JP5640313B2 - Biaxially stretched multilayer polyamide resin film - Google Patents

Description

  The present invention relates to a biaxially stretched multilayer polyamide resin having a multilayer structure that is tough and excellent in pinhole resistance and can be suitably used for packaging retort foods by laminating with an olefin resin film such as polyethylene or polypropylene. Related to film. More specifically, the present invention relates to a biaxially stretched multilayer polyamide resin film having a small boil distortion at the full width of the film roll when used as a packaging material.

  By providing the multilayer structure described in the present invention, the shrinkage stress can be reduced, and as a result, bowing that causes distortion during boiling can be reduced. Further, when the layered compound is added at the same time, gas barrier properties can be improved and boil distortion can be reduced at the same time.

  Biaxially stretched polyamide resin films are excellent in mechanical properties, barrier properties, pinhole resistance, transparency and the like, and are widely used as packaging materials. However, due to the high hygroscopic property derived from the amide bond in the resin skeleton, the mechanical strength is reduced, and hygroscopic elongation occurs. In addition, there are problems in various processes due to distortion and curl generated due to differences in shrinkage during boiling. Is likely to occur.

The distortion at the time of moisture absorption or boiling occurs due to the relaxation of the structure at the time of stretching. When a material having a high stretching stress is stretched, the shrinkage stress generated during relaxation increases and the strain increases. Therefore, it is considered that distortion can be suppressed by reducing the shrinkage stress, but in the case of polyamide resin, it is difficult to change the stretching stress due to its high intermolecular hydrogen bond, Reduction is difficult. Although several applications for reducing the boil distortion are found in the prior literature, there are no applications that disclose techniques for reducing stress (see Patent Documents 1 to 3).
JP 2006-96801 A JP 2006-88690 A JP 2007-237640 A

  As described above, with respect to the polyamide resin film with reduced boil distortion, there has been no study to reduce the boil distortion by paying attention to the stretching stress.

  The present invention reduces the shrinkage stress generated during boiling by reducing the stress during stretching, and as a result, by reducing bowing, it is excellent in terms of suppressing boil distortion, improving dimensional stability, and pinhole resistance. Another object of the present invention is to provide a biaxially stretched multilayer polyamide resin film.

The present inventor paid attention to the fact that the stress at the time of stretching decreases due to the multi-layering for these problems. That is, focusing on the fact that the stress necessary for deformation is reduced by reducing the entanglement of molecular chains in the thickness direction, it was considered possible to reduce shrinkage stress and boil distortion as described above. Then, this was confirmed experimentally and it came to this invention. That is, the present invention has the following configuration. A biaxially stretched multilayer polyamide resin film composed of the same resin composition with a total number of layers of 8 or more and a layer ratio of 80% or more, wherein the biaxially stretched multilayer polyamide resin film is a nylon 6 resin At least one resin layer mainly composed of a polyamide resin having a metaxylylene skeleton is laminated on a layer composed of nylon 6 or a layer composed of nylon 6 resin, 2.5 to 5.0 times in the longitudinal direction of the film, and 3.0 to 5.0 times in the width direction. A biaxially stretched multilayer polyamide resin film that is stretched, has a plane orientation coefficient (ΔP) of 0.057 to 0.07, and has a strain after boiling of 0.1 to 2.0%.
2. The inorganic substance containing a layered compound is added in an amount of 0.3 to 10% by weight, the layered compound is oriented in the plane, and the oxygen permeation amount in terms of 15 μm is 0.05 to 18 cc. biaxially stretched multilayer polyamide resin film.
the film.
3. The biaxially stretched multilayer polyamide resin film according to the first or second aspect, wherein a layered compound is added to each layer.

According to the present invention, under the conditions for producing a single-layer polyamide resin film, by stretching a resin sheet having the same composition having a multilayer structure, bowing is reduced, and a film with little boil distortion is obtained even at the end in the width direction. It becomes possible.
At the same time, when a resin in which a layered compound is uniformly dispersed is used as a polyamide resin, it becomes a film that is excellent not only in boil distortion but also in barrier properties, and extremely useful as a packaging material.

  In addition, although there is an application for a multilayer film in Japanese Patent Application Laid-Open No. 2007-196635, there is no description that the stress at the time of stretching or the like decreases due to the multilayering, which is a fact that has not been known so far. is there.

  For reducing the shrinkage stress during boiling, it is effective to reduce the shrinkage stress in addition to increasing the heat resistance of the resin. By reducing the entanglement density of molecular chains in the thickness direction by multilayering, the inventor can reduce the stretching stress by improving the ease of deformation of the molecular chains, resulting in a single-layer structure. In spite of having the same plane orientation as that of the film, the shrinkage stress can be reduced. It has been found that by these methods, bowing can be reduced, and a stretched film excellent in industrially practical production methods and characteristics can be realized.

  The present invention is described in detail below.

(Polyamide resin)
The polyamide resin used in the present invention is not particularly limited, such as a ring-opening polymer of a cyclic lactam, a condensate of diamine and dicarboxylic acid, and a self-condensate of amino acids. For example, nylon 6, nylon 7, nylon 66, Examples include, but are not limited to, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, nylon 612, and metaxylylenediamine-based nylon. It is also possible to use a copolymerized polyamide resin. Specifically, nylon 6 and nylon 66 copolymerized with metaxylylenediamine, nylon 6T, nylon 6I, nylon 6 / 6T copolymer, nylon 6 / 6I copolymer, nylon 6 / polyalkylene glycol resin, nylon 11 / Polyalkylene glycol resin, nylon 12 / polyalkylene glycol resin, nylon 6 / MXD6 copolymer and other aromatic polyamide resins can be used, but other components copolymerized can also be used, preferably nylon 6, nylon 66, and metaxylylenediamine-based nylon are preferable. In particular, gas permeability can be greatly reduced by laminating a small amount of a layer made of metaxylylenediamine-based nylon resin, which is one of the preferred examples in the present invention.

  In addition to the polyamide resin described later, other resins and additives may be added to these resins. 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. As other resins, known resins such as polyester resins, polyurethane resins, acrylic resins, polycarbonate resins, polyolefin resins, polyester elastomer resins, polyamide elastomer resins can be used, but are not limited thereto.

  Further, in terms of slipperiness, various lubricants can be added for the purpose of imparting surface roughness, and both organic lubricants and inorganic lubricants can be used, and particularly in the present invention. Although not limited, in the present invention, sufficient slipperiness can be imparted without the addition of these lubricants, and the type and amount of lubricant to be added should be determined in consideration of various characteristics. In the case of an inorganic lubricant, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more. The addition amount is preferably in the range of 100 to 5000 ppm in the layer forming the surface layer. If it is less than 100 ppm, the effect of addition is small, and if it exceeds 5000 ppm, the effect is saturated, so it is not economical.

(Polyamide resin in which layered compound is uniformly dispersed)
In the present invention, in addition to a normal polyamide resin, a polyamide resin in which a layered compound as described below is dispersed can also be used. In this case, the heat resistance, barrier properties, moisture absorption strain, etc. of the resin can be improved, which is one of the more preferable methods.

  A polyamide resin in which a layered compound is uniformly dispersed is generally called nanocomposite nylon. It is preferable that the layered compound is uniformly dispersed and does not contain a coarse material having a thickness of the layered compound exceeding 2 μm. Including a coarse product exceeding 2 μm is not preferable because transparency and stretchability are reduced.

  Examples of the layered compound include layered compounds such as swellable mica, clay, montmorillonite, smectite, and hydrotalcite, but are not limited to these and can be used regardless of inorganic or organic. The shape of the layered compound is not particularly limited, but the average length of the major axis is 0.01 to 50 μm, preferably 0.03 to 20 μm, particularly preferably 0.05 to 12 μm, and the aspect ratio is 5 to 5000. Preferably, those having 10 to 5000 can be suitably used. The amount of the inorganic layered compound added to the polyamide resin is preferably 0.3 to 10% by weight. The inorganic layered compound may be added as an organically treated layered compound, and the amount added may not always match the content of inorganic substances (added amount) due to the weight residue described below. In addition, if a method for obtaining from a weight residue as described later is employed, a small amount of an inorganic substance other than the layered inorganic compound may be added in addition, and in the present invention, it is obtained as an added amount of the inorganic substance containing the layered compound. become. In the present invention, the amount of the inorganic substance containing the layered compound is a value obtained by subtracting the ash from the weight residue obtained by the calorimeter (TGA). Specifically, the temperature increases from room temperature to 500 ° C. of the resin containing the layered compound. Obtained weight residue after warming, and then obtained by subtracting the value of resin ash. In the case of Example 1, the inorganic content was 2.6% by subtracting 4.4% weight residue by TGA and 1.8% weight residue from resin. Can be sought. Further, the ratio of the organic treating agent in the layered compound can be obtained separately by TGA and calculated from the numerical value.

  The lower limit value of the layered compound content is more preferably 0.3% or more, further preferably 0.5% or more, and most preferably 0.7% or more. If it is less than 1.0%, the effect of the addition of the layered compound is small because the dimensional stability and mechanical properties are small, which is not preferable. In addition, the coefficient of static friction increases and slipperiness may decrease.

  The upper limit is more preferably 10% or less, and still more preferably 8% or less. If it exceeds 10%, the effects in terms of dimensional stability and mechanical properties are saturated, which is not economical, and the fluidity at the time of melting is also lowered. In addition, the surface roughness becomes unnecessarily large or haze decreases.

  Although these layered compounds can be used in general, commercially available organically treated products that are suitably used in the monomer insertion polymerization method described below include Cloisite from Southern Clay Products, Somasif and Lucentite from Corp Chemical, Examples include Hosoon Sben.

In the present invention, it is preferable that the layered compound is uniformly dispersed in the above-described polyamide resin.
1. Intercalation method:
1) Monomer insertion polymerization method 2) Polymer insertion method 3) Organic low molecular insertion (organic swelling) kneading method In-situ method: In-situ filler formation method (sol-gel method)
3. The ultrafine particle direct dispersion method can be used. Examples of commercially available materials include Cress Alon NF3040 and NF3020 manufactured by Nanopolymer Composite Corp., NCH 1015C2 manufactured by Ube Industries, Imperm103 and Imperm105 manufactured by Nanocor, and the like. The layered compound is preferably treated with various organic treating agents for the purpose of enhancing the dispersibility of the layered compound in order to suppress the generation of coarse compounds of the layered compound contained in the polyamide resin. In order to avoid adverse effects due to thermal decomposition of the treatment agent, those obtained by using a low molecular weight compound having good thermal stability or a monomer insertion polymerization method without using a low molecular weight compound are preferred. Regarding thermal stability, a compound having a 5% weight loss temperature of 150 ° C. or higher of the treated layered compound is preferable. TGA etc. can be used for the measurement. Low thermal stability is undesirable because it may cause bubbles in the film or cause coloration (challenge nanotech materials, polymer nanocomposites with widespread use, published by Sumibe Tsutsunaka Techno Co., Ltd.) , See)

  These layered compounds are preferably oriented in the plane of the obtained film in order to develop the characteristics. The in-plane orientation can be confirmed by observing the cross section using a transmission electron microscope or a scanning electron microscope.

(Film forming method)
The biaxially stretched multilayer polyamide resin film of the present invention can be produced by ordinary methods, and is obtained by stretching a multilayer unstretched sheet obtained by various methods in the same manner as normal conditions. The thickness of each layer is controlled. By adjusting the stretching conditions so as to have a predetermined degree of plane orientation, a film having a small boil distortion and excellent in various properties can be obtained. The effect of multilayering is to reduce the entanglement of molecular chains in the thickness direction, thereby reducing the stretching stress and thus the contraction stress during boiling, resulting in a small bowing and a small boil distortion.

  The system in which the layered inorganic compound is added will be described below. In the stretching of the resin containing the layered compound, the problems in stretching using sequential biaxial stretching performed in the longitudinal-lateral order, which is generally advantageous in terms of economy, are as follows: In the stretching (hereinafter abbreviated as MD), crystallization progresses due to the heat during stretching, and the stretchability in the transverse direction (hereinafter abbreviated as TD) is lost after uniaxial stretching. (2) Breakage occurs during TD stretching. 3) There are three points: rupture occurs during heat setting after TD stretching. For (1), MD stretching conditions that allow TD stretching and MD stretching conditions that do not allow TD stretching are arranged. It was found that there was a difference in the refractive index in the width direction (refractive index in the Y-axis direction, hereinafter abbreviated as Ny) of the uniaxially stretched sheet after stretching. Specifically, Ny of a uniaxially stretched sheet capable of TD stretching is smaller than Ny after MD stretching, whereas TD stretching cannot be performed (that is, whitening or breaking occurs during TD stretching). Ny showed little or no change in Ny after MD stretching. In normal polyamide resin stretching, Ny after MD stretching causes necking in the width direction during MD stretching and Ny decreases at the same time, but when layered compounds are added, necking occurs but the layered It was found that Ny tends not to decrease due to the interaction between the compound and the polyamide resin molecule. This is because the molecular chains of the film before stretching are randomly oriented in the MD and TD directions, so when the molecular chains are stretched in the MD direction by MD stretching, force in the TD direction is also generated, but normal polyamide In the stretching of the resin, the force applied in the TD direction can be released by necking in the TD direction. On the other hand, in the case of the polyamide resin containing the layered compound, the molecular chain is constrained by the layered compound. Because the force in the direction cannot be released and the molecular chain is stretched in the TD direction as well, or the layered compound rotates during MD stretching. It was thought that the molecule was pulled in the direction of. That is, the surface orientation is already high after MD stretching. For this reason, it was thought that the stretching stress at the time of subsequent TD stretching increased, and the fracture occurred.

  As a method for solving this, by adopting a stretching condition in which Ny decreases after MD stretching, TD stretching performed subsequently can be stretched at a high magnification without causing breakage, etc. It became possible to manufacture on a scale.

  Ny (A) -Ny (B) is preferably 0.001 or more when the refractive index in the width direction before longitudinal stretching is Ny (A) and the refractive index in the width direction after longitudinal stretching is Ny (B). . Further, it is preferably 0.002 or more, most preferably 0.003 or more.

  As a method of lowering Ny after uniaxial stretching, a method of greatly reducing the MD stretching speed can be applied, but the same effect can be obtained by multilayering the unstretched sheet after melt extrusion. Ny can be reduced by reducing the molecular chain entanglement density in the thickness direction by multilayering, thereby improving the ease of deformation of the molecular chain, and as a result, the plane orientation during MD stretching Can be suppressed and TD stretchability can be improved. It has been found that these methods can improve the biaxial stretchability, and can realize a stretched film that is industrially highly practical and excellent in properties.

(Structure of the film)
The biaxially stretched multilayer polyamide resin film of the present invention is obtained by stretching an unstretched polyamide resin multilayer sheet having a total number of 8 layers or more.

  In the present invention, the number of layers is preferably at least 8 or more, preferably 16 or more. If it is less than 8 layers, the effect of lowering the entanglement density in the thickness direction is small and the effect for reducing the boil distortion is small, which is not preferable. The number of layers is preferably 10,000 layers or less, more preferably 5,000 layers. If it exceeds 10,000 layers, the thermal shrinkage after heat setting is not reduced, which is not preferable.

  The thickness of each layer before stretching is preferably in the range of 10 nm to 30 μm, more preferably 100 nm to 10 μm. If it is less than 10 nm, the heat shrinkage rate after heat setting is not small, which is not preferable. On the other hand, if it exceeds 30 μm, the effect of lowering the entanglement density in the thickness direction is small and the effect for reducing the boil distortion is small, which is not preferable.

  In addition, the biaxially stretched multilayer polyamide resin film of the present invention is preferably composed of the same resin composition with a layer number ratio of 80% or more. If it is less than 80%, the influence of the shrinkage stress derived from other resin layers becomes large, the effect of reducing the shrinkage stress is small, and the effect of reducing the boil distortion is small.

(Lamination method)
In the present invention, when the above-described polyamide resin is multilayered, it is possible to laminate the same kind of resin in addition to the lamination of different kinds of commonly employed resins. Here, it may be difficult at first glance to find out the physical meaning of multilayering the same kind of resin by the method described later, but in an actual system, the same kind of resin was melt-extruded and laminated at the same temperature. In some cases, the interface of the layers does not disappear and exists even after stretching. This is synonymous with the fact that it is very difficult to eliminate the weld line of the injection molded product. Thus, even if it is the same kind of resin, a multilayer state is maintained, and it is possible to maintain low molecular entanglement in the thickness direction. As a method of confirming the existence of the interface of the layers when melt-extrusion and lamination of the same kind of resin, after cooling the sample with ice or liquid nitrogen, cutting out with a razor or the like, creating a cross section, and then immersing it in a solvent such as acetone It can be observed by a method of observing the cross section with a microscope.

  Polyamide resin and, if necessary, the resin composition constituting the other layers are supplied to separate extruders and extruded at a temperature equal to or higher than the melting temperature, but the melting temperature is 5 ° C. lower than the decomposition start temperature or lower. It is preferable that Also, when using a resin containing a layered compound, the melting conditions and the melting temperature should be set carefully in order to suppress cracking of the layered compound in the resin. For example, in the case of a high molecular weight polyamide resin If the melting is performed at a low temperature such as a melting point of less than + 10 ° C., the layered compound is cracked, the aspect ratio becomes smaller than the initial state, and the effect of using the layered compound having a high aspect ratio is reduced. It is preferable to melt at a high temperature within a range where there is no problem in terms of stability.

  The polyamide resin and, if necessary, the resin composition constituting the other layer are laminated by various methods, and methods such as a feed block method and a multi-manifold method can be used. In the case of the feed block method, when the width is expanded to the die width after lamination, if there is a large difference in melt viscosity between the layers to be laminated or a temperature difference during lamination, lamination unevenness will occur, resulting in deterioration in appearance and thickness unevenness. Therefore, it is preferable to pay attention during the production. In order to suppress unevenness, etc., the melt viscosity at the time of extrusion is adjusted by (1) lowering the temperature, (2) adding various additives such as polyfunctional epoxy compounds, isocyanate compounds, carbodiimide compounds, etc. Preferably it is done.

  In the present invention, the in-plane orientation of the layered compound is promoted by the shearing force at the time of lamination, whereas the stress concentration at the time of stretching is concentrated at the tip of the layered compound, making it difficult to break. As a suitable method for such purpose, lamination by a feed block method or a static mixer method is preferable.

  The difference in melting temperature of each layer when the polyamide resin is laminated is 70 ° C. or less, preferably 50 ° C. or less, more preferably 30 ° C. or less. In addition, the difference in melt viscosity of the resin between the layers is within 30 times, preferably within 20 times, more preferably within 10 times the estimated shear rate in the die, thereby suppressing the appearance and unevenness during lamination. It becomes possible. In adjusting the melt viscosity, the addition of the aforementioned polyfunctional compound can be used. The static mixer temperature or feed block temperature at the time of lamination is 150 to 330 ° C, preferably 170 to 220 ° C, more preferably 180 to 300 ° C. A higher viscosity during laminating results in a better laminating state, so a lower feedblock temperature or static mixer temperature is preferable, but if the feedblock temperature or static mixer temperature is too low, the melt viscosity becomes too high and the extruder is fed. This is not preferable because the load on the surface becomes too large. When the temperature is high, the viscosity is too low and uneven lamination occurs, which is not preferable.

  Multi-manifold stacking is also possible, and the above-mentioned problem of uneven stacking is unlikely to occur. However, when laminating layers with different melt viscosities, poor wraparound of each layer resin occurs at the end. In this case, it is preferable to control the difference in melt viscosity.

  The 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.

(Stretching method)
The biaxially stretched multi-layer polyamide resin film of the present invention can be stretched by sequential biaxial stretching and simultaneous biaxial stretching of an unstretched sheet melt-extruded from a T die, and a method such as a tubular method can be used. In order to perform orientation, a method using a biaxial stretching machine is preferable. A preferable method from the standpoints of characteristics and economy includes a method of stretching in the longitudinal direction with a roll type stretching machine and then stretching in the transverse direction with a tenter type stretching machine (sequential biaxial stretching method). As for MD stretching, it is preferable to use MD multistage stretching because it is preferable to reduce the MD orientation during MD stretching in order to reduce bowing.

  A substantially unoriented polyamide resin sheet obtained by melt extrusion from a T-die is stretched 2.5 to 10 times in the longitudinal direction at a glass transition temperature Tg ° C. or higher and 150 ° C. or lower of the polyamide resin, and further obtained. It is preferable that the longitudinally stretched film is stretched 3.0 to 10 times at a temperature of 50 ° C. or more and 155 ° C. or less, and then the biaxially stretched polyamide resin film is heat-set at a temperature range of 150 to 250 ° C. .

  The temperature rising crystallization temperature can be determined by heating the sample that has been rapidly cooled after melting the resin by DSC.

  In MD stretching, when the temperature of the film is lower than the glass transition temperature Tg ° C. of polyamide, problems of breakage and thickness unevenness due to orientation crystallization due to stretching occur. On the other hand, when the temperature of the film exceeds 150 ° C., breakage occurs due to crystallization by heat, which is inappropriate. Further, the MD draw ratio in the present invention is preferably 2.5 to 5.0 times, and more preferably 2.8 to 4.5 times. If the draw ratio in MD drawing is less than 2.5 times, problems such as poor quality such as thickness unevenness and insufficient strength in the longitudinal direction occur, and if it exceeds 5 times, the effect of reducing the boil distortion is unfavorable. The MD stretching may be performed in a single stage or in multiple stages.

  Furthermore, when the temperature of the film in TD stretching is a low temperature of less than 50 ° C., the TD stretchability is poor and breakage occurs, and the thickness variation in the TD direction due to neck stretching increases, which is not preferable. When the temperature is higher than 155 ° C., thickness unevenness increases, which is not preferable. In addition, when the TD stretch ratio is less than 1.1 times, unevenness in the thickness of the TD direction increases, which is not preferable, and the strength in the TD direction is reduced. Is not preferable, and a draw ratio of 3 times or more is preferable. Further, when the TD stretch ratio is higher than 10 times, it is substantially difficult to stretch. A particularly preferable TD stretch ratio is 3.0 to 5.0 times.

  When the biaxially stretched multilayer polyamide resin film of the present invention is produced, the draw ratio in terms of area is preferably in the range of 6 to 25 times, more preferably in the range of 9 to 22 times. If it is less than 6 times, sufficient plane orientation is not obtained, and mechanical properties and the like are deteriorated. On the other hand, if it exceeds 25 times, the shrinkage stress increases, and the boil distortion does not decrease, which is not preferable.

  The stretching temperature is sufficient to exhibit the effect of adding the layered silicate, and stretching at a low temperature is preferred in terms of film thickness unevenness, gelboflex resistance and the like. Preferable conditions include stretching so that the film temperature is 155 ° C. or lower during stretching.

(Heat fixing)
When the heat setting temperature is lower than 150 ° C., the effect of heat setting by the heat of the film is small and inappropriate. On the other hand, a high temperature exceeding 250 ° C. is inappropriate because it causes poor appearance due to whitening caused by thermal crystallization of polyamide and a decrease in mechanical strength.

  In a system containing a layered compound, an increase in density due to crystallization and volume shrinkage associated therewith occur in heat setting after TD stretching, but in the case of a resin containing a layered compound, the generated stress is very large, Rapid heating causes stress in the MD direction and breaks. For this reason, as a heating method at the time of heat setting, it is preferable to increase the amount of heat in a stepwise manner to suppress the generation of a rapid contraction stress. As a specific method, there are methods such as gradually increasing the temperature or increasing the air volume from the vicinity of the entrance of the heat setting zone to the vicinity of the exit, and gradually reducing the air volume in terms of the heat shrinkage rate after stretching and heat setting. The heat setting method which raises is preferable.

  Regarding the relaxation treatment, it is preferable to determine the relaxation rate in consideration of the balance with the thermal contraction rate in the vertical direction. In the present invention, since the longitudinal dimension change in moisture absorption is small, the relaxation rate is preferably in the range of 0 to 5%. If it exceeds 5%, the effect for reducing the thermal shrinkage in the width direction is small, which is not preferable.

(Plane orientation)
The biaxially stretched multilayer polyamide resin film in the present invention preferably has a plane orientation (ΔP) of 0.057 to 0.07 after biaxial stretching, heat setting, and relaxation treatment. The plane orientation is obtained by the following formula, where birefringence is obtained from a refractometer, the refractive index in the longitudinal direction is Nx, the refractive index in the width direction is Ny, and the refractive index in the thickness direction is Nz.

ΔP = (Nx + Ny) / 2-Nz

  The increase in the plane orientation can be increased by increasing the biaxial stretch ratio, particularly the TD stretch ratio. If the plane orientation is less than 0.057, the mechanical strength as a film such as piercing strength decreases, which is not preferable. On the other hand, if it exceeds 0.07, productivity is lowered, which is not preferable.

(Boil distortion)
The boil distortion of the biaxially stretched multilayer polyamide resin film in the present invention is preferably 0.1 to 2.0%. Boil distortion is caused by being fixed to the clip at the end with respect to the shrinkage at the center during TD stretching, and is noticeable at the end in the film width direction. Boil distortion is reduced. In order to reduce the amount of shrinkage, in addition to the reduction of stretching stress due to multilayering, which is the point of the present invention, setting of stretching conditions is also important, but under conditions that greatly deviate from the conditions for stretching conventional polyamide resins. If not, it can be sufficiently reduced. When the boil distortion exceeds 2.0%, curling becomes remarkable, which is not preferable.

(Film characteristics-haze)
The haze of the biaxially stretched multilayer polyamide resin film in the present invention is preferably in the range of 1.0 to 20%. If the haze at the time of stretching is less than 1.0%, it is difficult to produce stably, which is not preferable. If the haze exceeds 20%, it is not preferable because the design properties are deteriorated in addition to making it difficult to see the contents during use.

  The haze in the system containing the layered compound of the present invention is the sum derived from the resin, the layered inorganic compound, and the void derived from the exfoliation of the resin at the time of stretching on the surface of the layered inorganic compound. It is preferable that the stretching conditions are set carefully. Specifically, when the MD temperature is too low, the haze increases due to the formation of voids, which is not preferable. Also, when the TD temperature is too high, haze increases due to crystallization, which is not preferable. The preferred temperature range is as described above, but can be adjusted with reference to this. Furthermore, it can adjust with the magnitude | size and kind of layered compound. For example, it is possible not only to reduce the haze by using a layered compound that is smaller than the wavelength of visible light, but also to employ a layered compound having a refractive index close to that of the resin. Can reduce the haze.

(Film characteristics-pinhole resistance)
The biaxially stretched multilayer polyamide resin film in the present invention is excellent in pinhole resistance, and the number of pinholes after 1000 gelboflex tests at 23 ° C. is preferably 0-30. It is mainly the stretching conditions that have an influence on the resistance to pinholes, and among them, it is preferable that the temperature during TD stretching is not particularly high. If the TD stretchability is poor, the temperature may be raised, but if the stretching temperature is raised too much above the low temperature crystallization temperature, crystallization proceeds partially without sufficient stretching, resulting in a thickness in a fine region. Unevenness and pinholes are likely to occur. Also, pinholes are likely to occur in the obtained film.

  Specifically, the TD stretching temperature is preferably lower than 155 ° C. If it exceeds 155 ° C., the film becomes fragile and the pinhole resistance deteriorates, which is not preferable.

(Film characteristics-equilibrium water absorption)
The polyamide resin film in the present invention preferably has an equilibrium water absorption in the range of 3.5 to 10%. A biaxially stretched film of a general polyamide resin has an equilibrium water absorption of about 3%, and the film of the present invention is preferably higher than that. Of the generally known layered compounds, montmorillonite and smectite, which are most commonly used, are generally used as thickeners for increasing the viscosity of aqueous solutions. As can be imagined from this, water is taken in between the layers, easily swells, and absorbs a large amount of water. If only these compounds are added to the resin, the montmorillonite absorbs a large amount of water. Therefore, the equilibrium water absorption of the resin composition is a large value, and the characteristics are also highly dependent on humidity. According to the present invention, the layered compound is highly oriented in the plane, and the equilibrium moisture content is 3.5% or more by subjecting the polyamide resin of the matrix to biaxial stretching at a high magnification and further orientational crystallization. Even with such an added amount, the humidity dependency of the characteristics can be kept low. If the equilibrium water absorption is less than 3.5%, the effect of adding the layered compound is small, and if it exceeds 10%, the addition amount is excessive and preferable characteristics cannot be obtained.

(Film characteristics-gas barrier properties)
In the present invention, the multilayer film containing a layered compound has excellent barrier properties because the layered compound is oriented in the plane, and the oxygen permeability in terms of 15 μm is 5 to 20 cc / m ² / day / atm. It is preferable that it exists in the range. The upper limit of the oxygen permeability is preferably at most ^{19cc / m 2 / day / atm} , more preferably not more than ^{18cc / m 2 / day / atm} . The oxygen barrier property depends on the in-plane orientation degree and addition amount of the layered compound in the polyamide resin. From the viewpoint of the oxygen barrier property, the preferred layered compound addition amount is in the range of 0.3 to 10% by weight based on the whole film. Is within. If it is less than 0.3% by weight, the effect of the barrier property is small, and if it exceeds 10% by weight, the balance of characteristics such as boil distortion is deteriorated. Further, for the purpose of further enhancing the gas barrier property, addition of a resin having a high barrier property and lamination of a resin layer having a high barrier property are also preferably used. Examples of the resin having a high gas barrier property include metaxylylenediamine nylon (MXD6), polyvinyl alcohol, and polyglycolic acid. The amount of addition or lamination is preferably 1 to 20%. If it is less than 1%, the effect of improving the barrier property is low, and if it exceeds 20%, the balance of stretchability with the added barrier resin is not preferred.

(Film characteristics-thermal shrinkage)
In the present invention, the biaxially stretched multilayer polyamide resin film preferably has a heat shrinkage rate at 160 ° C. of 10 minutes in the range of −0.5 to 1.5% in both the vertical and horizontal directions. In order to make the thermal shrinkage rate close to zero, it is preferable to optimize the layer thickness in addition to optimizing stretching conditions and heat setting conditions. It is advantageous to reduce the thickness of each layer in order to improve stretching stress reduction. However, if the layer becomes too thin, the heat shrinkage rate cannot be reduced due to heat fixation, etc., and the layer structure matches the desired heat shrinkage rate. However, in order to achieve both heat shrinkage and stretchability, the thickness of each layer before stretching is more preferably in the range of 1 to 30 μm, and still more preferably in the range of 2 to 20 μm. The lower limit value of the heat shrinkage rate is more preferably 0% or more, and further preferably 0.1% or more. The upper limit is preferably 1.5% or less, and more preferably 1.3% or less.

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

  The biaxially oriented multilayer polyamide resin film of the present invention has a hydrolysis resistance improver, antioxidant, colorant (pigment, dye), antistatic agent, conductive agent, flame retardant, reinforcing agent, filler, inorganic lubricant, organic A lubricant, a nucleating agent, a mold release agent, a plasticizer, an adhesion assistant, a pressure-sensitive adhesive, and the like can be optionally contained.

  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) Haze
The sample was measured at three different locations using a haze meter (Nippon Denshoku, NDH2000) by a method according to JISK7105, and the average value was defined as haze.

(2) Glass transition temperature (Tg) measurement and low-temperature crystallization temperature (Tc) measurement An unoriented polyamide resin sheet is frozen in liquid nitrogen, decompressed and thawed, using a DSC manufactured by Seiko Denshi Co., Ltd. Measured with

(3) Addition amount of inorganic substance including layered compound (weight residue)
Using TA Instruments TGA, the weight residue was obtained after heating up to a sample amount of 0.1 g, a nitrogen stream and a temperature increase rate of 20 ° C./min to 500 ° C.

(4) Plane orientation The plane orientation was determined by the following formula using an Abbe refractometer.

ΔP = (Nx + Ny) / 2-Nz

Here, Nx represents the refractive index in the longitudinal direction, Ny represents the refractive index in the width direction, and Nz represents the refractive index in the thickness direction.

(5) Boil distortion Samples were cut into a square shape with a side of 21 cm, and each sample was left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. The length of the two diagonals of each sample was measured and made the length before processing. Next, the sample was heat-treated in boiling water for 30 minutes, then taken out, wiped off moisture adhering to the surface, air-dried, and left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. Thereafter, the lengths of the two diagonal lines were measured again to obtain the length after treatment. From this value, the boiling water shrinkage in the 45 ° direction and the 135 ° direction was determined by the following formula, and the absolute value (%) of the difference was calculated as the boil strain. And the average value of the moisture absorption gap of each of those samples was computed.
Boiling water shrinkage rate = [(length before treatment−length after treatment) / length before treatment] × 100 (%)

(6) Relative viscosity 96% sulfuric acid solution 0.25 g of nylon resin was dissolved in 25 ml, and the relative viscosity was measured at 20 ° C.

(7) Observation of orientation state of layered compound in film A sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block. The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly. The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the images, 50 layered compounds were randomly extracted and the inclination of each was evaluated. When the variation in the inclination of any layered compound falls within an angle of 20 degrees or less, the in-plane orientation is indicated by ◯, and otherwise it is indicated by ×.

(8) Layer thickness and total number of layers in the film The film was cooled with liquid nitrogen and taken out immediately, and cut in the width direction of the cast film or stretched film with a feather blade to obtain a cross section. This cross section was observed using an optical microscope (Olympus BX60), and a value obtained by dividing the thickness of the layer for 5 to 20 layers by the number of layers was determined as the layer thickness. The total number of layers was determined by the same method.

When it was difficult to understand the interface of the layer by the above method, a sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block.
The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly. The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the image, the thickness of the layer having the maximum thickness was measured from the distance between the interfaces of each layer.

(9) Oxygen permeability An oxygen permeability measuring device (“OX-TRAN 10 / 50A” manufactured by Modern Controls) was used and measured at a humidity of 65% and a temperature of 23 ° C. The obtained results were converted to values at a thickness of 15 μm as oxygen permeability (cc / m ² / day / atm). Conversion to the value at 15μm thickness is

(15 μm thickness equivalent OTR) = (actually measured OTR) × (film thickness, μm) / 15 (μm)

As sought.

(10) The heat shrinkage test temperature was the same as the dimensional change test method described in JIS C2318 except that the test temperature was 160 ° C. and the heating time was 10 minutes.

Example 1
Nylon 6 resin pellets (T-814 manufactured by Toyobo Co., Ltd .: relative viscosity RV = 2.8, containing lubricant) were vacuum-dried at 100 ° C. overnight, and the same resin pellets were placed in two extruders. Supply and melt at 270 ° C, laminate the same type of resin using a 10-element static mixer, extrude from a T-die into a cooling roll adjusted to 20 ° C, and cool and solidify a multilayer unstretched sheet Produced. The ratio of the discharge amount of the two extruders was 1: 1. The thickness of the unstretched sheet was 250 μm, and the thickness of each layer from the cross section was about 1 μm. The sheet had a Tg of 35 ° C. and a melting point of 225 ° C. This sheet was first preheated at a temperature of 40 ° C., then longitudinally stretched 3.2 times at a stretching temperature of 60 ° C., and this sheet was continuously guided to a tenter, preheated at 60 ° C., 3.8 at 130 ° C. The film was transversely stretched twice, heat fixed at 210 ° C. and subjected to 5% lateral relaxation treatment, cooled, and both edges were cut and removed to obtain a biaxially stretched polyamide resin film having a thickness of 14 μm. The film had a width of 40 cm and a length of 1000 m and was wound around a paper tube. Table 1 shows the film physical properties at this time.

(Examples 2 to 10, Comparative Examples 1 to 8)
Examples 3 and 4 are 8-layer unstretched sheets using an 8-layer feedblock, and Comparative Examples 1-2, 5, and 7-8 are single-layer unstretched using a single-layer feedblock. Comparative Example 3 produced a 16-layer unstretched sheet, and Examples 2, 3, 4, 5, 6 and Comparative Example 5 were the same as Example 1 except that TD stretching was performed after MD two-stage stretching. Similarly, samples were produced under the conditions described in Table 1. Regarding film characteristics and the like, Examples 2 and 3 are shown in Table 1, Examples 4 to 10 are shown in Table 2, Comparative Examples 1 to 5 are shown in Table 1, and Comparative Examples 6 to 8 are shown in Table 3.

(Comparative Example 9)
Nylon 6 resin pellets (NF3040 manufactured by Nanopolymer Composite Corp., layered compound addition amount: 4%) in which montmorillonite was uniformly dispersed as a layered compound were vacuum-dried at 100 ° C. overnight. Next, it formed into a film using the single layer inflation film forming machine. The pellets were fed into an extruder and melted at 280 ° C. Subsequently, it was extruded from an annular die heated to 280 ° C., and while being air-cooled, it was adjusted so as to obtain a draw ratio of 4 times in terms of area from the discharge amount, winding speed, and tube diameter. The central part of the tube was cut to obtain a biaxially stretched polyamide resin film having a thickness of 25 μm. Table 3 shows the film physical properties at this time.

(Example 11)
Nylon 6 resin pellets (T-814 manufactured by Toyobo Co., Ltd .: relative viscosity RV = 2.8, containing lubricant), nylon 6 resin pellets in which montmorillonite is uniformly dispersed as a layered compound (NF3040 manufactured by Nanopolymer Composite Corp.) , Layered compound addition amount: 4%), MXD6 nylon resin pellets (S6001 manufactured by Mitsubishi Gas Chemical Co., Ltd.) having excellent barrier properties as a result of copolymerization of metaxylylenediamine were vacuum dried at 100 ° C. overnight. In a configuration where a 16-element static mixer heated to 275 ° C is introduced into the melt line between the extruder on the skin layer side and the feed block of a film forming machine capable of laminating two types and three layers, the skin Pellets prepared by blending T814 and NF3040 into a 50/50 ratio by dry blending were fed into two layer side extruders, and S6001 was introduced into the core layer side extruder. The skin layer side resin is melted at 270 ° C, the core layer side resin is melted at 280 ° C, and a structure (multilayer) in which a single layer sheet is sandwiched between two sheets of a multilayer structure with a feed block heated to 275 ° C, and at 20 ° C A multilayer unstretched sheet was produced by extruding the sheet from a T-die onto the adjusted cooling roll and allowing it to cool and solidify. The discharge rate ratio of the three extruders was 45:10:45. The thickness of the unstretched sheet was 250 μm, and the thickness of each layer on the skin layer side was about 1 μm from the cross section. This sheet was first preheated at a temperature of 70 ° C., then stretched at a stretching temperature of 80 ° C. 3.2 times and at a deformation rate of 4500% / min, and the sheet was continuously led to a tenter at 110 ° C. After preheating, it is transversely stretched to 3.8 times at 135 ° C, heat-fixed at 210 ° C and subjected to 5% transverse relaxation treatment, cooled, and both edges are cut and removed, and a biaxially stretched polyamide resin with a thickness of 15 µm. A film was obtained. The film had a width of 40 cm and a length of 1000 m and was wound around a paper tube. Table 3 shows the film physical properties at this time.

  In the conventional biaxially stretched polyamide resin film, when the plane orientation is increased to improve the mechanical strength, distortion during boiling is increased by bowing. In the biaxially stretched multilayer polyamide resin film of the present invention, by reducing the stretching stress, the boil distortion at the end in the film width direction is reduced, and the productivity of the low boil distortion film is improved. Further, by adding a layered compound to each layer, it is possible to obtain a film that is excellent not only in boil distortion but also in mechanical properties and barrier properties.

Claims (3)

  A biaxially stretched multilayer polyamide resin film composed of the same resin composition with a total number of layers of 8 or more and a layer ratio of 80% or more, wherein the biaxially stretched multilayer polyamide resin film is a nylon 6 resin At least one resin layer mainly composed of a polyamide resin having a metaxylylene skeleton is laminated on a layer composed of nylon 6 or a layer composed of nylon 6 resin, 2.5 to 5.0 times in the longitudinal direction of the film, and 3.0 to 5.0 times in the width direction. A biaxially stretched multilayer polyamide resin film that is stretched, has a plane orientation coefficient (ΔP) of 0.057 to 0.07, and has a strain after boiling of 0.1 to 2.0%. The inorganic material containing a layered compound is added in an amount of 0.3 to 10% by weight, the layered compound is oriented in the plane, and the oxygen transmission rate in terms of 15 μm is 0.05 to 18 cc. biaxially stretched multilayer polyamide resin film. The biaxially stretched multilayer polyamide resin film according to claim 1 or 2, wherein a layered compound is added to each layer.