JP6021529B2 - Laminated film - Google Patents

Description

  The present invention relates to a laminated film. More specifically, the present invention relates to a laminated film that is excellent in handling properties, hardly causes surface defects such as scratches, has high transparency, and is particularly suitable as an optical substrate film.

  Conventionally, an optical base film is required to have high transparency (light transmittance) and no surface defects such as scratches. For example, a base film used for a transparent electrode of a touch panel is used as a transparent electrode by applying a hard coating process to the transparent film, and this is incorporated into a liquid crystal display device as a touch panel module. In the touch panel thus created, the liquid crystal display is visually recognized through the transparent electrode. Therefore, in order to obtain a clear display, a substrate film that is highly transparent and free from surface defects is required. However, a conventional film with few surface defects is generally very difficult to achieve both reduction of surface defects and high transparency, and in recent years, higher light transmittance is required.

JP 2001-261856 A JP 2003-266622 A

  The present invention has been made in view of the above-described background art, and an object thereof is to provide a laminated film having high transparency (light transmittance) and excellent handling properties and hardly causing surface defects.

  As a result of intensive studies to solve the above problems, the present inventor has high transparency and few surface defects if a surface layer containing specific large particles is provided on at least one surface of a base material layer made of polyester. As a result of finding out that it can be achieved at the same time and further studying it, the present invention has been completed.

That is, the object of the present invention can be achieved by the following configuration.
1. A laminated film having a surface layer on at least one surface of a base material layer made of polyester (I) having an ethylene terephthalate unit as a main repeating unit, and the surface layer is made of massive particles having an average particle diameter of 5 to 12 μm. It is made of polyester (II) containing ethylene terephthalate unit as a main repeating unit, the center line average surface roughness Ra is 15 to 70 nm, the ten-point average roughness Rz is 400 to 10,000 nm, and the average of the massive particles A laminated film having a surface layer thickness (thickness of one surface layer) of 0.1 to 0.6 when the particle size is 1, and a total light transmittance of the laminated film of 91.0% or more.
2. 2. The laminated film according to 1 above, wherein the melting point Tm (I) of the polyester (I) and the melting point Tm (II) of the polyester (II) satisfy the following formula.
Tm (I) -5 <Tm (II)
3. 3. The laminated film according to 1 or 2 above, which has surface layers on both sides of the base material layer.
4). 4. The laminated film according to any one of 1 to 3, wherein the base material layer and the surface layer are laminated by a coextrusion method.
5). The laminated film according to any one of the above 1 to 4, which is used for optical applications.

  The laminated film of the present invention has a feature that it has high transparency and at the same time is excellent in handling properties, so that surface defects are unlikely to occur. Therefore, it can be particularly suitably used as an optical film that has recently been demanded for transparency.

  The laminated film of the present invention has a surface layer to be described later on at least one surface of a base material layer made of polyester (I) having ethylene terephthalate units as main repeating units.

[Base material layer]
The base material layer in the present invention is formed from polyester (I) having ethylene terephthalate units as main repeating units. Here, “main” means that the ethylene terephthalate unit is 80 mol% or more, preferably 85 mol% or more, more preferably 95 mol% or more, based on the total repeating units (100 mol%) of the polyester. From the viewpoint of heat resistance, a polyester having a low copolymerization component such as homopolyethylene terephthalate that does not contain a copolymerization component is preferred. In the case of copolymerized polyethylene terephthalate, as the copolymer component, the dicarboxylic acid component includes, for example, aromatic dicarboxylic acids such as isophthalic acid and naphthalenedicarboxylic acid, fats such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid. And alicyclic dicarboxylic acids such as aliphatic dicarboxylic acids and cyclohexanedicarboxylic acids. Examples of the diol component include 1,4-butanediol, 1,6-hexanediol, aliphatic diols such as diethylene glycol, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols such as bisphenol A. It can be illustrated. These may be used alone or in combination of two or more.

  The intrinsic viscosity of the polyester (I) is preferably 0.40 dl / g or more, more preferably 0.50 to 0.90 dl / g at 35 ° C. in o-chlorophenol. When the intrinsic viscosity is less than 0.40 dl / g, cutting may occur frequently during film formation, or the strength of the product after forming may be insufficient. On the other hand, if the intrinsic viscosity becomes too high, the melt viscosity becomes high, so that melt extrusion is difficult, and the polymerization takes a long time and the productivity may be deteriorated.

The melting point Tm of the polyester (I) is preferably 235 ° C. or higher, more preferably 240 ° C. or higher, further preferably 245 ° C. or higher, particularly preferably 250 ° C. or higher, from the viewpoint of heat resistance.
In addition, the polyester (I) may contain a small amount of additives within a range that does not impair the object of the present invention, such as a lubricant such as inert particles, an antioxidant, an ultraviolet absorber, an antistatic agent and the like. Additives are exemplified.

In addition, it is preferable that the base film of this invention does not contain an inert particle in a base material layer from a viewpoint of obtaining a high light transmittance. However, in order to prevent the generation of minute scratches in the manufacturing process and to improve the roll-up property of the film, the inert particles as a lubricant are 100 ppm or less, preferably 10 ppm or less, particularly preferably based on the mass of the base material layer. May be blended in small amounts of 1 ppm or less.
The base material layer made of such polyester (I) may be uniaxially or biaxially oriented. However, in terms of uniformity of in-plane mechanical properties and thermal properties, and suppression of deformation due to heat. To biaxial orientation.

[Surface layer]
The laminated film of the present invention has a surface layer made of the following polyester (II) containing massive particles to be described later on at least one surface, preferably both surfaces, of the above-mentioned base material layer.

(Polyester (II))
The polyester (II) forming the surface layer is a polyester having an ethylene terephthalate unit as a main repeating unit as in the above-described polyester (I), and has an intrinsic viscosity of 0.40 dl / g or more, particularly 0.50 to 0.90 dl. / G is preferable. The polyester (II) may be the same as or different from the polyester (I), but the melting point Tm (II) of the polyester (II) is higher than the melting point Tm (I) -5 ° C. of the polyester (I). High (Tm (I) -5 <Tm (II)), in particular, higher than Tm (I) -3 ° C. is preferable from the viewpoint of the heat resistance of the resulting laminated film, especially when both polyesters are the same. Further, it is preferable from the viewpoint of productivity and cost.
The melting point Tm of the polyester (II) is preferably 235 ° C. or higher, more preferably 240 ° C. or higher, further preferably 245 ° C. or higher, particularly preferably 250 ° C. or higher, from the viewpoint of heat resistance.

Polyester (II) may be added with a small amount of additives such as antioxidants, ultraviolet absorbers and antistatic agents in addition to the bulk particles described below, as long as the object of the present invention is not impaired. .
Such a surface layer made of polyester (II) may be unoriented or uniaxially or biaxially oriented in the same manner as the base material layer, but biaxially oriented is the mechanical property of the laminated film. It is more preferable from the viewpoint of characteristics and thermal characteristics.

(Lumped particles)
The massive particles contained in the polyester (II) are those in which primary particles aggregate to form secondary particles. By using such massive particles, even if the average particle diameter (secondary particle diameter) is coarse particles such as 4 to 12 μm, the massive particles are collapsed and deformed when the laminated film is stretched and oriented. It becomes possible to follow the stretching deformation of the surface layer, and as a result, generation of voids at the interface between the polyester and the particles can be suppressed. And by suppressing generation | occurrence | production of a void, even if it contains a coarse particle, the laminated | multilayer film which has a high light transmittance are obtained.

  The average particle size (secondary particle size) of the massive particles is 4 to 12 μm, preferably 5 to 12 μm, and more preferably 5 to 10 μm. When the average particle diameter is in the above range, the surface roughness described later can be achieved at the same time with a small amount of blending, and as a result, the characteristics that it is excellent in high transparency and handling properties and hardly causes surface defects can be achieved at the same time. . When the average particle size is too large, it becomes difficult to satisfy the centerline average surface roughness and the 10-point average roughness described later at the same time, while when too small, the centerline average surface roughness and the 10-point average roughness However, it is not preferable because the light scattering increases and the light transmittance decreases.

  The refractive index of the massive particles is preferably close to the refractive index of the polyester (II) constituting the surface layer from the viewpoint of transparency, and is usually 1.45 to 1.65. Preferably it is 1.50-1.65, More preferably, it is 1.55-1.65, Most preferably, it is 1.55-1.60.

Moreover, the scope of the BET specific surface area of 200~800m ² / g bulk particles, a range of more 250~750m ² / g, it is particularly preferably from 300~700m ² / g. When the BET specific surface area is within this range, the collapse and deformation of the massive particles when the laminated film is stretched and oriented becomes more appropriate, and the effect of suppressing the generation of voids is increased and the light transmittance is increased. it can. In addition, when the BET specific surface area becomes small, the effect of suppressing the generation of voids, which is a feature of the massive particles, tends to be reduced. On the other hand, massive particles having a large BET specific surface area are difficult to produce.

The lump particles preferably used include lump silica particles, lump barium sulfate particles, lump alumina particles, and lump calcium carbonate particles. Particularly, a lump film having high light transmittance can be obtained. Particles are preferred.
The content of the massive particles in the surface layer is adjusted so that the center line average surface roughness Ra and the ten-point average roughness Rz of the surface layer are within the ranges described below in consideration of the average particle diameter of the particles. Good. If the content is too small, Ra or Rz tends to be small and handling properties tend to be reduced. On the other hand, if the content is too large, transparency tends to be reduced, so depending on the thickness of the surface layer, Preferably 0.01 to 10% by mass, more preferably 0.05 to 1% by mass, still more preferably 0.05 to 0.20% by mass, particularly preferably 0.08 to 0.16% by mass based on the mass. Range.

(Thickness)
In the present invention, it is preferable that the thickness of the surface layer and the average particle size of the massive particles have a specific relationship. That is, the thickness of the surface layer when the average particle size of the massive particles is 1 (the thickness of one surface layer) is preferably 0.1 to 0.6, more preferably 0.1 to 0.5, particularly Preferably it is 0.2-0.5. When the thickness of the surface layer and the average particle size of the massive particles satisfy this relationship, high transparency and excellent handling properties can be easily achieved simultaneously.

[Laminated film]
(Total thickness)
The total thickness of the laminated film of the present invention is preferably 10 to 500 μm, more preferably 10 to 400 μm.

(Total light transmittance)
The laminated film of the present invention has a light transmittance of 91.0% or more, preferably 91.5% or more, more preferably 92.0% or more. When the light transmittance is 91.0% or more, the optical properties are excellent. For example, when used as a transparent electrode, the visibility of display on the touch panel can be increased.

(Surface roughness)
The laminated film of the present invention has a center line average surface roughness Ra on the surface layer surface of 15 to 300 nm, preferably 15 to 100 nm, more preferably 15 to 70 nm, and further preferably 20 to 50 nm. When Ra is within such a range, the slipperiness is excellent, the surface defects of the film are reduced, and the productivity is excellent. Moreover, it is excellent in transparency. When Ra is too low, the slipperiness tends to be inferior, the surface defects of the film increase, and the transparency tends to decrease. On the other hand, if it is too high, the transparency tends to decrease.

Further, the ten-point average roughness Rz on the surface layer surface is 400 to 9000 nm, preferably 600 to 8000 nm, more preferably 600 to 7000 nm, and particularly preferably 1000 to 5000 nm. When Rz is within such a range, the handling property is excellent and the surface defects of the film are reduced. When Rz is too low, the handling property tends to be inferior, and when it is too high, the transparency tends to decrease.
In order to make Ra and Rz on the surface layer surface within the above ranges, for example, the average particle size (secondary particle size) and content of the massive particles in the surface layer may be appropriately adjusted within the above-mentioned range. Ra and Rz tend to increase by increasing the secondary particle size or increasing the content.

(Haze)
The laminated film of the present invention preferably has a haze of 5% or less, more preferably 3% or less, even more preferably 2.5% or less, and particularly preferably 2% or less. Excellent visibility. In the present invention, low haze can be achieved by containing massive particles having an appropriate size in the surface layer and making the surface of the surface layer have an appropriate roughness.

  The surface of the laminated film of the present invention described above may be coated with a primer layer, or subjected to corona discharge treatment, plasma treatment, flame treatment, or the like. These treatments may be performed within the film production process or after the film production. Moreover, in the range which does not inhibit the objective of this invention, it can have another functional layer.

[Production method of laminated film]
In the present invention, the production method of the laminated film is not particularly limited, but it is preferable that the base material layer and the surface layer are laminated by a coextrusion method because of excellent productivity. For example, the production can be performed as follows. it can.

  That is, for example, (Tm (I) +10) to (Tm ()) in a state where both polyesters are melted together with the polyester (I) that forms the base layer and the lump-containing polyester (II) that forms the surface layer. I) At a temperature of +50) ° C., the sheet is extruded from a die so as to be in contact with each other to obtain an unstretched laminated sheet. This unstretched laminated sheet is placed in a uniaxial direction (longitudinal direction (machine axis direction) or transverse direction (direction perpendicular to the machine axis direction)) (glass transition temperature Tg (I) +5 of polyester (I)) to (Tg). (I) +50) The film is stretched at a temperature of 2 times or more, preferably 3 to 5 times, more preferably 3 to 4 times at a temperature of (° C.), and then (Tg (I) +5) to (Tg (I) +5) to (T The film is stretched at a temperature of Tg (I) +50) ° C. at a magnification of 2 times or more, preferably 3 to 5 times, more preferably 3 to 4 times. By adopting such stretching temperature and magnification conditions, the effect of suppressing the generation of voids in the surface layer can be increased, and the light transmittance of the resulting laminated film can be increased. Next, the biaxially oriented laminated film obtained by stretching is heat-treated at a temperature range of (Tm (I) -30) ° C. to (Tm (I) -5) ° C. The time for this heat treatment is, for example, about 1 second to 1 minute. By performing such heat treatment, crystal orientation of the base material layer can be promoted, and heat resistance can be increased. Note that it is preferable that Tm (II) is higher than the heat treatment temperature because the crystal orientation of the surface layer can be promoted and the heat resistance is further improved.

  The stretching of the laminated film may be either a sequential biaxial stretching method or a simultaneous biaxial stretching method, but if stretched by the simultaneous biaxial stretching method, voids are less likely to occur because stretching is performed simultaneously in the biaxial direction. Since transparency becomes high, it is more preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method.

(1) Average particle size of particles The average particle size was measured using a “CP-50 Centrifugal Particle Size Analyzer” manufactured by Shimadzu Corporation. The particle size corresponding to 50 mass percent was read from the cumulative curve of the particles of each particle size calculated based on the centrifugal sedimentation curve obtained by this measuring instrument and the abundance thereof, and this value was defined as the average particle size ( (Refer to “Particle Size Measurement Technology”, pages 242-247, published by Nikkan Kogyo Shimbun, 1975).

(2) BET specific surface area The specific surface area was calculated according to JIS Z 8901.

(3) Melting point (Tm) and glass transition temperature (Tg) of polyester
10 mg of the sample obtained by separating each layer from the film was sealed in an aluminum pan for measurement and attached to a differential calorimeter (DuPont V4.OB2000 DSC), and 25 ° C. to 20 ° C./min. The temperature was raised to 300 ° C. at a speed, and the melting point (Tm, unit: ° C.) was measured. After holding at 300 ° C. for 5 minutes, the product was taken out, immediately transferred onto ice and rapidly cooled. The pan was again attached to the differential calorimeter, and the glass transition temperature (Tg, unit: ° C) was measured by increasing the temperature from 25 ° C to 20 ° C / min.

(4) Presence / absence of voids A film sample was cut with a microtome in the thickness direction, and the cut surface was observed with a scanning electron microscope S-4700 (approximately 2000 times) manufactured by Hitachi, Ltd. The area ratio was calculated. The ratio was calculated for at least 10 points, the average was obtained, and evaluated according to the following evaluation criteria.
○: Void cross section is 30% or less △: Void cross section is more than 30%, 50% or less ×: Void cross section is more than 50%

(5) Thickness of each layer A film sample was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. And after slicing the embedded sample with a microtome (ULTRACUT-S) and making a thin film slice of 50 nm thickness so that a film cross section parallel to the longitudinal direction and the thickness direction can be observed, using a transmission electron microscope, The film was observed and photographed at an acceleration voltage of 100 kv, and the thickness of each layer was measured from the photograph. At this time, it measured in the location without particle | grains. It carried out about arbitrary 5 places, and calculated an average value as thickness of each layer, respectively.

(6) Total thickness of laminated film A film sample was measured with an electric micrometer (K-402B manufactured by Anritsu Corporation) for any 10 points, and the average value was taken as the total thickness of the film.

(7) Total light transmittance According to JIS K7361, the total light transmittance (unit:%) of the film was measured using the haze measuring device (NDH-2000) by Nippon Denshoku Industries Co., Ltd.

(8) Haze According to JIS K7136, the haze value of the film was measured using a haze measuring device (NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd.

(9) Centerline average surface roughness (Ra), Ten-point average surface roughness (Rz)
Using a surface roughness measuring instrument SE-3FAT manufactured by Kosaka Laboratory Ltd., the center line average roughness (Ra) and ten-point average roughness (Rz) on the surface of the optical functional layer of the film are measured according to the measurement method of JIS B0601. I asked for each. The cut-off was 0.25 mm, the measurement length was 1 mm, the scanning pitch was 2 μm, and the number of scans was 100.

(10) Ease (handling) property The friction coefficient was measured according to JIS K7125 (ISO 8295) on one side and the other side of the film sample, and evaluated according to the following criteria.
[Evaluation criteria for slipperiness]
◎: Less than 0.25 ○: 0.25 or more and less than 0.30 Δ: 0.30 or more and less than 0.40 ×: 0.40 or more

(11) Refractive index of particles The refractive index of particles was measured at room temperature by a refractive index dispersion method.

[ Comparative Example 1]
Polyethylene terephthalate (PET) as polyester (II) for forming the surface layer contains 0.08% by mass of bulk silica particles having an average particle diameter of 4 μm (manufactured by Fuji Silysia Co., Silicia, refractive index 1.45). A polyester composition was prepared. On the other hand, polyethylene terephthalate (PET) was prepared as polyester (I) for forming the base material layer.
These polyester compositions and PET are each sufficiently dried and melted in separate extruders, and these are laminated structures of surface layer / base material layer / surface layer, and the final thickness of each layer is In a state of being laminated so as to have the thickness shown in Table 1, it was extruded from a die and rapidly cooled on a casting drum to obtain an unstretched laminated sheet. Thereafter, this unstretched laminated sheet is preheated at 75 ° C., stretched 3.3 times in the machine direction at a stretch temperature of 110 ° C., preheated at 110 ° C., and 3.6 times in the transverse direction at a stretch temperature of 130 ° C. Stretched. Then, it heat-processed for 10 second at 235 degreeC in the crystallization zone, and obtained the laminated film. In the heat treatment, relaxation was adjusted to 1.5% in the vertical direction and 2.0% in the horizontal direction to adjust the heat shrinkage rate. The evaluation results of the obtained laminated film are shown in Table 1.

[Comparative Example 2, Example 3-15, Comparative Example 1-6]
A laminated film was obtained in the same manner as in Comparative Example 1, except that the polyester (I), polyester (II), particle type, particle content and thickness of each layer used were changed as shown in Tables 1 and 2. The evaluation results of the obtained laminated film are shown in Tables 1 and 2.

  In the table, PET represents polyethylene terephthalate, and IAnPET represents isophthalic acid n-mol copolymerized polyethylene terephthalate. At this time, the copolymerization amount is a value with respect to 100 mol% of all acid components.

The particles in the table are as follows.
Bulk silica: manufactured by Fuji Silysia Co., Silicia, refractive index 1.45
Spherical silicone: GE Toshiba Silicones, Tospearl, refractive index 1.43
Spherical silica: manufactured by Toa Gosei Co., Ltd., HPS, refractive index 1.45

  About the laminated | multilayer film obtained in the Example, the heat resistance test which assumed the lamination | stacking process of the highly crystallized ITO film | membrane was implemented. That is, the film was allowed to stand for 120 minutes in a 150 ° C. environment, and the flatness of the film was evaluated. No wrinkle generation or slight wrinkle generation after heat treatment is excellent in heat resistance of the film (evaluation ○), and wrinkle generation is enough to withstand use. Slightly excellent (evaluation Δ), wrinkles were so great that they could not be used, and the film was inferior in heat resistance (evaluation x).

Since the laminated film of the present invention has high transparency and at the same time has excellent handling properties, it has the feature that surface defects are unlikely to occur. It can be used suitably.
In addition, since the laminated film having the preferred embodiment of the present invention is excellent in heat resistance, a highly crystallized ITO film is formed in order to obtain a highly conductive electrode such as that used for an electrode of a capacitive touch panel, for example. Even if it is applied to the intended use, the planarity can be maintained, so that it can be suitably used for the intended use.

Claims (5)

A laminated film having a surface layer on at least one surface of a base material layer made of polyester (I) having an ethylene terephthalate unit as a main repeating unit, and the surface layer is made of massive particles having an average particle diameter of 5 to 12 μm. It is made of polyester (II) containing ethylene terephthalate unit as a main repeating unit, the center line average surface roughness Ra is 15 to 70 nm, the ten-point average roughness Rz is 400 to 10,000 nm, and the average of the massive particles A laminated film having a surface layer thickness (thickness of one surface layer) of 0.1 to 0.6 when the particle size is 1, and a total light transmittance of the laminated film of 91.0% or more. The laminated film according to claim 1, wherein the melting point Tm (I) of the polyester (I) and the melting point Tm (II) of the polyester (II) satisfy the following formula.
Tm (I) -5 <Tm (II)   The laminated film according to claim 1 or 2 which has a surface layer on both sides of a substrate layer.   The laminated film according to any one of claims 1 to 3, wherein the base material layer and the surface layer are laminated by a coextrusion method.   The laminated film according to any one of claims 1 to 4, which is used for optical applications.