, it is desirable to inspect the acetyl cellulose film for any scratches before adhering it to the polyvinyl alcohol film.

However, there have been no reports regarding the necessity or testing method of such testing.

"Problems to be Solved by the Invention" The present inventor has focused on alkaline hydrolysis treatment of triacetylcellulose film, which is particularly widely used among acetylcellulose films, and has developed manufacturing conditions for polarizing plates suitable for industrialization. While conducting evaluation studies, we discovered the following knowledge or problems.

In other words, in order to perform alkaline hydrolysis treatment on a triacetyl cellulose film without impairing its optical transparency, it is necessary to use an alkaline aqueous solution, for example, so that the alkaline hydrolysis treatment is carried out only on the surface layer of the film. Either use one with a normality of 2N or less, preferably 1N or less, or immerse it in an alkaline aqueous solution for a certain period of time.
&J It is necessary to perform the hydrolysis treatment within 5 minutes, preferably within 1 minute; For triacetyl cellulose films that have been appropriately subjected to alkaline hydrolysis treatment as described above, the hydrolysis treatment may be applied to the surface layer of the film. Since the coating is applied thinly only to the surface of the film, even the slightest amount of friction, such as rubbing it with the abdomen of a finger, can damage the surface layer of the film. This is sufficient to cause the film to lose its suitability as a polarizing plate.

The inventor of the present invention, based on the above knowledge and discovery of problems, thought of making the above-mentioned scratches that are difficult to observe with the naked eye so that they can be clearly observed with the naked eye, and further research results. A flaw detection method for the triacetylcellulose film for polarizing plates of the present invention, which is suitable for practical use, has been achieved.

``Means for solving the problems'' and ``effects'', that is, the present invention provides that the alkaline hydrolyzed surface of a triacetylcellulose film for a polarizing plate is treated with methyl ethyl ketone, ethyl acetate, acetone, and tetrahydrofuran. The present invention provides a flaw detection method for a triacetyl cellulose film for a polarizing plate, which is characterized in that the flaws on the hydrolyzed surface are brought into contact with a solvent to reveal the flaws.

The flaw detection method of the present invention has no effect on triacetylcellulose resin that has been subjected to alkaline hydrolysis treatment, and uses a solvent that dissolves or swells only untreated triacetylcellulose resin. By contacting the film, the parts of the triacetyl cellulose film that are exposed at the damaged parts of the film that have not undergone alkaline hydrolysis are dissolved or swollen, and the damaged parts are clearly visible to the naked eye by the whitening phenomenon of the parts. Make sure you are a friend.

The same principle should apply to diacetylcellulose films for polarizing plates, but according to the experiments of the present inventors, in the case of diacetylcellulose films, the same principle applies as in the case of triacetylcellulose films. , no clear effect of scarring was observed.

Theoretically, hydrolysis of the triacetylcellulose film for polarizing plates can be done only on the surface that will later be bonded to the polyvinyl alcohol film. In order to find such a triacetyl cellulose film that has been hydrolyzed only on one side, it is possible to apply the solvent of the present invention only to the side that has been hydrolyzed. The solvent of the present invention must be prevented from coming into contact with the surface of the film that is not exposed. If the solvent of the present invention comes into contact with the surface of the film that has not been hydrolyzed, the film will dissolve or swell and can no longer be used as a polarizing plate.

In other words, the flaw detection method of the present invention cannot be used for flaw detection on the surface of a triacetylcellulose film for polarizing plates that has not been subjected to hydrolysis treatment.

However, regardless of the theory, hydrolysis treatment of triacetylcellulose film for polarizing plate is not carried out over the entire surface of the film from the viewpoint of practical work.
Furthermore, since this is more suitable as a polarizing plate, the flaw detection method of the present invention is also carried out over the entire surface of the triacetylcellulose film.

In carrying out the present invention specifically, a hetriacetyl cellulose film may be immersed in a bath containing a solvent such as methyl ethyl ketone for 1 υ seconds to 2 minutes, and then the film may be air-dried directly or after washing with water.

"Effects of the Invention" As is clear from the above, according to the present invention, scratches that are difficult to see with the naked eye on the hydrolyzed surface of a triacetylcellulose film for a polarizing plate can be clearly visualized with the naked eye. be able to.

Furthermore, according to the present invention, it is also possible to detect portions that have not been partially hydrolyzed for some reason.

Moreover, since the flaw detection method of the present invention does not damage the intact portion of the film to be inspected, the test film can be advantageously used as a material for a polarizing plate.

"Example" Example 1゜A commercially available triacetylcellulose film (manufactured by Fuji Film Co., Ltd., product name: Fujitac, thickness 80μ) was coated with 3N
Immerse it in a sodium hydroxide aqueous solution according to the following article,
Obtain an alkali hydrolyzed product.

Immerse in alkaline aqueous solution at temperature 60°C for 1 minute. Rub several parts of the above alkaline hydrolyzed product with the pad of your finger to make scratches that are difficult to observe based on the amount of flesh. The transmittance of light (400 to 700 nm) of When the film was air-dried after 30 minutes, the damaged area of the film turned white and became visible to the naked eye.

Male side 2゜Example 10 A flaw detection test was conducted in the same manner as in Example 1, except that methyl ethyl ketone was replaced with ethyl acetate, tetrahydrofuran, and a mixed solvent of methyl ethyl ketone and ethyl acetate (1:1). Similar to Example 1, good results were obtained.

Claims (1)

[Claims] (1) A solvent selected from methyl ethyl ketone, ethyl acetate, acetone, and tetrahydrofuran is brought into contact with the alkaline hydrolyzed surface of a triacetyl cellulose film for polarizing plates to reveal scratches on the hydrolyzed surface. A flaw detection method for triacetylcellulose film for polarizing plates.