Method of manufacturing polyester film

Abstract

To provide a method of manufacturing a high-quality polyester film with few defects.SOLUTION: There is provided a method of manufacturing a polyester film having a film transport step by using rolls, wherein in the film transport step, an average wind speed in a width direction of the film within a range of 100 mm from each of front and rear surfaces of the film is 0.2 to 0.5 m / s in one direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a polyester film. [Background technology]

[0002] Polyester resins are used in a variety of applications due to their excellent mechanical properties, thermal properties, electrical properties, chemical resistance, moldability, etc. Polyester films made from polyester resins, particularly biaxially oriented polyester films obtained by stretching in two directions to achieve molecular orientation, are widely used as various industrial materials such as components for optical devices, solar cell backsheets, electrical insulating materials, thermal transfer applications, and process paper.

[0003] In particular, in optical applications having transparency, when used as a substrate for a hard coat layer of a liquid crystal device, defects in the film itself are small and difficult to notice, but when used as a component of a liquid crystal device, defects are easily noticeable due to diffusion of a light source, etc., and become product defects. In addition, when used as a protective film to suppress surface scratches of an optical film, if the protective film has a defect, it is not clear whether the defect is in the protective film or in the optical film, which is the product, and this may affect quality inspection.

[0004] One of these film defects is caused by dust that occurs during the film manufacturing process. This defect mainly occurs in the slitter process, where dust is likely to be generated from the slitting blades and people who approach the film when it is wound up and carry it out, and in the transfer and winder process near the slitter process. As a countermeasure against this dust-induced defect, dust is removed by providing a circulating flow that flows in the film transport direction on both the front and back sides of the film (Patent Document 1) or by providing an air flow from the top surface of the film to the film surface (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-298320 A [Patent Document 2] JP 2006-255559 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology in Patent Document 1 requires that there be circulating flows on both the front and back sides of the film that flow in the film transport direction, which raises the risk that the circulating flows will carry dust from places other than the film surface to the film surface, causing defects in the film.

[0007] In addition, the technology of Patent Document 2 requires an airflow that flows from the top surface of the film toward the film surface, and therefore, membrane vibration caused by the airflow colliding with the film surface may induce unexpected film defects.

[0008] Therefore, the present invention provides a method for producing a high-quality polyester film while suppressing the occurrence of defects. [Means for solving the problem]

[0009] [1] The method for producing a polyester of the present invention which solves the above-mentioned problems is a method for producing a polyester film, comprising a step of transporting a film with rolls, in which the transporting step includes a step (A) in which an average wind speed in the width direction of the film within a range of 100 mm from each of the front and back surfaces of the film is 0.2 to 0.5 m / s in one direction.

[0010] The method for producing the polyester film of the present invention is preferably any one of the following aspects [2] to [9]. [2] The method for producing a polyester film according to [1] above, wherein in the step (A), the average wind speed in the film transport direction and the average wind speed in the direction perpendicular to the film surface within the above range are each 10% or less of the average wind speed in the film width direction. [3] The method for producing a polyester film according to [1] or [2] above, wherein in step (A), the average number of dust particles having a particle size of 0.5 μm or more contained in 1 cubic foot of air within the range is 1,000 or less. [4] The method for producing a polyester film according to the above [1] or [2], wherein in the step (A), the turbulence intensity in the range is 0.05 or less. [5] The method for producing a polyester film according to the above [3], wherein in the step (A), the turbulence intensity in the range is 0.05 or less. [6] The method for producing a polyester film according to the above [1] or [2], wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less. [7] The method for producing a polyester film according to the above [3], wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less. [8] The method for producing a polyester film according to the above [4], wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less. [9] The method for producing a polyester film according to the above [5], wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less.

[0011] [Terminology] Next, the meaning of each term in the present invention will be explained. "Line direction" refers to the direction that coincides with the flow direction of a production line used to manufacture the polyester film. The term "vertical direction" refers to a direction that coincides with a direction perpendicular to the floor surface of a production line used in the manufacture of the polyester film. The term "film transport direction" refers to the direction that coincides with the direction in which a polyester film or a sheet-like molded product before becoming a polyester film is transported in a production line used for manufacturing the polyester film. The term "film thickness direction" refers to the direction that coincides with the thickness direction of the polyester film or a sheet-like molded product before it becomes a polyester film in a production line used for manufacturing the polyester film. The term "film width direction" refers to the direction that coincides with the width direction of the polyester film or a sheet-like molded product before it becomes a polyester film in a production line used for manufacturing the polyester film. "Turbulence intensity" refers to the standard deviation of velocity fluctuations (average flow velocity minus instantaneous flow velocity) at a certain point in a flow field and at a certain time period, divided by the average flow velocity. Effect of the Invention

[0012] According to the present invention, a method for producing a high-quality polyester film with few defects can be provided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing one embodiment of a method for producing a polyester film of the present invention as viewed in the production line direction and the film width direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below, but the present invention is not limited to the embodiments including the following examples. The method for producing a polyester film of the present invention is a method for producing a polyester film having a film transporting step using rolls, and is characterized in that the transporting step includes a step (A) in which the average wind speed in the film width direction within a range of 100 mm from each of the front and back surfaces of the film is 0.2 to 0.5 m / s in one direction.

[0015] The polyester film in the present invention is a non-stretched film or a film stretched at least in one direction, containing more than 50.0% by mass and 99.9% by mass or less of polyester resin among all the components constituting the film. The polyester resin that can be used in the present invention is not particularly limited, but is preferably polyethylene terephthalate or polyethylene-2,6-naphthalate. These may be polyester copolymers, but it is preferable that 80 mol % or more of the total repeating structural units are ethylene terephthalate units or ethylene-2,6-naphthalate units. As the copolymer component, for example, diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylene glycol, 1,4-cyclohexanedimethanol, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-hydroxyethoxybenzoic acid can be used.

[0016] In addition, the above polyester may be copolymerized or blended with one or more of an alkali metal salt derivative of sulfonic acid that is not reactive with the polyester, or a polyalkylene glycol or an aliphatic polyester that is insoluble in the polyester, in an amount not exceeding 5% by mass when the total components constituting the polyester film are taken as 100% by mass.

[0017] In the method for producing a polyester film of the present invention, as long as the above-mentioned step (A) is present, there is no particular limitation on the steps upstream and downstream thereof. That is, the polyester film obtained may be an unstretched film obtained in this step, or a uniaxially stretched film or a biaxially stretched film obtained by stretching this unstretched film in the production line direction and / or the film width direction.

[0018] An embodiment of the polyester film manufacturing method of the present invention will be described with reference to Fig. 1. Fig. 1 is a view of an embodiment of the polyester film manufacturing method of the present invention, observed from the production line direction and the film width direction. As shown in Fig. 1, an embodiment of the polyester film manufacturing method of the present invention has an air inlet 3 and an exhaust port 4 on the outer side in the film width direction of a film 2 transported by a roll 1. Air blown out from the air inlet 3 flows in the film width direction, passing near the front and back surfaces of the film, and is exhausted from the exhaust port 4 to the outside of the film-forming booth.

[0019] Here, as shown in the view of the film width direction in FIG. 1, in a polyester film manufacturing method having a step of transporting a film 2 by a roll 1, the film thickness direction and the film transport direction change in a complex manner via the roll 1. On the other hand, the film width direction does not usually change within the process. Therefore, in the step of transporting the film 2 by the roll 1, a uniform flow that flows in the film width direction to remove dust near the film 2 is always a uniform flow parallel to the film surface. By having a step (A) in which such a uniform flow has an average wind speed of 0.2 to 0.5 m / s in one direction in the film width direction within a range of 100 mm from each of the front and back surfaces of the film, it is possible to suppress the air flow from colliding with the film surface and causing membrane vibration.

[0020] In addition, in step (A), it is preferable that the average wind speed in the film transport direction and the average wind speed in the direction perpendicular to the film surface within the above range are each 10% or less of the average wind speed in the film width direction, since this can prevent dust from being transported to the film surface from places other than the film surface.

[0021] In step (A), it is also preferable that the average number of dust particles having a particle size of 0.5 μm or more contained in 1 cubic foot of air within the above range is 1000 or less, since this makes it possible to suppress defects caused by dust.

[0022] Furthermore, in step (A), it is preferable that the turbulence intensity in the above range is 0.05 or less, since this improves the effect of suppressing the air flow from colliding with the film surface and causing membrane vibration, and the effect of suppressing the transport of dust to the film surface from places other than the film surface.

[0023] In the step (A), the absolute value of the surface potential of the film is preferably 5 kV or less, since defects caused by dust adhesion due to potential can be suppressed. In theory, the closer the absolute value of the surface potential is to 0, the more effective it is at suppressing dust adhesion. However, in consideration of the cost of static electricity removal, the lower limit is practically 0.1 kV or more. A digital electrostatic potential meter (KSD-2000) manufactured by Kasuga Electric Co., Ltd. was used to measure the surface potential of the film in the present invention. In the step (A), the measurement distance was set to 100 mm from either the front or back side of the film, and measurements were taken at two points in the film width direction and three points in the production line direction, and the maximum absolute value among these six measured values ​​was taken as the final surface potential of the film. In addition, the measurement positions when measuring the three points in the production line direction were all measured at positions 100 mm or more away from the nearest roll.

[0024] The method of neutralization is not particularly limited, but various ionizers suited to the form of the manufactured product can be provided in a process prior to the process (A), and neutralization cloth, neutralization string, etc. can be appropriately selected and used. Among them, the use of a bar-type ionizer is preferred from the viewpoint of static electricity removal performance.

[0025] As described above, the polyester film manufacturing method of the present invention can prevent unexpected defects due to membrane vibration or dust adhesion to the film surface, and can produce a high-quality polyester film with few defects. EXAMPLES

[0026] [Example 1] A polyester film was actually produced using the polyester film production method shown in Fig. 1, and the results of evaluating the quality are described below. Specific film raw materials, polyester film production method, and quality evaluation method in this embodiment are as follows. ·Production method of polyester film (1) Raw material: polyester resin. (2) Drying: After drying at 160° C. for 2 hours under reduced pressure of 3.0 kPa or less using a rotary vacuum dryer, the mixture was fed to an extruder. (3) Extrusion: The material was extruded at 280°C, passed through a gear pump and a filter, and then fed to a T-shaped nozzle. (4) Molding: The material was extruded into a sheet from a T-shaped nozzle and wrapped around a mirror-finished cooling drum with a surface temperature of 20°C using an electrostatic casting method. (5) Cooling and solidification: Using an air blowing device having 13 air nozzles parallel to the cooling drum, air was blown at 12.4°C and at a speed of 19.4 m / sec onto the film on the cooling drum to cool and solidify it, obtaining an unstretched film. (6) Longitudinal stretching: The unstretched film was preheated to 80°C with a preheating roll, and then heated to 90°C with a radiation heater while being stretched 2.8 times in the longitudinal direction by utilizing the difference in peripheral speed between the rolls. The film was then cooled to 40°C with a cooling roll to obtain a uniaxially oriented film. (7) Transverse stretching: The uniaxially oriented film was held at both ends in the width direction with clips and preheated in an oven at an atmospheric temperature of 130°C, and then continuously stretched 3.3 times in the width direction. The resulting biaxially oriented film was then heat-treated in a heating zone at 230°C, and relaxed by 2.3% by reducing the distance between the clips facing each other in the width direction while cooling to 150°C. (8) Transfer / winder: The clips holding both ends of the film in the width direction were released to remove the film from the oven, and both ends of the film in the width direction were cut and removed. The film was transported by a transport roll and then wound up to obtain a biaxially oriented polyester film with a thickness of 250 μm. The process from the first transport roll after the clips were released to the winding process was a process (A) in which air was supplied and exhausted using the embodiment in FIG. 1 so that the average wind speed in the film width direction within a range of 100 mm from each of the front and back sides of the film was 0.3 m / s in one direction. The average wind speed in the film transport direction and the average wind speed in the film thickness direction within the above range were 0.09 m / s and 0.04 m / s, respectively. Furthermore, the average number of dust particles with a particle size of 0.5 μm or more contained in 1 cubic foot of air within the above range was 5,000 particles. The turbulence intensity in the above range was 0.11, and the surface potential of the film was −6 kV when measured using a Kasuga Electric digital electrostatic potential meter (KSD-2000) at a measurement distance of 100 mm. (9) Slitting: The wide polyester film wound around the roll was divided into four equal parts using three slit blades while being unwound, and then wound into four rolls. In the conveying process from unwinding to winding, the process (A) was carried out by supplying and exhausting air using the embodiment of FIG. 1 so that the average wind speed in the film width direction within a range of 100 mm from each of the front and back sides of the film was 0.3 m / s in one direction. In addition, the average wind speed in the film conveying direction and the average wind speed in the film thickness direction in the above range were 0.1 m / s and 0.04 m / s, respectively. Furthermore, the average number of dust particles with a particle size of 0.5 μm or more contained in 1 cubic foot of air in the above range was 5,000. In addition, the turbulence intensity in the above range was 0.11, and the surface potential of the film was measured at a measurement distance of 100 mm using a digital electrostatic potential measuring device (KSD-2000) made by Kasuga Electric Co., Ltd., and was -7 kV. How to evaluate quality The number of defects in each of the four rolls of polyester film was counted using a defect detector. 2 Average number of defects per unit (Unit: UN / 10m 2The average number of defects for each of the four rolls was then averaged to determine the quality evaluation value.

[0027] [Example 2] A polyester film was produced and evaluated in the same manner as in Example 1, except that in step (A) of the transfer / winder and slitting process, the average wind speed in the film transport direction and the average wind speed in the film thickness direction within the above-mentioned range were set to 0.02 m / s and 0.01 m / s, respectively.

[0028] [Example 3] A polyester film was produced and evaluated in the same manner as in Example 2, except that in step (A) of the transfer / winder and slitting process, the average number of dust particles having a particle size of 0.5 μm or more contained in 1 cubic foot of air in the above range was 800 particles.

[0029] [Example 4] A polyester film was produced and evaluated in the same manner as in Example 3, except that in step (A) of the transfer / winder and slitting process, the turbulence intensity in the above range was set to 0.03.

[0030] [Example 5] Polyester films were produced and evaluated in the same manner as in Example 4, except that in the transfer / winder and slitting steps (A), the surface potential of the film in each step was set to -0.2 and -0.3 kV.

[0031] [Comparative Example 1] A polyester film was produced and evaluated in the same manner as in Example 1, except that the process (A) was not included. The average wind speed in the film transport direction and the average wind speed in the film thickness direction in the transfer / winder and slitting processes were 0.09 m / s and 0.04 m / s, respectively. The average number of dust particles with a particle size of 0.5 μm or more contained in 1 cubic foot of air in the same process was 5,000. The turbulence intensity in the same process was 0.11. The surface potential of the film was measured using a Kasuga Electric digital electrostatic potential meter (KSD-2000) at a measurement distance of 100 mm, and was -6 kV and -7 kV in the transfer / winder and slitting processes, respectively.

[0032] [Evaluation of Results of Examples and Comparative Examples] The quality evaluation of the polyester film of each Example was carried out with a quality evaluation value of 1.1 UN / 10 m of Comparative Example 1. 2 The evaluation was based on the extent to which the effect was suppressed.

[0033] Example 1, which includes step (A), has a quality evaluation value of 0.2 UN / 10 m 2 The number of defects in the polyester film was improved to about 1 / 5 compared to Comparative Example 1.

[0034] Furthermore, in Example 2, in which the average wind speed in the film transport direction and the average wind speed in the film thickness direction in the above range were set to 0.02 m / s and 0.01 m / s, respectively, the quality evaluation value was 0.1 UN / 10 m 2 The number of defects was about 1 / 10 of that in Comparative Example 1. Furthermore, in Example 3, in which the average number of dust particles with a particle diameter of 0.5 μm or more contained in 1 cubic foot of air in the above range was set to 800, the quality evaluation value was 0.03 UN / 10 m 2 The number of defects was about 1 / 37 of that in Comparative Example 1. Furthermore, in Example 4, in which the turbulence intensity in the above range was set to 0.03, the quality evaluation value was 0.02UN / 10m 2 The number of defects was about 1 / 55 of that in Comparative Example 1. In Example 5, the surface potential of the film was set to -0.2 kV in the cross-winder process and -0.3 kV in the slit process, and the quality evaluation value was 0.004 UN / 10 m.2 The number of defects was about 1 / 275 of that in Comparative Example 1.

[0035] In comparison with Example 1, Examples 2 to 5 exhibited a greater effect of suppressing defects and improving quality.

[0036] [Table 1] [Industrial Applicability]

[0037] According to the present invention, a high-quality polyester film with few defects can be produced. [Explanation of symbols]

[0038] 1 roll 2. Film 3 Air supply port 4. Exhaust port

Claims

1. A method for producing a polyester film, comprising a step of transporting a film with rolls, the method comprising step (A) in which an average wind speed in the width direction of the film within a range of 100 mm from each of the front and back surfaces of the film is 0.2 to 0.5 m / s in one direction in the transporting step.

2. The method for producing a polyester film according to claim 1 , wherein in the step (A), the average wind speed in the film transport direction and the average wind speed in the film thickness direction within the range are each 10% or less of the average wind speed in the film width direction.

3. 3. The method for producing a polyester film according to claim 1, wherein in the step (A), an average number of dust particles having a particle size of 0.5 μm or more contained in 1 cubic foot of air in the range is 1,000 or less.

4. The method for producing a polyester film according to claim 1 or 2, wherein in the step (A), the turbulence intensity in the range is 0.05 or less.

5. The method for producing a polyester film according to claim 3 , wherein in the step (A), the turbulence intensity in the range is 0.05 or less.

6. The method for producing a polyester film according to claim 1 or 2, wherein in the step (A), an absolute value of a surface potential of the film is 5 kV or less.

7. The method for producing a polyester film according to claim 3 , wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less.

8. The method for producing a polyester film according to claim 4 , wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less.

9. The method for producing a polyester film according to claim 5 , wherein in the step (A), the absolute value of the surface potential of the film is 5 kV or less.

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