Method for manufacturing film using a tenter device and polyester film roll

Abstract

To provide a polyester film roll with excellent uniformity of refractive index in the film width direction, and a film manufacturing method that can simultaneously reduce oil adhesion to the film and overstretching of the film due to insufficient heat in the gripping portion in a tenter device. [Solution] A method for manufacturing a film using a tenter device having a gripping means for gripping both ends of a film and a heating means for blowing hot air onto the film, wherein the film gripping means comprises a clip chain having a clip cover that does not obstruct the airflow near the clip.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a film using a tenter device and a polyester film roll.

Background Art

[0002] Plastic films such as biaxially stretched polyester films are widely used in optical applications, release films, dry film resist applications, printer ribbon applications, etc. because of their excellent heat resistance and productivity. In recent years, with the growth of the IT field, the demand for engineering papers and release films used in the production of substrates such as anti-reflection films for displays, diffusion plates for backlights of liquid crystals, touch panels, and optical members such as optical display and liquid crystal retardation plates and polarizing plates has been increasing. Examples of the quality required for the film in such applications include reduction of adhered foreign substances such as oil and oligomers on the film surface, reduction of internal foreign substance defects, and reduction of film surface scratches.

[0003] When manufacturing a biaxially stretched film, a tenter device is generally used. This tenter device usually has gripping means for gripping both ends of the film, heating means for blowing hot air onto the film, and oil supply means for supplying oil to the gripping means. Further, the gripping means has a clip chain for gripping the film, a clip cover, a rail on which the clip travels, and power for driving the clip. In such a tenter device, problems such as oil scattered from the oil supply means to the film running from the gripping means and becoming oil defects, and over-stretching of the film at the gripping portion of the gripping means have become issues.

[0004] As a method for solving such problems, Patent Document 1 discloses a method of attaching cover means for rectifying the air flow near the clip by the gripping means. Patent Document 2 discloses a method of attaching gripping path cover means for protecting the clip chain from hot air to a part or all of the gripping means.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-3889 [Patent Document 2] Japanese Patent Publication No. 2015-30185 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the method described in Patent Document 1, the cover near the clip is an element that obstructs the airflow, and there was a problem that the airflow straightening effect could not be obtained when the airflow volume or turbulence near the gripping means decreased.

[0007] Furthermore, the method described in Patent Document 2 had the problem that the temperature of the film gripping portion did not rise because hot air did not hit the vicinity of the clip, causing the inside of the gripping portion to be overstretched and the film to break.

[0008] The present invention solves the above problems and provides a polyester film roll with excellent uniformity of refractive index in the film width direction, and a film manufacturing method that can simultaneously reduce oil adhesion to the film and overstretching of the film due to insufficient heat in the gripping portion in a tenter device. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have found a solution to the above problems and have arrived at the present invention. That is, the present invention is as follows. (1) A method for manufacturing a film using a tenter device having gripping means for gripping both ends of a film and heating means for blowing hot air onto a film, wherein the film gripping means comprises a clip chain having a clip cover that does not obstruct the airflow near the clip. (2) A method for manufacturing a film using a tenter device having gripping means for gripping both ends of a film and heating means for blowing hot air onto a film, wherein the film gripping means comprises a clip chain having a clip cover with an opening near the clip. (3) The method for manufacturing a film according to (1) or (2), wherein the coverage of the upper surface of the clip of the clip cover is 15% or more and 50% or less. (4) A method for manufacturing a film according to any one of (1) to (3), wherein the angle between the clip cover and the upper surface of the clip is 0° or less. (5) A method for manufacturing a film according to any one of (1) to (4), wherein the distance between the clip cover and the clip is 5 mm or more and 10 mm or less. (6) A polyester film roll in which the refractive index difference ΔR3 is the average value of the refractive index difference |ΔR1| between one end S1 and the center and the refractive index difference |ΔR2| between the other end S2 and the center, when the refractive index is measured at a total of three points: the center in the width direction of the film and points 600 mm inward from both ends in the width direction, and the number of oil defects is 4 or less per 1000 m length. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for manufacturing a film that can simultaneously reduce oil splashing onto the film during travel and overstretching of the film due to insufficient heat in the gripping portion. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing a first example of a gripping means in a tenter device that can be used in the film manufacturing method of the present invention. [Figure 2] This is a schematic cross-sectional view showing a second example of a gripping means in a tenter device that can be used in the film manufacturing method of the present invention. [Figure 3] This is a schematic plan view of a tenter apparatus that can be used in the film manufacturing method of the present invention. [Figure 4]This is a schematic cross-sectional view showing a third example of a gripping means in a tenter device that can be used in the film manufacturing method of the present invention. [Modes for carrying out the invention]

[0012] The method for manufacturing the film of the present invention will now be described in detail with reference to the drawings. The method for manufacturing the film of the present invention is a method for manufacturing a film using a tenter device having a gripping means for gripping both ends of the film and a heating means for blowing hot air onto the film, characterized in that the film gripping means comprises a clip chain having a clip cover that does not obstruct the airflow near the clip.

[0013] The tenter device used in the film manufacturing method of the present invention is equipped with gripping means for gripping both ends of the film, and the gripping means is equipped with a clip chain having a clip cover that does not obstruct the airflow near the clip. Here, "both ends of the film" refers to both ends in the width direction of the film, and the width direction refers to the direction perpendicular to the direction in which the film travels during the manufacturing process (sometimes called the flow direction or longitudinal direction) within the film surface. The configuration of such gripping means is not particularly limited as long as it can grip both ends in the width direction. Also, "near the clip" refers to the area within 50 mm from the clip unless otherwise specified. The length and shape of the clip cover are not limited as long as they do not obstruct the airflow near the clip, but preferred examples include those with an opening near the clip or those with a coverage rate of 15% to 50% of the top surface of the clip.

[0014] In the present invention, the coverage rate of the clip cover is preferably 15% or more and 50% or less. An example will be explained using Figure 1. The gripping means shown in Figure 1 consists of a clip 1 that grips the film 4, a rail 2 on which the clip chain runs, and a clip cover 3 that covers them, and shows a preferred example in which the coverage rate of the upper surface of the clip 1 is 15% or more and 50% or less. Here, the coverage rate of the upper surface of the clip 1 refers to the ratio of the length of the clip cover 3 to the length of the upper surface of the clip 1, and is L1 / L2 when the length of the upper surface of the clip 1 is L1 and the length of the clip cover portion of the upper surface of the clip 1 is L2. With this configuration, the temperature near the clip 1 rises without obstructing the hot air blown from the top of the tenter, and overstretching of the film near the clip is reduced.

[0015] By reducing the clip cover coverage to 50% or less, airflow is not obstructed, which improves temperature unevenness near the clip and prevents partial overstretching, thus preventing film breakage and making it preferable.

[0016] On the other hand, by setting the coverage rate to 15% or more, it is possible to prevent the inflow of hot air from above the rail and the generation of oil mist from the rail due to the inflow of hot air, so that the oil mist does not flow out of the gripping path cover, which is preferable. From these viewpoints, in the film manufacturing method of the present invention, it is more preferable that the coverage rate of the clip cover is 15% or more and less than 40%.

[0017] In the clip cover of the present invention, the angle formed with the upper surface of the clip is preferably 0° or less. The embodiments will be described with reference to FIG. 2. The gripping means shown in FIG. 2 is composed of a clip 1 and a clip cover 3 covering it. The angle θ between the clip cover 3 on the upper surface of the clip 1 and the upper surface of the clip 1 is preferably 0° or less. Here, the angle θ is defined as 0° when the clip cover 3 and the clip are parallel, with the direction in which the clip cover 3 and the clip 1 separate being positive and the direction in which the clip cover 2 and the clip 1 approach being negative. When the clip cover 3 is composed of a plurality of plate-like bodies, it is preferable that each plate is provided so as to be parallel to each other, but they may be attached at different angles. In the case where the plurality of plate-like bodies are attached such that the angles with the film are different from each other, it is more preferable that the angle θ between all of the plurality of plate-like bodies and the upper surface of the clip 1 is 0° or less. However, if the angle θ between at least one of the plurality of plate-like bodies and the upper surface of the clip 1 is 0° or less, it can be regarded as "the angle formed with the upper surface of the clip is 0° or less". By making the angle formed with the upper surface of the clip 0° or less, it is possible to prevent oil mist from coming out of the gripping path cover, which is preferable.

[0018] The tenter device used in the method for manufacturing the film of the present invention has a heating means for blowing hot air onto the film, and blows hot air onto both surfaces of the film from a direction perpendicular to the film. By having such means, it is possible to adjust the temperature of the film to a temperature suitable for stretching, and to thermally fix the stretched film at a high temperature.

[0019] Hereinafter, the tenter device used in the method for manufacturing the film of the present invention will be described with reference to the drawings. FIG. 3 is a schematic plan view of a tenter device that can be used in the method for manufacturing the film of the present invention. In FIG. 3, the film 4 is gripped at both ends in the width direction by a plurality of clips 1 (each clip is not shown, and the entire clip chain is shown) at the entrance of the tenter device 5, and is sent to the preheating zone 6 of the tenter device 5. The film 4 is heated by blowing hot air at a predetermined temperature in the preheating zone 6, and then in the stretching zone 7, it is heated by hot air at a temperature suitable for stretching and then stretched. Thereafter, the film 4 is heat-fixed by blowing hot air at a temperature suitable for heat-fixing in the heat-fixing zone 8. The heat-fixed film 4 is further cooled to a predetermined temperature in a cooling zone (not shown), discharged outside the tenter device 5, and released from the grip by the clip 1.

[0020] A plurality of clips 1 are connected in a clip chain and are covered by a clip cover 3 in the section from the entrance to the exit of the tenter device 5. Looking at one clip 1, the clip 1 grips the film at the entrance of the tenter device 5, passes through a plurality of bent portions of the gripping path in the tenter device 5, releases the film 4 at the exit, and returns to the entrance through the return path outside the tenter device 5. This movement is repeated by driving the clip chain.

[0021] Also, in the return path (the section from when the clip 1 releases the film 4 until it returns to the entrance), it is desirable to have cover means so that the clip 1 is not exposed to outside air. Since the cover means for the return path does not require a space for gripping the film 4, it is desirable that it is a sealed system and has heat insulation, and has a means for supplying cooling cold air and an exhaust means.

[0022] The gripping path within the tenter device 5 also has a clip cover 3 to prevent oil from splashing from the clip 1. The clip cover 3 is preferably structured in a way that does not obstruct the airflow near the clip, as shown in Figures 1 and 2. Although a sealed system is not possible because the film is being gripped, it is preferable that the distance (d (Figure 2)) between the tip of the clip cover and the clip is 5 mm or more and 10 mm or less. Setting the distance d between the tip of the clip cover and the clip to 5 mm or more is preferable as it prevents the clip cover from coming into contact with the clip and damaging the clip cover or clip. Setting the distance d between the tip of the clip cover and the clip to 10 mm or less is preferable as it suppresses the adhesion of oil mist to the film due to hot air blown from the gripping path through which the clip chain travels, thus preventing the occurrence of oil-related defects.

[0023] When film is manufactured using a tenter device equipped with clips that do not have clip covers, the oil supplied to the clip chain bearings may be blown off by the centrifugal force of the bearings and adhere to the film, resulting in oil-related defects.

[0024] The resin constituting the film in the film manufacturing method of the present invention is not particularly limited as long as it does not impair the effects of the present invention. For example, polyester resins such as polyethylene terephthalate, polyethylene isophthalate, and polybutylene terephthalate; polyolefin resins such as polyethylene and polypropylene; polyamide resins such as nylon 6, nylon 66, nylon 12, aromatic nylon, and aramid; and other polyimide resins, polysulfone resins, polyvinyl resins, polyester ether resins, polycarbonate resins, polyphenylene sulfide resins, polylactic acid resins, cellulose resins, and acrylic resins can be used individually or in combination. Among these, polyethylene terephthalate, polypropylene, aramid, and polyimide resins are preferred. The various resins may contain copolymer components in their molecular chains as long as they do not impair the effects of the present invention or the performance as a film, and may also contain additives such as antistatic agents, weathering agents, inorganic or organic particles, lubricants such as wax, and pigments.

[0025] The method for manufacturing the film of the present invention will be described below in detail using polyethylene terephthalate (PET) film as an example, but the present invention is not limited to the following embodiments.

[0026] PET is dried under reduced pressure at 100°C to 170°C for 8 hours, then supplied to a known molten lamination extruder and melt-extruded at 240°C to 310°C, and filtered through a high-precision filter with a collection efficiency of 95% or more for particles of 5 μm or larger. Subsequently, the obtained molten PET is extruded into a sheet through a slit die maintained at 280°C to 300°C, and cooled and solidified on a casting roll with a surface temperature of 20°C to 30°C using an electrostatic casting method to obtain an unstretched film. This unstretched film is heated to 60°C to 160°C using a roll heated to 60°C to 150°C and a radiation heater, and stretched 3 to 5 times in the longitudinal direction to obtain a uniaxially oriented film. Subsequently, the obtained uniaxially oriented film is transported to a tenter device, stretched 3 to 5 times in the width direction at 90°C to 130°C, heat-treated at 90°C to 240°C, then relaxed, and cooled in the transport process to obtain a biaxially oriented film. Subsequently, the biaxially oriented film is wound up under conditions of a winding speed of 75 m / min to 250 m / min and a winding tension of 40 N / m to 790 N / m to obtain a film roll.

[0027] The tenter device includes gripping means for gripping both ends of the film and heating means for blowing hot air onto the film. The film gripping means used is equipped with a clip chain that has a clip cover that does not obstruct the airflow near the clip.

[0028] Suitable clip covers that do not obstruct airflow near the clip include, for example, those with an opening near the clip or those with a coverage rate of 15% to 50% of the top surface of the clip. Here, "does not obstruct airflow" means a state in which there is no obstruction between the airflow flowing in from roughly above the clip (perpendicular to the film running direction) and the clip, and the airflow flows directly into the clip and its vicinity. By not obstructing the hot air blown from the top of the tenter, the temperature near the clip rises, and overstretching of the film near the clip is suppressed.

[0029] The biaxially oriented polyester film obtained by the film manufacturing method of the present invention has a refractive index difference ΔR3 of 0.15% or less, which is the average value of the refractive index difference |ΔR1| between one end S1 and the center, and the refractive index difference |ΔR2| between the other end S2 and the center, when the refractive index is measured at a total of three points: the center in the width direction of the film and points 600 mm inward from both ends in the width direction. The refractive index was measured using an Abbe refractometer (ATAGO Abbe refractometer NAR-4T). By making ΔR3 0.15% or less, the stretching in the width direction of the film becomes uniform, and breakage due to overstretching of the film near the clip can be reduced.

[0030] Furthermore, the biaxially oriented polyester film obtained by the film manufacturing method of the present invention has four or fewer oil defects per 1000m length. The number of oil defects can be measured by the method described later. By having four or fewer oil defects, the amount of foreign matter adhering to the film surface is reduced, making it preferable.

[0031] The biaxially oriented polyester film of the present invention may be a single-layer film or a laminated structure of two or more layers. When two or more layers are laminated, it consists of a polyester A layer and a polyester B layer, and in the case of three layers, it is a laminated film consisting of three layers: a polyester A layer, a polyester B layer, and a polyester A layer. In this case, by controlling the amount of particles contained in the layers constituting the surface layer (laminated portion), it is possible to reduce the consumption of petroleum resources and obtain cost benefits by appropriately mixing recovered raw materials from the edge portion generated in the film-making process, or recycled raw materials from other film-making processes, into the inner layer, within a range that does not adversely affect the characteristics of the film surface. In other words, it is preferable that the biaxially oriented polyester film of the present invention contains recovered raw materials and / or recycled raw materials.

[0032] The thickness of the biaxially oriented polyester film of the present invention is preferably 12 μm or more and 188 μm or less, and more preferably 25 μm or more and 50 μm or less. A thickness of 12 μm or more is preferable because it prevents the coating layer on the biaxially oriented polyester film from not being able to be supported, which can lead to uneven drying in subsequent processes and insufficient suppression of heat wrinkles. A thickness of 188 μm or less provides excellent resistance to heat wrinkles and a sufficient roll length, making it cost-effective as a base material.

[0033] The biaxially oriented polyester film roll of the present invention is preferably made by winding a polyester film having a length in the width direction (TD) of 400 mm or more and a length in the longitudinal direction (MD) of 500 m or more and a length in the longitudinal direction of 20,000 m or less, and more preferably having a length in the width direction of 500 mm or more and a length in the longitudinal direction of 1,000 m or more and a length in the longitudinal direction of 18,000 m or less. By making the length in the width direction and the length in the longitudinal direction of the polyester film within the above ranges, it is possible to prevent problems such as wrinkles caused by differences in roll hardness and circumference in the width direction of the wound polyester film roll, making it preferable. [Examples]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. The evaluations shown in the examples were performed using the methods and conditions described below.

[0035] (Evaluation method) (1) Oil splatter 1000m of film was unwound from the obtained film roll and inspected for oil defects using a reflective inspection machine (Hyutec Co., Ltd. "MaxEye.AQuO" (registered trademark) 2). The measurement conditions were set to a sensitivity of 10%, and oil defects with a detection width and detection length of 1 pixel or more were detected. Here, the sensitivity setting refers to the ratio of the set value to the maximum possible value. From the obtained inspection results, oil defects with a defect area of ​​10 pixels or more were evaluated according to the following criteria. ○: After inspecting a 1000m length of film, no oil defects were found in the film. △: After inspecting a 1000m length of film, 1 to 4 oil defects were found in the film. ×: After inspecting a 1000m length of film, more than 5 oil defects were found in the film.

[0036] (2) Whitening of the film edges 100m of film was unwound from the obtained film roll, and the whitening condition due to overstretching at the widthwise end of the film was visually observed and evaluated according to the following criteria. ○: No whitening was observed at the edges in the width direction of the film. △: Whitening with a width of 3 mm to 5 mm was found at the widthwise edge of the film. ×: Whitening exceeding 5 mm in width was found at the edges in the width direction of the film.

[0037] (3) Film breakage starting from whitening at the widthwise edge The extent of film breakage, starting from the whitened areas, was visually inspected and evaluated according to the following criteria. ○: Whitening did not occur at all. Or, film breakage originating from the whitened area did not occur for more than 48 hours from the start of production. △: Film rupture originating from the whitened area occurred between 24 and 48 hours after the start of production. ×: Film rupture originating from the whitened area occurred before 24 hours had passed since the start of production.

[0038] (4) Difference in refractive index of the film Three points were sampled from the obtained film: the center in the width direction and two points 600 mm inward from both ends in the width direction. The refractive index was measured using an Abbe refractometer (ATAGO Abbe refractometer NAR-4T). From the obtained results, the refractive index difference ΔR3 was calculated as the average of the refractive index difference |ΔR1| between one end S1 and the center, and the refractive index difference |ΔR2| between the other end S2 and the center.

[0039] (Example 1) Polyethylene terephthalate (PET) was dried under reduced pressure at 160°C for 8 hours, then supplied to a known melt lamination extruder and melt-extruded at 275°C. The resulting material was filtered through a high-precision filter with a 95% efficiency for capturing foreign matter larger than 5 μm. Subsequently, the obtained molten PET was extruded into a sheet through a slit die maintained at 285°C and cooled and solidified on a casting roll with a surface temperature of 25°C using an electrostatic casting method to obtain an unstretched film. This unstretched film was heated to 105°C using a roll heated to 103°C and a radiation heater, and stretched 4.3 times in the longitudinal direction to obtain a uniaxially oriented film. Subsequently, the obtained uniaxially oriented film was transported to the tenter apparatus shown in Figure 3, stretched 4.4 times in the width direction at 110°C, heat-treated at 210°C, then relaxed, and cooled during the transport process to obtain a biaxially oriented film. Subsequently, a film roll was obtained by winding the biaxially oriented film under conditions of a winding speed of 200 m / min and a winding tension of 150 N / m. The obtained film roll and the evaluation results of film breakage starting from whitening are shown in Table 1. The clip cover used in the tenter device was as shown in Figures 1 and 2, with a clip cover coverage rate of 30%, and the angle θ between the clip cover and the top surface of the clip and the distance d between the clip cover and the clip being 0° and 5 mm, respectively.

[0040] (Examples 2-5, Comparative Examples 1-3) A film roll was obtained in the same manner as in Example 1, except that the clip cover conditions were as shown in Table 1. The obtained film roll and the evaluation results of film breakage starting from whitening are shown in Table 1. In Comparative Example 2, the film was manufactured using a tenter device without a clip cover.

[0041] [Table 1] [Industrial applicability]

[0042] The present invention provides a method for manufacturing a film that can simultaneously reduce oil splashing onto the film and over-stretching of the film due to insufficient heat in the film gripping portion of a tenter device used for transverse stretching of a film. Films obtained by the manufacturing method of the present invention have fewer oil defects and whitening due to over-stretching, making them easy to process, and are therefore suitable for use in optical applications, release applications, dry film resist applications, printer ribbon applications, and the like. [Explanation of Symbols]

[0043] 1. Clip (gripping means) 2 rails 3 Clip Cover 4 Film 5. Tenter device 6 Preheating Zone 7 Extension Zone 8 Thermal Fixation Zones 9 Clipping Neighbors Length of the top of the L1 clip Length of the clip cover portion on the top surface of the L2 clip d Distance between the clip cover and the clip θ is the angle between the clip cover and the top surface of the clip.

Claims

1. A method for manufacturing a film using a tenter device having a gripping means for gripping both ends of a film and a heating means for blowing hot air onto the film, wherein the film gripping means comprises a clip chain having a clip cover that does not obstruct the airflow near the clip.

2. A method for manufacturing a film using a tenter device having a gripping means for gripping both ends of a film and a heating means for blowing hot air onto the film, wherein the film gripping means comprises a clip chain having a clip cover with an opening near the clip.

3. The method for manufacturing a film according to claim 1 or 2, wherein the coverage of the upper surface of the clip of the clip cover is 15% or more and 50% or less.

4. The method for manufacturing a film according to claim 1 or 2, wherein the angle between the clip cover and the upper surface of the clip is 0° or less.

5. The method for manufacturing a film according to claim 1 or 2, wherein the distance between the clip cover and the clip is 5 mm or more and 10 mm or less.

6. When the refractive index was measured at a total of three points: the center in the width direction of the film and a point 600 mm inward from both ends in the width direction, one end S １ and the refractive index difference in the central part |ΔR １ |, the other end S ２ and the refractive index difference in the central part |ΔR ２ The average value of the refractive index difference ΔR ３ A polyester film roll having an oil content of 0.15% or less and 4 or fewer oil defects per 1000m length.

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