JPH03219928A - Casting method of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To cast a thermoplastic resin sheet which is superior in plane properties, free from surface defect and stable and has little thickness irregularity, by making the diameter of a cooling drum into a specific one or larger. CONSTITUTION:It is necessary that the diameter of a cooling drum is 2.0m or larger, preferably 2.3m or larger, far preferably 2.5m or larger, further prefer ably 3.0m or larger. When the diameter for the drum is less than 2.0m, gripping of air at a high speed is generated and plane properties and thickness irregular ity become worse. The surface of the cooling drum may be the surface where publicly known mirror electroplated chrome finish is performed or the surface roughened with a device such as etching or sand blasting or further the surface to which an agent giving hydrophilic nature is applied. However, mirror finish is preferable from a view point of stabilized casting properties or reproducibility or stability in a change with a passage of time and the title resin sheet becomes a matter where thickness irregularity is favorable in both longitudinal and widthwise directions and superior in a quality also.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for casting thermoplastic resin sheets (including films, the same applies to the sheets described below). The present invention relates to a stable, high-speed, and highly efficient casting method for resin sheets.

[Conventional technology]

As a method of stably and rapidly casting a thermoplastic resin sheet, a method of casting the sheet in close contact with the surface of a cooling drum while applying an electrostatic charge is known, such as in Japanese Patent Publication No. 37-6142.

Furthermore, as a high-speed and highly efficient casting method, there are known Japanese Patent Application Laid-Open No. 58-63415, in which a thermoplastic resin sheet is cast by interposing water on the surface of a cooling drum, and Japanese Patent Publication No. 61-38133, which is an air chamber method.

In addition, in the conventional casting method of thermoplastic resin sheet,
In either method, the diameter of the cooling drum was approximately 1.5 m at most.

[Problem to be solved by the invention]

However, the above method has the following problems.

l) In the method of casting in close contact with the cooling drum surface while applying an electrostatic charge, stable and uniform casting without surface defects is not possible due to air being trapped during high speed casting.

2) In order to solve the above-mentioned problem 1), the method of interposing water on the surface of the cooling drum and casting it deteriorates the flatness, and as a result, the thickness unevenness also worsens.

3) In addition, in the air chamber method, if a small-diameter cooling drum is used, the higher the speed of casting, the worse the sealing performance becomes, and the stability and reproducibility of the cast deteriorates, resulting in problems such as worsening of thickness unevenness. has.

4) Furthermore, in any of the methods, with a small-diameter cooling drum, as the speed increases, there are problems such as uneven rotation of the drum and centrifugal force that cause air to become trapped and uneven thickness.

The present invention solves the problems of the above conventional casting method,
The purpose of the present invention is to provide a method for casting a stable thermoplastic resin sheet that can be cast at a high speed of 8 Qm/min or more, has excellent flatness, has little thickness unevenness, and has no surface defects.

[Means to solve the problem]

In order to achieve the above object, the present invention has the following configuration, namely, a method of casting a thermoplastic resin molten sheet onto a cooling drum, in which the diameter of the cooling drum is 2.0 m.
The present invention relates to a method for casting a thermoplastic resin sheet characterized by the above.

The thermoplastic resin referred to in the present invention is a resin that exhibits plasticity when heated, and representative resins (polymers) include polyethylene terephthalate, polyethylene naphthalate,
Polybutylene terephthalate, polyethylene α,β-dicarboxylate, polymers from P-hexahydro-xylylene terephthalate, polymers from l,4-cyclohexane dimetatool, polyP-ethyleneoxybenzoate, polyarylates, polycarbonates, etc. Polyesters having an ester bond in the main chain as represented by the copolymers of
Mainly only hydrocarbons, such as polyamides with amide bonds in the main chain, polyethylene, polypropylene, ethylene-vinyl acetate copolymers, polymethylpentene, polybutene, polyisobutylene, polystyrene, etc. polyolefins consisting of polyethersulfone (PES), polyphenylene oxide (PPO), polyetheretherketone (PEEK), polyethers represented by polyethylene oxide, polypropylene oxide, polyoxymethylene, etc., polyvinyl chloride , halogenated polymers represented by polyvinylidene chloride, polyvinylidene fluoride, polychlorotrifluoroethylene, etc., polyphenylene sulfide (PPS), polysulfone, and copolymers and modified products thereof.

In the case of the present invention, thermoplastic resins include polyesters, polyamides, polyethers, polyphenylene sulfide, etc., and polyesters such as polyethylene terephthalate and polyethylene naphthalate and polyphenylene sulfide are particularly effective in the present invention. Remarkable and desirable. Of course, the above polymer may contain known additives such as stabilizers, viscosity modifiers, antioxidants, fillers, slip agents, antistatic agents, antiblocking agents, release agents, mold release agents, and the like.

The cooling drum of the present invention refers to a drum-shaped rotating body. This cooling drum needs to have a drum diameter of 2.0 m or more, preferably 2.3 m or more, more preferably 2.5 m or more, and still more preferably 3.0 m or more. If the drum diameter is less than 2° Om, air will be trapped at high speeds, resulting in poor flatness and uneven thickness.

Further, even if the cast state appears to be problem-free, problems arise such as differences in surface conditions between the cooled drum surface and the non-cooled drum surface (phenomena such as protrusion between drum surfaces and non-drum surface).

For this purpose, the surface of this cooling drum may be finished with a known mirror chrome plating, or may be roughened by means such as etching or sandblasting if necessary, or may be coated with a hydrophilic agent. However, mirror finish is preferable from the viewpoint of stable castability, reproducibility, and stability over time, and surface roughness R is preferable to obtain a smooth sheet.
It is more preferable that t is 0°4 μm or less, and even more preferably that Rt is 0.2 μm or less.

Furthermore, in addition to the above-mentioned cooling drum, the angle between the final flow passage inside the nozzle and the sheet before landing on the cooling drum after being discharged from the nozzle is 140° to 180°, preferably 150 to 17°.
When the angle is set to 0°, the effect of the present invention becomes even more remarkable, which is preferable. If it is less than 140°, minute air is likely to be trapped, resulting in worsening of thickness unevenness. If the angle exceeds 180°, the same problem will occur, and the lower surface of the lip of the mouthpiece will become dirty, resulting in worsening of uneven thickness.

The method of casting while applying an electrostatic charge according to the present invention is as follows:
For example, Special Publication No. 37-6142, Special Publication No. 48-29311
As shown in
This is a method in which the molten material is brought into close contact with the cooling drum using electrostatic force applied to a cap or drum, etc., and when used in combination with the method of the present invention, it can achieve even better results such as increased speed, flatness, and improved thickness unevenness. You can get something.

In addition, an air chamber method (depressurization or pressurization) is the method shown in Japanese Patent Publication No. 62-38133, in which the chamber is attached to the opposite side of the sheet to be cast when depressurizing, and the sheet is placed on the opposite side when pressurizing. By attaching it to the side, you can achieve even better results such as faster speed, flatness, and improved thickness unevenness.

Further, at this time, if the electrostatic charge described above is applied, a sheet with excellent flatness and improved thickness can be obtained at a higher speed.

Further, by combining a casting method in which a water film of 0.1 to 2.0 μm is formed between the cooling drum and the sheet, it becomes possible to further increase the speed without sheet defects. The water film may be formed by any method such as a roll coater method or a method in which humid air is condensed on a cooling drum, but the latter method is particularly preferred. At this time, after the sheet leaves the cooling drum, it is important to completely remove water from the area where the water film has formed.

The cast sheet thus obtained can be used as an unstretched sheet, and it is obvious that it may be subsequently subjected to heat treatment, uniaxial stretching, or biaxial stretching, if necessary.

〔Effect of the invention〕

By using a casting method to increase the diameter of the cooling drum, the following excellent effects were achieved.

(1) A cast sheet with excellent flatness can be obtained,
Even when used as an unstretched sheet, a film with no problems can be obtained, and even when stretching is performed after casting, stable film formation is possible without meandering of the sheet.

(2) It also has excellent quality with good thickness unevenness in both the longitudinal and width directions.

(3) With these improvements, it becomes possible to perform high-speed, high-efficiency, stable casting over a long period of time without any problems in terms of quality.

〔Evaluation methods〕

(1) Sample the entire width of a flat cast sheet by 3 m, attach one end to a flat shaft, place it on a flat, freely rotating roll at an interval of 2.5 m, and place the sheet along this roll. The sheet is set so that a load of 50 g/mm2 is applied uniformly across the entire width at the edge. A thread is stretched horizontally over the entire width of the sheet at the center in the longitudinal direction, that is, at a position of 1°25 m.

This thread is set so that it contacts at least one location on the sheet. At this time, the sheet with poor flatness was located at a distance from this thread, and this distance was read and indicated using the following evaluation criteria.

If there is no problem with flatness, the entire width will be in contact with this thread.

Evaluation criteria (evaluation at the farthest part) ○: The distance between the sheetel yarns is less than 2 mm △: The distance between the sheetel yarns is 2 mm or more and less than 10 mm
Indicated with a mark. If the thickness is 10 mm or more, it cannot be used as an unstretched sheet, and cannot be used for stretching due to wrinkles, etc., and is indicated by an X mark.

Although it is recognized that the flatness is poor when the thickness is 2 mm or more and less than 10 mm, it can be used depending on the usage, and is indicated by a △ mark.

(2) Long-term cast stability is expressed as the time until sheet cracking, sheet slippage (with cooling drum), meandering, etc. occur. If there was no problem for more than 24 hours, long-term cast stability was indicated by a circle, and if it was less than 24 hours, stability was not indicated by an X.

(3) High-speed castability There are drawbacks such as air being trapped in the cast sheet.

The maximum speed is shown at which there are no problems with castability.

(4) Thickness unevenness The cast sheet was cut into 5 cm wide pieces and measured using an electronic micro thickness meter. In the width direction, 50 mm of the sheet edge was cut, and in the longitudinal direction, a length of 20 m was taken from the center in the width direction.

Longitudinal thickness unevenness tMo (%) However, the maximum thickness t MAX Minimum thickness t MIN Average thickness tx Width direction thickness unevenness tlo (%) I met.

(5) Regarding the cooling body surface roughness (μm) (μm) (μm), cut-off 0 is also determined according to J I 5-BO601-1976.
．． This is the maximum roughness Rt measured at 25 mm.

(6) A straight line between the final flow path inside the nozzle and the sheet after discharge from the nozzle, connecting the point where the molten sheet leaves the final flow path inside the square nozzle and the point where the sheet contacts the cooling drum, and the final flow inside the nozzle. This is the angle formed with the road on the non-drum surface side.

〔Example〕

The present invention will be explained below based on examples.

Examples 1-3. Comparative Examples 1-2 Polyethylene terephthalate (IV
= 0.60), vacuum-dried at 180°C, fed to an extruder, melted at 290°C, then discharged from a T-die, and placed in a cooling drum shown in Table 1 with a sheet thickness of 1.
The discharge rate of the extruder was adjusted so that the thickness was 0.00 μm, and casting was performed. The angle formed between the final flow path inside the nozzle and the sheet after discharge was 130°.

The results are shown in Table 1.

As is clear from this result, by using a cooling drum with a specific diameter, high-speed casting is possible, excellent flatness,
It can be seen that there is little thickness unevenness and stable casting is possible for a long period of time.

Examples 4 to 7 A cooling drum having a diameter of 2.6 m was used as in Example 1, and in Example 4, an electrostatic charge was applied (by a wire from the non-cooling drum surface side), and in Example 5, a 38133
In Example 6, the same chamber as in Example 4 was used, and the angle between the final flow path inside the nozzle and the sheet after discharge was 160°. Further, in Example 7, the diameter of the cooling drum was 3.2 m, similar to Example 4.

As is clear from this result, when conditions such as a large-diameter cooling drum of 2.0 m or more, application of static charge, and the angle between the final flow path inside the air chamber mouthpiece and the sheet after discharge are combined, flatness and thickness unevenness can be improved. It can be seen that it has excellent castability, no surface defects, and stable castability at high speed and over a long period of time.

Claims (5)

[Claims] (1) A method for casting a molten thermoplastic resin sheet onto a cooling drum, characterized in that the diameter of the cooling drum is 2.0 m or more. (2) The method for casting a thermoplastic resin sheet according to claim 1, wherein the thermoplastic resin sheet is cast onto a cooling drum while applying an electrostatic charge to the molten thermoplastic resin sheet. (3) Further, a water film having a thickness of 0.1 to 2.0 μm is cast on the cooling drum while being formed between the cooling drum and the sheet.
The method for casting a thermoplastic resin sheet as described in Section 1. (4) The heat according to any one of claims 1 to 3, characterized in that an air chamber (pressurized or reduced pressure) is used when casting the molten thermoplastic resin sheet onto a cooling drum. Casting method for plastic resin sheets. (5) The angle between the final flow path inside the nozzle that is discharged in the form of a sheet and the sheet before landing on the cooling drum after being discharged from the nozzle is 140
Claim 1 characterized in that the angle is 180°.
A method for casting a thermoplastic resin sheet according to any one of items 1 to 4.