JP2018094922A - Method for producing biaxially stretched polyamide resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a biaxially stretched polyamide resin film which is highly oriented to a surface direction of an inorganic laminar compound without impairing industrial productivity, and thereby is excellent in gas barrier property and mechanical strength in a vertical direction and is suitable for a package.SOLUTION: A method for producing a biaxially stretched polyamide resin film includes: a step of melt-extruding a polyamide resin composition containing 55-96.7 mass% of an aliphatic polyamide resin, 3-25 mass% of a m-xylylenediamine-based polyamide resin, and 0.3-20 mass% of an inorganic laminar compound from a T-die to obtain a non-stretched sheet; a step of stretching the sheet to 3.0-4.0 times in a vertical direction to obtain an uniaxially stretched film; and a step of stretching the uniaxially stretched film to a lateral direction so that an area ratio obtained by a product of a stretching ratio in the vertical direction and a stretching ratio in the lateral direction becomes 10.0 times or more to obtain a biaxially stretched film.SELECTED DRAWING: None

Description

  The present invention generally relates to a method for producing a biaxially stretched polyamide resin film made of a polyamide resin containing an inorganic layered compound called a nanocomposite resin. More specifically, the present invention relates to a method for producing a biaxially stretched polyamide resin film containing an inorganic layered compound having excellent gas barrier properties and excellent mechanical strength.

  Biaxially stretched polyamide resin films are excellent in gas barrier properties, mechanical strength, pinhole resistance, transparency and the like, and are widely used as packaging materials. However, further improvements in gas barrier properties and mechanical strength have been demanded.

As a method to improve oxygen and water vapor barrier properties and mechanical strength, a thermoplastic resin (nanocomposite resin) in which an inorganic layered compound such as layered silicate is uniformly dispersed is processed into a biaxially stretched film. However, in order to sufficiently enhance the gas barrier property and the effect of improving the mechanical strength, it has been said that it is necessary to add 1% by mass or more of the inorganic layered compound in the thermoplastic resin.
However, in the polyamide resin containing 1% by mass or more of the inorganic layered compound, it is particularly difficult to stretch in the transverse direction. Therefore, it is necessary to reduce the stretching ratio in the longitudinal direction as compared with the polyamide resin not containing 1% by mass or more of the inorganic layered compound, As a result, there were various problems such as poor mechanical strength in the vertical direction and reduced productivity.

Patent Document 1 and the like disclose a biaxially stretched polyamide resin film containing an inorganic stratiform compound. However, in order to overcome the difficulty of stretching of the polyamide resin, the temperature in the transverse stretching is followed by stretching in the longitudinal direction. It is essential to set the maximum temperature to 180 to 200 ° C.
However, not only is it difficult to produce, but also crystallization progresses excessively in the polyamide resin film before sufficient stretching in the transverse direction is achieved, resulting in thickness spots in fine regions. Further, since the inorganic layered compound is not sufficiently oriented in the polyamide resin film, there is a problem that the gas barrier property due to the inorganic layered compound is not sufficiently exhibited.

Patent Document 2 and the like disclose a technique for suppressing breakage troubles in the stretching process by adjusting the moisture content of an unstretched sheet made of a polyamide resin containing an inorganic layered compound to 1.3 to 10% by mass. However, since time and space for conditioning the unstretched sheet are required, loss during production occurs.
Further, since the apparent glass transition temperature of the polyamide resin is lowered due to moisture absorption, there is a problem that the gas barrier property is not sufficiently exhibited because the inorganic layered compound is not sufficiently oriented in the polyamide resin even if it is stretched. In addition, since the vertical orientation is weak, there is a problem that the mechanical strength in the vertical direction is weak.

Moreover, in patent document 3 etc., when extending | stretching the polyamide resin to which 0.3-10 mass% of inorganic layered compounds were added to the vertical direction, the refractive index (Ny) of the horizontal direction of a uniaxially stretched sheet may become small. By employing the stretching conditions, it is possible to stretch at a high magnification without causing breakage or the like even in the subsequent lateral stretching, and it is possible to produce a biaxially stretched polyamide resin film on an industrial scale. Are known.
However, this technique has a problem that it is necessary to introduce a static mixer or a multilayer feed block in order to make the layer structure of the film 8 layers or more, and the equipment needs to be modified for industrial productivity.

JP 2003-20349 A JP 10-138332 A JP 2010-132743 A

  The present invention solves the above-mentioned problems such as poor gas barrier properties, insufficient mechanical strength, and poor productivity, and is excellent in gas barrier properties and longitudinal mechanical strength without impairing industrial productivity. An object is to provide a biaxially stretched polyamide resin film suitable for a body.

As a result of examining in detail the factors causing breakage in the transverse stretching step of the polyamide resin in which the inorganic layered compound is dispersed, the present inventors have found that the polyamide after being longitudinally uniaxially stretched under the same conditions as the polyamide resin not containing the inorganic layered compound The abundance ratio (crystallinity) of the α-type crystals contained in the resin film is larger than that of the polyamide resin not containing the inorganic layered compound, which causes a defect structure and breaks the film in the subsequent transverse stretching process. I found it easier.
Furthermore, by adding a specific proportion of metaxylylenediamine-based polyamide resin to the polyamide resin in which the inorganic layered compound is dispersed, the abundance ratio of α-type crystals contained in the film after longitudinal uniaxial stretching is reduced. It was found that the defect structure in the film was suppressed. As a result, since the film breakage in the subsequent transverse stretching process can be suppressed, a biaxially stretched polyamide resin film excellent in gas barrier properties and longitudinal mechanical strength was obtained.

That is, this invention consists of the following structures.
1. A polyamide resin composition containing 55 to 96.7% by mass of an aliphatic polyamide resin, 3 to 25% by mass of a metaxylylenediamine-based polyamide resin, and 0.3 to 20% by mass of an inorganic layered compound is melt extruded from a T die. A step of obtaining an unstretched sheet, a step of stretching the sheet in the longitudinal direction by 3.0 to 4.0 times to obtain a uniaxially stretched film, and subsequently stretching the uniaxially stretched film in a longitudinal stretch ratio and a transverse stretch ratio. A method for producing a biaxially stretched polyamide resin film, comprising a step of stretching in a transverse direction so that an area ratio determined by product is 10.0 times or more to obtain a biaxially stretched film.
2. 2. The biaxially stretched polyamide resin film according to 1 above, wherein the aliphatic polyamide resin is a polyamide resin selected from nylon 6, nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, and nylon 612. Production method.

  INDUSTRIAL APPLICABILITY The present invention can provide a biaxially stretched polyamide resin film that is excellent in gas barrier properties and longitudinal mechanical strength and is suitable for a package without impairing industrial productivity.

An example of an infrared absorption spectrum corresponding to an amorphous component of a longitudinally uniaxially stretched film is shown. An example of an infrared absorption spectrum corresponding to an α-type crystal and a γ-type crystal of a longitudinally uniaxially stretched film is shown.

The present invention is described in detail below.
(Polyamide resin composition)
It is important that the polyamide resin composition used in the present invention contains an aliphatic polyamide resin, an inorganic layered compound, and a metaxylylenediamine-based polyamide resin. Further, it is preferable that the inorganic layered compound is uniformly dispersed in the polyamide resin.

(Aliphatic polyamide resin)
The aliphatic polyamide resin used in the present invention is a ring-opening polymer of cyclic lactam, a condensate of diamine and dicarboxylic acid. The self-condensate of amino acids is not particularly limited, but examples include nylon 6, nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, nylon 612 and the like. It is not something.
The addition amount of the aliphatic polyamide resin is preferably in the range of 55 to 96.7% by mass from the viewpoint of mechanical strength, pinhole resistance, and transparency. The addition amount of the aliphatic polyamide resin is more preferably 60% by mass or more, further preferably 70% by mass or more, still more preferably 75% by mass or more, and particularly preferably 80% by mass or more. When the addition amount of the aliphatic polyamide resin and the polyamide resin is less than 55% by mass, the mechanical strength, the pinhole resistance and the transparency are not sufficient, which is not preferable.

(Metaxylylenediamine-based polyamide resin)
The metaxylylenediamine-based polyamide resin used in the present invention is a condensate of metaxylylenediamine and dicarboxylic acid. Examples include those obtained by polycondensation of metaxylylenediamine and terephthalic acid, isophthalic acid, orthophthalic acid, 4-4′-diphenylcarboxylic acid, etc., but metaxylylene obtained by polycondensation of adipic acid and metaxylylenediamine. Adipamide resin is preferred.

The addition amount of the metaxylylenediamine-based polyamide resin is preferably in the range of 3 to 25% by mass from the viewpoint of the effect of suppressing α-type crystal formation and the barrier property due to the inorganic layered compound. The addition amount of the metaxylylenediamine-based polyamide resin is more preferably 4% by mass or more, and further preferably 5% by mass or more. Metaxylylenediamine-based polyamide resin When the addition amount of the polyamide resin is less than 3% by mass, the effect of suppressing α-type crystal formation is not sufficient, which is not preferable.
The upper limit is preferably 18% by mass or less, and more preferably 16% by mass or less. Even if the addition amount of the metaxylylenediamine-based polyamide resin is increased from 25% by mass, the effect of suppressing α-type crystal formation is saturated and not economical, which is not preferable.

(Inorganic layered compound)
Examples of inorganic layered compounds include, but are not limited to, inorganic layered compounds such as swellable mica, clay, montmorillonite, smectite, and hydrotalcite. In addition, inorganic layered compounds are organically treated organically modified inorganic layered compounds. It may be a compound. These inorganic layered compounds can use general ones, and examples of commercially available products include Cloisite manufactured by Southern Clay Products.

The shape of the inorganic layered compound includes various shapes including circular, non-circular, elliptical, substantially oval, and substantially bowl-shaped, but the length of the inorganic layered compound using an electron microscope is long. It is preferable that the average length of the side and the average thickness value are in a specific range.
In these calculation methods, it is preferable to analyze the shape of the inorganic layered compound by an image in a state where the resin is dispersed in the resin and the resin is oriented (reference document: Polymer 44 (2003) 4993-5013, TD). Fornes, D.R. Paul), specifically described in the Examples.

  The average length of the long side of the inorganic layered compound is preferably 70 nm or more. The inorganic layered compound is oriented in the film plane due to the stress generated during stretching, but if the average length of the long side of the inorganic layered compound is less than 70 nm, the degree of orientation is insufficient and sufficient oxygen permeation performance is obtained. Since it cannot be obtained, it is not preferable. The lower limit value of the average length of the long side of the inorganic layered compound in the film is more preferably 80 nm or more, and further preferably 90 nm or more. On the other hand, if the average length of the long side of the inorganic layered compound is 2000 nm or more, stress is concentrated during stretching and film breakage occurs, which is not preferable.

  About the thickness of an inorganic layered compound, it is preferable not to contain the coarse thing whose thickness exceeds 2 micrometers. Including a coarse product exceeding 2 μm is not preferable because transparency and stretchability are lowered.

  The ratio of the average length of the long sides and the average thickness of the inorganic layered compound ((average length of long sides) / (thickness average value)) is preferably 21 or more, more preferably 25 or more, and even more preferably. 30 or more. In addition, when the ratio of the average length of the long side to the average thickness of the inorganic layered compound is less than 21, it is difficult to form a dense layer, and the mechanical strength and gas barrier properties are deteriorated. The upper limit of the ratio between the average length of the long side and the thickness average value of the inorganic layered compound is not particularly limited, but when considering a commercially available general inorganic layered compound, the upper limit is about 200.

  The amount of the inorganic stratiform compound added to the polyamide resin composition is preferably 0.3 to 20% by weight. The lower limit is more preferably 1.0% by mass or more, further preferably 2.0% by mass or more, and particularly preferably 3.0% by mass or more. If the lower limit is less than 0.3% by mass, gas barrier properties cannot be obtained. The upper limit is more preferably 15% by mass or less, further preferably 10% by mass or less, and particularly preferably 6% or less. When the addition amount of the inorganic layered compound exceeds 20% by mass, there are problems that biaxial stretching becomes difficult and the transparency is remarkably lowered.

In the present invention, the content of the inorganic stratiform compound is the value of the weight residue obtained by a calorimeter (TGA). Specifically, the resin containing the inorganic stratiform compound is heated from room temperature at a rate of 10 ° C./min. The weight residue immediately after reaching 550 ° C. is obtained, and then the value of the weight residue derived from the resin is subtracted.
In the case of Example 1, the content of the inorganic layered compound can be determined to be 3.2% by mass from the weight residue by TGA.

In the practice of the present invention, in order to improve the slipperiness of the film, silica (SiO ₂ ) particles or the like may be added as an inorganic substance other than the inorganic layered compound, and the content of the added inorganic layered compound itself and the above The amount of inorganic material obtained by the method may not always match.
However, in general, the content of the inorganic substance other than the inorganic layered compound is small compared to the amount of the inorganic layered compound itself added, and the ratio of the inorganic layered compound itself to the amount of the inorganic substance obtained by the above method is Since it is usually 80% by mass or more, this may be used as an index.

(Other)
The polyamide resin composition may be used by adding resins and additives other than the above aliphatic polyamide resin and inorganic layered compound metaxylylenediamine-based polyamide resin.
As other resins, known resins such as polyester resins, polyurethane resins, and acrylic resins can be used, but are not limited thereto.
Additives include hydrolysis resistance improvers, antioxidants, colorants (pigments, dyes), antistatic agents, conductive agents, flame retardants, reinforcing agents, fillers, inorganic lubricants, organic lubricants, nucleating agents, mold release Known resins such as an agent, a plasticizer, an adhesion aid, and a pressure-sensitive adhesive can be used, but are not limited thereto.
Moreover, it is one of preferable embodiments that the collection film manufactured by this patent is used as a part or all of the polyamide resin from the economical aspect.

  Preferred embodiments of the present invention are described below, but are not limited thereto.

(Preparation method of polyamide resin composition in which inorganic layered compound is uniformly dispersed)
Examples of a method for producing a polyamide resin composition in which an inorganic layered compound is dispersed include a method in which a resin in which an inorganic layered compound is uniformly dispersed in an aliphatic polyamide resin and a metaxylylene-based polyamide resin are mixed, or an aliphatic polyamide resin and a metaxylylene. And a method of mixing a resin in which an inorganic layered compound is uniformly dispersed in a polyamide resin. Further, a material in which the inorganic layered compound is uniformly dispersed in both the aliphatic polyamide resin and the metaxylylene-based polyamide resin may be used.

As a method of uniformly dispersing the inorganic layered compound in the polyamide resin, an intercalation method is mainly used, and the following two methods a) and b) are mentioned.
a) Monomer Insertion Polymerization Method b) Polymer Insertion Method a) Monomer Insertion Polymerization Method The inorganic layered compound can be dispersed with molecular size along with polymer polymerization, so that gas barrier properties and mechanical strength, Excellent in terms of transparency. Specifically, CP Polymers Co. , Ltd., Ltd. Examples thereof include Criss Alon NF3040 and NF3020 manufactured by Ube Industries, NCH 1015C2 manufactured by Ube Industries, Imperm 103 and Imperm 105 manufactured by Nanocor, and the like.
On the other hand, since the b) polymer insertion method blends the polyamide resin and the inorganic layered compound, the inorganic layered compound does not peel sufficiently, resulting in poor dispersion compared to the a) monomer insertion polymerization method. When the inorganic layered compound is poorly dispersed, voids are formed at the interface between the inorganic layered compound and the polyamide resin during longitudinal stretching, which will be described later, resulting in poor transparency and difficulty in increasing the longitudinal orientation of the polyamide resin. , Gas barrier properties and mechanical strength are deteriorated. In order to improve dispersibility, when melt kneading is performed using a twin screw extruder or the like, the inorganic layered compound is broken by shearing in the extruder, so the length of the long side is shortened, and gas barrier properties and mechanical properties are reduced. This is not preferable because the strength deteriorates.

(Film forming method)
In the present invention, an unstretched polyamide resin composition sheet melt-extruded from a T-die is stretched in the longitudinal direction with a roll-type stretching machine and then stretched in the transverse direction with a tenter-type stretching machine (sequential biaxial stretching method). Is mentioned. The stretching may be multistage stretching.

(Extrusion method)
A polyamide resin composition obtained by blending an aliphatic polyamide resin and an inorganic layered compound with a metaxylylenediamine-based polyamide resin len or, if necessary, other polyamide resins or additives, is supplied to an extruder, and the polyamide resin An unstretched sheet is obtained by extruding from a T-die at a temperature equal to or higher than the melting temperature of the composition and bringing the extruded belt-like molten polyamide resin composition sheet into contact with a cooling roll to cool and solidify.
The T die temperature is the same as described above, but is preferably in the range of 150 to 300 ° C, preferably 170 to 290 ° C, more preferably 180 to 285 ° C. If the temperature is too low, the melt viscosity becomes too high and the surface becomes rough and the appearance deteriorates. An excessively high temperature is not preferable because, besides the thermal decomposition of the resin, the difference in melt viscosity becomes large and unevenness occurs as described above, and particularly unevenness with a small pitch occurs.
However, the temperature at which the polyamide resin composition is melted is preferably 5 ° C. or lower than the decomposition start temperature.
The cooling roll has a mirror finish, and cooling water circulates in the cooling roll and cools on the surface of the cooling roll, but it is preferably in the range of 10 to 30 ° C.

(Unstretched sheet)
The moisture content of the unstretched sheet before longitudinal stretching is preferably 1000 ppm or less, more preferably 800 ppm or less, and even more preferably 600 ppm or less. When the moisture content of the unstretched sheet before longitudinal stretching is larger than 1000 ppm, the thickness unevenness in the longitudinal direction of the film after biaxial stretching increases, and fluctuations and variations in film physical properties increase. On the other hand, if the moisture content of the unstretched sheet is less than 400 ppm, the viscosity becomes too high and it becomes difficult to stretch the film longitudinally.

(Longitudinal stretching)
A substantially unstretched polyamide resin composition sheet obtained by melt extrusion from a T-die is not less than the glass transition temperature (Tg (° C.)) of the polyamide resin composition, and the temperature rising crystallization temperature (Tc (° C.) of the polyamide resin. )) After stretching 2.5 to 10.0 times in the machine direction at a temperature of + 20 ° C. or less, the obtained longitudinally stretched film is further 50 ° C. or higher and the melting point temperature of polyamide resin (Tm (° C.)) − 20 ° C. It is preferable that the film is stretched 3.0 to 10.0 times at the following temperature, and then the biaxially stretched polyamide resin film is heat-set in a temperature range of 150 ° C to 250 ° C.

  The temperature rising crystallization temperature can be determined by heating the sample rapidly cooled after melting the polyamide resin composition by DSC.

In the longitudinal stretching, when the film temperature is lower than the glass transition temperature (Tg (° C.)) of the polyamide resin composition, problems such as breakage due to orientation crystallization due to stretching and thickness unevenness occur. On the other hand, when the temperature of the film is higher than the low-temperature crystallization temperature of polyamide (Tc (° C.)) + 20 ° C., it is not suitable because it breaks due to crystallization by heat.
Further, if the draw ratio in the longitudinal stretching is less than 2.5 times, problems such as poor quality such as thickness unevenness and insufficient mechanical strength in the longitudinal direction occur, and if it is more than 10 times, subsequent transverse stretching becomes difficult. There is. A preferable draw ratio is 3.0 to 4.0 times. Further, when the stretching ratio in the longitudinal direction is 2.5 times or less, the in-plane orientation of the inorganic layered compound due to the stress during stretching is insufficient, and the gas barrier property and the mechanical strength in the longitudinal direction are not improved. Since industrial productivity falls, it is not preferable.

(Α-type crystal)
General nylon 6 is composed of three phases, α-type crystal, γ-type crystal and amorphous. In the nylon 6 film forming process, molecular orientation proceeds by stretching, and the crystal structure (α crystal) accompanying orientation crystallization is Generated. When the α crystal is generated in the film, it is considered that the α crystal has a stable structure, so that it becomes a starting point for defect generation in the longitudinal stretching step and makes the horizontal stretching difficult. The abundance ratio (crystallinity) of α-type crystals in the film after longitudinal stretching in the present invention is related to the film forming property at the time of subsequent TD stretching, and the α-type crystal ratio of the film after longitudinal stretching is 20%. Must be less than. In addition, the α-type crystal ratio increases as the longitudinal stretching is performed at a higher magnification.
When the abundance ratio (crystallinity) of α-type crystals contained in the film after longitudinal uniaxial stretching is 20% or more, there are many defect structures due to α crystals that are stable structures inside the film after longitudinal uniaxial stretching. It occurs and the film breaks easily in the subsequent transverse stretching step.
The smaller the abundance ratio (crystallinity) of α-type crystals contained in the film after longitudinal uniaxial stretching is, the more preferable the defect structure inside the film is suppressed, and the α-type crystal ratio is more preferably 18% or less. % Or less is more preferable. From the viewpoint of suppressing the defect structure inside the film, it is preferable that the α-type crystal ratio of the film after longitudinal stretching is small, but it is difficult to reduce the α-type crystal ratio to 0% because α crystals are present in the unstretched film. And the practical lower limit is 5%.

By including a metaxylylenediamine-based polyamide resin in the polyamide resin composition in which the inorganic layered compound is dispersed as described above, the α-type crystal after the longitudinal uniaxial stretching can be performed even when the stretching ratio is 3.0 to 4.0 times. Since the abundance ratio can be less than 20% and the film breakage in the subsequent transverse stretching process can be suppressed, it is possible to obtain a film having excellent oxygen gas barrier properties and longitudinal mechanical strength, and also excellent productivity. It becomes possible.
The abundance ratio of α-type crystals contained in the film after longitudinal stretching depends on conditions such as stretching ratio and stretching temperature, but when the longitudinal stretching ratio is larger than 4.0 times, the longitudinal stretching step It should be noted that the abundance ratio of α-type crystals in this case may be greater than 20%.

  At this time, the stretching speed in the longitudinal stretching is preferably 10,000% / min or more, more preferably 13000% / min or more, and further preferably 14000% / min or more. When the stretching speed is lower than 10000% / min, the film stretching speed is low, and sufficient productivity cannot be obtained. On the other hand, when the stretching speed is too high, the film breaks during longitudinal stretching. Therefore, the longitudinal stretching speed is preferably 20000% / min or less, more preferably 18000% / min or less, and further preferably 16000% / min. Is less than a minute. The stretching speed here means the average value of the stretching speed in the longitudinal stretching step.

(Lateral stretching)
In the transverse stretching step, when the temperature of the film in the transverse stretching is a low temperature of less than 50 ° C., the transverse stretchability is poor and breakage occurs, and the thickness unevenness in the transverse direction due to neck stretching increases, which is not preferable. Moreover, when the temperature of the film is higher than (Tm (° C.)) − 20 ° C., thick spots increase, which is not preferable. If the transverse draw ratio is less than 3.0 times, the mechanical strength in the transverse direction becomes low, and the uneven thickness in the transverse direction due to neck stretching increases, which is not preferable. Further, at a high magnification of 10 times or more in the transverse draw ratio, it is substantially difficult to draw. A preferable draw ratio is 3.0 times to 5.0 times.

  When the product of the draw ratio in the machine direction and the draw ratio in the transverse direction is lower than 10.0 times, the in-plane orientation of the inorganic layered compound is insufficient and the gas barrier property and the mechanical strength in the machine direction are not improved. Moreover, since industrial productivity falls, it is not preferable. Further, when the product of the stretching ratio in the longitudinal direction and the stretching ratio in the transverse direction is a high ratio of 40 times or more, it is substantially difficult to stretch. The preferable draw ratio is preferably 10.0 to 20.0 times, more preferably 11.0 to 17.0 times, and still more preferably 12.0 to 14.0 times.

(Heat fixing)
When the heat setting temperature is a low temperature of less than 150 ° C., the dimensional stability due to heat of the film is poor and inappropriate. On the other hand, when the temperature is higher than 250 ° C., the appearance is poor due to whitening caused by thermal crystallization of the polyamide resin composition and the mechanical strength is lowered, which is inappropriate. Regarding the relaxation process, it is necessary to determine the relaxation rate in consideration of the balance with the heat shrinkage rate in the vertical direction.
Also. In order to reduce the vertical moisture absorption dimensional change, the relaxation rate is preferably in the range of 0 to 5%. If it is 5% or more, the effect on reducing the thermal shrinkage in the lateral direction is small, such being undesirable.

(Film thickness)
As long as the object of the present invention is not impaired, the film thickness is not particularly limited, but when used as a packaging material, a thickness of 300 μm or less, usually 5 to 50 μm is used.

(surface treatment)
In the present invention, corona treatment, coating treatment, and flame treatment may be performed in order to improve adhesion and wettability depending on applications. In the coating process, an in-line coating method in which a film coated during film formation is stretched is one preferred embodiment. In general, the biaxially stretched polyamide resin film of the present invention is further subjected to processing such as printing, vapor deposition, and lamination depending on the application.

(slit)
Subsequently, the stretched film is once released from the clip, and after trimming the unstretched remaining portion at the end, the stretched film is wound as a raw roll, separately slit into a desired width with a slitter, and wound as a product.

(Take-up)
Industrially, the film thus obtained is used for various applications as it is or in the form of a roll film wound around a paper tube or the like after undergoing processing such as printing or laminating. The roll film is preferably 30 cm or more in width. The length is preferably 500 m or more. The upper limit of the width is usually about 600 cm, and the upper limit of the length is about 20000 m. A wide film immediately after film formation or a long film is slit according to the application, and is usually used as a roll film having a width of 200 cm or less and a length of 8000 m or less.

The film obtained by the present invention preferably has the following characteristics.
(Extensible)
In the present invention, when the operation is continued under predetermined stretching conditions and the number of breaks in the stretching process is recorded, the number of breaks of the film per hour is preferably 3 or less. When the number of breaks of the film per hour is larger than 3, the operability is deteriorated and the productivity of the film is lowered, which is not preferable. The smaller the number of breaks of the film per hour, the better. The number of breaks is preferably 2 times or less, more preferably 1 time or less.

(Refractive index)
The film obtained by the present invention preferably has a longitudinal refractive index Nx of 1.560 or more after biaxial stretching, heat setting, and relaxation treatment. It is more preferably 1.563 or more, and further preferably 1.566 or more. When the refractive index Nx in the longitudinal direction is less than 1.560, the mechanical strength in the longitudinal direction is impaired, which is not preferable as a packaging material. On the other hand, if the refractive index Nx in the longitudinal direction is too high, it becomes difficult to produce stably, preferably 1.580 or less, and more preferably 1.575 or less. Here, the longitudinal direction is the flow direction of film formation.

  In order to satisfy the above-mentioned longitudinal refractive index Nx, although it depends on the conditions of biaxial stretching, heat setting, and relaxation treatment, the stretching ratio in the longitudinal direction should be 2.5 to 10.0 times. More preferably, it is more preferably 3.0 to 4.0. If it is less than 2.5 times, the gas barrier property and the mechanical strength in the longitudinal direction are not improved, and the industrial productivity is lowered. When it exceeds 10.0 times, there is a problem that subsequent transverse stretching becomes difficult.

  The film obtained by the present invention preferably has a lateral refractive index Ny of 1.560 or more after biaxial stretching, heat setting, and relaxation treatment. It is more preferably 1.563 or more, and further preferably 1.566 or more. If the lateral refractive index Ny is less than 1.560, the mechanical strength in the lateral direction is impaired, and the film thickness unevenness is large, which is not preferable. On the other hand, if the lateral refractive index Ny is too high, it becomes difficult to produce stably, preferably 1.580 or less, and more preferably 1.575 or less. In addition, a horizontal direction is a direction perpendicular | vertical to the flow direction of film forming here.

  In order to satisfy the above-mentioned transverse refractive index Ny, although it depends on the conditions of biaxial stretching, heat setting, and relaxation treatment, it is necessary to increase the stretching ratio in the transverse direction to 3.0 to 10.0 times. More preferably, it is more preferably 3.0 to 5.0 times. If the transverse draw ratio is less than 3.0 times, the mechanical strength in the transverse direction becomes low, and the uneven thickness in the transverse direction due to neck stretching increases, which is not preferable. Further, when the transverse stretching ratio exceeds 10 times, it is substantially difficult to stretch.

(Oxygen permeability)
The film obtained by the present invention has an inorganic layered compound oriented in-plane, excellent barrier properties, and an oxygen permeability of 15 to 15 μm (cc / m ² / day / atm). Is in range. The upper limit value of the oxygen permeability is more preferably 14 (cc / m ² / day / atm), and further preferably 13 (cc / m ² / day / atm). If the oxygen permeability in terms of 15 μm exceeds 15 (cc / m ² / day / atm), sufficient gas barrier performance cannot be obtained. On the other hand, the lower the oxygen permeability, the better. However, in the current technical level, the lower limit is about 5 (cc / m ² / day / atm).

(Mechanical strength)
The film obtained by the present invention is excellent in mechanical strength in the longitudinal direction, and has a tensile strength at break of 200 MPa or more measured at 23 ° C. and 60%. The upper limit value of the mechanical strength in the longitudinal direction is more preferably 220 MPa or more, and further preferably 240 MPa or more. If the tensile strength at break in the longitudinal direction is less than 200 MPa, the film does not have sufficient film strength, which is not preferable as a packaging material. On the other hand, if the tensile strength at break in the longitudinal direction is too high, the strength in the transverse direction is extremely impaired, so 400 MPa or less is more preferable, and 350 MPa or less is more preferable.

(Use)
By using the biaxially stretched polyamide resin film obtained by the present invention, a packaging bag can be formed. The packaging bag is formed by further laminating a sealant layer on a biaxially stretched polyamide resin film and heat-sealing the sealant layers. The heat-sealable resin can be composed of the same material as that conventionally used as a sealant layer for packaging materials. For example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer, etc. are used. be able to. The method for further laminating the sealant layer on the biaxially stretched polyamide resin film is not particularly limited, and methods such as a dry laminating method and an extrusion laminating method can be used.

  The form of the packaging bag is not particularly limited, and examples thereof include a three-sided bag, a four-sided bag, a pillow bag, a gusset bag, and a stick bag.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all to these examples, unless the summary is exceeded. The measurement method used in the present invention is shown below.

(1) Tg (glass transition point)
It calculated | required according to JISK7121-1987 using the differential scanning calorimeter (model | form: EXSTAR6000) made from SII nanotechnology. A 10 mg film sample was heated from −40 ° C. to 120 ° C. at a temperature rising rate of 20 ° C./min to obtain a temperature rising profile. The temperature at the intersection of the base line extension below the glass transition temperature and the tangent indicating the maximum slope at the transition was taken as the glass transition temperature.

(2) A 1 g sample was cut out from the central portion of the moisture ratio unstretched sheet and measured using a Karl Fischer moisture meter (CA-200 manufactured by Mitsubishi Chemical Analytech Co., Ltd.) at a sample heating temperature of 180 ° C.

(3) α-type crystal ratio of longitudinally uniaxially stretched film The method for measuring the α-type crystal ratio of the longitudinally uniaxially stretched film is as follows. First, 40 mm long and 20 mm wide sections were collected from the film after longitudinal uniaxial stretching, and the infrared of the film after uniaxial stretching was measured using an FT-IR measuring apparatus (infrared spectrometer FT-IR8400 manufactured by Shimadzu Corporation). The absorption spectrum was measured by the transmission method.

  FIG. 1 shows an example of an infrared absorption spectrum corresponding to an amorphous component of a longitudinally uniaxially stretched film.

As shown in FIG. 1, the amorphous component of the longitudinally uniaxially stretched film has a falling peak (hereinafter referred to as “first falling peak point Fp1”) in which the absorbance is the smallest between wave numbers 1140 cm ^{−1 to} 1080 cm ^−1. ), A falling peak with the second lowest absorbance (hereinafter referred to as “second falling peak point Fp2”), and a maximum rising peak Mp1 with the maximum absorbance. A line segment connecting the first falling peak point Fp1 and the second falling peak point Fp2 is defined as a base line. Here, when the infrared absorption spectrum in the predetermined wave number region is an ideal curve without unevenness, the above-mentioned peak means a point where the value when differentiating the infrared absorption spectrum curve is zero.

Then, a perpendicular line is drawn from the maximum rising peak point Mp1 toward the horizontal axis of the infrared absorption spectrum, and the absolute value of the difference between the absorbance at the intersection with the baseline and the absorbance at the maximum rising peak point Mp1 is determined as the maximum rising peak point. The height of Mp1 was taken as I (amorphous). Here, the wave number of the maximum rising peak is a slightly different value for each measurement. In the present invention, 1120 cm ⁻¹ was adopted as the absorption spectrum unique to the amorphous component as the wavelength of Mp1.

In the example shown in FIG. 1, Fp1 is 1135 cm ⁻¹ , and Fp2 is 1088 cm ⁻¹ (that is, the baseline is 1135 cm ^{−1 to} 1088 cm ⁻¹ ).

  FIG. 2 shows an example of an infrared absorption spectrum corresponding to an α-type crystal and a γ-type crystal of a longitudinally uniaxially stretched film.

As shown in FIG. 2, the α-type crystal and γ-type crystal of the longitudinally uniaxially stretched film have a falling peak (hereinafter referred to as “first falling peak”) at a wave number of 950 cm ^{−1 to} 870 cm ^−1. Point Fp1 "), a falling peak with the second lowest absorbance (hereinafter referred to as" second falling peak point Fp2 "), and a maximum rising peak with the maximum absorbance. A line segment connecting the first falling peak point Fp1 and the second falling peak point Fp2 is defined as a base line. Then, a perpendicular line is drawn from the peak point Mp2 having a wave number of 930 cm ⁻¹ toward the horizontal axis of the infrared absorption spectrum, and the absolute value of the difference between the absorbance at the intersection with the baseline and the absorbance at the peak point Mp2 is calculated as the peak point. The height of Mp2 was taken as I (α crystal). Similarly, a perpendicular line is drawn from the peak point Mp3 having a wave number of 920 cm ⁻¹ toward the horizontal axis of the infrared absorption spectrum, and the absolute value of the difference between the absorbance at the intersection with the baseline and the absorbance at the peak point Mp3 is The height of the point Mp3 was taken as I (γ crystal).

In the example shown in FIG. 2, Fp1 is 877 cm ⁻¹ and Fp2 is 944 cm ⁻¹ (that is, the baseline is 944 cm ^{−1 to} 877 cm ⁻¹ ).

From the absorbance at the peak of the infrared absorption spectrum of each of the amorphous, α-type crystal and γ-type crystal determined as described above, the α-type crystal ratio was calculated by the following formula (1).
Formula (1)
α-type crystal ratio = I (α crystal) / (I (amorphous) + I (α crystal) + I (γ crystal))

(4) Stability in transverse stretching process Continuous film formation for 1 hour under each film forming condition is performed, and the stretching stability is evaluated as ○ when the trouble of breaking in the transverse stretching process occurs 3 times or more, and when not. did.

(5) Refractive Index The refractive index was measured using a refractometer (NAGO-1 NAR-1T). The mount solution was methylene iodide, and the refractive index (Nx) in the vertical direction and the refractive index (Ny) in the horizontal direction were measured according to JIS K7142. The measurement was performed at the central portion of the biaxially stretched polyamide resin film as a sample in the lateral direction of the film.

(6) Content of inorganic layered compound (weight residue)
Using a TGA manufactured by TA Instruments, a sample amount of 0.1 g of a biaxially stretched polyamide resin film as a sample was heated from room temperature at a heating rate of 10 ° C./min in a nitrogen stream and immediately after reaching 550 ° C. The amount of weight residue.

(7) Average length and thickness of long side of inorganic layered compound A biaxially stretched polyamide resin film serving as a sample was embedded in an epoxy resin. An ultrathin section was cut out of the obtained embedded sample with a microtome equipped with an ultrasonic knife so that a cross section in the transverse stretching direction (TD stretching direction) of the film could be observed. An ultrathin section cut out by a microtome was collected on a transmission electron microscope observation mesh, and then thinly deposited with carbon. The transmission electron microscope observation was performed under the condition of an acceleration voltage of 200 kV using JEM-2100 manufactured by JEOL.

  Using the image analysis software “ImageJ”, which is an open source, the following analysis was performed on a film cross-sectional image having a magnification of 40000 times obtained as a result of observation with a transmission electron microscope.

  First, using the image analysis software “ImageJ”, image processing for classifying 256 levels of gray on a gray scale was performed. The gray scale is a technique for expressing an image only in shades (brightness and darkness) from white to black. In the present invention, the image is classified into 256 shades. The gradation is obtained for each pixel, the number of pixels and the gradation are histogrammed, the average gradation of the entire image is obtained, and binarization processing is performed using the average gradation as a threshold value.

  Next, in the observation image subjected to binarization processing, the length from one end to the other end in the long side direction was measured for one randomly extracted inorganic layered compound, and “the long side of the inorganic layered compound was measured. Length ".

  In addition, a straight line from one surface of the inorganic layered compound to the other surface in parallel to the thickness direction of the inorganic layered compound at the center point in the longitudinal direction from one end to the other end in the long side direction of the inorganic layered compound. Was taken, and the length of the straight line was measured to obtain “the thickness of the inorganic layered compound”.

  And in 130 layered compounds extracted at random, “the length of the long side of the layered compound” and “thickness of the layered compound” are measured by the above-mentioned method, and the average value of the 130 measurements is obtained as “ The average length of the long side and the average value of the thickness were used.

  Since the inorganic layered compound in the film is scaly and oriented in the plane direction, the length and thickness of the long side of the inorganic layered compound obtained from the cut cross section reflect the actual inorganic layered compound size well. .

(8) Oxygen permeability The oxygen permeability measuring device (“OX-TRAN 10 / 50A” manufactured by Modern Controls) is used, and the temperature and humidity on the high humidity side around the sample at the time of measurement are 23 ° C. and 65% humidity, respectively. The oxygen permeability was measured according to ASTM D-3985-81 in an atmosphere of% RH. The obtained result was converted into a value at a thickness of 15 μm as oxygen permeability (cc / m ² / day / atm).

(9) Tensile strength at break The film was cut into a length of 10 mm and a length of 100 mm in the longitudinal direction and left for 12 hours in an atmosphere of 23 ° C. and 60% RH. Using an autograph (AGS-1kNX) manufactured by Shimadzu Corporation, an average value of five measurement results was calculated under the conditions of a distance between chucks of 40 mm and a tensile speed of 200 mm / min in an atmosphere of 23 ° C. and 60% RH. .

Example 1
Nylon 6 resin pellets (CP Polymers Co., Ltd., Crystal Alon NF3040, Montmorillonite: 3.2 wt%) and metaxylenediamine-based polyamide resin pellets (manufactured by Toyobo Co., Ltd.) Each of T-600) was vacuum dried at 100 ° C. overnight, supplied to an extruder, melted at 270 ° C., extruded into a cooling roll adjusted to 20 ° C. from a T die, and cooled and solidified. A stretched sheet was prepared. The unstretched sheet had a thickness of 165 μm and a Tg of 45.4 ° C. The moisture content of this sheet was 600 ppm. This sheet was first preheated at a temperature of 40 ° C., and then longitudinally stretched 2.8 times at a stretching temperature of 70 ° C. and a stretching speed of 14400% / min. Subsequently, this sheet was continuously guided to a tenter, preheated at a temperature of 130 ° C., then transversely stretched 3.8 times at 140 ° C., heat-fixed at 215 ° C., and subjected to 5% lateral relaxation treatment. After cooling, both edges were cut and removed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm. Table 1 shows the film physical properties at this time.
The obtained film was excellent in productivity, longitudinal mechanical strength and oxygen barrier properties.

(Examples 2 to 4)
A film was obtained in the same manner as described in Example 1 except that the resin composition, the longitudinal stretching ratio, and the longitudinal stretching speed were changed as shown in Table 1. The obtained film was excellent in productivity and oxygen barrier properties.

(Comparative Example 1)
A film was obtained in the same manner as described in Example 1 except that the resin composition, the longitudinal stretching ratio, and the longitudinal stretching speed were changed as shown in Table 1. Although a film having good TD stretchability was obtained, the oxygen barrier property was poor.

(Comparative Example 2)
A film was obtained in the same manner as described in Example 1 except that the resin composition and the longitudinal draw ratio were changed as shown in Table 1. There were many breaks during TD stretching, and no film was obtained.

(Comparative Example 3)
A film was obtained in the same manner as described in Example 1 except that the resin composition, the longitudinal stretching ratio, and the longitudinal stretching speed were changed as shown in Table 1. Although a film having good TD stretchability was obtained, the oxygen barrier property was poor.

(Comparative Example 4)
A film was obtained in the same manner as described in Example 1 except that nylon 6 resin pellets (T-800 manufactured by Toyobo Co., Ltd.) containing no inorganic layered compound were used and the stretching conditions were changed as shown in Table 1. It was. Although a film having good lateral stretchability was obtained, the film had poor oxygen barrier properties.

(Comparative Example 5)
Nylon 6 resin pellets (NE 2640 manufactured by All Around Polymer Co., Ltd., Montmorillonite: 3.0% by mass) in which an inorganic layered compound is uniformly dispersed were used, and the stretching conditions were changed as shown in Table 1. A film was obtained in the same manner as described in Example 1. Although a film having good lateral stretchability was obtained, the ratio of the average length of the long side to the thickness average value of the inorganic layered compound was small, so that the oxygen barrier property was poor.

(Comparative Example 6)
Except for using nylon 6 resin pellets (Toyobo Co., Ltd. T-816 SiO ₂ : 0.63 mass%) in which silica (SiO ₂ ) particles are uniformly dispersed, and changing the stretching conditions as shown in Table 1. A film was obtained in the same manner as described in Example 1. Although a film having good lateral stretchability was obtained, the film had poor oxygen barrier properties.

  The biaxially stretched polyamide resin film obtained by the present invention is excellent in gas barrier properties and mechanical properties, has high productivity, and has high industrial utility value. In addition to packaging materials such as foods, pharmaceuticals, and miscellaneous goods, they can be suitably used as industrial materials.

Claims (2)

  A polyamide resin composition containing 55 to 96.7% by mass of an aliphatic polyamide resin, 3 to 25% by mass of a metaxylylenediamine-based polyamide resin, and 0.3 to 20% by mass of an inorganic layered compound is melt extruded from a T die. A step of obtaining an unstretched sheet, a step of stretching the sheet in the longitudinal direction by 3.0 to 4.0 times to obtain a uniaxially stretched film, and subsequently stretching the uniaxially stretched film in a longitudinal stretch ratio and a transverse stretch ratio. A method for producing a biaxially stretched polyamide resin film, comprising a step of stretching in a transverse direction so that an area ratio determined by product is 10.0 times or more to obtain a biaxially stretched film.   The biaxially stretched polyamide resin film according to claim 1, wherein the aliphatic polyamide resin is a polyamide resin selected from nylon 6, nylon 7, nylon 66, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, and nylon 612. Manufacturing method.