KR20180033118A - White reflective film - Google Patents

Abstract

(Problem) It is economical, excellent in film formability, whiteness, reflectivity, light weight, and surface shape, and by using this white reflective film, a backlight excellent in luminance characteristics and excellent compatibility with other members can be provided at low cost.
A white reflective film for an edge-type backlight satisfying the following (i) - (iii).
(i) a laminated film of two or more layers including at least a surface layer (A) and a base layer (B) containing bubbles.
(ii) the central surface average roughness (SRa) of the surface of the surface layer (A) is 90 nm or more and less than 300 nm.
(iii) the surface layer (A) has a domain composed of a polymer different from the polymer constituting the matrix.

Description

White reflective film

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a white reflective film for improving luminance unevenness of a liquid crystal backlight. And more particularly to a white reflective film suitably used for a backlight for a liquid crystal display of an edge light type, a planar light source for illumination such as a signboard, a vending machine, and the like.

BACKGROUND ART In a liquid crystal display, a backlight illuminating a liquid crystal cell is used, and it is divided into a direct-down type and an edge light type. In the direct-down type, a cold cathode tube or a light-emitting diode (LED) is disposed as a light source directly under the screen and is mainly used for TV applications requiring high brightness. In the edge light system, a light source is disposed at the end of the screen And it is adopted as a tablet light source, a notebook, a desktop monitor, and a TV which is required to be ultra thin. As these backlight reflecting films, porous white films formed by bubbles are generally used (Patent Document 1). Reflective films used in the edge light type are required not only to have high reflection performance, but also to be compatible with the light guide plate. In order to solve the problem that the printed portion on the light guide plate is scratched due to white dot unevenness (a portion visually brightly seen) caused by the contact between the light guide plate and the white film until now, and the unevenness of luminance is caused by the vibration, And improving the rigidity, reflection characteristics, and the like of the base material white film to improve brightness unevenness on the screen (Patent Documents 2 and 3).

Japanese Patent Laid-Open No. 8-262208 Japanese Patent Application Laid-Open No. 2003-92018 Japanese Patent No. 5578177

Recently, however, demands for long-term durability and impact durability of tablets and notebooks have been intensified, and a reflective film capable of withstanding the durability test described in the middle-load spot test has been demanded. There is a problem that scratches are generated on the surface of the light guide plate due to strong contact between the concavities and convexities on the surface of the reflective film and the light guide plate, resulting in luminance unevenness.

In the prior art described in Patent Documents 2 and 3, it was possible to suppress the generation of scratches on the printed layer on the light guide plate due to white dot unevenness (brightly visible portions) or vibration. However, Durability can not be sufficiently satisfied.

Therefore, an object of the present invention is to provide an inexpensive film having an impact resistance durability, an excellent reflectivity, and a surface shape that can not be attained in the above-mentioned conventional studies.

The present invention adopts any one of the following means (1) to (9) in order to solve the above problems.

(1) A white reflective film for an edge-type backlight satisfying the following (i) - (iii).

(i) a laminated film of two or more layers including at least a surface layer (A) and a base layer (B) containing bubbles.

(ii) the central surface average roughness (SRa) of the surface of the surface layer (A) is 90 nm or more and less than 300 nm.

(iii) a polymer having a domain in which the surface layer (A) is different from the polymer constituting the matrix.

(2) The white reflective film for edge-type backlight according to (1), wherein an interface thickness of the domain is 20 nm or more and 1,000 nm or less.

(3) When the shape of the domains described in (1) or (2) in (1) or (2) is a ratio of the length in the thickness direction to the length in the longitudinal direction when the cross section of the surface layer (A) 3 or more and 1: 50 or less.

(4) The white reflective film for edge-type backlight according to any one of (1) to (3), wherein the surface layer (A) contains particles and the content thereof is less than 5 mass%.

(5) The white reflective film for edge-type backlight according to any one of (1) to (4), wherein the difference in glossiness between 20 ° and 85 ° of the surface layer (A) is 50% or more.

(6) The white reflective film for edge-type backlight according to any one of (1) to (5), wherein the surface layer (A) contains at least a polyester or polyolefin having an alicyclic structure.

(7) The white reflective layer for edge-type backlight according to any one of (1) to (6) above, wherein the surface layer (A) is composed of two or more kinds of polymers and the difference in crystallization temperature (Tmc) film.

(8) A backlight for a liquid crystal display, comprising the film according to any one of (1) to (7).

(9) The backlight for a liquid crystal display according to (8), wherein the light source is a light emitting diode.

(Effects of the Invention)

According to the present invention, it is possible to select a polymer having a specific structure without adding particles to the surface layer (A) on the side of the white reflecting film facing the light guide plate (on the side of the reflecting surface and the light guide plate in use) It is possible to provide a white reflective film which suppresses the scratch adhesion to the light guide plate in the impact test of the backlight. The white reflective film obtained in the present invention is suitable for use in an edge light type backlight including an LED light source and a planar light source for illumination because it suppresses scratch adhesion to the light guide plate and can reduce luminance unevenness more than ever.

The present invention has been extensively studied on the above-mentioned problem, that is, the white reflecting film which suppresses the scratch adhesion to the light guide plate in the impact test of the edge light type backlight. As a result, (The side opposite to the reflecting surface side and the light guide plate) without adding particles to the surface layer (A), and the surface roughness is within a specific range.

Incidental luminance unevenness means unevenness described below which is visually observed when the backlight is lit.

(i) streak shape stains

(ii) a puddle-like stain

(iii) stain appearing to be dark

The white dot unevenness means a dot-like unevenness of an ellipsoid having a diameter of less than 5 cm, which is visually observed when the backlight is turned on.

Hereinafter, the white reflecting film according to the present invention will be described in detail.

[Basic structure of white reflective film]

The white reflecting film of the present invention is composed of a surface layer (A) and a base layer (B) containing bubbles. In consideration of easiness and effect of film formation, two or more layers are required. Particularly, the three-layer structure of the surface layer (A) / the base layer (B) / the surface layer (A) is preferable in the form in which the base layer (B) is protected in the surface layer (A). Further, in the case of multi-layered structure, it is more preferable that the deep layer is the base layer (B), and the surface layer portion on one side or both sides is the surface layer (A).

[Base layer (B) containing bubbles]

The white reflecting film of the present invention is required to have bubbles in the substrate layer (B) for whiteness and reflection characteristics, but it is preferable to contain a polyester or polypropylene constituting the base layer (B) Bubbles can be formed by stretching.

As examples of these production methods, there are disclosed examples of polyesters having barium sulfate described in Japanese Patent No. 3734172 as a component for use as an emulsion, and polypropylene having titanium dioxide as an emulsion component as disclosed in Japanese Patent Application Laid-Open Publication No. 2012-158167. In the case of the nonreinforced resin, specific examples of the organic material include linear, pulverized or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, cyclopentadiene and the like. The polyolefin may be a homopolymer or copolymer thereof, or two or more of them may be used in combination. Among these, polyolefins such as polypropylene and polymethylpentene are preferable in view of transparency and excellent heat resistance, and amorphous polyolefins such as cycloolefin copolymer are preferably used.

In the present invention, the addition amount of the non-functional phosphorus component is preferably 5 to 50 mass%, more preferably 5 to 30 mass%, based on 100 mass% of the total mass of the base material layer (B) . When the content of the nonconjugated phosphorous component is less than 5% by mass, bubbles are not sufficiently generated inside the film, resulting in poor whiteness and light reflection characteristics. On the other hand, when the content of the nonconjugated phosphorus component exceeds 50 mass%, the strength of the film is lowered, and the film tends to be broken at the time of stretching, which may cause problems such as generation of powder at the time of post-processing. When the content is within this range, sufficient whiteness, reflectivity and light weight can be exhibited.

[Surface roughness of surface layer (A)

In the white reflecting film of the present invention, the center plane average roughness (SRa) of the surface layer (A) surface should be 90 nm or more and less than 300 nm, preferably 120 to 300 nm, and most preferably 120 to 250 nm to be. When the thickness is less than 90 nm, the degree of gloss increases, dust adhering to the surface tends to be visually observed, and unevenness of brightness in the edge-light type backlight, particularly white dots, is likely to occur. On the other hand, when the thickness is 300 nm or more, the surface of the surface layer (A) is scraped off at the time of vibration test with the light guide plate, and the problem of transferring to the light guide plate dot is apt to occur.

The center-plane average roughness of the surface of the surface layer (A) is a value measured by the following method.

The center plane average roughness (SRa) was measured by a contact type surface roughness meter (Model number: ET 4000A) manufactured by Kosaka Laboratory Ltd. based on JIS B0601 (2001). The conditions were as follows, and the values were taken as an average value of five measurements.

· Radius of stylus tip: 0.1㎛

· Pushing load: 100 μN

Measuring length: 1.0 mm

Cutoff value: 0.25 mm

(The surface layer (A) has a domain composed of a polymer different from the polymer constituting the matrix)

It is necessary that the surface layer (A) has a domain made of a polymer different from the polymer constituting the matrix so as not to cause uneven luminance or uneven luminance after the impact test that occurs when the light guide plate comes into contact with the light guide plate. The domain can be easily recognized from the contrast of the cross-sectional SEM of the surface layer (A).

For example, when the center plane average roughness (SRa) of the present invention is achieved by using inorganic particles, for example, luminance unevenness occurs in the light guide plate due to scratching in the impact test. In addition, when the center-plane average roughness (SRa) is achieved in the organic particles, the organic particles fall off in the impact test, and adhere to the light guide plate, resulting in uneven brightness.

The interface thickness of the domain in the present invention is preferably 20 nm or more and 1,000 nm or less. When the thickness is less than 20 nm, voids tend to be formed between the matrix and the domains, and the matrix may be peeled off in the impact test and may adhere to the light guide plate to cause luminance unevenness. On the other hand, if it is larger than 1,000 nm, it may be too commercialized and sufficient surface roughness may not be obtained. A more preferable range of the domain thickness is 50 nm or more and 1,000 nm or less, and more preferably 50 nm or more and 500 nm or less.

In order to achieve the domain thickness range described above, a method of controlling the transesterification reaction using an ester exchange reaction inhibitor and a method of controlling the compatibility using a compatibilizing agent can be used.

The domain shape in the present invention is preferably a substantially flat shape coextruded together with the matrix. More specifically, when the cross section of the surface layer (A) is observed, the ratio of the length in the thickness direction to the length in the length direction is 1: 3 Or more and 1: 50 or less. If the ratio is less than 1: 3, the domain is not subjected to the performance enhancement, voids tend to be formed, and the matrix may be peeled off in the impact test, and may adhere to the light guide plate to cause luminance unevenness. If it is larger than 1:50, there is a possibility that unevenness is not formed due to excessive stretching with the matrix. A more preferable range of the domain shape is 1: 5 or more and 1:50 or less, more preferably 1:10 or more and 1:50 or less.

In order to achieve the shape of the domain described above, there is a method of controlling the Tg difference of the polymer constituting each of the matrix and the domain. Specifically, it is preferable to control the Tg difference of the polymer constituting each of the matrix and the domain to be 10 ° C or more and less than 40 ° C.

The surface roughness shape formed by having a domain made of a polymer different from the polymer constituting the matrix is not a sharp protrusion formed by particles or the like but a gentle protrusion, so that the aggressiveness to the light guide plate is low and the luminance unevenness after the impact test Can be greatly suppressed.

The thickness of the surface layer (A) is preferably from 4 탆 to 12 탆. If the thickness is less than 4 탆, cracking at the time of film formation may be large, resulting in reduced handleability or insufficient surface irregularities. If it is thicker than 12 탆, the luminance may be lowered. More preferably not less than 6 mu m and not more than 12 mu m.

[Temperature-decreasing crystallization temperature (Tmc)]

In the surface layer (A) of the present invention, it is preferable that the main protrusions are made of the polymer as nuclei so as to prevent uneven luminance after the impact test. In order to form the projections having the nucleus of the polymer, two or more kinds of polymers are preferably used, and it is preferable that the layer (A) is formed such that they are not used in an extruder or a film-forming process.

As a criterion which is not commercially available, for example, a difference in the temperature-drop crystallization temperature (Tmc) of the surface layer (A) is observed. Concretely, it is preferable that the crystallization temperature for cooling (Tmc) is 10 ° C or higher and 40 ° C or lower. If the temperature is higher than 40 ° C, the cold crystallization is promoted and the surface of the light guide plate may be uneven. More preferably not less than 15 ° C and less than 35 ° C.

As a method for suppressing commercial use, a method of adding a so-called transesterification inhibitor which inhibits the activity of a polymer polymerization catalyst in the case of a polyester or a method of suppressing thermal history in a film formation process can be mentioned.

[Polyester or polyolefin having alicyclic structure]

It is preferable that at least one of the two or more kinds of polymers in the present invention contains a polyester or polyolefin having an alicyclic structure. Among them, when a polyester or polyolefin having an alicyclic structure having a different compatibility is used, appropriate surface unevenness tends to be formed. The alicyclic structure is preferably a cyclopropane ring, a cyclopropane ring, a cyclopentane ring, or a cyclohexane ring. 1,3-cyclopentanediol, 1,3-cyclopentanediol, 1,4-cyclohexanedimethanol as a diol component and 200 ppm of butyltin tris (2- Ethylhexanoate) to obtain polyester pellets or polyolefin pellets having an alicyclic structure.

Examples of the polyester having a cyclic butane ring include "TRITAN" (trade name) (manufactured by Eastman Chemical Company), "EASTAR" (trade name) manufactured by Eastman Chemical Company) as a polyester having a cyclohexane ring, a polyolefin having a cyclopentane ring Quot; ZEONOR "(registered trademark) (manufactured by Zeon Corporation) can be suitably used.

The amount of the polyester (B) having an alicyclic structure is not particularly limited, but the total mass of the surface layer (A) is preferably 10% by mass or more and 40% by mass or less, more preferably 15% by mass or less, Or more and 35 mass% or less. When the amount is less than 10% by mass, unevenness of luminance in the edge light type backlight, particularly a white spot, is likely to occur.

As the polymer other than the polyester or polyolefin having an alicyclic structure among the two or more kinds of polymers in the present invention, a polyester in which a diol such as ethylene glycol or butanediol and a dicarboxylic acid component such as terephthalic acid or isophthalic acid are copolymerized can be used have. Among them, it is preferable to use polyethylene terephthalate (PET) which is a polymer of ethylene glycol and terephthalic acid. In addition to the above-mentioned PET, a copolymerized PET (PET-I) of ethylene glycol, isophthalic acid and terephthalic acid may also be used for imparting film-forming stability or for facilitating formation of surface unevenness. The amount of PET-I added is preferably 20% by weight or more but less than 50% by weight based on 100% by weight of the surface layer (A). If the content is less than 20% by weight, the effect of film forming stability may be low or the effect of forming surface irregularities may be low. When the content is more than 50% by weight, the heat resistance may be lowered.

[Particle content]

But may contain less than 5 mass% of the particles within the range not to impair the effect of the present invention. When the particles are contained in an amount of 5% by mass or more, scratches may be generated in the light guide plate, the polymer may be peeled off from the particle as a starting point, or the particles themselves may be detached to contaminate the light guide plate. A more preferable range of the content of the particles is 4 mass% or less, more preferably 3 mass% or less.

The particles of the present invention refer to inorganic particles or organic particles. Examples of the inorganic particles include titanium dioxide, calcium carbonate, barium sulfate, and silica. Examples of the organic particles include acrylic, polystyrene, and nylon.

[Gloss Tea]

The difference in glossiness between 20 DEG and 85 DEG of the surface layer (A) in the present invention is preferably 50% or more. It is possible to return light to the front of the display efficiently as a light reflecting film by a large difference in glossiness. More preferably 65% or more, and even more preferably 80% or more.

[Film forming method]

One example of the method for producing the biaxially oriented film of the present invention will be described, but the present invention is not limited to this example.

For the surface layer (A), a mixture containing polyester or polypropylene and polyester (B) having an alicyclic structure and, if necessary, various additives is thoroughly vacuum-dried and fed to a heated extruder. The addition of the polyester (B) having an alicyclic structure may be carried out using a master chip prepared by homogeneously melt-kneading the mixture, or may be directly supplied to a kneading extruder.

For the substrate layer (B) containing bubbles, a mixture containing polyester or polypropylene and a non-commercial component and, if necessary, a dispersant is thoroughly vacuum dried and fed to a heated extruder. The addition of the nonconjugated phosphorus component may be carried out by using a master chip prepared by homogeneously melt-kneading, or may be supplied directly to a kneading extruder.

Further, in the melt extrusion, it is preferable to obtain a molten sheet by extrusion molding after being filtered through a filter having a mesh of 40 탆 or less and then introduced into a T-die metal.

This molten sheet is closely cooled and solidified on a drum cooled to a surface temperature of 10 to 60 DEG C by static electricity to produce an unstretched A / B / A three-layer film. The unstretched three-layer film is led to a group of rolls heated to 70 to 120 캜, preferably 70 to 100 캜, stretched 2.5 to 4 times in the longitudinal direction (longitudinal direction, that is, the film advancing direction) Lt; 0 > C.

Subsequently, both ends of the film are guided by a tenter while grasping with a clip, and stretched 2.5 to 4 times in a direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated at a temperature of 90 to 150 캜.

The elongation magnification is 2.5 to 4 times in the longitudinal direction and in the width direction, respectively, but the area magnification (longitudinal stretching magnification x transverse stretching magnification) is required to be 9 to 16 times, more preferably 10 to 12 times. If the area magnification is less than 9 times, the formation of the bubbles and unevenness of the obtained white reflective film and the film strength become insufficient, and if the area magnification exceeds 16 times, cracking tends to occur at the time of stretching.

In order to complete the crystal orientation of the biaxially stretched film obtained and to provide dimensional stability, the film is subsequently subjected to heat treatment at a temperature of 150 to 240 DEG C for 1 to 30 seconds in a tenter, uniformly cooled to room temperature, If necessary, a corona discharge treatment or the like is carried out in order to further improve the adhesion to other materials, and the film can be wound to obtain a white reflecting film of the present invention. It is preferable to perform relaxation treatment of 3 to 12% in the width direction or the longitudinal direction during the heat treatment step.

[Edge light type backlight]

The white reflecting film of the present invention is suitably used for an edge light type backlight. In the edge light type backlight, for example, a white reflecting film and a light guide plate of the present invention are mounted in this order on a housing having projections and depressions, and the white film is mounted so that the side of the surface layer (A) faces the light guide plate. A light source such as an LED is provided at an edge portion of the light guide plate. Further, a diffusion plate, a prism, or the like may be provided on the front surface (opposite to the white reflective film) of the light guide plate.

[Use of white reflective film]

The white reflecting film of the present invention is used for a backlight, but it can be suitably used for an edge light type backlight for a liquid crystal display and a surface light source such as a signboard or a vending machine.

In addition, it can be suitably used as a reflecting film constituting various surface light sources and a sealing film or a back sheet of a solar cell module requiring reflection characteristics. In addition to paper, card substitute cards, labels, seals, courier slips, video printer receivers, inkjet, barcode printers, posters, maps, cardboard, signboards, whiteboards, thermal transfer, offset printing, It can also be used as an electronic part such as a base material of a receptacle sheet used for various printing records such as a card, a construction material such as a wallpaper, a lighting device used indoors and outdoors, an indirect lighting device, a member mounted on an automobile, a railroad, have.

[Measurement of physical properties and evaluation method of effect]

How to measure

The evaluation method and evaluation method of the physical property value of the present invention are as follows.

A. Surface roughness

The center plane average roughness (SRa) was measured by a contact type surface roughness meter (Model number: ET 4000A) manufactured by Kosaka Laboratory Ltd. based on JIS B0601 (2001). The conditions were as follows, and the value was taken as the average value of five measurements.

· Radius of stylus tip: 0.1㎛

· Pushing load: 100 μN

Measuring length: 1.0 mm

Cutoff value: 0.25 mm

B. Domain

The cross section of the white reflective film sample was cut out, and the domain (A) was magnified at 2,000 to 10,000 magnifications using a field emission scanning electron microscope "JSM-6700F" did. It was judged that the case where there was a roughly flat-shaped dense portion having no clear interface and had a coarse interface had a domain made of a polymer different from the polymer constituting the matrix. On the other hand, it was judged that the voids were formed around the particles.

Subsequently, in the case of a domain consisting of a polymer, an ultrathin slice of the surface layer (A) was prepared and stained with OsO ₄ , and then the shape of the domain and the interface thickness of the domain were observed with a transmission electron microscope TEM.

The shape of the domain was determined by measuring the length in the thickness direction: the length in the length direction by the distance between two points. Similarly, the interface of the domain (the width of the shaded portion) was measured as the distance between two points to obtain the interface thickness. The shape of the domain and the interface thickness of the domain are the average values obtained by measuring five points.

C. Particle content

A small piece obtained by cutting the surface of the white reflecting film with a taper was used as a sample, and the amount of the resultant obtained in accordance with JIS K7250-1: 2006 was measured. The same operation was performed on the other five white reflective films, and the average of the five values was used as the particle content.

D. Decrease in crystallization temperature (Tmc)

A small piece of the white reflective film surface was tapered and weighed to 5 ml on a sample pan and subjected to differential scanning calorimetry "Robot DSC-RDC220" manufactured by Seiko Instruments & Electronics Ltd. according to JIS K7122 (1987) The disk session "SSC / 5200" was used to perform the measurement in the following manner. Incidentally, the temperatures listed below were the average values measured by using five film samples.

Heated from 25 占 폚 to 300 占 폚 at a temperature raising rate of 20 占 폚 / min, held for 5 minutes in this state, and quenched to 25 占 폚 or lower. The temperature was elevated from room temperature to 300 ° C at a temperature rising rate of 20 ° C / minute, held for 5 minutes in this state, then decreased from 300 ° C to 25 ° C at a rate of 20 ° C / minute, The endothermic / exothermic peaks were measured during the temperature rise and the temperature decrease except for the respective temperatures.

The exothermic peak temperature in the process of lowering the temperature from 300 DEG C to 25 DEG C at the rate of 20 DEG C / minute was defined as the temperature-lowering crystallization temperature (Tmc).

The exothermic peak temperature at a high temperature and the exothermic peak temperature at a low temperature were defined as the differences between the temperature-decreasing crystallization temperatures (Tmc) and Tmc2 by the following equation.

Difference in crystallization temperature during cooling (Tmc) = Tmc1-Tmc2

E. Stability with LGP

(i) Pollution of light guide plate

A 40-inch liquid crystal television (manufactured by Sony Corporation, KDL-40EX700) was disassembled and an edge light type backlight using an LED as a light source was taken out. The size of the light emitting surface was 89 cm x 50 cm, and the diagonal length was 102.2 cm. The light guide plate was taken out from the backlight to cut the light guide plate to 5 cm x 5 cm and the surface layer (A) of the white reflection film of the present invention was superimposed on the irregular portion of the light guide plate to put a weight of 500 g on the opposite side of the surface layer The surface layer (A) of the white reflecting film of the present invention is reciprocated 3 cm x 5 times to rub. Thereafter, the surface layer (A) surface of the light guide plate of 5 cm x 5 cm which was in contact with the surface of the white reflecting film of the present invention was observed with a microscope, and the following evaluation results were obtained.

A: Good (no deposit is visible)

B: Good (Appearance is observed when observed well)

F: Lacking (attachment visible)

The above A and B were regarded as acceptable.

(ii) Heavy load test

The light guide plate drawn out from the backlight was cut out to a size of 5 cm x 5 cm and a concavo-convex portion of the light guide plate and the surface layer (A) of the white reflection film of the present invention were superimposed one on top of the other, The test is carried out 1000 times at a weight of 200 g. Thereafter, the surface of the light guide plate where the surface layer (A) of the white reflecting film was in contact was observed with a microscope, and the evaluation results were as follows.

A: Good (scratch not visible)

B: Good (scratch is seen when observed well)

F: Down (Scratch visible)

The above A and B were regarded as acceptable.

(iii) Brightness stain

The reflection film attached in the new HISENSE JAPAN CORPORATION Type 32 liquid crystal TV LHD32K15JP backlight was changed to the white reflection film of the present invention and lighted. The light source was stabilized by waiting for 1 hour in this state, and it was observed that it could be visually recognized as luminance unevenness under an illumination condition of 500 Lx or a dark environment, and the evaluation results were as follows. Incidentally, the brightness unevenness referred to herein is due to the bright spot caused by the contact between the reflective film and the light guide plate.

A: Good (no luminance speckle in 500Lx lighting environment and under cow environment)

B: Good (luminance unevenness is seen under a 500Lx dark environment, but luminance unevenness is not seen under an illumination environment)

F: Lacking (500Lx illumination environment, all cows environment shows uneven brightness)

The above A and B were regarded as acceptable.

F. Film forming property

In the examples and comparative examples, only film fragments were produced once or less per day when the film was formed, A without process contamination due to particle dropout or the like, and film cracking occurred only once or less per day. It is necessary to form film B which can confirm the accumulation of the contamination visually, film F to occur at a rate of 2 times / day to 3 times / day or less, and B at the time of mass production, and more than A, .

G. Glossiness

(A) side of the white reflecting film was measured according to JIS Z-8741 (1997) using a digital gloss gloss meter UGV-5B (manufactured by Suga Test Instruments Co., Ltd.). The measurement conditions are the values when the measurement conditions are 60 ° for the incident angle and 60 ° for the incident angle of 60 °. Likewise, the 20 ° gloss is 20 ° for the angle of incidence = 20 °, Is a value when the incident angle is 85 DEG and the light reception angle is 85 DEG.

Example

Hereinafter, the present invention will be described in more detail by way of examples and the like, but the present invention is not limited thereto.

(Raw material)

· Surface layer (A)

Terephthalic acid as an acid component and ethylene glycol as a diol component were added to polyester pellets in which antimony trioxide (polymerization catalyst) was obtained in an amount of 300 ppm in terms of antimony atom, and the resultant mixture was subjected to a polycondensation reaction to give an intrinsic viscosity of 0.63 dl / g To obtain a polyethylene terephthalate pellet (PET) having a carboxyl terminal group amount of 40 equivalents / ton.

Polyethylene terephthalate / isophthalate copolymer (PET-I) was obtained by adding isophthalic acid in the same manner.

By adding butanediol in the same manner, polybutylene terephthalate (PBT) was obtained.

· Polyester with alicyclic structure

Dimethyl terephthalate as an acid component and CHDM (cyclohexanedimethanol) as a diol component were subjected to a polycondensation reaction in the presence of 200 ppm of butyltin tris (2-ethylhexanoate) to obtain a copolymer polyester.

EASTAR " (trade name, manufactured by Eastman Chemical Company) as the alicyclic structure b), "ZEONOR (trade name, manufactured by Eastman Chemical Company) as the alicyclic structure c, (Registered trademark) (manufactured by Zeon Corporation)) was used.

These are characteristic of a copolymer component constituting the diol component. For example, EASTAR has a cyclohexane ring and TRITAN has a cyclobutane ring component.

(Examples 1 to 8)

57 parts by mass of PET, 5 parts by mass of a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG) (trade name: DU PONT-TORAY CO., LTD., Hytrel) 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 4-cyclohexane dimethanol was copolymerized in an amount of 33 mol%, 20 parts by mass of poly (5-methyl) norbornene and 10 parts by mass of rutile- ° C for 3 hours, and then supplied to an extruder B heated to 270 to 300 ° C (layer B).

On the other hand, as the layer A, PET, PET-I, alicyclic structure a "TRITAN" (manufactured by Eastman Chemical Company), alicyclic structure b "EASTAR" (manufactured by Eastman Chemical Company) Silica barium sulfate having particle diameter of 0.6 탆 and particle b having particle diameter of 3.5 탆 were used in particle b and vacuum dried at 180 캜 for 3 hours and then supplied to extruder A heated to 280 캜 , And these polymers were laminated through a lamination device so as to form an A layer / a B layer / an A layer (8 mu m / 137 mu m / 8 mu m), and formed into a sheet from a T die. Further, this film was led to a group of rolls heated to 85 to 98 占 폚 by cooling and solidifying the film by cooling with a cooling drum at a surface temperature of 25 占 폚 and longitudinally stretched 3.4 times in the longitudinal direction, and cooled in a roll group of 21 占 폚. Subsequently, both ends of the longitudinally stretched film were gripped with a clip, and were led into a tenter and stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated at 120 캜. Thereafter, heat setting at 200 DEG C was carried out in the tenter, uniformly cooled down to room temperature, and a biaxially stretched laminated film was obtained. The physical properties of the light-use substrate are shown in Table 1.

As described above, the white reflecting film of the present invention was able to form a film stably, and exhibited excellent surface characteristics (heavy load spot test, light guide plate contamination, luminance unevenness reduction).

(Example 9)

(Surface layer (A))

(Manufactured by Japan Polypropylene Corporation, product of Zeon Corporation, trade name "ZEONOR 1430R", density: ASTM D792: 1.01 g / cm 3, glass transition temperature Tg (JIS K7121) Novatec PPEA9 " in a mass ratio of 30:70 was fed to extruder A by the above-mentioned method.

(Base layer (B) containing bubbles)

(KRONOS 2230, rutile type titanium oxide, Al, Si surface treatment, content of TiO ₂ : 96.0%, manufactured by Japan Polypropylene Corporation, trade name: Novataek PP FY6HA, Chlorine method) at a mass ratio of 50:50 was fed to the extruder B by the above-mentioned method.

(Preparation of white reflective film)

After melt-kneading at 200 ° C and 230 ° C in each extruder, the resultant was joined to a two-kind three-layer T-die, and extruded into a three-layer structure of layer (A) / layer (B) / layer Cooled and solidified to form a laminated sheet. The resulting laminated sheet was subjected to 2-fold roll stretching at a temperature of 130 占 폚 in MD and then biaxially stretched by TD stretching three times in a TD at 130 占 폚 to obtain a laminate sheet having a thickness of 150 占 퐉 (resin layer (A): 8 占 퐉, ): 134 m) was obtained. The physical properties of the light-use substrate are shown in Table 1.

As described above, the white reflecting film of the present invention was able to form a film stably, and exhibited excellent surface characteristics (heavy load spot test, light guide plate contamination, luminance unevenness reduction).

(Examples 10 to 12)

57 parts by mass of PET, 5 parts by mass of a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG) (trade name: DU PONT-TORAY CO., LTD., Hytrel) 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 4-cyclohexane dimethanol was copolymerized in an amount of 33 mol%, 20 parts by mass of poly (5-methyl) norbornene and 10 parts by mass of rutile titanium oxide, For 3 hours, and then supplied to an extruder B heated to 270 to 300 DEG C (layer B).

On the other hand, PET, PET-I and alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used as the layer A in the proportions shown in Table 1, vacuum dried at 180 ° C. for 3 hours , And this was fed to an extruder A heated to 280 DEG C, and these polymers were laminated through a laminating apparatus so as to form an A layer / a B layer / an A layer, and the sheet was formed from a T die. Further, this film was led to a group of rolls heated to 85 to 98 占 폚, which was cooled and solidified in a cooling drum having a surface temperature of 25 占 폚, and was longitudinally stretched 3.4 times in the longitudinal direction, and cooled in a roll group of 21 占 폚. Subsequently, both ends of the longitudinally stretched film were gripped with a clip, and were led into a tenter and stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated at 120 캜. Thereafter, heat setting at 200 DEG C was carried out in the tenter, uniformly cooling down to room temperature, and a biaxially stretched laminated film having a thickness of 150 mu m was obtained. Further, by adjusting the discharge amounts of the extruder A and the extruder B, the total thickness was adjusted to 150 mu m to adjust the surface layer thickness to 8 mu m to 12 mu m.

The physical properties of the resultant laminated film as a light-mediated substrate are shown in Table 1. As described above, the white reflecting film of the present invention was able to form a film stably, and exhibited excellent surface characteristics (heavy load spot test, light guide plate contamination, luminance unevenness reduction).

(Comparative Examples 1 to 6)

In the composite film-forming apparatus having the main extruder and the secondary extruder, the composition shown in Table 2 was changed to perform film formation.

In Comparative Examples 1 and 6, scratches were generated on the light guide plate because the main protrusions were particles. EASTAR " (trade name, manufactured by Eastman Chemical Company) as the alicyclic structure b and "ECOZEN" (manufactured by SK chemicals) as the alicyclic structure d in Comparative Examples 3 to 6) Were mixed in the ratios shown in Table 2 and supplied to the extruder A under the same conditions as in Example 1 to prepare a white reflecting film. As a result, in Comparative Examples 2, 3 and 5, the SRa was small and luminance unevenness occurred, 4, SRa was large and light guide plate contamination occurred.

(Comparative Examples 7 and 8)

57 parts by mass of PET, 5 parts by mass of a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG) (trade name: DU PONT-TORAY CO., LTD., Hytrel) 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 4-cyclohexane dimethanol was copolymerized in an amount of 33 mol%, 20 parts by mass of poly (5-methyl) norbornene and 10 parts by mass of rutile- ° C for 3 hours, and then supplied to an extruder B heated to 270 to 300 ° C (layer B).

On the other hand, PET, PET-I and alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used as the layer A in the proportions shown in Table 1, vacuum dried at 180 ° C. for 3 hours , And this was fed to an extruder A heated to 280 DEG C, and these polymers were laminated through a laminating apparatus so as to form an A layer / a B layer / an A layer, and the sheet was formed from a T die. Further, this film was led to a group of rolls heated to 85 to 98 占 폚, which was cooled and solidified in a cooling drum having a surface temperature of 25 占 폚, stretched 3.4 times in the machine direction in the longitudinal direction, and cooled in a roll group of 21 占 폚. Subsequently, both ends of the longitudinally stretched film were led to a tenter while being gripped by a clip, and stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated at 120 캜. Thereafter, heat setting at 200 占 폚 was carried out in the tenter, uniformly thawed, and then cooled to room temperature to obtain a biaxially stretched laminated film having a thickness of 150 占 퐉. Further, by adjusting the discharge amounts of the extruder A and the extruder B, the total thickness was adjusted to 150 占 퐉 and the surface layer thickness was adjusted to 3 占 퐉.

The physical properties of the resultant laminated film as a light-mediated substrate are shown in Table 2. The SRa was small, resulting in luminance unevenness.

(Comparative Examples 9 to 10)

In the composite film-forming apparatus having the main extruder and the secondary extruder, the composition shown in Table 2 was changed to perform film formation.

Scratches were generated on the light guide plate because the main projection was particle c.

(Industrial applicability)

The white reflecting film of the present invention is used for a backlight, but it can be suitably used for an edge light type backlight for a liquid crystal display and a surface light source for a signboard or a vending machine. In addition, it can be suitably used as a reflecting film constituting various surface light sources and a sealing film or a back sheet of a solar cell module requiring reflection characteristics. In addition, there are various kinds of paper substitute, such as card, label, seal, courier slip, image printer, inkjet, image printer, barcode printer, poster, map, It can also be used as an electronic part such as a substrate of a receptacle sheet used for various printing records such as an IC card, a building material such as a wallpaper, a lighting device used indoors and outdoors, a member mounted on an automobile, a railroad, .

Claims (9)

A white reflective film for an edge-type backlight satisfying the following (i) - (iii).
(i) a laminated film of two or more layers including at least a surface layer (A) and a base layer (B) containing bubbles.
(ii) the central surface average roughness (SRa) of the surface of the surface layer (A) is 90 nm or more and less than 300 nm.
(iii) the surface layer (A) has a domain composed of a polymer different from the polymer constituting the matrix. The method according to claim 1,
Wherein an interface thickness of said domain is 20 nm or more and 1,000 nm or less. 3. The method according to claim 1 or 2,
The edge type backlight according to any one of claims 1 to 3, wherein the ratio of the length in the thickness direction to the length in the longitudinal direction when the cross section of the surface layer (A) is observed is from 1: 3 to 1: White reflective film for. 3. The method according to claim 1 or 2,
A white reflective film for edge-type backlight in which the surface layer (A) contains particles and the content of the particles is less than 5 mass%. The method according to claim 1,
A white reflective film for an edge-type backlight in which the difference in glossiness between 20 ° and 85 ° of the surface layer (A) is 50% or more. The method according to claim 1,
A white reflective film for an edge-type backlight comprising at least a polyester or polyolefin having an alicyclic structure in the surface layer (A). The method according to claim 1,
Wherein the surface layer (A) is composed of two or more kinds of polymers and the difference in crystallization temperature (Tmc) at a temperature lower than the temperature is not less than 10 占 폚 and less than 40 占 폚. A backlight for a liquid crystal display, comprising the film according to claim 1. 8. The method of claim 7,
A backlight for a liquid crystal display in which the light source is a light emitting diode.