JPH0316715A - Casting method of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To cast stable at a high speed and efficiently a thermoplastic resin molten sheet, by constituting the title method so that a thickness of a liquid film of water on the central part of the sheet is specified and the liquid film of water is not applied to both end parts of a widthwise direction of the sheet. CONSTITUTION:The title casting method is constituted so that at the time when a molten body is stuck close to a cooling drum by making use of static electric force, a thickness of a liquid film of water on the central part of a sheet is set to 0.1-3.0mum and the liquid film of water is not applied to both end parts of a widthwise direction of the sheet. Further, in the case where turning-up of at least 1mm is generated on an end part of the sheet when the sheet becomes thick even if a specific water film is applied to the sheet, it is preferable that both side end parts of a nondrum of the sheet are cooled at the same time. When this construction, a film where it is superior in plane properties as a cast sheet and there is no problem whatever even if it is used as an unsaturated sheet is obtained and in the case where stretching is performed after casting, the sheet is free from meandering and stable film making becomes possible.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for casting thermoplastic resin sheets (including films), and more specifically, to a method for casting thermoplastic resin sheets stably, at high speed, and at high speed. It is about efficient casting methods.

[Conventional technology]

A method of casting a thermoplastic resin sheet with water interposed on the surface of a cooling drum is known from Japanese Patent Laid-Open No. 58-63415.

Furthermore, a method of casting 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.

[Problem to be solved by the invention]

However, the above method has the following problems.

■ With the method of casting in close contact with the surface of the cooling drum while applying an electrostatic charge, it becomes difficult to cast at high speeds due to the entrainment of air, and stable and uniform casting without surface defects is not possible. Highly efficient cast cannot be obtained.

◎ In order to solve the above problem, there is a method of casting water on the surface of the cooling drum, but this method also has the following problems.

■ If a film of water is simply formed uniformly, the cast sheet will have poor flatness, and it will not be possible to form a stable film not only when used as an unstretched sheet, but also when stretching after casting. do not have.

(2) Also, the thickness unevenness becomes worse in both the longitudinal direction and the width direction.

Furthermore, during close-contact casting, both ends of the sheet (hereinafter also referred to as edge parts) curl up on the cooling drum, and end cracks may occur due to poor cooling.

An object of the present invention is to solve the above problems and provide a method for stably casting a molten thermoplastic resin sheet at high speed and efficiency.

[Means to solve the problem]

That is, the present invention provides a thermoplastic resin sheet casting method in which the thermoplastic resin sheet is tightly solidified on the surface of a cooling drum with a water film interposed therebetween while applying an electrostatic charge to the molten thermoplastic resin sheet. Water film thickness is 0
．． The present invention relates to a method for casting a thermoplastic resin sheet having a thickness of 1 to 3.0 μm and characterized in that a liquid film of water is not applied to both ends in the width direction of the sheet.

The cooling drum of the present invention refers to a drum-shaped rotating body.
It may be movable such as a belt. This surface may be finished with a well-known mirror chrome plating, or may be roughened by etching or sandblasting if necessary, or may be coated with a hydrophilic agent, but it is stable. A mirror finish is preferable in terms of castability, reproducibility, and oral stability, and a surface roughness Rt of 0.4 μm or less is preferable in terms of thin film coating with water.
More preferably, Rt is 0.2 μm or less.

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 1.4 cyclohexanedimethanol, poly-P-ethyleneoxybenzoate, polyarylates, polycarbonates, etc. and their Polyesters having ester bonds in the main chain as represented by copolymers, as well as nylon 6, nylon 66, nylon 6101, nylon 12, and nylon 11.
Polyamides with amide bonds in the main chain, such as polyamides, polyethylene, polypropylene, ethylene-vinyl acetate copolymers, polymethylpentene, polybutene, etc.
Polyolefins consisting mainly of hydrocarbons, such as polyisoptylene and polystyrene, polyether sulfone (PES), polyphenylene oxide (PPO), polyether ether ketone (PEEK), polyethylene, lene oxide, and polypropylene oxide. , polyethers such as polyoxymethylene, halogenated polymers such as polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polychlorotrifluoroethylene, polyphenylene sulfide (PPS), and polysulfon. and their copolymers and modified products.

In the case of the present invention, particularly preferred thermoplastic polymers are polyesters, polyamides, polyethers, polyphenylene sulfide, etc., and polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyphenylene sulfide are particularly preferred. In particular, the effects of the present invention are remarkable and are even more preferable. 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 electrostatic charge application method of the present invention is described in Japanese Patent Publication No. 37-6142, for example.
, Japanese Patent Publication No. 48-29311, etc., is a method in which a high DC or AC voltage is applied to the melt, a cap or a drum, and the melt is brought into close contact with the cooling drum using electrostatic force.

The thickness of the water film in the center of the sheet of the present invention (hereinafter referred to as water film thickness) needs to be 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm.

If the thickness is less than 0.1 μm, surface defects (irregularities) or thickness unevenness will occur on the sheet due to uneven air entrainment, and the adhesion will be too strong and the sheet will tear when the sheet is peeled off from the cooling drum. In addition, if the water film thickness exceeds 3.0 μm, the flatness of the sheet will be extremely poor, and surface defects (irregularities) will occur.
enters.

Furthermore, it is necessary that this liquid film of water not be applied to both ends of the sheet in the width direction. Here, the edge of the sheet to which the water film is not applied is defined as the width from the sheet edge to the center of the sheet where the water film is not applied, where a is 10 to 10.
It is necessary that it is 0 mm, preferably 15 to 75 mm. If a is less than 10 mm, the film will not roll up at the edges and its flatness will be poor, making it unusable. Also, a is 10
If Qmm is exceeded, surface defects (unevenness) will occur due to air entrapment.
, or it becomes difficult to cast stably and uniformly.

Furthermore, even if the specific water film coating mentioned above is applied, if the sheet becomes thick, the edge of the sheet may curl up by approximately 1 mm or more, and in this case, the edge of the sheet on the non-drum side may be cooled at the same time. It is preferable to do so. If it is not cooled, the flatness of the edges will deteriorate, and in severe cases, crystallization will occur and the sheet will crack at the edges.

This cooling method may be any method, such as a method in which nozzles are arranged in the flow direction of the sheet, a method in which a seepage roll is arranged in a row, or a method in which a nonwoven fabric is impregnated with water.

In order to prevent flatness from deteriorating and edge cracking, this cooling should be done in such a way that a continuous film of water is formed on the non-drum side edge of the sheet until the edge of the sheet reaches Tg+20°C or below. preferred.

In addition, this cooling area cools the sheet side at least 10 mm from the sheet edge in the sheet width direction, and at least 5 mm or more from the sheet edge at the part perpendicular to the drum and the drum surface where there is no sheet outside the sheet edge. Cooling is better from the viewpoint of preventing deterioration of flatness and edge cracking.

A method of forming a water film according to the present invention is a method in which humid air is blown onto the surface of a cooling drum kept at a temperature below its dew point to cause dew condensation. (condensation method), a method of spraying electrostatically charged water vapor, a method of seeping out with a roller, or a method of transfer coating.

The water film may be formed in the form of a continuous water film, condensation, or dots such as water vapor at the time of application, or may be formed in the form of a film when the sheet touches the ground.

The method of applying the water film is not particularly limited, and the areas where water is not applied at the edges may be coated once and then completely removed before the molten polymer comes into contact with the ground, or may not be coated from the beginning. There is no problem.

In addition, this water film is caused by water remaining on the surface of the cooling drum after the sheet formed on the drum is peeled off from the surface of the cooling drum, which often creates uneven thickness of the water film in both the width and length directions. After peeling, it is best to completely remove the water film using an air blower vacuum method, a suction roll, etc. before a new water film is formed.

In this way, a water-coated cast with good flatness and practical use can be obtained.

Of course, it is clear that heat treatment, uniaxial stretching, or biaxial stretching may be performed after this, if necessary.

〔Effect of the invention〕

By having a specific water film thickness and a specific distribution of the water film thickness in the width direction, that is, by not applying water to a specific range of the end portions, the following excellent effects were produced.

(1) A cast sheet with excellent flatness can be obtained,
Even when used as an unstretched sheet, a film without any problems can be obtained, and even when stretching is performed after casting, stable film formation is possible without meandering of the sheet.

■ It also has excellent quality, with good thickness unevenness in both the longitudinal and width directions.

(3) Furthermore, there is no curling up of both ends (edge parts) of the sheet, the flatness of the edge parts is good, and there is no occurrence of end cracking due to poor cooling.

(4) 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 to a length of 3 m, attach one end to a flat shaft, and place it on a free-rotating roll with good cylindricity (flatness) at an interval of 2.5 m. After aligning the sheet, set the sheet so that a load of 50 g/mm2 is applied uniformly to the edge of the sheet across the entire width. 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,
Sheets with poor flatness are located further away from this thread,
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) ○: Seat to thread distance is less than 2 mm Δ: Seat to thread distance is 2 mm or more and less than 10 mm ×: Seat to thread distance is 10 mm or more and seat to If the thread spacing is less than 2mm, there is no problem at all, so ○
Indicated with a mark. If it 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.

It is recognized that the flatness is poor if the thickness is 2 mm or more and less than 10 mm, but it can be used depending on the usage, and is indicated by a Δ symbol.

(2) Cracking of long-term cast stability sheet. It is expressed as the time until sheet meandering (with respect to the cooling drum) occurs.

If there was no problem for more than 8 hours, long-term casting stability was indicated by a circle, and if it was less than 8 hours, there was no stability, which was indicated by an x.

(3) High-speed castability If the cast sheet has no defects or troubles in castability and can achieve a casting speed of 80 m/min or more, it is considered to have good high-speed castability and is marked with an 80m/min or higher.
If it was less than m/min, it was considered defective and indicated by an x mark.

(4) Edge curling This is expressed as the amount of curling up of the sheet edge during casting. No lifting at all is marked with ◎, 1 mm or less is marked with ○, 5 mm or more is marked with ×, and the middle is marked with Δ. It was shown in

The measurement point is 1 point from the position where the sheet peels off from the cooling drum.
The location was set close to the 00mm cast position.

(5) Water film thickness Using an infrared trace moisture meter rM-300J manufactured by Chino ■, a calibration curve of the moisture meter output and water film thickness was determined in advance and determined from this.

(6) Cooling body surface roughness cutoff 0 according to JIS-BO601-1976
．． The maximum roughness Rt is measured at 25 mm.

〔Example〕

The present invention will be explained below based on examples.

Examples 1 to 6, Comparative Examples 1 to 4 Polyethylene terephthalate (IV
= 0.60), vacuum-dried at 180°C, fed to an extruder, melted at 290°C, then discharged the sheet from a T-die, and applied an electrostatic charge to the entire width of the sheet to improve surface roughness. Casting was performed on a cooling drum of RtO and 2 μm under the casting conditions shown in Table 1, with a sheet thickness of 40 μm, and casting speeds of 30.70 m/min and 100 m/min, respectively, for 24 hr of continuous operation.

The water film applicator used a dew condensation method, and the water film thickness was controlled by the amount of humid air supplied. After the water was once applied to the entire width of the drum, the water removal width was changed as shown in Table 1, and the water was completely removed using a mass roll.

In addition, after the sheet was peeled off from the cooling drum, a mass roll (manufactured by Masuda Seisakusho) with a hardness of 50 was attached to the water application area in the center, and the load was 0.7 kg.
g/cm, and excess water was removed with a suction pump of 5001/min-m2.

In Example 6, a width of 50 m is provided at the end of the sheet on the non-drum surface side.
Three mass rolls with a diameter of 50 mm and a diameter of 50 mm were attached in the sheet flow direction, water was allowed to seep out from the rolls, and the flow rate of the water was adjusted so as not to break the water film for cooling. The sheet cooling width at this time is 40 mm. : I installed the mass roll so that it would be.

As is clear from this result, by specifying the water film application range in the width direction with a specific amount of water film thickness, it is possible to achieve high efficiency with excellent flatness, less edge curling, and long-term casting stability. It turns out that it is possible to cast at high speed.

Claims (2)

[Claims] (1) In a method for casting a thermoplastic resin sheet, in which a static charge is applied to a molten thermoplastic resin sheet, the sheet is solidified in close contact with the surface of a cooling drum with a liquid film of water interposed therebetween. Film thickness is 0.1~3.0μ
1. A method for casting a thermoplastic resin sheet, characterized in that a liquid film of water is not applied to both ends of the sheet in the width direction. (2) The method for casting a thermoplastic resin sheet according to claim 1, characterized in that the non-drum surface side of both ends in the width direction of the molten thermoplastic resin sheet is cooled at the same time.