JPH0816175B2 - White polyester film for LCD reflector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film, and in particular, it is a white polyester film most suitable for use as a base material for a reflector of a liquid crystal display, and a liquid crystal screen is illuminated by a side light (also called an edge light). The present invention relates to a white polyester film for a liquid crystal display reflector, which can form a base material for a reflector that gives a brighter screen.

[0002]

2. Description of the Related Art When illuminating a liquid crystal display, a backlight system in which a light is illuminated from the back of the display has been conventionally used, but in recent years, it has been disclosed in JP-A-63-621.
The sidelight system as disclosed in Japanese Patent Publication No. 04 has been widely used because of its merit of being thin and uniformly illuminating. The sidelight method is a method in which halftone printing is performed on one side of a transparent base material such as an acrylic plate having a certain thickness, and the cold cathode tube or the like is illuminated from the edge of the acrylic plate. In addition, the illumination light is evenly dispersed, and a screen with uniform brightness can be obtained. Also,
Since the lighting is installed not at the back of the screen but at the edge, it can be thinner than the backlight system. Also, in order to prevent the 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 is required to be thin and highly reflective, so titanium oxide A film to which a white pigment such as is added is used.

The installation position of the reflector in this sidelight system will be described in advance with reference to FIG. FIG. 3 shows an example of the side light method, in which halftone printing 1 is performed 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 on which the diffused plate 13 and the liquid crystal screen 12 are located on the other screen. Light from the cold cathode tubes 16 is introduced from the edge of the transparent light guide plate 14, is uniformly dispersed by the dot printing 15, and the light reflected by the reflection plate 11 illuminates the screen brightly.

[0004]

However, the film whitened by the addition of titanium oxide or the like as described above can raise the light reflectance to a certain level, but there is a limit to the improvement of the reflectance. There is a problem that the screen brightness is not enough. Also, for titanium oxide,
Since light of a specific wavelength is absorbed, there is also a problem that the entire reflectance is lowered in a certain wavelength range and a sufficiently bright screen cannot be obtained. The market demands for a brighter screen, and there is a strong demand for a reflector having a higher reflectance over a wide wavelength range.

The present invention solves the above problems and provides a white polyester film for a liquid crystal display reflector, which is optimum for use as a base material for a liquid crystal display reflector having a higher reflectance and a brighter screen. With the goal.

[0006]

A white polyester film for a liquid crystal display reflector according to the present invention which meets this object has an average surface reflectance of 90% or more in the wavelength range of light of 400 to 700 nm. (Maximum value-minimum value) of 10% or less, and is used as a main constituent member of a substrate for a liquid crystal display reflector. (Hereinafter, it may be referred to as the first invention.)

Further, the present invention provides a white polyester film having a high reflectance for another specific wavelength range. That is, the above white polyester film contains a fluorescent whitening agent, and the average reflectance of the surface in the wavelength range of light of 330 to 380 nm is greater than 90%. . (Hereinafter, it may be referred to as the second invention.)

The characteristic of the first invention is shown as a characteristic H1 shown by the solid line in FIG. 1, for example. That is, it is a characteristic that the average reflectance is 90% or more in the main wavelength range of 400 to 700 nm. When this white polyester film is used as a base material for a liquid crystal display reflection plate, when the reflectance decreases, the screen becomes yellowish in the low wavelength region and bluish in the high wavelength region, but 90% or more. By setting the average reflectance of the above, these can be prevented and a sufficiently bright screen can be obtained. The characteristic of the above-mentioned second invention is shown as a characteristic H2 indicated by a chain line, for example. That is, when this white polyester film is used as a substrate for a liquid crystal display reflection plate, in addition to the characteristics of H1 described above, 90% even in the wavelength range of 330 to 380 nm.
The above reflectance is possible.

The polyester referred to in the present invention is a polymer obtained by polycondensation of a diol and a dicarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, And the diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specific examples thereof include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalene dicarboxylate. In the case of the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferable.

Of course, these polyesters may be homopolyesters or copolyesters, and examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol, adipic acid and sebacic acid. And dicarboxylic acid components such as phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid.

Various known additives such as antioxidants and antistatic agents may be added to the polyester. Polyethylene terephthalate is preferable as the polyester used in the present invention. Polyethylene terephthalate film is water resistant, durable,
It has excellent chemical resistance.

Conventionally, titanium oxide or the like was added to whiten the polyester film, but as described above, there is a limit to the improvement of reflectance, and it is difficult to obtain a brighter liquid crystal screen. In the present invention, fine bubbles are contained inside the film, and light is scattered by the bubbles to achieve whitening. As a result, a high reflectance, which cannot be obtained by the conventional film, is achieved, as shown in Examples described later.

The formation of the fine bubbles is caused by the film base material,
For example, it is achieved by finely dispersing an incompatible polymer having a high melting point in polyester and stretching it (for example, biaxial stretching). At the time of stretching, voids (air bubbles) are formed around the incompatible polymer particles, and this exerts a scattering effect on light, so that whitening occurs and high reflectance can be obtained. Incompatible polymers include poly-3-methylphthene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, Polymethylstyrene, polydimethylstyrene,
Polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate,
It is a polymer having a melting point of 200 ° C. or higher selected from polyvinyl fluoride, polychlorotrifluoroethylene and the like. Among them, polyolefin, particularly polymethylpentene, is preferable for the polyester base material.

The amount of the incompatible polymer (for example, polyolefin) added is preferably 2% by weight or more and 25% by weight or less. If the amount is less than this, the effect of whitening will fade,
If the reflectance is too high, the mechanical properties such as strength of the film itself may be too low.

It is preferable that the incompatible polymer is uniformly dispersed. Due to the uniform dispersion, bubbles are uniformly formed inside the film, and the degree of whitening and thus the reflectance is uniform. In the present invention, the value of (maximum value-minimum value) of the reflectance in the wavelength range of 400 to 700 nm is set to 10% or less in order to suppress variations in screen brightness. As a result, a screen with uniform brightness can be obtained as a liquid crystal screen.

In order to uniformly disperse the incompatible polymer, it is effective to add a low specific gravity agent as a dispersion aid.
The low specific gravity agent is a compound having an effect of reducing the specific gravity, and only the specific compound has the effect.
For example, for polyester, polyalkylene glycols such as polyethylene glycol, methoxy polyethylene glycol, polytetramethylene glycol, and polypropylene glycol, ethylenoxide / propylenoxide copolymers, and further sodium dodecylbenzenesulfonate and alkylsulfonates. Sodium salt,
Typical examples are glycerin monostearate and tetrabutylphosphonium paraaminobenzene sulfonate. In the case of the film of the present invention, polyalkylene glycol is preferable, and polyethylene glycol is particularly preferable. The addition amount is preferably from 0.1% by weight to 5% by weight. If it is too small, the effect of the addition will be weakened, and if it is too large, the original properties of the film base material may be impaired. Such a low specific gravity agent can be prepared as a master polymer (master chip) by previously adding it to the film base polymer.

As described above, since the white polyester film contains fine bubbles, the apparent specific gravity of the polyester film becomes lower than that of a normal polyester film. If a specific gravity lowering agent is further added, the specific gravity becomes lower. That is, a white and light film is obtained.
In order to reduce the weight of the white polyester film while maintaining the mechanical characteristics as a substrate for a liquid crystal display reflection plate, the apparent specific gravity is preferably 0.5 or more and 1.2 or less.

In the first aspect of the present invention, a laminated film structure may be used. For example, it has a two-layer structure of A layer / B layer or a three-layer structure of A layer / B layer / A layer. In this case, the layer B is a layer containing fine bubbles,
The layer A is preferably a layer in which inorganic particles (for example, calcium carbonate) are contained in polyester in an amount of 5% by weight or more and 25% by weight or less. With such a configuration, the layer A can maintain the surface characteristics of the laminated base material to the characteristics of the polyester itself while the layer B can obtain the target high reflectance, and the adhesion characteristics (for example, the surface characteristics of the base material) can be maintained. It is possible to maintain good ink adhesion and laminating characteristics). Also, by adding inorganic particles such as calcium carbonate to the surface layer,
The matte effect of the surface is obtained, and since calcium carbonate and the like themselves also have a void forming action, the reflection characteristics of the surface layer can be improved.

The second invention of the present invention is further 330-38.
It is a white polyester film whose average reflectance is greater than 90% even in the wavelength range of 0 nm light. Such a white polyester film is basically the first polyester film described above.
It is obtained by including an optical brightener in the white polyester film of the invention. That is, when the white polyester film contains fine bubbles inside the film, a fluorescent brightening agent is contained in the film, and when the film is composed of a laminated polyester film of a plurality of layers, It is sufficient that at least the outermost layer of the laminated film layer contains the optical brightener. further,
The film may include a white polyester film layer and an outermost coating layer, and at least the coating layer may contain an optical brightening agent.
The effect of improving the reflectance can be sufficiently obtained by adding the fluorescent whitening agent to the outermost layer.

The types of optical brighteners include OB-1 (manufactured by Eastman), Uvitex-OB (manufactured by Ciba Geigy), Uvitex-MD (manufactured by Ciba Geigy), and J.
P-Conc (manufactured by Nippon Kagaku Kogyo Co., Ltd.) and the like.

The amount of the fluorescent whitening agent added is 0.001% by weight or more and 0.1% by weight or more when added to the film.
It is 1% by weight or less, preferably 0.005 to 0.05% by weight, and more preferably 0.01 to 0.05% by weight. If it is less than 0.001% by weight, the reflectance in the wavelength range of light of 330 to 380 nm is lower than the above average reflectance, and the illuminance is not sufficient when the reflector is used. If it exceeds 0.1% by weight, the color peculiar to the fluorescent whitening agent appears, which is not preferable. In the case of coating, the solid content of the coating agent is 0.01% by weight or more and 2% by weight or less, preferably 0.05 to 1.5% by weight, more preferably 0.1 to
It is 1.5% by weight. The reason is the same as the above reason.

As the binder resin for the coating composition, various resins such as thermoplastic resins or thermosetting resins can be used. Examples thereof include polyester, polyamide, polyesteramide, polyvinyl chloride, poly (meth) acrylic acid ester, polyurethane, polyvinyl chloride, polystyrene, polyolefin, and copolymers and blends thereof. Of these, polyester, poly (meth) acrylic acid ester, and polyurethane are preferable. Further, it may be crosslinked by adding a crosslinking agent.

As a solvent for the coating agent, an organic solvent such as toluene, ethyl acetate, methyl ethyl ketone, or the like, or a mixture thereof can be used, and water may be used as a solvent.

In addition, particles may be added to the coating composition in order to change the roughness and gloss of the coating surface. Particles that do not absorb light are preferred because they do not prevent the effect of the optical brightener. For example, calcium carbonate, silica, barium sulfate, talc, clay and the like are preferable. The amount added is preferably 0.005% by weight or more and 25% by weight or less, more preferably 0.01 to
It is 20% by weight. If it is less than 0.005% by weight, the effect of adding particles is not obtained, and if it exceeds 25% by weight, the coating film becomes brittle and weak.

Further, as the coater, an ordinary gravure coater, coating with a metering bar, or the like can be used. The thickness of the coating film is 0.1μ after solvent drying.
m or more and 10 μm or less is preferable, and more preferably 0.5
~ 5 μm. If it is less than 0.1 μm, the effect of the fluorescent whitening agent does not appear, and if it exceeds 10 μm, the color change due to the binder resin becomes remarkable, which is not preferable.

In the white polyester film according to the first and second aspects of the present invention, the glossiness of at least one side is 80% or less, preferably 60%.
It is desirable that the amount is below, and more preferably 50% or less. By setting the glossiness to 80% or less, the brightness of the screen can be further improved without lowering the brightness of the screen.

Next, the method for producing the white polyester film of the present invention will be explained, but the present invention is not limited to this example. Extruder A was prepared by mixing polymethylpentene as an incompatible polymer and polyethylene glycol as a specific gravity reducing agent with polyethylene terephthalate, thoroughly mixing and drying the mixture and heating it to a temperature of 270 to 300 ° C.
Supply to. If necessary, polyethylene terephthalate containing an inorganic additive such as CaCO ₃ is supplied to the extruder B by a conventional method so that the polymer of the extruder B layer comes to both surface layers in the T die 3 layer die. You may laminate to 3 layers of the structure of A / B.

The melted sheet was contact-cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 to 60 ° C., and the unstretched film was introduced into a roll group heated to 80 to 120 ° C. The film is longitudinally stretched 2.0 to 5.0 times in the direction and cooled with a roll group at 20 to 50 ° C. Then, the both ends of the longitudinally stretched film are guided to a tenter while holding both ends of the film with clips, and transversely stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C. The stretching ratio is 2 to 5 times in each of the length and width, and the area ratio (longitudinal stretching ratio × horizontal stretching ratio) is preferably 6 to 20 times. If the area ratio is less than 6 times, the whiteness of the obtained film will be poor, and if it exceeds 20 times, tearing will tend to occur during stretching and the film-forming property will tend to be poor. In order to impart flatness and dimensional stability to the biaxially stretched film, heat setting is performed at 150 to 230 ° C. in a tenter, and after uniform slow cooling, it is cooled to room temperature to obtain the film of the present invention. .

[Measurement of Physical Properties and Evaluation Method of Effects] The evaluation method of physical properties and the evaluation method of effects of the present invention are as follows. (1) Average reflectance spectrophotometer (Shimadzu UV-26
0) is equipped with an integrating sphere, and the reflectance is 400-700 nm and 330-380 nm when the MgO white plate is 100%.
Measure over. The reflectance is read at intervals of 5 nm from the obtained chart, and the average value is calculated to obtain the average reflectance.

(2) Evaluation method of (maximum value-minimum value) physical property value of reflectance at light wavelength of 400 to 700 nm The reflectance was measured over 400 to 700 nm by the method described in the first paragraph, and the obtained chart Then, the maximum value and the minimum value of the reflectance are read and (maximum value-minimum value) is calculated.

(3) 100 × 1 apparent specific gravity film
Cut to a 00 mm square and dial gauge (N manufactured by Mitoyo Seisakusho)
o. 2109-10) with a probe having a diameter of 10 mm (No. 7).
The thickness of at least 10 points is measured with the one to which 002) is attached, and the average value d (μm) of the thickness is calculated. In addition, this film was weighed with a direct balance, and the weight w (g) was 10 ⁻⁴ g.
Read up to the unit of. At this time, apparent specific gravity = w / d × 100.

(4) Brightness of screen After setting a film as the reflection plate (11) of the apparatus shown in FIG. 3, the illuminance is measured on the screen (12) with an illuminometer (3421 manufactured by Hioki Electric Co., Ltd.). The screen brightness. To measure the illuminance, a black image paper having a width of 20 mm is wound around the size of the light receiver and a cylindrical one is attached to the light receiver, and the distance between the screen (12) and the light receiver is set to 20 mm.

(5) Color of the screen Visually judging the screen, "white" for white light, "yellow" for yellowish,
The reddish color was defined as "red" and the bluish color was defined as "blue".

(6) Glossiness A densitometer VG-107 manufactured by Nippon Denshoku Industries Co., Ltd. was used, and the incident angle and the light receiving angle were evaluated at 60 ° in accordance with JIS-Z-8741.

[0035]

EXAMPLES The present invention will be described based on examples. Example 1 A polyethylene terephthalate chip and a master chip in which polyethylene glycol having a molecular weight of 4000 was added during the polymerization of polyethylene terephthalate were 180
After vacuum drying at ℃ for 3 hours, 89% by weight of polyethylene terephthalate and 1% by weight of polyethylene glycol:
Mix so that polymethylpentene is 10% by weight, and mix.
It was supplied to an extruder heated to 70 to 300 ° C., and formed into a sheet from a T die. Further, an unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. is used.
2. Lead to a roll group heated to 5 to 98 ° C., and 3. in the longitudinal direction.
The film was longitudinally stretched 4 times and cooled by a roll group at 25 ° C. continue,
While holding both ends of the vertically stretched film with clips, the film was introduced into a tenter and horizontally stretched 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Then 2 in the tenter
The film was heat-set at 30 ° C., uniformly cooled slowly, and then cooled to room temperature to obtain a film having a winding thickness of 188 μm. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Example 2 In Example 1, a fluorescent whitening agent (OB manufactured by Eastman Co., Ltd.
-1) Master chip 0.03% by weight optical brightener
To obtain a thickness of 18 by the same method as in Example 1.
An 8 μm film was obtained. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Comparative Example 1 A master chip obtained by compounding polyethylene terephthalate with titanium dioxide particles and a polyethylene terephthalate chip were vacuum dried at 180 ° C. for 3 hours, and then,
The titanium dioxide particles were mixed so as to be 14% by weight, and a film having a thickness of 188 μm was obtained in the same manner as in Example 1. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Comparative Example 2 A master chip in which titanium dioxide particles were compounded in polyethylene terephthalate and a polyethylene terephthalate chip were vacuum dried at 180 ° C. for 3 hours, and then,
Titanium dioxide particles were mixed at 5% by weight and polypropylene at 15% by weight, and a film having a thickness of 188 μm was obtained in the same manner as in Example 1. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Example 3 A polyethylene terephthalate chip was prepared by extruding as in Example 1 from Extruder 1 using two extruders and adding 14% by weight of calcium carbonate particles (“Softon 3200” manufactured by Shiraishi Calcium Co.). After vacuum-drying as in Example 1, extrusion was carried out from the extruder 2, and coextrusion was carried out in a three-layer structure in which the extruder 1 was the inner layer and the extruder 2 was the outer layer. Then, a film having a thickness of 188 μm was obtained in the same manner as in Example 1. The laminated constitution of the obtained film was 12/164/12 μm. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Example 4 In Example 3, the raw material supplied to the extruder 2 was changed to Example 2
A thickness of 188 μm was obtained in the same manner as in Example 3 except that the same fluorescent whitening agent as in Example 1 was added so as to be 0.03% by weight.
m film was obtained. The physical properties of the obtained film as a substrate for a liquid crystal display reflector are shown in Table 1 and FIG.

Example 5 As in Example 3, a 188 μm film was obtained and subjected to corona discharge treatment. Next, acrylic resin (“Cotax” manufactured by Toray) / 2 silicon oxide (particle size 1 μm) / isocyanate / optical brightening agent (OB-1 manufactured by Eastman) = 1
Toluene / methyl ethyl ketone = 1/1 was diluted as a solvent so that 00/5/20/1 was 20%, and coating was performed with a gravure coater to obtain a coating film having a thickness of 3 μm. The physical properties of the obtained film as a substrate for a liquid crystal display reflection plate are as shown in Table 1 and FIG. 2, and almost the same physical properties as those of the film of Example 3 were obtained.

[0042]

[Table 1]

[0043]

The white polyester film of the present invention has an extremely high average reflectance of 90% or more in a specific wavelength range of light and has a small variation in the reflectance. When the white polyester film of the present invention is used as the base material for the substrate, it is possible to obtain a bright and easy-to-see liquid crystal screen in the sidelight system, which is unprecedented. Further, the white polyester film of the present invention has an excellent average reflectance in a specific wavelength range of light, so not only the liquid crystal display reflector base material, but also in other applications where high reflectance is required, It can exhibit excellent characteristics.

[Brief description of drawings]

FIG. 1 is a reflectance characteristic diagram of a white polyester film according to the present invention as a substrate for a liquid crystal display reflector.

FIG. 2 is a reflectance characteristic diagram of Examples and Comparative Examples.

FIG. 3 is a schematic cross-sectional view of a liquid crystal screen incorporating a reflector.

[Explanation of symbols]

H1 Reflectance characteristics showing an example of the white polyester film of claim 1 H2 Reflectance characteristics showing an example of the white polyester film of claim 10

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Claims (11)

[Claims] 1. In the wavelength range of light of 400 to 700 nm
Average reflectance of the surface is not less than 90%, the reflectivity of the wavelength range (maximum value - minimum value) Ri der 10% or less, and the liquid
Used as the main component of the base material for crystal display reflectors
A white polyester film for a liquid crystal display reflector, which is characterized by being applied. 2. The white polyester film for a liquid crystal display reflector according to claim 1, wherein the white polyester film is whitened by containing fine air bubbles inside the film. 3. The liquid crystal display according to claim 2, wherein the apparent specific gravity of the white polyester film is 0.5 or more and 1.2 or less.
White polyester film for spray reflectors . Wherein said white polyester film is a polyester polyolefin is contained more than 25 wt% 2 wt% or more, a liquid crystal display reflective plate for white polyester according to any of the biaxially claims 1 is stretched 3 Film. 5. The white polyester film for a reflector of a liquid crystal display according to claim 4 , wherein the polyolefin is polymethylpentene. 6. A liquid crystal disc of claim 4 or 5 polyalkylene glycol and / or its derivatives is contained 5 wt% or less than 0.1 wt% in the polyester
White polyester film for play reflectors . 7. The white polyester film has a two-layer structure of A layer / B layer or a three-layer structure of A layer / B layer / A layer, and the B layer is a layer containing the fine bubbles. ,
The layer A contains polyester with inorganic particles of 5% by weight or more 25
The white polyester film for a liquid crystal display reflector according to any one of claims 2 to 6 , which is a layer containing less than or equal to wt%. 8. The LCD display reflector for white polyester film of claim 7 wherein the inorganic particles are calcium carbonate. 9. The white polyester film is fluorescently enhanced.
Contains a whitening agent in the wavelength range of light from 330 to 380 nm
Characterized in that the average reflectance of the surface is greater than 90%
White polyester for a liquid crystal display reflector according to claim 1.
Film. 10. The white polyester film for a liquid crystal display reflector according to claim 9 , wherein the white polyester film comprises a laminated polyester film having a plurality of layers, and at least the outermost layer of the laminated film layer contains a fluorescent whitening agent. . 11. The liquid crystal display according to claim 9 , wherein the white polyester film has a coating layer as an outermost layer, and at least the coating layer contains an optical brightening agent.
White polyester film for play reflectors .