Plastic film manufacturing method

Abstract

To provide a method for manufacturing a plastic film capable of manufacturing the film at high speed and with high quality while reducing surface defects of the film.SOLUTION: A method for manufacturing a plastic film obtains the plastic film by sandwiching and pressing a molten resin discharged into a web form with two rollers and cooling and solidifying the molten resin. Droplets are deposited on a surface of at least one roller of the two rollers to cool the surface of the roller. A particle diameter and a flow rate of the droplets are a size and volume such that substantially all of the droplets evaporate before the droplets reach a portion that sandwiches and presses the molten resin with the two rollers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, one method for producing plastic films involves extruding molten resin into a web, pinching it between two rollers, a cooling roller and a nip roller, and cooling it to solidify it.

[0003] In the manufacturing method of such plastic films (hereinafter sometimes referred to as films), it is very important to lower the surface temperature of the nip rollers, because if the surface temperature of the nip rollers is too high when manufacturing films at high speed, the molten resin may adhere to and wrap around the surface of the nip rollers, resulting in an unintended rough surface for the manufactured film, or conversely, when embossing is performed using a rough nip roller surface, the resin may not be sufficiently cooled in the nip portion, resulting in an unintended smooth surface without embossing.

[0004] Therefore, in order to lower the surface temperature of the nip roller, a method has been proposed in which cooling water is passed through the inside of the nip roller to create a structure that allows cooling from the inside, and then an auxiliary cooling roller is brought into contact with the surface of the nip roller or a cooling gas is blown onto the surface of the nip roller, as described in Patent Document 1, for example.

[0005] Furthermore, as a method for cooling the surface of a roller used in producing a plastic film, a method has been proposed in which cooling water is sprayed onto the surface of the roller and the water is removed with an air knife, as described in Patent Document 2. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2009-501098 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-167909 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technologies described in Patent Documents 1 and 2 suffer from the following problems. First, the method described in Patent Document 1 lacks sufficient cooling capacity. In the method of contacting an auxiliary cooling roller with a nip roller, the temperature difference between the nip roller and the molten resin is at least 100°C or more, whereas the temperature difference between the nip roller and the auxiliary cooling roller is only a few tens of degrees at most. The contact time is also short, making sufficient cooling difficult. Furthermore, if the surface material of the nip roller is resin or rubber, the surface of the nip roller can be damaged by contact with the auxiliary cooling roller, resulting in defects in the surface of the produced plastic film. Furthermore, the method of spraying cooling gas onto the nip roller surface does not achieve sufficient heat transfer and therefore provides insufficient cooling capacity. Continuous spraying of low-temperature gas increases utility costs, and using gases other than air raises safety concerns and requires additional costs for safety assurance.

[0008] In addition, the method of spraying cooling water onto the roller surface and removing it with an air knife has a high cooling capacity, but it is difficult to completely remove the water from the cooling roller surface. As a result, the remaining water is carried into the area where the molten resin is pinched, resulting in defects on the surface of the produced plastic film. In addition, since the cooling water blown off with the air knife must be treated, there are issues such as the complexity of the equipment and increased costs.

[0009] The present invention solves the problems of the conventional techniques described above, and provides a method for producing a plastic film that can produce a high-quality film at high speed while suppressing the occurrence of defects on the film surface. [Means for solving the problem]

[0010] The plastic film manufacturing method of the present invention, which solves the above-mentioned problems, is a plastic film manufacturing method in which molten resin extruded in a web form is sandwiched between two rollers and the molten resin is cooled and solidified to obtain a plastic film, in which droplets are deposited on the surface of at least one of the two rollers to cool the surface of the roller, and the particle size and flow rate of the droplets are set to a size and amount such that the droplets substantially completely evaporate before reaching the part where the molten resin is sandwiched between the two rollers.

[0011] Another form of the plastic film manufacturing method of the present invention is a plastic film manufacturing method in which molten resin extruded in a web form is sandwiched between two rollers and the molten resin is cooled and solidified to obtain a plastic film, in which liquid droplets are deposited on the surface of at least one of the two rollers to cool the surface of the roller, and then gas is blown onto the surface of the roller to which the liquid droplets are deposited, causing substantially all of the liquid droplets to evaporate before they reach the part where the molten resin is sandwiched between the two rollers.

[0012] In addition, in the method for producing a plastic film of the present invention, the two rollers are preferably a cooling roller and an embossing roller, and the droplets are deposited on the surface of the embossing roller to cool the surface of the embossing roller.

[0013] The terms used in the present invention are defined as follows. The phrases "substantially all evaporate before reaching the area where the molten resin is clamped" and "substantially all evaporate the droplets before reaching the area where the molten resin is clamped" not only mean that the droplets attached to the roller surface become smaller and fewer through evaporation on the roller surface, and completely disappear in the area where the molten resin is clamped, but also mean that they are reduced to a size and amount that does not affect film production. Here, "not affecting film production" means that residual droplets do not cause detectable defects, or that defects are limited to a size and amount that do not pose a problem in terms of the required film quality.

[0014] The term "cooling roller" refers to a roller that comes into contact with the molten resin and cools it to solidify it. An "embossing roller" is a roller that, together with a "cooling roller," clamps and presses molten resin to cool and solidify it. It has a matte or specially shaped surface and is intended to transfer that surface shape to the surface of a plastic film. [Effects of the Invention]

[0015] According to the method for producing a plastic film of the present invention, it is possible to produce a plastic film at high speed and with high precision while suppressing the occurrence of defects on the surface of the film. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating one embodiment of the method for producing a plastic film of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing another embodiment of the method for producing a plastic film of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing an example of a spraying means that can be used in the plastic film manufacturing method of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing an embodiment of a conventional method for producing a plastic film. [Figure 5]FIG. 1 is a schematic diagram showing another embodiment of a conventional method for producing a plastic film. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing an embodiment of the plastic film manufacturing method of the present invention (hereinafter sometimes simply referred to as the manufacturing method). In the manufacturing method of the present invention, molten resin 2 is extruded into a web shape and pressed between two rollers consisting of a first roller 3 and a second roller 4, thereby cooling and solidifying the molten resin 2 to obtain a plastic film 6. Next, if necessary, the film is stretched in a stretching process, cut in a slitting process, or the edges 23 are trimmed, and then wound into a roll in a winding process 22 to form a film roll 10. Thereafter, if necessary, the film is again subjected to a slitting process or other processing steps to form a finished product.

[0018] A T-die method can be preferably used as a method for extruding the molten resin 2 in a web form. For example, the resin is melt-kneaded and fed using an extruder such as a single-screw extruder or a twin-screw extruder (not shown), and the molten resin 2 is extruded from a slit-shaped outlet provided in a T-die 1, thereby extruding the molten resin 2 in a web form.

[0019] The molten resin 2 is not particularly limited as long as it is a thermoplastic resin, but resins such as various polyethylene resins such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, and polyphenylene sulfide can be used.

[0020] The temperature of the molten resin 2 is determined appropriately based on the melting point, viscosity, melt index, and suppression of resin deterioration due to heat of the resin used. For example, in the case of polyethylene resin, it is generally discharged at a temperature of 180 to 260°C.

[0021] The core metals of the two rollers (first roller 3 and second roller 4) that clamp and cool and solidify the molten resin 2 preferably have a flow path structure inside to allow a heat transfer medium to pass through. By controlling the temperature and flow rate of the heat transfer medium, it is possible to control the surface temperature of the rollers to some extent.

[0022] The surface material and surface shape of the two rollers (3, 4) are each selected and designed appropriately depending on the plastic film to be produced. For example, when producing a highly transparent film for use in displays, the surface shapes of both the first roller 3 and the second roller 4 must be smooth. To achieve a smooth surface, the surface material can be made metal or ceramic and polished to obtain a mirror-like smooth surface. Furthermore, when producing masking film to be attached to the surface of an object for protection, one side is often made smooth and adhesive, and the other side is made matte and releasable. In this case, the desired film surface can be obtained by, for example, using the second roller 4 as a cooling roller with a mirror-finished metal surface and the first roller 3 as an embossing roller with a matte rubber surface.

[0023] Furthermore, when producing a thin film, for example, with a thickness of 300 μm or less, it is preferable to use rubber as the surface material for at least one of the two rollers (3, 4), as this allows the rubber to deform to conform to variations in the thickness of the extruded molten resin 2 across the width, enabling uniform clamping and cooling. The type of rubber used as the surface material can be appropriately selected from silicone rubber, butadiene-acrylonitrile copolymer (NBR), polychloroprene (CR), chlorosulfonated polyethylene (CSM), ethylene-propylene copolymer, ethylene propylene diene rubber (EPDM), or any of these rubbers containing additives or formulations that improve weather resistance, slip resistance, abrasion resistance, strength, etc. These rubbers can also be used in laminated configurations. For example, silicone rubber, which has high releasability and heat resistance against the molten resin 2, is preferably used for the rubber layer that comes into contact with the molten resin 2. Alternatively, a rubber layer can be provided inside an elastically deformable thin metal sleeve or fluororesin tube. Metallic thin-film sleeves can be made of nickel or stainless steel, or their surfaces can be plated, coated, or otherwise treated with various surface treatments. By using a material that can be easily mirror-finished, such as metal or fluororesin, as the surface material and providing a rubber layer as the inner layer, it is possible to obtain a smooth, thin plastic film.

[0024] The method for clamping the molten resin 2 between the two rollers (3, 4) is not particularly limited. It is possible to control the relative positions of the two rollers (3, 4), such as the gap between the two rollers (3, 4) or, if either roller is a rubber roller, the amount of rubber pressure applied by the rollers, by using a tapered block or the like. Alternatively, it is also possible to control the pressure applied to the first roller 3 using an air cylinder or the like. However, when producing a thin film in which the thickness of the molten resin 2 at the clamping point is 100 μm or less, or when the rubber coating the rollers has a hardness of 90 Hs JIS A or higher, controlling the pressure by the amount of pressure may result in excessively large pressure variations. Therefore, controlling the pressure is preferred. The pressure can be set as appropriate, preferably within the range of approximately 1 to 20 kN / m. A pressure within the above range facilitates successful transfer of the surface shape of the two rollers (3, 4) to the molten resin 2.

[0025] In the present invention, the surface of at least one of the two rollers (3, 4) is cooled by applying minute droplets to the surface of the roller using a spraying means 100. The particle size and flow rate of the droplets are such that all of the droplets adhering to the roller surface evaporate before reaching the pinching portion of the molten resin 2.

[0026] The spraying means 100 is not particularly limited, and various methods can be used. For example, a method of spraying droplets toward the roller surface using a two-fluid nozzle or a method of generating mist-like droplets using a commercially available mist generator such as an ultrasonic mist generator and spraying them onto the roller surface can be used. Another preferred method is to temporarily store the mist-like droplets generated by the above method in a chamber or the like, classify large droplets by gravity, and then spray them onto the roller at a desired wind speed and range using compressed air or a blower. For example, as shown in FIG. 3 , droplets are sprayed using a two-fluid nozzle 101 to fill a chamber 102, and air is then blown from a blower 103, allowing droplets of a certain size or smaller to be sprayed from a nozzle 104 with precision at a desired flow rate and range.

[0027] Any liquid can be used as the droplets to be deposited on the roller surface, but water is preferably used from the viewpoint of safety and cost.

[0028] The particle size and flow rate at which the droplets evaporate completely before reaching the pressing section of the molten resin 2 vary depending on the surface temperature of the cooling roller, the ambient temperature, humidity, the time it takes to reach the pressing section, the type of droplets, and the temperature, and are therefore set arbitrarily according to these factors. A preferred method is to spray droplets onto the roller surface while actually forming a film, and adjust the particle size and flow rate. Furthermore, the smaller the droplet size, the greater the surface area of ​​the droplets, which increases the evaporation rate and allows a greater flow rate of droplets to evaporate completely before reaching the pressing section of the molten resin 2. However, if the particle size is too small, the droplets will have difficulty adhering to the roller surface due to the accompanying flow of the roller, so it is advisable to adjust these values ​​appropriately according to the conditions of use.

[0029] The position where the droplets are deposited can be set as appropriate, but is preferably immediately after the area where the molten resin 2 is pinched. Because the temperature of the roller surface is highest immediately after the area where the molten resin 2 is pinched, the amount of droplets that can evaporate increases, allowing for more effective cooling of the roller surface. On the other hand, if droplets are sprayed at a position close to immediately after the area where the molten resin 2 is pinched, the droplets may adhere to the film 6, so it is preferable to install an adhesion prevention plate 110, as shown in Figure 1.

[0030] Another preferred method is to adhere droplets to the roller surface, as shown in Figure 2, and then spray gas onto the roller surface using gas spraying means 200 to promote evaporation of the droplets. By promoting droplet evaporation, larger droplets with a larger flow rate can be deposited, thereby enhancing the cooling effect. The gas spraying means 200 can be a known method, such as using a commercially available blower or compressor and air nozzle. The type and temperature of the gas to be sprayed may be any type that promotes evaporation of the droplets, and preferably, dry air with a humidity of 20% or less and a temperature of 20 to 40°C can be used.

[0031] In one embodiment of the present invention, the two rollers (3, 4) are a cooling roller and an embossing roller, and droplets are deposited on the surface of the embossing roller to cool the surface. For example, in FIG. 1 , the first roller 3 is an embossing roller and the second roller 4 is a cooling roller. The embossing roller is pressed against the molten resin 2 to form an embossed shape on the surface of the plastic film 6. The embossing roller surface imprints the molten resin 2 with the roller surface shape while simultaneously cooling and solidifying the molten resin 2, thereby fixing the imprinted shape. If the surface temperature of the embossing roller at the contact point with the molten resin 2 is high, the molten resin 2 may not be sufficiently cooled and solidified, resulting in a flattened surface. By depositing droplets on the surface of the embossing roller, allowing them to evaporate before reaching the nip and cooling the roller surface, the temperature of the roller surface can be effectively lowered, enabling stable and rapid embossing.

[0032] If necessary, a known roller surface cooling method such as spraying a cooling gas or contacting with an auxiliary cooling roller may be used in combination. [Example]

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Various evaluation and measurement methods are also described below.

[0034] [Film Haze] To evaluate whether the embossed shape was sufficiently formed into a film, the haze of the formed film was measured and compared. Using a measuring device and method conforming to JIS K7136:2000, measurements were taken at five points approximately in the center of the width direction of the formed film, and the average value was calculated.

[0035] [Surface defects] The formed film was visually inspected within a range of 1.5 m wide and 3 m long, and missing embossed areas, i.e., transparent areas, were regarded as defects, and the number of defects was counted.

[0036] [Example 1] A plastic film was produced using the plastic film manufacturing equipment shown in Figure 1. The first of the two rollers was used as an embossing roller, with a silicone rubber surface coating, and the second roller was used as a cooling roller with a chrome-plated and mirror-polished surface. The droplets were applied by generating a water mist using a two-fluid nozzle in the chamber as shown in Figure 3, and spraying it onto the surface of the embossing roller with a blower. A 0.93 g / cm2 density droplet was ejected from a T-die with a slit width adjusted to 0.9 mm. 3 Low-density polyethylene (LDPE) was extruded at 220°C in a single-layer configuration, and then pinched and cooled between a cooling roller and an embossing roller to obtain a plastic film 50 μm thick. The droplet size and flow rate were adjusted while observing the embossing roller and the surface of the film, and were set to a size and flow rate that would cause the droplets to completely evaporate before reaching the pinching section. The droplet size was adjusted by the flow rate of water supplied to the two-fluid nozzle and the pressure of the compressed air, and the flow rate to be deposited was adjusted by the air volume of the blower.

[0037] [Example 2] As shown in Figure 2, dry air at a temperature of 23°C and humidity of 15% was blown onto the surface of the embossing roller in front of the clamping section of the molten resin using an air nozzle. Blowing dry air increases the particle size of droplets that completely evaporate before reaching the clamping section and increases the flow rate, so adjustments were made to increase the particle size and flow rate of the droplets. A film was otherwise produced using the same equipment and method as in Example 1.

[0038] [Comparative Example 1] A plastic film was produced using the same apparatus and method as in Example 1, except that the step of attaching the droplets to the embossing roller was omitted.

[0039] Comparative Example 2 A plastic film was produced using the plastic film production apparatus shown in Figure 4. The two rollers and T-die were the same as those used in Example 1, and two auxiliary cooling rollers were brought into contact with the embossing roller. Apart from that, the same molten resin was used as in Example 1 under the same conditions to produce a plastic film.

[0040] Comparative Example 3 A plastic film was produced using the plastic film production apparatus shown in Figure 5. The two rollers and T-die were the same as those used in Example 1, and water was sprayed from a two-fluid nozzle onto the embossing roller in an amount that completely wetted the surface, after which the water on the surface was blown off with an air knife. A plastic film was produced using the same molten resin and under the same conditions as in Example 1.

[0041] The observation results and measurement results of the formed film are shown in Table 1.

[0042] [Table 1]

[0043] In Comparative Examples 1 and 2, the embossing roller was not cooled sufficiently, resulting in insufficient embossing of the film surface, and therefore a decrease in haze. In contrast, in Examples 1 and 2 and Comparative Example 3, the haze was high, indicating that the embossing roller surface was cooled sufficiently.

[0044] Furthermore, in Examples 1 and 2, when the film-forming speed was increased, in Example 2, in which the droplet size was increased and the flow rate was increased, the haze was maintained even at a film-forming speed that was 10% or more faster than in Example 1. In both Examples 1 and 2, the droplets completely evaporated before reaching the clamping section, even after the film-forming speed was increased.

[0045] In Comparative Example 2, the surface of the embossing roller was worn due to contact with the auxiliary cooling roller, and the worn powder adhered to the roller surface, causing defects on the film surface.

[0046] In Comparative Example 3, water remained on the surface of the embossing roller, causing many surface defects on the film surface. [Industrial Applicability]

[0047] The present invention is not limited to methods for manufacturing plastic films, but can also be applied to processes in which a plastic film is heated and nipped with rollers, such as embossing as a secondary process, but the scope of application is not limited to these. [Explanation of symbols]

[0048] 1 T-die 2. Molten resin 3 First Roller 4 Second Roller 5 Peeling roller 6. Plastic film 7 Cutter 8 Edge Suction Tube 9 Near Roller 10 film rolls 21 Slitting process 22 Winding process 23 Film Edge 100 Spraying means 101 Two-fluid nozzle 102 Chamber 103 Blower 104 Nozzle part 110 Droplet adhesion prevention plate 200 Gas spraying means 300 Auxiliary cooling roller 400 Air Knife

Claims

1. A method for producing a plastic film, comprising: nipping and pressing a molten resin discharged in a web shape between two rollers; and cooling and solidifying the molten resin to obtain a plastic film, cooling the surface of at least one of the two rollers by depositing droplets on the surface of the roller; without removing the droplets from the surface of the roller with a physical force and without blowing a gas onto the surface of the roller to evaporate the droplets; The particle size and flow rate of the droplets are set to a size and amount such that the droplets are substantially completely evaporated before reaching the portion where the molten resin is sandwiched between the two rollers. A method for manufacturing plastic films.

2. the two rollers being a cooling roller and an embossing roller, The droplets are deposited on the surface of the embossing roller to cool the surface of the embossing roller. A method for producing the plastic film of claim 1.

3. A method for producing a plastic film, comprising: nipping and pressing a molten resin discharged in a web shape between a cooling roller and an embossing roller; and cooling and solidifying the molten resin to obtain a plastic film, cooling the surface of the embossing roller by depositing droplets on the surface of the embossing roller at least in an area corresponding to the product portion of the plastic film; Next, a gas is blown onto the surface of the embossing roller on which the droplets are attached, so that the droplets are substantially completely evaporated before they reach a portion where the molten resin is sandwiched between the cooling roller and the embossing roller. A method for manufacturing plastic films.

Images