JPH0533891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for casting a thermoplastic resin film. [Prior art] As a casting method for thermoplastic resin film,
Attempts have been made to increase the casting speed and improve the surface properties of the film by coating the surface of a cooling roll (hereinafter referred to as a cast roll) with a liquid such as water. Kosho 61−
38012, JP-A-54-150477, JP-A-61-219621,
219622, 237619). [Problems to be Solved by the Present Invention] However, these methods cause the following problems. (1) Because the water film cannot be thinned, water boils on the film surface, creating uneven boiling marks (hereinafter referred to as boiling marks), or in the direction perpendicular to the film flow direction (width direction). small wavy defects occur. (2) Also, if a water film is made too thin, the film surface will have an uneven shape in areas where the water has drained and where it has not, which is the same as in the water-applied state. (3) Even in the mist method, unevenness occurs due to the water droplets, which causes defects on the film surface. In order to solve these problems, the present invention was arrived at as a result of intensive studies. [Means for Solving the Problems] The present invention provides a method for casting a thermoplastic resin film onto a cooling roll, in which the surface roughness Ra is
The maximum water droplet diameter is 0.04μm or less on a mirrored drum.
70μm or less, and the number of water droplets is 50 to 500/0.1mm ²
The present invention is characterized by a method for casting a thermoplastic resin film, in which water droplets are attached to the thermoplastic resin film, and the number of water droplets is larger at both ends in the width direction of the film than at the center. The term "thermoplastic resin film" as used in the present invention refers to a film-like material made of a thermoplastic polymer, and includes all materials generally called films, sheets, thin sheets, etc., regardless of thickness. Thermoplastic polymers are polymers that exhibit plasticity when heated.
Chemically, it is a linear polymer. Typical polymers include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyethylene α,β-bis(2-chlorophenoxy)ethane 4,4′-dicarboxylate, p-hexahydro-xylylene terephthalate, Polyesters having an ester bond in the main chain, as typified by polymers from 1,4 cyclohexanedimethanol, poly-p-ethyleneoxybenzoate, polyarylates, polycarbonates, etc., and copolymers thereof;
Furthermore, as represented by nylon 6, nylon 66, nylon 610, nylon 12, nylon 11, etc.
Polyamides having an amide bond in the main chain, polyolefins and polyethers mainly composed of hydrocarbons, such as polyamides, polyethylene, polypropylene, ethylene-vinyl acetate copolymers, polymethylpentene, polybutene, polyisobutylene, polystyrene, etc. Sulfon (PES), polyphenylene oxide (PPO), polyetheretherketone (PEEK), polyethylene oxide, polypropylene oxide,
Polyethers represented by polyoxymethylene, halogenated polymers represented by polyvinylidene chloride, polyvinylidene chloride, polyvinylidene fluoride, polychlorotrifluoroethylene, polyphenylene sulfide (PPS), polysulfon, etc. These include copolymers and modified products thereof. In the case of the present invention, the thermoplastic polymer is
In particular, polyesters, polyamides, polyethers, polyphenylene sulfide, etc.
Further, polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyphenylene sulfide are particularly preferable because the effects of the present invention are remarkable. 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 device is a movable device such as a roll-shaped rotating body or a belt, and the cooling surface is a well-known mirror chrome-plated one,
If necessary, the surface may be treated to be hydrophilic. However, Ra needs to be less than 0.04μm,
If it exceeds this range, it not only causes surface roughness of the film, but also makes it difficult to absorb water as described below, making it impossible to obtain a film with a maximum water droplet diameter of 70 μm or less, and causing surface defects due to water droplets. Moreover, this surface roughness Rmax is preferably 0.04 μm or less. Methods for attaching water droplets to the surface of the cooling device in the present invention include a method of blowing humid air onto the cooling surface kept below its dew point to cause dew condensation, and a method of spraying electrostatically charged water vapor. There is. The maximum water droplet diameter in the present invention must be 70 μm or less, preferably 50 μm or less. If the thickness exceeds 70 μm, uneven defects will occur on the film surface. Further, the number of water droplets must be 50 to 500 pieces/0.1 mm ² , preferably 70 to 400 pieces/0.1 mm ² . 50
If the amount is less than 0.1 mm ² , film surface defects occur due to air entrapment due to lack of water. If the number exceeds 500, it becomes impossible to reduce the maximum water droplet diameter to 70 μm or less. Furthermore, in order to obtain the maximum water droplet diameter and number of water droplets, it is important to remove the adhering water after the film leaves the cooling body surface. , Masuda Seisakusho Co., Ltd., air knives (hot air, dry air), and a combination of both. It is preferable to completely eliminate water droplets after passing through this removal device, but complete removal is impossible. In this case, the maximum water droplet diameter should be 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. There is a need. If the diameter exceeds 10 μm, when water droplets are reattached, the aforementioned maximum water droplet diameter will exceed 70 μm, causing defects on the film surface. In addition, in the present invention, a film with no surface defects can be obtained without applying an electrostatic charge, but in order to improve the uniformity of thickness unevenness in the width direction, it is better to cast while applying an electrostatic charge. is more preferable. Further, the number of water droplets in the present invention is preferably varied in the width direction within the above-mentioned range, and it is necessary to increase the number of water droplets at the edge portion (within 50 mm from the end of the film) than at the center portion in the width direction. When the edge portion is smaller than the center portion, the flatness deteriorates and the continuous stability of stretching deteriorates. [Effects of the Invention] The following effects are produced by keeping the cooling roll (cast roll) surface roughness Ra below a certain level and the water droplet shape within a specific range. (1) Even when applied in the form of water droplets, stable casting is possible without surface defects such as unevenness or small waves caused by water boiling. (2) Although it is not substantially a continuous film of water, molding defects due to unevenness of the film surface due to water drainage do not occur. (3) No unevenness transfer in the shape of water droplets occurs. (4) It is possible to achieve significantly higher speeds than conventionally known electrostatic charge casting methods, and stable casting for a long period of time is possible. [Evaluation method] (1) Water droplet diameter and number of water droplets After attaching water droplets to the surface of the cooling body, immediately set up a microscope (measurement after 30 seconds) and take a photograph. From the photograph, calculate the diameter and number of water droplets. I asked for it. (2) Cooling body surface roughness Measured based on JIS B0601. (3) Molding defects due to air entrapment Observe the film on the cast drum, and if air entrapment is clearly seen with the naked eye, it is marked as a molding defect and marked with an x mark, and if no air is found, it is marked as good and marked with an ○ mark. It was shown in (4) Irregularities due to water boiling When the molten film comes into contact with water droplets at the cast point, it boils, and this causes surface irregularities to be determined internally, and those with irregularities are marked as defective.
Indicated with a mark. In addition, those that were not observed were marked as good and marked with a circle. (5) Orange skin-like unevenness This is a surface defect caused by the transfer of the shape of water droplets.
In addition, even after biaxial stretching, orange skin-like defects are clearly observed (to the naked eye and thickness unevenness periodicity, but the periodicity increases by the stretching ratio).
are marked with an x as unusable. In addition, those that are observed in cast films but not after biaxial stretching are considered usable.
Those that were not observed even in the cast film were marked as good and were marked with a circle. (All judgments were made based on the center part of the film (product part).) (6) Continuous stability As the flatness deteriorates, meandering and wrinkling of the film occur, until stable film formation becomes impossible. If it is less than 8 hours, it is marked as unstable and marked with an ○, and if it is more than 48 hours, it is marked as stable, and in the middle of these, instability remains but relatively productive. It is indicated with a △ mark as there is no deterioration. Example 1 The present invention will be explained below based on examples. Examples 1 to 3, Comparative Examples 1 to 4 Polyethylene terephthalate (=0.6) was used as the thermoplastic resin, vacuum dried at 180°C, supplied to an extruder, melted at 285°C, and then a film was discharged from a T-die. A static charge was applied to the entire width of the sheet, and a film with a thickness of 100 μm was placed on a cooling roll (chrome plated roll) as shown in Attached Table 1.
It was cast at a speed of 90 m/min. Prior to this casting, humid air as shown in Attachment 1 is sent to the surface of the cooling roll on which the film is cast, causing dew to condense on the cooling roll so that the water droplet shape shown in Table 1 is formed on the part corresponding to the center of the film. I got it. In addition, moist air is sent through a separate circuit, and both ends of the film are 30 to 50 mm thick.
The temperature and air flow rate of the humid air were adjusted to separately form dew condensation within the range of 200 to 3000, and water droplets having the number of water droplets shown in Table 1 were obtained on the portion corresponding to the edge of the film. (Examples 1-3, Comparative Examples 1-3). In Comparative Example 4, separate dew condensation was not caused at the ends of the film, and the same dew condensation state as at the center of the film was created. In addition, between the place where the film is separated from the roll and the place where moist air is blown, a mass roll (Co., Ltd.)
(manufactured by Masuda Seisakusho) was installed, a load of 0.8 kg/cm was applied, and excess water was removed using a suction pump of 500/ ^m2 /min. This cast film was subjected to a conventional biaxial stretching device to obtain a biaxially stretched film. As a result, by providing water droplets with a specific shape on a cooling roll with a specific surface roughness, even when casting at high speed, molding defects due to air entrapment and water boiling may occur. A film was obtained that had no irregularities on the film surface or orange skin-like irregularities. Furthermore, the flatness was improved, and the stretching stability was accordingly improved. Also,
By increasing the number of water droplets at the end, it was possible to prevent width fluctuations when the speed was increased. 【table】

Claims (1)

[Scope of Claims] 1. In a method of casting a thermoplastic resin film on a cooling device, the surface of the cooling device has a surface roughness Ra of 0.04 μm or less, a maximum water droplet diameter of 70 μm or less, and a number of water droplets of 50 to 50. A method for casting a thermoplastic resin film, which is characterized by depositing 500 water droplets/0.1 mm ² and further casting by making the number of water droplets at both ends of the film larger than that at the center. 2. The method of casting a thermoplastic resin film according to claim 1, wherein the casting is carried out while applying an electrostatic charge from the non-cooled side of the thermoplastic resin film.