JPH04296819A - Reflecting plate base for surface light source - Google Patents

Abstract

PURPOSE:To obtain a reflecting plate base for surface light source that can obtain a bright. screen at high reflectance. CONSTITUTION:Expressions G1<=50%, G2/G1>=0.05, G3/G1>=0.05 are satisfied where G1 is glossiness of incident angle 60 deg.-light receiving angle 60 deg., G2 is glossiness of incident angle 60 deg.-light. receiving angle 45 deg., and G3 is glossiness of incident angle 60 deg.-light receiving angle 75 deg., and average reflectance in the wavelength region of the light of 400nm-700nm is not less than 90%. Since the glossiness is low, while scattering reflecting component is strong and the reflectance of the whole light is increased, a bright and clear screen of brightness higher than ever is obtained, when used as a reflecting plate 11 of a side-light type surface emitter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflector substrate for a surface light source. More specifically, the present invention relates to a reflector base material for a surface light source that provides a brighter screen when a sidelight (also referred to as edgelight) type surface light source is used as a method for illuminating a liquid crystal screen or the like.

0002

[Prior art] When lighting a liquid crystal display, etc.
Traditionally, a backlight method was used in which light is applied from the back of the display, but in recent years, Japanese Patent Application Laid-Open No. 63-6
The side light system as shown in No. 2104 has become widely used because of its thin design and ability to provide uniform illumination. The sidelight method involves halftone dot printing on one side of a transparent substrate such as a certain thickness of acrylic board.
By applying illumination from a cold cathode tube or the like from the edge of the acrylic plate, the illumination light is evenly dispersed for halftone dot printing, and a screen with uniform brightness can be obtained. Additionally, since the lighting is placed on the edge of the screen rather than on the back, it can be made thinner than the backlight method.

[0003]Also, in order to prevent illumination light from escaping to the back of the screen, it is necessary to install a reflector on the back of the screen, but this reflector needs to be thin and have high light reflectivity. , films containing white pigments such as titanium oxide are used.

The installation position of the reflector in this sidelight system will be explained in advance with reference to FIG. Figure 1 shows an example of the sidelight method, with 15 halftone dots printed on one side.
A reflective plate 11 is provided on one side of a transparent light guide plate 14 made of a transparent base material coated with a transparent light guide plate 14, and a diffuser plate 13 and a liquid crystal screen 12 are provided on the other side. Light from the cold cathode tubes 16 is introduced from the end face of the transparent light guide plate 14 and is uniformly dispersed by the dot printing 15, and the light reflected by the reflection plate 11 brightly illuminates the screen.

[0005]

[Problems to be Solved by the Invention] However, the above-mentioned films that have been whitened by adding titanium oxide, etc., have problems because pigment particles such as titanium oxide absorb light of specific wavelengths.
Films with these additives have lower overall reflectance,
There is a problem that sufficient screen brightness cannot be obtained. In terms of market demands, there is a tendency to desire brighter screens, and there is a strong demand for reflectors with higher reflectance.

The object of the present invention is to solve these problems and provide a reflector base material for a surface light source that has a higher reflectance and provides a brighter screen.

[0007]

[Means for Solving the Problems] A reflector base material for a surface light source according to the present invention that meets this objective has a glossiness G1 between an incident angle of 60° and an acceptance angle of 60°, and a glossiness between an incident angle of 60° and an acceptance angle of 45°. degree G
2. When G3 is the glossiness at an incident angle of 60° - an acceptance angle of 75°, G1 ≦50% G2 /G1 ≧0.05 G3 /G1 ≧0.05, and the wavelength range of light from 400 nm to 700 nm The average reflectance is 90% or more.

[0008] The glossiness G1 of the base material at an incident angle of 60° - an acceptance angle of 60° must be G1≦50%. Preferably, G1≦40%, more preferably G1≦
It is 30%. Light incident from the end face of the transparent light guide plate is scattered by the halftone dot printing and emitted from the screen, but light passing through the halftone dot printing is reflected by the reflecting plate. At this time,
When the gloss level G1 exceeds 50%, specular reflection is strong when reflected by a reflector, and the returned light is reflected again by the surface of the transparent light guide plate and is not emitted from the screen. This reflection on the surface of the transparent light guide plate is repeated, and the light escapes from the end face or is absorbed within the transparent light guide plate, making it impossible to obtain a bright screen. On the other hand, glossiness G
By setting 1 ≦50%, the scattered reflection becomes stronger when reflected by the reflector, so the light directly emitted from the screen becomes stronger, resulting in a high brightness, that is, a bright screen. .

[0009] Also, the angle of incidence of the base material is 60° - the angle of acceptance of light is 45°.
When the glossiness is G2 at an angle of incidence of 60° and the angle of acceptance is 75°, it is necessary that G2 /G1 ≧0.05 and G3 /G1 ≧0.05. Preferably, G2 /G1 ≧0.1 G3 /G1 ≧0.1, and more preferably G2 /G1 ≧0.2 G3 /G1 ≧0.2. As mentioned above, the stronger the scattered reflection, the brighter the screen will be obtained, and G1, which represents the intensity of specular reflection,
On the other hand, the larger G2 and G3, which represent the intensity of scattered reflection, are, the brighter the screen will be obtained. That is, G2 /G1 <0.05 or G3 /G1 <0
．． 05, even if G1≦50%, the intensity of scattered reflection is weak and a sufficiently bright screen cannot be obtained.

[0010] Furthermore, the base material is required to have an average reflectance of 90% or more in the wavelength range of 400 nm to 700 nm. Although the glossiness characteristics described above are required, if the average reflectance of the base material is less than 90%, sufficient brightness of the screen cannot be obtained. Only when the above-mentioned gloss characteristics, that is, scattering reflection characteristics, are imparted to the base material where there is no decrease in reflectance due to light absorption, etc.
A screen with high brightness, that is, sufficient brightness, can be obtained.

In the present invention, the surface roughness Ra of the base material is preferably 0.1 μm or more. More preferably, it is 0.15 μm or more. In order to design a surface with the above-mentioned glossiness, it is preferable to roughen the surface, and if Ra is less than 0.1 μm, it is difficult to obtain the above-mentioned glossiness characteristics.

[0012] Further, it is preferable that RT/Ra is 5 or more. More preferably, it is 10 or more. It is easier to obtain scattering and reflection characteristics when the surface roughness is at a low level on average and large roughness exists locally than when the surface roughness is at an average high level, and the brightness is more This is because a bright screen can be obtained.

[0013] The polyester referred to in the present invention is a polymer obtained by polycondensation from a diol and a dicarboxylic acid, and dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, adipic acid,
The diol is typified by sebacic acid, etc., and the diol is typified by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, etc. Specific examples include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalene dicarboxylate. Of course, these polyesters may be homopolymers or copolymers, and examples of copolymerization components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, Examples include dicarboxylic acid components such as isophthalic acid and 2,6-naphthalene dicarboxylic acid. In the case of the present invention,
In particular, polyethylene terephthalate is preferred from the viewpoints of water resistance, chemical resistance, durability, and the like.

[0014] Furthermore, various known additives such as antioxidants and antistatic agents may be added to the polyester.

Conventionally, a white pigment such as titanium oxide was added to whiten the polyester film, but
Because the particles themselves absorb specific wavelengths, there is a limit to how much reflectance can be improved, making it difficult to obtain a bright screen. Therefore, in the present invention, fine air bubbles are contained inside the film, and light is scattered by the air bubbles, thereby whitening the film. This achieves a high reflectance that cannot be obtained with conventional films.

[0016] The formation of these fine bubbles is caused by the film base material,
For example, it is formed by finely dispersing an incompatible polymer in polyester and stretching it uniaxially or biaxially. During stretching, voids (bubbles) are formed around the incompatible polymer particles, which exhibit a light scattering effect, resulting in whitening and a high reflectance. Incompatible polymers refer to polymers that do not dissolve in polyester, such as poly-3-methylbutene-1, poly-4-methylpentene-1, polypropylene, polyvinyl-t-
Butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene,
Examples include polyfluorostyrene, cellulose acetate, cellulose propionate, and polychlorotrifluoroethylene. Among these, polyolefins, particularly polymethylpentene, are preferred. The reasons for this are that voids are easily generated when stretched, and because the polymer has high transparency, it absorbs little light and does not absorb light scattered by voids, making it suitable for use as a reflector for surface light sources. When used, a screen with high brightness, that is, a bright screen can be obtained.

The amount of the incompatible polymer added is 2% by weight.
Above, 25% by weight or less is preferable. If it is less than this, sufficient whitening will not be achieved and high reflectance will be difficult to obtain, and if it is more than this, the strength of the film will become too low.

The film obtained in the above manner has a low specific gravity because it contains fine bubbles. The range of this specific gravity is preferably 0.5 or more and 1.2 or less. More preferably, it is 0.7 or more and 1.0 or less. If the specific gravity is less than 0.5, the strength of the film will be too low, and if it exceeds 1.2, sufficient whitening will not be achieved.

The whiteness of the film obtained as described above is preferably 70% or more. More preferably, it is 80% or more. When used as a reflector for a surface light source, it is required to obtain a screen with high luminance, that is, a bright screen, but there is also a strong demand for high whiteness of the screen. Therefore, the base material of the reflector needs to have high whiteness.

[0020] Furthermore, in order to uniformly disperse the incompatible polymer and to sufficiently generate fine bubbles, it is preferable to add a specific gravity lowering agent. A specific gravity lowering agent is a compound that is added as an auxiliary agent along with the above-mentioned incompatible polymer, and has the effect of promoting the creation of voids at the interface between the polyester and the incompatible polymer, thereby reducing the specific gravity. Only compounds have this effect. For example, polyesters include polyalkylene glycols and their derivatives such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, and polypropylene glycol, ethylene oxide/propylene oxide copolymers, and even sodium dodecylbenzenesulfonate and alkyl sulfones. Representative examples include sodium acid, glycerin monostearate, etc. In the present invention, polyalkylene glycols, particularly polyethylene glycols, are preferred. The amount added is preferably 0.1% by weight or more and 5% by weight or less. If it is too small, the effect of addition will be diminished, and if it is too large, the properties of the film base material may be impaired.

In the present invention, a laminated film structure is also preferably used. For example, it has a two-layer structure of A/B or a three-layer structure of A/B/A. In this case, it is preferable that the B layer is a layer containing microbubbles, and the A layer is a layer in which polyester contains inorganic particles in an amount of 5% by weight or more and 25% by weight or less. The amount added is more preferably 10% by weight or more and 20% by weight or less. By adopting a laminated structure, it is possible to achieve high reflectance due to microbubbles and then design surface properties such as glossiness. Furthermore, light scattering occurs at the lamination interface, resulting in higher reflectance. Further, if the amount of inorganic particles added to layer A is less than 5% by weight, the desired surface properties cannot be obtained, and if it exceeds 25% by weight, the stretchability of the film will deteriorate, which is not preferable.

[0022] Furthermore, the inorganic particles have an average particle size of 0.
．． Preferably, it is a mixture of particles having a diameter of 5 to 2 μm and particles having an average particle size of 2 to 10 μm. Average particle size 0.5-2
In order to obtain appropriate surface roughness and light scattering with particles of 2 to 10 μm in average diameter, sufficient scattering of light can be achieved with particles with an average particle size of 2 to 10 μm to obtain the desired surface characteristics. be. As the inorganic particles, particles that do not absorb light are preferable in order to obtain a high-brightness screen, and calcium carbonate, silica, and the like are preferable.

It is also preferable to coat such particles on a film instead of adding them during extrusion, and it is possible to obtain a screen with the same high brightness as when they are added during extrusion.

In the present invention, it is also preferred to add a fluorescent brightener. In the case of a laminated structure, it is preferable to add it to the outermost layer. By adding an optical brightener, it is possible to obtain a brighter screen.

Next, the manufacturing method of the present invention will be explained.
The invention is not limited to such examples.

[0026] Polymethylpentene as an incompatible polymer and polyethylene glycol as a specific gravity lowering agent are mixed with polyethylene terephthalate, thoroughly mixed and dried, and an extruder heated to a temperature of 270 to 300°C. Supply to B. When producing a single-layer film of this polymer, two or more types of inorganic particles having different average particle sizes as described above are added. Also, if a laminated structure is used at this time,
Polyethylene terephthalate containing two or more types of inorganic particles with different average particle sizes, such as calcium carbonate and silica, as described above, is supplied to extruder A by a conventional method, and is then fed into the extruder A before entering the T-die or inside the T-die laminated die. , two layers A/B, or three layers A/B/A are laminated.

This molten sheet is adhered and solidified by electrostatic force onto a drum cooled to a drum surface temperature of 10 to 60°C, and the unstretched film is guided to a group of rolls heated to 80 to 120°C to longitudinally stretched 2 to 5 times in the direction, 20 to
Cool with rolls at 50°C. Next, while holding both ends of the film with clips, guide it into the tenter and
Transverse stretching is carried out in a direction perpendicular to the longitudinal direction in an atmosphere heated to 0°C. The stretching magnification is 2 to 5 times in both length and width, and the area magnification is preferably 6 to 20 times. If the area magnification is less than 6 times, whitening will not be achieved sufficiently, and if it exceeds 20 times, tearing will easily occur during stretching. In order to impart flatness and dimensional stability to the biaxially stretched film, it is heat-set at 150 to 240°C in a tenter, uniformly cooled slowly, cooled to room temperature, and rolled up to form the base material of the present invention. obtain.

[0028]

[Evaluation method of physical property values] 1. Glossiness Using a glossmeter VG-107 manufactured by Nippon Denshoku Kogyo Co., Ltd.,
According to JIS Z-8741, the incident angle and the acceptance angle were measured according to the specified angles.

2. Average reflectance at light wavelengths of 400 to 700 nm An integrating sphere is attached to a spectrophotometer (UV-260, manufactured by Shimadzu Corporation), and the reflectance when the MgO white plate is taken as 100% is measured over a range of 400 to 700 nm. The reflectance was read at intervals of 5 nm from the obtained chart, the average value was calculated, and this was taken as the average reflectance.

3. Cut the apparent specific gravity film into a 100 x 100 mm square, and place it on a dial gauge (No. 2109-10 manufactured by Mitoyo Seisakusho) with a diameter of 10 mm.
Measure the thickness at a minimum of 10 points with a mm gauge head (No. 7002) attached, and calculate the average thickness d (μm).
Calculate.

Further, this film is weighed using a direct reading balance, and the weight w (g) is read to the nearest 10-4 g. At this time, the apparent specific gravity was set as w/d×100.

4. Screen Brightness As shown in FIG. 1, a 3 mm thick acrylic plate was printed with halftone dots, a film was set as a reflecting plate 11, and the screen was illuminated from one end with a 6W fluorescent tube. The brightness of the screen 12 was measured at 15 points using a brightness meter (Minolta LS-110), and the average value was taken as the brightness of the screen.

5. Surface roughness Ra, RT according to JIS B-0601, using a stylus type surface roughness meter (
The measurement was performed using ET-10 (manufactured by Kosaka Institute).

6. Average Particle Size of Inorganic Particles The inorganic particles were dispersed in ethanol and measured using a centrifugal sedimentation type particle size distribution analyzer (CAPA500 manufactured by Horiba, Ltd.) to calculate the volume average diameter, which was defined as the average particle size.

[0035]

EXAMPLES The present invention will be explained based on examples.

Example 1 Polyethylene terephthalate chips and a master chip to which polyethylene glycol with a molecular weight of 4000 was added during polymerization of polyethylene terephthalate were
After vacuum drying at ℃ for 3 hours, 89% by weight of polyethylene terephthalate, 1% by weight of polyethylene glycol,
Mix to make polymethylpentene 10% by weight, 2
It is fed to extruder B heated to 70-300°C. Further, polyethylene terephthalate containing 14% by weight of calcium carbonate with an average particle size of 1.1 μm and 3% by weight of silica with an average particle size of 4 μm is supplied to extruder A after being dried as described above. The polymer extruded from extruders A and B is
/B/A were laminated to form a three-layer structure, and formed into a sheet using a T-die. Furthermore, this film was heated to a surface temperature of 25
An unstretched film cooled and solidified in a cooling drum at 85 to
It was introduced into a roll set heated to 98°C, longitudinally stretched 3.4 times in the longitudinal direction, and cooled with a roll set heated to 25°C.

Subsequently, the lengthwise stretched film was held at both ends with clips and introduced into a tenter, and was laterally stretched 3.6 times in a direction perpendicular to its longitudinal direction in an atmosphere heated to 130°C. Thereafter, it was heat-fixed at 230° C. in a tenter, uniformly cooled slowly, and then cooled to room temperature and wound to obtain a film with a thickness of 188 μm. The laminated configuration was 12/164/12 μm.

The physical properties of the obtained film are shown in Table 1. It was possible to obtain a reflector base material for a surface light emitter with high screen brightness.

Example 2 In Example 1, master chips of optical brightener (OB-1 manufactured by Eastman) were added to the raw material supplied to extruder A so that the optical brightener amount was 0.03% by weight. A film with a thickness of 188 μm was obtained in the same manner as in Example 2.

The physical properties of the obtained film are shown in Table 1. By adding a fluorescent whitening agent, the reflectance increased and a base material for a surface light emitter with higher screen brightness could be obtained. Example 3 A 188 μm thick film with the same laminated structure was obtained in the same manner as in Example 1, except that the raw material supplied to extruder A was polyethylene terephthalate containing 14% by weight of calcium carbonate with an average particle size of 1.1 μm. After that, the surface of the film was subjected to corona discharge treatment.

Next, acrylic resin (“Kotax” manufactured by Toray) / silica particles (particle size 1 μm) / silica particles (particle size 4 μm) / isocyanate / optical brightener (Eastma
Diluted with toluene/methyl ethyl ketone = 1/1 as a solvent so that OB-1) = 100/5/3/20/1 was 20%, and coated with a gravure coater to form a 3 μm thick coating film. Obtained.

The physical properties of the obtained film are shown in Table 1. Even by coating two types of particles with different average particle diameters, a surface luminescent substrate with high screen brightness can be obtained as in Example 2. I was able to do that.

Comparative Example 1 After drying a master chip made of polyethylene terephthalate compounded with titanium dioxide particles and a polyethylene terephthalate chip at 180°C for 3 hours,
Titanium dioxide particles were mixed at 5% by weight and polypropylene at 15% by weight, and the mixture was supplied to an extruder and formed into a sheet using a T-die. Thereafter, a film with a thickness of 188 μm was obtained using the same method as in Example 1.

The physical properties of the obtained film are shown in Table 1. The screen brightness is low because the gloss is high, scattering reflection is weak, and titanium dioxide absorbs light. Comparative Example 2 In Example 1, dried polyethylene terephthalate chips were supplied to extruder A, and a film with a thickness of 188 μm was obtained in the same manner as in Example 1.

The physical properties of the obtained film are shown in Table 1. The screen brightness is low because the gloss is high and there are few scattered reflection components.

Example 4 A 188 μm film was obtained in the same manner as in Comparative Example 2, and subjected to corona discharge treatment.

Next, coating was performed as in Example 3 to obtain a coating film with a thickness of 3 μm.

The physical properties of the obtained film are shown in Table 1. Although the original film did not have sufficient screen brightness as in Comparative Example 2, it was coated as described above.
By increasing the scattering reflection, we were able to obtain high screen brightness.

[0049]

[Table 1]

[0050]

Effects of the Invention: In the reflector base material for a surface light emitter of the present invention, by lowering the gloss, further increasing the scattering reflection component, and increasing the overall light reflectance, the side light When used as a reflector for a surface light emitter, it is possible to obtain a bright, easy-to-see screen with unprecedented high brightness.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view when a reflector is incorporated into a sidelight type surface light emitter.

[Explanation of symbols]

11 Reflector 12 LCD screen 13 Diffusion plate 14 Transparent light guide plate 15 Halftone printing 16 Cold cathode tube

Claims (6)

[Claims] Claim 1: Glossiness G1 at an incident angle of 60° - acceptance angle of 60°, glossiness G2 at an incident angle of 60° - acceptance angle of 45°,
When the gloss level is G3 at an incident angle of 60° and an acceptance angle of 75°,
A reflection for a surface light source, which satisfies G1 ≦50% G2 /G1 ≧0.05 G3 /G1 ≧0.05 and has an average reflectance of 90% or more in the wavelength range of light from 400 nm to 700 nm. Board base material. 2. The reflector substrate for a surface light source according to claim 1, wherein the substrate has a surface roughness Ra of 0.1 μm or more and a RT/Ra of 5 or more. 3. The reflector base material for a surface light source according to claim 1, wherein the base material is made of a white polyester film containing microbubbles. 4. The reflector substrate for a surface light source according to claim 3, wherein the white polyester film has an apparent specific gravity of 0.5 or more and 1.2 or less. 5. The white polyester film is A/
It consists of a two-layer structure of B or a three-layer structure of A/B/A,
5. The reflective plate for a surface light source according to claim 3, wherein the layer B is a layer containing fine bubbles, and the layer A is a polyester containing 5% by weight or more and 25% by weight or less of inorganic particles. Base material. 6. The inorganic particles have an average particle size of 0.5 to 2 μm.
6. The reflector base material for a surface light source according to claim 5, wherein the base material is a mixture of particles having a particle size of m and particles having an average particle size of 2 to 10 μm.