JPH11309772A - Manufacture of thermoplastic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the upper limit of a sheet forming speed by giving electrostatic charges to a sheet by means of a tape-like electrode and a destaticization is executed at the separation of the sheet. SOLUTION: Electrostatic charges are uniformly given with a tape-like electrode 3 to a melt thermoplastic resin 2 extruded in a sheet out of a mouthpiece 1. An electrostatically charged resin sheet is cooled and solidified on the surface of a cooling drum 4 as the cooling drum 4 rotates so as to form a resin sheet 5, which is separated at its release point 6 so as to be sent through proper guide rolls 7, 8 and 9 to the following process. In this case, a destaticization is executed at a position ahead the release point 6. Since the resin sheet is uniformly given by electrostatic charges and the electrostatic charges are destaticized at the separation of the resin sheet, the favorably tightly adhered state of the resin sheet to the cooling drum is ensured so as to allow to suppress the development of ununiform application and the discharge between the sheet and the drum, resulting in allowing to increase the upper limit speed at the molding of the sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermoplastic resin sheet, and particularly to a method for forming a sheet by using an electrostatic application casting method, which greatly increases the forming speed without causing defects in the sheet. The present invention relates to a method for producing a thermoplastic resin sheet capable of being used.

[0002]

2. Description of the Related Art When a molten thermoplastic resin is extruded from a die into a sheet on a cooling drum and cooled and solidified on the cooling drum to form a thermoplastic resin sheet, the sheet-shaped molten resin is applied to the surface of the cooling drum. As a method of increasing the molding speed while adhering and molding to the desired surface form,
It is well known that an electrostatic application casting method for imparting an electrostatic charge to a sheet-like molten resin is effective.

In such an electrostatic application casting method,
To increase the adhesion of the resin sheet to the cooling drum,
It is effective to increase the amount of electrostatic charge applied to the sheet or increase its density. However, if the amount of electrostatic charge is too large, that is, if the voltage of the electrode to which the electrostatic charge is applied is too high, the cooling drum is discharged from the electrode and defects such as pinholes occur in the resin sheet. However, there is a limit to the increase in electrode voltage.

An electrostatic charge is applied from the electrode at a voltage within this upper limit. However, as the speed of the cooling drum is increased to increase the molding speed, the adhesion between the resin sheet and the cooling drum eventually becomes local. When the limit is reached and air is locally trapped, a surface defect called so-called application unevenness occurs.
Therefore, in the electrostatic application casting method, the upper limit of the sheet forming speed is firstly limited by the speed at which the application unevenness occurs.

On the other hand, the resin sheet adhered to the cooling drum in a state where an electrostatic charge is applied from the high voltage electrode as described above is cooled, solidified, peeled off from the cooling drum, and sent to the next step. At the time of this peeling, a discharge phenomenon may occur between the resin sheet provided with the electrostatic charge and the cooling drum. In particular, when the density of the charges applied to the sheet is not uniform, discharge is likely to occur. When such discharge occurs, the surface of the formed sheet is roughened, resulting in a surface defect, and may also cause surface damage of the cooling drum. This discharge generally tends to become more intense as the speed of the cooling drum, that is, the molding speed is increased. Therefore, the forming speed of the sheet is also limited by the discharge, and the upper limit speed at which no discharge occurs is to be suppressed.

Therefore, the upper limit of the sheet forming speed is ultimately limited to the lower one of the application unevenness generation speed and the discharge generation speed at the time of peeling. The fact is that the casting speed cannot be expected.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to dramatically increase the upper limit of a sheet forming speed at which no defects are caused in a thermoplastic resin sheet in an electrostatic application casting method.

[0008]

In order to solve the above-mentioned problems, a method for producing a thermoplastic resin sheet according to the present invention comprises extruding a molten thermoplastic resin from a die into a sheet shape, and casting a cooling drum by electrostatic application casting. When the sheet is cooled, solidified and molded, an electrostatic charge is applied to the sheet using a tape-shaped electrode having a uniform cross-section in the longitudinal direction, and a static elimination process is performed when the cooling drum and the sheet are separated. The method comprises the steps of:

That is, in the method according to the present invention,
By applying an electrostatic charge to the sheet using a tape-shaped electrode having a uniform cross-section in the longitudinal direction, evenly, or evenly impart an electrostatic charge in a very small uneven state,
First, the application unevenness generation speed is greatly increased. With the application unevenness generation speed greatly increased in this way, the resin sheet is brought into close contact with the cooling drum, cooled and solidified, and separated from the cooling drum after molding. When the resin sheet is peeled off from the cooling drum, a static elimination process is performed, so that the electrostatic charge held by the resin sheet is removed or extremely small, and the resin sheet is separated from the cooling drum at the time of peeling. Is suppressed. Therefore, the casting speed (cooling drum speed) at which electric discharge actually starts to occur is drastically increased. As a result, the upper limit of the sheet forming speed at which the lower one of the application unevenness generation speed and the discharge generation speed is the rule is drastically increased.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the method for producing a thermoplastic resin sheet according to the present invention, the type of resin to be molded is intended for a thermoplastic resin. It is difficult to apply the electrostatic application casting method to a thermosetting resin or the like, and even if it is applied, the effect is originally small. It is not particularly limited as long as it is a thermoplastic resin, and is typically a polyester resin such as polyethylene terephthalate or polyethylene naphthalate.

Such a thermoplastic resin is extruded in a molten state from a die into a sheet, adhered to a cooling drum by an electrostatic application casting method, cooled, solidified, and formed into a resin sheet.

A tape-shaped electrode having a uniform cross section in the longitudinal direction is used for applying an electrostatic charge in the electrostatic application casting method. Such a tape-shaped electrode can apply an electrostatic charge to the resin sheet at a uniform density from a tip end surface having a uniform shape as compared with a needle-shaped electrode or a wire electrode. Therefore, even if the voltage of the electrode is increased to some extent, the charges are not locally concentrated, and the electrostatic charges applied to the resin sheet can be made to have a relatively high potential, uniformity, and high density. As a result, so-called application unevenness is less likely to occur, in which air is locally bitten between the cooling drum and the sheet,
The occurrence of surface defects of the sheet due to unevenness in application is suppressed, and the casting speed can be substantially increased substantially.

The electrode for applying static electricity may be a tape-shaped electrode having a uniform cross section in the longitudinal direction, and the specific shape of the cross section is not particularly limited. Typically, a rectangular cross section is preferable, but other cross-sectional shapes such as a square shape and an elliptical shape are also possible.

The resin sheet to which the electrostatic charge has been applied by the tape-shaped electrodes is closely adhered to the surface of the cooling drum, cooled and solidified while being sent together with the surface in the rotating direction of the drum, and separated from the cooling drum at a predetermined position. To the next step.

At the time of this peeling, preferably, at a position before the peeling point, the resin sheet to which the electrostatic charge has been applied is subjected to a static elimination treatment. The resin sheet that has been neutralized at a stage before the peeling point has substantially no electrostatic charge or very little at the position where the resin sheet is peeled off. Generation of a discharge phenomenon between the cooling drum and the cooling drum is suppressed. Since the electrostatic charge often cannot be completely removed, as described above, an extreme increase in the casting speed (cooling drum speed) also tends to cause a discharge phenomenon. As a result, the casting speed at which the discharge starts can be dramatically increased. Since the casting speed at the start of the discharge is the upper limit of the sheet forming speed, the upper limit of the sheet forming speed is also dramatically increased.

Consequently, the use of the tape-shaped electrode results in a significant increase in the sheet forming speed determined by the occurrence of unevenness in application. In this state, the sheet forming speed controlled by the generation of electric discharge is further reduced by the discharge treatment upon peeling. Since it is dramatically increased, the upper limit of the sheet forming speed actually obtained in the entire casting process is also dramatically increased.

In the above-described method for producing a thermoplastic resin sheet according to the present invention, the method for removing static electricity can take various aspects.

For example, as shown in FIG. 1, a tape-shaped electrode 3 uniformly applies an electrostatic charge to a molten thermoplastic resin 2 extruded from a die 1 into a sheet. The resin sheet to which the electrostatic charge is applied is cooled and solidified on the surface of the cooling drum 4 with the rotation of the cooling drum 4, and the formed resin sheet 5 is peeled at a peeling point 6, and a suitable guide roll 7,
It is sent to the next step via 8 and 9. In the embodiment shown in FIG. 1, static elimination processing is performed at a position before (upstream side) the peeling point 6.

In the static elimination process, a static eliminator 10 of a type that blows ionized gas is used. That is, a high voltage of, for example, direct current is applied from the power supply 12 to the electrode 11 for static elimination, and the ionized gas (air) generated around the electrode 11 is blown from the blowing nozzle 14 toward the resin sheet 5 using the blower 13. It is.

In the embodiment shown in FIG. 2, a metal wire electrode 21 is used for static elimination, and a high DC voltage, for example, is applied from a power source 22 to neutralize the electrostatic charge applied to the resin sheet 5. As described above. Wire electrode 2
The material 1 is not particularly limited, and tungsten, stainless steel, or the like can be used. As a voltage to be applied, it is preferable to apply a negative voltage because it is effective for static elimination.

In the embodiment shown in FIG. 3, the needle 3 is
A needle-like electrode 32 in which 1 are arranged is used, and a negative DC high voltage is applied to the electrode 32 from a power supply 33, for example, to remove static charges applied to the resin sheet 5. Needle 3
1 are arranged in a direction perpendicular to the paper surface of FIG.
Although the interval of 1 is not particularly limited, for example, 3 to 10 mm
A range of degrees is preferred.

In the embodiment shown in FIG. 4, a blade electrode 41 made of metal, particularly stainless steel, is used for static elimination, and a negative DC high voltage, for example, is applied to the electrode 41 from a power supply 42 to remove the resin sheet 5. The static charge applied to is removed.

In the embodiment shown in FIG. 5, a self-discharge type static eliminator is used for static elimination. In this embodiment, the conductive cloth 51 is used as a static elimination electrode, and the conductive cloth 51 is grounded. 5
2) Has been done. The conductive cloth 51 is provided at a position on the upstream side of the peeling point 6 with an appropriate area and a length in the sheet traveling direction, and the electrostatic charge applied to the resin sheet 5 is transferred through the conductive cloth 51. Static electricity is removed by being released to the ground.

Further, in the embodiment shown in FIG. 6, a static eliminator of a type that blows ionized gas (air) is used.
The ionized gas is blown from the downstream side of the sheet peeling point 6 toward a wedge-shaped space formed between the resin sheet 5 and the surface of the cooling drum 4. Electrode 61 for static elimination
For example, a DC high voltage is applied to the
The ionized gas generated around 1 is blown toward the separation point 6 through the blowing nozzle 64 using the blower 63.

As described above, in the method for producing a thermoplastic resin sheet according to the present invention, various types of static elimination methods can be used. In particular, the charge is removed upstream of the peeling point 6,
It is preferable that the resin sheet 5 is peeled off from the cooling drum 4 in a state where the static elimination is sufficiently performed, thereby effectively suppressing a discharge phenomenon.

In order to suppress the discharge more effectively, it is preferable to increase the relative humidity of the atmosphere at the portion where the resin sheet 5 is peeled off.
More preferably, the relative humidity is set to 40% RH or more, and still more preferably, to 50% RH or more.

The resin sheet to which the electrostatic charge is applied at a uniform density by the tape-shaped electrode 3 is satisfactorily adhered to the surface of the cooling drum 4, cooled and solidified, and then the static charge applied up to that time is removed by static elimination. It is removed or reduced, and the discharge at the time of peeling the sheet is effectively suppressed. As a result, the upper limit of the casting speed at which the sheet can be formed without causing sheet surface defects is dramatically increased.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Examples 1 to 6 A polyethylene terephthalate (PET) pellet having a melting specific resistance of 5 × 10 ⁸ Ω · cm was dried at 180 ° C. in a vacuum for 4 hours, and then supplied to an extruder and melted at 280 ° C.
After passing through the filter, it is discharged by a T-die, cast on a cooling drum having a surface temperature of 25 ° C and a diameter of 1200 mmφ by the electrostatic application method under the following conditions. The sheet was obtained after the treatment.

(A) Electrode for Applying Electrostatic A. Material: SUS304H B. Shape: 0.04 mm thick x 8 mm wide tape-shaped electrode with rectangular cross section (b) Electrostatic application conditions Applied voltage: + DC voltage 14 kV B. Distance between molten thermoplastic resin and lower surface of electrode: 5mm

(C) Static elimination conditions Static electricity removal method: Example 1: A method in which ionized air is guided to the static electricity removal position by a nozzle using an AEROSTAT PC manufactured by SIMCO (as shown in FIG. 1). A method in which a wire is used as a charge removing electrode, and an applied voltage is set to a negative DC voltage of 10 kV (as shown in FIG. 2). Example 3: A charge removing electrode in which needles are arranged at intervals of 5 mm is used as a charge removing electrode, and a negative DC voltage is applied. Example 4: Method of applying a negative DC voltage of 10 kV to a 0.5 mm thick SUS blade (as shown in FIG. 4) Example 5: Conductivity Method of using a neutral cloth as a static elimination electrode and grounding the static elimination electrode (as shown in FIG. 5) Example 6: Air ionized using the same apparatus as in Example 1 is jetted from a downstream side of a separation point by a nozzle. A method in which the cooling drum and the thermoplastic resin sheet are guided to the peeling position and sprayed between the cooling drum and the thermoplastic resin sheet (as shown in FIG. 6). Static elimination position: 20 mm upstream from the position where the cooling drum and the thermoplastic resin sheet are separated, and the distance between the thermoplastic resin sheet and the static eliminator was 10 mm (Examples 1 to 5). C. The relative humidity of the atmosphere where the cooling drum and the thermoplastic resin sheet were peeled off was 30% RH.

The upper limit molding speed determined while adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet is 200 μm is as shown in Table 1. In each case, the high speed was achieved. The molded state of the thermoplastic resin sheets thus obtained was all good.

In Tables 1, 2 and 3, the measurement and evaluation of the applied unevenness generation speed, the peeling discharge at the applied unevenness generation speed, and the upper limit molding speed were based on the following criteria.

(1) Application unevenness generation speed The application unevenness of the thermoplastic resin sheet was classified into the following three ranks according to the state. ：: There is no defect on the film surface. わ ず か: Slight application unevenness occurs on the entire surface of the film. ×: Application unevenness occurs on the entire surface of the film, and air entrapment is observed. The speed was defined as the application unevenness generation speed (m / min).

(2) State of peeling discharge at applied unevenness generation rate The state of discharge at the peeling position of the thermoplastic resin sheet was visually observed and classified into the following three ranks according to the state. ：: No discharge was observed. Δ: Slight discharge was observed. X: Strong peeling discharge was observed and sometimes spark discharge was observed.

(3) Upper limit molding speed The upper limit molding speed was defined as a speed at which the state of peeling discharge changed from Δ to ○ (m / min) by decreasing the casting speed from the application unevenness generation speed.

[0036]

[Table 1]

Examples 7 to 12 The same thermoplastic resins and molding equipment as in Examples 1 to 6, respectively.
A sheet was obtained using the static elimination method under the following conditions. (A) Electrode for applying electrostatic force Material: SUS304H B. Shape: 0.04 mm thick x 8 mm wide tape-shaped electrode with rectangular cross section (b) Electrostatic application conditions Applied voltage: + DC voltage 14 kV B. Distance between molten thermoplastic resin and lower surface of electrode: 5 mm (c) Static electricity removal conditions Static elimination method: As shown in Table 2. Static elimination position: 20 mm upstream from the position where the cooling drum and the thermoplastic resin sheet are separated, and the distance between the thermoplastic resin sheet and the static eliminator was 10 mm (Examples 7-1)
1). C. The relative humidity of the atmosphere where the cooling drum and the thermoplastic resin sheet were separated was 50% RH.

The upper limit molding speed obtained by adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet is 200 μm is as shown in Table 2, and all of them are shown in Example 1.
6 could be achieved even faster than the results of. The molded state of the thermoplastic resin sheets thus obtained was all good.

Comparative Examples 1 to 4 Using the same thermoplastic resin and molding equipment as in the examples, the sheet was cast by the electrostatic application method under the following conditions and subjected to the following static elimination treatment to obtain a sheet. (A) Electrode for applying electrostatic force Material: As shown in Table 3 B Shape: As shown in Table 3 (b) Electrostatic application conditions A. Applied voltage: + DC voltage 14 kV B. Distance between molten thermoplastic resin and lower surface of electrode: 5 mm (c) Static electricity removal conditions Static elimination method: as shown in Table 3. Static elimination position: 20 mm upstream from the position where the cooling drum and the thermoplastic resin sheet are separated, and the distance between the thermoplastic resin sheet and the static eliminator was 10 mm (Comparative Examples 1 to 5).
3). C. The relative humidity of the atmosphere where the cooling drum and the thermoplastic resin sheet were separated was as follows. Comparative Example 1: 30% RH Comparative Example 2: 50% RH Comparative Examples 3, 4: 50% RH

The upper limit molding speed obtained by adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet is 200 μm is as shown in Table 3, and the high speed could not be achieved.

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

As described above, according to the method for producing a thermoplastic resin sheet of the present invention, an electrostatic charge is applied to a resin sheet at a uniform density, and an electrostatic charge that has been applied at the time of peeling is applied. Since the charge is removed, a good adhesion state of the resin sheet to the cooling drum can be secured to suppress the occurrence of uneven application, and at the time of peeling, the occurrence of discharge between the sheet and the drum can be suppressed. Speed can be increased dramatically.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a casting apparatus for performing a method according to an embodiment of the present invention.

FIG. 2 is a schematic structural view of a casting apparatus for performing a method according to another embodiment of the present invention.

FIG. 3 is a schematic structural view of a casting apparatus for performing a method according to still another embodiment of the present invention.

FIG. 4 is a schematic structural view of a casting apparatus for performing a method according to still another embodiment of the present invention.

FIG. 5 is a schematic structural view of a casting apparatus for performing a method according to still another embodiment of the present invention.

FIG. 6 is a schematic structural view of a casting apparatus for performing a method according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 cap 2 molten thermoplastic resin sheet 3 electrode for applying static electricity 4 cooling drum 5 resin sheet 6 peeling point 10 static eliminator 11, 21, 32, 41, 51, 61 static elimination electrode 14, 64 nozzle

Claims (10)

[Claims] 1. A molten thermoplastic resin is extruded from a die into a sheet shape, and is adhered onto a cooling drum by an electrostatic application casting method. When the sheet is cooled and solidified, a uniform cross section is formed in the longitudinal direction. A method for producing a thermoplastic resin sheet, comprising applying an electrostatic charge to a sheet using a tape-shaped electrode having the same, and performing a static elimination treatment when the cooling drum and the sheet are separated. 2. The method for producing a thermoplastic resin sheet according to claim 1, wherein a static elimination treatment is performed on the thermoplastic resin sheet before the cooling drum and the thermoplastic resin sheet are separated. 3. The method for producing a thermoplastic resin sheet according to claim 1, wherein a static eliminator of a type that blows ionized gas is used for static elimination. 4. The method for producing a thermoplastic resin sheet according to claim 1, wherein a metal wire is used for the static elimination electrode. 5. The method according to claim 1, wherein a needle-like electrode is used as the charge removing electrode.
Or the method for producing a thermoplastic resin sheet according to 2 above. 6. The method for producing a thermoplastic resin sheet according to claim 1, wherein a metal blade is used for the charge removing electrode. 7. The method for producing a thermoplastic resin sheet according to claim 1, wherein a self-discharge type static eliminator is used for static elimination. 8. The method for producing a thermoplastic resin sheet according to claim 1, wherein an ionized gas is blown between the cooling drum and the thermoplastic resin sheet using a static eliminator of a type that blows an ionized gas for static elimination. 9. The method for producing a thermoplastic resin sheet according to claim 1, wherein the relative humidity of the atmosphere between the cooling drum and the peeling portion of the sheet is 40% RH or more. 10. The thermoplastic resin is a polyester,
A method for producing the thermoplastic resin sheet according to claim 1.