JP4583105B2 - Coextrusion laminated polyester film - Google Patents

Description

  The present invention relates to a film or sheet that needs to prevent the occurrence of interference fringes that are problematic when used in close contact with a transparent member, such as a transparent conductive film for a touch panel, a diffusion plate for a backlight unit, and a reflector. The present invention relates to a polyester film excellent in transparency that can be suitably used as a film substrate such as an electromagnetic wave shielding film for plasma displays and prism sheets.

  Films and sheets that prevent the occurrence of interference fringes and the like that occur when the gap between the transparent members is in contact with each other when the transparent members are in contact with each other have been proposed in the past. For example, Patent Document 1 discloses a method of applying a transparent resin containing particles using a satin-like treated coating roll. Patent Document 2 discloses an interference fringe prevention sheet using an ultraviolet curable resin and spherical organic particles and having excellent transparency. However, any of these examples requires a coating layer coating step and a drying step, which limits the improvement in productivity, and requires attention to safety and health management.

JP 09-272183 A Japanese Patent Laid-Open No. 11-227088

  This invention is made | formed in view of the said situation, The solution subject is providing the coextruded laminated polyester film excellent in transparency which does not generate | occur | produce an interference fringe even if it closely_contact | adheres to another transparent member.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a laminated stretched polyester film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a coextruded biaxially stretched film composed of at least three layers of polyester, and the inner layer is selected from acrylic resin, melamine resin, polyethylene, polystyrene, organosilicone resin and acrylic-styrene copolymer. The coextruded biaxially stretched laminated polyester film contains 0.05 to 1.4% by weight of organic particles having an average particle diameter of 5 to 50 μm and a particle deformation degree of 2.0 to 8.0.

Hereinafter, the present invention will be described in detail.
The polyester in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1, This polyester is mainly composed of an ester with glycol such as 4-cyclohexanedimethanol. The polyester is obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by a transesterification reaction between an aromatic dicarboxylic acid dialkyl ester and a glycol, followed by polycondensation, or an aromatic dicarboxylic acid diglycol. It can also be obtained by a method such as polycondensation of an ester. Typical examples of the polyester include polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate (PEN), boribylene terephthalate, and the like. Such a polyester may be a homopolymer that is not copolymerized, 40 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and 40 mol% or less of the diol component is a diol component other than the main component. It may be a certain copolyester or a mixture thereof.

  The film of the present invention is a coextruded film composed of at least two layers, and has at least one coextruded layer (hereinafter simply referred to as a particle-containing layer) containing 5 to 50 μm of inert particles. The particle-containing layer may be an inner layer or a surface layer. For example, one of the two layers may be used, but it is preferable that the inner layer of the coextruded layer usually composed of at least three layers is a particle-containing layer. When the surface layer is a particle-containing layer, the inactive particles are likely to fall off, and the degree of cleanliness in the film forming process and the film processing process is lowered, resulting in adhered foreign matters.

  As the inert particles used in the particle-containing layer, organic particles or inorganic particles incompatible with polyester are used. These inert particles have a 5% thermal decomposition temperature of preferably 280 ° C. or higher, more preferably 290 ° C. or higher. If the 5% pyrolysis temperature of the inert particles is less than 280 ° C., the film becomes yellow or brown due to thermal deterioration. Specific examples of inert particles include organic fine particles such as acrylic resin, melamine resin, polyethylene, polystyrene, organic silicone resin, and acrylic-styrene copolymer, and calcium carbonate, silica, aluminum oxide, barium carbonate, barium sulfate, A simple substance or a mixture of inorganic fine particles such as glass.

  Further, the degree of particle deformation of the inert particles to be used is preferably in the range of 1.5 to 10, more preferably 2.0 to 8.0, and particularly preferably 2.0 to 5.0. When the degree of particle deformation is less than 1.5, voids are likely to be generated around the particles when the film is stretched, and the transparency may be lowered or the particles may fall off the film. On the other hand, if the degree of particle deformation exceeds 8, the height of the protrusion formed on the film surface becomes small, and the occurrence of interference fringes may not be prevented.

  The content of the inert particles in the particle-containing layer is 0.05 to 1.4% by weight, preferably 0.1 to 1.2% by weight. When the particle content is less than 0.05% by weight, the interference fringe prevention property is poor. On the other hand, if it exceeds 1.4% by weight, the transparency is lowered.

  Further, the average particle diameter of the inert particles is 5 to 50 μm, preferably 8 to 40 μm, and more preferably 12 to 30 μm. Inactive particles having an average particle size of less than 5 μm are inferior in interference fringe prevention. On the other hand, inactive particles exceeding 50 μm are inferior in film forming property and may cause optical defects in the film.

  In addition, in the particle size distribution of the inert particles, it is preferable that coarse particles of 70 μm or more are substantially zero, and it is more preferable that coarse particles of 50 μm or more are substantially zero. When coarse particles of 70 μm or more are present, optical defects due to foreign matters may be generated in the film. In order to make the coarse particles of 70 μm or more substantially zero, the inert particles are classified. There is a method of providing an appropriate filter in the melt extrusion process of polyester.

  The thickness of the particle-containing layer is preferably in the range of 0.1 d to 3.0 d (μm), more preferably 0.2 to 2.0 d (μm), where d (μm) is the average particle size of the inert particles. Range. When the thickness of particle eye transport is 0.1 d (μm) or less, co-extrusion tends to be difficult. On the other hand, when it exceeds 3.0 d (μm), the transparency is lowered.

  In addition, you may contain additives, such as a ultraviolet absorber, an antistatic agent, antioxidant, and a fluorescent whitening agent, in a particle | grain content layer as needed.

  The thickness of the coextruded layer constituting at least one surface layer of the film of the present invention is preferably in the range of 0.1 d to 1.0 d (μm), where the average particle diameter of the inert particles is d (μm). Preferably it is the range of 0.2d-0.8d (micrometer), Most preferably, it is the range of 0.3d-0.8d (micrometer). If the thickness is less than 0.1 d (μm), the inert particles may fall off, and if it exceeds 1.0 d (μm), the prevention of interference fringes tends to be reduced.

  On the surface of the film of the present invention, a coating layer having chargeability, slipperiness, and easy adhesion may be provided as necessary.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  When the film of the present invention is produced, the dried polyester is supplied to an extruder and heated to a temperature equal to or higher than the melting point of each polyester to be melted. Next, it is extruded as a molten sheet from a T die. In this case, a multilayer sheet is formed using two or more extruders. Subsequently, the molten sheet is rapidly cooled to below the glass transition temperature on a rotary cooling drum to obtain an amorphous unstretched film. At this time, in order to improve the flatness of the unstretched film, the adhesion between the unstretched film and the rotating cooling drum may be improved by an electrostatic application adhesion method, a liquid application adhesion method, or the like. And a uniaxially stretched film is obtained by extending | stretching an unstretched film in the longitudinal direction (longitudinal stretching) using a roll stretching machine. The stretching temperature at this time is stretched in a temperature range of minus 10 ° C. to plus 40 ° C. of the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.0 to 6.0 times. Furthermore, longitudinal stretching may be performed in only one stage, or may be performed in two or more stages. Then, it leads to a tenter and a biaxially stretched film is obtained by extending | stretching a uniaxially stretched film in the width direction (lateral stretching) using a tenter stretching machine. The stretching temperature at this time is stretched in a temperature range of + 50 ° C. from the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.5 to 6.0 times. Further, the transverse stretching may be performed only in one stage, or may be performed in two or more stages. Moreover, you may perform simultaneous biaxial stretching which performs vertical and horizontal simultaneously. And a laminated film is manufactured by heat-processing a biaxially stretched film. The heat processing temperature at this time is 130-250 degreeC. When the biaxially stretched film is heat-treated, the biaxially stretched film may be relaxed within 20%.

  INDUSTRIAL APPLICABILITY The present invention provides a coextruded biaxially stretched polyester film having good transparency and interference fringe prevention properties, and the industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement methods and terms used in the examples and the present invention are defined as follows.

(1) Average particle diameter The maximum diameter and the minimum diameter were obtained by observing particles using an electron microscope, and the average was defined as the particle diameter of one inert particle. This is done for at least 100 inert particles in the film. The average particle diameter of the particle group is the weight average diameter of these particles.

(2) Degree of particle deformation After fixing a small piece of film with an epoxy resin, it was cut with a microtome in the film thickness direction, and the cut surface was observed with a scanning electron microscope. The maximum diameter and the minimum diameter were determined for each particle, and the ratio of the maximum diameter to the minimum diameter was calculated for at least 50 particles in which the maximum diameter was within ± 10% of the average particle diameter, and the arithmetic average was used as the degree of deformation.

(3) Transparency The haze value was measured using a spheroid turbidimeter NDH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.), and the transparency was evaluated as follows.
A: Good transparency: haze value converted to 50 μm thickness is 3% or less ○: Good transparency: Haze value converted to 50 μm thickness exceeds 3% and 8% or less Δ: Transparency slightly good: converted to 50 μm thickness Haze value exceeds 8% and is 15% or less ×: Poor transparency: Haze value converted to 50 μm thickness exceeds 15% Note that the haze value converted to a thickness of 50 μm is L, the haze value of the sample film Is represented by H, it is a value defined by L / 50 × H.

(3) Interference fringe prevention property 100 g of a 5 mm square acrylic rod at an angle of 45 ° is superimposed on the surface of the polyester film having a surface roughness Ra of 8 nm and a thickness of 0.2 mm and the surface to be evaluated of the sample film (A layer surface). It was pressed from above with a load of 20 mm and moved to observe whether interference fringes were generated under a fluorescent lamp. The interference fringe prevention property was evaluated as follows.
○: A ring-shaped interference fringe is not observed even when the acrylic rod is pressed and moved 20 mm. Δ: A ring-shaped interference fringe is slightly observed during 20 mm movement, but disappears after 3 minutes. A clear ring-shaped interference fringe is observed and does not disappear after 3 minutes

The adjustment of the raw materials used in the following examples is as follows.
・ Polyester A
It is a polyethylene terephthalate resin having an intrinsic viscosity of 0.65 and a melting point of 253 ° C. synthesized by a conventional polycondensation.

・ Polyester B
A polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with organic particles having an average particle size of 13 μm and contained in an amount of 2.0% by weight.

・ Polyester C
A polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with organic particles having an average particle diameter of 8.2 μm and contained at 2.0% by weight.

・ Polyester D
Polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with 10% by weight of polyester C, and the concentration of 8.2 μm organic particles is 0.2% by weight. .

・ Polyester E
A polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with organic particles having an average particle diameter of 1.5 μm and contained in an amount of 2.0% by weight.

・ Polyester F
A polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with spherical silica particles having an average particle diameter of 10 μm and contained at 3.0% by weight .

Example 1:
A mixture of 40% by weight of polyester A and 60% by weight of polyester C is supplied to a twin-screw extruder with a vent (main), and polyester A is supplied to another twin-screw extruder with a vent (sub). Melted at ℃, the molten polymer from the sub-extruder and the molten polymer from the main extruder are separated by a feed block through a gear pump filter (50% particle collection rate is 75%), and taken through a die to a casting drum Two types and three layers of unstretched films were obtained. The unstretched film thus obtained was fed into a longitudinal stretching roll, first stretched 3.7 times at a film temperature of 83 ° C., then led to a tenter and stretched 4.0 times laterally at 95 ° C. to obtain a biaxially oriented film. It was. Next, the obtained biaxially oriented film was introduced into a heat setting zone, and heat-set while being relaxed by 3% in the width direction at 230 ° C. for 5 seconds to obtain a polyester film having a thickness structure described in Table 1 below.

Example 2:
Example 1 except that a mixture of 92.5% by weight of polyester A and 7.5% by weight of polyester C was fed to a twin-screw extruder with a vent (main) to obtain a film having the thickness structure shown in Table 1. A film was obtained under the same conditions.

Example 3:
A film was obtained under the same conditions as in Example 2 except that a mixture of 92.5% by weight of polyester A and 7.5% by weight of polyester B was supplied to a vented twin screw extruder (main).

(Comparative Example 1)
A mixture of 30% by weight of polyester A and 70% by weight of polyester B is fed to a vented twin screw extruder, melted at a melting temperature of 280 ° C., taken through a die to a casting drum to obtain a single-layer unstretched film, A film was obtained under the same conditions as in Example 1 except that the film having the thickness described in 1 was obtained.

(Comparative Example 2)
A film was obtained under the same conditions as in Example 3 except that a mixture of 75% by weight of polyester A and 25% by weight of polyester E was used to feed a vented twin-screw extruder (main).

(Comparative Example 3)
A film was obtained under the same conditions as in Example 2 except that a mixture of 90% by weight of polyester A and 10% by weight of polyester D was used to feed a vented twin-screw extruder (main).

(Comparative Example 4)
A film was obtained under the same conditions as in Example 2 except that 100% by weight of polyester F was supplied to a biaxial extruder with a vent (main) to obtain a film having a thickness structure described in Table 1.
The results thus obtained are summarized in Table 1.

The films of Examples 1 to 3 have good transparency and excellent interference fringe prevention properties. In particular, the film of Example 3 has high transparency and does not generate interference fringes. On the other hand, the film of Comparative Example 1 is inferior in transparency because it is a single layer film. The film of Comparative Example 2 had no interference fringe prevention property because the average particle diameter of the inert particles was small. The film of Comparative Example 3 could not prevent interference fringes due to the small content of inert particles. The film of Comparative Example 4 was inferior in transparency due to the large content of inert particles.

  The film of the present invention can be suitably used as a film substrate such as a transparent conductive film of a touch panel, a diffusion plate of a backlight unit, a reflection plate or a prism sheet, and an electromagnetic wave shielding film of a plasma display.

Claims (1)

Coextruded biaxially stretched film comprising at least three layers of polyester, and the inner layer is selected from acrylic resin, melamine resin, polyethylene, polystyrene, organic silicone resin and acrylic-styrene copolymer, and has an average particle size of 5 to 50 μm, A coextruded biaxially stretched laminated polyester film containing 0.05 to 1.4% by weight of organic particles having a particle deformation degree of 2.0 to 8.0.