JP4877786B2 - Laminated polyester film - Google Patents

Description

  The present invention resides in a laminated polyester film, more specifically, a laminated polyester film that is highly excellent in concealability and reflection characteristics and is suitably used for various optical reflecting members.

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 is inevitable if the film thickness is 19 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).
JP 2001-26087 A

  The present invention eliminates the above-mentioned drawbacks of the prior art, and provides a film useful as various reflecting members having high concealability and reflection characteristics in a specific thickness range and severely restricting light leakage. It is a problem to be solved.

  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, an object of the present invention is to provide a polyester resin containing 3 to 30% by weight of a white pigment having an average particle size of 0.1 to 1.0 μm on at least one surface of a polyester resin layer (B layer) containing a light-shielding agent. A laminated polyester film in which layers (A layer) are laminated, the total thickness of the film is 10 to 19 μm, the optical density (OD) of the film is 4.0 or more, and the surface of the A layer with respect to light having a wavelength of 460 nm The spectral reflectance of the laminated polyester film is 70% or more.

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 tends to be insufficient. On the other hand, if the average particle size of the white pigment is too large, the particles tend to 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.

  In order to obtain sufficient light reflectance, one layer (A layer) of the laminated film of the present invention needs to contain the above-mentioned white pigment. 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 25% 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 layer A, the content of the white pigment in the layer A is 5% by weight or more, preferably 10% by weight or more. Preferably it is 15 weight% or more.

  One of the layers constituting the laminated film of the present invention (B layer) needs to contain a light-shielding agent in order to enhance the concealability of the laminated film. Here, the light-shielding agent refers to, for example, a black, white, or colored organic or inorganic pigment.

  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 5 to 30 weight% similarly to the case of the above-mentioned A layer. The upper limit is more preferably 25% by weight or less from the viewpoint of film formation stability, and the lower limit is 10% by weight or more, and further 15% 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 spectral reflectance for light having a wavelength of 460 nm on the surface of the layer A of the laminated film of the present invention needs to be 70% or more. When the spectral reflectance is less than 70%, 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 tends to be insufficient. More preferably, the spectral reflectance is 75% or more, and more preferably 80% or more.

  In order to make the spectral reflectance of the surface of the A layer 70% or more, the A layer may contain a fluorescent whitening agent. 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. Therefore, the content in the layer A is preferably 5000 ppm or less. More preferably, it is 2000 ppm or less.

  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 the present invention, the total thickness of the laminated film is 10 to 19 μm. From the viewpoint of film waist and processability, a white (single layer) polyester film having a thickness of about 6 to 12 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 30 to 60% of the total thickness of the laminated film. When the thickness ratio of the B layer exceeds 60% 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 30% of the total thickness of the laminated film, the concealability of the laminated film tends to be insufficient. The ratio of the preferable B layer thickness to the total thickness is 40 to 50%.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, the white laminated polyester film which has the high concealability and reflection characteristic which was not obtained with the conventional white film 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, and its industrial value is very high.

  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 the value, the higher the concealment.) 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).

Comparative Example 1:
A polyethylene terephthalate chip (raw material A) having an intrinsic viscosity of 0.66 and containing 22% of anatase-type titanium dioxide particles having an average particle diameter of 0.3 μm was prepared. This is put into a twin screw extruder with a vent, 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. To obtain an unstretched sheet. Next, the unstretched sheet was stretched 2.7 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 220 ° C. for 5 seconds. Next, under a 190 ° C. atmosphere, 3% relaxation treatment (to narrow the tenter rail width) was performed in the width direction. Finally, a biaxially oriented film having a film thickness of 18 μm (single layer) was obtained. The film was inferior in concealability.

Comparative Example 2:
A polyethylene terephthalate chip (raw material B) having an intrinsic viscosity of 0.66 and containing 6% of carbon black having an average particle size of 0.02 μm was prepared. The raw material A (described in Comparative Example 1) and the raw material B are put into separate twin screw extruders with vents, melted and kneaded at 270 ° C., and the obtained melt is mixed with the raw materials A / B in a T die. After being laminated in such a manner, it was extruded into a slit shape and adhered and cooled on a cooling drum at 30 ° C. by an electrostatic application method to obtain an unstretched sheet. Next, the same stretching treatment and the like as in Comparative Example 1 were performed, and finally a biaxially oriented film having a film thickness of 18 μm (A / B thickness = 10/8 μm) was obtained. The film was inferior in concealability and spectral reflection characteristics.

Comparative Example 3:
A biaxially oriented film having a film thickness of 18 μm (A / B thickness = 10/8 μm) was finally obtained in the same manner as in Comparative Example 2, except that the carbon black content of the raw material B was changed to 12%. Although a film for confirming physical properties could be collected, sparks were intermittently generated in the step of bringing the film into close contact with the cooling drum by electrostatic application, and film formation continuity could not be ensured.

Example 1:
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. The raw material A (described in Comparative Example 1) and the raw material B ′ were used, and the subsequent manufacturing method was the same as in Comparative Example 2, and finally the film thickness was 18 μm (A / B thickness = 10/8 μm). A film was obtained.

Example 2:
In Example 1, except that the thickness of the A layer / B layer was changed to 12/6 μm, a biaxially oriented film having a final film thickness of 18 μm (A / B thickness = 12/6 μm) was obtained. Obtained.

Example 3:
A biaxially oriented film having a final film thickness of 18 μm (A / B thickness = 8/10 μm) was obtained in the same manner as in Example 1 except that the thickness of the A layer / B layer was changed to 8/10 μm. Obtained.

Comparative Example 4:
In Example 1, a biaxially oriented film having a final film thickness of 18 μm (A / B thickness = 14/4 μm) was obtained in the same manner except that the thickness of the A layer / B layer was changed to 14/4 μm. Obtained. The film was a film with poor concealability.

Comparative Example 5:
In Example 1, a biaxially oriented film having a final film thickness of 18 μm (A / B thickness = 6/12 μm) was obtained in the same manner except that the thickness of the A layer / B layer was changed to 6/12 μm. Obtained. The film was inferior in spectral reflection characteristics.

Example 4:
A biaxially oriented film having a film thickness of 18 μm (A / B thickness = 10/8 μm) was finally obtained in the same manner as in Example 1, except that 600 ppm of the optical brightener was added to the raw material A.

  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-based resin layer (A layer) containing 3 to 30% by weight of a white pigment having an average particle diameter of 0.1 to 1.0 μm was laminated on at least one surface of the polyester-based resin layer (B layer) containing a light-shielding agent. A laminated polyester film having a total film thickness of 10 to 19 μm, an optical density (OD) of the film of 4.0 or more, and a spectral reflectance of the surface of the A layer with respect to light having a wavelength of 460 nm of 70% or more. A laminated polyester film characterized by being: