JP7724101B2 - Processed film manufacturing method - Google Patents

Description

The present invention relates to a method for producing processed film using shot blasting, and more specifically, to a method for producing processed film in which residual sand is significantly reduced by removing coarse particles from the abrasive material added.

BACKGROUND ART Polymer films are subjected to surface roughening treatment to form 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.

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.

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

Patent Document 3 describes how applying fine irregularities to a film before hairline processing as a pre-treatment can reduce the occurrence of defects called whiskers, which are made up of shavings, after hairline processing, compared to when this pre-treatment is not performed. In the examples of Patent Document 3, shot blasting is used as a method for applying fine irregularities to the film.

In shot blasting, abrasives are recycled and reused, and various abrasive recycling devices and methods have been proposed (Patent Documents 4 to 6).

The particle size of recycled abrasives gradually decreases as they break and become rounded due to collisions with each other, the rotor, and the equipment walls. Abrasives with reduced particle size are unable to form sufficient irregularities, so to maintain the quality of the processed film, abrasives that have reached a certain particle size are collected and removed, and new abrasives are added to replace them. One method for collection and removal is to use air, as described in Patent Document 4, etc.

On the other hand, abrasives that break upon impact have sharp edges and can pierce the film upon impact with it. Such "abrasives that have pierced the film" (hereinafter sometimes referred to as "residual sand") can cause a decrease in yield when coating another material on the film after the texture has been formed.

For these reasons, there is a need to develop technology that can improve yield and productivity throughout the entire process, including coating.

Japanese Patent Application Laid-Open No. 2004-243497 Japanese Unexamined Patent Publication No. 62-279992 JP 2014-144539 A Japanese Patent Application Laid-Open No. 2016-168657 Japanese Patent Application Publication No. 8-267361 Japanese Patent Application Laid-Open No. 2002-210658

The present invention was made in consideration of the above-mentioned background art, and its objective is to provide a method for roughening a film surface by shot blasting that is less likely to result in the problem of residual sand remaining on the film after processing.

When abrasives are recycled during shot blasting, they become smaller in particle size and 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.

As a result of intensive research to solve the above problems, the inventors 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 new abrasives are added. From this, the 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 crack, and discovered that by removing 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.

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.

The present invention provides a method for roughening a film surface by shot blasting that is less likely to result in residual sand remaining on the film after processing.

In shot blasting, a larger average particle size of abrasive material makes it easier to increase the surface roughness (Ra) and the processing speed, which is advantageous for industrial production of roughened films. However, large particle size 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.

If sand remains on the film after roughening, the yield of the film (final product) that is subjected to coating or other processing 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.

1 shows a conceptual diagram of the shot blasting process of the present invention. 1 shows the particle size distribution of abrasive C used in Comparative Example 3. 1 shows the particle size distribution of abrasive E used in Example 2.

The present invention will be described below, but it is not limited to the following embodiments and can be implemented in any desired manner.

This invention is a method for producing processed film, in which the film is roughened by shot blasting.

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.

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 described as an example, but the abrasive in the present invention is not necessarily limited to sand (silica sand).

In the present invention, newly added abrasive material (hereinafter referred to as "new sand") 1 is introduced into the shot blasting device 10 from the tank 11. The introduced abrasive material is sent to the rotor 12, where it is ejected from the rotor 12 and collides with the surface of the traveling film F, roughening the surface of the film F.

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

If the particle size of the abrasive becomes too small, it will no longer be able to fully roughen the film. For this reason, the abrasive, whose particle size has been reduced through circulation, is collected, for example, by air and removed from the inside of the device 10 via the recovery path 14. Hereinafter, the abrasive removed from the recovery path 14 may be referred to as "recovered sand 3."

As the amount of abrasive circulating within the device 10 decreases due to the removal of the recovered sand 3, new abrasive (new sand) 1 is added to replace the reduced amount from the tank 11. The new abrasive (new sand) 1 has a larger volume average particle size than the abrasive (recovered sand) 3 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 instead, the abrasive's ability to roughen the surface (ability to reduce the surface roughness of the film) is maintained.

When abrasives collide with each other or with the rotor or equipment walls, the broken abrasives pierce the film when they collide, leaving sand residue on the film. The remaining sand in the film can cause problems when coating processes are applied to the roughened film, resulting in reduced yields. Abrasives are likely to break immediately after new sand is added, but become less likely to occur as the abrasives are circulated.

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 increases the amount of abrasive used or makes it necessary to slow down the processing speed (the running speed of the film), leading to reduced productivity and being undesirable from both an environmental and economic perspective.

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 large particles, 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.

There are no particular limitations on the method for removing coarse particles, but examples include sieving through a mesh, classifying using a centrifuge, and crushing coarse particles using a grinder, etc.

Depending on the type of abrasive, newly added abrasive particles are often not nearly spherical. In particular, when the abrasive is silica sand, the shapes often vary, 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.

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.

Even small amounts 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 coarse particles are breaking. As the abrasive circulation progresses (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 have broken or become rounded and become finer (smaller particle size).

For newly added abrasive (new sand), the value obtained by dividing the volume average particle diameter (Mv) by the number average particle diameter (Mn) (Mv/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 cracking of the coarse particles (and thus the resulting residual sand in the film).

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, and 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, and 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.

In the shot blasting process of the present invention, the workpiece, a film, is typically moved at a substantially constant speed while abrasive material is sprayed from a rotor installed along the film's path and collided with the film's surface.

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.

In the present invention, the abrasive particles having a 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.

New abrasive material equivalent to the amount removed from the device as recovered sand is added to the device. New abrasive material (new sand) can be added in batches on a regular basis, or it can be added all the time.

When new sand is added periodically in large quantities, the addition interval is preferably at least 4 minutes, more preferably at least 10 minutes, and particularly preferably at least 20 minutes. It is also preferable that the interval be no more than 180 minutes, more preferably no more than 120 minutes, and particularly preferably no more than 60 minutes.

In this case, the amount of material to be fed per load is preferably 5 kg or more, more preferably 10 kg or more, and particularly preferably 20 kg or more. It is also preferable that the amount be 100 kg or less, more preferably 80 kg or less, and particularly preferably 60 kg or less.

Whether adding new sand in batches periodically or continuously, 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. It is also preferably 100 kg/min or less, more preferably 80 kg/min or less, and particularly preferably 60 kg/min or less.

When the amount and interval of new sand added are within the above ranges, the surface roughness of the film can be sufficiently reduced and processing costs can be kept to a minimum.

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.

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 will be. If the average thickness of the film is below the upper limit, the significance of suppressing residual sand becomes greater, and the benefits of the present invention are more easily realized.

In the shot blasting treatment of the present invention, the running speed of the film 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.

The width of the film being run (the 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. It is also preferably 2000 mm or less, more preferably 1500 mm or less, and particularly preferably 1350 mm or less.

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 or more, 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.

In the present invention, the arithmetic mean 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.
When the film is uniformly processed, the arithmetic mean height (Sa) of the surface is the same value as Ra.

In the present invention, the maximum height (Sz) of the film surface after the shot blasting process is preferably approximately 1.0 to 40.0 μm, and particularly preferably approximately 5.0 to 35.0 μm.

The example explained was of collecting small particle size abrasives using air, but it is also possible to separate and collect them using a mesh sieve. In this case, the air sorts the particles by weight, while the sieve sorts them by size.

The present invention will be explained in more detail below using 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.

Comparative Example 1
Commercially available silica sand (hereinafter 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.

A 12-rotor shot blasting machine was used to blast a polyethylene terephthalate (PET) film (1,350 mm wide) with an average thickness of 25 μm. 36 kg of abrasive A was added to the tank of the shot blasting machine every 15 minutes as new sand. The machine was set up so that the abrasive (recycled sand), whose particle size had become smaller through recycling, was removed from the machine at the same rate, and the machine was set up so that around 400 kg of abrasive was circulating within it at steady state.

In a steady state, the film was roughened at a running speed of 15 m/min. After roughening, the film was washed with water and then dried. The dried film was observed using a laser microscope, and the number of abrasive particles (residual sand) that had penetrated the film per 100 m was calculated.

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 the volume average particle size (Mv) of Abrasive B was 166.12 μm and the number average particle size (Mn) of Abrasive B was 78.95 μm.

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 the volume average particle size (Mv) of Abrasive B was 141.82 μm and the number average particle size (Mn) was 78.64 μm.

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") obtained by removing coarse particles from abrasive B by in-line classification using a #70 mesh was used as new sand, and 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.

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") obtained by removing coarse particles from abrasive C by in-line classification using a #70 mesh was used as the new sand, and 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.

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") obtained by removing coarse particles from abrasive C by in-line classification using a #90 mesh was used as the new sand, and 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.

The results for each example and comparative example are shown in Table 1.

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, it was possible to dramatically reduce the amount of residual sand remaining on the film after the roughening process.
In Comparative Examples 1 to 3, the amount of residual sand was large. The residual sand tended to occur immediately after new sand was added.

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.

The process for producing processed films of the present invention is less likely to result in residual sand remaining on the film after roughening, and is therefore widely applicable to the production of base films and process films used in applications such as electronic devices and semiconductor manufacturing.

1 New sand 2 Circulating sand 3 Reclaimed sand 10 Equipment (shot blasting equipment)
11 Tank 12 Rotor 13 Circulation path 14 Recovery path F Film

Claims (6)

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. The method for manufacturing processed film according to claim 1, wherein the volume average particle diameter divided by the number average particle diameter of the newly added abrasive is 2.0 or less. 3. The method for producing a processed film according to claim 1, wherein the abrasive is silica sand. A method for producing a processed film according to any one of claims 1 to 3, wherein the coarse particles are removed by sieving through a mesh. A method for manufacturing a processed film according to any one of claims 1 to 4, wherein the average length of the long and short sides of the recovered abrasive material is 110 μm or less. A method for manufacturing processed film according to any one of claims 1 to 5, wherein the rate of abrasive material fed into the device is 5 kg/min or more and 100 kg/min or less.