KR101536024B1 - Multilayer film - Google Patents

Abstract

A laminated film comprising a polyester film and a coating layer containing a phosphor formed thereon is characterized in that the phosphor of the coating layer is made of an inorganic material and the content of the phosphor in the coating layer is 5 to 80% And the retardation of the yellowing over time is suppressed by the laminated film which has a high luminance and a small color deviation.

Description

[0001] MULTILAYER FILM [0002]

The present invention relates to a laminated film comprising a polyester film and a coating layer formed thereon.

BACKGROUND ART [0002] In recent years, liquid crystal display devices typified by liquid crystal televisions are rapidly spreading. The liquid crystal display device typically includes a backlight unit of a side-type light method or a direct-light type. In a backlight unit of a liquid crystal television, a direct lighting type is adopted. In this method, a cold cathode ray tube is provided in parallel between a liquid crystal cell and a reflector disposed therein. A high reflection performance is required for a reflector used in a backlight unit of a liquid crystal display device. Conventionally, a film containing a white pigment or a film containing fine bubbles therein has been used as the reflector. A film containing a white pigment therein has been widely used because it can obtain high luminance and uniform luminance and is disclosed in, for example, Japanese Patent Laid-Open Publication No. 2004-050479 and Japanese Patent Laid-Open Publication No. 2004-330727. A film containing fine bubbles therein is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 6-322153 and 7-118433.

As a method for improving the brightness of the backlight unit, it has been proposed to apply a fluorescent whitening agent to a film in addition to improving the reflectance of the film itself used for the reflector (Japanese Patent Application Laid-Open No. 2002-40214). However, when the fluorescent whitening agent is applied, the fluorescent whitening agent is deteriorated by the ultraviolet light emitted from the cold cathode ray tube, and the film is yellowed over time.

It is an object of the present invention to provide a laminated film in which time-wise yellowing is suppressed. Another object of the present invention is to provide a laminated film which can obtain a high luminance when used as a member of a backlight unit of a liquid crystal display device. Another object of the present invention is to provide a laminated film which is capable of achieving a high luminance by suppressing a time-wise yellowing and having a small color deviation, and which is suitable as a reflector.

That is, the present invention relates to a laminated film comprising a polyester film and a coating layer containing a phosphor formed thereon, wherein the phosphor of the coating layer is made of an inorganic material and the content of the phosphor in the coating layer is 5 to 80% Is a laminated film.

According to the present invention, it is possible to provide a laminated film in which time-wise yellowing is suppressed, and a laminated film which can obtain a high luminance when used as a member of a backlight unit of a liquid crystal display device. According to the present invention, it is also possible to provide a laminated film which is suppressed in time-wise yellowing to obtain a high luminance, and which is less suitable for use as a reflector because the color deviation is small.

Hereinafter, the present invention will be described in detail.

(Coated layer)

In the present invention, it is very important that the phosphor of the coating layer is made of an inorganic material. By using a phosphor made of an inorganic material as the phosphor, a laminated film having less color deviation can be obtained. On the other hand, when a phosphor composed of an organic material is used as a phosphor, the phosphor is decomposed by ultraviolet rays, and the laminated film is yellowed by ultraviolet rays for a long period of use.

The coating layer contains 5 to 80% by weight, preferably 15 to 50% by weight, of a phosphor made of an inorganic material per 100% by weight of the composition of the coating layer. If it is less than 5% by weight, a sufficiently high luminance can not be maintained when a white film is used as a film for use as a reflector. On the other hand, if it exceeds 80% by weight, a uniform coating layer can not be obtained and it is difficult to suppress the yellowing without irregularity throughout the film.

From the viewpoint of effectively suppressing the yellowing of the film, the coating layer preferably contains a compound capable of absorbing ultraviolet rays. When the coating layer contains a compound capable of absorbing ultraviolet rays, the content thereof is, for example, 20 to 95% by weight, preferably 20 to 50% by weight, per 100% by weight of the composition of the coating layer. The compound having an ultraviolet absorbing ability may be of a low molecular type or a high molecular type. As the polymer type, for example, a polymer obtained by polymerizing a small molecule having an ultraviolet ray absorbing ability on a main chain or a side chain of a polymer can be used. The polymer type ultraviolet absorbing compound is preferable because it has a function as a binder.

The coating layer preferably contains a resin as a binder in addition to a compound having an ultraviolet absorbing ability. In the case where the coating layer contains a resin of a binder, the binder resin may occupy a portion other than the phosphor made of the inorganic material in the composition of the coating layer, or may contain a phosphor other than the phosphor and an ultraviolet absorbing compound Can take part.

These components constituting the coating layer are dissolved or dispersed in an organic solvent to be used as a coating liquid.

Examples of the binder resin include polyolefins such as polyester, polyurethane, acrylic, polyamide, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, Mixtures of more than two kinds can be used. Further, a binder resin obtained by copolymerizing a compound having an ultraviolet absorbing ability as a copolymerization component may be used.

The thickness of the coating layer is preferably 2 to 10 mu m. By setting the thickness within this range, it is possible to obtain a laminated film which does not drop off the inorganic phosphor well and has good sliding properties.

(A phosphor made of an inorganic material)

It is preferable that the phosphor of the inorganic material in the present invention has an excitation wavelength of 400 to 450 nm. By using a phosphor made of an inorganic material having an excitation wavelength within this range, a high luminance can be obtained when used as a reflector, and a laminated film free from coloration due to absorption can be obtained. Hereinafter, a " phosphor made of an inorganic material " may be simply referred to as an " inorganic phosphor ".

The inorganic phosphor of the present invention preferably has an emission peak wavelength of 500 to 600 nm. When the emission wavelength is less than 500 nm or exceeds 600 nm, the effect of improving the luminance when used as a reflector is not preferable.

An inorganic phosphor satisfying the above requirements for the excitation wavelength and emission peak wavelength is made of an alkaline earth metal sulfide having an alkali salt crystal structure, an alkaline earth metal complex oxide or a lanthanum phosphate compound as a host, Can be used.

As the alkaline earth metal sulfide, for example, zinc sulfide (ZnS), strontium sulfide (SrS) and yttria (Y ₂ O ₂ ) can be used.

As the alkaline earth metal composite oxide, for example, a barium-magnesium-aluminum composite oxide (BaMgAl ₁₀ O ₁₇ ) can be used.

Eu, Cu, Al, Ce, Tb, Ba, Sr and Ag can be used as the material for the electroluminescence. A combination of Ba and Eu, and a combination of Ba, Sr and Eu can be used.

Particularly preferred inorganic phosphors are inorganic phosphors containing europium (Eu) and / or copper (Cu) as a host material, made of strontium sulfide (SrS) or yttria (Y ₂ O ₂ ) (LaPO ₄ ), which is made of an aluminum composite oxide (BaMgAl ₁₀ O ₁₇ ) as a host and contains europium (Eu) and / or manganese (Mn) And is an inorganic phosphor containing Ce and / or Tb as a material.

When the activated substance is Eu, for example, Eu ₂ O ₃ can be used as the activating agent. In this case, the content of the activator Eu ₂ O _{3 in} the inorganic phosphor is, for example, 0.01 to 10% by weight based on the total weight of the inorganic phosphor.

When the activated substance is Mn, for example, MnO may be used as the activating agent. In this case, the content of the activator MnO in the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

If the revival material of Ce, for example, as the activator may be used CePO _4. In this case, the content of the activator CePO _{4 in} the inorganic phosphor is, for example, from 0.01 to 35% by weight based on the total weight of the inorganic phosphor.

If the rejuvenated material is Tb, for example, Tb ₄ O ₇ may be used as the activator. In this case, the content of the activator Tb ₄ O _{7 in} the inorganic phosphor is, for example, 0.01 to 25% by weight based on the total weight of the inorganic phosphor.

If the rejuvenated material is Cu, for example, Cu ₂ S may be used as the activator. In this case, the content of the activator Cu ₂ S in the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

When the activated substance is Al, for example, Al ₂ S ₃ can be used as the activating agent. In this case, the content of the activator Al ₂ S _{3 in} the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

The inorganic phosphor is, for example, in the form of a particle, and the shape of the particle is not critical, but a spherical phosphor can be used, for example. The average particle diameter of the particles is, for example, 2 to 10 占 퐉, preferably 3 to 7 占 퐉. By using the inorganic fluorescent material having the particle size of the average particle diameter in this range, it is possible to uniformly disperse the inorganic fluorescent substance in the coating liquid and to obtain a coated layer in which the fluorescent substance is uniformly distributed.

Inorganic phosphors are commercially available, and for example, the following can be used.

As the green luminescent inorganic phosphor, 2210 (made of ZnS made by Kasei Optonics Co., Ltd., made of Cu-activating material), E7031-2 (La ₂ O ₂ S produced by Nemoto specialties Co., ), E4011-1 (made up of SrAl ₂ O ₄ produced by Nemoto Specialty Chemicals Co., Ltd., and Eu as a reductant) can be used.

As the red inorganic phosphor, D1110 (manufactured by Nemoto special chemical Co., Ltd., Y ₂ O ₃ is used as a host and Eu is used as the activating material) can be used.

As the blue inorganic phosphor, D1230 (SrS produced by Nemoto Specialty Chemicals Co., Ltd. is used as a matrix and Eu is used as the activating material), E2031-2 (BaMgAl ₁₀ O ₁₇ manufactured by Nemoto Specialty Chemicals Co., ) Can be used.

As the green inorganic phosphor, KX732A (manufactured by Kasei Optonics, a barium-magnesium-aluminum composite oxide (BaMgAl ₁₀ O ₁₇ ) is used as a matrix and Eu and Mn are used as the activating material) can be used.

Yellow-green inorganic phosphor P22-GN4 as (a Kasei opto matrix a ZnS of Phoenix Corp., and is achieved by a Cu, Al as a resurrection material), LP-G2 (the LaPO ₄ of Kasei Optonix Co., Ltd. as a matrix, and Ce , And Tb is used as the rejuvenating material).

(Compound having ultraviolet absorbing ability)

Examples of the compound having an ultraviolet ray absorbing ability include organic ones such as benzophenone type, benzotriazole type, cyanoacrylate type, salicylic acid type, triazine type, benzoate type, and oxalic acid anilide type, Can be used. A compound having an ultraviolet absorbing ability of organic base may be used in the form of being copolymerized with a polymer.

Compounds having ultraviolet absorbing ability are exemplified below.

Benzophenone compounds such as 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy- , 4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, bis 4-hydroxy-5-benzoylphenyl) methane.

Benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, (2'-hydroxy-5'-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'- , 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) benzotriazole, 2- (2'- Benzotriazol-2-yl) phenol], 2 (2'hydroxy-5'- methacryloxyphenyl) -2H- benzotriazole, 2- [2'- - (3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl] benzotriazole.

Cyanoacrylate-based, ethyl-2-cyano-3,3'-diphenylacrylate.

P-t-butylphenyl salicylate, and p-octylphenyl salicylate, which are salicylic acid-based.

(Polyester film)

As the polyester film, a film made of a thermoplastic aromatic polyester is used. The thermoplastic aromatic polyester includes, for example, polyethylene terephthalate, polyethylene naphthalene dicarboxylate and polybutylene terephthalate. These polyesters may be copolymerized with copolymerization components. In this case, the proportion of the copolymerization component is, for example, 20 mol% or less based on the total dicarboxylic acid component.

When the laminated film of the present invention is used as a reflector, it is preferable to use a white polyester film as the polyester film.

The white polyester film may be obtained by stretching a sheet of a composition in which particles are blended with a polyester or a composition in which a non-compatible resin is blended with a polyester, and at the time of stretching the polyester- A white polyester film in which fine voids are formed in the inside of the film by causing peeling at the interface between the polyester resin and the nonconductive resin can be used. As the particles, for example, inorganic particles, organic particles, and composite particles thereof can be used.

As the white polyester film, it is preferable to use a white laminated film comprising a reflective layer and a supporting layer for supporting the reflective layer. In this case, a coating layer is formed on the reflection layer to suppress the yellowing of the reflection layer.

The void volume ratio of the reflective layer in the white laminated film is preferably 30 to 80%, more preferably 35 to 75%, particularly preferably 38 to 70%. This void volume ratio can be obtained by causing the interface between the polyester and the particle or the non-dispersible resin to peel off during drawing to generate voids.

When particles are used as the material forming the void, the average particle diameter of the particles is preferably 0.3 to 3.0 mu m, more preferably 0.4 to 2.5 mu m, particularly preferably 0.5 to 2.0 mu m. If the average particle diameter is less than 0.3 탆, aggregation tends to occur, which is undesirable. If the average particle diameter exceeds 3.0 탆, the film may be broken. The particles are preferably contained in an amount of 31 to 60 parts by weight, more preferably 35 to 55 parts by weight, particularly preferably 37 to 50 parts by weight, per 100 parts by weight of the polyester composition of the reflection layer. If it is less than 31% by weight, the reflectance decreases or the deterioration due to ultraviolet rays becomes worse. If it exceeds 60% by weight, the film tends to be torn, which is not preferable. The particles are preferably inorganic particles.

In particular, a white pigment is preferably used as the inorganic particles from the viewpoint of obtaining high reflection performance. As the white pigment, for example, particles of titanium oxide, barium sulfate, calcium carbonate, silicon dioxide, and preferably barium sulfate particles are used. By using barium sulfate particles, particularly good reflectance can be obtained. The barium sulfate particles may have any of a plate shape and a spherical shape.

As the organic particles, for example, particles of a non-resisting resin described below can be used.

When an emergency resin is used as the material forming the void, for example, a polyolefin resin or a polystyrene resin can be used as the nonreciprocal resin, and specific examples thereof include poly-3-methylbutene- Polypropylene, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polyfluorostyrene, cellulose acetate cellulose propionate Polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, and polychlorotrifluoroethylene. Particularly preferably, polypropylene and polymethylpentene are used. Polypropylene and polymethylpentene are the most preferable since the resin itself is highly transparent and can suppress the absorption of light and improve the reflectance.

When an emergency resin is used, the amount is preferably 5 to 30 parts by weight, more preferably 8 to 25 parts by weight, and particularly preferably 10 to 20 parts by weight per 100 parts by weight of the composition of the polyester of the reflection layer. When the amount is more than 30 parts by weight, the film tends to be very easily broken. When the amount is less than 5 parts by weight, sufficient void formation is not achieved and the reflectance of the film is lowered. It is not preferred because the resistance is lowered.

The support layer is composed of a polyester composition, and preferably contains 0.5 to 30% by weight, more preferably 1 to 27% by weight, and particularly preferably 2 to 25% by weight, of inorganic particles per 100 parts by weight of the polyester composition. If it is less than 0.5% by weight, sufficient sliding property can not be obtained, and if it is more than 30% by weight, strength as a support layer for supporting the reflective layer can not be maintained, leading to breakage of the film.

The average particle diameter of the inorganic particles is preferably 0.1 to 5 占 퐉, more preferably 0.5 to 3 占 퐉, and particularly preferably 0.6 to 2 占 퐉. If it is less than 0.1 mu m, agglomeration of the particles tends to occur, which is undesirable. If it exceeds 5 mu m, coarse protrusions may be formed, leading to film breakage.

(Manufacturing method)

Hereinafter, a method for producing the laminated film of the present invention will be described as an example of a laminated film in which a coating layer is formed on a white polyester film comprising a reflective layer containing barium sulfate particles and a support layer.

The blending of the barium sulfate particles in the polyester composition may be carried out during the polymerization of the polyester, or may be carried out after the polymerization. In the case of carrying out the polymerization, it may be added before the transesterification reaction or the end of the esterification reaction, or may be added before the polycondensation reaction is started.

When the polymerization is carried out after the polymerization, it may be added to the polyester after polymerization and melt-kneaded. In this case, a master pellet containing barium sulfate particles at a relatively high concentration is prepared and blended with polyester pellets not containing barium sulfate particles, whereby a polyester composition containing barium sulfate particles with a desired content can be obtained.

It is preferable to filter the polyester composition by using a nonwoven fabric filter made of a stainless steel fine wire having a line diameter of 15 mu m or less as a filter at the time of film production and having an average mesh of 10 to 100 mu m and preferably an average mesh of 20 to 50 mu m. By carrying out this filtration, it is possible to suppress coagulation of particles which are generally aggregated and tend to become coarse aggregated particles, and a film with few coarse foreign matters can be obtained.

A multilayer undrawn sheet is produced by simultaneous multilayer extrusion using a feed block in the polyester composition molten from a die. That is, the melt of the polyester composition constituting the reflection layer and the melt of the polyester composition constituting the support layer are laminated so as to become a reflection layer / support layer by using a feed block, and the melt is expanded on a die and extruded. At this time, the polyester composition laminated by the feed block maintained a laminated form.

The unstretched sheet extruded from the die is cooled and solidified in the casting drum to become an unstretched film.

The coating liquid used for the application of the coating layer is preferably applied to the unstretched film or to the longitudinally stretched film after the subsequent vertical stretching.

An unstretched film is heated by roll heating, infrared heating or the like, and stretched in the machine direction to obtain a longitudinally stretched film. This stretching is preferably carried out using a difference in peripheral speed of two or more rolls. The stretching temperature is preferably a temperature higher than the glass transition point (Tg) of the polyester, and more preferably, the temperature is from Tg to (Tg + 70 deg. C). The stretching magnification is preferably 2.2 to 4.0 times, more preferably 2.3 to 3.9 times in both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter, referred to as the transverse direction) although it depends on the required characteristics of the application. If it is less than 2.2 times, unevenness in thickness of the film deteriorates and a good film can not be obtained. If it exceeds 4.0 times, breakage tends to occur during film production, which is not preferable.

The longitudinally stretched film is successively subjected to transverse stretching, heat fixing, and heat relaxation in sequence to form a biaxially oriented film. These processes are carried out while the film is running. The transverse stretching treatment is carried out while raising the temperature from (Tg + 5) to (Tg + 70) ° C, starting from a temperature higher than the glass transition point (Tg) of the polyester. The temperature increase during the transverse stretching process may be continuous or stepwise (recursive), but is usually repeatedly raised. For example, the transverse stretching zone of the tenter is divided into a plurality of zones along the film running direction, and the temperature is raised by flowing a heating medium at a predetermined temperature for each zone. The magnification of transverse stretching is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times. If the ratio is less than 2.5 times, the thickness unevenness of the film becomes worse and a good film can not be obtained, which is undesirable. If it exceeds 4.5 times, breakage tends to occur during film production.

It is preferable that the film after transverse stretching is heat-treated at a (Tm-20) to (Tm-100) ° C, holding both ends, at a constant width or a width reduction of 10% or less to lower the heat shrinkage. If the temperature is higher than the above range, the flatness of the film is deteriorated and the thickness irregularity becomes large. If the heat treatment temperature is lower than (Tm-100) ° C, the heat shrinkage ratio may be increased.

After the heat treatment, in order to regulate the amount of heat shrinkage of the film in the temperature range of (Tm - 20) to (Tm - 100) ° C in the process of returning the film temperature to room temperature, both ends of the holding film were cut out, Or may be relaxed in the longitudinal direction by adjusting the pulling speed in the direction. To relax, you can adjust the speed of the rolls in the tent. The relaxation can be carried out by lowering the speed of the roll group relative to the film line speed of the tenter, preferably by reducing the speed to 0.1 to 1.5%, more preferably 0.2 to 1.2%, particularly preferably 0.3 to 1.0%. By loosening the film in this manner, the heat shrinkage ratio in the longitudinal direction can be adjusted. In addition, the transverse direction of the film may be reduced in width during the process of cutting both ends to obtain a desired heat shrinkage ratio.

Here, the case of stretching by the sequential biaxial stretching method has been described in detail as an example. However, the laminated film of the present invention may be stretched by either the axial biaxial stretching method or the simultaneous biaxial stretching method.

In the present invention, the coating layer may be formed directly on the polyester film as the substrate, but when the adhesion is insufficient, the surface of the polyester film is preferably subjected to corona discharge treatment or undercoating treatment. The undercoating treatment may be carried out in a polyester film production process (in-line coating method), or the polyester film may be separately coated (offline coating method). The material to be used for the undercoating treatment may be appropriately selected, but copolymerized polyester, polyurethane, acrylic, and various coupling agents can be preferably used.

The coating layer containing the inorganic phosphor can be applied by any method. For example, gravure, roll, spin, reverse, bar, screen, dipping and the like can be used. As the curing method after application, known methods can be used. For example, a method using active lines such as thermal curing, ultraviolet rays, electron beams, and radiation can be applied. The application may be carried out before the completion of the crystal orientation of the film in the production of the polyester film, or after the completion of crystal orientation of the film.

Example

Hereinafter, the present invention will be described in detail by way of examples.

Measurement and evaluation were carried out in the following manner.

(1) Film thickness

The film sample was measured by a 10-point thickness with an electric micrometer (K-402B, manufactured by Anritsu), and the average value was determined to be the film thickness.

(2) Thickness of Coating Layer

The sample was cut into triangles, fixed in a capsule, and embedded in an epoxy resin. Then, the embedded sample was taken as a thin film section in parallel with the longitudinal direction using a microtome (ULTRACUT-S), and then observed and photographed using an optical microscope. The thickness ratio of the coating layer to the film was measured from the photograph , And the thickness of the coating layer was calculated from the thickness of the entire film.

(3) Emission and emission peak wavelength at excitation wavelength 400 to 450 nm

The excitation light emission spectrum in the range of the excitation wavelength 400 to 450 nm and the emission wavelength 300 to 800 nm was collected using a fluorescence spectrophotometer F-4500 (manufactured by Hitachi), and the presence or absence of fluorescence emission was evaluated based on the following criteria Respectively. The measurement was carried out on the surface on which the phosphor-containing coating layer was formed. For fluorescence emission, the emission peak wavelength was determined from the excitation emission spectrum.

◎: Fluorescent light is available

X: No fluorescence emission

(4) Time course of yellowing

Was irradiated with light for 50 hours by a high-pressure mercury lamp (manufactured by Harrison Toshiba Lighting, "Tosecure 401": with a glass filter), and the color change before and after the light irradiation was observed. The irradiance for light irradiation was 18 mW / cm 2. In the case where the constitution of the film is two layers of the reflection layer / support layer, light is irradiated from the reflection layer side and measured.

The initial film color (L ₁ ^* , a ₁ ^* , b ₁ ^* ) and the film color after irradiation (L ₂ ^* , a ₂ ^* , b ₂ ^* ) were measured with a color difference meter (SZS- Σ90 COLOR manufactured by Nippon Denshoku Industries Co., MEASURING SYSTEM), and the color change (dE *) represented by the following formula was calculated and evaluated according to the following criteria.

dE * = {(L ₁ ^* -L ₂ ^* ) ² + (a ₁ ^* -a ₂ ^* ) ² + (b ₁ ^* -b ₂ ^* ) ² } ^1/2

5?: DE *

5

10?: 5 < dE *

10

15?: 10 <dE *

15

×: 15 <dE *

(5) Average particle diameter

The particles in the powder state before the addition to the polyester were subjected to scanning electron microscopy (SEM), a double-sided tape was attached to the sample table, the particles were thinly layered thereon and carbon was deposited, and then the particle size was measured using a scanning electron microscope The photographs were taken at appropriate magnification. The circle equivalent diameter of particles of at least 100 points or more was obtained by an image processing apparatus and divided by the number of particles, and the average particle diameter (占 퐉) on the number basis was obtained.

(6) Luminance and chromaticity

(Examples 1 to 5 and Comparative Examples 1 to 3) in which the object to be measured was a white polyester film was evaluated by the methods described in the following (6-1) to (6-5).

(6-1) Production of backlight unit for evaluation

A direct-type backlight unit (20 inches) was taken out from a liquid crystal television (AQUOS LC-20S4, manufactured by SHARP) prepared for evaluation, replaced with a light reflecting sheet originally attached to the backlight unit, Thereby producing a backlight unit.

The backlight side of the backlight unit for evaluation was divided into 4 sections of 2 × 2, and the backlight was turned on. The luminance and chromaticity of the front side after 1 hour were measured using a BM-7 luminance meter manufactured by Topcon Co., And the backlight distance was measured as 50 cm. The measurement was carried out for each of the four sections of the backlight surface, and a simple average of brightness was obtained to obtain an average brightness, and a simple average of the chromaticity was obtained to obtain an average brightness.

(6-2) Brightness Improvement Rate

The average luminance before coating was measured by the method described in (6-1) above, with the film before application of the phosphor-containing coating layer as an object to be measured. Next, the average brightness after coating was measured by the method of (6-1) above, with the film after application of the phosphor-containing coating layer as an object to be measured. From the average luminance obtained, the luminance improvement rate was calculated using the following equation.

Brightness Improvement (%)

= (Average luminance after coating) / (average luminance before coating) x 100

(6-3) chromaticity difference

The average chromaticity (x, y) before coating was measured by the method described in (6-1) above, with the film before application of the phosphor-containing coated layer as an object to be measured. Next, the average chromaticity (x, y) after coating was measured by the method of (6-1) above, with the film after application of the phosphor-containing coating layer as an object to be measured. The chromaticity difference? Xy was calculated from the obtained average chromaticity (x, y) using the following equation.

Δxy = (Δx ² + Δy ² ) ^1/2

? X = (x component of average chromaticity after coating) - (x component of average chromaticity before coating)

? Y = (y component of average chromaticity after coating) - (y component of average chromaticity before coating)

Using the obtained? Xy, the chromaticity difference? Xy was evaluated based on the following criteria.

?:? X <0.05

Δxy＜0.10?: 0.05

? X <0.10

Δxy×: 0.10

Δxy

(6-4) Brightness maintenance ratio in the durability test

The average luminance was measured by the method described in (6-1) above, with the film after application of the phosphor-containing coating layer (film before the durability test) as an object to be measured. Next, a durability test was performed in which the backlight was turned on for 3000 hours. The average luminance after the durability test was measured for the film subjected to the durability test by the method of (6-1).

The luminance retention ratio was calculated by the following equation.

Brightness Retention Rate (%)

= (Average luminance after durability test) / (average luminance before durability test) x 100

(6-5) Change in chromaticity in durability test

The average chromaticity (x, y) was measured by the method described in the above (6-1), with the film (the film before the durability test) coated with the phosphor-containing coating layer as the measurement target. Next, a durability test was performed in which the backlight was turned on for 3000 hours. The average chromaticity (x, y) of the film after the durability test was measured by the method of (6-3) above. From the average chromaticity (x, y) thus obtained,? Xy was calculated using the following equation.

Δxy = (Δx ² + Δy ² ) ^1/2

? X = (x component of average chromaticity after durability test) - (x component of average chromaticity before durability test)

? Y = (y component of average chromaticity after durability test) - (y component of average chromaticity before durability test)

Using the obtained? Xy, the chromaticity change? Xy was evaluated on the basis of the following criteria.

?:? X <0.05

Δxy＜0.10?: 0.05

? X <0.10

Δxy×: 0.10

Δxy

(7) Luminance and chromaticity

When the object to be measured was a transparent polyester film (Reference Example 6 and Comparative Example 4), evaluation was made by the methods described in (7-1) to (7-5).

(7-1) Production of backlight unit for evaluation

The backlight unit (20 inches) was taken out from a liquid crystal television (AQUOS LC-20S4, manufactured by SHARP) for evaluation and replaced with a light diffusion sheet originally attached to the backlight unit. A backlight unit was manufactured.

The backlight side of the backlight unit for evaluation was divided into 4 sections of 2 × 2, and the backlight was turned on. The luminance and chromaticity of the front side after 1 hour were measured using a BM-7 luminance meter manufactured by Topcon Co., And the backlight distance was measured as 50 cm. The measurement was carried out for each of the four sections of the backlight surface, and a simple average of brightness was obtained to obtain an average brightness, and a simple average of the chromaticity was obtained to obtain an average brightness.

(7-2) Brightness Improvement Rate

The average luminance before coating was measured by the method described in (7-1) above, with the film before the application of the phosphor-containing coated layer as an object to be measured. Next, the average brightness after coating was measured by the method of (7-1) above, with the film after application of the phosphor-containing coating layer as an object to be measured. From the average luminance obtained, the luminance improvement rate was calculated using the following equation.

Brightness Improvement (%)

= (Average luminance after coating) / (average luminance before coating) x 100

(7-3) The chromaticity difference

The average chromaticity (x, y) before coating was measured by the method described in (7-1) above, with the film before application of the phosphor-containing coating layer as an object to be measured. Next, the average chromaticity (x, y) after coating was measured by the method of (7-1) above, with the film after application of the phosphor-containing coating layer as an object to be measured. The chromaticity difference? Xy was calculated from the obtained average chromaticity (x, y) using the following equation.

Δxy = (Δx ² + Δy ² ) ^1/2

? X = (x component of average chromaticity after coating) - (x component of average chromaticity before coating)

? Y = (y component of average chromaticity after coating) - (y component of average chromaticity before coating)

Using the obtained? Xy, the chromaticity difference? Xy was evaluated on the basis of the following criteria.

?:? X <0.05

Δxy＜0.10?: 0.05

? X <0.10

Δxy×: 0.10

Δxy

(7-4) Brightness retention rate in the durability test

The average luminance was measured by the method described in (7-1) above, with the film (the film before the durability test) coated with the phosphor-containing coated layer as the measurement target. Next, a durability test was performed in which the backlight was turned on for 3000 hours. The average brightness after the durability test was measured for the film subjected to the durability test by the method of (7-1).

The luminance retention ratio was calculated by the following equation.

Brightness Retention Rate (%)

= (Average luminance after durability test) / (average luminance before durability test) x 100

(7-5) Change of chromaticity in durability test

The average chromaticity (x, y) was measured by the method described in the above (7-1), with the film (the film before the durability test) coated with the phosphor-containing coating layer as an object to be measured. Next, a durability test was performed in which the backlight was turned on for 3000 hours. The average chromaticity (x, y) of the film after the durability test was measured by the method of (7-3) above. From the average chromaticity (x, y) thus obtained,? Xy was calculated using the following equation.

Δxy = (Δx ² + Δy ² ) ^1/2

? X = (x component of average chromaticity after durability test) - (x component of average chromaticity before durability test)

? Y = (y component of average chromaticity after durability test) - (y component of average chromaticity before durability test)

Using the obtained? Xy, the chromaticity change? Xy was evaluated on the basis of the following criteria.

?:? X <0.05

Δxy＜0.10?: 0.05

? X <0.10

Δxy×: 0.10

Δxy

Reference Example 1 (Production of white polyester film)

132 parts by weight of dimethyl terephthalate, 18 parts by weight of dimethyl isophthalate (12 mol% based on the total dicarboxylic acid component of the polyester), 96 parts by weight of ethylene glycol, 3.0 parts by weight of diethylene glycol, 0.05 part by weight of manganese acetate, 0.012 part by weight of lithium was injected into a flask equipped with a rectification tower and a distillation condenser and heated at 150 to 235 DEG C with stirring to carry out an ester exchange reaction in which methanol was flowed out. After the methanol had spilled out, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to the reactor. Subsequently, the inside of the reactor was gradually reduced to 0.5 mmHg while stirring, and the temperature was raised to 290 占 폚 to carry out a polycondensation reaction. The content of the diethylene glycol component in the obtained copolymer polyester was 2.5% by weight, the content of germanium element was 50 ppm, and the content of lithium element was 5 ppm.

To the polyester was added 50 wt% of barium sulfate particles having an average particle diameter of 1.5 mu m to obtain a polyester composition for a reflection layer. Further, 5 wt% of barium sulfate particles having an average particle diameter of 1.5 mu m was added to the polyester to obtain a polyester composition for a support layer. Each of the compositions was fed to two extruders heated to 280 DEG C and joined together using a two-layer feed block device so that the ratio of the thickness of the reflective layer / support layer was 3/1 to form a two-layer laminate, Extruded from a die to form a two-layer sheet. The film was cooled and solidified in a cooling drum having a surface temperature of 25 ° C to form an unstretched film. The film was further heated to 95 ° C and stretched in the longitudinal direction (longitudinal direction), and cooled in a roll group of 25 ° C. Subsequently, both ends of the longitudinally stretched film were led to a tenter while being held by a clip, and stretched in a direction perpendicular to the longitudinal direction (transverse direction) in an atmosphere heated to 120 占 폚. Thereafter, heat setting was carried out at a temperature of 200 ° C in the tenter, and the longitudinal relaxation and the lateral width were carried out at a temperature of 130 ° C at 0.5% and 1%, respectively, Mu] m of a biaxially oriented polyester film.

Reference Example 2 (Production of transparent polyester film)

96 parts by weight of dimethyl terephthalate, 58 parts by weight of ethylene glycol, and 0.03 part by weight of manganese acetate were charged into the reactor, and the transesterification reaction was carried out while allowing methanol to flow out until the internal temperature became 240 캜 under stirring. After completion, 0.097 part by weight of trimethyl phosphate and 0.041 part by weight of antimony trioxide were added. Subsequently, the temperature of the reaction product was raised, and polycondensation was finally carried out under high vacuum at 280 ° C to obtain a polyester pellet having an intrinsic viscosity ([?]) Of 0.64.

The obtained polyester pellets were dried at 160 DEG C for 3 hours, then melt-extruded at 280 DEG C, cooled and solidified on a cooling drum having a surface temperature of 20 DEG C to obtain an unstretched film. Subsequently, the film was stretched 3.2 times in the longitudinal direction (longitudinal direction) by heating at 95 占 폚, cooled in a roll group of 25 占 폚, and both ends of the longitudinally stretched film were guided by a tenter while being gripped by a clip, , Stretched 3.6 times in the direction perpendicular to the longitudinal direction (transverse direction), and then heat-set at 220 캜. Thereafter, in the tenter at a temperature of 130 캜, the stretching in the longitudinal direction and the widthwise stretching in the transverse direction were carried out by 0.5% and 1.0%, respectively, and then cooled to room temperature to obtain a biaxially oriented film.

Example 1 (Example of white polyester film)

The following composition was dissolved in a toluene / butyl acetate mixed solution to prepare a coating liquid having a solid concentration of 45% by weight. Toluene / butyl acetate mixed solution at a weight ratio of 1: 1 was used.

(Solid content of coating liquid)

Green light emitting inorganic phosphor 2210 (manufactured by Kasei Optonics) 30 parts by weight

Ultraviolet absorbing material: Udouble UV6010 (manufactured by Nippon Shokubai Co., Ltd.) 15 parts by weight

This coating liquid was applied on the reflective layer of the white polyester film obtained in Reference Example 1 so that the thickness after drying became 5 占 퐉 and dried by hot air at 150 占 폚 for 2 minutes to obtain a coated film.

The luminance increase rate of the obtained coating film was 104%. The other evaluation results are shown in Table 1.

Further, the green light emitting inorganic phosphor 2210 (manufactured by Kasei Optonics) is an inorganic phosphor made of ZnS as a host and Cu as a recycling material.

Example 2 (Example of white polyester film)

A coating film was obtained in the same manner as in Example 1 except that the fluorescent substance of the coating liquid was changed to red inorganic phosphor D1110 (manufactured by Nemoto Specialty Chemicals). The evaluation results are shown in Table 1.

The red inorganic phosphor D1110 (manufactured by Nemoto specialties Co., Ltd.) is an inorganic phosphor made of Y ₂ O ₃ as a matrix and containing Eu as a reductant.

Example 3 (Example of white polyester film)

A coating film was obtained in the same manner as in Example 1 except that the fluorescent substance of the coating liquid was changed to a blue inorganic fluorescent substance D1230 (manufactured by Nemoto Specialty Chemicals). The evaluation results are shown in Table 1.

Further, the blue inorganic phosphor D1230 (manufactured by Nemoto specialties Co., Ltd.) is an inorganic phosphor made of SrS as a matrix and using Eu as the activating material.

Example 4 (Example of white polyester film)

A coating film was obtained in the same manner as in Example 1 except that the fluorescent substance of the coating liquid was changed to the green inorganic fluorescent substance KX732A (manufactured by Kasei Optonics). The evaluation results are shown in Table 1.

Further, the green inorganic phosphor KX732A (manufactured by Kasei Optonics) is an inorganic phosphor comprising a barium-magnesium-aluminum composite oxide (BaMgAl ₁₀ O ₁₇ ) as a matrix and using Eu and Mn as the activator.

Example 5 (Example of white polyester film)

A coating film was obtained in the same manner as in Example 1 except that the ultraviolet absorbing material was changed to acrylic binder type double S-2840 (manufactured by Nippon Shokubai Co., Ltd.). The luminance improvement rate was 104%. The evaluation results are shown in Table 1.

Comparative Example 1 (Example of white polyester film)

The following composition was dissolved in a toluene / butyl acetate mixed solution to prepare a coating liquid having a solid concentration of 45% by weight. Further, a toluene / butyl acetate mixed solution having a weight ratio of 1: 1 was used.

(Solid content of coating liquid)

- 5 parts by weight of organic fluorescent whitening agent OB-1 (manufactured by Eastman)

Ultraviolet absorbing material: Udouble UV6010 (manufactured by Nippon Shokubai Co., Ltd.) 15 parts by weight

This coating solution was applied onto the reflective layer of the white polyester film obtained in Reference Example 1 so as to have a thickness of 5 mu m after drying and dried at 150 DEG C for 2 minutes to obtain a coated film.

The obtained coating film exhibited a luminance increase rate of 105%, but the difference in chromaticity due to coloring was large, and the luminance after the durability test was also deteriorated to a great extent. The evaluation results are shown in Table 1.

Comparative Example 2 (Example of white polyester film)

A coating film was obtained in the same manner as in Example 1 except that the fluorescent substance shown in Table 1 was changed to an organic fluorescent whitening agent UVITEX-OB (manufactured by Ciba Specialty Chemicals) and the amount thereof was changed to 5 parts by weight. The luminance increase rate at this time was about 100%, and the improvement of the luminance was not confirmed. This film is a film having a large difference in chromaticity due to coloring and a large decrease in luminance after the durability test, so that it is difficult to use the film practically. The evaluation results are shown in Table 1.

Comparative Example 3 (Example of white polyester film)

A coating film was obtained in the same manner as in Comparative Example 1 except that the amount of the organic fluorescent whitening agent OB-1 was changed to 30 parts by weight. The evaluation results are shown in Table 1.

Reference Example 6 (Example of transparent polyester film)

The following composition was dissolved in butyl acetate to prepare a coating liquid having a solid concentration of 45% by weight.

(Solid content of coating liquid)

10 parts by weight of Inorganic Phosphor 2210 (manufactured by Kasei Optonics)

Acryl beads (MBX-15, manufactured by Sekisui Chemical Co., Ltd.) 60 parts by weight

25 parts by weight of an acrylic binder (Yueda Double S2740, manufactured by Nippon Shokubai Co., Ltd.)

5 parts by weight of a crosslinking agent (Colonate HL, manufactured by Nippon Urean Co., Ltd.)

A coating film was obtained in the same manner as in Example 1 except that the coating liquid was applied so as to be 8 g / m 2 after solidification. The evaluation results are shown in Table 1.

Further, the green light emitting inorganic phosphor 2210 (manufactured by Kasei Optonics) is an inorganic phosphor made of ZnS as a host and Cu as a recycling material. MBX-15 is an acrylic particle having an average particle diameter of 15 mu m.

This coating liquid was applied onto the transparent polyester film obtained in Reference Example 2 so as to have a thickness of 5 mu m after drying, and dried by hot air at 150 DEG C for 2 minutes to obtain a coated film. The evaluation results are shown in Table 1.

Comparative Example 4 (Example of transparent polyester film)

The following composition was dissolved in butyl acetate to prepare a coating liquid having a solid concentration of 45% by weight.

(Solid content of coating liquid)

Acryl beads (MBX-15, manufactured by Sekisui Chemical Co., Ltd.) 60 parts by weight

32 parts by weight of an acrylic binder (Yueda Double S2740, manufactured by Nippon Shokubai Co., Ltd.)

8 parts by weight of a crosslinking agent (Colonate HL, manufactured by Nippon Polyurethane Industry Co., Ltd.)

A coating film was obtained in the same manner as in Reference Example 6, except that this coating liquid was applied as a coating liquid so that it became 8 g / m 2 after solidification. The evaluation results are shown in Table 1.

Industrial availability

The laminated film of the present invention can be widely used for optical use, and can be suitably used, for example, as a member of a backlight unit of a liquid crystal display device, particularly as a reflector of a backlight unit of a liquid crystal display device.

Claims (3)

In a laminated film comprising a white polyester film and a coating layer containing a phosphor formed thereon, it is preferable that the phosphor of the coating layer is made of an alkaline earth metal sulfide having an alkali salt crystal structure, an alkaline earth metal complex oxide or a lanthanum phosphate compound as a matrix Wherein the inorganic phosphor is an inorganic phosphor containing a red phosphor and a phosphor and the content of the phosphor in the coating layer is 5 to 80 wt% and is used as a reflector. delete The method according to claim 1,
A laminated film used as a reflector of a backlight unit of a liquid crystal display device.