JPH0460812B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for molding a thermoplastic resin sheet, and more specifically, when molding a film from a molten thermoplastic polymer using an electrostatic application method, it is necessary to The present invention relates to a method for producing a polymer film that uses ultrafine wires as electrodes to tightly adhere the film to the surface of a rotating cooling body. [Prior art and problems to be solved by the invention] Among film molded products made from thermoplastic resins, polyester films, especially polyethylene terephthalate films, have poor mechanical properties, electrical properties, chemical resistance, and dimensional stability. Because of its excellent properties, it is used as a base material in many fields such as magnetic tapes, capacitors, packaging, plate making, electrical disconnections, and photographic films. Incidentally, in recent years, the requirements for film quality have become increasingly strict, and in particular, improving thickness accuracy has become an indispensable condition. It is known that when a thermoplastic resin is formed into a film by a melt molding method, the degree of thickness unevenness is determined when the molten material is cooled and solidified on a rotary cooling body, regardless of whether stretching is performed or not. To improve this thickness unevenness, for example,
As described in Publication No. 6142, it is known that the so-called electrostatic application cooling method, in which an electrostatic charge is applied to the surface of the film when it is cooled and solidified into a film, and the film is brought into close contact with the cooling surface, is effective. It is widely used industrially. However, in this electrostatic cooling method, when the speed of the rotary cooling body is increased for the purpose of increasing productivity, the adhesion between the film and the rotary cooling body decreases, resulting in so-called trapped bubbles, which are required for the product. This will reduce quality characteristics. Various methods have been proposed to improve the above problems, such as those disclosed in JP-A-52-68262, JP-A-54-34370, and JP-A-56-53037. The technology is known. These methods include irradiating the wire with infrared rays, bringing a grounded separate covered electrode close to the electrode, and using a blade-shaped electrode with a curved end, but all of these methods have little effect. Even if it was effective, it had drawbacks such as the large scale of the device and the difficulty of installation. When using a linear electrode, the easiest way to increase the adhesion between the film and the rotary cooling body is to reduce the diameter of the wire. However, when the wire diameter is reduced, although the adhesion strength increases, the tensile strength at break decreases due to the decrease in wire diameter, so it is necessary to reduce the tension to prevent the wire from breaking. This causes the wire itself to vibrate, which causes the thickness of the film to fluctuate, causing the film to lose its commercial value, making spark discharge more likely to occur, and often making stable operation impossible. Conventionally, tungsten wires have been mainly used as linear electrodes, but for the reasons mentioned above, the wire diameter is about 80 μm, which is the practical limit, and as a result, the speed of the rotary cooling body cannot be increased that much. [Means for Solving the Problems] In view of the above circumstances, the inventors of the present invention have made extensive studies, and have found that if a specific ultra-thin wire with a high tensile breaking stress is used as an electrode, the electrostatic cooling capacity can be dramatically increased. The present inventors have discovered that the present invention can be improved in terms of performance, and have completed the present invention. That is, the gist of the present invention is to provide a method of molding a sheet by applying an electrostatic charge to a molten thermoplastic resin extruded from a die into a sheet using a linear electrode, thereby solidifying the resin in close contact with a rotary cooling body. , a thermoplastic resin sheet molding method characterized in that a wire having a diameter of 100 μm or less, a tensile breaking stress of 300 Kg/cm ² or more, and a surface roughness Ra of 0.1 μm or less is used as an electrode. The present invention will be explained in more detail below. Examples of the molten thermoplastic resin applicable to the present invention include polyesters, polyester ethers, polyamides, polycarbonates, polyester carbonates, polysulfones, polyethersulfones, polyetherimides, and polyolefins, such as ethylene. , propylene, butene, 4-methylpentene-1, and the like. Among the above-mentioned thermoplastic resins, the present invention is particularly effective in producing films of polyesters, such as polyethylene terephthalate, copolymers thereof, and polyethylene naphthalate. Furthermore, since the present invention is effective regardless of the electrical resistivity of the thermoplastic resin when it is melted,
It is also effective against polysulfones and polyamides. Next, details of the present invention will be explained with reference to the drawings. FIG. 1 is a schematic diagram of a cooling and solidifying apparatus for electrostatic adhesion according to the present invention. In FIG. 1, a film 1 of molten thermoplastic resin extruded from a die is cooled by an electrically grounded metal rotary cooling body 2.
It is solidified and taken away. At this time, a linear electrode 3 is provided near where the film first contacts the rotary cooling body, and a high voltage is applied. The linear electrode is placed on the upper surface of the film at a slight distance from the die in a direction perpendicular to the film flow direction. The wire used as the linear electrode in the present invention must have a diameter of 100 μm or less, preferably 80 μm or less, and more preferably 60 μm or less. Wire diameter (means the diameter of the wire)
If it exceeds 100 μm, the effect of improving electrostatic adhesion, which is the objective of the present invention, will hardly be observed, which is not preferable. Further, the wire must have a tensile breaking stress of 300 Kg/mm ² or more. Preferably 330Kg/ ^mm2 or more,
More preferably, it is 360 Kg/mm ² or more. If the tensile breaking stress is less than 300 Kg/ ^mm2 , when thinner wire is used for the purpose of improving electrostatic adhesion, the wire cannot be stretched with sufficient tension, and the wire tends to vibrate, causing the film to deteriorate. This is undesirable because it causes thickness fluctuations and spark discharge is more likely to occur. Further, in the case of a winding wire, the wire may break due to slight fluctuations in tension during the winding process, which is not preferable. The tensile breaking strength determined from the wire diameter and tensile breaking stress described above is preferably 100 g or more, more preferably 300 g or more, and most preferably 600 g or more. This tensile breaking strength is 100
If the weight is less than g weight, handling becomes extremely difficult and operation becomes extremely complicated, which is not preferable. Even if a sufficient tension (approximately 80 to 95% of the tensile breaking strength) is applied to the wire so that it does not break when installed, the vibration of the wire cannot be suppressed and the thickness of the film will vary. Furthermore, in extreme cases, spark discharge may occur and it may become impossible to form a film at all, which is not preferable. Furthermore, the wire used in the present invention must have a surface roughness (Ra) of 0.1 μm or less, preferably 0.05 μm or less, and more preferably 0.01 μm or less. If the surface roughness (Ra) exceeds 0.1 μm, electric field concentration will occur due to unevenness on the surface of the wire, making spark discharge more likely to occur, which is not preferable. Specific examples of wires that meet the above characteristics include wires made of various amorphous metals or amorphous alloys (amorphous wires); is preferable. The composition of amorphous metal or amorphous metal is one of transition metals such as iron, cobalt, and nickel.
The main component is beryllum, magnesium, aluminum, titanium, vanadium, chromium, manganese, copper, zinc, diluconium, niobium, molybdenum, silver, indium, platinum, gold, etc. and/or one or more nonmetals/metalloids selected from the group of nonmetals/metals such as boron, carbon, silicon, phosphorus, germanium, antimony, etc. Add or not add
It is composed of a single element or multiple elements, and the composition ratio can be selected arbitrarily. Any known method can be used for its production, and the main methods include the gun method, piston anvil method, atomization method, centrifugal quenching method, twin roll method, and single roll method. , the molten metal or alloy is cooled at a cooling rate higher than the critical cooling rate at which the metal or alloy becomes amorphous, and any manufacturing method may be used as long as it satisfies this condition. Further, there is no problem in performing post-treatment such as heat treatment after cooling. The amorphous metal or amorphous alloy manufactured by such a manufacturing method has a so-called glass-like structure, and the arrangement of its structural atoms has virtually no long-period order. Therefore, the X-ray diffraction pattern is halo-like and clearly different from that of crystalline metals. The amorphous wire preferably used in the present invention has a mainly amorphous structure, preferably 50% or more of which is amorphous, but it may partially have a crystalline structure. Examples of the compositions of the above amorphous wires include FeCoSiB, CoCrSiB, FeCoCrSiB,
Fe _75-85 , B _15-25 , Fe _75-85 P _10-16 C _4-10 ,
Fe _59-67 Cr _4-9 Mo _1-6 B _27-29 , Fe ₇₈ B ₁₀ Si ₁₂ ,
Fe ₆₂ Mo ₂₀ C ₁₈ , Fe ₆₂ Cr ₁₂ Mo ₁₈ C ₁₈ ,
Fe ₄₆ Cr ₁₆ Mo ₂₀ C ₁₈ , Co ₇₃ Si ₁₅ B ₁₂ , Co ₅₆ Cr ₂₅ C ₁₈ ,
_{Co44Mo36C20 , Co34Cr28Mo20C18 , _ _ _}
Examples include Ni ₃₄ Cr ₂₄ Mo ₂₄ C ₁₈ . In the above compositional formula, the subscript numbers represent the atomic composition ratio or the range of the composition ratio (both percentages). Those without subscripts represent arbitrary composition ratios. However, the present invention is not limited to these, and various composition ratios that meet the requirements of the present invention can be used. Furthermore, there are no particular regulations regarding trace elements that are necessarily included within a practically acceptable range. The present invention has been explained above, but the gist is that the diameter
By using a wire with a diameter of 100 μm or less, a tensile breaking stress of 300 Kg/mm ² or more, and a surface roughness Ra of 0.1 μm or less for the electrostatic adhesion electrode, it increases electrostatic adhesion, suppresses spark discharge, and reduces thickness fluctuation. The object of the present invention is to provide a defect-free film and to improve the film production speed. Therefore, the present invention is not limited to the embodiment shown in FIG. 1 or the content described above, unless this spirit is impaired. For example, using multiple wires, heating the wires, irradiating infrared rays to the close contact parts, attaching a cover to at least part of the top or side of the wires, or using a roll or pear cloth with an insulating layer. It is also possible to use a combination of known techniques such as using a roll with a roughened surface. [Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. The surface roughness Ra of the present invention was measured by the following method. Measurement of Surface Roughness In the present invention, the centerline average roughness Ra (μm) is defined as surface roughness. The surface roughness was determined using a measuring instrument (SE-3FK manufactured by Kosaka Institute) as follows. That is, from the curve measured in the longitudinal direction of the surface of the wire, a part of standard length L (2.5 mm) is extracted in the direction of its center line, and the center line of this extracted part is
Line, roughness curve Y = f with the direction of vertical magnification as the Y axis
When expressed as (X), the value given by the following formula is expressed in μm. However, the tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 80 μm. Measurement was performed at 10 points, and the average value was taken as Ra. Ra=1/L ₀ ^L | f(X) | dx Example 1 After drying polyethylene terephthalate pellets with an intrinsic viscosity of 0.65, they were heated to 290°C using an extruder.
The mixture was melted and rapidly cooled using the cooling and solidifying apparatus shown in FIG. 1 to form a film. At this time, an electrically grounded metal rotating roll with a length of 600 mm and a chrome-plated surface and a mirror finish was used as the rotating cooling body. A diameter of 60μm is placed 5mm away from the rotary cooling body.
An amorphous wire made of Co ₃₄ Cr ₂₈ Mo ₂₀ C ₁₈ was used as an electrode, and while applying a DC voltage of 6 KV to the electrode, the extrusion amount and width were adjusted to a thickness of 150 μm.
I took over the film. The surface roughness (Ra) of the wire was 0.010 μm. Table 1 shows the maximum rotational speed of the rotary cooling body at which no trapped air bubbles are introduced into the film, the film thickness unevenness, the number of spark discharges, the number of wire cuts, etc. In this example, a defect-free film was stably obtained and the productivity was good. Practical Example 2 A polyethylene terephthalate film with a thickness of 150 μm was obtained in the same manner as in Example 1, except that the diameter of the amorphous wire used in Example 1 was 55 μm. The results are shown in Table 1. The speed with which trapped bubbles were not introduced was increased, and there were no problems with uneven thickness, spark discharge, wire breakage, etc., and productivity was good. Example 3 The diameter of the linear electrode used in Example 1
The thickness was the same as in Example 1 except that the amorphous wire made of 50 μm Fe ₆₀ Cr ₆ Mo ₆ B ₂₈ was used.
A 150 μm polyethylene terephthalate film was obtained. The results are shown in Table 1. The speed at which trapped bubbles were not introduced was further increased, there were no problems such as thickness unevenness, spark discharge, wire breakage, etc., and the productivity was extremely good. Comparative Example 1 The diameter of the linear electrode used in Example 1 was
A polyethylene terephthalate film with a thickness of 150 μm was obtained in the same manner as in Example 1 except that a 60 μm tungsten wire was used. The results are shown in Table 1, but the wire tension could not be increased very much and the thickness was uneven. In addition, spark discharge and wire breakage are likely to occur, and it can be seen that the productivity is considerably inferior to that of the above-mentioned embodiments. Comparative Example 2 The diameter of the linear electrode used in Example 1 was
A polyethylene terephthalate film with a thickness of 150 μm was obtained in the same manner as in Example 1, except that an amorphous wire made of Co ₃₄ Cr ₂₈ Mo ₂₀ C ₁₈ with a diameter of 60 μm and a surface roughness of 0.5 μm was used. The results are shown in Table 1. Spark discharge occurred in the film, and productivity was poor.

【table】

〔Effect of the invention〕

As detailed above, the present invention enhances electrostatic adhesion by using a wire with a diameter of 100 μm or less, a tensile breaking stress of 300 Kg/mm ² or more, and a surface roughness Ra of 0.1 μm or less as a linear electrode. The present invention has great industrial significance because it improves production speed, provides stable operation without spark discharge or wire breakage, and dramatically improves productivity.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an apparatus for carrying out the method of the invention. The symbols in the figure are as follows. DESCRIPTION OF SYMBOLS 1... Molten thermoplastic resin film, 2... Rotating cooling body, 3... Linear electrode, 4... End insulating support of linear electrode.

Claims (1)

[Claims] 1. In a method of molding a sheet by applying an electrostatic charge to a molten thermoplastic resin extruded from a die into a sheet using a linear electrode and solidifying the same resin in close contact with a rotary cooling body, the resin has a diameter of 100 μm or less,
Tensile fracture stress is 300Kg/ ^cm2 or more, surface roughness Ra is
A method for molding a thermoplastic resin sheet, characterized in that a wire having a diameter of 0.1 μm or less is used as an electrode.