阅读说明：本技术 双轴取向的聚酯反射膜及其制造方法 (Biaxially oriented polyester reflective film and method for producing same ) 是由 金志赫 金吉中 朴瑞镇 于 2019-12-18 设计创作，主要内容包括：本发明涉及双轴取向的聚酯反射膜以及生产其的方法,所述双轴取向的聚酯反射膜通过在模制期间抑制反射膜的内部多孔层的变形而即使在真空压缩模制和热压模制之后也能够保持优异的反射特性。(The present invention relates to a biaxially oriented polyester reflective film capable of maintaining excellent reflective characteristics even after vacuum compression molding and hot press molding by suppressing deformation of an inner porous layer of the reflective film during molding, and a method of producing the same.)

1. A biaxially oriented polyester reflective film comprising:

a light reflecting layer having a hole in an interior thereof; and

a support layer formed on at least one surface of the light reflection layer,

wherein the light reflecting layer comprises a polyester composition comprising a homopolyester, a copolymer polyester, a resin incompatible with the polyester, and inorganic particles,

the support layer comprises a polyester composition comprising a homopolyester, a copolymeric polyester, and inorganic particles, and

a plurality of light collecting structures depressed at the center thereof are arranged in a lattice shape and holes are formed in the depressed portions.

2. The biaxially oriented polyester reflective film of claim 1, wherein the polyester composition of the light reflective layer satisfies the following conditions (1) to (3):

(1) vo + Vi is more than or equal to 8 percent and less than or equal to 20 percent

(2)0.5≤Vo/Vi≤1.6

(3)0.6≤(Vo+Vi)/Vc≤3

Wherein Vo represents a volume% of the polyester-incompatible resin, Vi represents a volume% of the inorganic particles, and Vc represents a volume% of the copolymer polyester, when the weight of each component of the polyester composition based on 100% by weight of the total is divided by the specific gravity.

3. The biaxially oriented polyester reflective film of claim 1 wherein the biaxially oriented polyester reflective film has a storage elastic modulus E' at 200 ℃ of from 40MPa to 100 MPa.

4. The biaxially oriented polyester reflective film of claim 1, wherein the copolymer polyester is a polymer obtained by a polycondensation reaction of: 100 mole% of an aromatic dicarboxylic acid as an acid component, 60 to 90 mole% of ethylene glycol as a total glycol component, and 10 to 40 mole% of one or more glycol components selected from trimethylene glycol, tetramethylene glycol, 2 dimethyl (1, 3-propane) glycol, and 1, 4-cyclohexanedimethanol.

5. The biaxially oriented polyester reflective film of claim 1, wherein the polyester incompatible resin is at least one selected from the group consisting of: crystalline polyolefin resin, amorphous cycloolefin resin, thermosetting polystyrene resin, thermosetting polyacrylate resin, polyphenylene sulfide resin, and fluorine-based resin, or a homopolymer or a copolymer thereof.

6. The biaxially oriented polyester reflective film of claim 5, wherein the glass transition temperature of the resin incompatible with polyester is 160 ℃ or greater.

7. The biaxially oriented polyester reflective film of claim 1, wherein the inorganic particles comprise at least one inorganic particle selected from the group consisting of silica, alumina, barium sulfate, titanium dioxide, and calcium carbonate.

8. The biaxially oriented polyester reflective film of claim 1, wherein the average particle size of the inorganic particles of the light reflective layer is greater than 0.2 μ ι η and less than 1.2 μ ι η.

9. The biaxially oriented polyester reflective film of claim 1 wherein the average particle size of the inorganic particles of the support layer is greater than 0.1 μ ι η and less than 10.0 μ ι η.

10. The biaxially oriented polyester reflective film of claim 1 wherein the total thickness of the biaxially oriented polyester reflective film is from 150 μ ι η to 400 μ ι η.

11. The biaxially oriented polyester reflective film of claim 1, wherein the thickness of the support layer is greater than 1.0% and less than 10.0% of the thickness of the light reflecting layer.

12. The biaxially oriented polyester reflective film of claim 1, wherein the biaxially oriented polyester reflective film has a specific gravity of 0.7g/cm³To 1.2g/cm³。

13. The biaxially oriented polyester reflective film according to one of claims 1 to 12, wherein the physical property variation of the central portion of the depressed portion depressed at the center thereof in the biaxially oriented polyester reflective film before and after molding with a molding die satisfies the following conditions (4) to (7):

(4) optical Density before Molding (OD) >1.4

(5) OD reduction <0.15 before and after molding

(6) OD deviations after moulding were < 7%

(7) The reduction in thickness (d) before and after molding was < 30%.

14. The biaxially oriented polyester reflective film according to one of claims 1 to 12, wherein the biaxially oriented polyester reflective film satisfies the following formula 1 after molding using a molding die

(formula 1)

Wherein WA_mRepresenting the wall angle of said moulding tool, and WA_rRepresenting the wall angle of the reflective film after molding.

15. A method of producing a biaxially oriented polyester reflective film, the method comprising:

a first step of drying each of the polyester composition of the support layer a and the polyester composition of the light reflection layer B;

a second step of preparing an unstretched sheet by melt-extruding the composition of the first step;

a third step of preparing a uniaxially stretched reflective film by uniaxially stretching the unstretched sheet in the longitudinal direction;

a fourth step of preparing a biaxially stretched reflective film by re-stretching the uniaxially stretched reflective film in a transverse direction;

fifthly, performing heat treatment on the biaxial stretching reflective film;

sixthly, cooling and winding the heat-treated reflecting film;

a seventh step of molding the reflective film produced in the sixth step into a form in which a plurality of depressed light collecting structures are arranged in a lattice shape using a molding die; and

an eighth step of forming (punching) a hole for mounting an LED in the recessed light collecting structure of the reflective film produced in the seventh step.

16. The method according to claim 15, wherein the polyester composition of the light reflection layer satisfies the following conditions (1) to (3):

(1) vo + Vi is more than or equal to 8 percent and less than or equal to 20 percent

(2)0.5≤Vo/Vi≤1.6

(3)0.6≤(Vo+Vi)/Vc≤3

Wherein Vo represents the volume% of the resin incompatible with the polyester, Vi represents the volume% of the inorganic particles, and Vc represents the volume% of the copolymer polyester, when the weight of each component of the polyester composition based on 100% by weight of the total is divided by the specific gravity.

17. The method according to claim 15, wherein the change in physical properties of the central portion of the concave portion that is concave at the center thereof in the biaxially oriented polyester reflective film before and after molding using a molding die in the seventh step satisfies the following conditions (4) to (7):

(4) optical Density before Molding (OD) >1.4

(5) OD reduction <0.15 before and after molding

(6) OD deviations after moulding were < 7%

(7) The reduction in thickness (d) before and after molding was < 30%.

18. The method according to claim 15, wherein the biaxially oriented polyester reflective film after molding using a molding die in the seventh step satisfies the following formula 1

(formula 1)

Wherein WA_mRepresenting the wall angle of said moulding tool, and WA_rRepresenting the wall angle of the reflective film after molding.

Technical Field

The following description relates to a biaxially oriented polyester reflective film and a method for producing the same, and more particularly to such a biaxially oriented polyester reflective film: which has excellent moldability and can maintain excellent reflection characteristics even after vacuum compression molding and hot press molding by suppressing deformation of an inner porous layer of a reflective film during molding, and a method of producing the same.

Background

Liquid crystal displays, which have been widely used in all application fields such as mobile devices, tablet devices, monitors, notebook computers, and televisions, are not self-luminous devices, and thus a backlight unit providing light from the back side is required. In the past, a line light source using a cold cathode ray tube was generally used as a light source of a backlight unit, but recently, a point light source using a Light Emitting Diode (LED) was widely used.

It is necessary to convert a point/line light source of the backlight unit into a surface light source for the display. For this reason, in addition to the light source, the point light source is converted into a surface light source by various optical sheet configurations such as a light guide plate transmitting LED light emitted from one side to the front surface, a reflection film reflecting light lost to the rear side of the display back to the front surface, a diffusion film uniformly diffusing light irradiated to the front surface, and a prism film concentrating the diffused light into front light. A liquid crystal display using a surface light source converted by a backlight unit includes a polarizing film, a Thin Film Transistor (TFT), a liquid crystal, a color filter, a polarizing filter, etc. in a panel part to realize R/G/B colors in each pixel unit. In the case of a liquid crystal display, contrast of brightness and darkness of surface light is achieved by applying a voltage to a panel portion to block or transmit light by an arrangement of liquid crystals, but there is a problem in that contrast of color is significantly lower than that of an Organic Light Emitting Diode (OLED) which is a self-luminous element in which each pixel emits light by itself.

For this reason, the display industry is actively developing a method of improving the contrast of a liquid crystal display using a local dimming method in which point light sources are individually turned on/off using a plurality of LEDs. In the case of separately driving a plurality of LEDs, as one of methods for solving light interference between LED elements, a method of repeatedly forming recesses and holes on a reflective film and mounting LEDs therein is being studied.

However, when the reflective film is molded at a high temperature, the conventional reflective film may not be sufficiently molded into a desired shape, or the holes inside the reflective film are deformed during molding, so that the reflective characteristics are rapidly deteriorated. Therefore, a reflective film having excellent moldability and retaining the reflective characteristics after molding is required.

As a related art, japanese laid-open patent publication No. 2007-261260 discloses a reflective film containing a polyester resin as a main component, in which an attempt is made to improve the reflective performance of the film by improving the manufacturing method with an optimum combination of the weight ratio of inorganic particles and a resin incompatible with polyester. However, since the above-described related art improves only general reflection performance, it cannot overcome problems of insufficient moldability and deformation of holes during molding.

Disclosure of Invention

Technical problem

The present invention is conceived to solve the aforementioned problems and to satisfy conventional requirements. An object of the present invention is to provide a biaxially oriented polyester reflective film capable of improving moldability and maintaining excellent reflection characteristics after molding, and a method for producing the same.

The above and other objects and advantages of the present invention will become more apparent from the following disclosure of preferred exemplary embodiments.

Technical scheme

In one general aspect, there is provided a biaxially oriented polyester reflective film comprising: a light reflecting layer having a hole in an interior thereof; and a support layer formed on at least one surface of the light reflection layer, wherein the light reflection layer comprises a polyester composition comprising a homopolyester, a copolymer polyester, a resin incompatible with the polyester, and inorganic particles, the support layer comprises a polyester composition comprising a homopolyester, a copolymer polyester, and inorganic particles, and a plurality of light collecting structures depressed at the center thereof are arranged in a lattice shape and holes are formed in depressed portions.

The polyester composition of the light reflection layer may satisfy the following conditions (1) to (3):

(1) vo + Vi is more than or equal to 8 percent and less than or equal to 20 percent

(2)0.5≤Vo/Vi≤1.6

(3)0.6≤(Vo+Vi)/Vc≤3

Wherein Vo represents the volume% of the resin incompatible with the polyester, Vi represents the volume% of the inorganic particles, and Vc represents the volume% of the copolymer polyester, when the weight of each component of the polyester composition based on 100% by weight of the total is divided by the specific gravity.

The biaxially oriented polyester reflective film may have a storage elastic modulus E' at 200 ℃ of 40MPa to 100 MPa.

The copolymer polyester may be a polymer obtained by polycondensation of: 100 mole% of an aromatic dicarboxylic acid as an acid component, 60 to 90 mole% of ethylene glycol as a total glycol component, and 10 to 40 mole% of one or more glycol components selected from trimethylene glycol, tetramethylene glycol, 2 dimethyl (1, 3-propane) glycol, and 1, 4-cyclohexanedimethanol.

The resin incompatible with the polyester may be at least one selected from the group consisting of: crystalline polyolefin resin, amorphous cycloolefin resin, thermosetting polystyrene resin, thermosetting polyacrylate resin, polyphenylene sulfide resin, and fluorine-based resin, or a homopolymer or a copolymer thereof.

The glass transition temperature of the resin incompatible with the polyester may be 160 ℃ or higher.

The inorganic particles may include at least one inorganic particle selected from the group consisting of silica, alumina, barium sulfate, titanium dioxide, and calcium carbonate.

The inorganic particles of the light reflecting layer may have an average particle diameter of more than 0.2 μm and less than 1.2 μm.

The inorganic particles of the support layer may have an average particle diameter of more than 0.1 μm and less than 10.0 μm.

The total thickness of the biaxially oriented polyester reflective film is 150 to 400 μm.

The thickness of the support layer may be greater than 1.0% and less than 10.0% of the thickness of the light reflection layer.

The specific gravity of the biaxially oriented polyester reflective film may be 0.7g/cm³To 1.2g/cm³。

The change in physical properties of the central portion of the concave portion depressed at the center thereof in the biaxially oriented polyester reflective film before and after molding using the molding die may satisfy the following conditions (4) to (7):

(4) optical Density before Molding (OD) >1.4

(5) Reduction of OD before and after molding <0.15

(6) Deviation of OD after moulding < 7%

(7) Reduction in thickness (d) before and after molding < 30%.

After molding using a molding die, the biaxially oriented polyester reflective film satisfies the following formula 1:

(formula 1)

Wherein WA_mIndicating the wall angle of the moulding tool, and WA_rIndicating the wall angle of the reflective film after molding.

In another general aspect, there is provided a method of producing a biaxially oriented polyester reflective film, the method comprising: a first step of drying each of the polyester composition of the support layer a and the polyester composition of the light reflection layer B; a second step of preparing an unstretched sheet by melt-extruding the composition of the first step; a third step of preparing a uniaxially stretched reflective film by uniaxially stretching an unstretched sheet in a longitudinal direction; a fourth step of preparing a biaxially stretched reflective film by re-stretching the uniaxially stretched reflective film in the transverse direction; fifthly, performing heat treatment on the biaxial stretching reflective film; sixthly, cooling and winding the heat-treated reflecting film; a seventh step of molding the reflective film produced in the sixth step into a form in which a plurality of depressed light collecting structures are arranged in a lattice shape using a molding die; and an eighth step of forming (punching) a hole for mounting the LED in the recessed light collecting structure of the reflective film produced in the seventh step.

Advantageous effects

According to the present invention, excellent moldability, light reflection characteristics, film forming stability, and low molding deviation are achieved before and after molding.

In addition, the present invention can be effectively applied to a reflective film for a local dimming liquid crystal display.

However, the effects of the present invention are not limited to the above-described effects, and other effects not mentioned above will be apparent to those skilled in the art from the foregoing description.

Drawings

FIG. 1 is a cross-sectional view of a biaxially oriented polyester reflective film according to one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a biaxially oriented polyester reflective film according to one embodiment of the present invention.

FIG. 3 is a plan view of a biaxially oriented polyester reflective film according to one embodiment of the present invention.

Fig. 4 is a view for describing a molding process of a biaxially oriented polyester reflective film according to an embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so as to be easily practiced by those of ordinary skill in the art. It should be understood that the present invention should not be construed as limited to the embodiments set forth herein, but may be embodied in many different forms.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. In addition, although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

As used herein, the terms "comprises," "comprising," "includes," "including," "contains," "characterized by," "has/having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, "or" refers to an inclusive "or" rather than an exclusive "or" unless specifically indicated to the contrary.

In describing and/or claiming the present invention, the term "copolymer" is used to refer to a polymer formed from the copolymerization of two or more monomers. Such copolymers include copolymers, terpolymers or higher order copolymers.

Fig. 1 is a sectional view of a biaxially oriented polyester reflective film according to an embodiment of the present invention, fig. 2 is an enlarged sectional view of a biaxially oriented polyester reflective film according to an embodiment of the present invention, fig. 3 is a plan view of a biaxially oriented polyester reflective film according to an embodiment of the present invention, and fig. 4 is a view for describing a molding process of a biaxially oriented polyester reflective film according to an embodiment of the present invention.

Referring to fig. 1 to 3, a biaxially oriented polyester reflective film 10 according to one aspect of the present invention has a multi-layer structure including a light reflection layer B having holes 24 therein and a support layer a formed on at least one surface of the light reflection layer B, and the biaxially oriented polyester reflective film 10 has a structure and a raw material composition which will be described below.

As shown in fig. 1 to 3, a biaxially oriented polyester reflective film 10 according to an embodiment of the present invention has a structure in which: a plurality of concave light collecting structures having a concave portion 12 at the center thereof are arranged in a lattice shape, and a hole 13 is formed on the concave portion 12. The convex portions 11 and the concave portions 12 are repeatedly formed on the reflective film according to the lattice shape of the concave light collecting structure. By reflecting light via the recessed light collecting structure such that the light is not scattered in all directions but concentrated in the center, the influence of the reflected light of the bright area on the dark area can be minimized during local dimming, thereby enabling local dimming of the individual Light Emitting Diodes (LEDs).

In fig. 3, the square-shaped depressed light collecting structures are arranged in a lattice shape, but this is only an example, and the lattice shape is not limited to a square, so that various lattice shapes such as a circular shape, an elliptical shape, and a regular hexagonal shape may be possible.

The biaxially oriented polyester reflective film 10 according to one embodiment of the present invention may be produced as an a/B double layer structure of a support layer a/a light reflection layer B, in which the support layer a is formed on only one surface of the light reflection layer B. Further, the biaxially oriented polyester reflective film 10 according to an embodiment of the present invention may be produced as an a/B/a three-layer structure of a support layer a/a light reflection layer (B)/a support layer, wherein the support layer a is formed on both surfaces of the light reflection layer B. For example, an a/B/a three-layer structure is preferable in view of film forming stability, defect control, and processing stability. In the case of the a/B bilayer structure, the support layer a serving as a support layer is formed only on one surface of the film when forming the film, and thus a processing defect such as film tearing may occur due to the lack of the support layer during film processing, which may result in a reduction in productivity. Further, the light reflection layer B in which the holes 24 are formed forms a surface layer on the other surface, so that the holes 24 may cause a crater-like appearance on the surface layer, and defects such as cracks or dents may be caused on the surface of the reflection film due to the holes 24 during secondary processing such as bead coating, or when the reflection film is inserted into the backlight unit, there is a high possibility that cracks or dents occur on the surface of the reflection film at the contact surface with the light guide plate. Therefore, more preferably, the multilayer structure of the biaxially oriented polyester reflective film 10 according to an embodiment of the present invention has an a/B/a triple layer structure of a support layer a/a light reflection layer B/a support layer a. For example, fig. 2 shows a biaxially oriented polyester reflective film 10 formed as an a/B/a three-layer structure of support layer (a)/light reflection layer (B)/support layer (a).

In one embodiment, the light reflection layer B may include a polyester composition including homopolyester as a main component and including a copolymer polyester, a resin 23 incompatible with the polyester, and inorganic particles 22.

Further, the support layer a may comprise a polyester composition comprising a homopolyester as a main component and comprising a copolymer polyester and inorganic particles.

The homopolyester is a polymer obtained by a polycondensation reaction of a dicarboxylic acid component and a diol component. As the dicarboxylic acid component, it is preferable to use one selected from the following alone: dimethyl terephthalate, terephthalic acid, isophthalic acid, 2, 6-naphthalenedicarboxylic acid, sebacic acid, adipic acid, diphenyldicarboxylic acid, 5-t-butylisophthalic acid, 2,6, 6-tetramethyldiphenyl-4, 4-dicarboxylic acid, 1, 3-trimethyl-3-phenylphosphate-4, 5-dicarboxylic acid, sodium 5-sulfoisophthalate, trimellitic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, palmitic acid, azelaic acid, pyromellitic acid, 1, 4-cyclohexanedicarboxylic acid, 1, 3-cyclohexanedicarboxylic acid, and the like, and dimethyl terephthalate, terephthalic acid, and a selected one are more preferably used. As the diol component, one selected from ethylene glycol, trimethylene glycol, tetramethylene glycol, 2-dimethyl (1, 3-propane) diol, 1, 4-cyclohexanedimethanol, and the like is preferably used alone, and ethylene glycol is more preferably used.

Further, the copolymer polyester is a polymer obtained by polycondensation of two or more dicarboxylic acid components or diol components in the homopolyester component. As the dicarboxylic acid component, besides terephthalic acid, preferably with terephthalic acid, 2, 6-naphthalene two formic acid combined use, as the glycol component, besides ethylene glycol, preferably with three methylene glycol, four methylene glycol, 2 two methyl (1, 3-propane) glycol, 1, 4-cyclohexane dimethanol and combination of copolymer polyester.

In one embodiment, the copolymer polyester according to the invention is preferably a polymer obtained by polycondensation of: 100 mole% of an aromatic dicarboxylic acid as an acid component, 60 to 90 mole% of ethylene glycol as a total glycol component, and 10 to 40 mole% of one or more glycol components selected from trimethylene glycol, tetramethylene glycol, 2 dimethyl (1, 3-propane) glycol, and 1, 4-cyclohexanedimethanol.

The polyester-incompatible resin 23 is preferably at least one selected from the group consisting of: a crystalline polyolefin resin, an amorphous cycloolefin resin, a thermosetting polystyrene resin, a thermosetting polyacrylate resin, a polyphenylene sulfide resin and a fluorine-based resin, or a homopolymer or a copolymer thereof, and more preferably an amorphous cyclic polyolefin resin.

Further, the glass transition temperature Tg of the resin incompatible with polyester is preferably 160 ℃ or more. When the glass transition temperature Tg of the polyester-incompatible resin is lower than 160 ℃, the polyester-incompatible resin particles formed in the pores in the light reflection layer are easily deformed during a high-temperature molding process, which may cause a problem of deterioration in light reflection performance.

The inorganic particles 22 preferably include at least one inorganic particle selected from the group consisting of: silica, alumina, barium sulfate, titanium dioxide, and calcium carbonate, and more preferably calcium carbonate particles.

Further, among the inorganic particles, the average particle diameter of the inorganic particles 22 used in the light reflection layer B is preferably more than 0.2 μm and less than 1.2 μm. This is because, if the diameter of the inorganic particles used for the light reflection layer B is 1.2 μm or more, the density of the aperture layer formed by the inorganic particles is significantly reduced, so that the reflection characteristics are significantly deteriorated. If the diameter is 0.2 μm or less, dispersion in the light reflection layer is difficult and particle aggregation is easily caused. Further, when the produced polyester reflective film is subjected to press molding or vacuum compression molding at high temperature, the deformation of the holes 24 in the polyester reflective film is caused by high-temperature heat and pressure. In this case, when the size of the inorganic particles is 0.2 μm or less, the particles cannot act as a support for minimizing the variation of the pores 24 in the film, so that a problem occurs in that the specific gravity of the reflective film rises after molding and the reflective characteristics are significantly deteriorated.

Further, among the inorganic particles, the average particle diameter of the inorganic particles used for the support layer a is preferably more than 0.1 μm and less than 10.0 μm, and more preferably more than 1.0 μm and less than 5.0 μm. This is because, if the size of the inorganic particles used for the support layer a is 0.1 μm or less, the running characteristics of the film during film formation are significantly insufficient, so that a large number of scratches are generated on the surface of the film. If the size of the particles is 10.0 μm or more, processing defects such as film tearing during a stretching process may be caused by the large-sized particles during film formation.

In one embodiment, the polyester composition of the light reflection layer B contains homopolyester as a main component, and contains a copolymer polyester, a resin incompatible with polyester, and inorganic particles, wherein when the weight of each component of the copolymer polyester, the resin incompatible with polyester, and the inorganic particles is divided by a specific gravity based on 100% by weight of the polyester composition forming the light reflection layer, the following conditions (1) to (3) are preferably satisfied to achieve moldability at high temperature and excellent reflection characteristics after molding.

(1) Vo + Vi is more than or equal to 8 percent and less than or equal to 20 percent

(2)0.5≤Vo/Vi≤1.6

(3)0.6≤(Vo+Vi)/Vc≤3

Here, Vo represents the volume% of the resin incompatible with the polyester, Vi represents the volume% of the inorganic particles, and Vc represents the volume% of the copolymer polyester.

Based on a large number of experiments, the inventors of the present invention confirmed that when the contents of a homopolyester resin, a copolymer polyester resin, a resin incompatible with polyester, and inorganic particles in a polyester composition constituting a light reflection layer B of a biaxially oriented polyester reflection film satisfy the above conditions, excellent reflection characteristics before and after press molding and vacuum compression molding and excellent molding processability are achieved at high temperatures.

That is, as can be confirmed in the following examples and comparative examples, when the value of the condition (1) is less than 8 vol%, the void density in the light reflective layer is reduced, and thus it is difficult to achieve sufficient light reflection efficiency, and when the value exceeds 20 vol%, many pores (voids) are formed in the film, and thus the stretchability is significantly reduced, which is likely to cause processing defects such as film tearing during film formation.

Further, when the value of the condition (2) is less than 0.5, the storage elastic modulus of the reflective film at 200 ℃ increases, so that the film may be torn or difficult to be sufficiently molded during the molding process, and when the value exceeds 1.6, the storage elastic modulus of the reflective film at 200 ℃ decreases, so that the moldability during the molding process increases, but the film thickness and the optical density may be drastically reduced due to deformation. The deterioration of the optical characteristics after molding is caused by the deformation of the holes 24 in the polyester reflective film due to high-temperature heat and pressure when the press molding or the vacuum compression molding is performed at high temperature. In this case, the inorganic particles serve as a support that minimizes the variation of pores in the membrane.

Further, when the value of the condition (3) is less than 0.6, the relative content of the copolymer polyester resin increases, thus improving the stretchability during the film forming process, whereas the storage elastic modulus E' of the reflective film at 200 ℃ decreases, which may result in a drastic decrease in the film thickness and optical density due to deformation during molding processing. When the value of the condition (3) exceeds 3, the relative content of the copolymer polyester resin is decreased, and thus the storage elastic modulus E' of the reflective film at 200 ℃ is increased, and the film may be torn during the molding process or sufficient molding may not be performed.

In one embodiment, the polyester composition of the support layer a may comprise homopolyester as a main component, and comprises a copolymer polyester and inorganic particles, wherein the content of the copolymer polyester is preferably 30.0 wt% and the content of the inorganic particles is more than 0.01 wt% and less than 20 wt% based on 100 wt% of the total composition.

When the content of the copolymer polyester in the polyester composition of the support layer a is 30% by weight or more, the heat resistance of the support layer is deteriorated, and thus there arises a problem that various surface defects such as peeling, dents, scratches, etc. are generated on the film surface due to adhesion to a mold during press processing or vacuum compression molding.

Further, when the content of the inorganic particles in the polyester composition of the support layer a is 0.01 wt% or less, there is a problem in that a large number of scratches are caused on the film surface due to insufficient running characteristics during the film forming process, and when the content of the inorganic particles is 20 wt% or more, problems such as film tearing may easily occur during the stretching process of the film forming process.

In one embodiment, the storage elastic modulus E' of the reflective film at 200 ℃ is preferably 40MPa to 100 MPa. The biaxially oriented polyester reflective film produced in the present invention deforms due to high temperature heat and pressure when subjected to press molding or vacuum compression molding at a high temperature of 190 ℃ or higher during the molding process. When the storage elastic modulus E' of the reflective film at 200 ℃ is less than 40MPa, the molding workability is excellent, but the holes 24 in the polyester reflective film are easily deformed, and thus the reflective property is deteriorated. When the storage elastic modulus E' of the reflective film exceeds 100MPa, variation of pores in the film during molding process is minimized, but molding processability is deteriorated.

In one embodiment, the total thickness of the biaxially oriented polyester reflective film is preferably from 150 μm to 400 μm. This is because, if the total thickness of the reflective film is less than 150 μm, there is a problem in that molding workability is significantly reduced or the film is torn during the molding process due to too thin thickness. If the total thickness of the reflective film exceeds 400 μm, it is difficult to stably produce, for example, cracks occur during a process of forming the polyester reflective film, manufacturing costs increase due to thick thickness, and the total thickness of the manufactured liquid crystal display increases, which makes it challenging to realize a thin design.

In one embodiment, the thickness of the support layer a is preferably greater than 1.0% and less than 10.0% of the thickness of the light reflection layer B. That is, the thickness ratio between the support layer a and the light reflection layer B (thickness of the support layer a/thickness of the light reflection layer B) × 100% is preferably greater than 1.0% and less than 10.0%. This is because, if the thickness ratio of the support layer a with respect to the thickness of the light reflection layer B is 1.0% or less, since the support layer a cannot function as a sufficient support during the film forming process, processing defects such as film tearing or the like are likely to occur during the film stretching process. If the thickness ratio is 10.0% or more, since the support layer a in which the holes 24 are not formed is too thick, sufficient moldability cannot be obtained during the reflective film molding process at high temperature.

In one embodiment, the specific gravity of the biaxially oriented polyester reflective film is preferably 0.7g/cm³To 1.2g/cm³. This is because, if the specific gravity of the reflective film is less than 0.7g/cm³It is difficult to stably produce, for example, cracks occur during the process of forming the polyester reflective film, and dimensional stability is significantly reduced due to heat treatment during the molding process. If the specific gravity of the reflective film exceeds 1.2g/cm³The manufacturing cost increases and the reflection characteristics are significantly deteriorated since the holes are not sufficiently formed in the light reflection layer of the polyester reflection film.

A method of producing a biaxially oriented polyester reflective film according to another aspect of the present invention will then be described. Redundant description of the above-described biaxially oriented polyester reflective film according to an aspect of the present invention will be omitted.

A method of producing a biaxially oriented polyester reflective film according to another aspect of the present invention comprises: a first step of drying each of the polyester composition of the support layer a and the polyester composition of the light reflection layer B; a second step of preparing an unstretched sheet by melt-extruding the composition of the first step; a third step of preparing a uniaxially stretched reflective film by uniaxially stretching the unstretched sheet in the longitudinal direction; a fourth step of preparing a biaxially stretched reflective film by re-stretching the uniaxially stretched reflective film in a transverse direction; fifthly, performing heat treatment on the biaxial stretching reflective film; sixthly, cooling and winding the heat-treated reflecting film; a seventh step of molding the reflective film produced in the sixth step into a form in which a plurality of depressed light collecting structures are arranged in a lattice shape using a molding die; and an eighth step of forming (punching) a hole for mounting the LED in the recessed light collecting structure of the reflective film produced in the seventh step.

In the first step, the polyester composition of the support layer a and the polyester composition of the light reflection layer B are each dried at a temperature of 100 ℃ to 200 ℃ in each dryer, wherein moisture present in the resin is removed by drying the compositions under high vacuum for 3 to 10 hours. The reason why the moisture is removed by the drying process is to overcome the following problems that may occur: if the polyester resin is hydrolyzed by residual moisture in the resin during the melt extrusion process, sheet molding proceeds poorly in the T-die extrusion process or bubbles are generated in the discharged polymer due to rapid decrease in melt viscosity of the polyester, and thus the film cannot be formed.

The second step obtains an unstretched sheet by melt-extruding the composition of the first step, wherein the dried polyester composition of the support layer a and the dried polyester composition of the light reflection layer B are melt-extruded at 250 to 300 ℃ using a co-extrusion apparatus having an extruder a 'and an extruder B', and then introduced into a T-die multi-nozzle. In the T-die multi-nozzle, an a/B/a layered structure in which the support layer a is positioned on each surface of the light reflection layer B is formed, and the molten resin is cooled and solidified using a T-die and a casting drum to obtain an unstretched sheet.

The third step is to produce a uniaxially stretched film by uniaxially stretching the obtained unstretched sheet in the longitudinal direction, wherein the unstretched sheet is heated to a temperature equal to or higher than the glass transition temperature of the polyester resin by heating means such as roller heating and heating by an infrared heater, and then stretched preferably by three to five times by a difference in peripheral speed of two or more rollers.

A fourth step of producing a biaxially stretched film by redrawing the film uniaxially stretched in the longitudinal direction in the transverse direction, wherein an oven apparatus called a tenter that stretches the film in the width direction using a running nip (travel nip) is used to preheat the film stretched in the longitudinal direction in the third step in an oven having formed therein a plurality of heating zones and a plurality of stretching zones to a temperature within 50 ℃ of the glass transition temperature of the polyester resin, and then stretches the film in the transverse direction three to five times in the same temperature range.

The fifth step is to perform a heat treatment to ensure dimensional stability and orientation relaxation (orientation relaxation) of the film stretched in the tenter device, wherein the heat treatment is performed in a plurality of heat treatment zones formed in the same tenter device at a temperature of less than or equal to the melting point of the polyester plus 30 ℃. In this case, in order to secure high dimensional stability and molding characteristics during heat treatment, orientation relaxation and uniform orientation in the transverse direction of the biaxially stretched film are required, which can be performed by the following method.

When a film biaxially stretched in the longitudinal direction and the transverse direction is subjected to heat treatment in a tenter, relaxation of transverse orientation chains occurs, in which the central portion in the width direction is sufficiently relaxed in the transverse direction, while the portions adjacent to the clips may not be sufficiently relaxed in the transverse direction due to the clips, so that a bending phenomenon occurs in which bow-shaped over-orientation occurs in the tenter. In order to overcome such a phenomenon, it is preferable to maintain the temperature difference between the transverse stretching end region where the bending phenomenon seriously occurs in the fourth step and the heat treatment initiation region of the fifth step within 30 ℃.

Further, for orientation relaxation, it is preferable to provide a plurality of heat treatment regions and perform heat treatment by gradually increasing the temperature from the start region to the end region, the temperature difference between the heat treatment start region and the heat treatment end region is preferably 30 ℃ to 100 ℃, and the temperature of the heat treatment end region is preferably greater than or equal to the melting point of the polyester. Also, when the stretching is additionally 0.05 times to 0.5 times in the transverse direction in the heat-treated region, the bending phenomenon is alleviated, so that uniform orientation in the width direction can be achieved.

The sixth step is to stably cool and wind the biaxially stretched film by using a plurality of heat treatment zones in the above tenter device, and a biaxially oriented polyester reflective film can be obtained by this step of winding the cooled film.

The seventh step molds the reflective film prepared in the sixth step into a form in which the plurality of light collecting structures having the depressions 12 are arranged in a lattice shape using a molding die 200 in which the plurality of light collecting structures each having the depression part 12 at the center thereof are arranged. By the light collecting structure, the light reflected by the reflective film is not scattered in all directions but reflected in a center concentrated form, thereby achieving local dimming of the individual LEDs. In this case, the prepared biaxially oriented polyester reflective film preferably satisfies the conditions for the inner angle (wall angle) of the reflective film and the inner angle (wall angle) of the molding die shown in fig. 4. The condition of the internal angle will be described in detail with reference to formula 1 which will be described below.

The eighth step is to form (stamp) a hole 13 for mounting an LED in the recessed light collecting structure of the reflective film prepared in the seventh step, and the shape of the hole 13 may be various shapes such as a circle, an ellipse, a rectangle, etc., and is preferably a circle, according to the shape of the LED.

The biaxially oriented polyester reflective film according to one embodiment prepared by the above method preferably has the technical features shown below.

First, in the biaxially oriented polyester reflective film according to one embodiment, the change in physical properties of the central portion of the concave portion 12 recessed at the center thereof (before the hole processing) before and after the molding using the molding die preferably satisfies the following conditions (4) to (7).

(4) Optical Density before Molding (OD) >1.4

(5) Reduction of OD before and after molding <0.15

(6) Deviation of OD after moulding < 7%

(7) Reduction in thickness (d) before and after molding < 30%

That is, the OD of the biaxially oriented polyester reflective film before molding preferably satisfies the condition of more than 1.4. When the OD is 1.4 or less, the transmittance increases so that sufficient reflection performance cannot be achieved, thereby reducing the luminance (brightness) of the manufactured liquid crystal display. Further, when comparing the OD before and after the molding process of the seventh step in the process of producing the reflective film, it is preferable that the reduction of the OD before and after the molding of the reflective film satisfies less than 0.15. This is because the molded reflective film cannot provide sufficient reflective performance even when the reduction in OD before and after molding is 0.15 or more, and thus has the same disadvantage of a decrease in brightness (brightness) of the manufactured liquid crystal display. Further, if the deviation of the OD after molding measured at the central portion of each recessed portion before hole-processing the recessed portion recessed at the center thereof is 7% or more, it can be seen that molding is not uniformly performed over the entire surface of the reflective film, and there is a problem that the manufactured liquid crystal display device exhibits luminance unevenness (brightness difference). Further, when the reduction of the thickness d before and after molding is 30% or more, the shape of the hole in the light reflection layer is deformed, so that the molded reflection film cannot provide sufficient reflection performance and the rigidity of the film deteriorates.

Then, the biaxially oriented polyester reflective film according to one embodiment preferably satisfies the following formula 1. Equation 1 is a measure for evaluating moldability of the reflective film.

(formula 1)

Here, WA_mIndicating the wall angle of the moulding tool, and WA_rIndicating the wall angle of the reflective film after molding. Namely, WA_rRepresents an internal angle between the broken lines connecting the convex portion 11 as the highest point of the reflective film 10 after molding and the contact point 32 where the reflective film 10 contacts the molding die 200, and the concave portion 12, WA of the reflective film 10_mShowing the interior corners of the molding die 200.

In the biaxially oriented polyester reflective film according to an embodiment, the relationship according to formula 1 between the inner angle of the molding die 200 and the inner angle of the reflective film 10 preferably satisfies 5% or less. This is because, if the value of equation 1 exceeds 5%, there is a limitation in reducing the size of the light collecting structure of the plurality of depressions in the molded reflective film, and thus there is a limitation in mounting the plurality of LEDs to improve the efficiency of local dimming.

Hereinafter, the structure of the present invention and the effects obtained thereby will be described in detail with reference to examples and comparative examples. However, examples are provided to describe the present invention in more detail, and the scope of the present invention is not limited to the examples.

[ examples ]

[ example 1]

Support layers a were formed on both sides of the light reflection layer B to form a reflection film in which layers were laminated in the order of support layer a/light reflection layer B/support layer a, and the thickness ratio of the support layer a with respect to the light reflection layer B was 5% based on the total thickness of 250 μm. The starting material is designed such that the support layer a has a composition such that: 89.9% by weight of polyethylene terephthalate (Toray Advanced Materials Korea inc., a9093) as a homopolyester, 10% by weight of a copolymer polyester (Eastman Chemical Company, GN071), and 0.1% by weight of silica having an average particle diameter of 2.0 μm as inorganic particles, and such that the support layer B has such a composition: 63% by weight of polyethylene terephthalate as a homopolyester (Toray Advanced Materials Korea Inc., A9093), 15% by weight of a copolymer polyester (Eastman Chemical Company, GN071), 8% by weight of a copolymer resin of ethylene and norbornene as a resin incompatible with the polyester, which is an amorphous cycloolefin copolymer (polyplasics Co., Ltd., Topas6017, Tg 170 ℃ C.), and 14% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm as inorganic particles, followed by co-extrusion of the support layer A of the extruder A 'and the light reflection layer B of the extruder B' at 280 ℃ into an A/B/A layer, and cooling and curing using a T die and a casting drum to obtain an unstretched sheet.

Thereafter, a reflective film was produced by subjecting the unstretched sheet to biaxial stretching 3.2 times in the longitudinal direction and 3.6 times in the transverse direction by the above-described production method. Then, the biaxially oriented polyester reflective film was prepared in the form shown in FIG. 1 using a prepared molding die having a width of 200mm and a length of 300 mm. At this time, after a pretreatment at a film heating temperature of 200 ℃ for a heating time of 10 seconds using a small-sized vacuum compression molding machine (FKS-0632-20) of Asano Laboratories co.ltd., a biaxially oriented polyester reflective film, which is a molded article in the same shape as a molding die, was prepared by vacuum compression molding.

[ examples 2 to 6]

A biaxially oriented polyester reflective film was produced in the same manner as in example 1 except that the content of the constituent material in the light reflective layer B was changed as shown in table 1 below, and was taken as each of example 2 to example 6, respectively.

[ comparative example ]

Comparative examples 1 to 6

A biaxially oriented polyester reflective film was produced in the same manner as in example 1 except that the content of the constituent material in the light reflective layer B was changed as shown in table 1 below, and was taken as each of comparative examples 1 to 6, respectively.

Comparative example 7

A biaxially oriented polyester reflective film was produced in the same manner as in example 1 except that the polyester incompatible resin in the light reflective layer B in example 1 was changed to an amorphous cycloolefin copolymer having a Tg of 150 ℃ (polyplases co., ltd., Topas6015, Tg 150 ℃).

Comparative example 8

A biaxially oriented polyester reflective film was produced in the same manner as in example 1, except that the thickness ratio of the support layer a to the light reflective layer B was changed to 0.7%.

Comparative example 9

A biaxially oriented polyester reflective film was produced in the same manner as in example 1, except that the thickness ratio of the support layer a to the light reflective layer B was changed to 13%.

Constituent materials and contents thereof of the biaxially oriented polyester reflective films according to the above-described examples 1 to 6 and comparative examples 1 to 9 are shown in table 1 below.

TABLE 1

Physical properties were measured by the following experimental examples using the biaxially oriented polyester reflective films according to the above examples 1 to 6 and comparative examples 1 to 9, and the measurement results are shown in the following table 2.

[ Experimental example ]

1. Thickness measurement

The thickness of the prepared biaxially oriented polyester reflective film was measured according to JIS C2151-2006 (which is a test method for plastic films for electrical use) of the japanese standards institute. The biaxially oriented polyester reflective film according to the present invention was cut in the thickness direction using a microtome to obtain a cross-sectional sample. Then, the thicknesses of the support layer a and the light reflection layer B were measured by a cross-sectional photograph of a cross-sectional sample produced by Hitachi, ltd. using a transmission electron microscope S800 at a magnification of 250 times.

Further, after the prepared biaxially oriented polyester reflective film was subjected to molding processing by a molding die 200, a cross-sectional sample was obtained, and the thickness of the central portion of each of the plurality of depressed light collecting structures arranged in a lattice shape was measured in the same manner as described above.

2. Measurement of storage elastic modulus E

In order to measure the storage elastic modulus E' of the prepared biaxially oriented polyester reflective film, the biaxially oriented polyester reflective film according to the present invention was cut into a size of 16mm in width and 5mm in length to obtain a cross-sectional sample. Subsequently, the storage elastic modulus E' of the reflective film was measured using a dynamic viscoelasticity measuring apparatus (DMA, TI Instruments, Q800) under conditions of a temperature range of 30 ℃ to 220 ℃, a temperature rise rate of 3 ℃/minute, a strain of 1.0%, and a static force of 0.05N.

3. Optical Density (OD) measurement

The OD of the prepared biaxially oriented polyester reflective film was measured using a densitometer (Gretag D200-II) manufactured by Gertag Macbeth. Each of the central portions of the plurality of recessed light collecting structures arranged in the lattice shape is measured before molding using the molding die and after the molding process by the molding die 200.

4. Measurement of specific gravity

The prepared biaxially oriented polyester reflective film was cut into a size of 10cm × 10cm, and then the weight of the sample was accurately weighed by an electronic balance (AC 100 produced by Mettle) with an accuracy of 0.1 mg. Thereafter, the thickness of the sample was measured at 10 points by a static pressure thickness meter to obtain an average value, and the specific gravity was calculated by the following equation.

Specific gravity (g) of film/thickness (um) of film 100

5. Interior angle measurement

The shape and size of the prepared biaxially oriented polyester reflective film were measured using a three-dimensional surface shape measuring instrument (VR-3200) manufactured by Keyence.

6. Testing of stability of film formation

The stability of film formation was evaluated according to the following criteria.

O: the film formation is stably carried out for 6 hours or more without breaking the film

X: rupture of the film occurred within 6 hours

TABLE 2

As can be seen from table 2, it was confirmed that the biaxially oriented polyester reflective films according to examples 1 to 6 of the present invention had excellent moldability, light reflection characteristics, film forming stability and low molding deviation.

In contrast, comparative example 1 has a value of 2.21 under condition (2), and thus condition (2) is not satisfied where the value of volume% with respect to the components of the light reflection layer composition should be 1.6 or less. That is, the volume% of the inorganic particles contained is small as compared with the volume% of the resin incompatible with polyester, and therefore the storage elastic modulus E' of the reflective film at 200 ℃ is lowered, which may cause the film to be easily deformed during molding at high temperature. Therefore, the film may be torn during the molding process, or its thickness is significantly reduced and the OD is reduced after molding, so that sufficient reflection performance cannot be achieved, thereby reducing the brightness of the produced display. Further, since uniform molding is not achieved in the molding process, there is a problem in that OD deviation after molding increases.

Further, comparative example 2 has a value of 0.43 under the condition (2), and thus the condition (2) in which the value of volume% with respect to the components of the light reflection layer composition should be 0.5 or more is not satisfied. That is, the volume% of the inorganic particles contained is large compared to the resin incompatible with polyester, and thus the storage elastic modulus E' of the reflective film at 200 ℃ is increased, and thus the film is difficult to be deformed during hot-temperature molding (hot-temperature molding) of the depressed reflective structure in a lattice shape with a molding die. In addition, the value calculated by equation 1 is 22%, and the condition that the value is required to be 5% or less is not satisfied, so moldability is significantly reduced, making it difficult to form a desired molded article, thereby having a limitation in mounting a plurality of LEDs to improve local dimming efficiency.

Further, comparative example 3 has a value of 21 vol% under the condition (1), and thus the condition (1) in which the value of vol% with respect to the components in the light reflection layer composition should be 20 vol% or less is not satisfied. That is, the resin and the inorganic particles incompatible with the polyester are contained at a large volume%, and therefore the pore density of the light reflective layer increases during film formation, which results in a drastic decrease in stretchability, and a high possibility of processing defects such as tearing of the light reflective film. Further, due to low specific gravity, a thickness reduction may occur during molding, and thus a problem of OD reduction after molding is likely to occur.

Comparative example 4 has a value of 7.6 vol% under condition (1), and thus condition (1) in which the value of vol% with respect to the components of the light reflection layer composition should be 8 vol% or more is not satisfied. That is, the resin and the inorganic particles incompatible with the polyester are contained at a small volume%, and thus pores are not sufficiently formed during the film forming process of the reflective film, so that the specific gravity increases and the storage elastic modulus E' at 200 ℃, and thus the film is difficult to be deformed during the hot-temperature molding into the lattice-shaped depressed reflective structure with the molding die, and the moldability calculated by equation 1 is significantly reduced, which makes it difficult to form a desired molded article.

Further, comparative example 5 has a value of 3.53 under condition (3), and thus condition (3) in which the value of volume% with respect to the components of the light reflection layer composition should be 3 or less is not satisfied. That is, the volume% of the copolymer polyester resin is lower than the volume% of the resin and inorganic particles incompatible with the polyester, and therefore crystallization is not sufficiently suppressed during film formation of the reflective film, which results in a rapid decrease in stretchability during stretching and a high possibility of processing defects such as tearing of the light reflective film. In addition, since the storage elastic modulus E' is increased, the film is difficult to be deformed during the hot-warm molding into the lattice-shaped depressed reflective structure with the molding die. Further, the value calculated from formula 1 is 17%, which does not satisfy the condition that the value is required to be 5% or less, and therefore moldability is significantly reduced, which makes it difficult to form a desired molded article.

Further, comparative example 6 has a value of 0.48 under condition (3), and thus condition (3) in which the value of volume% with respect to the components of the light reflection layer composition should be 0.6 or more is not satisfied. That is, the volume% of the copolymer polyester resin is higher than the volume% of the resin and inorganic particles incompatible with the polyester, and thus crystallization is sufficiently suppressed, but the storage elastic modulus E' of the reflective film at 200 ℃ is lowered, so that the film is easily deformed during molding at high temperature. Therefore, the film may be torn during the molding process, or its thickness is significantly reduced and the OD is reduced after molding, so that sufficient reflection performance cannot be achieved, thereby reducing the brightness of the produced display. Further, since uniform molding cannot be achieved in the molding process, there is a problem in that OD deviation after molding increases.

Comparative example 7 an amorphous cycloolefin copolymer having a glass transition temperature (Tg) of 150 ℃ of a resin incompatible with polyester was used in the light reflection layer composition, which did not satisfy the condition of Tg of 160 ℃ or more. The resin incompatible with the polyester particles formed in the holes of the light reflection layer is easily deformed during molding processing at high temperature, so that the thickness is significantly reduced and the OD is reduced after molding, and thus sufficient reflection performance cannot be achieved, thereby reducing the luminance of the produced display. Further, since uniform molding cannot be achieved in the molding process, there is a problem in that OD deviation after molding increases.

In comparative example 8, the thickness ratio of the support layer a to the light reflection layer B was 0.7%, which does not satisfy the condition in which the thickness ratio of the support layer a to the light reflection layer B exceeded 1%. Therefore, in the film forming process of the reflective film, the film is not sufficiently supported during stretching, so the stretchability is rapidly reduced, and processing defects such as tearing of the light reflective film occur.

In comparative example 9, the thickness ratio of the support layer a with respect to the light reflection layer B was 13%, which does not satisfy the condition in which the thickness ratio of the support layer a with respect to the light reflection layer B was less than 10%, and the value calculated from formula 1 was 12%, which does not satisfy the condition that the required value was 5% or less. Therefore, moldability is greatly reduced, making it difficult to form a desired molded article.

As described above, according to the biaxially oriented polyester reflective film and the method of producing the same according to one embodiment of the present invention, such a biaxially oriented polyester reflective film can be obtained by multilayer design of the reflective film, modification of raw materials, adjustment of thermal characteristics of a resin incompatible with polyester and a volume ratio of inorganic particles, orientation relaxation production method, and the like: its thickness is not significantly reduced even after molding and excellent reflection characteristics are maintained. Therefore, the reflective film can be used for various applications, and in particular, it was confirmed that the reflective film can be suitably used as a reflective film for local dimming.

Although preferred embodiments of the present invention have been described in detail above, it should be understood that the present invention is not limited to and by the embodiments shown, and those skilled in the art can modify and improve in various forms within the concept of the present invention set forth in the appended claims.