JP2009202404A - Laminated polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polyester film having high shielding performance and excellent reflection characteristics in a specified range of thicknesses and combining antistatic performance. <P>SOLUTION: The laminated polyester film includes a polyester type resin layer (A layer) containing 3-30 wt.% of a white pigment of an average particle size of 0.1-1.0 μm and 400-5,000 ppm of a fluorescent whitener, on at least one side of a polyester type resin layer (B layer) containing a shading agent. It has a total thickness of 20-40 μm, an optical density (OD) of 4.0-8.0 and a spectral reflectance of the surface of the A layer to the 460-nm light ray of 85-105%. It has a coating layer on at least one side of the A layer, and the coating layer has a surface specific resistivity of 1×10<SP>6</SP>to 1×10<SP>12</SP>Ω. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laminated polyester film, and more particularly relates to a laminated polyester film which is suitably used for various optical reflecting members having high concealability and reflection characteristics and having antistatic performance. is there.

  A technique for imparting concealability to a film by adding a white pigment such as titanium oxide, such as a white polyester film for a prepaid card, is conventionally known. In addition, a technique for maintaining the whiteness of the film at a high level by adding a fluorescent brightening agent in combination as required is also known. However, in a reflective member application in which light leakage is severely limited, a lack of concealment cannot be avoided if the film thickness is 40 μm or less. Conventionally, in order to compensate for this, a light-shielding coating layer has been provided on a white film, but a plurality of coating steps are required to obtain a predetermined ink thickness (hiding property). This is a disadvantageous method from the viewpoint of manufacturing cost and quality control (occurrence of coating omission).

Furthermore, when a film is printed and applied in the process of passing between rolls, there is a tendency to be charged with static electricity, and the occurrence of sparks in an atmosphere using a solvent may lead to an explosion. Also, if foreign matter is attracted by charging, printing and coating may be lost, which is a big problem in the quality of the processed product.
JP 2001-26087 A

  The present invention eliminates the above-mentioned drawbacks of the prior art, and in a specific thickness range, the leakage of light is severely limited in a laminated polyester film having high concealment and reflection characteristics and also having antistatic performance. It is set as a solution subject to provide as various reflective members.

  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 adopting a specific configuration, and the present invention has been completed.

That is, the gist of the present invention is that at least one side of a polyester-based resin layer (B layer) containing a light-shielding agent contains 3 to 30% by weight of a white pigment having an average particle size of 0.1 to 1.0 μm and a fluorescent brightening agent. Is a laminated polyester film having a polyester-based resin layer (A layer) containing 400 to 5000 ppm, the total thickness of the film is 20 to 40 μm, and the optical density (OD) is 4.0 to 8.0, The spectral reflectance of the surface of the A layer with respect to light having a wavelength of 460 nm is 85 to 105%, the coating layer is provided on at least one surface of the A layer, and the surface specific resistance value of the coating layer is 1 × 10 ⁶ to 1 × 10. It exists in the laminated polyester film characterized by being ¹² ohms.

Hereinafter, the present invention will be described in more detail.
As the polyester constituting the laminated polyester film of the present invention, typically, for example, polyethylene terephthalate in which 80 mol% or more of the structural unit is ethylene terephthalate, and 80 mol% or more of the structural unit is ethylene-2,6-naphthalate. Polyethylene-2,6-naphthalate, and poly-1,4-cyclohexanedimethylene terephthalate in which 80 mol% or more of the structural unit is 1,4-cyclohexanedimethylene terephthalate. Other examples include polyethylene isophthalate and polybutylene terephthalate.

  Examples of copolymer components other than the above-described dominant components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, and polytetramethylene glycol, isophthalic acid, 2,7-naphthalenedicarboxylic acid, and 5-sodium dicarboxylic acid. Ester-forming derivatives such as diasulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid and oxymonocarboxylic acid can be used. Further, as the polyester, in addition to a homopolymer or a copolymer, a small proportion of a blend with another resin can also be used.

  As the white pigment used in the present invention, conventionally known pigments can be used. For example, titanium dioxide, barium sulfate, calcium carbonate, zinc oxide, zinc sulfide and the like can be used. In particular, titanium oxide is preferably used because it has a high refractive index and can impart high concealability to a film with a relatively small amount.

  The average particle diameter of the white pigment used in the present invention is 0.1 to 1.0 μm, and more preferably 0.2 to 0.6 μm. When the average particle diameter of the white pigment is too small, the concealability of the laminated film is insufficient. On the other hand, when the average particle diameter of the white pigment is too large, the particles fall off from the surface of the laminated film. Here, a white pigment may be used individually by 1 type, and may use 2 or more types together.

  The layer A of the laminated film of the present invention needs to contain a predetermined white pigment in order to obtain sufficient light reflectance. As will be described later, since the thickness of the A layer preferably occupies a considerable proportion with respect to the total thickness of the laminated film, it is required to maintain the film forming stability of the laminated film in the A layer. Therefore, the content of the white pigment in the A layer is 30% by weight or less, preferably 20% by weight or less. On the other hand, for the purpose of improving the concealability of the laminated film and improving the light reflectance of the surface of the A layer, the content of the white pigment in the A layer is 3% by weight or more, preferably 7% by weight or more. Preferably it is 10 weight% or more.

  The layer B of the laminated film of the present invention needs to contain a light shielding agent in order to make the laminated film highly concealed. Specific examples of the light shielding agent include black pigments, white pigments, and other colored pigments.

  As the black pigment, conventionally known pigments can be used, and examples thereof include carbon black, iron oxide, and aniline black. Carbon black is preferable from the viewpoint of the effect of improving the concealability and the material cost.

  In the B layer of the present invention, black pigments, white pigments, and colored pigments can be used alone or in combination of two or more. However, the concealability is improved, the laminated film itself is regenerated and blended, etc. From this point of view, it is preferable to use a black pigment and a white pigment in combination. In particular, in the case of carbon black that is suitably used as a black pigment, it is difficult to add a high concentration due to its electrical conductivity (electrostatic application adhesion is performed when extruding from a die onto a cast roll in a manufacturing process. However, in this process, problems such as sparks occur). Therefore, when the concealing property is insufficient, it is preferable to supplement by adding a white pigment.

  When carbon black is used for the B layer of the film of the present invention, the content is preferably 1 to 10% by weight, more preferably 3 to 9% by weight. When the content of carbon black exceeds 10% by weight, productivity problems such as sparking in the production process of the laminated film (electric contact process on the cast roll) tend to occur. On the other hand, when the content of carbon black is less than 2% by weight, the concealability of the laminated film tends to be insufficient.

  When using a white pigment for B layer of this invention, it is preferable that the content is 3 to 30 weight% similarly to the case of the above-mentioned A layer. The upper limit is more preferably 20% by weight or less from the viewpoint of film formation stability, and the lower limit is 7% by weight or more, further 10% by weight or more from the viewpoint of improving the concealability of the laminated film. Is more preferable.

  The average particle diameter of the light-shielding agent (excluding the white pigment) used in the present invention is preferably 0.01 to 0.5 μm, more preferably 0.02 from the viewpoints of improving concealability and productivity of laminated film. ~ 0.3 μm.

  The optical density (OD) of the laminated film of the present invention needs to be 4.0 or more. When a film having an OD of less than 4.0 is used for a reflecting member that does not allow slight light leakage, defects tend to occur. A preferable OD value is 5.0 or more, and more preferably 5.5 or more. The upper limit of the OD value is 8.0, and even if the OD value exceeds this, the concealability of the film is already saturated.

  The spectral reflectance with respect to light having a wavelength of 460 nm on the surface of layer A of the laminated film of the present invention needs to be 85 to 105%. When the spectral reflectance is less than 85%, the light amount is lost when the light is reflected on the A layer (white) surface of the laminated film, and the brightness of the display surface illuminated by the reflected light is insufficient. More preferably, the spectral reflectance is 88% or more, and more preferably 90% or more. The upper limit of the spectral reflectance is 105%.

  In order to make the spectral reflectance of the surface of the A layer 85% or more, it is necessary that the A layer contains 400 ppm or more of the fluorescent brightening agent. When the content of the fluorescent brightening agent is less than 400 ppm, the blue region reflectance tends to be insufficient. Further, if the fluorescent brightening agent is added in a large amount, the effect of the fluorescent brightening agent is saturated and the weather resistance tends to deteriorate, so the content in the A layer needs to be 5000 ppm or less. More preferably, it is 2000 ppm or less.

In the laminated film of the present invention, the surface specific resistance value of at least one surface of the A layer needs to be in the range of 1 × 10 ⁶ to 1 × 10 ¹² Ω. When the surface specific resistance value on the surface of the A layer exceeds 1 × 10 ¹² Ω, it becomes a problem that the film is charged with static electricity when passing the film between rolls to process the foreign material to the film surface. The surface specific resistance value (upper limit) of the surface of the preferred A layer is 1 × 10 ¹¹ Ω or less, more preferably 1 × 10 ¹⁰ Ω or less. On the other hand, when the surface specific resistance value is less than 1 × 10 ⁶ Ω, the antistatic effect is saturated and a large amount of antistatic material needs to be added, and the uniformity of the coated surface tends to be impaired. The surface specific resistance value (lower limit) on the surface of layer A is preferably 1 × 10 ⁷ Ω or more, more preferably 1 × 10 ⁸ Ω or more.

The composition of the coating layer is not particularly limited as long as it satisfies the required surface specific resistance value (1 × 10 ⁶ to 1 × 10 ¹² Ω). For example, the composition can be as follows. is there.

  (A) a polymer having a pyrrolidinium ring in the main chain, (b) at least one polymer selected from polyesters, polyacrylates, polyurethanes and chlorine-containing polymers, and (c) a melamine-based and / or epoxy-based crosslinking agent; A coating layer containing

  The polymer having a pyrrolidinium ring in the main chain, which is one of the coating agent components, is, for example, a polymer having a structure of the following formula (I) or (II) as a main component.

In the above formulas (I) and (II), R ¹ and R ² are each independently an alkyl group, a phenyl group or the like, and these alkyl groups and phenyl groups may be substituted with the groups shown below. Good. That is, the substitutable group is, for example, a hydroxyl group, an amide group, a carbo lower alkoxy group, a lower alkoxy group, a thiophenoxy group, a cycloalkyl group, a tri- (lower alkyl) ammonium lower alkyl group, and the nitro group is Only on alkyl groups and halogen groups can be substituted only on phenyl groups. Further, ^{R 1} and ^{R 2} may be chemically bonded, for _{example, - (CH 2) m -} (m is integer of 2 to _{5), - CH (CH 3)} -CH (CH 3) - , -CH = CH-CH = CH -, - CH = CH-CH = N -, - CH = CH-N = CH -, - (CH 2) 2 O (CH 2) 2 -, - (CH 2) ₂ -O _{(CH 2) 2} - and the like. X ⁻ in the above formula is an inorganic acid residue such as Cl ⁻ , Br ⁻ , 1 / 2SO ₄ ²⁻ , or 1 / 3PO ₄ ^3−, a sulfone of CH ₃ SO ₄ ⁻ , C ₂ H ₅ SO ₄ ^— . Acid residues are indicated.

  The polymer (I) can be obtained, for example, by subjecting a compound represented by the following formula (III) to cyclopolymerization using a radical polymerization catalyst.

  The polymer of the formula (II) can be obtained by cyclopolymerizing the compound of the formula (III) in a system using sulfur dioxide as a solvent. The polymerization is carried out by using a polymerization initiator such as hydrogen peroxide, benzoyl peroxide, tertiary butyl peroxide in a polar solvent such as water or methanol, ethanol, isopropanol, formamide, dioxane, acetonitrile, sulfur dioxide as a solvent. Although it can implement by a method, it is not limited to these.

  The polymer having a pyrrolidinium ring in the main chain may use a compound having a polymerizable carbon-carbon unsaturated bond as a copolymerization component with the compound of the above formula (III).

  The molecular weight of the polymer having a pyrrolidinium ring in the main chain in the present invention is preferably 500 to 1,000,000, more preferably 1000 to 500,000. When the molecular weight of the polymer is less than 5000000, although there is an antistatic effect, the strength of the coating film tends to be weak or it tends to block. When the molecular weight of the polymer is higher than 1,000,000, the viscosity of the coating solution becomes high, and the handleability and applicability tend to deteriorate.

  The polyester, polyacrylate, polyurethane and chlorine-containing polymer used as the coating layer component of the present invention are not particularly limited as long as they are usually used as a coating agent. For example, examples of the chlorine-containing polymer include polyvinylidene chloride, polyvinyl chloride, chlorinated polyolefin, vinyl chloride-vinyl acetate copolymer, and chloroprene.

  These polymers can be dispersed in water by imparting hydrophilicity by copolymerizing nonionic, cationic or amphoteric hydrophilic components as one component of the monomer. Alternatively, nonionic, cationic or amphoteric surfactants may be used for water dispersion by so-called forced emulsification, or emulsion polymerization may be carried out using nonionic, cationic or amphoteric surfactants to form an aqueous dispersion. it can.

  These polymers can also be used as copolymers, and may be random copolymer block copolymers or graft copolymers, or may be a conjugate of different polymers. Examples include, but are not limited to, polyurethane-graft-polyacrylate or polyester-graft-polyacrylate obtained by emulsion polymerization of an acrylic monomer in the presence of an aqueous solution or dispersion of polyurethane or polyester.

  Examples of the melamine-based crosslinking agent used in the present invention include methoxymethylated melamine and butoxymethylated melamine which are alkylol or alkoxyalkylolated melamine compounds, and those obtained by co-condensing urea or the like with a part of melamine. Can be used.

  Moreover, as an epoxy type crosslinking agent, what is necessary is just a compound which has an epoxy group whose water solubility or water-solubilization rate is 50% or more.

  By adding the cross-linking agent, the adhesion, water resistance, solvent resistance and mechanical strength of the coating layer are improved. As a result, in addition to improving the adhesion to the base film, the antistatic property is surprisingly improved. In particular, the melamine-based crosslinking agent has a high curing rate, and is more effective when used in combination with a curing catalyst such as a protonic acid or its ammonium salt.

  In this invention, the compounding quantity of the polymer which has a pyrrolidinium ring in the principal chain mix | blended with a coating liquid is 5 to 40 weight% normally, Preferably it is 10 to 30 weight%. When the blending amount is less than 5% by weight, the antistatic performance of the surface on which the coating layer is formed tends to be insufficient. On the other hand, when the blending amount exceeds 40% by weight, the antistatic performance is saturated and the surface of the coating layer tends to be non-uniform.

  The total amount of at least one polymer selected from the polyester, polyacrylate, polyurethane and chlorine-containing polymer blended in the coating solution for obtaining the coating layer of the film of the present invention is usually 20 to 60% by weight, Preferably it is 30 to 50% by weight. When the blending amount is less than 20% by weight, the adhesion of the coating layer to the base film tends to be insufficient. On the other hand, if the blending amount exceeds 60% by weight, the coating layer tends to block when the film is wound into a roll.

  The total amount of the melamine-based or epoxy-based crosslinking agent blended in the coating solution is usually 10 to 60% by weight, preferably 20 to 50% by weight. If the blending amount is less than 10% by weight, the antistatic performance and the anti-blocking effect tend to be insufficient. On the other hand, if the blending amount exceeds 60% by weight, the adhesion between the coating layer and the base film is poor. There is a tendency to be sufficient.

  In the present invention, slipping property and appropriate releasability can be imparted by further blending a lubricant in the coating layer. Examples of the lubricant include polyolefin waxes, mineral oils, animal and vegetable oils, waxes, esters, metal soaps, and the like. Usually, since polyolefin waxes do not impair adhesiveness, they are used.

  Furthermore, the coating layer of the film of the present invention contains an antifoaming agent, a coating property improving agent, a thickener, inorganic particles, organic polymer particles, an antioxidant, an ultraviolet absorber, a foaming agent, a dye and the like as necessary. You may contain.

  Specifically, the layer constitution of the laminated film of the present invention is A / B or A / B / A. However, one surface of the laminated film is not necessarily white, and is preferably composed of two layers of A / B from the viewpoint of rationalization of the constituent materials. In addition, as long as it is in the range which does not impair the summary of this invention, you may laminate | stack a 3rd layer between A layer and B layer.

  In the present invention, the total thickness of the laminated film is 20 to 40 μm. From the viewpoint of film waist and processability, a white (single layer) polyester film having a thickness of about 25 to 38 μm and a black coating layer is conventionally used, and the laminated film of the present invention is used. This is because the purpose of substituting this is taken into consideration.

The thickness ratio of the B layer is preferably 15 to 40% of the total thickness of the laminated film.
When the thickness ratio of the B layer exceeds 40% of the total thickness of the laminated film, the thickness of the A layer becomes relatively thin, so that a predetermined light reflectance tends not to be obtained. The properties also deteriorate (the color of the B layer is affected). On the other hand, when the thickness ratio of the B layer is less than 15% of the total thickness of the laminated film, the concealability of the laminated film tends to be insufficient. A more preferable ratio of the B layer thickness to the total thickness is 20 to 35%.

  As a method for adding a light-shielding agent to the film raw material for forming the layer B of the laminated film of the present invention, the light-shielding agent may be directly added to the polyester resin as a powder in the melt extruder in the film production process. In addition, it is preferable to prepare a master pellet in which a light-shielding agent is kneaded with a polyester resin in advance, because the dispersibility of the pigment can be further improved by re-kneading with the polyester resin by an extruder in the film manufacturing process. Is the method.

  As a method for producing the laminated polyester film of the present invention, a polymer blended in each of the A layer and the B layer is supplied to separate extruders, and then laminated in a molten state and extruded from the same die. Is preferably adopted. The obtained unstretched film may be stretched in at least a uniaxial direction according to a roll stretching method, a tenter method or the like. In order to appropriately satisfy mechanical strength and thermal dimensional stability, it is preferable to use a biaxial stretching method and a heat treatment method in combination.

  Here, although an example at the time of using biaxial stretching is demonstrated in detail, unless the summary of this invention is exceeded, this invention is not limited to the following examples.

  First, different raw materials constituting the laminated film are supplied to separate extruders, and after melt-kneading, the molten polymer is laminated in a slit shape and extruded on a slit. Next, the molten sheet extruded from the die is rapidly cooled and solidified on the rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the planar uniformity and cooling effect of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and in the present invention, an electrostatic application adhesion method is preferably employed. Next, the obtained sheet is stretched in a biaxial direction to form a film. First, the unstretched sheet is stretched under the conditions of a stretching temperature of usually 70 to 150 ° C., preferably 75 to 130 ° C., usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. Stretch in one direction (longitudinal direction). A roll and tenter type stretching machine can be used for such stretching. Next, at a stretching temperature of usually 75 to 150 ° C., preferably 80 to 140 ° C., orthogonal to the first stage under the conditions of a stretching ratio of usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. The film is stretched in the direction (transverse direction) to obtain a biaxially oriented film. For such stretching, a tenter type stretching machine can be used.

  A method of performing the above-mentioned unidirectional stretching in two or more stages can also be adopted, but in this case as well, it is preferable that the final stretching ratio falls within the above-described range. The unstretched sheet can be simultaneously biaxially stretched so that the area magnification is 6 to 30 times. Next, heat treatment in the tenter is usually performed at 180 to 240 ° C., preferably 200 to 235 ° C., for 1 second to 5 minutes. In this heat treatment step, relaxation of 0.1 to 20% in the transverse direction and / or the longitudinal direction is performed in the zone of the highest temperature of the heat treatment and / or the cooling zone immediately before the heat treatment outlet, in order to impart thermal dimensional stability. Is preferable.

  In the above, a coating layer is provided on the film after longitudinal stretching. As a method of providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. However, in general, the post-coating process is performed at 70 to 280 ° C. for 3 to 200 seconds. It is preferable to perform heat treatment.

  Moreover, you may use together heat processing and active energy ray irradiation, such as ultraviolet irradiation, as needed. The laminated polyester film of the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  ADVANTAGE OF THE INVENTION According to this invention, the white laminated polyester film which was excellent in the concealability and the reflective characteristic which was not obtained with the conventional white film, and had both antistatic performance can be provided. Furthermore, the film of the present invention is suitably used as an optical reflecting member that does not allow slight light leakage, has high processability, and has a very high industrial value.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples, unless the summary is exceeded. In addition, the various physical property in this invention, its measuring method, and a definition are as follows. In Examples and Comparative Examples, “parts” and “%” mean “parts by weight” and “% by weight”, respectively.

(1) Average particle size of white pigment (μm)
Using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation, the particle size was measured by a sedimentation method based on Stokes' resistance law. The average particle diameter was determined by using a value of 50% of integration (volume basis) in the equivalent spherical distribution of particles obtained by measurement.

(2) Intrinsic viscosity (dl / g)
A mixed solvent of phenol / tetrachloroethane: 50/50 (weight ratio) was added to 1 g of polyester at a ratio of 100 ml, and the mixture was measured at 30 ° C.

(3) Optical density A single film was measured using a Macbeth densitometer TD-904 type. (The higher this value, the higher the concealment property.) After the displayed value was stabilized, reading was performed.

(4) Spectral reflectance, hue (L *, a *, b *)
Using a spectrocolorimeter CM-3700d manufactured by Minolta, the reflectance at a light wavelength of 460 nm was measured by a reflection method. (Using a white standard plate) A 2 ° field of view, a C light source were used, and the color system was L * a * b * (CIE 1976). In addition, about the laminated | multilayer film, A layer surface (white surface) was measured.

(5) Layer thickness ratio (μm)
The cross section of the laminated film was observed with a scanning electron microscope (SEM).

(6) Surface resistivity of layer A (Ω)
A sample film was placed in a Yokogawa Hewlett Packard concentric circular electrode “16008A (trade name)” (inner electrode 50 mm, outer electrode 70 mm diameter) in an atmosphere of 23 ° C. and 50% RH, and a voltage of 100 V was applied. The surface resistance of the film surface (A layer side) was measured with the company's high resistance meter “4329A (trade name)”.

Comparative Example 1:
Preparation of polyethylene terephthalate chip (raw material A) having an intrinsic viscosity of 0.66 containing 15% of anatase-type titanium dioxide particles having an average particle size of 0.3 μm and 900 ppm of a fluorescent brightening agent (OB-1 manufactured by Eastman Chemical Co., Ltd.) did. Next, a polyethylene terephthalate chip (raw material B) having an intrinsic viscosity of 0.66 containing 15% of anatase-type titanium dioxide particles having an average particle diameter of 0.3 μm and 6% of carbon black having an average particle diameter of 0.02 μm was prepared. Raw material A and raw material B are put into separate twin-screw extruders with vents, melted and kneaded at 270 ° C., and the obtained melt is laminated so as to become raw material A / B in a T-die. The sheet was extruded into a shape and adhered and cooled on a cooling drum at 30 ° C. by an electrostatic application method to obtain an unstretched sheet. Next, the unstretched sheet was stretched 3.2 times at 82 ° C. in the longitudinal direction, and further stretched 3.6 times at 115 ° C. in the transverse direction. After the temperature was raised stepwise, heat treatment was performed at 230 ° C. for 5 seconds. Next, under a 180 ° C. atmosphere, 2% relaxation treatment (to narrow the tenter rail width) was performed in the width direction. Finally, a biaxially oriented film having a film thickness of 30 μm (A / B thickness = 25/5 μm) was obtained. Since the layer A of the film has a high surface resistivity, it is easily charged with static electricity and easily adsorbs foreign substances in the environment.

Comparative Example 2:
A biaxially oriented film having a final film thickness of 30 μm (A / B thickness = 22/8 μm) was prepared in the same manner as in Comparative Example 1 using the raw material A / raw material B described in Comparative Example 1 above. Obtained. Since the layer A of the film has a high surface resistivity, it is easily charged with static electricity and easily adsorbs foreign substances in the environment.

Example 1:
In the same manner as in Comparative Example 1, an unstretched sheet was obtained. Next, the unstretched sheet is stretched 3.2 times in the longitudinal direction at 82 ° C., and then a coating solution (5 wt% aqueous dispersion) having the coating composition shown below is applied to a coating thickness of 4.5 μm (wet). And applied to the layer A side of the laminated film. Further, after stretching in the transverse direction at 115 ° C. by 3.6 times, a biaxially oriented film having a final film thickness of 30 μm (A / B thickness = 25/5 μm) was obtained in the same manner as in Comparative Example 1. The A layer of the film had a surface specific resistance within a suitable range, was hardly charged with static electricity, and was a film that solved the problem of adsorbing foreign substances in the environment.

Coating composition (wt%): X / Y / Z = 20/40/40
X: polydimethyldiallylammonium chloride (molecular weight = 30000)
Y: Nonionic aqueous dispersion of methyl methacrylate / ethyl acrylate / methylol acrylamide copolymer (monomer ratio: 47.5 / 47.5 / 5 mol%)
Z: Methoxymethylmelamine aqueous solution

Example 2:
In Example 1, a biaxially oriented film having a final film thickness of 30 μm (A / B thickness = 22/8 μm) was obtained in the same manner except that the thickness of the A layer / B layer was changed to 22/8 μm. Obtained. The A layer of the film had a surface specific resistance within a suitable range, was hardly charged with static electricity, and was a film that solved the problem of adsorbing foreign substances in the environment.

Comparative Example 3:
A polyethylene terephthalate chip (raw material A ′) having an intrinsic viscosity of 0.66 containing 15% of anatase-type titanium dioxide particles having an average particle diameter of 0.3 μm and 600 ppm of an optical brightener (OB-1 manufactured by Eastman Chemical Co., Ltd.) Prepared. This is put into a twin screw extruder with a vent and melted and kneaded at 270 ° C., and the obtained melt is extruded into a slit shape through a T-die, and is adhered and cooled on a cooling drum at 30 ° C. by an electrostatic application method. Thus, an unstretched sheet was obtained. The subsequent manufacturing method was carried out in the same manner as in Example 1 including the application step, and finally a biaxially oriented film having a film thickness of 38 μm (single layer) was obtained. The film was inferior in concealability.

Comparative Example 4:
In Example 1, instead of the raw material B (described in Comparative Example 1), a polyethylene terephthalate chip containing 8% carbon black having an average particle size of 0.02 μm (not containing titanium dioxide) and having an intrinsic viscosity of 0.66 ( A biaxially oriented film having a film thickness of 30 μm (A / B thickness = 25/5 μm) was finally obtained in the same manner except that the raw material B ′) was used. The film was inferior in concealability.

Comparative Example 5:
In Comparative Example 4, the film thickness was 30 μm (A / B thickness) in the same manner except that the carbon black content of the raw material B ′ was 12% and the thickness of the A layer / B layer was 21/9 μm. A biaxially oriented film having a thickness of 21/9 μm was obtained. Although a film for confirming physical properties could be collected, sparks were intermittently generated in the process of making the film adhere to the cooling drum by electrostatic application, and film formation continuity could not be ensured, and the coating process was carried out. I couldn't.

Comparative Example 6:
In Example 1, a biaxially oriented film having a final film thickness of 30 μm (A / B thickness = 15/15 μm) was prepared in the same manner except that the thickness of the A layer / B layer was changed to 15/15 μm. Obtained. The film was inferior in spectral reflection characteristics.

Comparative Example 7:
In Example 2, a biaxially oriented film having a final film thickness of 30 μm (A / B thickness = 22/8 μm) was obtained in the same manner except that the content of the fluorescent brightener in the raw material A was changed to 300 ppm. It was. The obtained film was a film having poor spectral reflection characteristics.

  The characteristics of the obtained film are summarized in Table 1 below.

  The film of the present invention can be suitably used as an optical reflecting member, for example.

Claims (1)

A polyester system containing 3 to 30% by weight of a white pigment having an average particle size of 0.1 to 1.0 μm and 400 to 5000 ppm of a brightening agent on at least one surface of a polyester resin layer (B layer) containing a light shielding agent. A laminated polyester film having a resin layer (A layer), the total thickness of the film is 20 to 40 μm, the optical density (OD) is 4.0 to 8.0, and the surface of the A layer with respect to light having a wavelength of 460 nm Characterized by having a spectral reflectance of 85 to 105%, a coating layer on at least one surface of the layer A, and a surface resistivity of the coating layer of 1 × 10 ⁶ to 1 × 10 ¹² Ω. Laminated polyester film.