JP2009139829A - Light-diffusing film and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-diffusing film with high practicality, having good passing property of the film in a heat treatment step in a post process, over the whole length of the roll regardless of conditions of the post process. <P>SOLUTION: The light-diffusing film has a Δn<SB>ab</SB>(relating to the refractive index) of from 0.015 to 0.060, and is characterized in that (1) the film has a light-diffusing layer containing a light-diffusing component inside; (2) the light-diffusing layer does not substantially contain a void; and (3) the light-diffusing layer comprises at least a light-transmitting resin and fine particles as a light-diffusing component. The light-diffusing film is controlled in such a manner that: heat shrinkage percentages HS150 close to both ends in the width direction of the film range from 0.7% to 2.0%, with the difference in the HS150 between close to both ends being not more than 0.1%; and the amount of variation in the longitudinal direction in the HS150 close to both ends is not more than 0.25%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light diffusing film, and more particularly to a light diffusing film having excellent processing characteristics.

  A light diffusing film using a biaxially stretched polyethylene terephthalate film as a base film is used as a backlight film for a liquid crystal display because of its excellent light transmittance, light diffusing property, and chemical resistance. In particular, a light diffusing film excellent in light transmittance, light diffusibility, and mechanical strength while having a smooth surface has been proposed (Patent Documents 1 and 2). Such a light diffusing film is stretched in the longitudinal direction between rolls having a difference in rotational speed, and then stretched in the width direction in a state where the end of the film is gripped in a tenter, and is thermally fixed. Manufactured. In this case, since the longitudinal direction cannot be relaxed at the end of the film in the width direction at the time of heat fixing, the heat shrinkage rate in the longitudinal direction varies depending on the position in the film width direction. Therefore, in the slit roll corresponding to the edge of the mill roll, the thermal contraction rate at the one end edge in the width direction (thermal contraction rate in the longitudinal direction) is larger than the thermal contraction rate at the other end edge. When such a slit roll is used, functions other than light diffusibility such as a prism lens layer, a hard coat layer, and an adhesive layer are added to the surface of a smooth film during post-processing when another layer is laminated. The film passability deteriorates in the heat treatment step. In some cases, the film is rubbed and scratched by the frame of the machine base and others. In addition, adjusting the post-processing conditions in order to prevent the film from being damaged is a very time-consuming operation. For the above reasons, only slit rolls other than the edge of the mill roll could be used without adjusting the post-processing conditions. However, due to the recent demand for improvement in production efficiency, the post-processing conditions have become high-speed and high-temperature. Under such conditions, even if the post-processing conditions are adjusted according to the roll characteristics, the post-processing conditions can rub against the machine base. There have been cases where scratches are not suppressed.

JP 2001-272508 A JP 2001-324606 A

  On the other hand, the demand for wide slit rolls has been increasing in order to reduce post-processing costs. In order to collect a wide slit roll, it is desirable to increase the width of the mill roll. However, when the width of the mill roll is widened, it becomes difficult to keep the temperature in the width direction uniform during heat setting. That is, the temperature fluctuation range is large both in terms of position and time. Therefore, in order to increase the width of the mill roll, it is necessary to finely adjust the hot air blowing amount and the like to maintain the temperature uniformity in the width direction of the heat fixing device. However, even when fine adjustments such as the amount of blown hot air are made, it is not possible to reduce the difference in thermal shrinkage at the film edge to a level sufficient to improve the film passability in post-processing.

  Until now, as a method of reducing the difference in thermal shrinkage in the width direction of the film, the applicant has increased the temperature in the width direction of the film from the center to the end by the following means, thereby relaxing the edge. A method of bringing the amount closer to the relaxation amount in the central portion has been proposed (Patent Document 3). That is, in the heat fixing process of the film, (1) covering a plenum duct (hot air outlet) arranged vertically at a certain interval with respect to the film traveling direction, and (2) shielding the film. The width of the plate is gradually widened according to the film traveling direction side.

JP 2001-138462 A

  Further, as a method for reducing the difference in the heat shrinkage rate in the width direction of the film, the applicant attached discontinuous shielding plates to the five plenum ducts in the film heat setting step, and from each plenum duct, per unit time Discloses a method of increasing the amount of hot air impinging on the end by increasing the speed of air blown from the plenum duct while keeping the amount of hot air blown to the outside (Patent Document 4).

JP 2002-79638 A

  In the case of the light diffusing film of Patent Documents 1 and 2, when post-processing, the productivity is remarkably lowered and post-processing is required, or the post-processing conditions such as tension must be adjusted. It was not a high-quality light-diffusing film that could satisfy the demand for improved efficiency.

  In the future, it is predicted that the line speed of post-processing will be further improved from the viewpoint of productivity improvement, and it is considered that a film that can be suitably used even in high-temperature post-processing is required. However, in the method of Patent Document 3 in which a continuous shielding plate is simply placed on the plenum duct, the heat treatment in post-processing (coating and drying) is improved to some extent at about 120 ° C. The film relaxation is still inadequate. That is, in the above method, the passability when heat treatment at about 160 ° C. is performed for a relatively long time (10 to 60 seconds) (formation of a hard coat film, etc.) is not improved so much. Therefore, when post-processing is performed at a high temperature for a long time, the conditions must be adjusted, or the adjustment may not be possible.

  In addition, in the method of Patent Document 3, since temperature turbulence occurs in the heat setting zone, when a long film (mill roll) having a length of 1,000 m or more is manufactured, there is a difference in heat shrinkage rate in the width direction of the film. A big part arises.

  Moreover, in the method of patent document 4, since the air volume of each plenum duct is constant, since a wind speed differs for each plenum duct, a turbulent flow arises in a heat fixing apparatus. Therefore, the temperature in the heat setting zone is greatly inhomogeneous, which is inconvenient. Moreover, the effect of reducing the difference in the heat shrinkage rate in the width direction due to the shielding plate was not satisfactory.

  The object of the present invention is to solve the above-mentioned problems, and to pass through the film in the heat treatment step during post-processing, and to achieve a high-quality polyethylene terephthalate light diffusing film over the entire length of the roll, and a method for producing the same. It is to provide.

Among the present inventions, the first invention relates to a refractive index in a direction that forms an angle of 45 degrees with the winding direction of the film and a refractive index in a direction that forms an angle of 135 degrees with the winding direction of the wound film. Δn _ab which is the difference is 0.015 or more and 0.060 or less and satisfies the following requirements (1) to (3), and the first sample cutout portion is within 2 m from the end of winding of the film. A total of 10 samples are provided by providing a final cutout portion within 2 m from the beginning of winding of the film, and providing a sample cutout portion for each length obtained by dividing the distance between the first cutout portion and the final cutout portion into nine equal parts. When the cutout part is provided, the following requirements (5) to (6) are satisfied.
(1) It has a light diffusion layer having a light diffusion component inside at least one surface of a biaxially stretched polyethylene terephthalate film. (2) The light diffusion layer does not substantially contain voids. (3) The light diffusing layer is composed of at least a light-transmitting resin and fine particles as a light diffusing component. (4) In each of the cutout portions, a position within 50 mm from one edge in the film width direction and within 50 mm from the other edge. Samples were cut out from the respective positions, and HS150, which is the heat shrinkage rate in the film winding direction when heated at 150 ° C. for 30 minutes, was obtained for the two samples, and the difference in heat shrinkage rate, which was the difference between the HS150, was obtained. Sometimes, the thermal contraction rate difference in all cutouts is 0.1% or less. (5) In each cutout, When the sample is cut out from a position within 50 mm from the one end edge and a position within 50 mm from the other end edge in the width direction of the rumm, and HS 150 is obtained for each sample, the HS 150 of the sample at both end edges in all cut portions is (6) The fluctuation amount of HS150 on the one end edge side in the width direction of the film obtained in each cutout part, and the film obtained in each cutout part are 0.7% or more and 2.0% or less. The fluctuation amount of the HS 150 on the other end edge side in the width direction is 0.25% or less. The second invention is the light having a total light transmittance of 80% or more and a haze of 60% or more. It is a diffusive film.
3rd invention exists in the thickness of the said light diffusable film being 80 micrometers or more and 450 micrometers or less.
4th invention is a manufacturing method for manufacturing the said light diffusable film, Comprising: The film formation process which forms an unstretched sheet | seat by melt-extruding raw material resin from an extruder, and obtained in the film formation process A biaxial stretching step of biaxially stretching the unstretched sheet to be machined in the longitudinal direction and the transverse direction, and a heat fixing step of heat fixing the film after biaxial stretching. ) To (9).
(7) A plurality of wide plenum ducts for blowing hot air are arranged vertically opposite to the film traveling direction. (8) Shielding for shielding hot air outlets from the plurality of plenum ducts. (9) The dimension of each shielding plate in the traveling direction of the film is adjusted to be substantially the same as the dimension of the outlet of each plenum duct in the traveling direction of the film. The dimension in the width direction of the film is adjusted so as to become gradually longer with respect to the traveling direction of the film. In the fifth aspect of the invention, the biaxial stretching step in the transverse direction after the film is stretched in the longitudinal direction. And an intermediate zone in which no blowing of wind is performed is provided between the zone where the transverse stretching is performed and the heat setting device.
According to a sixth invention, in the above invention, the heat setting device is divided into a plurality of heat setting zones, and the product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. -It is set so that it may become m / s or less.

  The light diffusing film of the present invention has excellent film passability during post-processing such as prism lens processing, hard coat processing, adhesive processing, and AR processing, and can be post-processed with a very high yield. . In particular, the light diffusive film of the present invention can be suitably used for processing in which heat treatment in post-processing is performed at a high temperature (about 160 ° C.) for a relatively long time (10-60 seconds).

  The polyethylene terephthalate film, which is a base film of the light diffusing film of the present invention, contains ethylene glycol and terephthalic acid as main components. Other dicarboxylic acid components and glycol components may be copolymerized as long as the object of the present invention is not impaired. Examples of the other dicarboxylic acid components include isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-dicarboxybenzophenone, bis- (4-carboxyphenylethane), adipine Examples include acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4-dicarboxylic acid, and the like. Examples of the other glycol component include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, ethylene oxide adducts such as bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In addition, oxycarboxylic acid components such as p-oxybenzoic acid can also be used.

  The light diffusing film of the present invention has a structure in which a light diffusing layer having a light diffusing component is laminated on at least one surface of a polyethylene terephthalate film.

  The light diffusion layer of the present invention comprises at least a light transmissive resin and a light diffusion component.

  Examples of the light transmissive resin preferably used in the present invention include polyesters such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, and polybutylene terephthalate, polyolefins such as polycarbonate, polystyrene, and polypropylene, polyamides, polyethers, Polyester amide, polyether ester, polyvinyl chloride, polymethacrylic acid ester, a copolymer containing these as main components, a mixture of these resins, or the like can be suitably used.

  The light-transmitting property of the light-transmitting resin here means that it is transparent with respect to light rays in the visible light region. Specifically, it refers to a resin having a total light transmittance of 80% or more in a film having a thickness of 450 μm made of only those resins. Here, the total light transmittance can be measured using a haze meter.

  In addition, the refractive index of the resin is generally preferably about 1.3 to 1.7.

  The light diffusing component used in the present invention may be any material that diffuses incident light, and various fine particles are preferably used.

Examples of the fine particles used in the present invention include inorganic fine particles such as glass, silica, barium sulfate, titanium oxide, magnesium sulfate, magnesium carbonate, and calcium carbonate, or acrylic resin, organic silicone resin, polystyrene, polyolefin, polyester, and urea resin. And organic fine particles such as formaldehyde condensate and fluororesin.

  Further, in the production process (melting / extrusion process) of the biaxially stretched film, in the matrix made of the light-transmitting resin, by dispersing and forming the domain made of the incompatible thermoplastic resin in the light-transmitting resin, The fine particles may be formed. Examples of the thermoplastic resin incompatible with the light transmissive resin include polyolefins such as polyethylene, polypropylene, polymethylpentene, and various cyclic olefin polymers, polycarbonate, atactic polystyrene, syndiotactic polystyrene, isotactic polystyrene, and the like. Acrylic resins such as polystyrene, polyamide, polyether, polyesteramide, polyphenylene sulfide, polyphenylene ether, polyether ester, polyvinyl chloride, polymethacrylic acid ester, and copolymers containing these as main components, or of these resins A mixture etc. can be mentioned.

The shape of these fine particles is preferably substantially spherical or true spherical. The substantially spherical shape here may be a shape having at least a spherical portion on the surface of the fine particles. Furthermore, an aggregate of these fine particles may be present. When the fine particles are substantially spherical or spherical, a uniform diffusion effect without directionality can be obtained. In this respect, the fine particles are more preferably spherical. These average particle diameters are usually 0.1 to 50 μm, more preferably 0.1 to 30 μm, and most preferably 0.1 to 20 μm. By making the particle diameter of the fine particles larger than 0.1 μm, the total light transmittance of the film is increased, and by making the particle diameter smaller than 50 μm, a good light diffusion effect can be obtained without reducing the film strength.

  Further, it is important that the refractive index of the fine particles is different from the refractive index of the light-transmitting resin. If the refractive indexes of the fine particles and the light-transmitting resin are the same, the refractive scattering phenomenon does not occur at the interface between the resin and the fine particles, and as a result, a desired light diffusion effect cannot be obtained. Furthermore, in order to obtain substantially effective light diffusibility, it is preferable that the difference in refractive index between the light-transmitting resin and the fine particles is 0.012 or more. If the refractive index difference is less than 0.012, the light diffusion effect is small, and in order to obtain a good diffusion effect, it is necessary to add a large amount of fine particles or increase the film thickness, and the mechanical strength becomes weak or desired. It is not preferable because the influence is too thick.

  The light-transmitting resin used as the raw material of the light diffusing layer of the present invention and the fine particles as the light diffusing component are supplied to pellets prepared by being melt-kneaded and blended uniformly in advance or directly kneaded extruder. Melt knead.

  Moreover, the ratio of the fine particles blended in the light diffusion layer is appropriately selected depending on the desired degree of light diffusion. Preferably, the volume fraction is 1 to 75%, more preferably 1 to 50%.

  The total light transmittance of the light diffusing film is 80% or more, preferably 83% or more, more preferably 86% or more, further preferably 89% or more, and the haze is 60% or more, preferably 70% or more. More preferably, it is 80% or more, More preferably, it is 90% or more.

  Moreover, it is preferable that a light-diffusion layer does not contain a void substantially. A void here refers to the fine bubble produced | generated inside the film. This void can be confirmed by using a scanning electron microscope, a transmission electron microscope, or the like for the film cross section.

  The light diffusing film of the present invention is constituted by laminating a light diffusing layer on a biaxially stretched polyethylene terephthalate film that is a base film. A film consisting of a single film consisting only of the light diffusing layer can be obtained as a film having a high total light transmittance and a high haze, but is not preferred because it is inferior in the mechanical strength of the film such as bending rigidity. If the bending rigidity is weak, a handling problem such as a crease tends to occur during handling after film formation is not preferable. Moreover, the light diffusion component contained inside inhibits the flatness of the surface. Therefore, the light diffusing film of the present invention is formed by laminating a light diffusing layer and a biaxially stretched polyethylene terephthalate film excellent in mechanical strength and surface flatness. Here, the lamination method will be described. For example, a raw material for the light diffusion layer and a raw material for the biaxially stretched polyethylene terephthalate film are melted by separate extruders, and a method such as coextrusion molding through a T-die or the like. After forming into a film, a desired light diffusion layer is obtained through a stretching process, a heat setting process, a heat treatment process, and the like as necessary. Here, when a stretching process is required, voids may be generated in the film after stretching. When a large amount of voids are generated in the film, the total light transmittance may be lowered. Therefore, it may be necessary to eliminate the voids through processes such as heat setting and heat treatment.

  As a polymerization method of polyethylene terephthalate (hereinafter simply referred to as PET) used as the base film, for example, the following method can be used. (1) A direct polymerization method in which terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid components and diol components are reacted directly. (2) A transesterification method in which a dimethyl ester of terephthalic acid (including a methyl ester of another dicarboxylic acid if necessary) and ethylene glycol (including another diol component if necessary) are subjected to a transesterification reaction.

  When the base film of the present invention is mainly formed of PET, the intrinsic viscosity (IV) of the PET raw material is preferably in the range of 0.45 to 0.70 dl / g. It is preferable that the intrinsic viscosity of the PET raw material is 0.45 or more because the stretchability and tear resistance of the film are improved. In addition, when the intrinsic viscosity is 0.70 dl / g or less, the filtration pressure becomes moderately low, and high-precision filtration is possible. In addition, IV of resin raw material is calculated | required with the following methods, for example.

[Intrinsic viscosity (IV)]
After the PET ground sample is dried, it is dissolved in a mixed solvent of phenol / tetrachloroethane = 60/40 (weight ratio), and a solution having a concentration of 0.4 (g / dl) is obtained at 30 ° C. using an Ostwald viscometer. Measure the flow time and the flow time of the solvent alone. From these time ratios, IV is calculated using the Huggins equation, assuming that the Huggins constant is 0.38. The intrinsic viscosity is also expressed as [η].

The light diffusing film of the present invention is derived from a slit roll obtained by slitting a mill roll once produced in a wide width, and Δn _ab (base in a direction forming an angle of 45 degrees with the winding direction of the wound film). The difference (absolute value) between the refractive index on the material film side and the refractive index on the base film side in the direction forming an angle of 135 degrees with the winding direction of the wound film is 0.015 or more in all regions It is limited to what is .060 or less. That is, in the case of a distorted slit roll having Δn _ab of 0.015 or more, the above-described problem of “distortion (that is, physical property difference in the width direction)” occurs. Further, in the case of a slit roll having Δn _ab of 0.060 or less, the heat shrinkage rate difference or the like can be adjusted so as to satisfy the requirements of the present invention.

  The light diffusing film of the present invention has a position within 50 mm from one edge in the width direction of the film and a position within 50 mm from the other edge in the width direction of the film when the sample cutout is set by the method described later. When each sample was cut out from the two samples, HS150, which is the heat shrinkage rate in the film winding direction when heated at 150 ° C. for 30 minutes, was obtained, and the difference in heat shrinkage rate, which is the difference between the HS150, was obtained. In addition, it is necessary that all the heat shrinkage difference in all cutout portions is 0.1% or less.

  That is, the light diffusive film of the present invention has a total of 10 heat shrinkage ratio differences (difference in HS150 at both end edges in the film sample cut out from each cutout portion) obtained in a total of 10 cutout portions. It must be 1% or less. It is preferable that the difference in thermal shrinkage at each cut-out portion is 0.1% or less because the film can be easily passed in post-processing. Further, the difference in heat shrinkage rate between the cutout portions is more preferably 0.08% or less, and particularly preferably 0.06% or less. In addition, although the heat shrinkage rate difference in each cut-out part is preferably as low as possible, 0.05% is considered to be the lower limit in design.

A film sample used for the measurement of HS150 is cut out from 10 cutout portions provided by the following procedure.
(1) The first sample cutout is provided within 2 m from the end of winding of the film.
(2) A value obtained by dividing the length of the wound film by 9 (hereinafter, referred to as “cut section interval”) is calculated.
(3) A sample cutout portion is provided at a position within 10 m before and after each “cutout portion interval” from the end of winding of the film.
(4) A final cutout portion is provided within 2 m from the start of film winding.

  The cutting of the sample will be described more specifically. For example, when a film having a length of 500 m is wound on a roll, the first sample (1) is cut within 2 m from the end of winding of the film. The sample is cut out in the film winding direction (longitudinal direction) including the position within 50 mm from one end edge and the position within 50 mm from the other end edge in the roll width direction (direction orthogonal to the film winding direction). Direction) and a rectangular shape so as to have a side along the width direction (not diagonally cut). Next, the “cutting portion interval” is calculated by dividing the winding length of the film by 9. Note that the “cutout interval” is calculated to the unit of “1 m”. Therefore, as described above, when the winding length is 500 m, 2 m from the winding end where the first cutout portion can be provided and 2 m from the winding start where the final cutout portion can be provided are subtracted from 500 m in advance, and the remaining 496 m is obtained. 55 m divided into nine equal parts is defined as “interval of cutout portions”. Subsequently, the second sample (2) is cut off at a distance of 55 ± 10 m from the winding end of the film. Thereafter, similarly, samples are sequentially cut out at intervals of 55 m on the winding start side to obtain a total of 10 samples. That is, the first sample (first sample) is cut out at a position within 2 m from the end of winding, the second sample is cut out at a position near 57 m from the end of winding, and the third sample is cut at a position near 112 m from the end of winding. Similarly, the fourth to ninth samples are cut out at every position 55 m away from the end of winding, and the final sample (10th sample) is cut out at a position within 2 m from the start of winding.

  Furthermore, when the sample cutout portion is set by the above-described method, the light diffusive film is sampled from the position within 50 mm from one end edge and the position within 50 mm from the other end edge in each rollout portion. When HS150 is obtained for each sample, it is necessary that the HS150 of the samples at both ends in all cutout portions is 0.7% or more and 2.0% or less.

  That is, in the light diffusing film of the present invention, the HS150 values (the values of 20 HS150 in total) at both ends of the cut out film sample are 0.7% or more in a total of 10 cutout portions. It must be 0% or less. It is preferable that the value of HS150 at both ends of the film sample cut out from each cut-out portion is 2.0% or less because the film can be easily passed in post-processing. Further, the value of HS150 at both ends of the film sample cut out from each cut-out portion is more preferably 1.5% or less, and particularly preferably 1.2% or less. In addition, although the value of HS150 in the both ends of the film sample cut out from each cutout part is so preferable that it is low, it considers that 0.7% is a minimum from the point of productivity.

  Furthermore, the light diffusive film of the present invention has a fluctuation amount of HS 150 on one end edge side in the width direction of the roll obtained in each cutout portion, and a fluctuation amount of HS150 on the other end edge side in the width direction of the roll obtained in each cutout portion. The amount must be 0.25% or less in all cases.

  That is, the light diffusing film of the present invention obtains HS150 on one end edge side (one end edge side in the width direction) and HS150 on the other end side (the other end edge side in the width direction) for 10 films cut out from each cutout portion. The fluctuation amount of 10 HS 150 on the one edge side (difference between the maximum value and the minimum value) is 0.25% or less, and the fluctuation amount of 10 HS 150 on the other edge side is 0.25%. It is necessary that: It is preferable that the fluctuation amount of the ten HS 150 on either edge side is 0.25% or less because the film can be easily passed during post-processing. Further, the fluctuation amount of the ten HS 150 on each edge side is more preferably 0.20% or less, still more preferably 0.18% or less, still more preferably 0.016% or less, and 0.15 % Or less is particularly preferable. In addition, although the variation | change_quantity of 10 HS150 of each edge side is so preferable that it is low, 0.05% is considered to be a minimum by design.

  The light diffusing film of the present invention is a non-stretched sheet (unstretched laminated film or unstretched laminated film) obtained by melting the raw material of the light diffusing layer and the polyethylene terephthalate resin with separate extruders and coextrusion through a T die or the like. The sheet is biaxially stretched in the longitudinal direction (longitudinal direction) and the lateral direction (width direction), and then wound into a roll and heat-fixed by the method described later.

  As a method for obtaining an unstretched sheet, a method in which a resin melted at about 285 ° C. is melt-extruded into a sheet shape, and the molten sheet is cooled and solidified with a cooling roll can be suitably employed. Note that. It is desirable that the resin pellets used in the extruder are sufficiently dried.

  As a method for bringing the sheet-like melt into close contact with the rotary cooling drum, for example, a method using an air knife or a method of applying an electrostatic charge can be preferably applied. In those methods, the latter is preferably used.

  In addition, as a method of cooling the sheet-like melt, for example, a method of bringing the sheet surface into contact with the cooling liquid in the tank, a method of applying a liquid that evaporates with a spray nozzle to the sheet air surface, and blowing a high-speed air flow A method of cooling may be used in combination. The unstretched sheet thus obtained is stretched in the biaxial direction to obtain a film.

  As a method of stretching the film in the biaxial direction, the obtained unstretched sheet is stretched in the longitudinal direction by a roll or a tenter-type stretching machine, and then stretched in the width direction orthogonal to the first-stage stretching direction. A method can be mentioned. The stretching temperature in the longitudinal direction is preferably 75 to 120 ° C., and the stretching ratio in the longitudinal direction is 2.5 to 4.5 times, preferably 3.0 to 4.3 times. A stretching temperature in the longitudinal direction of 75 ° C. or higher is preferable because the film is difficult to break. Moreover, since it becomes difficult to produce the thickness spot of the obtained film at 120 degrees C or less, it is preferable. A stretching ratio in the longitudinal direction of 2.5 times or more is preferable in terms of the flatness of the film. Moreover, it is preferable that it is 4.6 times or less because the frequency of fracture due to orientation decreases.

  In the case of stretching in the width direction, the stretching temperature needs to be 80 to 210 ° C, and preferably 130 to 200 ° C. A stretching temperature in the width direction of 80 ° C. or higher is preferable because the film is difficult to break. Moreover, at 210 degrees C or less, it is preferable at the point of the planarity of the obtained film. The draw ratio in the width direction is 3.0 to 5.0 times, preferably 3.6 to 4.8 times. If the draw ratio in the width direction is 3.0 times or more, it is preferable because uneven thickness of the obtained film hardly occurs. It is preferable that the draw ratio in the width direction is 5.0 times or less because the breaking frequency due to orientation decreases.

  Subsequently, heat setting is performed. The temperature in the heat setting treatment step is preferably 180 ° C. or higher and 240 ° C. or lower. When the temperature of the heat setting treatment is 180 ° C. or higher, the absolute value of the heat shrinkage ratio is preferably reduced. Moreover, it is preferable that the temperature of the heat setting treatment is 240 ° C. or less because the frequency of breakage is reduced. A suitable heat setting method will be described later.

  It is effective to control the heat shrinkage rate, particularly the heat shrinkage rate in the width direction, by narrowing the guide rail of the gripping tool by the heat setting process. The temperature for the relaxation treatment can be selected in the range from the heat setting treatment temperature to the glass transition temperature Tg of the polyethylene terephthalate resin film, and is preferably (heat setting treatment temperature) −10 ° C. to Tg + 10 ° C. The width relaxation rate is preferably 1 to 6%. If it is less than 1%, the effect is small, and if it is 6% or less, it is preferable in terms of the flatness of the film.

  Here, although the method of extending | stretching to the width direction after extending | stretching first to a longitudinal direction was described, the extending | stretching order may be reverse. In addition, the longitudinal stretching and the lateral stretching may be performed in one stage, or may be performed in two or more stages. In addition, as described above, in addition to the method of sequentially biaxial stretching, it is also possible to employ a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal direction and the transverse direction. However, in order to satisfy the characteristics of the present invention, it is important to take optimum temperature conditions and longitudinal and lateral draw ratios, and it is sufficient that the finally obtained film characteristics satisfy the requirements of the present invention.

  Moreover, in order to give functionality other than light diffusibility to a film, it is good also as a polyethylene terephthalate type | system | group light diffusive film which has a multilayered structure of three or more layers. When the surface on which the slippery layer or the easy-adhesion layer is applied is the A layer, the light diffusion layer is the B layer, and the other surface is the C layer, the layer structure in the film thickness direction is A / B, A / B / A , A / B / C, A / C / B, A / C / B / C / A, etc. are conceivable. The layers A to C may be made of the same material or different materials.

  The thickness of the light diffusing film of the present invention is preferably 80 μm or more and 450 μm or less. The upper limit of the thickness of the light diffusing film is more preferably 400 μm or less, and further preferably 300 μm or less.

  In addition, the film width is preferably 0.7 m or more, and more preferably 1.0 m or more, from the viewpoint of ease of handling. On the other hand, the upper limit of the width of the film is determined by the size of the post-processing apparatus, but at present, 2.2 m is considered the maximum width, more preferably 2.0 m or less, and 1.5 m or less. And more preferred. In addition, the winding length of the film is preferably 7,000 m or less and more preferably 6,000 m or less when the film has a thickness of about 80 μm from the viewpoint of ease of winding and handling. In addition, when the film has a thickness of about 450 μm, it is preferably 1,100 m or less, and more preferably 1,000 m or less. Therefore, when the thickness of the film is in the middle of 80 to 450 μm, it is preferable to set the film length to be 400 m or more and 7,000 m or less. As the take-up core, usually, paper of 3 inches, 6 inches, 8 inches, etc., a plastic core, a metal core, and a conductive core can be used.

  It is preferable to use various coatings applied during film formation for the purpose of imparting easy adhesion or slipperiness to one side or both sides of the light diffusing film of the present invention.

  Moreover, in the resin which forms the polyethylene terephthalate film which comprises the film of this invention, microparticles | fine-particles can be added as needed. Examples of the fine particles added at that time include known inorganic fine particles and organic fine particles. Furthermore, in the resin forming the film, various additives as necessary, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stabilizers, coloring pigments, An anti-coloring agent, an ultraviolet absorber and the like can be added. It is preferable to add fine particles to the polyethylene terephthalate film in the present invention to make the film slippery. Examples of the fine particles include inorganic particles such as silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of the organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle diameter of the fine particles can be selected as necessary within a range of 0.05 to 2.0 μm.

  As a method for blending the above-mentioned particles into the film, for example, it can be added at the stage of producing a polyethylene terephthalate resin, but preferably at the stage of esterification or the stage before the start of the polycondensation reaction after completion of the transesterification reaction. May be added as a slurry dispersed in ethylene glycol or the like to proceed with the polycondensation reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyethylene terephthalate resin raw material, or a dried particle and a polyethylene terephthalate system using a kneading extruder It can be performed by a method of blending with a resin raw material.

  Further, the light diffusing film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion of the film surface.

  Next, the preferable manufacturing method for obtaining the light diffusable film of this invention is demonstrated.

  Usually, the heat setting process of the stretched film is carried out in a heat setting device in which a plurality of plenum ducts having long hot air outlets are arranged perpendicular to the longitudinal direction. In such a heat fixing device, “circulation of hot air” is performed in order to improve the heating efficiency. Air in the heat fixing device is sucked by a circulation fan installed in the heat fixing device, the temperature of the sucked air is adjusted, and the air is again discharged from the hot air outlet of the plenum duct. In this manner, “hot air circulation” of “hot air blowing → suction by circulation fan → temperature adjustment of sucked air → hot air blowing” is performed.

  Further, as described above, the difference in thermal shrinkage in the width direction of the film roll (difference between HS 150 at the edge of one end and HS 150 at the edge of the other end) is that relaxation of the edge of the film does not occur when heat fixing is performed. It occurs because it is enough. As shown in FIG. 1, in the heat setting process, a continuous large shielding plate S is placed on the central portion of the hot air outlets 2, 2,... Of each plenum duct 3, 3,. See) improves the passage when short films are processed at relatively low temperatures (eg 120 ° C.) in post-processing. However, the permeability in a long film and the permeability when heat treatment in post-processing is performed at a high temperature (for example, 160 ° C.) are not improved.

  In order to understand why the method shown in FIG. 1 does not improve the "passability in a long film" or "passability when heat-setting treatment in post-processing is performed at a high temperature", The analysis of the phenomenon in the heat setting device was done in detail. As a result, when a continuous large shielding plate that spans multiple plenum ducts is placed over the hot air outlet of the plenum duct, the flow of hot air is restricted by the shielding plate, and the above-mentioned "hot air circulation" is performed smoothly. As a result, it was found that temperature turbulence (temperature hunting phenomenon) occurred in the heat fixing device.

Since the above-mentioned “temperature hunting phenomenon” causes insufficient thermal relaxation at the edge of the film, the present inventors have made “passability in a long film” and “heat setting treatment in post-processing high temperature. It was speculated that the “passability” would worsen. Therefore, the present inventors can improve the “passability in a long film” and the “passability when a heat setting process in post-processing is performed at a high temperature” by smoothing “circulation of hot air”. I thought that. And, as a result of trial and error to grasp the relationship between the temperature air volume condition of the heat setting device, the covering mode of the shielding plate, and the film permeability in the post-processing, the following means (1) There was a tendency that “passability in a long film” and “passability when heat-setting in post-processing was performed at a high temperature” were improved. And based on the knowledge, as a result of further trial and error, the present inventors have taken the following means (1) and then taken the following means (2) and (3). It has been found that a film having good permeability can be obtained. Furthermore, by taking the means of the following (4), a light diffusing layer substantially free of voids can be obtained, and a film excellent in light transmittance and light diffusibility while having a smooth surface is obtained. As a result, the present invention has been devised.
(1) Adjustment of temperature and air volume of plenum duct in heat fixing device (2) Adjustment of shut-off condition of hot air outlet of plenum duct in heat fixing device (3) Shut off of heat between drawing zone and heat fixing device ( 4) Adjustment of heat setting temperature Hereinafter, each above-mentioned means is demonstrated one by one.

(1) Adjusting the temperature and air volume of the plenum duct in the heat setting device In order to heat and cool the heat setting process step by step, the heat setting device is generally divided into several sections (heat setting zones) with different temperatures. I know. In the production of the film of the present invention, from each plenum duct, the product of the temperature difference and the wind speed difference between adjacent heat setting zones of the heat setting device is 250 ° C. · m / s or less. It is essential to adjust the temperature and air volume of the hot air blown out. For example, when the heat setting device is divided into first to third heat setting zones, the product of the temperature difference and the wind speed difference between the first zone and the second zone, and between the second zone and the third zone. Both products of the temperature difference and the wind speed difference are adjusted to be 250 ° C. · m / s or less. Thus, by adjusting the temperature and air volume of hot air, “circulation of hot air” becomes smooth. When combined with a method of attaching a discontinuous shielding plate, which will be described later, to the hot air outlet, the “temperature hunting phenomenon” is effectively suppressed. Thus, for the first time, it is possible to obtain a long film having good passability when the heat setting treatment in the post-processing is performed at a high temperature.

  If the product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. · m / s or less (for example, the temperature difference between adjacent heat setting zones is set to 20 ° C. The temperature difference between adjacent heat setting zones is set to 10 m / s), “circulation of hot air” in the heat setting device is smoothly performed, and “temperature hunting phenomenon” is effectively suppressed. This is preferable. In addition, if the product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. · m / s or less, the heat setting zone downstream from the heat setting zone upstream as an accompanying flow caused by the passage of the film The temperature difference of the air flowing into Therefore, it is preferable because the temperature in the width direction of the downstream heat setting zone is stabilized. The product of the temperature difference and the wind speed difference is preferably 200 ° C. · m / s or less, and more preferably 150 ° C. · m / s or less. Further, as in Patent Document 4, if the air volume of each plenum duct is made constant and the air speed of each plenum duct is made different, a “temperature hunting phenomenon” occurs. In the present invention, the “temperature hunting phenomenon” is effectively suppressed by making the wind speed in each zone constant.

(2) Adjustment of Plenum Duct Cut-off Conditions in Heat Fixing Device In the production of the film of the present invention, individual plenum ducts 3 are not attached as shown in FIG. It is necessary to attach rod-shaped shielding plates S, S,... To shield the hot air outlets (nozzles) 2, 2,. By using such a discontinuous shielding plate, “circulation of hot air” is performed smoothly. Moreover, it is preferable not to attach the same length of the shielding plate to each plenum duct, but to gradually increase the length of the shielding plate from the inlet of the heat fixing device to the outlet (film passing direction) (see FIG. 4). . Thus, by adjusting the length, the temperature of the hot air exposed to the film edge is adjusted, and the elimination of distortion at the film edge is promoted. The material of the shielding plate may be any material as long as it can withstand the temperature of the heat fixing device and does not stain the film or adhere the film, but it is the same material as the plenum duct from the viewpoint of thermal expansion. Is preferably used. Further, in order to suppress the difference in thermal contraction rate of the film edge portion due to the shielding plate to the level of the present invention, it is preferable that the number of shielding plates is large, and it is desirable to use 15 or more.

(3) Blocking of heating between the stretching zone and the heat setting device (installation of an intermediate zone)
A light diffusing film based on a biaxially stretched polyethylene terephthalate film is usually heat-set after being stretched in the longitudinal and transverse directions. In the production of the film of the present invention, it is desirable to install an intermediate zone in which active hot air is not blown between the zone that is longitudinally and laterally stretched and the heat setting device that is heat-set. As a result, the heat is completely shut off between the stretching zone and the heat setting device. More specifically, when a strip-shaped paper piece is hung between the stretching zone and the heat setting device in the state where the drawing zone and the heat setting device are in the same condition as in film production, the paper piece is almost completely removed. It is preferable to block the hot air from the stretching zone and the heat fixing device so as to hang down in the vertical direction. Note that such an intermediate zone may be surrounded by a housing, or may be provided so that a continuously manufactured film is exposed. When the hot air is sufficiently blocked in the intermediate zone, the shielding effect of the shielding plate in the heat fixing device is exhibited, and good film passage during post-processing can be obtained.

(4) Adjustment of heat setting temperature The light diffusive film of the present invention is formed by laminating a light diffusion layer on at least one surface of a polyethylene terephthalate film as described above, and the melting point of the polyethylene terephthalate film on the surface layer side is Tm1. When Tg1 is the glass transition temperature and Tm2 is the melting point of the thermoplastic resin having the highest melting point among the thermoplastic resins used in the light diffusion layer, heat setting is performed at a temperature Ts that satisfies Tm1>Ts> Tm2 and Ts> Tg1. It is characterized by including a process. By heat-fixing at a temperature lower than Tm1, work problems such as adhesion during the treatment process do not occur, and by heat-treating at a temperature higher than Tm2, defects such as internal unevenness of the stack are eliminated and the surface Flattening is possible. Moreover, by heat-fixing at a temperature higher than Tg1, the fluidity of the thermoplastic resin in the surface layer increases, and the surface layer can be easily flattened. Here, the magnitude relationship between Tm2 and Tg1 is not particularly limited.

  Although effective surface heat treatment is possible with Ts satisfying Tm1> Ts, it is preferable to perform treatment at a temperature Ts that preferably satisfies Tm1> Ts + 10 (° C.), more preferably Tm1> Ts + 20 (° C.). In order to effectively eliminate internal defects, Ts> Tm2 + 10 (° C.) is preferable, and Ts> Tm2 + 20 (° C.) is more preferable.

Moreover, the ratio for which a light-diffusion layer accounts among the light diffusable films of this invention is although it does not specifically limit, Usually, it selects in the range of 1-50 micrometers, Preferably it is 1-30 micrometers.

  As described above, by adopting the above methods (1) to (3), the “hot air circulation” in the heat fixing device can be smoothly executed, and the “temperature hunting phenomenon” can be suppressed. As a result, it is possible to sufficiently promote relaxation in the longitudinal direction at the edge of the width direction, such as “passability in a long film” and “passability when heat setting treatment in post-processing is performed at a high temperature”. Can be improved. In the above description, the method of suppressing the “temperature hunting phenomenon” by smoothly executing “circulation of hot air” in the heat fixing device in which the plenum duct is installed. The above description discloses the technical idea of how the film of the present invention can be obtained by applying thermal energy to the film at the production level. The film of the present invention can be easily obtained by a different method from that described above. For example, instead of providing a shielding plate, an infrared heater may be used to increase the temperature in the film width direction from the center to the end. In other words, even with another type of heat fixing device, the "circulation of hot air" is smoothly executed to suppress the "temperature hunting phenomenon" and then sufficiently relaxed in the longitudinal direction at the edge of the width direction. By applying sufficient heat energy to the film, it is possible to improve the “passability in a long film” and the “passability when heat-setting treatment in post-processing is performed at a high temperature” like the film of the present invention. Film can be obtained.

  In addition, by adopting the above method (4), it is possible to improve the “void when the cross section of the light diffusion layer is observed”. In the above description, a method of processing at the heat fixing temperature Ts is shown. The above description discloses the technical idea of how the film of the present invention can be obtained by processing at a temperature Ts satisfying Tm1> Ts> Tm2 and Ts> Tg1 at the production level. If so, the technical idea can be easily implemented by a method different from the above-described method, and the film of the present invention can be obtained by a different method. That is, even if another type of heat treatment apparatus is used, by treating at a temperature Ts that satisfies Tm1> Ts> Tm2 and Ts> Tg1, “voids when observing the cross section of the light diffusion layer” as in the present invention can be obtained. It is possible to obtain an improved film.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the embodiments of the examples, and can be appropriately changed without departing from the spirit of the present invention. . In addition, the evaluation method of a film characteristic is as follows.

[Δn _ab ]
Sample films were sampled from a position within 50 mm and a center position from both edges parallel to the film winding direction of the obtained slit roll. The cut sample film was allowed to stand for 2 hours or more in an environment of 23 ° C. and 65% RH. For each sample sample, using an “Abbe refractometer 4T type” manufactured by Atago Co., Ltd., the refractive index (n _a ) on the base film side in the direction forming an angle of 45 degrees with the film winding direction, and the film winding The refractive index (n _b ) on the base film side in a direction that forms an angle of 135 degrees with the direction (that is, a direction that forms an angle of 45 degrees and an angle of 90 degrees) is measured. The absolute value of the difference between these two refractive indexes is Δn _ab, and Δn _ab = | n _a −n _b | It was confirmed that Δn _ab at both ends and the center of the film roll was 0.015 or more and 0.060 or less, and the largest value was designated as Δn _ab in the table.

[Heat Shrinkage Ratio of Film] The first sample cut-out portion is provided within 2 m from the end of winding of the film, and the sample cut-out portion is provided for each length obtained by dividing the film winding length into nine from the end of film winding. By providing the final cutout portion within 2 m from the beginning of winding, a total of 10 sample cutout portions were provided for one film roll. For each cut-out part, a sample film having a width of 20 mm and a length of 250 mm is cut out along the film winding direction from the left and right edge parts (the part within 50 mm from the edge) of the film roll, and the left edge part and the right edge part Ten sample films were obtained for each part. Each sample film was marked at intervals of 200 mm, placed in a heating oven adjusted to 150 ° C., and the amount of heat shrinkage was measured in accordance with JIS C-2318. In the table, “thermal contraction rate at each cutout portion” indicates a combination of the thermal contraction rate difference between the minimum and the maximum in the width direction.

[Passability of film]
The flatness of the film after the heat treatment was evaluated by the following method. As a heat treatment step, a coater having a distance between two rolls of 1,900 mm was used, the temperature was set to 100 ° C. or 160 ° C., and the furnace tension was set to 100N. Next, two rolls are horizontally arranged so that the roll interval is 2,000 mm, and further, the iron bar is positioned at the center position of the two rolls at a position 30 mm below the common tangent of the roll upper surface. Arranged. The film passed through the heat treatment step was passed between two rolls under a tension of 98N. When the film was allowed to pass through, it was marked as ◯ when the film was not in contact with the iron bar, and x when it was in contact with the iron bar. These steps were performed continuously, and it was visually confirmed whether or not the film contacted the iron bar.

  In addition, Table 1 shows the film forming conditions of the film rolls in Examples and Comparative Examples.

[Example 1]
[Preparation of coating solution (M1)]
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared.

  Next, 51.4 parts by weight of water, 38 parts by weight of isopropyl alcohol, 5 parts by weight of n-butyl cellosolve, 0.06 parts by weight of a nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by weight of the water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer solidified, the resin water dispersion is cooled to room temperature, and the solid content concentration is 5.0% by weight. A uniform water-dispersible copolymerized polyester resin liquid was obtained.

  Further, after 3 parts by weight of aggregate silica particles (manufactured by Fuji Silysia Co., Ltd., Silicia 310) are dispersed in 50 parts by weight of water, 99.46 parts by weight of the water-dispersible copolyester resin solution is mixed with 99.46 parts by weight of the silicia 310. 0.54 parts by weight of the aqueous dispersion was added, and 20 parts by weight of water was added with stirring to obtain a coating liquid (M1).

In a main extruder, true spherical silica particles (refractive index 1.46) having an average particle diameter of 4.5 μm are added to a polyester resin (refractive index 1.61) obtained by copolymerizing 23 mol% of an isophthalic acid component with polyethylene terephthalate (PET). Pellets blended to a volume ratio of 10% were supplied and melted at a temperature of 280 ° C. in an extruder. Separately, PET having a refractive index of 1.61 that does not contain fine particles is supplied to the sub-extruder and melted at a temperature of 285 ° C. in the extruder, and the molten resin is filtered into a stainless steel sintered body (nominal filtration accuracy) in the extruder. : Particles of 10 μm or more were cut by 90%). Next, the melted resin was melted and co-extruded from a T-shaped die, and cooled on a mirror-casting drum by an electrostatic application method to produce a two-layer laminated sheet. At this time, extrusion was performed so that the PET layer containing particles contacted the cast drum.

The above-mentioned unstretched sheet is heated to 100 ° C. by a heated roll group and a near infrared heater, and then continuously stretched 3.5 times in the longitudinal direction with a roll group having a difference in peripheral speed. It was.

After the longitudinal stretching is completed, the coating liquid (M1) is coated on one side (non-light diffusion layer side) of the obtained uniaxially stretched film so that the final coating layer thickness becomes 0.08 g / m ^2, and then a drying furnace And dried.

  Next, the end of the uniaxially stretched film was gripped with a clip, led to a hot air zone heated at 130 ° C., and continuously stretched 4.0 times in the width direction. Further, after heat setting by a method described later, 1.7% transverse relaxation was performed at 225 ° C. By winding this in a roll shape, a biaxially oriented light diffusing film roll (mill roll) in which a film having a thickness of 100 μm and a width of 3,300 mm was wound up by 6,500 m was produced. While rewinding the mill roll, both ends are removed by 150 mm, and the remaining part is slit into three at equal intervals in the width direction, and by removing approximately 200 m from the surface layer (winding end portion) of the mill roll, Six slit rolls having a width of 1,000 mm and a winding length of 3,010 m were obtained. Of the six slit rolls obtained as described above, using the slit roll corresponding to one edge side of the mill roll (the right side when viewed from the upstream to the downstream of the film flow), except for the optical characteristics of the film Was evaluated. The evaluation results are shown in Table 4. The cross section, total light transmittance, haze, and diffusive optical properties of the film are evaluated in the width direction of the slit roll corresponding to one edge side of the mill roll (right side when viewed from upstream to downstream of the film flow). This was done using a film located in the center.

  When the cross section of the obtained light diffusive film was cut out and the cross section was observed using the transmission electron microscope HU-12 type (Hitachi Ltd.), the void was not observed but disappeared.

  About the obtained light diffusable film, the total light transmittance and haze were measured using fully automatic direct reading haze computer HGM-2DP (made by Suga Test Instruments Co., Ltd.). The total light transmittance was 89% and haze was 87%.

Moreover, in order to actually visually evaluate the diffusion performance of the obtained light diffusive film, the following experiment was conducted. That is, a visible light laser (He-Ne laser, wavelength 632.8 nm) is irradiated onto the obtained light diffusive film, and the transmitted light is projected onto a screen to observe how much the incident light is spread. And evaluated. The case where the intensity distribution was not observed and which had a uniform and wide diffusion range was marked with ◯, and the case where the intensity distribution was narrow or the narrow diffusion range or the amount of transmitted light was dark was marked with x. It was found that the laser beam spreads through the film and shows good diffusion performance. Moreover, the surface flatness was good and the bending rigidity was also excellent. The evaluation results are shown in Table 4.

[Heat setting]
The said heat setting process was performed with the heat setting apparatus which has a structure shown in FIG. The heat setting device is divided into four heat setting zones called first to fourth zones. Eight plenum ducts a to x are provided in the first to third zones, respectively. Eight plenum ducts are also provided in the fourth zone. Each plenum duct is vertically installed at 400 mm intervals with respect to the film traveling direction so as to be perpendicular to the film traveling direction. Hot air is blown to the stretched film from the hot air outlet (nozzle) of the plenum duct.

  In Example 1, discontinuous rod-shaped shielding plates S, S,... Were attached to hot air outlets of 15 plenum ducts a to o in the manner shown in FIG. FIG. 4 shows a state where the heat fixing device having the shielding plates S, S... Attached to the hot air outlets of the plenum ducts a to o is viewed from above. The longitudinal center of each of the attached shielding plates S, S... Is set so as to substantially coincide with the center of the width of the film passing through the heat fixing device. Further, the length of each shielding plate S, S... (The dimension in the width direction of the produced film) was set so as to gradually increase from the inlet to the outlet of the heat fixing device. Table 2 shows the shielding ratio of the hot air outlets of each of the plenum ducts a to o (the shielded area of the hot air outlet by the shielding plate / the area of the hot air outlet). In addition, let the shielding aspect by the shielding board in Example 1 be "A aspect."

  Table 3 shows the adjustment values of the temperature and wind speed in the first to fourth zones of the heat setting device in Example 1. In addition, as for the temperature conditions of the 1st-4th zone of the heat setting apparatus of Example 1, and the wind speed conditions, the product of the temperature difference between adjacent heat setting zones and a wind speed difference is 250 degrees C * m / s or less. Set to. The temperature and wind speed conditions in the first to fourth zones in Example 1 are defined as “I condition”.

[Example 2]
In a main extruder, a spherical resin having a spherical average particle size of 4.5 μm (refractive index of 1.1) is added to a polyester resin (refractive index of 1.61) obtained by copolymerizing 23 mol% of an isophthalic acid component with polyethylene terephthalate (PET). 46) is supplied at a volume ratio of 10%, and the sub-extruder is supplied with PET having a refractive index of 1.61 that does not contain fine particles. The surface of the containing PET was melt co-extruded with particle-free PET, and cooled on a mirror-casting drum by an electrostatic application method to prepare a three-layer laminated sheet. This three-layer sheet has a structure in which both surfaces of particle-containing PET are coated with non-particle PET. At this time, the extrusion amount of the extruder was increased to increase the width of the unstretched sheet.

After the longitudinal stretching was completed, the coating solution (M1) was applied on both sides of the obtained uniaxially stretched film so that the final coating layer thickness was 0.08 g / m ^2, and then dried in a drying furnace.

  The shielding plate attached to the hot air outlet of each plenum duct of the heat setting device is changed to have the shielding rate shown in Table 2, and the temperature and wind speed of the first to fourth zones of the heat setting device are adjusted values shown in Table 3. A mill roll was obtained in the same manner as in Example 1 except that the film having a thickness of 100 μm and a width of 5,300 mm was wound up by 6,500 m. While rewinding the mill roll, both ends are removed by 150 mm, and the remaining part is slit into five at equal intervals in the width direction. By removing approximately 200 m from the surface layer of the mill roll, the width is 1,000 mm. 10 slit rolls having a winding length of 3,010 m were obtained. And among the 10 slit rolls obtained as described above, the slit roll corresponding to one edge side of the mill roll (the right side when viewed from the upstream to the downstream of the film flow) is used. Evaluation was performed. The evaluation results are shown in Table 4. In addition, the shielding aspect by the shielding board in Example 2 is set to "B aspect", and the temperature and wind speed conditions of the 1st-4th zone in Example 2 are set to "II conditions."

  When the cross section of the obtained film was observed in the same manner as in Example 1, no voids were observed inside the film.

[Example 3] The extrusion amount of the extruder is increased, the thickness of the unstretched sheet is increased to 2,440 μm, and cooling air at 16 ° C. is used in combination with the casting drum for cooling in the longitudinal direction. Except having changed the draw ratio to 3.3 times, it carried out similarly to Example 1, and obtained the mill roll which wound up the film of thickness 188 micrometers and width 3,300mm to 4,500m. While rewinding the mill roll, the process of removing both ends at 150 mm each and slitting the remaining part into three at equal intervals in the width direction was performed, and by removing approximately 200 m from the surface layer of the mill roll, the width was 1,000 mm. Six slit rolls having a winding length of 2,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

Example 4 Crosslinked acrylic resin fine particles (refractive index) having a spherical shape and an average particle diameter of about 8 μm were added to 100 parts by weight of a polyester resin (refractive index 1.61) obtained by copolymerizing 23 mol% of an isophthalic acid component with polyethylene terephthalate (PET). 1.47) Using 20 parts by weight of pellets, and changing the shielding plate attached to the hot air outlet of each plenum duct of the heat setting device so as to have the shielding rate shown in Table 2, the first heat setting device Ten slit rolls were obtained in the same manner as in Example 2 except that the temperature and wind speed of the -4 zone were changed to the adjustment values shown in Table 3. Note that the temperature and wind speed conditions in the first to fourth zones in Example 4 are referred to as “III conditions”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

  When the cross section of the obtained film was observed in the same manner as in Example 1, no voids were observed inside the film.

[Example 5]
While adjusting the take-up speed of the unstretched sheet to change the thickness of the unstretched sheet to 1,030 μm, the ratio of the lateral relaxation treatment is changed to 2.3%, the temperature of the first to fourth zones of the heat setting device, Except that the wind speed was changed to each adjustment value shown in Table 3, a mill roll was obtained in the same manner as in Example 1 except that a film having a thickness of 75 μm and a width of 3,300 mm was wound up by 12,300 m. While rewinding the mill roll, remove both ends by 150 mm and repeat the process of slitting the remaining part into three at equal intervals in the width direction. By removing approximately 150 m from the surface layer of the mill roll, the roll is wound at a width of 1,000 mm. Six slit rolls having a length of 6,010 m were obtained. Note that the temperature and wind speed conditions in the first to fourth zones in Example 5 are referred to as “VIII conditions”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

[Example 6]
Mill roll obtained by winding 6,500 m of a film having a thickness of 125 μm and a width of 3,300 mm in the same manner as in Example 1 except that the take-up speed of the unstretched sheet was adjusted and the thickness of the unstretched sheet was changed to 1,720 μm. Got. While rewinding the mill roll, both ends were removed by 150 mm, and the remaining part was slit into three at equal intervals in the width direction. By removing about 300 m from the surface of the mill roll, the width was 1,000 mm. Six slit rolls having a winding length of 3,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

[Example 7]
While adjusting the take-up speed of the unstretched sheet to change the thickness of the unstretched sheet to 3,250 μm, a cooling air of 16 ° C. is used in combination with the cooling with the casting drum, and the stretching ratio in the longitudinal direction is 3. A film having a thickness of 250 μm and a width of 3,300 mm is 2,500 m in the same manner as in Example 1, except that the temperature and wind speed of the first to fourth zones of the heat setting device are changed to VIII conditions. A wound mill roll was obtained. While rewinding the mill roll, the process of removing both ends by 150 mm and slitting the remaining part into three at equal intervals in the width direction was performed, and by removing approximately 200 m from the surface layer of the mill roll, the width was 1,000 mm. Six slit rolls having a winding length of 1,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

[Example 8]
While adjusting the take-up speed of the unstretched sheet to change the thickness of the unstretched sheet to 1,030 μm, the ratio of the lateral relaxation treatment is changed to 2.3%, the temperature of the first to fourth zones of the heat setting device, Except that the wind speed was changed to each adjustment value shown in Table 3, a mill roll was obtained in the same manner as in Example 2 by winding a film having a thickness of 75 μm and a width of 5,200 mm for 12,300 m. After that, while the mill roll is rolled back, the process of slitting the remaining portions into 5 parts at equal intervals in the width direction is repeated while removing both ends by 100 mm, and approximately 200 m is excluded from the surface layer (winding end portion) of the mill roll. Thus, 10 slit rolls having a width of 1,000 mm and a winding length of 6,010 m were obtained. The temperature and wind speed conditions in the first to fourth zones in Example 4 are referred to as “IX conditions”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

[Example 9]
A mill roll in which a film having a thickness of 125 μm and a width of 5,200 mm was wound up by 6,500 m, except that the undrawn sheet take-up speed was adjusted and the thickness of the unstretched sheet was changed to 1,720 μm. Got. While rewinding the mill roll, remove both ends by 100 mm and repeat the process of slitting the remaining part into five at equal intervals in the width direction. By removing about 300 m from the surface of the mill roll, the width is 1,000 mm. Ten slit rolls having a winding length of 3,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

[Example 10]
While adjusting the take-up speed of the unstretched sheet to change the thickness of the unstretched sheet to 2,440 μm, a cooling air of 16 ° C. is used in combination with the cooling with the casting drum, and the stretching ratio in the longitudinal direction is 3. Except having changed to 3 times, it carried out similarly to Example 8, and obtained the mill roll which wound up the film of thickness 188 micrometers and width 5200mm 4,500m. While rewinding the mill roll, remove both ends by 100 mm and repeat the process of slitting the remaining part into five at equal intervals in the width direction. By removing about 200 m from the surface of the mill roll, the width is 1,000 mm. Ten slit rolls having a winding length of 2,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

[Example 11]
The thickness of the unstretched sheet was changed to 3,250 μm by adjusting the take-up speed of the unstretched sheet, and the same procedure as in Example 10 was performed except that a cooling air of 16 ° C. was used at the time of cooling with the casting drum. A mill roll was obtained by winding 2,500 m of a film having a thickness of 250 μm and a width of 5,200 mm. While rewinding the mill roll, remove both ends by 100 mm and repeat the process of slitting the remaining part into five at equal intervals in the width direction. By removing about 200 m from the surface of the mill roll, the width is 1,000 mm. Ten slit rolls having a winding length of 1,010 m were obtained. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

[Comparative Example 1]
Six slit rolls were obtained in the same manner as in Example 1 except that an integrated large shielding plate was attached to the hot air outlets of the plenum ducts a to o of the heat fixing device. The shape of the large shielding plate was adjusted so that each shielding rate was the same as in Example 1. Using the slit roll in the same position as in Example 1, the characteristics of the film were evaluated. The evaluation results are shown in Table 4.

[Comparative Example 2]
A large shielding plate integrated with the hot air outlets of the plenum ducts a to v of the heat fixing device by changing the temperature and wind speed of the first to fourth zones of the heat fixing device to the adjustment values shown in Table 3. 10 slit rolls were obtained in the same manner as Example 2 except that was attached. The shape of the large shielding plate was adjusted so that each shielding rate was the same as in Example 2. The temperature and wind speed conditions in the first to fourth zones in Comparative Example 2 are defined as “IV conditions”. Using the slit roll in the same position as in Example 2, the characteristics of the film were evaluated. The evaluation results are shown in Table 4.

[Comparative Example 3]
A large shielding plate integrated with the hot air outlets of the plenum ducts a to v of the heat fixing device by changing the temperature and wind speed of the first to fourth zones of the heat fixing device to the adjustment values shown in Table 3. 10 slit rolls were obtained in the same manner as Example 2 except that was attached. The shape of the large shielding plate was adjusted so that each shielding rate was the same as in Example 2. Using the slit roll in the same position as in Example 2, the characteristics of the film were evaluated. The evaluation results are shown in Table 4.

[Comparative Example 4]
While changing the shielding mode by the rod-shaped shielding plate attached to the hot air outlet of each plenum duct of the heat fixing device a to o as shown in Table 2, the temperature and wind speed of the first to fourth zones of the heat fixing device are also shown. Except having changed to each adjustment value shown in 3, it carried out similarly to Example 1, and obtained six slit rolls. In addition, the length of the film width direction of each shielding plate in Comparative Example 4 is adjusted so as to become gradually narrower from the inlet to the outlet of the heat fixing device. Further, the shielding mode by the shielding plate in Comparative Example 4 is set as “C mode”, and the temperature and wind speed conditions in the first to fourth zones in Comparative Example 4 are set as “V condition”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

[Comparative Example 5]
Except that the heat fixing is performed without attaching a shielding plate to the hot air outlet of each plenum duct, and the temperature and wind speed of the first to fourth zones of the heat fixing device are changed to the adjustment values shown in Table 3, respectively. 6 slit rolls were obtained in the same manner as in Example 1. The temperature and wind speed conditions in the first to fourth zones in Comparative Example 5 are referred to as “VI conditions”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 1. The evaluation results are shown in Table 4.

[Comparative Example 6]
Except that the heat fixing is performed without attaching a shielding plate to the hot air outlet of each plenum duct, and the temperature and wind speed of the first to fourth zones of the heat fixing device are changed to the adjustment values shown in Table 3, respectively. Ten slit rolls were obtained in the same manner as described above. Note that the temperature and wind speed conditions of the first to fourth zones in Comparative Example 6 are referred to as “VII conditions”. And the characteristic of the film was evaluated using the slit roll in the same position as Example 2. The evaluation results are shown in Table 4.

[Comparative Example 7]
While adjusting the take-up speed of the unstretched sheet with the same raw material type as in Example 1, heat fixing is performed by a heat fixing device having five plenum ducts to which discontinuous shielding plates are attached, and each of the shielding plates is attached. Except for changing the air speed blown out of the plenum duct while keeping the plenum duct's hot air flow constant for each plenum duct, and changing the conditions of the heat fixing device as shown in Tables 1, 2, and 3, the same as in Example 1. 6 slit rolls were obtained. In addition, the wind speed shown in Table 3 has shown the wind speed of the first plenum duct and the wind speed of the last plenum duct. Further, the shielding mode by the shielding plate in Comparative Example 7 is set as “D mode”, and the temperature and wind speed conditions of the heat fixing device are set as “X conditions”. Using the slit roll in the same position as in Example 1, the characteristics of the film were evaluated. The evaluation results are shown in Table 4.

[Effects of Example Film]
From Table 4, all of the films of the examples are excellent in light transmittance and light diffusibility, have a small difference in thermal shrinkage rate (that is, difference in thermal shrinkage rate) over the entire width of the roll, and further in the longitudinal direction. The amount of fluctuation of the heat shrinkage rate in is small, and the permeability during post-processing is good, which is suitable for post-processing. On the other hand, the film roll of the comparative example has a large difference in heat shrinkage rate over the entire width of the roll, and also has a large fluctuation amount of the heat shrinkage rate in the longitudinal direction, and the passability during post-processing is poor.

  Since the light diffusing film of the present invention has excellent processing characteristics as described above, heat treatment in post-processing such as prism lens processing, hard coat processing, adhesive processing, AR processing is performed in a high temperature zone (about 160 ° C.). Can be suitably used as a processing film for a relatively long time (10 to 60 seconds).

Explanatory drawing (a) which shows the shielding aspect by the conventional shielding board shows the vertical cross section of a part of heat setting apparatus, (b) is the state which attached the shielding board to the hot-air blowing outlet of the plenum duct Is a view from above.) It is explanatory drawing which shows the shielding aspect by the shielding board in this invention, (a) shows the vertical cross section of a part of heat setting apparatus, (b) shows a shielding board in the hot-air blowing outlet of a plenum duct. The state which attached the state seen from the top is shown. It is explanatory drawing which shows the state which saw through the heat fixing apparatus used by the Example and the comparative example from the top. It is explanatory drawing which shows the shielding aspect by the shielding board in Example 1. FIG.

Explanation of symbols

1: Heat fixing device 2: Hot air outlet 3, a to x: Plenum duct F: Film S: Shielding plate A: Film winding direction Z1: First zone Z2: Second zone Z3: Third zone Z4: First 4 zones

Claims (6)

Δn _ab is 0.015 or more and 0.060 or less, which is the difference between the refractive index in the direction that forms an angle of 45 degrees with the winding direction of the film and the refractive index in the direction that forms an angle of 135 degrees with the winding direction of the film. A light diffusing film satisfying the following requirements (1) to (3),
The first sample cutout is provided within 2 m from the end of winding of the film, the final cutout is provided within 2 m from the start of winding of the film, and the length between the first and final cutout is divided into nine equal parts. A light diffusing film characterized by satisfying the following requirements (4) to (6) when a total of 10 sample cutout portions are provided by providing sample cutout portions in the plate.
(1) It has a light diffusion layer having a light diffusion component inside at least one surface of a biaxially stretched polyethylene terephthalate film. (2) The light diffusion layer does not substantially contain voids. (3) The light diffusing layer is composed of at least a light-transmitting resin and fine particles as a light diffusing component. (4) In each of the cutout portions, a position within 50 mm from one edge in the film width direction and within 50 mm from the other edge. Samples were cut out from the respective positions, and HS150, which is the heat shrinkage rate in the film winding direction when heated at 150 ° C. for 30 minutes, was obtained for the two samples, and the difference in heat shrinkage rate, which was the difference between the HS150, was obtained. Sometimes, the thermal contraction rate difference in all cutouts is 0.1% or less. (5) In each cutout, When the sample is cut out from a position within 50 mm from the one end edge and a position within 50 mm from the other end edge in the width direction of the rumm, and HS 150 is obtained for each sample, the HS 150 of the sample at both end edges in all cut portions is (6) The fluctuation amount of HS150 on the one end edge side in the width direction of the film obtained in each cutout part, and the film obtained in each cutout part are 0.7% or more and 2.0% or less. The amount of fluctuation of the HS 150 on the other end side in the width direction is 0.25% or less.   The light diffusing film according to claim 1, wherein the light diffusing film has a total light transmittance of 80% or more and a haze of 60% or more.   The light diffusive film according to claim 1, wherein the light diffusive film has a thickness of 80 μm or more and 450 μm or less. A manufacturing method for manufacturing the light diffusing film according to claim 1,
A film forming process for forming an unstretched sheet by melt-extruding a raw material resin from an extruder, a biaxial stretching process for biaxially stretching the unstretched sheet obtained in the film forming process in the longitudinal direction and the transverse direction, A heat setting step of heat fixing the film after axial stretching,
The heat setting process is performed in the heat setting apparatus which satisfy | fills the following requirements (7)-(9), The manufacturing method of the light diffusable film characterized by the above-mentioned.
(7) A plurality of wide plenum ducts for blowing hot air are arranged vertically opposite to the film traveling direction. (8) Shielding for shielding hot air outlets to the plurality of plenum ducts. (9) The dimension of each shielding plate in the traveling direction of the film is adjusted to be substantially the same as the dimension of the outlet of each plenum duct in the traveling direction of the film. The dimension in the width direction of the film is adjusted so as to become gradually longer with respect to the film traveling direction.   In the biaxial stretching process, the film is stretched in the transverse direction after stretching the film in the longitudinal direction, and an intermediate zone that does not perform wind blowing is provided between the zone that performs the transverse stretching and the heat setting device. The method for producing a light diffusing film according to claim 4.   The heat setting device is divided into a plurality of heat setting zones, and the product of the temperature difference and the wind speed difference between adjacent heat setting zones is set to be 250 ° C. · m / s or less. 6. The method for producing a light diffusing film according to claim 4, wherein the light diffusing film is formed.

Images