JPH1073816A - Reflection member for liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a colorless half-transmitting film having a high transmittance and a reflectance by forming a transparent layer having a high refractive index on a transparent film. SOLUTION: This half-transmitting reflection member for a liquid crystal display element has >=30% reflectance and >=40% transmittance for 550nm wavelength. This member is obtd. by alternately depositing transparent high refractive index layers 20 and transparent low refractive index layers 30 on one surface of a transparent polymer film 40. The transparent high refractive index layer 20 consists of a transparent material having a higher refractive index than that of the transparent polymer film 40 as the base body. The transparent low refractive index layer 30 consists of a transparent material having a lower refractive index than that of the transparent polymer film 40 as the base body. As for the transparent high refractive index layer 20, a transparent material having high refractive index such as titanium oxide, oxide of indium and tin and zinc oxide can be used. As for the transparent low refractive index layer 30, silicon oxide or magnesium fluoride is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transflective film having both high transmissivity and high reflectivity, and relates mainly to a reflection member which can be suitably used as a reflection type reflection member for a liquid crystal display.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) have been widely applied to one another by taking advantage of their features of thinness, light weight, and low power consumption. Currently, about 70% of LCDs are for notebook computers and word processors, but it is expected that demand for car navigation and PDAs (personal information terminals) will increase in the future. LCDs for notebook PCs and word processors are mainly backlit LCDs. However, small-sized portable information devices that are expected to spread in the future use reflection light liquid crystal display devices that use external light and consume less power. Is expected. In a reflection type liquid crystal display, when displaying characters or the like in a dark color (for example, black or dark blue), the display surface needs to be white like paper. Making the display surface of the LCD white like paper is called paper whitening of the LCD.

As a reflection sheet generally used at present, a white pigment-containing resin sheet, an aluminum reflection sheet, a silver reflection sheet and the like can be mentioned. As the aluminum reflection sheet, a reflection sheet made of aluminum foil or PET /
A reflection sheet made of an aluminum thin film layer is exemplified. Also,
The silver reflection sheet is made of a PET / silver thin film layer similarly to aluminum, but is a reflection sheet having a higher reflectance since silver having higher reflectance than aluminum is used.

However, a reflection type LCD of a scattering mode
For example, when the display portion is transparent and the non-display portion is relatively light, a colored reflection sheet is required. If a conventional reflection sheet is used for these reflection-type LCDs, the display portion becomes white or metal-colored, and it is not suitable because it is reflected and becomes very difficult to see. However, if a dark sheet is used to make the display part darker, the non-display part becomes darker, far from paper white, and the contrast between the display part and the non-display part is lost, making it hard to see.

[0005]

In order to obtain a display screen which is easy to see in this way, it is inserted between a reflective LCD in a scattering mode and a dark sheet. The display portion transmits the color of the dark sheet and does not display. There is a demand for a film that has appropriate reflectance and transmittance so that the portion reflects external light to obtain contrast with the display portion, and that has low absorption.

[0006]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by forming a transparent and high-refractive-index layer on a transparent film, A colorless transflective film having both high transmittance and high reflectance could be obtained.

That is, the present invention provides a semi-transmissive reflective member for a liquid crystal display device having a reflectance of 30% or more and a transmittance of 40% or more at a wavelength of 550 nm, and a transparent polymer film on at least one surface of the transparent polymer film. A layer of a transparent substance having a higher refractive index (a transparent high refractive index layer) and a layer of a transparent substance having a lower refractive index than the transparent polymer film (a transparent low refractive index layer). The described transflective reflective member for a liquid crystal display element formed by forming a film, the liquid crystal display element formed by alternately forming a transparent high refractive index layer and a transparent low refractive index layer on both surfaces of a transparent polymer film, or The transflective reflection member for liquid crystal display element according to any one of-, wherein the transparent high-refractive index layer is made of titanium oxide, an oxide of indium and tin, zinc oxide, indium oxide, or aluminum nitride. The semi-transmissive reflective member for a liquid crystal display element according to any one of the above items, wherein the transparent reflective member comprises a silicon oxide or magnesium fluoride.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the reflectance at a wavelength of 550 nm is 30% or more and the transmittance is 4%.
It is a semi-transmissive reflective member for a liquid crystal display element of 0% or more. In order to realize this, the most preferable specific embodiment is to form a transparent high refractive index layer 20 and a transparent low refractive index layer 30 on at least one surface of a transparent polymer film 40 as shown in FIG. This is a semi-transmissive reflective member for a liquid crystal display element formed by alternately forming a film. Here, the transparent high-refractive-index layer is a layer made of a transparent substance having a higher refractive index than the transparent polymer film serving as the base material, and the transparent low-refractive-index layer is referred to as a transparent base material. This is a layer made of a transparent material having a lower refractive index than the polymer film.

As shown in FIG. 2, a transparent high refractive index layer 20 and a transparent low refractive index layer 30 may be alternately formed on both surfaces of a transparent polymer film 40. As shown in FIG. 3, the reflection member of the present invention is a scattering mode reflection type liquid crystal cell 1.
It can be used by being inserted between 0 and a dark sheet 50 such as black.

The material of the polymer film used in the present invention is not particularly limited as long as it is transparent. Examples thereof include polyester, polyether, polyarylate, acrylic resin, methacrylic resin, polyolefin, and polyvinyl chloride. And a homopolymer or a copolymer such as polyethersulfone. More preferably, polyethylene terephthalate or polyethersulfone is used.

The film material can be easily confirmed by measuring an infrared absorption spectrum (IR).
There is no critical limit on the thickness of the film;
１５０150 μm is preferably used.

It is easily understood by those skilled in the art that a chemical cleaning treatment, a surface roughening treatment, a glow discharge treatment, a corona discharge treatment and the like are applied to the surface of the transparent polymer film in advance to improve the adhesion and the like. Will.

For the transparent high refractive index layer, a transparent and high refractive index material such as titanium oxide, indium and tin oxide (ITO), zinc oxide (ZnO), indium oxide or aluminum nitride is used. You. The high refractive index is a refractive index higher than the transparent polymer film to be used, and the refractive index is preferably 1.6 or more. For example, the refractive index of a titanium oxide thin film is usually 2.3.
It is about.

On the other hand, silicon oxide or magnesium fluoride is used for the transparent low refractive index layer. The refractive index of the silicon oxide thin film is usually about 1.3 to 1.4, and an appropriate refractive index difference is generated between the transparent high refractive index layer and the transparent high refractive index layer.

Both the transparent high refractive index layer and the transparent low refractive index layer
It is preferable that the film be formed using a vacuum such as a vacuum evaporation method or a sputtering method. In the vacuum evaporation method, a metal oxide as a material is melted in a crucible by resistance heating or electron beam heating, and the vapor pressure is increased to form a thin film on a desired substrate. As the sputtering method, a high-frequency sputtering method, a direct-current sputtering method, a high-frequency magnetron sputtering method, a direct-current magnetron sputtering method, an electron cyclotron resonance sputtering method, or the like can be applied.

The thicknesses of the transparent high-refractive index layer and the transparent low-refractive index layer are not particularly defined because they differ depending on the required balance between the reflectance and the transmittance, the transparent polymer film used, the material used and the like.

The refractive index n and the film thickness d when the reflectance at the wavelength λ is maximum have the following relationship. λ / 4 = n · d In the present invention, the product of the refractive index n and the transparent high (low) refractive index layer thickness d is preferably 50 to 200, more preferably 75 to 150, and still more preferably. Is 100
~ 125. For example, when the refractive index of the transparent high refractive index layer is 2.2 and the refractive index of the transparent low refractive index layer is 1.3, the thickness of the transparent high refractive layer that maximizes the reflectance at a wavelength of 550 nm is 62. 0.5 nm, the transparent low refractive index layer thickness is 105.8
nm. Note that a preferable film thickness can be obtained using the above equation.

In the present invention, as the transflective reflection member for a liquid crystal display element, the values of the transmittance and the reflectance at a wavelength of 550 nm are 30% or more and the transmittance is 40%.
Or more, more preferably, a reflectance of 32.
% Or more and a transmittance of 42% or more, more preferably a reflectance of 35% or more and a transmittance of 45% or more.

In order to obtain such a transflective film having the desired reflectance and transmittance, a vector method using the refractive index and the extinction coefficient of the transparent polymer film and the transparent high refractive index layer material is used.
An optical design using a method using an admittance diagram or the like is performed to determine the material of the transparent high refractive layer, the number of layers, the film thickness, and the like. For example, if polyethylene terephthalate is used for the transparent polymer film, ITO is used for the transparent high-refractive index layer, and silicon oxide is used for the transparent low-refractive index layer, and it is desired to obtain high reflectance with as few layers as possible, use ITO for the polymer film. Optical calculations show that a total of three layers, 68 nm, silicon oxide 94 nm and ITO 68 nm, should be stacked in total.

Even if the film thickness is too large, the reflectivity does not increase, and the adhesion of the transparent high refractive index layer and the transparent low refractive index layer to the polymer film decreases, which is not preferable from the viewpoint of effective use of resources. .

For measuring the film thickness of the transparent high refractive index layer and the transparent low refractive index layer, there are a stylus roughness meter, a repetitive reflection interferometer, a microbalance, a quartz oscillator method, and the like. Since the film thickness can be measured in the film, it is suitable for obtaining a desired film thickness. There is also a method in which the conditions for film formation are determined in advance, a film is formed on a sample substrate, the relationship between the film formation time and the film thickness is examined, and the film is controlled by the film formation time.

The types of metal oxides used for the transparent high refractive index layer and the transparent low refractive index layer were determined by X-ray diffraction (XRD).
Or electron beam diffraction, or Auger electron spectroscopy (AES). The layer structure can be measured by observing a cross section with a transmission electron microscope.

The transflective film of the present invention thus obtained can be suitably used as a transmissive reflection member for a liquid crystal element, that is, as a reflection member of a reflection type LCD. Reflective LC
In addition to clarifying the contrast between the display part and the non-display part by inserting it between D and a dark sheet, when the backlight is provided on the back of the LCD, the LCD and the back light are used for turning off the backlight. It can be inserted between lights.

In addition to using the semi-permeable film of the present invention as it is, it can be easily inferred that it can be used by applying an adhesive and bonding it to another film or a plate-like molded product. For example, if it is used by being attached to a dark sheet, it is excellent in workability and can be suitably used. Even if release paper is attached to the adhesive-applied surface without immediately bonding, workability is improved.

[0025]

The present invention will be described below with reference to examples. [Example 1] Polyethylene terephthalate (PET) film (O-100 manufactured by Teijin Limited, film thickness: 100)
μm), a transparent high-refractive index layer / a transparent low-refractive index layer / a transparent high-refractive index layer having a total of three layers, ITO of 68.5 nm as a transparent high-refractive index layer and oxidation as a transparent low-refractive index layer Three layers of silicon were alternately laminated at 94.2 nm. That is, PET / I
A total of three layers were sequentially laminated in a configuration of TO / silicon oxide / ITO. The film was formed by a sputtering method using argon gas as a sputtering gas. [Example 2] Polyethylene terephthalate (PET) film (O-100 manufactured by Teijin Limited, film thickness: 100)
μm), a transparent high-refractive index layer / a transparent low-refractive index layer / a transparent high-refractive index layer having a total of three layers, ITO of 68.5 nm as a transparent high-refractive index layer and oxidation as a transparent low-refractive index layer Five layers of silicon were alternately laminated at 94.2 nm. In other words, PET /
A total of five layers were sequentially laminated in a configuration of ITO / silicon oxide / ITO / silicon oxide / ITO. The film was formed by a sputtering method using argon gas as a sputtering gas.

For Examples 1 and 2, the reflectance and the transmittance at a wavelength of 550 nm were measured. The reflectance was measured by installing a 150φ integrating sphere on a Hitachi automatic recording spectrophotometer (U-3400), installing a black plate with low reflectance on the back surface of the sample, and measuring the reflectance from the film forming surface side, ie, the mirror surface. The reflectance + diffuse reflectance was measured. The reflectance of the back black plate was measured by the same apparatus, and the reflectance of the sample was determined by calculation. Also,
The transmittance measured the parallel light transmittance. Table 1 shows the measured values of the reflectance and the transmittance. The values of the PET film used for both reflectance and transmittance are presented for comparison.

[0027]

[Table 1]

Next, as shown in FIG. 3, the transflective film was sandwiched between a scattering type reflective liquid crystal cell and a black sheet, and the visibility of the display portion was checked. A comparison was also made when only a black sheet was provided on the back surface of the reflective liquid crystal cell in the scattering mode. The results are shown in (Table 2). At this time, an adhesive was applied to the front and back surfaces of the semi-transmissive film, and a black sheet was bonded to the PET film surface, and a scattering mode reflective liquid crystal cell was bonded to the film forming surface.

[0029]

[Table 2]

[0030]

According to the present invention, high transmittance and reflectance can be obtained by alternately forming a transparent layer having a higher refractive index and a transparent layer having a lower refractive index on a transparent polymer film. A transparent translucent film having the same was obtained. Thus, a reflecting member that can be used as a reflector of a liquid crystal display device can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a reflection member according to the present invention.

FIG. 2 is an explanatory view showing an example of a reflecting member according to the present invention.

FIG. 3 is an explanatory view showing an example of a practical structure of a reflecting member according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 scattering mode reflection type liquid crystal cell 20 transparent high refractive index layer 30 transparent low refractive index layer 40 transparent polymer film 50 black sheet

Claims (5)

[Claims] 1. The reflectance at a wavelength of 550 nm is 30%.
As described above, a transflective reflection member for a liquid crystal display device having a transmittance of 40% or more. 2. A layer (transparent high refractive index layer) made of a transparent substance having a higher refractive index than the transparent polymer film on at least one surface of the transparent polymer film, and a lower refractive index than the transparent polymer film. 2. The transflective reflection member for a liquid crystal display element according to claim 1, wherein a layer made of a transparent substance (a transparent low refractive index layer) is alternately formed. 3. A transparent high-refractive index layer and a transparent low-refractive index layer are alternately formed on both surfaces of a transparent polymer film.
Or a semi-transmissive reflective member for a liquid crystal display element according to item 2. 4. The half for a liquid crystal display device according to claim 1, wherein the transparent high refractive index layer is made of titanium oxide, an oxide of indium and tin, zinc oxide, indium oxide, or aluminum nitride. Transmission type reflection member. 5. The transflective reflection member for a liquid crystal display device according to claim 1, wherein the transparent low refractive index layer is made of silicon oxide or magnesium fluoride.