JP5987412B2 - Laminated film - Google Patents

Description

  The present invention relates to a laminated film having an excellent thermal diffusivity. More specifically, it is suitable as a base film in applications that require heat dissipation (thermal diffusibility) and reflectivity, such as LCD TV backlight members, personal computer backlight members, and small monitor light source members. It is related with the laminated film used for.

  In recent years, in order to make liquid crystal displays such as televisions and personal computers thinner and more functional, backlight devices have been improved and replaced by LED light sources. Further, in the next generation liquid crystal display, the brightness is increased in order to make it look bright and beautiful, and the light reflecting film used in the backlight device corresponding to the brightness has been improved. It is known that the current generation of liquid crystal televisions and liquid crystal display devices for personal computers increase the amount of heat generated in the device by reducing the size and improving the performance and are likely to cause failure.

  The cause of the increase in the amount of heat generation is the heat generation of the light source (for example, LED) used in the backlight of the liquid crystal display, and depending on the long-term use of the liquid crystal display device, the light source (for example, LED) structure may deteriorate and fail. In particular, since the lifetime of the LED is shortened when the temperature is 78 ° C. to 100 ° C. or higher, it is necessary to take appropriate heat dissipation measures to control the LED temperature to 78 ° C. or lower.

  Therefore, the light reflection film has been required to have high light reflectivity and heat diffusibility.

  On the other hand, for example, Patent Document 1 discloses a white laminated film that contains fine bubbles inside and refracts and reflects light at the bubble interface, and is often used in a reflector for backlight. Since this laminated film has a low heat diffusion and heat tends to accumulate with respect to the heat generation of the LED of the light source part of the liquid crystal display device, the LED part tends to become hot due to long-term use, and the LED main body is thermally deteriorated. If this occurs, the liquid crystal display device may be damaged.

  Further, in the liquid crystal display device as disclosed in Patent Document 2, since the amount of heat is increased by using a plurality of LEDs, it is not preferable because the LED main body is likely to be thermally deteriorated due to the temperature rise in the device.

  The film disclosed in Patent Document 3 can obtain heat dissipation by laminating a heat conductive composition layer capable of reflecting light, but it cannot be used as a white reflector unlike the point that it has a metallic gloss surface, Even when the side facing the light source is a white film layer, the reflectance may decrease due to a refractive difference at the interface with the heat conductive composition layer, which is not preferable.

  The film disclosed in Patent Document 4 also has insufficient heat dissipation and may be inferior in light reflectivity. Under such circumstances, a laminated film excellent in light reflectivity and heat dissipation is demanded.

JP 2003-160682 A JP 2010-278071 A JP 2008-169513 A JP 2009-170770 A

To provide a laminated film superior in light reflectivity and heat dissipation (heat diffusibility).
It is an object of the present invention to provide a laminated film having a reflectance equivalent to that of a conventional reflective film for a liquid crystal display and improving a low thermal diffusivity which is a weak point of the film. Another object of the present invention is to provide a method for producing a laminated film that is optimal for a backlight base material, with selection of the thermal diffusivity and refractive index of the inorganic particles and a blending method using a master pellet.

A laminated film having at least an A layer and a B layer,
(A) A layer contains a polyester resin and inorganic particles,
(B) The refractive index of the inorganic particles is 1.65 to 2.40,
(C) The content of the inorganic particles is 5% by weight to 60% by weight with respect to the A layer,
(D) The bubble content in the A layer is 10% by volume or less with respect to the A layer,
(E) The thermal diffusivity of the A layer is 1.4 × 10 ⁻⁷ m ² s ⁻¹ or more,
(F) The density of the A layer is 1100 kgm ^{−3 to} 2500 kgm ⁻³ ,
(G) It is a laminated film used for a back sheet of a liquid crystal display light source part, wherein the B layer is a layer formed using a polyester resin.

  In the present invention, the A layer is preferably the outermost layer, the B layer is preferably a layer using a polyester resin, the B layer contains bubbles, and the bubble content in the B layer is 15 The volume is preferably 50% by volume to 50% by volume, and is optimally used for the back sheet of the liquid crystal display light source part.

Further, in the present invention, the A layer is formed using a polyester composition containing inorganic particles (1) and a polyester composition containing inorganic particles (2).
The median diameter D1 of the inorganic particles (1) is 3 μm to 20 μm,
The median diameter D2 of the inorganic particles (2) is 0.1 μm to 10 μm,
D1 and D2 are manufacturing methods of a laminated film in which the following formula is satisfied.
D1 (μm) / D2 (μm) ≧ 2

  A laminated film excellent in light reflectivity and heat dissipation (heat diffusibility) can be provided. Further, by using the laminated film of the present invention as a backlight member of a liquid crystal display, the temperature of the light source part of the backlight is lowered to prevent deterioration of the light source or failure of the liquid crystal display device. be able to.

FIG. 1 is a schematic view when the temperature of an LED is measured in the characteristics evaluation of the laminated film of the example.

  The film of the present invention is a laminated film having at least an A layer and a B layer.

In the laminated film of the present invention, it is necessary that the thermal diffusivity of the A layer is 1.4 × 10 ⁻⁷ m ² s ⁻¹ or more. By setting the thermal diffusivity of the A layer to 1.4 × 10 ⁻⁷ m ² s ⁻¹ or more, the thermal diffusibility of the film can be enhanced. In the present invention, heat diffusibility refers to the ability to diffuse heat within the film (in the film plane) when the film is irradiated with heat rays. For example, even when a heat ray is incident on a specific part of the film surface, the heat is diffused in the film (in the film surface), and as a result, heat is applied from a part different from the part where the heat ray is incident on the film surface. Will be released.

In order to set the thermal diffusivity of the A layer to 1.4 × 10 ⁻⁷ m ² s ⁻¹ or more, it is important that the A layer contains inorganic particles.

  In particular, it is important to use inorganic particles having a refractive index of 1.65 to 2.40. When the refractive index is 1.65 or more, heat can be diffused efficiently. This is because the heat rays are electromagnetic waves (far infrared rays), and the heat rays can be refracted and diffused inside the film by containing particles having a high refractive index in the film. The upper limit of the refractive index is limited to 2.40 or less. This is because inorganic particles exceeding the upper limit reflect heat rays (regularly) with a high refractive index, so that the contribution to the diffusion of the heat rays is small and the diffusion efficiency is lowered.

  In the present invention, the refractive index of the inorganic particles is indicated by the refractive index in the visible light region, because the refractive index in the visible light region is correlated with the refractive index of heat rays (far infrared rays). And the particle | grains whose refractive index is 1.65 or more are higher than the refractive index of a polyester resin. Therefore, when heat rays are incident from a direction perpendicular to the film surface, when heat rays (far infrared rays) pass through the inside of the particles, they are refracted at the interface between the polyester resin and the inorganic particles, and the heat rays are transmitted in the film surface direction. It becomes easy to (heat propagation). Then, the heat ray collides with another inorganic particle, and is refracted and diffused. Thereby, the thermal diffusibility of the A layer can be dramatically increased.

  Moreover, it is preferable that content of the inorganic particle in A layer is 5 to 60 weight% with respect to A layer. By setting the content of the inorganic particles to 5% by weight or more, the thermal diffusivity of the A layer can be efficiently increased. Moreover, the intensity | strength of a film can be maintained by content of an inorganic particle being 60 weight% or less. Moreover, when the film of the present invention is obtained by a biaxial stretching method, tearing can be reduced during film formation.

  The layer A preferably contains the inorganic particles and a polyester resin. Thereby, the light reflectivity of a laminated film can be improved. This is because the refractive index of the polyester resin is greatly different from the refractive index of the inorganic particles, so that the light reflectance at the interface between the polyester resin and the inorganic particles can be increased.

  Moreover, it is preferable that the content rate of the bubble in A layer is 10 volume% or less with respect to A layer. This is because bubbles reduce the thermal diffusivity.

Further, it is important that the density of the A layer is 1100 kgm ^{−3 to} 2500 kgm ⁻³ . This is because the density of the A layer greatly affects the thermal diffusivity of the A layer. The density of the A layer is preferably smaller from the viewpoint of heat capacity. This is because the thermal diffusivity increases if the heat capacity is small. Therefore, it is important that the density of the A layer is 2500 kgm ⁻³ . Even considering the amount of inorganic particles that can be contained in the A layer, 2500 kgm ⁻³ is a practical upper limit.

On the other hand, the lower limit is not particularly defined, but is preferably 1100 kgm ⁻³ or more. In order to reduce the density, it is effective to allow bubbles to exist inside the A layer. However, as described above, since the bubbles have a function of lowering the thermal diffusivity, it is not possible to include a large amount of bubbles. It is because it is not preferable. Therefore, if the content rate of bubbles in the A layer is about 10% by volume or less with respect to the A layer, the substantial lower limit of the density of the A layer is 1100 kgm ⁻³ .

  In order to make the density of the A layer within the above range, it can be achieved by controlling the content of inorganic particles and the content of bubbles. Particularly preferably, the content of the inorganic particles is within the above range, and the content rate of the bubbles is within the above range.

  It is preferable that the heat ray is used in a mode of being incident from the A layer. That is, in the present invention, since the layer having a function of diffusing heat rays is the A layer, it is preferable that the heat rays are used in a mode of being incident from the A layer. Moreover, it is preferable that A layer exists in at least one outermost layer. By setting it as such a structure, a heat | fever can be efficiently diffused in air | atmosphere from A layer, and the thermal diffusivity of the whole laminated film can be raised.

  Moreover, the film of this invention has B layer which uses a polyester resin. The B layer preferably contains bubbles. When the film of the present invention has such a B layer, the thermal diffusibility of the film can be further increased. The reason for this is as follows. In the laminated film having the A layer / B layer, when the heat ray is incident from the A layer side, the heat ray reaches the B layer while being refracted and diffused in the A layer. Here, the B layer is a layer containing bubbles, and the refractive index of the bubbles and the refractive index of the polyester resin are greatly different. Therefore, the heat rays incident on the B layer are reflected (positively) at the polyester resin / bubble interface in the B layer, and are incident on the A layer again (return). The heat rays re-entering the A layer are further refracted and diffused in the A layer, and finally exit from the surface of the A layer to the outside of the film.

  Furthermore, when light reflectivity is calculated | required, the light reflectivity of a laminated | multilayer film can also be improved by making a B layer contain a polyester resin and a bubble.

  As a means of incorporating bubbles in the B layer, a polyester having a high melting point and an incompatible polymer that can be a nucleating agent for bubbles, an amorphous cyclic olefin resin, a crystalline olefin resin, and the like are finely dispersed in the polyester. For example, a means for forming voids (bubbles) around the incompatible polymer particles by stretching (for example, biaxial stretching) is exemplified.

  Moreover, it is preferable that the content rate of the bubble in B layer is 15 volume%-50 volume%. By setting the bubble content to 15% by volume or more, the heat ray reflectivity of the B layer and the reflectivity of the film can be improved efficiently. On the other hand, the bubble content is preferably 50% by volume or less. The mechanical properties of the film can be maintained by setting the bubble content to 50% by volume or less. Moreover, since air bubbles are inferior in thermal diffusivity, a film having excellent light reflectivity while maintaining excellent thermal diffusivity can be obtained by controlling the bubble content to 50% by volume or less. Further, when the film of the present invention is obtained by the biaxial stretching method, tearing can be reduced during film formation by controlling the bubble content to 50% by volume or less.

The thermal diffusivity of the laminated film of the present invention is preferably 0.7 × ^10- 7 ^{m 2} s ^-1 or more. The thermal diffusivity of the whole film can be improved as a thermal diffusivity is 0.7 * 10 < ^-7 > m < ² > s < ^-1 > or more.

  The laminated film of the present invention preferably has a reflectance of 90% or more. When the reflectance is 90% or more, the film of the present invention can be suitably used as a back sheet for a liquid crystal display light source part. In particular, when the back sheet also serves as a light reflecting plate, the film of the present invention having a reflectance of 90% or more can be particularly preferably used. This is because the liquid crystal display can be brightly displayed with this reflectance. Thus, the film of the present invention can also be used as a light reflecting plate of a liquid crystal display light source part.

In order to increase the reflectance of the laminated film, it is effective to adopt the following means.
(1) Inorganic layers having a refractive index of 1.65 to 2.40 are included in the A layer.
(2) The content of the inorganic particles is 5% by weight to 60% by weight with respect to the A layer.
(3) The A layer is at least one outermost layer,
(4) Make B layer contain air bubbles.
(5) Let the content rate of the bubble in B layer be 15 volume%-50 volume%.

In particular, it is preferable to adopt the means (1), (3) and (4). When light is incident from the surface on the A layer side, the A layer contains 1.65 to 2.40 inorganic particles, so that the light reflects the polyester at the interface of the inorganic particles. Some light passes through the A layer and enters the B layer. However, since the B layer contains bubbles, the light that has entered the B layer is reflected to the A layer side at the interface between the polyester and the bubbles. As a result, the two kinds of reflected light are combined on the film surface on the A layer side, and the reflectance of the laminated film can be increased efficiently. By further taking the means of (2) and (5), the reflectance of the laminated film can be increased more efficiently.
In the present invention, the A layer preferably contains inorganic particles having different particle diameters. Specifically, it is preferable to include inorganic particles having a large particle size (inorganic particles (1)) and inorganic particles having a small particle size (inorganic particles (2)). Such inorganic particles (1) and inorganic particles When the A layer is formed using (2), the inorganic particles (2) having a small particle diameter enter the gap between the inorganic particles (1) and the inorganic particles (1) having a large particle diameter in the A layer, and the A layer This is because the inorganic particles are densely packed. That is, since the distance between the particles is reduced, the heat propagation is improved and the thermal diffusivity is increased.

More specifically, the median diameter D1 of the inorganic particles (1) is 3 μm to 20 μm, the median diameter D2 of the inorganic particles (2) is 0.1 μm to 10 μm, and D1 and D2 satisfy the following formula: Is preferred. The median diameter in the present invention is a particle diameter corresponding to 50% in a cumulative distribution curve of volume-based particle diameter measured by a laser diffraction particle size distribution measuring apparatus (for example, Microtrack MT3000II manufactured by Nikkiso Co., Ltd.). I mean.
D1 (μm) / D2 (μm) ≧ 2
By setting D1 (μm) / D2 (μm) to 2 or more, the inorganic particles can be more efficiently and densely packed. As a result, the heat transfer (heat propagation) between the particles is improved, and the thermal diffusibility of the A layer can be dramatically increased.

  In the present invention, the median diameter D1 of the inorganic particles (1) is preferably 3 μm to 20 μm. This is because the thermal diffusivity of the A layer can be more efficiently increased by setting the median diameter D1 within such a numerical range. In addition, it is because particles having such a median diameter are easily available and easily contained in a film. In particular, when a polyester composition containing inorganic particles (1) is obtained by the master pellet method described later, the yield of the polyester composition is controlled by setting the median diameter D1 of the inorganic particles (1) to 20 μm or less. Can be increased.

  On the other hand, the median diameter D2 of the inorganic particles (2) is preferably 0.1 μm to 10 μm. This is because the thermal diffusivity of the A layer can be more efficiently increased by setting the median diameter D2 in such a numerical range. In addition, it is because particles having such a median diameter are easily available and easily contained in a film. In particular, when the median diameter D2 of the inorganic particles (2) is 0.1 μm or more, aggregation of the inorganic particles (2) can be suppressed, and the inorganic particles can be more efficiently and densely packed.

  In order to pack the inorganic particles densely, the mixing ratio “inorganic particles (1) / inorganic particles (2)” (volume ratio) between the inorganic particles (1) and the inorganic particles (2) is from 85/15 to 50. / 50 is preferable. By setting the mixing ratio (volume ratio) in the range, the A layer is densely filled with inorganic particles, so that heat propagation is improved and thermal diffusivity can be more efficiently increased.

  Further, the inorganic particles used in the present invention preferably have a major axis / minor axis ratio of 5 or less, more preferably 3 or less, and most preferably 1.8 or less. This is because by setting the major axis / minor axis ratio within the above numerical range, the inorganic particles are dispersed in the polyester resin and the thermal diffusibility is increased. If the major axis / minor axis ratio is outside the above numerical range, the inorganic particles tend to aggregate during film production (particularly during melting and kneading). Aggregation of the inorganic particles is not preferable because sufficient thermal diffusivity may not be exhibited.

  Moreover, it is preferable that the laminated | multilayer film of this invention are used for the backsheet of a liquid crystal display light source part. Since the liquid crystal display light source unit is also a heat source, the temperature in the vicinity of the light source and the light source unit increases as the lighting time increases. On the other hand, a light source is generally weak against heat, and deterioration is promoted when exposed to heat for a long time. Here, if the film of the present invention is used as a back sheet, the heat rays irradiated from the light source and the heat in the vicinity of the light source part can be quickly diffused, and the temperature rise in the vicinity of the light source and the light source part can be suppressed. . As a result, deterioration of the light source can be suppressed and the life of the light source can be extended. In particular, when an LED is used as the light source, this effect is particularly noticeable. This is because the LED light source uses resin as its constituent member. This is because the resin generally tends to be thermally deteriorated, and the deterioration of the resin has a great influence on the life of the light source. Therefore, by using the film of the present invention, the deterioration of the resin can be suppressed, and as a result, the lifetime of the LED light source can be greatly extended.

  Hereinafter, the polyester and inorganic particles that are suitably used in the present invention will be described.

  In the present invention, it is preferable that a polyester having a melting point of 250 ° C. or higher is preferably used. Specifically, polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate Rate and so on. Particularly preferred is polyethylene terephthalate. By using such a polyester, it becomes possible to produce a laminated film by a biaxial stretching method.

  In the present invention, the inorganic particles suitably used include magnesium oxide (refractive index: 1.74), calcined kaolin (refractive index: 1.66), magnesium carbonate (refractive index: 1.70), zinc oxide (refractive index). : 1.95). Particularly preferred are magnesium oxide and calcined kaolin. By using such inorganic particles, the thermal diffusibility of the laminated film can be increased.

  Further, the inorganic particles used in the present invention do not include carbon particles (carbon black, carbon fiber, etc.). This is because carbon particles and organic particles easily absorb heat rays and inhibit heat diffusion. Further, when the film is required to have light reflectivity, black carbon particles are not particularly preferable. The inorganic particles do not include aluminum oxide (alumina) particles. This is because the aluminum oxide particles have a high surface activity, decompose polyester, and generate a large number of bubbles in the film layer to inhibit heat diffusion.

  Moreover, it is preferable that the surface of the inorganic particles contained in the A layer is treated. By performing the surface treatment, the bubble content in the A layer can be reduced. This is because the laminated film of the present invention is preferably produced by the biaxial stretching method as described above, but if inorganic particles are present in the polyester, peeling occurs at the interface between the polyester and the inorganic particles during stretching. This is because bubbles with inorganic particles as nuclei may be generated. By treating the surface of the inorganic particles, the affinity of the polyester can be increased, and as a result, the generation of bubbles can be suppressed.

  In the present invention, the surface treating agent preferably used is a phosphate ester, a silane coupling agent, a titanate coupling agent, or siloxane. Particularly preferred are phosphate esters and silane coupling agents.

Although the manufacturing method of the laminated | multilayer film of this invention is demonstrated, it is not limited to this example (1) The polyester composition formed by containing inorganic particle (1) and inorganic particle (2) are contained. Production method of polyester composition (master pellet method)
Polyester, inorganic particles (1) having a median diameter D1, and a surface treatment agent are mixed, the mixture is put into an extruder, melt-kneaded and extruded, pelletized, and master pellets containing inorganic particles (1) ( A polyester composition comprising inorganic particles (1) is obtained.

  Polyester, inorganic particles (2) having a median diameter D2 and a surface treatment agent are mixed, the mixture is put into an extruder, melt-kneaded and extruded, pelletized, and master pellets containing inorganic particles (2) ( A polyester composition comprising inorganic particles (2) is obtained. Note that D1 (μm) / D2 (μm) is preferably 2 or more.

  When inorganic particles having different particle diameters are mixed into a master pellet, the inorganic particles are aggregated, and the filter is likely to be clogged during pelletization, and the inorganic particles are likely to be poorly dispersed. Therefore, as follows, a master pellet containing inorganic particles (1) and a master pellet containing inorganic particles (2) are prepared separately. By making it separate, a master pellet in which inorganic particles are well dispersed in polyester can be obtained. By manufacturing a film using the master pellet obtained in this way, the inorganic particles (1) and the inorganic particles (2) can be closely packed in the A layer.

(2) Film production method (biaxial stretching method)
Using an extruder having an extruder A, an extruder B, and a T-die three-layer die, the raw materials are charged into the extruder A and the extruder B, melt-kneaded, and melt extrusion comprising A layer / B layer / A layer Create a sheet.

  Specifically, as a raw material for the A layer, a master pellet containing inorganic particles (1) and a master pellet containing inorganic particles (2) obtained in (1) and polyester as necessary are mixed. , Dried and fed to an extruder A heated to a temperature of 270-300 ° C.

  Next, as a raw material for the B layer, a resin incompatible with polyester (for example, polymethylpentene) and polyester are mixed, dried, and supplied to an extruder B heated to a temperature of 270 to 300 ° C. To do.

  Lamination is performed so that the polyester composition charged into the extruder A in the T-die three-layer die comes to both surface layers, and the polyester composition thrown into the extruder B comes to the inner layer. The extruded sheet is discharged.

  This melted sheet is closely cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 to 60 ° C., and the unstretched film is led to a group of rolls heated to 80 to 120 ° C. in the longitudinal direction. The film is stretched 2.0 to 5.0 times longitudinally and cooled with a roll group of 20 to 50 ° C. Subsequently, the film was stretched in a longitudinally heated atmosphere at 90 ° C. to 150 ° C. while being held at both ends of the longitudinally stretched film with clips, and gradually cooled through heat setting at 150 to 230 ° C. Then, after cooling to room temperature and winding up, slitting is performed to obtain the laminated film of the present invention.

[Measuring method]
(1) Refractive Index of Inorganic Particles 100 g of laminated film was dispersed in ethanol using a plasma low-temperature ashing treatment device (device name: Plasma Asher, manufactured by J-Science Co., Ltd.), and precipitated after centrifugation. The inorganic particles are vacuum-dried to obtain a measurement sample.

The refractive index of the obtained measurement sample is measured by using an immersion liquid at room temperature by the B method (Becke line method) of the plastic measurement method shown in JIS-K7142 (2008). As the immersion liquid, bromonaphthalene or methylene iodide is used alone or in combination depending on the range of the refractive index. The polarizing microscope uses “Optiphoto” (Nikon).
(2) Median diameter (D1, D2) of inorganic particles (1) and inorganic particles (2)
Measurement is performed using a laser diffraction particle size distribution measuring apparatus (Nikkiso Co., Ltd., Microtrac MT3000II). 1 g of the inorganic particle (1) is put in a cell block attached to the laser diffraction particle size distribution measuring device, and then measured at room temperature. The particle size corresponding to 50% in the cumulative distribution curve of the volume-based particle size is the inorganic particle (1 ) Median diameter D1. The median diameter D2 is similarly determined for the inorganic particles (2).
(3) Content of inorganic particles in layer A Inorganic deposited from 100 g of laminated film obtained by ashing with a plasma low-temperature ashing treatment device (device name: Plasma Asher, manufactured by J Science Co., Ltd.) The particles are vacuum dried to obtain a measurement sample. The obtained measurement sample is quantitatively analyzed using an ICP emission analyzer (device name: OPTIMA4300DV, manufactured by PerkinElmer).
(4) Particle size ratio of inorganic particles contained in layer A Cut the laminated film into strips with a width of 10 mm, apply adhesive tape to the edges, peel off the interface, take out only 50 g of layer A, and plasma low-temperature ashing Ashing was performed using a treatment method (device name: Plasma Asher, manufactured by J-Science Co., Ltd.) to obtain inorganic particles. 1 g of the obtained inorganic particles were placed in a cell block attached to a laser diffraction particle size distribution measuring apparatus (manufactured by Nikkiso Co., Ltd., Microtrac MT3000II), and then measured at room temperature. In the frequency distribution curve of the volume-based particle diameter, two peaks are taken from the higher frequency distribution, and the arithmetic average diameter of the peak seen on the larger particle diameter side is the inorganic particle D1 particle diameter and particle contained in the A layer The arithmetic average diameter of the peak seen on the smaller diameter side is measured as the particle diameter of D2, and the particle size ratio (D1 / D2) of the inorganic particles contained in the A layer is calculated.
(5) Content ratio of bubbles in the A layer and the B layer The laminated film is cut in the cross-sectional direction (thickness direction), and a transmission electron microscope HU-12 type (manufactured by Hitachi, Ltd.) is used. , Observe the cross section of the B layer, and obtain a cross-sectional photograph magnified 2000 times. From the obtained cross-sectional photograph, the bubble portion is traced on the transparent film for OHP with an oil pen, and the bubble portion is filled with the oil pen to obtain an analysis film in which the bubbles are traced. Using the image analyzer, the area (a) of the air bubbles filled with the oil-based pen and the area (b) corresponding to the A layer are calculated from the obtained A layer analysis film, and the B layer analysis film From this, the area (c) of the bubbles filled with the oil pen and the area (d) corresponding to the B layer are calculated. The value calculated by the following formula using (a) to (d) is defined as the bubble content in the A layer and the B layer.
Bubble content in layer A = (a) / (b) × 100 (%)
Bubble content in layer B = (c) / (d) × 100 (%)
(6) Density of the A layer The laminated film is cut into a strip having a width of 10 mm, an adhesive tape is attached to the end portion, interface peeling is performed, only the A layer is taken out, and an A layer sample having a width of 10 mm and a length of 10 mm is made. The specific gravity of the layer A sample was measured in an atmosphere at room temperature of 23 ° C. and relative humidity of 65% using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.). The measurement is performed three times, and the average value is defined as the specific gravity ρ of the A layer, and the value calculated by the following formula is defined as the density of the A layer.
Density of layer A (kgm ⁻³ ) = ρ of layer A × 0.9997538 × 1000
(7) Thermal diffusivity of layer A A layer sample in which a laminated film was cut into a strip with a width of 20 mm, an adhesive tape was attached to the end, interface peeling was performed, and only layer A was taken out to form a disk shape with a diameter of 10 mm. make. This A layer sample is measured using a xenon flash method measuring device (device name: TC9000, manufactured by ULVAC-RIKO).
(8) Density of Laminated Film Collect a total of 15 sheets of N = 5 in a square of 3 cm, width 10 cm, and length 10 cm at both ends and center in the width direction of the laminated film. Measure the weight of 15 samples and measure the total weight of the samples. Further, the thickness of the central part of the four sides of the sample is measured with a micrometer at N = 2, and the average value is taken as the thickness of the sample, and the total volume of the sample is calculated from the thickness and area. From the total weight of the sample and the total volume of the sample, the density of the laminated film is calculated from the following formula.
Density of laminated film (kgm ⁻³ ) = (total weight of sample (kg)) / (total volume of sample (m ³ ))
(9) Thermal diffusivity of the entire laminated film The thermal diffusivity of the entire laminated film is determined according to the method described in (7).
(10) Reflectivity of laminated film A spectrophotometer (U-3310) manufactured by Hitachi High-Technologies is attached with a 60 mmφ integrating sphere, and a standard white plate made of aluminum oxide (Part No. 210-0740 manufactured by Hitachi High-Technologies) is 100%. The reflectivity is measured over 400 to 700 nm. The reflectance is read at intervals of 5 nm from the obtained chart, and the arithmetic average value is calculated to obtain the reflectance. The number of samples is 3, and the reflectance obtained in each measurement is averaged to obtain the reflectance of the laminated film.
(11) LED temperature (characteristic evaluation of laminated film)
LED (width 3.5 mm, length 2.8 mm, thickness 1.9 mm) at the center of an aluminum plate (width 4 mm, length 120 mm, thickness 1.2 mm) (Bright Corporation, 3528 (SMD) white / 0 .2 W)) are arranged in a row at regular intervals (interval: 10 mm) and fixed to obtain a light source device. The lighting of the LEDs is adjusted by using a power source (180 mA, voltage 12 V) so that the total output of all the LEDs is 2.2 W, and all the LEDs are turned on.

  Next, as shown in FIG. 1, a laminated film of the same size is laid on a stainless steel plate (width 200 mm, length 200 mm, thickness 5 mm), and the aluminum substrate side of the light source device is placed at the center of the film surface. I put it like a knot. After turning on the power and lighting the LEDs for 30 minutes, the LED side surface temperature is measured by using a radiation thermometer (Horiba IT-340) and the total number (12) is measured, and the average value of the LED light source temperature is obtained. When the average value of the LED temperature exceeds 78 ° C., the lifetime of the LED is remarkably reduced. If it is 78 degrees C or less, the lifetime of LED will become long to the level which is practically satisfied, and there exists a tendency for a lifetime to become long, so that the average value of LED temperature is low.

  The present invention will be described based on examples.

[Example 1]
Inorganic particles (1) Polyethylene terephthalate resin master pellets containing 50% by weight of magnesium oxide having a median diameter D1 of 3 μm and a refractive index of 1.74, and inorganic particles (2) median diameter D2 of 1.5 μm, refractive index A raw material (D2 (μm) / D1 (μm) = 2) prepared by blending master pellets made of polyethylene terephthalate resin containing 50% by weight of magnesium oxide having a weight of 1.74 with a weight ratio of 50/50, and pellets of polyethylene terephthalate The amount of inorganic particles of magnesium oxide in the total amount of polyethylene terephthalate raw material of 100% by weight was adjusted to 5% by weight in 90% by weight of the raw material. The polyethylene terephthalate raw material is vacuum dried and then supplied to an extruder A heated to 280 ° C. to form a polyester (A layer). In the composite film forming apparatus having an extruder B, a polyester layer (B layer) is formed. Extruder B heated to 260-300 ° C. in which 95% by weight of a dried polyethylene terephthalate raw material and 5% by weight of a dried Mitsui Chemicals polymethylpentene resin (hereinafter abbreviated as PMP) were mixed. Was melted and introduced into the T-die composite die. These polymers were laminated through a laminating apparatus so as to be A layer / B layer / A layer and formed into a sheet form from a T die. Furthermore, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction and then passed through a cooling roll, While holding both ends of the longitudinally stretched film with clips, the film was guided to the tenter and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Thereafter, a heat setting temperature treatment of 180 to 240 ° C. was performed in a tenter to obtain a target laminated film. For design verification of the obtained laminated film, the refractive index of the inorganic particles in the A layer, the content of the inorganic particles in the A layer, and the like were measured. The properties of the laminated film are shown in Table 1. The bubble content in layer A of the obtained laminated film was 1.0% by volume, and the bubble content in layer B was 15% by volume. In addition, the obtained laminated film has a density of A layer of 1510 kgm ⁻³ , the thermal diffusivity of the A layer is as good as 1.5 × 10 ⁻⁷ m ² s ^−1, and the thermal diffusivity of the entire laminated film is also 1 0.0 × 10 ⁻⁷ m ² s ⁻¹ and good. The laminated film density was as light as 1000 kgm ⁻³ and the reflectivity was as good as 95%. Moreover, in the characteristic evaluation of a laminated film, the temperature of LED was as low as 75 degreeC, for example, was a laminated film suitable as a back sheet | seat of a liquid crystal display light source part.

[Examples 2-3]
A laminated film was obtained in the same manner as in Example 1, except that the content of the magnesium oxide particles in the A layer was changed to the content and content shown in Table 1. Table 1 shows the characteristics of the obtained laminated film. When the content of the magnesium oxide particles in the A layer was increased, the thermal diffusivity of the A layer, the thermal diffusivity of the laminated film, and the reflectance of the laminated film increased. Therefore, the temperature of LED became low, for example, it was a laminated film suitable as a back sheet | seat of a liquid crystal display light source part.

[Examples 4 to 9]
A laminated film was obtained in the same manner as in Examples 1 to 3 except that the content of the polymethylpentene resin in the B layer was changed and the content of the bubbles in the B layer was changed to the content shown in Table 1. . Table 1 shows the characteristics of the obtained laminated film. The obtained laminated film had good thermal diffusivity and reflectance, and was a laminated film suitable as a back sheet for a liquid crystal display light source part, for example.

[Examples 10 to 12]
A laminated film was obtained in the same manner as in Example 2 except that the median diameters of the inorganic particles (1) and the inorganic particles (2) were changed to the particle diameters shown in Table 1. Table 2 shows the characteristics of the obtained laminated film. The obtained laminated film had good thermal diffusivity and reflectance, and was a laminated film suitable as a back sheet for a liquid crystal display light source part, for example.

[Examples 13 to 21]
A laminated film was obtained in the same manner as in Examples 1 to 9, except that calcined kaolin having a refractive index of 1.66 was used as the inorganic particles. The properties of the obtained laminated film are shown in Tables 2 and 3. The obtained laminated film had good thermal diffusivity and reflectance, and was a laminated film suitable as a back sheet for a liquid crystal display light source part, for example.

[Examples 22 to 24]
A laminated film was obtained in the same manner as in Examples 1 to 3, except that zinc oxide having a refractive index of 1.95 was used as the inorganic particles. Table 3 shows the properties of the obtained laminated film. The obtained laminated film had good thermal diffusivity and reflectance, and was a laminated film suitable as a back sheet for a liquid crystal display light source part, for example.

[Comparative Examples 1 to 9]
A laminated film was obtained in the same manner as in Examples 1 to 9 except that calcium carbonate having a refractive index of 1.58 was used as the inorganic particles. Table 4 shows the properties of the obtained laminated film. In Comparative Examples 1 to 9 using inorganic particles having a low refractive index, the thermal diffusivity of the A layer and the thermal diffusivity of the laminated film were low. Therefore, the temperature of the LED is increased in the characteristic evaluation of the laminated film, and for example, it is a laminated film that is not suitable as a back sheet for a liquid crystal display light source part.

[Comparative Examples 10-12]
A laminated film was obtained in the same manner as in Examples 1 to 3, except that the inorganic particle content of the A layer was changed to the content shown in Table 5. Table 5 shows the characteristics of the obtained laminated film. In Comparative Examples 10 to 12 having a small inorganic particle content, the thermal diffusivity of the A layer, the thermal diffusivity of the laminated film, and the reflectance of the laminated film were low. Therefore, in the characteristic evaluation of the laminated film, the temperature of the LED becomes high, and for example, the laminated film is not suitable as a back sheet for a liquid crystal display light source part.

[Comparative Examples 13 to 15]
A laminated film was obtained in the same manner as in Examples 1 to 3, except that the inorganic particle content of the A layer was changed to the content shown in Table 5. Table 5 shows the characteristics of the obtained laminated film. In Comparative Examples 13 to 15 having a large inorganic particle content, although the thermal diffusivity of the A layer, the thermal diffusivity of the laminated film, and the reflectance of the laminated film increased, troubles in the film forming process frequently occurred and productivity was poor. Met.

  The laminated film of the present invention can be widely used in applications that require heat dissipation and reflectivity, such as a backlight member for a liquid crystal television, a backlight member for a personal computer, and a light source member for a small monitor.

1 LED
2 Aluminum plate 3 Laminated film 4 Stainless steel plate 5 Radiation thermometer

Claims (4)

A laminated film having at least an A layer and a B layer,
(A) A layer contains a polyester resin and inorganic particles,
(B) The refractive index of the inorganic particles is 1.65 to 2.40,
(C) The content of the inorganic particles is 5% by weight to 60% by weight with respect to the A layer,
(D) The bubble content in the A layer is 10% by volume or less with respect to the A layer,
(E) The thermal diffusivity of the A layer is 1.4 × 10 ⁻⁷ m ² s ⁻¹ or more,
(F) The density of the A layer is 1100 kgm ^{−3 to} 2500 kgm ⁻³ ,
(G) A laminated film used for a back sheet of a liquid crystal display light source section, wherein the B layer is a layer formed using a polyester resin.   The laminated film according to claim 1, wherein the A layer is an outermost layer.   The laminated film according to claim 1 or 2, wherein the B layer contains bubbles, and the content of bubbles in the B layer is 15% by volume to 50% by volume. The laminated film according to claim 1, wherein the laminated film has a thermal diffusivity of 0.7 × 10 ⁻⁷ m ² s ⁻¹ or more and a reflectance of 90% or more .

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