JPS6058830A - Manufacture of polyamide film - Google Patents

Abstract

PURPOSE:To obtain the titled film with higher uniformity of thickness at a high efficienty by a method wherein a polyamide resin with a specified melt specific resistance containing a metal compound is melted and extruded like a film and put electrostatically tight on a rotary cooling roll to be taken off being quenched and solidified. CONSTITUTION:A polyamide resin (e.g. nylon 6) with the melt specific resistance of 1.5X10<5>OMEGAcm or less at 260 deg.C containing a metal compound (e.g. sodium stearate) is melted and extruded like a film with a screw extruder, put electrostatically tight on a rotary cooling roll and then, taken off being quenched and solidified to obtain a desired film. It is desirable that the film thus obtained is stretched by 1.1 times at lest in one direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly efficient method for producing a polyamide film with excellent thickness uniformity.

Polyamide films, especially N4-6 films obtained by ring-opening polymerization of ε-caprolactam, are widely used in the food packaging field due to their toughness, impact resistance, pinhole resistance, and high oxygen barrier properties. There is.

As a method for manufacturing polyamide films, a melt extrusion method using an inflator method or a T-die method is generally used. When obtaining a boronamide film by the T-die method, the molten film is extruded from a goose and first cast onto a rotating cooling roll. At this time, in order to bring the film into close contact with the cooling rotating roll, there is a method of blowing air with an air knife (hereinafter referred to as the air knife method), a method of depositing a charge on the molten film from a high voltage electrode and making it adhere electrostatically (hereinafter referred to as the electrostatic (called the close contact method) etc. are performed.
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However, even in casting using the air knife method or electrostatic adhesion method, when the take-up speed increases, air is drawn between the rotating cooling roll and the film due to the accompanying flow generated by rotation, making it difficult to form a uniform film. You won't be able to get it.・In the case of Bo1 amide resin, a polyamide-based thermoplastic polymer sheet characterized by performing corona discharge in a streamer corona discharge state and depositing charges on the molten film (±1), which is electrostatically brought into close contact with a rotating cooling roll. The cooling power method for
Publication No.). It is also known that this method is effective for synthetic resins having a melt specific resistance of 6.0×10 6 Ω or less.

(Japanese Unexamined Patent Publication No. 56-105930) However, even with this improved electrostatic adhesion method, the adhesion to the rotating cooling roll cannot be said to be sufficient, and the film thickness uniformity and productivity cannot be satisfied. I can't say that I do. Therefore, the present inventors have conducted intensive studies to efficiently produce a polyamide film with excellent thickness uniformity, and as a result, have arrived at the present invention.

The present invention involves melting and extruding a polyamide resin containing a metal compound and having a melt specific resistance of 1°5×10'Ω or less at 260°C, and then electrostatically transferring the melt-extruded film to a rotating cooling roll. The present invention relates to a method for producing a stretched polyamide film in polyamide by secretly infiltrating the film and rapidly solidifying it.

That is, by incorporating a metal compound into a polyamide resin, the Kel melt specific resistance at 260°C can be increased to 1.
It has been found that by setting the resistance to 5×10 5 Ωα or less, electrostatic adhesion is significantly improved and unstretched and stretched polyamide films with excellent thickness uniformity can be efficiently produced.

The specific melting resistance of polyamide resin that does not contain metal compounds at 260°C is usually 1XIO3Ωctn ~ 5X for nylon 6, nylon 66, and polymethaxylylene adipamide.
105Ωα, 5X105 to 10X105 with nylon 12
The Ω saw is a thermoplastic synthetic resin having a specific melting resistance of 6,0×10' Ω (7) or less, which is disclosed in Japanese Patent Application Laid-Open No. 56-105930. However, compared to polyamide resins that do not contain metal compounds and are used as starting materials in the present invention, polyamide resins that contain metal compounds and have a specific melting resistance of 1.5 x 105 Ωm or less at 260°C have significantly improved electrostatic adhesion. I found something to do.

The present invention will be explained in more detail below.

Examples of the polyamide resin in the present invention include homopolymers and copolymers of nylon 6, Tyron 66, nylon J2, and polymethaxylylene adipamide. In addition, thermoplastic polyamide resins having film-forming properties can also be used. When not containing a metal compound, the melting resistivity of these polyamide resins at 260° C. is usually larger than 10 × 10 11 Ωm. A mixture of these polyamide resins can also be used. These resins also contain small amounts of other resins, lubricants, antioxidants,
Organic or inorganic substances such as antistatic agents and colorants may be added.

The metal compounds used in the present invention include alkali metals, alkaline earth metals, aluminum group elements, transition metal halide compounds, sulfur oxygen acid compounds, phosphorus oxygen acid compounds, hydroxides, organic carboxylates, organic There are sulfonates, specifically sodium chloride, lithium chloride,
Potassium chloride, magnesium chloride, calcium chloride, aluminum chloride, zinc chloride, copper chloride, cobalt chloride, sodium bromide, lithium bromide, magnesium bromide, potassium iodide, sodium iodide, sodium sulfate, magnesium sulfate, zinc sulfate , sodium phosphate, potassium phosphate, sodium phosphite, sodium hypophosphite, calcium hypophosphite, sodium hydroxide, lithium hydroxide, sodium stearate, potassium stearate, magnesium stearate, calcium stearate, aluminum stearate , zinc stearate, potassium oleic acid, sodium acetate, potassium acetate, sodium benzoate, thorium lauryl sulfonate, sodium benzene sulfonate, and the like.

In addition, a metal base-containing compound capable of forming an amide bond, such as 5-sodium sulfoisophthalic acid, may be added to bond the metal base directly to the polyamide chain. The present invention is not limited to full flexure in polyamide. Furthermore, in the case of metals with low ionization potential, such as alkali gold and alkaline earth metals, it is also possible to use them alone. If the content of these metal compounds is 0.0005% to 5% by weight based on the polyamide resin and the content is 0.0005% by weight or less, the effect of improving electrostatic adhesion is small. Metal compound content is 5%
In the above case, the physical properties of the film deteriorate, which is not preferable. However, the present invention is not limited to these metal compound content ranges.

The metal compound can be added to the raw material before polymerization, during the polymerization process, during the extraction process, or when the pellets are dried. I don't mind. It is effective as long as the metal compound is contained in the final melt-extruded polyamide resin, and the present invention is not limited to these methods of addition.

In the present invention, as a method for electrostatically bringing the rotary cooling four into close contact with each other, a method in which a charge is applied by performing corona discharge in a streamer corona state (Japanese Patent Application Laid-Open No. W3SS-1755
9) is valid. However, the present invention is not limited to this method only, and can be applied to devices that apply a charge by bringing a normal high-voltage charging electrode close to a molten film, to an electrostatic adhesion device that uses an air knife in combination, and to rotating It is also possible to apply the present invention to a device in which a cooling roll is coated with a dielectric material and a charge having a sign opposite to that of a high-voltage charging electrode is deposited on the rotating cooling roll. In the case of polyamide resins that contain metal compounds and have a melting specific resistance of 1.5X105Ωα or less at 260°C, the electrostatic adhesion of the molten resin to the rotating cooling roll during installation is lower than that of polyamide resins that do not contain metal compounds. This improves the quality of life.

The take-up speed of the unstretched film in the present invention is not particularly limited. If the drawing speed is increased, air will be trapped between the rotary cooling wheel and the molten film, making it impossible to obtain a good unstretched film. Does not contain conventional metal compounds, melting resistivity at 260℃ is 1.5X10
When taking polyamide resin larger than 5 Ωm onto a rotating cooling roll using the electrostatic adhesion method, the maximum υ1 removal speed is usually 10 to 20 m7 minutes, but in the present invention, even at this drawing speed or higher, the rotating cooling roll This prevents air from entering between the molten film and the molten film, resulting in an unstretched film with a uniform thickness. The unstretched polyamide as it is is suitable for packaging foods and the like. However, the unstretched polyamide film can be further reduced by 1.1 times or more in one direction, preferably by 2.0 to 5.0 times in each of two orthogonal directions.
A double-stretched biaxially stretched film further improves mechanical strength, transparency, and oxygen barrier properties, and is suitable for various packaging films.

The present invention will be explained in more detail by showing examples below.

In addition, the melting specific resistance of the resin in the present invention is the melting temperature maintained at 260°C! Insert stainless steel M electric razor into d fat, 100
This is a value calculated from the formula of specific resistance ρ=(S/L)X(V/I) from the current value flowing for 1 to 5 seconds when a DC voltage of V is applied. Here, ρ is specific resistance (Ωcrn),
S is the electrodeposition area (crA), L is the distance between electrodes (crn),
■ represents the voltage (V), and 〇 represents the current (A). In the measurement in this example, S was 0.12 cd% and L was 1.5 cm. In addition, the relative viscosity of the resin in the examples is 96
．． This is the value measured using an Ostwald viscometer in a constant temperature bath at 20° C. after dissolving in 3% concentrated sulfuric acid at a concentration of 1.0 f/100 me.

Example 1 Naipun 6 pellets with a relative viscosity of 2.6 containing 0.4% by weight of silicon dioxide with an average particle size of 3 μtn as a lubricant were mixed with sodium stearate in a rotary vacuum dryer. After mixing and drying, the resin was extruded into a film at 260°C through a T-die using a 90-die screw extruder and cast onto a rotating cooling roll at 20°C. Next, apply a DC voltage to the multi-acicular high-voltage charge '@ pole and bring it close to the surface of the molten resin.
After J-Mafrona was discharged to give an electric charge and brought into close contact with the cooling roll, the take-up speed of the rotating cooling roll was gradually increased. At this time, up to a take-up speed of 55 m/min, air was not entrained between the resin and the rotating cooling roll, and a transparent unstretched film with little thickness unevenness was obtained.
The melt specific resistance at 60° C. was 4.7×10′Ωm.

Example 2.3 In the same manner as in Example 1, magnesium bromide and zinc chloride were added to the contents shown in the table and a casting test was conducted. It was possible to prevent air from getting caught between the rotating cooling rolls.

Comparative Example 1 Same as Examples 1 to 3.
．． Nylon 6 containing 4% by weight and having a relative viscosity of 2.6 was dried in a rotary vacuum dryer without the addition of metal compounds. When a casting test similar to that in Example 1 was conducted, the take-up speed was 35 m. /min, air gets caught between the resin and the rotating cooling roll, causing vertical streaks.
Thickness spots and opaque areas occurred. The melt specific resistance of this resin was 1.8 x 10'Ω-.

Example 4 To 10 parts by weight of epsilonkab tetralactam, 0.05 parts by weight of trisodium phosphate dodecahydrate, 1.5 parts by weight of 0.05 heavy weight water, and 0.4 parts by weight of silicon dioxide having an average particle size of 3 μm were added. Then, ring-opening polymerization was performed to obtain pellets of nylon 6 having a melting specific resistance of 0.58 x 105 Ωm1 and a relative viscosity of 2.6 at 260°C. As in Example 1, after drying this in a rotary vacuum dryer, a casting test was performed, and it was found that no air was caught between the resin and the rotating cooling roll up to 55 m/min, resulting in a transparent unfinished product with little thickness unevenness. A stretched film was obtained.

An unstretched film with a uniform thickness with no air caught between the rotating cooling roll and an unstretched film with vertical stripes with air caught between the resin and the cooling rotating roll were heated to 70°C at different circumferential speeds. After stretching 3.5 times in the longitudinal direction between rolls, stretching 3.7 times in the transverse direction in a tenter at 100°C, and further heat-setting at 200°C to obtain a biaxially stretched nylon 6 film. A biaxially stretched film was obtained from an unstretched film that did not involve air, but an unstretched film that involved air was broken in a tenter, making it extremely difficult to obtain a biaxially stretched film.

In addition, the thickness of the unstretched film at this time is 180 to 200
μm, and the thickness of the film after biaxial stretching is 15 to 16
It was μm.

Example 6 440ii parts of metaxylene diamine, 470 parts of adipic acid
1 part by weight of trisodium phosphate dodecahydrate
Polymethaxylylene adipamide with a relative viscosity of 2.1 obtained by polycondensation with addition of 450 parts and 450 parts of water was extruded at 260°C from a T-die in the same manner as in Example 1, and a casting test was conducted. As a result, the pick-up speed was 55m/
No air was trapped between the resin and the rotary cooling roll even when the stretching time was longer than 30 minutes, and an unstretched film with good thickness uniformity and transparency was obtained. The melt specific resistance of this resin is 3.9X10'
It was Ωα.

Comparative Example 2 When polymethaxylylene adipamide was obtained by polycondensation in the same manner as in Example 5, polymethaxylylene with a relative viscosity W of 2.1 and containing no metal compound was produced without adding trisodium phosphate dodecahydrate. Obtained adipamide.

This resin was extruded through a T-die at 260°C in the same manner as in Example 1, and a casting test was conducted. At a casting speed of 40 m/min, air was caught between the resin and the rotating cooling roll, causing vertical streaks to form in the film. spots occurred. The melting specific resistance number of this resin at 260°C is 1.6X105
It was an Ω saw.

Margin table 1 below. Maximum melting speed and specific melting resistance at 260'C of polyamide pre-blending with various metal salts added

Claims (1)

[Claims] 1. Melt-extrude a polyamide resin containing a metal compound and having a melt specific resistance of 1.5 x 10'Ω or less at 260°C, and pass the melt-extruded film onto a rotating cooling roll. A method for producing a polyamide film, which is characterized by electrostatically adhering to the film and removing it while rapidly cooling and solidifying it. 2. Method 0 of further stretching the film according to claim 1 by 1.1 times or more in at least one direction.