JPH0688309B2 - Method for rapid film formation of polyamide-based multilayer film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyamide-based high-layer film, and a multilayer polyamide-based film provided with a layer having a low specific resistance in order to impart a special function to the film. The method provides a method of rapidly cooling by adhering to a cooling roll by electrostatic pinning.

(Prior Art) A method of rapidly forming a polyamide film by electrostatic pinning has been known, for example, Japanese Patent Publication No. 59-23270.
The publication describes a method of corona discharge in a streamer corona state when cooling a polyamide-based film and applying a high current to the film to bring it into close contact with a cooling roll.

In addition, the inventors of the present invention filed Japanese Patent Application No. 59-217521 (Japanese Patent Publication No. 1-463).
No. 04), in order to improve work safety and film homogeneity, a method of electrostatically pinning a polyamide-based film with a low current discharge that does not reach a streamer state, that is, a dielectric breakdown voltage of 5 KV or more on the surface of a cooling roll. We propose a method of applying an electric insulating coating to the film to impart an electric charge of an apparent applied density of ² μC / cm ² or less to the film.

(Problems to be Solved by the Invention) The method of Japanese Patent Application No. 59-217521 (Japanese Patent Publication No. 1-4630) is
The specific resistance in the molten state is about 10 ⁵ Ω · cm and other thermoplastic resins such as polyethylene terephthalate (specific resistance
This is an advantageous method for electrostatically pinning a polyamide-based film with a smaller specific resistance at a safe low current than that of 10 ⁸ to 10 ⁹ Ω ・ cm). It is possible to perform electrostatic pinning on a film whose specific resistance has dropped to 5.0 × 10 ⁴ Ω · cm or less by adding. However, the inventors of the present invention further improved the method of Japanese Patent Application No. 59-217521 (Japanese Patent Publication No. 1-46304), and as a result of diligent research to develop applied technology,
It was found that a larger specific resistance is more advantageous in the range of 10 ⁴ to 10 ⁶ Ω · cm. In the case of electrostatic pinning by high-current streamer corona discharge as in the method of Japanese Patent Publication No. 59-23270, it is advantageous to reduce the specific resistance and increase the flow rate for streamer corona discharge. For example, as is clear from the description in Japanese Patent Laid-Open No. 60-58830, Japanese Patent Application No. 59-217521 (Japanese Patent Publication No. 1-46304)
Since the method of (1) aims to limit the current by providing an electric resistance layer on the cooling roll and safely perform electrostatic pinning with a minimum amount of current, it is disadvantageous if the specific resistance is too small.

Ordinary polyamide resin such as nylon 6 and nylon 66
The specific resistance in the molten state is 1.0 × 10 ^{5 to} 3.0 × 10 ⁵ Ω
・ Approximately cm, and in this case, the method of Japanese Patent Application No. 59-217521 is extremely effective. For example, when this method is applied to the biaxially stretched film manufacturing process, the casting speed is the rate-determining step of the line speed. There is no such thing.

However, if the specific resistance is in the range of 1.0 × 10 ^{4 to} 5.0 × 10 ⁴ Ω · cm by adding an ionic antistatic agent, heat-resistant agent, and antioxidant, the casting speed that allows electrostatic piniog is set. Start to be rate controlled. That is, even when electrostatic pinning is performed using a cooling roll provided with an electrically insulating coating, if the specific resistance is too small, the current begins to increase, and finally a streamer state is reached, which is a work safety problem and the thickness It was necessary to slow down the casting speed to lower the current in order to disturb the temperature.

(Means for Solving Problems) The present inventors have found that when the polyamide-based film is electrostatically pinned by using a cooling roll provided with an electrically insulating coating, the current increases when the specific resistance decreases. As a result of the investigation, it was found that the cause is that when the specific resistance becomes small, the electric charge that conducts through the film and escapes to the T-die increases. As the leakage current to the T-die increases, the extra current is needed to provide the film with the charge necessary for sufficient electrical attraction between it and the chill roll.

On the other hand, polyamide films, especially their biaxially stretched films, are widely used in various fields of application such as packaging films, and ionic antistatic agents, antioxidants, and heat-resistant agents are added due to the requirements of the application. In this case, the specific resistance in the molten state decreases, and as a result, the film forming rate is limited.

The inventors of the present invention have a multilayer structure of a polyamide-based film and add an antistatic agent and an antioxidant only to a layer in which they are required, but in many cases, the additive function does not deteriorate so much, and The electric resistance in the molten state is maintained to some extent by co-extruding as a multi-layer structure of a layer having a lowered specific resistance by kneading an ionic additive and a layer not kneading them and thus not lowering the specific resistance. The present invention has been achieved by knowing that the leakage current to the T-die can be limited. That is, a polyamide-based multilayer film containing a layer with a specific resistance in the molten state of 5.0 × 10 ⁴ Ω · cm or less was extruded from the die, and a dielectric breakdown voltage of 5 KV was applied to the surface.
When the film is cast on a cooling roll provided with the above electrically insulating coating, an electrostatic charge is applied by an electrode arranged above the film, and the film is applied to the cooling roll by an electric attraction acting between the film and the cooling roll. In the method of closely contacting and cooling, by combining layers with a specific resistance of 1.4 × 10 ⁵ Ω · cm or more, the average resistance of the film averaged by thickness is 1.0 × 10 ⁵ Ω · cm or more. And a method for rapidly cooling a polyamide-based multilayer film.

Leakage current to the T-die when electrostatically pinning a multi-layer film composed of layers having different specific resistances using a cooling roll provided with an insulative coating determines the specific resistance of each layer by the thickness of that layer. It is almost inversely proportional to the weight-averaged film average resistivity. When kneading an ionic antistatic agent, antioxidant, etc., selecting the type and concentration of the additive required to fully exhibit each performance, the specific resistance in the molten state is 5.0 × 10 ⁴ Ω.・ It is often less than cm, and when trying to electrostatically pin films in this range in a non-streamer state using a chill roll with an insulating coating, the casting speed is limited to, for example, 40 m / min or less. However, since the film has a multi-layer structure and contains additives, the surface layer is composed of a polyamide resin that has a resistivity of 5.0 × 10 ⁴ Ω · cm or less, and the inner layer contains no ionic additives and has a resistivity of 1.
By using a polyamide-based resin of 4 × 10 ⁵ Ω · cm or more and setting the average resistance of the film weight averaged to 1.0 × 10 ⁵ Ω · cm or more, the effect of the additive does not decrease so much.
Moreover, there are almost no restrictions on the casting speed, and it becomes possible to perform uniform quench film formation at 50 m / min or higher, for example.

The method of the present invention reduces the leakage current between the electrode and the cooling roll by providing an electrically insulating coating on the surface of the cooling roll,
Holds the specific resistance of the film above a certain range to reduce the leakage current between the electrode and the T-die, and due to these effects, contains a ionic additive with a low current discharge that does not reach a streamer state,
It is intended to provide a method for rapidly and rapidly forming a polyamide-based multilayer film including a functional layer having a reduced specific resistance by an electrostatic pinning film forming method.

The polyamide-based multilayer film to which the present invention is applied is
Homopolymers such as Nylon 6, Nylon 66, Nylon 6-10, etc. or mixtures thereof and copolymers of these polyamides within the range not changing the basic properties, and multilayers composed of materials to which various additives are added. The film is usually a two-layer or three-layer film composed of the same material except for the presence or absence or concentration of the ionic additive. The electrically insulating coating is an organic polymer material such as a fluorine resin, an acrylic resin, a polyester resin, or the like.
It is an electrically insulating ceramic material such as Al ₂ O ₃ , and usually a combination of these is the most suitable. The material and thickness of the coating layer are selected in consideration of the condition that the dielectric breakdown voltage is 5 KV or more, more preferably 10 KV or more. This is because it is necessary to avoid damage to the coating layer when arcing occurs due to some trouble during the film forming operation. However, since the electrically insulating coating material generally has low thermal conductivity, if the coating layer is made too thick, the cooling efficiency of the cooling roll deteriorates. For this reason, the covering layer is generally suitable in the range of dielectric breakdown voltage of 5 KV or more and 15 KV or less. From this range, the most suitable one according to the film forming conditions such as polymer resistivity, film thickness, speed, and cooling roll temperature. Select. The electrode is a steel wire with a diameter of 0.1 to 0.3 mm,
A method of arranging the tongue-stain wire at a position 1 to 10 mm above the film surface above the position where the film contacts the cooling roll is common. A DC high voltage generator is used to apply a positive or negative DC voltage of 5 to 15 KV to the electrodes. The polarity may generally be positive or negative, but it is often more preferable to apply a voltage having a polarity opposite to the charging polarity of the coating material, which is determined from the charging sequence of the insulating coating material and the film, to the electrodes.

The weighted average of the specific resistance thickness in the molten state means, for example, a polymer having a specific resistance at the extrusion temperature of 4.0 × 10 ⁴ Ω · cm and a thickness of 25 μm after cooling. In the case of a three-layer film composed of a polymer with a specific resistance of 1.6 × 10 ⁵ Ω · cm, the average specific resistance is That is 1.2 × 10 ⁵ Ω · cm. When a film of polyamide resin having a viscosity suitable for extrusion molding and having a total thickness of 100 to 500 μ is subjected to electrostatic pinning by the method of the present invention, the average resistance of the film averaged by weight is at least 1.0 × 10 ⁵
Ω · cm or more, more preferably 1.2 × 10 ⁵ Ω · cm or more is suitable.

(Operation) By applying the method of the present invention, in the non-streamer electrostatic pinning technology, it is possible to perform rapid cooling film formation without restriction on a polyamide-based film including a low-resistivity functional layer whose casting speed is restricted. Become.

In addition, the polyamide-based film can be adhered to the cooling roll at a low current to perform rapid cooling film formation, ensuring work safety,
A uniform film can be formed without the thickness irregularity occurring at the streamer discharge point.

When the polyamide-based multilayer film formed by the method of the present invention is further biaxially stretched, the biaxially stretched film has good thickness accuracy, optical uniformity, and the like, and has improved antistatic property and heat resistance. And the effect of the method of the present invention is further enhanced.

(Examples and Comparative Examples) Example 1 A film forming apparatus comprising two extruders, a feed block type three-layer die, and a cooling roll having a surface coated with ceramics (Al ₂ O ₃ ) to a thickness of 0.15 mm. The film was formed. Nylon 6 (manufactured by Unitika Ltd.) is used for both side surface layer forming extruders.
A1030BRF) with 1% by weight of an anionic antistatic agent (Chemistat 3033, Sanyo Kasei Co., Ltd.) added, the same nylon 6 raw material with no additive added to the extruder for forming the inner layer, and the extrusion temperature 260 A three-layer nylon film was extruded at ° C. A tungsten wire having a diameter of 0.2 mm was stretched in parallel with the cooling roll above the position where the film discharged from the T-die was in contact with the cooling roll, to form an electrostatic pinning electrode.

The specific resistance of each raw material was measured by a separate device consisting of a small extruder and a specific resistance measuring cell. The specific resistance of the raw material added with the antistatic agent at 260 ° C was 2.2 × 10 ⁴ Ω · cm, no addition. The raw material was 1.7 × 10 ⁵ Ω · cm.

After the film was cooled and solidified, electrostatic pinning was performed while adjusting the discharge rate of the extruder so that the surface layer thickness was 23μ on both sides and the inner layer thickness was 124μ.
A uniform rapid cooling film can be formed without streamer discharge up to min, and the obtained film is simultaneously biaxially stretched 3.3 times in the longitudinal direction and 3.5 times in the transverse direction, resulting in excellent antistatic effect, thickness accuracy, and optical uniformity. A film was obtained. In this example, the average resistance of the film averaged by the weight is 1.3 × 1
It is 0 ⁵ Ω · cm.

Comparative Example 1 Using the same apparatus as in Example 1, the same antistatic additive raw material as that charged in the surface layer extruder in Example 1 was supplied to both the surface layer and inner layer extruders, and two extruders were used. A 170 μm-thick film was formed by electrostatic pinning while maintaining the same discharge amount ratio as in Example 1.

When the speed of the chill roll exceeds 30 m / min, local streamer discharge occurs, making it impossible to evenly adhere the film to the chill roll, and a uniform rapid film-forming speed of about 25 m / mi.
It was n.

Further, when the film formed at 25 m / min was simultaneously biaxially stretched under the same conditions as in Example 1, the antistatic effect of the obtained film was similar to the film obtained in Example 1 in practical use. Met.

(Effect of the invention) By adding an ionic additive to the polyamide film,
The method of giving a special function to the film is useful as a modification technology for polyamide film, but when combined with the non-streamer method electrostatic pinning technology, there was a problem that the film formation speed was conventionally limited. . The method of the present invention makes it possible to increase the film formation rate without losing the function of the ionic additive, and its economic effect is great.

Claims (1)

[Claims] 1. The specific resistance in the molten state is 5.0 × 10 ⁴ Ω · cm.
When a polyamide-based multilayer film containing the following layers was extruded from a die and cast on a chill roll having an electrically insulating coating with a dielectric breakdown voltage of 5 KV or more on its surface, an electrostatic charge was applied by electrodes placed above the film. In the method in which the film is brought into close contact with the cooling roll by an electric attraction acting between it and the cooling roll to cool it, by combining layers with a specific resistance of 1.4 × 10 ⁵ Ω · cm or more, the load average by thickness is obtained. The average resistivity of the film was 1.0 x 1
A method for forming a rapid cooling film of a polyamide-based multilayer film, which is characterized in that it is at least ⁵ Ω · cm.