JP2002240123A - Method for producing polyester resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a quality polyester resin sheet. SOLUTION: The polyester resin sheet which is made a sheet in which a layer of a thermoplastic resin A having melt resistivity at least ten times as large as that of the polyester resin is laminated on at least one side of the main layer of the polyester resin sheet is melt and discharged from a nozzle onto a rotary cooling body. Voltage is applied between electrodes installed on the sheet to charge the sheet, and the sheet is cooled while being adhered to the rotary cooling body to produce the polyester resin sheet. The polyester resin sheet obtained by cooling is biaxially oriented in turn to obtain the oriented 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 producing a polyester resin sheet of good quality at low cost and with good productivity, and more particularly to a method of producing a polyester resin sheet suitable for high-speed film formation. .

[0002]

2. Description of the Related Art As a method for producing a polyester resin sheet, for example, a polyester resin containing inorganic particles as an anti-blocking agent is melt-extruded, and the molten sheet is brought into close contact with a rotary cooling body by an electrostatic application casting method and cooled. In general, a method of obtaining an amorphous unoriented sheet and stretching the sheet in a uniaxial or biaxial direction is employed.
Among the series of sheet manufacturing steps, the casting step of cooling and solidifying the molten sheet to obtain an amorphous unoriented sheet is an important step that determines the quality of the sheet and the film forming speed.

[0003] In the case of a polyester resin sheet, cooling by an electrostatic application casting method is effective. However, due to the limit of the electrostatic adhesion between a molten sheet and a cooling medium, a transparent sheet having low crystallinity and a smooth surface can be obtained. Maximum speed is 60m /
It could not be faster than about a minute, and there was a limit to productivity improvement.

Therefore, in the electrostatic application casting method, various techniques have been proposed for lowering the melting specific resistance of the polyester resin in order to improve the adhesion between the molten sheet and the rotary cooling body and increase the cooling rate. For example, Japanese Patent Publication No. 53-40231 proposes a method of improving the casting speed by lowering the melting specific resistance of a resin by adding an alkali metal salt or an alkaline earth metal salt, and a quaternary phosphonium sulfonate. Japanese Patent Publication No. 7-5765 proposes a method of improving the casting speed by lowering the melting specific resistance of the resin by incorporating a salt. Further, in order to prevent electrode contamination due to scattering of the quaternary phosphonium salt of sulfonic acid, a laminated sheet in which the sheet has a laminated structure and a layer containing no quaternary phosphonium salt of sulfonic acid on the electrode side is disclosed in Japanese Patent Application Laid-Open No. 2000-211009. Has been proposed.

[0005]

However, such a conventional method has the following disadvantages. In other words, even if the melting specific resistance of the polyester resin is lowered, most of the electric charges given from the electrodes flow out of the molten sheet to the rotary cooling body by itself, so that the effective cooling is effective between the molten sheet and the rotary cooling body. It is difficult to generate a strong adhesion. Even when a polyester resin adjusted to an appropriate melting specific resistance was used, the maximum speed by the electrostatic application casting was only about 80 m / min.

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 polyester resin sheet having excellent quality with high productivity.

[0007]

Means for Solving the Problems In view of the problems described above, the present inventors have conducted intensive studies and as a result, have found that at least one surface of a polyester resin is made of a layer of a thermoplastic resin A having a higher melting specific resistance than the polyester resin. It has been found that the above-mentioned problem can be solved by the provision of the present invention, and the present invention has been accomplished.

That is, according to the method for producing a polyester resin sheet of the present invention, the thermoplastic resin A having a melting specific resistance of at least 10 times the melting specific resistance of the polyester resin is formed on at least one surface of the main layer of the polyester resin sheet. A polyester resin sheet is melt-discharged from a die onto a rotary cooling body, and the sheet is charged by applying a voltage to an electrode placed on the sheet, and the polyester resin sheet is brought into close contact with the rotary cooling body. This is a method for producing a polyester resin sheet while cooling while heating.

According to the manufacturing method of the present invention, the cooling speed of the molten sheet in the cooling step by close contact with the rotary cooling body is greatly increased, and casting at a high speed of 80 to 120 m / min becomes possible. Further, by increasing the adhesion between the molten sheet and the rotary cooling body, even in high-speed casting, no defects are generated in the sheet, and the thickness unevenness in the longitudinal direction of the film can be improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

The polyester resin in the present invention is a high molecular compound having an ester bond in the main chain. Representative examples thereof include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene terephthalate, and polycyclohexane dimethylene terephthalate. And blends thereof with other copolymers and other resins, but are not limited thereto as long as melt extrusion is possible. In the present invention, particularly preferably used polyester resins include polyethylene terephthalate, polyethylene naphthalate and copolymers and blends thereof,
The intrinsic viscosity of the polyester resin is 0.5 to 1.2.
It is good to be in the range. Of course, various additives such as an antiblocking agent, a bulking agent, a stabilizer, an antioxidant, a viscosity reducing / thickening agent, and other resins can be added to these polyester resins.

The sheet produced by the production method of the present invention is a sheet obtained by laminating a surface layer made of a thermoplastic resin A on at least one surface of a sheet main layer made of a polyester resin. The melting specific resistance of the thermoplastic resin A is required to be 10 times or more the melting specific resistance of the polyester resin forming the sheet main layer, preferably 50 times or more, particularly preferably 100 times or more. is there.

The melting specific resistance is a volume specific resistance at a temperature at which the resin is melt-extruded. Generally, the higher the temperature, the smaller the melting specific resistance. If a layer made of thermoplastic resin A having a melting specific resistance 10 times or more higher than that of the polyester resin is laminated on at least one surface of the sheet main layer made of the polyester resin, the charge given from the electrostatic application electrode is melted. It is difficult for the sheet to escape from the sheet to the cooling body, and electric charges are easily accumulated in the molten sheet. As a result, the charge accumulated in the molten sheet increases,
A stronger adhesive force is generated between the cooling body and the casting, and higher-speed casting can be performed. Specifically, 80-1
Casting at 20 m / min becomes possible. Therefore, if the melting specific resistance of the thermoplastic resin A is less than 10 times that of the polyester resin, the charge cannot sufficiently be prevented from flowing out to the rotary cooling body, and it becomes difficult to improve the casting speed.

When the melting specific resistance of the entire molten sheet is lowered, most of the applied electric charge escapes from the molten sheet to the cooling body, so that it is difficult for the electric charge to accumulate in the molten sheet itself. When the specific resistance is high, it is difficult to receive the charge from the electrode, so that it is difficult for the charge to accumulate in the molten sheet, and in any case, a strong adhesion between the molten sheet and the cooling body cannot be generated.

On the other hand, in the present invention, the surface layer made of the thermoplastic resin A whose melting specific resistance is ten times or more that of the polyester resin is laminated on at least one surface of the main sheet layer made of the polyester resin. The surface layer functions as a charge trapping layer, and can strongly charge the molten sheet. As a result, casting at a higher speed than before can be performed. Further, by improving the adhesive force between the molten sheet and the cooling body, thickness unevenness in the length direction of the obtained sheet can be improved.

The surface layer made of the thermoplastic resin A may be laminated on only one surface of the polyester resin sheet main layer, or may be laminated on both surfaces. When laminating only on one surface, when cooling the polyester resin sheet while keeping the polyester resin sheet in close contact with the rotating cooling body, the surface layer made of the thermoplastic resin A is so contacted that the layer made of the thermoplastic resin A contacts the rotating cooling body. Are preferably laminated.
Lamination is performed by using two or more extruders and melting each resin, then joining and laminating these resins with a lamination adapter and guiding them to the die, or merging and laminating each resin in the die. And extruded as a molten sheet without any particular limitation.

In the present invention, the thermoplastic resin A forming the surface layer is a thermoplastic resin having a predetermined melting specific resistance, for example, a polyolefin resin represented by polyethylene and polypropylene, polyethylene terephthalate,
Polybutylene terephthalate, polyester resin represented by polyethylene naphthalate, polyvinyl chloride resin, polyvinylidene chloride resin, ionomer resin, etc. can be mentioned, and it is appropriately selected according to the use of the polyester resin sheet. In order to collect and reuse the film scraped in the film forming process or the film forming process, it is preferable that the thermoplastic resin A is also a polyester resin, and is a polyester resin of the same type as the polyester resin to be the main layer of the sheet. Is preferred.

In the present invention, the polyester resin constituting the main sheet layer preferably has a melting specific resistance in the range of 10 ⁶ to 10 ¹¹ Ω · cm in order to accumulate more charges given from the electrodes. Furthermore, 5 × 10 ^{6 to} 5 × 10 ⁸ Ω
-The range of cm is preferable. Further, the melting specific resistance of the thermoplastic resin A forming the surface layer is 10 ⁸ to 10 ¹² Ω · c.
m is preferably in order to suppress escape of electric charges to the cooling body, and more preferably 10 ⁹ to 10.
The range is ¹¹ Ω · cm.

As a means for adjusting the melting specific resistance of the polyester resin forming the sheet main layer or the polyester resin of the thermoplastic resin A forming the surface layer to a desired level, a known method may be used. For example, the melting specific resistance can be reduced by adding a compound comprising an alkali metal and an alkaline earth metal to a polyester resin.

These metal species may be added as a catalyst for transesterification during polymerization of the polyester resin. Further, in order to increase the melting specific resistance, it is necessary to reduce the amount of the metal compound including the polyester polymerization catalyst. Further, by adding a phosphorus compound, the metal ions are deactivated and the melting specific resistance is reduced. Can also be increased. Furthermore, the melting specific resistance of the polyester resin can be adjusted to an arbitrary value by adjusting the addition amount of these metal species and the addition amount of a phosphorus compound such as a phosphoric acid compound and a phosphorous acid compound.

The surface layer made of the thermoplastic resin A plays a role in preventing electric charge from escaping from the molten sheet.
The thickness of the surface layer made of is preferably in the range of 5 to 60% of the total sheet thickness in order to accumulate charges in the molten sheet.

In the manufacturing method of the present invention, a known electrode can be used as the voltage applying electrode, and for example, a wire electrode or a tape electrode can be used. This is because even if these electrodes are used, the casting speed can be effectively improved.

In the present invention, a known rotary cooling body for cooling the molten sheet can be used, and a metal drum is preferable. The surface is preferably smooth, for example, the surface roughness is less than 0.5S, more preferably less than 0.2S. It is preferable to apply chrome plating to the drum surface from the viewpoint of surface smoothness,
A sprayed ceramic material may be used. The drum surface temperature can be controlled by passing cooling water or a heat medium through the inside of the drum. It is preferable that the drum is electrically grounded. In this case, an arbitrary resistor may be provided between the drum and the ground point.

The polyester resin sheet obtained by the method of cooling while being brought into close contact with the rotary cooling body by the production method of the present invention is subjected to stretching and / or stretching following casting.
Alternatively, heat treatment can be performed. Stretching of the polyester resin sheet can be performed by various methods such as longitudinal uniaxial stretching, horizontal uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching, and the sequential biaxial stretching method is particularly preferable. Usually, a sheet with good mechanical balance can be obtained by biaxial stretching.

The stretching of the polyester resin sheet can be carried out between rolls having different peripheral speeds, or by a tenter method in which the sheet is gripped by a clip and the interval between the clips is changed. The stretching ratio is not particularly limited, but it is preferable to stretch in one direction by 2 to 6 times.

Next, the method for producing a polyester resin sheet according to the present invention will be described with reference to polyethylene terephthalate (PE).
T) The resin will be shown more specifically as an example.

The PET resin used as a raw material may be, if necessary, other compounds, for example, other thermoplastic resins, silicon oxide, magnesium oxide, calcium carbonate, titanium oxide, titanium oxide, as long as the melting specific resistance condition of the present invention is satisfied. Aluminum, crosslinked polyester, crosslinked polystyrene, mica, talc, kaolin and other inorganic and organic compounds, ethylenebisstearylamide, ionic polymer compound ionomers and other organic compounds, etc. may be added and blended. Raw materials, and further, raw materials recovered from the polyester resin sheet and the like may be mixed. Two types of PET raw materials having melting specific resistances different by 10 times or more are prepared by applying the above-mentioned melting specific resistance adjusting means,
After drying and dehydrating these, single screw extruder, twin screw extruder,
The mixture is supplied to a melt extruder such as a vent extruder or a tandem extruder, and is melt-extruded under a nitrogen stream or vacuum so as to minimize the molecular weight (eg, intrinsic viscosity [η]). At this time, in order to remove foreign matter in the raw material, the molten resin is filtered with an appropriate filter (for example, sintered metal,
It is preferable to extrude while filtering through a porous ceramic, sand, wire mesh, or the like.

The molten resin filtered and extruded by each extruder is laminated by a lamination adapter and guided to a T-die die.

Thus, the molten sheet is extruded from the die and brought into close contact with a cast drum (rotary cooling body). A wire-like electrode is placed near the upper portion of the molten sheet, and a high DC voltage is applied to this electrode. Casting.

The cast sheet thus obtained is subjected to a stretching treatment as required. For example, in the case of a sequential biaxial stretching method, the cast sheet is firstly subjected to Tg by a preheating roll.
The sheet is heated as described above, stretched 2 to 4 times in the longitudinal direction by rolls having different peripheral speeds, and the sheet is cooled by a cooling roll. Next, the sheet stretched in the longitudinal direction is guided to a tenter-type transverse stretching machine, and the sheet is heated to Tg or more by hot air while holding both ends of the sheet with clips. The sheet is stretched 2 to 4 times in the lateral direction by increasing the width of the clips at both ends, and the sheet is heat-treated by hot air as needed.

[Measurement Methods for Physical Properties] Next, the measurement methods used in the present invention will be described below. 1. Cast Adhesion On a cast drum (rotary cooling body), the case where air or the like was caught or sagged, and no other casting defects were observed, was evaluated as ○, and the case where any defects were observed with the naked eye was evaluated as ×. 2. Cast surface properties Light is applied to a cast sheet surface of 10 m ² or more, and the reflected light is visually observed to determine whether or not surface irregularities such as craters are recognized. Judgment criteria are as follows: o, when no irregularities are found on the surface, o, when there is irregularities on the surface, but when the depth is less than 0.1 μm, which is shallow and disappears by stretching, x when the entire surface is uneven. And 3. Melting specific resistance of thermoplastic resin After vacuum drying the thermoplastic resin, put it in a test tube with an inner diameter of 50 mm, melt it under a nitrogen atmosphere, insert a pair of copper electrodes into the molten resin, and melt according to the type of polyester. A DC voltage was applied at the temperature during sheet extrusion (for example, 280 ° C. in the case of the PET resin sheet of the following example), and the melting specific resistance [ρ] was determined by the following equation. The unit is Ω · cm. [Ρ] = V × S / (I × D) where V is the applied voltage (V) and S is the electrode area (c
m ² ), I is the current value (A), and D is the electrode distance (cm). 4. Thickness unevenness (%) 30 m width using Anritsu Film Thickness Tester KG601A and Electronic Micrometer K306C
The thickness of a film sampled at m and 40 m in length is continuously measured. The fluctuation width R is obtained from the maximum thickness value T _MAX (μm) and the minimum thickness value T _MIN (μm) by R = T _MAX −T _MIN , and the thickness unevenness (%) = R / R from the average thickness T _AVE (μm).
It was determined as T _AVE × 100.

[0032]

The present invention will be described in more detail by way of examples.

Example 1 As a polyester resin, 2
PE having a melting specific resistance of 4 × 10 ⁶ Ω · cm at 80 ° C.
T resin (1) was used, and as thermoplastic resin A, 2
PET resin (2) having a melting specific resistance of 8 × 10 ⁹ Ω · cm at 80 ° C. was used. In PET resin (1), P
The melting specific resistance is adjusted by adding 1% by weight of calcium acetate during the ET polymerization, and the PET resin (2) is polymerized without adding a metal compound except for adding 0.03% by weight of antimony trioxide as a polymerization catalyst. By doing so, the melting specific resistance was adjusted.

After drying each resin thus prepared, it is supplied to a usual melt extruder, melted at 280 ° C., filtered through a 10 μm cut fiber sintered metal filter, and then filtered to form a laminated adapter. Introduce and PET
The sheet main layer made of the resin (1) and both surface layers made of the PET resin (2) were laminated in a sheet shape, and were melt-extruded at 280 ° C. from a T-die die.

The molten sheet is extruded onto a casting drum having a surface roughness of 0.1 S and a surface having a diameter of 1.5 m, which is hard chrome-plated. A 2 mm tungsten wire electrode was arranged, and a positive DC voltage of +8 KV was applied to perform casting. Cooling water was passed through the casting drum to adjust the surface temperature to 25 ° C.

As a result of casting in this manner,
A casting sheet having good cast adhesion could be produced at a high speed of 100 m / min.
A surface layer of thermoplastic resin A having a thickness of 10 μm was laminated on both surfaces of the obtained casting sheet, and the total sheet thickness was 270 μm. The adhesiveness of the cast sheet was good, and the cast surface property was good. The thickness unevenness of the cast film was as good as 1%.

Subsequently, the casting sheet was stretched 3.5 times at a stretching temperature of 90 ° C. with a roll-type longitudinal stretching machine, and then cooled to 30 ° C. or less. After completion of the roll stretching, the stretched sheet is guided to a tenter while holding both ends of the stretched sheet with clips, stretched three times in the width direction in a hot air atmosphere heated to a stretching temperature of 100 ° C., and then heat-set at 200 ° C. As a result, a biaxially stretched polyester resin sheet having a thickness of 25 μm was wound up at a high speed of about 350 m / min in a stable state without being broken.

[Comparative Example 1] Casting was performed in the same manner as in Example 1 except that a single-layer sheet was formed using only the PET resin (2) having a melting specific resistance of 8 × 10 ⁹ Ω · cm used in Example 1. Was done. However, in the region where the casting speed exceeded 25 m / min, the airflow between the molten sheet and the casting drum could not be eliminated, and the cast adhesion was × and the cast surface property was ×. The thickness unevenness of the cast sheet was also 8%.

[Comparative Example 2] Casting was performed in the same manner as in Example 1 except that a single-layer sheet was formed using only the PET resin having a melting specific resistance of 4 × 10 ⁶ Ω · cm used in Example 1. . However, casting speed is 45m
In the region exceeding / min, airflow between the molten sheet and the casting drum could not be eliminated, and the cast adhesion and the cast surface property were x. The thickness unevenness was also 7%.

Example 2 Casting was performed in the same manner as in Example 1 except that the surface layer made of the thermoplastic resin A of Example 1 was laminated only on the drum surface side of the molten sheet.
As a result, even at a casting speed of 100 m / min, the cast adhesion and the cast surface property were ○. The thickness of the surface layer made of the thermoplastic resin A in the cast sheet was 30 μm, the total sheet thickness was 300 μm, and the thickness unevenness was 1.5%.

[Example 3, Comparative Examples 3 and 4] By adjusting the amount of calcium acetate added during the polymerization of the PET resin,
PET resin (3) having a melting specific resistance of 10 ⁷ Ω · cm at 80 ° C., and a melting specific resistance of 2 × 10 ^{8 at} 280 ° C.
Ω · cm PET resin (4) was produced.

The above-mentioned PET resin (3) is used as the polyester resin, and the above-mentioned PET is used as the thermoplastic resin A.
Casting was performed in the same manner as in Example 1 except that the resin (4) was used. As a result, the cast adhesion and the cast surface property were ○ until the casting speed reached 90 m / min. The thickness unevenness was 2%. When the casting speed was 100 m / min, the cast adhesion was 性, the cast flatness was △, and the thickness unevenness was 3%.

Further, PE having a melting specific resistance of 10 ⁷ Ω · cm
A single-layer sheet using only the T resin (3) or a PET resin (4) having a melting specific resistance of 2 × 10 ⁸ Ω · cm
When only a single-layer sheet was used, the casting speed could not be made higher than 60 m / min.

[0044]

According to the present invention, a surface layer made of a thermoplastic resin A having a melting specific resistance 10 times or more higher than that of the polyester resin is laminated on at least one surface of a sheet main layer made of a polyester resin and subjected to electrostatic application casting. Thereby, the adhesive force between the molten sheet and the rotary cooling body is greatly increased, and the casting speed can be increased to 80 m / min or more,
Further, since a high quality sheet having good thickness unevenness in the longitudinal direction of the film can be produced, a high quality polyester resin sheet can be produced with high productivity.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4F100 AK01B AK01C AK41A AK41B AK41C BA02 BA03 BA06 BA10A BA10B BA10C BA15 BA16 BA26 EC032 EH202 EJ373 EJ383 EJ423 EJ502 JB16B JB16C JG00A JG04AJK02AJK02A

Claims (7)

[Claims] 1. A sheet in which a layer made of a thermoplastic resin A having a melting specific resistance not less than 10 times the melting specific resistance of the polyester resin is laminated on at least one surface of a main sheet layer made of a polyester resin, Polyester, wherein a polyester resin sheet is melted and discharged from a die onto a rotary cooling body, the sheet is charged by applying a voltage to an electrode provided on the sheet, and cooled while being in close contact with the rotary cooling body. A method for manufacturing a resin sheet. 2. The method for producing a polyester resin sheet according to claim 1, wherein a layer made of the thermoplastic resin A is laminated on the sheet surface on the side contacting the rotary cooling body. 3. The method for producing a polyester resin sheet according to claim 1, wherein the polyester resin constituting the sheet main layer has a melting specific resistance in the range of 10 ⁶ to 10 ¹¹ Ω · cm. 4. The thermoplastic resin A has a melting specific resistance of 10 ^8.
10 characterized in that it is a ¹² Omega · cm range polyester resin of producing a polyester resin sheet according to claim 1. 5. The polyester resin sheet according to claim 1, wherein the layer thickness of the layer made of the thermoplastic resin A is in the range of 5 to 60% of the total sheet thickness. Method. 6. The method for producing a polyester resin sheet according to claim 1, wherein the electrode for voltage application provided on the sheet is a wire-shaped or tape-shaped electrode. 7. The method for producing a polyester resin sheet according to claim 1, wherein the polyester resin sheet cooled by close contact with the rotary cooling body is stretched and / or heat-treated.