JPS60255413A - Preparation of polyamide film - Google Patents

Abstract

PURPOSE:To obtain the titled film excellent in thickness uniformity, by a method wherein a composition containing a polyamide resin having a metal base introduced into the main chain thereof and other polyamide resin is extruded under melting and the extrudate is electrostatically and closely contacted with a cooling roll to be solidified under cooling. CONSTITUTION:A composition consisting of 1-100pts.wt. of a polyamide resin (A) having a metal base contained in the main chain thereof and 99-0pts.wt. of a polyamide resin (B), of which the melt specific resistance at 260 deg.C is 1.5X 10<5>OMEGA.cm or more, is extruded in a film form under melting. Subsequently, this melt-extrusion film is electrostatically and closely contacted with a rotary cooling roll and solidified under cooling to obtain the objective polyamide film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly efficient method for producing a polyamide film with excellent thickness uniformity.

<Object of the Invention> Polyamide films are widely used in the field of food packaging, where they can take advantage of their properties such as toughness, impact resistance, pinhole resistance, and oxygen barrier properties. In recent years, with the growth of retort food products, the demand for polyamide films has also increased, and there is a desire to supply high-quality and inexpensive films.

<Relationship with Prior Art> Polyamide films are usually produced by melt extrusion using an inflation method or a T-die method. When obtaining a polyamide film by the T-die method,
The molten film extruded from the die is 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 (referred to as the close contact method). However, even in casting using the air knife method or electrostatic adhesion method, when the take-up speed increases, air is caught between the rotating cooling roll and the film due to the accompanying flow generated by rotation, making it difficult to obtain a uniform film. It disappears.

Therefore, the present inventors conducted intensive studies to efficiently produce a polyamide film with excellent thickness uniformity.As a result of repeated studies, we found that adding a metal compound to polyamide resin improves electrostatic adhesion. I found out. However, among polyamide resins, in the case of polyamides that require an extraction step for monomers and oligomers after polymerization, if metal compounds are added to both the raw materials and the raw materials before polymerization, some of the metal compounds may be eluted by water extraction. Yes, electrostatic adhesion may deteriorate. As a result of further intensive studies, the present inventors discovered that polyamide with a metal base introduced into the main chain has excellent electrostatic adhesion, and that the electrostatic adhesion decreases little even after water extraction. reached.

<Structure of the Invention> That is, the present invention comprises 1 to 100 parts by weight of a polyamide resin (A) containing a metal base in its main chain and a polyamide resin (A) having a specific melting resistance at 260°C of 1.5×10'0 cm or more. B) A polyamide film characterized by melt-extruding a composition containing 99 to 0 parts by weight into a film, electrostatically adhering the melt-extruded film to a rotating cooling roll, and solidifying it by cooling. The present invention relates to a manufacturing method.

The present invention will be explained in more detail below.

The polyamide resin (A) containing a metal base in the main chain in the present invention is a polyamide containing a sulfonic acid group, a phosphonic acid group, etc. in the main chain. Specifically, metal salts of sulfoterephthalic acid, metal salts of sulfoisophthalic acid,
Polyamide-forming dicarboxylic acids, diamines, aminocarboxylic acids or lactams containing metal bases such as metal salts of phosphoinphthalic acid and metal salts of biscarboxyphenylphosphonic acid are combined with adipic acid, sebacic acid, terephthalic acid, hexa It can be obtained by copolymerizing with metal base-free polyamide-forming dicarboxylic acids, diamines, aminocarboxylic acids, lactams, etc., such as methylene diamine, metaxylene diamine, ε-caprolactam, and ε-laurolactam. Preferred examples of the polyamide-forming monomer containing a metal base include sodium sulfoterephthalate, sodium sulfoisophthalate, potassium sulfoisophthalate, etc., but the present invention is not limited to these specific examples.

The content of the metal base introduced into the main chain is not particularly limited, but is preferably 10 to 0.0003% by weight based on the polyamide resin (A) based on the metal base.O, OOO
If it is less than 3% by weight, sufficient electrostatic adhesion cannot be obtained;
When the amount exceeds % by weight, gelation of the resin becomes significant.

The polyamide resin (A) containing a metal base in the main chain has a lower melting resistivity than the polyamide resin not containing a metal base in the main chain. preferable.

The specific melting resistance at 260°C in the present invention is 1.5
Polyamide resin with XIC1' 00111 or higher (
B) means nylon 6, nylon 66, nylon 11.
Nylon 12. Examples include homopolymers and copolymers with polyhexamethylene terephthalamide and polymethaxylylene adipamide. The mixing ratio of polyamide resin (A) and polyamide resin (B) is preferably 1.5 x 1050 cm or less depending on the specific melt resistance of the composition.

The mixing ratio of the polyamide resin (A) varies depending on the amount of metal base in the resin (A), but the content of the metal base relative to the composition weight of the resin (A) and resin (B) is The mixing ratio is preferably such that the metal content is 0.0003% by weight to 1% by weight. The mixing ratio of the resin (A) in the polymer mixture can be 1% by weight or more and 100% by weight or less.

In the present invention, the method of electrostatically bringing the roller into close contact with the rotating cooling roll includes, for example, applying a high voltage to a wire-like electrode, knife-like electrode, or probe-like electrode disclosed in Japanese Patent Publication No. 37-6142, and melting the roll. A method of imparting charge to the film can be applied. However, the present invention is not limited to this method only, and can be applied to an electrostatic adhesion device that uses an air knife in combination, or by coating a rotating cooling roll with a dielectric material and rotating a charge having the opposite sign to that of a high-voltage charged electrode. Application to a device for depositing on a cooling roll is also possible. Regardless of which device is used, in the case of the polyamide resin composition of the present invention, the electrostatic adhesion of the molten resin to the rotating cooling roll in these devices is improved compared to polyamide resins other than the polyamide resins of the present invention. The unstretched polyamide obtained in the present invention is suitable as it is for packaging foods and the like. However, the unstretched polyamide film is further expanded by at least 1.1 times in one direction, preferably by 2.0 to 5 times in each of two orthogonal directions.
A biaxially stretched film stretched 0 times has further improved mechanical strength, transparency, and oxygen barrier properties, and is suitable for various packaging films.

<Effects of the Invention> The speed at which the unstretched film is taken off in the method of the present invention is not particularly limited. When the take-up speed is increased, air is caught between the rotating cooling roll and the molten film.
A good unstretched film cannot be obtained. Does not contain conventional metal compounds and has a melting resistivity of L5X1 at 260℃
When taking polyamide resin larger than 05ΩCIN onto a rotating cooling roll using an electrostatic adhesion device, the maximum taking-up speed is usually 10 to 20 m/min. The entrainment of air between the molten film and the molten film is prevented, and an unstretched film with a uniform thickness can be obtained.

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

In addition, the melt specific resistance of the resin in the present invention is determined by inserting a stainless steel electrode into the molten resin kept at 260°C.
This value is calculated from the formula of specific resistance ρ=(S/L)X(V/I) from the current value after 1 second to 5 seconds after applying a DC voltage of v. Here, ρ is specific resistance (Ωc+o)
, S is the electrode area (c-7), L is the distance between the electrodes (am),
V represents voltage (V), and ■ represents current (A). S in the measurement in this example is o, 12cJ11. was 1.5 cm. In addition, the relative viscosity of the resin in the examples is 98,
Dissolved in 3% concentrated sulfuric acid at a concentration of 1.0/100ml,
This is a value measured using an Ostwald viscometer in a constant temperature bath at 20°C.

Example 1 To 100 parts by weight of epsilon caprolactam, 0.3 parts by weight of a 25% by weight aqueous solution of nylon salt of sodium sulfoisophthalate and hexamethylene diamine salt was added,
Ring-opening polymerization was performed to obtain nylon 6 pellets. After extracting the residual lactam with hot water, the extracted content is 1.0% by weight or less, and the specific melt resistance at 260°C is 0.72X10.
Pellets of nylon 6 with a relative viscosity of 2.6 and a relative viscosity of 5 Ωcm1 were obtained. When the maximum take-up speed was set using the pellets dried and mixed in a rotary vacuum dryer, it was possible to prevent air from being entrained between the rotary cooling roll and the molten film at a speed of 51 m/min.

Example 2 To 100 parts by weight of epsilon caprolactam, 0.5 parts by weight of a 25% by weight aqueous solution of nylon salt of sodium sulfoisophthalate and hexamethylene diamine was added, ring-opening polymerization was carried out, and pellets of nylon 6 were obtained. . After extraction of the residual lactam with hot water, the extracted content is 1.0% by weight or less, and the specific melt resistance at 260°C is 0.54X1.
Nylon 6 pellets having a relative viscosity of 2.6 and a relative viscosity of 0'Ωcm were obtained. Using the pellets dried and mixed in a rotary vacuum dryer, the maximum take-up speed was 57 m/min, and air entrainment between the rotary cooling roll and the molten film could be prevented.

Example 3 100 parts by weight of epsilon caprolactam, 25% of hexamethylene diamine salt of sodium sulfoisophthalate
Ring-opening polymerization was performed by adding 5 parts by weight of a wt% aqueous solution to obtain nylon 6 pellets. After extraction of residual lactam with hot water, nylon 6 pellets were obtained with an extracted content of 1.0% by weight or less, a specific melting resistance at 260° C. of 0.16×10 5 ΩCm, and a relative viscosity of 2.6.

The pellet has a melting specific resistance of 1.9X at 260°C.
105Ωcm1 Nylon 6 pellets with relative viscosity 2.6)1
Adding 5 parts by weight to 00 parts by weight and drying and mixing the pellets in a rotary vacuum dryer, the maximum take-up speed was 57 m/min. Air was drawn between the rotating cooling roll and the molten film. could be prevented.

Comparative example 1 Melting specific resistance at 260°C 1.9XI05 ΩC
After drying only Nine 6 pellets with a relative viscosity of 2.6 in a rotary vacuum dryer, air was caught between the rotating cooling roll and the molten film at the maximum take-up speed of 34 m/min. Thickness unevenness and opaque areas appeared on the film.

Comparative Example 2 0.5 parts by weight of trisodium phosphate dodecahydrate and 1.5 parts by weight of water were added to 100 parts by weight of epsilon caprolactam, and ring-opening polymerization was performed to obtain nylon 6 pellets. After extraction of residual lactam with hot water,
Nylon 6 pellets having an extractability of 1.0% by weight or less, a specific melting resistance at 260° C. of 1.0×10′ Ωcm, and a relative viscosity of 2.6 were obtained. After drying the pellets in a rotary vacuum dryer, the maximum take-up speed was determined, and at 48 m/min, air was caught between the rotary cooling roll and the molten film, causing uneven thickness and opaque areas on the film. .

Comparative Example 3 0.3 parts by weight of potassium stearate and 1.5 parts by weight of water were added to 100 parts by weight of epsilon caprolactam, and ring-opening polymerization was carried out to obtain pellets of nylon 6. After extraction of residual lactam with hot water, extractability 1.
0% by weight or less, melt specific resistance at 260°C is 1.2
Nylon 6 pellets with a relative viscosity of 2.6 were obtained. After drying the pellets in a rotary vacuum dryer, at the maximum take-up speed of 46 m/min, air was drawn in between the rotating cooling roll and the molten film, resulting in uneven thickness and opaque areas on the film. occured.

Table 1. Maximum take-up speed and specific melt resistance of polyamide resin containing metal base

Claims (1)

[Scope of Claims] 1) Polyamide resin containing a metal base in the main chain (A
) 1 to 100 parts by weight and melt specific resistance at 260°C is 1
．． Polyamide resin (B) with a resistance of 5 x 105 Ωcm or more
A method for producing a polyamide film, which comprises melt-extruding a composition containing 99 to 0 parts by weight into a film, electrostatically adhering the melt-extruded film to a rotating cooling roll, and solidifying it by cooling. 2. A method for producing a polyamide film, which further stretches the film according to claim 1 by at least 1.1 times.