JPS6210820B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a stretched film made of a thermoplastic resin, and more specifically, to a method for producing a stretched film made of a thermoplastic resin, and more specifically, by applying an electrostatic charge to an extrudate melted and extruded from an extruder nozzle, the film is applied to the surface of a cooling body such as a casting drum. The present invention relates to an improvement in a method for manufacturing a stretched film from an amorphous sheet or film (the sheet and the film are collectively referred to simply as a film in the following description) obtained by adhering them together and cooling and solidifying them.

When manufacturing thermoplastic resin stretched film,
In order to stretch uniformly, it is necessary to produce a non-crystallized amorphous film that is as uniform as possible, but the method for manufacturing these amorphous sheets is usually to pass it through an extruder and from a die such as a T-die or an I-die. A method is used in which the extruded sheet-like melt is immediately brought into contact with the surface of a rotary cooling body maintained at a predetermined temperature, and rapidly cooled and solidified. The most important thing in such a method is the state of contact between the sheet-like melt and the cooling body, which can determine most of the properties of the stretched film. For example, if there is local entrainment of air between the sheet-like melt and the cooling body, or if low-molecular substances, ie, oligomers, adhere to nylon or polyester resin, causing cooling spots, The amorphous film partially crystallizes and becomes non-uniform, causing uneven stretching in the next stretching step and increased unevenness in thickness, significantly reducing the quality of the stretched film.

As a means to avoid such inconveniences, a method is known in which an electrostatic charge is applied to the sheet-like melt extruded from the extruder nozzle to improve the adhesion with the cooling body (for example, the No. 6142, Tokko Akira
48-3535, Special Publication No. 48-14784),
This method is extremely effective, especially when using a resin that has low molecular weight substances attached to the cooling body, such as when using nylon or polyester resin as a film material. First, it is possible to obtain an amorphous film that is more uniform and complete than conventional products.

However, when adopting this electrostatic charge application method,
It turned out that there was a problem from another aspect. That is, if only the method described in the above-mentioned known document is carried out, a problem will arise in the quality of the film. This is because during the rapid cooling and solidification process, a high voltage is applied to the sheet-like material in a state close to melting, and then it is rapidly cooled, so that charges are captured (or confined) inside the cooled and formed film. (Even if you get it, you get it). When this film is stretched, charges are confined within the crystal structure of the stretched film and are fixed as extremely stable charges. Such trapped charges can hardly be removed by ordinary static eliminating means. A film having such trapped charges causes various problems when it is used for various processing to obtain the final product. For example, when performing vapor deposition processing to obtain desired products such as capacitors or gold and silver threads, even when using conventional films without trapped charges,
Stable charges are generated by tightly winding the roll after vapor deposition, but if stable trapped charges already exist in the film before vapor deposition, the generation of trapped charges is further promoted, and it is difficult to perform the next coating or slitting. During processing, the slipperiness with metal rolls becomes poor, and work efficiency is significantly reduced. In particular, films thinner than 25 μm become wrinkled and become impossible to work with. Furthermore, even in applications where vapor deposition is not performed, very unstable charges called triboelectric charges are usually generated due to friction between the metal roll and the film during processing. This charge can usually be removed by a static elimination bar installed in the device, but with films that already have trapped charges, the charges generated by frictional charging tend to be drawn in and stabilized by the trapped charges inside the film. Not only does this further reduce workability, but also the amount of charge generated by frictional electrification is large, resulting in a significant decrease in workability during processing, particularly during dry periods such as winter.

In view of this background, the present invention provides a method for manufacturing a stretched film from an amorphous film obtained by applying an electrostatic charge and cooling and solidifying with a cooling body.
The purpose of the present invention is to provide a method for efficiently manufacturing a stretched film made of a thermoplastic resin that does not have the above-mentioned trapped charges after stretching and does not adversely affect subsequent work. In a method for manufacturing a stretched film by stretching an amorphous sheet or film made of a thermoplastic resin obtained by applying an electrostatic charge and cooling and solidifying on the surface of a cooling body, prior to the stretching process, While maintaining the temperature T of the amorphous film or sheet within the range of Tg-20℃≦T≦Tg+50℃ (here, Tg is the glass transition temperature of the amorphous sheet or film), When one or both sides of the film are subjected to static elimination treatment and the amount of charge retained in a stretched sheet or film is measured in the temperature range from room temperature to Tg + 40°C, the amount of charge of the thermal stimulation current is 0.7 × 10 ^-10 coulombs. /cm ² or less.

The method of the present invention will be explained in detail below.

Any conventionally known method can be used to obtain an amorphous thermoplastic resin film by applying an electrostatic charge to the sheet material melted and extruded from an extruder, and cooling and solidifying it on a continuous cooling surface such as a casting drum. There is no harm in twisting it. In the method of the present invention, in the preheating stage before stretching, the temperature of the amorphous film is kept in the range of Tg - 20°C to Tg + 50°C, preferably Tg to Tg + 30°C, and subjected to static elimination treatment. If the temperature is lower than 0.degree. C., the trapped charges will not be removed sufficiently, and if the temperature is higher than Tg+50.degree. C., the film will stick to a metal roll such as a preheating roll, making it impossible to obtain a uniform stretched film. As the static eliminator used for static neutralization, a conventional commercially available device (for example, a corona discharge type static eliminator) used to eliminate electric charges caused by frictional electrification in film processing can be used. The degree of charge removal treatment is determined by stretching the amorphous film that has undergone this treatment, and measuring the amount of charge retained in the stretched film using thermally stimulated current measurement in the temperature range from room temperature to Tg + 40℃, which is 0.7×
Adjust so that it is 10 ^-10 coulombs/cm ² or less.
If the above charge amount is larger than 0.7×10 ⁻¹⁰ coulombs/cm ² , the secondary processability of the film will be significantly reduced. In particular, it is 25μ that the amount of charge above is a problem.
In the case of a stretched film having the following thickness,
With films thicker than 25μ, this problem is relatively rare because the film has stiffness due to its thickness.

Conventionally, methods for improving workability during film processing include adding additives such as lubricants and sliding agents to improve slipperiness. Although workability can be improved to a considerable extent by
For films that require transparency, the incorporation of additives cannot be carried out because it leads to a decrease in transparency and also degrades other properties, so it is essential to remove trapped charges by the method of the present invention.

In addition, the trapped charges can be removed even if the stretched sheet with trapped charges is held at a temperature above the glass transition point, preferably above Tg + 40°C, and below the melting point of the film for a long time without losing the film's properties. can do. However, this requires time on the order of several tens of minutes, and
At present, where stretching is carried out at speeds ranging from 100 m/min to several hundred m/min, the above-described static elimination treatment is unsuitable from a practical standpoint.

As mentioned above, the degree of static elimination treatment is such that the amount of charge of the thermal stimulation current is below a certain level when the stretched film is measured at a temperature in a predetermined area. This can be done depending on factors such as the flow speed of the film, the thickness of the film, the size of the electrode of the static eliminating bar of the static eliminating device, the static eliminating ability, the distance between the film and the static eliminating bar, and the installation position of the static eliminating device. Among these factors, the film thickness remains constant once the film to be processed is determined.
Since the film flow rate is also limited within a substantially fixed range in conjunction with other processing, adjustments are made by a combination of other factors. Then, for the amorphous film obtained by applying a constant electrostatic charge, the charge amount of the thermally stimulated current in the above temperature range of the stretched product is repeatedly measured, and once the conditions for obtaining the desired value are found, from then on, Reproducible implementation can be achieved without measuring the amount of charge of the thermal stimulation current each time.

One of the main means for adjusting the degree of charge removal of the trapped charges is the distance between the amorphous film and the charge removal bar, and the distance is selected from the range of 10 to 100 mm, preferably 15 to 50 mm. In other words, the shorter the distance, the better; on the contrary, if the distance is closer than 10 mm, an increase in the trapped charge will be observed, while if it is farther than 100 mm, the static elimination effect will be lost. Also, it is preferable to perform static elimination treatment on both sides of the film.
It may be done only on one side.

FIG. 1 shows an apparatus for measuring thermally stimulated current. Figure 1 is a schematic diagram of the device, and in the figure, 1
2 is a film sample coated with conductive paint on both the front and back sides, 3 is an electrode, and 4 is a vibratory capacitance type microcurrent meter (TR-84 model manufactured by Takeda Riken) was used in the examples of the present invention. be. To make measurements,
Apply conductive paint to both sides of the film sample,
Place it between the electrodes 3, raise the temperature inside the constant temperature chamber 1 at a constant temperature increase rate (1.5℃/min), read the current value (depolarization current, amperage) at that time, and divide the value by the electrode area. , plot each temperature and create a chart. An example of the chart is shown in Figure 2. In this chart, the vertical axis is depolarization current (amp) per unit area (1 cm ² ), and the horizontal axis is temperature (° C.).

In FIG. 2, the solid line 5 is the temperature characteristic of the stimulation current measured as described above on a film with trapped charges, and the dotted line 6 is the temperature characteristic of the same sample after the above measurement, cooled to room temperature, and then heated again. This is the temperature characteristic of the measured thermal stimulation current. The amount of charge is the area surrounded by solid line 5 and dotted line 6 (shaded area in the figure)
This is what it means. Note that the polarity of the current may be opposite to that shown in FIG.

The method of the present invention can be applied to any stretchable thermoplastic resin, but is particularly applicable to resins containing a large amount of low molecular weight substances (oligomers) in the polymer, such as nylon, polyester (such as polyethylene terephthalate or ethylene). It is effective in producing stretched films such as copolymers containing 70 mol% or more of terephthalate structural units, or blends thereof. The stretched film obtained by the method of the present invention is extremely suitable for finishing into products such as capacitors and gold and silver threads.

Next, examples of the present invention will be described. In these examples, an apparatus having the configuration shown in FIG. 3 was used. In Fig. 3, 11 is the extruder mouthpiece, 12
13 is a high voltage generator for applying static charge; 14 is a casting drum; 15
is a guide roll, 16 and 17 are preheating rolls, 1
Reference numeral 8 denotes a low-speed stretching roll, 19 a high-speed stretching roll, 20 a cooling roll, 21 a sheet-like material melt-extruded from an extruder die, and 22 a stretched film.

In addition, the glass transition temperature of the material resin was determined by differential thermal analysis (DSC manufactured by Perxielmer), which was measured while raising the temperature of the film from room temperature at a constant rate of 5°C/min.
In the diagram line obtained by -1B use),
The intersection of the rising tangent of the first endothermic peak and the baseline tangent is the glass transition temperature (Tg).
That is. For polyethylene terephthalate, the Tg is approximately 70°C.

In addition, in the examples, the workability of the obtained film is determined by the degree of wrinkles generated during printing and coating processing, which is divided into five levels. The appearance is good, but there are some wrinkles, and the number 5 is that there are no wrinkles at all. From a practical standpoint, a value of about 4 to 5 can be used.

Example 1 Using the apparatus shown in Fig. 3, polyethylene terephthalate with an intrinsic viscosity of 0.62 was melt-extruded from the die 21 at an extrusion temperature of 290°C, and an electrostatic charge was applied to this sheet-like extrudate (voltage 20 kilovolts, current 10 The film was cooled and solidified in close contact with the casting drum 14 to obtain a quenched film with a width of 700 mm and a thickness of 150 μm. Subsequently, the film was heated and maintained at 85 to 95°C (measured with an infrared radiation thermometer) using preheating rolls 16 and 17, and a static eliminator (KSC-325-S type manufactured by Kasuga Denki Co., Ltd.) was installed at the position indicated by C in the figure. According to
The distance from the film to the electrode was set to 25 mm, and the static electricity was removed from both sides of the film. Immediately at the same temperature,
It was stretched 3.2 times in the machine direction between the low-speed stretching roll 18 and the high-speed roll 19, then stretched 3.9 times in the cross direction at 90°C in a tenter (not shown), and then heat-set at 200°C (not shown). (omitted), and then cooled to obtain a biaxially stretched film with a thickness of 12 μm and an extremely good appearance. (Tg of film is 70℃). The amount of electric charge of the obtained film in thermally stimulated current measurement from 20°C to 110°C was 0.10 x 10 ^-10 coulombs/cm ² , and the workability was evaluated as 5.

Comparative Example 1 A stretched film was produced in exactly the same manner as in Example 1, but no charge removal process was performed on the charges trapped in the film, and the thermal stimulation current was similarly measured for the stretched film obtained. ,
The amount of electric charge was 5×10 ⁻¹⁰ coulombs/cm ² and the workability was evaluated as 1.

Comparative Example 2 A stretched film was produced in exactly the same manner as in Example 1, except that the static elimination treatment was not performed before the stretching process, and the film was biaxially stretched and heat-set at 85°C.
The amount of charge measured by thermally stimulated current on the stretched film is 5.
×10 ^-10 coulombs/cm ² (that is, the same result as in Comparative Example 1 in which no static elimination treatment was performed), and the workability evaluation of the film was 2.

Example 2 A biaxially stretched polyethylene terephthalate film with a thickness of 12μ and a very good appearance was obtained by operating under the same conditions as in Example 1 except that the static elimination bar was installed only on the opposite side (one side) from the casting surface. Ta. The amount of charge of this film in heat-stimulated current measurement from 20°C to 110°C was 0.15 x 10 ^-10 coulombs/cm ² , and the workability was evaluated as 5.

Example 3 The static eliminating bar was installed at the position shown in Figure 3B, the distance from the film to the electrode was 50 mm, the film temperature was maintained at approximately 75°C, and static electricity was removed from the film surface until 85~ The process was carried out under the same conditions as in Example 1, except for uniaxial stretching in the longitudinal direction at 95°C, and the thickness was 12 μm.
A stretched film with an extremely good appearance was obtained. The amount of charge of this film in thermally stimulated current measurement from 20°C to 110°C was 0.28 x 10 ^-10 coulombs/cm ² , and the workability was evaluated as 5.

Example 4 A stretched film having a thickness of 12 μm and having an extremely good appearance was obtained by operating under the same conditions as in Example 3 except that the static elimination bar was installed only on the opposite side (one side) to the casting surface. The charge amount of this film in heat-stimulated current measurement from 20°C to 110°C was 0.30×10 ^-10 coulombs/cm ² , and the workability was evaluated as 5.

Example 5 A biaxially stretched film with a thickness of 12 μm and an extremely good appearance was obtained by operating under the same conditions as in Example 2 except that the film temperature during static elimination was 110° C. and the longitudinal stretching temperature was 110° C. 110 from 20℃ for this film
The amount of charge in thermally stimulated current measurement up to ℃ is 0.15×
10 ^-10 coulombs/cm ² , and the workability evaluation was 5.

Example 6 The distance from the electrode of the static elimination bar to the film is 100
The operation was carried out under the same conditions as in Example 4 except that the thickness was 12 mm, and a stretched film having a thickness of 12 μm and having an extremely good appearance was obtained.
The amount of charge of this film in thermally stimulated current measurements from 20℃ to 110℃ is 0.45×10 ^-10 coulombs/cm ²
The workability evaluation was 4.

Comparative example 3 The distance from the electrode of the static elimination bar to the film is 120
A biaxially stretched film having a thickness of 12 μm and having an extremely good appearance was obtained by operating under the same conditions as in Example 1 except that the film was set to mm. The amount of charge of this film in thermally stimulated current measurement from 20°C to 110°C was 0.75 x 10 ^-10 coulombs/cm ² , and the workability was evaluated as 3.

Comparative example 4 Distance from the electrode of the static elimination bar to the film is 5 mm
The operation was carried out under the same conditions as in Example 1 except that the thickness
A biaxially stretched film with a thickness of 12μ and a good appearance was obtained. The amount of charge of this film in thermally stimulated current measurement from 20°C to 110°C is 0.93 × 10 ^-10 coulombs,
The workability evaluation was 3.

Comparative Example 5 The static eliminator was installed at the location shown in Figure 3A, the distance from the film to the electrode was 25 mm, and the film temperature was maintained at 35°C to perform static neutralization on both sides.
A biaxially stretched film with a thickness of 12 μm and a good appearance was obtained by operating under the same conditions as in Example 1 except for longitudinal stretching at 85 to 95°C. The charge amount of this film in heat-stimulated current measurement from 20°C to 110°C was 2.3 x 10 ^-10 coulombs/cm ² , and the workability was evaluated as 2.

Comparative Example 6 An attempt was made to produce a biaxially stretched film under the same conditions as in Example 1 except that the film temperature during static elimination was maintained at 120°C, but adhesion occurred on the preheating roll and the appearance of the film actually sampled was poor. It was very bad. Note that the amount of charge of this film was 0.10×10 ⁻¹⁰ coulombs/cm ² as determined by thermally stimulated current measurement from 20° C. to 110° C.

What has been explained above and described in the examples is for the purpose of helping the understanding of the present invention, and the present invention is not limited thereto, and other changes and modifications may be made within the gist of the invention. It is something that can be done.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the device for measuring thermally stimulated current;
Fig. 2 is a chart showing the results of measuring thermally stimulated current by heating a film sample at a constant heating rate using the apparatus shown in Fig. 1, and Fig. 3 explains the apparatus for carrying out the method of the present invention. FIG. In the figure, 1 is a constant temperature bath, 2 is a film sample, and 3
1 is an electrode, 4 is a vibratory capacitance type microammeter, 11 is an extruder mouthpiece, 12 is an electrode for applying static electricity, 13 is a high voltage generator, 14 is a casting drum, 15 is a guide roll, 16 and 17 are preheating rolls , 18 are low-speed stretching rolls, and 19 are high-speed stretching rolls.

Claims (1)

[Scope of Claims] 1. A method for producing a stretched film by stretching an amorphous sheet or film made of a thermoplastic resin obtained by applying an electrostatic charge and cooling and solidifying on the surface of a cooling body. First, while maintaining the temperature T of the amorphous film or sheet within the range of Tg-20℃≦T≦Tg+50℃ (here, Tg is the glass transition temperature of the amorphous sheet or film), When static electricity removal treatment is applied to one or both sides of a sheet or film, and the amount of charge retained in a stretched sheet or film is measured in the temperature range from room temperature to Tg + 40℃, the amount of charge of the thermally stimulated current is 0.7 × 10 ^-10 coulombs/cm ² or less, a method for producing a stretched film.