JP4923378B2 - Light reflecting film and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-reflecting film excellent in reflecting characteristics and opacifying properties. <P>SOLUTION: The light-reflecting film has foam in the interior of the film. In the film, a ratio (L/R) of a length (L) of foam in a surface direction of the film to a length (R) of foam in the thickness direction of the film is obtained, a simple average value d1 and a standard deviation &sigma; of the L/R satisfy formula (1): &sigma;1/d1&ge;0.5. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a light reflecting film used for a reflecting member, and more particularly, a light reflecting film suitable as a reflector for a surface light source and a reflector, which is brighter and has a superior illumination efficiency. It is related with the light reflection film which can be obtained.
[0002]
[Prior art]
In recent years, many displays using liquid crystals have been used as display devices for personal computers, televisions, mobile phones, and the like. Since these liquid crystal displays themselves are not light emitters, they can be displayed by irradiating light using a surface light source called a backlight installed from the back side. Further, the backlight has a structure of a surface light source called a side light type or a direct type in order to meet the requirement that the entire screen should be irradiated uniformly, not just light. In particular, for thin LCD displays used in notebook PCs, where thinness and miniaturization are desired, there is a sidelight type, that is, a backlight that illuminates the screen from the side. Applied (Patent Document 1 claims (1) to (4)).
[0003]
Generally, in this sidelight type backlight, a cold cathode ray tube is used as an illumination light source from the edge of a plate called a light guide plate made of a transparent plate provided on one side even if there are at least one irregular reflection surface, and light is uniformly propagated and diffused. A light guide plate system that uniformly irradiates the entire liquid crystal display using a light guide plate is adopted. In this illumination method, in order to use light more efficiently, a reflector made of a white film or white tape is provided around the cold cathode ray tube and on the side surface of the light guide plate that does not have the cold cathode tube. Further, in order to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side, a reflection layer called a reflection plate is provided under the irregular reflection surface of the light guide plate. Thereby, the loss of light from the cold cathode ray tube is reduced, and the function of brightening the liquid crystal screen is provided.
[0004]
On the other hand, for large screens such as liquid crystal televisions, the edge-light method has been adopted because it is not possible to increase the screen brightness. In this method, a cold cathode ray tube is provided in parallel at the lower part of the liquid crystal screen, and the cold cathode ray tubes are arranged in parallel on the reflector. The reflecting plate may be a flat plate or a cold cathode ray tube formed into a semicircular concave shape.
[0005]
Reflectors and reflectors used in such surface light sources for liquid crystal screens (collectively referred to as surface light source reflecting members) are required to have a high reflection function as well as a thin film. A film containing fine bubbles inside is used alone, or a film in which these films are bonded to a metal plate, a plastic plate or the like has been used. In particular, when a film containing fine bubbles inside is used, it is widely used because of its excellent brightness improvement effect and uniformity. Such fine bubbles can be obtained by causing a resin to contain an incompatible component (void nucleating agent) and stretching it in one or more directions. Such a film containing fine bubbles inside is disclosed in Patent Gazettes (Patent Documents 2 and 3). Moreover, although there are usually many types of void nucleating agents, examples in which two or more types of void nucleating agents are used in combination are also disclosed (Patent Documents 4 and 5).
[0006]
In addition, a film that has been whitened by containing a large number of fine bubbles inside the film has high reflectivity and high whiteness, so it is preferably used for image printing media, particularly image receiving paper for sublimation transfer systems. It has been.
[0007]
[Patent Document 1]
JP 63-62104 A
[0008]
[Patent Document 2]
JP-A-6-322153
[0009]
[Patent Document 3]
JP-A-7-118433
[0010]
[Patent Document 4]
JP 2001-225433 A
[0011]
[Patent Document 5]
JP 2001-288291 A
[0012]
[Problems to be solved by the invention]
By the way, in addition to conventional notebook PCs, LCD screens have been used in various devices such as stationary PCs, TVs, and mobile phone displays in recent years, and demand is rapidly increasing. . On the other hand, with the demand for higher-definition images on liquid crystal screens, improvements have been made to increase the brightness of liquid crystal screens to make the images clearer and easier to see. Tubes) are also becoming brighter and more powerful. However, when the above film is used as a reflector or reflector that is a surface light source reflecting member, a part of the light from the illumination light source is transmitted to the opposite surface because of its poor concealment property. (Brightness) is insufficient, and further problems such as a reduction in illumination efficiency due to light transmission loss from the illumination light source have been pointed out. In order to solve such a problem, a reflection film in which the amount of void nucleating agent is simply increased and a reflection film using two or more kinds of void nucleating agents have been proposed, but the light reflectivity and backlight luminance characteristics are dramatically improved. It does not lead to improvement, and further improvement in reflectivity and concealment of the light reflection film is required.
[0013]
Also in the field of image printing media, with higher image quality and higher definition of digital photos, image receiving paper is required to have higher whiteness and improved reflectivity of light reflecting films.
[0014]
In view of the above, in both the field of surface light sources used for liquid crystal screens and the like and the field of image printing media, it is an object to provide a light reflecting film having excellent reflection characteristics and concealment properties.
[0015]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention,
Inside the filmVoid nucleating agents and flat independenceWhen the ratio of the bubble length (L) in the plane direction of the film and the length (R) of the bubble in the thickness direction of the film (L / R) is obtained for each bubble, The simple average value d1 and standard deviation σ1 of those L / Rs satisfy the formula (1)And
In addition, two or more kinds of components are used as the void nucleating agent, and the simple average d2 and standard deviation σ2 of the particle diameter or dispersion diameter of the void nucleating agent contained in the film satisfy the formula (2).A light reflecting film characterized by,and,
A method for producing a film having a void nucleating agent and flat closed cells inside the film, wherein for each bubble, the bubble length (L) in the plane direction of the film and the bubble length (R) in the thickness direction of the film ) Ratio (L / R), the simple average value d1 and standard deviation σ1 of these L / R satisfy the formula (1),
And the manufacturing method of the reflective film characterized by satisfy | filling Formula (2) and (3),
Is the essence of this.
[0016]
σ1 / d1 ≧ 0.5 (1)
σ2 / d2 ≧ 0.5 (2)
However, d2 is a simple average of the particle diameter or dispersion diameter of the void nucleating agent contained in the film, and is a σ2 standard deviation.
ΔM = | Mmd−Mtd | ≧ 0.3 (3)
However, Mmd is a draw ratio in the film longitudinal direction, and Mtd is a draw ratio in the film width direction.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
  The light reflecting film of the present invention has a film inside.Void nucleating agents and flat independenceWhen the ratio of the bubble length (L) in the plane direction of the film and the length (R) of the bubble in the thickness direction of the film (L / R) is obtained for each bubble, It is necessary that the simple average value d1 and standard deviation σ1 of L / R satisfy the formula (1).
[0018]
σ1 / d1 ≧ 0.5 (1)
In the present invention, the light reflecting film is not necessarily limited, but is particularly preferably used as an image printing medium such as a light reflecting member (reflecting plate, light guide plate side reflector, lamp reflector) and image receiving paper in a surface light source. A film that is made.
[0019]
As described above, as one of the manufacturing methods widely used in producing a light reflecting film, as described above, the main resin component constituting the light reflecting film and a component (void) that is incompatible with the resin component There is a technique of generating bubbles by melt-extruding a mixture containing a nucleating agent) and stretching it in at least one direction. However, merely increasing the void nucleating agent has little effect in the range where film formation is possible.
[0020]
As a result of earnestly examining the problem, the inventor of the present invention has a certain degree of distribution in the shape of bubbles existing inside the film, so that the light reflecting film has reflectivity, concealment, light diffusibility, and backlight. I found out that the brightness is dramatically improved. According to the study by the present inventors, such a light reflecting film could not be obtained by any conventional technique.
[0021]
As a result of further investigation of such a phenomenon, the present inventors have simply determined the light reflectivity, light diffusibility, and backlight luminance characteristics by the bubble volume and the amount of void nucleating agent added as described above. It has not been done, but has been found to be greatly influenced by the shape distribution of bubbles inside the film, particularly the L / R ratio distribution. Furthermore, the light reflecting film to be obtained has been found that the standard deviation σ1 and the simple average value d1 of the L / R ratio of bubbles inside the film can be satisfied by satisfying the formula (1), and the present invention has been achieved.
[0022]
Although the detailed reason why the fulfillment of such requirements greatly contributes to the improvement of light reflectivity, luminance characteristics, etc. is unclear, the inclusion of various shapes of bubbles mainly produces the following effects. This seems to be the reason.
[0023]
(1) Since the size of the generated bubbles is not uniform in the thickness direction and the surface direction, the bubbles are filled more densely. Therefore, the number of gas-solid interfaces per thickness can be increased efficiently, and the light reflectivity is improved.
[0024]
(2) The effect of improving the light diffusibility by appropriately scattering the light inside the film because the shape of the bubbles is various.
[0025]
It is considered that the backlight luminance characteristic is drastically improved because such an effect of improving the light reflectivity and the light diffusibility is exhibited at the same time.
[0026]
In addition, in the conventional reflection film, the detailed reason why the simple increase of the void nucleating agent did not greatly contribute to the improvement of the light reflectivity or the like is unknown, but the increase in visible light absorption by the void nucleating agent and the bubble It is conceivable that the effective light reflection inside the film is suppressed by the connection.
[0027]
In the present invention, it is necessary that the ratio L / R of the bubble length L in the plane direction of the bubbles in the film and the bubble length R in the thickness direction of the film has a certain distribution or more.
[0028]
The distribution above a certain level refers to a distribution in which the simple average value d1 and standard deviation σ1 of the L / R ratio of bubbles contained in the reflective film satisfy the formula (1).
[0029]
Here, the bubble length L in the plane direction of the bubble film and the bubble length R in the film thickness direction can be obtained by observing a cross section in the film thickness direction. This will be described with reference to the schematic model diagram shown in FIG. 1-3, the state of bubbles in the film cross section is shown as a model in relation to the measurement method. 1 is resin, 2 is bubble, 3 is void nucleating agent, 4 is particle or non- It is a compatible resin.
[0030]
That is, the bubble length L in the surface direction of the bubble film and the bubble length R in the film thickness direction can be obtained by observing a cross section in the film thickness direction (FIG. 1). In addition, when the method of generating bubbles inside the film using a void nucleating agent described later is used, the cavity length of the bubbles in the film surface direction is L, and the thickness direction of the void nucleating agent generating the bubbles Is set to R (FIG. 2). However, if there are no cavities around the particles or incompatible resin, they are not subject to measurement (FIG. 3). Even if bubbles are generated, the cross-sectional area of the bubbles is 1 μm.²The following are not subject to measurement.
[0031]
A specific method for measuring the cross-sectional area of the bubbles in the present invention is shown below. (1) Take a picture of the cross-sectional image obtained in accordance with the method described later (the cross-sectional image may be obtained electronically). (2) Overlay a sufficiently transparent film or tracing paper on the photograph and trace the shape of the bubbles in the photograph. However, the thickness of the pen tip used for tracing is 0.5 mm or less. (3) The image of the film or tracing paper traced using a CCD camera or the like was taken into a personal computer, and the cross-sectional area of the bubbles was determined using image analysis software. In addition, the spherical equivalent diameter of the void nucleating agent described later was also obtained from the cross-sectional area of the void nucleating agent using the same method.
[0032]
By measuring L and R for each bubble present inside the film, then calculating L / R, calculating the simple average of those L / R, and determining the standard deviation of those L / R σ1 can be obtained.
[0033]
Here, σ1 / d1 obtained by dividing σ1 by d1 is an index indicating the size of the distribution of the (L / R) ratio of bubbles existing inside the film. It is preferable to make the size of the distribution (σ1 / d1) larger in view of luminance characteristics and light reflectivity. σ1 / d1 needs to be 0.5 or more, but a more preferable range is 0.6 or more, and further preferably 0.7 or more. The upper limit of σ1 / d1 is not particularly defined, but is preferably 2.0 or less from the standpoint of productivity.
[0034]
Σ1 / d1 is measured for commercially available white films (E60L, E20 (above, Toray Industries, Inc.), WS-100, WS-180 (Mitsui Chemicals), MC-PET (Furukawa Electric), etc.) As a result, it was less than 0.4. Further, when these films were actually incorporated into a backlight and the luminance was measured, sufficient luminance could not be obtained. Although the details of the reason are unclear, it is considered that these films focus on the expression of high reflectivity. Therefore, it must be said that it is insufficient for the light reflector application aimed at in the present invention.
[0035]
  From the point of light reflectivity, the shape of the bubbles inside the film is an elliptical shape that is elongated with respect to the film surface direction, that is, a flat shape.is necessary. By flattening the shape of the bubbles, a large number of bubbles can be formed in the film thickness direction, and the light reflectivity can be dramatically improved. Further, it is preferable that the bubbles in the film are independent from the viewpoint of productivity and backlight luminance characteristics.
[0036]
In the present invention, “flat shape” means that L / R is 1.5 or more. In the light reflecting film of the present invention, the ratio of the bubbles having a flat shape among all the bubbles is preferably 20% or more, more preferably 30% or more, and further preferably 40% or more. By setting the ratio of flat bubbles to such a range, a light reflecting film that is more excellent in light reflectivity can be obtained.
[0037]
As a method of forming such flat closed cells,,
A method in which a void nucleating agent is contained inside the light reflecting film and fine bubbles are generated inside by stretching it in at least one direction;
More specifically,
(A) Using two or more kinds of components as the void nucleating agent, the simple average d2 and standard deviation σ2 of the particle diameter or dispersion diameter of the void nucleating agent contained in the film satisfy the formula (2),
σ2 / d2 ≧ 0.5 (2),
Or
(B) satisfying formulas (2) and (3),
ΔM = | Mmd−Mtd | ≧ 0.3 (3)
However, Mmd is a draw ratio in the film longitudinal direction, Mtd is a draw ratio in the film width direction,
Can be mentioned.
[0038]
In the present invention, it is desired to form a large number of fine closed flat bubbles,the aboveUsing a techniqueis necessary.the aboveThe technique is a technique for generating flat bubbles by utilizing the fact that peeling occurs at the interface between the resin component constituting the light reflecting film and the void nucleating agent during stretching. Therefore,the aboveWhen using the technique, biaxial stretching is more preferable than uniaxial stretching in order to increase the bubble occupied volume and increase the number of bubbles per thickness.
[0039]
Less than,the aboveThe resin component and void nucleating agent that can be suitably used in the method will be described in detail.
[0040]
As a main resin component which comprises a light reflection film, what does not have absorption in visible region is preferable. In addition, since the light reflecting film in the present invention reflects and diffuses light at the gas-solid interface between the bubbles inside the film and the resin, the refractive index of the resin component forming the solid phase is the refractive index of the gas phase. It is preferable that the difference is large. When the refractive index difference is small, reflection at the gas-solid interface does not occur so much, and as a result, a desired light reflection effect cannot be obtained. Since the refractive index of gas and vacuum is substantially 1.0, in order to obtain substantially effective light reflectivity, the refractive index of the resin component is preferably 1.4 or more, more preferably 1 .5 or more. Examples of resins that satisfy such conditions include polyolefins and polyesters. Among them, an aromatic polyester having favorable dimensional stability, mechanical properties, handling properties (handling properties) and a high refractive index can be preferably used.
[0041]
Furthermore, among aromatic polyesters, polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate, and the like Since it can be obtained at a low cost and the film-forming property is good, it can be particularly preferably used.
[0042]
These polyesters may be homopolymers or copolymers, but are preferably homopolymers. Examples of copolymer components in the case of a copolymer include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and diol components having 2 to 15 carbon atoms. Examples of these components include isophthalic acid. , Adipic acid, sebacic acid, phthalic acid, sulfonate group-containing isophthalic acid, and ester-forming compounds thereof, diethylene glycol, triethylene glycol, neopentyl glycol, polyalkylene glycol having a molecular weight of 400 to 20,000, and the like. .
[0043]
In these polyester resins, various additives within the range in which the effect of the present invention is not impaired, for example, fluorescent brightener, crosslinking agent, heat stabilizer, oxidation stabilizer, ultraviolet absorber, organic lubricant, organic, Inorganic fine particles, fillers, light proofing agents, antistatic agents, nucleating agents (excluding nucleating agents for forming voids), dyes, dispersing agents, coupling agents and the like may be added.
[0044]
Next, the void nucleating agent added to form bubbles will be described. The void nucleating agent is not necessarily the same as the main resin component constituting the light reflecting film, and may be any material that can be dispersed in the resin component, for example, inorganic fine particles, organic fine particles, various thermoplastic resins, and the like. It is done.
[0045]
The void nucleating agent is preferably one that can form bubbles with itself as a nucleus, such as calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide (anatase type, rutile type), zinc oxide, barium sulfate, zinc sulfide, basic Lead carbonate, mica titanium, antimony oxide, magnesium oxide, calcium phosphate, silica, alumina, mica, talc, kaolin, polyolefin resin such as polyethylene, polypropylene, polybutene, polymethylpentene, polystyrene resin, polyacrylate resin, polycarbonate resin, polyacrylonitrile Resins, polyphenylene sulfide resins, fluororesins and the like are preferably used.
[0046]
The void nucleating agent may be a single type, but it is preferable to use two or more types of components. By using two or more kinds of void nucleating agents, various bubbles having different L / R ratios can be generated, and as a result, σ1 / d1 can be increased. Although the details of the reason why such a phenomenon occurs are unknown, it can be considered as follows.
[0047]
Dispersibility and solubility (compatibility) in the resin component constituting the light reflecting film vary depending on the type of void nucleating agent selected. Therefore, the shape of the bubbles generated by the void nucleating agent also differs depending on the type of the void nucleating agent. Therefore, it is considered that the use of plural kinds of void nucleating agents is effective in generating bubbles having various L / R ratios, and as a result, σ1 / d1 becomes larger.
[0048]
When two or more kinds of void nucleating agents are used, the combination is not particularly limited, and any combination of inorganic components, organic components, and inorganic and organic components may be used. Examples of combinations include barium sulfate-calcium carbonate, barium sulfate-alumina, polymethylpentene-polystyrene, polymethylpentene-polypropylene, barium sulfate-polymethylpentene, calcium carbonate-polymethylpentene, and the like.
[0049]
However, if the distribution of the particle size of the void nucleating agent (or the dispersion diameter, or the equivalent sphere diameter if it is not a perfect sphere) is small, σ1 / d1 jumps even when two or more void nucleating agents are used. Does not improve. In order to drastically increase σ1 / d1 indicating the size of the L / R ratio distribution of the bubbles generated by the void nucleating agent, it is particularly preferable to have a certain distribution in the particle size of the void nucleating agent. . The particle size distribution of the void nucleating agent is determined by a value σ2 / d2 obtained by dividing σ2 by d2, where d2 is a simple average value of the particle size of the void nucleating agent and σ2 is a standard deviation.
[0050]
In the present invention, σ2 / d2 indicating the particle size distribution of the void nucleating agent preferably satisfies the formula (2).
[0051]
σ2 / d2 ≧ 0.5 (2)
Σ2 / d2, which is a value indicating the distribution of the particle size distribution of the void nucleating agent, is preferably greater than 0.5, more preferably 0.6 or more, and even more preferably 0.7 or more.
[0052]
By using a void nucleating agent satisfying such conditions, bubbles having various L / R values can be efficiently generated, and σ1 / d1 can be further increased.
[0053]
Further, if σ2 / d2 is increased, the light diffusibility can be greatly improved because the size of the generated bubbles in the thickness direction and the surface direction may not be uniform. At the same time, since the close-packing of bubbles can be promoted, the light reflectivity is also greatly improved. The backlight luminance characteristic can be greatly improved by further improving the light reflectivity and further improving the light diffusibility.
[0054]
Conventionally, a light reflecting film using two or more kinds of void nucleating agents has been proposed (Patent Documents 4 and 5). When the present inventors made additional trials in accordance with such known examples, the light reflectivity improvement effect and the luminance characteristic improvement effect were poor. The details of this reason are unknown, but when σ2 / d2 was measured, all were less than 0.4. Also, σ1 / d1 was less than 0.4. In such a known example, since the shape of the bubbles and the particle size of the void nucleating agent are not controlled, it is presumed that as a result, sufficient light reflectivity improvement effect and luminance characteristic improvement were not expressed.
[0055]
Further, it is not impeded to form a skin layer on one side or both sides of a film in which fine bubbles are formed by a method such as coextrusion. Furthermore, various particles, a fluorescent brightening agent, and the like may be added to the skin layer. By laminating such a skin layer, mechanical strength, surface smoothness and the like can be imparted to the light reflecting film.
[0056]
Furthermore, it is not impeded to add various particles that do not generate air bubbles in the light reflecting film or the skin layer in order to improve surface slippage and running durability during film formation.
[0057]
In addition, various coating liquids are applied using well-known techniques in order to impart easy adhesion, antistatic properties, ultraviolet light absorption performance, etc. to the surface of the light reflecting film within the range where the effects of the present invention are not impaired. A hard coat layer or the like may be provided for application or to improve impact resistance. The application may be performed at the time of film production (in-line coating) or may be applied on the light reflecting film after completion of crystal orientation (off-line coating).
[0058]
Furthermore, for the purpose of imparting electromagnetic wave shielding properties or bending workability, aluminum, silver, or the like may be bonded or vapor-deposited on one surface of the light reflecting film.
[0059]
The apparent specific gravity, which is a measure of the bubble content of the light reflecting film of the present invention, is preferably 0.1 or more and less than 1.5. More preferably, it is 0.3 or more and less than 1.3. When the specific gravity is less than 0.1, the mechanical strength as a film may be insufficient, or problems such as easy breakage and poor handleability may occur. On the other hand, when it exceeds 1.3, the bubble content is too low, the reflectance is lowered, and the luminance tends to be insufficient.
[0060]
10-500 micrometers is preferable and, as for the thickness of the light reflection film in this invention, 20-300 micrometers is more preferable. When the thickness is less than 10 μm, it becomes difficult to ensure the flatness of the film, and unevenness in brightness tends to occur when used as a surface light source. On the other hand, when it is thicker than 500 μm, when it is used as a light reflecting film in a liquid crystal display or the like, the thickness may be too large.
[0061]
In the light reflecting film of the present invention, the light reflectance is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more from the viewpoint of light reflectivity and backlight luminance characteristics. When the light reflectance is less than 80%, the film is inferior in concealability, and when used as a light reflecting film in a liquid crystal display or the like, sufficient luminance may not be obtained. The upper limit of the reflectance is not particularly specified, but is preferably 200% or less from the viewpoint of light reflectance and color.
[0062]
Here, the light reflectivity is obtained by irradiating a film with a light beam having a light wavelength of 560 nm whose angle formed by the optical axis is 10 degrees or less with respect to the normal line of the film surface at an incident angle of 10 °. It is obtained by collecting and reflecting light reflected at an angle. However, if an integrating sphere is used, the sum of the areas of all openings must not exceed 10%.
[0063]
Next, although an example is demonstrated about the manufacturing method of the light reflection film of this invention, it is not limited to this example.
[0064]
In a composite film-forming apparatus having a main extruder and a sub-extrusion machine, a mixture of aromatic polyester resin chips and a void nucleating agent constituting a light-reflective film that was sufficiently vacuum-dried as needed was heated. Supply to the main extruder. Moreover, in order to laminate | stack a skin layer, the chip | tip of the aromatic polyester resin which performed sufficient vacuum drying as needed, an inorganic particle, and a fluorescent whitening agent are supplied to the heated subextruder.
[0065]
Here, as a first method for obtaining the reflective film of the present invention, it is desirable to use a void nucleating agent having a large particle size distribution (σ2 / d2). By using such particles, bubbles having various L / R ratios can be generated, and as a result, σ1 / d1 can be increased.
[0066]
Moreover, it is desirable to use two or more types of void nucleating agents as the second method for obtaining the reflective film of the present invention. By using different types of void nucleating agents, bubbles having different L / R ratios can be efficiently generated, and σ1 / d1 can be increased.
[0067]
In this way, the raw materials are supplied to each extruder and laminated (A / B or A / B / A) so that the polymer of the sub-extruder comes to one side of the polymer of the main extruder in the T die composite die. Co-extruded into a sheet shape to obtain a melt-laminated sheet.
[0068]
The melt-laminated sheet is tightly cooled and fixed on a cooled drum to produce an unstretched laminated film. At this time, in order to obtain a uniform film, it is desirable to apply static electricity to make it adhere to the drum. Thereafter, if necessary, a desired light reflecting film is obtained through a stretching step, a heat treatment step, and the like.
[0069]
The stretching method is not particularly limited, and there are a sequential biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are separated and a simultaneous biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are performed simultaneously.
[0070]
As a method of sequential biaxial stretching, for example, there is a method in which the unstretched laminated film is guided to a heated roll group, stretched in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and then cooled by a cooling roll group. It is common.
[0071]
In the stretching process in the longitudinal direction, it is effective to use a multistage stretching method in which stretching is performed in two or more stages in order to increase σ1 / d1. When performing multistage stretching, it is desirable that the stretching temperature in the previous stretching stage is lower than the stretching temperature in the subsequent stretching stage. It is also a desirable stretching method to increase the stretching ratio in the subsequent stretching step as much as possible. Hereinafter, one of the preferable aspects in the case of performing two-stage stretching will be exemplified. First, regarding the stretching temperature, when the stretching temperature in the first stage is T1, and the stretching temperature in the second stage is T2, it is preferable that the stretching temperature difference ΔT obtained by the following formula is 5 ° C. or more.
[0072]
ΔT = T2-T1
Next, with respect to the draw ratio, when the draw ratio of the first stage is M1, the draw ratio of the first stage (referring to the draw ratio of the film after completion of the first stage of stretching) is M2, the stretch represented by the following formula: It is preferable that the magnification ratio M21 is 0.7 or more.
[0073]
M21 = M2 / M1
When performing two-stage stretching, it is possible to efficiently generate bubbles with various L / R ratios by setting the stretching temperature difference ΔT and the stretching ratio M21 within this range, and as a result, σ1 / d1 Can be made larger.
[0074]
After stretching in the longitudinal direction, stretching in the width direction can be subsequently performed. In the sequential biaxial stretching method, both ends of the film are guided to a heated tenter while being held by clips, and can be stretched in a direction perpendicular to the longitudinal direction (lateral direction or width direction).
[0075]
On the other hand, as a method of simultaneous biaxial stretching, for example, the both ends of the above-mentioned unstretched laminated film are guided to a heated tenter while being gripped by clips, and stretched in the width direction and simultaneously accelerated the clip traveling speed. Thus, there is a method of simultaneously stretching in the longitudinal direction. This simultaneous biaxial stretching method has an advantage that the film surface does not come into contact with the heated roll, and therefore there is no scratch that becomes an optical defect on the film surface.
[0076]
Here, as a third method for obtaining the film of the present invention, when the draw ratio in the width direction is Mtd and the draw ratio in the longitudinal direction is Mmd, the draw ratio difference ΔM shown by the following formula is 0.2 or more. It is preferable.
[0077]
ΔM = | Mmd−Mtd |
By providing a difference in the draw ratio in each drawing direction, flat bubbles having various L / R ratios can be efficiently generated in the film plane, and σ1 / d1 can be further increased.
[0078]
As a fourth method for obtaining the film of the present invention, the effective surface magnification is preferably 10 times or less. By setting the effective surface magnification within such a range, the connection of bubbles due to excessive stretching can be prevented, and independent flat bubbles can be contained in the light reflecting film.
[0079]
In order to impart planar stability and dimensional stability to the biaxially stretched laminated film thus obtained, heat treatment (heat setting) is subsequently performed in the tenter, and after uniform cooling, cooling to near room temperature and winding up Thus, the light reflective film of the present invention can be obtained.
[0080]
Thus, the light reflecting film of the present invention can be prepared by continuously stretching and heat treating after extrusion. That is, it is possible to obtain a light reflecting film that is extremely excellent in light reflectivity, light diffusibility, backlight luminance characteristics, surface flatness, mechanical characteristics, heat resistance and productivity in a stroke.
[Measurement and evaluation method of characteristics]
(1) Bubble L / R ratio distribution (σ1 / d1)
(i) Using a microtome, the film cross section is cut vertically without being stretched or crushed in the thickness direction. Here, whether it is “stretched” or “crushed” is determined by the following operation.
[0081]
(i-i) The film thickness is measured before cutting.
[0082]
(i-ii) The sample after cutting is observed with a scanning electron microscope S-2100A type (Hitachi Ltd.), and the length in the film thickness direction is measured.
[0083]
(i-iii) If the measured value obtained in (i-ii) is within ± 10% with respect to the film thickness obtained in (ii), “It is not stretched and is not crushed”. to decide.
[0084]
(ii) Using a scanning electron microscope S-2100A type (Hitachi Ltd.) (hereinafter SEM), the cross section is cut at an appropriate magnification (500-200) so that 100 to 200 bubbles are included in one screen. (10,000 times magnification) and take a picture of the screen to obtain a screen image. In the present invention, with the aim of 150 in principle, the enlargement magnification is determined so as to be within ± 10, and in the examples described later, the total number of bubbles that are effective as measurement objects included in the screen is measured. When taking a picture of the screen, an electronic method may be used.
[0085]
(ii-1) Here, when the thickness of the film is too large and the whole film thickness direction does not fit in the measurement screen (when the edges on both surfaces of the film are not observed on the screen), one screen The screen image is enlarged to an appropriate magnification (500 to 10000 times) so that 100 to 200 bubbles are contained in the film, and from the end portion related to one surface of the film to the end portion related to the other surface. A screen image of the SEM observation image is obtained by dividing the image into two or more times so that the images can be connected. The screen images obtained by division are connected to form one image.
[0086]
(ii-2) If the film thickness is too small to fit 100-200 bubbles in the measurement screen, move the field of view horizontally in the direction of the film surface and connect the screen images together. So that the screen image of the SEM observation image is obtained by dividing into two or more times. The screen images obtained by division are connected to form one image. However, the total number of bubbles to be measured should be at least 150.
[0087]
(iii) From the image obtained by the magnified observation, for each bubble, the bubble length (L) in the film surface direction, the bubble length (R) in the film thickness direction, and the ratio (L / R) ) Here, L and R are not necessarily the length in the surface direction and the length in the thickness direction of the actual bubbles in the film, but are determined by the length in the surface direction of the bubbles and the length in the thickness direction obtained from the image. Shall.
[0088]
In addition, the cross-sectional area of the bubble is 1 μm²Anything less than that is not subject to measurement. Also, bubbles that are not entirely contained in the screen (for example, bubbles that are partially missing at the edge of the screen) are not measured.
[0089]
(iv) The simple average of the obtained L / R ratio is d1, and the standard deviation is σ1.
[0090]
(v) σ1 is divided by d1 to obtain σ1 / d1.
[0091]
(vi) The operations of (i) to (v) are repeated three times, each σ1 / d1 is obtained, and the average of them is σ1 / d1.
[0092]
(vii) The cut surface of the film is shifted by 45 °, 90 ° and 135 ° with respect to the film surface direction, and the operations (i) to (vi) are performed, and each σ1 / d1 is obtained and averaged. Is σ1 / d1.
[0093]
(viii) According to the various findings of the present inventors, one location is usually sufficient, but in a wide sample or a long sample, if there is any structural unevenness, It is also possible to take a method such as measuring and determining the average value by measuring at about three locations (preferably at least three locations in the width direction for wide samples and at least three locations in the length direction for long samples). .
[0094]
In the present invention, the case where σ1 / d1 is less than 0.5 is evaluated as small, the case where 0.5 or less is less than 0.6 is evaluated as medium, and the case where 0.6 or more is evaluated as large.
(2) Particle size distribution of void nucleating agent (σ2 / d2)
(i) Using a microtome, the film cross section is cut vertically without being stretched or crushed in the thickness direction. Here, whether it is “stretched” or “crushed” is determined by the following operation.
[0095]
(i-i) The film thickness is measured before cutting.
[0096]
(i-ii) The sample after cutting is observed with an SEM, and the length in the film thickness direction is measured.
[0097]
(i-iii) If the measured value obtained in (i-ii) is within ± 10% with respect to the film thickness obtained in (ii), “It is not stretched and is not crushed”. to decide.
[0098]
(ii) Using a SEM, the cut section is enlarged and observed at an appropriate magnification (500 to 10000 times) so that the void nucleating agent is 100 to 200 in one screen. get. In the present invention, with the aim of 150 in principle, the enlargement magnification is determined so as to be within ± 10, and in the examples described later, the total number of void nucleating agents effective as measurement targets contained in the screen is measured. did. When taking a picture of the screen, an electronic method may be used.
[0099]
(ii-1) Here, when the thickness of the film is too large and the whole film thickness direction does not fit in the measurement screen (when the edges on both surfaces of the film are not observed on the screen), one screen The screen is enlarged to an appropriate magnification (500 to 10000 times) so that 100 to 200 void nucleating agents can be contained in the screen, from the end portion related to one surface of the film to the end portion related to the other surface. In order to be able to connect the images, the screen image of the SEM observation image is obtained by dividing the image into two or more times. The screen images obtained by division are connected to form one image.
[0100]
(ii-2) If the film thickness is too small to fit 100-200 void nucleating agents in the measurement screen, the measurement field of view is moved horizontally in the direction of the film surface to connect the screen images. The screen images of the SEM observation images are acquired in two or more times so that they can be matched. The screen images obtained by division are connected to form one image. However, the total number of measurement void nucleating agents should be at least 150.
[0101]
(iii) From the image obtained by magnified observation, the particle diameter (or equivalent sphere diameter if not completely spherical) is determined for each void nucleating agent. The particle size of the void nucleating agent obtained by such a method is not limited to the actual void nucleating agent in the film, but is determined by the particle size of the void nucleating agent obtained from the image. Note that void nucleating agents that are not entirely contained in the screen (for example, void nucleating agents that appear partially missing at the edge of the screen) are not subject to measurement.
[0102]
(iv) The simple average d2 and standard deviation σ2 of the particle diameters are calculated.
[0103]
(v) σ2 is divided by d2 to obtain σ2 / d2.
[0104]
(vi) The operations of (i) to (v) are repeated three times, and each σ2 / d2 is obtained and the average of them is σ2 / d2.
[0105]
(vii) The cut surfaces of the film are shifted by 45 °, 90 ° and 135 ° with respect to the film surface direction, and the operations (i) to (vi) are performed to obtain the respective σ2 / d2 and average them. σ2 / d2.
[0106]
(viii) According to the various findings of the present inventors, one location is usually sufficient, but in a wide sample or a long sample, if there is any structural unevenness, It is also possible to take a method such as measuring and determining the average value by measuring at about three locations (preferably at least three locations in the width direction for wide samples and at least three locations in the length direction for long samples). .
[0107]
In the present invention, the case where σ2 / d2 is less than 0.5 is evaluated as small, the case where it is 0.5 or more and less than 0.6 is evaluated as medium, and the case where it is 0.6 or more is evaluated as large.
(3) Reflectance
A reflectance of 560 nm is obtained on both sides of the film with a spectrophotometer U-3410 (Hitachi Ltd.) and a φ60 (diameter 60 mm) integrating sphere 130-0632 (Hitachi Ltd.) and a 10 ° C. inclined spacer attached. The higher value was adopted as the reflectance. The standard white plate attached to the machine was used.
(4) Backlight brightness
A film was incorporated into the backlight, and the luminance was measured. The backlight used is a straight single-light sidelight type backlight (14.1 inches) used for a notebook computer prepared for evaluation. Here, no sheet such as a diffusion sheet or a prism sheet is placed on the backlight. The measurement was performed by dividing the backlight surface into 4 × 2 × 2 sections and determining the luminance after 1 hour of lighting. The luminance was measured using BM-7 manufactured by Topcon Corporation. A simple average of the luminance at four locations in the plane was determined and used as the average luminance.
[0108]
【Example】
The present invention will be described with reference to the following examples and comparative examples, but is not particularly limited thereto.
Reference example 1
To the extruder, 82% by weight of PET as a resin component, 7% by weight and 10% by weight of two components of polymethylpentene and calcium carbonate (average particle size 3 μm) are added as void nucleating agents, respectively, and polyethylene glycol is added as a dispersant. The pellets added and mixed by weight were supplied and cooled on a mirror-casting drum by a predetermined method to prepare an unstretched sheet.
[0109]
Next, this sheet was stretched 3.5 times in the longitudinal direction by a two-stage stretching method. The first stage stretching was performed at a stretching temperature of 84 ° C. and a stretching ratio of 2.0 times, and the second stage stretching was performed at a stretching temperature of 95 ° C. and a stretching ratio of 1.75 times. The stretching temperature difference ΔT is 11 ° C., and the stretching ratio M21 is 0.875. Subsequently, after passing through a 100 ° C. preheating zone with a tenter, the film was stretched 3.1 times in the width direction at 110 ° C. ΔM is 0.3 and the effective surface magnification is 8.90 times. Furthermore, this biaxially stretched film was heat-treated at 210 ° C. for 30 seconds to obtain a light reflecting film having a thickness of 100 μm. Although the σ2 / d2 distribution of the obtained light reflecting film was small, the σ1 / d1 distribution was medium. Further, the reflectance was as high as 95% and the backlight luminance was as high as 2300 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Reference example2
Pellets mixed with 86% by weight of PET as a resin component and calcium carbonate (average particle size: 2 μm) as a void nucleating agent were supplied to an extruder, and an unstretched sheet was produced using the same method as in Reference Example 1. . The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a medium σ1 / d1 distribution and a medium σ2 / d2 distribution. The reflectivity was 95%, and the backlight luminance was as high as 2340 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Reference example3
Pellets prepared by adding 86% by weight of PET as a resin component and 14% by weight of barium sulfate (average particle size 2 μm) as a void nucleating agent were fed into an extruder and cooled on a mirror-cast drum by a predetermined method. An unstretched sheet was produced. Next, the sheet was stretched in one stage so that the stretching ratio was 3.4 times at a stretching temperature of 92 ° C. in the longitudinal direction. Subsequently, after passing through a 100 ° C. preheating zone with a tenter, the film was stretched 3.1 times in the width direction at 110 ° C. ΔM is 0.3 and the effective surface magnification is 8.59 times. Furthermore, this biaxially stretched film was heat-treated at 210 ° C. for 30 seconds to obtain a light reflecting film having a thickness of 100 μm. The obtained light reflecting film had a medium σ1 / d1 distribution and a medium σ2 / d2 distribution. Further, the reflectance was 96% and the backlight luminance was as high as 2350 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Example 4
In the extruder, 79% by weight of PET as the resin component, 2% of polymethylpentene and barium sulfate (average particle size 1.5 μm) as the void nucleating agent, 7% by weight and 10% by weight, respectively, and polyethylene glycol as the dispersing agent 1% by weight of the pellets was supplied, and an unstretched sheet was prepared using the same method as in Reference Example 1. The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a medium σ1 / d1 distribution and a medium σ2 / d2 distribution. Further, the reflectance was 96% and the backlight luminance was as high as 2370 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Example 5
Supplying the extruder with 84% by weight of PET as a resin component, 10% by weight of barium sulfate having an average particle size of 3.5 μm and 6% by weight of barium sulfate having an average particle size of 1.5 μm as a void nucleating agent, An unstretched sheet was produced using the same method as in Reference Example 1. The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a medium σ1 / d1 distribution and a large σ2 / d2 distribution. Further, the reflectance was 97% and the backlight luminance was as high as 2420 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Example 6
The extruder was supplied with 84% by weight of PET as a resin component, 10% by weight of barium sulfate having an average particle size of 3 μm as a void nucleating agent, and 6% by weight of calcium carbonate having an average particle size of 0.7 μm. An unstretched sheet was produced by cooling on a mirror cast drum by the method. Next, the sheet was stretched in one stage so that the stretching ratio was 3.4 times at a stretching temperature of 92 ° C. in the longitudinal direction. Subsequently, after passing through a 100 ° C. preheating zone with a tenter, the film was stretched 3.3 times in the width direction at 110 ° C. ΔM is 0.1, and the effective surface magnification is 9.20 times. Furthermore, it heat-processed for 30 seconds at 210 degreeC, and obtained the light reflection film with a film thickness of 100 micrometers. The obtained light reflecting film had a medium σ1 / d1 distribution and a large σ2 / d2 distribution. Further, the reflectance was 96% and the backlight luminance was as high as 2390 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Example 7
A pellet containing 84% by weight of PET as a resin component, 10% by weight of barium sulfate having an average particle diameter of 3 μm and 6% by weight of calcium carbonate having an average particle diameter of 0.7 μm as a void nucleating agent is supplied to an extruder. 1 was used to produce an unstretched sheet. The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a large σ1 / d1 distribution and a large σ2 / d2 distribution. Further, the reflectance was 96% and the backlight luminance was as high as 2470 cd / m 2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Example 8
In the main extruder, 82% by weight of PET as a resin component, two components of polymethylpentene and barium sulfate (average particle size 1 μm) as a void nucleating agent are 7% by weight and 10% by weight, respectively, and polyethylene glycol as a dispersing agent. 1% by weight of the mixed pellets was supplied, and a sub-extruder was used separately from the main extruder, and 86% by weight of PET and 14% by weight of calcium carbonate having an average particle diameter of 2 μm were mixed in this sub-extruder. Pellets are supplied, and by a predetermined method, melt three-layer lamination co-extrusion is carried out so as to have the component layers supplied to the sub-extruder on both sides of the component layers supplied to the main extruder, and mirror cast drums are applied by electrostatic application method. By cooling above, a three-layer laminated unstretched sheet was prepared. The thus obtained three-layer laminated sheet was stretched and heat-treated in the same manner as in Reference Example 1 to obtain a laminated light reflecting film having a total film thickness of 100 μm. In the obtained laminated light reflecting film, the thickness of the skin layer derived from the sub-extruder is 5 μm, and the thickness of the inner layer derived from the main extruder is 90 μm. The obtained light reflecting film had a medium σ1 / d1 distribution and a medium σ2 / d2 distribution. The reflectivity was 97%, and the backlight luminance was as high as 2520 cd / m2. Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent practicality was obtained.
Comparative Example 1
Pellets mixed with 90% by weight of PET as a resin component and 10% by weight of polymethylpentene as a void nucleating agent were fed into an extruder and cooled on a mirror-casting drum by a predetermined method to produce an unstretched sheet. . Next, this sheet was stretched in one step so that the stretching ratio was 3.3 times at a stretching temperature of 92 ° C. in the longitudinal direction. Subsequently, after passing through a preheating zone of 100 ° C. with a tenter, the film was stretched 3.0 times in the width direction at 110 ° C. ΔM is 0.3 and the effective surface magnification is 8.12 times. Furthermore, this biaxially stretched film was heat-treated at 210 ° C. for 30 seconds to obtain a light reflecting film having a thickness of 100 μm. The obtained light reflecting film had a small σ1 / d1 distribution and a small σ2 / d2 distribution. The reflectance was 85%, and the backlight luminance was 1660 cd / m 2.
Comparative Example 2
Pellets prepared by mixing 90% by weight of PET as a resin component and 10% by weight of polymethylpentene as a void nucleating agent were supplied to an extruder, and an unstretched sheet was produced using the same method as in Reference Example 1. The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a small σ1 / d1 distribution and a small σ2 / d2 distribution. Further, the reflectance was 88% and the backlight luminance was 1720 cd / m 2.
Comparative Example 3
Pellets mixed with 86% by weight of PET as a resin component and calcium carbonate (average particle size: 2 μm) as a void nucleating agent were supplied to an extruder, and an unstretched sheet was produced using the same method as in Reference Example 1. . Next, this sheet was stretched in one step so that the stretching ratio was 3.2 times at a stretching temperature of 92 ° C. in the longitudinal direction. Subsequently, after passing through a preheating zone of 100 ° C. with a tenter, the film was stretched 3.1 times in the width direction at 110 ° C. ΔM is 0.1, and the effective surface magnification is 8.23 times. Furthermore, this biaxially stretched film was heat-treated at 210 ° C. for 30 seconds to obtain a light reflecting film having a thickness of 100 μm.
The obtained light reflecting film had a small σ1 / d1 distribution and a medium σ2 / d2 distribution. The reflectance was 89%, and the backlight luminance was 1880 cd / m 2.
Comparative Example 4
Supplying the extruder with 84% by weight of PET as a resin component, 10% by weight of barium sulfate having an average particle size of 3.5 μm and 6% by weight of calcium carbonate having an average particle size of 3.5 μm as a void nucleating agent, An unstretched sheet was produced using the same method as in Reference Example 1. The unstretched sheet was stretched and heat treated in the same manner as in Reference Example 1 to obtain a light reflecting film. The obtained light reflecting film had a small σ1 / d1 distribution and a small σ2 / d2 distribution. Further, the reflectance was 87%, and the backlight luminance was 1860 cd / m 2.
Comparative Example 5
Japanese Patent Laid-Open No. 2001-2001226501Described in the GazetteExampleIn accordance with No. 1, an extruder was charged with 88% by weight of PET as a resin component, 10% by weight of polymethylpentene as a void nucleating agent, 1% by weight of polyethylene glycol as a dispersing agent, and “Adekastab” LA-31 ( Asahi Denka Kogyo Co., Ltd.) was added and mixed with 1% by weight of pellets, and cooled on a mirror cast drum maintained at 25 ° C. by a predetermined method to prepare an unstretched sheet. Next, this sheet was stretched in one step so that the stretching temperature was 98 ° C. and the stretching ratio was 3.2 times in the longitudinal direction, and cooled in a roll group at 25 ° C. Subsequently, the film was stretched 3.4 times in the width direction at 125 ° C. with a tenter. ΔM is 0.2 and the effective surface magnification is 8.72 times. Furthermore, this biaxially stretched film was heat-treated at 220 ° C. to obtain a light reflecting film having a thickness of 100 μm. The obtained light reflecting film had a small σ1 / d1 distribution and a small σ2 / d2 distribution. The reflectance was 85% and the backlight luminance was 1600 cd / m 2.
[0110]
【The invention's effect】
The light reflecting film of the present invention is lightweight and excellent in reflection characteristics, luminance characteristics, concealment properties, etc., and when used as a reflector or reflector in a surface light source that illuminates a liquid crystal screen, the liquid crystal screen is illuminated brightly, and the liquid crystal image Is clearer and easier to see.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional model view of a bubble-containing film, which is shown to explain a method for measuring bubble length.
FIG. 2 is a schematic cross-sectional model view of a bubble-containing film having a void nucleating agent, which is shown to explain a method for measuring the bubble length.
FIG. 3 is a schematic cross-sectional model view of a film containing no air bubbles, which is shown for explaining a method for measuring the length of air bubbles.
[Explanation of symbols]
1 ... Resin
2 ... Bubble
3. Void nucleating agent
4 ... Particle or incompatible resin

Claims (4)

A film having a void nucleating agent and flat closed cells inside the film, and for each bubble, a ratio of the bubble length (L) in the film surface direction to the bubble length (R) in the film thickness direction When (L / R) is determined, the simple average value d1 and standard deviation σ1 of these L / R satisfy the formula (1),
In addition, the light reflection is characterized by using two or more kinds of components as a void nucleating agent, and the simple average d2 and standard deviation σ2 of the particle diameter or dispersion diameter of the void nucleating agent contained in the film satisfy the formula (2). the film.
σ1 / d1 ≧ 0.5 (1)
σ2 / d2 ≧ 0.5 (2)
However, as for σ1 / d1, L / R is obtained for 150 bubbles, and d1 and σ1 are obtained. As for σ2 / d2, the particle diameter or the dispersion diameter is obtained for 150 void nucleating agents, and σ2 and d2 are obtained. 2. The light reflecting film according to claim 1, wherein the main resin component constituting the light reflecting film is an aromatic polyester resin and is used for a surface light source. A method for producing a film having a void nucleating agent and flat closed cells inside the film, wherein for each bubble, the bubble length (L) in the plane direction of the film and the bubble length (R) in the thickness direction of the film ) Ratio (L / R), the simple average value d1 and standard deviation σ1 of these L / R satisfy the formula (1),
And the manufacturing method of the light reflection film characterized by satisfy | filling Formula (2) and (3).
σ1 / d1 ≧ 0.5 (1)
σ2 / d2 ≧ 0.5 (2)
However, d2 is a simple average of the particle diameter or dispersion diameter of the void nucleating agent contained in the film, and is a σ2 standard deviation.
However, as for σ1 / d1, L / R is obtained for 150 bubbles, and d1 and σ1 are obtained. As for σ2 / d2, the particle diameter or the dispersion diameter is obtained for 150 void nucleating agents, and σ2 and d2 are obtained.
ΔM = | Mmd−Mtd | ≧ 0.3 (3)
However, Mmd is a draw ratio in the film longitudinal direction, and Mtd is a draw ratio in the film width direction.   The light reflecting film according to claim 3, wherein two or more kinds of components are used as a void nucleating agent, and the main resin component constituting the light reflecting film is an aromatic polyester resin, and is used for a surface light source. Manufacturing method.

Images