JPH11961A - Surface protective film or sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a float phenomenon from being generated even though a surface protective film or sheet is restored to ordinary temperature by thermopressure fixing with an autoclave or the like by a method wherein a film in which oxygen permeability at specific temperature and specific relative humidity is under specific numerical value is used as a base material, and a pressure-sensitive adhesive layer is provid on its one side. SOLUTION: A film of 25 μm thickness consisting of ethylene-vinyl alcohol copolymer is used as a base material film. One side surface of the film is treated with corona, and a pressure sensitive adhesive is applied to this surface. Though a permeation amount of oxygen receives influences from a thickness of the film, temperature and humidity, the permeation amount is inversely proportional to the thickness of the film, and linearity is realized between a logarithm of the permeation amount and a reciprocal of absolute temperature. Though oxygen transmission at temperature and pressure under the same conditions as those for an autoclave is intrincically important, when a film wherein oxygen permeability at 20 deg.C and 0%RH is under 40 cc/m<2> 24 hrs-atm (a film wherein oxygen permeability at ordinary temperature, ordinary humidity, and ordinary pressure is very low) is used as the base material, occurrence of float is very little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface protective film or sheet, and more particularly to a surface protective film or sheet suitable for thermocompression bonding, such as a surface protective film or sheet for a polarizing plate.

[0002]

2. Description of the Related Art Conventionally, a polyester film has often been used as a surface protective film or sheet of a polarizing plate. The adhesive-processed polarizing plate is heated and pressed by an autoclave in order to bring the polarizing plate into close contact with the glass substrate. However, when the temperature is returned to room temperature after the heating and pressing, countless floating bubbles are generated in the film. If such bubbles are present, there is a problem that a foreign substance inspection in a later process cannot be performed.

[0003] Although the above-mentioned floating phenomenon is less in a polyester film than polyethylene and polypropylene, it is not absent, and bubbles tend to be generated as the temperature and pressure of the autoclave become higher.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface protective film or sheet which does not cause a floating phenomenon even when the temperature is returned to room temperature by heating and pressure bonding in an autoclave or the like.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the oxygen permeability at 20 ° C. and 0% RH (relative humidity) is 4%.
0 (cc / m ² · 24 hrs · atm), preferably 30 (cc / m ² · 24 hrs · atm) or less, more preferably 20 (cc / m ² · 24 hrs · atm)
By using the following film as a base material, it has been found that a surface protective sheet in which floating is prevented can be obtained, and the present invention has been completed.

Although the amount of oxygen permeation is affected by the thickness of the film and the temperature and humidity, the amount of permeation is inversely proportional to the thickness of the film, and linearity is established between the logarithm of the amount of permeation and the reciprocal of the absolute temperature. I know it.

In actual use, the oxygen permeability at the same temperature and pressure as the autoclave is originally important.
Oxygen permeability at 40 ° C. and 0% RH is 40 (cc / m ² · 24
When the base material is a film having an oxygen permeability at room temperature, normal humidity, and normal pressure, the occurrence of the float is extremely small under practical autoclave conditions. I found

[0008] The plastic film having a low oxygen permeability, which is the basis of the present invention, has a thickness of 10 to 30.
Oxygen permeability at 20 ° C. and 0% RH at about μm is 40
(Cc / m ² · 24 hrs · atm), a plastic film of less than 10 g is preferred, for example, ethylene vinyl alcohol copolymer, polyvinyl alcohol, vinylidene chloride, vinylidene chloride-methyl acrylate copolymer, acrylonitrile copolymer, polyamide and the like. Used.
These may be used alone as a base film, or a multilayer film of these composite multilayer films or other resins (for example, general polyethylene, polypropylene, polyester, etc.) that satisfies the above oxygen permeability conditions. If there is no problem. Also, the thickness of the plastic film is not particularly limited as long as it satisfies the above oxygen permeability conditions, but is preferably 10 to 200 μm.
m, especially 15 to 40 μm.

The oxygen permeability is measured by using oxygen in a dry state and using a gas permeation measuring selmanometer according to JI.
Performed according to SZ1707.

The substrate having such an oxygen permeability can be obtained, for example, by selecting the material of the plastic film, adjusting the thickness, and combining with a different kind of film.

Oxygen permeability at 20 ° C. and 0% RH is 40
If it is more than (cc / m ² · 24 hrs · atm), after heating and pressure bonding by an autoclave, when the temperature is returned to normal temperature, bubble-like floating occurs. When a base film having a high oxygen permeability is used, a large amount of air enters the autoclave through the base film and is compressed at the interface between the polarizing plate surface and the adhesive. It is considered that when the temperature is returned to normal temperature, the compressed air expands, and a bubble-like floating occurs.

The pressure-sensitive adhesive used in the present invention may be any of a pressure-sensitive adhesive composition of an acrylic type, a synthetic rubber type, and a rubber type, but an acrylic pressure-sensitive adhesive whose adhesive strength is easily controlled by the composition is desirable. The pressure-sensitive adhesive is applied to one side of the base material of the plastic film so that the thickness after drying is 1 to 50 μm, preferably 5 to 30 μm.

[0013]

The present invention will now be described more specifically with reference to examples and comparative examples. Note that the present invention is not limited to these examples.

[Preparation of Pressure-Sensitive Adhesive] An acrylic ester of 2-ethylhexyl acrylate (96 mol) and hydroxyethyl acrylate (4 mol) having an average molecular weight of 700,000 (polystyrene equivalent) in ethyl acetate was prepared using a conventional method. A polymer (25% solution) was obtained. This solution 10
With respect to 0 parts (solid content), a crosslinking agent (polyisocyanate,
Nippon Polyurethane Industry Co., Ltd., trade name Coronate L)
Three parts were added to obtain a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition was applied to the substrate films of the following Examples and Comparative Examples so that the thickness after drying was 20 μm to obtain a surface protection sheet. Table 1 shows the oxygen permeability at 20 ° C. and 0% RH of the base films of the respective examples and comparative examples.

Example 1 As a substrate film, a 25 μm-thick film made of an ethylene vinyl alcohol copolymer (EVAL EF-
F, manufactured by Kuraray Co., Ltd.). One surface of the film was subjected to corona treatment, and an adhesive was applied to this surface.

Example 2 A 25 μm-thick film made of polyvinyl alcohol (Boblon, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used as a base film. Corona treatment on one side of the film,
An adhesive was applied to this surface.

Example 3 As a base film, a multilayer film in which a vinylidene chloride resin was coated on a polyester film (thickness: PET)
(Polyethylene terephthalate) = 12 μm, vinylidene chloride resin layer = 2 μm) (Seneshi KET # 6000, manufactured by Daicel Chemical Industries, Ltd.) was used. An adhesive was applied to the polyester side.

Example 4 As a base film, OPP (stretched polypropylene film) 20 μm / EVAL EF-F 15 μm / CPP
(Polypropylene film by T-die method (cast)) A 50 μm three-layer film (laminated product using a urethane-based adhesive) was used. Corona treatment on OPP side,
An adhesive was applied to this surface.

Example 5 A 20 μm thick polyamide (nylon-6) film was used as a base film. An adhesive was applied to one side of the film.

Comparative Example 1 A biaxially stretched polyester film (25 μm in thickness) was used as a base film. An adhesive was applied to one side of the film.

Comparative Example 2 A biaxially stretched polypropylene film (thickness: 40 μm) was used as a base film. An adhesive was applied to one side of the film.

[Test Method] After the surface protective sheets obtained in Examples and Comparative Examples were attached to a polarizing plate with a laminator, the polarizing plate was attached to a glass plate with a laminator. NPF-F manufactured by Nitto Denko Corporation as an adhesive-processed polarizing plate
1225 DUAG25 was used. A 0.7 mm-thick non-alkali glass plate was used as a substrate to which the adhesive-processed polarizing plate was attached.

In an autoclave, it was heated and pressed at 70 ° C. and 5 atm for 30 minutes, and then returned to normal temperature and normal humidity, and the floating phenomenon of the surface protective sheet was observed. Table 1 summarizes the results.

[0025]

[Table 1]

[0026]

The surface protective film or sheet of the present invention can prevent the occurrence of a floating phenomenon even when the surface protective film or sheet is heated and pressed by an autoclave or the like to return to room temperature. Therefore, when used as a surface protective film or sheet for a polarizing plate, generation of bubbles is suppressed, and foreign matter inspection in a later step is facilitated.

Claims (2)

[Claims] 1. Oxygen permeability at 20 ° C. and 0% RH is 40
(Cc / m ² · 24 hrs · atm) A surface protection film or sheet comprising a plastic film as a base material and an adhesive layer provided on one side thereof. 2. The surface protective film or sheet according to claim 1, which is a surface protective film or sheet for a polarizing plate.