JP5284877B2 - Method for producing simultaneous biaxially stretched film - Google Patents

Description

  The present invention relates to a method for producing a simultaneous biaxially stretched film that can be stably produced without cutting even if a large amount of inorganic pigment is contained.

  In order to improve the brightness of a liquid crystal television, a white film having a high reflectivity and a high concealment property is used as a reflection sheet for a backlight. For example, Patent Document 1 reflects light by containing a large amount of an inorganic pigment in the film. It has been proposed to improve the rate and brightness.

  Moreover, in patent document 2, the manufacturing method of the simultaneous biaxially stretched film which increased the thickness of the film edge 1-3 times as a manufacturing method suitable for the said reflective film is disclosed. However, in this simultaneous biaxial stretching method, since the edge end portion is gripped with a clip and stretched in the vertical and horizontal directions, stress concentrates on the film end portion, and many tears occur at the time of stretching, resulting in a reduction in productivity. It was.

  Therefore, in order to solve this problem, it is necessary to increase the thickness of the edge portion within an appropriate range. However, when forming a white film with high concealment by forming inert voids in the film and forming voids around the particles during stretching to form a white film with high concealment, it is easy to tear due to the low density. There is a problem of becoming. In particular, the problem of tearing and cutting at the edge portion gripped by the clip was significant. Therefore, cutting cannot be prevented simply by increasing the edge thickness.

JP 2007-320238 A JP-A-11-105131 JP-A-8-207119

  The object of the present invention is to manufacture a novel simultaneous biaxially stretched film that can be stably produced without being cut at the time of stretching even in the case where a large amount of inert particles are contained, in view of the problems of the conventional technology described above. It is to provide a method.

The inventions described in the following (1) to (6) for solving the above problems are provided.
(1) In a method of simultaneously biaxially stretching a thermoplastic resin A layer and a thermoplastic resin B layer containing 40 to 80% by weight of an inert particle alternately at least two layers to form a sheet, extruded from a die Both edge portions of the sheet are single layers of only the A layer, the density of the central portion is high compared to the edge when unstretched, and the density of the central portion is low compared to the edge after stretching. Manufacturing method of simultaneous biaxially stretched film.
(2) A ratio (ρe / ρc) of the density (ρc) of the central portion after stretching and the density (ρe) of the edge portion is 1.05 to 1.40, as described in (1) Manufacturing method of simultaneous biaxially stretched film.
(3) The ratio (ρc / ρb) of the density ρb of the central part before stretching and the density (ρc) of the central part after stretching is 0.5 to 0.9 (1), The manufacturing method of the simultaneous biaxially stretched film as described in (2).
(4) The method for producing a simultaneous biaxially stretched film according to any one of (1) to (3), wherein the inert particles are barium sulfate and / or titanium oxide.
(5) The method for producing a simultaneous biaxially stretched film according to any one of (1) to (4), wherein an unstretched width of the edge portion of only the A layer is 20 to 100 mm on one side.
(6) The ratio (te / tc) of the total thickness (tc) of the unstretched central portion A layer and the thickness (te) of the A layer at the edge portion is 3 to 50, (1) to The manufacturing method of the simultaneous biaxially stretched film as described in (5).

  According to the present invention, even when a large amount of inert particles are contained in the film, simultaneous biaxial stretching can be performed while preventing cutting.

Hereinafter, the manufacturing method of the biaxially stretched film of this invention is demonstrated.
The method for producing a simultaneous biaxially stretched film of the present invention is a multilayer film containing a large amount of inactive particles in the center as a product, whereas both edge portions held by a clip have few inactive particles. An unstretched film composed of a single layer film is subjected to a simultaneous biaxial stretching process.

  Therefore, in the biaxially stretched film produced in the present invention, voids due to stretching cannot be formed in a single layer portion with a small amount of inert particles, and therefore simultaneous biaxial stretching can be performed with good productivity without tearing even in the gripping portion. Become. In addition, after stretching, the central portion containing a large amount of inert particles becomes a low-density film, while the edge portion becomes a relatively high-density film and is tough and difficult to tear during stretching.

  However, if it is a multi-layer up to the edge part, when it passes through the simultaneous biaxial stretching process, it tears from the edge part in the stretching process, and cutting often occurs, and film formation may not be performed at all. The ratio (ρe / ρc) between the density (ρc) at the center and the density (ρe) at the center of the product is preferably 1.05 to 1.40. Unfavorable because the thickness unevenness occurs due to stretch spots due to, and conversely, if it is less than the lower limit, the gripping part at the time of simultaneous biaxial stretching can not withstand stress concentration frequently, and film tearing frequently occurs, greatly increasing productivity It is not preferable because it is lowered.

  On the other hand, the present invention is characterized in that the voids are generated in the product part before and after stretching to reduce the density and to exhibit the reflection performance of the film. For this reason, the ratio (ρc / ρb) between the density (ρb) before stretching and the density (ρc) after stretching is preferably 0.5 to 0.9. This is because when the upper limit is exceeded, voids are reduced and the reflection performance of the film is lowered. Conversely, when the lower limit is exceeded, the void layer itself tears and a phenomenon of opening a hole occurs.

  In the present invention, the ratio (te / tc) between the total thickness (tc) of the unstretched central portion A layer and the thickness (te) of the A layer at the edge portion is preferably from 3 to 50. When the thickness of the A layer is reduced, the product part is cut during stretching, and if the thickness is smaller than the lower limit, the ratio of the B layer in the product part is reduced, resulting in poor film reflection performance.

  Further, in the present invention, the polyester A layer constituting the white laminated polyester film preferably contains 1 to 15% by weight of inert particles. This is because if the content of the inert particles is less than 1% by weight, the slipperiness of the film is lowered and winding becomes difficult, and conversely, if it exceeds 15% by weight, the film is easily broken, and the film is formed. This is because the properties are lowered and the generation of chips is increased.

  On the other hand, the ratio of the inert particles contained in the B layer is preferably 40 to 80% by weight. This is because if the content of the inert particles is less than 40% by weight, the reflective performance of the film is deteriorated. On the other hand, if the content exceeds 80% by weight, the void layer of the B layer itself is torn when stretched, resulting in holes. This is because an opening phenomenon occurs. In addition, the inert particles contained in the A layer and the B layer preferably have an average particle size of 0.3 to 3.0 μm, and if the average particle size is less than 0.3 μm, the dispersibility becomes extremely poor. Due to the aggregation of particles, troubles in the production process are likely to occur.

  The average particle size of the particles was measured using a CP-50 type Centrifuggle Particle Size Analyzer manufactured by Shimadzu Corporation. A particle size corresponding to 50 mass percent is read from an integrated curve of particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is used as the average particle size (see “Particle Size Measurement Technology”). "See Nikkan Kogyo Shimbun, 1975, pages 242-247).

  As the inert particles, a white pigment is preferably used from the viewpoint of reducing the visible light transmittance of the film and improving the reflection performance. As the white pigment, for example, titanium oxide, barium sulfate, calcium carbonate, silicon dioxide, preferably barium sulfate and / or titanium oxide are used. Barium sulfate may have a plate-like or spherical particle shape. By using barium sulfate, better reflectance can be obtained. When titanium oxide is used, a rutile type titanium oxide can be exemplified.

  The thermoplastic resin in the present invention includes polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6 and nylon 66, polyimides, and polystyrenes. It is a resin used for melt extrusion molding such as polycarbonates and polyvinyls. Polyesters are polyesters composed of a dicarboxylic acid component and a glycol component. The dicarboxylic acid component is preferably an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, and the glycol component is preferably ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol. Glycols such as are preferred.

  The polyester in the present invention can be obtained by, for example, direct polycondensation of an aromatic dicarboxylic acid and a glycol, but can also be obtained by a method of polycondensation after a dialkyl ester of an aromatic dicarboxylic acid and a glycol are transesterified. be able to. Representative examples of such polymers include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like. However, the polyester may be a copolymer of these, or may be a copolymer of a third component other than these. The thermoplastic resin may contain a stabilizer, a lubricant, a pinning agent, a viscosity modifier, an antioxidant, a pigment, a coloring dye, a fluorescent whitening agent, an ultraviolet absorber, an antistatic agent, and the like.

  Known simultaneous biaxial stretching methods in the present invention can be used. From the viewpoint of achieving both cutting prevention and thickness unevenness, the unstretched width of the edge portion of only the A layer is preferably 20 to 100 mm on one side. If it is wide, product loss will increase.

  In the present invention, the multilayer film is obtained by laminating a thermoplastic resin into two or more layers by a conventionally known method and extruding from a die. For example, as proposed in Japanese Patent Application Laid-Open No. 2002-225107, the product relevant part is laminated in two or more layers in the state of molten resin by a known feed block method, and only the A layer is merged and laminated at both ends thereof. The sheet can be extruded from the die. Further, as proposed in Japanese Patent Application Laid-Open No. 9-76323, a die in which a feed block is laminated in multiple layers and the A layer of the edge portion is individually joined at both ends of the die can be exemplified. Note that the sheet-like molten resin discharged from the die in this manner is tightly cooled and solidified on the cast drum by applying static electricity.

  The obtained unstretched film is subjected to simultaneous biaxial stretching using a tenter, and stretching is simultaneously started and terminated in the longitudinal direction and the width direction. The simultaneous biaxial stretching temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin and less than (Tg + 100 ° C.). The film thus obtained is excellent in dimensional stability and is effective, for example, as a film for a reflector for a liquid crystal display device.

Hereinafter, the present invention will be further described by way of examples. The values in the table were measured or evaluated in the following manner.
(1) Unstretched film thickness at the edge (te)
The film sample was measured with an electric micrometer (K-402B manufactured by Anritsu).
(2) Thickness of each layer (te, tc)
An unstretched film or a biaxially stretched film sample was cut into a triangle, fixed to an embedding capsule, and then embedded with an epoxy resin. And after making the embedded sample into a thin film slice of 50 nm thickness with a microtome (ULTRACUT-S) in a cross section parallel to the vertical direction, it was observed and photographed at an acceleration voltage of 100 kv using a transmission electron microscope, and the photograph taken The thickness of each layer was measured.
(3) Density (ρe, ρc, ρb)
The density of the unstretched film or the biaxially stretched film sample was measured with a vibration digital density meter DMA4500 manufactured by Anton Paar.
(4) Edge cutting The frequency of edge cutting in 24 hours of production was evaluated as “◯: no cutting”, “Δ: cutting 1 to 3 times”, and “x: cutting 4 times or more”.

[Example 1]
Hereinafter, the configuration and effects of the present invention will be described more specifically using examples and comparative examples.
Polyethylene terephthalate with an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.64 dl / g as a thermoplastic resin contains 12 mol% of copolymer components and 4 wt% of barium sulfate with an average particle size of 0.8 μm in the A layer. And 50% by weight contained in the B layer.
Each polyethylene terephthalate pellet was dried at 160 ° C. for 4 hours, supplied to an extruder, melted at 275 ° C., and laminated with a feed block so as to consist of three layers of A layer, B layer, and A layer. The layers were laminated in the width direction so as to be positioned at 30 mm at both ends of the die, and extruded from the die to obtain an unstretched sheet. The obtained unstretched sheet was taken up at a speed of 6 m / min on a casting drum while being electrostatically applied, and rapidly cooled and solidified. The center density (ρb) of the unstretched film thus obtained was 1.81 g / cc, the thickness (tc) of the center part of the A layer was 47 um, the thickness (te) of the edge part was 565 um, and te / tc was 12 Met. This film was guided to a simultaneous biaxial stretching machine and simultaneously biaxially stretched by 3.2 and 3.6 times in the longitudinal direction and the width direction in an atmosphere heated at 90 to 120 ° C. while holding both ends with clips, Thereafter, it was cooled to room temperature to obtain a biaxially stretched polyester film having a winding thickness of 188 um. The density (ρb) at the center was 1.10 g / cc, and the density (ρe) at the edge portion was 1.35 g / cc.
The state of film formation for 24 hours in this manner and the obtained characteristics are shown in Table 1. It was found that a biaxially stretched polyester film can be obtained without cutting.

[Examples 2 and 3]
A film was formed under the same conditions as in Example 1 except that the pigment concentration of the B layer was changed. The results are shown in Table 1. It was found that a biaxially stretched polyester film can be obtained without cutting.

[Example 4]
Films were formed under the same conditions as in Example 1 except that the pigments of the A layer and B layer were changed. The results are shown in Table 1.

[Comparative Example 1]
A film was formed in the same manner as in Example 1 except that the A layer, the B layer, and the A layer were formed up to both edge portions. Edge cutting occurred frequently, resulting in poor film formation. It was found that the edge portion was cut because of its low density. The results are shown in Table 1.

[Comparative Example 2]
A film was formed in the same manner as in Example 3 except that the A layer, the B layer, and the A layer were formed up to both edge portions. The film was cut at the stretching zone of the simultaneous biaxial stretching apparatus, and a stretched film could not be collected. The results are shown in Table 1. It was found that it is important to make the edge part a single layer and to have a high density.

Claims (7)

  Layers consisting of a thermoplastic resin containing 1 to 15% by weight of inert particles (A layer) and layers consisting of a thermoplastic resin containing 40 to 80% by weight of inert particles (B layer) are alternately stacked. In the method of simultaneously biaxially stretching as a sheet, both edge portions of the sheet extruded from the die are single layers of only the A layer, and in the unstretched state, the density of the central portion is high in comparison with the density of the edge portion. The method for producing a simultaneous biaxially stretched film is characterized in that after stretching, the density of the central portion is low compared with the edge portion.   The ratio of the density (ρc) of the center portion after stretching and the density (ρe) of the edge portion (ρe / ρc) is 1.05 to 1.40. A method for producing an axially stretched film.   The ratio (ρc / ρb) between the density (ρb) of the central portion before stretching and the density (ρc) of the central portion after stretching is 0.5 to 0.9, or 2. A method for producing a simultaneous biaxially stretched film according to 2.   The method for producing a simultaneous biaxially stretched film according to any one of claims 1 to 3, wherein the inert particles are barium sulfate and / or titanium oxide.   The method for producing a simultaneous biaxially stretched film according to any one of claims 1 to 4, wherein the unstretched width of the edge portion of only the A layer is 20 to 100 mm on one side.   The ratio (te / tc) between the total thickness (tc) of the unstretched central portion A layer and the thickness (te) of the A layer at the edge portion is 3 to 50, characterized in that 5. A method for producing a simultaneous biaxially stretched film according to 5.   The method for producing a simultaneous biaxially stretched film according to claim 1, wherein the laminated film is used as a reflector for a liquid crystal display device.