JPH0573575B2 - - Google Patents

Description

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

[Conventional technology]

Polyamide films, especially polycapramide 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. . In recent years, with the spread of retort food, the demand for polyamide film has also increased.
It is desired to supply high quality and inexpensive film.

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 film is brought into close contact with it electrostatically (hereinafter referred to as "electrostatic adhesion"). law) etc. are being carried out. 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, there is provided a method for cooling a polyamide thermoplastic polymer film, which is characterized by performing corona discharge in a streamer corona discharge state between polyamide resins, 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, heat transfer between the cooling roll and the film is poor, and uneven cooling occurs between the fully adhered areas and the incompletely adhered areas, resulting in significantly poor uniformity and transparency of the product sheet. 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 sheet will break during the stretching process, making it impossible to form the film itself.

[Problem that the invention seeks to solve]

The present invention aims to overcome these drawbacks of the prior art and to provide a technology that can efficiently produce polycapramide films at high speed without impairing the uniformity and transparency.

The present inventors copolymerized an appropriate amount of a monomer having an aromatic ring such as a benzene ring with a generally widely used aliphatic polyamide resin, without impairing the performance of the aliphatic polyamide. , found that it was possible to improve electrostatic adhesion and increase production speed, and proposed it earlier. This time, we further improved the electrostatic adhesion by lowering the content of methanol extractables in the resin by special treatment of the aliphatic polycapramide resin copolymerized with monomers having aromatic rings. It has been found that the production speed can be achieved.

[Means to solve the problem]

That is, the present invention provides aromatic aminocarboxylic acid residues, aromatic dicarboxylic acid residues, and/or aromatic diamine residues of 2% by weight or more and 20% by weight or less, and aliphatic aminocarboxylic acid residues, aliphatic dicarboxylic acid residues, and/or aromatic dicarboxylic acid residues. A polyamide resin consisting of 80% by weight or more and 98% by weight or less of residues and/or aliphatic diamine residues, and a polycapramide resin in which 80% by weight or more of capramide units has a methanol extractable content of 1.5% by weight or less. A method for producing a polycapramide film, characterized in that the melt-extruded film is electrostatically brought into close contact with a rotating cooling roll, and then taken off while being rapidly solidified, and the polycapramide resin further contains a metal compound. , melting specific resistance at 260℃ is 1.5×10 ⁵ Ω
The present invention relates to a method for producing a polycapramide film having a thickness of 1.5 cm or less, and a method for producing a polycapramide film by further stretching the film obtained by the above method by 1.1 times or more in at least one direction. According to the present invention, a polycapramide film with excellent uniformity and transparency can be efficiently produced.

The present invention will be explained in more detail below.

Polyamide resins generally contain oligomers and monomers in the resin. In particular, polycapramide-based polymers contain large amounts of oligomers and caprolactam immediately after polymerization, and a method is disclosed in which the impurities are removed by water extraction or the like, followed by drying and feeding into an extruder. (for example,
(described in US 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 methanol extraction is further performed, more than 1.5% by weight of methanol extractables are obtained.

The present inventors have discovered that by copolymerizing an appropriate amount of an aliphatic polyamide aromatic ring-containing monomer, electrostatic adhesion can be improved and production speed can be increased. The methanol extractables content is reduced by removing residual monomers and oligomers through a special treatment.
It has been found that when the content is 1.5% by weight or less, electrostatic adhesion is further improved and production speed can be increased.

Aromatic aminocarboxylic acid residues in the present invention,
Aromatic dicarboxylic acid residues and/or aromatic diamine residues include aminomethylbenzoic acid, terephthalic acid, isophthalic acid, 2,4-bis(carboxymethyl)toluene, paraxylylenediamine,
It is a residue obtained by polymerizing metaxylylene diamine, 2,4-bis(aminomethyl)toluene, etc.

On the other hand, aliphatic aminocarboxylic acid residues, aliphatic dicarboxylic acid residues, and/or aliphatic diamine residues include epsilon caprolactam, omega laurolactam, aminocaproic acid, aminoundecanoic acid, aminododecanoic acid, adipic acid, and sebacin. It is a residue obtained by polymerizing acids, hexamethylene diamine, etc. Aromatic residues are 2% by weight
Above, 20% by weight or less is preferable. If it is less than 2% by weight, the effect of improving the electrostatic adhesion of the molten resin is small, and if it is more than 20% by weight, the softening temperature will be low and pellets will fuse, making it difficult to handle, or conversely, the melting point of the resin will increase. molding becomes difficult.

The content of methanol extractables in the polycapramide resin is preferably 1.5% by weight or less. When the content of methanol extractables is reduced, the voltage applied to the electrode when winding the molten film onto a cooling roll by the electrostatic adhesion method can be increased, and a larger electrostatic adhesion force can be obtained.

The polyamide resin having a methanol extractable content of 1.5% by weight or less can be obtained by washing the polymer chips or pellets obtained by a conventional polymerization method with a solvent such as alcohol that has a strong affinity with oligomers and monomers, or It can be obtained by extracting it with hot water, by conducting polymerization under reduced pressure or in an inert gas atmosphere to obtain a polymer containing few oligomers and monomers, or by combining these methods.

The polycapramide resin contains a small amount of other resins,
Organic or inorganic substances such as lubricants, antioxidants, antistatic agents, and colorants may be added. In particular, when a soluble metal compound is added to the polycapramide resin, the electrostatic adhesion can be further improved and the production rate can be increased. Examples of metal compounds include alkali metals, alkaline earth metals, aluminum group elements, transition metal halides, sulfur oxygen acid compounds, phosphorus oxygen acid compounds, hydroxides, organic carboxylates, organic sulfonates, etc. Can be mentioned. 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, iodide. sodium, 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, stear Calcium phosphate, aluminum stearate, zinc stearate, potassium oleate, sodium acetate, potassium acetate,
Examples include sodium benzoate, sodium lauryl sulfonate, and sodium benzenesulfonate.

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. Further, in the case of metals having a small ionization potential such as alkali metals and alkaline earth metals, it is also possible to use them alone. It is preferable that the melting specific resistance at 260° C. be 1.5×10 ⁵ Ωcm or less by containing these metal compounds in a metal content of 0.0003% to 3% by weight based on the polyamide resin. When the metal content is 0.0003% by weight or less, the effect of improving electrostatic adhesion is small. If the metal content is 3% by weight or more, the physical properties of the film will deteriorate, which is not preferable. However, the present invention is not limited to these metal compound content ranges.

Methods for adding a metal compound include adding it to the raw material monomer before polymerization, adding it during the progress of polymerization, adding it during the extraction process, adding it when drying the pellets,
Either is fine. It is effective if the metal compound is finally contained in the melt-extruded polycapramide 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, and can be applied to devices that apply a charge by bringing a normal high-voltage charging electrode close to a molten film, to electrostatic adhesion devices that use 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. No matter which device is used, in the case of the polycapramide resin of the present invention,
Compared to polycapramide resins other than those of the present invention, the electrostatic adhesion of the molten resin to the rotating cooling roll in these devices is improved.

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 specific resistance 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. Air is prevented from getting caught between the rotating cooling roll and the molten film even at higher take-up speeds.
An unstretched film with a uniform thickness can be obtained. The unstretched polycapramide as it is is suitable for packaging foods and the like. However, if the unstretched polycapramide film is further stretched 1.1 times or more in at least one direction, preferably 2.0 to 5.0 times in each of two orthogonal directions, it is possible to obtain a biaxially stretched film with improved mechanical strength, transparency, oxygen It has improved shielding properties and is suitable for various packaging films.

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 polycapramide resin A stainless steel electrode is inserted into the molten resin kept at 260°C, a DC voltage of 100V is applied, and the specific resistance is determined from the current value after 1 to 5 seconds. This is a value calculated from the formula ρ=(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), and I is current (A). In the measurement in this example, S was 0.12 cm ² and L was 1.5 cm.

(2) Content of methanol extractables in raw material polycapramide resin. Accurately weigh 4 to 5 g of raw material polycapramide resin chips into the glass filter of a Soxhlet extractor.
~Pour 150m of methanol into the flask and 90~
After soaking in a hot water bath at 95℃ and extracting for 15 hours, the chips remaining on the filter are dried under reduced pressure in a desiccator for 1 to 2 hours, then dried in a vacuum dryer at 105℃ for 15 hours, and then left to cool in the desiccator. Weigh accurately,
It was calculated from the weight before and after extraction using the following formula.

(Methanol extractables content) = (Methanol extractables content) - (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 90mm diameter screw, extrude the resin into a film from a T-die at 260 to 280℃, cast it on a rotating cooling roll at 10 to 20℃, and extrude it from a high-pressure charged electrode. After applying an electric charge to the molten film and bringing it into close contact with the rotating cooling roll, the take-up speed of the rotating cooling roll is gradually increased to the maximum take-up speed that can prevent air from being drawn in between the rotating cooling roll and the molten film. showed that.

Example 1 To 100 parts by weight of ε-caprolactam, an aqueous nylon salt solution in which 6.9 parts by weight of metaxylylene diamine and 7.4 parts by weight of adipic acid were dissolved in 14.3 parts by weight of hot water was added, and the mixture was heated under pressure at 180 to 240°C. After the condensation, normal pressure polycondensation was further performed at 240 to 270°C to obtain a copolyamide. The pellets were subjected to conventional batchwise hot water extraction 8 times until the methanol extractables content was 0.8.
Polyamide resin pellets having a weight% melting specific resistance of 1.8×10 ⁵ 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 it was possible to prevent air from being drawn in between the rotary cooling roll and the molten film up to 50 m/min.

Example 2 To 100 parts by weight of ε-caprolactam, an aqueous nylon salt solution in which 13.8 parts by weight of metaxylene diamine and 14.8 parts by weight of adipic acid were dissolved in 28.6 parts by weight of hot water was added, and the mixture was heated under pressure in the same manner as in Example 1. After condensation and atmospheric polycondensation, ordinary batch hot water extraction was repeated seven times to determine the methanol extractables content.
0.8% by weight, specific melt resistance 1.8×10 ⁵ Ωcm, relative viscosity
2.6 polyamide resin pellets were obtained. After drying the pellets in a rotary vacuum dryer, the maximum take-up speed was determined to be 52 m/min, which was sufficient to prevent air from being drawn in between the rotary cooling roll and the molten film.

Example 3.4 0.02 parts by weight of trisodium phosphate dodecahydrate was added to 100 parts by weight of the polyamide resin pellets obtained in Examples 2 and 3, and the pellets were dried and mixed in a rotary vacuum dryer. When we determined the maximum take-up speed, we were able to prevent air from getting caught between the rotating cooling roll and the molten film even at a speed of 65 m/min.

The melt specific resistances of the resins after melt extrusion were 0.88×10 ⁵ Ωcm and 0.90×10 ⁵ Ωcm, respectively.

Comparative Example 1 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.
Using nylon 6 pellets containing 0.4% by weight of 3μm silicon dioxide and no added metal compounds, the maximum take-up speed was determined in the same manner as in Example 1. At 35m/min, the rotating cooling roll Air was trapped between the molten films, and a uniform unstretched film could not be obtained at higher speeds. The melt specific resistance of this resin is 1.8×10 ⁵ Ωcm
It was hot.

Comparative Example 2 The content of methanol extractables is 0.8% by weight, the relative viscosity is 2.6, the specific melting resistance is 1.9×10 ⁵ Ωcm, and it contains 0.4% by weight of silicon dioxide with an average particle size of 3 μm as a lubricant.
In particular, using nylon 6 pellets to which no metal compounds were added, the maximum take-up speed was determined in the same manner as in Example 1, and air entrainment between the rotating cooling roll and the molten film was prevented until it reached 47 m/min. did it.

Example 3 In Example 1, the batch hot water extraction was carried out only once as usual, and the methanol extractables content was 1.6% by weight.
Copolyamide resin pellets having a specific melt resistance of 1.8×10 ⁵ 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 to be 36 m/min, and air was caught between the rotary cooling roll and the molten film.
At higher speeds, a uniform unstretched film could not be obtained.

〔Effect of the invention〕

As is clear from the Examples and Comparative Examples, by copolymerizing an appropriate amount of aromatic residues with a polycapramide resin and reducing the content of methanol extractables in the polycapramide resin, polyamide can be produced more quickly and efficiently. based films can be produced.

Example 4 An unstretched film with a uniform thickness in which no air was caught between the resin obtained in Examples 1 to 4 and Comparative Example 1 and the rotating cooling roll, and a film in which air was drawn between the resin and the cooling rotating roll. Each unstretched film with longitudinal stripes was stretched 3.5 times in the longitudinal direction between rolls heated to 70°C with different circumferential speeds, then stretched 3.7 times in the transverse direction in a tenter at 100°C, and then heat-set at 200°C. When an operation was carried out to obtain a biaxially stretched polycapramide film, a biaxially stretched film was obtained from the unstretched film that did not involve air.
The unstretched film containing air is 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.

Claims (1)

[Scope of Claims] 1 Aromatic aminocarboxylic acid residues, aromatic dicarboxylic acid residues and/or aromatic diamine residues of 2% to 20% by weight, and aliphatic aminocarboxylic acid residues, aliphatic dicarboxylic acid residues Acid residues and/or aliphatic diamine residues: 80% or more by weight, 98% by weight
A polyamide-based resin consisting of the following, in which at least 80% by weight of the polycapramide-based resin has a methanol extractable content of 1.5% by weight or less, is melt-extruded, and the melt-extruded film is electrostatically adhered to a rotating cooling roll. A method for producing a polycapramide film, which is characterized in that it is removed while being rapidly cooled and solidified. 2. A method for producing a polycapramide film, wherein the polycapramide resin according to claim 1 further contains a metal compound, and has a specific melting resistance of 1.5×10 ⁵ Ωcm or less at 260°C.