JPS6362723A - Manufacture of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To permit the regulation of the position of an electrode to the optimum position whereat a good sheet molding condition can be obtained in a short period of time, by a method wherein the variations of thickness in the direction of the flow of a resin sheet and the widthwise direction of the same are detected by a detecting means while the variation is separated into the components of variation of a thickness in a plural frequency areas by an analyzing means. CONSTITUTION:Molten resin is extruded through a die 1 to obtain a sheet 2 while static electric charge is impressed on the sheet in a space until the sheet arrives at a cooling roll 3 by the electric bulb 4 of a needle type electrode, in which a multitude of needles is arranged. A detecting means 9 is a device for measuring the thickness of the sheet by the absorption of infrared rays of a thermoplastic resin and measures the fluctuation with time of the thickness of the sheet at positions near both ends in the widthwise direction of the sheet and at the center of the same while the measured values are separated into the frequency area of 0.5-2Hz and the same area of 10-30Hz to operate respective components of fluctuation by an analyzing means 10 and set the optimum distance between the electrode and the resin sheet. The position of electrode rays is regulated based on the variation of the thickness of 'components of undulation', further, the variation of thickness of the component of striping is also controlled by means 5, 6 to minimize it.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is an electrostatic method used in producing sheets or films (including sheets thicker than a film may also be referred to as a film) from thermoplastic resin. The present invention relates to an improvement in pinning technology, and relates to a manufacturing/detachment technology that can maintain a stable electrostatic pinning state and can obtain a film with a high level of uniformity in thickness.

[Prior Art 1] It is well known to form a sheet by a method in which a thermoplastic resin is thermally melted, extruded from a slit die into a band (sheet) shape, and cooled and solidified on the surface of a rotating cooling roll. There are known methods such as adjusting the lip interval of a slit die to make the sheet thickness uniform, and rolling an unsolidified sheet at a temperature higher than the softening point between a pair of rolls to make the sheet thickness uniform. This is a means for adjusting the sheet thickness.

In applications where the quality and uniformity of melons are required, various means are used, either alone or in combination, to ensure uniformity of sheet thickness. Thermoplastic resin is kneaded in a molten state so that it has a uniform heating temperature and a uniform melt viscosity, and a metering pump is used to maintain a constant flow rate per hour when extruding into a sheet. Sometimes.

Furthermore, in order to avoid local fluctuations in the amount of molten resin flowing out in the die portion, a set of adjustment bolts that expand or narrow the gap between the die lips as described above may be provided along the slit of the die, or Uniform thickness control means are known, such as arranging a large number of fine heating and cooling means along the slit of the die to adjust the amount of localized melt outflow.

It is also known that these local flow adjustments of the melt are associated with automatic control devices that correct differences between the measured sheet thickness and a reference value. The thickness of the sheet can be measured using optical means, such as changes in infrared ω (transmitted light ω), β-ray thickness meter, etc. ) can be measured.

Further, by scanning the thickness measuring means in the sheet width direction, the thickness state in the sheet width direction can be detected. In the conventional technology, the thickness of the sheet in the width direction is detected during the sheet manufacturing process, and the thickness detection results are fed back to control the local molten material of the die so that the thickness in the sheet width direction is constant. Thickness control technology that adjusts flow rate has been put into practical use.

By the way, even if the molten resin is extruded to a uniform thickness along the die width direction and the extrusion amount is completely constant, a sheet of molten resin will be deposited on the cooling roll surface to a uniform thickness. If it is not solidified, it will not be possible to obtain a sheet of uniform thickness. The technology for cooling and solidifying a molten resin sheet requires that the cooling roll rotates at a uniform speed with almost no fluctuation even momentarily, and that the molten resin sheet contacts the cooling roll at a predetermined position without fluctuation. (
It is essential that the touchdown condition is stable. The latter technique, a film forming technique using electrostatic pinning that electrostatically brings a molten resin sheet into close contact with a cooling roll, is effective (Japanese Patent Publication No. 37-6142 No. 1).
. In this electrostatic pinning, if the resin sheet and the cooling roll do not come into perfect contact with each other, air will be drawn in and the sheet surface will become in close contact. A condition for good electrostatic pinning is to maintain a stable state in which the air accompanying the resin sheet as it travels is removed at the position where it contacts the cooling roll. From another point of view, in order to form a uniform thickness as a sheet, it is necessary that the state of the resin sheet in contact with the cooling roll is constant, and that the position n in contact with the surface of the cooling roll is also spatially constant. .

[Technical problem to be solved] In the electrostatic pinning method, in order to obtain a good and stable film casting state and a resin sheet with a uniform thickness, it is necessary to use a live part exposed electrode, such as a needle-like electrode or a wire-like electric pinning method. It is necessary to place it in an appropriate spatial position. For example, the distance between the electrode and the resin sheet must be appropriate in the relative position of the electrode and the touchdown line (also called landing line) of the molten resin sheet to the surface of the cooling roll. If the electrode and the resin sheet are too close together, the molten sheet receives excessive static electricity and vibrates, changing the touchdown line and causing uneven thickness of the resin sheet in the flow direction. This is because the vibration causes unevenness in the amount of deposit over time, and pulsating thickness unevenness is observed in the longitudinal direction of the resin sheet. Furthermore, when the electrode is moved closer to the die than the touchdown line, the potential gradient becomes smaller as the electrode moves away, reducing the electrostatic charge applied to the molten resin sheet, and increasing the adhesion of the resin sheet to the cooling roll. becomes weaker. If the entrained air cannot be completely removed when the resin sheet is brought into close contact with the cooling roll, air will be drawn into or removed from the sheet, and the entrained air will be scattered as fine bubbles on the sheet surface, making it impossible to make it come into close contact with the cooling roll. Traces of these air bubbles will remain on the surface of the resin sheet. Such a resin sheet with scattered air bubbles also has "undulation"-like thickness unevenness.

As described above, the electrodes must be positioned appropriately depending on the thermoplastic resin used to form the sheet.

In conventional technology, adjustment of the electrode position relies on the operations of a skilled operator based on the measured value of the sheet thickness during manufacturing, and in reality, the thickness unevenness is determined based on the state of the final product. , the position of the electrodes was finely adjusted based on inspection results such as the presence or absence of traces of microbubbles.

However, this method requires a high degree of skill on the part of the operator, and as the molding speed increases, the range of optimal positions for the electrode narrows, so if adjustment takes time, there will be a lot of loss. Technical issues have been pointed out, such as the use of opaque sheets and other brands that make it difficult for workers to make judgments and require automatic adjustment technology.

[Object of the Invention] In order to solve the above-mentioned problems, the present invention aims to provide a method that can quickly and quantitatively adjust the position of an electrode to an optimal position that provides a good sheet forming condition. .

[Structure of the Invention] In order to achieve this object, the method for manufacturing a thermoplastic resin sheet of the present invention has the following structure.

In the present invention, when extruding a molten thermoplastic resin in the form of a sheet onto the surface of an electrically grounded cooling roll, the resin sheet is In the method of manufacturing a thermoplastic resin sheet that is electrostatically brought into close contact with the cooling roll and cooled, a change in the thickness of the resin sheet at a predetermined position in the width direction of the resin sheet (in the flow direction and in the longitudinal direction) is detected by a detection means. The detected thickness change is separated into thickness change components in a plurality of frequency ranges by an analysis means, and the electrode and the resin are separated at positions corresponding to the predetermined position in the sheet width direction according to the thickness change components in each frequency range. Adjust the distance of the sheet to minimize each thickness change component, and then detect the thickness change at another predetermined position in the width direction of the resin sheet in the same way as the first position example, and detect multiple frequency ranges. By repeating separating the thickness change components into thickness change components and adjusting the distance between the electrode and the resin sheet at a position corresponding to another predetermined position according to the thickness change component, the thickness change over the entire width of the resin sheet can be reduced. This is a method for producing a thermoplastic resin sheet characterized by a tightening property.

The present invention will be explained.

The present invention can be applied to forming sheets, films, and webs from general thermoplastic resins. Electrostatic pinning can increase production speed and produce sheets through uniform cooling and solidification, making it suitable for molding (film forming) where quality and productivity are requirements. Typical examples of thermoplastic resins include linear saturated aromatic polyesters such as polyethylene terephthalate, polyethylene naphthalene dicarboxylate, and polyhexamethylene naphthalene dicarboxylate; Naturally, thermoplastic resins such as polyamide and polyolefin can also be used.

In the present invention, known means can be applied as a technique for melting the resin, extruding it through a die, and casting it onto the surface of the cooling roll. That is, the resin is melt extruded at a temperature above its melting point and cast onto a cooling roll whose surface is cooled to about room temperature. The cooling roll is usually composed of a surface made of a material such as metal or ceramic, and a cavity for storing (circulating) a coolant, and is electrically grounded or connected to a power source to form a counter electrode.

To explain this with reference to Figure 1 of the drawings, the molten resin is extruded from the die 1 onto the sheet 2, and in the space until it reaches the cooling roll 3, it is placed in a position close to the resin sheet but not in contact with it. An electrostatic charge is applied to the sheet by the placed light bulb 4. This light bulb uses a needle-like electrode with a large number of needles densely arranged at approximately equal intervals across the width of a resin sheet, or a wire such as a piece of piano wire stretched across the width of the sheet. Electrodes are appropriate. In either case, the surface of the electrode placed near the sheet is exposed and is not covered with an insulator. This light bulb is connected to a power source, and during operation, an electrostatic charge is deposited on the surface of the sheet from the electrodes.

In the present invention, as will be described later, the electrode 4 is provided with means for adjusting in the horizontal direction 5 and the vertical direction 6 to maintain the distance between the electrode and the resin sheet within an appropriate range. Note that the electrodes are connected to a high voltage static electricity generation source 7.

In the present invention, a detection means 9 is provided for detecting the thickness of the sheet 8 at a position away from the cooling roll, usually before and after the stretching process, and as described later, detects the thickness of the sheet and changes in the thickness. is analyzed by the analysis means 10.

The sheet is subjected to biaxial stretching and heat treatment via a stretching machine 11, a stitcher 12, etc., and then taken to a winding means 13 according to a conventional method.
It is wound up by.

The present invention mainly comprises these electrostatic pinning means, a sheet thickness sensing means, and a means for adjusting the electrode position based on the sheet thickness variation obtained by the sensing means. In addition to the above-mentioned electrostatic pinning means, automatic position l+ control of the electrodes is performed by detecting changes in the thickness of the sheet during operation during the manufacturing process of the sheet.

In the present invention, the thickness measuring device 9 disclosed in Japanese Unexamined Patent Publication No. 59-70904, for example, can be used as the sheet thickness detecting means 9 incorporated during the manufacturing process. This device is an infrared thickness measuring device that utilizes the infrared absorption characteristics of thermoplastic resin, and when the resin is polyethylene terephthalate, it uses infrared rays with a wavelength of 5.8 μm, and compares it with a standard thickness using the double beam method. However, the sheet thickness at a predetermined position can be measured with high precision, and a highly sensitive element made of indium antimony is used as the sensor. Such a thickness measuring device can be installed in any space from the position where the sheet leaves the cooling roll to the position where the sheet is rolled up, and can measure changes in thickness while the sheet is running.

The thickness of the sheet can be measured at any position in the width direction. However, in the present invention, since the electrode position is divided by w4 by means 5 and 6 so as to make the sheet thickness uniform, the sheet thickness can be adjusted at an effective position when adjusting the electrode position. It is desirable to measure patterns. Therefore, in the width direction of the sheet, changes in the thickness of the sheet over time are measured at positions close to both ends of the sheet, and at positions where there is a means to adjust the distance between the electrode wire and the molten resin sheet, such as at the center of the sheet. It is preferable to do so.

The thickness of the sheet changes over time, in other words in the longitudinal direction.
It fluctuates like curve P in FIG.

Changes in thickness are observed as a combination of "undulations" with a relatively long period and small changes with a short period.

That is, in Fig. 2, the undulation (fluctuation component; R11 curve and 10 to 30H7
Striped changes in frequency (fluctuation component: R21 song FJS
) is recognized as a composite variation (component: Ro, curve P).

In the present invention, the variation in the sheet thickness detected by the thickness detection means 9 is separated into the frequency range ft of 0.5 to 2l-1z and 10 to 30Hz as shown in F, and the analysis means 10 analyzes each variation component. The optimum distance between the electrode and the resin sheet is set by calculating the following.

FIG. 3 schematically shows the relationship between the position of the sheet and the wire electrode and the fluctuation component.

If the distance between the electrode at the position corresponding to the predetermined position (the position of the electrode that causes the most change in the thickness of the part of the sheet whose thickness is being observed) and the resin sheet is moved so as to reduce the thickness variation of the waviness component, The difference between the maximum value and the minimum value of the waviness changes as shown by the 0 curve in FIG. And up to 31 for position adjustment! ! It turns out that the value exists.

This U4 adjustment can be carried out by trial and error, but if the manufacturing conditions are the same, it is possible to start production with the optimum value based on actual performance as the initial value and gradually optimize it. After repeating trial and error several times, you will come to know the following. That is, if the distance between the Wi pole and the molten sheet is too short, a strong charge will be applied to the molten sheet, but as a result of the sheet oscillating at this time, there is a tendency for sheet thickness unevenness to become large (third
Area A in the figure). Furthermore, if the electrode is too far away from the molten sheet, the electrostatic pinning effect will weaken, making the casting state unstable and tending to increase sheet thickness unevenness (
Area C in Figure 3). These conditions are from 0.5 to 0.5 in Figure 3.
The zero curve is shown as the relationship between the fluctuation component in the 2Hz frequency region and the distance between the electrode and the sheet.

Next, regarding the fluctuation component in the frequency domain from 10 to 301-IZfW degrees, the optimum W-A--! It is necessary to determine the pole position. In this case as well, there is an appropriate distance between the electrode and the molten resin sheet that minimizes thickness unevenness. and,
It must be noted that this striped component has an optimal distance only within a very narrow range. (See S curve in Figure 3).

In the present invention, the position of the electrode wire corresponding to a predetermined position in the sheet width direction is adjusted based on the change in the thickness unevenness of the "wavy component", and furthermore, the change in the thickness unevenness of the striped component is also minimized. tIIIm.

Moreover, the conditions for determining the position of the electrode wire for optimizing the change in the waviness component and the adjustment of the change in striped thickness are performed completely independently.

In the prior art, it is hardly known that adjustment of sheet thickness is performed as position control of electrode wires. Of course, it is presumed that they tried to obtain a high-quality sheet by determining the position empirically, but as in the present invention, the thickness unevenness is divided into specific frequency regions υ1 and each component is optimized. By doing this, the optimum position of the electrode wire (8 areas in FIG. 3) can be determined in a short period of time. Furthermore, the accuracy is higher than when processing is performed based on actual thickness variation data.

The present invention measures the sheet thickness and analyzes (computes) the thickness fluctuations to separate them into long-period region fluctuations and short-period region fluctuations.
Based on the results, the optimal position is independently determined by the adjusting means 5 and 6 for 'Fi1 & position, but automatic adjustment can be performed by linking this adjusting means and the analysis means.

[Example] Using the apparatus shown in Fig. 1, the film was stretched to a thickness of 200μ
m polyethylene terephthalate (intrinsic viscosity 0.60
) was formed into a film. For casting, the circumferential speed of the cooling roll was set at 37.57 FL/min, and an infrared thickness measuring device (Japanese Patent Application Laid-Open No. 70904/1986) was used as a thickness detection means.
(described in the publication) was used. The measurement was carried out at three locations at the center 9 of the sheet, at both ends, three times for 3 seconds each, and the average value was used to repeat the adjustment in order.The fourth adjustment of the position of the wire electrode resulted in a good sheet thickness uniformity. was achieved.

Adjustments are made by sequentially measuring thickness variations at the edge, center, and other edges of the sheet, then adjusting the wire electrode according to the waviness component, and then adjusting the variation in the striped component to determine the thickness at that position. The first rough adjustment is completed. in a different position,
This adjustment is repeated, and the first rough adjustment is completed at three locations. This process was repeated three times and the average thickness unevenness of the 200 μm sheet was controlled to within 1.5 μm when all locations were subjected to c-3 order. The position of the wire electrode was connected to the wire support and the step motor, and the position of the wire electrode could be changed based on the analysis results, making it possible to adjust the position automatically and in a short time. . If a conversion table (calculation table) is prepared for each production condition, data with good reproducibility can be obtained from the analysis results and the motor drive base.

As explained above, the present invention reduces sheet thickness unevenness by adjusting the electrode position in electrostatic pinning. In addition to unstretched sheets, the sheet thickness is determined after one step of stretching.
It is possible to optimize the electrode distance by detecting at a position such as after the two wheels have been stretched, and based on the analysis results of the thickness variation. Therefore, the installation location of the thickness detection means can be arbitrarily selected. Furthermore, as an analysis means for adjusting the electrode position, in this example, approximately 1 Hz (0.5 to 2H2) and approximately 20H2 (1
0 to 301→2), but the frequency range may be selected as appropriate based on analysis of the periodicity of thickness variation.

Furthermore, in this embodiment, the electrode position is adjusted for each variation component by dividing into two parts, but it is also possible to separate the thickness variation component into three or more parts and adjust the electrode position based on each variation component. be.

In this example, wire electrodes were used as an example, so the thickness of the sheet was measured at three points (the center and both ends), and the position of the wire was adjusted at only three points. A method of adjusting the position of the needle electrode is also within the scope of the technical idea of the present invention.

[Effect of the Invention 1] According to the present invention, a resin sheet having an extremely uniform thickness can be obtained. This uniform thickness can be achieved by adjusting the distance between the electrode and the melted sheet in electrostatic pinning, and the adjustment of the electrode position can be optimized automatically and in a short time, which increases production efficiency. This is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus implementing the invention. FIG. 2 is a curve showing changes in thermoplastic resin sheet thickness. Further, FIG. 3 is a curve schematically showing the state of change in thickness when the positions of the sheet and the electrode are changed. In the drawings, 1 is a die, 2 is a resin sheet, 3 is a cooling roll, 4
1 is an electrode, 5 and 6 are electrode position adjustment means, and 9 is a sheet thickness detection means. 10 is a thickness variation analysis means, 11 is a primary drawing machine, 12
1 is a second drawing machine, and 13 is a winding means.

Claims (5)

[Claims] (1) When extruding molten thermoplastic resin into a sheet onto the surface of an electrically grounded cooling roll, a high DC voltage is applied to the exposed electrode of the live part installed above the resin sheet to extrude the resin sheet. A method for manufacturing a thermoplastic resin sheet that is electrostatically brought into close contact with a cooling roll for cooling, the method comprising: detecting a change in the thickness of the resin sheet in the flow direction (longitudinal direction) at a predetermined position in the width direction of the resin sheet using a detection means; The detected thickness change is separated into thickness change components in multiple frequency regions by an analysis means, and the distance between the electrode and the resin sheet at the corresponding position in the sheet width direction is determined according to the thickness change component in each frequency region. The thickness change component is adjusted to the minimum by changing the thickness change component, and the thickness change at another predetermined position in the width direction of the resin sheet is similarly detected, and the other predetermined position is adjusted according to the thickness change component. A method for manufacturing a thermoplastic resin sheet, characterized in that by repeatedly adjusting the distance between an electrode at a position and the resin sheet, changes in thickness over the entire width of the resin sheet are reduced. (2) Detected thickness change in flow direction at 0.5-2Hz
The thickness change component in the frequency range of 10 to 30 Hz is separated into the thickness change component in the frequency range of 10 to 30 Hz. A method for producing a thermoplastic resin sheet according to claim 1, which comprises adjusting the distance. (3) The method for producing a thermoplastic resin sheet according to claim 1 or 2, wherein the thermoplastic resin is polyalkylene terephthalate. (4) The method for producing a thermoplastic resin sheet according to claim 1, wherein the live portion exposed electrode is wire-shaped. (5) The method for producing a thermoplastic sheet according to claim 1, wherein the live portion exposed electrodes include a number of needle-like electrodes.