JPH0570574B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a highly efficient method for producing a polycapmid film with excellent thickness uniformity. <Prior art> Polyamide films, especially polycapramide films obtained by ring-opening polymerization of ε-caprolactam, are used in the food packaging field because of their toughness, impact resistance, pinhole resistance, and high oxygen barrier properties. widely used in In recent years, with the spread of retort food, the demand for polyamide films has also increased, and there is a desire to supply high-quality and inexpensive films. Conventionally, polycapramide films have been produced by a melt extrusion method using an inflation method or a T-die method. When a polycapramide film is obtained 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 roll, there is a method of blowing air with an air knife (hereinafter referred to as the "air knife method"), a method in which charges are deposited on the molten film from a high-voltage electrode, and the method is made to adhere electrostatically (hereinafter referred to as the "electrostatic" method). (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 air flow generated by the rotation, resulting in a uniform film. You won't be able to get it. The electrostatic adhesion method involves inserting, for example, a wire-shaped electrode between the die and the cooling roll to impart an electrostatic charge to the film-like material, and then bringing the film-like material and the cooling roll into close contact with each other electrostatically. , a method for improving the uniformity and transparency of a formed film, is disclosed in, for example, Japanese Patent Publication No. 37-6142. According to this method, the melt-extruded film is brought into close contact with the cooling roll due to static electricity and is rapidly cooled, so that a thermoplastic resin film can be efficiently produced. Furthermore, in the case of polyamide resin, there is a method for cooling a polyamide-based thermoplastic polymer film, which is characterized by performing corona discharge in a streamer corona discharge state, depositing charges on the molten film, and bringing it into close contact with a rotating cooling roll electrostatically. It has been disclosed (Japanese Unexamined Patent Publication No. 17559/1983). However, when manufacturing polycapramide film, even if the electrostatic adhesion method is used, if the rotation speed of the cooling roll is increased in an attempt to increase production efficiency, the adhesion force will be insufficient, resulting in a partial gap between the film and the rotating cooling roll. air is caught in. In such areas, the heat transfer between the cooling roll and the film is poor, and uneven cooling occurs between the fully adhered parts and the incompletely adhered parts, resulting in significantly poor uniformity and transparency of the product film. The value of the product is lost. Moreover, the film can be continuously rolled on one or two shafts.
When stretching in the axial direction, there is a possibility that the film will break during the stretching process, making it impossible to form the film itself. <Problems to be Solved by the Invention> The present invention provides a technology that overcomes the drawbacks of the prior art and can efficiently produce a polycapramide film at high speed without impairing its uniformity and transparency. This is what I am trying to do. <Means for solving the problems> That is, the present invention contains a metal compound and 260
A polycapramide resin having a melt resistivity of 1.5×10 ⁵ Ωcm or less at ℃ and a methanol extractable content of 1.5% by weight or less is melt-extruded into a film, and the melt-extruded film is electrostatically adhered to a rotating cooling roll, The present invention relates to a method for producing a polycapramide film, which is characterized in that a film is obtained by pulling the film while rapidly cooling and solidifying it, and a method for producing a stretched polycapramide film by further stretching the film by 1.1 times or more in at least one direction. be. According to the present invention, a polycapramide film with excellent uniformity and transparency can be efficiently produced. Polycapramide-based polymers contain large amounts of oligomers and caprolactam immediately after polymerization, and after removing these impurities by water extraction etc.
A method of drying and feeding to an extruder is disclosed. (For example, described in U.S. Pat. No. 3,245,964) However, in polycapramide-based polymers that have only been subjected to a normal water extraction process, these impurities remain, and when further methanol extraction is performed, more than 1.5% by weight of methanol extractables remain. can get. The present inventors used a polycapramide polymer whose methanol extractables content was reduced to 1.5% by weight or less through special treatment as a raw material resin, and by melt extrusion using a T-die using the electrostatic adhesion method. The voltage that can be applied to the electrodes can be increased when the film is wound onto a cooling roll, and even when wound onto a cooling roll at higher speeds, unstretched and stretched polycapramide films with excellent thickness and transparency can be obtained. I discovered this and proposed it first. According to the present invention, the methanol extractables content is
By incorporating an appropriate amount of metal compound into a polycapramide resin of 1.5 weight or less, the temperature at 260°C
It is now possible to reduce the specific melt resistance to 1.5×10 ⁵ Ωcm or less, and the electrostatic adhesion is significantly improved.
Unstretched polycapramide films and stretched films with excellent uniformity and transparency can be obtained even when wound around a cooling roll at higher speeds. The polycapramide resin used in the present invention includes a polycapramide homopolymer, copolymer, and/or mixture of polycapramide in which 70% by weight or more is composed of capramide units. Examples of copolymers include hexamethylene diamine, metaxylylene diamine, aminododecanoic acid, aminoundecanoic acid, adipic acid, sebacic acid, isophthalic acid, terephthalic acid, laurolactam, etc. together with ε-caprolactam and/or aminocaproic acid. Examples include polymers. Examples of mixtures include mixtures with other polyamide resins, such as polyhexamethylene adipamide, polymethaxylylene adipamide, etc., and mixtures with other polyolefin-based or polyester-based resins. Further, inorganic particles such as titanium oxide, silicon oxide, magnesium silicate, etc. may be included. In addition, it may contain an antistatic agent, a stabilizer, an antigelation agent, a slip agent, a light stabilizer, a coloring agent, and the like. The content of methanol extractables in these polycapramide resins must be 1.5% by weight or less.
More preferably, it is 0.9% by weight or less. By reducing the content of methanol extractables in the raw material polycapramide resin, it is possible to increase the voltage applied to the electrodes when winding the molten resin film onto a cooling roll using the electrostatic adhesion method, resulting in greater electrostatic adhesion. These polycapramide resins with a low methanol extractable content can be obtained by washing polymer chips or pellets obtained by conventional continuous or batch polymerization with a solvent that has a strong affinity for oligomers such as alcohol, and then by washing the chips with hot water. It can be obtained by a method of extracting in two or more stages. Also, during polymerization or before chipping, the oligomer and caprolactam are removed from the system by passing the molten polymer under reduced pressure or an inert gas atmosphere, and the resulting polymer is further heated with hot water. It can be obtained by extraction or/and extraction with a solvent such as alcohol that has a strong affinity with the oligomer. However, the present invention is not limited to these methods. The metal compounds used in the present invention include alkali metals, alkaline earth metals, aluminum group elements,
There are transition metal halides, sulfur oxygen acid compounds, phosphorus oxygen acid compounds, hydroxides, organic carboxylates, organic sulfonates, etc. Specifically, sodium chloride, lithium chloride, potassium chloride, chloride Magnesium, 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, potassium hypophosphite, sodium hydroxide, lithium hydroxide, sodium stearate, potassium stearate, magnesium stearate, calcium stearate, aluminum stearate, zinc stearate, potassium oleate, sodium acetate, Examples include potassium acetate, sodium benzoate, sodium lauryl sulfonate, sodium benzene sulfonate, and ethylene ionomer. 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 contains a metal compound and 260
It is sufficient to use a polycapramide resin having a melting specific resistance of 1.5×10 ⁵ Ωcm or less at °C and a methanol extractable content of 1.5% by weight or less, and is not limited to the above-mentioned metal compounds. Also, alkali metals,
In the case of metals with small ionization potential, such as alkaline earth metals, it is also possible to use them alone. By containing these metal compounds in the polyamide resin in an amount of 0.0003 to 3% by weight, preferably 0.0003 to 0.5% by weight, the melting specific resistance at 260°C can be adjusted to 1.5×10 ⁵ Ωcm.
It is possible to do the following. When the metal compound content is 0.0003% by weight or less as the amount of metal, the effect of improving electrostatic adhesion is small. If the metal compound content is 3% by weight or more as the amount of metal, the physical properties of the film will deteriorate, which is undesirable. However, the present invention is not limited to these metal compound content ranges. The metal compound may be added to the raw material monomer before polymerization, during the polymerization process, during the extraction process, or when drying the pellets. . It is effective if the metal compound is finally contained in the 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 film into close contact with the rotating cooling roll, a method in which a charge is applied by performing corona discharge in a streamer corona state (Japanese Unexamined Patent Publication No. 17559/1983) is particularly effective. 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 charged electrode close to a molten film, an electrostatic adhesion device that uses an air knife in combination, and rotation. 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. Contains a metal compound and has a specific melting resistance of 1.5×10 ⁵ at 260℃
Less than Ωcm, methanol extractables content is 1.5% by weight
In the case of the following polycapramide resins, the electrical adhesion of the molten resin to the rotating cooling roll in these devices is improved compared to polycapramide resins that do not contain metal compounds. The take-up speed of the unstretched film in the present invention is not particularly limited. If the take-up speed is increased, air will be caught between the rotating cooling roll and the molten film, making it impossible to obtain a uniform unstretched film. Contains no conventional metal compounds,
The melting resistivity at 260℃ is greater than 1.5×10 ⁵ Ωcm,
When a polycapramide resin with a methanol extractable content of more than 1.5% by weight is taken onto a rotary cooling roll by electrostatic adhesion, the maximum take-up speed is usually 10 to 35 m/min. Even at a take-up speed or higher, air entrainment between the rotating cooling roll and the molten film is prevented, and an unstretched film with a uniform thickness can be obtained. The unstretched polyamide as it is is suitable for packaging foods and the like. However, the unstretched polyamide film is further expanded by 1.1 times or more in at least one direction, preferably
A biaxially stretched film that is stretched 2.0 to 5.0 times in two orthogonal directions each has further improved mechanical strength, transparency, and oxygen barrier properties, and is suitable for various packaging films. <Function> The function of the present invention will be explained below. usually,
If a high voltage is applied to the high-voltage charged electrode when winding the film onto a rotating cooling roll using the electrostatic adhesion method, more charges can be applied to the molten film, and a larger electrostatic adhesion force can be obtained. However, if the applied voltage is increased, dielectric breakdown occurs, so no higher voltage can be applied. Although the detailed mechanism is not clear, the content of methanol extractables in the present invention is
When 1.5% by weight or less of polycapramide resin is used, the voltage applied to the high-voltage charge electrode can be made higher than usual, and even at a higher take-up speed, air entrainment can be prevented and a uniform unstretched film can be obtained. Furthermore, by containing a metal compound and lowering the specific melting resistance of the resin, more charge can be applied to the molten film at the same voltage, resulting in more electrostatic adhesion and a faster take-up speed. seems to have been obtained. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. The measurement methods used in the Examples and Comparative Examples are shown below. (1) Melting specific resistance of raw material polycapramide resin 260
A stainless steel electrode is inserted into the molten resin kept at ℃, and a DC voltage of 100V is applied, and from the current value after 1 to 5 seconds, the specific resistance ρ =
This is a value calculated from the formula (S/L)×(V/I). Here, ρ is specific resistance (Ωcm), S is electrode area (cm ² ), L is distance between electrodes (cm), V is voltage (V),
I represents current (A). S in the measurement in this example
was 0.12 cm ² and L was 1.5 cm. (2) Methanol extractable content of raw material polycapramide resin Chips of raw material polycapramide resin are crushed,
Precisely weigh 5 g of powder with a particle size of 0.3 to 1.0 mm into the glass filter of a Soxhlet extractor, add 150 ml of methanol to the flask, soak in hot water at 95°C, extract for 24 hours, and remove the powder remaining on the filter. was dried under reduced pressure in a desiccator for 2 hours, and then
After drying in a vacuum dryer at 105°C for 15 hours, the mixture was allowed to cool in a desiccator, accurately weighed, and calculated from the weights before and after extraction using the following formula. (Methanol extractables content) = (Weight before methanol extraction) - (Weight after methanol extraction) / (Weight before methanol extraction) x 100 (3) Relative viscosity 1.0g/100ml of raw polycapramide resin chips in 96.3% concentrated sulfuric acid. This is the value measured using an Ostwald viscometer in a constant temperature bath at 20°C. (4) Maximum withdrawal speed Using an extruder with a screw of 90 mmφ in diameter, extrude the resin into a film from a T-die at 260 to 280°C, cast it on a rotating cooling roll at 10 to 20°C, and melt it using a high-pressure charged electrode. After applying an electric charge to the film and bringing it into close contact with the rotating cooling roll, the take-up speed of the rotating cooling roll is gradually increased until the maximum take-up speed that prevents air from being caught between the rotating cooling roll and the molten film is reached. Indicated. Note that due to equipment limitations, measurements were taken up to 65 m/min, and if air entrainment could be prevented even at that point, the speed was set at 65 m/min or higher. Example 1 Silicon dioxide with a methanol extractable content of 0.8% by weight, a relative viscosity of 2.6, and an average particle size of 3 μm as a lubricant.
Polycapramide chips containing 0.4% by weight were mixed and dried in a rotary vacuum dryer with the addition of trisodium phosphate dodecahydrate at a content of 0.02% by weight based on the polycapramide, and then the chips were used as raw materials. When the maximum take-up speed was determined, it was possible to prevent air from being drawn in between the rotating cooling roll and the molten film even at 65 m/min, which is the maximum usable speed of the device. The melt specific resistance of this resin at 250°C was 8.8×10 ⁴ Ωcm. Examples 2 and 3 Casting tests were conducted by adding magnesium bromide and zinc chloride to the contents shown in the table in the same manner as in Example 1. 65, which is the limit speed that can be used.
Even at m/min, it was possible to prevent air from getting caught between the resin and the rotating cooling roll. Comparative Example 1 A normal hot water extraction process was carried out. A casting test was conducted in the same manner as in Example 1 using polycapramide chips containing 0.4% by weight of silicon dioxide with a methanol extractable content of 1.7%, a relative viscosity of 2.6, and an average particle size of 3 μm. At a speed of 35 m/min, air was trapped between the rotating cooling roll and the molten film, and a uniform unstretched film could not be obtained at a speed higher than that. Comparative Example 2 Methanol extractables content was 1.7% by weight, relative viscosity was 2.6, and average particle size was subjected to normal hot water extraction treatment.
Polycapramide chips containing 0.4% by weight of 3 μm silicon dioxide were treated with trisodium phosphate decahydrate at 0.02% by weight per polycapramide in a rotary vacuum dryer.
After adding it to a weight% content and mixing and drying,
Next, when the maximum take-up speed was determined using the chips as a raw material, air was caught between the rotating cooling roll and the molten film at a speed of 54 m/min, and a uniform unstretched film could not be obtained at speeds higher than that. Example 4 Silicon dioxide with a methanol extractable content of 0.8% by weight, a relative viscosity of 2.6, and an average particle size of 3 μm as a lubricant
The experiment was carried out by blending 1% by weight of an ionomer resin with a melt index (MI) of 2.8 [trade name "Himilan 1605" manufactured by Mitsui Polychemical Co., Ltd.] containing sodium as a metal ion with polycapramide chips containing 0.4% by weight. When a casting test was carried out in the same manner as in Example 1, it was possible to prevent air from being entrained between the rotating cooling roll and the molten film even at the maximum usable speed of the apparatus, 65 m/min. Example 5 An unstretched film with a uniform thickness that did not involve air between the resin obtained in Examples 1 to 3, 4 and Comparative Examples 1 to 2 and the rotating cooling roll, and a film with a uniform thickness between the resin and the cooling rotating roll. Each unstretched film with longitudinal stripes that incorporates air is stretched 3.5 times in the longitudinal direction between rolls heated to 70°C and at different circumferential speeds, and then stretched at 100°C.
When a biaxially stretched nylon 6 film was obtained by stretching 3.7 times in the transverse direction using a tenter and further heat-setting at 200°C, it was found that a biaxially stretched film was obtained from an unstretched film that did not involve air. However, the unstretched film containing air was broken in the tenter, making it extremely difficult to obtain a biaxially stretched film. The thickness of the unstretched film at this time was 150 to 200 μm, and the thickness of the film after biaxial stretching was 12 to 16 μm. The results of Examples 1-3, 4 and Comparative Examples 1-2 are summarized in Table 1.

【table】

[Table] <Effects of the Invention> As is clear from the examples, according to the present invention, a polycapramide film with excellent uniformity and transparency can be efficiently produced at high speed.

Claims (1)

[Scope of Claims] 1. A polycapramide resin containing a metal compound, having a melt specific resistance of 1.5×10 ⁵ Ωcm or less at 260°C, and a methanol extractable content of 1.5% by weight or less, is melt-extruded into a film, A method for producing a polycapramide film, which comprises the steps of electrostatically bringing the melt-extruded film into close contact with a rotating cooling roll, and taking it off while rapidly cooling and solidifying it. 2. The method for producing a polycapramide film according to claim 1, wherein the metal compound is an ethylene ionomer resin. 3. The obtained film is further processed in at least one direction.
A method for producing polycapramide film that stretches more than 1.1 times.