JPH11156922A - Cast method for thermoplastic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent induction of a sheet surface defect, a thickness irregularity, and a width fluctuation even when a thickness of the sheet is thick by a method wherein when a thermoplastic resin molten sheet is stuck close to a transfer cooling medium by impressing an electrostatic charge thereto, costing is executed by making a water liquid film lie only at both end parts of the thermoplastic resin sheet. SOLUTION: In a cast method wherein a thermoplastic resin molten sheet is cooled by sticking that close to a transfer cooling medium by impressing electrostatic charge thereto, intensive adhesion to the transfer cooling medium is obtained over the whole of a sheet width by improving adhesion at an end part by making a water liquid film lie practically only at both end parts of the thermoplastic resin sheet. A thickness of the water liquid film formed at the sheet end part is further preferably 0.03 to 0.2 μm. Formation of the water liquid film can be executed by applying a water film and a water drop. As a method wherein such the water film and the water drop are applied, a comparatively simple roller coating method is preferable. It is important that a surface roughness of the transfer cooling medium is 0.2 μm or under and smooth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for high-speed casting of a thermoplastic resin sheet.

[0002]

2. Description of the Related Art As a method of casting a thermoplastic resin sheet, a method of applying an electrostatic charge to only a central portion of the melt sheet to improve the adhesion to a cooling medium (for example, Japanese Patent Publication No. 37-6142). , Tokiko Sho 48-
29311).

[0003]

In the casting method for applying an electrostatic charge as described above, the application electrodes are arranged in parallel with the width direction of the melt sheet, but the application width is smaller than the width of the sheet. It can only be installed and applied to only. This is because when an electrode wider than the sheet width is used, an electric discharge occurs between the electrode and the cooling medium, so that no improvement in the adhesive strength of the melt is recognized.

As described above, if the applied width is made smaller than the sheet width, a strong adhesive force is obtained at the center of the sheet due to the electrostatic charge, but the adhesive force with the cooling medium is weak at the end of the sheet. During the cooling process, the thermoplastic resin crystallized and turned up (curled) at the edges, which caused unevenness in drawing and tearing in the subsequent drawing step. Of course, with such a casting method, it was impossible to cast at high speed.

For this purpose, there has been proposed a casting method in which a liquid film of water is interposed over the entire width of the sheet to improve the adhesion not only at the end but also at the center of the sheet. No. 63415). However, in this method, although the moving sheet surely adheres to the cooling medium uniformly in the entire sheet width direction, since the entire melt sheet film is on the water film, the slip resistance, which is a shearing force, is small. In particular, when the sheet thickness is large, the entire sheet moves relatively freely up and down, left and right on the moving cooling medium due to gravity, volume shrinkage, etc., which causes sheet surface defects, thickness unevenness, and width fluctuation. It was not a preferable casting method.

In view of the above-mentioned points, the present invention provides a casting method at a high speed which does not induce sheet surface defects, thickness unevenness, width fluctuation, etc., even when the sheet thickness is large, It is intended to provide a new casting method that also realizes cost reduction.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a casting method for applying an electrostatic charge to a thermoplastic resin melt sheet to make it adhere to a moving cooling medium and to cool the thermoplastic resin sheet. A method of casting a thermoplastic resin sheet, wherein a casting is performed with a liquid film of water interposed between the sheets.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In the present invention, the thermoplastic resin is
A resin that exhibits fluidity when heated, polyester,
Typical resins include resins selected from polyamides, polyolefins, vinyl polymers, and mixtures and modified products thereof. In the case of the present invention, polyester resins and polyamide resins are particularly preferred. Polyester resin is a polymer compound having an ester bond in the molecular main chain,
Usually, it is often synthesized by a polycondensation reaction between a diol and a dicarboxylic acid. However, a compound which self-condenses like a hydroxycarboxylic acid represented by hydroxybenzoic acid may be used. Representative diol compounds include ethylene glycol, propylene glycol, butylene glycol, hexene glycol represented by HO (CH ₂ ) nOH, further diethylene glycol, polyethylene glycol, ethylene oxide adduct, propylene oxide adduct and the like. And diols such as ether-containing diols, and the like, alone or in combination. Representative examples of dicarboxylic acid compounds include phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid. , And mixtures thereof.

In the present invention, in particular, polyethylene terephthalate (PET) and its copolymer, polybutylene naphthalate (PBN) and its copolymer, polybutylene terephthalate (PBT) and its copolymer, polyethylene naphthalate (PEN) ) And its copolymers,
Polyethylene terephthalate / adipate (PET / A), which is a resin having a lower glass transition temperature Tg;
Polyethylene terephthalate / sebacate (PET /
S), polybutylene terephthalate / isophthalate (PBT / I), polyethylene terephthalate-polyethylene glycol copolymer (PET-PEG), polyhexamethylene terephthalate (PHT), and mixtures and copolymers thereof are preferred. The number of repeating units of these polymer compounds is 100 or more, preferably 150 or more. The intrinsic viscosity was 0.5 (dl / d) as measured in orthochlorophenol (OCP).
g) or more, preferably 0.6 (dl / g) or more. Needless to say, various additives such as a slipping agent, a stabilizer, an antioxidant, a viscosity modifier, an antistatic agent, a colorant, and a pigment can be arbitrarily used in these polymer compounds.

A polyamide resin is a polymer compound having an amide bond in the main chain, and typical examples thereof include nylon 6, nylon 66, nylon 610, nylon 12, nylon 11, nylon 7, nylon 7, / Paraxylylene adipamide, polyhexamethylene terephthalamide / isophthalamide, and polyamide compounds selected from copolymers and mixtures thereof. Of course, these may be a polyamide ether obtained by copolymerizing a polyether compound such as polyethylene glycol, polypropylene glycol or polytetramethylene glycol, or a polyester amide compound obtained by copolymerizing with a polyester. Particularly excellent effects are exhibited for polymers and amorphous polyamide resins having many or large substituents in side chains.

In a casting method in which an electrostatic charge is applied to a thermoplastic resin melt sheet to adhere to a moving cooling medium and cooled, in a conventional casting method in which an electrostatic charge is not applied to an end portion, an end portion adheres to a cooling medium. Insufficient force causes crystallization or curling of the edge at the end, which causes stretching unevenness and tearing in the subsequent stretching step. In such a casting method, It was impossible to cast at high speed. Of course, in the conventional casting method, if the width of the applied electrode is simply widened, such an electrode cannot be used as it is because discharge occurs on the cooling medium because there is no molten resin sheet outside the end of the sheet. Therefore, in the present invention, the strong adhesive force to the moving cooling medium over the entire width of the sheet is first obtained by improving the adhesive force at the edges by interposing a liquid film of water substantially only at both ends of the thermoplastic resin sheet. As a result, crystallization of the sheet edge can be suppressed, and not only a sheet having excellent flatness and thickness uniformity can be obtained, but also stable stretching can be performed, and the casting speed and film forming speed can be increased. is there.

On the other hand, in the casting method in which a liquid film of water is interposed over the entire width of the sheet so as to improve the adhesion not only at the end but also at the center of the sheet, the entire melt sheet film is used. Is on the water film, so the slip resistance, which is the shearing force, is small.If the sheet is particularly thick, the entire sheet moves up and down on the moving cooling medium due to gravity and volume shrinkage. It moves relatively freely to the left and right, which leads to defects on the sheet surface, uneven thickness and width fluctuation, which is not preferable.

In the method of the present invention, "adhesion" means that the molten sheet is in contact with the moving cooling medium substantially without air or the like, so that the sheet can be uniformly and efficiently cooled. Say the state.

In the present invention, "water" refers to a liquid medium that forms a meniscus by being interposed between a molten sheet and a cooling medium, and is not necessarily limited to pure water itself. Water to which an appropriate surfactant or the like is added may be used.

The term “liquid film” often refers to a state in which a liquid is continuously formed as a film, but here, a liquid state such as a droplet is referred to as a discontinuous state. Is a concept that also includes That is, the present invention is not limited to a state in which a thin layer of water exists continuously without interruption.

In the present invention, as the electrode shape, a substantially wire-shaped, tape-shaped, blade-shaped or needle-shaped electrode can be used. There is also a method in which an electrode for applying an electrostatic charge is constituted by a moving cooling medium. In this case, since the apparatus is relatively simple and excellent in operability, the electrostatic charge is applied over the entire width or more. It is also possible to improve the adhesion at both the end portion and the center portion of the sheet, which is a more preferable embodiment of the present invention. Further, in order to further improve the adhesive force of the sheet edge, an electrostatic charge may be applied to the sheet edge, but the shape of the electrode to be applied may be needle-like, tape, blade-like, or the like. Since the electric charge can be concentrated only on the portion, it is possible to improve the adhesion at the end without discharging to the cooling medium, which is preferable. In addition, it is also possible to further improve the adhesion at the edge by using an electrode different from that at the center only at the edge of the sheet and applying an electrostatic charge from the electrode.

In the present invention, the thickness of the liquid film of water formed at the edge of the sheet is not particularly limited, but according to the knowledge of the present inventors, it is preferably 0.01 to 3 μm, more preferably 0 to 3 μm. 0.03 to 0.2 [mu] m, and a thinner one is preferable because of excellent adhesion. 0.01μ
If it is less than m, a uniform liquid film may not be formed between the sheet and the cooling medium, so that a uniform adhesion may not be obtained. Conversely, if it exceeds 3 μm, high surface tension of water cannot be exhibited. It is not preferable because a strong adhesive force is not obtained and the end portion may move freely.

In the present invention, the formation of a liquid film of water can be performed by applying a water film or a water droplet. As a method of applying such a water film or a water droplet, air containing moisture is exposed to the dew point. The method of dew condensation by spraying on the cooling medium kept below, the method of spraying electrostatic water vapor,
A method of applying water vapor generated by ultrasonic vibration,
There is a method in which water is extruded with a roller formed of a porous material and transfer coating is performed. There is no particular limitation on the coating method, but a relatively simple roller coating method is preferable. In addition,
Before forming a water film or a water droplet, the water droplet or the liquid film remaining on the cooling medium is preferably completely removed by air blow, vacuum suction, or a water absorbing roll.

The surface roughness of the moving cooling medium is preferably 0.6 μm or less, more preferably 0.2 μm or less.
The smoothness of not more than μm is important for realizing the smoothness of the obtained sheet. Cooling body surface material is SU
Any material such as S metal, chromium plating, nickel plating, and ceramic spraying can be used. The surface temperature of the moving cooling medium is the glass transition temperature T of the thermoplastic resin.
g−50 ° C. or higher and Tg + 100 ° C. or lower,
More preferably, Tg−25 ° C. or higher, Tg + 60 ° C. or lower,
More preferably, by maintaining the temperature at Tg−20 ° C. or higher and Tg + 10 ° C., not only the sheet edge, but also the center of the sheet significantly improves the adhesiveness to the cooling medium, and also facilitates handling such as peelability. Therefore, it is preferable as a method for casting a thermoplastic resin sheet. Of course, when the temperature of the cooling medium is increased, the adhesion between the medium and the molten sheet is improved. However, it is not preferable because the stretchability may be extremely deteriorated or the film may not be peeled off from the cooling medium.

Next, a specific example of a method for producing a thermoplastic resin sheet using the casting method of the present invention will be described.

As the thermoplastic resin raw material used for the melt extrusion, a raw material obtained by blending a raw material such as polyester and polyamide with other compounds as necessary, for example, a liquid crystal polymer and another polyester resin, furthermore, silicon oxide,
Magnesium oxide, calcium carbonate, titanium oxide, aluminum oxide, crosslinked polyester, crosslinked polystyrene,
Raw materials to which inorganic compounds such as mica, talc, kaolin, etc., organic compounds such as ethylenebisstearylamide, ionic polymer compound ionomers, etc. are added, raw materials once melted, and raw materials obtained by mixing the raw materials for collecting the film of the present invention After preparing and drying and dewatering this, it is supplied to a melt extruder such as a single-screw extruder, a twin-screw extruder, a vent extruder, a tandem extruder, etc. so as not to lower the molecular weight, for example, the intrinsic viscosity [η]. Under a nitrogen stream or under vacuum. Of course, the melting temperature is usually higher than the melting point of the thermoplastic resin. However, once the resin is melted at a temperature higher than the melting point of the resin, it is cooled to the melting point or lower, and the melt crystallization temperature Tmc or higher. Extrusion may be performed. Such supercooled extrusion not only has the effect of reducing the thermal decomposition and gelation of the resin, but also reduces the production of low molecular weight oligomers, so that the drum is less contaminated and therefore easier to cast. There is also an effect. In addition, various filters, such as sintered metal, porous ceramic, sand, and wire mesh, can be used to remove foreign matter. The draft ratio (= lip lip interval / extruded film thickness) when extruding from the die is preferably 7 or more, and more preferably 10 or more, so that thickness unevenness is small and transparency is better. It is possible to obtain a suitable film.

According to the present invention, according to the present invention, the molten thermoplastic resin sheet is applied with an electrostatic charge to a central portion thereof, brought into close contact with a moving cooling medium, such as a casting drum, and rapidly cooled to be cast. By improving the adhesive force at the edge of the resin sheet, a strong adhesive force to the moving cooling medium is obtained over the entire sheet width, and as a result, crystallization at the edge of the sheet can be suppressed, and the flatness and uniform thickness can be obtained. A sheet having excellent properties can be obtained. Note that an additional electrostatic charge may be applied to further improve the adhesion at the sheet end.

The cast film is subsequently subjected to a stretching step, and can be stretched according to a stretching method such as longitudinal uniaxial stretching, horizontal uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching. Even in the case, since the crystallization of the sheet edge is suppressed, problems such as tearing substantially do not occur,
Stretching can be performed more stably than the conventional method. The stretching temperature is not particularly limited, but may be any temperature as long as it is equal to or higher than the glass transition temperature Tg of the resin, and any temperature can be selected as needed. The stretching ratio in one direction is 2 to 8 times, preferably 3 to 6 times.
About twice as good. After stretching, appropriate heat setting may be performed as necessary.

The process according to the invention is especially suitable for
The present invention can be applied to a wide range of casts of 0 μm and exhibits an effect. According to the method of the present invention, high-speed casting can be realized, and more specifically, casting at a very high speed of 40 to 120 m / min can be performed stably without causing sheet defects. This is 200-600 m
Per minute, which is very useful in film production.

Therefore, according to the present invention, a high-speed casting of 10 to 100 m / min can be realized even in a case where the thickness of the melt sheet is relatively large, for example, 1000 to 3000 μm. This area was considered difficult to achieve. Needless to say, the present invention can be suitably applied to a casting process at a low or medium speed that does not reach the above speed, and is effective.

The thus obtained thermoplastic resin sheet according to the method of the present invention can be used for packaging applications conventionally used,
Not only magnetic recording applications, electrical applications such as capacitors and electrical insulation, graphic applications, receiving paper applications,
It is effective for a new film application excellent in thermal dimensional stability, moldability, shape stability and toughness.

[0027]

[Measurement Methods for Physical Properties] Next, the measurement methods used in the present invention will be described.

1. Intrinsic viscosity [η] of polyester: 25
At ゜ C, the value was determined by the following formula using o-chlorophenol as a solvent.

[Η] = lm [ηsp / c] The specific viscosity ηsp is obtained by subtracting 1 from the relative viscosity ηr. c is the concentration. The unit is expressed in dl / g.

2. Surface roughness Rt (μm): JIS B0
Measured at room temperature with a cutoff of 0.25 mm according to 601-1976. 3. Glass transition temperature Tg (° C), cold crystallization temperature Tcc
(° C.): Using a DSC-II type measuring device manufactured by Perkin Elmer, the sample was heated at a rate of 20 ° C./min under a nitrogen flow with a sample weight of 10 mg. Tg, and the exothermic peak at a higher temperature is Tcc.

4. Casting property: The melt was brought into close contact with a cast drum as a cooling medium, and judged from the state of close contact, the shape and crystal state of the sheet edge, and the like.

The criteria are as follows.

[0033]

[Table 1] 5. Stretchability: A 12 μm-thick biaxially stretched film was subjected to continuous film-forming operation for 3 days, and judged mainly from a film-forming trouble state such as sheet cutting or tearing caused by the sheet edge.

[0034]

[Table 2]

[0035]

EXAMPLES Hereinafter, in order to make it easier to understand the specific structure and effect of the present invention, description will be made using examples and comparative examples.

Example 1 As a thermoplastic resin, polyethylene terephthalate (P
ET) (intrinsic viscosity [η] = 0.65, glass transition temperature 70)
At 25 ° C., containing 0.1 wt.% Of spherical silica having an average particle size of 0.2 μm as an additive).
After feeding to a 0 mm melt extruder and melting, after passing through a filter for removing foreign substances of 10 μm or less, 900 mm
It was formed into a sheet from a T-die die having a width of 1200 m and maintained at 75 ° C. while applying an electrostatic charge to the center of the sheet.
m-diameter drum (water film thickness of 0.5 μm only at the part where the sheet edge contacts to improve the adhesion of the melt sheet edge
The surface of the drum is closely adhered and cooled at a speed of 70 m / min onto a cooling medium of a chrome-plated roll mirror-finished to a maximum roughness Rt = 0.1 μm. did. The application electrode used at this time was a tungsten wire electrode having a diameter of 0.1 mm, and a voltage of 15 kv was applied to the electrode.

The thickness of the cast sheet thus obtained was 200 μm at the center and 800 μm at the end of the cast sheet.
m. The resulting sheet is a non-crystalline sheet having a small thickness unevenness, excellent flatness, no surface defects such as craters, and has no edge portion width fluctuation, and is transparent and amorphous, Excellent castability (Evaluation of castability: ○). Subsequently, the extruded film is stretched 5 times in multiple stages at a stretching temperature of 105 ° C. with a roll-type longitudinal multi-stage stretching machine, once cooled to Tg or less, and then while holding both ends of the longitudinally stretched film with clips. In the hot air atmosphere heated to 100 ° C. at a stretching temperature of 4
After doubling stretching, heat fixed at 210 ° C for a fixed length and relaxed at 150 ° C for 3% in the width direction. After cooling to Tg or less, the edge end is cut and a 12 μm thick biaxially oriented polyester is cut. The film could be wound and formed at a high speed of about 350 m / min in a stable state without breaking (evaluation of stretchability: ○). The obtained film had no surface defects and was excellent in flatness and thickness uniformity (5% in thickness in the longitudinal direction).

Example 2 The thickness of the end of the sheet formed in Example 1 was 1000
μm, and in addition to the water application method of Example 1 for the edge contact, in order to further improve the adhesiveness of the edge, a pin electrode having a diameter of 0.4 mm is formed along the edge. The three electrodes were arranged in close contact with each other. The castability of this example was good (（). A film was formed in exactly the same manner as in Example 1 under the same conditions as in Example 1, and the biaxially stretched polyethylene terephthalate film having a thickness of 12 μm was stabilized to have no surface defects and excellent flatness. It was possible to form a film at high speed with a film castability (evaluation of stretchability: ○).

Example 3 The temperature of the cooling medium employed in Example 1 was increased from 75 ° C. to 25 ° C.
A film was formed in the same manner as in Example 1 except that the film thickness was reduced to 12 μm. As a result, a biaxially oriented film having a thickness of 12 μm could be formed stably at a high speed, and an excellent film could be obtained as in Example 1. . Both castability and stretchability were good (○).

Comparative Examples 1 to 4 In Example 3, when nothing was used only at the sheet edge instead of the water film for contacting the edge (Comparative Example 1), electrostatic printing was performed using three needle electrodes. Method (Comparative Example 2), using an air knife (Comparative Example 3), and using a presser roll coated with a polyfluoroethylene resin (Comparative Example 4). The film was cast on a moving cooling medium at a high speed of 70 m / min (surface temperature: 75 ° C.) and biaxially stretched and heat-treated in the same manner as in Example 1 to obtain a film having a thickness of 12 μm.

[0041]

[Table 3] As described above, it can be understood that casting and stretching film formation can be performed at high speed and stably only when a water film is present at the sheet edge.

[0042]

According to the present invention, not only high-speed casting is possible, but also the stretchability is stable, and a stable film formation can be realized with significant cost reduction, and excellent film properties can be obtained. .

The method of the present invention generally has a thickness of 10 to 3000
It can be used for casting in a wide range of μm,
It is more effective when employed in a casting process of a melt sheet having a thickness of 20 to 1000 μm. Conventionally, it is difficult to cast such a thickness satisfactorily. According to the present invention, by improving the adhesive force at the end of the thermoplastic resin melt sheet, a strong adhesive force to the moving cooling medium is obtained over the entire sheet width, and as a result,
Crystallization at the sheet edge can be suppressed, and a sheet excellent in flatness and thickness uniformity can be obtained. The productivity is also greatly improved, and high-quality films can be produced while reducing costs.

According to the second to fifth aspects of the present invention, the adhesive force at the end of the thermoplastic resin melt sheet is further improved, and a stronger adhesive force to the moving cooling medium can be obtained over the entire sheet width. Thus, the effect of the method of the present invention is further enhanced.

Further, according to the method of claim 6, wherein the electrode for applying an electrostatic charge to the molten sheet is constituted by a moving cooling medium and applied, it is possible to realize a large adhesive force while rapidly cooling the film. The effect of the present invention can be further enhanced.

According to the method of the seventh aspect, it is possible to achieve a very high speed casting while achieving a strong adhesion to the moving cooling medium over the entire sheet width.

According to the method of claim 8, a high-quality film can be manufactured at low cost while realizing the above-mentioned cast state.

Claims (8)

[Claims] 1. A casting method in which an electrostatic charge is applied to a thermoplastic resin melt sheet to make it adhere to a moving cooling medium for cooling, wherein a liquid film of water is interposed substantially only at both ends of the thermoplastic resin sheet. A method for casting a thermoplastic resin sheet. 2. The method for casting a thermoplastic resin sheet according to claim 1, wherein the thickness of the liquid film of the water is 0.01 to 3 μm. 3. The surface temperature of the moving cooling medium is set to a glass transition temperature Tg of the thermoplastic resin of 50 ° C. or higher, and Tg + 100 ° C.
The method for casting a thermoplastic resin sheet according to claim 1, wherein the temperature is maintained at the following temperature. 4. The thermoplastic resin sheet according to claim 1, wherein an electrostatic charge is applied only to the end of the sheet from an electrode different from that of the center to improve the adhesion at the end. How to cast. 5. An electrode according to claim 1, wherein said electrostatic charge is applied by an electrode, and said electrode shape is an electrode selected from a wire shape, a tape shape and a needle shape.
The method for casting a thermoplastic resin sheet according to the above. 6. The method for casting a thermoplastic resin sheet according to claim 1, wherein an electrode for applying an electrostatic charge to the melt sheet is constituted by a moving cooling medium and applied. . 7. The casting speed according to claim 1, wherein the casting speed is 40 to 120 m / min.
The method for casting a thermoplastic resin sheet according to the above. 8. A method for producing a thermoplastic resin sheet using the casting method according to claim 1, 2, 3, 4, 5, 6, or 7.