JPH09316221A - White-colored film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a white-colored film which is suitable for a substrate for a liquid crystal display reflection plate giving a bright screen due to its high reflectance, excellent print quality by forming voids on an undrawn film made of a polyester composition containing a prescribed amount of white particles under specific conditions. SOLUTION: A static discharge with an electric field strength of >=1kv/cm is applied to an undrawn film comprising a polyester composition containing 5-30vol% of white particles such as calcium carbonate with an average reflectance of >=80% in 500-600nm light wavelength range and the film is oriented at least in one direction to form voids by interfacial peeling at the interface of the white particles whereby the objective film is obtained, whose at least one face (face A) satisfies the formula [R is an average reflectance (in %) in the light wavelength range from 500-600μm calculated as the film thickness is 100μm; OD is the optical density calculated as the film thickness is 100μm] and which has a resistivity of 1×10<7> to 1.9×10<12> Ω.cm when it is molten.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a white film and a method for producing the same. More specifically, the present invention relates to a receiving paper for bar code printers, a receiving paper for match printing, a receiving paper for video printers and the like, and a printing substrate, a wrapping paper, a copying paper, a poster, a delivery slip,
Cards, labels, photographic paper, display boards, white boards, magnetic cards,
TECHNICAL FIELD The present invention relates to a receiving film for heat-sensitive recording, a prepaid card, a white film used as a base material for a reflector for a liquid crystal display, etc., and particularly to a high brightness white film preferably used for a reflector base material for an area light source and a method for producing the same. It is a thing.

[0002]

2. Description of the Related Art Conventionally, when illuminating a liquid crystal display, a backlight system in which a light is illuminated from the back surface of the display has been used, but in recent years, it has been disclosed in JP-A-63-621.
The sidelight type as disclosed in Japanese Patent Publication No. 04 has been widely used because of its thinness and uniform illumination.

As shown in FIG. 1, the sidelight system is a transparent light guide plate (base material) 4 such as an acrylic plate having a certain thickness, on one side of which halftone dot printing 3 is applied, and on one side of the reflective plate 2, The diffuser plate 5 and the screen 1 are installed on the other surface, and the illumination light is uniformly dispersed for the halftone dot printing 3 by a method of illuminating the cold cathode tubes 6 and the like from the edges of the transparent light guide plate 4 and the like. The feature is that a screen with uniform brightness can be obtained. Further, since the illumination is installed not on the back surface of the screen but on the edge portion, there is an advantage that the backlight system can be made thinner. However, in order to prevent the illumination light from escaping to the back of the screen, it is necessary to install a reflector 2 on the screen. However, since this reflector 2 is required to be thin and highly reflective, the titanium oxide A film to which a white pigment such as is added is used.

[0004]

However, although the film whitened by the addition of titanium oxide or the like as described above can increase the light reflectance to a certain level, there is a limit to the improvement of the reflectance. However, there was a problem that the screen brightness was still insufficient.

As a result of diligent investigations on such problems, the present inventors have found that titanium oxide or the like absorbs light of a specific wavelength due to the inclusion of a specific impurity in the manufacturing process, and the overall reflectance decreases in a certain wavelength range. It has been found that this is due to the reason that a sufficiently bright screen cannot be obtained and that the hiding property is insufficient due to the inadequate particle size distribution of particles such as titanium oxide. As the market demands,
There is a tendency to desire a brighter screen, and there is a strong demand for a reflector having a higher reflectance over a wide wavelength range. Also,
It has been found that when the workability to be incorporated into a liquid crystal display panel and the market as a reflector substrate for a surface light source are used in the market, it is preferable that a value obtained by multiplying the reflectance of the front and back surfaces and the concealing property is a certain value or more.

An object of the present invention is to solve such a problem,
An object of the present invention is to provide an optimal white film for use as a reflector base material for surface light sources such as a base material for a liquid crystal display reflector, which has a higher reflectance and a brighter screen, and a manufacturing method thereof.

Another object of the present invention is to provide a receiving paper for bar code printers, a receiving paper for match printing, a receiving paper for video printers and the like and a printing substrate, a packaging paper, a copying paper, a poster, a delivery slip, and a card. Another object of the present invention is to provide a high brightness white film which is preferably used for a label, a photographic paper, a display plate, a white plate, a magnetic card, a heat-sensitive recording receiving sheet, a prepaid card and the like, and a method for producing the same.

[0008]

The white film of the present invention which achieves the above object has as its essence a white film having at least one surface (A surface) satisfying the following expression (1).

300 ≧ (R) × (OD) ≧ 50 Equation (1) (where R is the average reflectance (%) in the light wavelength region of 500 to 600 nm when the white film is converted to 100 μm) , OD is the optical density when the white film is converted to 100 μm.) The present invention also includes the following preferred embodiments a to e.

A. The white film consists of polyester and white particles.

B. Light wavelength region of the white particles 500 to 6
The light average reflectance at 00 nm is 80% or more.

C. Containing 100 ppm or more of a phosphorus compound, at least uniaxially stretched, and containing a void.

D. The specific resistance of the white film when melted is 1 × 10 ^{7 to} 1.9 × 10 ¹² Ω · cm.

E. The white film is used as a reflector substrate for a surface light source.

In the white film of the present invention, at least after applying an electrostatic charge having a DC electrolytic strength of 1 kV / cm or more to an unstretched film made of a polyester composition containing 5 to 30% by volume of white particles. By stretching in the uniaxial direction, interfacial peeling is caused at the interface of the white particles to form a void, which can be preferably manufactured.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the above formula (1) is used.
However, a more preferable range of the (R) × (OD) value is 100 or more, and a more preferable range is 110 or more. In the present invention, this value is 1000 or 50.
A larger value such as 0 is more preferable, but considering practical industrial manufacturing, etc., about 300 is practical, and the effect is sufficient. When the white film of the present invention is used for a liquid crystal display reflector substrate, the above (R) ×
If the (OD) value is too low, the hiding property is insufficient and the back side becomes transparent,
Moreover, since the reflectance is low, a sufficiently bright screen cannot be obtained.

Average reflectance (R) and optical density (OD)
The measuring method of will be described later, but in the present invention,
The higher the value of R at 600 nm, the more preferable. This wavelength region corresponds to yellow and is the wavelength region most sensitive to human eyes. That is, in the present invention, the white film may be a white film having a hiding property that satisfies the above formula (1), and may be slightly colored. When it is colored in this way, it is not particularly limited, but a preferable color is a blue to yellowish white in terms of a color wheel.

In the white film of the present invention, if necessary, a fluorescent whitening agent containing an organic and / or inorganic fluorescent agent may be added to enhance whiteness and give a high-class feeling. In particular, in order to obtain these preferable whiteness, in the case of a composite film, at least some layers such as the outermost layer may contain a fluorescent whitening agent, but all layers contain a fluorescent whitening agent. It may be contained. In this case, it is desirable that the content of the optical brightening agent in the outermost layer is higher than the contents of the other layers.

The fluorescent whitening agent may be any one that can be added to the film or one that can be laminated and / or coated on the film using various binders, but those developed especially for polyester are durable. It tends to have good properties and is optimal. Product names include, for example, "Uvitex" OB, MD (manufactured by Ciba Geigy), "Mikawhit"
Examples include e "(Nippon Kayaku-Mitsubishi Chemical Co., Ltd.)," OB-1 "(Eastman Chemical Japan Co., Ltd.) and the like.
The amount of the fluorescent whitening agent added is 100 to 1 with respect to the film substrate.
0000 ppm is preferable, and more preferably 200 to 5
000 ppm. If it is less than 100 ppm, the yellow tint due to the particles may be strong, which is not preferable, and if the amount of the fluorescent whitening agent added is too large, the reflectance may be decreased.

The material of the white film of the present invention may be any thermoplastic resin that can be formed into a sheet, and polyolefin, polyester, polyester carbonate, vinyl chloride, polystyrene and the like are preferable because they have good stretchability. Polyester is particularly preferable because it can impart more preferable dimensional stability and flatness.

Here, the polyester is a polymer obtained by polycondensation of a diol and a dicarboxylic acid, and the dicarboxylic acid is represented by terephthalic acid, isophthalic acid, phthalic acid naphthalene dicarboxylic acid, adipic acid, sebacic acid, etc. It is what is done. The diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specifically, for example, polyethylene terephthalate (PET), polytetramethylene terephthalate (PBT), polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate (PCHDMT), polyethylene-2,6-naphthalene diene. Carboxylate (PEN) or the like can be used.

As the polyester in the film of the present invention, PET and PEN are particularly preferable. Various additives such as an antioxidant and an antistatic agent may be added to the polyester as long as the effects of the present invention are not impaired.

Further, in order to obtain a preferable whiteness of the film, particularly in order to make it difficult to form a coloring matter during extrusion, it is preferable to add an antioxidant, a light resistance stabilizer and / or a heat resistance additive. The preferred content of these additives is 10 to 20000 p based on the film substrate.
pm. If it is less than 10 ppm, it may be colored by light from a fluorescent lamp or the like, which is not preferable.
If it exceeds pm, it may undesirably bleed out and contaminate the surface. Among these additives, phosphorus compounds, hindered amine-based or phenol-based antioxidants are particularly preferable. In particular, a polymer type phenol type is particularly preferable because it is difficult to bleed and the effect is stable.

The content of the phosphorus compound is preferably 100 ppm or more as elemental phosphorus. More preferably 200
To 20000 ppm, more preferably 300 to 1000
It is 0 ppm. Particularly preferably 400 to 8000 pp
m.

If the content of the phosphorus compound exceeds 20,000 ppm, the surface may be contaminated due to bleed-out. On the other hand, when the phosphorus element content in the film is less than 100 ppm, the dispersibility of the white inorganic particles is inferior, and when the resin composition retains at a high temperature, foreign matter is generated and foaming occurs, and preferable whiteness cannot be obtained. Therefore, it may not be preferable. The type of phosphorus compound is not particularly limited, but, for example, phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid and their derivatives, or metal phosphates can be used. Specifically, phosphoric acid, phosphorous acid, trimethyl phosphate, tributyl phosphate, mono- or dimethyl phosphate, dimethylphosphinic acid, finylphosphinic acid, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, etc. Further, metal phosphates such as calcium phosphate, sodium phosphate, magnesium phosphate, manganese phosphate, and phosphorus compounds such as ammonium phosphate can be used.

The dispersibility of inorganic particles in the obtained polyester and composition, the quality stability of the polyester composition, the foamability of the polymer when the polyester composition stays at a high temperature, the generation of foreign matters due to the inorganic particles, etc. From the viewpoint, the above-mentioned phosphorus compound is preferably phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid and derivatives thereof or metal salts of phosphoric acid, more preferably phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid or These are alkyl ester compounds having 3 or less carbon atoms. Moreover, you may use together 2 or more types of these phosphorus compounds.

In producing the white film of the present invention,
It is desirable to use polymeric phenolic antioxidants, especially FDA (FOOD AND DRUG AD- MINISTRATION)
It is preferable to use those listed on the positive list added to the polyesters or olefins of. In particular, tetrakis- [methylene-3- (3 ', 5'-di-
t-Butyl-4'-hydroxyphenyl) propionate] methane is preferred. The addition amount of the antioxidant is preferably 10 ppm to 20000 ppm with respect to the film substrate. More preferably 200 ppm to 20000 pp
m, more preferably 300 ppm or more and 10000 pp
m. Particularly preferably, it is 400 to 8000 ppm.

If the content of the antioxidant exceeds 20,000 ppm, the surface may be contaminated by bleeding out. On the other hand, when the content of the phenolic antioxidant in the film is less than 10 ppm, the dispersibility of the white inorganic particles may be poor, or foreign matter may be generated or foaming may occur when the resin composition stays at high temperature, which is not preferable. is there.

The white film of the present invention preferably contains voids and / or white particles. Conventionally,
In order to whiten the film, it was possible to add inorganic particles such as titanium oxide without particularly examining the particle size and the light average reflectance (R), but in such a film, the reflectance is improved as described above. However, it was difficult to obtain a brighter LCD screen.

In the present invention, the white particles have a light average reflectance (R) of 80 in the light wavelength region of 500 to 600 nm.
% Or more white particles are preferably used. The higher the (R) of the white particles, the better, but the upper limit is 150%.
It is a degree. A more preferable range is 95 to 120%. When (R) is less than 80%, a white film having a preferable high reflectance may not be obtained in some cases. This white particle having a high reflectance can be obtained by removing a coloring compound having a light absorption at a wavelength of 500 to 600 nm. Specifically, there is a method in which particles are dissolved, a coloring compound is removed by a column that adsorbs, and particles are formed while being precipitated.

The white particles in the present invention are inorganic white particles and / or organic white particles. Examples of the inorganic white particles include calcium carbonate, alumina, magnesium oxide, barium sulfate and silica. In the case of the present invention, it is particularly preferable to use calcium carbonate. Further, it is more preferable that 50% by weight or more of the crystalline form of calcium carbonate is a calcite type, since impurities can be reduced and a substance with few impurities can be easily obtained.

The organic white particles can be obtained, for example, by melt-mixing a thermoplastic resin having a parallel light transmittance of 80% or more with polyester to form dispersed particles. In this case, a compatibilizing agent for reducing the dispersed particle size is also preferably used. The compatibilizer has an effect of reducing the dispersed particle size of the incompatible resin by adding it, as compared with the case where it is not added.

When obtaining the film of the present invention, the film is preferably stretched in at least a uniaxial direction in a subsequent step. In this stretching step, voids (bubbles) are generated by interfacial peeling at the white particle interface, and light is scattered by the voids, which has the effect of improving the reflectance. The amount of white particles used is preferably 5 to 30% by volume, more preferably 4 to 15%, based on the film substrate.
% By volume. If the amount of white particles added is less than 5% by volume, it may be difficult to bring the reflectance and optical density of the white film of the present invention into the ranges of the present invention. On the contrary, when the amount of the white particles added exceeds 30% by volume, not only the mechanical properties of the white film of the present invention are inferior, but also the white film is often torn during film formation and the thermal dimensional stability is improved. Problems such as inferiority may occur.

In the present invention, the white particles preferably used have an average particle size of 0.01 to 20 μm, more preferably 0.1 to 10 μm, and most preferably 0.4.
Is about 5 μm. Here, the average particle diameter means the “equivalent spherical diameter” of particles at a point of 50% by weight of all measured particles. Here, the “equivalent spherical diameter” means an imaginary sphere having the same volume as a particle, and can be calculated from measurement by a usual sedimentation method or the like. If the average particle size is larger than 20 μm, generally there are many coarse particles and the optical density is low, which is not preferable. If the average particle size is smaller than 0.01 μm, it may be difficult to set the value of R × OD within the range of the present invention.

Various methods can be used for incorporating the white particles, the antioxidant and the various additives into the film. In the case of polyester used preferably, the following methods can be used as typical methods.

A method of adding before completion of transesterification or esterification reaction during polyester synthesis, or addition before polycondensation reaction.

A method of adding to polyester and melt-kneading.

In the above method, a large amount of additives are added to prepare a masterbatch, or a masterbatch containing white inorganic particles, an antioxidant and various additives in an amount of one or two types is prepared. A method in which a polyester containing no particles is kneaded to contain a predetermined amount of an additive.

As a method of adding the antioxidant, a method of previously adsorbing it on the inorganic particles and then adding it together with the inorganic particles is also preferably used.

When the white film of the present invention is made of polyester, the specific gravity is preferably 0.5 or more.
3 or less. If the specific gravity is more than 1.3, the softness and flexibility of the film tend to be poor, and the thermal conductivity is not sufficiently lowered, so that high quality printing cannot be performed when used as a thermal transfer receiving paper. This is because there are cases and the like. On the other hand, if the specific gravity is less than 0.5, the mechanical strength of the film is generally low, and handling may be difficult.

The excellent flexibility of the white film of the present invention is that an image can be clearly transferred even when the pressure of the thermal recording head is reduced when it is used as a receiving paper for a video printer or the like. This is a desirable property. Of course, the feel when touching the hand is also an important factor. For this reason, it is important that wrinkles are hard to enter during handling.

While not limiting to the invention, suitably made white films of the invention exhibit cushioning values of generally greater than 4%. Preferably 1
It is 0% to 40%, more preferably 20% to 40%.
If the cushion ratio is less than 4%, for example, when it is used as a receiving paper for a video printer or the like, lowering the pressing force of the thermal recording head causes a hard contact with the head and missing dots, resulting in a clear image transfer. Is not preferable, and the touch when touched by the hand may be unfavorable.

In the present invention, it is also preferable that the voids (air bubbles) are efficiently generated by injecting an electrostatic charge in advance at the interface of the dispersed particles and then stretching.
In particular, a manufacturing method using an electrostatically applied casting method is preferable because static electricity can be injected during melting. This electrostatically applied casting method is a preferable means because it can cool the front and back surfaces rapidly and has the effect of reducing the difference in (R) × (OD) between the front and back surfaces of the film. The difference of (R) × (OD) between the front and back of the film is preferably 10 or less, more preferably 5 or less, and most preferably 2 or less.

The specific resistance of the white film of the present invention when melted is preferably 1 × 10 ^{6 to} 1.9 × 10 ¹² Ω · cm. More preferably 1 × 10 ^{7 to} 1.9 × 10 ^10.
Ω · cm. If it is less than 1 × 10 ⁶ Ω · cm, the thermal stability at the time of melting is inferior, which is not preferable in some cases. 1.9 x 10
If it exceeds ¹² Ω · cm, the adhesion to the cast drum may be poor, which may be undesirable.

Further, the color tone b value determined by a color difference meter is preferably -20 or more and 4 or less. The smaller the b value is, the more the whiteness of the apparent film is improved, giving a high-grade image, and it is also preferable for a reflector for a liquid crystal display.

In order to improve the winding property during the production of the film and to improve the glossiness of the surface, it may be used by further laminating.

The preferred surface roughness (Ra) of the white film in the present invention is 1 μm or less. It is more preferably 0.5 μm or less, and most preferably 0.2 μm or less. If the surface roughness is larger than this value, the printability may not be good when used as a printing substrate. In addition, in a magnetic card or the like, the electromagnetic conversion characteristics are inferior, which may be undesirable. However, when (Ra) is less than 0.01 μm, the slipperiness of the film is deteriorated and handling becomes difficult, and luster is generated to make the film feel cheesy, which may lower the commercial value, so caution is required.

In the present invention, the void shape caused by the white particles in the film preferably has a shape factor of 10 or more and 100 or less. If it is out of this range, creases are likely to occur during use, and it may be difficult to use it with a magnetic card or the like.

Next, the method for producing the white film of the present invention will be described, but the present invention is not limited to such a method.

White particles are previously sprinkled with an antioxidant and thoroughly mixed with a resin to form a resin composition. The resin composition is supplied to an extruder heated to a temperature equal to or higher than the melting point of the resin and extruded from a die. Form into a film. Here, the resin composition may be extruded with a vented twin-screw extruder after removing water during extrusion. At this time, it may be passed through a filter in order to obtain a film having desirable surface characteristics. At this time, the film extruded from the die can also be electrostatically adhered to the drum for cooling and solidification. The surface of this drum is preferably a smooth metal-plated surface.

Next, after the unstretched film thus cooled and solidified is longitudinally stretched in the machine axis direction at the stretching temperature of the resin,
The both ends of this uniaxially stretched film are guided to a tenter while gripping both ends with clips, and transversely stretched in the direction perpendicular to the machine direction at the stretching temperature of the resin. At this time, a void can be generated by stretching, and a desired white film can be obtained.

The method for producing a white film using a polyester, which is more preferably carried out, will be described more specifically.

Polyethylene terephthalate was blended with calcium carbonate, which was synthesized by the carbon dioxide gas synthesis method and whose impurities were sufficiently removed, as white particles, and trimethylphosphoric acid, as an antioxidant, respectively, which were thoroughly mixed and dried. , Extruded by supplying to an extruder heated to a temperature of 270 to 300 ° C. Here, the polyester composition can be extruded with a vented twin-screw extruder after removing water during extrusion. At this time, in order to obtain a film having preferable surface characteristics, it is desirable to pass through the filter in a molten state at least once before forming the film in order to remove coarse foreign matters. The filtration accuracy of the filter used is 400
μm or less. It is preferably 100 μm or less, more preferably 50 μm or less.

The sheet thus melt-extruded is then contact-cooled and solidified by static electricity on a drum cooled to a drum surface temperature of 10 to 60 ° C. In the present invention, it is preferable to inject static electricity because if the static electricity is injected into the interface of the dispersed particles in advance and the film is stretched, interfacial peeling occurs effectively. The static electricity may be injected before the longitudinal stretching and before the lateral stretching, but an electrostatic application cast that adds an electrostatic charge during melting is preferable. DC electrolysis having a load electrolytic strength of 1 kV / cm or more, preferably 1 kV / cm or more. 20 kV / c
If it is more than m, corona discharge may occur, which is not preferable.

The surface of this drum is preferably a smooth metal-plated surface. The surface roughness of the drum is preferably 1S or less. It is more preferable to use 0.5S or less, and further preferably 0.3S or less. If the surface of the drum is rough, the surface roughness of the drum is transferred and the surface of the film is rough, which is not preferable.

Then, for example, the unstretched film thus cooled and solidified is guided to a roll group heated to 75 to 120 ° C., longitudinally stretched in the machine axis direction by 2 to 5 and cooled by a roll group at 20 to 50 ° C. . At this time, the inside of the film has a structure containing voids. Voids may be generated in this step in order to obtain the desired white film.

Further, the uniaxially stretched film obtained at this time can be subjected to corona discharge treatment for coating. Next, both ends of this uniaxially stretched film are guided to a tenter while gripping both ends with clips, and transversely stretched in a direction perpendicular to the machine direction in an atmosphere heated to 90 to 140 ° C. The stretching ratio is 2 to 5 times in the longitudinal and lateral directions,
The area magnification is preferably 6 to 15 times. If the area magnification is less than 6 times, the whiteness is insufficient, and conversely, if it exceeds 15 times, tearing tends to occur during stretching, and the film-forming property tends to be poor.

The film biaxially stretched in this manner has a flatness of 15 and a dimensional stability of 15 in a tenter.
It is heat-set at 0 to 230 ° C., uniformly cooled slowly, then cooled to room temperature and wound. At the time of heat setting, it is possible to add a relaxation of 10% or less in order to reduce the heat shrinkage rate. In this way, the white polyester film of the present invention can be obtained.

Alternatively, as described above, a white film made of polyester may be first produced under the above conditions, and a coating layer may be separately melt-extruded or laminated thereon by coating.

In the white film made of the polyester of the present invention, fine particles of calcium carbonate, amorphous zeolite particles, calcium phosphate, silica, kaolin, talc, clay or the like may be used in combination. The addition amount of these is preferably 0.005 to 1 part by weight with respect to 100 parts by weight of the polyester composition. In addition to such fine particles,
Fine particles precipitated by the reaction of the catalyst residue and the phosphorus compound in the polyester polycondensation reaction system can also be used in combination. As the deposited particles, for example, those composed of calcium, lithium and phosphorus compounds, or calcium,
Those composed of magnesium and phosphorus compounds can be used, and the content of these particles in the polyester is preferably 0.05 to 1 part by weight with respect to 100 parts by weight of the polyester.

The white film of the present invention is used as a receiving paper for bar code printers, a receiving paper for match printing, a receiving paper for video printers and the like, and a printing substrate, a wrapping paper, a copying paper, a poster, a delivery slip, a card, It is preferably used as a base material for a label, a photographic paper, a display plate, a white plate, a magnetic card, a heat-sensitive recording receiving sheet and a prepaid card, a reflector for a liquid crystal display, and the like, and a reflector substrate for an area light source.

In the present invention, the method of measuring physical properties and the method of evaluating effects are as follows.

1. Specific gravity The film is cut into 100 x 100 mm square and the dial gauge (Mitoyo Seisakusho No. 2109-10) has a diameter of 10 m.
The thickness of at least 10 points is measured with a probe attached with an m measuring element (No. 7002), and the average value d (μm) of the thickness is calculated. In addition, this film is weighed with a direct balance and the weight w (g) is read up to the unit of 10 ⁴ g. At this time,
Specific gravity = w / d × 100.

2. Optical Density One or several sheets of film are stacked and an optical densitometer (TR9
27, manufactured by Macbeth Co.) is used to measure the transmission density. The film thickness and the optical density were plotted, and the optical density corresponding to a thickness of 100 μm was determined by the interpolation method or the extrapolation method.

3. Cushion rate (%) Dial gauge No. of Mitoyo Manufacturing Co., Ltd. 2109-10
The standard gauge head 900030 is used for the dial gauge stand No. It was calculated from the following formulas from the thicknesses d ₅₀ and d ₅₀₀ of the respective films when a dial gauge pressing partial load of 50 g and 500 g was applied using 7001DGS-M.

Cushion ratio = 100 × (d ₅₀ −d ₅₀₀ ) / d ₅₀ 4. Surface roughness Ra, Rt According to JIS B-0601, it measured with the stylus type surface roughness meter (ET-10 made by Kosaka Laboratory).

5. Average Particle Diameter of Inorganic Particles Inorganic particles were dispersed in ethanol and measured using a centrifugal sedimentation type particle size distribution measuring device (CAPA500 manufactured by Horiba Ltd.), and the volume average diameter was calculated and used as the average particle diameter.

6. Light Transmittance It is melted above the melting point with an extruder and extruded, and a test piece is adjusted to a thickness of 1 mm with a T-die, and the measurement is performed according to JIS-7105 measuring method A. The total light transmittance and the scattered light amount were measured using an integrating sphere type light transmittance measuring device, and the total light transmittance, the diffuse transmittance, and the parallel light transmittance as the difference between them were determined.

7. Optical Average Reflectance of White Particles Hitachi Ltd. spectrophotometer U-3410 type MgO
After adjusting 100% using a white plate as a standard plate, white particles are put into an optical quartz glass (cell optical path length 1 cm) for measurement.

The white particles in the film are collected by dissolving the matrix resin in a solvent which does not affect the white particles, separating the matrix resin from the white particles by centrifugation and washing, and drying. . Particularly in the case of a polyethylene terephthalate film, an orthochlorophenol / chloroform mixed solution is preferable as a solvent.

8. Optical Average Reflectance of Film An integrating sphere is attached to a spectrophotometer U-3410 manufactured by Hitachi, Ltd., 100% is adjusted using a MgO white plate as a standard plate, and then measured over 500 to 600 nm. The reflectance is read from the obtained chart at intervals of 5 nm, and the average value is calculated to obtain the average reflectance. The thickness of the film and the light average reflectance were plotted, and the light average reflectance corresponding to a thickness of 100 μm was determined by the interpolation method or the extrapolation method.

9. BRITISH JOURNAL OF APPLIED PHYSICS Vol.17, Vol.1
The method described on pages 149 to 1154 (1966) was followed. However, in this case, the temperature at the time of melting the polymer composition is 300 ° C., and the value immediately after applying a DC voltage of 3,000 V is the specific resistance at the time of melting.

10. Screen Brightness and Colors In the device shown in FIG. 1, a 3 mm thick acrylic plate was subjected to halftone dot printing, a film was set as the reflecting plate 2, and then a 6 W fluorescent lamp was illuminated from one end face. Screen 1
Measure the illuminance with an illuminometer (3421 made by Hioki Denki),
Set the screen brightness. The illuminance is measured by mounting a black image paper having a width of 20 mm on the light receiver in the size of the light receiver to form a cylinder, and setting the distance between the screen 1 and the light receiver to be 20 mm. Those of 1000 (Lx) or more were accepted.

Also, by visually observing the screen, the white light is "white", the yellowish one is "yellow", the red one is "red", and the blue one is bluish. "Blue".

11. Brightness of screen In FIG. 1, a brightness meter (LS-110 made by Minolta) is displayed on the screen 1.
At 15 points, the luminance was measured, and the average value was taken as the luminance of the screen. Those of 200 (cd / m ² ) or more were accepted.

12. Printing quality A heat-sensitive transfer receiving layer was applied to the obtained white film and cut into 4 plates. Thermal transfer recording was performed on this film using a CX-5000 color printer manufactured by Sharp Corporation, and the obtained hard copy was visually evaluated for print density, print unevenness and the degree of contrast in the following five grades, and the average value was calculated. 4 or more were passed.

[0077]

[0078]

EXAMPLES The present invention will be described below based on examples.

Example 1 20% by weight of calcium carbonate having an average particle size of 1.4 μm, 80% by weight of polyethylene terephthalate (PET) and 1000 ppm of trimethyl phosphate (TMPA) were mixed,
Extrusion was performed while degassing and drying with a vacuum pump so that the vent pressure was 5 (mmHg) from an extruder with a biaxial vent heated to 270 to 300 ° C, and a sheet was formed from a T die. At this time, the electrostatically applied casting method was used.
+ 0.5mm diameter tungsten wire as electrode
Charge and casting drum set to earth (0 potential) 7
A DC electric field of kV was applied. At this time, the distance between the ground point of the molten film and the casting drum and the tungsten wire was 1 cm. 500 of calcium carbonate
The average reflectance in nm-600 nm is 90%,
The specific resistance when melted was 1 × 10 ⁸ Ω · cm. Further, this film was cooled and solidified with a cooling drum having a surface temperature of 25 ° C., led to a roll group heated to 100 ° C., longitudinally stretched 3 times in the machine axis direction, and cooled with a roll group of 25 ° C. Subsequently, the both ends of this longitudinally stretched film were guided to a tenter while gripping both ends with clips, and laterally stretched 3.6 times in a direction perpendicular to the machine axis direction in an atmosphere heated to 125 ° C. Thereafter, the film was heat-set at 220 ° C. in a tenter, gradually cooled, and then cooled to room temperature to obtain a film having a winding thickness of 100 μm. As for the obtained film, as shown in Table 1, the print quality was at the highest level, the brightness was large, and the white and bright screen was obtained.

Comparative Example 1 Trimethyl phosphate (TMP used in Example 1
A film was obtained in the same manner as in Example 1 except that A) was not added and the amount of calcium carbonate added was 10 wt%. The physical properties of the obtained film are shown in Table 1. The value of R × OD of the film was less than 50, the brightness of the screen was not sufficient and the print quality was poor.

Example 2 20% by weight of titanium dioxide having an average particle size of 0.1 μm, 80% by weight of polyethylene terephthalate (PET) and 1000 ppm of trimethyl phosphate (TMPA) were mixed, and 2
Extruded while being degassed and dried with a vacuum pump so that the vent pressure was 10 (mmHg) from an extruder with a biaxial vent heated to 70 to 300 ° C, and formed into a sheet from a T die. A film was obtained in the same manner as in.
As for the obtained film, as shown in Table 1, a high print quality level, a large brightness and a bright screen were obtained.

Comparative Example 2 A film was obtained in the same manner as in Example 2 except that TMPA was not added. The physical properties of the obtained film are shown in Table 1.

Since TMPA was not added, a film having a low average reflectance was obtained, and the screen using this film was not sufficiently bright. Also, the print quality was slightly degraded.

Example 3 10% by weight of calcium carbonate having an average particle diameter of 0.8 μm and 90% by weight of polyethylene terephthalate (PET) were mixed, and the vent pressure was increased by the extruder A with a twin-screw vent heated to 270 to 300 ° C. Extruded while being degassed and dried by a vacuum pump so as to be 5 (mmHg), and 80% by weight of PET, 20% by weight of calcium carbonate having an average particle size of 1.4 μm, and 1000 ppm of trimethyl phosphate (TMPA) were added to 1%.
It is vacuum dried at 80 ° C. for 3 hours and extruded from extruder B. Extruder A is an inner layer, and extruder B is an outer layer and is coextruded so as to have a three-layer structure (B / A / B). After that, a film was obtained in the same manner as in Example 1 thereafter. The average reflectance of the used calcium carbonate at 500 nm to 600 nm was 90%. As for the obtained film, as shown in Table 1, the print quality level was high,
A bright and bright screen was obtained.

[0085]

[Table 1]

[0086]

According to the present invention, a white film having a large value obtained by multiplying the average reflectance and the hiding property can be obtained.
By using such a white film, it is possible to obtain an effect that a bright screen with higher reflectance can be obtained and at the same time excellent printing quality can be obtained by using it as a reflector substrate for a surface light source such as a substrate for a liquid crystal display reflector. In addition, when used as a receiving paper or a printing substrate, the printing contrast is good and a high-grade feeling is given.

[Brief description of drawings]

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

[Explanation of symbols]

 1 ... Screen 2 ... Reflector 3 ... Halftone dot printing 4 ... Transparent light guide plate 5 ... Diffusion plate 6 ... Cold cathode tube (fluorescent lamp)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G02F 1/1335 520 B41M 5/26 H // B29K 67:00 C08L 67:02

Claims (7)

[Claims] 1. A white film having at least one surface (A surface) satisfying the following expression (1). 300 ≧ (R) × (OD) ≧ 50 Equation (1) (where R is the average reflectance (%) in the light wavelength region of 500 to 600 nm when the white film is converted to 100 μm, and OD is Optical density when the white film is converted to 100 μm.) 2. The white film as claimed in claim 1, wherein the white film comprises polyester and white particles. 3. The light wavelength range of the white particles 500 to 600
The white film according to claim 2, having a light average reflectance in nm of 80% or more. 4. The white film according to any one of claims 1 to 3, which contains a phosphorus compound in an amount of 100 ppm or more, is stretched in at least a uniaxial direction, and contains a void. 5. The specific resistance of the white film when melted is 1 ×.
It is 10 < ⁷ > -1.9 * 10 < ¹² > (ohm) * cm, The white film in any one of Claims 1-4 characterized by the above-mentioned. 6. The use as a reflector substrate for a surface light source.
The white film as described in any one of to 5. 7. An unstretched film made of a polyester composition containing 5 to 30% by volume of white particles is added at 1 kV / cm.
A method for producing a white film, which comprises applying an electrostatic charge having the above DC electrolytic strength and then stretching the film in at least a uniaxial direction to cause interfacial peeling at the interfaces of the white particles to form voids.