Film manufacturing method

Abstract

To provide a film manufacturing method that identifies the process that caused the film to tear. [Solution] A method for manufacturing a film, comprising two or more steps for continuously measuring the temperature in the width direction of the transported film, wherein the steps are located immediately after the casting step and immediately after the uniaxial stretching step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a film.

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 they are excellent in heat resistance and productivity. In recent years, with the growth of the IT field, the use in optical applications has increased, such as anti-reflection films for displays, diffusion plates for backlights of liquid crystals, substrates such as touch panels, process papers for optical members such as optical displays and liquid crystal retardation plates, polarizing plates, and release films.

[0003] In manufacturing the above film, temperature control in the film manufacturing process is important. As a means for measuring and controlling temperature unevenness of the film, a method is known (Patent Document 1) in which the temperature in the width direction of the film is measured after the preheating process and before the stretching process, and the information is fed back to the preheating process to control the width direction temperature distribution of the film before the stretching process within a certain range while stretching the film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When manufacturing a biaxially stretched film, generally, a casting process is provided in which the molten polymer discharged from the die is cooled on a rotating drum to form an unstretched sheet, and a uniaxial stretching process is provided in which the film is heated (preheated) to a temperature required for stretching and then stretched in the conveyance direction immediately thereafter.

[0006] In these processes, it is crucial whether the amount of heat applied to the film is appropriate, and consequently, whether the film temperature is appropriate, as this greatly affects the thickness variations of the film and the molding condition of the film edges. Furthermore, if the thickness variations and the molding condition of the film edges deteriorate, it can cause the film to tear.

[0007] However, the method described in Patent Document 1 only measures film temperature unevenness at one location after the preheating process and before the stretching process, and therefore cannot capture temperature changes before and after the process.

[0008] The object of this invention is to resolve the above-mentioned issues and provide a method for manufacturing a film that identifies the process that caused the film to tear. [Means for solving the problem]

[0009] To solve the aforementioned problems, the present invention has the following configuration.

[0010] (1) A method for manufacturing a film, comprising a casting step in which a polymer constituting the film is melted, extruded from a die, and cooled on a rotating drum to form an unstretched sheet, and a uniaxial stretching step in which the film is heated to a temperature necessary for stretching and then stretched, wherein the method comprises two or more steps for continuously measuring the temperature in the width direction of the conveyed film, and the steps are located immediately after the casting step and immediately after the uniaxial stretching step.

[0011] (2) The method for manufacturing a film according to (1), wherein when the temperature of one end in the width direction measured immediately after the casting process is X1 and the temperature of the other end is X2, and the temperature of one end in the width direction measured immediately after the uniaxial stretching process is Y1 and the temperature of the other end is Y2, |X1-X2| and |Y1-Y2| are controlled to be less than 3.0°C.

[0012] (3) The method for manufacturing a film according to (1) or (2), wherein the step of continuously measuring the temperature in the width direction of the transported film immediately after the casting step is located within 1.0 m of the film travel distance after the casting step, and the step of continuously measuring the temperature in the width direction of the transported film immediately after the uniaxial stretching step is located within 3.0 m of the film travel distance after the uniaxial stretching step.

[0013] (4) A method for manufacturing a film according to any one of (1) to (3), wherein in the step of continuously measuring the temperature of the transported film in the width direction, the temperatures of both ends in the width direction are compared and the temperature difference is evaluated.

[0014] (5) A method for manufacturing a film according to any one of (1) to (4), wherein a non-contact infrared thermometer is used in the step of continuously measuring the temperature in the width direction of the transported film.

[0015] (6) A method for manufacturing a film, comprising a quality prediction step for predicting the quality of the film and a step for controlling the film manufacturing conditions based on the quality prediction results of the film, The quality prediction step for predicting the quality of the film includes a step of outputting a quality prediction result for the quality information of the film after a predetermined time, by taking process information obtained from the film manufacturing process over a predetermined period and quality information of the film manufactured by the manufacturing process as input parameters, and performing calculations based on a trained model generated by machine learning using the process information and quality information for the manufactured film, thereby obtaining a quality prediction result for the quality information of the film after a predetermined time. A method for manufacturing a film according to any one of (1) to (5), wherein the step of controlling the film manufacturing conditions based on the quality prediction results of the film comprises a step of controlling the film temperature at least immediately after the casting step and immediately after the uniaxial stretching step in the film manufacturing process based on the quality prediction results of the film.

[0016] (7) The method for manufacturing a film according to (6), wherein the process information obtained from the film manufacturing process includes |X1-X2| and |Y1-Y2|, where X1 is the temperature of one end in the width direction measured immediately after the casting process, X2 is the temperature of the other end, Y1 is the temperature of one end in the width direction measured immediately after the uniaxial stretching process, and Y2 is the temperature of the other end. [Effects of the Invention]

[0017] The present invention provides a method for manufacturing a film that identifies the process that caused the film to tear. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram of a method for manufacturing a film according to one embodiment of the present invention. [Modes for carrying out the invention]

[0019] The method for manufacturing the film of the present invention will be described in detail below.

[0020] The resin constituting the film in the method for producing the film of the present invention is not particularly limited as long as the effects of the present invention are not impaired, and examples thereof include thermoplastic resins. Among them, 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; other polyimide resins, polysulfone resins, polyvinyl resins, polyester ether resins, polycarbonate resins, polyphenylene sulfide resins, polylactic acid resins, cellulose resins, acrylic resins, etc. can be used alone or in combination. Among them, it is preferable to use polyethylene terephthalate, polypropylene, aramid, and polyimide resins. In addition, various resins may contain a copolymer component in the molecular chain as long as the effects of the present invention and the performance as a film are not impaired, and may also contain additives such as antistatic agents, weathering agents, inorganic or organic particles, lubricants such as waxes, and pigments.

[0021] Hereinafter, the method for producing the film of the present invention will be specifically described by taking a polyethylene terephthalate (PET) film as an example, but the present invention is not limited to the following embodiments.

[0022] After drying PET under reduced pressure at 100°C to 170°C for 8 hours, it is supplied to a known melt extrusion machine for a melt extrusion at 240°C to 310°C, and filtered with a high-precision filter having a collection efficiency of 95% or more for foreign matters of 5 μm or more. Subsequently, the obtained molten PET is extruded in a sheet form from a slit die maintained at 280°C to 300°C, and cooled and solidified on a casting roll having a surface temperature of 20°C to 30°C using an electrostatic printing casting method to obtain an unstretched film. This unstretched film is heated to 60°C to 160°C with a roll and a radiation heater heated to 60°C to 150°C, and stretched 3 to 5 times in the longitudinal direction to obtain a uniaxially stretched film. Subsequently, the obtained uniaxially stretched film is conveyed 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, and then subjected to relaxation treatment, and cooled in the conveying process to obtain a biaxially stretched film. Thereafter, the biaxially stretched film is wound 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.

[0023] The method for manufacturing a film of the present invention has two or more steps of continuously measuring the temperature in the width direction of the conveyed film, and is characterized in that the steps are located immediately after the casting step and immediately after the uniaxial stretching step.

[0024] The present invention provides a film manufacturing method that, more specifically, includes a casting step in which molten polymer extruded from a die is cooled on a rotating drum to form an unstretched sheet, and a uniaxial stretching step in which the film is heated (preheated) to the temperature required for stretching and immediately stretched in the transport direction, with a step of continuously measuring the temperature in the width direction of the transported film immediately following each step. Figure 1 shows a schematic configuration diagram. In the casting and uniaxial stretching steps, it is necessary to heat (preheat) the film in order to form it into a sheet or stretch it, but after such a change in the state of the film occurs, it is necessary to cool the film. This is to prevent crystallization of the film. If crystallization of the film progresses, problems in film formation occur such as loss of strength of the film itself and reduction of the film width, and in the worst case, it can cause the film to tear. It is important to measure the film temperature immediately after these steps in order to perform appropriate heating (preheating) and cooling. In addition, in order to establish preventive actions against tearing, it is important to identify which step is causing the tearing. This is made possible by having two or more steps for continuously measuring the temperature in the width direction of the transported film. Furthermore, when sequential stretching is performed in two axes, it is preferable that the step for continuously measuring the temperature is located immediately after the first stretching step in one axis direction.

[0025] In the film manufacturing method of the present invention, when the temperature of one end in the width direction measured immediately after the casting process is X1 and the temperature of the other end is X2, and the temperature of one end in the width direction measured immediately after the uniaxial stretching process is Y1 and the temperature of the other end is Y2, it is preferable to control |X1-X2| and |Y1-Y2| to less than 3.0°C, more preferably to less than 2.0°C, and even more preferably to less than 1.0°C. Here, the width direction is the direction perpendicular to the direction in which the film is transported, and the end refers to the range of 50 mm from the end in the width direction of the film. It is preferable that the temperature be the maximum value at the end. Controlling |X1-X2| and |Y1-Y2| to less than 3.0°C is preferable because it prevents differences in the condition of both ends of the film from occurring, which would impair the film-forming stability. In particular, the temperature difference at both ends is a factor that determines the film thickness and film width at the ends and has a large impact on film-forming stability, so it is most preferable that there is no temperature difference.

[0026] This configuration helps to suppress film tearing. The means for controlling the film temperature are not particularly limited as long as they do not impair the effects of the present invention, and examples include changing the temperature of the water passing through the roll used for heating (preheating) and cooling.

[0027] In the present invention, the method for manufacturing a film preferably involves a step of continuously measuring the temperature in the width direction of the transported film immediately after the casting step, located within 1.0 m of the film's travel distance after the casting step, and a step of continuously measuring the temperature in the width direction of the transported film immediately after the uniaxial stretching step, located within 3.0 m of the film's travel distance after the uniaxial stretching step. The casting step involves heating (preheating) the film before cooling it, and the longer the travel distance of the film after the casting step, the longer the time the film is in contact with the surrounding air. Therefore, it is preferable to measure the film temperature while the film is still traveling a short distance after the casting step. The same applies after the uniaxial stretching step. Measuring the film temperature within the above range prevents discrepancies between the film temperature assumed in the casting and uniaxial stretching steps and the actual film temperature, thus making the method preferable. Furthermore, the lower limit of the installation position is preferably 0.1 m or more after the casting and uniaxial stretching steps. By positioning the device at least 0.1m after each process, variations in film temperature measurement due to the influence of internal process temperature can be reduced, making it preferable.

[0028] In the film manufacturing method of the present invention, it is preferable to compare the temperatures at both ends in the width direction and evaluate the temperature difference in the step of continuously measuring the temperature in the width direction of the conveyed film. Comparing the temperatures at both ends in the width direction of the film and evaluating the temperature difference is preferable because it prevents excessive temperature differences from significantly affecting the film formation stability. It is preferable that the temperature to be compared and evaluated is the maximum value at the end.

[0029] In the film manufacturing method of the present invention, it is preferable to use a non-contact infrared thermometer in the step of continuously measuring the temperature in the width direction. It is preferable to measure the temperature without contact because directly touching the film may cause defects such as scratches and dirt on the film surface, which are problematic for quality control, and depending on the strength of the contact, it may cause the film to tear. It is preferable to measure the temperature from at least two points at both ends in the width direction of the film, three points including the center, and more precisely, a line profile over the entire width direction. By measuring the temperature line profile, the thickness distribution in the width direction and the film width of the film can be indirectly measured, and important indicators for evaluating the condition of the film and film formation stability can be obtained.

[0030] The present invention provides a method for manufacturing a film, comprising a quality prediction step for predicting the quality of the film and a step for controlling the film manufacturing conditions based on the film quality prediction results, wherein the quality prediction step for predicting the quality of the film includes a step of outputting a quality prediction result for the quality information of the film after a predetermined time, by performing calculations based on a trained model generated by machine learning using process information and quality information of the film manufactured by the manufacturing process, using process information obtained from the film manufacturing process over a predetermined period and quality information of the film manufactured by the manufacturing process as input parameters, and the step of controlling the film manufacturing conditions based on the film quality prediction results preferably includes a step of controlling the film temperature at least immediately after the casting step and immediately after the uniaxial stretching step in the film manufacturing process based on the film quality prediction results.

[0031] The quality prediction process in this invention refers to the process of predicting the quality of a film after a predetermined time, based on process information obtained from the film manufacturing process and quality information of the manufactured film. Here, "process information" includes information on manufacturing conditions such as temperature, speed, tension, and humidity during film manufacturing, and "quality information" refers to the quality evaluation results of the manufactured film, such as thickness, optical properties, and mechanical strength. In the quality prediction process, a trained model constructed by machine learning using past process information and quality information is used to output prediction results through computational processing.

[0032] In this invention, the trained model refers to a model generated by machine learning using film manufacturing process information and quality information collected over a predetermined period as input data. This model learns the correlation between input parameters and quality results, and is capable of predicting quality for unknown manufacturing conditions.

[0033] The trained model in this invention is a model constructed using a machine learning algorithm to predict quality, taking film manufacturing process information and quality information as input. It is preferable to use an algorithm capable of accurately representing nonlinear correlations when constructing the trained model. Specifically, the following algorithms are examples.

[0034] Neural networks: These networks, with their multi-layered structure, can learn the complex relationships between process information and quality information. For example, they can take input such as casting process temperature, stretching ratio, and line speed to predict film thickness and optical properties.

[0035] Random Forest: By combining multiple decision trees, it is possible to learn patterns in past manufacturing conditions and quality results, thereby improving prediction accuracy. In particular, by evaluating the importance of features, it is possible to extract key parameters that affect quality.

[0036] Gradient boosting: This method builds a model by sequentially correcting errors, enabling highly accurate predictions even with small amounts of data.

[0037] These algorithms have the advantage of being able to handle the nonlinearity and multidimensionality between parameters in the film manufacturing process. Furthermore, in quality prediction, simple linear models often lack sufficient accuracy, and improvements in prediction accuracy can be expected by using techniques such as neural networks and gradient boosting. In addition, random forests are useful for extracting key parameters that affect quality because they can evaluate the contribution of features.

[0038] The trained models built using these algorithms can predict film quality (e.g., thickness uniformity, optical anisotropy, tensile strength, etc.) after a predetermined time, based on the latest input process information.

[0039] The step of controlling the film manufacturing conditions in this invention refers to the step of adjusting the conditions of the film manufacturing process based on the prediction results obtained in the quality prediction step. In particular, it is preferable to control the film temperature immediately after the casting step and immediately after the uniaxial stretching step. This allows for appropriate control of film cooling and stretching, and enables the stable acquisition of the desired quality.

[0040] The present invention's method for manufacturing a film preferably includes process information obtained from the film manufacturing process, where X1 is the temperature of one end in the width direction measured immediately after the casting process, X2 is the temperature of the other end, and Y1 is the temperature of one end in the width direction measured immediately after the uniaxial stretching process, Y2 is the temperature of the other end. Here, the width direction is the direction perpendicular to the direction in which the film is transported, and the end refers to a range of 50 mm from the end in the width direction of the film. The temperature is preferably the maximum value at the end. By inputting the film temperature immediately after the casting process and immediately after the uniaxial stretching process, which are related to the cooling and stretching of the film, as process information used in the quality prediction process, more accurate quality prediction can be achieved. [Examples]

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0042] (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 longitudinally stretched 4.2 times at a temperature of 110°C using a stretching roll with a surface roughness of Ra 0.2 μm to obtain a uniaxially oriented film. Subsequently, the obtained uniaxially oriented film was transported to a tenter device, stretched 4.5 times in the width direction at 115°C, heat-treated at 215°C, then relaxed, and cooled during the transport process to obtain a biaxially oriented film. Subsequently, the biaxially oriented film was wound up under conditions of a winding speed of 180 m / min and a winding tension of 150 N / m to obtain a film roll.

[0043] At this time, non-contact infrared thermometers were placed at a position where the film had traveled 0.16m after the casting process and at a position where the film had traveled 2.5m after the uniaxial stretching process to measure the film temperature. By checking the temperature data when tears occurred, it was possible to identify that the tears were caused by the uniaxial stretching process. A Fluke RAYTMP150P30 was used for the measurements, and it was installed perpendicular to the film's width and transport direction, with a distance of 1050mm from the film.

[0044] (Comparative Example 1) Under the conditions of Example 1, a non-contact infrared thermometer was installed only at a position where the film had traveled 0.16m after the casting process, and the film temperature was measured. By checking the temperature data when tearing occurred, it was possible to identify that the tearing was caused by a process after the uniaxial stretching process, but it was not possible to determine whether the tearing was caused by the uniaxial stretching process or a later process. A Fluke RAYTMP150P30 was used for measurement, and it was installed perpendicular to the film's width and transport direction, with a distance of 1050mm from the film.

[0045] (Comparative Example 2) Under the conditions of Example 1, a non-contact infrared thermometer was installed only at a position where the film had traveled 2.5m after the uniaxial stretching process, and the film temperature was measured. By checking the temperature data when tearing occurred, it was possible to identify that the tearing was caused by a process prior to the uniaxial stretching process, but it was not possible to determine whether the tearing was caused by the uniaxial stretching process or an earlier process (casting process). A Fluke RAYTMP150P30 was used for measurement, and it was installed perpendicular to the film's width and transport direction, with a distance of 1050mm from the film.

[0046] (Example 2) Under the conditions of Example 1, non-contact infrared thermometers were placed at a position where the film had traveled 0.16m after the casting process and at a position where the film had traveled 2.5m after the uniaxial stretching process. Film temperature was measured, and when |X1-X2| and |Y1-Y2| were controlled to less than 3.0℃, no film tearing occurred. A Fluke RAYTMP150P30 was used for measurement, and it was installed perpendicular to the film's width and transport direction, with a distance of 1050mm from the film. Temperature control was achieved by changing the temperature of the water passing through the roll.

[0047] From the above, it was confirmed that the process causing film tearing can be identified, and that the stability of the film can be maintained by suppressing the temperature difference at both ends of the film. The results obtained are shown in Table 1.

[0048] [Table 1] [Explanation of symbols]

[0049] 1. Casting Process 2 Uniaxial stretching process 3 Films 4a non-contact radiation thermometer 4b Non-contact radiation thermometer

Claims

1. A method for manufacturing a film, comprising a casting step in which a polymer constituting the film is melted, extruded from a die, and cooled on a rotating drum to form an unstretched sheet, and a uniaxial stretching step in which the film is heated to a temperature necessary for stretching and then stretched, wherein the method further comprises two or more steps for continuously measuring the temperature in the width direction of the conveyed film, and the steps are located immediately after the casting step and immediately after the uniaxial stretching step.

2. A method for manufacturing a film according to claim 1, wherein when the temperature of one end in the width direction measured immediately after the casting process is X1 and the temperature of the other end is X2, and the temperature of one end in the width direction measured immediately after the uniaxial stretching process is Y1 and the temperature of the other end is Y2, |X1-X2| and |Y1-Y2| are controlled to be less than 3.0°C.

3. A method for manufacturing a film according to claim 1 or 2, wherein a step of continuously measuring the temperature in the width direction of the transported film immediately after the casting step is located within 1.0 m of the film travel distance after the casting step, and a step of continuously measuring the temperature in the width direction of the transported film immediately after the uniaxial stretching step is located within 3.0 m of the film travel distance after the uniaxial stretching step.

4. A method for manufacturing a film according to claim 1 or 2, comprising the step of continuously measuring the temperature of the transported film in the width direction, wherein the temperatures of both ends in the width direction are compared and the temperature difference is evaluated.

5. A method for manufacturing a film according to claim 1 or 2, wherein a non-contact radiation thermometer is used in the step of continuously measuring the temperature in the width direction of the transported film.

6. A method for manufacturing a film, comprising a quality prediction step for predicting the quality of the film and a step for controlling the film manufacturing conditions based on the quality prediction results of the film, The quality prediction step for predicting the quality of the film includes a step of outputting a quality prediction result for the quality information of the film after a predetermined time, by taking process information obtained from the film manufacturing process over a predetermined period and quality information of the film manufactured by the manufacturing process as input parameters, and performing calculations based on a trained model generated by machine learning using the process information and quality information for the manufactured film, thereby obtaining a quality prediction result for the quality information of the film after a predetermined time. The method for manufacturing a film according to claim 1 or 2, wherein the step of controlling the film manufacturing conditions based on the film quality prediction results includes a step of controlling the film temperature at least immediately after the casting step and immediately after the uniaxial stretching step in the film manufacturing process based on the film quality prediction results.

7. The method for manufacturing a film according to claim 6, wherein the process information obtained from the film manufacturing process includes |X1-X2| and |Y1-Y2|, where X1 is the temperature of one end in the width direction measured immediately after the casting process, X2 is the temperature of the other end, and Y1 is the temperature of one end in the width direction measured immediately after the uniaxial stretching process, and Y2 is the temperature of the other end.

Images