KR101453811B1 - Polyester film for reflecting plate - Google Patents

Abstract

[PROBLEMS] To provide a laminated polyester film which can provide a high-quality image without any spots or defects when used as a member of a liquid crystal display (LCD) of a large screen.

[MEANS FOR SOLVING PROBLEMS] A laminate film having fine pores in at least a polyester layer (A) and having a light transmittance of 5.0% or less at a wavelength of 550 nm and having a film length of 88 cm in the longitudinal direction and 60 cm in the width direction , The difference between the maximum value and the minimum value of the nine light transmittance at the intersection when a line of 22 cm in lengthwise direction and 15 cm in widthwise direction is drawn is 0.5% or less.

Polyester film for reflector

Description

POLYESTER FILM FOR REFLECTING PLATE [0002]

The present invention relates to an optical polyester film, and more particularly to a laminated polyester film for a reflector used in a liquid crystal display of large screen, preferably 40 inch or more (hereinafter, referred to as LCD) It can contribute to the improvement of the quality of optical products.

BACKGROUND ART Conventionally, a biaxially oriented film of a polyester film, particularly polyethylene terephthalate or polyethylene naphthalate, has excellent mechanical properties, heat resistance and chemical resistance, and is widely used as a magnetic tape, a ferromagnetic thin film tape, a film for packaging, And is widely used as a material such as an electric insulating film, a metal laminate film, a film attached to a glass surface such as a glass display, and a protective film for various members.

BACKGROUND OF THE INVENTION [0002] Polyester films are widely used in various optical films in recent years. They are widely used for base films such as prism sheets, light diffusion sheets, reflectors, and touch panels of LCD members, base films for anti- And the like. In these optical products, a base film used as an optical film for obtaining a bright and clear image is required to have good transparency in its use form and to be free from defects such as foreign objects or scratches which affect the image.

The polyester film is usually obtained by stretching an amorphous sheet obtained by melt extrusion into a sheet form and quenching and solidifying it in the machine direction and the transverse direction, and performing heat treatment. If the uniformity of cooling or stretching is insufficient in these processes, there is a problem that the physical property deviation occurs in the film and deterioration of the image and image unevenness occur when used for optical use.

Brightness is an important characteristic in displays, but it is known that polyester film used as a member greatly affects this brightness. In particular, when obtaining a high-quality image, a high brightness is required. If the deformation of the used polyester film or the difference in physical properties in the polyester film is large, it causes defects on the screen. For this purpose, it is needless to say that the polyester film as the optical member needs to have flatness, but it is important that the phenomenon of lacking the flatness of physical properties during use as an optical member does not occur.

In addition, due to recent large screen display of a liquid crystal display, a distortion of a film and a difference in physical properties within a large screen display tends to remarkably appear as display performance. For example, in Patent Document 1, it has been proposed to use a specific auxiliary cooling device in a process of cooling and solidifying a molten resin sheet in order to produce an oriented polyester film having no thickness fluctuation that causes a luminance deviation. In Patent Document 2, when using the film as a liquid crystal display member, there is no deviation or defect, and in order to realize a high luminance, the film haze and the film thickness are specified so that a biaxially oriented polyester for a light diffusion sheet of a large screen liquid crystal display of 40 inches or more Film production. In Patent Document 3, in order to provide a base film which has a high reflection luminance and a low directivity, a polyester film is coated with a thin coating containing fine particles to form a liquid crystal having a fine concavo- A base film for a display reflector is manufactured.

However, in the above-mentioned prior art, color deviation and brightness deviation occur in the display when the liquid crystal display is used as a member of a large screen liquid crystal display of 40 inches or more in size, and film distortion due to lighting of the display for a long time is also seen. It was necessary to further improve the deviation of the light transmittance, the deviation of the luminance, and the light resistance.

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-281531

[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-184368

[Patent Document 3] JP-A-61-102687

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a polyester film which can provide a high-quality image without any spots or defects when used as a member of a large screen liquid crystal display.

That is, the gist of the present invention is

(1) A polyester film comprising a polyester layer (A) having fine voids and having a light transmittance of 5.0% or less at a wavelength of 570 nm and having a film length of 88 cm in the longitudinal direction and 60 cm in the width direction, 22 cm, a line at intervals of 15 cm in the width direction, and the difference between the maximum value and the minimum value of the light transmittance at nine wavelengths of 550 nm is 0.5% or less,

(2) a polyester film for a reflector according to (1), wherein a polyester layer (B) containing inorganic particles is laminated on one side of the polyester layer (A)

(3) The polyester layer (A) contains 10 to 80% by weight of a void forming agent and 2 to 25% by weight of a thermoplastic polyester elastomer having a melting point of 160 to 230 캜, , A polyester film for a reflector according to (1) or (2) which is formed by forming fine voids,

(4) The polyester film for reflector according to (3), wherein the void-forming agent is a polymethylpentene or cycloolefin copolymer,

(5) A line of 22 cm in the lengthwise direction and 15 cm in the widthwise direction was drawn in the range of the size of 88 cm in the length direction and 60 cm in the width direction in the film, and a line width of 100 mm x 10 mm The heat shrinkage ratio of the film when heated at 80 DEG C for 30 minutes in nine samples each in the longitudinal direction or in the width direction was cut in the longitudinal direction and the width direction (such that the direction of 100 mm was the longitudinal direction or the width direction) Is 1.0% or less in both the width direction and the longitudinal direction,

The polyester film for reflector according to any one of (1) to (4), wherein the difference between the maximum value and the minimum value is within 0.3%

(6) The polyester film for a reflector according to any one of (1) to (5), which is used for a large screen liquid crystal display of 40 inches or more.

EFFECTS OF THE INVENTION [

INDUSTRIAL APPLICABILITY When used as a member of a large screen liquid crystal display, the present invention can provide a high-quality image without any spots or defects.

Hereinafter, the present invention will be described in more detail.

The polyester used in the polyester layer (A) and the polyester layer (B) of the present invention is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid. Examples of the dicarboxylic acid include those represented by terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like, and examples of the diol include ethylene glycol, trimethylene glycol, tetramethylene glycol , Cyclohexane dimethanol, and the like.

Specific examples of the polyester to be used for the polyester layer (A) and the polyester layer (B) of the present invention include polyethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene Polyethylene naphthalene dicarboxylate (polyethylene naphthalate), and the like, and they may be the same or different.

These polyesters may be homopolyesters or copolyesters. Examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid A dicarboxylic acid component such as a carboxylic acid, a 5-sodium sulfoisophthalic acid, or the like may be used.

As the polyester used in the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferable because they have excellent strength, heat resistance, water resistance and chemical resistance.

The polyester to be used in the present invention may contain a resin other than a polyester, an additive such as an ultraviolet absorber, a UV stabilizer, a heat stabilizer, an oxidation stabilizer, an organic Lubrication Now organic microparticles, fillers, nucleating agents, dyes, dispersants, coupling agents and the like may be blended.

The polyester layer (A) and the polyester layer (B) may be made of the same kind of polyester component or may be made of different kinds of polyester component. When the polyester layer (B) is laminated on one side of the polyester layer (A), the polyester layer (B) preferably contains the inorganic fine particles to be described below, . It is also effective to improve the optical pick-up value and the reflectance, and has an excellent effect on the ultraviolet ray resistance. Examples of the inorganic fine particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium dioxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, silica, alumina, mica, mica titanium, talc, clay, kaolin, , Calcium fluoride and the like can be used.

Among these, calcium carbonate, barium sulfate, magnesium carbonate, etc. having bubble forming properties may be used.

In addition, particles that whiten the film due to the difference in refractive index between the titanium oxide, zinc oxide, cerium oxide, and mica titanium may be used.

These inorganic fine particles may be used alone or in combination of two or more. The inorganic fine particles may be in the form of porous or hollow porous or the like and may be subjected to a surface treatment in order to improve the dispersibility of the resin within a range not hindering the effect of the present invention.

As the raw material used for the polyester layer (B) in the present invention, it is preferable to use, for example, a master chip in which polyethylene terephthalate (PET) and inorganic particles are uniformly mixed and PET and inorganic particles are synthesized in advance Do. The master concentration (weight ratio of the inorganic particles to the master chip) of these inorganic particles is preferably 60% by weight or less. When the concentration of the master is larger than 60 wt%, the dispersibility of the inorganic particles is lowered, resulting in a concentration deviation when synthesized. In addition, while PET is in the form of a chip, many inorganic particles are processed into a powder state. If the PET is produced by synthesis without using a master chip, a step of pulverizing PET into a powder form at the time of synthesis is required, There are many things that fall.

The amount of the inorganic fine particles to be added to the polyester layer (B) is not particularly limited, but is preferably 0.05 to 30% by weight, more preferably 3 to 20% by weight, based on the total weight of the polyester layer (B) Is particularly preferable. When the addition amount is less than the above range, it may become difficult to improve the whiteness and hiding properties (optical density) of the film. On the other hand, if it is more than the above range, the gloss or smoothness of the film surface may be lowered , Problems such as tearing of the film at the time of stretching and generation of powder at the time of post-processing may occur.

The polyester layer (A) in the present invention needs to have a fine cavity. In order to form fine pores, in the present invention, it is preferable to add a void-forming agent composed of an inorganic particle or polyester and a resin for non-use. The void-forming agent means inactive particles such as inorganic particles and organic particles, and a cavity when the polyester layer is stretched out of the polyester and the resin for non-use. Representative examples of the inorganic particles that are the void forming agents include calcium carbonate, barium sulfate, magnesium carbonate, titanium dioxide, zinc oxide, cerium oxide, and mica titanium.

In addition, a resin that is non-reactive with polyester is a thermoplastic resin other than polyester and is also incompatible with the polyester, and is dispersed in the form of particles in the polyester and forms bubbles in the film by stretching The effect is great.

Examples of the emulsion resin include olefin resins such as polyethylene, polypropylene, polybutene and polymethylpentene; styrene resins; polyacrylate resins; polycarbonate resins; Polyacrylonitrile resin, polyphenylene sulfide resin, and fluorine resin are preferably used. These may be homopolymers or copolymers, or two or more types of nonconstituent resins may be used in combination. Of these, polyolefins such as polypropylene, polymethylpentene and cycloolefin copolymers having a small critical surface tension are preferable, and polymethylpentene and cycloolefin copolymers are particularly preferably used.

Polymethylpentene is particularly preferable as a non-resisting resin because it has a large difference in surface tension with respect to the polyester and a high melting point, and thus has a large effect of forming bubbles per added amount. As an example of using polymethylpentene, a composition containing 80 wt% of polyethylene terephthalate (PET), 10 wt% of polymethylpentene (PMP), and 10 wt% of polyethylene glycol (PEG) as a dispersing agent of PMP is mixed and melted . When the composition obtained by melting and mixing is measured by differential scanning calorimetry (DSC) to 25 to 300 ° C, the first peak observed at a temperature higher than 200 ° C and near 230 ° C is the melting point (Tm) of the PMP, The peak is the melting point of PET. Since this temperature is higher than the normal heat treatment temperature of 200 to 230 DEG C, PMP is a non-resisting resin and exhibits the function of pore forming agent even after the heat treatment in the film production step.

As described above, a cycloolefin copolymer resin is also preferably used as the void forming agent.

The glass transition temperature of the cycloolefin copolymer resin is preferably 120 ° C to 230 ° C, more preferably 180 ° C to 220 ° C, and still more preferably 190 ° C to 220 ° C. With respect to the glass transition temperature, in the region where the glass transition temperature is lower than 180 占 폚, the cycloolefin copolymer as an emulsion resin is deformed in the heat treatment step in the film production process to lose its function as a porogen, Is deformed and may be distorted. Particularly, in the voids (voids) that are finely dispersed and hardened, small deformation causes void disappearance, which may adversely affect the reflectance of the white polyester film and hence the luminance.

The glass transition temperature is the temperature at which the noncrystalline state transitions from the glassy state to the rubbery state in an amorphous or semi-crystalline material, and is abbreviated as Tg. In the present invention, the Tg is measured by reading out the heat due to the non-trains in both states when the temperature is changed by using the differential scanning calorimeter (DSC) to obtain Tg.

The method of controlling the Tg can be arbitrarily changed by controlling the copolymerization ratio of the straight chain olefin portion (ethylene portion) and the cycloolefin portion (methyl-norbornene portion), and the ratio of cycloolefin can be increased to increase Tg have. The ratio of the cycloolefin moiety to the cycloolefin moiety = cycloolefin moiety = 3: 7 can be further increased to 180 DEG C or higher.

When the Tg is within the above range, voids are hardly lost at the time of heat treatment. In addition, since the rigidity of the cycloolefin serving as the nucleus when the void is expressed during drawing is high and the void generation rate is very high, it is preferable. Since the voids can be laminated in multiple layers, it is effective to improve the reflectance and further improve the brightness.

In the present invention, the content of the void forming agent is preferably in the range of 10 to 80% by weight based on the total weight of the polyester layer (A). If the content is less than 10% by weight, the number of voids may be small and the ability as an LCD member may be lowered. On the other hand, if it is larger than 80% by weight, the pore-forming agent may not be mixed well with the PET, or the pore-forming agents may aggregate, resulting in a decrease in pore-forming property and a tendency for film breakage to occur.

Due to the presence of the voids, the light incident on the film causes reflection at the interface between the polymer constituting the film and the air, thereby improving the reflectance of the film. The size and shape thereof are not particularly limited, but it is preferable that the pores are fine and the size is uniform because the reflectance is improved. In the present invention, it is preferable that the voids exist uniformly over a wide range because of the polyester film for a large liquid crystal display. In the present invention, it is effective to add a thermoplastic elastomer as a dispersing aid in order to uniformly disperse the void forming agent. Examples of the thermoplastic polyester elastomer include polyalkylene glycols such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol and polypropylene glycol, ethylene oxide / propylene oxide copolymers, sodium dodecylbenzenesulfonate, alkylsulfonate Sodium salt, glycerin monostearate, tetrabutylphosphonium paraaminobenzenesulfonate, and the like. In the case of the film of the present invention, a polyalkylene glycol, especially polyethylene glycol, and a copolymer of polybutylene terephthalate and polytetramethylene glycol are particularly preferable. The amount added is preferably from 2% by weight to 25% by weight, based on 100% by weight of the entire layer containing the nonconjugated polymer. When the amount is less than 2% by weight, the addition is not effective and the dispersibility is deteriorated. When the amount is more than 25% by weight, the inherent characteristics of the film base material may be impaired. Such a thermoplastic polyester elastomer can be previously added to the film base material polymer and adjusted as a master polymer (master chip). The thermoplastic polyester elastomer used in the present invention preferably has a melting point in the range of 130 ° C to 230 ° C. More preferably in the range of 180 to 220 占 폚. If the melting point of the thermoplastic polyester elastomer is less than 160 캜, it may become difficult to obtain a uniform dispersion, which may cause variations in physical properties in the film or lower the luminance when used as a reflector. On the other hand, if it is higher than 230 ° C, the dispersion effect is hardly confirmed, which is not preferable.

A stabilizer, an ultraviolet absorber, a thickening branching agent, a gloss removing agent, a colorant, and various other improvers may be added to the thermoplastic polyester elastomer as needed.

In the present invention, it is preferable to laminate the polyester layer (A) and the polyester layer (B), but as the method in this case, a method of forming a composite by coextrusion in a molten film or a method of lamination However, the former method is more preferable in terms of cost and the like. Further, since a large number of voids exist in the polyester layer (A), the film tends to be broken during stretching of the film, so that the former method is more preferable in terms of productivity.

The film of the present invention has a light transmittance of 5.0% or less, preferably 3.0% or less, at a wavelength of 550 nm. That is, the reflectance is 95% or more, and more preferably 98% or more. When it is 95% or less, the screen as a whole becomes dark when used as a liquid crystal display member, and a beautiful image may not be developed. The difference between the maximum value and the minimum value of the light transmittance at 550 nm of nine intersections when a line of 22 cm in the lengthwise direction and 15 cm in the widthwise direction was drawn in the film phase range of 88 cm in the lengthwise direction and 60 cm in the widthwise direction was 0.5% Or less. Here, the longitudinal direction is the film roll releasing direction, and the width direction is the direction perpendicular to the film roll releasing direction. The difference between the maximum value and the minimum value is required to be 0.5% or less, particularly preferably 0.2% or less, in order to uniformly achieve high brightness when the reflective film is mounted on the liquid crystal display.

In the present invention, in order to make the difference between the maximum value and the minimum value of the nine light transmittances to 0.5% or less, the present invention uses a method of introducing a static mixer into a short tube immediately before introduction into the T- Or a method of making the temperature within the single tube uniform. More specifically, the method of introducing the static mixer into the single tube immediately before introduction into the T-die composite detachment can improve the dispersibility of the void forming agent by applying a shearing force immediately before melt extrusion. Therefore, it is preferable to install a static mixer having four or more stages in front of the nipping. Further, since the void-forming agent once dispersed by the extruder generates a flow difference due to a temperature difference and a viscosity difference in a single pipe until being introduced into the T-die composite separator, the polymer near the pipe wall tends to cause re- It can be alleviated by applying a shearing force just before the composite detachment.

Further, the polyester film of the present invention was cut into a size of 88 cm in the longitudinal direction x 60 cm in the width direction, and a line of 22 cm in the longitudinal direction and 15 cm in the width direction was drawn, A sample for measuring the heat shrinkage ratio is prepared. Here, the longitudinal direction is the film roll releasing direction, and the width direction is the direction perpendicular to the film roll releasing direction. The samples for measurement in the longitudinal direction were 10 cm in length and 1 cm in width direction, while samples for measurement in the width direction were 1 cm in the longitudinal direction and 10 cm in the width direction. It is preferable that the heat shrinkage ratio of the heated film is 1.0% or less, preferably 0.5% or less in both the width direction and the length direction, and the difference between the maximum value and the minimum value of the heat shrinkage is 0.3% or less, preferably 0.2% .

If it exceeds this range, heat shrinkage occurs due to the heat of the fluorescent tube or the base, which is a member of the liquid crystal display, when used for a large liquid crystal display, which causes wrinkles and causes color deviation or luminance deviation on the liquid crystal display screen. .

When the thickness of the white laminated polyester film of the present invention is too thin, the stickiness is lost and the workability is deteriorated. When the thickness is excessively large, the price per unit area is increased and the productivity is lowered. In addition, the white laminated polyester film is used as a liquid crystal display It is preferable that the total film thickness of the film is in the range of 150 탆 to 500 탆, more preferably 170 탆 to 300 탆, which is excellent in practical handling. In addition, even when bonded to other materials, the upper limit of the thickness of the base polyester film for reflectors of the present invention is preferably 500 탆 or less from the viewpoint of handling.

Next, the production method in the case where the laminated structure is B / A / B in the polyester film for a reflector of the present invention will be described below, but the present invention is not limited to this example, And a polyester layer (A) such as a monolayer.

In the composite film-forming apparatus having the extruder (A) and the extruder (B), in order to form the polyester layer (A), the dried polyester chips, the dried non- And the polyester chips are supplied to an extruder (A) heated to 260 to 300 占 폚 in such a manner that the final addition amounts are as shown in Table 1, melted and introduced into the T-die composite detergent. On the other hand, as a resin to be used for the polyester layer (B), a polyester chip and a master chip of inorganic fine particles are sufficiently vacuum dried. Next, these dry materials are supplied to an extruder (B) heated to 260 to 300 占 폚 to be melted and introduced into a T-die composite separator, and the polymer of the extruder (B) (Both surfaces) or both surface layers (both surfaces), and co-extruded in a sheet form to obtain a melt-laminated sheet.

Further, a static mixer is introduced into a single tube immediately before introduction into the T-die composite separator, and a shearing force is applied immediately before melt extrusion. This melt-laminated sheet is closely cooled and solidified on a drum cooled to a surface temperature of 10 to 60 占 폚 by static electricity to produce an unstretched laminated film. The unstretched laminated film is guided by a roll group heated at 70 to 120 캜 and is stretched 2 to 5 times in the longitudinal direction (longitudinal direction, that is, the film advancing direction) and chilled by a roll group of 20 to 30 캜.

Subsequently, the white polyester layer (A) side of the film stretched in the longitudinal direction was subjected to corona discharge treatment, and both ends of the film were guided by a tenter while grasping with a clip. In the direction perpendicular to the longitudinal direction (width direction).

The area ratio of stretching (longitudinal stretching magnification x transverse stretching magnification) is preferably 6 to 20 times. If the area ratio is less than 6 times, the whiteness and the film strength of the resulting film tends to become insufficient. On the other hand, if the area ratio exceeds 20 times, tearing tends to occur at the time of stretching.

The biaxially oriented laminated film thus obtained is subjected to a heat treatment at 150 to 230 DEG C for 1 to 30 seconds in a tenter to complete planarity and dimensional stability by completing the crystal orientation, uniformly whirling, cooling to room temperature and winding The polyester film for a reflector of the present invention can be produced.

In the heat treatment step, a relaxation treatment of 3 to 12% in the transverse direction or the longitudinal direction may be carried out, if necessary. The biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, and may be repeated in either the longitudinal or transverse direction or in both directions after biaxial stretching.

The stretching temperature and the stretching ratio are determined in the case of the polyester film (A) monolayer film and the lamination ratio of the polyester layer (A) and the polyester layer (B) or the addition amount of the inorganic fine particles added to the polyester layer It is preferable to appropriately select correspondingly.

Since the polyester film for reflector thus obtained is excellent in the optical properties in the film, the difference in heat shrinkage in the longitudinal and width directions is small, and the thermal deformation is small. Therefore, the polyester film for a reflection plate of the present invention is a film having preferable characteristics as a base film for a reflection plate for a large liquid crystal display.

[Method and Apparatus for Measuring Characteristics]

The characteristic values of the present invention are based on the following evaluation methods and evaluation criteria.

(1) Melting point, glass transition temperature (Tg)

Using a differential scanning calorimeter DSC7 (manufactured by Perkin Elmer), 5 mg of a sample sample is dissolved in a test container at a temperature of 300 캜 for 5 minutes based on JIS K7121, and then quenched at room temperature. The sample was heated at a rate of 10 占 폚 / min, the intermediate glass transition temperature was detected, and the temperature was further increased to obtain an endothermic peak based on crystal melting as a melting point.

(2) Number average particle diameter of inorganic particles

Sectional image of the polyester layer (A) or the polyester layer (B) was observed at a magnification of 10,0000 times using a transmission electron microscope HU-12 type (manufactured by Hitachi, Ltd.). That is, the particle portion of the cross-section photograph is marked along the particle shape, and the particle portion is subjected to image processing using a high vision image analyzing apparatus PIAS-IV (manufactured by Pierce), and a total of 100 particles in the measurement field Circle) was calculated as the number average particle diameter of the inorganic fine particles.

(3) Film Thickness

The thickness of the polyester film for the reflector was measured using a Micrometer M-30 (manufactured by Sony Corporation).

(4) Diameter of pore forming in film

A cross-section observation sample prepared by cutting the film by freezing with a rotary type microtome (manufactured by Nippon Microtom) was subjected to Pt-Pd sputtering and then subjected to cross-sectional photographing with a scanning electron microscope ABT-32 (top cone) at a magnification of 1000 times.

From the photographed cross-sectional photograph, traces of traces of 100% voiding agent were traced with a tracing paper, and the longest side diameter and the shortest side diameter of the pore forming agent were measured based on the scale of the sectional photograph, An average value of 100 values of one value was defined as the cavity forming diameter.

Cavity formation diameter = (longest displacement diameter + shortest displacement diameter) / 2.

When the void-forming agent is not spherical or ellipsoidal, the cross-sectional shape is approximated to an ellipse closest to the shape, and the ellipse is taken as (long diameter + short diameter) / 2.

(5) Light transmittance at a wavelength of 550 nm

The light transmittance at a wavelength of 550 nm in the thickness direction of the film was measured using a fully automatic Hayes computer HGM-2DP (manufactured by Suga Shiken K.K.). The direction parallel to the film roll releasing direction was the longitudinal direction and the direction perpendicular to the film roll releasing direction was the width direction. The maximum value and the minimum value of the total light transmittance at nine intersections when the line was drawn, and the difference therebetween were obtained.

(6) Heat shrinkage

The direction parallel to the film roll releasing direction is the longitudinal direction, and the direction perpendicular to the film roll releasing direction is the width direction. The length in the longitudinal direction of 22 cm and the width in the width direction of 15 cm The sample was cut in the longitudinal direction and the width direction (the direction of 100 mm was in the longitudinal direction or the width direction) with a size of 100 mm x 10 mm centered on the nine intersections, and nine samples in the longitudinal direction and a width 9 samples were obtained. Nine samples in the longitudinal direction or nine samples in the widthwise direction were uniformly subjected to a load of 3 g and the original length was measured with an automatic heat shrinkage measuring instrument (manufactured by TechnoNiz). Subsequently, the resultant was placed in an oven at 80 ° C for 30 minutes, heat-treated, and then subjected to automatic heat shrinkage measurement to determine the heat shrinkage rate from the following equation.

Heat shrinkage (%) = (original length - length after treatment) / original length x 100.

(7) Deviation of luminance due to film origin (direct-type luminance)

In order to measure the luminance deviation of the film origin rather than the backlight originated luminance deviation, the direction parallel to the film roll releasing direction is the longitudinal direction, and the direction perpendicular to the film roll releasing direction is the width direction. A line of 22 cm in the lengthwise direction and 15 cm in the widthwise direction was drawn in the range of 60 cm in size, and each of the nine samples was cut in the size of 100 mm (longitudinal direction) × 100 mm (width direction) As shown in Fig. 1, the reflecting film fused in the backlight of 181BLM07 (manufactured by NEC) was removed, and film samples were placed in the center of each of the above nine sections in order and turned on. The light source was stabilized by waiting for 1 hour in that state, and then the liquid crystal screen was photographed with a CCD camera DXC-390 (manufactured by Sony Corporation), and an image was introduced into an image analyzer system, EyeScale. Thereafter, the luminance level of the photographed image was controlled to be 30,000 steps, automatically detected, and converted into luminance. Thereafter, the difference in luminance in the nine samples was obtained from the following equation to obtain the luminance deviation.

(Cd / m 2) - minimum value (cd / m 2) x 100 / maximum value (cd / m 2)

In addition, within the range of the luminance deviation (%) of 0.8%, it was determined to be acceptable, and more than that.

(8) Film deformation by long-time display

A 40-inch large liquid crystal display was marked on the center of a film cut into a size of 40 inches. After marking, the display was turned on for 100 hours continuously, the display was disassembled, the inserted film was taken out, Mark the center of the paper and the marking cut in 40 inch size. The dimensional difference in the longitudinal and transverse directions at four corners at that time was measured with an ABS Digimatic caliper (manufactured by Mitsutoyo). The evaluation criteria are as follows.

[Evaluation standard]

?: The difference in dimension from the four blanks is 1 mm or less, and the maximum (mm) - minimum (mm) is 0.3 mm or less

?: The difference in dimension from the four blanks is 1 mm or less, and the maximum (mm) - minimum (mm) is 0.3 to 0.5 mm

X: The difference in dimension from the four blanks is 1 mm or more, or the maximum (mm) - minimum (mm) is 0.5 mm or more

<Examples>

The present invention will be described with reference to the following examples and comparative examples, but the present invention is not limited thereto.

(Example 1)

The raw material composition of the polyester (B) layer is as follows. (Silicon dioxide content: 2% by weight, Dore's F118) was used as a polyethylene terephthalate chip (Doreis F20S), the content of silicon dioxide was 0.08% by weight based on the polyester layer (B) , Vacuum-dried at 180 ° C for 3 hours, and then supplied to an extruder (B). The resulting mixture was melted at 285 ° C and introduced into a T-die composite detergent.

The raw material composition of the polyester (B) layer

PET chips 99.92 wt%

0.08 wt% of silicon dioxide (number average particle diameter 3 mu m)

On the other hand, the raw material composition of the polyester (A) layer is as follows. A copolymer obtained by mixing 10 parts by weight of isophthalic acid and 5 parts by weight of polyethylene glycol with PET as a thermoplastic polyester elastomer and mixing the PET chips (DOREES F20S) with polymethylpentene (PMP, "TPX" DX820 by Mitsui Chemicals) (Abbreviated as "PBT / PTMG", manufactured by Toray DuPont "Hytrel") of 10% by weight of a thermoplastic polyester elastomer, polybutylene terephthalate and polytetramethylene glycol, Was added so that the total weight of the thermoplastic elastomer was 15% by weight.

- Raw material composition of polyester (A) layer -

PET chips 65.00 wt%

PMP 20.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

This composition was vacuum-dried at 180 占 폚 for 3 hours and then fed to an extruder (A), treated with a static mixer in front of the spinneret, melted at 285 占 폚 and a white polyester layer (B) A) was obtained by extrusion lamination on both surface layers. The laminated melt sheet was closely cooled and solidified on a cooling drum maintained at a surface temperature of 25 캜 by an electrostatic method to obtain an unstretched film. Thereafter, the unstretched film was guided by a roll group heated to 85 to 98 캜 and longitudinally stretched 3.1 times in the longitudinal direction.

Subsequently, both ends of the longitudinally stretched film were guided into the tenter while grasping with a clip, and stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated at 130 캜. Thereafter, heat setting at 230 캜 was carried out in the tenter, uniformly thawing, cooling to room temperature, and winding to obtain a film having a thickness of 188 탆.

The properties of this film were as shown in Table 1, and a film having a small deviation was obtained as a polyester film for reflector.

(Example 2)

A film having a thickness of 188 탆 was obtained in the same manner as in Example 1 except that the melting point of the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chips 65.00 wt%

PMP 20.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG Melting point 170 占 폚 5.00 wt%

(100% by weight in total)

The properties of this film were as shown in Table 1, and a film having a small deviation was obtained as a polyester film for reflector.

(Example 3)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chips 45.00 wt%

PMP 40.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

The properties of this film were as shown in Table 1, and a film having a small deviation was obtained as a polyester film for reflector.

(Example 4)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chips 25.00 wt%

PMP 55.00 wt%

PET / I / PEG 13.00 wt%

PBT / PTMG 7.00 wt%

(100% by weight in total)

The properties of this film were as shown in Table 1, and a film having a small deviation was obtained as a polyester film for reflector.

(Example 5)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder (B) in Example 1 and the composition to the extruder (A) were changed.

- Raw material composition of polyester (B) layer -

PET chips 95.00 wt%

Silicon dioxide (number average particle diameter 1 mu m) 5.00 wt%

- Raw material composition of polyester (A) layer -

PET chip 35.00 wt%

Barium sulfate (number average particle diameter 1 mu m) 50.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

The properties of this film are shown in Table 1, and a polyester film for a reflector having a very small variation in transmittance and heat shrinkage was obtained.

(Example 6)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chip 10.00 wt%

Barium sulfate (number average particle diameter 1 mu m) 70.00 wt%

PET / I / PEG 13.00 wt%

PBT / PTMG 7.00 wt%

(100% by weight in total)

The properties of this film are shown in Table 1, and a polyester film for a reflector having a very small variation in transmittance and heat shrinkage was obtained.

(Example 7)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1, except that the polyester layer (A) was formed into a single film without using the extruder (B).

The characteristics of the polyester film for the reflection plate are shown in Table 1, and there was no problem in particular with respect to the characteristics.

(Example 8)

A film having a thickness of 188 탆 was obtained in the same manner as in Example 1 except that cycloolefin copolymer ("TOPAS" Tg made by Polyplastics Co., Tg: 160 캜) was used as a void forming agent in Example 1.

- Raw material composition of polyester (A) layer -

PET chips 65.00 wt%

Cycloolefin copolymer (Tg 160 DEG C) 20.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

The properties of this film are shown in Table 1, and a polyester film for a reflector having a very small variation in transmittance and heat shrinkage was obtained.

(Example 9)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that cycloolefin copolymer ("TOPAS" Tg made by Polyplastics Co., Ltd., 220 ° C) was used as the porogen.

- Raw material composition of polyester (A) layer -

PET chips 65.00 wt%

Cycloolefin copolymer (Tg 220 캜) 20.00% by weight

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

The properties of this film are shown in Table 1, and a polyester film for a reflector having a very small variation in transmittance and heat shrinkage was obtained.

(Comparative Example 1)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the static mixer was not used in the extrusion molding. The characteristics of the polyester film for the reflector are as shown in Table 2, and the color and luminance variation in the display were a little seen, and the film distortion was large and did not satisfy the function as the reflector film of the liquid crystal display.

(Comparative Example 2)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder (B) was changed.

- Raw material composition of polyester (B) layer -

PET chip 80.00 wt%

PMP 20.00 wt%

(100% by weight in total)

The properties of the polyester film for the reflector are as shown in Table 2, and the transmittance maximum-minimum was large, and similarly, the absolute value of the heat shrinkage and the difference between the maximum value and the minimum value of the heat shrinkage were large.

(Comparative Example 3)

A film having a thickness of 188 占 퐉 was obtained in the same manner as in Example 1 except that the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chips 85.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG 5.00 wt%

(100% by weight in total)

The characteristics of the polyester film for the reflector are as shown in Table 2, and voids were not formed in the polyester layer (B) because no void forming agent was added, and the transmittance was very high, so that the function as a polyester film for a reflector was low.

(Comparative Example 4)

A film having a thickness of 188 탆 was obtained in the same manner as in Example 1 except that the melting point of the raw material composition to be fed to the extruder A was changed.

- Raw material composition of polyester (A) layer -

PET chips 85.00 wt%

PET / I / PEG 10.00 wt%

PBT / PTMG Melting point 150 占 폚 5.00 wt%

(100% by weight in total)

The properties of the polyester film for the reflector are as shown in Table 2 and a static mixer was used. However, since the melting point of the thermoplastic elastomer was low and the dispersibility was not improved, the difference between the maximum value and the minimum value of the transmittance was large.

(Comparative Example 5)

In Example 3, film formation was carried out in the same manner as in Example 1 except that the raw material composition to be fed to the extruder A was changed and a static mixer was not used. However, film breakage occurred frequently and no target film was obtained .

- Raw material composition of polyester (A) layer -

PET chip 5.00 wt%

Barium sulfate (number average particle diameter 1 mu m) 90.00 wt%

PET / I / PEG 3.00 wt%

PBT / PTMG 2.00 wt%

(100% by weight in total)

(Comparative Example 6)

In Example 4, the raw material composition to be fed to the extruder A was changed, and a static mixer was not used.

- Raw material composition of polyester (A) layer -

PET chips 85.00 wt%

Barium sulfate (number average particle diameter 1 mu m) 5.00 wt%

PET / I / PEG 7.00 wt%

PBT / PTMG 3.00 wt%

(100% by weight in total)

The characteristics of the polyester film for the reflector were as shown in Table 2, and the absolute value of the transmittance was high and the heat shrinkage was large, so that it could not be used as a polyester film for a reflector.

(Comparative Example 7)

In Example 1, the raw material composition to be fed to the extruder A was changed and a static mixer was not used.

- Raw material composition of polyester (A) layer -

PET chips 85.00 wt%

PMP 5.00 wt%

PET / I / PEG 7.00 wt%

PBT / PTMG 3.00 wt%

(100% by weight in total)

The characteristics of the polyester film for the reflection plate are shown in Table 2, and the absolute value of the transmittance was high, so that the function as the polyester film for reflector was low.

(Comparative Example 8)

In Example 1, the raw material composition to be fed to the extruder A was changed and a static mixer was not used.

- Raw material composition of polyester (A) layer -

PET chip 5.00 wt%

PMP 90.00 wt%

PET / I / PEG 3.00 wt%

PBT / PTMG 2.00 wt%

(100% by weight in total)

The properties of the polyester film for the reflector are shown in Table 2, and the dispersibility was poor and the function as the polyester film for reflector was not satisfied.

(Comparative Example 9)

In Example 1, the raw material composition to be fed to the extruder A was changed, and a static mixer was not used.

- Raw material composition of polyester (A) layer -

PET chips 78.00 wt%

PMP 15.00 wt%

PET / I / PEG 5.00 wt%

PBT / PTMG 2.00 wt%

(100% by weight in total)

The characteristics of the polyester film for the reflector are as shown in Table 2. Since the pores were small, the transmittance was high and the polyester film for the reflector did not function as a polyester film.

1 is a schematic cross-sectional view of a liquid crystal display (direct light type) provided with a reflector and a direct view type light type luminance measurement method.

Description of the Related Art

1: reflector 2: cold cathode tube

3: Milk white plate 4: Diffusion plate

5: prism sheet 6: polarizing prism sheet

7: CCD camera 8: Image analyzing apparatus (eye scale)

Claims (6)

The polyester layer (A) contains 10 to 80% by weight of a void forming agent based on the total weight of the polyester layer (A), 2 to 25% by weight of a thermoplastic polyester elastomer having a melting point of 160 to 230 캜 Wherein the thermoplastic polyester elastomer is a copolymer of polybutylene terephthalate and polytetramethylene glycol and a copolymer of isophthalic acid and polyethylene glycol in polyethylene terephthalate as the thermoplastic polyester elastomer, A light transmittance at 550 nm of not more than 5.0%, and a line of 22 cm in the lengthwise direction and 15 cm in the widthwise direction in a film-shaped range of 88 cm in the lengthwise direction and 60 cm in the widthwise direction of the film, Wherein the difference between the maximum value and the minimum value of the light transmittance of the film is 0.5% or less. The polyester film for a reflector according to claim 1, characterized in that at least a polyester layer (B) containing inorganic particles is laminated on one side of the polyester layer (A). delete The polyester film for a reflector according to claim 1, wherein the void-forming agent contains a polymethylpentene or cycloolefin copolymer. 3. The film according to claim 1 or 2, wherein a line of 22 cm in the longitudinal direction and 15 cm in the width direction is drawn in the range of the size of 88 cm in the longitudinal direction x 60 cm in the width direction in the film, The sample was cut in a longitudinal direction and a width direction (such that the direction of 100 mm was the longitudinal direction or the width direction) with a size of mm x 10 mm, and heating for nine samples each in the longitudinal direction or the width direction at 80 캜 for 30 minutes Is 1.0% or less in both the width direction and the longitudinal direction, and the difference between the maximum value and the minimum value is 0.3% or less. The polyester film for a reflector according to claim 1 or 2, which is for a large screen liquid crystal display of 40 inches or more.

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