KR102272984B1 - White polyester film and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a white polyester film comprising: a layer B including a polyester resin, an amorphous cyclic olefin copolymer and inorganic particles; and a layer A located on at least one side of the layer B and containing a polyester resin, PCT, and PET-I. PCT in the layer A aggregates in the form of particles to form surface roughness, so a light guide plate is not damaged and the light leakage phenomenon does not occur because the light guide plate and a reflector do not stick together.

Description

White polyester film and its manufacturing method {WHITE POLYESTER FILM AND MANUFACTURING METHOD THEREOF}

The present invention relates to a white polyester film, and more specifically, to a white polyester film that can form surface roughness and prevent damage to the light guide plate without separately coating organic particles on the surface of the reflective film used for edge-type backlight units. It relates to a polyester film.

In general, a liquid crystal display (LCD) emits light itself to display an image, unlike a plasma display panel (PDP), a field emission display (FED), etc., which are light-emitting display devices. It is a light-receiving type display device in which light is incident from outside to form an image without being formed. For this reason, in the liquid crystal display, a backlight unit (BLU) for emitting light is positioned on the rear surface of the liquid crystal display to ensure high luminance.

Such a backlight unit needs to uniformly illuminate the entire screen as well as irradiate light. As a way to solve this problem, a direct-type or edge-type surface light source structure is used. In the direct-type backlight unit, the LED is embedded in the bottom of the BLU and located at the rear of the display to irradiate the light directly to the front, and in the edge-type backlight unit, the LED is It is installed on the edge of the BLU and directs the light to the front using the light guide plate. Such a backlight unit uses a diffusion film or a diffusion plate to widely diffuse the light emitted from the LED, and also induces light scattering by increasing the surface roughness of the reflective film to further diffuse the light. On the other hand, as disclosed in Korean Patent Application Laid-Open No. 2004-0021274 and Korean Patent Application Laid-Open No. 2009-0071425, a white polyester film used for a reflector is mixed with a polyolefin resin in a polyester resin, and a white pigment is added. It is common to form a cavity inside the film by extruding it together with the polyester resin.

In addition, in order to increase the surface roughness of the reflective film, it is common to laminate the reflective film in the form of a three-layer film of A/B/A structure, and include inorganic particles such as _{SiO 2} or CaCO _{3 in the A layer.} At this time, in the case of an edge-type backlight unit, the light guide plate comes into contact with the reflective film, and the reflective film comes into contact with the light guide plate, so that the light guide plate is split by the surface of the reflective film or the reflective film is split by the light guide plate. Because sufficient illuminance is not formed on the surface of the reflective film, and a sufficient gap is not formed between the film and the light guide plate, causing light leakage (wet out), an illuminance of sufficient size is required on the surface of the reflective film. In some cases, a process of additionally coating the particles is performed, or large inorganic particles are dispersed in the surface layer during co-extrusion to induce surface roughness to be formed in the stretching process. However, when large inorganic particles are added to the surface layer during co-extrusion to form surface roughness, the inorganic particles may protrude to the film surface and there is a high risk of damaging the light guide plate. Particle coated products are often used.

However, in order to coat the separate organic particles, an offline coating process for coating the organic particles on the surface of the reflective film must be added, and the price of the reflective film is high because the price of the organic particles used is high.

Korean Patent Publication No. 2004-0021274 Korean Patent Publication No. 2009-0071425

The present invention has been devised to solve the above problems, and an object of the present invention is to improve the surface roughness without separately coating organic particles on the surface of the reflective film and without adding inorganic particles to the surface layer of the reflective film through copolymerization during film production. It is to provide a white polyester film capable of forming and preventing damage to the light guide plate or adhesion to the light guide plate while having excellent productivity, and a method for manufacturing the same.

These and other objects and advantages of the present invention will become apparent from the following description of preferred embodiments.

The above object includes a layer B and a layer A located on at least one surface of the layer B, wherein the layer A is polyethylene terephthalate (PET), poly-1,4-cyclohexylenedimethylene terephthalate (PCT) and polyethylene terephthalate. A phthalate/isophthalate copolymer (PET-I) is included, and layer B is achieved by a white polyester film comprising a polyester resin, an amorphous cyclic olefin copolymer and inorganic particles.

Preferably, layer A contains 35 to 70% by weight of polyethylene terephthalate, 15 to 30% by weight of poly-1,4-cyclohexylenedimethylene terephthalate, and 15 to 35% by weight of polyethylene terephthalate/isophthalate copolymer. can do.

Preferably, poly-1,4-cyclohexylenedimethylene terephthalate (PCT) comprises 70 mol% of 1,4-cyclohexanedimethanol-terephthalic acid (CHDM-TPA) and 1,4-cyclohexanedimethanol-isophthalic acid. (CHDM-IPA) may be a copolymer copolymerized at 30 mol%.

Preferably, the polyethylene terephthalate/isophthalate copolymer (PET-I) is an ethylene glycol-terephthalic acid (EG-TPA) and ethylene glycol-isophthalic acid (EG-IPA) copolymer, wherein ethylene glycol and terephthalic acid (EG-TPA) ) 80 to 85 mol% and ethylene glycol and isophthalic acid (EG-IPA) may contain 15 to 20 mol%.

Preferably, the poly-1,4-cyclohexylenedimethylene terephthalate may be agglomerated into non-spherical particles in layer A, and the non-spherical particles may have an aspect ratio of 3 to 20.

Preferably, the white polyester film may have a three-dimensional surface roughness (SRa) of 100 to 300 nm.

Preferably, layer B may contain 60 to 94% by weight of a polyester resin, 5 to 40% by weight of an amorphous cyclic olefin copolymer, and 1 to 40% by weight of inorganic particles.

Preferably, the glass transition temperature of the amorphous cyclic olefin copolymer may be 120 to 200 ℃.

Preferably, the average particle diameter of the amorphous cyclic olefin copolymer may be 0.5 to 5.0 μm.

Preferably, the average particle diameter of the inorganic particles may be 0.1 to 3.0㎛.

Preferably, the inorganic particles may include at least one of barium sulfate, titanium dioxide, and calcium carbonate.

In addition, the above object is to prepare a B-layer composition comprising a polyester resin, an amorphous cyclic olefin copolymer and inorganic particles, polyethylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate and polyethylene terephthalate / Preparing an A-layer composition comprising an isophthalate copolymer, co-extruding the B-layer composition and the A-layer composition to prepare an unstretched film, uniaxially stretching the unstretched film in the longitudinal direction, uniaxial It is achieved by a method for producing a white polyester film comprising the steps of biaxially stretching the stretched film in the width direction and heat-treating the biaxially stretched film.

Preferably, the step of uniaxial stretching is a step of stretching 2.5 to 4.0 times at a temperature above the glass transition temperature of the polyester resin and below the glass transition temperature of poly-1,4-cyclohexylenedimethylene terephthalate, and biaxial stretching The stretching step starts at a temperature above the glass transition temperature of the polyester resin and poly-1,4-cyclohexylenedimethylene terephthalate and increases to a temperature 5 to 70° C. higher than the glass transition temperature of the polyester resin, while raising the temperature to 2.5 to 4.5. It may be a step of double stretching.

Preferably, the step of heat treatment may be heat treatment at a temperature of 120 to 220 °C for 1 to 30 seconds.

As described above, according to the white polyester film and the method for manufacturing the same according to an embodiment of the present invention, damage to the light guide plate or adhesion to the light guide plate can be prevented without additional organic particles being coated.

In addition, according to the white polyester film and its manufacturing method according to an embodiment of the present invention, there is an effect such as being able to form surface roughness without putting inorganic particles in the surface layer of the reflective film through copolymerization during film production.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a cross-sectional view of a white polyester film according to an embodiment of the present invention.

With reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. Throughout the specification, like reference numerals are assigned to similar parts. When a part of a layer, film, region, plate, etc. is said to be “on” another part, it includes not only cases where it is “directly on” another part, but also cases where there is another part in between. Conversely, when we say that a part is "just above" another part, we mean that there is no other part in the middle.

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. Also, 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.

Hereinafter, a polyester film according to an embodiment of the present invention will be described in detail with reference to FIG. 1 , which is a cross-sectional view of a white polyester film according to an embodiment of the present invention.

Referring to FIG. 1 , the polyester film according to an embodiment of the present invention includes a layer B 20 and a layer A 10 positioned on at least one surface of the layer B 20 . 1 shows that the A layer 10 is formed on both sides of the B layer 20, but is not limited to that the A layer 10 is formed on both sides as described above, and the A layer 10 is the B layer ( 20), or may be located on both sides of the layer B (20).

First, the B layer 20 will be described in detail.

The layer B 20 may include a polyester resin, an amorphous cyclic olefin copolymer, and inorganic particles 24 . In addition, the B layer 20 may include a plurality of bubbles 22 therein.

The polyester resin included in the layer B 20 may be formed by polymerizing dicarboxylic acid and diol, and may include polyethylene terephthalate (PET). In the case of containing polyethylene terephthalate, copolymerization of 1 to 15 mol%, preferably 3 to 14 mol%, more preferably 5 to 13 mol% of the total dicarboxylic acid or diol component from the viewpoint of polyester film film forming stability It may include a co-polyester comprising a component. This is because, when the copolymer component is less than 1 mol% or more than 15 mol%, it may be difficult to prepare the B layer 20 including the air bubbles 22 .

Here, the dicarboxylic acid is terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenyl carboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfone dicarboxylic acid, phthalic acid, etc. Aromatic dicarboxylic acids, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimasic acid, maleic acid, and fumaric acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, paraoxybenzoic acid, etc. oxycarboxylic acid and the like.

In addition, diols include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentine glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, and polypropylene glycol, cyclohexane dimethanol, etc. Aromatic glycols, such as alicyclic glycol of , bisphenol A, and bisphenol S, etc. can be used.

Layer B 20 is preferably formed by using isophthalic acid or naphthalenedicarboxylic acid as dicarboxylic acid from the viewpoint of stability of the amorphous cyclic olefin copolymer, which will be described later, and polymerizing cyclohexane dimethanol as a diol. It may include polyester, but is not limited thereto, and may include polyester formed through various combinations.

In one embodiment, the polyester resin may include 60 to 94% by weight relative to the total weight of the layer B 20, more preferably including 70 to 90% by weight. This is because when the content of the polyester resin is out of 60 to 94% by weight relative to the total weight of the B layer 20 , it may be difficult to form the plurality of bubbles 22 in the B layer 20 . More specifically, if it is less than 60% by weight, there is a problem that the film formability is lowered and a lot of fracture occurs, and if it is more than 94% by weight, void formation is less and the luminance is lowered.

In one embodiment, the amorphous cyclic olefin copolymer included in the layer B 20 includes bicyclo[2,2,1]hepto-2-ene, 6-methylbicyclo[2,2,1]hepto-2 -ene, 5,6-dimethylbicyclo[2,2,1]hepto-2-ene, 1-methylbicyclo[2,2,1]hepto-2-ene, 6-ethylbicyclo[2,2 ,1]hepto-2-ene, 6-n-butylbicyclo[2,2,1]hepto-2-ene, 6-i-butylbicyclo[2,2,1]hepto-2-ene, 7 -Methylbicyclo[2,2,1]hepto-2-ene, tricyclo[4,3,0,12.5]-3-decene, 2-methyl-tricyclo[4,3,0,12.5]-3 -decene, 5-methyl-tricyclo[4,3,0,12.5]-3-decene, tricyclo[4,4,0,12.5]-3-decene and 10-methyl-tricyclo[4,4, 0,12.5]-decene, and may include a copolymer of an amorphous cyclic olefin resin and a crystalline polyolefin resin such as ethylene, propylene, butene, or methylpentene. However, as a resin that is difficult to be deformed by heat treatment after stretching of the polyester film, it is preferable to include a copolymer between ethylene and norbornene.

In one embodiment, the amorphous cyclic olefin copolymer preferably has a glass transition temperature (Tg) of 120 to 200 °C, more preferably 135 to 185 °C, even more preferably 140 to 150 °C. This is when the glass transition temperature is less than 120 ℃, the amorphous cyclic olefin copolymer is plastically deformed in the stretching process of the polyester film, and the generation of the bubbles 22 in the B layer 20 may be inhibited, and if it is more than 200 ℃, amorphous It is because dispersion of the cyclic olefin copolymer becomes insufficient, and it is difficult to produce the shape and number of the cells 22 to a desired level.

In addition, the amorphous cyclic olefin copolymer preferably contains 5 to 40% by weight, more preferably 10 to 30% by weight, based on the total weight of the layer B (20). This is that when the amorphous cyclic olefin copolymer is less than 5% by weight, the whitening effect of the polyester film is weak and it is difficult to implement high reflectivity, and when it exceeds 40% by weight, the mechanical properties of the film itself are lowered and the amorphous cyclic olefin This is because aggregation of the copolymer may occur.

Moreover, it is preferable that the average particle diameter of an amorphous cyclic olefin copolymer is 0.5-5.0 micrometers. This is because, when the average particle diameter is less than 0.5 μm, it is difficult to generate the bubbles 22 in the layer B 20, and when it is more than 5.0 μm, the polyester film may be torn in the stretching process.

In one embodiment, the inorganic particles 24 included in the layer B 20 may include at least one of barium sulfate, titanium dioxide, and calcium carbonate.

In this case, the inorganic particles 24 preferably have an average particle diameter of 0.1 to 3.0 μm, more preferably 0.2 to 2.0 μm, and even more preferably 0.3 to 1.0 μm. When the average particle diameter of the inorganic particles 24 is less than 0.1 μm, the degree of scattering light is lowered and there is a problem in that the luminance is lowered, and when the average particle diameter of the inorganic particles 24 is more than 3.0 μm, voids are excessively formed in the stretching process and breakage occurs.

In addition, the inorganic particles 24 are preferably included in an amount of 1 to 40% by weight, more preferably 2 to 30% by weight, even more preferably 3 to 25% by weight, based on the total weight of the B layer 20 . This is because when the inorganic particles 24 are less than 1% by weight, the scattered light by the inorganic particles 24 is insufficient to obtain sufficient reflection performance, and when it is more than 40% by weight, the film forming stability of the polyester film may be significantly reduced. to be.

In addition, in the B layer 20, various additives such as a fluorescent whitening agent, a crosslinking agent, a heat-resistant stabilizer, an oxidation-resistant stabilizer, an ultraviolet absorber, an organic lubricant, an inorganic fine particle, a filler, a light-resistant agent, an antistatic agent, as long as the effects of the present invention are not impaired. , a nucleating agent, a dye, a dispersing agent, a coupling agent, and the like may be further included.

Next, the A-layer 10 will be described in detail.

In one embodiment, layer A 10 may include a polyester resin, poly-1,4-cyclohexylenedimethylene terephthalate (PCT) and polyethylene terephthalate/isophthalate copolymer (PET-I). . In this case, the PCT 15 included in the A layer 10 may be aggregated in the form of non-spherical particles.

In one embodiment, the A layer 10 may include 35 to 70% by weight of polyester resin, 15 to 30% by weight of PCT, and 15 to 35% by weight of PET-I.

The polyester resin included in the layer A 10 is the same as the polyester resin included in the layer B 20 described above, and overlapping descriptions will be omitted.

In one embodiment, the PCT 15 is terephthalic acid (hereinafter 'TPA'), isophthalic acid (hereinafter 'IPA'), or dimethyl terephthalate (hereinafter 'DMT') and 1,4-cyclo Preferably, it is a crystalline polyester prepared by esterification or transesterification of hexanedimethanol (1,4-cyclohexanedimethanol, hereinafter 'CHDM'). PCT is a copolymer of CHDM-TPA and CHDM-IPA, and CHDM- It is preferable to include 70 to 80 mol% of TPA and 20 to 30 mol% of CHDM-IPA.

More specifically, PCT according to an embodiment is a copolymer copolymerized with 70 mol% of CHDM-TPA and 30 mol% of CHDM-IPA, and it is preferable to add it in the form of a master pellet consisting of 50% by weight of polyester and 50% by weight of PCT. Do.

The present invention is characterized in that surface roughness is formed by putting a resin containing CHDM (1,4-cyclohexanedimethanol) in the surface layer using copolymerization technology. It can be lowered, and the price of the resin used is also cheaper than the organic particles used in the existing OFF LINE COATING, so it has the effect of significantly lowering the price of the existing product.

In one embodiment, the PCT 15 is preferably 15 to 30% by weight in the A layer 10, and if the PCT 15 is less than 15% by weight, the PCT agglomerate size in the A layer 10 is small enough This is because the roughness cannot be formed, and when it is greater than 30% by weight, a problem of poor film forming stability occurs.

At this time, the glass transition temperature of the PCT (15) is preferably 85 ℃ or more, more preferably 90 ℃ or more is more preferable. In the stretching process for the A layer 10, when biaxial stretching is performed at a temperature higher than the glass transition temperature (78° C.) of polyester and lower than the glass transition temperature of PCT, surface roughness is formed, and surface roughness is decreased in the film heat treatment process. goes down again

In an embodiment, the organic particles 15 made of PCT are aggregated in a non-spherical form, and the aspect ratio is preferably 3 to 20, more preferably 5 to 15. As an example, the PCT 15 may be an elliptical particle. This is because it is difficult for the aspect ratio of the PCT 15 to exist if it is 3 or less, and if it is 20 or more, sufficient surface roughness is not formed.

In one embodiment, PET-I increases the film forming stability in the A layer 10 and controls the size of the PCT aggregation in the A layer 10 to be large and uniform to form a uniform surface roughness.

It is preferable to use a copolymer of 80 to 85 mol% of EG-TPA and 15 to 20 mol% of EG-IPA for PET-I. This is because, when EG-IPA exceeds 20 mol%, PET-I does not crystallize, resulting in a problem that CHIP is fused and adhered to the hopper in the raw material drying process for film forming.

In one embodiment, PET-I is preferably included in the 15 to 35% by weight in the A layer (10). When PET-I is less than 15% by weight, the effect of increasing film-forming stability and controlling the size of the agglomeration of PCT (15) decreases, and when it exceeds 35% by weight, the orientation of the film is disturbed and film-forming properties of the film, This is because thickness stability and strength may be insufficient.

The white polyester film prepared in this way preferably has a three-dimensional surface roughness of 100 to 300 nm. Due to this surface roughness range, the light leakage phenomenon does not occur when the white polyester film of the present invention is in contact with the light guide plate.

The thickness of the layer A 10 in the white polyester film according to an embodiment of the present invention is preferably 5 to 20㎛. When the thickness of the layer A 10 is more than 20 μm, there is a problem in that the thickness of the layer B is low among the entire film, so that the luminance is insufficient, and when it is less than 5 μm, there is a problem that sufficient illuminance is not formed.

And it is preferable that the thickness of the B layer 20 is 50 to 250 μm. When the thickness of the layer B 20 is more than 250 μm, there is a problem in that it is difficult to form a film, and when it is less than 50 μm, there is a problem in that the luminance is deteriorated because it does not provide sufficient reflection performance.

Next, a method for producing a white polyester film according to another embodiment of the present invention will be described. However, the description overlapping with the white polyester film according to an embodiment of the present invention described above will be omitted.

The method for producing a white polyester film according to another embodiment of the present invention comprises the steps of preparing a B-layer composition comprising a polyester resin, an amorphous cyclic olefin copolymer and inorganic particles, a polyester resin, PCT and PET-I Preparing an A-layer composition comprising the step of co-extruding the B-layer composition and the A-layer composition to prepare an unstretched film, uniaxially stretching the unstretched film in the longitudinal direction, and uniaxially stretching the uniaxially-stretched film in the width direction Including the step of biaxially stretching and heat-treating the biaxially stretched film.

In the step of preparing an unstretched film by co-extruding the B-layer composition and the A-layer composition, the B-layer composition including polyester, an amorphous cyclic olefin copolymer and inorganic particles and A including polyester, PCT and PET-I An unstretched film having a laminated form of A layer/B layer/A layer or A layer/B layer may be prepared by co-extruding the layer composition.

The stretching temperature in the step of uniaxial stretching is preferably performed at a draw ratio of 2.5 to 4.0 times at a glass transition temperature (Tg) of 78° C. or higher and below the glass transition temperature (Tg) of PCT.

In addition, the stretching temperature in the biaxial stretching step is a temperature higher than the glass transition temperature of the polyester resin and poly-1,4-cyclohexylenedimethylene terephthalate, 5 to 70 ℃ higher than the glass transition temperature of the polyester resin. It is preferable to perform stretching at a draw ratio of 2.5 to 4.5 times while raising the temperature to . Here, the temperature increase process may be continuously increased or the temperature may be increased in stages.

The thus obtained biaxially oriented film may be subjected to heat treatment at a temperature of 120 to 220° C. for 1 to 30 seconds, and then cooled to room temperature to prepare a white polyester film of the present invention. At this time, during the heat treatment process, 3 to 12% relaxation treatment may be additionally performed in the width or length direction as needed.

Hereinafter, the configuration of the present invention and its effects will be described in more detail through Examples and Comparative Examples. However, these examples are for explaining the present invention in more detail, and the scope of the present invention is not limited to these examples.

[Example]

[Example 1]

As a B-layer composition, 75 wt% of PET, 5 wt% of a copolymer between ethylene and norbornene, which are an amorphous cyclic olefin copolymer (average particle diameter of 1.0 μm), and titanium dioxide (average particle diameter of 0.3 μm) were mixed and prepared by mixing 20 wt%.

And as the A-layer composition, PET 5% by weight, PCT master pellets 60% by weight, and PET-I 35% by weight were mixed and prepared. At this time, PCT master pellets were used by diluting a mixture of 50% by weight of PCT resin and 50% by weight of polyester resin copolymerized with 70 mol% of CHDM-TPA and 30 mol% of CHDM-IPA. The content of PCT in the A-layer composition is set to 30% by weight. In addition, in the case of PET-I, a copolymer of 80 mol% of EG-TPA and 20 mol% of EG-IPA was used.

Next, the B-layer composition and the A-layer composition were co-extruded in a T-die to prepare a sheet, which was cooled and solidified in a casting drum having a surface temperature of 20° C. to prepare an unstretched film. The prepared unstretched film was stretched 3.5 times in the longitudinal direction of the film at 85° C., cooled, and stretched 3.7 times in the width direction while starting at 85° C. and raising the temperature to 120° C. Thereafter, heat setting was performed at 190° C. in a tender and cooled to room temperature to prepare a biaxially stretched white polyester film.

[Example 2]

In the A-layer composition, the PCT master pellet content was reduced to 45% by weight, so that the content of PCT in the A-layer was 22.5% by weight, and 20% by weight of PET was added through the same process as in Example 1, except that the white poly An ester film was prepared.

[Example 3]

White polyester through the same process as in Example 1, except that the PCT master pellet content in the A-layer composition was reduced to 30% by weight, so that the content of PCT in the A-layer was 15% by weight, and 35% by weight of PET was added. A film was prepared.

[Example 4]

A white polyester film was prepared in the same manner as in Example 1, except that the content of PET-I was reduced to 25% by weight in the A-layer composition and 15% by weight of PET was added.

[Example 5]

A white polyester film was prepared in the same manner as in Example 1, except that the content of PET-I was reduced to 15% by weight in the A-layer composition and 25% by weight of PET was added.

[Example 6]

Example except that the PCT master pellet content in the A-layer composition was 30% by weight, so that the PCT in the A-layer was 15% by weight, the PET-I content was 15% by weight, and 55% by weight of PET was added. A polyester film was prepared through the same process as in 1.

[Example 7]

A polyester film was prepared in the same manner as in Example 1, except that PET-I was copolymerized with 85 mol% of EG-TPA and 15 mol% of EG-IPA in the A-layer composition.

[Comparative example]

[Comparative Example 1]

Through the same process as in Example 1, except that the PCT master pellet content in the A-layer composition was increased to 65% by weight so that the PCT content in the A-layer was 32.5% by weight, and no separate PET was added except for the PCT master pellets. A polyester film was prepared.

[Comparative Example 2]

A polyester film was prepared through the same process as in Example 1 except that the PCT master pellet content in the A-layer composition was reduced to 28% by weight so that the PCT content in the A-layer was 14% by weight, and 37% by weight of PET was added. did.

[Comparative Example 3]

A polyester film was prepared in the same manner as in Example 1, except that the content of PET-I was increased to 36% by weight in the A-layer composition and 4% by weight of PET was used.

[Comparative Example 4]

A polyester film was prepared in the same manner as in Example 1, except that the content of PET-I was reduced to 14% by weight in the A-layer composition and 26% by weight of PET was added.

[Comparative Example 5]

A polyester film was prepared in the same manner as in Example 1, except that PET-I was copolymerized with 75 mol% of EG-TPA and 25 mol% of EG-IPA in the A-layer composition.

[Comparative Example 6]

In Example 1, the B-layer composition and the A-layer composition were co-extruded in a T-die to prepare a sheet, which was cooled and solidified in a casting drum having a surface temperature of 20° C. to prepare an unstretched film, and then the prepared unstretched film was stretched 3.5 times in the longitudinal direction of the film at 95° C. and then cooled, and stretched 3.7 times in the width direction while raising the temperature from 85° C. to 120° C., heat setting was performed at 230° C. in a tender, and cooled to room temperature. A polyester film was prepared in the same manner except for preparing an axially stretched white polyester film.

For the films prepared in Examples 1 to 7 and Comparative Examples 1 to 6, physical properties were evaluated through the following experimental examples, and the results are shown in Tables 1 and 2.

[Experimental example]

(1) Measurement of three-dimensional surface roughness (SRa) of the film

The roughness (SRa) value of the surface of the polyester film was measured using a three-dimensional surface shape measuring device (KOSAKA, SE-600K).

(2) Evaluation of film forming stability

When the prepared white polyester film can be stably formed for 20 minutes or more, it is indicated by "○", and when it is not possible to form a stable film due to breakage within 20 minutes, it is indicated by "X". In addition, in the case of the fusion of CHIP sticking to the hopper during the raw material drying process, it was also marked with X.

(3) Measurement of aspect ratio of PCT particles

Cut the cross section of the prepared white polyester film and measure 5 sheets at 5,000 magnification with SEM, measure the particle size of the aggregated PCT particles in horizontal and vertical sizes, and then calculate the ratio of length and width to aspect ratio [aspect ratio = width] /vertical] and the average value of 20 samples was used.

PET
(weight%) PCT
(weight%) PET-I
(85:15) PET-I
(80:20) PET-I
(75:25) Sum surface
illuminance
(nm) film-forming light leak
phenomenon Example 1 35 30 - 35 - 100 280 ○ ○ Example 2 42.5 22.5 - 35 - 100 180 ○ ○ Example 3 50 15 - 35 - 100 140 ○ ○ Example 4 45 30 - 25 - 100 240 ○ ○ Example 5 55 30 - 15 - 100 200 ○ ○ Example 6 70 15 - 15 - 100 130 ○ ○ Example 7 35 30 35 - - 100 270 ○ ○ Comparative Example 1 32.5 32.5 - 35 - 100 300 X ○ Comparative Example 2 51 14 - 35 - 100 80 ○ X Comparative Example 3 34 30 - 36 - 100 280 X ○ Comparative Example 4 56 30 - 14 - 100 180 X ○ Comparative Example 5 35 30 - - 35 100 310 ○ ○

In Table 1, the PET content represents the combined content of the directly added PET and the PET contained in the PCT masterbatch.

As shown in Table 1, in the case of Example 1, it is confirmed that the surface roughness is 280 nm, the film forming property is good, and there is no light leakage. In addition, in the case of Examples 2 and 3, it can be seen that the surface roughness is slightly reduced as the PCT content is decreased. The surface roughness was good at 140 nm until the PCT content was 15% by weight, so that no light leakage occurred when the BLU was connected. In addition, in the case of Examples 4 and 5, it can be seen that the surface roughness decreases as the PET-I content is reduced to 15% by weight, which is because the PCT aggregation in the A layer is reduced when the PET-I content is small, Until the PET-I content was 15% by weight, film forming stability was good and light leakage did not occur. In addition, in the case of Example 6, the PCT content was further reduced compared to Example 5, and it was confirmed that the surface roughness was lowered to 130 as the PCT content was further reduced, but light leakage did not occur and the film forming property was good. In addition, in the case of Example 7, EG-TPA:EG-IPA was changed to 85:15 as a copolymerization molar ratio of PET-I, and there was no significant effect on film formability and surface roughness.

On the other hand, in the case of Comparative Example 1, the PCT content was increased to 32.5% by weight, and the film forming stability was poor due to an excessive amount of PCT, and many fractures occurred.

In addition, in the case of Comparative Example 2, the PCT content was reduced to 14% by weight, and the PCT content was too small to form a sufficient surface roughness, and light leakage occurred when the BLU was connected.

In addition, in the case of Comparative Example 3, the PET-I content was increased to 36% by weight compared to Example 1, and the PET-I content was too high, resulting in non-uniform film thickness and reduced strength, and film formability This has gotten worse.

In addition, in Comparative Example 4, compared to Example 1, the PET-I content was lowered to 14% by weight, and the PET-I content was too low, resulting in poor film forming properties and many fractures.

In addition, in the case of Comparative Example 5, EG-TPA:EG-IPA was changed to 75:25 in the copolymerization molar ratio of PET-I. In this case, the PCT particle size was made large, the surface roughness was increased, and the film was formed in addition to the results shown in Table 1 For this purpose, it was confirmed that the PET-I chip was fused to the hopper during drying of the raw material and the discharge port was blocked.

PET
(weight%) PCT
(weight%) PET-I
(85:15) PET-I
(80:20) PET-I
(75:25) Sum aspect ratio surface
illuminance
(nm) film-forming light leak
phenomenon Example 1 35 30 - 35 - 100 6 280 ○ ○ Example 2 42.5 22.5 - 35 - 100 12 180 ○ ○ Comparative Example 6 35 30 - 35 - 100 21 90 ○ X

As shown in Table 2, Examples 1 and 2, which satisfy the aspect ratio of the aggregated PCT of 3 to 20, satisfy that the surface roughness is 100 to 300 nm and have good film forming properties and light leakage, while the aspect ratio In Comparative Example 6 exceeding 20, sufficient surface roughness was not formed, and light leakage occurred when BLU was connected.

As described above, according to the white polyester film according to the present invention, it is possible to prevent damage to the light guide plate or sticking to the light guide plate while being excellent in productivity.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

10: A floor 20: B floor
15: Agglomerated PCT 22: Bubbles
24: inorganic particles

Claims (15)

Including a layer B and an A layer located on at least one surface of the B layer,
The A layer comprises 35 to 70% by weight of polyethylene terephthalate (PET), 15 to 30% by weight of poly-1,4-cyclohexylenedimethylene terephthalate (PCT), and polyethylene terephthalate/isophthalate copolymer (PET-I). ) comprising 15 to 35% by weight,
The layer B is a polyester resin, an amorphous cyclic olefin copolymer and an inorganic particle, a white polyester film. delete According to claim 1,
The poly-1,4-cyclohexylenedimethylene terephthalate (PCT) contains 70 mol% of 1,4-cyclohexanedimethanol-terephthalic acid (CHDM-TPA) and 1,4-cyclohexanedimethanol-isophthalic acid (CHDM- IPA) 30 mol% copolymer copolymerized, white polyester film. According to claim 1,
The polyethylene terephthalate / isophthalate copolymer (PET-I) is an ethylene glycol-terephthalic acid (EG-TPA) and ethylene glycol-isophthalic acid (EG-IPA) copolymer, ethylene glycol and terephthalic acid (EG-TPA) 80 to A white polyester film comprising 85 mol% and 15 to 20 mol% of ethylene glycol and isophthalic acid (EG-IPA). According to claim 1,
The poly-1,4-cyclohexylenedimethylene terephthalate is agglomerated into non-spherical particles in the layer A, a white polyester film. 6. The method of claim 5,
The non-spherical particles have an aspect ratio of 3 to 20, a white polyester film. According to claim 1,
The white polyester film has a three-dimensional surface roughness (SRa) of 100 to 300 nm, a white polyester film. According to claim 1,
The B layer comprises 60 to 94 wt% of a polyester resin, 5 to 40 wt% of an amorphous cyclic olefin copolymer, and 1 to 40 wt% of inorganic particles, a white polyester film. According to claim 1,
The glass transition temperature of the amorphous cyclic olefin copolymer is 120 to 200 ℃, a white polyester film. According to claim 1,
The average particle diameter of the said amorphous cyclic olefin copolymer is 0.5-5.0 micrometers, The white polyester film. According to claim 1,
The average particle diameter of the inorganic particles is 0.1 to 3.0㎛, a white polyester film. According to claim 1,
The inorganic particles include at least one of barium sulfate, titanium dioxide and calcium carbonate, a white polyester film. Preparing a B-layer composition comprising a polyester resin, an amorphous cyclic olefin copolymer, and inorganic particles;
35 to 70% by weight of polyethylene terephthalate, 15 to 30% by weight of poly-1,4-cyclohexylenedimethylene terephthalate, and 15 to 35% by weight of polyethylene terephthalate / isophthalate copolymer A-layer composition comprising: step;
Co-extruding the B-layer composition and the A-layer composition to prepare an unstretched film;
uniaxially stretching the unstretched film in the longitudinal direction;
biaxially stretching the uniaxially stretched film in the width direction; and
heat-treating the biaxially stretched film;
A method for producing a white polyester film comprising a. 14. The method of claim 13,
The step of uniaxial stretching is a step of stretching 2.5 to 4.0 times at a temperature above the glass transition temperature of the polyester resin and below the glass transition temperature of poly-1,4-cyclohexylenedimethylene terephthalate,
The step of biaxial stretching starts from a temperature above the glass transition temperature of the polyester resin and poly-1,4-cyclohexylenedimethylene terephthalate, while raising the temperature to a temperature 5 to 70° C. higher than the glass transition temperature of the polyester resin. A method for producing a white polyester film, which is a step of stretching 2.5 to 4.5 times. 14. The method of claim 13,
The heat treatment step is a method for producing a white polyester film, heat treatment for 1 to 30 seconds at a temperature of 120 to 220 ℃.

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