Processed film manufacturing method

Abstract

To provide a method which makes a problem of sand remaining in a film after processing less likely to occur in surface roughening of the film by shot blasting.SOLUTION: Shot blasting of the invention uses an abrasive material in a circulating manner. The abrasive material (reclamation sand 3) whose particle diameter is reduced through circulation is recovered from a recovery passage 14 and is removed from a device 10. A new abrasive material (new sand 1) is placed into the device 10 from a tank 11. The abrasive material (the new sand 1) placed into the device 10 and the abrasive material (circulation sand 2) circulated through a circulation passage 13 are sent to a rotor 12, are jetted from the rotor 12, and are collide with a surface of a traveling film F to roughen a surface of the film F. In the invention, the abrasive material from which coarse particles are removed is used as the new abrasive material (the new sand 1) to achieve the above object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing processed films using shot blasting, and more particularly to a method for producing processed films in which residual sand is significantly reduced by removing coarse particles from the abrasive material being added. [Background technology]

[0002] Surface roughening is performed on polymer films to create minute irregularities on their surfaces for the purposes of suppressing reflection, improving adhesive strength control such as lamination and peeling properties, and improving printability. One such roughening method is shot blasting, which creates fine irregularities on the surface of an object by spraying abrasive material from blades attached to a rotor rotating at high speed onto the object. Shot blasting is used to process films for a variety of purposes.

[0003] For example, Patent Document 1 discloses a processing method in which the film surface is shot blasted and then air blasted across the entire width of the film, which is said to be applicable to films with aluminum vapor-deposited on a non-matte surface.

[0004] Patent Document 2 discloses an identification sheet in which the area where visible identification information is present is roughened by sandblasting and then covered with a synthetic resin film having a rough surface with an average roughness within a specific range.

[0005] Patent Document 3 describes that by forming fine irregularities as a pretreatment on a film before hairline processing, it is possible to suppress the occurrence of defective parts called whiskers, which are made up of shavings, after hairline processing, compared to when this pretreatment is not performed. In the examples of Patent Document 3, shot blasting is used as a method for forming fine irregularities on a film.

[0006] In shot blasting, the abrasive is circulated and reused, and various abrasive circulating devices and methods have been proposed (Patent Documents 4 to 6).

[0007] The particle size of recycled abrasives gradually decreases as they collide with each other, the rotor, or the equipment walls, causing them to crack and lose their edges. Abrasives with reduced particle size are unable to form sufficient irregularities, so to maintain the quality of the processed film, abrasives whose particle size has been reduced to a certain extent are collected and removed, and new abrasives are added in their place. One method for collection and removal is to use air, as described in Patent Document 4, etc.

[0008] On the other hand, the abrasive broken by the collision has sharp edges, which may pierce the film upon collision with it. Such "abrasive stuck in the film" (hereinafter sometimes referred to as "residual sand") can cause a decrease in yield when coating another material on the film after forming the irregularities.

[0009] In view of the above circumstances, there is a need for the development of technology that can improve yield and productivity in a series of processes, including coating processing. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-243497 [Patent Document 2] Japanese Patent Publication No. 62-279992 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-144539 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-168657 [Patent Document 5] Japanese Patent Application Publication No. 8-267361 [Patent Document 6] Japanese Patent Application Laid-Open No. 2002-210658 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above-mentioned background art, and an object of the present invention is to provide a method for roughening a film surface by shot blasting, which is less likely to cause the problem of residual sand remaining on the film after processing. [Means for solving the problem]

[0012] When abrasives are recycled in shot blasting, the particle size becomes smaller and they are collected and removed, and new abrasives are added. The particle size of the newly added abrasives is not uniform, but has a particle size distribution.

[0013] The present inventors have conducted extensive research to solve the above problems and have found that the residual sand stuck in the film after shot blasting is about several tens to several hundreds of μm in size, and that such residual sand tends to be generated immediately after newly adding abrasives. Based on this, the present inventors have speculated that the newly added abrasives, in other words, the abrasives immediately after starting use, are the main cause of the residual sand generated during the roughening process. The inventors then considered that if the average particle size of the newly added abrasive is large, the particles of the abrasive will be more likely to break, and discovered that by removing the coarse particles (particles with large particle sizes) from the newly added abrasive in advance by classification, crushing, etc., it is possible to dramatically reduce the amount of residual sand remaining on the film after roughening processing, which led to the completion of the present invention.

[0014] That is, the present invention relates to a method for producing a processed film in which a film is roughened by a shot blasting process in which an abrasive is circulated and used, and the abrasive whose particle size has become smaller through the circulation is removed from the device by collecting it, and new abrasive having a volume average particle size larger than that of the removed abrasive is introduced into the device, The present invention provides a method for producing a processed film, characterized in that the newly added abrasive is one from which coarse particles have been removed. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for roughening a film surface by shot blasting, which is less likely to cause the problem of residual sand remaining on the film after processing.

[0016] In shot blasting, the larger the average particle size of the abrasive, the easier it is to increase the surface roughness (Ra) and the faster the processing speed, which is advantageous when producing roughened films industrially. However, large abrasive particles tend to break and become stuck in the film, causing residual sand. In the present invention, even when an abrasive having a large average particle size is used, the generation of residual sand can be dramatically reduced by removing the coarse particles in advance.

[0017] If sand remains on the film after roughening, the yield of the film (final product) that is processed by coating or other processes after roughening will decrease. In the method of the present invention, even when an abrasive having a large average particle size is used, the amount of sand remaining on the film after the surface roughening process is very small, thereby improving the yield of films that have been processed, such as coated films. When roughening is performed using the method of the present invention, even when the cost of removing coarse particles is taken into consideration, the productivity of the roughening process can be improved and the yield of the final product can also be improved, thereby reducing the costs of the entire process. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a conceptual diagram of the shot blasting process of the present invention. [Figure 2] 1 shows the particle size distribution of abrasive C used in Comparative Example 3. [Figure 3] 1 shows the particle size distribution of abrasive E used in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described below, but the present invention is not limited to the following embodiments and can be practiced with any modifications.

[0020] The present invention is a method for producing a processed film, in which a film is roughened by shot blasting.

[0021] A conceptual diagram of the shot blasting treatment of the present invention is shown in Figure 1. In the shot blasting treatment of the present invention, the abrasive is recycled for use. In the present invention, as the shot blasting machine (hereinafter sometimes simply referred to as "machine"), any known shot blasting machine capable of recycling abrasives can be used as appropriate.

[0022] There is no particular limitation on the abrasive material used in the present invention, and examples thereof include silica sand, alumina, carborundum, ceramic beads, and glass beads. Among these, silica sand, which has a broad particle size distribution and often contains coarse particles, is the most suitable for application of the present invention. In the following description, the case where the abrasive is sand (silica sand) will be mainly explained as an example, but the abrasive in the present invention is not necessarily limited to sand (silica sand).

[0023] In the present invention, newly added abrasive (hereinafter referred to as "new sand") 1 is added into the shot blasting device 10 from a tank 11. The added abrasive is sent to the rotor 12, and is ejected from the rotor 12, colliding with the surface of the traveling film F, thereby roughening the surface of the film F.

[0024] The abrasive that collides with the surface of film F breaks up upon impact, reducing its particle size. The abrasive sprayed from rotor 12 passes through circulation path 13 within device 10, is collected back into tank 11, is sent back to rotor 12, is sprayed from rotor 12, and collides with the surface of film F. Hereinafter, the abrasive circulating within device 10 may be referred to as "circulating sand 2."

[0025] If the particle size of the abrasive becomes too small, it will no longer be able to fully perform the function of roughening the film. Therefore, the abrasive whose particle size has been reduced by circulation is collected, for example, by air, and removed from the inside of the device 10 via the collection path 14. The abrasive removed from the collection path 14 may be referred to as "recovered sand 3" hereinafter.

[0026] As the recovered sand 3 is removed, the amount of abrasive circulating within the device 10 decreases, so new abrasive (new sand) 1 is added from the tank 11. The new abrasive (new sand) 1 has a larger volume average particle size than the abrasive (recovered sand) 3 that is being removed. The particle size of the abrasive decreases as it is recycled, but by removing the recovered sand 3 with a smaller particle size and adding new sand 1 with a larger particle size in its place, the abrasive's roughening ability (the ability to reduce the surface roughness of the film) is maintained.

[0027] When abrasives collide with each other or with the rotor or equipment walls, the broken abrasives pierce the film when they collide with it, leaving sand residue on the film. The sand residue in the film can cause problems when coating the film after roughening, resulting in reduced yields. The phenomenon of abrasives breaking tends to occur immediately after new sand is added, but becomes less likely as the abrasives are circulated.

[0028] Since it is thought that the phenomenon of abrasive cracking is more likely to occur the larger the particle size of the abrasive, one approach to suppress the generation of residual sand is to reduce the average particle size of new abrasive (new sand). However, doing so reduces the abrasive's ability to roughen the surface (its ability to reduce the surface roughness of the film), which means that the amount of abrasive used increases or the processing speed (the film's running speed) has to be reduced, leading to a decrease in productivity and being undesirable from both an environmental and economic perspective.

[0029] In the present invention, the abrasive (new sand) newly charged from the tank 11 has had coarse particles removed. The particle size of the abrasive is not uniform, but has a particle size distribution. The problem of residual sand in the film is caused by coarse particles, especially those with large particle sizes, among the new sand (which has an average particle size larger than the recycled sand). The inventors have discovered that by removing such coarse particles in advance, the amount of residual sand caused by the cracking of the coarse particles can be dramatically reduced. In this invention, by removing the coarse particles from the new sand, the amount of residual sand generated in the film after surface roughening can be dramatically reduced.

[0030] The method for removing coarse particles is not particularly limited, but examples include sieving with a mesh, classification with a centrifuge, and crushing of coarse particles with a grinder or the like.

[0031] Although it depends on the type of abrasive, newly added abrasive particles are often not nearly spherical. In particular, when the abrasive is silica sand, the shape often varies, and the value (L / S) obtained by dividing the particle's long side length (L) by its short side length (S) is often around 1 to 3.

[0032] In the present invention, newly added abrasive (new sand) has had coarse particles removed, and "coarse particles" refers to particles whose average value (L+S) / 2 of the long side length (L) and short side length (S) of the particle is, for example, 300 μm or more, 310 μm or more, 330 μm or more, 350 μm or more, 370 μm or more, 400 μm or more, 450 μm or more, 500 μm or more, etc.

[0033] Even a small amount of coarse particles of this size contained in the abrasive (new sand) can cause residual sand to be generated. In other words, it is thought that the phenomenon of the coarse particles breaking occurs. As the abrasive circulation progresses (after sufficient time has passed since the new sand was added), residual sand is less likely to be generated, which is presumably because the coarse particles break or become rounded and become finer (smaller particle size).

[0034] For newly added abrasive (new sand), the value (Mv / Mn) obtained by dividing the volume average particle diameter (Mv) by the number average particle diameter (Mn) is preferably 2.0 or less, more preferably 1.8 or less, particularly preferably 1.6 or less, and most preferably 1.5 or less. When Mv / Mn is equal to or less than the upper limit, coarse particles are sufficiently removed, and the abrasive material can be prevented from piercing the film due to cracks in the coarse particles (and the resulting residual sand in the film).

[0035] In the present invention, the coarse particles are removed by the above-mentioned method, and the amount of the coarse particles removed by the operation of removing the coarse particles is generally 0.5% by mass or more, generally 1.0% by mass or more, based on the total amount of the abrasive particles subjected to the operation, and is generally 10.0% by mass or less, generally 5.0% by mass or less. That is, although only a very small number of coarse particles are removed, these very small number of coarse particles break and cause sand residue after film processing.

[0036] In the shot blasting process of the present invention, a film, which is the object to be processed, is usually run at a substantially constant speed, and an abrasive ejected from a rotor installed on the running path of the film is made to collide with the surface of the film.

[0037] In the present invention, in a steady state, a substantially constant amount of abrasive circulates inside the shot blasting device. The amount of abrasive circulating inside the device is preferably 50 kg or more, more preferably 100 kg or more, and particularly preferably 200 kg or more, and is preferably 5000 kg or less, more preferably 3000 kg or less, and particularly preferably 2000 kg or less. When the content is equal to or greater than the lower limit, the surface roughness of the film can be sufficiently reduced, and when the content is equal to or less than the upper limit, the processing costs can be sufficiently reduced.

[0038] In the present invention, the abrasive particles having reduced particle size are collected by air. The particle size (average of the long and short sides) of the collected abrasive particles (recovered sand) is preferably 110 μm or less, more preferably 90 μm or less, and particularly preferably 75 μm or less. By adjusting the thickness to the above upper limit or less, both the surface roughness of the film and economic efficiency can be achieved.

[0039] The amount of abrasive material equivalent to the amount removed from the device as recovered sand is newly added to the device. The newly added abrasive material (new sand) may be added in batches periodically or continuously.

[0040] When new sand is periodically added in bulk, the interval between additions is preferably 4 minutes or more, more preferably 10 minutes or more, and particularly preferably 20 minutes or more, and is preferably 180 minutes or less, more preferably 120 minutes or less, and particularly preferably 60 minutes or less.

[0041] In this case, the amount of material to be added at one time is preferably 5 kg or more, more preferably 10 kg or more, and particularly preferably 20 kg or more, and is preferably 100 kg or less, more preferably 80 kg or less, and particularly preferably 60 kg or less.

[0042] Whether it is added periodically in a lump or constantly, the amount of new sand added is preferably 5 kg / min or more, more preferably 10 kg / min or more, and particularly preferably 20 kg / min or more, and is preferably 100 kg / min or less, more preferably 80 kg / min or less, and particularly preferably 60 kg / min or less.

[0043] When the amount and interval of new sand addition are within the above ranges, the surface roughness of the film can be sufficiently reduced, and processing costs can be sufficiently reduced.

[0044] In the present invention, there are no particular limitations on the material of the film to be processed (the film to be roughened), and films such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), polycarbonate, polyarylate, polyethylene, polypropylene (PP), unstretched polypropylene film (CPP), oriented polypropylene film (OPP), diacetyl cellulose, triacetyl cellulose (TAC), polyacrylate, polymethacrylate, polyimide (PI), polyamide, and polyphenylene sulfide (PPS) can be used in the present invention.

[0045] In the present invention, the average thickness of the film to be roughened before processing is not particularly limited, but is preferably 4 μm or more, more preferably 12 μm or more, and particularly preferably 25 μm or more, and is preferably 2000 μm or less, more preferably 1000 μm or less, and particularly preferably 250 μm or less. The thinner the film, the more likely it is that residual sand will be generated due to the abrasive penetrating the film, and the thinner the film, the more significant the effects (defects) caused by residual sand. If the average thickness of the film is equal to or less than the upper limit, the significance of suppressing residual sand becomes greater, and the benefits of the present invention are more easily realized.

[0046] In the shot blasting treatment of the present invention, the film running speed is preferably 1 m / min or more, more preferably 3 m / min or more, and particularly preferably 5 m / min or more, and is preferably 100 m / min or less, more preferably 70 m / min or less, and particularly preferably 50 m / min or less. A thickness equal to or greater than the lower limit is preferred from the viewpoint of productivity, whereas a thickness equal to or less than the upper limit allows the film surface to be suitably roughened.

[0047] The width of the film to be run (length perpendicular to the running direction) is preferably 300 mm or more, more preferably 400 mm or more, and particularly preferably 500 mm or more, and is preferably 2000 mm or less, more preferably 1500 mm or less, and particularly preferably 1350 mm or less.

[0048] The rate of abrasive sprayed from the rotor toward the film is preferably 146 kg / Hr or more, more preferably 188 kg / Hr or more, and particularly preferably 230 kg / Hr or more, and is preferably 1800 kg / Hr or less, more preferably 1500 kg / Hr, and particularly preferably 1200 kg / Hr or less. Within the above range, the film surface can be sufficiently roughened, and this is also preferable from the standpoint of cost.

[0049] In the present invention, the arithmetic mean line height (Ra) (JIS B 0601) of the film after the shot blasting step is preferably about 0.1 to 2.0 μm, and particularly preferably about 0.2 to 1.2 μm. If the film is processed uniformly, the arithmetic mean height (Sa) of the surface will be the same value as Ra.

[0050] In the present invention, the maximum height (Sz) of the film surface after the shot blasting step is preferably about 1.0 to 40.0 μm, and particularly preferably about 5.0 to 35.0 μm.

[0051] Although the example described above uses air to collect the abrasive particles with reduced particle size, it is also possible to separate them using a mesh sieve and then collect them. In this case, the air classifies the particles by weight, while the sieve classifies them by size. [Example]

[0052] The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention.

[0053] Comparative Example 1 Commercially available silica sand (hereafter referred to as "Abrasive A") was used as new sand for shot blasting without any treatment to remove coarse particles. Measurements using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3000II, manufactured by Microtrac Bell Co., Ltd.) revealed that the volume mean particle size (Mv) of Abrasive A was 188.38 μm and the number mean particle size (Mn) was 90.89 μm.

[0054] A shot blasting machine with 12 rotors was used for a polyethylene terephthalate (PET) film (1350 mm wide) with an average thickness of 25 μm. 36 kg of abrasive A was added to the tank of the shot blasting machine as new sand every 15 minutes. The machine was set up so that the abrasive (recovered sand), whose particle size had become smaller through recycling, was removed from the machine at the same pace, and the machine was set up so that around 400 kg of abrasive was circulating within the machine in a steady state.

[0055] The film was subjected to a surface roughening process at a steady state running speed of 15 m / min. After the roughening process was completed, the film was washed with water and then dried. The dried film was observed under a laser microscope, and the number of abrasive particles (residual sand) that had penetrated the film per 100 m was calculated.

[0056] Comparative Example 2 A PET film was roughened by shot blasting in the same manner as in Comparative Example 1, except that another commercially available silica sand (hereinafter referred to as "Abrasive B") was used as new sand instead of Abrasive A, and the number of sand particles remaining on the film after washing and drying was calculated. Abrasive B was not treated to remove coarse particles, and its volume average particle size (Mv) was 166.12 μm and its number average particle size (Mn) was 78.95 μm.

[0057] Comparative Example 3 A PET film was roughened by shot blasting in the same manner as in Comparative Example 1, except that another commercially available silica sand (hereinafter referred to as "Abrasive C") was used as new sand instead of Abrasive A, and the number of sand particles remaining on the film after washing and drying was calculated. Abrasive B was not treated to remove coarse particles, and its volume average particle size (Mv) was 141.82 μm and its number average particle size (Mn) was 78.64 μm.

[0058] Example 1 In Comparative Example 2, a PET film was roughened by shot blasting in the same manner as in Comparative Example 2, except that a new abrasive (hereinafter referred to as "Abrasive D"), which had been prepared by in-line classification using a #70 mesh to remove coarse particles from Abrasive B, was used as the new sand. The number of sand particles remaining on the film after washing and drying was calculated. The volume average particle size (Mv) of Abrasive D was 134.94 μm, and the number average particle size (Mn) was 89.10 μm.

[0059] Example 2 In Comparative Example 3, a PET film was roughened by shot blasting in the same manner as in Comparative Example 3, except that a new abrasive (hereinafter referred to as "Abrasive E"), which had been prepared by in-line classification using a #70 mesh to remove coarse particles from Abrasive C, was used as the new sand. The number of sand particles remaining on the film after washing and drying was calculated. The volume average particle size (Mv) of Abrasive E was 131.00 μm, and the number average particle size (Mn) was 86.85 μm.

[0060] Example 3 In Comparative Example 3, a PET film was roughened by shot blasting in the same manner as in Comparative Example 3, except that a new abrasive (hereinafter referred to as "Abrasive F"), which had been prepared by in-line classification using a #90 mesh to remove coarse particles from Abrasive C, was used as the new sand. The number of sand particles remaining on the film after washing and drying was calculated. The volume average particle size (Mv) of Abrasive F was 131.39 μm, and the number average particle size (Mn) was 89.91 μm.

[0061] The results for each of the Examples and Comparative Examples are shown in Table 1.

[0062] [Table 1]

[0063] As is clear from the results in Table 1 above, in Examples 1 to 3, by performing shot blasting using an abrasive from which coarse particles had been removed, the amount of residual sand remaining on the film after roughening processing could be dramatically reduced. The amount of residual sand was large in Comparative Examples 1 to 3. The residual sand tended to occur immediately after new sand was added.

[0064] The particle size distributions of Abrasive C used in Comparative Example 3 and Abrasive E used in Example 2 are shown in Figures 2 and 3, respectively. In Abrasive C, coarse particles with a value obtained by dividing the sum of the long and short sides by 2 exceeding 310 μm can be seen (Figure 2), but in Abrasive E, no coarse particles with this value exceeding 310 μm can be seen (Figure 3). Furthermore, the particle size distribution of particles with this value less than 310 μm is almost the same between Abrasive C and Abrasive E. This indicates that the small amount of coarse particles present is the cause of residual sand remaining on the film. [Industrial Applicability]

[0065] The method for producing processed films of the present invention is less likely to cause problems with residual sand in the film after roughening, and is therefore widely used in the production of base films and process films used in applications such as electronic devices and semiconductor manufacturing. [Explanation of symbols]

[0066] 1 Shinsuna 2 Circulating sand 3. Reclaimed sand 10 Equipment (Shot Blasting Equipment) 11. Tank 12 rotors 13 Circulation route 14 Recovery Route F film

Claims

1. In a method for producing a processed film, a film is roughened by a shot blasting process in which an abrasive is circulated and used, and the abrasive whose particle size has become smaller through the circulation is removed from the device by collecting it, and new abrasive having a volume average particle size larger than that of the removed abrasive is introduced into the device. A method for producing a processed film, characterized in that the newly added abrasive has had coarse particles with an average length of 300 μm or more on its long and short sides removed.

2. 2. The method for producing a processed film according to claim 1, wherein the value obtained by dividing the volume average particle diameter by the number average particle diameter of the newly added abrasive is 2.0 or less.

3. A method for manufacturing a processed film as described in claim 1 or claim 2, wherein the abrasive is silica sand.

4. 4. The method for producing a processed film according to claim 1, wherein the coarse particles are removed by sieving through a mesh.

5. 5. The method for producing a processed film according to claim 1, wherein the average length of the long and short sides of the recovered abrasive is 110 [mu]m or less.

6. 6. The method for producing a processed film according to claim 1, wherein the rate of abrasive material fed into the device is 5 kg / min or more and 100 kg / min or less.

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