JP2002197926A - Plastic film with transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems in a plastic film with a transparent conductive film having a protection film wherein (2) a first protection film made of thermoplastics resin, (3) a second protection film having difference coefficient of linear expansion between the plastic film constituting the plastic film with the transparent conductive film is 30 ppm/ deg.C or less on the other surface of (1) the plastic film with transparent conductive film on one surface are laminated in the order of (1), (2), (3), and bubbles generated in the protection film in a heating process of the working process of a touch panel. SOLUTION: By using a film in which the height of a projection on the film surface is 25 μm or less as the first protection film, the plastic film with the transparent conductive film having the protection film generating no bubble is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plastic film with a transparent conductive film used for a transparent touch panel and the like, and more particularly, to a plastic film with a transparent conductive film with a protective film.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have attracted attention as image display devices, and as one of their uses, application to portable electronic notebooks, information terminals, and the like is expected. Further, as an input device such as a portable information terminal, a device in which a transparent touch panel is mounted on a liquid crystal display element is used. Conventionally, glass has been used as a substrate for a touch panel, but recently, a plastic film has attracted attention from the viewpoint of weight reduction and resistance to cracking. As used herein, the term “substrate” refers to a substrate with a transparent conductive film formed by forming a transparent conductive film such as ITO on the surface of a glass or plastic film. As a plastic film used for such an application, conventionally, polyethylene terephthalate (PE) is used.
T) has been used. However, since there are many problems in terms of optical characteristics, in recent years, solution casting using a material having a high glass transition temperature such as polycarbonate (PC), polyarylate (PAR), polysulfone (PSF), or polyethersulfone (PES) has been proposed. The film formed by the method
Attention has been paid to the surface smoothness and optical isotropy. When manufacturing a touch panel using these substrates,
In order to prevent the film surface from being damaged during the process, a protective film is usually attached to the surface opposite to the surface on which the transparent conductive film is formed, and the process is performed.

[0003] As the protective film used for the above purpose, a PET film is usually used from the viewpoint of heat resistance and mechanical strength. PET film is one of plastic films having a small linear expansion coefficient. Therefore, in various heat treatments during the process, warping of the film due to a difference in linear expansion coefficient between the film with the transparent conductive film and the protective film occurs. In addition, PET film is usually 1
1% mainly in MD (winding direction) when heat over 00 ° C is applied
As described above, there has been a problem in that even if heat shrinkage occurs and the temperature is returned to room temperature after the heat treatment, warpage remains or a pattern shift occurs due to heat shrinkage. In order to solve such a problem, a method of using a plastic film having a coefficient of linear expansion close to that of a plastic film constituting a plastic film with a transparent conductive film as a protective film, as shown in, for example, JP-A-7-68690, has been proposed. Well known. The present invention is based on the premise that a processing process is performed in a roll shape. However, in actual processing of a touch panel or the like, in many cases, a roll-shaped film is cut into a fixed size and processed through a single wafer. When the film is processed in a roll, the film is run under a certain tension in order to run the film. In this case, even if the laminated film has a slight curl, it is stretched by the tension and becomes flat. Therefore, it does not pose a major problem, but when cut into single sheets, processing becomes difficult even with a slight curl.

[0004]

In order to solve the above-mentioned problems, as disclosed in JP-A-11-320744, a plastic film with a transparent conductive film is formed on a plastic film with a transparent conductive film via a first protective film. It has been found that a laminated film having a warp in a wide tension range at the time of lamination can be obtained by laminating a plastic film to be laminated and a second protective film having a close linear expansion coefficient. However, if the laminated film is cut into sheets and passed through a heating process for a touch panel or the like, bubbles may be generated in the adhesive layer used for bonding, and as a result, bubble marks may be formed on the plastic film with a transparent conductive film. Not only cause poor appearance such as
Electricity of assembled touch panel and liquid crystal display element,
There is a problem that optical characteristics are also impaired. In particular, when the thickness of the second protective film is increased to increase the rigidity of the entire laminated film in order to improve the handleability of the film at the time of processing, there has been a problem that the number of generated bubbles is greatly increased.

[0005]

As a result of repeated studies to solve the above problems, a film having protrusions on the film surface of 25 μm or less is used as a first protective film to be bonded to a plastic film with a transparent conductive film. Thereby, it was found that the generation of the bubbles can be prevented.

That is, the present invention provides (1) a first protective film made of thermoplastic plastic, (3) a transparent conductive film, A second protective film having a linear expansion coefficient difference of 30 ppm / ° C. or less from a plastic film constituting the plastic film with a film, and a protective film formed by laminating (1), (2) and (3) in this order. In a plastic film with a transparent conductive film,
A plastic film with a transparent conductive film with a protective film, wherein the height of the protrusion on the first protective film surface is 25 μm or less.

[0007] The first protective film (2) is preferably a polyolefin-based film.

In particular, the first protective film (2) is preferably a non-stretched polypropylene film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a plastic film constituting a plastic film with a transparent conductive film will be described.

As the plastic film, a transparent plastic film is preferable, and polycarbonate (P
C), polyarylate (PAR), polysulfone (P
SF), polyethersulfone (PES) and the like are used. In particular, when these resins are used for applications requiring optical isotropy such as a liquid crystal substrate, a solution casting method using these resins is used. It is desirable to use a film formed by using a film. In addition, these materials have a P value in terms of mechanical strength.
Since it is inferior to ET, it is necessary to attach a protective film to the back surface in order to suppress the occurrence of defects during the processing step. Furthermore, since there is usually a heating step of 100 ° C. or more in the liquid crystal panel or touch panel processing step, the heat deformation temperature is desirably 100 ° C. or more, and more preferably, in that this step does not cause thermal deformation. Is 120 ° C. or higher. Also in this respect, the above resin is suitably used. The heat deformation temperature indicates a temperature at which deformation of a TMA curve measured by thermomechanical analysis (TMA) starts. As a film support used in the solution casting method, a resin film or the like can be used in addition to a stainless steel belt and a stainless steel drum, but is not limited thereto. A so-called retardation film obtained by stretching these films to have birefringence can also be suitably used for the purpose. Film thickness is usually 5
It is about 0 μm to 250 μm and is appropriately selected depending on the device to be used. it can.

As a transparent conductive film formed on a transparent plastic film, a material obtained by doping a metal oxide such as indium oxide, tin oxide or zinc oxide to increase conductivity is generally used. Although not particularly limited, a composite oxide of indium oxide and tin oxide is preferable in terms of conductivity, etching properties, and the like. As a method for forming the transparent conductive film, a method such as DC magnetron sputtering, EB vapor deposition, or CVD is used, and among these, DC magnetron sputtering is particularly preferable in terms of resistance stability and adhesion to the film. Used.

The first protective film to be bonded to the other surface of the plastic film having a transparent conductive film formed on one side has an effect of softening in a heating step at the time of processing a liquid crystal panel or a touch panel, thereby suppressing curling or deformation of the laminated film. Since it is necessary, a film made of a thermoplastic plastic is preferable, and the heat distortion temperature is desirably 100 ° C. or less. As a film with such characteristics,
Examples include polyethylene, polypropylene, vinyl chloride, acrylic, nylon, and the like, and mixtures thereof, but are not particularly limited thereto. Among these films, a polyolefin-based film is preferable because it is suitable for a heating step at about 100 ° C., and is easily available. ) Films are more preferred. Among the unstretched polypropylene (cPP) films, homopolymer type unstretched polypropylene (cPP) is particularly preferable from the viewpoint of heat resistance. The thickness of the first protective film is at least 20 μm from the viewpoint of the total film thickness of the plastic film with a transparent conductive film with the protective film of the present invention and the handling property at the time of bonding.
It is not more than 00 μm.

[0013] Since the first protective film is bonded to the first protective film via an adhesive, the film surface is preferably smooth. That is, the projections on the first protective film surface generate a space between the first protective film and the second protective film when the second protective film is bonded, and cause air bubbles at the time of bonding. Not only that, there is a possibility that even if no space is generated, the nucleus may generate bubbles at the time of heating. Therefore, it is preferable that the height of the protrusion is as small as possible and the number of the protrusion is small. The protrusion on the film surface referred to here indicates a part which abnormally protrudes, not a periodic waviness or waving. Such protrusions include, for example, foreign matter, fish eyes, and bubbles during film formation. Fish eyes are defects generated in a film formed by a melt extrusion method like a general polyolefin film, and are generated due to a gel component, a foreign substance, and the like contained in a resin. In particular, unstretched polypropylene (cPP) films may generally contain many fish eyes. In order to suppress the generation of bubbles in the heating step of a touch panel or the like, the height of these projections is preferably 25 μm or less, more preferably 10 μm or less. The height of the protrusion shown here is JIS
Using a surface roughness measuring device as shown in B0651 and B0562, a cross-sectional curve (JIS)
B0601). Taking measures such as adding an additive at the time of melt extrusion in order to suppress the generation of projections due to fish eyes in the film can also be expected to have an effect of making the surface state of the film smoother. As a result, it is possible to reduce bubbles generated in portions other than the fish eyes, and such a measure is one of more effective means as a measure for preventing the generation of bubbles.

The adhesive for bonding the first protective film to the plastic film with a transparent conductive film desirably does not cause foaming, deterioration, or the like during various heat treatments during the process. In addition, since it is finally peeled off from the plastic film with the transparent conductive film, the adhesive strength is preferably 0.5 N / 25 mm or less, more preferably 0.3 N / 25 mm or less so that the film can be easily peeled off. Is desirable. As an adhesive having such characteristics, an acrylic adhesive, a silicone adhesive, a urethane adhesive and an EVA adhesive are generally used, but are not limited thereto.

The second protective film bonded to the first protective film may be a plastic film forming a plastic film with a transparent conductive film in order to suppress curling during the heating step of the laminated film and thermal deformation after heating. It is preferable that the difference in the coefficient of linear expansion from the film is 30 ppm / ° C. or less, more preferably 20 ppm / ° C. or less. The heat distortion temperature is 100 as in the case of the plastic film constituting the plastic film with a transparent conductive film.
C. or higher, more preferably 120 ° C. or higher. The linear expansion coefficient is determined from the slope of a TMA curve measured by thermomechanical analysis (TMA). From these points, PAR, PC, and a mixture thereof are preferably formed into a film by a method such as melt extrusion in terms of cost and the like. Also, if the thickness of the second protective film and the plastic film with a transparent conductive film are significantly different, curl may occur even with a slight difference in the coefficient of linear expansion. It is desirable that the thickness be 0.5 times or more and 2 times or less.

The adhesive strength of the adhesive for bonding the second protective film to the first protective film is ultimately peeled off between the plastic film with a transparent conductive film and the first protective film. It is desirable that the adhesive strength between the protective film and the plastic film with a transparent conductive film is larger than the adhesive strength.

As a method of attaching the first and second protective films to the plastic film with a transparent conductive film,
Paste the first and second protective films on the plastic film with the transparent conductive film in this order, after first bonding the first and second protective films, and then laminating on the plastic film with the transparent conductive film, or co-extrusion,
There is a method such as adhesive processing on a two-layer film of a first protective film and a second protective film, which is produced by thermal lamination or the like, and the method is not particularly limited thereto.

[0018]

The present invention will be described below with reference to specific examples. The thermal deformation temperature and the coefficient of linear expansion described in Examples and Comparative Examples are TMA (tensile mode, sample size 20 mm × 3 m).
m, a load of 3 g, a heating rate of 10 ° C./min, and a linear expansion coefficient calculation temperature range of 20 to 100 ° C.). The maximum height of the projection on the film surface is 1 m
After sampling the appearance abnormal part visually observed in the film of No. ² , the cross-sectional curve of the abnormal appearance part was measured with a surface roughness meter. Find the height of the projection from the obtained cross-sectional curve,
The maximum value in 1 m ^{2 was} defined as the maximum height.

Example 1 A 60 μm-thick polycarbonate (PC) film formed by depositing ITO (indium tin oxide) as a transparent conductive film (heat deformation temperature: 165 ° C.)
Polyethylene (PE) with a thickness of 65 μm, which has a maximum height of projections of 8 μm on the film surface (measured from a cross-sectional curve of the projections), on the side opposite to the ITO film formation surface having a linear expansion coefficient of 60 ppm / ° C. Protective film (Acrylic adhesive applied to PE base film. Adhesive strength 0.3N / 25m
m adherend SUS JIS Z 0237), and an acrylic pressure-sensitive adhesive layer (adhesive force 9 N / 25 mm)
130 μm thick PC film (Iupilon film having a linear expansion coefficient of 60 ppm /
° C). 80 ℃ hot air drying oven 30
After heating for minutes, no bubbles were generated in the protective film.

Example 2 A 75 μm-thick polyarylate film (product name: Elmec F-110) formed by forming ITO (indium tin oxide) as a transparent conductive film
0, heat deformation temperature 240 ° C, linear expansion coefficient 70ppm / ° C)
A non-stretched polypropylene (cPP) protection film (thickness: 8 μm, maximum height of projections on the film surface: 45 μm) (an acrylic adhesive is applied to a cPP base film. 3N / 25mm adherend SUS JIS Z 0237) and a 130-μm-thick PC film (Iupilon film with a linear expansion coefficient of 60 ppm / ° C) on which an acrylic pressure-sensitive adhesive layer (adhesive strength 9N / 25mm) is formed. I combined. 8
When heated in a hot air drying oven at 0 ° C for 30 minutes,
No bubbles were generated in the protective film.

Comparative Example 1 A 75 μm-thick polyarylate film (product name: Elmec F-110) formed by forming ITO (indium tin oxide) as a transparent conductive film
0, heat deformation temperature 240 ° C, linear expansion coefficient 70ppm / ° C)
A non-stretched polypropylene (cPP) protective film (thickness: 33 μm) having a maximum height of projections on the film surface of 45 μm (an acrylic adhesive applied to a cPP base film. 3N / 25mm
An adherend SUS JIS Z 0237) was attached, and a 130-μm PC film (Iupilon film having a linear expansion coefficient of 60 ppm / ° C.) on which an acrylic pressure-sensitive adhesive layer (adhesive strength 9 N / 25 mm) was formed was further attached. 80
When heated in a hot air drying oven for 30 minutes, foaming (1
2 pieces / m ² ).

[0022]

According to the present invention, it is possible to process a plastic film with a transparent conductive film without causing bubbles in the protective film due to heating or the like in a processing process of the plastic film with a transparent conductive film with a protective film without impairing electrical and optical characteristics. Can be.

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Claims (3)

[Claims] 1. A plastic film with a transparent conductive film having a transparent conductive film on one side, (1) a first protective film made of thermoplastic plastic, and (3)
With a protective film formed by laminating a second protective film having a linear expansion coefficient difference of 30 ppm / ° C. or less with the plastic film constituting the plastic film with a transparent conductive film in the order of (1), (2) and (3) The plastic film with a transparent conductive film with a protective film, wherein the height of the protrusion on the surface of the first protective film is 25 μm or less. 2. The plastic film with a transparent conductive film with a protective film according to claim 1, wherein the first protective film of (2) is a polyolefin film. 3. The plastic film with a transparent conductive film with a protective film according to claim 1, wherein the first protective film of (2) is a non-stretched polypropylene film.