KR20160043277A

KR20160043277A - White polyester film and method of manufacturing white polyester film and reflective sheet using the same

Info

Publication number: KR20160043277A
Application number: KR1020140137402A
Authority: KR
Inventors: 김창주; 한승훈; 이문복
Original assignee: 도레이첨단소재 주식회사
Priority date: 2014-10-13
Filing date: 2014-10-13
Publication date: 2016-04-21

Abstract

The present invention relates to a white polyester film, a method of producing the same, and a reflective sheet using the same, and more particularly, to a white polyester film having excellent uniformity of organic particles that are compatible with polyester, A method of manufacturing the same, and a reflective sheet using the same. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film, and more particularly, to a white polyester film and a reflective sheet using the white polyester film.

Description

TECHNICAL FIELD [0001] The present invention relates to a white polyester film, a method of producing the same, and a reflective sheet using the white polyester film,

The white polyester film used in the conventional reflector is a polyester film obtained by mixing a polyolefin resin with a polyester resin and mixing the polyester resin with a white pigment added thereto Extruded, and a cavity is formed inside the film.

As is known in the related art, in the case of a white polyester film in which a cavity is formed inside the film and a white pigment is added, pores inside the film are formed depending on the polyolefin resin and the inorganic particles to achieve a somewhat good optical characteristic , A high brightness can not be achieved due to the uneven pore size, and a process instability problem such as frequent breakage at the time of film formation at an excessive stretching magnification occurs.

On the other hand, when the stretching magnification is reduced in order to achieve film forming stability, problems such as failure to satisfy desired optical characteristics have occurred.

The present inventors have made efforts to solve the problems inherent in the white polyester film used in the conventional reflector plate. As a result, the present inventors have found that when the distribution of polyester and non-organic organic particles is 1.0 or less, The present invention has been accomplished to adjust the retention time and adjust the stretching magnification and the heat fixing temperature after stretching to improve the uniformity of the pores while maintaining stable film formability and maintaining high luminance and good physical properties.

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

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a stable film forming material by controlling the retention time, the draw ratio and the heat fixing temperature after stretching of organic particles in a single tube by using organic particles having improved particle- And to provide a white polyester film, a method of manufacturing the same, and a reflective sheet using the same.

These and other objects and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof.

The above object is achieved by the following formulas (1) and (2)

(1) 1.0? 0.523 (A ² CR ³ )? 30.0

(2) 3.0? A / C? 9.0

A is the X axis length (탆) of the pores, C is the Z axis length (탆) of the pores, and R is the particle diameter (탆) of the organic particles.

Here, the white polyester film is characterized in that the polyester resin contains organic particles having particle diameters of 0.5 to 2.5 占 퐉 which are nonconductive.

Preferably, the organic particles have a glass transition temperature of 120 to 200 캜.

Preferably, the particle size distribution of the organic particles is 1.0 or less.

Preferably, the residence time in the single tube of the organic particles is 10 minutes or less.

Preferably, the white polyester film is stretched at a stretch ratio of 3.0 to 5.0 both in the longitudinal direction and in the transverse direction.

Preferably, the heat-setting temperature of the white polyester film is 170 to 200 ° C.

Preferably, the white polyester film has a reflectance of 101% or more.

The present invention also provides a method for producing an unstretched sheet, comprising the steps of: melting and extruding a raw material composition containing a polyester resin, polyester and non-emulsifiable organic particles having a particle size distribution of 1.0 or less as a main component, A second step of cooling the unstretched sheet by a casting drum; a third step of stretching the cooled unoriented sheet by one to 3.0 to 5.0 times the uniaxial stretching to produce a uniaxially stretched film; A fourth step of biaxially stretching the film in a biaxially stretched state to produce a biaxially stretched film; and a fifth step of heat-treating the biaxially stretched film, wherein the biaxially stretched film is biaxially stretched .

Here, the raw material composition in the first step is characterized by having a residence time in a single tube of 10 minutes or less.

Preferably, the thermal fixing temperature in the fifth step is 170 to 200 ° C.

The above object is also achieved by a reflective sheet using the above white polyester film.

According to the present invention, a raw material composition containing an organic particle resin and a polyester resin as main components, which is incompatible with polyester and has a particle diameter distribution of 1.0 or less, is extruded while controlling retention time in a single tube, It is possible to improve the pore uniformity of the obtained film and to provide stable film formability while maintaining good physical properties.

Further, even if the stretching magnification of the white polyester film of the present invention is adjusted to 3.0 to 5.0 times, the uniformity of the pores reduces the risk of breakage during film formation, thereby improving the film forming stability. In addition, since the film is not broken during film formation, a high film-forming yield can be achieved, thereby reducing the manufacturing cost.

Thus, the reflective sheet using the white polyester film of the present invention can be usefully used for a backlight device for image display, a reflective sheet of a lamp reflector, a reflective sheet of an illumination device, a reflective sheet for an illuminated signboard, .

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

FIG. 1 is a schematic view of organic particles inducing voids and pores of a spheroid type.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. It will be apparent to those skilled in the art that these embodiments are provided by way of illustration only for the purpose of more particularly illustrating the present invention and that the scope of the present invention is not limited by these embodiments .

Unless otherwise defined, 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.

The white polyester film according to one aspect of the present invention satisfies the following equations (1) and (2).

(1) 1.0? 0.523 (A ² CR ³ )? 30.0

(2) 3.0? A / C? 9.0

A is the X axis length (占 퐉) of the pores, C is the Z axis length (占 퐉) of the pores, and R is the particle diameter (占 퐉) of the organic particles.

Although the present specification describes a white polyester film used as a planar light source for a liquid crystal display, it is not limited thereto. For convenience of description, the white polyester film will be described together with the white polyester film according to another embodiment of the present invention.

A method of producing a white polyester film according to another aspect of the present invention includes melting a raw material composition containing a polyester having a particle size distribution of 1.0 or less and a non-compatible organic particle and a polyester resin as main components, extruding the mixture, Stretching the unstretched sheet by a casting drum, stretching the unstretched sheet by 3.0 to 5.0 times the uniaxially stretched film, stretching the unstretched sheet by biaxial stretching at the same stretching ratio as the uniaxially stretched film, And adjusting the heat setting temperature.

The white polyester film according to the present invention can provide a high film forming stability by uniformizing the pores in the film even at a high stretching magnification so that the problem of breaking at the time of film formation can be prevented.

The raw material composition of the first step is prepared by mixing 100 parts by weight of a polyester resin and 100 parts by weight of a resin mixture composed of a particulate mixture formed of an amorphous cyclic olefin copolymer resin having a particle size distribution of 1.0 or less, Is preferably contained. At this time, it is preferable that the polyester resin used as the base resin of the white polyester film is composed of a dicarboxylic acid component and a diol component, and has a basic constitution of polyethylene terephthalate with high film-forming stability and low cost. As the dicarboxylic acid component, it is preferable to use terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid and sebacic acid. Can be selected from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like.

The content of the polyester resin in the resin composition is preferably 65 to 95% by weight, more preferably 70 to 90% by weight. If the content of the polyester resin is out of the above range, it is impossible to form a film containing a large number of voids. When polyethylene terephthalate is used as the base resin, it is preferably 1 to 15 mol%, more preferably 3 to 14 mol%, and most preferably 5 to 13 mol%, based on the total dicarboxylic acid component, % Of copolymerized polyester or a copolymerized polyester containing 1 to 15 mol%, more preferably 3 to 14 mol%, and most preferably 5 to 13 mol% of a copolymerizable component per total diol component It is good to use. At this time, if it is less than 1 mol%, it is difficult to form a film containing a large number of voids, whereas when it exceeds 15 mol%, film formation is also difficult. The dicarboxylic acid component may be selected from the group consisting of isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid and sebacic acid. And the diol component may be selected from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like. Among the above copolymerization components, isophthalic acid or 2,6-naphthalenedicarboxylic acid is preferably used in order to obtain good film formability, and 1,4-cyclohexane, which has an effect of stabilizing the dispersion state of the non- It is preferable to use dimethanol.

In the resin composition in the raw material composition, an amorphous cyclic olefin copolymer is used as a non-crystalline resin for the polyester resin. At this time, as the amorphous cyclic olefin copolymer used in the present invention, there may be mentioned bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept- 2,2,1] hept-2-ene, 6-dimethylbicyclo [2,2,1] 2-ene, 6-n-butylbicyclo [2,2,1] hept-2-ene, 6-i-butylbicyclo [2,2,1] hept- 2,2,1] hept-2-ene, tricyclo [4,3,0,12,5] -3-decene, 2-methyl-tricyclo [ Decene, 5-methyl-tricyclo [4,3,0,12,5] -3-decene, tricyclo [4,4,0,12,5] , 4,0,12,5] -decene, or the above-mentioned amorphous cyclic olefin resin and a crystalline polyolefin resin such as ethylene, propylene, butene, methylpentene or the like can be used.

These may be homopolymers or may be used in combination of two or more. Particularly, a resin having a large difference in critical surface tension from the polyester resin and hardly being deformed by heat treatment after stretching is preferable, and a copolymer of ethylene and bicycloalkene is most preferable. The content of the amorphous cyclic olefin copolymer of the present invention is preferably 5 to 35% by weight, more preferably 10 to 30% by weight, based on the resin composition. If it is contained in an amount of less than 5% by weight, the effect of whitening becomes faint and it becomes difficult to obtain a high reflectance. When the content exceeds 35% by weight, mechanical properties such as strength of the film itself are deteriorated, This is because the coagulation occurs a lot and the risk of breakage increases when the film is formed. At this time, the amorphous cyclic olefin copolymer to be used is obtained by separating from the polyester composition and using a differential scanning calorimeter and measuring the transition temperature according to JIS K7121-1987 measurement method, .

In an embodiment of the present invention, a copolymer resin between ethylene and norbornene is used as an amorphous cyclic olefin copolymer which is an incompatible resin for a polyester resin as a most preferable example. The copolymer resin between ethylene and norbornene can be prepared by the liquid phase polymerization method exemplified in the well-known Japanese Patent Application Laid-Open No. 61-271308.

The amorphous cyclic olefin copolymer of the present invention obtained by the above method preferably has a glass transition temperature of 120 to 200 캜 or less. If the glass transition temperature is less than 120 캜, the cyclic olefin copolymer is plastically deformed when the film is stretched to inhibit the formation of voids. On the other hand, when the glass transition temperature exceeds 200 캜, when the polyester resin and the amorphous cyclic olefin copolymer are melt-kneaded using an extruder or the like and discharged into a sheet, the dispersion of the amorphous cyclic olefin copolymer becomes insufficient The shape and number of the voids can not be attained to a desired level. The glass transition temperature can be adjusted by changing the copolymerization ratio of the cyclic olefin and the non-cyclic olefin in the amorphous cyclic olefin copolymer. The glass transition temperature is elevated at a rate of 20 ° C / min using a differential scanning calorimeter Is determined by the midpoint of JIS K7121-1987.

The amorphous cyclic olefin copolymer having a particle diameter of 0.5 to 2.5 μm or less is selected and used. If the particle size is less than 0.5 mu m, it is difficult to form a void at the time of stretching, and if it exceeds 2.5 mu m, film tearing may occur during stretching, which may deteriorate film formability. Further, the particle size distribution of the amorphous cyclic olefin copolymer is selected to be 1.0 or less. If the particle diameter distribution exceeds 1.0, the pores are uneven at the time of stretching, which is disadvantageous in terms of optical properties and film formability.

The residence time in the single tube of the polyester resin, the polyester resin and the amorphous cyclic olefin copolymer which is non-recyclable is preferably 10 minutes or less, more preferably 5 minutes or less. If the retention time in the single tube exceeds 10 minutes, the organic particles are maintained at a high temperature for a long time, and the particle size becomes uneven due to the re-agglomeration of the particles in the single tube, thereby preventing the formation of uniform voids.

Next, preferable examples of the inorganic particles used in the raw material composition of the present invention include titanium dioxide particles, barium sulfate particles, calcium carbonate particles alone, or a combination thereof. Particularly, titanium dioxide particles are preferable for imparting light resistance. The average particle diameter of the inorganic particles is 0.1 to 2.0 占 퐉, more preferably 0.2 to 2.0 占 퐉, and most preferably 0.3 to 1.0 占 퐉 to obtain good dispersibility and film-forming stability. Here, the average particle diameter refers to the number average particle diameter, and the particle diameter is arbitrarily determined for each particle before being added to the resin (film) at a magnification of 10,000 at a scanning electron microscope to determine the average particle diameter size . In this case, when the particle is not spherical, it is approximated to the closest ellipse, and the ellipse (long diameter + short diameter) / 2 is determined. Here, particles smaller than 0.01 탆 in diameter and particles of 10 탆 or larger in diameter are excluded do. The content of the white inorganic particles used in the present invention is 0 to 40 parts by weight, more preferably 2 to 30 parts by weight, and most preferably 3 to 20 parts by weight based on 100 parts by weight of the resin composition. If the content of the white inorganic particles is less than 1 part by weight, scattering light due to the inorganic particles is insufficient and sufficient light reflectivity can not be obtained. If the content is more than 40 parts by weight, the film forming stability remarkably decreases.

The method of blending the white inorganic particles in the polyester composition can be carried out by using the known methods (A) to (D).

Concretely, the method (A) is a method in which particles are added before the transesterification reaction or the end of the esterification reaction in the synthesis of the polyester, or the addition of the particles before the initiation of the polycondensation reaction. When added at the time of synthesis, the titanium dioxide particles are preferably prepared as a slurry dispersed in glycol, and then added to the reaction system. The method (B) is a method in which particles are added to a polyester and melt-kneaded, and the method (C) is a method of producing a master pellet in which a large amount of particles are added in the method And then kneading these and a polyester not containing an additive to make a predetermined amount of the additive. In addition, the method (D) can be carried out by directly using the master pellet (C). At this time, in the embodiment of the present invention, barium sulfate particles or titanium dioxide particles are mixed according to the method (c) or (d) in consideration of the dispersibility of the particles.

The raw material composition of the present invention may contain various additives such as fluorescent whitening agents, crosslinking agents, heat stabilizers, oxidation stabilizers, ultraviolet absorbents, organic lubricants, inorganic fine particles, fillers , An anti-light agent, an antistatic agent, a nucleating agent, a dye, a dispersing agent, a coupling agent and the like may be added.

Next, the second step of the manufacturing method of the present invention is to cool the unstretched sheet formed in the first step in the casting drum. Since this step is well known to those skilled in the art, detailed description is omitted.

Next, the third step of the present invention is a step of uniaxially stretching the cooled unoriented sheet to produce a uniaxially stretched film, wherein the cooled unoriented sheet is heated by a heating means such as a roll heating or an infrared heating And then stretching in the longitudinal direction to obtain a uniaxially stretched film. It is preferable that the stretching is performed using the main speed difference of two or more rolls and that the stretching temperature is set to a temperature not lower than the glass transition temperature (Tg) of the polyester resin and the stretching magnification is 3.0 to 5.0 times. When the draw ratio is less than 3.0 times, desired optical characteristics can not be obtained sufficiently, and when it is more than 5.0 times, the film formation stability is deteriorated.

Next, the fourth step of the manufacturing method of the present invention is a step of biaxially stretching a uniaxially stretched film to produce a biaxially stretched film, wherein the uniaxially stretched film in the longitudinal direction of the third step is continuously Is a biaxial stretching step in a direction perpendicular to the longitudinal direction (hereinafter also referred to as " width direction "). At this time, the transverse stretching is performed while raising the temperature to 5 to 70 캜 higher than the glass transition point (Tg) starting from a temperature higher than the glass transition point (Tg) of the polyester resin. The temperature rise in the widthwise stretching process may be continuous or may be stepwise (sequential), but the temperature is usually increased sequentially. For example, the width direction stretching zone of the tenter is divided into a plurality of portions along the film running direction, and the temperature is raised by flowing a heating medium at a predetermined temperature for each zone. At this time, the magnification of the widthwise stretching is set to 3.0 to 5.0 times the same magnification as that of the uniaxial stretching magnification. If the magnification is not set at the same magnification, thermal stability in the longitudinal direction and in the width direction is shifted to one side, and a void having a uniform shape can not be obtained.

Next, the fifth step of the manufacturing method of the present invention is a step of heat-treating the biaxially stretched film, wherein the biaxially stretched film is subjected to heat treatment such as heat fixing or thermal relaxation while running the film, . Thus, in order to complete the crystal orientation of the obtained biaxially stretched film and to impart planarity and dimensional stability, heat treatment is performed in the tenter at a temperature of 170 to 200 캜 for 1 to 30 seconds. When the heat treatment temperature is lower than 170 ° C, the crystal orientation is less, which adversely affects the strength of the film. If the heat treatment temperature is higher than 200 ° C, the Tg of the organic particles causing voids is exceeded, It is difficult to form a pore. After the film is cooled uniformly to room temperature, it is wound up to obtain a white polyester reflection film according to the present invention. At this time, during the heat treatment step, a relaxation treatment of 3 to 12% in the width direction or the longitudinal direction may be performed, if necessary.

The white polyester film produced as described above preferably has a reflectance of 101% or more.

Further, the white polyester film produced according to the above production method may have a single layer or a laminated structure of a multilayer coating of two or more layers.

Further, the present invention provides a reflective sheet using a white polyester film according to an aspect.

The white polyester film can be produced by controlling the retention time in the single tube, the stretching magnification and the heat fixing temperature by using organic particles having a particle size distribution of 1.0 or less to form uniform voids, and thereby to obtain a good overall physical property to the reflective sheet used for the liquid crystal display backlight unit And a stable film-forming property is realized.

Hereinafter, the structure and effect of the present invention will be described in more detail with reference to examples and comparative examples. However, this embodiment is intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

[Example 1]

Wherein 20% by weight of a copolymer resin of ethylene and norbornene as an amorphous cyclic olefin copolymer as a non-crystalline resin for the polyester resin and 80% by weight of a polyester resin in the raw material composition have a mean particle diameter And 20 parts by weight of inorganic particles having a particle size of 0.3 mu m were added to an extruder heated to 280 DEG C and molded into a sheet from a die. At this time, the residence time of the resin in the single tube was 10 minutes and the temperature of the resin was 300 占 폚. The additives such as the above-mentioned emergency polyolefin resin and inorganic particles were used in the form of master pellets previously compounded with a polyester resin. The average particle diameter of the polyolefin resin for emergency use in the master pellet was 1.5 占 퐉, the average particle diameter of the titanium dioxide particles was 0.2 占 퐉, and the particle diameter distribution was 1.0.

The molded sheet was cooled and solidified in a casting drum having a surface temperature of 20 DEG C to obtain an unstretched film, which was then heated to 3.0 times in the longitudinal direction and then cooled. Subsequently, the film was uniaxially stretched in the longitudinal direction while being held at both ends of the film by a clip, and the film was led into a tenter and stretched in a direction perpendicular to the length (width direction) at a magnification of 3.0 in a heated atmosphere.

Thereafter, heat fixation was carried out at 190 DEG C in a tenter, and the solution was cooled to room temperature to obtain a biaxial oriented film.

[Example 2]

The film was formed in the same manner as in Example 1 except that the film was stretched 4.0 times in the longitudinal direction and the transverse direction at the time of film formation in Example 1.

[Example 3]

The film was formed in the same manner as in Example 1 except that the film was stretched 5.0 times in the longitudinal direction and the transverse direction at the time of film formation in Example 1.

[Example 4]

The same procedure as in Example 1 was carried out except that, at the time of film formation in Example 1, the heat fixing temperature was 170 占 폚.

[Example 5]

The procedure of Example 1 was repeated except that the heat-setting temperature was changed to 200 ° C at the time of film formation in Example 1.

[Comparative Example 1]

The same procedure as in Example 1 was carried out except that the particle size distribution of the non-commercial polyolefin resin was 1.2 at the time of film formation in Example 1.

[Comparative Example 2]

The procedure of Example 1 was repeated except that the retention time of the resin in the short tube at the time of film formation in Example 1 was 11 minutes.

[Comparative Example 3]

The film was formed in the same manner as in Example 1, except that the film was stretched 2.0 times in the longitudinal direction and the transverse direction at the time of film formation in Example 1.

[Comparative Example 4]

The film was formed in the same manner as in Example 1, except that the film was stretched 6.0 times in the longitudinal direction and in the transverse direction at the time of film formation in Example 1.

[Comparative Example 5]

The procedure of Example 1 was repeated except that the heat-setting temperature was changed to 160 캜 at the time of film formation in Example 1.

[Comparative Example 6]

The procedure of Example 1 was repeated, except that the heat-setting temperature was changed to 210 캜 at the time of film formation in Example 1.

The properties of the polyester films according to Examples 1 to 5 and Comparative Examples 1 to 6 were measured through the following experimental examples, and the results are shown in Table 1 below.

[Experimental Example]

1. Measurement of particle size distribution

In each of Examples 1 to 5 and Comparative Examples 1 to 6, the film was section cut in the longitudinal direction and the width direction, and the center portion was measured 5 times at 5,000 magnification by SEM. The particle size of each particle was measured and data of 10% D10) from the maximum value and data (D90) of 10% from the maximum value were obtained, and the particle diameter distribution was obtained by the following formula.

Particle size distribution = (D90 - D10) / D50

2. Reflectance measurement

An integral sphere was attached to a spectrophotometer (UV-3600, manufactured by Shimazu Co., Ltd.) of the films prepared in Examples 1 to 5 and Comparative Examples 1 to 6, and 100% of a standard white plate (BaSO ₄ ) The reflectance was measured over the range of 400 to 700 nm. From the obtained data, the reflectance was read at intervals of 5 nm, and an average value was calculated to calculate an average reflectance.

3. Evaluation of void volume and pore uniformity

The cross sections of the films prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were measured at 5,000 magnification at 5,000 magnification and 5 times at the center of the film, The volume and uniformity were calculated using the following equations (1) and (2) as the average value of the X-axis and Z-axis lengths and the particle size of the organic particles in the pores.

(1) Volume of pores = 0.523 A ² C - 0.523 R ³

(2) Uniformity of air gap = A / C

A: X-axis length (탆)

C: Z-axis length of the gap (탆)

R: particle size of organic particles (占 퐉)

On the other hand, the total volume of the pores and the volume of the organic particles can be obtained as shown in Fig. 1, which is a schematic diagram of the organic particles inducing pores and pores in the spheroid type.

Total volume of pores = (4? / 3) a ² c? 4.19 a ² c (If 2a = A & 2c = C)

= (? / 6) A ² C? 0.523 A ² C

Volume of organic particles = ( ⁴ ? / 3) r ³ ? 4.19 r ³ ( ² r = R)

= (? / 6) R ³ ? 0.523R ³

4. Evaluation of Film Stability

If it is possible to form the film stably for one hour or more, it is judged as "? &Quot;, and breakage occurs within one hour, and if stable film formation is impossible, the film produced in Examples 1 to 5 and Comparative Examples 1 to 6, X ".

division Particle size
Distribution visit
time
(min) Stretching magnification Freeze heat
Temperature (℃) reflectivity
(%) air gap Film forming property Lengthwise Width direction Volume (탆 ³ ) Uniformity Example 1 1.0 10 3.0 3.0 190 101.4 1.8 3.2 O Example 2 1.0 10 4.0 4.0 190 102.9 19.9 6.5 O Example 3 1.0 10 5.0 5.0 190 103.0 27.8 8.7 O Example 4 1.0 10 3.0 3.0 170 101.7 21.1 4.1 O Example 5 1.0 10 3.0 3.0 200 101.1 11.3 3.8 O Comparative Example 1 1.2 10 3.0 3.0 190 100.3 2.1 3.4 X Comparative Example 2 1.0 11 3.0 3.0 190 99.2 0.9 2.4 X Comparative Example 3 1.0 10 2.0 2.0 190 100.5 0.7 1.5 O Comparative Example 4 1.0 10 6.0 6.0 190 103.2 31.6 10.5 X Comparative Example 5 1.0 10 3.0 3.0 160 101.8 17.2 4.4 X Comparative Example 6 1.0 10 3.0 3.0 210 98.4 0.3 2.6 O

As can be seen from the above Table 1, in the case of the polyester films prepared in Examples 1 to 5, all the uniform pores were found to be good in terms of optical characteristics and film-forming stability. In Comparative Example 1, non-uniform pores were formed due to a large particle size distribution as compared with Examples 1 to 5, so that reflectance was not good. In Comparative Example 2, too, particle re-aggregation occurred due to a long residence time, The reflectance was disadvantageous. Compared with Examples 1 to 5, Comparative Example 3 and Comparative Example 6 exhibited excellent film-forming stability due to a low draw ratio and high crystallinity, but the volume of pores was reduced, , But the film stability was not achieved due to frequent breakage of the film due to unfavorable stretching magnification. In Comparative Example 5, relatively good optical properties were obtained, but crystallization was less and the mechanical properties of the film were low, which was disadvantageous to the film formation.

Thus, the reflective sheet using the white polyester film according to the present invention can be used effectively for a backlight device for image display, a reflective sheet of a lamp reflector, a reflective sheet of an illumination device, a reflective sheet for an illuminated signboard, have.

It is to be understood that the present invention is not limited to the above embodiments and various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

10: Organic particles
20: Pore
30: X-axis radius of the gap
40: Z-axis radius of the gap
50: Radius of organic particles

Claims

In the white polyester film,
Satisfy the following equations (1) and (2)
(1) 1.0? 0.523 (A ² CR ³ )? 30.0
(2) 3.0? A / C? 9.0
A is the X axis length (탆) of the pores, C is the Z axis length (탆) of the pores, and R is the particle diameter (탆) of the organic particles.

The method according to claim 1,
Wherein the white polyester film comprises organic particles having a particle diameter of 0.5 to 2.5 占 퐉 which is non-compatible with the polyester resin.

3. The method of claim 2,
Wherein the organic particles have a glass transition temperature of from 120 to < RTI ID = 0.0 > 200 C. < / RTI >

3. The method of claim 2,
Wherein the particle diameter distribution of the organic particles is 1.0 or less.

3. The method of claim 2,
Wherein the retention time in the short tube of the organic particles is 10 minutes or less.

The method according to claim 1,
Wherein the white polyester film is stretched at a stretch ratio of 3.0 to 5.0 both in the longitudinal direction and in the transverse direction.

The method according to claim 1,
Wherein the heat-setting temperature of the white polyester film is 170 to 200 ° C.

The method according to claim 1,
Wherein the white polyester film has a reflectance of 101% or more.

A first step of melting and extruding a raw material composition containing a polyester resin, polyester and organic particles having a particle size distribution of not more than 1.0 as a main component, and molding the resultant into a sheet to form an unoriented sheet;
A second step of cooling the unstretched sheet in a casting drum,
A third step of stretching the cooled unoriented sheet by 3.0 to 5.0 times the uniaxial length to produce a uniaxially stretched film;
A fourth step of biaxially stretching the film in the same stretching ratio as the uniaxially stretched film to produce a biaxially stretched film,
And a fifth step of heat-treating the biaxially stretched film.

10. The method of claim 9,
Wherein the raw material composition in the first step has a retention time in a single tube of 10 minutes or less.

10. The method of claim 9,
Wherein the thermal fixing temperature of the heat treatment temperature in the fifth step is 170 to 200 占 폚.

A reflective sheet using the white polyester film according to any one of claims 1 to 8.