JPS6153292B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a film roll formed by rolling up a polyester film. Conventional techniques for forming a film roll by winding a film made of synthetic resin such as polyester resin include a center wind method and a surf S wind method. In the former method, the film is directly wound on a driven winding drum, and nothing is brought into contact with the surface of the film winding layer. The latter is a method in which the winding drum is rotatably supported without being driven, and brought into contact with a surface drive roll that drives the surface of the film layer, and the winding drum is rotated by the frictional force. Further, as a winding method, there is a SURF S-center wide method which combines the features of both of the above. This method is essentially a center wind method in that it directly drives the winding drum, but in order to stabilize the running film and apply pressing force to the film roll to obtain a good winding shape. This is a method in which the winding drum is brought into contact with a rotatably supported tatsuchi roll separate from the winding drum. When winding a polyester resin film or the like using such a winding method, the film is wound up together with the accompanying air present near the film surface. A film roll formed into a roll shape by a winding drum is composed of a film and an air layer interposed between the wound layers of each film. However, when winding the film, it is necessary to keep the amount of air interposed between the winding layers of the film within a certain appropriate range.
That is, in general, if the amount of air between the film winding layers is too large, the coefficient of friction between the film winding layers will be significantly reduced, and when the film is wound onto a winding drum, the film will meander in the width direction, causing the film to roll on both end sides of the film roll. This results in a defect called "end face misalignment" in which the edges become uneven. Also, when the film shrinks, which is its own characteristic, the air interposed between the film winding layers is discharged from both end sides of the film roll due to the tightening phenomenon, and the inner layer of the film roll is compressed by the compressive force of the outer layer. Defects such as distortion and deformation may occur. On the other hand, if the amount of air between the winding layers of the film is too small, if there is unevenness in the thickness along the width direction of the film, the thicker parts will overlap one after another on the winding drum and will stand out compared to other parts. do. As a result, band-like bulges are formed on the circumference of the film roll, and the film may lose its flatness and other physical properties. For the above reasons, when winding up a film roll, in the prior art, a winding method is adopted in which a suitable amount of air can be interposed between the film winding layers.
Among the above-mentioned winding methods, in the center wind method, a large amount of air accompanying the film wound on the winding drum is caught between the film winding layers of the film roll, resulting in an excessive amount of air. Therefore, the winding tension must be relied upon as a means of controlling the amount of air. However, if the winding tension is low, the excessive amount of air will not be resolved, and if the winding tension is too high, wrinkles will occur in the film and the wrinkles will be rolled into the film roll. have. In addition, in the surf-swind method, it is necessary to maintain surface pressure between the film roll and the surface drive roll in order to obtain drive stability of the winding drum, but as the winding diameter of the film roll increases, external disturbances It is difficult to keep the surface pressure constant against the changing load. In this case, since the air layer between the film winding layers is also inevitably influenced by the surface pressure, it is very difficult to control the air layer. However, in the Surf S Center Wind method, the film roll is wound around a driven winding drum and is pressed by a separate tatsuchi roll, so by changing the surface shape of the tatsuchi roll and changing the pressing force, the air layer between the film winding layers can be reduced. It has the advantage of being able to control. For this reason, the surf S-center wind method is often used in slitters that slit film to a predetermined width in the width direction and wind it into a film roll. Recently, the focus of winding technology has been on controlling the amount of air between layers of film, and film rolls are created with specific air layer thicknesses (air amounts) depending on the brand of film. On the other hand, due to rapid advances in film forming technology, uneven thickness such as the formation of band-like bulges in the circumferential direction of the film roll hardly occurs when the film is wound. As a result, it is becoming an important condition for winding technology in slivers that the wound film roll has excellent shape stability as a product. In other words, in the case of polyester film, quality control is necessary to ensure that the rolled film roll does not lose its rolled shape over time by appropriately controlling the amount of air between the film winding layers. The main points of the matter are changing. Here, the change in shape of a film roll over time means that if the film roll is left as it is, moisture contained in the atmosphere will gradually be absorbed into the film from the surface layer and end surfaces of the film roll, and as a result of this moisture absorption, the film will gradually absorb moisture from the atmosphere. This indicates that "wrinkles" occur in the film roll as a result of the film being slightly stretched. These "wrinkles" occur over time on a flat film roll several days after it is rolled up. Such "wrinkles" over time are particularly likely to occur in thin polyester films with relatively high surface smoothness. In the conventional technology, it is a thin film of 16 μ or less, and the center line average roughness of the film surface (center line average roughness: defined in JIS B 0601-1976, hereinafter indicated by the symbol Ra) is 0.05 μ or less. For typical polyester film brands, it has been difficult to avoid "wrinkles" over time due to the winding method in which an air layer of an appropriate thickness is interposed between the film winding layers. Traditionally, we have made great efforts to determine the winding conditions that will give the optimal air layer thickness through preliminary tests, by varying the winding tension and Tatsuchiroll pressing force each time the brand changes, but it just so happens that the results are good. Even if a good film roll is obtained, the basis for obtaining it is unknown, so reproducibility is poor. Furthermore, it is impossible to guarantee that "wrinkles" will not develop over time after the product film roll is shipped. As described above, it has not yet been possible to provide users with a product that is completely free from "wrinkling" over time. As mentioned above, "wrinkles" over time will appear within about a week if the film roll is left in a normal atmosphere after winding, and depending on the film roll, wrinkles will appear up to half the diameter of the film roll. There were also cases where "wrinkles" appeared. Films with such "wrinkles" must be unrolled and removed, resulting in a significant loss of product value. An object of the present invention is to provide a film roll that does not develop wrinkles over time. According to the present invention, a thin film having a film thickness of 16 μm or less is formed and stretched so as to have a surface roughness within a specific range, and is rolled up in accordance with the film surface roughness to form a film roll. By this method, a polyester film roll that does not wrinkle over time due to moisture absorption and elongation even when left in an atmosphere can be obtained. That is, the present invention provides a film roll formed by rolling up a polyester film having a film thickness of 16 microns (μ) or less and a center line average roughness (Ra) of the film surface in the range of 0.001 to 0.05. and the winding hardness (H) of the film roll is between the center line average roughness and H≧
0.67x ³ −10.61x ² +55.54x−1.16where x=ln
The film roll is characterized by satisfying the relationship (1/Ra). The present invention will be explained. The present invention was made by accidentally discovering that "wrinkles over time" do not occur when the winding hardness of a film roll and the centerline average roughness of the film surface satisfy the above relationship. In the prior art, the measure against "wrinkles over time" was to wrap the film roll with a moisture-proof material to avoid moisture absorption. Suppressing the occurrence of "target wrinkles" is a completely unexpected solution. Even in the case of a film roll that does not "wrinkle" over time, there will still be a slight air layer between the film winding layers. However, there is no way to accurately measure this air layer. Therefore, the hardness of the rolled-up film roll (hereinafter indicated by symbol H) is made to correspond to the air layer. Assuming that the thickness of the film is constant, if the air layer is thick, the hardness H tends to be low, and if the air layer is thin, the hardness H tends to be high.
Therefore, the hardness H can be made to correspond to the amount of air in the film roll. On the other hand, the surface roughness of the film changes depending on the additives added to the film raw material, and the user can adjust the surface roughness by adding and dispersing substances that form the core of the surface roughness in advance, or by generating the core through a reaction. However, after forming the film, the general characteristics described above are
Represented by Ra. The polyester film to which the present invention can be applied must have a surface roughness Ra of 0.05 or less. Ra is
If it exceeds 0.05, slippage will occur between the film layers regardless of the winding hardness of the film roll, so "wrinkles over time" will hardly occur. In cases where the surface roughness is large and the films tend to slip between layers, conventional techniques must be used to prevent wrinkles over time due to moisture absorption and elongation. In the prior art, a film that has been pre-absorbed with moisture must be rolled up to prevent moisture absorption and elongation, or the winding hardness should be lowered so that the film hardly wrinkles due to interlayer slippage. In addition, if Ra is less than 0.001, it is possible to manufacture a film roll by rolling it up hard and prevent "wrinkling over time," but the film lacks slipperiness and is difficult to call practical in terms of workability. . The film of the present invention is limited to a thickness of 16 μm or less. For thick polyester films, wrinkles over time are not a practical problem. When "wrinkles" occur on thin films of about 2 to 16μ, these "wrinkles"
becomes permanently distorted and impairs its utility value. Especially when it comes to magnetic tape base materials, a film with "wrinkles" is not practical. As described above, the present invention is specified to a rolled-up film roll that is effective for very thin films in which "wrinkling over time" is a problem. To measure the hardness H of the film roll, a general-purpose hardness tester that presses a steel ball against the surface layer of the film roll can be used. In particular, the present invention uses a hardness tester manufactured by Kobunshi Keiki Co., Ltd.
Use TYPE C. Further, as the actual value of H, measurements are taken at five points along the axial direction of the film roll, and the average value thereof is adopted. Kaolin, an inert inorganic substance, is added to polyester.
Various types of calcium carbonate, silica, etc. with different particle sizes (average particle size and particle size distribution) and different additive amounts are selected to form and stretch biaxially stretched films with different Ra values. The Ra of the resulting film is determined by determining the type (average particle size and particle size distribution) of the inert inorganic substance added to the film, the amount added, etc., and the film forming and stretching conditions. In the present invention, through trial and error, Ra was 0.001 μm, 0.01 μm, 0.03 μm and 0.05 μm.
A large amount of four levels of μm was prepared in the polymerization process. These polyester films can be obtained by using a winding machine of the Surf S center wind type, and by appropriately changing the pressing force of the tatsuchi roll and the winding tension of the film, film rolls having different hardnesses can be obtained. The film roll thus obtained was left in an atmosphere with a temperature of 35°C and a relative humidity of 70% for 7 days and nights to determine the film roll winding hardness H and film surface roughness.
When the relationship with Ra was investigated, as shown in Table 1, the minimum hardness H at which "wrinkles over time" do not occur was found. Table 1 was obtained by organizing a large number of experimental data. For example, for a film with Ra = 0.05μ, about 60 film rolls with hardness (H) in the range of 84 to 95 As a result of testing the occurrence of wrinkles, it was found that a hardness of 88 is a critical value at which wrinkles occur over time. Table 1 shows the center line average roughness of the film surface and the critical value of the winding hardness that determines the occurrence of "wrinkles over time."

[Table] According to the results in Table 1, the lower the Ra on the film surface, the higher the H, otherwise wrinkles will occur over time.
It is clear that it is not possible to prevent the occurrence of The reason for this is understood to be that in a film roll with a small Ra, the films between the winding layers are difficult to slide against each other, and as a result, the film partially sticks between the winding layers (blocking phenomenon). In other words, when the film absorbs moisture from the outside air, the film's elongation due to moisture absorption is suppressed by the blocking phenomenon between the films, and as a result, elongation is actually hindered.
It can be understood that it does not develop wrinkles over time even if it absorbs moisture. In addition, when winding a film with a small Ra, by making the air layer between the film winding layers as thin as possible and discharging the air uniformly, a film roll is formed with the films in close contact with each other, and the air layer between the film winding layers is made to be as thin as possible. It can also be assumed that there is a self-sealing effect that prevents the penetration of moisture. The film roll wound in this manner has a very thin air layer between the film winding layers, so that H is high. On the other hand, Ra on the film surface is
Brands with a value larger than 0.05 have a low coefficient of friction between the film layers, so the films will not stick to each other partially, regardless of the thickness of the air layer between the layers, and the film will not slip between the layers. Easy to occur. In such a case, it is thought that the elongation of the film due to moisture absorption is released toward the edge of the film without being restricted, and wrinkles do not occur over time. Since the relationship shown in Table 1 exists between the centerline average roughness Ra of the film surface and the winding hardness H of the film roll, the regression equation between Ra and H can be determined by mathematical means. . The regression equation thus obtained is as follows. H≧0.67x ³ −10.61x ² +55.54x−1.16 where x=ln(1/Ra) The above regression equation is based on the center line average roughness (Ra) of the film surface and the winding hardness of the film roll (Table 1). In H), this is nothing but a mathematical expression that shows the critical conditions under which wrinkles do not occur over time. In other words, as shown in Table 1, when the above formula is satisfied, a film roll without "wrinkling over time" can be obtained. The polyester film roll obtained by the present invention has the advantage that it does not wrinkle over time, so it can be used as a base material for magnetic tapes, a base material for vapor-deposited films, and the like. Example: Polyethylene terephthalate containing 0.5% by weight of clay with an average particle size of 0.6μ as an additive was used to prepare a film with a thickness of 8μ with an Ra of 0.04 (μ) using a conventional method.
A biaxially stretched film material was obtained. This raw film was rolled up by a sliver into a film roll having a width of 650 mm and a total length of 6000 m at a winding speed of 150 m/min.
At this time, a film roll having a hardness H of 98 was obtained under the conditions that the winding tension was 1.2 Kg/mm ² and the pressing force of Tatsuchi Roll was 80 Kg. Further, under the condition that the Tatsuchi roll pressing force was 20 kg, a film roll with a hardness H of 88 was obtained under the same winding tension. Heat these two film rolls to 40
When left for 7 days at ℃ and 75% humidity, H
The film roll of H=88 had deep "wrinkles over time" reaching 1500 m from the surface layer, but the film roll of H=98 had no "wrinkles over time" at all.

Claims (1)

[Claims] 1. The film has a thickness of 16μ or less and a center line average roughness (Ra) of 0.001 on the surface of the film.
A film roll formed by rolling up a polyester film in the range of 0.05 to 0.05, which satisfies the following formula between the winding hardness (H) of the film roll and the center line average roughness of the film surface. Characteristic film roll. H≧0.67x ³ −10.61x ² +55.54x−1.16 where x=ln(1/Ra)