KR102590694B1 - white reflective film - Google Patents

Abstract

(Problem) To provide an inexpensive backlight with excellent economic efficiency, film forming properties, whiteness, reflectivity, lightness, and surface shape, and excellent luminance characteristics and compatibility with other members by using this white reflective film.
(Solution) White reflective film for edge-type backlight that satisfies the following (i) to (iii).
(i) It is a laminated film of two or more layers including at least a surface layer (A) and a base layer (B) containing air bubbles.
(ii) The average roughness (SRa) of the center 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.

Description

white reflective film

The present invention relates to a white reflective film that improves luminance unevenness of a liquid crystal backlight. More specifically, it relates to a white reflective film that is suitably used for backlights for edge light-type liquid crystal displays and surface light sources for lighting signs, vending machines, etc.

Liquid crystal displays use backlights to illuminate the liquid crystal cells, and are divided into direct and edge light types. In the direct method, a large number of cold cathode tubes or light emitting diodes (LEDs) are placed directly below the screen as a light source and are mainly used for TV applications that require high brightness, while in the edge light method, the light source is placed at the end of the screen and a light guide plate is used. Since it is a surface light source, it can be made ultra-thin, so it is used in tablets, laptops, desktop monitors, and TV applications that require ultra-thinness. As these reflective films for backlights, porous white films formed by air bubbles are generally used (Patent Document 1). Reflective films used in edge light types require not only high reflective performance but also compatibility with the light guide plate. Until now, we have applied spherical particles of appropriate hardness to address the problems of white spot stains (parts that are brightly visible as dots) caused by contact between the light guide plate and white film, or luminance stains caused by scratches on the printed area on the light guide plate due to vibration. By improving the rigidity, reflection characteristics, etc. of the base white film, an attempt is made to improve luminance unevenness on the screen (Patent Documents 2 and 3).

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

However, recently, the demand for long-term durability and impact durability of tablets and laptops has become stronger, and there is a demand for reflective films that can withstand durability tests such as heavy load spot tests. In this localized impact test, the uneven surface of the reflective film and the light guide plate come into strong contact, causing scratches on the surface of 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 occurrence of scratches on the printed layer on the light guide plate due to white dot stains (parts that are brightly visible as dots) or vibration, but shock resistance in tablets and laptops has recently been requested. Durability cannot be fully satisfied.

Therefore, the object of the present invention is to provide, at low cost, a film having impact resistance, durability, excellent reflectivity, and surface shape that could not be achieved in the above-described conventional studies.

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

(1) White reflective film for edge-type backlight that satisfies the following (i) to (iii).

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

(ii) The surface center surface average roughness (SRa) 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 domain has an interface thickness of 20 nm or more and 1,000 nm or less.

(3) In (1) or (2), when the shape of the domain described in (1) or (2) is observed in the cross section of the surface layer (A), the ratio of the length in the thickness direction to the length in the longitudinal direction is 1: White reflective film for edge-type backlight, characterized in that the ratio is 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 particle content is less than 5% by mass.

(5) The white reflective film for edge-type backlight according to any one of (1) to (4), wherein the difference in gloss 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 polyester or polyolefin having an alicyclic structure.

(7) White reflection for edge-type backlight according to any one of (1) to (6), wherein the surface layer (A) is composed of two or more types of polymer, and the difference in cooling crystallization temperature (Tmc) is 10°C or more and less than 40°C. film.

(8) A backlight for a liquid crystal display constructed 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 with 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 reflective surface side during use, the side facing the light guide plate), and a specific range is selected. By controlling the surface roughness of , it is possible to provide a white reflective film that suppresses scratches from adhering to the light guide plate in a backlight impact test. The white reflective film obtained in the present invention is suitable for use in edge light backlights equipped with LED light sources and surface light sources for illumination, as it can reduce luminance unevenness more than before by suppressing scratches on the light guide plate.

The present invention has been intensively studied for the above-described problem, namely, a white reflective film that suppresses scratches on the light guide plate in an impact test for an edge light type backlight, and as a result, the side in contact with the light guide plate of the white reflective film (when in use) It was discovered that the above problems can be solved at once by selecting a polymer with a special structure without adding particles to the surface layer (A) on the reflective surface side (side opposite to the light guide plate) and when the surface roughness is within a specific range.

In addition, brightness unevenness means the unevenness described below that is observed with the naked eye when the backlight is turned on.

(i) Stripe-shaped stains

(ii) Puddle-shaped stains

(iii) Stains that appear dark

In addition, white dot stain refers to an ellipsoid-shaped dot-shaped stain with a major diameter of less than 5 cm that is observed with the naked eye when the backlight is turned on.

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

[Basic composition of white reflective film]

The white reflective film of the present invention consists of a surface layer (A) and a base layer (B) containing bubbles. Considering the ease and effectiveness of film formation, a two-layer or more configuration is required, and a three-layer configuration is preferable. In particular, a form in which the surface layer (A) protects the base layer (B), that is, a three-layer structure of surface layer (A)/base layer (B)/surface layer (A), is preferable. In addition, in the case of multiple layers, it is more preferable that the deep layer is the base layer (B) and the surface layer on one or both sides is the surface layer (A).

[Base layer containing air bubbles (B)]

The white reflective film of the present invention needs to have bubbles inside the base layer (B) for whiteness and reflective properties, but it contains a component incompatible with polyester or polypropylene constituting the base layer (B) to form a biaxial film. Bubbles can be formed by stretching.

Examples of these manufacturing methods include polyester containing barium sulfate as an incompatible component described in Japanese Patent No. 3734172 and polypropylene containing titanium oxide as an incompatible component described in Japanese Patent Application Laid-Open No. 2012-158167. In the incompatible resin, specific examples of organic substances include linear, ground, or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene. This polyolefin may be a homopolymer or a copolymer, and two or more types may be used together. Among these, polypropylene, polymethylpentene, etc. are preferably used as the crystalline polyolefin, and cycloolefin copolymers, etc. are preferably used as the amorphous polyolefin because they are excellent in transparency and heat resistance.

In the present invention, the amount of the incompatible component added is preferably 5 to 50% by mass, more preferably 5 to 30% by mass, based on 100% by mass of the total mass of the base material layer (B) containing bubbles. . If the content of the incompatible component is less than 5% by mass, bubbles are not sufficiently generated inside the film, and whiteness and light reflection characteristics may be poor. On the other hand, if the content of the incompatible component exceeds 50% by mass, the strength of the film decreases, rupture occurs easily during stretching, and problems such as powder generation may occur during post-processing. By keeping the content within this range, sufficient whiteness, reflectivity, and lightness can be achieved.

[Surface roughness of surface layer (A)]

In the white reflective film of the present invention, the center surface average roughness (SRa) of the surface layer (A) is required to be 90 nm or more and less than 300 nm, preferably 120 to 300 nm, and most preferably 120 to 250 nm. am. In the case of less than 90 nm, the gloss increases, dust adhering to the surface becomes easily visible, and luminance unevenness, especially white spots, in the edge light type backlight becomes easy to occur. On the other hand, in the case of 300 nm or more, the problem of the surface layer A being chipped and transferred to the light guide plate dots during a vibration test with the light guide plate is likely to occur.

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

Based on JIS B0601 (2001), the center surface average roughness (SRa) was measured using a stylus surface roughness meter (model number: ET 4000A) manufactured by Kosaka Laboratory Ltd. The conditions were as follows, and the value was taken as the average value of 5 measurements.

·Stylus tip radius: 0.1㎛

·Stylus load: 100μN

·Measurement length: 1.0mm

·Cutoff value: 0.25mm

[The surface layer (A) has a domain made 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 to prevent brightness unevenness that occurs when in contact with the light guide plate or brightness unevenness after an impact test. The domain can be easily recognized from the contrast of the cross-sectional SEM of the surface layer (A).

If it does not have a domain made of a polymer, for example, if the central plane average roughness (SRa) of the present application is achieved with inorganic particles, the light guide plate will be scratched in an impact test and luminance unevenness will occur. In addition, when the center surface average roughness (SRa) is achieved for organic particles, the organic particles fall off in the impact test and adhere to the light guide plate, resulting in luminance unevenness.

The interface thickness of the domain in the present invention is preferably 20 nm or more and 1,000 nm or less. In the case of less than 20 nm, voids are likely to form between the matrix and the domain, and there is a possibility that the matrix may peel off and adhere to the light guide plate during an impact test, causing luminance unevenness. Additionally, if it is larger than 1,000 nm, it may become too compatibilized and sufficient surface roughness may not be obtained. A more preferable range of 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 domain thickness range, it can be controlled by controlling the transesterification reaction using a transesterification reaction inhibitor or controlling compatibility using a compatibilizer.

The shape of the domain in the present invention is preferably a substantially flat shape co-stretched together with the matrix, and specifically, when observing the cross section of the surface layer (A), the ratio of the length in the thickness direction to the length in the longitudinal direction is 1:3. It is preferable that it is 1:50 or less. If it is less than 1:3, the domain is not co-extended, voids are likely to form, and the matrix may peel off and adhere to the light guide plate during an impact test, causing luminance unevenness. Additionally, if it is greater than 1:50, there is a possibility that unevenness may not be formed due to excessive stretching along with the matrix. 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-described domain shape, one method is to control the Tg difference between the polymers constituting the matrix and each domain. Specifically, it is desirable to control the Tg difference between the polymers 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 a gentle protrusion rather than a steep protrusion formed by particles, etc., so the aggressiveness toward the light guide plate is low, resulting in brightness unevenness or brightness unevenness after an impact test. can be greatly suppressed.

The thickness of the surface layer (A) is preferably 4 μm or more and 12 μm or less. If it is less than 4㎛, there are many cracks during film forming, which reduces handling properties, or sufficient surface irregularities may not be formed. Additionally, if it is thicker than 12㎛, luminance may decrease. More preferably, it is 6 ㎛ or more and 12 ㎛ or less.

[Crystallization temperature (Tmc)]

As for the surface layer (A) in the present invention, it is preferable that the main protrusions are made of polymer as the core to prevent brightness unevenness after the impact test. In order to form protrusions with polymer as the core, it is preferable that the layer (A) is formed of two or more types of polymers without mixing them in the extruder or film forming process.

The criteria for non-commercial use include, for example, observation of a difference in the crystallization temperature (Tmc) of the surface layer (A). Specifically, it is preferable that the crystallization temperature on cooling (Tmc) is 10°C or more and 40°C or less. If the temperature exceeds 40°C, cold crystallization is promoted, forming a hard surface irregularity, which may cause problems with cutting the light guide plate. More preferably, it is 15°C or more and less than 35°C.

Methods for suppressing compatibility include, in the case of polyester, adding a so-called transesterification inhibitor that suppresses the activity of the polymer polymerization catalyst, or suppressing heat history during the film forming process.

[Polyester or polyolefin with an alicyclic structure]

Among the two or more types of polymers in the present invention, it is preferable that at least one type contains a polyester or polyolefin having an alicyclic structure. Among these, when polyester or polyolefin having an alicyclic structure with different compatibility is used, appropriate surface irregularities are easily 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, and 1,3-cyclopropanediol, 1,3-cyclobutanediol, 1,3-cyclopentanediol, and 1,4-cyclohexanedimethanol as diol components were mixed with 200 ppm of butyltintris (2- By performing a polycondensation reaction in the presence of ethylhexanoate), polyester pellets or polyolefin pellets having an alicyclic structure can be obtained.

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), polyolefin having a cyclopentane ring As such, "ZEONOR" (registered trademark) (manufactured by Zeon Corporation) can be suitably used.

The amount of polyester (B) having an alicyclic structure added is not particularly limited, but is preferably 10% by mass or more and 40% by mass or less, and particularly preferably 15% by mass, based on 100% by mass of the total mass of the surface layer (A). It is 35% by mass or less. If it is less than 10% by mass, luminance unevenness, especially white spots, will easily occur in the edge light type backlight.

Among the two or more types of polymers in the present invention, as polymers other than polyester or polyolefin having an alicyclic structure, polyester copolymerized with a diol such as ethylene glycol or butanediol and a dicarboxylic acid component such as terephthalic acid or isophthalic acid can be used. there is. 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 PET, PET (PET-I), a copolymer of ethylene glycol, isophthalic acid, and terephthalic acid, can also be used for the purpose of providing film forming stability or making it easier to form 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. Additionally, at 50% by weight or more, heat resistance may decrease.

[Particle content]

It may contain less than 5% by mass of particles as long as the effect of the present invention is not impaired. If the particles contain more than 5% by mass, the light guide plate may be scratched, the polymer may peel off from the particles, or the particles themselves may fall off and contaminate the light guide plate. A more preferable range of 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 inorganic particles include titanium dioxide, calcium carbonate, barium sulfate, and silica. Examples of organic particles include acrylic, polystyrene, and nylon.

[Glossiness is also different]

In the present invention, it is preferable that the difference in gloss between 20° and 85° of the surface layer (A) is 50% or more. Because the difference in gloss is large, light can be efficiently returned to the front of the display as a light reflection film. More preferably, it is 65% or more, and even more preferably, it is 80% or more.

[How to unveil]

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 this example.

For 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. Polyester (B) having an alicyclic structure may be added using a master chip prepared by uniformly melting and kneading in advance, or may be directly supplied to a kneading extruder.

For the base material layer (B) containing bubbles, a mixture containing a component incompatible with polyester or polypropylene and, if necessary, a dispersant is sufficiently vacuum dried and supplied to a heated extruder. Incompatible components may be added using a master chip prepared by uniformly melting and kneading in advance, or may be directly supplied to a kneading extruder.

In addition, in melt extrusion, it is preferable to filter through a filter with a mesh of 40 μm or less, then introduce it into a T-die metal mold and obtain a molten sheet by extrusion molding.

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 produce an unstretched A/B/A three-layer film. The unstretched three-layer film is guided to a roll group heated to 70 to 120°C, preferably 70 to 100°C, and stretched 2.5 to 4 times in the longitudinal direction (vertical direction, i.e., the film moving direction) to 20 to 50° C. Cool in the roll group at a temperature of ℃.

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

The stretch ratio is 2.5 to 4 times in the longitudinal direction and the width direction, but the area magnification (vertical stretch ratio x horizontal stretch ratio) is required to be 9 to 16 times, and is more preferably 10 to 12 times. If the area magnification is less than 9 times, the formation of bubbles or irregularities in the resulting white reflective film and the film strength will be insufficient, and if the area magnification exceeds 16 times, cracking will easily occur during stretching.

In order to complete the crystal orientation of the obtained biaxially stretched film and provide dimensional stability, heat treatment is continuously performed in a tenter at a temperature of 150 to 240°C for 1 to 30 seconds, and then uniformly slowly cooled to room temperature. If necessary, the white reflective film of the present invention can be obtained by performing corona discharge treatment and winding to further increase adhesion to other materials. During the heat treatment process, it is preferable to carry out a relaxation treatment of 3 to 12% in the width or length direction.

[Edge light type backlight]

The white reflective film of the present invention is suitably used for edge light type backlight. An edge light type backlight is formed, for example, by mounting the white reflective film of the present invention and the light guide plate in this order on a housing having concavo-convex surfaces, and the white film is mounted so that the surface layer (A) side faces the light guide plate. Additionally, a light source such as an LED is installed at the edge of the light guide plate. Additionally, a diffusion plate, prism, etc. may be installed on the front side of the light guide plate (opposite to the white reflective film).

[Uses of white reflective film]

The white reflective film of the present invention is used for backlights, and is particularly suitable for use as backlights for edge light-type liquid crystal displays and surface light sources for lighting such as signboards and vending machines.

In addition, it can be suitably used as a reflector that constitutes various surface light sources, or as a sealing film or backsheet for solar cell modules that require reflective properties. Other paper substitutes include cards, labels, seals, delivery slips, image paper for video printers, inkjet, image paper for barcode printers, posters, maps, blank paper, signs, white boards, thermal transfer, offset printing, telephone cards, IC It can also be used as a substrate for receiving sheets used for various printing records such as cards, building materials such as wallpaper, lighting equipment and indirect lighting equipment used indoors and outdoors, members mounted on automobiles, railways, aircraft, etc., and electronic components such as circuit materials. there is.

[Method for measuring physical properties and evaluating effects]

measurement method

The evaluation method of the physical properties and effect of the present invention are as follows.

A. Surface roughness

Based on JIS B0601 (2001), the center surface average roughness (SRa) was measured using a stylus surface roughness meter (model number: ET 4000A) manufactured by Kosaka Laboratory Ltd. The conditions were as follows, and the value was taken as the average value of 5 measurements.

·Stylus tip radius: 0.1㎛

·Stylus load: 100μN

·Measurement length: 1.0mm

·Cutoff value: 0.25mm

B. Domain

Cut a cross-section of a white reflective film sample, observe the surface layer (A) at 2,000 to 10,000 times magnification using a field emission scanning electron microscope "JSM-6700F" (manufactured by JEOL Ltd.), and observe the domain from a cross-sectional photograph taken. did. A case where there was a co-stretched, roughly flat dark and dark portion without a clear interface was judged to have a domain made of a polymer different from the polymer constituting the matrix. On the other hand, those with voids formed around them were judged to be particles.

Next, in the case of a domain made of a polymer, an ultra-thin section of the surface layer (A) was prepared and stained with OsO ₄ , and then the shape of the domain and the thickness of the domain interface were observed using a transmission electron microscope TEM.

For the shape of the domain, the ratio was obtained by measuring the length in the thickness direction: the length in the longitudinal direction as the distance between two points. Similarly, the interface of the domain (width of the dark part) was measured as the distance between two points and used as the interface thickness. The shape of the domain and the thickness of the domain's interface were the average values measured at five locations.

C. Particle content

A small piece obtained by tapering the surface of the white reflective film was used as a sample, and the obtained ash content was measured based on JIS K7250-1:2006. The same operation was performed on five other white reflective films, and the average value of the five was used as the particle content.

D. Cooling crystallization temperature (Tmc)

A small piece obtained by tapering the surface of the white reflective film was weighed in a sample pan of 5 mg, and a differential scanning calorimetry device "RobotDSC-RDC220" manufactured by Seiko Instruments & Electronics Ltd. was used for data analysis in accordance with JIS K7122 (1987). Measurements were performed using disk session "SSC/5200" in the following manner. In addition, the temperatures listed below were the average values measured using five film samples.

It was heated from 25°C to 300°C at a temperature increase rate of 20°C/min, maintained at that state for 5 minutes, and then rapidly cooled to 25°C or lower. Immediately, the temperature was again raised from room temperature to 300°C at a rate of 20°C/min and maintained at that state for 5 minutes, and then the temperature was lowered from 300°C to 25°C at a rate of 20°C/min, followed by a rapid cooling process. The endothermic/exothermic peaks were measured during each temperature increase and temperature decrease process except.

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 taken as the cooling crystallization temperature (Tmc).

Among the crystallization temperatures on cooling, the higher exothermic peak temperature was Tmc1, the lower exothermic peak temperature was Tmc2, and the difference in crystallization temperature on cooling (Tmc) was determined by the following equation.

Difference in crystallization temperature (Tmc) = Tmc1-Tmc2

E. Compatibility with light guide plate

(i) Light guide plate contamination

A 40-inch liquid crystal television (KDL-40EX700, manufactured by Sony Corporation) was disassembled to extract an edge-light type backlight using LED as a light source. The size of the emitting surface was 89 cm x 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 into 5 cm The surface layer (A) of the white reflective film of the invention is reciprocated at 3 cm After that, the surface layer (A) surface in contact with the surface of the white reflective film of the present invention of the 5 cm x 5 cm light guide plate was observed under a microscope, and the evaluation results were as follows.

A: Excellent (no visible adhesion)

B: Good (attachment can be seen if observed closely)

F: Falling behind (attachments visible)

The above A and B were accepted as passes.

(ii) Medium load RBI test

The light guide plate taken out from the backlight is cut into 5 cm The dot test is performed 1000 times with a bar of 200 g. After that, the surface of the light guide plate with which the surface layer (A) of the white reflective film was in contact was observed under a microscope, and the evaluation results were obtained as follows.

A: Excellent (no visible scratches)

B: Good (scratches can be seen if observed closely)

F: Falling behind (scratches visible)

The above A and B were accepted as passes.

(iii) Luminance staining

The reflective film attached to the backlight of a new 32-inch liquid crystal TV LHD32K15JP manufactured by HISENSE JAPAN CORPORATION was changed to the white reflective film of the present invention and turned on. After waiting in that state for 1 hour to stabilize the light source, it was observed that something that could be recognized as a luminance spot with the naked eye under a lighting environment of 500 Lx or a dark environment was used as the evaluation result as follows. In addition, the brightness unevenness referred to here is caused by bright spots resulting from contact between the reflective film and the light guide plate.

A: Rainy weather (no luminance unevenness visible under 500Lx lighting environment or dark environment)

B: Good (luminance unevenness is visible in a dark environment of 500Lx, but brightness unevenness is not visible in a lighting environment)

F: Poor (luminance unevenness is visible both under a 500 Lx lighting environment and in a dark environment)

The above A and B were accepted as passes.

F. Membranability

In Examples and Comparative Examples, when forming a film, film cracking occurs no more than once per day, and there is no process contamination due to particle dropping, etc. A, film cracking occurs only once per day, but there is no film cracking on the roll surface. B indicates that the accumulation of contamination can be confirmed with the naked eye, F indicates that film cracks occur more than 2 times/day but less than 3 times/day, film forming ability of B or higher is required for mass production, and if it is A or higher, there is a greater cost reduction effect. .

G. Glossiness

Measurements were made based on JIS Z-8741 (1997) on the surface layer (A) side of the white reflective film using a digital variable-angle glossmeter UGV-5B (manufactured by Suga Test Instruments Co., Ltd.). In addition, the measurement conditions are: 60° gloss is the value when the measurement conditions are incident angle = 60°, light received angle = 60°, and similarly, 20° gloss is the value when incident angle = 20°, light received angle = 20°, 85° gloss. The degree is the value when the angle of incidence = 85° and the angle of light reception = 85°.

Example

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

(Raw material)

·Surface layer (A)

A polycondensation reaction was performed by adding terephthalic acid as an acid component and ethylene glycol as a diol component to a polyester pellet from which antimony trioxide (polymerization catalyst) was obtained at a concentration of 300 ppm in terms of antimony atoms, resulting in an intrinsic viscosity of 0.63 dl/g. , polyethylene terephthalate pellets (PET) with a carboxyl terminal group weight of 40 equivalents/ton were obtained.

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.

·Polyester with an alicyclic structure

A polycondensation reaction was performed using dimethyl terephthalate as an acid component and CHDM (cyclohexanedimethanol) as a diol component in the presence of 200 ppm butyltintris(2-ethylhexanoate) to obtain a copolyester.

In addition, commercially available products (e.g., "TRITAN" (manufactured by Eastman Chemical Company) as alicyclic structure a, "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) as alicyclic structure b), and "ZEONOR" (manufactured by Eastman Chemical Company) as alicyclic structure c. "(registered trademark) (manufactured by Zeon Corporation) was used.

These are characterized by the copolymerization component constituting the diol component, for example, EASTAR has a cyclohexane ring component, and TRITAN has a cyclobutane ring component.

(Examples 1 to 8)

57 parts by mass of PET, 5 parts by mass of a (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (Product name: Hytrel, manufactured by DU PONT-TORAY CO., LTD.), 1 to ethylene glycol, 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) copolymerized with 33 mol% 4-cyclohexanedimethanol, 20 parts by mass of poly(5-methyl)norbornene, and 10 parts by mass of rutile type titanium oxide were adjusted and mixed, 180% After drying at ℃ for 3 hours, it was supplied to extruder B heated at 270-300℃ (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), particle a has a particle size of 0.6 ㎛. Silica, silica with a particle size of 3.5㎛ for particle b, and barium sulfate with a particle size of 0.6㎛ for particle c were mixed in the ratio shown in Table 1, dried in vacuum at 180°C for 3 hours, and then supplied to extruder A heated to 280°C. , these polymers were laminated through a lamination device to form A layer/B layer/A layer (8 μm/137 μm/8 μm), and were molded into a sheet shape using a T die. Additionally, the unstretched film, which was solidified by cooling with a cooling drum with a surface temperature of 25°C, was guided to a roll group heated to 85 to 98°C, stretched 3.4 times longitudinally in the longitudinal direction, and cooled in a roll group at 21°C. Subsequently, both ends of the vertically stretched film were held by clips and guided to a tenter, and horizontally stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated to 120°C. After that, heat setting was performed at 200°C in a tenter, uniformly cooled slowly, and then cooled to room temperature to obtain a biaxially stretched laminated film. The physical properties as a light reflection substrate are shown in Table 1.

In this way, the white reflective film of the present invention could be stably formed and showed excellent surface morphology (medium load spot test, light guide plate contamination, and reduction of luminance unevenness).

(Example 9)

(Surface layer (A))

Pellets of amorphous cycloolefin resin A (manufactured by Zeon Corporation, brand name "ZEONOR 1430R", density (ASTMD792): 1.01 g/cm3, glass transition temperature Tg (JISK7121): 133°C) and polypropylene resin (manufactured by Japan Polypropylene Corporation) , product name “Novatech PPEA9”) pellets were mixed at a mass ratio of 30:70 and supplied to the extruder A by the above method.

(Base layer containing air bubbles (B))

Pellets of polypropylene resin (manufactured by Japan Polypropylene Corporation, brand name "Novatech PP FY6HA"), titanium oxide (manufactured by KRONOS, brand name "KRONOS2230", rutile-type titanium oxide, Al, Si surface treatment, TiO ₂ content 96.0%, manufacturing method : chlorine method) was mixed at a mass ratio of 50:50 and supplied to extruder B using the above method.

(Production of white reflective film)

In each extruder, after melt-kneading at 200°C and 230°C, it is joined to a T-die for two types of three layers and extruded into a sheet shape to form a three-layer structure of layer (A)/layer (B)/layer (A). and cooled and solidified to form a laminated sheet. The obtained laminated sheet was roll-stretched 2 times in MD at a temperature of 130°C, and then biaxially stretched by tenter stretching 3 times in TD at 130°C to obtain a thickness of 150 ㎛ (resin layer (A): 8 ㎛, resin layer (B) ): 134㎛) white reflective film was obtained. The physical properties as a light reflection substrate are shown in Table 1.

In this way, the white reflective film of the present invention could be stably formed and showed excellent surface morphology (medium load spot test, light guide plate contamination, and reduction of luminance unevenness).

(Examples 10 to 12)

57 parts by mass of PET, 5 parts by mass of a (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (Product name: Hytrel, manufactured by DU PONT-TORAY CO., LTD.), 1 to ethylene glycol, 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) copolymerized with 33 mol% 4-cyclohexanedimethanol, 20 parts by mass of poly(5-methyl)norbornene, and 10 parts by weight of rutile titanium oxide were adjusted and mixed at 180°C. After drying for 3 hours, it was supplied to extruder B heated to 270-300°C (layer B).

Meanwhile, PET, PET-I, and alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used as the layer (A), mixed in the ratio shown in Table 1, and dried under vacuum at 180°C for 3 hours. , were supplied to extruder A heated to 280°C, these polymers were laminated through a lamination device to form A layer/B layer/A layer, and were molded into a sheet shape using a T die. Additionally, the unstretched film, which was cooled and solidified in a cooling drum with a surface temperature of 25°C, was introduced into a roll group heated to 85 to 98°C, stretched 3.4 times longitudinally in the longitudinal direction, and cooled in a roll group at 21°C. Subsequently, both ends of the vertically stretched film were held by clips and guided to a tenter, and horizontally stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated to 120°C. After that, heat setting was performed at 200°C in a tenter, uniformly cooled slowly, and then cooled to room temperature to obtain a biaxially stretched laminated film with a thickness of 150 μm. Additionally, by adjusting the discharge amounts of extruder A and extruder B, the surface layer thickness was adjusted to 8 μm to 12 μm while maintaining the total thickness of 150 μm.

The physical properties of the obtained laminated film as a light reflection substrate are shown in Table 1. In this way, the white reflective film of the present invention could be stably formed and showed excellent surface morphology (medium load spot test, light guide plate contamination, and reduction of luminance unevenness).

(Comparative Examples 1 to 6)

In a composite film forming apparatus having a main extruder and a secondary extruder, film forming was performed by changing the formulation shown in Table 2.

In Comparative Examples 1 and 6, scratches occurred on the light guide plate because the main protrusions were particles. In Comparative Examples 3 to 6, alicyclic structure a "TRITAN" (manufactured by Eastman Chemical Company), "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) as alicyclic structure b, and "ECOZEN" (manufactured by SK chemicals) as alicyclic structure d. The mixture was mixed in the ratio shown in Table 2 and supplied to extruder A under the same raw materials and conditions as in Example 1 to produce a white reflective film. As a result, in Comparative Examples 2, 3, and 5, SRa was small and luminance unevenness occurred, and Comparative Example 4 In this case, SRa was large and contamination of the light guide plate occurred.

(Comparative Examples 7, 8)

57 parts by mass of PET, 5 parts by mass of a (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (Product name: Hytrel, manufactured by DU PONT-TORAY CO., LTD.), 1 to ethylene glycol, 8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) copolymerized with 33 mol% 4-cyclohexanedimethanol, 20 parts by mass of poly(5-methyl)norbornene, and 10 parts by mass of rutile type titanium oxide were adjusted and mixed, 180% After drying at ℃ for 3 hours, it was supplied to extruder B heated at 270-300℃ (layer B).

Meanwhile, PET, PET-I, and alicyclic structure b "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) were used as the layer (A), mixed in the ratio shown in Table 1, and dried under vacuum at 180°C for 3 hours. , were supplied to extruder A heated to 280°C, these polymers were laminated through a lamination device to form A layer/B layer/A layer, and were molded into a sheet shape using a T die. Additionally, the unstretched film, which was cooled and solidified in a cooling drum with a surface temperature of 25°C, was introduced into a roll group heated to 85 to 98°C, stretched 3.4 times longitudinally in the longitudinal direction, and cooled in a roll group at 21°C. Subsequently, while holding both ends of the vertically stretched film with clips, it was guided to a tenter and horizontally stretched 3.6 times in the direction perpendicular to the length in an atmosphere heated to 120°C. After that, heat setting was performed at 200°C in a tenter, uniformly cooled slowly, and then cooled to room temperature to obtain a biaxially stretched laminated film with a thickness of 150 μm. Additionally, by adjusting the discharge amounts of extruder A and extruder B, the surface layer thickness was adjusted to 3 μm while the overall thickness was 150 μm.

The physical properties of the obtained laminated film as a light reflection substrate are shown in Table 2. Since SRa was small, luminance unevenness occurred.

(Comparative Examples 9 to 10)

In a composite film forming apparatus having a main extruder and a secondary extruder, film forming was performed by changing the formulation shown in Table 2.

Because the main protrusion was particle c, scratches occurred on the light guide plate.

The white reflective film of the present invention is used for backlighting, and is particularly suitable for use in backlights for edge light-type liquid crystal displays and surface light sources for lighting such as signboards and vending machines. In addition, it can be suitably used as a reflector that constitutes various surface light sources, or as a sealing film or backsheet for solar cell modules that require reflective properties. In addition, paper substitutes such as cards, labels, seals, delivery slips, video printers, inkjet, barcode printers, posters, maps, blank paper, signs, white plates, thermal transfer, offset printing, telephone cards, etc. It can also be used as a base material for receiving sheets used for various printing records such as IC cards, construction materials such as wallpaper, lighting equipment and indirect lighting equipment used indoors and outdoors, members mounted on automobiles, railways, aircraft, etc., and electronic components such as circuit materials. You can.

Claims (9)

White reflective film for edge-type backlight that satisfies the following (i) to (iv).
(i) It is a laminated film of two or more layers including at least a surface layer (A) and a base layer (B) containing air bubbles.
(ii) The surface center surface average roughness (SRa) of the surface layer (A) is 120 nm or more and less than 250 nm.
(iii) The surface layer (A) has a domain made of a polymer different from the polymer constituting the matrix.
(iv) Containing polyester having an alicyclic structure in the surface layer (A). According to claim 1,
A white reflective film for an edge-type backlight wherein the domain has an interface thickness of 20 nm or more and 1,000 nm or less. The method of claim 1 or 2,
An edge-type backlight, wherein the shape of the domain according to claim 1 or 2 has a ratio of the length in the thickness direction to the length in the longitudinal direction of 1:3 or more and 1:50 or less when observing the cross section of the surface layer (A). For white reflective film. The method of claim 1 or 2,
A white reflective film for an edge-type backlight in which the surface layer (A) contains particles and the particle content is less than 5% by mass. According to claim 1,
White reflective film for edge-type backlight with a gloss difference of more than 50% between 20° and 85° of the surface layer (A). delete According to claim 1,
A white reflective film for edge-type backlights whose surface layer (A) is composed of two or more types of polymers and whose temperature-fall crystallization temperature (Tmc) difference is 10°C or more and less than 40°C. A backlight for a liquid crystal display constructed using the film according to claim 1. According to claim 8,
A backlight for liquid crystal displays whose light source is a light-emitting diode.