Manufacturing method for resin film

Abstract

To provide a manufacturing method capable of suppressing process contamination caused by the precipitation of oligomers and coating sublimates generated in large quantities during a heat treatment process in a tenter oven and reducing a foreign matter adhering to a film by controlling an air flow flowing from the upstream side to the downstream side of a film transport direction and / or from the downstream side to the upstream side of the film transport direction.SOLUTION: A resin film manufacturing method includes means for controlling a specific air flow in a manufacturing method for a resin film using a tenter oven having a heat treatment step and one or more of a preheating step, a stretching step, and a cooling step.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a resin film, and more particularly to a method for producing a resin film that can suppress process contamination caused by precipitation of oligomers and sublimated coating agents that occur when a resin film is heat-treated, and reduce foreign matter adhering to the film. [Background technology]

[0002] Known methods for producing resin films include a sequential biaxial stretching method and a simultaneous biaxial stretching method. In the sequential biaxial stretching method, an unstretched resin film is stretched in its longitudinal direction to obtain a uniaxially stretched film, and the obtained uniaxially stretched film is then introduced into a tenter oven and stretched in its width direction. In the simultaneous biaxial stretching method, an unstretched resin film is introduced into a tenter oven and simultaneously stretched in its longitudinal direction and its width direction in the tenter oven.

[0003] Resin films produced by the sequential biaxial stretching method or the simultaneous biaxial stretching method are widely used for packaging applications, as well as for various industrial material applications, etc. In particular, sequential biaxially stretched films of polyester, polyolefin, and polyamide resins are widely used in applications where unstretched resin films cannot be used due to their excellent mechanical properties, thermal properties, electrical properties, etc., and the demand for such films is also increasing.

[0004] Problems with tenter ovens used to manufacture resin films include the phenomenon that air circulation is not complete within the chambers that make up the tenter oven, and air with a different set temperature flows into adjacent chambers, outside air flows into the tenter oven from outside, and air inside the tenter oven is blown out of the oven. All of these are phenomena in which air flows in the film transport direction, and this type of air flow is called MD (Machine Direction) flow. MD flow occurs due to the accompanying air flow when the resin film is transported, the difference between the amount of heated air supplied into the tenter oven and the amount of air exhausted from the tenter oven, etc.

[0005] When an MD flow occurs, air of different temperatures that flows in from outside the room flows near the resin film and mixes with the heated air inside the room, causing unevenness in the efficiency of heating the resin film and large temperature unevenness in the resin film. In a tenter oven, at least one of the following processes is performed: a preheating process to heat the resin film to a desired temperature, a stretching process to expand the resin film to a desired width, a heat treatment process to heat treat the resin film at a desired temperature, and a cooling process to cool the resin film to a desired temperature. If temperature unevenness occurs in the resin film in any of these processes, it can cause uneven thickness and properties of the resin film, resulting in a decrease in product quality. In addition to the decrease in product quality, film breakage can occur in the tenter oven, reducing productivity.

[0006] In particular, in the production of polyethylene terephthalate (hereinafter referred to as PET) films, low molecular weight substances such as oligomers (hereinafter simply referred to as oligomers) volatilize from the film during the heat treatment process, so the air in the heat treatment process contains a large amount of oligomers. When the air from the heat treatment process containing a large amount of oligomers enters the adjacent stretching process or cooling process, the saturation amount of the oligomers decreases as the temperature of the air containing the oligomers decreases, and the oligomers eventually precipitate in the tenter oven. The precipitated oligomers cause process contamination in the tenter oven and foreign matter adhering to the film.

[0007] Furthermore, in films for optical applications or displays, in order to provide a functional layer to a base film, a coating liquid may be applied to a resin film and the coating liquid may be heated and dried in a tenter oven. In this case, sublimates of the coating agent (e.g., melamines, etc.) volatilize in the heat treatment process environment, and the sublimates of the coating agent may precipitate in the stretching and cooling processes, similar to oligomers, and may cause contamination in the tenter oven or foreign matter attached to the film.

[0008] As a technique for reducing film-attached foreign matter caused by oligomers and coating agent sublimates, Patent Document 1 discloses a technique for controlling the pressure difference between the stretching step, the heat treatment step, and the cooling step, and discloses controlling the pressure difference in the furnace in an intermediate chamber equipped with air supply and exhaust. Further, Patent Document 2 discloses a technique of providing an intermediate chamber between the heat setting chamber and the cooling chamber and blocking the contaminated air accompanying the transport film with the injection air from the air injection nozzles installed in the intermediate chamber.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] By the way, the method disclosed in Patent Document 1 can be expected to have a certain effect in reducing film-attached foreign matter when it can be controlled to a desired pressure difference. However, when airflow control is performed only by the pressure difference between chambers, it is affected by the pressure fluctuations in the tenter oven, and the film-attached foreign matter may sometimes increase suddenly. Therefore, there is room for improvement in the airflow control of the tenter oven aimed at reducing film-attached foreign matter.

[0011] Further, in the method disclosed in Patent Document 2, since the injection nozzles and the exhaust passage are configured in a circulation system, from the viewpoint of the balance of the air mass in the tenter oven, the total amount of the entrained air and the air from the injection nozzles cannot all be discharged through the exhaust passage, and there are problems such as the generation of foreign matter due to the outflow of contaminated air and temperature unevenness due to the outflow of the air from the injection nozzles.

[0012] The present invention has been made in consideration of the above-mentioned problems, and provides a manufacturing method that controls the airflow flowing from the upstream side to the downstream side in the film transport direction and / or from the downstream side to the upstream side in the film transport direction, thereby making it possible to suppress process contamination caused by precipitation of oligomers and sublimated coating agents that are generated in large quantities during the heat treatment process, and to reduce foreign matter adhering to the film. [Means for solving the problem]

[0013] The resin film manufacturing method of the present invention that solves the above problems is a method for manufacturing a resin film using a tenter oven having a heat treatment step, and one or more steps selected from a preheating step, a stretching step, and a cooling step, comprising the steps of: a means for controlling an air flow flowing from the upstream side to the downstream side in the film transport direction and / or from the downstream side to the upstream side in the film transport direction between the heat treatment step and a step in which the resin film is treated at a temperature lower than that in the heat treatment step, the means for controlling the air flow is a blow-out nozzle that blows air onto the resin film being transported, the blow-out nozzles being at least a pair of blow-out nozzles that face each other across a plane through which the resin film passes; a suction and exhaust mechanism that sucks and exhausts air inside the tenter oven, the suction and exhaust mechanism being located upstream of the pair of blowing nozzles in the conveying direction of the resin film and facing each other across the film passing plane; at least a pair of downstream suction and exhaust mechanisms are located downstream of the pair of blow-out nozzles in the transport direction of the resin film and face each other across the film passing plane.

[0014] In the method for producing a resin film of the present invention, the upstream suction exhaust mechanism and the downstream suction exhaust mechanism are adjusted so that a total exhaust amount from the upstream suction exhaust mechanism and the downstream suction exhaust mechanism is greater than a blow-out amount from the blow-out nozzle, It is preferable that the exhaust volumes of the upstream suction exhaust mechanism and the downstream suction exhaust mechanism are each adjusted to be greater than zero.

[0015] In the resin film manufacturing method of the present invention, it is preferable that the direction of the air blown out from the blowing nozzle is perpendicular to the film transport direction of the resin film.

[0016] In the resin film manufacturing method of the present invention, it is preferable that the static pressure on the side closer to the boundary with the means for controlling the air flow in the heat treatment process and the static pressure on the side closer to the boundary with the means for controlling the air flow in a process in which the resin film is treated at a temperature lower than that in the heat treatment process are each 1 to 30 Pa higher than the static pressure in the space in which the means for controlling the air flow is provided.

[0017] In the resin film manufacturing method of the present invention, the tenter oven includes at least the heat treatment step and the cooling step, It is preferable that a means for controlling the air flow is provided between the heat treatment step and the cooling step.

[0018] In the resin film manufacturing method of the present invention, the tenter oven includes at least the stretching step and the heat treatment step, It is preferable that the means for controlling the air flow is provided between the stretching step and the heat treatment step. Effect of the Invention

[0019] According to the present invention, a manufacturing method can be provided that can suppress process contamination caused by precipitation of oligomers, coating agent sublimation products, and the like that occurs when a resin film is heat-treated, and can reduce foreign matter adhering to the film. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic plan view showing the configuration of a tenter oven. [Diagram 2] FIG. 2 is a diagram showing a method for producing a resin film provided with a means for controlling an air flow according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiment of the method for producing a resin film of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments. Furthermore, each drawing referred to in the following description merely shows the shape, size, and positional relationship in a schematic manner to the extent that the contents of the present invention can be understood. In other words, the present invention is not limited to only the shape, size, and positional relationship exemplified in each drawing. Furthermore, in the description of the drawings, the same parts are given the same reference numerals.

[0022] Fig. 1 is a schematic plan view showing the overall structure of a typical tenter oven used in a method for producing a resin film. A tenter oven is a device that holds both ends of a resin film 3 with continuously running clips 2, and heats and stretches the film 3 to a desired temperature with a circulation nozzle 1 inside the tenter oven. Air from inside the tenter oven taken in through a return port 4 is heated to a desired temperature by a heat exchanger 6 provided either before or after a fan 5 and then supplied to the circulation nozzle 1. In addition, an air supply line 7 and an exhaust line 8 may be provided to ventilate the tenter oven and control the room pressure.

[0023] A tenter oven used in a general sequential biaxial stretching method often has a preheating step, a stretching step, a heat treatment step, and a cooling step in this order. However, for example, the preheating step, the stretching step and the heat treatment step, and the cooling step may be performed in separate tenter ovens, and are appropriately selected according to the purpose. The present invention controls the air flow flowing from the upstream side to the downstream side in the film conveyance direction FR and / or the air flow flowing from the downstream side to the upstream side in the film conveyance direction FR, so that oligomers and coating agent sublimates generated when the resin film 3 is heat-treated are cooled and deposited, preventing them from adhering to the resin film 3 and becoming defects. It is a technology that exerts an effect when manufacturing the resin film 3 using a tenter oven having a heat treatment step and any one or more of the preheating step, the stretching step, and the cooling step. Therefore, it is effective not only for a tenter oven having a preheating step, a stretching step, a heat treatment step, and a cooling step in this order, but also for a case where the preheating step, the stretching step and the heat treatment step, and the cooling step are in separate tenter ovens.

[0024] Here, the preheating step is a step before the stretching step, and means a step of heating the resin film 3 at a temperature equal to or higher than its glass transition temperature. When the resin film 3 is a PET film, its glass transition temperature is about 70 to 90 °C, and its crystallization temperature is about 140 to 170 °C. Therefore, although it also depends on the heat transfer efficiency and the longitudinal length in the preheating step, it is preferable to heat the resin film 3 to 80 °C or higher and 140 °C or lower in the preheating step. If the temperature of the resin film 3 in the preheating step exceeds 140 °C, partial crystallization of PET may proceed, and the resin film 3 may break in the stretching step.

[0025] The stretching step refers to a step of stretching the resin film 3 at least in one axial direction. In this stretching step, it is common to stretch at least in the width direction, but it may be stretched in the width direction and the longitudinal direction simultaneously. The stretching ratio in the width direction and / or the longitudinal direction is appropriately selected depending on the purpose, but generally, 1.2 times or more is selected for the purpose of improving toughness and flexibility, and a range of 1.5 times to 5 times is selected for the purpose of strength and retardation expression. In addition, when the resin film 3 is a PET film, it is preferable to heat the resin film 3 to 80°C or more and 140°C or less in the stretching step, as in the preheating step. If the temperature of the resin film 3 is 140°C or more, crystallization of the PET progresses in part, and the resin film 3 may not be stretched and may break.

[0026] The heat treatment step refers to a step of holding and / or relaxing the resin film 3 while heating the resin film 3 at a temperature higher than the maximum temperature during the stretching step. When the resin film 3 is a PET film, the temperature of the resin film 3 during this heat treatment step is preferably a relatively high temperature of 180°C or higher and 250°C or lower. By providing a heat treatment step, the dimensional stability is improved when exposed to high temperatures in the subsequent processing steps or when used as a final product. In addition, in the heat treatment step, it is possible to narrow the gap between the clips 2 in the width direction and length direction of the resin film 3, which causes the resin film 3 to relax and thermally shrink, thereby further improving the dimensional stability and thickness uniformity.

[0027] The cooling step refers to a step of gripping and / or relaxing the resin film 3 while cooling the resin film 3 at a temperature lower than the lowest temperature in the heat treatment step. As in the heat treatment step, the cooling step can also narrow the gaps between the clips 2 in the width direction and length direction of the resin film 3, which relaxes the resin film 3 and causes thermal shrinkage, thereby improving the dimensional stability and thickness uniformity. When the resin film 3 is a PET film, the temperature of the resin film 3 in the cooling step is preferably 50°C or higher and lower than 180°C.

[0028] Fig. 2 is a diagram showing a method for producing a resin film comprising a means for controlling an airflow according to an embodiment of the present invention. In the present invention, between the heat treatment step and a step in which the temperature for treating the resin film 3 is lower than that of the heat treatment step, a means for controlling an airflow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR is provided. The means for controlling the airflow shown in Fig. 2 comprises blowing nozzles 11, 21 that blow air toward the resin film 3 being transported, and a suction and exhaust mechanism that sucks and exhausts air inside the tenter oven. Specifically, the suction and exhaust mechanism comprises upstream suction and exhaust mechanisms 12, 22 located upstream of the blowing nozzles 11, 21 in the film transport direction FR, and downstream suction and exhaust mechanisms 13, 23 located downstream of the blowing nozzles 11, 21 in the film transport direction FR.

[0029] As the source of air supply to the blowing nozzles 11 and 21, blowers B1 and B2, heat exchangers H1 and H2, and ducts D11, D12, D21 and D22 are provided. As the source of air suction from the tenter oven, blowers B3 and B4 and ducts D31, D32, D33, D41, D42 and D43 are connected to the upstream suction exhaust mechanism 12 and 22 and the downstream suction exhaust mechanism 13 and 23. In other words, the volume of air blown out from the blowing nozzles 11 and 21 and the volume of air sucked and exhausted from the upstream suction exhaust mechanism 12 and 22 and the downstream suction exhaust mechanism 13 and 23 can be adjusted independently. In order to adjust the volume of air supplied to the blowing nozzles 11 and 21 and the volume of air sucked from the upstream suction exhaust mechanism 12 and 22 and the downstream suction exhaust mechanism 13 and 23, an air volume adjustment mechanism (not shown) is provided. The air volume adjustment mechanism is not particularly limited, but for example, an inverter that adjusts the blower frequency, a damper, a valve, an orifice, etc. may be attached to the duct. In addition, in FIG. 2, the ducts D11, D12, D21, D22 of the blow-off nozzles 11, 21 are not connected to the ducts D31, D32, D33, D41, D42, D43 of the upstream suction exhaust mechanism 12, 22 and the downstream suction exhaust mechanism 13, 23. However, the ducts D31, D32, D33, D41, D42, D43 of the upstream suction exhaust mechanism 12, 22 and the downstream suction exhaust mechanism 13, 23 may be connected to the ducts D11, D12, D21, D22 of the blow-off nozzles 11, 21 by separate ducts (not shown), and some of the air sucked from the upstream suction exhaust mechanism 12, 22 and the downstream suction exhaust mechanism 13, 23 may be supplied to the ducts D11, D12, D21, D22 of the blow-off nozzles 11, 21. Since the air sucked from the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 contains hot air from within the tenter oven, it is preferable to return some of that air to the ducts D11, D12, D21, D22 of the blow-out nozzles 11, 21, as this reduces the energy required to heat the blow-out nozzles 11, 21 to the desired temperature. In this case, it is preferable to provide an air volume adjustment mechanism in the ducts connecting the blow-out nozzles 11, 21 to the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23, and adjust the air volume to the desired level.

[0030] The air flow inside the tenter oven in the present invention will be described with reference to Figure 2. The air blown out from the blowout nozzles 11, 21 toward the resin film 3 collides with the resin film 3, changes direction of flow to the upstream and downstream sides in the film transport direction FR, becomes return air, and is sucked and exhausted from the upstream suction and exhaust mechanisms 12, 22 and the downstream suction and exhaust mechanisms 13, 23, respectively. At this time, it is possible to cause the return air to collide with the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR, so that the energy of the air flow is lost, and the stagnant air flow can be sucked and exhausted from the upstream suction and exhaust mechanisms 12, 22 or the downstream suction and exhaust mechanisms 13, 23, respectively. This allows the air current flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR to flow into other processes, suppressing process contamination caused by the precipitation of oligomers and sublimated coating agents generated when the resin film 3 is heat-treated in the tenter oven, and reducing foreign matter adhering to the film.

[0031] The blowing nozzles 11, 21, upstream suction and exhaust mechanisms 12, 22, and downstream suction and exhaust mechanisms 13, 23 are arranged above and below the film passing plane 30, respectively, so that their air blowing surfaces 31 and air suction surfaces 32, 33 face the film passing plane 30. This makes it possible to control the airflow flowing from the upstream to the downstream side in the film conveyance direction FR and / or from the downstream to the upstream side in the film conveyance direction FR, above and below the film passing plane 30, suppressing process contamination caused by precipitation in the tenter oven of oligomers and sublimates of coating agents generated when the resin film 3 is heat-treated, and reducing foreign matter adhering to the film.

[0032] In the present invention, the shape of the opening on the air blowing surface 31 of the blowing nozzles 11, 21 is not particularly limited, but it is preferably a slit shape extending in the width direction. This makes it easier to control the airflow flowing from the upstream side to the downstream side in the film transport direction FR and / or the airflow flowing from the downstream side to the upstream side in the film transport direction FR in the width direction of the resin film 3, thereby suppressing process contamination caused by precipitation in the tenter oven of oligomers and sublimates of coating agents generated when the resin film 3 is heat-treated, and improving the effect of reducing foreign matter adhering to the film.

[0033] The blowing air speed from the blowing nozzles 11, 21 is not particularly limited, as long as it is set to a magnitude capable of controlling the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or the air flow flowing from the downstream side to the upstream side in the film transport direction FR. The wind speed distribution of the blowing nozzles 11, 21 in the width direction of the resin film 3 (the value obtained by dividing the difference between the maximum wind speed and the minimum wind speed by the average wind speed in the width direction) is also not particularly limited, but if the wind speed distribution of the blowing nozzles 11, 21 becomes large, the ability to control the air flow in places where the wind speed is locally low decreases, so the wind speed distribution is preferably within 10%, more preferably within 5%, and even more preferably within 2%.

[0034] The direction of the air blown out from the blowing nozzles 11, 21 is preferably perpendicular to the film transport direction FR of the resin film 3. Perpendicular here means that the angle between the blown air and the film transport direction FR is 90±10 degrees, and the angle is preferably 90±5 degrees, and more preferably 90±2 degrees. This is preferable because it makes it easier to control both the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or the air flow flowing from the downstream side to the upstream side in the film transport direction FR. However, if the air flow flowing from the upstream side to the downstream side in the film transport direction FR or the air flow flowing from the downstream side to the upstream side in the film transport direction FR is known in advance, a so-called inclined nozzle that blows out air in a direction against the air flow may be provided. Alternatively, a mechanism for adjusting the air blowing direction may be provided, and for example, it is sufficient if the angle of the blowing nozzles 11, 21 can be adjusted using general mechanical elements, and is configured by combining one or more of a stage, shaft, gear, joint, hinge, rail, pin, jack, air cylinder, hydraulic cylinder, etc. When the resin film 3 is being produced, the temperature inside the tenter oven is high in order to heat the resin film 3 to the desired temperature, so it is preferable that the air blowing direction can be adjusted from the external space of the tenter oven.

[0035] The distance between the blowing nozzles 11, 21 and the resin film 3 is not particularly limited, and may be set to a size that can control the airflow flowing from the upstream side to the downstream side in the film transport direction FR and / or the airflow flowing from the downstream side to the upstream side in the film transport direction FR. However, the greater the distance between the blowing nozzles 11, 21 and the resin film 3, the greater the blowing wind speed required to control the airflow, and therefore the heating energy required to heat the blown air to a desired temperature increases. Therefore, when the opening of the blowing surface 31 is slit-shaped, it is preferable that the slit gap t and the distance Ls between the blowing nozzles 11, 12 and the resin film 3 are Ls / t≦8. This setting is preferable because it allows the airflow to be controlled in an area where the blown air has a high straightness. When the opening of the blowing surface 31 is hole-shaped, it is preferable that Ls / D≦8, where D is the major diameter of the hole.

[0036] The shape of the openings of the air suction surfaces 32, 33 of the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 may be a slit extending in the width direction or a hole shape of punched metal or the like, and is not particularly limited.

[0037] The wind speed of the air sucked and exhausted from the openings of the air suction surfaces 32, 33 of the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 is not particularly limited because it is determined by the volume of air blown out from the blowout nozzles 11, 21 and the aperture ratio of the openings of the air suction surfaces 32, 33 of the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23. The widthwise distribution of the wind speed sucked and exhausted from the openings of the air suction surfaces 32, 33 of the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 is also not particularly limited, but if the wind speed distribution becomes large, the ability to control the airflow at locations where the suction wind speed is locally low decreases, so the wind speed distribution is preferably within 30%, more preferably within 20%, and even more preferably within 10%.

[0038] The distance Le between the air suction surfaces 32, 33 of the upstream suction / exhaust mechanisms 12, 22 and the downstream suction / exhaust mechanisms 13, 23 and the resin film 3 is preferably greater than the distance Ls between the blowout nozzles 11, 21 and the resin film 3, and the distance Le is preferably 10 to 500 mm greater than the distance Ls, and more preferably 100 to 200 mm greater. This is preferable because it allows the return air to be sucked and exhausted without impeding the straightness of the air blown out from the blowout nozzles 11, 21. If the distances Le and Ls are made equal, the straightness of the air blown out from the blowout nozzles 11, 21 will be impeded, and the ability to control the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR will be reduced. On the other hand, if the distance Le is more than 500 mm relative to the distance Ls, it becomes easier to suck in and exhaust air near the air suction surfaces 32, 33 that are away from the film surface, but it becomes difficult to suck in and exhaust the air blown out from the blowing nozzles 11, 21 and the airflow flowing from the upstream to downstream in the film transport direction FR and / or from the downstream to upstream in the film transport direction FR.

[0039] The numbers of blow-out nozzles 11, 21, upstream suction / exhaust mechanisms 12, 22, and downstream suction / exhaust mechanisms 13, 23 are not particularly limited, and may be set to any number that can control the air flow flowing from the upstream side to the downstream side in the film transport direction FR, and / or the air flow flowing from the downstream side to the upstream side in the film transport direction FR.

[0040] In the present invention, it is preferable that the total exhaust volume from the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 is adjusted to be greater than the blowout volume from the blowout nozzles 11, 21. This makes it easier for the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanisms 13, 23 to suck and exhaust not only the return air after the air blown out from the blowout nozzles 11, 21 collides with the resin film 3, but also the airflow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR, thereby improving the airflow disruption effect and making it easier to suppress process contamination caused by precipitation in the tenter oven of oligomers and sublimates of a coating agent generated when the resin film 3 is heat-treated, and thus improving the effect of reducing foreign matter adhering to the film.

[0041] It is also preferable that the exhaust rates of the upstream suction and exhaust mechanisms 12, 22 and the downstream suction and exhaust mechanisms 13, 23 are each adjusted to be greater than zero. The air blown out from the blowout nozzles 11, 21 collides with the resin film 3 and changes direction of flow to the upstream and downstream sides in the film transport direction FR to become return air, but since the exhaust rates of the upstream suction and exhaust mechanisms 12, 22 and the downstream suction and exhaust mechanisms 13, 23 are each adjusted to be greater than zero, it becomes easier to suck in and exhaust the return air flowing to the upstream and downstream sides in the film transport direction FR, thereby enhancing the airflow disruption effect, making it easier to suppress process contamination caused by precipitation in the tenter oven of oligomers and sublimates of a coating agent generated when the resin film 3 is heat-treated, and improving the effect of reducing foreign matter adhering to the film.

[0042] Preferably, the static pressure on the side closer to the boundary with the means for controlling the air flow in the heat treatment step is 1 to 30 Pa higher than the static pressure in the space provided with the means for controlling the air flow. Similarly, preferably, the static pressure on the side closer to the boundary with the means for controlling the air flow in the step where the temperature for treating the resin film 3 is lower than that in the heat treatment step is 1 to 30 Pa higher than the static pressure in the space provided with the means for controlling the air flow. The present invention provides, between the heat treatment step and the step where the temperature for treating the resin film 3 is lower than that in the heat treatment step, means for controlling the air flow flowing from the upstream side to the downstream side in the film conveyance direction FR and / or the air flow flowing from the downstream side to the upstream side in the film conveyance direction FR. The means includes air blowing nozzles 11 and 21 that blow air toward the resin film 3, upstream suction and exhaust mechanisms 12 and 22, and downstream suction and exhaust mechanisms 13 and 23. Therefore, even when pressure fluctuations occur inside and outside the tenter oven within the above-described pressure difference range, the air flow can be controlled. Thus, it is possible to suppress process contamination caused by the deposition of oligomers, coating agent sublimates, etc. generated when the resin film 3 is heat-treated inside the tenter oven, and to reduce foreign matter adhering to the film. At this time, the smaller the above-described pressure difference, the smaller the amount of air blown out from the air blowing nozzles 11 and 21, and the smaller the amount of air suctioned and exhausted from the upstream suction and exhaust mechanisms 12 and 22 and the downstream suction and exhaust mechanisms 13 and 23. That is, it becomes possible to easily control with less energy consumption. Therefore, preferably, the static pressure on the side closer to the boundary with the means for controlling the air flow in the heat treatment step and the static pressure on the side closer to the boundary with the means for controlling the air flow in the step where the temperature for treating the resin film 3 is lower than that in the heat treatment step are 1 to 15 Pa higher than the static pressure in the space provided with the means for controlling the air flow, and more preferably 1 to 8 Pa higher.

[0043] As described above, a tenter oven used in a general sequential biaxial stretching method often has a preheating step, a stretching step, a heat treatment step, and a cooling step in this order, but the preheating step, the stretching step, the heat treatment step, and the cooling step may be performed in different tenter ovens, and may be appropriately selected according to the purpose. In the heat treatment step, oligomers and sublimates of the coating agent generated when the resin film 3 is heat treated flow from the heat treatment step to the cooling step due to the air flow flowing from the upstream side to the downstream side in the film transport direction FR, and often precipitate in the cooling step. Alternatively, the cold air of the cooling step may flow into the heat treatment step due to the air flow flowing from the downstream side to the upstream side in the film transport direction FR, and the oligomers and sublimates of the coating agent may precipitate in the heat treatment step. Therefore, it is preferable to provide a means for controlling the air flow of the present invention between the heat treatment step and the cooling step, since it is possible to suppress the precipitation contamination of oligomers and sublimates of the coating agent in the heat treatment step and the cooling step, and reduce the amount of foreign matter attached to the film.

[0044] Similarly, from the stretching step to the heat treatment step, the oligomers and sublimates of the coating agent generated in the heat treatment step may be precipitated in the stretching step or the heat treatment step due to the air flow flowing from the upstream side to the downstream side in the film transport direction FR or the air flow flowing from the downstream side to the upstream side in the film transport direction FR. Therefore, it is preferable to provide the means for controlling the air flow of the present invention between the stretching step and the heat treatment step, since it is possible to suppress the deposition contamination of the oligomers and sublimates of the coating agent in the stretching step and the heat treatment step and to reduce the foreign matter attached to the film. In addition, since the air flow may flow reciprocally between the stretching step, the heat treatment step, and the cooling step, it is even more preferable to provide the means for controlling the air flow of the present invention between the stretching step and the heat treatment step and between the heat treatment step and the cooling step, since it is possible to suppress the deposition contamination of the oligomers and sublimates of the coating agent between each step and to reduce the foreign matter attached to the film.

[0045] Resins constituting the film to which the present invention can be applied include, but are not limited to, thermoplastic resins, thermosetting resins, etc. Thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene, polyamide resins such as nylon 6 and nylon 66, polyester resins such as polyethylene terephthalate (PET), polybutylene naphthalate (PBT), polyethylene-2,6-naphthalate (PEN), polybutylene naphthalate (PBN), polytrimethylene terephthalate (PPT), polyethylene-p-oxybenzoate, and poly-1,4-cyclohexylene dimethylene terephthalate (PCT), polycarbonate resins, and polyester resins obtained by copolymerizing polyethylene terephthalate with, for example, diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, and dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, as copolymerization components, polyacetal resins, polyphenylene sulfide resins, etc. Thermosetting resins include epoxy resins, polyimide resins, etc. They can also be suitably used in optical applications where strict control of retardation and thickness unevenness is required, and are also effective in stretching materials that contain amorphous resins such as polycarbonate resins, polyolefin resins, cyclic polyolefin resins, and polyacrylic resins as their constituent components.

[0046] In addition, various additives can be added to the above-mentioned resins depending on the purpose. For example, in order to impart slipperiness, inert particles such as colloidal silica, alumina, calcium carbonate, organic silicone, and polydivinylbenzenesulfonic acid can be added. In addition, antistatic agents, antioxidants, etc. can be added to the film composed of the above-mentioned resins.

[0047] As a polymerization method for PET, any production method can be used, such as a direct polymerization method in which terephthalic acid is directly reacted with ethylene glycol, and, if necessary, with other dicarboxylic acid components and diol components, and an ester exchange method in which a dimethyl ester of terephthalic acid (containing, if necessary, a methyl ester of another dicarboxylic acid) is subjected to an ester exchange reaction with ethylene glycol (containing, if necessary, a diol component).

[0048] Next, a method for producing the resin film 3 of the present invention will be described below, taking as an example the production of a PET film by a successive biaxial stretching method.

[0049] When melt extruding the raw resin (hereinafter simply referred to as the resin raw material), it is preferable to dry the resin raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the resin raw material in this way, the resin melted by the melt extrusion device or the like is metered by a gear pump, the heated and melted resin is extruded, and foreign matter, gelled matter, etc. are removed through a filter or the like. At this time, the extruder may be one or more, and when multiple extruders are used, the resin raw material that has passed through the filter is sent to a lamination device. As the lamination device, a multi-manifold die, a feed block, a static mixer, etc. can be used, and these may be combined arbitrarily.

[0050] The melt of the resin raw material thus obtained is discharged from a die as a sheet-like melt, and is extruded onto a cooling body such as a casting drum to be cooled and solidified, thereby obtaining a non-oriented film. A specific method for obtaining a non-oriented film from a sheet-like melt is preferably a method in which the sheet-like melt is brought into close contact with a cooling body such as a casting drum by electrostatic force using a wire-shaped, tape-shaped, needle-shaped, or knife-shaped electrode to rapidly solidify the melt. Other preferred methods include a method in which air is blown out from a slit-shaped, spot-shaped, or planar device to rapidly solidify the sheet-like melt by bringing it into close contact with a cooling body such as a casting drum, a method in which the sheet-like melt is brought into close contact with a cooling body such as a nip roll to rapidly solidify the melt, and a method in which the back side of the sheet-like melt is depressurized by discharging air between the sheet-like melt and a cooling body such as a casting drum in a decompression chamber to rapidly solidify the sheet-like melt by bringing it into close contact with a cooling body.

[0051] Next, the obtained non-oriented film is stretched in the machine direction (longitudinal stretching) to obtain a uniaxially oriented film. The longitudinal stretching can be performed in one step using one or multiple stretching rolls with the same peripheral speed, or in multiple steps using multiple stretching rolls with different peripheral speeds. In this case, the uniaxial stretching ratio is appropriately selected depending on the purpose, but generally, 1.2 times or more is selected for the purpose of improving toughness and flexibility, and 1.5 times to 5 times is selected for the purpose of strength and retardation expression. The uniaxial stretching can be performed in one step or in two or more steps, but it is preferable to select a stretching method that is less likely to cause defects such as scratches on the film surface and adhesive marks on the roll. In addition, in the longitudinal stretching, it is also possible to further heat the non-oriented film by an infrared heater or the like after heating the non-oriented film with a preheating roll.

[0052] In addition, after the longitudinal stretching, a step of coating a functional layer such as an easy-adhesion layer on both sides or one side of the obtained uniaxially oriented film can be provided. The method of coating the functional layer is not particularly limited, but for example, a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a wire bar coating method, a die coating method, a spray coating method, etc. can be used.

[0053] The uniaxially oriented film obtained by the longitudinal stretching is introduced into a tenter apparatus and stretched in the width direction (transverse stretching) to obtain a biaxially oriented film. The tenter apparatus used for transverse stretching generally has a preheating step, a stretching step, a heat setting step, and a cooling step in this order. In the present invention, between the heat setting step and the step in which the temperature for treating the resin film 3 is lower than that of the heat treatment step, a means for controlling the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or the air flow flowing from the downstream side to the upstream side in the film transport direction FR is provided, and the means for controlling the air flow includes blowing nozzles 11 and 21 for blowing air onto the resin film 3 being transported, and a suction and exhaust mechanism for sucking and exhausting the air in the tenter oven, which includes upstream suction and exhaust mechanisms 12 and 22 located upstream of the blowing nozzles 11 and 21 in the film transport direction FR, and downstream suction and exhaust mechanisms 13 and 23 located downstream of the blowing nozzles 11 and 21 in the film transport direction FR. This embodiment makes it possible to control the airflow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR, thereby suppressing process contamination caused by precipitation of oligomers, sublimated coating agents, etc. in the tenter oven and reducing the occurrence of foreign matter adhering to the film. Note that the preheating process, stretching process, heat setting process, and cooling process in the tenter apparatus may be composed of only one zone, or may be composed of multiple zones in which the temperature setting can be changed for each zone.

[0054] In the manufacturing method of resin film 3 of the present invention, the thickness of the resin film 3 to be stretched (hereinafter, an unstretched film or a uniaxially stretched film is referred to as the resin film 3 to be stretched) is appropriately selected depending on the purpose, but generally, it is preferable that the thickness of the resin film 3 before the manufacturing method of the present invention is within the range of 5 to 1500 μm. If the thickness of the resin film 3 before the manufacturing method of the present invention is less than 5 μm, the yield may be reduced, for example, the resin film may be more likely to break when stretched, and if it exceeds 1500 μm, the transparency may decrease or the thickness as a component may become too large.

[0055] The thickness unevenness in any direction of the resin film 3 (resin film 3 to be stretched) before the manufacturing method of the present invention is applied is preferably 0% to 2.5% of the thickness of the resin film 3, and for example, when the thickness of the resin film 3 is 1000 μm, it is desirable that the thickness unevenness is 0 μm to 25 μm in both the longitudinal and width directions of the resin film 3. This is because, depending on the shape and location of the thickness unevenness, the thinner parts may be locally stretched during stretching, causing unevenness in the physical properties in the width and longitudinal directions. EXAMPLES

[0056] The present invention will be described in more detail below with reference to examples, but the present invention should not be construed as being limited to these examples. As a resin raw material, polyethylene terephthalate (PET) pellets with an intrinsic viscosity of 0.65 dl / g and Tg of 80°C were used, which contained as little internal particles and inactive particles as possible based on polymerization catalyst residues, etc. The pellets were thoroughly vacuum-dried at a temperature of 180°C for 5 hours under a reduced pressure of 3 torr, and the discharge amount was made constant using a gear pump. After filtering through a filter with a filtration accuracy of 5 μm, the pellets were discharged in a sheet form from a die with a width of 2100 mm. The obtained sheet-like melt was cooled and solidified on a casting drum with a surface temperature of 30°C to form a non-oriented film, and stretched in the longitudinal direction at a temperature of 90°C and a magnification of 3.5 times using a longitudinal stretching machine having multiple rolls. The obtained uniaxially oriented film was introduced into a tenter oven having a preheating process, a stretching process, a heat treatment process, and a cooling process in this order, and stretched in the width direction at a temperature of 115°C and a magnification of 3.5 times to form a biaxially oriented film, and then heat-treated in an environment controlled at a temperature of 210°C. The biaxially oriented film was then cooled to below 70°C and wound up at a speed of 180 m / min on a winding machine to obtain a biaxially oriented film with a thickness of 25 μm. The number of foreign particles adhering to the resin film 3 was obtained by counting the number of foreign particles adhering to the film surface with a major axis of 15 μm or more using a transmission and reflection type defect inspection device for the resin film 3 after stretching in a tenter oven. At this time, the number of foreign particles adhering to the film surface with a major axis of 15 to 150 μm was 2.0 particles / 1000 m. 2The following cases were judged to be good:

[0057] Example 1 Between the heat treatment process and the cooling process, the blowing nozzles 11 and 21, the upstream suction exhaust mechanisms 12 and 22, and the downstream suction exhaust mechanisms 13 and 23 for controlling the air flow were installed. The shape of the opening on the air blowing surface 31 of the blowing nozzles 11 and 21 was a slit shape (slit width 20 mm), the blowing wind speed was 10 m / s, and the angle between the wind direction of the blowing air from the blowing nozzles 11 and 21 and the film conveying direction FR of the resin film 3 was 90°. The distance between the air blowing surface 31 of the blowing nozzles 11 and 21 and the resin film 3 was 150 mm. The total exhaust volume of the upstream suction exhaust mechanisms 12 and 22 and the downstream suction exhaust mechanisms 13 and 23 was the same as the air volume blown out from the blowing nozzles 11 and 21, and the exhaust ratio of the upstream suction exhaust mechanisms 12 and 22 and the downstream suction exhaust mechanisms 13 and 23 was 50%:50%. The distance between the resin film 3 and the air suction surfaces 32, 33 of the upstream suction and exhaust mechanisms 12, 22 and the downstream suction and exhaust mechanism 13 was 250 mm. The static pressure at the outlet of the heat setting process was set to 5 Pa higher than the static pressure in the space in which the air flow control means was installed, and the static pressure at the inlet of the cooling process was set to 3 Pa higher than the static pressure in the space in which the air flow control means was installed. At this time, the number of foreign matter particles adhering to the film was 1.5 pieces / 1000 m. 2 Thus, a resin film 3 with a small amount of resin particles was obtained.

[0058] Example 2 The conditions were the same as in Example 1, except that the total exhaust volume of the upstream suction exhaust mechanisms 12 and 22 and the downstream suction exhaust mechanisms 13 and 23 was set to 1.2 times the volume of air blown out from the blowing nozzles 11 and 21. Under these conditions, the number of foreign particles adhering to the film surface was 0.8 particles / 1000 m 2 This is because not only the air blown out from the blow-out nozzles 11, 21 but also the air flowing in the film transport direction FR was sucked in by the upstream suction and exhaust mechanisms 12, 22 and the downstream suction and exhaust mechanisms 13, 23, so process contamination by oligomers and foreign matter adhering to the film were reduced compared to Example 1.

[0059] Example 3 The conditions were the same as in Example 1, except that the static pressure at the outlet of the heat setting process was 30 Pa higher than the static pressure in the space in which the airflow control means was installed, and the static pressure at the inlet of the cooling process was 30 Pa higher than the static pressure in the space in which the airflow control means was installed. Under these conditions, the number of foreign particles adhering to the film surface was 2.0 pieces / 1000 m 2 The larger the pressure difference between the processes, the larger the airflow in the film transport direction FR becomes, but the airflow control means was able to prevent the airflow on the surface of the resin film 3 between the heat setting process and the cooling process, so there was little foreign matter adhering to the film and the resin film 3 was produced in good condition.

[0060] Example 4 Between the stretching steps, the blowing nozzles 11 and 21, the upstream suction exhaust mechanisms 12 and 22, and the downstream suction exhaust mechanisms 13 and 23 for controlling the airflow were installed. The shape of the opening on the blowing surface 31 of the blowing nozzles 11 and 21 was a slit shape (slit width 20 mm), the blowing wind speed was 10 m / s, and the angle between the wind direction of the blowing air from the blowing nozzles 11 and 21 and the film conveying direction FR of the resin film 3 was 90°. The distance between the blowing nozzles 11 and 21 and the resin film 3 was 150 mm. The total exhaust volume of the upstream suction exhaust mechanisms 12 and 22 and the downstream suction exhaust mechanisms 13 and 23 was the same as the air volume blown out from the blowing nozzles 11 and 21, and the exhaust ratio of the upstream suction exhaust mechanisms 12 and 22 and the downstream suction exhaust mechanisms 13 and 23 was 50%:50%. The conditions were the same as in Example 1, except that the distance between the air suction surfaces 32, 33 of the upstream suction exhaust mechanisms 12, 22 and the downstream suction exhaust mechanism 13 and the resin film 3 was 250 mm. Under these conditions, the number of foreign particles adhering to the film surface was 1.2 pieces / 1000 m 2 It was possible to obtain a resin film 3 with a small amount of contamination by oligomers and foreign matter attached to the film, because the airflow between the heat treatment step and the cooling step, as well as between the stretching step and the heat treatment step, could be controlled.

[0061] Comparative Example 1 The resin film 3 was produced without installing the blowing nozzles 11, 21, the upstream suction exhaust mechanisms 12, 22, or the downstream suction exhaust mechanisms 13, 23 for controlling the airflow between the heat treatment process and the cooling process. At this time, the static pressure at the outlet of the heat treatment process was 2 Pa higher than the static pressure at the inlet of the cooling process, and the airflow from the heat treatment process flowed into the cooling process. Under these conditions, the number of foreign particles adhering to the film was 3.2 pieces / 1000 m 2 It was. The following is evident from the above examples and comparative examples. In other words, the manufacturing method of the present invention can control the air flow flowing from the upstream side to the downstream side in the film transport direction FR and / or from the downstream side to the upstream side in the film transport direction FR, thereby providing a manufacturing method that can suppress process contamination due to precipitation of oligomers and coating agent sublimations that occur when the resin film 3 is heat-treated, and reduce foreign matter adhering to the film. [Industrial Applicability]

[0062] The present invention described above can provide a resin film with little attached foreign matter such as oligomers and sublimated coating agents, and can therefore be suitably used in films for optical applications and release applications. [Explanation of symbols]

[0063] 1 Circulation nozzle 2 Clips 3. Resin film 4 Return port 5 Fan 6, H1, H2 heat exchanger 7 Air supply line 8 Exhaust Line 11, 21 Blowing nozzle 12, 22 Upstream suction exhaust mechanism 13, 23 Downstream suction exhaust mechanism 30 Film passing surface 31 Air outlet surface 32, 33 Air suction surface B1, B2, B3, B4 Blowers D11, D12, D21, D22, D31, D32, D33, D41, D42, D43 Duct FR Film transport direction

Claims

1. A method for producing a resin film using a tenter oven, the method comprising the steps of: a heat treatment step; and at least one of a preheating step, a stretching step, and a cooling step, a means for controlling an air flow flowing from the upstream side to the downstream side in the film transport direction and / or from the downstream side to the upstream side in the film transport direction between the heat treatment step and a step in which the resin film is treated at a temperature lower than that in the heat treatment step, the means for controlling the air flow is a blow-out nozzle that blows air onto the resin film being transported, the blow-out nozzles being at least a pair of blow-out nozzles that face each other across a plane through which the resin film passes; a suction and exhaust mechanism that sucks and exhausts air inside the tenter oven, the suction and exhaust mechanism being located upstream of the pair of blowing nozzles in the conveying direction of the resin film and facing each other across the film passing plane; at least a pair of downstream suction and exhaust mechanisms are located downstream in the transport direction of the resin film relative to the pair of blow-out nozzles and opposed to each other across the film passing plane, A method for producing a resin film.

2. the upstream suction exhaust mechanism and the downstream suction exhaust mechanism are adjusted so that a total exhaust volume from the upstream suction exhaust mechanism and the downstream suction exhaust mechanism is greater than a blow-out volume from the blow-out nozzle; The exhaust amounts of the upstream suction exhaust mechanism and the downstream suction exhaust mechanism are adjusted to be greater than zero. A method for producing the resin film of claim 1.

3. a static pressure on a side close to the boundary with the means for controlling the air flow in the heat treatment process and a static pressure on a side close to the boundary with the means for controlling the air flow in a process in which the temperature for treating the resin film is lower than that in the heat treatment process are each 1 to 30 Pa higher than the static pressure in a space in which the means for controlling the air flow is provided; A method for producing the resin film of claim 1.

4. The direction of the air blown out from the blowing nozzle is perpendicular to the film transport direction of the resin film. A method for producing the resin film of claim 1.

5. The tenter oven comprises at least the heat treatment step and the cooling step, A means for controlling the air flow is provided between the heat treatment step and the cooling step. A method for producing the resin film of claim 1.

6. The tenter oven includes at least the stretching step and the heat treatment step, A means for controlling the air flow is provided between the stretching step and the heat treatment step. A method for producing the resin film according to claim 1 or 5.

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