JPH0356889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of cooling a plastic film, and more particularly to a method of heating a plastic film, stretching it in the longitudinal direction, and then cooling it with a cooling roll.

[Prior Art] Generally, in order to continuously stretch a plastic film in the longitudinal direction, a roll stretching method is used in which a predetermined stretching ratio is applied between rolls. The continuously conveyed plastic film is heated to a predetermined temperature by a heating roll (or by adding heating by an auxiliary heater to the heating by the heating roll), and then stretched at a predetermined ratio between it and a cooling roll. The stretched film is cooled by cooling rolls.

In such stretching apparatuses, conventionally, a chrome-plated roll whose surface is usually mirror-finished is used as a cooling roll. Regarding the heating roll side, rolls with various surface materials have been proposed in order to suppress the adhesion of the film heated to high temperatures.However, the controlled temperature of the cooling roll after stretching is also low, so that the adhesion with the film is reduced. In order to cool and form the film surface to be as smooth as possible, and to maintain good heat transfer for cooling, a mirror-finished metal roll such as the one described above is usually used.

[Problems to be Solved by the Invention] However, in the case of certain types of plastic films, such as polyester films, triangular defects as shown in FIG. 2 may occur on a cooling roll having a chrome-plated surface. . The triangular defect 1 mainly occurs when the plastic film 2 passes over the cooling roll 3 immediately after being stretched.
The size varies depending on conditions such as film thickness, stretching temperature, cooling temperature, etc.
It has a length l of about 5 to 20 mm.

Triangular defect 1 is quite difficult to distinguish with the naked eye, but can be definitely recognized when viewed with a polarizing plate, and the film 2 (especially its surface) is slightly deformed into a triangular shape in this area. It is.
As a result of investigating the cause of this triangular defect 1, it was found that the deformation was caused by air being trapped on the cooling roll 3. The trapped air tries to escape to the rear side in the width direction and transport direction of the film 2, but since the film is cooled, it does not slip on the cooling roll 3, and since the surface of the cooling roll 3 is a mirror surface, The trapped air cannot escape completely, resulting in a triangular defect as shown in the figure. If such a triangular defect 1 occurs, it will cause a major quality defect in secondary processing, such as magnetic layer coating processing, so film manufacturers have no choice but to reject the product. The occurrence of 1 was a cause of a large decrease in yield.

Conventionally, when the above-mentioned triangular defect 1 occurs, it has been dealt with by changing conditions such as stretching temperature, cooling roll temperature, and lowering the film transport speed, but in doing so, undesirable conditions have to be adopted. This has also led to a decline in the quality of the films produced.

An object of the present invention is to provide a method that can prevent the above-mentioned triangular defect from occurring without the need to substantially change the manufacturing conditions and without creating another defect.

[Means for Solving the Problems] The plastic film cooling method of the present invention in accordance with this objective involves heating a continuously conveyed plastic film, stretching it in the longitudinal direction, and then cooling the plastic film with a cooling roll. In the method, the cooling roll is a ceramic roll whose surface material is made of ceramic.

Here, the ceramic layer constituting the roll surface is formed by, for example, thermal spraying ceramic onto the surface of the roll body. The thickness of this ceramic layer is not particularly limited, but since a coolant is usually passed through the inside of the cooling roll, it is preferable to form the ceramic layer to be as thin as possible without impairing the cooling performance of the cooling roll for the film.

The surface roughness of the ceramic roll is preferably in the range of 0.02μ≦Ra≦2μ in terms of center line average roughness (Ra). Preferably, the range of Ra is
It is 0.05μ to 1.0μ, more preferably 0.08 to 0.7μ.

In addition, the types of ceramics include, for example:
Examples include ceramics containing aluminum oxide, titanium oxide, chromium oxide, zirconium oxide, and the like.

[Operation] The ceramic constituting the surface of the cooling roll has essentially minute irregularities on the surface even after thermal spraying or mechanical finishing. Therefore, the air trapped between the plastic film after stretching and the surface of the cooling roll escapes through the surface due to the minute irregularities on the surface of the cooling roll, causing triangular defects that occur when air is trapped. Prevented. However, if triangular defects can be prevented only by minute irregularities on the surface, the cooling roll should be a metal roll.
A similar effect could be obtained by making the surface rough, but in reality, the triangular defects could not be completely eliminated using a metal cooling roll with a rough surface. By using a ceramic roll as described above as the cooling roll, it was possible to completely eliminate the triangular defect for the first time. This is because ceramic is essentially a porous material, so the trapped air escapes into the porosity, and this escape of air compensates for the escape of air that travels along the roll surface. considered to be a thing.

Then, the surface roughness of the ceramic roll was set to 0.02μ.
By setting the value within the range of ≦Ra≦2μ, the trapped air will be completely released, and no triangular defects will occur. In other words, if the surface roughness is 0.02μ or less, it approaches the surface roughness of a conventional mirror-finished metal roll (Ra is usually 0.01μ or less), and the air release effect becomes too small.On the other hand, if the surface roughness is 2μ or more, it becomes too rough. Doing so may cause scratches on the film.
It is preferable to set the surface roughness within the above range.

Since prevention of such defects is achieved by the surface shape and porous properties of the ceramic layer, the stretching conditions, temperature conditions, or film transport speed may be substantially changed in order to prevent the occurrence of defects. There's no need at all. Furthermore, although ceramic does not have high thermal conductivity compared to metal, by configuring only the surface of the cooling roll with ceramic, there is no need to substantially impair the film cooling performance of the cooling roll.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the roll arrangement of a film stretching apparatus embodying the present invention. In this embodiment, the plastic film 10 is made of polyester film, is continuously conveyed in the X direction, and is gradually heated to the stretching temperature by heating rolls 11, 12, 13, and 14. 15 indicates a nip roll, and up to the nip point between the roll 15 and the heating roll 14,
The film 10 is stretched at a predetermined stretching temperature (for example, 90°C).
is heated to. 16, 17, 18, and 19 are cooling rolls, and 20 is a nip roll. Between the heating roll 14 and the cooling roll 16, the film 1
0 is continuously stretched in the longitudinal direction at a predetermined magnification (for example, 3.3 times). Cooling rolls 16, 17, 1
8 is temperature controlled to, for example, about 225°C.

In this embodiment, the cooling roll 16 was a ceramic roll as used in the present invention. That is, the roll body was made of metal, and a ceramic layer was formed on the surface by plasma spraying ceramic. Ceramics with chromium oxide as the main component were selected, and the roll surface roughness was determined by the center line average roughness (Ra).
So, Ra=0.15μ.

Using such a stretching device, the thickness is 300 μ~
When various polyester films 10 of 2500μ were stretched under predetermined conditions (same conditions as before), the triangular defects that had been a problem did not occur at all, and a film was obtained that had no surface defects and had the targeted physical properties. It was done.

In the above embodiment, only the cooling roll 16 was used as the ceramic roll, but for films where the cooling rate is inevitably slow (for example, thick film), the cooling roll downstream of the ceramic roll may be used as the main cooling roll as necessary. It may also be a ceramic roll as used in the invention.
Moreover, the temperature conditions of the cooling roll are not limited to the above-mentioned temperature conditions, and can be freely set. For example, in the case of a polyester film, the temperature may be at least 10°C lower than the temperature of the film immediately after stretching, and may be appropriately set within a range of 80°C to -10°C.

Furthermore, the surface roughness Ra of ceramic roll is
As mentioned above, the range is preferably 0.02 to 2μ, preferably 0.05 to 1.0μ, more preferably 0.08 to 0.7μ. this is,
When the surface roughness is 0.02μ or less, air trapped between the film and roll will travel along the roll surface and will have a hard time escaping, and since the film is also cooled, it will hardly slip on the cooling roll, so it will not get caught. This is because air becomes more likely to be trapped, and the effect of preventing triangular defects from occurring is weakened. Further, if the film has a roughness of 2 μm or more, it is not preferable because if a slight slip occurs on the film, scratches are likely to occur due to the surface unevenness.

[Effects of the Invention] As explained above, when using the plastic film cooling method of the present invention, the surface of the cooling roll is made of ceramic, and due to the action of the fine irregularities and pores of the ceramic, the film and the roll are bitten. Since air can escape easily, the effect of completely preventing the occurrence of triangular defects under optimal conditions can be obtained without changing the stretching conditions, temperature conditions, speed conditions, etc.

Furthermore, if the roughness of the surface of the ceramic roll is set within an appropriate range, the triangular defects described above can be effectively prevented without producing new film defects such as scratches.

In addition, since the air trapped on the surface of the ceramic roll escapes, the volatile matter from the film also escapes along with the air flow, and the effect of suppressing the attachment of volatile matter to the cooling roll can also be obtained.

Furthermore, since the ceramic that makes up the surface of the cooling roll is extremely hard, roll scratches are significantly reduced compared to conventional metal rolls, which reduces the number of scratches transferred to the film and improves the roll's durability. You can also get the effect of being able to improve.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a film stretching apparatus used in carrying out a method according to an embodiment of the present invention, and FIG. 2 is a plan view of a film on a cooling roll showing the occurrence of triangular defects. 1... Triangular defect, 2... Plastic film, 3... Cooling roll, 10... Plastic film, 11, 12, 13, 14... Heating roll, 16... Cooling roll of ceramic roll, 1
7, 18, 19...Cooling roll, X...Film transport direction.

Claims (1)

[Claims] 1. A method for cooling a plastic film in which a continuously conveyed plastic film is heated, stretched in the longitudinal direction, and then cooled by a cooling roll, in which a ceramic roll whose surface material is made of ceramic is used as the cooling roll. A method for cooling plastic film, characterized by: 2. The method of cooling a plastic film according to claim 1, wherein the ceramic roll has a centerline average roughness (Ra) in the range of 0.02μ≦Ra≦2μ.