JPH10151661A - Manufacture of polyester sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the adhesion of a polyester sheet to the surface of a rotary cooling drum and, at the same time, suppress the lowering of the intrinsic viscosity of the polyester sheet by a method wherein a metal salt is added to the polyester, the polymerization of which has finished. SOLUTION: Magnesium decanedicarboxylate is added to polyester, the specific resistance of which is 1×10<7> Ωcm or more, so as to realize the magnesium atom density in the polyester of 0.5-1,000ppm. The above-mentioned mixture is melted in a vent type twin-screw extruder and, in succession, extruded from a mouthpiece in a sheet-like fashion through a gear pump so as to electrostatically bond to the surface of a rotary cooling drum by means of wire electrodes in order to obtain a sheet. Thus, the specific resistance is reduced under the condition that the lowering of the degree of polymerization of the polyester after melt-extrusion is checked as small as possible so as to produce a high quality polyester sheet at high productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyester sheet, and more particularly, to an industrially advantageous method for producing a polyester sheet to which an electrostatic adhesion method is applied.

[0002]

2. Description of the Related Art Biaxially oriented polyester films typified by polyethylene terephthalate are known for their excellent mechanical properties, electrical properties, chemical resistance, dimensional stability, etc., for their use in information recording materials, capacitors, packaging and plate making. , Electrification,
It is used as a substrate in many fields such as photographic films.

[0003] The polyester film is prepared by first bringing a molten polyester sheet extruded from an extruder onto a rotary cooling drum into close contact with the surface of the rotary cooling drum to produce a polyester sheet, and then stretching the polyester sheet. Can be Therefore, in the production of a polyester film, it is important to efficiently produce a polyester sheet having no surface defects.

Conventionally, in the production of a polyester sheet, an electrostatic adhesion method has been employed in order to increase the adhesion of a molten polyester sheet to the surface of a rotating cooling drum. Here, the electrostatic contact method generally means that a linear electrode is provided on the upper surface of a sheet extruded on a rotary cooling drum in a direction orthogonal to the flow of the sheet, and a DC voltage of about 5 to 10 kV is applied to the electrode. A method in which an electrostatic charge is applied to the sheet by applying the voltage to improve the adhesion between the rotary cooling drum and the sheet (Japanese Patent Publication No. 37-6124).

[0005] However, in the electrostatic contact method, if the speed of the rotary cooling drum is increased for the purpose of increasing the productivity, the adhesive force between the sheet and the rotary cooling drum decreases. As a result, so-called bound bubbles that cause crater-like quality defects in the sheet are generated in the product.

It is known that the above-mentioned bound cells are more likely to be generated as the specific resistance of the raw material polyester at the time of melting becomes higher. Therefore, conventionally, various methods have been proposed for adding a metal compound to the polyester in order to reduce the specific resistance of the raw material polyester at the time of melting. Among these, a method of adding a metal compound to the polyester after polymerization is proposed in, for example, JP-A-57-18534.

[0007] The above-mentioned method involves adding a metal salt of an aliphatic monocarboxylic acid or a dicarboxylic acid to a polyester by 0.04%.
This is a method of adding 1 to 1% by weight. In the above method, a method of producing a so-called masterbatch containing a metal salt at a high concentration and blending the chips with a polyester is preferably employed from the viewpoint of uniformity and operability of blending the metal salt. . However, in the case of using the master batch method, there is a problem such as a decrease in the molecular weight of the polyester due to a high concentration of the metal salt.

In order to solve the above problem, Japanese Patent Publication No.
Japanese Patent No. 4328 proposes a method in which the melting temperature of polyester to which a metal salt is added is limited. However, this method is applied only to polyesters having a low melting point, such as isophthalic acid copolymerized polyester and polybutylene terephthalate, and has a drawback that it cannot be applied to other polyesters.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to rotate a molten polyester sheet extruded from an extruder onto a rotary cooling drum by the above-mentioned rotating method using an electrostatic adhesion method. This is a method for producing a polyester sheet that is in close contact with the surface of a cooling drum, wherein a metal salt is added to the polyester after the polymerization to enhance the adhesion of the polyester sheet to the surface of the rotating cooling drum, and furthermore, the inherent properties of the polyester sheet An object of the present invention is to provide an industrially advantageous method for producing a polyester sheet in which a decrease in viscosity is suppressed.

[0010]

The present inventor has made various studies to achieve the above object, and as a result, disclosed in Japanese Patent Application Laid-Open No. 6-916.
As described in Japanese Patent No. 35, a vented twin-screw extruder, which is adopted only in special cases such as when compounding a particle slurry with polyester, is used. It has been found that if the content is limited to a certain range, the above object can be easily achieved by avoiding problems such as a decrease in the molecular weight of the polyester due to the metal salt.

The present invention has been accomplished on the basis of the above findings, and the gist of the invention is that a molten polyester sheet extruded from an extruder onto a rotary cooling drum is coated on the surface of the rotary cooling drum by an electrostatic adhesion method. In a method for producing a polyester sheet to be in close contact with, a vent-type twin-screw extruder is used as an extruder, and a polyester having a specific resistance of 1 × 10 ⁷ Ωcm or more as a raw material polyester is used. A method for producing a polyester sheet, characterized in that a metal salt of an aliphatic monocarboxylic acid or a dicarboxylic acid is supplied to an extruder in such an amount that the concentration of metal atoms becomes 0.5 to 1,000 ppm.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a side view illustrating an example of a vent-type twin-screw extruder used in the production method of the present invention. In FIG. 1, (1) is a molding machine (extruder), (2) is a heating cylinder, 3) is a screw, (4) is an extrusion port, M is a screw driving device, (6) is a vent hole, (8) is a reverse screw,
(9) represents a material input port.

The polyester used in the present invention refers to a polyester comprising an aromatic dicarboxylic acid component and a glycol component. In particular, 80% or more of the repeating units are ethylene terephthalate units or ethylene 2,6-naphthalate units or Polyesters having 1,4-cyclohexylene dimethylene terephthalate units are preferred. The polyester may have another third component copolymerized.

The aromatic dicarboxylic acid component includes:
Besides terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid,
Sebacic acid, 4,4'-diphenyldicarboxylic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid and the like) and the like. On the other hand, examples of the glycol component include, in addition to ethylene glycol and 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, neopentyl glycol, and the like. In the present invention, a polyester in which 80% or more of the repeating units are ethylene terephthalate units or ethylene-2,6-naphthalate units is suitably used.

The polyester used in the present invention does not require the addition of a metal salt during polymerization to reduce the specific resistance. Accordingly, the specific resistance of the polyester used in the present invention at the time of melting is 1 × 10 ⁷ Ωcm or more, preferably 3 × 10 ⁷ Ωcm.
It is more preferably 5 × 10 ⁷ Ωcm or more. Further, the polyester used in the present invention may contain inorganic and / or organic fine particles according to a known method, or may contain fine particles based on a catalyst residue at the time of polymerization.

The metal salt of an aliphatic monocarboxylic acid or dicarboxylic acid used in the present invention is, for example, a compound having 4 carbon atoms.
Lithium salts, sodium salts, potassium salts, manganese salts, zinc salts, calcium salts, aluminum salts and the like of about 30 to about 30 aliphatic monocarboxylic acids or dicarboxylic acids. Among these metal salts, magnesium salts, manganese salts, zinc salts and calcium salts are preferred. In particular, magnesium salts are preferred because they have excellent thermal stability when the polyester is melted and generate less fish eyes.

Specific examples of the above metal salts include magnesium decanedicarboxylate, magnesium palmitate,
Manganese palmitate, zinc palmitate, magnesium stearate, zinc stearate, potassium oleate, sodium oleate, magnesium oleate,
Examples include zinc oleate, magnesium sebacate, and manganese sebacate. In particular, magnesium decane dicarboxylate has a high melting point of 275 ° C., and thus has good heat resistance and can maintain a high degree of polymerization of the polyester.

The vent-type twin-screw extruder used in the present invention (hereinafter simply referred to as an extruder) may have a screw rotating in a different direction or in the same direction. Ratio (L / D) of cylinder length (L) and cylinder inner diameter (diameter D)
Is usually from 20 to 60, preferably from 22 to 50. L
When / D exceeds 60, the residence time in the extruder increases, and the temperature of the polyester in the extruder is unavoidably increased, and the degree of polymerization of the polyester tends to decrease. Also,
When L / D is less than 20, melting of the polyester and degassing under a vent tend to be insufficient.

In the present invention, the polyester and the metal salt are supplied from the raw material inlet (9) of the extruder. The raw material polyester may be a dried polyester, but it is not necessary to use a dried polyester. Therefore, it is preferable to use an undried polyester. The use of undried polyester has the advantage that the drying step and the preceding crystallization step can be omitted. The metal salt is
You may mix | blend previously in polyester, and may add as a mixture of polyester and a metal salt.

The supply amount of the metal salt is 0.5 to 1,000 ppm, preferably 10 to 800 ppm, more preferably 15 to 500 ppm as the concentration of metal atoms in the polyester.
It must be in the ppm range. If the concentration of the metal atoms in the polyester is less than 0.5 ppm, the specific resistance of the polyester at the time of melting does not sufficiently decrease, and a large amount of bound bubbles are generated in the sheet obtained by the electrostatic adhesion method. When the concentration of metal atoms in the polyester exceeds 1,000 ppm, the polyester is decomposed by the action of the metal salt, and the intrinsic viscosity (IV) decreases.

That is, in the present invention, the kneading action and the degassing action of water in the extruder successively renew the polyester surface, thereby avoiding the local presence of metal salts and suppressing the polyester decomposition. If the concentration of metal atoms in the polyester exceeds 1,000 ppm,
The effect of preventing the decomposition of the polyester by the above action is not sufficiently exhibited.

The polyester and the metal salt supplied from the raw material charging port (9) are transferred toward the extrusion port (4) by the screw (3) in the heating cylinder (2). Then, diffusion degassing (hereinafter simply referred to as degassing) of water occurs from the surface of the polyester transferred from the reverse screw (8) to the vent hole (6), and the water is removed.
In order to efficiently perform such deaeration, the degree of pressure reduction in the vent hole (6) is usually 40 hectopascals or less, preferably 30 hectopascals or less.
It is less than hectopascal, more preferably less than 20 hectopascal.

By the way, when the screw rotation speed is increased for a certain amount of extrusion in the extruder, the polyester surface existing on the screw surface can be forcibly renewed, and accordingly, degassing from the molten polyester is correspondingly performed. Efficiency will increase. In other words, it can be said that the deaeration efficiency is better when the screw rotation speed is higher for a certain amount of extrusion. However, as a result of the study by the present inventor, it has been found that when the screw rotation speed is increased for a certain amount of extrusion, the IV holding ratio is improved or held, and then the IV holding ratio is lowered.

The above-mentioned phenomenon that the IV holding ratio is lowered is due to the accelerated deterioration of the resin by heating due to the rise in the resin temperature. Therefore, in the present invention, it is preferable that the extrusion amount of the polyester and the screw rotation speed are appropriately selected in order to secure the IV retention of polysyl.

That is, in the present invention, when the internal diameter (diameter) of the cylinder of the twin-screw extruder is D (mm), the extrusion rate Q (kg / hr.) Per unit time and the screw rotation speed N (rpm) Is the following formula (1), preferably the formula (I
I), and more preferably, melt extrusion is performed under conditions satisfying the formula (III).

[0026]

## EQU1 ## 5.2 × 10 ⁻⁶ × D ^2.8 ≦ Q / N ≦ 15.8 × 10 ⁻⁶ × D ^2.8 (I) 6.0 × 10 ⁻⁶ × D ^2.8 Q / N ≦ 15 0.0 × 10 ⁻⁶ × D ^2.8 … (II) 6.3 × 10 ⁻⁶ × D ^2.8 ≦ Q / N ≦ 14.7 × 10 ⁻⁶ × D ^2.8 (III)

Under the condition of 5.2 × 10 ⁻⁶ × D ^2.8 > Q / N, the number of revolutions is too high with respect to the extruded amount, so that excessive heat generation due to shearing of the screw results in deterioration of the IV retention, which is preferable. Absent. Also, Q / N> 15.8 × 10 ⁻⁶ ×
Under the condition of D ^2.8 , the rotational speed is too low with respect to the extruded amount, so that the degree of renewal of the molten resin surface under vacuum is reduced and sufficient degassing cannot be performed, and the IV retention rate is unfavorably deteriorated. .

In the present invention, the polyester melted by the extruder is extruded from an extrusion port (4) into a sheet on a rotary cooling drum through a metal opening and held tightly by an electrostatic adhesion method to form a substantially amorphous material. Sheets are used (note that the metal mouth, the rotary cooling drum and the peripheral equipment are not shown). At this time, in order to improve the thickness uniformity in the longitudinal direction of the sheet (the rotating direction of the rotary cooling drum), if necessary, a metering pump (a so-called gear pump) is arranged between the extruder and the die and introduced into the die. The flow rate of the molten polyester to be produced may be made uniform.

The electrode in the electrostatic contact method may be either a wire electrode or a blade electrode. The DC voltage applied to the electrodes is usually in the range of about 5 to 10 kV. In the present invention, an electrostatic adhesion method may be applied by forming a water film or the like on the surface of the rotary cooling drum.

The surface of the rotary cooling drum may be metal or nonmetal, but is preferably made of a conductor from the viewpoint of enhancing the adhesion due to static electricity. The surface temperature of the rotary cooling drum is usually 0 to 80C, preferably 10 to 70C, and more preferably 15 to 60C. When the surface temperature of the rotary cooling drum is lower than 0 ° C., the adhesiveness between the sheet end and the rotary cooling drum deteriorates, and the flatness of the obtained sheet deteriorates. On the other hand, when the surface temperature of the rotating cooling drum exceeds 80 ° C., the adhesion between the sheet and the rotating cooling drum is excessively increased, and it becomes difficult to separate the sheet. Although the surface speed of the rotary cooling drum is not particularly limited, it is 30 m / min. It is preferable that this is the case.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the examples and comparative examples, “%” simply means “% by weight”.

(1) Melt specific resistance: 12 g of polyester is put into a test tube with branches, immersed in an oil bath at 285 ° C. and completely melted, and the process of reducing pressure and replacing with nitrogen gas is repeated to completely remove bubbles. . Then, after inserting a stainless steel electrode into the molten polyester and holding for 10 minutes,
A DC voltage of 3 kV is applied, the current value immediately after the application is read, and the specific resistance is calculated according to the following equation. Where ρv is the specific resistance (Ωcm), I is the current value (A), and S is the cross-sectional area of the electrode (c
m ² ) and L is the distance (cm) between the electrodes.

Ρv = (3,000 / I) × (S / L) (Ωcm)

(2) Polyester IV (dl / g):
Incompatible with the polyester, 100 g of a mixed solvent of phenol / tetrachloroethane: 50/50 (weight ratio) is added to 1 g of the polyester from which other polymer components and particles are removed.
Then, the mixture was dissolved by adding ml, and measured at 30 ° C.

(3) Comprehensive evaluation: The polyester sheet after melt extrusion has an IV reduction rate of less than 10%, and the rotational cooling drum speed is 30 m / min. When the sheet quality was good without any defects due to the restrained bubbles under the conditions of less than ○, the speed of the rotating cooling drum was 30 m / min. Under the above conditions, if there is no defect due to bound bubbles and the sheet quality is good,
The case where the IV reduction rate was 10% or more, and there were restrained air bubbles in the sheet or stable electrostatic adhesion was not obtained, was evaluated as x.

Example 1 A polyester having a specific resistance of 200 × 10 ⁷ Ωcm and an IV of 0.640 was added to a polyester having an Mg atom concentration of 60 pp.
m, and melted in a vent-type twin-screw extruder having a cylinder diameter of 120 mm. Subsequently, the mixture was extruded into a sheet shape from a mouthpiece via a gear pump, and 30 mm was passed through a wire electrode having a diameter of 0.04 mm. The sheet was electrostatically brought into contact with the surface of a rotating cooling drum (made of metal) at a temperature of 200 ° C. to obtain a 230 μm thick sheet. The screw rotation speed of the twin screw extruder is 167 rpm, and the extrusion rate is 1,000.
kg / h, the voltage applied to the electrode was 5.0 kV, the current flowing through the electrode was 1.2 mA, and the surface speed of the cooling roll was 20 m.
/ Min. Met. The obtained sheet had a specific resistance at the time of melting of 5.7 × 10 ⁷ Ωcm and an IV of 0.627,
There were no defects such as restrained bubbles, and the thickness uniformity was good.

Example 2 An amorphous sheet was prepared in the same manner as in Example 1, except that manganese sebacate was used as the metal salt and the concentration in the polyester was 400 ppm. Obtained. The obtained sheet had a specific resistance of 7.0 × 10 ⁷ Ωcm when melted, an IV of 0.620 and good quality.

Example 3 In Example 1, when the Mg atom concentration in the polyester was 3
An amorphous sheet was obtained in the same manner as in Example 1 except that magnesium decane dicarboxylate was added so as to be 0 ppm. The current flowing through the electrode when a voltage of 5.0 kV was applied was 1.3 mA. The resulting sheet is
The specific resistance at the time of melting is 3.7 × 10 ⁷ Ωcm, and the IV is 0.6.
23, and the quality was good as in Example 1.

Example 4 In Example 1, the Mg atom concentration in the polyester was 1
An amorphous sheet was obtained in the same manner as in Example 1 except that magnesium decane dicarboxylate was added to 20 ppm. The current flowing through the electrode when a voltage of 7.0 kV was applied was 2.6 mA. The obtained sheet had a specific resistance of 2.4 × 10 ⁷ Ωcm and an IV of 0.619 when melted, and the quality was as good as in Example 1.

Examples 5 to 7 In Example 1, the speed of the rotary cooling drum was set to 3
0 m / min. , 70 m / min. , 80 m / min.
An amorphous sheet was obtained in the same manner as in Example 1, except for the following. Specific resistance and IV of the obtained sheet during melting
Are shown in Table 1. The sheet quality was as good as in Example 1 as shown in Table 2.

Comparative Example 1 An amorphous sheet was obtained in the same manner as in Example 1 except that no metal salt was added. The obtained sheet had a specific resistance of 168 × 1 when melted.
0 ⁷ Ωcm, IV was 0.629, and there were many crater-like quality defects due to restrained air bubbles, and the quality was rejected.

Comparative Example 2 In Example 1, the speed of the rotary cooling drum was increased to 70 m / min without adding a metal salt. Example 1 except for changing to
In the same manner as above, an amorphous sheet was obtained, but the sheet did not adhere to the rotating cooling drum due to insufficient electrostatic adhesion,
The melted polyester wrapped around the electrode, making it impossible to obtain an amorphous sheet. The specific resistance of the polyester melted in the electrode at the time of melting was 168 × 10 ⁷ Ωcm, and the IV was 0.629.

Comparative Example 3 An amorphous sheet was obtained in the same manner as in Example 1, except that a single screw extruder having a cylinder diameter of 200 mm was used. The obtained sheet has a specific resistance of 4.
It was 0 × 10 ⁷ (Ωcm), and the IV was significantly reduced to 0.495, so that it could not be put to practical use.

Comparative Example 4 An amorphous sheet was obtained in the same manner as in Example 1 except that magnesium decanedicarboxylate was added so that the Mg atom concentration in the polyester became 2,000 ppm. However, the melt viscosity was remarkably reduced, and an amorphous sheet could not be stably obtained.
Further, the specific resistance at the time of melting of the polyester which was extruded from the die was 0.5 × 10 ⁷ Ωcm, and the IV was 0.400.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

According to the present invention described above, a high-quality polyester sheet can be produced with high productivity by suppressing the decrease in the degree of polymerization of the polyester after melt extrusion to a minimum and reducing the specific resistance. You can do it.

[Brief description of the drawings]

FIG. 1 is an explanatory side view of an example of a vented twin-screw extruder used in the production method of the present invention.

[Description of Signs] 1: Vent type twin screw extruder 2: Heating cylinder 3: Screw 4: Extrusion port 6: Vent hole 9: Raw material input port 8: Reverse screw M: Screw driving device

Claims (4)

[Claims] 1. A method for producing a polyester sheet in which a molten polyester sheet extruded from an extruder onto a rotary cooling drum is brought into close contact with the surface of the rotary cooling drum by an electrostatic adhesion method. Machine, the specific resistance at the time of melting as raw material polyester is 1
A polyester having a density of 10 ⁷ Ωcm or more is used, and the concentration of metal atoms in the polyester together with the polyester is 0.
A method for producing a polyester sheet, comprising supplying an extruder with a metal salt of an aliphatic monocarboxylic acid or dicarboxylic acid in an amount of 5 to 1,000 ppm. 2. The method according to claim 1, wherein magnesium decane dicarboxylate is used as the metal salt. 3. When the inside diameter (diameter) of a cylinder of a vented twin-screw extruder is D (mm), the extrusion rate Q (kg / hr.) Per unit time and the screw rotation speed N (rpm) are set.
3. The production method according to claim 1, wherein the melt extrusion is performed under conditions satisfying the following expression (1). ## EQU1 ## 5.2 × 10 ⁻⁶ × D ^2.8 ≦ Q / N ≦ 15.8 × 10 ⁻⁶ × D ^2.8 (I) 4. The rotating cooling drum has a surface speed of 40 m / m.
in. The manufacturing method according to any one of claims 1 to 3, which is as described above.