JPH0316714A - Casting method of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To cast stably at a high speed and efficiently a thermoplastic resin sheet, by a method wherein a thickness of a liquid film of water on the central part of a sheet is specified and the same on both end parts of a widthwise direction of the sheet is made thicker than the same on the central of the sheet. CONSTITUTION: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 0.1-30mum. Further, the liquid film of water is made thicker at both end parts of a widthwise direction of the sheet than at the central part and an end part of a nondrum surface side of the sheet is cooled at the same time. With this construction, a cast sheet superior in plane properties is obtained, there is no problem whatever even if the same is used as an unstreached sheet and even 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, 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]

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 has poor flatness and cannot be used because it cannot be used as a stable film not only when used as an unstretched sheet but also when stretched after casting. .

■Also, in the longitudinal direction. Thickness unevenness becomes worse in both 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 thermoplastic molten resin sheet at high speed and with high 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, in which the thickness of the water film at both ends in the sheet width direction is thicker than at the center.

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 a well-known mirror chrome plated surface, a surface roughened by means such as etching or sandblasting if necessary, or a surface coated with a hydrophilic agent. A mirror finish is preferable from the viewpoint of stability, reproducibility, and oral stability, and a surface roughness Rt of 0.4 μm or less is preferable from the viewpoint of thin film application 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-hexahide/xylylene terephthalate, polymers from 1.4 cyclohexanedimethanol, polyP-ethyleneoxybenzoate, polyarylates, polycarbonates, etc. Polyesters having an ester bond in the main chain as represented by their copolymers, as well as nylon 6, nylon 66, nylon 6101, nylon 12, and nylon 11
Polyamides having an amide bond in the main chain, such as polyethylene, polypropylene, ethylene vinyl acetate copolymer, polymethylpentene, polybutene, etc.
Polyolefins consisting mainly of hydrocarbons, such as polyisobutylene and polystyrene, polyether sulfone (PES), polyphenylene oxide (PPO), polyether ether ketone (PEEK), polyethylene oxide, and polypropylene. oxide, polyethers represented by polyoxymethylene, halogenated polymers represented by polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polychlorotrifluoroethylene, etc., and polyphenylene sulfide (PPS), These include polysulfone and their copolymers and modified products.

In the case of the present invention, particularly preferred thermoplastic polymers include polyesters, polyamides, polyethers, polyphenylene sulfide, etc., and polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyphenylene sulfide. The effect of the present invention is particularly remarkable and is 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 at the center of the sheet of the present invention (hereinafter referred to as water film thickness) must 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, the water film thickness needs to be thicker at both ends in the sheet width direction than at the center, and the thickness ratio of the ends/center is 1.1 to 1.
30 is better. If the water film thickness at the edges is the same as or less than the water film thickness at the center, the sheet will have poor flatness and cannot be used.

Here, the sheet edge where the water film thickness is increased is 200 mm or less from the sheet edge toward the sheet center, preferably <15 mm.
It is preferable to set it to 0 mm or less. If the thickness exceeds 200 mm, the flatness will worsen. Further, it is preferable that the width of the sheet end portion where the water film thickness is increased is at least 30 m or more from the sheet end toward the center of the sheet. If the thickness is less than 30 mm, no improvement in flatness is observed.

Furthermore, the area where there is no sheet outside the sheet edge is also 5mm.
It is preferable to apply the same water film thickness over the above width from the viewpoint of maintaining flatness and preventing rolling up.

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 range cools the sheet side 10 mm or more from the sheet edge in the sheet width direction, and cools the drum surface that is perpendicular to the drum or outside the sheet edge without sheets at least 5 mm or more from the sheet edge. It is better to do this from the viewpoint of preventing deterioration of flatness and preventing edge cracking.

Methods for forming the water film of the present invention include a method in which humid air is sprayed onto the surface of a cooling drum kept at a temperature below its dew point to form dew (dew condensation method), and a method in which electrostatically charged water vapor is sprayed. There are methods such as bleed-out with a roller, or transfer coating.

The shape of the water film may be a continuous water film, condensation, or dots like water vapor at the time of application, or it may be in the form of a film when the sheet touches the ground. The method of coating the center and end portions is not particularly limited, and may be the same method, different methods, or may be applied in one step or in multiple steps. It is sufficient that the above-mentioned specific water film is formed when the molten polymer contacts the cooling drum.

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 setting the water film thickness in the width direction to a specific distribution with a specific water film thickness, the following excellent effects are produced.

(1) A cast sheet with excellent flatness can be obtained,
Even when used as an unstretched sheet, a sheet without any 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 direction and the width direction.

(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 cast at high speed, with no quality problems, with high efficiency, and with stability over a long period of time.

〔Evaluation methods〕

{1} Sample the entire width of the flat cast sheet to a length of 3 m, attach one end to a flat shaft, and measure the cylindricity (
The sheet is passed over a freely rotating roll with good flatness, and then set so that a load of 50 g/mm2 is applied uniformly to the edge of the sheet over 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, 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 (evaluated at the farthest part) O: Seat to thread distance is less than 2 mm △: Seat to thread distance is 2 mm or more and less than 10 mm ×: Seat to thread distance is 10 mm or more 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 A cast sheet that has no defects or troubles in castability, and that can achieve a casting speed of 80 m/min or more is considered to have good high-speed castability and is marked with an 8.
If it was less than 0 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 indicated by ◎, 1 mm or less is indicated by ○, 5 mm or more is indicated by ×, and the middle is Δ. Indicated with a mark.

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 needle rM-300J manufactured by Chino ■, a calibration curve of moisture meter output and water film thickness was determined in advance and calculated from this.

e) Cooling body surface roughness cutoff 0 according to JIS-BO601-1976
．． Maximum set length Rt measured at 25 mm.

(7) Edge water application position The range in which the water film thickness differs from the center of the sheet is indicated by - (negative) in the direction toward the center in the sheet width direction, with the sheet edge as the reference point, and the outside area where there is no sheet. is indicated by + (positive).

〔Example〕

The present invention will be explained below based on examples.

Examples 1 to 4, Comparative Examples 1 to 4 Polyethylene terephthalate (IV
= 0.65), vacuum-dried at 180°C, supplied 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 the surface roughness. A sheet with a thickness of 50 μm was cast on a cooling drum with an Rt of 0.2 μm under the casting conditions shown in Table 1. Casting was performed under various casting speed conditions of 30.70 m/min and 100 m/min, respectively, and continuous operation for 24 hr.

The water film coating equipment used a dew condensation method, and the water film thickness was controlled by the amount of humid air supplied. Separate dew condensation devices were used for the center and ends. For all water-coated sheets, after the sheet was peeled off from the cooling drum and before the next coating, a mass roll with a hardness of 50 (■Masuda Seisakusho Co., Ltd.) was attached, a load of 0.7 kg/cm was applied, and 500 1 was applied. /min
Excess water was removed with @m2 suction pump.

In Example 3, 15 nozzles with a slit of 0.2 mm and a width of 30 mm were arranged in the sheet flow direction at the end of the sheet on the non-drum surface side, and the flow rate of water was adjusted so as not to break the water film for cooling. .

As is clear from this result, by specifying the water film thickness distribution 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
m, and a method for casting a thermoplastic resin sheet, characterized in that the thickness of the water film at both ends in the width direction of the sheet is thicker than at the center. (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.