JP2818367B2 - Detecting method of film position corresponding to die - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a position of a film corresponding to a die, and more particularly, to extruding a molten polymer into a film from a die to produce an unstretched film or a stretched film. When the electrostatic force is applied to the cooling drum, a change in thickness is applied to the unstretched film by locally changing the strength of the adhesion, and the mark is detected in a subsequent process, and the mark of the corresponding die is detected. The present invention relates to a method for specifying a width direction position.

[0002]

2. Description of the Related Art In recent years, as the use of a film has become more sophisticated, the required level of uniformity of the thickness in the film width direction has become extremely severe.

In order to correct the unevenness of the thickness of the film, a method of adjusting the opening in the width direction of the die (die) or partially adjusting the temperature in the width direction of the die is generally adopted. In order to reliably correct even small thickness unevenness, it is necessary to narrow the arrangement interval of the opening degree adjuster and the temperature adjuster (hereinafter, these are referred to as controllers) arranged in the width direction of the base. .

However, as the spacing between the controllers is reduced, it becomes difficult to identify the position of the controller corresponding to the thickness unevenness of the film, and if the position of the corresponding controller is adjusted incorrectly. However, the unevenness in thickness is worsened.

For the purpose of solving such a problem, for example, Japanese Unexamined Patent Publication No. Sho 59-89119 proposes that a mark is formed in a space extending from a die to a forming roll. Film-like material in a molten state,
Especially when the temperature of the film-like material is high or the thickness is thin, it is difficult to mark with a magic ink pen as in this proposal, and even if the mark is made,
Since a different colorant adheres to the film, it cannot be used as a product film, and that part cannot be collected and reused, which adds to the trouble that the film must be cut off and disposed of.

There is also a method in which a projection piece is attached to the tip of the base to change the unevenness on the film. However, this method may cause a new problem when the molten polymer adheres to the tip of the projection. Many.

[0007] In addition, there is a method in which a thickness unevenness is intentionally partially formed with a specific control element and this is used as a mark. Difficulties arise when stretching. That is,
In many cases, the stretch ratio of the thickness uneven portion is different from that of the other portions. For example, when the uneven portion is thick, the stretch ratio of the portion is smaller than that of the other portion, and when the uneven portion is thin, the reverse is true. When the controller is returned to the original state after specifying the position of the die corresponding to the thickness unevenness of the stretched film, the stretching ratio changes to a nearly uniform state. The position is greatly shifted, and wrong information is obtained.

[0008]

SUMMARY OF THE INVENTION The present inventors have been keen to develop a method which does not have the drawbacks of the prior art and has no particularly difficult problems in implementation, and a method which does not generate wrong information. As a result of research, when forming a film by the electrostatic adhesion method, by applying a local change to the adhesion force,
The thickness of the film can be varied with a small width at any point in the width direction of the film, the method is easy to be embodied, the film can be marked without generating new problems, and the film die Have the advantage that the corresponding position can be detected quickly and reliably,
The present invention has been reached.

[0009]

That is, according to the present invention, a molten polymer is extruded from a die into a film, and static electricity is applied to the extruded film by a corona discharge electrode provided on a cooling drum in a width direction. When the film-like material is cooled while being brought into close contact with the cooling surface of the drum by the electrostatic adhesion force, the unstretched film is stretched in at least one direction, if desired, to produce a stretched film. The thickness of the unstretched film is marked by changing the electrostatic adhesion force locally in the width direction of the film, and the mark is detected in a subsequent step. The position of the mark on the film and the position of the die This is a method of detecting a die-corresponding position of a film, characterized by specifying a correspondence with a width direction position.

The polymer in the present invention is a thermoplastic polymer, and examples thereof include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and vinyl polymers such as polyvinyl chloride. it can. Of these, polyester is particularly preferred.

The die in the present invention is a die for extruding a molten polymer into a film, and is, for example, a coat hanger die, a fish tail die, or a manifold die.

The corona discharge electrode according to the present invention generates an electrostatic charge and deposits on a molten film (film-like material).
An electrostatic charge generator for producing an unstretched film by bringing the film into close contact with a cooling drum which is grounded by Coulomb force, and is generally made of a conductive thin metal wire such as tungsten or stainless steel. At a distance of 3 to 15 mm, stretch in parallel with the width direction on the grounded cooling drum,
An electrostatic charge is generated by applying a high DC voltage (generally a positive electrode) to the fine wire. Further, the fine wire may be covered with a conductive cover (for example, a semi-cylindrical member) that is open at one end and grounded to enhance the discharge capability of corona discharge. The voltage applied to the corona discharge electrode is preferably 4 to 15 KV, more preferably 5 to 10 KV.

In order to locally change the electrostatic adhesion, a method of forming a local unevenness in the electric field formed by the corona discharge electrode is preferable. Specifically, for example, by bringing an electrically insulating rod-shaped object close to or in contact with a corona electrode from a right angle, or by bringing a conductive or semi-conductive rod-like object grounded closer, It forms localized spots in the corona discharge electric field, causing strong spots in the electrostatic adhesion. This causes a local thickness change (thickness reduction) in the unstretched film at the corresponding portion.

When an object approaching the electrode is conductive or semi-conductive, it depends on the magnitude of the electric resistance of the object. Excessive approach to the electrode may cause a spark discharge. It is easier to handle.

The magnitude of the thickness change (spot) caused by the change in the strength of the electrostatic adhesion depends on the voltage applied to the corona discharge electrode, the method of forming a local spot in the electric field, the thickness of the film, and the casting. Since the speed varies greatly depending on the speed and the like, it is better to determine the optimum conditions in a preliminary experiment. In general, it is convenient for the unstretched film after cooling and solidification to have a thickness change (thickness) of 1 to 10 μm. This thickness change preferably corresponds to 5 to 10% of the thickness of the unstretched film.

Next, although the width of the thickness change depends on the casting conditions as in the case of the depth, there are also portions depending on the method and conditions for forming a local unevenness in the electric field.
When an electrically insulating rod is approached or brought into contact with the corona electrode at right angles, the width of the rod is preferably 1 to 10 mm. In this case, the unstretched film after cooling and solidifying usually has a width of about 7 to 10 mm. A thickness change (spot) of a width of 30 mm results.

The local thickness change (spot) generated in this way can be measured as a non-stretched film solidified by cooling or as a film after uniaxial stretching or biaxial stretching, using a known thickness unevenness measuring instrument, for example, radiation ( Generally, β-ray) is detected by a thickness measuring device, an infrared thickness measuring device, or the like. The detected thickness change is used as a mark, and the position of the mark in the film width direction is a position where the electrostatic adhesion is changed, and this position corresponds to a specific position in the die width direction. Therefore, by detecting the position of this mark in the film width direction, it is possible to specify the corresponding position in the die width direction of the die.

Hereinafter, the present invention will be further described with reference to the drawings.

FIG. 1 is a view showing one embodiment of the present invention, and is a perspective view schematically showing a casting process.
In FIG. 1, 1 is a die, 2 is a molten film (film-like material), 3 is a cooling drum, 4 is a corona discharge electrode, and 5 is a rod-like object. The molten film (film-like material) 2 extruded from the die 1 deposits a positive charge generated by the corona discharge electrode 4 installed near the point of attachment to the cooling drum 3, and the Coulomb force causes the cooling drum 3 Firmly adheres to the cooling surface. Here, in order to form a local thickness change (spot) as a mark on the film, the rod-shaped object 5 approaches the corona discharge electrode 4 corresponding to a specific position in the width direction of the die 1 from the vertical direction of the electrode. Let it. If the rod-shaped object 5 is an insulator, it may be brought into contact. This causes a local disturbance of the electric field. When the rod-shaped object is an insulator, the amount of electrostatic charge deposited on the film at a position corresponding to the disturbance of the electric field is reduced. As a result, air is entrapped between the cooling drum and the film, and the film at that portion is removed. Is thinner than the thickness of the enclosure. On the other hand, when the rod-shaped object is a semi-conductor or a conductor, the amount of electrostatic charge deposited on the film at a position corresponding to the disturbance of the electric field increases, and as a result, the adhesion between the cooling drum and the film increases, and The thickness of the portion of the film-like material is thinner than the thickness of the enclosure.

FIG. 2 is a chart showing the change in thickness in the width direction of the unstretched film obtained by the method of the present invention, and FIG. 3 is a chart of the unstretched film obtained by the conventional method, from which an object causing disturbance in the electric field has been removed. 6 is a chart showing a thickness change in a width direction.

The V-shaped line substantially at the center in FIG. 2 is where the thickness is reduced, and differs from FIG. 3 in comparison.

[0022]

The present invention will be described in more detail with reference to the following examples.

[0023]

EXAMPLE 1 Polyethylene terephthalate was melted to a thickness of 200 μm and extruded from a die by the apparatus shown in FIG. 1 and solidified in close contact with a cooling drum by a corona discharge electrode loaded with a 7 KV DC positive electrode. The obtained unstretched film was taken out at a casting speed of 30 m / min.

At this time, a Teflon rod having a thickness of 1 mm and a width of 5 mm was brought into contact with the center of the corona discharge electrode in the width direction from the side of the die in a direction perpendicular to the electrode.

The unstretched film thus obtained was successively stretched 3.6 times in the machine direction and 3.9 times in the transverse direction to obtain a 14 μm-thick biaxially stretched film.

The unstretched film has a width of 18 mm at the center,
There was a thin streaky thickness unevenness with a height of 12 μm, and the biaxially stretched film had a thin streaky thickness unevenness with a width of 62 mm and a height of 1.1 μm, all of which were clearly detected by a β-ray thickness measuring instrument. .

After obtaining the correspondence between the position of the die in the width direction and the position of the biaxially stretched film in the width direction, the Teflon rod in contact with the electrode is removed, and the unstretched film solidified on the cooling drum is magically formed. When a mark was made with a pen and the corresponding position in the biaxially stretched film was examined, there was almost no deviation from the method of the present invention.

[0028]

According to the present invention, the position in the width direction of the die and the position in the width direction of the film can be corresponded quickly and reliably without the disadvantages of the conventional method. The thickness unevenness in the direction can be easily and quickly corrected.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a casting process, showing one embodiment of the present invention.

FIG. 2 is a chart showing a change in thickness in the width direction of an unstretched film when the present invention is used.

FIG. 3 is a chart showing a change in thickness in the width direction of an unstretched film according to a conventional method.

[Description of Signs] 1 Die 2 Fused film 3 Cooling drum 4 Corona discharge electrode 5 Rod-shaped object

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-293874 (JP, A) JP-A-63-81018 (JP, A) JP-A-63-62723 (JP, A) JP-A 48-48 36260 (JP, A) JP-A-2-72923 (JP, A) JP-A-51-114466 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 47/00-47 / 96

Claims (4)

(57) [Claims] 1. A molten polymer is extruded from a die into a film, and static electricity is applied to the extruded film by a corona discharge electrode installed on a cooling drum in a width direction. When the unstretched film is cooled by bringing the unstretched film into close contact with the cooling surface of the drum, and the unstretched film is stretched in at least one direction as desired, the adhesion of static electricity to the unstretched film is reduced. Marking the thickness change on the unstretched film by locally changing it in the width direction, detecting this mark in a subsequent process, and specifying the correspondence between the position of the mark on the film and the width direction position of the die. A method for detecting a position corresponding to a die of a film. 2. An insulator at an arbitrary position of the corona discharge electrode,
The method according to claim 1, wherein the semi-conductor or the conductor is brought closer to change the amount of static electricity on the film corresponding to the semi-conductor, thereby marking the unstretched film with a thickness change. 3. An unstretched film is marked with a thickness change on an unstretched film by changing an amount of static electricity on a film-like material corresponding to the portion by contacting an insulator with an arbitrary portion of the corona discharge electrode. the method of. 4. The mark on the unstretched film is 1 to 10 μm.
The method according to claim 1, wherein the thickness is changed.