JPH10128828A - Manufacture of crystallized resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a transparent and high quality crystallized sheet free from the difference in physical properties in the thickness direction and also from surface defects. SOLUTION: In a sheet manufacturing method in which crystallizable resin 2 is melt-extruded into the sheet shape, brought into close contact with a rotary cooling drum 3 to be quenched and solidified, a refrigerant is discharged from a refrigerant discharge die 5 onto a surface opposite to the drum of the sheet in the position where the sheet temperature on the drum 3 is in the range of at most melting point of resin 2 and at least maximum crystallization speed temperature, and the refrigerant is flowed down in a film shape on the sheet at the flow rate and in the amount not boiling nor evaporating on the sheet surface, and cooled also from the face opposite to the drum surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a crystalline resin sheet. More specifically, the present invention relates to a method for producing a crystalline resin sheet with a small difference in physical properties in the front and back thickness directions and without causing surface defects.

[0002]

2. Description of the Related Art As a method for producing a crystalline resin sheet, a method of extruding a molten polymer into a sheet and bringing the molten polymer into close contact with a rotary cooling drum to rapidly cool and solidify is known and widely used. However, this method is disadvantageous in that since the cooling is performed substantially from one side, the resulting sheet has a difference in physical properties in the thickness direction between the front and back sides. This drawback is not so problematic when the sheet is thin, but becomes significant as the thickness of the sheet increases, especially when the thickness is 1 mm or more, and it is required to eliminate it.

[0003] Therefore, as a method of cooling and forming a sheet of a crystalline polyolefin resin or a polyester resin, particularly a sheet having a thickness of 1 mm or more (including an original sheet of a biaxially stretched film), its transparency and non- In order to ensure crystallinity, the melt-extruded sheet is brought into close contact with the rotating cooling drum with static electricity or an air knife, and then the air drum, a refrigerant mixed with air and water mist is blown against the film on the anti-drum surface, A method of immersing the entire drum inside the drum has been proposed. (Japanese Unexamined Patent Publication No. 62-214921, Japanese Unexamined Patent Publication No. 1-21442
No. 2, JP-A-3-180317)

[0004]

However, according to the research results of the present inventors, the above-mentioned air knife method exhibits a certain effect, but the cooling speed is still slower than the cooling speed from the rotating cooling drum side. When the thickness of the sheet becomes thicker, a difference in crystallinity occurs between the front and back of the sheet, and it is insufficient to produce a sheet with uniform front and back characteristics, and the water mist method aimed at the cooling effect by boiling of the refrigerant or latent heat of evaporation Although the cooling effect is large, there is a problem that irregularities are likely to occur on the sheet surface due to cooling spots. Also,
The method of immersing in a water tank has a problem that although the cooling rate is higher than that of the above method, the cooling start position is fixed, and the sheet cannot be freely set to a position where crystallization of the sheet occurs rapidly. There is a problem in that the apparatus becomes large-scale, and it is difficult to perform a threading operation such as threading, and it is difficult to cope with an emergency such as winding a sheet around a drum.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing a crystalline resin film having the same front and back characteristics.

[0006]

The present invention has the following construction. In a method for producing a sheet in which a crystalline resin is melt-extruded into a sheet form and closely contacted with a rotary cooling drum to be rapidly cooled and solidified, the temperature of the sheet on the drum is in a range of not more than the melting point of the resin and not less than a maximum crystallization rate temperature. The refrigerant is discharged from the refrigerant discharge die onto the opposite surface of the sheet from the refrigerant discharge die, and the refrigerant is caused to flow down on the sheet in a film shape at a flow rate and an amount that does not cause boiling or evaporation on the sheet surface, and is also cooled from the opposite surface of the sheet. A method for producing a crystalline resin sheet.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a side view of a cooling device showing one embodiment of the present invention. FIG. 2 is a graph showing the relationship between the crystallization speed of the crystalline resin and the temperature. In FIG. 1, 1 is a resin extrusion die, 2 is an extruded resin, 3 is a rotary cooling drum, 4 is an electrostatic adhesion wire, 5 is a refrigerant discharge die, 6 is a refrigerant flow, 7 is a pan, 8 is a squeeze rubber roll, 9, 9 'are suction mass rolls.

In the present invention, the crystalline thermoplastic resin is melt-extruded into a sheet form from an extrusion die 1, and a rotating cooling drum 3 for cooling from the inside through a cooling medium controlled at a constant temperature, an electrostatic wire 4, or other material. (For example, an air knife). The sheet-like thermoplastic resin adhered to the rotary cooling drum is cooled and solidified. In this cooling process, the drum surface of the sheet is rapidly cooled, but the opposite drum surface is cooled in the thickness direction by heat conduction of the sheet, so that the cooling speed is slow and the heat is easily crystallized.

As can be understood from the curve in FIG. 2, the crystallization speed of the crystalline resin is temperature-dependent, and there is a region where the crystallization of the resin proceeds in a specific temperature range, and the crystallization is the fastest in that region. There is an advancing temperature (maximum crystallization rate temperature). The crystallization temperature range and the temperature of the maximum crystallization rate vary depending on the type of the resin. The present invention is characterized in that the crystallization temperature region is cooled and passed in a short time, for example, several seconds, and at the same time, cooled so that there is no difference in front and back physical properties.

Therefore, in the present invention, as means for cooling the sheet from the surface opposite to the drum, a refrigerant having a cooling capacity equivalent to or similar to the refrigerant flowing through the drum is discharged from the discharge nozzle 5 to the surface opposite to the drum of the sheet. The film is caused to flow down in a film form on the anti-drum surface. The nozzle 5 can be installed at any position in the cooling process, and has an advantage that it can be installed freely aiming at a temperature zone where crystallization of the resin starts.

[0011] When the refrigerant flows down on the surface of the high-temperature sheet,
The refrigerant may receive heat from the sheet and boil and evaporate. Another feature of the present invention is that the boiling phenomenon is suppressed by the flow rate and amount of the refrigerant flowing down.

The problem caused by the boiling of the refrigerant is that since the boiling film is not necessarily generated uniformly, the cooling action is locally changed and cooling spots, that is, temperature spots are generated on the sheet surface. In this case, a slight uneven defect which is considered to be a contraction unevenness due to a temperature difference occurs on the sheet surface. Depending on the required level of sheet quality, this defect may not be a serious defect. However, especially in a sheet (raw sheet) where importance is placed on flatness and transparency for a biaxially stretched film, this irregular defect is a problem. Become.

An object of the present invention is to provide a method for producing a high-quality raw sheet even in an application requiring high quality, without a difference in front and back physical properties. On the other hand, for example, as described above, the water mist method aims at a cooling effect by boiling or latent heat of evaporation of the refrigerant, and has a large cooling effect, but has a problem that a surface irregularity defect is generated. This is not preferable for the production of the raw sheet.

Generally, the cooling effect of the latent heat of vaporization of the liquid is at least 10 times higher than that of the flowing water. This is an effective means, but the uniformity of the mist is extremely good for uniform evaporation. It is industrially extremely difficult to apply a mist applying means for obtaining high quality uniformity as the object of the present invention. In the present invention, the above-described means which is superior in quality to cooling efficiency is used.

In the present invention, the conditions under which the flowing refrigerant is not evaporated by boiling are, of course, affected by the amount of heat carried by the sheet, that is, the amount of extruded sheet, the extruded temperature, the specific heat of the resin, and the like. In order to lower the temperature of the outermost surface of the sheet below a certain level, a necessary and sufficient flow rate of the refrigerant is set. In the supply of the refrigerant from one cooling nozzle, there is a possibility that the temperature may increase during the flow and boiling may occur. In this case, it is preferable to provide a plurality of refrigerant supply nozzles in the flow direction.

When the sheet cooled to a predetermined temperature is left as it is with the refrigerant adhered thereto, the refrigerant evaporates and dries at random from the sheet surface. In this drying process, the latent heat of evaporation is deprived and a random temperature distribution is obtained. There is a possibility of making it unintentionally, which is not preferable for precise physical property control. Therefore, in the present invention, it is preferable that the cooling step under the flow of the coolant be completed by removing the coolant all at once and uniformly in the sheet width direction. For example, it is preferable to terminate the cooling from the side opposite to the drum surface by installing a squeeze roll for substantially squeezing the refrigerant with a nip roll at the position shown in FIG. Further, as shown in this figure, when a cooling means is arranged particularly on the lower surface of the rotary cooling drum, a bath or a pan having a liquid reservoir may be used as the means. However, in general, cooling by a pool bath or pan is generally not necessarily provided at a relatively upstream position where the flow rate is small and the heat transfer efficiency is low, and the temperature difference from the sheet is large and the cooling capacity is required. Absent. As shown in FIG. 1, it is preferable to install at a position that does not require much cooling capacity at the end of cooling, and a function that also serves to receive the water flowing down from the nozzle is preferable. If the bus is to be installed at the upstream nozzle position shown in FIG. 1, it is necessary to immerse the entire rotary cooling drum in the bath or to provide a seal structure to prevent the liquid from leaking to the side of the drum. . In this case, as described above, there is a problem that it is difficult to handle the membrane or to deal with abnormal winding, which is not preferable.

The sheet which has been cooled in this way is
When the process is shifted to the next step, for example, the stretching step, it is preferable that the sheet is wiped on both sides of the sheet under reduced pressure with a mass roll coated with a nonwoven fabric in order to further remove the residual refrigerant.

The present invention can be widely applied to thermoplastic resins having thermocrystallinity. Examples of the thermoplastic resin include polyolefins represented by polypropylene and polyethylene, and polyethylene terephthalate, polyethylene-2,
Polyesters represented by 6-naphthalate are preferred. These resins may be copolymers as long as they have crystallinity.

In the present invention, the thickness of the sheet is set to 0.1.
5 mm or more and 4 mm or less are appropriate, and 2 mm or more and 4 mm are more preferable. Water is mainly used as a refrigerant applied to the sheet, and a small amount of alcohol and / or a surfactant can be added and contained in the water, and this case is often preferable.

According to the method of the present invention, a crystalline thermoplastic sheet can be cooled in an amorphous state with uniform physical properties in the thickness direction without causing surface defects, curling, and the like. It can be manufactured efficiently.

[0021]

The present invention will be further described with reference to the following examples.

Example 1 Using an apparatus shown in FIG. 1, polyethylene-2,6-naphthalate (PEN) was extruded from a die 1 into a sheet 2 at a resin temperature of 295.degree.
The sheet was brought into close contact with the mirror rotating cooling drum 3 having a peripheral velocity of 5 m / min through which water at 0 ° C. was passed by an electrostatic wire 4 to obtain a sheet having a thickness of 2 mm. At this time, at a position where the sheet surface temperature is 230 ° C., water whose temperature has been adjusted from the nozzle 5 to the same temperature as the drum passage water temperature is 0.3 m ³ / min per 1 m width, and the flow rate is 1 m / sec.
And cooled down by flowing down on the sheet surface in the form of a film. At the lower part of the drum, a water pan 7 was installed at the position shown in the figure, so that a part of the drum was immersed. The conditions under which the flowing water stream during this period was not interrupted and did not evaporate were selected. A squeeze rubber roll 8 for removing water was placed at a position where the sheet left the cooling drum, and cooling was stopped all at once in the width direction. After that, the water adhering to the sheet was able to be almost completely removed from the water remaining in the form of water droplets or a film by the suction mass rolls 9 and 9 'shown in the figure. As a result of inspecting the sheet selected by the above method, the density of the sheet was 1.332 g / cm ³ , and it was possible to obtain a sheet almost similar to amorphous PEN.

The raw sheet thus obtained was biaxially stretched in the vertical and horizontal directions, and the surface properties of the biaxially stretched film were examined. As a result, no problematic levels of irregularities and curls were found.

[Comparative Example 1] A sheet was extruded under the same conditions as in Example 1, water was sprayed at the same position as in Example 1, and residual water was squeezed with a squeeze rubber roll 8 to obtain a sheet having a thickness of 2 mm. Obtained. The sprayed water evaporates violently to the squeeze position, causing mottled drying. The density of this sheet was about 1.340 g / cm ³ , and crystallization had progressed from the sheet of Example 1. The raw sheet obtained by this cooling method is stretched in the vertical and horizontal directions,
When the surface of the axially stretched film was observed, countless crater-like irregularities were observed on the water spray surface, and large curl defects were also generated.

[0025]

According to the method for cooling a thermoplastic film of the present invention, it is possible to obtain a transparent and extremely flat film having no surface defects without crystallizing a sheet having a thickness of 2 mm or more, and to produce a high quality film. It can be manufactured while ensuring the performance.

[Brief description of the drawings]

FIG. 1 is a side view of a cooling device showing one embodiment of the present invention.

FIG. 2 is a graph showing measurement results of one crystalline resin of the present invention by a differential scanning calorimeter.

[Explanation of symbols]

 1: resin extrusion die 2: resin 3: cooling drum 4: electrostatic contact wire 5: refrigerant discharge die 6: refrigerant flow 7: pan 8: squeeze rubber roll 9, 9 ': suction mass roll

Claims (7)

[Claims] 1. A method for producing a sheet in which a crystalline resin is melt-extruded into a sheet form and then rapidly cooled and solidified by closely adhering to a rotary cooling drum, wherein the temperature of the sheet on the drum is lower than the melting point of the resin and higher than the maximum crystallization rate temperature. At a position within the sheet, a refrigerant is discharged from a refrigerant discharge die to the opposite surface of the sheet from the refrigerant discharge die, and the refrigerant is caused to flow down on the sheet in a film shape at a flow rate and amount that does not cause boiling or evaporation on the sheet surface. A method for producing a crystalline resin sheet, comprising cooling from a surface. 2. The crystalline resin sheet according to claim 1, wherein the refrigerant on the sheet is removed after the temperature of the sheet becomes equal to or lower than the boiling point of the refrigerant, and the cooling of the refrigerant from the side opposite to the drum surface is substantially terminated. Production method. 3. The method for producing a crystalline resin sheet according to claim 2, wherein a press roll is applied to the sheet on the rotary cooling drum to squeeze and remove the refrigerant on the sheet. 4. The method for cooling a crystalline resin sheet according to claim 3, wherein a suction roll is applied to one or both sides of the sheet detached from the pressing roll to remove residual refrigerant. 5. The cooling sheet has a thickness of 0.5 mm or more and 4 m or more.
The method for producing a crystalline resin sheet according to claim 1, which is not more than m. 6. The method for producing a crystalline resin sheet according to claim 1, wherein the crystalline resin is a polyester resin. 7. The method according to claim 1, wherein the crystalline resin is a polyolefin resin.