JP2006168313A - Co-extruded laminated polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellently transparent co-extruded polyester laminated film having a surface generating no interference fringe even in contact with another transparent member and another surface which is flat. <P>SOLUTION: The co-extruded polyester laminated film comprises at least two polyester layers. One surface has not less than 0.7 (pieces/mm<SP>2</SP>) of a density of protrusion showing the interference fringes of 5 order or more observed by double beam interferometry, and another surface has a surface roughness Ra of not more than 0.4 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a surface that can prevent the occurrence of interference fringes that become a problem when used in close contact with a transparent member of a sheet glass, a transparent resin film, a sheet, or a molded product that is used for optical applications having ordinary transparency. The other surface is relatively flat on the other surface and excellent in transparency, for example, transparent conductive film for touch panel, diffuser plate for backlight unit, reflector plate and prism sheet, and electromagnetic wave shielding film for plasma display The present invention relates to a co-extruded polyester film used as a film substrate for applications such as.

  Preventing interference fringes generated when the transparent members are in close contact with each other is an important issue in optical applications. As a countermeasure, a method of widening an interval generated between the two or more, a method of scattering light, and a method of combining them are taken. Conventionally, the film and sheet for preventing the occurrence of interference fringes, etc., have been used to roughen the surface that adheres to the transparent member, and in many cases, coated with a transparent resin layer containing particles having light scattering properties A film is disclosed. For example, Patent Document 1 discloses a method of applying a transparent resin containing particles using a coated roll that has been treated in a satin-like manner. Patent Document 2 discloses an interference fringe preventing sheet having excellent light transmittance by using an ultraviolet curable resin and spherical organic particles. However, in any case, a coating layer coating process and a drying process are necessary, and there is a limit to improvement in productivity, and attention should be paid to safety and health management. On the other hand, many optical polyester films may be provided with a coating layer or a vapor deposition layer, or may be formed with prism-shaped protrusions in order to have various functions depending on the application. In that case, the film surface is preferably flat. In the conventional polyester film base material, there was no thing in which surface characteristics differed greatly by front and back.

JP 09-272183 A JP-A-11-227088

  An object of the present invention is to provide a coextruded laminated polyester film excellent in transparency having a surface on which interference fringes do not occur even when it comes into contact with another transparent member, and the other surface is flat. To do.

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

That is, the gist of the present invention is a film comprising at least two polyester layers, and the density of protrusions having interference fringes of the fifth order or higher observed by two-beam interference method on one surface (pieces / mm ² ). The coextruded laminated polyester film is characterized in that the surface roughness Ra of the other surface is 0.04 μm or less.

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, A polyester 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, 20 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and / or 20 mol% or less of the diol component is other than the main component. It may be a copolyester such as a diol component. Moreover, those mixtures may be sufficient.

  The film of the present invention usually comprises at least two layers forming a surface (hereinafter referred to as a flat surface) opposite to a layer forming a surface (hereinafter referred to as a concavo-convex surface) on the side in contact with the transparent member. It is a coextruded laminated film. As the layer structure, for example, A layer / B layer, A layer / B layer / A ′ layer, A layer / B layer / C layer can be employed. Here, the difference between the A layer and the B layer (C layer) means that the type of polyester resin used or the type and concentration of the contained inert particles are different. Further, the difference between the A layer and the A ′ layer means that the thicknesses of the layers are different.

In the present invention, the density (number / mm ² ) of projections having fifth-order interference fringes observed by the two-beam interference method on the uneven surface of the polyester film in the present invention is 0.7 or more, preferably 0.8 or more. . If the density (number / mm ² ) of projections having fifth or higher order interference fringes observed by the two-beam interference method is less than 0.7, the interference fringes generated when contacting the transparent member cannot be suppressed. Further, the upper limit value of the density (number / mm ² ) of projections having fifth-order interference fringes observed by the two-beam interference method is preferably 20, more preferably 15 or less, particularly preferably 10 or less. It is. If it exceeds 20, the film transparency tends to decrease.

  In the polyester film of the present invention, in order to provide protrusions having fifth or higher order interference fringes on the concavo-convex surface, an inert particle is usually contained in the layer or inner layer forming the concavo-convex surface.

  These inert particles have a 5% thermal decomposition temperature of preferably 280 ° C. or higher, more preferably 290 ° C. or higher. When the 5% pyrolysis temperature of the inert particles is less than 280 ° C., the film may be yellowish or brownish 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 is preferably in the range of 1.5 or more and 10 or less, more preferably 2.0 or more and 8.0 or less, and particularly preferably 2.0 or more and 5.0 or less. When the degree of particle deformation is less than 1.5, voids tend to be generated around the particles when the film is stretched, and the transparency tends to decrease and the particles are likely to fall off the film. On the other hand, if the degree of particle deformation exceeds 10, 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 inert particles in the particle-containing layer is preferably 0.05 to 1.4% by weight, more preferably 0.1 to 1.2% by weight. If it is less than 0.05% by weight, the interference fringe prevention property tends to be inferior, and if it exceeds 1.4% by weight, the transparency tends to decrease.

  The average particle diameter of the inert particles is preferably 4 to 40 μm, more preferably 5 to 30 μm. Inactive particles having an average particle size of less than 4 μm tend to be 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 further preferable that coarse particles of 50 μm or more are substantially zero. When coarse particles of 70 μm or more are present, optical defects may occur in the film. In order to make the coarse particles of 70 μm or more substantially zero, the inert particles may be classified. There is also a method of providing an appropriate filter in the polyester melt extrusion process.

  The layer that contains the inert particles may be either the surface layer or the inner layer that forms the uneven surface, but the inner layer that is in contact with the surface layer that forms the uneven surface may contain the film itself against scratching or the transparent member that comes into contact This is preferable in order to improve scratch resistance. In this case, the thickness of the inner layer is preferably 0.05d to 5d (μm), more preferably 0.1 to 4d (μm), where d (μm) is the average particle diameter of the inert particles. If it is 0.05 d (μm) or less, coextrusion is difficult and the interference fringe prevention performance tends to be inferior. On the other hand, if it exceeds 5 d (μm), the surface roughness of the flat surface may increase or the transparency may decrease. Further, the thickness of the surface layer that forms the irregular surface when the inert particles are contained in the inner layer is preferably 0.1 d to 1.5 d (μm), where d (μm) is the average particle diameter of the inert particles. More preferably, it is 0.1 to 1.0 d (μm). If it is 0.1 d (μm) or less, co-extrusion becomes difficult. On the other hand, if it exceeds 1.5 d (μm), interference fringe prevention performance and scratch resistance tend to be inferior. In addition, when inert particles are included in the layer forming the irregular surface, the thickness of the surface layer forming the irregular surface is preferably 0.1d to 10d (μm), where d (μm) is the average particle diameter of the inert particles. More preferably, it is 0.2d-5d (micrometer). If it is 0.1 d (μm) or less, coextrusion tends to be difficult, and particles tend to fall off easily. On the other hand, if it exceeds 10 d (μm), the transparency may decrease.

  Each co-extruded layer may contain additives such as inert fine particles having an average particle size of 2 μm or less, an ultraviolet absorber, an antistatic agent, an antioxidant, and a fluorescent brightening agent as necessary. .

  In the present invention, the surface roughness (Ra) of the flat surface is 0.04 μm or less, preferably 0.03 μm or less. When surface roughness Ra exceeds 0.04 micrometer, the transparency of a film will fall and a processing characteristic and a reflective characteristic will fall depending on a use.

  The layer constituting the flat surface may or may not contain inert particles, but preferably does not contain substantially. In this case, the thickness of the flat layer is preferably 1.0 d or more, more preferably 1.2 d or more, where d is the average particle diameter of the inert particles contained in the other layers. If it is less than 1.0 d, the surface flatness may be impaired.

  Although the thickness of the film of this invention is not specifically limited, it is 20-300 micrometers. If the thickness is less than 20 μm, the workability of the film tends to be poor. If the thickness exceeds 300 μm, the weight may increase or the handleability may deteriorate.

  Moreover, you may provide the coating layer which has electrification property, slipperiness | lubricity, and easy-adhesion as needed on the surface of the film of this invention.

  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 forming each layer is supplied to a separate extruder and heated to a temperature equal to or higher than the melting point of each polyester to be melted. Next, each polyester is laminated and extruded as a molten sheet from a T die. 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.

  The obtained unstretched film is stretched (longitudinal stretching) in the longitudinal direction using a roll stretching machine to obtain a uniaxially stretched film. The stretching temperature at this time is stretched in a temperature range of (raw material resin glass transition temperature (Tg-10) to (Tg + 40) ° C.) The stretching ratio is preferably 2.5 to 7.0 times, more preferably It is 3.0 to 6.0 times, and the longitudinal stretching may be performed only in one stage, or may be performed in two or more stages.

  Next, the biaxially stretched film is obtained by stretching the 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 the glass transition temperature (Tg) to (Tg + 50) ° C. 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%.

  The present invention provides a polyester film in which interference fringes do not occur even if one surface is in close contact with another transparent member, the other surface is flat, and has excellent transparency and scratch resistance. The industrial value of the 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 are obtained for each particle, and the ratio of the maximum diameter to the minimum diameter is calculated for at least 50 particles in which the maximum diameter falls within ± 10% of the average particle diameter, and the arithmetic average is defined as the degree of deformation.

(3) Surface roughness Measured according to JIS-B-0601-1982 using a surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory. However, the cut-off value is 80 μm and the measurement length is 2.5 mm.

(4) Aluminum is vapor-deposited on the surface of the density film of the projections having fifth-order or higher interference fringes observed by the two-beam interference method, and measurement is performed by the two-beam method using a Nikon Optiphoto interference microscope. A measurement wavelength is 0.54 μm, and the number of protrusions showing fifth or higher order interference fringes is measured over an area of 100 mm ² to obtain the number of protrusions per 1 mm ² area.

(5) Interference fringe prevention property Measured according to JIS-B-0601-1982 using a surface roughness Ra (surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory Ltd.), cut-off value of 80 μm, measurement length 20 mm by pressing a 5 mm square acrylic rod from the top with a load of 100 g at an angle of 45 ° on the surface of the polyester film with a thickness of 8 nm and a 0.2 mm thick polyester film. Move and observe if interference fringes occur under fluorescent lights. The interference fringe prevention property is 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. X: During 20 mm movement. A clear ring interference fringe is observed and does not disappear after 3 minutes

(6) Scratch prevention property Using a rubbing tester manufactured by Ohira Rika Kogyo Co., Ltd., a 2 mm thick methacrylic resin plate specified in JIS k6718 is fixed to a reciprocating plate with a double-sided adhesive tape. Next, a plate on which a test film having 24 sheets of 5 cm × 5 cm gauze and a cushion is attached is placed. Reciprocate 10 times in the state. Thereafter, a scratch having a length of 5 mm or more generated on the surface of the methacrylic plate is visually observed under a fluorescent lamp. The test is performed three times per sample, the average value of the number of scratches is determined, and the evaluation is performed as follows.
○: The number of scratches is 1 or less, and the scratch resistance is excellent. Δ: The number of scratches is more than 1 and 3 or less, and the scratch resistance is slightly good. X: The number of scratches is more than 3, preventing scratches. Poor

(Raw material adjustment)
・ 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 crosslinked styrene-acrylic organic particle having an average particle size of 11 μm and a 5% thermal decomposition temperature of 331 ° C. is kneaded into a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation of 2.0 weight. %.

・ Polyester c
Contains 2.0% by weight of crosslinked acrylic organic particles with an average particle size of 13μm, a 5% thermal decomposition temperature of 290 ° C, and a polyethylene terephthalate resin with an intrinsic viscosity of 0.68 and a melting point of 253 ° C synthesized by conventional polycondensation It has been made.

・ Polyester d
A synthetic calcium carbonate particle having an average particle diameter of 0.8 μm was added at the time of polycondensation of polyethylene terephthalate, and was synthesized with a polyethylene terephthalate resin having an intrinsic viscosity of 1.08% and a melting point of 253 ° C. is there.

・ Polyester e
1. Kneaded crosslinked styrene-acrylic organic particles having an average particle size of 8.2 μm and a 5% pyrolysis temperature of 365 ° C. into polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation. 0% by weight is contained.

・ 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 porous silica particles having an average particle diameter of 10 μm and contained at 2.0% by weight.

  The raw material mixed with 70% by weight of polyester a and 30% by weight of polyester b is supplied to a twin screw extruder with a vent (sub), and polyester a is supplied to another twin screw extruder with a vent (main). Then, after melting at a melting temperature of 280 ° C., it is divided into two to form layers constituting the front and back of the film, and the molten polymer from each sub-extruder and the molten polymer from the main extruder are separated by a gear pump filter (particle The filter of the sub-extruder containing the molten polymer containing 50 μm was used as a filter having a particle collection rate of 50 μm and 75%). A stretched film was 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.

  The raw material mixed with 82% by weight of polyester a and 18% by weight of polyester c is supplied to a twin screw extruder with a vent (sub), and polyester a is supplied to another twin screw extruder with a vent (main). Then, after melting at a melting temperature of 280 ° C., the melt polymer from each extruder was used as a gear pump filter (the filter of the sub-extruder containing the melt polymer containing particles was a filter having a particle collection rate of 50 μm and 75%. )), And was fed to a casting drum through a die to obtain an unstretched film of two types and two layers. Thereafter, the film was stretched and heat-set in the same manner as in Example 1 to obtain a film having a thickness structure described in Table 1.

  Using three vented twin screw extruders, the inner layer was fed with a raw material in which 64% by weight of polyester a and 36% by weight of polyester c were mixed, and the surface layer was fed with polyester a to obtain a melting temperature. After melting at 280 ° C., the molten polymer from each extruder was passed through a gear pump filter (the filter of the extruder containing the molten polymer containing particles used a filter having a particle collection rate of 50 μm and 75%). Two types and three layers of unstretched films were obtained using a multi-manifold die. Thereafter, the film was stretched and heat-set in the same manner as in Example 1 to obtain a film having a thickness structure described in Table 1.

(Comparative Example 1)
The raw material in which 60% by weight of polyester a and 40% by weight of polyester d are mixed is supplied to an extruder with a vent, melted at a melting temperature of 280 ° C., and then the molten polymer is passed through a die through a gear pump filter to a casting drum. A single layer unstretched film was obtained. Thereafter, the film was stretched and heat-set in the same manner as in Example 1 to obtain a film having the thickness described in Table 1.

(Comparative Example 2)
The raw materials mixed with 92.5% by weight of polyester a and 7.5% by weight of polyester e were supplied to a twin-screw extruder with a vent (main) to obtain a film having the thickness described in Table 1. A film was obtained in the same manner as in Example 1.

(Comparative Example 3)
A raw material in which 55% by weight of polyester a and 45% by weight of polyester f were mixed was supplied to the inner layer, and a film having the thickness described in Table 1 was obtained. .

  In Examples 1-3, it is excellent in transparency and interference fringe prevention property. In particular, Example 3 also has good scratch resistance. On the other hand, Comparative Example 1 is inferior in transparency because it is a single layer film, and has no interference fringe prevention property because it uses inert particles having a small average particle diameter, so that projections having fifth-order interference fringes are not formed. It was. In Comparative Example 2, since the degree of deformation of the particles was large, the density of protrusions having fifth-order or higher interference fringes on the uneven surface was small and did not exhibit interference fringe prevention. Since the comparative example 3 had large surface roughness, transparency was inferior.

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

Claims (1)

It is a film composed of at least two polyester layers, and on one surface, the density (number / mm ² ) of projections having fifth-order interference fringes observed by two-beam interference method is 0.7 or more, A co-extruded laminated polyester film characterized in that the roughness Ra of the other surface is 0.04 μm or less.