JP5604994B2 - Lens sheet base film - Google Patents

Description

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

  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 generated in the film forming process.

  Then, in order to reduce the oligomer in a polyester film, it is proposed to propose the oligomer amount of the polyester raw material by a solid phase polymerization method (patent documents 1 to 4).

  On the other hand, 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 5 and Patent Document 6 propose to use both inert particles having different particle sizes to achieve both transparency and scratch resistance. Patent Document 7 proposes that the surface layer portion of the 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-A-9-99530 JP 2000-141570 A JP 2003-191413 A Japanese Patent Laid-Open No. 2003-301057 Japanese Patent No. 3311591 Japanese Patent No. 3235759 JP 2003-231229 A

  However, in the methods proposed in Patent Documents 1 to 4, although the amount of oligomer in the polyester can be reduced by solid phase polymerization, the polycondensation reaction of the polyester proceeds at the same time, and the degree of polymerization of the obtained polyester is increased. For this reason, the intrinsic viscosity of the polyester is increased, and the load during extrusion molding is increased, or the temperature of the polyester is increased by shearing heat generation, which may cause thermal decomposition. Moreover, although the amount of oligomers can be reduced by these, it is inevitable that oligomers are generated as by-products due to the thermal history in film melt film formation.

  Furthermore, the display definition has been greatly improved, and it has been considered that 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 5 to 7. However, if fine particles with an average particle size of 1 μm or less are used as in Patent Documents 5 and 6, they cannot be uniformly dispersed in the resin due to the aggregation of the fine particles, and the fisheye-like defects are generated by the aggregated particles. However, the optical defects could not be suppressed to a level that can solve the above problems.

  Further, as in Patent Document 7, if the resin layer is 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.

  In this way, measures have been established to stably obtain a high-quality lens sheet film with less oligomer precipitation and fewer optical defects, which can respond to future high definition and productivity improvements. I found out that it was not.

  As a result of intensive studies to solve the above problems, the present inventors have found that the oligomer regenerated when the polyester is melted depends on the amount of hydroxyl (OH) ends of the molecular chain, and further contains an inert particle-containing layer. By controlling the surface protrusions having a specific ratio of the thickness of the protrusion and the particle diameter of the inert particles and the ratio of the specific protrusion diameter to the protrusion height, there are few optical defects due to powder falling or oligomer precipitation, This led to the provision of highly transparent films.

1st invention in this invention which can solve the said subject is a biaxially oriented laminated polyester film, Comprising: It is the base film for lens sheets which satisfy | fills the following structural requirements (1)-(7).
(1) It has a laminated structure of three or more layers by a coextrusion method.
(2) Both outermost layers of the film contain inert particles having an average particle diameter of 2.1 to 2.5 μm. (3) The thickness of the outermost layer is not less than 5 times and less than 11 times the average particle diameter of the inert particles. (4) Of the surface protrusions having a height of 2 nm or more observed by the atomic force microscope (AFM) on the outermost surface, the ratio L / h of the surface protrusion diameter L to the surface protrusion height h is 50 or less. The ratio of the number of surface protrusions is 30% or less. (5) Change in film haze ΔHz (ΔHz = haze after heating haze before heating) when heated at 170 ° C. for 20 minutes is less than 1.0 (6) At least the hydroxyl (OH) terminal amount in the outermost polyester layer is 70 eq / ton or less. (7) The cyclic trimer content in at least the outermost layer is 0.45% by mass or less.

  In a second aspect of the present invention, 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. The lens sheet base film.

  In a third aspect of the present invention, 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. It is the said base film for lens sheets which is 0.015-0.03 mass%.

  4th invention in this invention is the said base film for lens sheets whose number of the particles which have a particle size of 10 micrometers or more among the said inert particles is 1% or less of the whole.

  5th invention in this invention is a 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 said base film for lens sheets.

6th invention in this invention is a manufacturing method of the said polyester film, Comprising: It is a manufacturing method of the polyester film using the polyester resin which heat-processed satisfy | fills the following requirements (8)-(10).
(8) A crude polyester having an intrinsic viscosity of 0.50 to 0.70 dl / g obtained by a polycondensation reaction between a dicarboxylic acid component and a glycol component has a water content of 3.5 to 30.0 g / Nm ³ . (9) Heat treatment is performed at 190 ° C. to 260 ° C. (10) Changes in the intrinsic viscosity of the polyester are as follows. Heat treatment is performed so as to satisfy the equation −0.05 dl / g ≦ Intrinsic viscosity before heat treatment−Intrinsic viscosity after heat treatment ≦ 0.05 dl / g

  The film obtained by the present invention is excellent in transparency, the precipitation of oligomers is suppressed, and the generation of minute scratches in the processing process and the film forming process is small. 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.

  The film haze change ΔHz (ΔHz = haze before heating haze before heating) when the biaxially oriented laminated polyester film of the present invention is heated at 170 ° C. for 20 minutes needs to be less than 0.5. In the case where ΔHz is 0.5 or more, oligomers may precipitate in the film post-processing step, which may contaminate the step. On the contrary, when ΔHz is less than 0.5, whitening by heating is suppressed even in heat treatment in post-processing, and it can be suitably used in optical applications. In the invention, the preferable upper limit of ΔHz is 0.3, more preferably 0.1. ΔHz is preferably small, and the lower limit of ΔHz is zero.

  It is important that the hydroxyl (OH) terminal amount in at least the outermost polyester layer of the biaxially oriented laminated polyester film of the present invention is 70 eq / ton or less. Since the polyester film of the present invention has a hydroxyl (OH) terminal amount reduced to the above range, the production of a cyclic trimer can be suitably reduced. Therefore, regeneration of the cyclic trimer in the melting step at the time of film formation can be suppressed, and the low oligomer amount of the film raw material can be suitably maintained. The hydroxyl (OH) terminal amount is more preferably 68 eq / ton or less, and still more preferably 65 eq / ton or less. The hydroxyl (OH) terminal amount is preferably small, but if it is too small, hydrolysis of the polyester resin tends to occur. Therefore, from the viewpoint of the durability of the film, the lower limit of the hydroxyl (OH) terminal amount is preferably 40 eq / ton or more, and more preferably 50 eq / ton or more. In the present invention, it is important to find out the influence of hydroxyl (OH) terminal in the polyester resin on oligomer regeneration, and the method for controlling the amount of hydroxyl (OH) terminal of the polyester film is not particularly limited. By performing the heat treatment under an atmosphere, the amount of hydroxyl (OH) end can be suitably controlled.

  The cyclic trimer content in at least the outermost layer of the biaxially oriented laminated polyester film of the present invention needs to be 0.45% by mass or less. When the cyclic trimer content is 0.45% by mass or more, oligomers are precipitated in the film-forming process, and heat whitening is likely to occur, or the film-forming process and subsequent processes are contaminated with optical defects. May occur. In order to make the amount of the cyclic trimer of the polyester film within the above range, it is preferable to heat-treat the polyester raw material. However, in the present invention, by reducing the amount of terminal hydroxyl (OH), the cyclic trimer in the film is reduced. The body weight can be suitably reduced within the above range. The upper limit of the preferable cyclic trimer content in the present invention is 0.40% by mass. Although the amount of cyclic trimer is preferably small, in view of productivity, the lower limit of the amount of cyclic trimer is preferably 0.05% by mass, more preferably 0.10% by mass, and 0.20% by mass. % Is more preferable.

  The intrinsic viscosity of the biaxially oriented laminated polyester film of the present invention is preferably in the range of 0.40 dl / g to 0.68 dl / g. When the intrinsic viscosity is lower than 0.40 dl / g, the film is easily torn, and when it is higher than 0.70 dl / g, the increase in filtration pressure is increased and high-precision filtration becomes difficult. The upper limit of the intrinsic viscosity of PET is preferably 0.65 dl / g, more preferably 0.63 dl / g. Furthermore, the lower limit is preferably 0.50 dl / g, more preferably 0.55 dl / g.

  The film of the present invention comprises a polyester resin obtained by a polycondensation reaction between a dicarboxylic acid component and a glycol component. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and examples of the glycol component include ethylene glycol, diethylene glycol, 1,4-butanediol, and neopentyl glycol. In the present invention, polyethylene terephthalate and polyethylene naphthalate are preferable from the viewpoint of strength and transparency, and polyethylene terephthalate is particularly preferable.

  Polymerization of polyethylene terephthalate (hereinafter simply referred to as PET) includes direct polymerization of terephthalic acid and ethylene glycol and, if necessary, other dicarboxylic acid components and diol components directly, and dimethyl ester of terephthalic acid (required) Depending on the method, any production method such as a transesterification method in which a transesterification reaction of ethylene glycol (including other diol components as necessary) and ethylene glycol (including other dicarboxylic acid methyl esters) can be used.

  The intrinsic viscosity of the polyester is preferably in the range of 0.45 dl / g to 0.70 dl / g. When the intrinsic viscosity is lower than 0.45 dl / g, the film is easily torn, and when it is higher than 0.70 dl / g, the increase in filtration pressure is increased and high-precision filtration becomes difficult. The upper limit of the intrinsic viscosity of PET is preferably 0.68 dl / g, more preferably 0.65 dl / g. Further, the lower limit is preferably 0.48 dl / g, more preferably 0.50 dl / g.

  Conventionally known Mn, Mg, Ca, Ti, Ge, Al, Sb, Co compound, phosphorus compound, antimony compound and the like are used as a catalyst for preparing the crude polyester. A method of deactivating the catalyst has been proposed as a method for suppressing the regeneration of the oligomer when the polyester is melted. However, in the present invention, the regeneration of the oligomer can be suitably suppressed without going through the steps. Here, “crude polyester” is expressed by classifying polyester before heat treatment described later.

  The composition containing the dicarboxylic acid component and the glycol component includes a stabilizer, a pigment, a dye, a nucleating agent, a filler, an ultraviolet absorber, an antioxidant, an antibacterial agent, and an antistatic agent, depending on the final use of the polyester. Additives such as lubricants and mold release agents can be contained.

  Next, the obtained crude polyester is appropriately formed into a chip shape (for example, a cylindrical shape), a particle shape, or the like by a sheet cutting method, a strand cutting method, or the like. For example, in forming a chip, a melt of crude polyester is extruded from a die with a gear pump to form a strand, and this strand is cut with a cutter, and a major axis × minor axis × length is about 2.2 × 3.1 ×. A 3.4 mm elliptical columnar chip is formed. By molding into such a chip shape, the humidity control effect can be suitably exerted to the inside of the chip while suitably reducing the oligomer amount of the film raw material by heat treatment described later.

  Examples of a method for reducing the hydroxyl (OH) terminal amount of polyester include a method of increasing the molecular weight of polyester to reduce the terminal amount per unit, and a method of water-saturating a raw material chip. Among them, in the present invention, the crude polyester as a film raw material is preferably heat-treated in a water atmosphere, so that the oligomer content can be suitably reduced and the hydroxyl (OH) terminal amount can be suitably reduced. The heat treatment is characterized by performing a high-temperature heat treatment at 190 to 260 ° C. under a flow rate of a moisture-containing inert gas containing water. By performing the heat treatment under an inert gas flow rate, oligomers can be suitably reduced without increasing the PET intrinsic viscosity more than necessary. This point is different from the conventional solid phase polymerization. Further, unlike the solid phase polymerization method conventionally performed by the batch method, the productivity is excellent in that the treatment can be continuously performed under a flow rate.

  Furthermore, the amount of hydroxyl (OH) ends in the polyester resin can be suitably reduced by performing the heat treatment in a predetermined water atmosphere. The reason why the amount of hydroxyl (OH) ends is reduced in a water atmosphere is considered as follows. That is, the hydroxyl (OH) ends are bonded by a deethylene glycol reaction by heat treatment, and the hydroxyl (OH) ends are consumed. On the other hand, the reverse reaction of the ester reaction occurs in a water atmosphere, the polyester molecular weight is reduced, and a new molecular chain end is generated. Since these reactions occur as a mixture, it is believed that the resulting hydroxyl (OH) end will be reduced.

The heat treatment conditions for the crude polyester in the present invention are described in detail below.
In the heat treatment, the water content in the inert gas is preferably 3.5 to 30.0 g / Nm ³ , more preferably 4.0 to 20.0 g / Nm ³ . When the moisture content in the humidity control inert gas is less than 3.5 g / Nm ³ , the increase in intrinsic viscosity of the resulting polyester is remarkable. When the moisture content in the humidity control inert gas is excessive, a hydrolysis reaction may occur, and the intrinsic viscosity of the resulting polyester may be reduced.

  As the inert gas, a gas inert to polyester is used, and examples thereof include nitrogen gas, carbon dioxide gas, and helium gas. Nitrogen gas is particularly preferable because it is inexpensive.

  As the heat treatment apparatus, an apparatus that can uniformly contact the crude polyester and the inert gas is desirable. Examples of such a heat treatment apparatus include a stationary dryer, a rotary dryer, a fluidized bed dryer, and a dryer having a stirring blade.

  Further, it is more preferable to partially crystallize the polymer in order to appropriately remove moisture from the polyester before the heat treatment and to prevent fusion of the polymers during the heat treatment.

  In heat processing, heat processing temperature becomes like this. Preferably it is 190 to 260 degreeC, More preferably, it is 200 to 250 degreeC. When the heat treatment temperature is less than 190 ° C., the rate of reduction of the cyclic trimer in the crude polyester may be small. When the heat treatment temperature exceeds the melting point of the polyester, the polyester melts and adhesion is likely to occur. Therefore, it is difficult to take out the obtained polyester from the heat treatment apparatus, and the molding operation may be difficult.

  The heat treatment time is usually preferably 1 to 70 hours, more preferably 2 to 60 hours, and further preferably 4 to 50 hours. If it is less than 1 hour, the cyclic trimer in the crude polyester is not sufficiently reduced, and if it exceeds 70 hours, the rate of reduction of the cyclic trimer in the crude polyester is small, and conversely thermal degradation, etc. May occur, and the color tone is impaired.

  The flow rate of the inert gas is closely related to the intrinsic viscosity of the polyester. Further, the water content contained in the humidity control inert gas also affects the change in the intrinsic viscosity of the polyester. Therefore, the flow rate of the inert gas should be appropriately selected according to the water content, the desired intrinsic viscosity of the polyester, the heat treatment temperature, and the like.

  For example, when the moisture content of the humidity control inert gas is high, the flow rate is preferably increased in order to avoid adverse effects such as hydrolysis by water. Moreover, when making heat processing temperature high, in order to suppress the raise of the intrinsic viscosity of polyester, it is preferable to reduce the flow volume of an inert gas.

  The flow rate of the inert gas is preferably at least 1 liter per hour per kg of polyester, more preferably at least 5 liters. When the flow rate of the inert gas is less than 1 liter per hour per 1 kg of polyester, there is a risk of adverse effects such as yellowing of the resulting resin due to oxygen contamination. The upper limit of the flow rate of the inert gas is determined by the water content contained in the inert gas and the heat treatment temperature. 1,000 liters or less. Even if the flow rate of the inert gas is set to 10,000 liters or more, it does not deviate from the object of the present invention.

  The heat treatment of the present invention is carried out by heat treatment while circulating an inert gas under normal pressure to slightly pressurized pressure.

In this case, since the purpose of pressurization is to prevent moisture and oxygen in the atmosphere from being mixed into the reactor during the heat treatment, the pressurization condition of 5.0 kg / cm ² or less is sufficient. Even when the pressurization condition exceeds 5.0 kg / cm ² , the object of the present invention is not deviated, but since the equipment is costly, it is meaningless to increase the pressure more than necessary.

  Furthermore, the oxygen concentration in the inert gas circulated from the viewpoint of color tone is required to be 50 ppm or less, preferably 25 ppm or less. When the oxygen concentration is 50 ppm or more, the color tone deteriorates due to the deterioration of the polyester of the present invention, specifically, yellowing is severe, resulting in a problem in product quality.

The polyester thus obtained preferably satisfies the following formula.
−0.05 dl / g ≦ Intrinsic viscosity before heat treatment −Intrinsic viscosity after heat treatment ≦ 0.05 dl / g

  By these treatments, the intrinsic viscosity (B) of the polyester composition after the heat treatment is preferably 0.50 dl / g or more and 0.70 dl / g or less, and further the intrinsic viscosity of the polyester composition (crude polyester) before the heat treatment. Between (A) and -0.05 dl / g≤ {(A)-(B)} ≤0.05 dl / g, and preferably -0.02 dl / g≤ {(A) -(B)} ≦ 0.02 dl / g is preferably satisfied. By setting the intrinsic viscosity (B) after the heat treatment to 0.50 dl / g or more, the occurrence of film breakage during film formation is reduced, which is advantageous. Moreover, by setting it as 0.70 dl / g or less, it can reduce that a temperature rises by the shear heat_generation | fever at the time of melt molding, and it is advantageous in suppressing the amount of oligomers in a product.

  Further, by satisfying −0.05 dl / g ≦ {(A) − (B)} ≦ 0.05 dl / g, there is no unnecessary temperature rise during film formation, and the amount of polyester oligomer is small and the color tone is reduced. In addition to obtaining a good film, it is not necessary to newly provide a low-viscosity or high-viscosity brand for a polyester composition (crude polyester) before heat treatment, and an existing polymer that can be used as another product is used. Thus, the amount of oligomer can be reduced, which is economically advantageous.

  Further, the content of the cyclic trimer of the polyester composition after the heat treatment needs to be 0.4% by mass or less. More preferably, it is 0.35 mass%. When the content exceeds 0.4% by mass, the oligomer may be regenerated during film forming, and the oligomer may be deposited on the film surface during film production or in the film processing process, causing problems such as film production defects and film product defects. .

  Furthermore, the hydroxyl (OH) terminal amount of the polyester composition after heat treatment needs to be 65 eq / ton or less. The lower the hydroxyl (OH) terminal amount, the more the oligomer regeneration during the melt extrusion in the film forming process of the polyester raw material can be suppressed. 60 eq / ton or less is more preferable.

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 is conceivable. 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).

  As described above, the polyester having a reduced amount of the cyclic trimer can be applied to each layer of the film, but at least the polyester constituting the outermost layer is a polyester having a reduced amount of the cyclic trimer. Thereby, precipitation of the oligomer on the film surface can be suppressed suitably.

  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 diameter 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 diameter 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. 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 0.03% by mass, and more preferably 0.02 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 0.03 mass% or less, it is preferable when maintaining high transparency.

  As a result of studying how to reduce optical defects due to the provision of surface irregularities and powder fall off caused by high-speed processing, the present inventor has found that both of these characteristics are remarkably compatible when having a specific surface structure. I found out. That is, according to 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 with a height of 2 nm or more observed by the atomic force microscope (AFM) on the surface of the outermost layer. 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 present inventor does not determine the ease of particle removal depending on the height of the surface protrusion, but the shape of the peak of the surface protrusion 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. This is not preferable because the transparency is lowered. The upper limit of the thickness of the outermost layer was set to less than 11 times from the range in which the haze increase can be allowed. 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 fine scratches having a height difference of 0.3 μm are preferably 2 or less per 1 m ² , more preferably 1 or less, and even more preferably 0. . 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 per 1 m ² , more preferably 1 or less, and even more preferably 0. 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.

  Next, the effect of this invention is demonstrated using an Example and a comparative example. First, the evaluation method of the characteristic values used in the present invention is shown below.

[Evaluation method]
(1) Thickness of outermost layer (inert 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.

(2) Evaluation of protrusion shape on outermost layer surface Prepare a base film for lens sheet prepared without providing an adhesive modified resin layer in each example and comparative example, and cut out the base film for lens sheet at any place 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.

(3) Total light transmittance A base film for a lens sheet prepared without providing an adhesive modification resin layer in each example and comparative example, and a base film for a lens sheet with an adhesive modification layer were prepared. According to K7105, the haze and total light transmittance of the base film were measured using a turbidimeter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

(4) 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.

(5) Average particle diameter of inert particles, number of particles of 10 μm or more Inactive particles are observed with a scanning electron microscope (manufactured by Hitachi, 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.

(6) 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. 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, the Nikon universal projector V-12 (projection lens 50x, transmitted illumination light beam switching knob 50x, transmitted light inspection) is used for 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.

(7) Haze Measured according to JIS K 7105 “Testing method for optical properties of plastic” haze (cloudiness value). NDH-300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measuring instrument.

(8) Evaluation of Haze Change (ΔHz) The film was cut into a 50 mm square, and the haze before heating was measured according to JIS K 7105 “Testing Method for Optical Properties of Plastics” haze (cloudiness value). NDH-300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measuring instrument. After the measurement, the film is set in an oven heated to 170 ° C., and the film is taken out after 20 minutes. After heating, the film is measured for haze by the same method as described above to obtain haze after heating. The haze difference before and after heating is set to ΔHz.
ΔHz = (Haze after heating) − (Haze before heating)

(9) Hydroxyl (OH) terminal amount of polyester film or polyester resin The polyester film or resin was finely pulverized, and 15 mg was weighed. After completely dissolving in 0.1 ml of hexafluoroisopropanol (HFIP) -d2, it was diluted with 0.6 ml of deuterated chloroform. Furthermore, in order to shift the OH group peak of HFIP, 30 μl of pyridine-d5 was added, and measurement was performed by H-NMR (BBO-5 mm probe).

(10) Cyclic trimer amount The polyester film or polyester resin was finely pulverized, and 0.1 g was dissolved in 3 ml of a mixed solvent of hexafluoroisopropanol (HFIP) / chloroform (2/3 (volume ratio)). To the resulting solution, 20 ml of chloroform was added and mixed uniformly. 10 ml of methanol was added to the resulting mixture to reprecipitate the linear polyester. Next, this mixed solution was filtered, and the precipitate was washed with 30 ml of a mixed solvent of chloroform / methanol (2/1 (volume ratio)) and further filtered. The obtained filtrate was concentrated to dryness on a rotary evaporator. 10 ml of dimethylformamide was added to the concentrated dried product to prepare a cyclic trimer measurement solution. This measurement solution was quantified using LC100 type high performance liquid chromatography manufactured by Yokogawa Electric Corporation.

(11) Amount of cyclic trimer of outermost layer Using an unstretched sheet, the surface trimmed from the surface to a portion of 50% or less of the thickness of the outermost layer, and the amount of cyclic trimer is quantified using the same method as above. .

(11) Intrinsic viscosity 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60/40 (weight ratio)), and an Ostwald viscometer was used at 30 ° C. It was measured. The unit is dl / g.

(12) Melting | fusing point measurement It measured with the differential thermal analyzer (DSC) by Seiko-electronic industry Co., Ltd., RDC-220. Using 10 mg of the sample, the temperature was raised at a rate of temperature rise of 20 ° C./min and held at 290 ° C. for 3 minutes. The peak temperature of the melting peak observed when the temperature was raised was defined as the melting point (Tm).

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 the 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 polyester resin (A))
1,000 parts of dimethyl terephthalate, 700 parts of ethylene glycol, and 0.3 part of zinc acetate dihydrate were charged into a transesterification reaction can and subjected to a transesterification reaction at 120 to 210 ° C., and the produced methanol was distilled off. When the transesterification reaction was completed, 0.13 phosphoric acid and 0.3 part antimony trioxide were added, and the pressure in the system was gradually reduced to 1 mmHg or less in 75 minutes. At the same time, the temperature was gradually raised to 280 ° C. A polycondensation reaction was carried out for 70 minutes under the same conditions, and the molten polymer was extruded into water from a discharge nozzle and formed into a cylindrical chip having a diameter of about 3 mm and a length of about 5 mm by a cutter. The obtained crude polyester had an intrinsic viscosity of 0.610 dl / g, a hydroxyl (OH) terminal amount of 70 eq / ton, a cyclic trimer content of 1.05% by mass, and a melting point of 252 ° C. It was. In the examples, “parts” are all parts by weight. Let the obtained crude polyester be a polyester resin (A).

The polyester resin (A) was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 6.4 g / Nm ³ was circulated at a rate of 70 liters per kg of crude polyester at 207 ° C. For 48 hours. The obtained polyester had an intrinsic viscosity of 0.631 dl / g, a hydroxyl (OH) end amount of 59 eq / ton, and a cyclic trimer content of 0.27% by mass. Let the obtained crude polyester be a polyester resin (B).

(Creation of polyester resin (C))
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 of terephthalic acid and 64.4 parts of ethylene glycol, and antimony trioxide and magnesium acetate (tetrahydrate) are 250 ppm as Sb atoms and 65 ppm as Mg atoms with respect to polyethylene terephthalate (PET). After the addition, it 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 performed 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. The hydroxyl (OH) terminal amount was 71 eq / ton, the content of the cyclic trimer was 1.03% by mass, and the melting point was 253 ° C. Let the obtained crude polyester be a polyester resin (C).

The polyester resin (C) was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 6.4 g / Nm ³ was circulated at a rate of 70 liters per kg of the crude polyester at 207 ° C. For 48 hours. The obtained polyester had an intrinsic viscosity of 0.639 dl / g, a hydroxyl (OH) terminal amount of 58 eq / ton, and a cyclic trimer content of 0.28% by mass. Let the obtained crude polyester be a polyester resin (D).

(Preparation of lens sheet base film)
The polyester resin (A) as a raw material for the A layer was dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours. Subsequently, the polyester resin (A) after drying was supplied to the extruder for A layer (1). As the raw material for the B layer, the above-mentioned polyester resin (B) and polyester resin (D) were mixed at a ratio of 90:10, and then dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours. Subsequently, the mixed polyester resin after drying was supplied to the extruder for B layer (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 PET is applied by a roll coating method so that the coating amount after drying becomes 7 mg / m 2. It was applied to one side of the 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.

Example 4
(Preparation of polyester resin E)
The polyester resin (A) was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a moisture content of 15.3 g / Nm ³ was circulated at 300 liters per kg of crude polyester at 12 hours at 230 ° C. Heat treatment was performed for a time. The obtained polyester had an intrinsic viscosity of 0.617 dl / g, a hydroxyl (OH) terminal amount of 63 eq / ton, and a cyclic trimer content of 0.28% by mass. Let the obtained crude polyester be a polyester resin (E).

(Preparation of polyester resin F)
The polyester resin (B) was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a moisture content of 15.3 g / Nm ³ was circulated at 300 liters per kg of crude polyester at 12 hours at 230 ° C. Heat treatment was performed for a time. The obtained polyester had an intrinsic viscosity of 0.617 dl / g, a hydroxyl (OH) terminal amount of 62 eq / ton, and a cyclic trimer content of 0.29% by mass. Let the obtained crude polyester be a polyester resin (F).

  A biaxially stretched polyethylene terephthalate film was obtained in the same manner as in Example 1, except that the polyester resin (B) used in the B layer of Example 1 was changed to the polyester resin (E) and the polyester resin (F).

(Example 5)
(Preparation of polyester resin G)
Using a method similar to the production of the polyester resin (A), the intrinsic viscosity is 0.648 dl / g, the hydroxyl (OH) terminal amount is 64 eq / ton, and the cyclic trimer content is 1.2. A crude polyester having a mass% and a melting point of 245 ° C. was obtained. The obtained crude polyester was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 15.3 g / Nm ³ was circulated at 300 liters per kg of the crude polyester at 220 ° C. Heat treatment was performed for 24 hours. The obtained polyester had an intrinsic viscosity of 0.623 dl / g, a hydroxyl (OH) terminal amount of 57 eq / ton, and a cyclic trimer content of 0.27% by mass. Let the obtained crude polyester be a polyester resin (G).

(Preparation of polyester resin H)
Using a method similar to the production of the polyester resin (C), the intrinsic viscosity is 0.648 dl / g, the hydroxyl (OH) terminal amount is 64 eq / ton, and the cyclic trimer content is 1.2. A crude polyester having a mass% and a melting point of 245 ° C. was obtained. The obtained crude polyester was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 15.3 g / Nm ³ was circulated at 300 liters per kg of the crude polyester at 220 ° C. Heat treatment was performed for 24 hours. The obtained polyester had an intrinsic viscosity of 0.623 dl / g, a hydroxyl (OH) terminal amount of 57 eq / ton, and a cyclic trimer content of 0.27% by mass. Let the obtained crude polyester be a polyester resin (H).

  A biaxially stretched polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the polyester resin (B) of Example 1 was changed to the polyester resin (G) and the polyester resin (D) was changed to the polyester resin (H).

(Example 6)
(Preparation of polyester resin (I))
Using a method similar to the production of the polyester resin (A), the intrinsic viscosity is 0.613 dl / g, the hydroxyl (OH) terminal amount is 70 eq / ton, and the cyclic trimer content is 1.03. A crude polyester having a mass% and a melting point of 255 ° C. was obtained. The polyester was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 6.4 g / Nm ³ was circulated at a rate of 70 liters per kg of the crude polyester. The pressure was adjusted to 2 kg / cm 2 and heat treatment was performed at 207 ° C. for 48 hours. The obtained polyester had an intrinsic viscosity of 0.629 dl / g, a hydroxyl (OH) terminal amount of 60 eq / ton, and a cyclic trimer content of 0.28 weight. Let the obtained crude polyester be polyester resin (I).

(Preparation of polyester resin (J))
Using the same method as the production of the polyester resin (C), the intrinsic viscosity is 0.613 dl / g, the hydroxyl (OH) terminal amount is 70 eq / ton, and the cyclic trimer content is 1.03. A crude polyester having a mass% and a melting point of 255 ° C. was obtained. The polyester was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a water content of 6.4 g / Nm ³ was circulated at a rate of 70 liters per kg of the crude polyester. The pressure was adjusted to 2 kg / cm 2 and heat treatment was performed at 207 ° C. for 48 hours. The obtained polyester had an intrinsic viscosity of 0.629 dl / g, a hydroxyl (OH) terminal amount of 60 eq / ton, and a cyclic trimer content of 0.28 weight. Let the obtained crude polyester be a polyester resin (J).

  A biaxially stretched polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the polyester resin (B) of Example 1 was changed to polyester resin (I) and the polyester resin (D) was changed to polyester resin (J).

(Comparative Example 1)
A biaxially stretched polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the polyester resin (B) of Example 1 was changed to the polyester resin (A) and the polyester resin (D) was changed to the polyester resin (C).

(Comparative Example 2)
(Creation of polyester resin (K))
The polyester resin (A) obtained in the same manner as in Example 1 was dried at 160 ° C. under reduced pressure, adjusted to a slight pressure of 0.1 kg / cm 2 under a nitrogen atmosphere, and heat-treated at 215 ° C. for 24 hours. It was. The obtained polyester had an intrinsic viscosity of 0.622 dl / g, a hydroxyl (OH) terminal amount of 73 eq / ton, and a cyclic trimer content of 0.30% by mass. Let the obtained crude polyester be a polyester resin (K).

(Creation of polyester resin (L))
The polyester resin (C) obtained in the same manner as in Example 1 was dried at 160 ° C. under reduced pressure, adjusted to a slight pressure of 0.1 kg / cm 2 under a nitrogen atmosphere, and heat-treated at 215 ° C. for 24 hours. It was. The obtained polyester had an intrinsic viscosity of 0.625 dl / g, a hydroxyl (OH) terminal amount of 74 eq / ton, and a cyclic trimer content of 0.30% by mass. Let the obtained crude polyester be a polyester resin (L).

  Biaxially stretched polyethylene terephthalate in the same manner as in Example 1 except that the polyester resin (B) used in the B layer of Example 1 is changed to the polyester resin (K) and the polyester resin (D) is changed to the polyester resin (L). A film was obtained.

(Comparative Example 3)
In Example 1, in place of the polyester resin (D), 2000 ppm of amorphous bulk silica having an average particle diameter of 1.3 μm obtained by sieving coarse silica having an average particle diameter of 2.3 μm through a sieve and removing coarse particles. A base film for a lens sheet was obtained in the same manner as in Example 1 except that the polyester resin having an intrinsic viscosity of 0.621 dl / g was used and the polyester resin (B) was changed to the polyester resin (A). 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 4)
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 5)
In Example 1, instead of the polyester resin (D), a polyester resin having an intrinsic viscosity of 0.620 dl / g and containing 2000 ppm of amorphous bulk silica having an average particle size of 2.0 μm and a pore volume of 1.2 ml / g is used. A base film for a lens sheet was obtained in the same manner as in Example 1 except that the polyester resin (B) was used and the polyester resin (A) was used. The obtained film was inferior in transparency, easily caused by process contamination due to dropping of particles, and had a tendency to increase scratches generated in the film forming process.

(Comparative Example 6)
In Example 1, instead of the polyester resin (D), a polyester resin having an intrinsic viscosity of 0.621 dl / g containing 2000 ppm of amorphous bulk silica having an average particle diameter of 3.5 μm and a pore volume of 1.6 ml / g was used. A base film for a lens sheet was obtained in the same manner as in Example 1 except that the polyester resin (B) was changed to the polyester resin (A). The obtained film was inferior in transparency and had many fish-eye-like foreign matters.

(Comparative Example 7)
In Example 1, a lens sheet base film was obtained in the same manner as in Example 1 except that the ratio of the polyester resin (D) to the polyester resin (B) was 75:25. The obtained film was inferior in transparency.

(Comparative Example 8)
(Creation of polyester resin (M))
The polyester resin (C) obtained in the same manner as in Example 1 was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a moisture content of 18.1 g / Nm ³ was added per 1 hour of crude polyester per hour. It was distributed at 40 liters and heat-treated at 170 ° C. for 24 hours. The content of the cyclic trimer in the obtained polyester was 1.03% by mass and did not decrease at all. Let the obtained crude polyester be a polyester resin (M).

(Creation of polyester resin (O))
The polyester resin (A) obtained in the same manner as in Example 1 was dried at 160 ° C. under reduced pressure, and then nitrogen gas conditioned to a moisture content of 18.1 g / Nm ³ was added per 1 hour of crude polyester per hour. It was distributed at 40 liters and heat-treated at 170 ° C. for 24 hours. The content of the cyclic trimer in the obtained polyester was 1.05% by mass and did not decrease at all. Let the obtained crude polyester be a polyester resin (O).

  Biaxially stretched polyethylene terephthalate in the same manner as in Example 1 except that the polyester resin (B) used in the B layer of Example 1 is changed to the polyester resin (M) and the polyester resin (D) is changed to the polyester resin (O). A film was obtained.

(Comparative Example 9)
The polyester resin (A) obtained in the same manner as in Example 1 was dried at 160 ° C. under reduced pressure, and then nitrogen gas adjusted to a moisture content of 18.1 g / Nm ³ was added per 1 kg of crude polyester. The mixture was circulated at 40 liters per hour and heat-treated at 263 ° C. for 12 hours. The treated polyester was melted in the can and could not be obtained.

  The film for a lens sheet of the present invention is excellent in transparency, has little oligomer precipitation, 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 base film for a lens sheet, which is a biaxially oriented laminated polyester film and satisfies the following structural requirements (1) to (8) .
(1) Having a laminated structure of three or more layers by coextrusion method (2) Both outermost layers of the film contain inert particles having an average particle diameter of 2.1 to 2.5 μm (3) The thickness of the outermost layer is not The average particle diameter of active particles is 5 times or more and less than 11 times (4) Among surface protrusions having a height of 2 nm or more observed by an atomic force microscope (AFM) on the outermost layer surface, The ratio of the number of surface protrusions having a surface protrusion height h ratio L / h of 50 or less is 30% or less. (5) Change in film haze ΔHz (ΔHz = (Haze after heating haze before heating) is less than 1.0 (6) At least the hydroxyl (OH) terminal amount in the outermost polyester is 70 eq / ton or less. (7) At least the outermost cyclic trimer content is 0.45 wt. %Less than
(8) 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. 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 0.03% by mass. The base film for lens sheets according to claim 1, wherein The base film for a lens sheet according to claim 1 or 2, wherein the number of particles having a particle size 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 Claims 1-3 . A method of manufacturing a lens sheet for the base fill beam according to claim 1, the lens base film sheet using a polyester resin obtained by the heat treatment satisfies the following requirements (9) - (11) Production method.
(9) A crude polyester having an intrinsic viscosity of 0.50 to 0.70 dl / g obtained by a polycondensation reaction between a dicarboxylic acid component and a glycol component has a water content of 3.5 to 30.0 g / Nm ³ . The humidity-conditioning inert gas is circulated at a flow rate of 1 to 10,000 liters / kg of crude polyester per hour.
(10) Heat treatment is performed at 190 ° C to 260 ° C.
(11) Heat treatment is performed so that the change in intrinsic viscosity of the polyester satisfies the following formula: -0.05 dl / g≤ (Intrinsic viscosity before heat treatment-Intrinsic viscosity after heat treatment) ≤0.05 dl / g