TWI422481B - Production method of white film - Google Patents

Description

White film manufacturing method

The present invention relates to a method of producing a white film. More specifically, the present invention relates to a method for producing a white film which is suitable as a white film for a surface light source reflecting member (reflector and reflector) and which can coexist both in reflection property and film formability.

In recent years, displays using liquid crystals have been widely used as display devices for computers, televisions, portable telephones, and the like. Since these liquid crystal displays are not themselves illuminants, a surface light source called "backlight" is provided to illuminate light from the back side. Further, the backlight is not simply used for illuminating light, but also adopts a surface light source structure called "side light-type or direct-type" in response to the requirement of uniformly illuminating the entire screen. In the use of a thin liquid crystal display such as a notebook computer that is expected to be thin and compact, a sidelight type backlight is applied. The edge-lit backlight is a type of backlight that illuminates the screen from the side.

The "sidelight type backlight" uses a cold cathode tube as an illumination source to cause light to enter from the end portion of the light guide plate, and uniformly spreads the light by the light guide plate to diffuse and uniformly illuminate the entire liquid crystal display. In this illumination method, in order to utilize light efficiently, a reflector is provided around the cold cathode conduit. Further, in order to efficiently reflect the light diffused through the light guide plate to the liquid crystal screen side, a reflector is provided below the light guide plate. Thereby, the loss of light from the cold cathode conduit can be reduced, making the liquid crystal picture brighter.

On the other hand, in the case of a large screen application such as a liquid crystal television, a "direct type light mode" is employed. In this method, cold cathode conduits are arranged side by side in the lower portion of the liquid crystal screen, and cold cathode conduits are arranged in parallel on the reflector. The reflector is formed in a planar shape or formed by forming a portion of the cold cathode conduit into a semicircular concave shape.

A reflector or a reflection plate (hereinafter, collectively referred to as a "surface light source reflecting member") for a surface light source for such a liquid crystal screen is required to have a high reflection function at the same time as the film. . The film used for the surface light source reflecting member has been disclosed as a film which allows fine bubbles to be contained inside the film to utilize light reflection at the gas-solid interface, and the refractive index difference between the fine bubbles contained in the film and the matrix resin. Film (Patent Document 1).

A method of forming fine bubbles inside a film, and a manufacturing method comprising: a step of allowing an inert gas to be contained in a polyester resin sheet under pressure, and heating the inert resin-containing polyester resin sheet under normal pressure The step of foaming it (Invention Patent Document 2).

Further, a method for producing a white film having resin particles having incompatibility inside and extending to form bubbles around the resin particles has been disclosed (Patent Document 3).

On the other hand, a method for producing a film which is a single layer and which contains both incompatible resin particles and a light-resistant component has been disclosed (Patent Documents 4 to 6).

Further, a method of heating using an infrared heater during stretching in a method of producing a white film containing bubbles has been disclosed (Patent Document 7).

[Previous Technical Literature]

(Invention patent document)

(Invention Patent Document 1) Japanese Patent Laid-Open Publication No. 2002-40214

(Invention Patent Document 2) Japanese Patent Laid-Open Publication No. 2006-249158

(Invention Patent Document 3) Japanese Patent Laid-Open Publication No. 2009-98660

(Invention Patent Document 4) Japanese Patent Application Laid-Open No. 8-48792

(Invention Patent Document 5) Invention Patent No. 4306294

(Invention Patent Document 6) Japanese Patent Application Publication No. 2009-516049

(Invention Patent Document 7) Japanese Patent Laid-Open Publication No. 2006-241471

However, the techniques of Patent Documents 2 to 7 have the following problems.

The technique of Patent Document 2 is a method for producing a film which is difficult to be thinned and which is not suitable for use in a surface light source reflecting member.

In order to improve the reflectance, improve the light resistance, and stabilize the productivity, it is necessary to add an inner layer for forming a non-coherent component of a bubble at a high concentration and a titanium oxide having a function of light resistance. The bubbles are layered with a small outer layer. Since the titanium oxide of the outer layer absorbs a part of the light, the increase in reflectance is hindered. In addition, in order to laminate, large-scale equipment is required, and therefore, it is not good in terms of cost.

The techniques of the patent documents 4 to 6 are such that when the bubbles are extended to form bubbles, bubbles are also generated on the surface of the film to cause the non-compatible resin particles to fall off and contaminate the production line. Further, although the measure for increasing the bubble to increase the reflectance is effective, the film is easily broken due to a decrease in specific gravity, and film formation cannot be performed stably.

The technique of the invention patent document 7 is that the output energy of the infrared heater is small, and only the extent to which the roller is used to heat the film is assisted, and bubbles are formed on the surface of the film, so that the non-compatible resin particles fall off and contaminate the production line.

The present invention provides a method for producing a white film which can solve such technical problems and which has no line contamination, has less film breakage, and can be stably produced.

The present invention relates to a method for producing a white film for producing a white film containing bubbles inside and having a specific gravity of 0.55 or more and 1.30 or less, which includes:

A film having a layer containing a main resin component and a layer which is an incompatible component to the resin component is heated while heating at least one surface of 8.5 W/cm or more and 40 W/cm or less per one surface. The circumferential speed difference of the rolls is extended by 3.0 times or more and 4.5 times or less in the film length-wise direction, and then extended by 3 times or more and 5 times or less in the film width-wise direction.

According to the method for producing a white film of the present invention, there is no contamination of the production line, the film is less broken, and a white film can be stably produced.

[Best Embodiment of the Invention] (1) White film (1.1) Composition of white film

The white film produced according to the present invention is a white film containing bubbles inside and having a specific gravity of 0.55 or more and 1.30 or less.

The white film must contain bubbles inside. The white film is preferably a film of a single layer containing bubbles inside, or a film having at least one outer layer of a layer containing bubbles inside. Since a layer containing bubbles is present in the outermost layer of the film, a white film having high reflection characteristics can be obtained. Examples of such a laminated white film are two or more layers in which a layer containing bubbles and a layer containing no bubbles or a layer of bubbles may be different.

In the present invention, the bubbles contained inside the film may be independent bubbles or a plurality of continuous bubbles. Further, the shape of the bubble is not particularly limited, and a plurality of interfaces are formed in the thickness direction of the film, and the cross-sectional shape of the bubble is preferably a circular shape or an elliptical shape elongated in the direction of the film surface.

Further, the method of forming the bubbles is preferably carried out by melt-extruding a mixture containing a main resin component (a) for constituting a layer having bubbles therein and a mixture of the non-compatible component (b) for the resin component (a). After the exit, at least one direction is extended to form a bubble inside. Here, the "main resin component (a)" means a component having a mass ratio of more than 50% with respect to the entire layer having bubbles inside. This method can form fine and flat bubbles, and can produce a white film with high reflectivity under good productivity.

This method is a method in which a flat bubble is formed by peeling off at the interface between the main resin component (a) and the incompatible component (b) during stretching. Therefore, in order to increase the bubble occupying volume and increase the average thickness of the film thickness to improve the reflective performance, the biaxial stretching is superior to the uniaxial stretching.

The presence or absence of air bubbles inside the film can be confirmed by the following methods. That is, a cross section of the film in the TD direction (film width direction) and the parallel direction is cut out using a sheet slicer. After the platinum-palladium was vapor-deposited in a cross section, the cross section was observed with a scanning electron microscope (hereinafter referred to as "SEM") at an appropriate magnification (500 to 10,000 times). The bubbles can be confirmed by observing the images obtained.

The thickness of the white film is preferably 30 μm or more and 500 μm or less. The lower limit of the thickness is more preferably 50 μm or more. The upper limit of the thickness is more preferably 300 μm or less. If the thickness is less than 30 μm, there is a possibility that sufficient reflectivity cannot be obtained. When the thickness is more than 500 μm, it is too thick for a liquid crystal display which is required to be thinned. Further, when the white film is a laminate, the thickness means the thickness of the entire laminate.

The specific gravity of the white film is 0.55 or more and 1.30 or less, more preferably 0.55 or more and 0.99 or less, still more preferably 0.55 or more and 0.90 or less. The term "specific gravity" as used herein means the proportion of the overall white film. When the specific gravity is less than 0.55, the strength of the film is lowered, and the film is easily broken to cause poor productivity, which is not preferable. Further, wrinkles are likely to occur in the assembly operation of the liquid crystal display, which is not preferable. If the specific gravity is more than 1.30, the reflectance obtained by containing bubbles will become insufficient, which is not preferable.

The method of controlling the white film to have a specific gravity of 0.55 or more and 1.30 or less includes: 1) increasing the content of the incompatible component (b); 2) using the resin particles as the incompatible component (b); 3) reducing the incompatibility The volume average particle diameter Dv of the component (b); and 4) the magnification ratio is increased to a high magnification.

The density of the depressions on the surface of the white film is preferably 1/100 μm ² or less. According to the review by the inventors of the present invention, the reason why the production line is contaminated is that particles (incompatible components) fall off from the depressions and the particles adhere to the production equipment. Therefore, if the density of the depression of the surface of the control film is 1/100 μm ² or less, contamination of the production line can be prevented. The lower limit of the density of existence is 0/100 μm ² or more. Further, in order to obtain the present effect, it is preferred that the density of the depressions on both surfaces of the film is controlled to be 1/100 μm ² or less. In the present invention, the term "crater" means a concave pupil having a long diameter of 1 μm or more as observed on an SEM photograph having a magnification of 2,500 times on the surface of the film.

The method of controlling the presence density of the depressions to be 1/100 μm ² or less is a method of extending the film while supplying a certain amount of heat (heating) to the surface of the film by using an infrared heater of a high output power as described later. .

(1.2) Main resin component (a)

The main resin component (a) is a matrix resin component constituting a layer containing bubbles. The main resin component (a) is preferably a polyester resin (a1). The "polyester resin" is a polymer obtained by polycondensation of a diol component and a dicarboxylic acid component. Representative examples of the "dicarboxylic acid component" include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like. Further, representative examples of the "diol component" include ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexane dimethanol, and the like. Specific examples of "polyester resin" are polyethylene terephthalate, polyethylene-2,6-naphthalate (polyethylene naphthalate), polytrimethylene terephthalate. Ester, polybutylene terephthalate, and the like.

Needless to say, these polyesters may be homopolyester or copolymerized polyester. The "copolymerization component" is a "diol component" such as diethylene glycol, neopentyl glycol or polyalkylene glycol; adipic acid, sebacic acid, phthalic acid, isophthalic acid, A "dicarboxylic acid component" such as 2,6-naphthalenedicarboxylic acid or sodium 5-sulfoisophthalate.

When the resin is used as the polyester resin (a1) as described above, high mechanical strength can be imparted while being formed into a film while maintaining high coloring resistance. From the viewpoint of being inexpensive and excellent in heat resistance, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) is more preferable.

(1.3) Incompatible components (b)

When it is incompatible with the main resin component (a) constituting the matrix resin component, the incompatible component (b) is not particularly limited, and a thermoplastic resin (b1) which is incompatible with the matrix resin can be used. Any one of the inorganic particles (b2). These components may be used singly or in combination of two or more. The use of the thermoplastic resin (b1) and the inorganic particles (b2) as the incompatible component (b) is one of the more preferable modes.

Further, the white film preferably has a layer containing the polyester resin (a1) and the polyester resin (a1) as the incompatible component (b), and the outermost layer of at least one side of the white film is the layer. According to the configuration described above, since bubbles are efficiently obtained, it is possible to produce a white film having high reflection characteristics. More preferably, the white film is composed of a layer containing the polyester resin (a1) and the incompatible component (b). Further, when a layer containing no bubbles is provided on the surface layer of the white film, yellowing may occur due to deterioration of the polymer due to ultraviolet rays, which is not preferable.

(1.3.1) Thermoplastic Resin (b1)

When the non-compatible component (b) is a thermoplastic resin (b1), the resin may be either crystalline or amorphous. Specific examples thereof include: a linear, branched chain or cyclic polyolefin resin such as polyethylene, polypropylene, polybutene, polymethylpentene, cyclopentadiene or the like; poly( Acrylic resin such as methyl acrylate; polystyrene; fluorine resin. These non-compatible resins may be homopolymers or copolymers, or two or more kinds of incompatible resins may be further used. Among these, polyolefin is preferably used because it is excellent in transparency and has excellent heat resistance. Specifically, it is preferable to use polypropylene or polymethylpentene as the crystalline resin, and a cycloolefin copolymer or the like as the amorphous resin.

In the case where the main resin component (a) is a polyester resin (a1) and the polyester resin (a1) is a non-compatible component, a thermoplastic resin (b1) is used, and a specific example of the crystalline resin is from transparency. From the viewpoint of heat resistance, it is more preferable to use polymethylpentene. The polymethylpentene is preferably a derivative derived from 4-methylpentene-1 in a molecular skeleton of 80 mol% or more, more preferably 85 mol% or more, particularly preferably 90 mol% or more. By. Further, other derivatization units are exemplified by an ethylene unit, a propylene unit, a butene-1 unit, a 3-methylbutene-1, or a hydrocarbon having a carbon number of 6 to 12 other than 4-methylpentene-1. . Polymethylpentene can be a homopolymer or a copolymer. Further, it is possible to use several kinds of polymethylpentenes having different compositions or melt viscosities, or to use them with other olefin resins or other resins.

Further, in the case where the thermoplastic resin (b1) is an amorphous resin, a cyclic olefin copolymer resin is particularly preferably used. The "cyclic olefin copolymer" is a copolymer composed of at least one cyclic olefin selected from the group consisting of a cyclic olefin, a bicycloolefin, a tricycloolefin, and a tetracycloolefin, and a linear olefin such as ethylene or propylene. Things.

Representative examples of "cyclic olefin" in the cyclic olefin copolymer resin include: bicyclo[2,2,1]hept-2-ene, 6-methylbicyclo[2,2,1]hept-2 - alkene, 5,6-dimethylbicyclo[2,2,1]hept-2-ene, 1-methylbicyclo[2,2,1]hept-2-ene, 6-ethylbicyclo[2, 2,1]hept-2-ene, 6-n-butylbicyclo[2,2,1]hept-2-ene, 6-isobutylbicyclo[2,2,1]hept-2-ene, 7- Methylbicyclo[2,2,1]hept-2-ene, tricyclo[4,3,0,1 ^2.5 ]-3-decene, 2-methyl-tricyclo[4,3,0,1 ^2.5 ]-3-decene, 5-methyl-tricyclo[4,3,0,1 ^2.5 ]-3-decene, tricyclo[4,4,0,1 ^2.5 ]-3-decene, 10- Methyl-tricyclo[4,4,0,1 ^2.5 ]-3-decene, and the like.

Further, representative examples of the "linear olefin" in the cyclic olefin copolymer resin include: ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-anthracene Alkene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and the like.

The thermoplastic resin (b1) is particularly preferably a cyclic olefin copolymer resin belonging to an amorphous resin among those described above. The cyclic olefin copolymer resin is further finely dispersed due to the interaction with the alicyclic diol or the alicyclic dicarboxylic acid contained in the matrix as described later, and as a result, the reflection characteristics can be further improved.

The thermoplastic resin (b1) preferably has a glass transition temperature Tg of 170 ° C or more, more preferably 180 ° C or more. When it is controlled to 170 ° C or more, it is more finely dispersed in the matrix resin at the time of kneading, bubbles are formed in the stretching step, and the disappearance of the bubbles in the heat treatment step can be further suppressed. The upper limit is preferably 250 °C. If it exceeds 250 ° C, the extrusion temperature at the time of film formation will need to be increased, so that the workability may be deteriorated.

In particular, when the thermoplastic resin (b1) is a cyclic olefin copolymer resin, when the glass transition temperature Tg is less than 170 ° C, when heat treatment of the film is performed to impart dimensional stability, it may cause The case where the cyclic olefin copolymer resin of the nucleating agent is deformed. As a result, there is a possibility that the bubbles formed by the nucleus are reduced or disappeared, and the reflection characteristics are lowered. Further, if the heat treatment temperature is lowered while maintaining the reflection characteristics, the dimensional stability of the film may be lowered.

In the case where the thermoplastic resin (b1) is a cyclic olefin copolymer resin, if the glass transition temperature Tg is to be controlled in the range of 170 ° C or more and 250 ° C or less, for example, a ring in the cyclic olefin copolymer may be added. A method of reducing the content of a linear olefin component such as ethylene by the content of the olefin component. Specifically, the cyclic olefin component in the cyclic olefin copolymer is preferably 60 mol% or more, and the content of the linear olefin component such as ethylene is less than 40 mol%. More preferably, the cyclic olefin component is 70 mol% or more, and the content of the linear olefin component such as ethylene is less than 30 mol%, and more preferably the cyclic olefin component is 80 mol% or more and ethylene. The content of the linear olefin component is less than 20 mol%. It is particularly preferable that the cyclic olefin component is 90 mol% or more, and the content of the linear olefin component such as ethylene is less than 10 mol%. When set to such a range, the glass transition temperature Tg of the cyclic olefin copolymer can be increased to 170 °C.

In the case where the thermoplastic resin (b1) is a cyclic olefin copolymer resin, the linear olefin component is not particularly limited, but from the viewpoint of reactivity, an ethylene component is preferred.

Further, the cyclic olefin component is not particularly limited, but from the viewpoint of productivity, transparency, and high Tg, bicyclo[2,2,1]hept-2-ene (norbornene) is preferred. ) or a derivative thereof.

Therefore, the white film preferably has a layer containing the polyester resin (a1) and the incompatible component (b), and the non-compatible component (b) is a thermoplastic resin having a glass transition temperature of 170 ° C or more and 250 ° C or less ( B1). Further preferably, the thermoplastic resin (b1) is an amorphous resin. Particularly preferably, the thermoplastic resin (b1) is an amorphous cyclic olefin copolymer resin.

The content of the thermoplastic resin (b1) is preferably 3% by mass or more and 25% by mass or less based on the entire layer containing the bubbles. The lower limit of the content is more preferably 5% by mass or more. The upper limit of the content is more preferably 10% by mass or less. When the content of the thermoplastic resin (b1) is less than 3% by mass, sufficient bubbles cannot be formed inside the film, and whiteness or light reflection characteristics may be deteriorated. When the content of the thermoplastic resin (b1) is more than 25% by mass, the strength of the film may be lowered, and the film may be easily broken during stretching. When the controlled content is in the range of 3% by mass or more and 25% by mass or less, sufficient whiteness, reflectivity, and lightness can be exhibited.

(1.3.2) Inorganic particles (b2)

In the case where "inorganic particles (b2)" is used as the incompatible component (b), examples thereof include glass, ceria, barium sulfate, titanium oxide, magnesium sulfate, magnesium carbonate, calcium carbonate, talc, and the like.

In the case where the main resin component (a) is a polyester resin (a1), in particular, from the viewpoint of comprehensive effects such as bubble formation, whiteness, and optical density, among these inorganic particles, it is preferred that At least one or more inorganic particles (b2) selected from the group consisting of titanium oxide, calcium carbonate, and barium sulfate are used, and particularly preferably titanium oxide.

The content of the inorganic particles (b2) is preferably 5% by mass or more and 60% by mass or less based on the entire layer containing the bubbles. The lower limit of the content is more preferably 10% by mass or more. The upper limit of the content is more preferably 20% by mass or less. When the content of the inorganic particles (b2) is less than 5% by mass, sufficient bubbles cannot be formed inside the film, and whiteness or light reflection characteristics may be deteriorated. When the content of the inorganic particles (b2) is more than 60% by mass, the strength of the film is lowered, and the film may be easily broken during stretching. When the controlled content is in the range of 5% by mass or more and 60% by mass or less, sufficient whiteness, reflectivity, and lightness can be exhibited.

The use of the thermoplastic resin (b1) and the inorganic particles (b2) as the incompatible component (b) is one of preferable modes. Particularly preferably, the white film is a layer having a layer containing a polyester resin (a1) and an incompatible component (b), and a thermoplastic resin (b1) having a glass transition temperature of 170 ° C or more and 250 ° C or less, and a titanium oxide, At least one or more inorganic particles (b2) of the group consisting of calcium carbonate and barium sulfate are used as the incompatible component (b). Moreover, it is preferable that the content of the thermoplastic resin (b1) is 3% or more and 25% by mass or less with respect to the entire layer containing the bubbles, and the content of the inorganic particles (b2) is based on the entire layer containing the bubbles. 5 mass% or more and 60 mass% or less.

(1.4) Other additives

The matrix resin component of the layer containing the bubbles may be a mixture of the copolymerized polyester resin (c) obtained by introducing a copolymerization component into the polyester resin (a1). The amount of the copolymerization component is not particularly limited, but from the viewpoints of transparency, moldability, and the like, and from the viewpoint of amorphization described in the following paragraphs, the dicarboxylic acid component and the diol component are preferably relatively. Each component is 1 mol% or more and 70 mol% or less, more preferably 10 mol% or more and 40 mol% or less.

Further, the copolymerized resin (c) is preferably a polyester which is copolymerized to be amorphous. Examples thereof include a copolymerized polyester resin in which a main component of the diol component is an alicyclic diol, or a copolymerized polyester resin in which an acid component is an alicyclic dicarboxylic acid. In particular, from the viewpoints of transparency, moldability, or microdispersion efficiency of the incompatible resin as described later, cyclohexanedimethanol which is one of a diol component and an alicyclic diol can be used. The amorphous polyester obtained by copolymerization is carried out. In this case, from the viewpoint of amorphization, it is preferred that the cyclohexane dimethanol component of the diol component of the copolymerized polyester resin (c) is 30 mol% or more.

The copolymerized polyester resin (c) is introduced into the matrix resin containing the layer of the bubble, and the cyclic olefin copolymer resin as the thermoplastic resin (b1) is used as the incompatible component (b) due to the copolymerization polymerization. The cyclic aliphatic hydrocarbon portion of the ester resin (c) interacts with the cyclic olefin portion of the cyclic olefin copolymer resin, and the cyclic olefin copolymer resin can be finely dispersed in the matrix resin, and as a result, it can be achieved. Highly reflective, high white, and lightweight. Further, since the copolymerized polyester resin (c) is added, the elongation or film formability can be improved.

The content of the copolymerized polyester (c) is preferably 1% by mass or more and less than 50% by mass based on 100% by mass of the total of the resins constituting the layer containing the bubbles. The lower limit of the content is more preferably 1.5% by mass or more. The upper limit of the content is more preferably 40% by mass or less, particularly preferably 35% by mass or less. When the content of the copolymerized polyester (c) is less than 1% by mass, there is a possibility that it may become difficult to finely disperse the thermoplastic resin (b1) in the matrix. When the content of the copolymerized polyester (c) is 50% by mass or more, the heat resistance is lowered, so that the matrix resin may be softened when the film is subjected to heat treatment for imparting dimensional stability, and as a result, it may be caused. The case where the bubble is reduced or disappeared and the reflection characteristics are lowered. Further, if the heat treatment temperature is lowered while maintaining the reflection characteristics, the dimensional stability of the film may be lowered. When the content of the control copolymerized polyester (c) is in the range of 1% by mass or more and less than 50% by mass, the film forming property can be maintained while sufficiently exhibiting the dispersion efficiency of the incompatible component as described above or Mechanical properties. As a result, both high reflectance and dimensional stability can coexist.

In order to make the thermoplastic resin (b1) more slightly dispersed in the matrix resin containing the layer of the bubble, it is preferably in the matrix resin, except for the polyester resin (a1) and the copolymerized polyester resin (c) as described above. Further containing a dispersing agent (d). When the dispersing agent (d) is contained, the dispersion diameter of the thermoplastic resin (b1) can be made smaller. As a result, the flat bubbles formed by the stretching can be made finer, and as a result, the whiteness, reflectivity, and lightness of the film can be improved.

The type of the dispersing agent (d) is not particularly limited, and an olefin-based polymer or copolymer having a polar group such as a carboxyl group or an epoxy group or a functional group reactive with a polyester, diethylene glycol, or poly An alkyl diol, a surfactant, a thermal adhesive resin, and the like. Needless to say, these may be used alone or in combination of two or more. Among them, a polyester-polyalkylene glycol copolymer (d1) containing a polyester component and a polyalkylene glycol component is particularly preferred.

In this case, the polyester component is preferably an aliphatic diol component having a carbon number of 2 or more and 6 or less, and a polyester component composed of a terephthalic acid and/or an isophthalic acid component. Further, the polyalkylene glycol component is preferably a component such as polyethylene glycol, polypropylene glycol or polytetramethylene glycol.

A particularly preferred combination includes: the polyester component is polyethylene terephthalate or polybutylene terephthalate, and the polyalkylene glycol component is polyethylene glycol or polytetrazene. A combination of methyl glycols. Among them, it is particularly preferred that the polyester component is a polybutylene terephthalate, and the polyalkylene glycol component is a combination of polytetramethylene glycol; or the polyester component is a polyparaphenylene. Ethylene glycolate, and the polyalkylene glycol component is a combination of polyethylene glycol.

The content of the dispersant (d) is preferably 0.1% by mass or more and 30% by mass or less based on 100% by mass of all the resins constituting the matrix. The lower limit of the content is more preferably 1% by mass or more, and particularly preferably 1.5% by mass or more. The upper limit of the content is more preferably 25% by mass or less, and particularly preferably 20% by mass or less. When the content is less than 0.1% by weight, there is a possibility that the effect of refining the bubbles becomes small. When the content is more than 30% by weight, the heat resistance is lowered, and when the heat treatment of the film is performed to impart dimensional stability, the matrix is softened, and as a result, the bubbles are reduced or disappeared, so that the reflection characteristics are lowered. Further, if the heat treatment temperature is lowered while maintaining the reflection characteristics, the dimensional stability of the film may be lowered. In addition, there are problems such as reduced production stability or increased costs. When the content of the controlled dispersant (d) is in the range of 0.1% by mass or more and 30% by mass or less, the film forming property or mechanical properties of the film can be maintained under the effect of sufficiently exhibiting the dispersion efficiency of the thermoplastic resin (b1). Both high reflectivity and dimensional stability are allowed to coexist.

In addition, suitable amounts of additives which do not impair the efficacy of the present invention, such as heat-resistant stabilizers, antioxidant stabilizers, ultraviolet absorbers, ultraviolet stabilizers, organic lubricants, organic fine particles, may be blended as needed. Fillers, nucleating agents, dyes, dispersants, coupling agents, and the like.

(2) Film properties

The total light transmittance of the white film is preferably 1.5% or less, more preferably 1.2% or less, still more preferably 1.0% or less. In addition, the "total light transmittance" herein means a value measured according to the criteria of JIS-K7361-1 (1997 edition). When the total light transmittance is controlled to 1.5% or less, light leakage to the back surface can be suppressed. As a result, a white film excellent in whiteness and reflection characteristics can be obtained. In particular, when used as a liquid crystal display device, high luminance improvement efficiency can be obtained.

The relative reflectance of the white film is preferably 100% or more, more preferably 100.5% or more, still more preferably 101% or more. There is no special limit on the upper limit, but it is below 120% in practical applications. When the controlled relative reflectance is 100% or more, a white film excellent in whiteness and reflection characteristics can be obtained. In particular, when used as a liquid crystal display device, high luminance improvement efficiency can be obtained.

In order to adjust the total light transmittance or the relative reflectance of the white film to the range as described above, the dispersion diameter and density of the resin particles inside the film can be controlled by 1) in the range as described above; 2) Measures such as increasing the thickness of the film are obtained.

(3) Manufacturing method

Hereinafter, the method for producing the white film of the present invention will be described, but it is not limited thereto except for the stretching method.

If necessary, the mixture containing the polyester resin (a1) and the incompatible component (b) may be sufficiently vacuum dried and then supplied to a heated extrusion equipped with a film forming apparatus of an extruder (main extruder). machine. The addition of the incompatible component (b) is a master batch pellet obtained by blending by pre-uniformly melt-kneading, or may be directly supplied to a kneading extruder or the like. Since the dispersion of the incompatible component (b) can be promoted, it is preferred to use a masterbatch pellet obtained by uniformly melt-kneading a mixture containing the polyester resin (a1) and the incompatible component (b) in advance.

Further, in the case of melt extrusion, it is preferably filtered through a sieve having a mesh size of 40 μm or less, and then introduced into a T-die to obtain a molten sheet by extrusion molding. Then, the molten flakes are cooled to a temperature of 10 ° C or more and 60 ° C or less at a surface temperature, and are cooled and solidified by static electricity to produce an unstretched film.

The unstretched film is introduced into a roll group heated to a temperature of 40 ° C or higher and 120 ° C or lower, and stretched in the film forming direction (film length direction) between the two sets of rolls at different peripheral speeds. That is, it is extended by the circumferential speed difference of the rolls. In this extension, at least one surface of the film is heated with a heat Q of 8.5 W/cm or more and 40 W/cm or less per one side. The lower limit of the heat Q is preferably 10 W/cm or more. The upper limit of the heat amount Q is preferably 25 W/cm or less. The term "heat quantity Q" means heat applied to the surface of the film per 1 cm of the film width direction.

When the amount of heat Q is less than 8.5 W/cm, the temperature of the surface of the film may not rise sufficiently, and the surface may be dented to cause process contamination due to generation of powder or the like. When the amount of heat Q is more than 40 W/cm, the film is softened when the longitudinal direction is extended, so that film formation cannot be performed stably.

The heat source for heating can use an infrared heater or hot air. From the viewpoint of energy efficiency, an infrared heater is preferred.

The type of the infrared heater is not particularly limited, and a near-infrared heater or a carbon heater can be used. From the standpoint of the balance between heating performance and durability, it is more preferable to be a pure carbon heater. The infrared heater preferably has a gold reflective film attached to the back surface. In addition, a light collecting device can also be used. Such a heater is a pure carbon heater made of Twin Tube transparent quartz glass manufactured by Heraeus Ltd.

The infrared heater is disposed such that the length direction of the heater is parallel to the film width direction. The length of the infrared heater is preferably longer than the width of the film so that the film surface can be uniformly heated in the film width direction. The infrared heater can be one or several rows side by side in the length direction of the film. If the film forming speed is slow, it may be one. If the film forming speed is fast, it is preferably a side row. The upper limit is not particularly limited, but due to the gap between the rolls, the practical application is limited to four.

In addition, the infrared heater is disposed on one side or both sides of the film. It is disposed at least on one side of the layer having bubbles.

The output power (heat) S of the infrared heater to the film side is preferably 35 W/cm or more and 150 W/cm or less per one side of the film. Further, in the case where a plurality of infrared heaters are provided on one side of the film, the output power of each side of the infrared heater to the film side is multiplied by the value obtained by the number of heaters per one side of the film. The output power of the infrared heater is not all toward the film side, but also includes the loss points that do not reach the film surface. The output power to the film side is calculated by multiplying the rated output power (W/cm) of the infrared heater by the irradiation efficiency inherent to the infrared heater. Here, the "output power of the infrared heater to the film side" is a value calculated by the following formula.

‧ S=S'×E×N

S: output power of the infrared heater to the film side (W/cm);

S': rated output power (W/cm) of each infrared heater;

E: irradiation efficiency of the infrared heater;

N: The number of heaters per one side of the film.

The lower limit of the output power to the film side is more preferably 40 W/cm or more, and particularly preferably 50 W/cm or more. The upper limit of the output power to the film side is more preferably 100 W/cm or less, and particularly preferably 80 W/cm or less. When extending in the longitudinal direction, if the output power of the infrared heater to the film side is more than 150 W/cm, there is a possibility that the film is softened when it is extended in the longitudinal direction. As a result, there is a possibility that the film formation cannot be performed stably. When the output power of the infrared heater to the film side is less than 35 W/cm in the longitudinal direction, the temperature of the film surface may not be sufficiently raised. As a result, there is a possibility that a depression is formed on the surface to cause contamination of the process caused by powder or the like.

The distance from the infrared heater to the surface of the film is preferably 5 mm or more and 100 mm or less. The lower limit of the distance is preferably 10 mm or more. The upper limit of the distance is preferably 50 mm or less, and particularly preferably 20 mm or less. If the distance from the infrared heater to the surface of the film is more than 100 mm, the output power range of the infrared heater as described above may cause attenuation due to the infrared rays before reaching the film, and the surface temperature of the film may not be sufficiently increased. Case. If the distance between the infrared heater and the film is less than 5 mm, the output power range of the infrared heater may cause the entire thickness direction of the film to soften. As a result, there is a possibility that the film formation cannot be performed stably. Further, the term "distance from the infrared heater to the surface of the film" means the distance from the central axis of the heating tube of the infrared heater to the surface of the film.

The time during which the film passes through the irradiation zone is preferably 0.2 seconds or more and less than 2 seconds. The lower limit of the passage time is more preferably 0.4 seconds or more. The upper limit of the passage time is preferably 1 second or shorter. The term "irradiation zone" means an area in which the length of the film is 40 mm (20 mm from the position of the heating pipe to the upstream side and 20 mm to the downstream side) centering on the heating tube. In the case where the infrared heaters are arranged in two or more rows, the total distance is other than the overlapping portion of the irradiation regions occupied by the respective heaters. If the passage time is shorter than 0.2 seconds, the temperature rise of the film may be insufficient. When the passage time is 2 seconds or longer, there is a possibility that the temperature inside the film becomes high and the bubble cannot be increased. As a result, there is a possibility that the reflectance becomes small.

In the extension, when the surface of the film is heated, the stretching tension at the surface portion of the film becomes small, so that the formation of bubbles is hindered. At the same time, in the inside of the film, the thermal conductivity becomes lower due to the bubble formed at the beginning, so that it is less heated than the surface portion of the film. As a result, in the inside of the film, the stretching tension due to the stretching sufficiently occurs to promote the formation of bubbles. That is, the surface of the film can be formed into a white film having a small number of bubbles and a large number of bubbles inside the film.

When the glass transition temperature of the main resin component (a) is Tg (° C.), the film temperature before stretching is preferably (Tg - 20 ° C) or more and Tg or less. The "film temperature before stretching" means the film temperature before passing through the heated roll group and heating the surface with heat Q. The film temperature before stretching is set to 1.0 times in the longitudinal stretching ratio at the time of film formation, and is obtained by measuring the film temperature of the extending region in a state where the surface is not heated Q, and is measured by a radiation thermometer. The lower limit of the film temperature before stretching is more preferably (Tg - 15 ° C) or more. The upper limit of the film temperature before stretching is more preferably (Tg - 5 ° C) or less. In particular, when the main resin component (a) is PET, the film temperature before stretching is preferably 60 ° C or more and 80 ° C or less. When it is set to (Tg-20 ° C) or more and Tg or less, the formation of bubbles inside the film can be increased, so that the reflection performance can be improved. If it is lower than (Tg - 20 ° C), the elongation of the film becomes small, which may cause the film to rupture. When it is higher than Tg, the stretching tension generated by the film is insufficient, and the peeling at the interface between the main resin component (a) and the incompatible component (b) is less likely to occur, so that it is difficult to form voids. As a result, there is a possibility that the reflection performance as the reflecting plate is insufficient. The method of controlling the film temperature before stretching has a method of adjusting the roll temperature of the heated roll group in accordance with the speed of the film and the material of the roll or the heat transfer coefficient of the material of the film.

While heating as described above, it is extended by 3.0 times or more and 4.5 times or less in the longitudinal direction of the film, and then cooled by a roll group having a temperature of 20 ° C or more and 50 ° C or less. The stretching ratio in the longitudinal direction of the film is preferably 3.4 times or more and 4.5 times or less. If the stretching ratio is less than 3.0 times, the bubbles cannot be formed in a sufficient size, and thus sufficient reflectance cannot be obtained. When the stretching ratio is more than 4.5 times, in the subsequent transverse stretching (extension in the film width direction), the film is easily broken and the productivity is deteriorated, which is not preferable.

Next, the both ends of the film are sandwiched between the cookers and introduced into the tenter, and in an atmosphere heated to a temperature of 90 ° C or higher and 150 ° C or lower, at a right angle to the longitudinal direction of the film. (film width direction) is extended by 3 times or more and 5 times or less. If the stretching ratio is less than 3 times, the bubble size is small, so that sufficient reflectance cannot be obtained. When the stretching ratio is more than 5 times, it is liable to be broken and the productivity is deteriorated, which is not preferable. When the product of the stretching ratio in the longitudinal direction of the film and the stretching ratio in the film width direction is set to be large, the reflection performance can be further improved.

In order to impart planarity and dimensional stability to the completion of the alignment crystallization of the obtained biaxially stretched film, it is then carried out at a temperature of 150 ° C or more and 240 ° C or less in a tenter for 1 second or more and 30 After heat treatment for a second or less, then slowly and uniformly cooled, and then cooled to room temperature. Thereafter, corona discharge treatment or the like may be applied to further improve the adhesion to other materials, and then wound up. In the heat treatment step, a relaxation treatment of 3% or more and 12% or less may be applied in the film width direction or the film length direction as needed. Depending on the backlight, the temperature of the atmosphere inside the backlight may rise to about 100 ° C, and the white film needs to have a certain thermal dimensional stability. In general, the higher the heat treatment temperature, the higher the thermal dimensional stability. Therefore, it is preferred to carry out heat treatment at a high temperature of 190 ° C or higher.

(4) Determination method A. Heat Q

The amount of heat Q reaching the film surface was measured as follows. The distance from the film to the heat source is adjusted to conform to the film forming conditions. A thermocouple was mounted on both surfaces of the film, and the average of the temperatures on both sides was taken as the film temperature. The film was heated by a heat source in the state of a stationary film, and the temperature increase rate α (° C./sec) was measured. The heat Q is calculated by the following formula. Fig. 1 is a schematic view showing a state in which measurement is being performed.

‧ Q=α×D×M×C

Q: the amount of heat reaching the film surface (per single-sided film) (W/cm);

α: heating rate α (° C / sec);

D: the length direction (cm) of the film in the heated portion of the film surface;

M: film weight per 1 cm ² of the film surface (g/cm ² );

C: specific heat of the film (J/(g‧°C)).

In the case of using an infrared heater, "length D (cm)" is the length of the irradiation zone. The "irradiation zone" is an area in which the length of the film is 40 mm (20 mm from the position of the heating pipe to the upstream side and 20 mm to the downstream side) centering on the heating tube. When the infrared heaters are arranged in two or more rows, the total length is excluding the overlapping portions of the irradiation regions occupied by the respective heaters.

The specific heat C (J/(g‧°C)) is measured in accordance with the guidelines of JIS K7123 (1987 edition). In the case of a PET film, it is C = 1.25 (J / (g ‧ ° C)).

Further, in the case of using an infrared heater, the amount of heat Q reaching the film surface can also be calculated by the following formula. However, in the case where a plurality of infrared heaters are provided, the distance from each infrared heater to the film surface is applicable to all cases.

‧ Q=S×(0.4-0.055×ln(L))

S=S’×E×N

Q: the amount of heat reaching the film surface (per single-sided film) (W/cm);

S: output power of the infrared heater to the film side (per single-sided film) (W/cm);

L: distance from the infrared heater to the surface of the film (mm);

S': rated output power (W/cm) of each infrared heater;

E: irradiation efficiency;

N: The number of heaters per one side of the film.

B. Density in the presence of depressions on the surface of the film

After depositing platinum-palladium on the surface of the film, it was magnified 2500 times by a field emission scanning electron microscope to obtain a magnified image. The number of concave depressions having a long diameter of 1 μm or more in a 10 μm square was counted by the enlarged image. The same operation was performed for different 10 fields of view, and the average value thereof was used as the density of existence of the depression. The two sides of the film were measured as described above and then the higher values were used. The field emission scanning electron microscope was JSM-6700F manufactured by JEOL Ltd.

C. Relative reflectivity

The light reflectance at 560 nm was measured by attaching a Φ 60 integrating sphere and a 10° tilting locator to a spectrophotometer. Further, the light reflectance was measured on both sides of the white film, and the higher value was used as the reflectance of the white film. The spectrophotometer is U-3410 manufactured by Hitachi, Ltd. (Hitachi, Ltd.), and the Φ 60 integrating sphere is 130-0632 manufactured by Hitachi, Ltd. (the inner surface is made of barium sulfate), and the standard white plate is used. It is 210-0740 (aluminum oxide) manufactured by Hitachi Instruments Service Co., Ltd. The relative reflectance is judged at the following levels. If the result of the determination is S, A or B, it is qualified. If it is S or A, it is preferable.

‧ The relative reflectivity is above 101% and below 120%: S;

‧ The case where the relative reflectivity is 100% or more and less than 101%: A;

‧ The case where the relative reflectance is 99% or more and less than 100%: B;

‧ Case where the relative reflectance is less than 99%: C.

D. Proportion

The white film was cut into a size of 5 cm × 5 cm, and then measured using an electronic hydrometer according to the guidelines of JIS K7112 (1980 edition). Further, five sheets of each of the white films were separately measured, and the average value thereof was used as the specific gravity of the white film. The electronic hydrometer was SD-120L manufactured by Mirage Co., Ltd. The specific gravity is determined by the following levels. If the result of the determination is S, A or B, it is qualified.

‧ The case where the specific gravity is 0.55 or more and 0.9 or less: S;

‧ The case where the specific gravity is greater than 0.9 and less than 1.0: A;

‧ The case where the specific gravity is greater than 1.0 and less than 1.3: B;

‧ Case where the specific gravity is greater than 1.3: C.

E. Film formation

The film formation property was evaluated at the following grades by the frequency of film breakage at the time of film formation. For mass production, the film forming properties of S, A or B are required. If it is S or A, there is a further cost reduction effect.

‧ film rupture in less than one time a week: S;

‧ The film ruptures in more than 2 times and less than 5 times a week: A;

‧ The film ruptures in 6 or 7 times a week: B;

‧ The film ruptures in more than 8 times a week: C.

F. Pollution assessment of film production line

In the longitudinally extending chill roll group in the film formation, the film line contamination was evaluated by observing the contamination at the entire or end of the surface through which the film of any of the rolls passed after the film was passed. When contamination is observed, cleaning is required, and production cannot be performed during cleaning. Therefore, from the viewpoint of productivity, it is acceptable if it is S or A, and more preferably S.

‧ No pollution observed after passing 5 meters: S;

‧ Although no pollution was observed after passing 10,000 meters, pollution was observed after passing 50,000 meters: A;

‧ Although no pollution was observed after passing 2000 meters, pollution was observed after passing 10,000 meters: B;

‧ Contamination was observed after 2000 meters: C.

G. Glass transition temperature of incompatible component (b)

In the case where the incompatible component (b) can be obtained alone, a sample obtained by melting and quenching 5 mg of the incompatible component (b) is subjected to a differential scanning calorimeter from 25 ° C to 20 The temperature rise rate of ° C / min was raised, and the intermediate point glass transition temperature of JIS K7121 (1987 edition) criteria was measured as the glass transition temperature. The differential scanning calorimeter was a DSC-2 type manufactured by Perkin Elmer, Inc.

Further, when the incompatible component (b) cannot be obtained alone, the glass transition temperature is measured using a differential scanning calorimeter after the incompatible component (b) is separated from the white film. For example, in the case of a white film composed of a polyester resin (a1), a cyclic olefin copolymer as the incompatible thermoplastic resin (b1), and inorganic particles (b2), the white film is dissolved in a volume fraction. The undissolved matter of a mixed solution of methanol and chloroform at a ratio of 1:1 was filtered and taken out. The undissolved matter was redissolved in chloroform, and the undissolved matter was taken out and dissolved in a mixed solution of hexafluoroisopropanol and chloroform having a volume fraction of 1:1. After the solution is centrifuged in a centrifugal separator, a cyclic olefin copolymer can be obtained by taking a float. A sample obtained by melting and quenching 5 mg of the cyclic olefin copolymer obtained as described above was heated from 25 ° C at a temperature increase rate of 20 ° C / min using a differential scanning calorimeter, and JIS K7121 ( 1987 edition) The intermediate point glass transition temperature of the guideline is determined as the glass transition temperature. The differential scanning calorimeter is, for example, a DSC-2 type manufactured by Bojing Instruments.

H. Film temperature before extension

The longitudinal stretching ratio in the film forming conditions was set to 1.0 times, and the heating using the infrared heater was stopped. The film temperature of the longitudinally extending extension region was measured 5 times using the radiation temperature, and the average value thereof was taken as the film temperature before the extension. At this time, the emissivity correction of the film of the target is performed in advance. The radiation thermometer was an IT2-80R manufactured by Keyence Corporation.

"Embodiment"

Hereinafter, the present invention will be more specifically described with reference to the embodiments, but the present invention is not limited thereto.

(raw material) ‧ polyester resin (a1-1)

The acid component is a terephthalic acid, a glycol component is ethylene glycol, and antimony trioxide (polymerization catalyst) is added in an amount of 300 ppm in terms of a ruthenium atom relative to the obtained polyester pellet. The condensation reaction was carried out to obtain polyethylene terephthalate pellets (PET) having an ultimate viscosity of 0.63 dl/g and a carboxyl terminal group of 40 equivalents/ton. When the crystal melting heat was measured by using a differential thermal analyzer, it was 1 cal/g or more, which is a crystalline polyester resin. The melting point Tm of the resin was measured and found to be 250 °C.

‧ cyclic olefin copolymer resin (b1-1)

A cyclic olefin resin "TOPAS" (manufactured by Polyplastics Co., Ltd.) having a glass transition temperature of 178 ° C and an MVR (260 ° C / 2.16 kg) of 4.5 ml / 10 min was used. Further, when the heat of crystal melting was measured by using a differential thermal analyzer, it was less than 1 cal/g, which is an amorphous resin.

‧ cyclic olefin copolymer resin (b1-2)

A cyclic olefin resin "TOPAS" (manufactured by Polyplastics Co., Ltd.) having a glass transition temperature of 158 ° C and an MVR (260 ° C / 2.16 kg) of 4.5 ml / 10 min was used. Further, when the heat of crystal melting was measured by using a differential thermal analyzer, it was less than 1 cal/g, which is an amorphous resin.

‧ olefin resin (B1-3)

An olefin resin PMP (polymethylpentene) "TPX" having a glass transition temperature of 25 ° C, a melting point of 235 ° C, and an MFR (260 ° C / 5 kg) of 8 g/10 min (Mitsui Chemicals Co., Ltd.) , Inc.) Manufacturing).

‧ Copolymerized polyester resin (c-1)

PET was copolymerized using CHDM (cyclohexanedimethanol). The resin is a PET obtained by copolymerizing 30 mol% of cyclohexanedimethanol in a copolymerized diol component. The result of measuring the heat of crystal melting using a differential thermal analyzer is less than 1 cal/g, which is an amorphous resin.

‧ Copolymerized polyester resin (c-2)

PET was copolymerized using CHDM (cyclohexanedimethanol). The resin is a PET obtained by copolymerizing a copolymerized diol component with 60 mol% of cyclohexanedimethanol. The result of measuring the heat of crystal melting using a differential thermal analyzer is less than 1 cal/g, which is an amorphous resin.

‧Copolymerized polyester resin (c-3)

Copolymerized PET using isophthalic acid. The resin is a PET obtained by copolymerizing a copolymerized dicarboxylic acid component with 17.5 mol% of phthalic acid. The result of measuring the heat of crystal melting using a differential thermal analyzer is less than 1 cal/g, which is an amorphous resin.

‧Dispersant (d-1)

A PBT-PAG (polyalkylene glycol) copolymer was used. The resin is a block copolymer of PBT (polybutylene terephthalate) and PAG (mainly polytetramethylene glycol). The result of measuring the heat of crystal melting by using a differential thermal analyzer is 1 cal/g or more, which is a crystalline resin.

[Example 1]

The mixture of the raw materials as shown in Table 1 was vacuum dried at 180 ° C for 3 hours and then supplied to an extruder. After melt extrusion at a temperature of 280 ° C, it was filtered through a 30 μm cut filter and then introduced into a T-die.

Next, it was extruded into a sheet shape from a T-die as a molten single layer sheet. The molten single layer sheet was held on a drum at a surface temperature of 25 ° C, and electrostatically adhered thereto to be cooled and solidified to obtain an unstretched single layer film. At this time, it is assumed that the film surface attached to the drum is the back surface, and the surface connected to the air is the front surface. Next, the unstretched single-layer film was preheated by a roll group heated to a temperature of 85 ° C, and then irradiated from both sides of the film under the conditions of an infrared heater as shown in Table 4, while using the circumferential speed difference of the roll toward the film length. The direction was extended by 3.6 times and then cooled by a roll group having a temperature of 25 ° C to obtain a uniaxially stretched film. The infrared heater is a pure carbon heater "CZB8000/1000G" manufactured by Heraeus Co., Ltd. and is disposed on both sides with two sides on one side. The heater is a heater with a length of 1 m and a rated output of 80 W/cm per one. Also, the power supplied to the heater was adjusted to meet the conditions of the infrared heater as shown in Table 4. In addition, the numerical values regarding the heating conditions as shown in the table are values per one side.

While holding both ends of the obtained uniaxially stretched film with a cooker, the film is introduced into a preheating zone at a temperature of 95 ° C in the tenter, and secondly, continuously in a heating zone at a temperature of 105 ° C toward the length of the film. The direction orthogonal to the film (the width direction of the film) was extended by 3.6 times. Further, heat treatment is applied to the heat treatment zone in the tenter at 190 ° C for 20 seconds, and further, after the relaxation treatment is applied to the 6% width direction at a temperature of 180 ° C, and then to the 1% width direction at a temperature of 140 ° C. A relaxation treatment is applied. Secondly, it is uniformly cooled slowly and then taken up. A single-layer white film having a thickness of 188 μm was obtained as described above. As a result of observing the cross section of the white film, many fine bubbles were contained inside. Further, the number of depressions on the surface of the film is small, and there is no roll contamination and excellent film formability. The various characteristics of the film are shown in Table 7.

[Examples 2 to 7]

Film formation was carried out in the same manner as in Example 1 except that the conditions of the infrared heaters shown in Table 4 were respectively set to obtain a single-layer white film having a thickness of 188 μm. As a result of observing the cross section of the white film, many fine bubbles were contained inside. Further, the number of depressions on the surface of the film is small, and there is no roll contamination and excellent film formability. The various characteristics of the film are shown in Table 7.

[Examples 8 to 15, 17, 22 to 24]

Film formation was carried out in the same manner as in Example 1 except that the raw material compositions shown in Tables 1 and 2 were respectively set to obtain a single-layer white film having a thickness of 188 μm. As a result of observing the cross section of the white film, many fine bubbles were contained inside. Further, the number of depressions on the surface of the film is small, the roller contamination is small, and the film formation property is also excellent. The various characteristics of the film are shown in Tables 7 and 8.

[Example 16]

The mixture of the raw materials as shown in Table 2 was vacuum dried at 180 ° C for 3 hours and then supplied to the extruder (A). Further, the polyester resin (a1-1) was additionally dried at a temperature of 180 ° C for 3 hours and then supplied to an extruder (B). The raw materials supplied to the extruder (A) and the raw materials supplied to the extruder (B) were separately melted at a temperature of 280 ° C and supplied to a feed tap block. In the feed splitter sleeve, the layer (layer A) composed of the raw material supplied to the extruder (A) and the layer (layer B) composed of the raw material supplied to the extruder (B) are oriented in the thickness direction. The two layers of the A layer/B layer are laminated and then introduced into the T-die.

Next, it was extruded into a sheet shape from the T-die, and it was a molten two-layer laminated unstretched sheet composed of the A layer/B layer. The molten laminated sheet was adhered to a rotating cylinder maintained at a surface temperature of 25 ° C, and electrostatically adhered thereto to be cooled and solidified to obtain an unstretched laminated film. At this time, the surface of the layer B is connected to the drum and the surface of the layer A is connected to the air. That is, the surface of the layer B is the back surface, and the surface of the layer A is the front surface.

Then, the unrolled film was preheated by a roll group heated to a temperature of 85 ° C, and then irradiated only by the surface side (front side) of the layer A under the conditions of the infrared heater shown in Table 5, and the circumferential speed difference of the rolls was used. The film was stretched 3.6 times in the longitudinal direction of the film and cooled by a roll group at a temperature of 25 ° C to obtain a uniaxially stretched film.

While holding both ends of the obtained uniaxially stretched film with a cooker, the film is introduced into a preheating zone at a temperature of 95 ° C in the tenter, and then continuously heated at a temperature of 105 ° C toward the length of the film. The direction orthogonal to the film (the width direction of the film) was extended by 3.6 times. Further, heat treatment is applied to the heat treatment zone in the tenter at 190 ° C for 20 seconds, and further, after the relaxation treatment is applied to the 6% width direction at a temperature of 180 ° C, and then to the 1% width direction at a temperature of 140 ° C. A relaxation treatment is applied. Secondly, it is uniformly cooled slowly and then taken up. A laminated white film having a thickness of 188 μm was obtained as described above. As a result of observing the cross section of the white film, many fine bubbles were contained inside the layer A. Further, both the front surface and the back surface have a small number of depressions on the surface of the film, and there is no roll contamination and excellent film formability. The various characteristics of the film are shown in Table 8.

[Examples 18 to 21, 27]

Film formation was carried out in the same manner as in Example 1 except that the stretching ratios shown in Table 5 were respectively set to obtain a single-layer white film having a thickness of 188 μm. As a result of observing the cross section of the white film, many fine bubbles were contained inside. Further, the number of depressions on the surface of the film is small, the roller contamination is small, and the film formation property is also excellent. The various characteristics of the film are shown in Table 8.

[Examples 25, 26]

The film formation was carried out in the same manner as in Example 1 except that the preheat roll temperature and the infrared heater conditions were set as shown in Table 5, respectively, to obtain a single-layer white film having a thickness of 188 μm. As a result of observing the cross section of the white film, many fine bubbles were contained inside. Further, the number of depressions on the surface of the film is small, the roller contamination is small, and the film formation property is also excellent. The various characteristics of the film are shown in Table 8.

[Comparative Examples 1, 2, 4]

Film formation was carried out in the same manner as in Example 1 except that the conditions of the infrared heater shown in Table 6 were respectively set to obtain a single-layer white film having a thickness of 188 μm. The film forming property was inferior to that of Example 1. As a result of observing the cross section of the white film, fine bubbles were contained inside. Since the heat Q is less than 8.5 W/cm, the temperature of the surface of the film cannot be sufficiently raised, so that the number of depressions on the surface of the film increases. Therefore, the roll is contaminated, resulting in frequent cleaning. The various characteristics of the film are shown in Table 9.

[Comparative Example 3]

Film formation was carried out in the same manner as in Example 1 except that the conditions of the infrared heater shown in Table 6 were set. Since the heat Q exceeds 40 W/cm, when the longitudinal direction (longitudinal direction) is extended, the film is softened and the film is thermally sag, resulting in failure to form a film.

[Comparative Example 5]

Film formation was carried out in the same manner as in Example 16 except that the conditions of the infrared heater shown in Table 6 were set to obtain a laminated white film having a thickness of 188 μm. The film forming property was repeatedly broken and was inferior to that of Example 16. As a result of observing the cross section of the white film, fine bubbles were contained inside the layer composed of the mixed raw materials as shown in Table 3. Since the heat Q is less than 8.5 W/cm, the temperature of the surface of the film cannot be sufficiently raised, so that the number of depressions on the surface of the film increases. Therefore, the roll is contaminated, resulting in frequent cleaning. The various characteristics of the film are shown in Table 9.

[Comparative Example 6]

Film formation was carried out in the same manner as in Example 1 except that the composition of the raw materials as shown in Table 3 was set to obtain a single-layer transparent film having a thickness of 188 μm. When extending in the longitudinal direction, the edge portion is thermally swelled, so that the width of the film after the longitudinal stretching is varied, so that a film having a large thickness unevenness is obtained. Since there is no incompatible component, there is no roll contamination. However, since there is no air bubble inside the film and the reflectance is small, it is not suitable for use as a film of a reflective film. The various characteristics of the film are shown in Table 9.

[Comparative Examples 7, 12]

Film formation was carried out in the same manner as in Example 1 except that the raw material composition was as shown in Table 3, respectively, to obtain a single-layer white film having a thickness of 188 μm. Comparative Example 7 is a result of observing the cross section of the white film, and the voids are joined to form a large void. Film formation is unstable and cracks occur repeatedly.

Comparative Example 12 is a cross-sectional result of observing a white film, and contains fine bubbles inside. Since the heat Q is less than 8.5 W/cm, the temperature of the surface of the film cannot be sufficiently raised, so that the number of depressions on the surface of the film increases. Therefore, the roll is contaminated, resulting in frequent cleaning.

The various characteristics of the film are shown in Table 9.

[Comparative Examples 9 to 11, 13]

Film formation was carried out in the same manner as in Example 1 except that the stretching ratios shown in Table 6 were respectively set to obtain a single-layer white film having a thickness of 188 μm. As a result of observing the cross section of the white film, many fine bubbles were contained inside.

In Comparative Example 9, the stretching ratio in the longitudinal direction of the film was more than 4.5 times, and in Comparative Example 11, the stretching ratio in the film width direction was more than 5 times, so that the number of depressions on the surface of the film was increased. Therefore, the roll is contaminated, resulting in frequent cleaning.

In Comparative Example 10, the stretching ratio in the film width direction was less than 3 times, and in Comparative Example 13, the stretching ratio in the film width direction was less than 2.9 times. Therefore, the number of depressions on the surface of the film was small, and the contamination of the roll was small. However, the reflectance is small, so it is not suitable for use as a film of a reflective film. Further, Comparative Example 13 was prone to cracking when it was extended in the lateral direction.

The various characteristics of the film are shown in Table 9.

The items "heat Q (W/cm)" in Tables 4 to 6 are the heat reaching the film surface per one side of the film.

The items "infrared heater/output power (W/cm)" in Tables 4 to 6 are the output power of the infrared heater to the film side per one side of the film.

The items "infrared heater/distance (mm)" in Tables 4 to 6 are the distance from the infrared heater to the film surface.

The items "infrared heater/time (seconds)" in Tables 4 to 6 are the time required for the film to pass through the irradiation zone.

[Industry use possibility]

According to the method for producing a white film of the present invention, a white film excellent in film formability, whiteness, and reflectivity can be provided. Further, by using the white film of the present invention, it is possible to provide a surface light source excellent in luminance characteristics.

1. . . film

2. . . Thermocouple

3. . . Heat source (infrared heater)

D. . . Length of film length direction of the heated portion of the film surface (length of film length direction of the irradiation zone)

L. . . Distance from heat source (infrared heater) to film surface

Fig. 1 is a schematic view showing a method of measuring the amount of heat Q observed from the width direction of the film.

Claims (9)

A method for producing a white film for producing a white film having bubbles inside and having a specific gravity of 0.55 or more and 1.30 or less, which is a film having a layer containing a main resin component and an incompatible component to the resin component. While heating at least one surface thereof at a heat of 8.5 W/cm or more and 40 W/cm or less per one surface, the film is extended by 3.0 times or more and 4.5 times or less in the longitudinal direction of the film by the circumferential speed difference of the rolls, and then in the film. The width direction is extended by 3 times or more and 5 times or less. The method for producing a white film according to the first aspect of the invention, wherein the stretching ratio of the film in the longitudinal direction is 3.4 times or more and 4.5 times or less. The method for producing a white film according to claim 1 or 2, wherein when the glass transition temperature of the main resin component is Tg (° C.), preheating is applied so that the film temperature before extending in the longitudinal direction of the film is at Tg-20. (°C) or more and Tg (°C) or less. The method for producing a white film according to claim 1 or 2, wherein an infrared heater is provided on at least one surface side of the film, and a distance from the surface of the film to the infrared heater is set to be 5 mm or more and 100 mm or less. The output power of the infrared heater to the film side per one side of the film is set to be 35 W/cm or more and 150 W/cm or less, and the surface of the film is 8.5 W/cm or more and 40 W/cm or less per one side. The heat is heated. A method of manufacturing a white film according to item 1 of the patent application, wherein The white film has a layer containing a polyester resin and an incompatible component to the polyester resin, and the outermost layer of at least one side of the white film is the layer, and the incompatible component has a glass transition temperature of 170 ° C. The above thermoplastic resin of 250 ° C or less and/or at least one or more inorganic particles selected from the group consisting of titanium oxide, calcium carbonate and barium sulfate. The method for producing a white film according to claim 5, wherein the incompatible component is a thermoplastic resin having a glass transition temperature of 170 ° C or more and 250 ° C or less, and a group selected from the group consisting of titanium oxide, calcium carbonate and barium sulfate. At least one or more inorganic particles. The method for producing a white film according to the fifth or sixth aspect of the invention, wherein the content of the inorganic particles is 5% by mass or more and 60% by mass or less based on the layer containing the polyester resin and the incompatible component. The method for producing a white film according to claim 1 or 2, wherein the density of the depression on the surface of the white film is 1/100 μm ² or less. The method for producing a white film according to claim 1 or 2, wherein the white film has a relative reflectance of 100% or more and 120% or less.