JPH0762747B2 - Base film for liquid crystal display reflector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base film for a liquid crystal display reflection plate, and more particularly to a base film for a liquid crystal display reflection plate having a high reflection brightness of light and a small directivity. .

2. Description of the Related Art Liquid crystal display devices have large characteristics such as thinness, low voltage operation, and low power consumption that cannot be imitated by other display devices, and are widely used mainly for displays of small devices such as wristwatches and calculators. In recent years, technological developments such as display for duty board, display of OA equipment, display of small TV, display enlargement, color display, increase of display information amount, etc. have been promoted due to the electronicization of automobiles. The department is in practical use.

A liquid crystal display device usually has two polarizing plates arranged on the lower side of a liquid crystal display element such as a TN (twisted nematic) type, and a reflection plate provided on the lower layer (the side opposite to the visible side). There is. As the reflector, an aluminum foil or a plastic film, especially a polyester film, on which the metal such as Al or Cr is vacuum-deposited, is used.

Along with the increase in size of the liquid crystal display device, it is required to increase the size of the reflection plate, but when increasing the size of the reflection plate in which the Al foil is attached with an adhesive, vertical stripes occur during the rolling process of the Al foil, Further, there is a problem that wrinkles and fluffs of the Al foil are generated and the product yield is reduced. On the other hand, the plastic film formed by vacuum-depositing a metal such as Al has a strong directivity of light because the reflecting surface is too flat and is a mirror surface.For example, the reflection from one direction is also a little different from the one direction. When viewed from an angle, the display signal is dark and unclear. Since the drawback of a narrow viewing angle is further increased with the increase in size, it is necessary to eliminate the directivity on the visible side with a large reflector.

Further, since the liquid crystal display device usually uses two polarizing plates, the amount of transmitted light is significantly reduced. Therefore, it is necessary for the reflector to reflect the transmitted light as much as possible, and a reflector having a large reflectivity is required.

OBJECT OF THE INVENTION It is an object of the present invention to provide a base film for a liquid crystal display reflector, in which such drawbacks are improved. Another object of the present invention is to provide a base film which forms a reflecting surface having a high reflection brightness and a small light directivity. Still another object of the present invention is to provide a base film useful for manufacturing a reflector of a large liquid crystal display device.
Further objects and advantages of the present invention will be apparent from the following description.

According to the present invention, the object of the present invention is to provide an average particle size of 1 to 15 μm on the surface of the plastic film on which the metal thin film layer is provided.
By coating with a paint containing m spherical organic filler, fine irregularities capable of forming a metal thin film layer with a white light reflection brightness of 10% or more and a reflection brightness half-value angle of 30 ° or more are formed. And a base film for a liquid crystal display reflector.

As is apparent from the above, the base film of the present invention has fine irregularities formed on at least one surface thereof by a coating method. The fine irregularities are formed on the metal thin film layer provided thereon with a reflection brightness of 10% or more of white light and a half-value angle of the reflection brightness (an angle showing half the maximum reflection brightness (symmetrical with respect to 45 reflection angles). )] It exerts the effect of imparting 30 ° or more.

There are various methods for changing the surface morphology of the plastic film. For example, as a technique for changing the surface morphology of a polyester film, (1) a method of mixing fine particles of clay, calcium carbonate, titanium oxide, etc. with polyester to form a film (2) a fine sand (SiO ₂ sand) film There is a sand matting method in which the surface of the film is roughened by hitting it against the surface. (3) There is a coating method in which the plastic film is thinly coated with a coating material containing fine particles to change the surface shape.

However, the first method has a defect that the size of the projections on the film surface changes depending on where in the thickness direction of the film kneaded fine particles exist, and as a result, an imperfect uneven surface is formed. is there.

In the second method, the unevenness of the surface of the film obtained due to the uneven shape of the hard sand is also harsh and uneven. For example, this is treated with an alkaline solution to dissolve a part of the surface. However, there is a drawback that the roughness cannot be made sufficiently uniform and the surface morphology of the obtained film is still non-uniform.

On the other hand, the third method is effective for surface design because it is possible to form unevenness with a uniform surface morphology by selecting a large particle size, uniformity and coating thickness according to the purpose and coating it. It can be called a means. Since the base film of the present invention is surface-treated by this coating method, its advantages are fully utilized.

Examples of the plastic film in the present invention include films such as polystyrene, polymethyl acrylate, polycarbonate, acetate, polysulfone and polyester. Of these films, polyester film is preferred. Polyester film has a small surface irregularity formed in the film-forming step, and when the surface irregularity is formed by coating a paint on it,
It has the advantage that the unevenness of the substrate film can be ignored, and also has the advantages of good solvent resistance and excellent mechanical performance.

The composition of the paint applied to the plastic film basically consists of a filler, a binder and a solvent. In order to improve the dispersibility of the filler, a dispersion aid such as a surfactant can be blended, and in order to improve the coating work, a wetting agent, a leveling agent or the like can be added in a small amount.

Although spherical organic fine particles are used as the filler (fine particles), it is preferable that the fine particles have a uniform particle size.

Preferable examples of the uniform spherical organic filler include benzoguanamine resin (Nippon Shokubai Kagaku KK. Trade name “Eposter”), cross-linked styrene resin (Sumitomo Chemical KK. Trade name Huinvar), nylon resin and the like.

The size of the filler is in the range of 1 to 15 μm in average particle size. A filler having an average particle size of less than 1 μm has a strong cohesive force and is difficult to uniformly disperse. Therefore, irregularity of the surface due to the agglomerated particles is likely to occur, and surface irregularities are small in the absence of the agglomerated particles. Further, a filler having an average particle size of more than 15 μm is difficult to apply uniformly to spread the filler on the surface of the film, and the obtained surface is not always uniformly uneven.

As the binder, for example, acrylic resin, urethane resin, nitrocellulose, melamine resin, epoxy resin,
A polyester resin or the like can be used. What is particularly desired for the binder is to show high adhesive strength to both the plastic film and the filler so that the coating film does not peel off or the filler is missing. A heat-resistant binder is preferable since a metal, especially aluminum, is vacuum-deposited on the surface as post-processing.

The ratio of filler to binder is an important factor in terms of coating surface design. In particular, in the case of a binder having a flat coating film forming ability without the projection performance of the binder itself, only the presence of the filler is a factor for forming fine unevenness. If the proportion of the filler is too small, projections will be scattered in places on the flat portion of the coated surface, and it will not be possible to impart desirable reflection performance.
In addition, the proportion of filler is too high and the critical pigment volume concentration (CP
VC) causes the binder to penetrate into the stacking of fillers, and the recesses of the protrusions do not become flat, and the amount of reflected light drops sharply. Therefore, there is a suitable range for the ratio of the filler to the binder, and the ratio of the filler to the total weight of the filler and the binder is preferably 1 to 50% by weight, more preferably 5 to 30% by weight.

The solvent is not particularly limited as long as it does not substantially attack the film and the organic filler, and the solvent conventionally used for film coating can be used. Specific examples of such a solvent include methyl ethyl ketone, toluene, cyclohexanone, butyl acetate and the like. The concentration of filler and binder in the paint is preferably about 10 to 50% by weight, more preferably about 20 to 40% by weight.

Various methods can be used for coating the plastic film, for example, Mayer bar coating, reverse coating, kiss roll coating, gravure coating, or the like.

The coating layer is based on the average particle size (μm) of the filler.
The thickness is preferably 0.8 to 3 times, more preferably 1 to 2 times, and preferably 0.5 to 50 μm, further preferably 0.8 to 30 μm on a dry basis. The fine irregularities of the coating layer preferably have a surface roughness CLA of 0.1 to 1 μm, more preferably 0.4 to 0.8 μm.

The distribution of the reflected light brightness of a reflector, in which a metal, especially Al is vacuum-deposited, is greatly affected by the uneven shape of the film surface. When the surface is too flat and has no unevenness or is very small even at all, the light reflection has a strong directivity, and the light has a strong directivity in which the light is reflected only in the regular reflection angle direction opposite to the incident angle. Also, if the film surface forms a surface with large irregularities of large and small, the light diffusion on the surface increases and the reflected light is radiated in all directions to improve the directivity, while the brightness of the reflected light decreases. It is in a dark state as a whole. The base film of the present invention is
Since the surface has unevenness with a gentle inclination, and the size and number of the unevenness are uniform, the specularly reflected light has a spread and can form a reflecting surface which gives a reflected light curve with a skirt. The base film of the present invention has, for example, Al on its surface.
By vacuum deposition, the reflective brightness is 10% or more, and the angle at half height of the peak value (half-value angle) is 30 ° or more. A liquid crystal display reflection plate having a reflective function with low property is formed.

The method for forming the metal thin film layer on the base film is not particularly limited, and a physical vapor deposition method such as a vacuum vapor deposition method, a sputtering method or an ion plating method can be used. The thickness of the metal thin film layer may be the thickness conventionally used, for example, about 100Å to about 5 μm, and further about 200Å to about 3
It is desirable to be in μm.

EXAMPLES The present invention will be described in more detail with reference to the following examples.

The formation of the metal thin film and the measurement of various characteristics of the film were carried out by the following methods.

1. Vacuum deposition method: Vacuum deposition of Al (aluminum) thin film on the coated film surface is performed using JEE-4B equipment of JEOL Ltd. under a vacuum degree of 2 × 10 ⁻⁵ mmHg. Natsuta.

2. Measurement of glossiness: The surface glossiness of the Al-deposited surface was measured using GONIOPHOTO METER GP-1R of Murakami Color Research Laboratory. According to JIS Z-8741 (1959), the reflected brightness G _S (45 °) is the following formula G _S (45 °) = ( _S / _O ) × 100 (%) where _S is the sample brightness , _O is an uncoated blank film (commercially available transparent polyester film)
Indicates the brightness of.

I asked more.

In addition, the scattering of reflected light was connected at a point showing half the luminance of the peak value of the reflection luminance obtained by the above method, and the angle φ _1/2 (degree) was shown as the half value (the reflection luminance curve is Since it is shown in logarithm, it was calculated from the value at half-value angle φ _1/2 log G45 °).

A halogen lamp of 12 V and 50 W was used as the light source, and a slit of 10 mmφ was used on both the light source side and the light receiving side.

3. CLA value: The surface of the coated film was measured using a stylus surface roughness meter (Surcom 8B) from Tokyo Seimitsu Co., Ltd.
Under the condition of a load of 0.1g, write a chart with a standard length of 26mm 50 times in the standard length direction and 2000 times in the vertical direction with respect to the surface, and measure length L (L = 2m in the direction of the center line).
When the roughness curve is represented by Y = f (x) with the center line at this portion as the X axis and the vertical magnification direction as the Y axis, the value given by the following equation is μ Expressed in units of (microns), CLA (μ).

Example 1 A 30% solution of polyester in methyl ethyl ketone (manufactured by Soken Kagaku KK, trade name "Thermologic B101") was added to spherical benzoguanamine particles having an average particle size of 2.5μ (manufactured by Nippon Shokubai Kagaku KK, trade name "Eposter M"). ") Was added at the ratio shown in Table-1 and the paint was prepared by a ball mill.

A commercially available transparent and smooth polyethylene terephthalate film was uniformly coated with this coating material (after drying) to a thickness of 6 μm. Furthermore, Al (aluminum) was vacuum-deposited on the coated surface to form a reflective surface. Each performance of this anti-slope is shown in Table-1.
Shown in.

Comparative Example 1 The ratio of benzoguanamine particles used in Example 1 is shown in Table-1.
The performance of the anti-slope surface was examined in the same manner as in Example 1 except that the coating material changed as shown in Table 1 was used. The results are shown in Table 1.

Example 2 Spherical cross-linked styrene particles having an average particle size of 5 μm (manufactured by Sumitomo Chemical KK, trade name “Huain Pearl 3000F”) were added to the Thermorad B101 solution of Example 1 at a ratio of Table-2,
The paint was prepared with a ball mill.

This paint was uniformly coated on a commercially available transparent and smooth polyethylene terephthalate film so that the thickness after drying was about 10 μm. Further, Al was vacuum-deposited on the coated surface to form a reflective surface. Each performance of this reflecting surface is shown in Table-2.

Comparative Example 2 A reflective surface was prepared in the same manner as in Example 2 except that a coating composition was used in which the proportion of crosslinked styrene particles used in Example 2 was changed as shown in Table 2. The performance of this reflective surface was investigated and the results are shown in Table-2.

Example 3 100 g of a 30% methyl-ethyl-ketone solution of polyester (manufactured by Soken Kagaku KK, trade name "Thermologic B101") was added to spherical benzoguanamine particles having an average particle size of 10 μ (manufactured by Nippon Shokubai Kagaku KK, trade name "Eposter L"). ") Was added in the ratio shown in Table-3, and the paint was prepared by a ball mill.

This paint was uniformly coated on a commercially available transparent and smooth polyethylene terephthalate film so that the thickness after drying was about 15 μm. Furthermore, vacuum-deposit Al on this coated surface,
I made a reflective surface. Each performance of this anti-slope is shown in Table-3.

Comparative Example 3 Table 3 shows the proportion of benzoquanamine particles used in Example 3.
A reflective surface was prepared in the same manner as in Example 3 except that the coating material changed as shown in FIG. The performance of this reflective surface was investigated and the results are shown in Table-3.

Claims (2)

[Claims] 1. A surface of a plastic film on which a metal thin film layer is provided is coated with a coating material containing a spherical organic filler having an average particle diameter of 1 to 15 μm, whereby the reflection brightness of white light is 10% or more and the reflection brightness is half-valued. A base film for a liquid crystal display reflection plate, which is formed with fine irregularities capable of forming a metal thin film layer having an angle of 30 ° or more. 2. The base film according to claim 1, wherein the film is a polyester film.