JP6363334B2 - White reflective film - Google Patents

Description

  The present invention relates to a white reflective film. In particular, it is related with the white reflective film used for a liquid crystal display device.

  A backlight unit of a liquid crystal display device (LCD) includes a direct type provided with a light source and a reflective film on the back surface of the liquid crystal display panel, and a light guide plate provided with a reflective plate on the back surface of the liquid crystal display panel. There is an edge light type provided with a light source on the side surface. Conventionally, as a backlight unit used in a large-sized LCD, a direct type (mainly direct type CCFL) has been mainstream from the viewpoint of excellent screen brightness and uniformity of brightness within the screen.

  On the other hand, the edge light type is often used for a comparatively small LCD such as a conventional notebook PC, but the light guide plate made of a relatively soft material because the light guide plate and the reflection film are in direct contact with each other. Is damaged by the reflective film. As a countermeasure, for example, as disclosed in Patent Documents 1 and 2, there is a report of a reflective sheet including a scratch-preventing layer using elastomeric beads. Furthermore, there is a report that adjusts the average particle diameter and burial rate of beads to suppress the dropping of beads and suppress the occurrence of white spot defects (Patent Document 3).

  In recent years, with the development of light sources and light guide plates, the brightness and uniformity of brightness within the screen have been improved even in edge-light type backlight units, and the LCD can be made thinner. In addition, edge-light type backlight units have come to be used even in large LCDs.

JP 2003-92018 A Special table 2008-512719 gazette JP 2009-244509 A

  Since the edge light type backlight unit has a structure in which the light guide plate and the reflective film are in direct contact as described above, in order to suppress the in-plane variation in luminance due to the sticking, the light guide plate and the reflective film are reflected. It is necessary to have a gap with the film and keep this gap constant. And since a reflective film has a bead on the surface, the gap between a light-guide plate and a reflective film can be kept constant, and these sticking can be prevented.

  However, as described in Patent Documents 1 to 3, the present inventors collect a film that does not become a product from a film in which an anti-scratch layer is formed by applying a paint containing elastomeric beads or rubber beads. When a new film is produced again using it as a self-recovery raw material, if the beads remaining in the recovered raw material are present in the film and particularly in the reflective layer without being melted, the film thickness The number of voids per unit was reduced, and it was difficult to obtain a high reflectance, and the film forming property was lowered. As a result, a new problem was found that was not substantially self-collectable, and was focused on.

  Therefore, the present invention provides a recoverable white reflective film in which a film is recovered and the resulting film is excellent in reflection characteristics and film formability even when the film is manufactured using the raw material as a self-collecting raw material. Objective.

The present invention adopts the following configuration in order to achieve the above-described problems.
1. A white reflective film having a void-containing polyester base film and a coating layer,
The coating layer forms at least one surface of the white reflective film and is formed from a coating liquid. The coating liquid mainly includes a polyester binder and polyester particles having a melting point of 200 to 270 ° C. in the solid content of the coating liquid. As a component, the content of the polyester particles is 5 to 60% by mass based on the solid content mass of the coating liquid,
Coating layer is less than a thickness of 1μm or more 10 [mu] m, has a projection on the surface, the height 5μm or more protrusions frequency in the surface is ¹⁰ 4 ^{-10 10} / ^{m 2,} for an edge light type backlight unit White reflective film.
2. 2. The edge-light type back as described in 1 above, wherein the melting point Tm1 of the polyester particles and the melting point Tm2 of the polyester resin constituting the polyester base film satisfy 200 ≦ Tm2 ≦ 270 and Tm1-40 ≦ Tm2 ≦ Tm1 + 40. White reflective film for light unit .
3. The white reflective film for an edge light type backlight unit according to the above 1 or 2, wherein the coating liquid further contains 1 to 15% by mass of a crosslinking agent based on the solid content mass of the coating liquid.
4). The white reflective film for an edge-light type backlight unit according to any one of 1 to 3 above, wherein the coating liquid further contains 0.1 to 10% by mass of silicone oil based on the solid content mass of the coating liquid. .
5. The white reflective film for an edge light type backlight unit according to any one of the above 1 to 4, which is used as a surface light source reflecting plate including a light guide plate.

  According to the present invention, there is provided a recoverable white reflective film in which the obtained film is excellent in reflection characteristics and film formability even if the film is recovered and the film is manufactured again using the self-collecting raw material. be able to.

It is a schematic diagram which shows the structure used for the adhesion spot evaluation in this invention. It is a schematic diagram which shows the method of the damage evaluation of the light-guide plate in this invention, and the drop-off evaluation of particle | grains.

  Hereafter, each structural component which comprises this invention is demonstrated in detail.

[Polyester base film containing voids]
The polyester base film containing a void in the present invention is a film composed of a polyester resin and a void forming agent, containing a void forming agent by containing the void forming agent, and exhibiting a white color. The void forming agent will be described in detail later, but for example, inorganic particles and a resin that is incompatible with the polyester resin constituting the polyester base film (hereinafter may be referred to as incompatible resin) are used. be able to.
Further, the reflectance of the polyester base film at a wavelength of 550 nm is preferably 95% or more, more preferably 96% or more, and particularly preferably 97% or more.

  Further, the polyester base film in the present invention may be a single layer film or a laminated film. In the case of a laminated film, it can be composed of, for example, a reflective layer having a relatively large void content and a support layer having a relatively small void content. When it has a reflective layer (A) and a support layer (B), it consists of two layers of A / B, three layers of A / B / A and B / A / B, and similarly four or more layers A multilayer structure may be used, and there is no particular limitation as long as the structure of the present application is satisfied. With the support layer having a relatively small void content, the effect of improving the film forming property can be enhanced.

(Polyester resin)
The polyester resin constituting the polyester base film is preferably a polyester composed of a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, sebacic acid, and the like. Examples of the diol component include components derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like. Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable. Polyethylene terephthalate may be a homopolymer, but crystallization is suppressed when the film is stretched uniaxially or biaxially, and the film-forming stability (also referred to as stretchability or film-forming property) of the film is improved. From the viewpoint, a copolymer is preferable. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and an isophthalic acid component and a 2,6-naphthalenedicarboxylic acid component are preferable from the viewpoint of achieving both heat resistance and film forming properties. The ratio of the copolymerization component is, for example, 0.5 to 20 mol%, preferably 1 to 18 mol%, particularly preferably 2 to 15 mol%, based on 100 mol% of all dicarboxylic acid components of the polyester. By making the ratio of a copolymerization component into this range, it is excellent in the improvement effect of film forming property. Moreover, it is excellent in thermal dimensional stability.

  In addition to the polyester resin and void forming agent described above, the polyester base film contains a self-recovery raw material that collects a product that does not become a product or an end gripped by a clip in the production of a white reflective film. Can do. In the present invention, since the polyester base film and the coating layer are mainly composed of polyester, a white reflective film excellent in reflectance can be obtained even if a self-recovery raw material is contained. Examples of such a self-recovery raw material include a pulverized recovered film, a pulverized film made into a chip shape by pressure or the like, and a pulverized film melt-extruded into a chip shape.

  The content of the self-collecting raw material is not particularly limited as long as the object of the present invention is not impaired, but is, for example, 10 to 60% by mass, preferably 15 to 55% by mass based on the mass of the polyester base film. Within such a range, it is difficult to adversely affect the reflectance, and the productivity is excellent.

  In this invention, when a polyester base film has a reflection layer and a support layer, it is preferable to mainly contain a self-recovery raw material in a reflection layer. This is because, when it is contained in the support layer, the effect of improving the film forming property by the support layer is hardly achieved with the void forming agent or the like of the self-recovery raw material. Since the coating layer in the present invention has a specific configuration, even if the self-recovery raw material is mainly contained in the reflective layer, the film forming property and the reflectance are excellent.

(Void forming agent)
In the polyester base film, when inorganic particles are used as the void forming agent, the inorganic particles are preferably white inorganic particles. Examples of the white inorganic particles include barium sulfate, titanium dioxide, silicon dioxide, and calcium carbonate particles. For these inorganic particles, the average particle size and content may be selected so that the white reflective film has an appropriate reflectance, and preferably has an appropriate film forming property, and these are not particularly limited. The average particle diameter of the inorganic particles is, for example, 0.2 to 3.0 μm, preferably 0.3 to 2.5 μm, and more preferably 0.4 to 2.0 μm. Moreover, the content is preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and most preferably 31 to 53% by mass based on the mass of the polyester base film. By using inorganic particles in this range, it is easy to achieve a preferable reflectance. Further, by adopting the above-described particle mode, it is possible to appropriately disperse in the polyester, it is difficult for the particles to aggregate, and a film without coarse protrusions can be obtained. Breaking at the time of stretching starting from the particles is also suppressed, and the effect of improving the film forming property can be enhanced. The inorganic particles may have any particle shape, for example, a plate shape or a spherical shape. The inorganic particles may be subjected to a surface treatment for improving dispersibility.

When an incompatible resin is used as the void forming agent, polyolefin, polystyrene, or the like is preferable as the incompatible resin. These may be in the form of particles. In addition, as in the case of inorganic particles, the content may be selected as the average particle size and content so that the white reflective film has an appropriate reflectance, and preferably has an appropriate film forming property. These are not particularly limited. Preferably, the reflectance of the white reflective film may be within a preferable range in the present invention. In consideration of this, the content is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and most preferably 10 to 32% by mass based on the mass of the polyester base film. By using an incompatible resin in such a range, it becomes easy to achieve a preferable reflectance.
In the present invention, inorganic particles and an incompatible resin can be used in combination, and even when they are used in combination, the content and the like may be appropriately adjusted according to the target reflectance.

(Other ingredients)
As long as the object of the present invention is not impaired, the polyester base film is different from other components such as ultraviolet absorbers, antioxidants, antistatic agents, fluorescent brighteners, waxes, void forming agents, and the like. Can be contained.

[Coating layer]
The coating layer of the present invention is formed from a coating liquid, and the coating liquid has a solid content mainly composed of a polyester binder and polyester particles. In the present invention, it is particularly preferable that the polyester particles and the polyester binder constituting the coating layer are not crosslinked (sometimes referred to as non-crosslinked polyester binder and non-crosslinked polyester particles, respectively). When at least one of these is crosslinked (sometimes referred to as crosslinked polyester binder and crosslinked polyester particles, respectively), foreign matter such as unmelted matter is generated in film formation using self-recovery raw materials. And the effect of improving the film forming property may be reduced. Further, the reflectance of a film obtained by forming a film using a self-recovery raw material tends to be low. Furthermore, when the polyester particles are crosslinked particles, the particle hardness tends to increase, and the improvement effect of suppressing damage to the light guide plate tends to decrease. In addition, it can be judged that it is what was bridge | crosslinked here, for example, what does not have melting | fusing point is the aspect bridge | crosslinked.

  In addition, the above-mentioned "contains a polyester binder and polyester particles as main constituents" does not exclude the inclusion of components other than the polyester binder and the polyester particles, and forms the coating layer (or the coating layer in the present invention). The solid content of the coating liquid to contain can contain other optional components. At that time, the coating layer (or the solid content of the coating liquid forming the coating layer) is added with a specified amount of polyester particles, and with an optional amount of other optional components, and the remaining portion becomes a polyester binder. What is necessary is just to set it as an aspect.

(Polyester binder)
It does not specifically limit as a polyester binder which comprises the coating layer in this invention, For example, aromatic polyester, aliphatic polyester, etc. can be mentioned. Moreover, when laminating a polyester base film and a coating layer, the interlaminar adhesion is improved by adopting a polyester binder. Furthermore, as a polyester resin constituting these, a similar polyester resin (for example, a copolymer component is included). By using the same or similar copolymerization amount, the adhesion between layers is further improved.

  Examples of the polyester used as the polyester binder include the same polyesters as those exemplified as the polyester resin in the polyester base film. Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable. Polyethylene terephthalate may be a homopolymer, but a copolymer is preferred from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the film forming property of the coating layer is improved. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoint of achieving both heat resistance and film-forming properties. The proportion of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 17 mol%, and particularly preferably 12 to 16 mol%, based on 100 mol% of the total dicarboxylic acid component of the polyester. Mol%. By making the ratio of a copolymerization component into this range, it is excellent in the effect of improving the film forming property of the coating layer. Moreover, it is excellent in heat resistance. Furthermore, it becomes easy to achieve the aspect of the melting point described later. In addition, a modified polyester having components other than polyester, such as a block copolymer or a graft copolymer, can also be used as the polyester binder in the present invention, but the polyester component is based on the weight of the modified polyester. 50% by mass or more, more preferably 60% by mass or more, and most preferably 70% by mass or more in terms of film-forming properties and reflectivity after recovery of raw materials, and adhesion to a substrate mainly composed of polyester. Desirable from a viewpoint.

  Moreover, from the viewpoint of reducing raw material recoverability and environmental load, it is preferable to use an aqueous polyester binder made of a water-soluble polyester or a water-dispersible polyester and to make an aqueous coating liquid as a coating liquid. The water-based polyester binder preferably includes a dicarboxylic acid component containing a sulfonic acid metal salt, preferably a Na sulfoisophthalic acid component as a copolymerization component. The copolymerization amount is preferably 1 to 20 mol%, more preferably 2 to 15 mol%. When the copolymerization amount of the dicarboxylic acid component containing the sulfonic acid metal salt is too large, the blocking resistance tends to be inferior.

(Polyester particles)
Examples of the polyester particles in the coating layer of the present invention include polyethylene terephthalate particles, polybutylene terephthalate particles, polyethylene naphthalate particles, and the like. These are particularly high in thermal stability, and the film is recovered and self-collected. It is particularly preferable from the viewpoints of being easy to handle when used as a raw material, excellent in reflectivity of the resulting film, and excellent in film forming properties in which foreign matters such as gas marks and unmelted materials are hardly generated.

  The average particle diameter of the polyester particles is preferably 5 to 70 μm from the viewpoint that the gap between the light guide plate and the film can be kept constant and that they can be prevented from sticking and the particles are prevented from falling off. When the average particle size is too small, the white reflective film is partially adhered to the light guide plate, and there is a tendency that the possibility of becoming adhesion spots increases. From such a viewpoint, the average particle diameter is more preferably 6 μm or more, further preferably 7 μm or more, and particularly preferably 8 μm or more. On the other hand, if the particle size is too large, the particles tend to drop off. If the dropout occurs, the backlight unit partially contacts the light guide plate and becomes white as a brightness spot, which can be seen visually. It becomes a drawback. From such a viewpoint, the average particle diameter is more preferably 65 μm or less, further preferably 60 μm or less, and particularly preferably 55 μm or less.

The polyester particles are particularly preferably non-spherical particles having a minor axis / major axis in the range of 0.9 to 0.3. Since the polyester particles are non-spherical particles, the mechanism is unknown. However, the particles themselves tend to be moderately aggregated, and the moderately aggregated particles can preferably form high protrusions. It is advantageous that the gap between the optical plate and the film can be easily maintained, and that the luminance uniformity is excellent. From such a viewpoint, the ratio of the minor axis / major axis is more preferably 0.8 or less, and even more preferably 0.7 or less. On the other hand, when the ratio of the minor axis / major axis is less than 0.3, it tends to be difficult to form a projection having a preferred height.
In addition, what is necessary is just to select the range which satisfies the protrusion frequency mentioned later, after considering the average particle diameter of particle | grains etc., as content of the polyester particle in an application layer. For example, preferably 5 to 60% by mass, more preferably 6 to 55% by mass, and particularly preferably 7 to 50% by mass based on the mass of the coating layer (the mass of the solid content of the coating liquid forming the coating layer). is there.

  Here, an example is shown below about the manufacturing method of a polyester particle. That is, after freezing the polyester resin, the polyester resin can be finely cut and then the desired particle size can be obtained by air classification. In such a production method, the polyester resin is preferably on a chip or in a fibrous form, but when made from a fibrous polyester resin, the ratio of the short diameter / long diameter of the resulting particles can be easily controlled. This is particularly preferable because the size can be easily obtained.

(Other ingredients)
The coating layer (solid content of the coating liquid forming the coating layer) may contain components other than the above-described constituent components as long as the object of the present invention is not impaired. Examples of such components include crosslinking agents, silicone oils, UV absorbers, antioxidants, antistatic agents, fluorescent brighteners, waxes, particles and resins different from the polyester particles.

(Crosslinking agent)
The coating layer in the present invention may have a crosslinked structure with a crosslinking agent. Use of a crosslinking agent has an effect of improving the blocking resistance of the coating layer. On the other hand, in film formation using a self-recovery raw material, foreign matters such as unmelted materials are likely to be generated, and the effect of improving film formation may be reduced. Moreover, the reflectance of the film after self-collection may be lowered. From the viewpoint of achieving these balances, the content of the crosslinking agent is preferably 1 to 15% by mass, preferably 1 to 10% by mass, based on the mass of the solid content in the solid content of the coating liquid forming the coating layer. Is more preferable, and 2 to 5% by mass is even more preferable. If priority is given to recoverability (film-formability and reflectance after self-recovery), it is preferable not to contain a crosslinking agent.
As the crosslinking agent, epoxy-based, oxazoline-based, melamine-based and isocyanate-based crosslinking agents are preferable. Examples of the epoxy crosslinking agent include polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds.

(Silicone oil)
The coating layer (solid content of the coating liquid forming the coating layer) in the present invention can contain silicone oil. When the coating layer contains silicone oil, it is possible to impart lubricity and antistatic properties to the film. On the other hand, when there is too much content, it will become easy to drop | omit from an application layer, and if silicone oil falls, it will become process contamination. From these viewpoints, the content of the silicone oil is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, based on the solid content mass of the coating liquid forming the coating layer, and 0.3 -3 mass% is still more preferable.

In the present invention, the silicone oil is a silicone compound having an organosiloxane skeleton, for example, dimethyl silicone, methylphenyl silicone, methyl hydrogen silicone, fluorosilicone, silicone polyether copolymer, alkyl-modified silicone, higher fatty acid-modified silicone. Can be mentioned.
In addition, it is preferable to use a silicone compound having a reactive group. By containing a reactive group, the slipperiness decreases due to the lack of silicone oil from the coating layer, the antistatic property decreases, and the production process due to the missing component. Contamination can be suppressed.

  Silicone oils having this reactive group have a reactive group directly bonded to a silicon atom, and include an organic group containing an amino group, an organic group containing an epoxy group, an organic group containing a carboxylic acid group, a silanol group, or a hydrolized group. It is preferable to use one containing at least one reactive group selected from organic groups that generate silanol groups by decomposition. Examples of the organic group containing an amino group include primary aminoalkyl groups such as 3-aminopropyl group, 3-amino-2-methyl-propyl group, and 2-aminoethyl group, and N- (2-aminoethyl) -3-amino. Examples thereof include organic groups having primary and secondary amino groups such as propyl group and N- (2-aminoethyl) -2-aminoethyl group. Examples of the organic group containing an epoxy group include glycidoxyalkyl groups such as γ-glycidoxypropyl group, β-glycidoxyethyl group, γ-glycidoxy-β-methyl-propyl group, and 2-glycidoxycarbonyl-ethyl. And a glycidoxycarbonylalkyl group such as a 2-glycidoxycarbonyl-propyl group. Examples of organic groups that generate silanol groups by hydrolysis include alkoxy groups such as methoxy, ethoxy, butoxy, and 2-ethylhexyloxy, methoxy-β-ethoxy, ethoxy-β-ethoxy, and butoxy-β-. Alkoxy-β-ethoxy groups such as ethoxy groups, acyloxy groups such as acetoxy groups and propoxy groups, N-alkylamino groups such as methylamino groups, ethylamino groups and butylamino groups, N, N-dialkyl groups such as dimethylamino groups and diethylamino groups Examples include nitrogen-containing heterocyclic groups such as amino groups, imidazole groups, and pyrrole groups.

[Aspect of coating layer surface]
(Protrusion frequency)
The white reflective film of the present invention has a coating layer on at least one surface, and the coated layer has the above-described polyester particles on the surface, and the polyester particle covers the surface of the white reflective film. Become. And the protrusion is formed in the white reflective film surface by this polyester particle. On such a surface, by having protrusions with an appropriate height at an appropriate frequency, sticking to the light guide plate can be suppressed. Specifically, the protrusion frequency with a height of 5 μm or more is 10 ⁴ to 10. It is usually necessary to be ¹⁰ pieces / m ² . When the protrusion frequency is within the range, the effect of maintaining the gap between the light guide plate and the white reflective film can be obtained, and problems such as luminance spots (defects in which the adhered part appears white) do not occur. If the protrusion frequency is less than 10 ⁴ / m ² , the gap may not be maintained, and luminance spots due to sticking between the light guide plate and the reflective film (a defect in which the sticking part appears white) occur. There is a fear. Further, the friction between the light guide plate and the reflective film tends to increase, and the light guide plate is easily scratched. In addition, when the projection frequency exceeds 10 ¹⁰ pieces / m ² , the projection becomes dense, and the proper gap between the reflective film and the light guide plate can be secured and the sticking can be suppressed, or the film surface can be damaged. In this case, they overlap and become easy to drop off. From these viewpoints, the more preferable protrusion frequency is 10 ⁵ / m ² or more, and more preferably 10 ⁶ / m ² or more. Further, it is more preferably 5 × 10 ⁹ pieces / m ² or less, further preferably 10 ⁹ / m ² or less, particularly preferably 5 × 10 ⁸ pieces / m ² or less.

(Average protrusion height)
In the present invention, the average protrusion height on the surface of the coating layer refers to the most frequent height from the center line of the surface of the coating layer, which is determined by the measurement method described later. The average protrusion height is preferably 5 to 70 μm, and it is easy to secure a gap with the light guide plate, and particle dropping is further suppressed. When the average protrusion height is less than 5 μm, contact with the light guide plate is likely to occur, and when the average protrusion height exceeds 70 μm, the particles forming the protrusion easily fall off. Therefore, the height of the protrusion is more preferably 6 to 65 μm, the more preferable range is 7 to 60 μm, and the most preferable range is 8 to 55 μm.

[Melting point of each component]
In the present invention, when the melting point of the polyester particles in the coating layer is Tm1 (unit: ° C.), it is necessary to satisfy the following formula.
200 ≦ Tm1 ≦ 270
By setting it as such an aspect, the heat resistance of particle | grains can be maintained and it is excellent in recoverability (film forming property and reflectance after collection | recovery) when raw material collection | recovery is performed from a film. If Tm1 is too low, the particles tend to melt in the formation of the coating layer, making it difficult to form protrusions on the surface of the coating layer. On the other hand, if Tm1 is too high, the polyester particles tend to remain in the film formation using the self-recovery raw material, and the effect of improving the film formability and reflectance of the film to be obtained decreases. From this viewpoint, Tm1 is preferably 205 to 268 ° C, and more preferably 210 to 260 ° C.

Moreover, it is more preferable that the following formula is satisfied when the melting point of the polyester resin constituting the polyester base film containing voids is Tm2 (unit: ° C.). Here, when the polyester base film has a plurality of layers such as a reflective layer and a support layer, the Tm2 may be considered as the melting point of the polyester resin constituting the layer containing the self-recovery raw material. In the present invention, as described above, the self-recovery raw material is preferably contained in the reflective layer. Therefore, in such an aspect, the Tm2 is the melting point of the polyester resin constituting the reflective layer.
200 ≦ Tm2 ≦ 270
Tm1-40 ≦ Tm2 ≦ Tm1 + 40

  By making Tm2 into such a melting point mode together with the above-described Tm1, the white reflective film can maintain a gap with the light guide plate, and at the same time, the white reflective film of the present invention can be collected and self-collected. Even when the white reflective film of the present invention is produced by using it again as a raw material for forming a film, particularly for forming a reflective layer, the obtained white reflective film is excellent in film forming properties and reflectance. That is, particles are present in the coating layer, and it is possible to secure a gap. At the same time, when the particles are collected, the particles can be sufficiently melted in the film. While maintaining the performance, the reduction in the number of voids due to self-recovered raw material particles, etc. is suppressed, resulting in a void aspect similar to that of the void when the raw material is not recovered, resulting in reduced reflectivity and other optical properties An excellent film that does not affect the film can be obtained. From such a viewpoint, Tm2 is more preferably 205 to 268 ° C, and further preferably 210 to 260 ° C. More preferably, Tm1-30 ≦ Tm2 ≦ Tm1 + 30, and further preferably Tm1-25 ≦ Tm2 ≦ Tm1 + 25.

[Configuration of white reflective film]
The thickness of the polyester base film in the present invention is preferably 70 to 400 μm. Thereby, the improvement effect of a reflectance can be made high. If it is too thin, the effect of improving the reflectance is low, while if it is too thick, it is inefficient. From such a viewpoint, the thickness is more preferably 80 to 350 μm.

  Moreover, the thickness of the coating layer (when there are a plurality of coating layers, the thickness of one layer on the surface on the light guide plate side) is 1 μm or more and less than 10 μm. Thereby, even if it is an application layer formed by application | coating of a coating liquid, the aspect of protrusion frequency can be satisfied and the gap with a light-guide plate can be ensured. Moreover, a reflectance fall can be suppressed and a reflectance can be made high. If it is too thin, it is difficult to achieve both the projection frequency and the suppression of particle dropout. From this viewpoint, it is preferably 2 μm or more. On the other hand, if it is too thick, it becomes difficult to achieve the necessary projection frequency in the coating layer formed by coating the coating liquid, and the tendency of the reflectance to decrease is significant. Furthermore, when the coating layer is too thick, there is a problem that the film forming property is inferior in the film formation using the recovered raw material obtained by recovering the film. From these viewpoints, it is preferably 8 μm or less, more preferably 5 μm or less.

The coating layer should just have on the surface of at least one side of a white reflective film, and may have it on both surfaces.
Moreover, in this invention, you may have other layers, unless the objective of this invention is impaired other than the polyester base film and coating layer which contain a void. For example, you may have the layer for providing functions, such as antistatic property, electroconductivity, and ultraviolet durability.

[Production method]
Hereinafter, an example of the method for producing the white reflective film of the present invention will be described.
First, when manufacturing a polyester base film, after sufficiently drying a polyester composition containing a polyester resin and, for example, inorganic particles as a void forming agent, the polyester composition is put into an extruder, melted, and wire It is preferable to perform filtration using a nonwoven fabric type filter having an average opening of 10 to 100 μm made of a fine stainless steel wire having a diameter of 15 μm or less. By performing this filtration, it is possible to suppress aggregation of particles that normally tend to aggregate into coarse aggregated particles, and to obtain a film with few coarse foreign matters. The average opening of the nonwoven fabric is preferably 20 to 50 μm. When the filtered polyester composition is, for example, a laminated layer of a reflective layer and a support layer, the polyester composition for forming each layer is melted by a simultaneous multilayer extrusion method using a feed block. Then, an unstretched laminated sheet is produced by extruding from a die in a multilayer state. The unstretched laminated sheet extruded from the die is cooled and solidified with a casting drum to obtain an unstretched laminated film. Next, this unstretched laminated film is heated by roll heating, infrared heating, or the like, and stretched in the machine axis direction (hereinafter, sometimes referred to as the longitudinal direction or the longitudinal direction or MD) to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls.

Next, a coating liquid containing a polyester binder, polyester particles and other optional components for forming a coating layer is coated on one or both sides of the film after longitudinal stretching by a solution coating method, a melt extrusion resin coating method, or the like. To do.
For example, the coating liquid used for the solution coating method can be obtained by mixing each component constituting the coating layer and appropriately diluting with a solvent. Here, as the solvent, water is preferable, that is, an aqueous coating liquid is preferable. The solid content concentration of the coating liquid may be a concentration suitable for various known coating methods.
Thereafter, the coating liquid is dried by a tenter, and stretched in a direction orthogonal to the machine axis direction (hereinafter sometimes referred to as a transverse direction, a width direction, or TD) while preheating the resin of each layer. Get a film.

  The stretching described above is preferably performed at a temperature not lower than the glass transition temperature (Tg) of the polyester constituting the polyester base film and not higher than Tg + 30 ° C., and has excellent film forming properties, and voids are preferably formed. Here, when a film consists of a plurality of layers, the highest Tg is usually adopted, but a Tg of a layer having a high thickness ratio may be adopted as appropriate. The stretching ratio is preferably 2.5 to 4.3 times, more preferably 2.7 to 4.2 times in both the longitudinal direction and the transverse direction. If the draw ratio is too low, uneven thickness of the film tends to be worsened, and voids tend not to be formed. On the other hand, if it is too high, breakage tends to occur during film formation. In the case of sequential biaxial stretching in which longitudinal stretching is performed and then lateral stretching is performed, the second stage (in the above case, transverse stretching) is determined from the stretching temperature of the first stage (in the above case, longitudinal stretching). Also, it is preferable to increase the temperature by 10 to 50 ° C. This is due to the fact that the Tg as a uniaxial film is increased due to the orientation in the first stage of stretching.

Moreover, it is preferable to preheat a film before each extending | stretching. For example, the pre-heat treatment for transverse stretching may be started from a temperature higher than Tg + 5 ° C. of the polyester constituting the polyester base film and gradually raised. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone.
The film after biaxial stretching is subsequently subjected to heat-fixing and heat-relaxing treatments in order to obtain a biaxially oriented film. However, following melt-extrusion to stretching, these treatments can also be performed while the film is running. it can.

  The film after biaxial stretching is heat-fixed by heat treatment under a constant width or a width reduction of 10% or less while holding both ends with a clip (Tm-20 ° C) to (Tm-100 ° C), It is better to reduce the shrinkage rate. Here, when the film is composed of a plurality of layers, the lowest Tm is usually adopted, but a Tm of a layer having a high thickness ratio may be adopted as appropriate. When the heat treatment temperature is too high, the flatness of the film tends to deteriorate, and the thickness unevenness tends to increase. On the other hand, if it is too low, the thermal shrinkage tends to increase.

Further, in order to adjust the amount of heat shrinkage, both ends of the film being held can be cut off, the take-up speed in the film vertical direction can be adjusted, and the film can be relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, preferably 0.1 to 2.5%, more preferably 0.2 to 2.3%, particularly preferably 0.3. The film is relaxed by performing a speed reduction of ˜2.0% (this value is referred to as “relaxation rate”), and the longitudinal heat shrinkage rate is adjusted by controlling the relaxation rate. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, and a desired heat shrinkage rate can be obtained.
In the biaxial stretching, a lateral-longitudinal sequential biaxial stretching method may be used in addition to the longitudinal-lateral sequential biaxial stretching method as described above. Moreover, it can form into a film using a simultaneous biaxial stretching method. In the case of the simultaneous biaxial stretching method, the stretching ratio is, for example, 2.7 to 4.3 times, preferably 2.8 to 4.2 times in both the longitudinal direction and the transverse direction.

  In the above, the coating layer is formed by applying the coating liquid after the longitudinal stretching, but a polyester base film having no coating layer in the above can be prepared, and the coating layer can be provided by so-called off-line coating. Moreover, the polyester base material which does not have a coating layer is produced by applying a coating liquid containing a polyester binder, polyester particles and other optional components to another arbitrary base material to form a coating layer. It is also possible to obtain a polyester base film having a coating layer by laminating to the film by a laminating method or the like so that the coating layer becomes the surface.

Thus, the white reflective film of the present invention can be obtained.
In addition, a white reflective film can be produced in the same manner as described above by adding the obtained white reflective film into a chip by pulverization or melt extrusion as a self-collecting raw material and adding it to the base film. In that case, the concentration of each component may be adjusted so as to obtain a target concentration as a whole in consideration of the amount of each component contained in the self-recovery raw material.

[Characteristics of reflective film]
(Reflectance, brightness)
The reflectance of the white reflective film of the present invention is preferably 95% or more, more preferably 96% or more, and still more preferably 97% or more on the coating layer side. When the reflectance is 95% or more, high luminance can be obtained when used in a liquid crystal display device or illumination.
Moreover, although a brightness | luminance is calculated | required with the measuring method mentioned later, 5500 cd / m < ² > or more is preferable, 5510 cd / m < ² > or more is more preferable, 5520 cd / m < ² > or more is especially preferable.

(Amount of volatile organic solvent)
In the white reflective film of the present invention, the amount of volatile organic solvent measured by the method described later is preferably 10 ppm or less. Thereby, when a self-recovery raw material is obtained and a film is formed using the raw material, a gas mark is hardly generated, and the film forming property is improved. From this viewpoint, it is more preferably 5 ppm or less, further preferably 3 ppm or less, and ideally 0 ppm. In the present invention, in order to reduce the amount of the volatile organic solvent, it is preferable to employ the above-described method without adopting the solution coating method using the organic solvent in forming the coating layer.

Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.
(1) Light reflectance The integrating sphere was attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), the reflectance when the BaSO ₄ white plate was 100% was measured at a wavelength of 550 nm, and this value was defined as the reflectance. In addition, the measurement was performed on the surface of the coating layer for those having the coating layer. What is necessary is just to measure in the side which contacts the light-guide plate side, when having a different coating layer on the front and back, or in the case of only a polyester base material.

(2) Average particle size of void forming agent (inorganic particles) Particle size distribution (standard deviation of particle size) of particles was determined with a laser scattering particle size distribution analyzer (SALD-7000 manufactured by Shimadzu Corporation), and particles at d50 The diameter (particle diameter with 50% distribution from the smaller side on the volume distribution basis) was defined as the average particle diameter.

(3) Average particle diameter of polyester particles Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., 100 particles were arbitrarily measured at a magnification of 1000 times to obtain an average particle diameter, a long diameter, and a short diameter. It was. In addition, in the case other than spherical, the average particle diameter was determined by (major axis + minor axis) / 2. Here, the major axis represents the maximum diameter, and the minor axis represents the maximum diameter perpendicular to the major axis.

(4) Amount of Volatile Organic Solvent At room temperature (23 ° C.), 1 g of a film sample was placed in a 10 L fluororesin bag, which was purged with pure nitrogen and sealed. Next, immediately from the nitrogen in the bag, 0.2 L and 1.0 L of nitrogen were collected in two analytical TENAX-TA collection tubes at a flow rate of 0.2 L / min. The mass of the organic solvent component contained in the collected nitrogen was quantified by HPLC, GCMS. The obtained value is converted into the amount in 10 L of nitrogen, and the mass of the organic solvent volatilized in 10 L of nitrogen is obtained from 1 g of the film sample, and the amount of volatile organic solvent (unit: ppm, based on the mass of the film sample) did. The aldehydes were quantified by HPLC by eluting the aldehyde derivatized product from the collection tube with acetonitrile. Moreover, when the value was different between HPLC and GCMS, the value of the more detected one was adopted.

(5) Film thickness A white reflective film is sliced with a microtome to obtain a cross section, and the cross section is observed at a magnification of 500 times using a S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd. The thickness of each of the polyester base material and the coating layer was determined. In addition, the thickness of the whole film and the coating layer was made into the thickness of the part except the part which particle | grains protruded from the coating layer surface.

(6) Melting point, glass transition temperature Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 ° C./min.

(7) Average protrusion height A 1 mm × 1 mm film sample (measured on the coating layer side) is prepared using a laser microscope (VK-X100) manufactured by Keyence Corporation. The shape of the objective lens is measured by autofocus at a magnification of 50 times. Set the height threshold to 5 μm using the analysis application stored in the device for the stored shape measurement data, and set the median value of the measured most frequent protrusion height range (μm) as the protrusion height (μm). did.

(8) Protrusion frequency The projection profile on the film surface was cut off by a three-dimensional roughness measuring device SE-3CKT (manufactured by Kosaka Laboratory Ltd.) with a cutoff of 0.25 mm, a measurement length of 1 mm, a scanning pitch of 2 μm, and a scanning number of 100. The protrusion profile was recorded at a height magnification of 1000 times and a scanning direction magnification of 200 times. For the analysis, a three-dimensional roughness analyzer SPA-11 (manufactured by Kosaka Laboratory Ltd.) was used. From the obtained projection profile (horizontal axis: projection height, vertical axis: projection profile of the number of projections), the number of projections having a height of 5 μm or more (pieces / m ² ) was obtained and used as the projection frequency.

(9) Luminance The reflective film is taken out from the LED liquid crystal television (LG42LE5310AKR) manufactured by LG and the reflective film obtained in the example is the screen side (surface in contact with the light guide plate) when the coated layer is present. Using the luminance meter (Model MC-940, manufactured by Otsuka Electronics Co., Ltd.) in the state of the backlight unit, the luminance was measured at a measurement distance of 500 mm from the front of the center of the backlight.

(10) Evaluation of scratches on light guide plate (evaluation of shaving property) and evaluation of particle dropout As shown in FIG. 2 is firmly attached, and a reflective film (reference numeral 9 in FIG. 2) having a width of 250 mm × length of 200 mm with the evaluation surface facing upward is 25 mm from both ends in the width direction. Was pasted so that the part of the plate protruded from the iron plate (so that the central 200 mm × 200 mm portion overlapped the iron plate). At this time, the evaluation surface (coating layer surface) of the reflective film was placed outside. In addition, the 25 mm portion remaining at both ends in the width direction of the reflective film is folded back to the back side of the iron plate, and the end portion of the reflective film (the portion where the blade is inserted with a knife or the like at the time of sampling) has the effect of scraping the light guide plate. Eliminated.
Next, the light guide plate (with a size of at least 400 mm × 200 mm) with the dot surface up is fixed on a horizontal desk, and the evaluation film and the light guide plate are in contact with the reflection film fixed on the iron plate created above. As described above, the reflective film side is placed on the light guide plate with the surface facing downward, and a 500 g weight (reference numeral 10 in FIG. 2) is placed thereon, and fixed to the iron plate at a distance of 200 mm (400 mm × 200 mm region) The reciprocating film was moved 15 times at a speed of about 5 to 10 seconds. Then, on the surface of the light guide plate, the degree of shaving and the presence or absence of organic particles dropped off from the reflective film were observed with a 20-fold magnifier and evaluated according to the following criteria.
In the entire range of 400 mm × 200 mm rubbed on the light guide plate, if there are no scratches that can be observed with a magnifying glass after 15 reciprocating movements, “scratch is not evaluated” (scraping evaluation ○), and scratches that can be observed after 10 reciprocating movements are observed. Although there were no scratches that could be observed after 15 reciprocating movements, “scratch was difficult” (shave evaluation Δ), and when there were scratches that could be observed after 10 reciprocations, “scraped” (scraping evaluation ×).
Moreover, after 15 reciprocating movements, if there was no white foreign matter that could be observed with a loupe in the entire range of 400 mm × 200 mm rubbed on the light guide plate, it was determined that “particles did not fall off” (dropout evaluation ○). In addition, when there is a white foreign matter that can be observed, the white foreign matter is observed with a microscope to confirm that it is a polyester particle. (Dropout evaluation Δ), and if 6 or more, “particles dropped out” (dropout evaluation ×).
In the evaluation, in order to suppress the influence of the dot size as much as possible, an area having a large dot size was selected as much as possible on the light guide plate, and the evaluation samples were aligned.

(11) White spot evaluation Using the reflective film and the light guide plate used in the evaluation of (10) above, place the reflective film on the desk so that the coating layer faces upward, and the dot surface faces downward on it. Place the light guide plate, place and fix each 200 g weight on each of the four sides of the light guide plate, and use the backlight light source of the LED liquid crystal television (LG42LE5310AKR) manufactured by LG Inc. If there were bright spots other than light guide plate dots that could be observed visually, white spots were generated (evaluation x). On the other hand, if there were no abnormal bright spots that could be observed visually, no white spots were generated (evaluation ○).

(12) Adhesion spots evaluation (adhesion evaluation)
Take out the chassis from the LED liquid crystal television (LG42LE5310AKR) manufactured by LG and place it on a horizontal desk so that the inside of the television is facing upward. Further, a light guide plate and three optical sheets (two diffusion films and one prism) originally provided in the television were placed thereon. Next, an equilateral triangular base having three columnar legs with a diameter of 5 mm as shown in FIG. 1 is placed in the area including the most severely uneven portion of the chassis in the plane, and a weight of 15 kg is further placed thereon. The area surrounded by these three legs was visually observed, and if there was no abnormally bright part, “no adhesion spots” (adhesion spots evaluation ○) was designated. If there is an abnormally bright part, place the DBEF sheet originally provided on the television on top of the three optical sheets and observe it in the same manner. When there was a spot (evaluation x), and when there was no abnormally bright part, it was set as "there was almost no adhesion spot" (evaluation (triangle | delta)). In addition, the area surrounded by the three legs was a substantially equilateral triangle having a side length of 10 cm.

(13) Film formability (stretchability)
The film formation stability when the film described in the Examples was formed by a continuous film formation method using a tenter was observed and evaluated according to the following criteria.
○: A film having a film length of 10,000 m or more can be stably formed.
(Triangle | delta): The cutting | disconnection produced once during winding of film length 10,000m.
X: Cutting occurred multiple times during the film length of 10,000 m, and stable film formation was not possible.

(Production Example 1: Synthesis of isophthalic acid copolymerized polyethylene terephthalate 1)
136.5 parts by mass of dimethyl terephthalate, 13.5 parts by mass of dimethyl isophthalate (9 mol% with respect to 100 mol% of total acid components of the obtained polyester), 98 parts by mass of ethylene glycol, 1.0 part by mass of diethylene glycol , 0.05 parts by mass of manganese acetate and 0.012 parts by mass of lithium acetate were charged into a rectification column and a flask equipped with a distillation condenser, and heated to 150 to 240 ° C. with stirring to distill methanol to conduct a transesterification reaction. went. After methanol was distilled, 0.03 parts by mass of trimethyl phosphate and 0.04 parts by mass of germanium dioxide were added, and the reaction product was transferred to the reactor. Next, while stirring, the pressure in the reactor was gradually reduced to 0.3 mmHg and the temperature was raised to 292 ° C. to carry out a polycondensation reaction to obtain isophthalic acid copolymerized polyethylene terephthalate 1. The melting point of this polymer was 235 ° C.

(Production Example 2: Preparation of inorganic particle master chip 1)
Using a part of the isophthalic acid copolymerized polyethylene terephthalate 1 obtained above and barium sulfate particles having an average particle diameter of 1.0 μm (in the table, indicated as BaSO ₄ ) as a void forming agent, manufactured by Kobe Steel In a NEX-T60 tandem extruder, mixing is performed so that the content of barium sulfate particles is 63% by mass with respect to the mass of the obtained master chip, and the mixture is extruded at a resin temperature of 260 ° C. A particle master chip 1 was prepared.

(Production Example 3: Polyester Particle A)
The raw materials described below were charged into an autoclave and heated at 180 to 240 ° C. for 120 minutes to conduct a transesterification reaction. Next, the temperature of the reaction system was raised to 245 ° C., and the reaction was continued for 60 minutes at an internal pressure of 1-10 mmHg. As a result, a copolyester was obtained.
134 parts by weight of dimethyl terephthalate 5 parts by weight of dimethyl isophthalate 3 parts by weight of 5-sodium sulfodimethylisophthalate 5 parts by weight of methyl paraterbutyl benzoate Ethylene glycol 136 parts by weight Tetrabutoxy titanate 0.1 parts by weight The particles were slowly agglomerated to obtain particles (polyester particles A) shown in the table.

(Production Example 4: Polyester particles B to F)
Polyethylene terephthalate pellets (melting point: 255 ° C.) are frozen and frozen, and then micronized with a cutter. The finely divided particles were subjected to air classification to obtain particles B having an average particle diameter of 55 μm (major axis average: 60 μm / minor axis average: 50 μm). Particles C to F were subjected to a change in resin cutting conditions and air classification to obtain particles having the sizes shown in Table 1.

[Example 1]
(Manufacture of white reflective film)
Using the isophthalic acid copolymerized polyethylene terephthalate 1 and the inorganic particle master chip 1 obtained above as a raw material for the reflective layer (A layer) and a raw material for the support layer (B layer), the respective layers described in Table 1 So that the melt extrusion temperature of layer A is 275 ° C. and the melt extrusion temperature of layer B is 270 ° C., so that B layer / A layer / B layer is obtained as shown in Table 1. And a three-layer feed block device, and the sheet was formed into a sheet from a die while maintaining the laminated state. At this time, it adjusted with the discharge amount of each extruder so that the thickness ratio of B layer / A layer / B layer might become 10/80/10 after biaxial stretching. Further, this sheet was an unstretched film cooled and solidified with a cooling drum having a surface temperature of 25 ° C. This unstretched film is led to a longitudinal stretching zone maintained at 92 ° C. through a preheating zone at 73 ° C., followed by a preheating zone at 75 ° C., stretched 2.9 times in the longitudinal direction, and cooled by a roll group at 25 ° C. did.
Subsequently, the coating liquid 1 having the composition shown in Table 1 containing the polyester particles A obtained in the above production example was applied to one side of the film, put into a stenter, and 115 ° C. while holding both ends of the film with clips. The film was led to a transverse stretching zone maintained at 130 ° C. through a preheating zone, and stretched 3.6 times in the transverse direction. After that, heat setting is performed at 192 ° C in the tenter, the width is set to 2%, the width is set in the horizontal direction at a temperature of 130 ° C, then both ends of the film are cut off and heat relaxed at a longitudinal relaxation rate of 2%. After cooling, a biaxially stretched film having a base film thickness of 250 μm and a coating layer thickness of 2 μm was obtained.
This film is recovered, pulverized, melt extruded at 275 ° C. to form chips, and a self-recovered raw material is prepared. 35% by mass of the self-recovered raw material is added to the reflective layer A based on the weight of the reflective layer A. The raw material is blended so that the composition of the reflective layer A is the same as that of the original film, and a biaxially stretched film having a base film thickness of 250 μm and a coating layer thickness of 2 μm is obtained in the same manner as described above. Obtained. The evaluation results of the obtained film are shown in Table 2.

[Examples 2 to 5, 7 and Comparative Examples 1 to 3]
A self-recovery raw material was prepared in the same manner as in Example 1 except that the coating liquid was as shown in Table 1, and a white reflective film was prepared using the self-recovery raw material. The evaluation results are shown in Table 2.
In Comparative Example 1, no protrusion having a height of 5 μm or more was observed.

[Example 6]
Using coating liquid 6 described in Table 1 containing polyester particles D as the coating liquid, cycloolefin resin (“TOPAS6017S-04” manufactured by Polyplastics Co., Ltd.) is used instead of barium sulfate as a void forming agent in reflective layer A. A self-recovery raw material was prepared in the same manner as in Example 1 except that the mass was 18% by mass based on the mass of the layer A, and a white reflective film was prepared and evaluated. The evaluation results are shown in Table 2.

[Comparative Example 4]
A self-recovered raw material was prepared in the same manner as in Example 1 except that the coating liquid was changed to the coating liquid 11 shown in Table 1, and a white reflective film was prepared using the self-recovery raw material. The results are shown in Table 2.
In Comparative Example 4, crosslinked polymethylmethacrylate (PMMA) particles (MBX-40 manufactured by Sekisui Plastics Kogyo Co., Ltd.) contained in the coating layer do not melt at the time of recovery, and the film-forming property is greatly reduced due to the formation of coarse voids. did. In addition, it was observed and confirmed by the cross-sectional photograph by the same electron microscope as film thickness measurement that PMMA particle | grains remained in the film obtained by the comparative example 4. FIG.

[Comparative Example 5]
After producing a polyester base film without applying the coating liquid in Example 1, the coating liquid 12 shown below was applied to one side of this film, and dried in a dryer set at a maximum temperature of 115 ° C. A sample was obtained.
(Coating liquid 12, solid content concentration 35% by mass)
・ Particles: Sekisui Plastics Co., Ltd. MBX-40 (cross-linked PMMA, no melting point due to cross-linking system) ... 10.5% by mass
-Acrylic binder: DIC Acrydic A-817BA 31.5% by mass
・ Crosslinking agent: Nippon Polyurethane Industry Co., Ltd. Coronate HL ... 11.7% by mass
・ Organic solvent: butyl acetate: 46.3 mass%
In addition, the solid content ratio of each component in the bead layer obtained from the above recipe is as follows.
・ Particles: 30% by mass
・ Binder: 45% by mass
・ Crosslinking agent: 25% by mass

[Comparative Example 6]
The same operation as in Example 1 was performed except that the coating liquid was not applied in Example 1. The results are shown in Table 2.

[Comparative Example 7]
It was produced in the same manner as Example 1 except that the coating liquid of Example 1 was changed to the coating liquid 13 shown in Table 1. The results are shown in Table 2. Polyethylene particles (Miplon PM-200 manufactured by Mitsui Chemicals) were melted in the film forming process, and surface protrusions could not be formed.
In Comparative Example 7, no protrusion having a height of 5 μm or more was observed because the polyethylene particles were melted.

Polyester binder: Product name, plus coat Z465
Cross-linking agent: manufactured by Takamatsu Yushi, product name Pesresin A-645GH
Silicone oil: NOF Corporation, product name MODIPER FS770
ND: not detected (detection limit)

  The white reflective film of this invention can be used suitably as a reflective film used for a liquid crystal display device, a lighting fixture, etc., and also as a reflective film of a surface light source having a light guide plate. In particular, it can be suitably used as a reflection film used in a display device such as an LCD, particularly as an edge light type backlight unit used in an LCD including a large LCD.

4 Chassis 5 Reflective film, light guide plate, optical sheet laminate 6 Weight 7 Handle portion 8 Iron plate 9 Reflective film 10 Weight 11 Light guide plate 1101 dots

Claims (5)

A white reflective film having a void-containing polyester base film and a coating layer,
The coating layer forms at least one surface of the white reflective film and is formed from a coating liquid. The coating liquid mainly includes a polyester binder and polyester particles having a melting point of 200 to 270 ° C. in the solid content of the coating liquid. As a component, the content of the polyester particles is 5 to 60% by mass based on the solid content mass of the coating liquid,
Coating layer is less than a thickness of 1μm or more 10 [mu] m, has a projection on the surface, the height 5μm or more protrusions frequency in the surface is ¹⁰ 4 ^{-10 10} / ^{m 2,} for an edge light type backlight unit White reflective film. The edge light type according to claim 1, wherein the melting point Tm1 of the polyester particles and the melting point Tm2 of the polyester resin constituting the polyester base film satisfy 200 ≦ Tm2 ≦ 270 and Tm1-40 ≦ Tm2 ≦ Tm1 + 40. White reflective film for backlight unit . The white reflective film for an edge-light type backlight unit according to claim 1 or 2, wherein the coating liquid further contains 1 to 15% by mass of a crosslinking agent based on the solid content mass of the coating liquid. The white color for an edge-light type backlight unit according to any one of claims 1 to 3, wherein the coating solution further contains 0.1 to 10% by mass of silicone oil based on the solid content mass of the coating solution. Reflective film. The white reflective film for edge light type backlight units according to any one of claims 1 to 4, wherein the white reflective film is used as a surface light source reflector including a light guide plate.