JP2011005648A - Base film for lens sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film that has high transparency and most suitable as a base film for a lens sheet while suppressing minute damage generated in a machining process.SOLUTION: The base film for the lens sheet is a biaxially oriented polyester film having three or more layers of laminated structure by a co-extrusion method, and is characterized in that both outermost layers of the film contain inert particles having an average grain size of 2.1-2.5 μm, and the thickness of the outermost layers is five times or more and less than 11 times the average grain size of the inert particles, and the ratio of the number of the surface projections having the ratio L/h of the diameter L and the height h of the surface projections of 50 or less, of the surface projections having a height of 2 nm or higher as observed by an atomic force microscope (AFM) in the outermost layer surface is 30% or below.

Description

  The present invention relates to a lens sheet base film. More specifically, the present invention relates to a biaxially oriented laminated polyester film that is optimal when used as a base film for lens sheets, having few micro scratches generated in the film forming process, few optical defects, and excellent transparency.

  As represented by the colorization and the reduction in size and weight of notebook personal computers in recent years, there has been a remarkable spread of reduction in size and weight and colorization of portable electric devices. In addition, for example, products using color liquid crystal displays are not limited to color notebook computers, such as portable color liquid crystal televisions, video integrated color liquid crystal televisions, handy label printers, portable communication devices (mobile gears, etc.) A wide variety of products have been put into practical use.

  In such a device, a battery is used to be portable, but its operating time is limited. In particular, the power consumption of liquid crystal displays, especially color liquid crystal displays, greatly affects the operating time of the battery. Reducing this power consumption as much as possible is a practical product for portable electric devices as described above. In addition to increasing value, it is also meaningful for energy saving.

  As a method for reducing power consumption, it is the simplest method to suppress power consumption of a backlight used in a liquid crystal display. However, when the amount of power is reduced, the luminance of the backlight is lowered, so that the luminance of the liquid crystal display is also lowered, and the display function is significantly lowered.

  In order to solve these problems, methods for improving the optical efficiency of the backlight unit have been proposed. For example, a backlight in which a lens sheet such as a lens sheet in which a large number of lens units in a prism array are formed on one side or a sheet in which a large number of lens units in a lenticular array are formed is provided on the outgoing light surface side of the light guide of the backlight. Proposed.

  These lens sheets improve the front luminance by directing the light emitted from the backlight toward the front of the display by refraction. Usually, a lens sheet uses a transparent plastic resin such as a polycarbonate resin, an acrylic resin, or a polyester resin as a base material (base film) because of its good moldability. Among these, polyester resins are widely used from the viewpoints of excellent transparency, dimensional stability, and chemical resistance.

  The biaxially oriented polyester film is generally biaxially stretched in the winding direction (MD direction) and the width direction (TD direction) of the film after a polyester resin is melt-extruded and formed into a sheet, followed by a transport roll. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method is generally employed, but the sequential biaxial stretching method is most widely employed. In the sequential biaxial stretching method, the film is stretched in the MD direction using the speed difference between the transport rolls, and then stretched in the TD direction by a tenter clip.

  When the film passes through the transport roll during the film-forming process, fine scratches may be generated on the film due to foreign matters on the transport roll. These foreign substances are mainly caused by oligomers and the like generated during the film forming process. In order to obtain a high-quality film, periodic roll cleaning, use of a low oligomer raw material as in Patent Document 1, etc. Countermeasures have been proposed.

  In addition, it has been studied to reduce minute scratches by providing protrusions on the film surface. The effect on scratches generally corresponds to SRa (center plane average roughness), which is an index of surface roughness, and it is known that the higher the SRa, the higher the effect on scratches. As a measure for imparting protrusions to the film surface, there is a method in which the film has a three-layer structure and inert particles are imparted to the film surface layer. However, when the inert particles are provided in the film, there is a difference in the refractive index between the inert particles and the resin, so that the haze that is an index of transparency of the film is increased and the transparency is impaired.

  In order to solve these problems, Patent Document 2 and Patent Document 3 propose to use both inert particles having different particle sizes to achieve both transparency and scratch resistance. Patent Document 4 proposes that the surface layer portion having a three-layer structure is made very thin so that the number of particles that do not contribute to the protrusions is reduced and the transparency is improved.

JP 2007-130984 A Japanese Patent No. 3311591 Japanese Patent No. 3235759 JP 2003-231229 A

  Regarding the reduction of scratches and foreign matters that become optical defects, it has been conventionally used without any problems by the proposal of disclosure of Patent Document 1 and the like. However, it has been considered that the display definition has been greatly improved, and minute scratches and foreign matters that are not regarded as problems in the past are recognized as optical defects.

  In addition, due to the improvement in productivity, the line speed in processing and film forming processes has been dramatically improved, and it has become necessary to reduce optical defects even under high-speed processing conditions. Therefore, it has been studied to reduce optical defects due to minute scratches by providing protrusions on the film surface as in Patent Documents 2 to 4. However, if fine particles having an average particle size of 1 μm or less are used as in Patent Documents 2 and 3, the fine particles cannot be uniformly dispersed in the resin due to aggregation of the fine particles, and the fisheye-like defects occur due to the aggregated particles. However, the optical defects could not be suppressed to a level that can solve the above problems.

  Furthermore, as in Patent Document 4, if the resin layer is made too thin with respect to the particles, there is a concern that the particles may fall off due to high-speed processing in processing or film formation, which may cause new optical defects. It was.

  As described above, it has been found that there is no established method for stably obtaining a high-quality lens sheet film with few optical defects that can cope with future high definition and productivity improvement. It was.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors set the thickness of the inert particle-containing layer and the particle diameter of the inert particles in a specific range, and further, the ratio between the diameter of the specific protrusion and the height of the protrusion. By controlling the surface protrusions having the above, there are few optical defects due to powder falling and the like, and a highly transparent film has been provided.

  Specifically, it is a biaxially oriented polyester film having a laminated structure of three or more layers by a coextrusion method, and both outermost layers of the film contain inert particles having an average particle diameter of 2.1 to 2.5 μm. The thickness of the outermost layer is not less than 5 times and less than 11 times the average particle size of the inert particles, and the surface of the surface protrusions having a height of 2 nm or more observed by the atomic force microscope (AFM) on the outermost layer surface By setting the ratio of the number of surface protrusions having a ratio L / h of the protrusion protrusion diameter L to the surface protrusion height h of 50 or less to 30% or less, the film has excellent transparency and few optical defects. It became possible to obtain an optimal film.

  The film obtained according to the present invention is excellent in transparency and has few generation of fine scratches in the processing step and the film forming step. By using the film of the present invention as a base film for a lens sheet, it is possible to stably obtain a high-performance lens sheet with few optical defects.

(Polyester raw material)
In the present invention, the polyester used for the polyester film may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by condensation polymerization of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2.6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, 1.4-butanediol, and 1.4-cyclohexanedimethanol. . Examples of such polyester include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like. Among these, polyethylene terephthalate can be suitably used from the viewpoint of physical strength, heat resistance, and chemical resistance.

  On the other hand, the dicarboxylic acid component of the copolyester includes one or more of isophthalic acid, phthalic acid, terephthalic acid, 2.6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxylcarboxylic acid, and the like. Examples of the component include one or more of ethylene glycol, diethylene glycol, propion glycol, 1.4-butanediol, 1.4-cyclohexanedimethanol, neopentyl glycol and the like. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

  Polyester is produced by a conventionally known method such as a polycondensation method in which a dicarboxylic acid and a glycol are esterified and then a polycondensation reaction, or a transesterification method in which a dicarboxylic acid salt and a glycol are transesterified and then a polycondensation reaction is performed. Manufactured.

Typical polycondensation catalysts for polyester include Sb-based catalysts such as antimony trioxide and antimony glycolate, Ge-based catalysts, Ti-based catalysts, etc. Of these, from the viewpoint of transparency, thermal stability, and price In general, antimony trioxide (Sb ₂ O ₃ ) is used as a polymerization catalyst for the polyester resin for film.

  The polyester film may contain various additives. Examples of the additive include an antistatic agent, an ultraviolet absorber, and a stabilizer.

  The film of the present invention has a laminated structure of three or more layers by a coextrusion method, and contains inert particles in both outermost layers. For example, if the outermost layer is the B layer, the other layers are the A layer, and the C layer, the layer structure in the film thickness direction is B / A / B, B / A / C / B, or B / A / C / A. A configuration such as / B can be considered. Each of the layers A to C may have the same or different polyester resin configuration, but in order to suppress the occurrence of curling due to the bimetal configuration, the polyester resin of each layer has the same configuration. And / or a B / A / B configuration (two-kind three-layer configuration).

  In the present invention, the polyester resin constituting the central layer other than the outermost layer (for example, the A layer in the B / A / B configuration) may contain particles, but in order to obtain high transparency, the central layer It is preferable that the polyester resin that constitutes substantially contains no particles. By containing inert particles only in the outermost layer, high transparency can be obtained more suitably. When particles are added to the central layer other than the outermost layer, it is preferably 50 ppm or less, preferably 10 ppm or less.

  The inert particles contained in the outermost layer include calcium carbonate, calcium phosphate, amorphous silica, spherical silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, fluoride. Inorganic particles such as calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, Examples thereof include heat-resistant polymer fine particles such as polytetrafluoroethylene particles. Of these, silica is most suitable in that it can ensure a film with higher transparency because its refractive index is relatively close to that of polyester.

  The average particle size of the inert particles contained in the outermost layer of the film of the present invention is 2.1 to 2.5 μm, more preferably 2.2 to 2.4 μm. If the average particle size of the inert particles is 2.1 μm or less, the agglomeration force of the particles is very large, and coarse abnormal particles are easily generated due to the aggregation of the particles, which is not preferable. Furthermore, in order to construct a surface shape as described later, it is desirable that the average particle diameter of the inert particles is 2.1 μm or more. Moreover, when the average particle diameter is 2.5 μm or more, the content of coarse particles as a single particle increases, which is not preferable. In the present invention, in order to reduce the coarse particles that cause optical defects to the utmost limit, a specific very narrow range of particles is used.

  The range of the average particle diameter of an inert particle here is measured with the measuring method mentioned later. For example, in the case of secondary particles in which primary particles are aggregated as described later, it means the average particle size of the secondary particles. That is, the average particle diameter of the inert particles here is an average particle diameter in an aspect that can actually exist as inert particles in the film.

  The content of the inert particles in the outermost layer is desirably 0.015 to 0.030% by mass, and more preferably 0.020 to 0.025% by mass. When the content of the inert particles is 0.015% by mass or more, it is preferable from the viewpoint of exhibiting an effective slipping property to the extent that fine scratches are reduced. When content of an inert particle is 0.030 mass% or less, it is preferable when maintaining high transparency.

  The inventor of the present application has studied how to reduce optical defects due to surface irregularities and powder fall off caused by high-speed processing, and as a result, when both have a specific surface structure, both of these characteristics are remarkably compatible. I found out. That is, in the present invention, the ratio L / h between the diameter L of the surface protrusion and the height h of the surface protrusion among the surface protrusions having a height of 2 nm or more observed on the surface of the outermost layer by an atomic force microscope (AFM). The ratio of the number of protrusions that is 50 or less is 30% or less.

  In order to exhibit slipperiness that suppresses optical defects, it is important to have surface protrusions having a protrusion height of 2 nm or more due to inert particles. If the height of the surface protrusion is less than 2 nm, the surface shape of the macro becomes almost flat, and it is difficult to effectively contribute to slipperiness. However, when the surface protrusions become high, particles forming the protrusions fall off due to rubbing between rolls and films in ultra-high speed processing. A slight powder fall during such a process causes the process to become dirty due to long-term operation, and causes a minute scratch. The same applies to the case where a coating layer described later is provided on the film. Therefore, as a result of examining the surface shape that causes powder falling off, the inventor of the present application does not determine the ease of particle removal depending on the height of the surface protrusion, but the shape of the surface protrusion peak is that of the inert particle. The present inventors have found a new finding that it affects the ease of dropping off, and have reached the present invention. That is, among the surface protrusions having a height of 2 nm or more, the surface protrusion having a gentle skirt in which the ratio L / h of the diameter L of the surface protrusion to the height h of the surface protrusion exceeds 50 is less likely to drop off particles. On the other hand, surface protrusions with a relatively small skirt having a ratio L / h of the diameter L of the surface protrusions to the height h of the surface protrusions of 50 or less are likely to cause the particles to fall off.

  The film of the present invention is a projection having a ratio L / h of the surface projection diameter L to the surface projection height h of 50 or less among surface projections having a height of 2 nm or more observed by an atomic force microscope (AFM). The ratio of the number is 30% or less, preferably 25% or less, more preferably 20% or less, and still more preferably 15% or less. When the ratio of the surface protrusions having a ratio L / h of the diameter L to the height h of 50 or less exceeds 30%, an optical defect due to powder falling tends to occur. The ratio of the surface protrusions having the shape is preferably small, but it is considered that the lower limit is about 1% from the viewpoint of productivity.

  In order to form the specific surface configuration, it is desirable to increase the number of surface protrusions having a gentle crest. Therefore, the thickness of the outermost layer needs to be at least 5 times the average particle diameter of the inert particles. The surface protrusions are formed by inert particles present in the outermost layer. In order to form gentle surface protrusions, it is desirable that the particles having a certain size or more exist with an appropriate depth, rather than the inert particles being directly below the surface. When the thickness of the outermost layer is less than 5 times the average particle diameter of the inert particles, the shape of the surface protrusions due to the inert particles becomes relatively sharp, so that powder falling easily occurs. The upper limit of the thickness of the outermost layer is not particularly provided from the viewpoint of occurrence of powder falling, but if the thickness becomes too thick, the amount of inactive particles inside the film becomes too large, and scattering of light generated inside the film is large. Therefore, it is not preferable in a field where high transparency is required as a lens sheet. The upper limit of the thickness of the outermost layer was set to less than 11 times from the range in which haze increase can be allowed as a lens sheet. Here, the thickness of the outermost layer is the thickness of one side of the outermost layer laminated on both sides of the film.

  By controlling the thickness of the inert particles and the inert particle-containing layer as described above, it is possible to suitably control the protrusion shape on the film surface, and to reduce the inclination angle of each protrusion as much as possible, resulting in a decrease in transparency. It is possible to enhance the effect of reducing optical defects while suppressing as much as possible.

  Furthermore, in order to form the specific surface shape more preferably, for example, (1) a method of smoothing the surface shape by increasing the intrinsic viscosity of the polyester resin, and (2) processing at a high heat setting temperature. It is also possible to combine the method of smoothing the surface shape. In addition, as will be described later, it is also preferable to use (3) inert particles that are likely to undergo follow-up deformation when the film is stretched.

Inactive particles that are likely to undergo follow-up deformation when the film is stretched are secondary particles in which primary particles of several to several hundred nm are aggregated and have a pore volume of 1.5 ml / g or more. Is preferred. In particular, amorphous bulk silica is preferable from the viewpoints of transparency, handleability, and cost. By setting the pore volume of the inert particles to 1.5 ml / g or more, deformation of the particles due to stretching tends to occur, and the protrusion shape can be easily controlled within the scope of the present invention. The pore volume of the inert particles can be calculated by known nitrogen desorption such as BJH method. If the inert particles are present in the film, for example, dissolve them with a phenol / tetrachloroethane mixed solution, collect the inert particles that are the residue, dry well, and calculate by known nitrogen desorption such as the BJH method. Can do.
The

  As a method of blending the inert particles with polyester, a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder It can be carried out.

  Among them, in the present invention, after the aggregated inorganic particles are homogeneously dispersed in the monomer liquid that is part of the polyester raw material, the filtered material is the polyester raw material before the esterification reaction, during the esterification reaction, or after the esterification reaction. The method of adding to the remainder of is preferable. According to this method, since the monomer liquid has a low viscosity, homogeneous dispersion of particles and high-accuracy filtration of the slurry can be easily performed, and when added to the remainder of the raw material, the dispersibility of the particles is good and new aggregation is achieved. Aggregation is unlikely to occur.

  In particular, in the case of using the above-mentioned amorphous bulk silica, the particles may be aggregated and aggregated coarse particles may be generated by adding and mixing the slurry. Since silica agglomeration is likely to occur at high temperatures, an esterification reaction or a transesterification reaction is required when adding an ethylene glycol solution containing the above-mentioned irregularly-shaped bulk silica in order to reduce aggregated coarse particles that cause optical defects. In the step before the production of the oligomer, it is preferably blended with the polyester raw material while maintaining the temperature within the range of 10 to 50 ° C, more preferably 10 to 30 ° C. By adding the slurry at this timing, it becomes possible to add the slurry while keeping the slurry temperature at a low temperature, and generation of new aggregates can be suppressed.

  In general, the particle size of the inert particles shows a distribution having a certain width, but the inert particles used in the present invention preferably have 1% or less of the total number of inert particles having a particle size of 10 μm or more. Is preferred. If the number of inert particles having a particle diameter of 10 μm or more exceeds 1%, the number of coarse particles that cause optical defects increases, which is not preferable. As a method for bringing the distribution of the inert particles into the above range, (1) a method of microfiltration of ethylene glycol or polyester in which inert particles are dispersed, and (2) a batch of ethylene glycol or polyester in which inert particles are dispersed. For example, a method of processing with a centrifugal separator of a type or an intermittent type, (3) a method of selecting inert particles having a predetermined particle size distribution, and the like can be used.

  In the present invention, the haze of the film is preferably 2.0% or less, more preferably 1.5% or less, and further preferably 1.0% or less. When the haze is 2.0% or more, when used as a lens sheet, the front luminance of the backlight unit may be lowered, which is not preferable. Moreover, when the adhesive property modification layer containing the particle | grains mentioned later is laminated | stacked, it is preferable that the haze of a film with an adhesive property modification layer is 3.0% or less, and it is 2.5% or less. Is more preferable, and it is further more preferable that it is 2.0% or less.

  The three-dimensional center plane average roughness (SRa) of the film of the present invention is preferably 0.008 to 0.015 μm. Further, the ten-point average roughness (SRz) is preferably 0.5 to 1.5 μm, and more preferably 0.6 to 1.0 μm. It is preferable that the three-dimensional center plane average roughness (SRa) or the ten-point average roughness (SRz) is within the above range because light transparency can be maintained while effectively suppressing minute scratches.

  The present invention has the above-mentioned specific surface structure, and preferably has the above-mentioned specific surface roughness, so that it exhibits good slipperiness that can suppress micro-scratches generated in the processing step and the film-forming step. Can do. Therefore, the dynamic friction coefficient (μd) of the film of the present invention measured by the measurement method described later is preferably 1.5 or less, and more preferably 1 or less. When the dynamic friction coefficient is within the above range, scratch resistance is maintained, and scratches are less likely to occur during the process.

  Although the thickness of the film of this invention is not specifically limited, Preferably it is 75-350 micrometers, More preferably, it is 100-300 micrometers. When the thickness of the film is 75 μm or more, the strength as the base film is easily maintained. Moreover, it is preferable at the point of weight reduction of a lens sheet that film thickness is 350 micrometers or less.

Since the film of the present invention has the specific surface structure described above, it is possible to suppress optical defects that occur during film formation while being light transparent. When the film of the present invention is measured by the method described later, the number of fine scratches having an elevation difference of 0.3 μm is preferably 2 or less, more preferably 1 or less, and even more preferably 0 per 1 m ^2. . Micro scratches having a very shallow depth with a height difference of 0.3 μm are caused by rubbing with films or guide rolls during the film forming process or the processing process. Such microscopic scratches have not been a major problem in the past, but can be an optical defect to be a problem in order to cope with the higher definition that will be developed in the future. For this reason, the film of the present invention is particularly suitable for a lens sheet that requires high definition.

Moreover, since the film of this invention has the said specific particle structure, it becomes possible to suppress the aggregation foreign material which becomes a factor of an optical defect to the limit, containing a particle in a film. When the film of the present invention is measured by the method described later, the number of foreign matters having a major axis of 20 μm or more is preferably 2 or less, more preferably 1 or less, and even more preferably 0 per 1 m ² . Foreign matter having a major axis of 20 μm or more is caused by coarse particles formed by aggregation of fine particles. For this reason, the film of the present invention is particularly suitable for a lens sheet that requires high definition.

  In the present invention, in order to improve the adhesiveness with the lens resin, it is also a preferable aspect to have an adhesive property-modified resin layer on at least one surface of the biaxially oriented polyester film. The component of the adhesive modification layer is not particularly limited, but it is preferable that at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin is a main component. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the adhesive modified resin layer. The coating solution used for forming the adhesive modified resin layer of the present invention is preferably an aqueous coating solution containing at least one of water-soluble or water-dispersible copolyester resin, acrylic resin and polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

  The adhesive property-modified resin layer can be obtained by applying the coating solution on one or both sides of a uniaxially stretched film in the longitudinal direction, drying at 100 to 150 ° C., and further stretching in the transverse direction. The thickness of the adhesive modified resin is not particularly limited, but is usually preferably in the range of 0.01 to 5 μm, more preferably 0.02 to 2 μm, and most preferably 0.05 to 0.5 μm. If the thickness is too thin, there is a possibility of poor adhesion. In addition, within the scope of the present invention, it is also possible to laminate a plurality of adhesion modifying resins, to use a mixture of a plurality of adhesion modifying resins, and to apply different adhesion modifying resins on both sides. Is possible.

  It is preferable to add particles to the adhesiveness-modified resin layer in order to provide easy slipping. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the coating layer. Examples of the particles to be contained in the adhesive modified resin layer include the same particles as those described above.

  Moreover, a well-known method can be used as a method of apply | coating a coating liquid. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc. can be mentioned. Or it can carry out in combination. In addition, about the film for lens sheets with an adhesion modification resin layer of the present invention, when evaluating the characteristics of the film surface shape, for example, a film obtained by removing the adhesion modification resin layer from a solvent such as methyl ethyl ketone is used. Can be evaluated.

  In the present invention, the lens sheet is a resin sheet provided with a light condensing function, and is used as an optical member of a liquid crystal display device, a screen projection device, and other display devices. The condensing functional layer applied to the film of the present invention as a lens sheet is not particularly limited as long as it has a condensing function, and examples thereof include a prism lens, a microlens, and a Fresnel lens. Examples of the resin for forming such a condensing functional layer include an ultraviolet curable type or an electron beam curable type acrylic resin.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with modifications within a scope that fits the gist of the present invention. All of these are possible within the scope of the present invention. Moreover, about the characteristic and physical property of the obtained film, it evaluated using the following method.

(1) Intrinsic Viscosity of Polyester Resin 0.1 g of polyester was dissolved in 25 g of a mixed solution of phenol / tetrachloroethane (volume ratio 3/2) and measured at 30 ° C. using an Ostwald viscometer.

(2) Thickness of outermost layer (inactive particle-containing layer) A base film for a lens sheet was cut out perpendicular to the film flow direction and embedded with a photo-curing resin. The embedded sample was made into an ultrathin section having a thickness of about 70 to 100 nm with a microtome and stained in ruthenium tetroxide vapor for 30 minutes. This dyed ultrathin section was cross-sectionally observed using a transmission electron microscope (TEM 2010, manufactured by JEOL Ltd.), and the thickness of the outermost layer (inactive particle-containing layer) was determined from the position of the inert particles. The observation magnification was appropriately set in the range of 1500 to 10,000 times.

(3) Evaluation of protrusion shape on outermost layer surface Prepare a base film for a lens sheet prepared without providing an adhesive modification resin layer in each example and comparative example, and cut out the base film for a lens sheet at an arbitrary location. Then, using an atomic force microscope (SII, SPI3800), observation mode = DFM mode, scanner = FS-20A, cantilever = DF-3, observation field = 5 × 5 μm ² , resolution 1024 × 512 pixels Surface morphology was observed to obtain an observed image. Subsequently, the cross-sectional profile display mode of the same measurement visual field was displayed. On the cross-sectional movement screen, the cursor was moved at both ends so as to be along the longitudinal direction of the surface protrusion having a height of 2 nm or more and so as to pass through the maximum height position of the surface protrusion. The distance between two intersections where the cross-sectional profile curve and the 0 nm-high line that is the average height line within the measurement range intersect was read, and the diameter of the surface protrusion was measured. Furthermore, the height of the surface protrusion is measured with a height of 0 nm which is an average height line within the measurement range. From the observation image thus obtained, for at least 100 protrusions having a height of 2 nm or more, the diameter L of the protrusions and the height h of the protrusions are measured to calculate the ratio L / h of the diameter and the height. The ratio of protrusions where h is 50 or less was calculated.

(4) Haze, total light transmittance In each example and comparative example, a lens sheet base film prepared without providing an adhesive modified resin layer, and a lens sheet base film with an adhesive modified layer were prepared. According to JIS-K7105, the haze and total light transmittance of the base film were measured using a turbidimeter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

(5) Three-dimensional surface roughness (SRa, SRz) of the outermost layer surface
In each example and comparative example, a lens sheet base film prepared without providing an adhesive modified resin layer was prepared, and the outermost surface of the lens sheet base film was measured with a stylus type three-dimensional roughness meter (SE- 3AK (manufactured by Kosaka Laboratory Co., Ltd.) using a needle radius of 2 μm and a load of 30 mg with a cut-off value of 0.25 mm in the longitudinal direction of the film, a measurement length of 1 mm, and a needle feed rate of 0. The measurement was performed at 1 mm / second, divided into 500 points at a pitch of 2 μm, and the height of each point was taken into a three-dimensional roughness analyzer (SPA-11). The same operation was performed 150 times continuously at intervals of 2 μm in the width direction of the film, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Next, the center plane average roughness (SRa) and the ten-point average roughness (SRz) were determined using an analyzer.

(6) Average particle diameter of inert particles, number of particles of 10 μm or more Inert particles are observed with a scanning electron microscope (manufactured by Hitachi, Ltd., S-51O type), and the magnification is appropriately changed according to the size of the particles. An enlarged copy of the photo was taken. Next, the outer circumference of each particle was traced for at least 200 particles selected at random, the equivalent circle diameter of the particles was measured from these trace images with an image analyzer, and the average of these was taken as the average particle diameter. Further, the ratio of particles of 10 μm or more was calculated from the particle diameter of 200 or more particles thus obtained.

(7) Scratch and foreign matter detection method In each example and comparative example, a lens sheet base film prepared without providing an adhesive modified resin layer was prepared, and 100 mm × 100 mm was obtained using an optical defect detection apparatus described below. The 20 film pieces were inspected and converted into the number of defects per 1 m ² .

(Optical defect detection method)
The produced film piece is sandwiched between two polarizing plates to form a crossed Nicol state and set to a state where the vanishing position is maintained. In this state, Nikon Universal Projector V-12 (projection lens 50x,
Inspection is performed using the transmitted illumination light beam switching knob 50x, transmitted light inspection). When there are scratches and foreign matter on the film piece, light having a major axis of 20 μm or more that is transmitted through the part and appears to shine is detected.

(Scratch depth measurement)
From the defect portions detected by the above-described optical defect detection method, defects due to scratches were selected. Further cut out to an appropriate size, and observed from a direction perpendicular to the film surface using a three-dimensional non-contact shape measurement system Micromap MM500N-M100 (manufactured by Ryoka System, measurement conditions: wave mode, objective lens 10 times). The cross-sectional shape of the scratch was measured. The height difference of the scratch (difference between the highest place and the lowest place) was calculated from this cross-sectional shape. The number of scratches having an elevation difference of 0.3 μm or more was measured.

(Measurement of foreign substance size)
Defects due to foreign matters were selected from the defect portions detected by the optical defect detection method described above. Furthermore, it cut out to a suitable magnitude | size, and observed with the transmitted light using the optical microscope, and made the maximum diameter of the part observed as an optically abnormal range the magnitude | size (major axis) of a foreign material. The optically abnormal range refers to a range in which light leaks and transmits when in a crossed Nicol state (dark field). When a cavity (void) existing around the foreign object is observed as an optically abnormal range, the size of the foreign object including the cavity is set. The number of foreign matters having a size of 20 μm or more thus measured was measured.

Example 1
(Preparation of adhesive modified resin solution)
(Synthesis of copolymer polyester resin)
Dimethyl terephthalate (95 parts by mass), dimethyl isophthalate (95 parts by mass), ethylene glycol (35 parts by mass), neopentyl glycol (145 parts by mass), zinc acetate (0.1 parts by mass) and antimony trioxide (0. 1 part by mass) was charged into a reaction vessel, and a transesterification reaction was performed at 180 ° C. over 3 hours. Next, 5-sodium sulfoisophthalic acid (6.0 parts by mass) was added and the esterification reaction was performed at 240 ° C. over 1 hour, and then at 250 ° C. under reduced pressure (10 to 0.2 mmHg) for 2 hours. The polycondensation reaction was carried out to obtain a copolymerized polyester resin (A) having a number average molecular weight of 19,500 and a glass transition temperature of 62 ° C.
300 parts by mass of the obtained copolyester resin and 140 parts by mass of butyl cellosolve were stirred at 160 ° C. for 3 hours to obtain a viscous melt, water was gradually added to the melt, and a uniform light white color was added after 1 hour. An aqueous dispersion having a solid concentration of 30% was obtained.

(Synthesis of polyurethane resin)
100 parts by mass of a polyester diol (OHV: 2000 eq / ton) having a composition of adipic acid // 1.6-hexanediol / neopentyl glycol (molar ratio: 4/2/2/3), and 41.4 xylylene diisocyanate After mixing by mass and reacting at 80 to 90 ° C. for 1 hour under a nitrogen stream, the mixture was cooled to 60 ° C. and dissolved by adding 70 parts by mass of tetrahydrofuran to obtain a urethane prepolymer solution (NCO / OH ratio: 2.2). , Free isocyanate group: 3.30% by mass). Subsequently, the urethane prepolymer solution was brought to 40 ° C., then, 45.5 parts by mass of a 20% by mass aqueous sodium bisulfite solution was added, and the mixture was reacted at 40-50 ° C. for 30 minutes while vigorously stirring. After confirming the disappearance of the free isocyanate group content (in terms of solid content), the aqueous solution of the self-crosslinking polyurethane resin containing an isocyanate group diluted with emulsified water and blocked with sodium bisulfite having a solid content of 20% by mass (B) Got. The glass transition temperature was 45 ° C.

  7.5 parts by mass of a 30% by mass aqueous dispersion of the obtained copolymer polyester (A), 11.3 parts by mass of a 20% by mass aqueous solution of self-crosslinking polyurethane (B), catalyst (dibutyltin laurate) ) 0.02 parts by mass, water 37.9 parts by mass and isopropyl alcohol 39.6 parts by mass. Further, 0.3 parts by mass of a 10% by mass aqueous solution of a fluorine-based nonionic surfactant, 2.3 parts by mass of a 20% by mass aqueous dispersion of spherical silica having an average particle size of 40 nm as particles A, and average particles as particles B 0.5 parts by mass of a 3.5 mass% aqueous dispersion of dry silica having a diameter of 200 nm (average primary particle diameter of 40 nm) was added. Next, the pH of the coating solution was adjusted to 6.2 with an aqueous sodium bicarbonate solution, and the solution was precisely filtered with a filter having a filtration particle size (initial filtration efficiency: 95%) of 10 μm to obtain an adhesive modified resin solution.

(Preparation of PET pellet B)
Amorphous bulk silica particles having an average particle size of 2.3 μm and a pore volume of 1.6 ml / g were dispersed in ethylene glycol to prepare an ethylene glycol slurry containing 15 mass% of the amorphous bulk silica particles.

86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol, and antimony trioxide and magnesium acetate (tetrahydrate) are 250 ppm as Mg atoms and 250 ppm as Mg atoms with respect to the resulting polyethylene terephthalate (PET). After adding 65 ppm, the mixture was stirred. Thereafter, the glycol slurry was added to 2000 ppm with respect to the generated PET while being kept at 30 ° C. or lower, and then the temperature was increased by pressurizing with nitrogen. The esterification reaction was carried out at 240 ° C. for 2 hours under a pressure of 3.5 kg / cm ² G (gauge pressure: 0.34 MPa). The obtained esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C.

  After completion of the polycondensation reaction, it is extruded into a strand form from a nozzle, cooled and solidified using cooling water that has been previously filtered (pore size: 1 μm or less), cut into pellets, and has an intrinsic viscosity of 0 containing inert particles. A resin pellet B of .62 dl / g was produced.

(Preparation of lens sheet base film)
A polyethylene terephthalate (PET) resin pellet A containing no inert particles and having an intrinsic viscosity of 0.62 dl / g was dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours. Subsequently, the dried PET pellets were supplied to the A layer extruder (1). As a raw material for layer B, resin pellet B having an intrinsic viscosity of 0.62 dl / g, containing 2000 ppm of the above-described resin pellet A and irregular-shaped massive silica particles having an average particle size of 2.3 μm and a pore volume of 1.6 ml / g Were mixed at a ratio of 90:10, and then dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours. Next, the dried PET pellets were supplied to the B layer extruder (2). After the polymer supplied to the extruder is melted at 285 ° C., each is filtered with a filter medium having a filtration particle size (initial filtration efficiency of 95%) of 15 μm, and laminated so as to be B layer / A layer / B layer, After adjusting the discharge rate of the extruder so that the lamination ratio becomes 8/84/8, it is extruded in a layer form from a T die at 285 ° C., and solidified tightly on a rotary cooling roll at 25 ° C. to obtain an unstretched PET film It was.

The obtained unstretched PET film was heated to 95 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a peripheral speed difference to obtain a uniaxially oriented PET film. . Next, the adhesive modified resin liquid is microfiltered with a filter medium having a filtration particle size (initial filtration efficiency: 95%) of 10 μm, and uniaxially oriented by a roll coating method so that the coating amount after drying becomes 7 mg / m ^2. It apply | coated to the single side | surface of PET film.

  Subsequently, this uniaxially stretched PET film was guided to a clip-type transverse stretching machine, stretched 4.0 times in the transverse direction at 130 ° C, then heat-set at 230 ° C, and then 3% relaxed in the transverse direction at 200 ° C. Thus, a base film for a lens sheet having a thickness of 188 μm was obtained.

(Example 2)
In Example 1, a lens sheet base film was obtained in the same manner as in Example 1 except that the film thickness was 250 μm.

(Example 3)
In Example 1, a base film for a lens sheet was obtained in the same manner as in Example 1 except that the ratio of B layer / A layer / B layer was set to 12/76/12.

(Comparative Example 1)
In Example 1, instead of the resin pellet B, 2000 ppm of amorphous bulk silica having an average particle diameter of 1.3 μm obtained by removing coarse particles by sieving the bulk silica having an average particle diameter of 2.3 μm through a sieve. A base film for a lens sheet was obtained in the same manner as in Example 1 except that the resin pellet D having an intrinsic viscosity of 0.62 dl / g was used. Although the obtained film was excellent in transparency, scratches generated in the film forming process could not be reduced. Moreover, the aggregation foreign material by a silica was confirmed.

(Comparative Example 2)
A base film for a lens sheet was obtained in the same manner as in Example 1, except that the ratio of B layer / A layer / B layer was changed to 3/94/3. Although the obtained film was excellent in transparency, process contamination due to particle dropping was likely to occur, and there was a tendency that scratches generated in the film forming process increased.

(Comparative Example 3)
In Example 1, instead of resin pellet B, resin pellet E having an intrinsic viscosity of 0.62 dl / g and containing 2000 ppm of irregular-shaped massive silica having an average particle size of 2.0 μm and a pore volume of 1.2 ml / g is used. A lens sheet base film was obtained in the same manner as in Example 1 except that. The obtained film was inferior in transparency, easily caused by process contamination due to dropping of particles, and tended to increase scratches generated in the film forming process.

(Comparative Example 4)
In Example 1, instead of resin pellet B, resin pellet E having an intrinsic viscosity of 0.62 dl / g and containing 2000 ppm of irregular-shaped massive silica having an average particle diameter of 3.5 μm and a pore volume of 1.6 ml / g is used. A lens sheet base film was obtained in the same manner as in Example 1 except that. The obtained film was inferior in transparency and had many fish-eye-like foreign matters.

(Comparative Example 5)
In Example 1, a lens sheet base film was obtained in the same manner as in Example 1 except that the ratio of resin pellet A to resin pellet B was 75:25. The obtained film was inferior in transparency.

  The film for lens sheets of the present invention is excellent in transparency and has few optical defects. Therefore, by using the lens sheet film of the present invention as the base film of the lens sheet, it is possible to easily obtain a lens sheet with few optical defects and excellent brightness enhancement performance.

Claims (5)

A biaxially oriented polyester film having a laminated structure of three or more layers by a coextrusion method,
Both outermost layers of the film contain inert particles having an average particle size of 2.1 to 2.5 μm,
The thickness of the outermost layer is 5 times or more and less than 11 times the average particle size of the inert particles,
Of the surface protrusions with a height of 2 nm or more observed by the atomic force microscope (AFM) on the outermost layer surface, the surface protrusion whose ratio L / h of the diameter L of the surface protrusion to the height h of the surface protrusion is 50 or less The ratio of the number is 30% or less,
Base film for lens sheets.   2. The lens according to claim 1, wherein the center surface average roughness (SRa) of the outermost layer surface is 0.008 to 0.015 μm and the ten-point average roughness (SRz) is 0.5 to 1.5 μm. Base film for sheet.   The inert particles in the outermost layer are amorphous bulk silica having a pore volume of 1.5 to 2.0 ml / g, and the inert particle content in the outermost layer is 0.015 to 0.030% by mass. The base film for lens sheets according to any one of claims 1 and 2.   The base film for a lens sheet according to any one of claims 1 to 3, wherein the number of particles having a particle diameter of 10 µm or more among the inert particles is 1% or less.   The base film for lens sheets with an adhesive property modification resin layer which has an adhesive property modification resin layer in the at least single side | surface of the base film for lens sheets in any one of Claim 1 to 4.