JPH06246828A - Warpage correction method and device for plastic sheet - Google Patents

Abstract

PURPOSE:To efficiently obtain a plastic sheet having a superior appearance and no warpage by a low-cost equipment without a need for a large equipment for pressing or the like. CONSTITUTION:In a plastic sheet warpage correction method and device, after the last roll 6 in an extrusion process for producing a plastic sheet, either or both surfaces of a sheet is heated or warmed and held at -1 deg.C<=DELTAt<=3 deg.C, where (sheet top surface temperature)-(sheet rear surface temperature) = DELTAt.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a plastic sheet,
For example, the present invention relates to a method and apparatus for correcting warpage of a thermoplastic resin sheet such as a polycarbonate resin, an acrylic resin, or a vinyl chloride resin during the production thereof.

[0002]

2. Description of the Related Art Thermoplastic plastic sheets, for example, sheets of polycarbonate resin, acrylic resin, vinyl chloride resin and the like are used for various purposes due to their excellent characteristics such as transparency. The sheet may be used as it is as a flat plate at the time of sheet production, at the time of construction by bending along a frame into a curved surface, or by press molding.

The present invention is an effective means for a sheet extrusion manufacturing apparatus in a general three-roll system as a thermoplastic plastic sheet manufacturing system, and a technique which is extremely useful especially when it is installed as a flat plate shipped from the factory. It is provided. That is, when the sheet has a warp, when setting it in the frame or tightening the bolt to the frame, it is necessary to perform the work while correcting the warp manually, which requires a great deal of labor, time, or warpage. When it was severe, there were inconveniences such as difficulty in construction.

As a method for correcting this warp off-line, press work has been known. This is a method of cold pressing for a long time or pressing while heating at a temperature lower than the glass transition temperature. As a method to reduce warpage online, the method of controlling by adjusting the temperature of each roll is "Kenkichi Murakami: Extrusion molding.
Revised 7th edition, (1989) p66 Plastics Age ".

Further, as a method for heating or cooling during the process, Japanese Patent Application Laid-Open No. 56-93520 discloses a method of blowing air to a thinner portion of the film to cool it, and Japanese Patent Application Laid-Open No. 59-14929 discloses a method for cooling the film. Japanese Patent Application Laid-Open No. 59-33121 discloses a method of installing and heating a heater in the width direction of a film, as a method of cooling air by blowing air on a roll according to the plate thickness.

The above-mentioned pressing method requires equipment such as a pressing machine, a large heating furnace, and a sheet conveying device, which requires a large investment. Further, the control by the roll temperature has a problem that the appearance is deteriorated even if the warp can be reduced. That is, since the roll temperature has a great influence on the appearance of the sheet, it is impossible to manufacture a sheet having excellent warpage and appearance unless the optimum roll temperature is the same for the warpage and the appearance.

All of the methods of heating and cooling during the process (JP-A-56-93520, JP-A-59-14929, and JP-A-59-33121) have a temperature in the width direction of the film. The purpose is to make the plate thickness uniform in the width direction by control. Therefore, these methods cannot correct the warp of a thick sheet.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for reducing the warp of a sheet at a low cost and efficiently without using a large amount of equipment and without deteriorating the appearance of the sheet. To do.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors found that the warp of a plastic sheet is faster than the lower surface after the upper surface of the sheet rolls out from the final roll. Therefore, we found that warpage is caused by heat shrinkage, and found that it can be solved by keeping the temperature of the front and back of the sheet within a certain range by heating or keeping the sheet after passing the final roll, Completed the invention.

That is, the present invention is as follows. (1) In the extrusion process for producing a plastic sheet, after the step of winding the sheet around the final roll is finished, one or both sides of the sheet is heated or kept warm, thereby (sheet front temperature)-(sheet back temperature). ) = Δt is maintained within a range of −1 ° C. ≦ Δt ≦ 3 ° C., a warp correction method for a plastic sheet.

(2) The material of the plastic sheet is any one of polycarbonate resin, acrylic resin and vinyl chloride resin, (sheet front temperature)-(seat back temperature) =
By setting the temperature difference of Δt to be −1 ° C. ≦ Δt ≦ 3 ° C.,
The warpage rate φ represented by the amount of warp / length × 100 = φ with respect to the manufacturing direction and the direction of 90 ° with the manufacturing direction is −0.1%
The method for straightening the warp of the plastic sheet according to the above item (1), wherein ≦ φ ≦ 0.2%.

(3) Behind the final roll, a heating device is provided on either the upper surface or the upper and lower surfaces of the sheet passing surface, (sheet upper surface temperature)-(sheet lower surface temperature) = Δt.
Is a device for correcting warpage of a plastic sheet, which maintains the range of -1 ° C ≤ Δt ≤ 3 ° C.

(4) The plastic sheet according to the above (3), wherein the heating device is any one of a thermal resistance heating device, an infrared heating device, a heat storage heating device, a combustion heating device, and a heating medium heating device. Warp correction device.

(5) Behind the final roll, a heat-retaining device is provided on either the upper surface or the upper and lower surfaces of the sheet passing surface, and (sheet upper surface temperature)-(sheet lower surface temperature) = Δt -1 ° C. ≦ A warp straightening device for plastic sheets that maintains a range of Δt ≦ 3 ° C.

(6) The plastic sheet according to the above (5), wherein the heat insulating material used in the heat retaining device is at least one selected from solid materials (polymers, ceramics, metals), hollow materials and porous materials. Warp correction device.

The present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of the sheet manufacturing process. Resin 8 is extruder 7
Is extruded in a molten state from the die and is cooled and solidified by the rolls 4 and 5 to form a sheet (at this point, the sheet temperature is
For example, in the case of polycarbonate (PC), it is around 125 ° C}. However, during the production of the sheet, the sheet having no warp warps when cooled to room temperature.

As a result of various studies, the inventors of the present invention have (sheet upper surface temperature) of the sheet after passing through the auxiliary roll 6 (roll 5 if the auxiliary roll 6 is not present)-( If the temperature difference Δt is −1 ° C. ≦ Δt ≦ 3 ° C., the sheet flow direction (MD direction) and the sheet in both the sheet flow direction and the 90 ° C. direction (TD direction) are set. Many experiments have found that the warp of the can be corrected at the same time.

In FIG. 2 (a diagram corresponding to Table 1), the difference in the surface temperature of the sheet immediately after passing through the roll 6 (the temperature on the front side of the sheet-the temperature on the back side of the sheet = Δt) is the warp of the sheet after cooling. The effect on the ratio φ (warpage / length × 100) is shown. However, φ> 0 when warping upward, φ when warping convex
<0. Resin is polycarbonate, plate thickness is 8mm
Is.

When the upper part of the sheet is not heat-retained (Comparative Example 1), Δt = −2.9 ° C., and the warpage rate φ shows a considerably large value. φ (TD) = 0.81, φ (M
D) = 0.32 and a considerably large warp in the upper part. As shown in FIG. 3, when only the upper part of the sheet is properly heat-retained (heat-retention length = 900 mm) and the surface temperature difference is small (−1 ° C. ≦ Δt ≦ 3 ° C.), the warpage rate of the sheet is −
The sheet becomes flat when 0.1% ≦ φ ≦ 0.2%. On the contrary, if the temperature of the upper part rises too much (Comparative example 2, Δt =
(6.3 ° C.), a large warp occurs in the upward convex (φ <0).

In Examples 2 to 4 of Table 1, when the same polycarbonate (plate thickness 8 mm) was heat-retained on the upper surface and the lower surface (Example 2), it was positively heated instead of heat-retained (Implementation). The influence of the surface temperature difference Δt on the warpage rate φ in Examples 3 and 4) is shown. In any case, it can be seen that if Δt is made extremely small, the warp is significantly reduced. Similar effects were confirmed with other resins such as acrylic resin and vinyl chloride resin in addition to polycarbonate.

A heating device for carrying out the method of the present invention is shown in FIG. Immediately after the auxiliary roll 6 (or roll 5 if there is no auxiliary roll) of the sheet manufacturing apparatus, the sheet heater 1,
Install 1 '. As the heater system, any one of an electric resistance type heater, an infrared heater, a heat storage type heating device, a combustion type heating device and a heat medium type heating device may be adopted. Further, the heater may be divided in the longitudinal direction or the width direction so as to correspond to a wide range of manufacturing conditions, and the temperature may be controlled in each zone using an infrared surface temperature measuring device or the like (FIG. 5).

The method of dividing the heater in the width direction is shown in Japanese Patent Laid-Open No. 59-33121, but differs from the present invention in the following points. That is, JP-A-59-33121
The purpose of the method of the publication is to control the temperature of the film in the plate width direction, but the object of the present invention is to equalize the temperatures of the front and back sides (the plate thickness direction) of the sheet.

Generally, the temperature distribution on the front and back of the sheet after the final rolling step is as shown in FIG. This is because the plate edge easily gets cold. Therefore, in order to make the front and back temperatures in the plate width direction equal, it is necessary to heat the plate width center weakly and strongly heat the plate edge.

Regarding the control of the heater temperature, the temperature control device 2 is attached to the heater 1. This device has a control function and a temperature display function. The heating device may be installed only on the surface having a low temperature (FIG. 7).

If there is sufficient space after the roll 6, a heat retaining device may be attached instead of the heating device as shown in FIG. Since it does not actively heat,
Although the length of the heat retention device is longer than that of the heating device, since a power source or the like is not required, it is possible to correct the warp at low cost. In addition, it is preferable that the heat retention length can be changed so as to be able to correspond to various manufacturing conditions. Also in this case, the heat retention device may be installed only on the surface having a low temperature. In addition,
The position for heating or heat retention is preferably immediately after passing through the final-stage roll because it means that the heat of the resin itself is used.

[0026]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. According to the examples and the comparative examples, it is understood that the present invention significantly reduces the warpage rate. Tables 1 to 4 are examples and comparative examples when the plate thickness of polycarbonate (PC) is changed, and Table 5 is an acrylic resin,
Table 6 shows the case of vinyl chloride resin.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

[Table 6]

[0033]

According to the present invention, since it is possible to efficiently manufacture a warp-free plastic sheet having an excellent appearance with inexpensive equipment, it is possible to mass-produce an excellent polymer material.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a warp correction method of the present invention.

FIG. 2 shows the influence of the difference in the sheet surface temperature on the warpage rate of the sheet after cooling.

FIG. 3 shows a warp correction method by heat retention.

FIG. 4 shows a warp correction device (heating method) of the present invention.

FIG. 5 shows a warp straightening device (heating system, heater division) of the present invention.

FIG. 6 shows temperature distributions on the front and back of the sheet in the width direction of the sheet.

FIG. 7 shows a warp straightening device of the present invention (heating method, only upper surface is heated).

FIG. 8 shows a warp straightening device (heat retaining system) of the present invention.

[Explanation of symbols]

 1 Flat Heater 2 Temperature Control Device 3 Roll 4 Roll 5 Roll 6 Auxiliary Roll 7 Extruder Die 8 Resin 9 Heat Retaining Plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Yamazaki 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (6)

[Claims] 1. In an extrusion process for producing a plastic sheet, after the step of winding the sheet around the final stage of the roll is completed, one or both sides of the sheet are heated or kept warm to obtain (sheet surface temperature)-(sheet surface temperature). Back temperature) = Δt is maintained within a range of −1 ° C. ≦ Δt ≦ 3 ° C., a method of straightening a warp of a plastic sheet. 2. The material of the plastic sheet is any one of polycarbonate resin, acrylic resin and vinyl chloride resin, and the temperature difference of (sheet front temperature)-(seat back temperature) = Δt is −1 ° C. ≦ Δt ≦ 3 ° C. As a result, the warpage rate φ represented by the amount of warpage / length × 100 = φ with respect to the manufacturing direction and the direction 90 ° from the manufacturing direction is −0.1% ≦ φ ≦
The warping correction method for a plastic sheet according to claim 1, wherein the warping correction is 0.2%. 3. A heating device is provided on the upper surface or both upper and lower sides of the sheet passing surface behind the final roll,
(Seat upper surface temperature)-(Sheet lower surface temperature) = Δt -1
A warp straightening device for a plastic sheet, which is maintained in the range of ℃ ≤ Δt ≤ 3 ℃. 4. The warp of the plastic sheet according to claim 3, wherein the heating device is any one of a thermal resistance heating device, an infrared heating device, a heat storage heating device, a combustion heating device, and a heating medium heating device. Straightening device. 5. A heat retaining device is provided on the upper surface or both upper and lower sides of the sheet passing surface behind the final roll,
(Seat upper surface temperature)-(Sheet lower surface temperature) = Δt -1
A warp straightening device for a plastic sheet, which is maintained in the range of ℃ ≤ Δt ≤ 3 ℃. 6. The warp correction of a plastic sheet according to claim 5, wherein the heat insulating material used for the heat retaining device is at least one selected from solid materials (polymers, ceramics, metals), hollow materials and porous materials. apparatus.