JP6862829B2 - White reflective film - Google Patents

Description

The present invention relates to a white reflective film for improving the brightness unevenness of a liquid crystal backlight. More specifically, the present invention relates to a white reflective film preferably used for an edge light type liquid crystal display backlight and a surface light source for lighting such as signboards and vending machines.

A backlight that illuminates a liquid crystal cell is used in a liquid crystal display, and is divided into a direct type and an edge light type. In the direct method, a large number of cold cathode fluorescent lamps and light emitting diodes (LEDs) are placed directly under the screen as a light source, which is mainly used for TV applications that require high brightness, while in the edge light method, the light source is placed at the edge of the screen. Since it is used as a surface light source by using a light guide plate, it can be made thinner, and it is used in tablets, notebook computers, desktop monitors, and TV applications that require thinning. As these reflective films for backlight, a porous white film formed by air bubbles is generally used (Patent Document 1). The reflective film used for the edge light type is required to have high reflection performance as well as compatibility with a light guide plate in particular. To solve the problem of uneven white spots (parts that are visually recognized as bright dots) caused by contact between the light guide plate and the white film and scratches on the printed part on the light guide plate due to vibration, resulting in uneven brightness. By improving the rigidity, reflection characteristics, etc. of the base white film to which spherical particles of appropriate hardness are applied, the uneven brightness on the screen is improved (Patent Documents 2 and 3).

Japanese Unexamined Patent Publication No. 8-262208 Japanese Unexamined Patent Publication No. 2003-92018 Japanese Patent No. 5578177

However, in recent years, there has been an increasing demand for long-term durability and impact durability of tablets and notebook computers, and a reflective film capable of withstanding a durability test called a heavy load dot test is required. By performing this local impact test, the unevenness of the surface of the reflective film and the light guide plate are in strong contact with each other, so that the surface of the light guide plate is scratched, resulting in uneven brightness.
In the prior art described in Patent Documents 2 and 3, it was possible to suppress the occurrence of scratches on the printing layer on the light guide plate due to uneven white spots (parts that are brightly visible in dots) and vibration, but tablets that have been demanded in recent years. And the impact durability of a laptop computer cannot be fully satisfied.

Therefore, an object of the present invention is to provide a film having impact resistance, excellent reflectivity, and a surface shape, which cannot be achieved by the above-mentioned conventional studies, at low cost.

The present invention employs any of the following means (1) to (9) in order to solve the above problems.
(1) A white reflective film for an edge-type backlight that satisfies the following (i) to (iii).
(I) A laminated film having at least two layers including a surface layer (A) and a base material 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 made of a polymer different from the polymer constituting the matrix.
(2) The white reflective film for an edge type backlight according to (1), wherein the interface thickness of the domain is 20 nm or more and 1,000 nm or less.
(3) The ratio of the length in the thickness direction: the length in the longitudinal direction when the shape of the domain described in (1) or (2) is observed in the cross section of the surface layer (A) is 1: 3 or more. The white reflective film for an edge type backlight according to (1) or (2), which is characterized by having a ratio of 1:50 or less.
(4) The white reflective film for an edge type backlight according to any one of (1) to (3), wherein the surface layer (A) contains particles and the particle content is less than 5% by mass.
(5) The white reflective film for an 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 an edge-type backlight according to any one of (1) to (5), which contains at least polyester or polyolefin having an alicyclic structure in the surface layer (A).
(7) The method according to any one of (1) to (6), wherein the surface layer (A) is composed of two or more kinds of polymers, and the difference in the temperature lowering crystallization temperature (Tmc) is 10 ° C. or higher and lower than 40 ° C. White reflective film for edge-type backlight.
(8) A backlight for a liquid crystal display configured by using 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.

According to the present invention, a polymer having a special structure is selected without adding particles to the surface layer (A) of the white reflective film on the side in contact with the light guide plate (the side facing the light guide plate during use). However, by controlling the surface roughness in a specific range, it is possible to provide a white reflective film that suppresses scratches on the light guide plate in the impact test of the backlight. The white reflective film obtained in the present invention suppresses scratches on the light guide plate when used for an edge light type backlight equipped with an LED light source and a surface light source for illumination, thereby causing uneven brightness more than ever. Can be reduced, which is preferable.

The present invention has made a diligent study on a white reflective film that suppresses scratches on the light guide plate in the above-mentioned problem, that is, an impact test on an edge light type backlight. As a result, the side of the white reflective film in contact with the light guide plate (reflection surface side during use). , A polymer having a special structure is selected without adding particles to the surface layer (A) on the side facing the light guide plate, and when the surface roughness is within a specific range, the above-mentioned problems can be solved at once. It should be noted that the brightness unevenness means the unevenness described below that is visually observed when the backlight is turned on.
(I) Streak-like unevenness (ii) Puddle-like unevenness (iii) Unevenness that appears as a dark part In addition, white spot unevenness is an ellipsoid with a major axis of less than 5 cm that is visually observed when the backlight is turned on. It means the point-like unevenness of.

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

[Basic configuration of white reflective film]
The white reflective film of the present invention is composed of a surface layer (A) and a base material layer (B) containing bubbles, and in consideration of ease and effect of film formation, a configuration of two or more layers is required, and a three-layer configuration is required. preferable. In particular, a form in which the base material layer (B) is protected by the surface layer (A), that is, a three-layer structure of the surface layer (A) / base material layer (B) / surface layer (A) is preferable. Further, when the number of layers is further increased, it is preferable that the core layer portion is the base material layer (B) and the surface layer portion on one side or both sides is the surface layer (A).

[Base material layer (B) containing air bubbles]
The white reflective film of the present invention is required to have air bubbles inside the base material layer (B) for whiteness and reflection characteristics, but is incompatible with polyester or polypropylene constituting the base material layer (B). Bubbles can be formed by biaxially stretching the mixture containing various components.

As examples of these production methods, examples of polyesters containing barium sulfate as an incompatible component described in Japanese Patent No. 3734172 and polypropylene containing titanium oxide as an incompatible component described in JP2012-158167 are disclosed. Specific examples of organic substances in organic incompatible resins include linear, demarcated or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene and cyclopentadiene. This polyolefin may be a homopolymer or a copolymer, and more than two kinds may be used in combination. Among these, polypropylene and polymethylpentene are preferably used as the crystalline polyolephy, and cycloolefin copolymers and the like are preferably used as the amorphous polyolefin in terms of excellent transparency and heat resistance. ..

In the present invention, the amount of the incompatible component added is preferably 5 to 50% by mass, preferably 5 to 30% by mass, when the total mass of the base material layer (B) containing bubbles is 100% by mass. More preferably. If the content of the incompatible component is less than 5% by mass, bubbles are not sufficiently generated inside the film, and the whiteness and light reflection characteristics may be inferior. On the other hand, if the content of the incompatible component exceeds 50% by mass, the strength of the film is lowered, breakage is likely to occur during stretching, and inconvenience such as powder generation during post-processing may occur. .. By setting the content within such a range, sufficient whiteness, reflectivity, and lightness can be exhibited.

[Surface roughness of surface layer (A)]
In the white reflective film of the present invention, the central surface average roughness (SRa) of the surface layer (A) surface needs to be 90 nm or more and less than 300 nm, preferably 120 to 300 nm, most preferably 120 to 250 nm. is there. If it is less than 90 nm, the glossiness becomes high, dust adhering to the surface becomes easy to see, and uneven brightness, particularly white spots, are likely to occur in the edge light type backlight. On the other hand, when it is 300 nm or more, the surface of the surface layer (A) is scraped during the vibration test with the light guide plate, and the problem of transfer to the light guide plate dots is likely to occur.

The average roughness of the central surface of the surface of the surface layer (A) is a value measured by the following method.
Based on JIS B0601 (2001), the central surface average roughness (SRa) was measured using a stylus type surface roughness meter (model number: ET 4000A) manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 5 measurements was used as the value.
・ Radius of stylus tip: 0.1 μm
・ Needle load: 100 μN
・ Measurement 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]
The surface layer (A) needs to have a domain made of a polymer different from the polymer constituting the matrix so that the brightness unevenness generated when it comes into contact with the light guide plate and the brightness unevenness after the impact test do not occur. The domain can be easily recognized from the contrast of the cross-sectional SEM of the surface layer (A).

When it does not have a domain made of a polymer, for example, when the central surface average roughness (SRa) of the present application is achieved with inorganic particles, the light guide plate is scratched in the impact test and uneven brightness occurs. Further, when the central surface average roughness (SRa) is achieved with the organic particles, the organic particles fall off in the impact test and adhere to the light guide plate, causing uneven brightness.

The interface thickness of the domain in the present invention is preferably 20 nm or more and 1,000 nm or less. If it is less than 20 nm, voids are likely to occur between the matrix and the domain, and the matrix may be rolled up and adhered to the light guide plate in the impact test, resulting in uneven brightness. Further, if it is larger than 1,000 nm, it may be too compatible with each other 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 above-mentioned range of domain thickness, the transesterification reaction can be controlled by using a transesterification reaction inhibitor, or the compatibility can be controlled by using a compatibilizer.

The shape of the domain in the present invention is preferably a substantially flat shape co-stretched together with the matrix. Specifically, when the cross section of the surface layer (A) is observed, the length in the thickness direction: the length in the longitudinal direction. The ratio of the above is preferably 1: 3 or more and 1:50 or less. If it is less than 1: 3, the domain is not co-stretched and voids are likely to occur, and the matrix may be rolled up and adhered to the light guide plate in the impact test, resulting in uneven brightness. On the other hand, if it is larger than 1:50, it may be stretched too much together with the matrix and unevenness may not be formed. A more preferable range of the domain shape is 1: 5 or more and 1:50 or less, and more preferably 1:10 or more and 1:50 or less.

In order to achieve the above-mentioned domain shape, 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 between the polymers constituting the matrix and the domain to be 10 ° C. or higher and lower 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 steep protrusion formed by particles or the like, but a gentle protrusion, so that the aggression to the light guide plate is high. It is low and can significantly suppress brightness unevenness and brightness unevenness after impact test.

The thickness of the surface layer (A) is preferably 4 μm or more and 12 μm or less. If it is less than 4 μm, the film may be torn during film formation and the handleability may be deteriorated, or sufficient surface unevenness may not be formed. Further, if it is thicker than 12 μm, the brightness may decrease. More preferably, it is 6 μm or more and 12 μm or less.

[Low temperature crystallization temperature (Tmc)]
In the surface layer (A) in the present invention, it is preferable that the main protrusions have a polymer as a core so that uneven brightness does not occur after the impact test. In order to form protrusions centered on the polymer, it is preferable that the polymer is composed of two or more kinds of polymers and the layer (A) is formed without being compatible with each other in the extruder or the film forming process.

The criteria for not being compatible is, for example, that a difference in the temperature-decreasing crystallization temperature (Tmc) of the surface layer (A) is observed. Specifically, the temperature-lowering crystallization temperature (Tmc) is preferably 10 ° C. or higher and 40 ° C. or lower. If the temperature exceeds 40 ° C., cold crystallization is promoted, resulting in hard surface irregularities, which may cause a problem of scraping the light guide plate. More preferably, it is 15 ° C. or higher and lower than 35 ° C.

Examples of the method of suppressing the compatibility include, in the case of polyester, a method of adding a so-called transesterification inhibitor that suppresses the activity of the polymer polymerization catalyst, a method of suppressing the thermal history in the film forming process, and the like.

[Polyester or polyolefin with alicyclic structure]
Of the two or more types of polymers in the present invention, it is preferable that at least one type contains polyester or polyolefin having an alicyclic structure. Above all, when polyester or polyolefin having an alicyclic structure having different compatibility is used, appropriate surface irregularities are likely to be formed. As such an alicyclic structure, a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, and a cyclohexane ring are preferable. Dimethyl terephthalate as an acid component, 1,3-cyclopropanediol, 1,3-cyclobutanediol, 1,3-cyclopentanediol, 1,4-cyclohexanedimethanol as a diol component, and 200 ppm butyltintris (2-). The polycondensation reaction can be carried out in the presence of (ethylhexanoate) to obtain polyester pellets or polyolefin pellets having an alicyclic structure.

As a polyester having a cyclobutane ring, "TRITAN" (registered trademark) (manufactured by Eastman Chemical Company), as a polyester having a cyclohexane ring, "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company), as a polyolefin having a cyclopentane ring. Can preferably use "Zeonoa" (registered trademark) (manufactured by Nippon Zeon Co., Ltd.) and the like.

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 with respect to 100% by mass. Particularly preferably, it is 15% by mass or more and 35% by mass or less. If it is less than 10% by mass, uneven brightness in the edge light type backlight, particularly white spots, is likely to occur.

Among the two or more types of polymers in the present invention, as the polymer other than polyester or polyolefin having an alicyclic structure, a diol such as ethylene glycol or butanediol is copolymerized with a dicarboxylic acid component such as terephthalic acid or isophthalic acid. Polyester can be used. Of these, polyethylene terephthalate (PET), which is a polymer of ethylene glycol and terephthalic acid, is preferably used. In addition to the PET, a copolymer PET (PET-I) of ethylene glycol, isophthalic acid, and terephthalic acid can also be used for the purpose of imparting film-forming stability and facilitating the formation of surface irregularities. The amount of PET-I added is preferably 20% by weight or more and less than 50% by weight when the surface layer (A) is 100% by weight. If it 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. Further, if it is 50% by weight or more, the heat resistance may decrease.

[Particle content]
The particles may be contained in an amount of less than 5% by mass as long as the effects of the present invention are not impaired. If the particles are contained in an amount of 5% by mass or more, the light guide plate may be damaged, the polymer may be peeled off from the particles, or the particles themselves may fall off to contaminate the light guide plate. The range of the more preferable particle content is 4% by mass or less, more preferably 3% by 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, silica and the like. Examples of the organic particles include acrylic, polystyrene, nylon and the like.
[Gloss difference]
The difference in glossiness between 20 ° and 85 ° of the surface layer (A) in the present invention is preferably 50% or more. Since the difference in glossiness is large, light can be efficiently returned to the front of the display as a light-reflecting film. It is more preferably 65% or more, still more preferably 80% or more.
[Film formation method]
An example of the method for producing a biaxially stretched film of the present invention will be described, but the present invention is not limited to such an example.

Regarding the surface layer (A), a mixture containing polyester or polypropylene, polyester (B) having an alicyclic structure, and various additives as necessary is sufficiently vacuum-dried and supplied to a heated extruder. The polyester (B) having an alicyclic structure may be added by using a master chip produced by uniformly melt-kneading in advance, or by directly supplying the polyester (B) to a kneading extruder.
Regarding the base material layer (B) containing bubbles, a mixture containing components incompatible with polyester or polypropylene and, if necessary, a dispersant is sufficiently vacuum-dried and supplied to a heated extruder. The addition of incompatible components may be carried out using a master chip produced by uniformly melt-kneading in advance, or may be directly supplied to a kneading extruder.

Further, in the case of melt extrusion, it is preferable that after filtering with a filter having a mesh of 40 μm or less, the melt sheet is introduced into a T-die base and extruded to obtain a melt sheet.

This molten sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to prepare an unstretched A / B / A 3-layer film. The unstretched three-layer film was led to a roll group heated to 70 to 120 ° C., preferably 70 to 100 ° C., stretched 2.5 to 4 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and 20. Cool with a group of rolls at a temperature of ~ 50 ° C.

Subsequently, the film is guided to the tenter while grasping both ends with clips, and stretched 2.5 to 4 times in the direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated to a temperature of 90 to 150 ° C. ..

The stretching ratio is 2.5 to 4 times in each of the longitudinal direction and the width direction, but the area ratio (longitudinal stretching ratio x lateral stretching ratio) needs to be 9 to 16 times, and is 10 to 12 times. More preferably. If the area magnification is less than 9 times, the formation of bubbles and irregularities of the obtained white reflective film and the film strength become insufficient, and if the area magnification exceeds 16 times, tearing is likely to occur during stretching.

In order to complete the crystal orientation of the obtained biaxially stretched film and impart dimensional stability, heat treatment was subsequently carried out in a tenter at a temperature of 150 to 240 ° C. for 1 to 30 seconds, and after slow cooling uniformly. The white reflective film of the present invention can be obtained by cooling the film to room temperature, and then, if necessary, performing a corona discharge treatment or the like in order to further enhance the adhesion with other materials and winding the film. During the heat treatment step, it is preferable to perform a relaxation treatment of 3 to 12% in the width direction or the longitudinal direction.

[Edge light type backlight]
The white reflective film of the present invention is suitably used for an edge light type backlight. In the edge light type backlight, for example, the white reflective film of the present invention and the light guide plate are incorporated in this order in a housing having irregularities, and the white film is incorporated so that the surface layer (A) side faces the light guide plate. Is done. Further, a light source such as an LED is installed at the edge portion of the light guide plate. Further, a diffuser plate, a prism, or the like may be installed on the front surface of the light guide plate (on the side opposite to the white reflective film).

[Use of white reflective film]
The white reflective film of the present invention is used for a backlight, and among them, it can be suitably used for an edge light type liquid crystal display backlight and a surface light source for lighting such as a signboard or a vending machine.

In addition, it can also be suitably used as a reflector constituting various surface light sources, a sealing film or a back sheet of a solar cell module that requires reflective characteristics. Other paper alternatives: cards, labels, stickers, home delivery slips, image-receiving paper for video printers, inkjet, image-receiving paper for bar code printers, posters, maps, dust-free paper, display boards, white boards, heat-sensitive transfer, offset printing, telephone Base materials for receiving sheets used for various printing records such as cards and IC cards, building materials such as wallpaper, lighting equipment and indirect lighting equipment used indoors and outdoors, members mounted on automobiles, railways, aircraft, etc., for circuit materials, etc. It can also be used as an electronic component of.

[Measurement of physical properties and evaluation method of effect]
Measurement method The evaluation method of the physical property value and the evaluation method of the effect of the present invention are as follows.

A. Surface Roughness Based on JIS B0601 (2001), the central surface average roughness (SRa) was measured using a stylus type surface roughness meter (model number: ET 4000A) manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 5 measurements was used as the value.
・ Radius of stylus tip: 0.1 μm
・ Needle load: 100 μN
・ Measurement length: 1.0 mm
・ Cutoff value: 0.25 mm
B. A cross section of a domain white reflective film sample was cut out, and the surface layer (A) was magnified 2,000 to 10,000 times using a field emission scanning electron microscope "JSM-6700F" (manufactured by JEOL Ltd.). The domain was observed from the cross-sectional photograph taken. It was judged that the case where there is a co-stretched substantially flat shade portion without a clear interface has a domain composed of a polymer different from the polymer constituting the matrix. On the other hand, those having voids formed around them were judged to be particles.
Then, if a domain consisting of a polymer, to create a super-thin section of the surface layer (A), then stained with OsO _4, a transmission electron microscope TEM, were observed interfacial thickness of shape and domain domains.
For the shape of the domain, the length in the thickness direction: the length in the longitudinal direction was measured by the distance between two points, and the ratio was obtained. Similarly, the interface of the domain (width of the shaded portion) was measured at the distance between the two points and used as the interface thickness. For the shape of the domain and the interface thickness of the domain, the average value measured at 5 points was used.

C. Particle content A small piece obtained by tapering the surface of the white reflective film was used as a sample, and the amount of ash obtained based on JIS K7220-1: 2006 was measured. The same operation was measured with another five white reflective films, and the average value of the five was taken as the particle content.

D. Temperature down crystallization temperature (Tmc)
Weigh 5 mg of small pieces from the surface of the white reflective film with a taper into a sample pan, and use the differential scanning calorimetry device "Robot DSC-RDC220" manufactured by Seiko Electronics Co., Ltd. in accordance with JIS K7122 (1987). The disk session "SSC / 5200" was used for data analysis, and the measurement was carried out as follows. Incidentally, for the temperatures listed below, the average value measured using five film samples was used.

It was heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min, held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately subsequently, the temperature was raised again from room temperature to 300 ° C. at a heating rate of 20 ° C./min, held in that state for 5 minutes, and then lowered from 300 ° C. to 25 ° C. at a rate of 20 ° C./min. The endothermic / exothermic peaks were measured in each of the temperature raising and lowering processes except the quenching process.
The exothermic peak temperature in the process of lowering the temperature from 300 ° C. to 25 ° C. at a rate of 20 ° C./min was defined as the temperature lowering crystallization temperature (Tmc).
Among the temperature-decreasing crystallization temperatures, the high exothermic peak temperature was defined as Tmc1 and the lower exothermic peak temperature was defined as Tmc2, and the difference in temperature-decreasing crystallization temperature (Tmc) was defined by the following equation.
Difference in temperature-decreasing crystallization temperature (Tmc) = Tmc1-Tmc2
E. Compatibility with the light guide plate (i) Dirt on the light guide plate A 40-inch LCD TV (KDL-40EX700 manufactured by Sony Corporation) 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 × 50 cm, and the diagonal length was 102.2 cm. A light guide plate is taken out from this backlight, the light guide plate is cut out into a 5 cm square, the uneven portion of the light guide plate and the surface layer (A) of the white reflective film of the present invention are overlapped, and 500 g is placed on the opposite side of the surface layer (A). The weight of the above is placed, and the surface layer (A) of the white reflective film of the present invention is reciprocated by 3 cm × 5 so as to rub. Then, the surface layer (A) of the 5 cm square light guide plate in contact with the surface of the white reflective film of the present invention was observed with a microscope, and the evaluation results were as follows.
A: Excellent (no deposits visible)
B: Good (If you look closely, you can see the deposits)
F: Inferior (adhesion can be seen)
The above A and B were accepted.

(Ii) Heavy load dot test A light guide plate taken out from the above backlight is cut out into a 5 cm square, and the uneven portion of the light guide plate and the surface layer (A) of the white reflective film of the present invention are overlapped with each other on the opposite side of the surface layer (A). A SUS columnar rod having a diameter of 1 mm is used to perform a dot test 1000 times with a load of 200 g. Then, the surface of the light guide plate to which the surface layer (A) of the white reflective film was in contact was observed with a microscope, and the evaluation results were as follows.
A: Excellent (no scratches visible)
B: Good (scratches can be seen when observed closely)
F: Inferior (scratches can be seen)
The above A and B were accepted.

(Iii) Luminance unevenness The reflective film laminated in the new Hisense Japan Co., Ltd. 32-inch liquid crystal TV LHD32K15JP backlight was changed to the white reflective film of the present invention and turned on. After waiting for 1 hour in that state to stabilize the light source, what could be visually recognized as uneven brightness under a lighting environment of 500 Lx or a dark environment was observed, and the following evaluation results were obtained. The luminance unevenness referred to here is due to a bright spot caused by contact between the reflective film and the light guide plate.
A: Excellent (No uneven brightness can be seen in both a 500Lx lighting environment and a dark environment.)
B: Good (Uneven brightness is visible in a dark environment of 500 Lx, but uneven brightness is not visible in a lighting environment.)
F: Inferior (brightness unevenness can be seen in both a 500 Lx lighting environment and a dark environment.)
The above A and B were accepted.

F. Film-forming property When film-forming in Examples and Comparative Examples, film tearing occurs only once / day or less, and film tearing occurs only once / day or less if there is no process contamination due to particle shedding or the like. However, B is the one in which the accumulation of dirt on the roll surface can be visually confirmed, F is the one in which the film tear occurs 2 times / day or more and 3 times / day or less, and B or more film forming property is required for mass production. Yes, if it is A or more, there is a further cost reduction effect.
G. Glossiness Using a digital variable angle gloss meter UGV-5B (manufactured by Suga Test Instruments Co., Ltd.), measurement was performed from the surface layer (A) side of the white reflective film according to JIS Z-8741 (1997). The measurement condition is that the 60 ° glossiness is a value when the measurement conditions are the incident angle = 60 ° and the light receiving angle = 60 °. Similarly, the 20 ° glossiness is the incident angle = 20 ° and the light receiving angle = The 20 ° and 85 ° glossiness are values when the incident angle = 85 ° and the light receiving angle = 85 °.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited thereto.

(material)
・ Surface layer (A)
Using terephthalic acid as the acid component and ethylene glycol as the diol component, they are added to polyester pellets from which antimony trioxide (polymerization catalyst) can be obtained so as to be 300 ppm in terms of antimony atom, and a polycondensation reaction is carried out to obtain the ultimate viscosity. Polyethylene terephthalate pellets (PET) having 0.63 dl / g and a carboxyl terminal group amount of 40 equivalents / ton were obtained.
A polyethylene terephthalate / isophthalate copolymer (PET-I) was obtained by adding isophthalic acid in the same manner.
Polybutylene terephthalate (PBT) was obtained by adding butanediol in the same manner.

-Dimethyl terephthalate as a polyester acid component having an alicyclic structure, CHDM (cyclohexanedimethanol) as a diol component, and polycondensation reaction in the presence of 200 ppm butyltin tris (2-ethylhexanoate) to copolymerize. Obtained polyester.
In addition, products on the market (for example, "TRITAN" (manufactured by Eastman Chemical Company) as the alicyclic structure a, "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) as the alicyclic structure b), alicyclic. “Zeonoa” (registered trademark) (manufactured by Nippon Zeon Corporation) was used as the structure c.
These are characterized by a copolymerization component constituting a 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 (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont Co., Ltd.), 33 mol% of 1,4-cyclohexanedimethanol with respect to ethylene glycol. 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET), 20 parts by mass of poly (5-methyl) norbornene, and 10 parts by weight of rutile-type titanium oxide are adjusted and mixed, and dried at 180 ° C. for 3 hours. After that, it was supplied to the 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" (registered trademark) (manufactured by Eastman Chemical Company), particles. Using silica with a particle size of 0.6 μm for a, silica with a particle size of 3.5 μm for particle b, and sulfur burr with a particle size of 0.6 μm for particle c, they were mixed at the ratios shown in Table 1 and vacuum dried at 180 ° C. for 3 hours. After that, the polymer was supplied to the extruder A heated to 280 ° C., and these polymers were laminated through a laminating device so as to form an A layer / B layer / A layer (8 μm / 137 μm / 8 μm), and formed into a sheet from a T die. Molded. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., vertically stretched 3.4 times in the longitudinal direction, and cooled by the roll group at 21 ° C. .. Subsequently, both ends of the vertically stretched film were gripped by clips and guided to a tenter, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Then, the film was heat-fixed at 200 ° C. in a tenter, cooled slowly, and then cooled to room temperature to obtain a biaxially stretched laminated film. Table 1 shows the physical characteristics of the base material for light reflection.
As described above, the white reflective film of the present invention was able to form a stable film, and exhibited excellent characteristics in the surface shape (heavy load dot test, light guide plate stain, reduction of luminance unevenness).

(Example 9)
(Surface layer (A))
Amorphous cycloolefin resin A (manufactured by Nippon Zeon Co., Ltd., trade name "ZEONOR 1430R", density (ASTMD792): 1.01 g / cm ³ , glass transition temperature Tg (JISK7121): 133 ° C. pellets and polypropylene resin ( Pellets of the trade name "Novatec PPEA9" manufactured by Japan Polypropylene Corporation were mixed at a mass ratio of 30:70 and supplied to the extruder A by the above method.

(Base material layer (B) containing bubbles)
Polypropylene resin (manufactured by Nippon Polypro Co., Ltd., trade name "Novatec PP FY6HA" pellets and titanium oxide (manufactured by KRONOS, trade name "KRONOS2230", rutile-type titanium oxide, Al, Si surface treatment, TiO ₂ content 96. A mixture of 0% (manufacturing method: chlorine method) at a mass ratio of 50:50 was supplied to the extruder B by the above method.

(Making a white reflective film)
In each extruder, after melt-kneading at 200 ° C. and 230 ° C., they are merged with a T-die for two types and three layers so as to have a three-layer structure of layer (A) / layer (B) / layer (A). It was extruded into a sheet and cooled and solidified to form a laminated sheet. The obtained laminated sheet was roll-stretched twice to MD at a temperature of 130 ° C., and then further rolled at 130 ° C.
A white reflective film having a thickness of 150 μm (resin layer (A): 8 μm, resin layer (B): 134 μm) was obtained by biaxial stretching by tenter stretching to TD three times. Table 1 shows the physical characteristics of the base material for light reflection.
As described above, the white reflective film of the present invention was able to form a stable film, and exhibited excellent characteristics in the surface shape (heavy load dot test, light guide plate stain, reduction of luminance unevenness).

(Examples 10 to 12)
57 parts by mass of PET, 5 parts by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont Co., Ltd.), 33 mol% of 1,4-cyclohexanedimethanol with respect to ethylene glycol. 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET), 20 parts by mass of poly (5-methyl) norbornene, and 10 parts by weight of rutile-type titanium oxide are adjusted and mixed, and dried at 180 ° C. for 3 hours. After that, it was supplied to the extruder B heated to 270 to 300 ° C. (layer B).

On the other hand, as the layer (A), PET, PET-I, and an alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used, mixed at the ratio shown in Table 1, and mixed at 180 ° C. for 3 hours. After vacuum drying, the polymer was supplied to an extruder A heated to 280 ° C., and these polymers were laminated through a laminating device so as to form an A layer / B layer / A layer, and formed into a sheet from a T die. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., vertically stretched 3.4 times in the longitudinal direction, and cooled by the roll group at 21 ° C. .. Subsequently, both ends of the vertically stretched film were gripped by clips and guided to a tenter, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Then, the film was heat-fixed at 200 ° C. in a tenter, slowly cooled uniformly, cooled to room temperature, and biaxially stretched to obtain a laminated film having a thickness of 150 μm. Further, by adjusting the discharge amounts of the extruder A and the extruder B, the total thickness was adjusted to be 150 μm, and the surface layer thickness was adjusted to be 8 μm to 12 μm.

Table 1 shows the physical characteristics of the obtained laminated film as a base material for light reflection. As described above, the white reflective film of the present invention was able to form a stable film, and exhibited excellent characteristics in the surface shape (heavy load dot test, light guide plate stain, reduction of luminance unevenness).

(Comparative Examples 1 to 6)
In a composite film-forming apparatus having a main extruder and a sub-extruder, film formation was performed by changing the composition shown in Table 2.
In Comparative Examples 1 and 6, since the main protrusions were particles, the light guide plate was scratched. In Comparative Examples 3 to 6, the alicyclic structure a "TRITAN" (manufactured by Eastman Chemical Company), the alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company), and the alicyclic structure d "ECOZEN". (Manufactured by SK chemicals)) was mixed at the ratio shown in Table 2 and supplied to the extruder A under the same raw materials and conditions as in Example 1 to prepare a white reflective film. , SRa was small and uneven brightness occurred, and in Comparative Example 4, SRa was large and the light guide plate was contaminated.

(Comparative Examples 7 and 8)
57 parts by mass of PET, 5 parts by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont Co., Ltd.), 33 mol% of 1,4-cyclohexanedimethanol with respect to ethylene glycol. 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET), 20 parts by mass of poly (5-methyl) norbornene, and 10 parts by weight of rutile-type titanium oxide are adjusted and mixed, and dried at 180 ° C. for 3 hours. After that, it was supplied to the extruder B heated to 270 to 300 ° C. (layer B).

On the other hand, as the layer (A), PET, PET-I, and an alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used, mixed at the ratio shown in Table 1, and mixed at 180 ° C. for 3 hours. After vacuum drying, the polymer was supplied to an extruder A heated to 280 ° C., and these polymers were laminated through a laminating device so as to form an A layer / B layer / A layer, and formed into a sheet from a T die. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., vertically stretched 3.4 times in the longitudinal direction, and cooled by the roll group at 21 ° C. .. Subsequently, both ends of the vertically stretched film were gripped by clips and guided to a tenter, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Then, the film was heat-fixed at 200 ° C. in a tenter, slowly cooled uniformly, cooled to room temperature, and biaxially stretched to obtain a laminated film having a thickness of 150 μm. Further, by adjusting the discharge amounts of the extruder A and the extruder B, the total thickness was adjusted to be 150 μm and the surface layer thickness was adjusted to 3 μm.

Table 2 shows the physical characteristics of the obtained laminated film as a base material for light reflection. SRa was small and uneven brightness occurred.

(Comparative Examples 9 to 10)
In a composite film-forming apparatus having a main extruder and a sub-extruder, film formation was performed by changing the composition shown in Table 2.
Since the main protrusion is the particle c, the light guide plate is scratched.

The white reflective film of the present invention is used for a backlight, and among them, it can be suitably used for an edge light type liquid crystal display backlight and a surface light source for lighting such as a signboard or a vending machine. In addition, it can also be suitably used as a reflector constituting various surface light sources, a sealing film or a back sheet of a solar cell module that requires reflective characteristics. Other paper alternatives: cards, labels, stickers, home delivery slips, image-receiving paper for video printers, inkjet, image-receiving paper for bar code printers, posters, maps, dust-free paper, display boards, white boards, heat-sensitive transfer, offset printing, telephone Base materials for receiving sheets used for various printing records such as cards and IC cards, building materials such as wallpaper, lighting equipment and indirect lighting equipment used indoors and outdoors, members mounted on automobiles, railways, aircraft, etc., for circuit materials, etc. It can also be used as an electronic component of.

Claims (8)

A white reflective film for edge-type backlight that satisfies the following (i) to (iv).
(I) A laminated film having at least three layers including a surface layer (A) and a base material 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 made of a polymer different from the polymer constituting the matrix.
(Iv) The surface layer (A) contains 10% by mass or more and 40% by mass or less of polyester or polyolefin having an alicyclic structure with respect to 100% by mass of the total mass of the surface layer (A). The white reflective film for an edge-type backlight according to claim 1, wherein the interface thickness of the domain is 20 nm or more and 1,000 nm or less. The ratio of the length in the thickness direction: the length in the longitudinal direction when the shape of the domain according to claim 1 or 2 is observed in the cross section of the surface layer (A) is 1: 3 or more and 1:50 or less. The white reflective film for an edge-type backlight according to claim 1 or 2, wherein the white reflective film is provided. The white reflective film for an edge-type backlight according to claim 1 or 2, wherein the surface layer (A) contains particles and the particle content thereof is less than 5% by mass. The white reflective film for an edge-type backlight according to claim 1, wherein the difference in glossiness between 20 ° and 85 ° of the surface layer (A) is 50% or more. The white reflective film for an edge-type backlight according to claim 1, wherein the surface layer (A) is composed of two or more kinds of polymers, and the difference in temperature-decreasing crystallization temperature (Tmc) is 10 ° C. or higher and lower than 40 ° C. A backlight for a liquid crystal display configured by using the film according to claim 1. The backlight for a liquid crystal display according to claim 7, wherein the light source is a light emitting diode.