JP2018070786A - Matte-like barrier polyamide film and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matte-like gas barrier polyamide film excellent in impact strength, dimensional stability, oxygen barrier property and vapor barrier property.SOLUTION: There is provided a polyamide film having a multilayered structure including a polyamide film (X) consisting of a polyamide resin containing silica and a barrier layer (Y), in which the barrier layer is formed by a polyvinylidene chloride-based copolymer, and satisfying following (1) to (6) conditions at same time. (1) glossiness is 50% or less. (2) porosity of the film is 0.1 to 5%. (3) impact strength measured under 20°C condition is 0.35 J or more. (4) difference of hot water shrinkage factor in a 45 degree direction and a 135 degree direction to a width direction (TD direction) of the film is 2.0% or less. (5) oxygen permeation degree is 100 ml/mday MPa or less under 20°C and 65%RH. (6) water vapor permeation degree is 20 ml/mday or less under 40°C and 90%RH.SELECTED DRAWING: None

Description

  The present invention relates to a mat-like barrier polyamide film having a multilayer structure including a polyamide film made of a polyamide resin containing silica and a barrier layer.

  Polyamide resin films have good mechanical properties, thermal properties, and transparency, and are therefore widely used for packaging applications, particularly food packaging applications. In recent years, as one application among the diversification of applications, a matte-like film in which fine irregularities are provided on the film surface to form a ground glass has been demanded in order to improve design properties. By using such a matte tone, the gloss of the film surface is eliminated (matte), the content is blurred, and further, a Japanese paper texture is imparted, whereby a high-quality packaging can be obtained. As one of means for imparting a matte tone to the film, a method of incorporating inorganic particles, organic synthetic resin, or the like into the resin constituting the film can be mentioned. Moreover, the improvement of oxygen barrier property is calculated | required from a viewpoint of improving the preservability of the contents.

  Patent Document 1 includes a method of matting the surface of a film by adding a certain amount of specific silica, a vinylidene chloride copolymer, and a resin layer in which an inorganic layered compound is blended with a high hydrogen bonding resin. A method for providing oxygen barrier properties by laminating is described.

JP2014-037122

  In Patent Document 1, a film having a matte surface and an oxygen barrier property can be obtained. However, since it contains silica particles, the mechanical properties are not fully satisfactory. That is, when a filler such as silica is contained, the stretching stress becomes high when the unstretched film is stretched. For this reason, the resin that is in close contact with the filler peels off due to the stretching stress, and voids are generated. When a large number of voids are generated or large voids are generated and the void ratio is increased, the impact strength and the strong elongation of the film are remarkably lowered. In addition, when the stretching stress increases, the bowing phenomenon (a phenomenon in which a straight line marked perpendicular to the film traveling direction on the unstretched film deforms into a bow shape with a delayed center after stretching and heat treatment). The film becomes large and has a large thermal shrinkage in the length direction and the width direction. It was very difficult to achieve both impact strength and dimensional stability in the matte barrier film.

  The present invention is a polyamide film made of silica-containing polyamide resin, has a matte surface with a matte surface, and is excellent in impact strength, dimensional stability, oxygen barrier property and water vapor barrier property. An object of the present invention is to provide a mat-like gas barrier polyamide film and a method for producing the same.

  As a result of studying the present inventors to solve the above-mentioned problems, an unstretched film made of a polyamide resin containing silica is allowed to absorb water so as to have a specific water absorption rate, and a specific preheating / stretching temperature / heat setting temperature condition. It was found that the stretching stress can be reduced by simultaneously biaxially stretching under. As a result, it has been found that the voids generated in the film can be reduced, the bowing phenomenon can be reduced, a matte polyamide film having high impact strength and excellent dimensional stability can be obtained. Furthermore, it has been found that a matte-like barrier polyamide film excellent in oxygen barrier property and water vapor barrier property can be obtained by forming a barrier layer or a vapor deposition layer comprising a polyvinylidene chloride copolymer on this film.

The gist of the present invention is as follows.
(A) A polyamide film having a multilayer structure comprising a polyamide film (X) comprising a polyamide resin containing silica and a barrier layer (Y),
A mat-like barrier polyamide film characterized by simultaneously satisfying the following conditions (1) to (6):
(1) Glossiness is 50% or less (2) Porosity of film is 0.1 to 5%
(3) Impact strength measured at 20 ° C. is 0.35 J or more. (4) The difference in hot water shrinkage between the direction of 45 degrees and the direction of 135 degrees with respect to the film width direction (TD direction) is 2. 0.05% or less (5) Oxygen permeability at 20 ° C. under 65% RH, 100 ml / m ² · day · MPa or less (6) Water vapor permeability at 40 ° C. under 90% RH, 20 g / m ² · day or less
(B) The matte barrier polyamide film according to (a), wherein the barrier layer (Y) is formed of a polyvinylidene chloride copolymer.
(C) A method for producing a matte-like barrier polyamide film as described in (a) or (b), wherein the steps (1) and (2) are sequentially performed. Method.
(1) A barrier layer-forming coating material comprising a polyvinylidene chloride copolymer on at least one surface of an unstretched film after water absorption in a hot water tank so that the moisture content of the unstretched film is 3 to 9%. Apply.
(2) Preheating is performed at a preheating temperature of 180 to 250 ° C., stretching is performed at a temperature of 170 to 230 ° C., and heat setting is further performed at a temperature of 180 to 230 ° C.

  The matte barrier polyamide film of the present invention has a matte surface with a matte surface, is excellent in impact strength and dimensional stability, and has excellent oxygen barrier properties and water vapor barrier properties as barrier performance. . For this reason, the film of this invention is excellent in the design property, the mechanical characteristic, and the characteristic of the content preservation property, and can be used for various packaging uses including a foodstuff and a medical product. Moreover, according to the method for producing a matte-like barrier polyamide film of the present invention, the film of the present invention can be obtained with high productivity.

Hereinafter, the present invention will be described in detail.
[Polyamide film (X)]
The polyamide film (X) of the matte-like barrier polyamide film of the present invention is made of a polyamide resin containing silica.

  In the present invention, the polyamide resin is a melt-moldable thermoplastic resin having an amide bond (—CONH—) in the molecule, such as polycoupleramide (nylon 6), polyhexamethylene adipamide (nylon 66), poly Hexamethylene sebacamide (nylon 610), polyaminoundecamide (nylon 11), polylauryl amide (nylon 12), and copolymers and mixtures thereof may be mentioned, with nylon 6 being particularly preferred. In addition, the polyamide has a lubricant, such as talc, silica, alumina, magnesia, calcium carbonate, ethylene bisstearylamide, calcium stearate, pigments, heat stabilizers, antioxidants, weathering agents, as long as the performance of the film is not impaired. A flame retardant, a plasticizer, and a mold release agent can also be mix | blended.

  The relative viscosity that serves as an index of the molecular weight of the polyamide resin is preferably in the range of 1.5 to 5.0, more preferably in the range of 2.5 to 4.0 from the viewpoint of mechanical properties. Here, the relative viscosity is a value measured in 96% by mass sulfuric acid at a concentration of 1 g / dl and a temperature of 25 ° C.

  In the present invention, it is necessary to add silica to the polyamide resin in order to make the film surface glossiness of the matte-like barrier polyamide film 50% or less.

  As a method of adding silica, a method of internally adding before or after the start of polymerization of polyamide resin, a method of melt-kneading polyamide resin and silica in an extruder, a dry blend of polyamide resin and silica The method of doing is mentioned. Among these, addition of silica to the polyamide resin is preferably performed by a method of internal addition at the start of polymerization or at any time after the start of polymerization from the viewpoint of dispersibility of silica in the film.

  Silica may be subjected to a surface treatment such as an inorganic treatment or an organic treatment in order to improve dispersibility, weather resistance, heat resistance, adhesion to a polymer, and the like.

  The content of silica in the polyamide film (X) of the present invention is preferably 0.1 to 12% by mass, more preferably 0.5 to 10% by mass, and still more preferably 1.5 to 7% by mass. It is. When the content of silica in the polyamide film (X) is less than 0.1% by mass, the glossiness of the film surface becomes high, and it becomes difficult to have a matte tone in which the surface is matte. On the other hand, when the content exceeds 12% by mass, voids are greatly generated, and mechanical properties including impact strength are deteriorated.

  The average particle diameter of silica is preferably in the range of 1.0 to 5.0 μm. If it is smaller than 1.0 μm, it becomes difficult to form protrusions on the film surface, so that the matte tone is lowered. On the other hand, if it exceeds 5.0 μm, voids in the film become enormous, which causes a decrease in mechanical properties including impact strength.

[Barrier layer (Y)]
The matte-like barrier polyamide film of the present invention is a polyamide film having a multilayer structure including a polyamide film (X) and a barrier layer (Y), and the barrier layer (Y) is formed on at least one surface of the polyamide film (X). It is provided. The barrier layer (Y) is preferably formed of a polyvinylidene chloride copolymer.

  Polyvinylidene chloride copolymer is prepared by polymerizing 50 to 99% by mass of vinylidene chloride as a raw material and one or more other monomers copolymerizable with vinylidene chloride by a known emulsion polymerization method, and dispersing it in a medium It is preferable that it is obtained as a latex. If the proportion of the other monomer that can be copolymerized is less than 1% by mass, plasticization inside the resin is insufficient, and the film-forming property of the film is lowered, and the proportion of the other monomer is 50% by mass. When it exceeds, gas barrier property will fall, and it is unpreferable for both. In addition, since a polyvinylidene chloride copolymer having a higher crystal melting point is obtained as the ratio of vinylidene chloride is higher, the vinylidene chloride ratio is polymerized in a ratio close to the above upper limit, for example, in the range of 95 to 99% by mass of vinylidene chloride. Thus, a polyvinylidene chloride copolymer can be obtained.

  Examples of the monomer copolymerizable with vinylidene chloride include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate, methyl methacrylate, and methacrylic acid. Examples thereof include methacrylic acid esters such as glycidyl acid, nitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and maleic acid, and vinyl chloride. These monomers may be used alone or in combination.

  The polyvinylidene chloride copolymer is used as a barrier layer-forming paint (latex) in a state of being dispersed in water, and is coated on at least one surface of the polyamide film (X). The average particle size of the polyvinylidene chloride copolymer in the barrier layer-forming coating material is preferably 0.05 to 0.5 μm, and particularly preferably 0.07 to 0.3 μm. The polyvinylidene chloride copolymer may be used in combination with various additives such as an antiblocking agent, a crosslinking agent, a water repellent, and an antistatic agent, as long as the effects of the present invention are not impaired.

The method of coating is not particularly limited. For example, gravure roll method, reverse roll method, air knife method, reverse gravure method, Mayer bar method, inverse roll method, or a combination thereof, or various sprays A method etc. can be adopted.
The polyamide film (X) may be subjected to corona discharge treatment immediately before coating.

  The thickness of the barrier layer (Y) formed of the polyvinylidene chloride copolymer is preferably in the range of 0.5 μm to 3.5 μm, more preferably in the range of 0.7 μm to 3.0 μm, particularly preferably. It is in the range of 1.0 μm to 2.5 μm. When this barrier layer (Y) is thinner than 0.5 μm, sufficient barrier properties (oxygen barrier properties and water vapor barrier properties) are hardly exhibited. On the other hand, when the barrier layer (Y) is thicker than 3.5 μm, not only the effect is saturated but also the physical properties of the film may be impaired.

  The adhesion strength between the polyamide film (X) and the barrier layer (Y) is preferably 0.3 N / cm or more. If the adhesion strength is lower than this value, the polyamide film (X) and the barrier layer (Y) may be peeled off during the boil treatment or retort treatment, or sufficient sealing strength may not be obtained.

  The mat-like barrier polyamide film having the structure in which the barrier layer (Y) is laminated in this way has excellent oxygen barrier properties and water vapor barrier properties in addition to excellent strength and mechanical properties as a polyamide film. Since it is excellent, it can be suitably used as a packaging material.

Further, the barrier layer (Y) may be a vapor deposition layer. A compound made of an inorganic substance or an organic substance is used for the vapor deposition layer. As the inorganic substance, a metal such as aluminum or an inorganic oxide such as aluminum, silicon, magnesium, or titanium is used.
Examples of a method for forming such an inorganic layer include a vacuum deposition method, a sputtering method, a chemical vapor deposition (CVD) method, and a physical vapor deposition (PVD) method. In particular, the vacuum deposition method is excellent in practicality.

When the polyamide film (X) is subjected to vapor deposition, in order to improve the adhesion between the polyamide film (X) and the vapor deposition layer, the polyamide resin layer is previously coated with corona treatment, plasma treatment or inorganic or organic compound. Processing may be performed.
In the case of vacuum deposition, aluminum (Al), alumina (Al ₂ O ₃ ), silicon (Si), silica (SiO ₂ ), or a combination thereof is used as a deposition raw material. Examples of the method for heating the raw material include resistance heating, high frequency induction heating, electron beam heating, and laser heating. Further, a gas such as oxygen can coexist during heating, ozone can be added, or an ion assist method can be employed.

  As for the thickness of the barrier layer (Y) which consists of a vapor deposition layer, about 1-1000 nm is preferable. If it is 1 nm or less, the barrier properties (oxygen barrier property and water vapor barrier property) are not exhibited, and if it is 1000 nm or more, the plasticity of the processed film as a whole is lost and the practicality is lowered.

[Characteristics of polyamide film]
The matte-like barrier polyamide film of the present invention satisfies all the above-mentioned characteristic values (1) to (6).
First, the glossiness needs to be 50% or less, more preferably 40% or less, and further preferably 30% or less. If the glossiness exceeds 50%, the matte tone cannot be obtained with a matte surface, and the desired high-quality feeling and Japanese paper texture cannot be obtained.

  The porosity of the matte-like barrier polyamide film of the present invention needs to be 0.1 to 5%, preferably 0.1 to 4%, and more preferably 0.3 to 3%. When the porosity in the film is less than 0.1%, there are few voids, and the required gloss may not be obtained only by blending silica. On the other hand, when the porosity in the film exceeds 5%, the impact strength and the high elongation decrease, and further, breakage easily occurs in the stretching process and the secondary processing process.

  The impact strength of the matte-like barrier polyamide film of the present invention is required to be not less than 0.35J, preferably not less than 0.4J, more preferably not less than 0.3J, as measured at 20 ° C. 45J or more. If the impact strength is less than 0.35 J, it is easy to break in the secondary processing step such as the printing step, and it is difficult to use because it does not have sufficient practicality. Moreover, there is a concern that the film may be broken by falling after the bag making, or the film may be cracked to spill the contents.

  Furthermore, the matte-like barrier polyamide film of the present invention has a difference in hot water shrinkage between the direction of 45 degrees and the direction of 135 degrees with respect to the width direction (TD direction) of the film (hereinafter referred to as “diagonal of hot water shrinkage” May be abbreviated as “difference”) is 2.0% or less, preferably 1.8% or less, and more preferably 1.6% or less.

The “diagonal difference in hot water shrinkage” in the present invention is measured as follows.
First, the width direction (TD direction) of the film is specified, and when the width direction is set to 0 degree, strip-shaped test pieces are cut with the directions of 45 degrees and 135 degrees as the length direction with respect to 0 degrees. The test piece has a width of 10 mm and a length of 100 mm. The obtained 45 degree test piece and 135 degree direction test piece were each boiled in 100 ° C. hot water for 5 minutes and then left at 23 ° C. and 50% RH for 2 hours. The dimensions are measured, and the hot water shrinkage rate of the test piece in the 45 ° direction and the hot water shrinkage rate of the test piece in the 135 ° direction are obtained by the following formulas. Furthermore, the diagonal difference of the hot water shrinkage is calculated from the hot water shrinkage of the test pieces in both directions.

The original length is the length of the test piece before performing the hot water treatment. In the present invention, both (L0 ₄₅ ) and (L0 ₁₃₅ ) are 100 mm.
Hot water shrinkage (%) in the 45 degree direction = {original length (L0 ₄₅ ) −post-treatment length (L ₄₅ )} / original length (L0 ₄₅ ) × 100
Hot water shrinkage (%) in the direction of 135 degrees = {original length (L0 ₁₃₅ ) −post-treatment length (L ₁₃₅ )} / original length (L0 ₁₃₅ ) × 100
Diagonal difference in hot water shrinkage rate (%) = | (hot water shrinkage rate in 45 ° direction) − (hot water shrinkage rate in 135 ° direction) |

  When the diagonal difference of the hot water shrinkage ratio exceeds 2.0%, the dimensional stability of the resulting matte-like barrier polyamide film is insufficient, resulting in deviation in color matching during printing. Moreover, when it is set as a packaging bag, it is twisted and warped due to the influence of the temperature and humidity of the atmosphere, resulting in poor flatness. Further, when filling the contents, a gripping error may occur at the gripping portion of the filling machine, or a sealing failure may occur. Furthermore, due to the distortion of the packaging bag, the bag breaking rate upon impact from the outside increases.

The oxygen permeability of the matte-like barrier polyamide film of the present invention is required to be 100 ml / m ² · day · MPa or less at 20 ° C. and 65% RH, particularly 80 ml / m ² · day · MPa or less. It is preferable that

Furthermore, the water vapor permeability of the matte-like barrier polyamide film of the present invention is required to be 20 g / m ² · day or less at 40 ° C. and 90% RH, and more preferably 15 g / m ² · day or less. It is preferable.
If the oxygen permeability and water vapor permeability of the matte-like barrier polyamide film of the present invention do not satisfy the above values, the contents will be inferior in storage stability, and difficult to use for food, medical products and medicine packaging applications. Become.

  The tensile strength of the matte-like barrier polyamide film of the present invention is preferably 175 MPa or more in both the length direction (MD) and the width direction (TD) of the film. When the tensile strength of the film is less than 175 MPa, the problem that the strength required for packaging foods, medical products, medicines and the like is insufficient tends to occur.

  The tensile elongation of the matte-like barrier polyamide film of the present invention is preferably 65% or more in both the length direction (MD) and the width direction (TD) of the film. If the tensile elongation of the film is less than 65%, the inconvenience that the strength required for packaging foods, medical products, medicines and the like is insufficient as well as the tensile strength tends to occur.

  The thickness of the matte-like barrier polyamide film of the present invention is not particularly limited as long as both impact strength and dimensional stability can be achieved, but is preferably 10 to 30 μm, and more preferably 12 to 18 μm. If the thickness is less than 10 μm, the impact strength tends to be very low. On the other hand, if the thickness exceeds 30 μm, the cost increases, which is not preferable.

Next, a method for producing the matte-like barrier polyamide film of the present invention will be described.
As described above, when a film is formed using a polyamide resin containing inorganic particles such as silica, the stretching stress increases when the unstretched film is stretched, leading to the generation of voids and an increase in the bowing phenomenon. In the present invention, in order to eliminate such a phenomenon, in the production of the polyamide film (X), (1-a) after adjusting the unstretched film to have a specific moisture content, at least the unstretched film It is important to apply a coating for forming a barrier layer containing a polyvinylidene chloride copolymer on one surface, and (1-b) to perform stretching under specific temperature conditions. And it became possible to obtain the polyamide film which satisfy | fills the above characteristic values by having discovered the conditions of such (1-a) and (1-b).

  As a method for producing the polyamide film (X), a tubular method, a tenter type simultaneous biaxial stretching method, and a tenter type sequential biaxial stretching method are generally known. The tubular method is advantageous in that the equipment cost of the equipment is cheaper than other methods, but it is difficult to increase the film thickness accuracy, and the tenter-type biaxial stretching method is also better in terms of quality stability and dimensional stability. Are better. As a method for producing the matte barrier polyamide film of the present invention, a tenter simultaneous biaxial stretching method is preferred.

  First, raw material resin pellets are supplied to a hopper, plasticized and melted with a melt extruder, and the melted resin is extruded into a sheet form from a T-die attached to the tip of the extruder, and cooled and solidified with a cast roll. At this time, the polyamide resin is pressed against the cast roll with air to obtain an unstretched film.

  And adjustment of the moisture content of an unstretched film and application | coating of the coating material for barrier layer formation are performed on the conditions of (1-a). Specifically, water is absorbed by a hot water bottle so that the moisture content of the unstretched film is 3 to 9%. The temperature of the hot water tank is preferably 45 to 90 ° C. If it is less than 45 ° C., the water absorption rate to the polyamide is slow, so it is necessary to lengthen the water absorption time, which is uneconomical. If it exceeds 90 ° C, crystallization of the polyamide proceeds and stretching becomes difficult. Furthermore, since the temperature is high, the stiffness of the film is eliminated, film wrinkles in the hot water layer are likely to occur, and the operability is significantly reduced.

  The moisture content of the unstretched film in the water absorption step needs to be 3 to 9%, and preferably 3.5 to 8.5%. If the moisture content is less than 3%, the amount of moisture that becomes a plasticizer is small, so that the stretching stress becomes high. Therefore, since bowing becomes large, a hot water shrinkage | contraction diagonal difference becomes large. Moreover, since the porosity in a film becomes high, the impact strength of a film falls or a cutting | disconnection occurs frequently. On the other hand, if the moisture content exceeds 9%, the water absorption in the width direction (TD direction) becomes non-uniform, resulting in poor film thickness. Furthermore, since it becomes difficult to obtain the film temperature required for stretching, neck stretching occurs or cutting frequently occurs.

Next, a barrier layer-forming coating material (latex) containing a polyvinylidene chloride copolymer is applied to at least one surface of the unstretched film. Specifically, after applying the barrier layer-forming coating to an unstretched film, the method of simultaneously applying the stretching process and the film-forming process as it is, or applying the coating layer for the barrier layer by spraying hot air with a drier etc. A method of performing a stretching process and a film forming process simultaneously after evaporating and drying the moisture of the paint and heat-sealing can be used. The latter method, which can promote the crystallization of the polyvinylidene chloride copolymer in advance before the stretching treatment, is more preferable in terms of brushing resistance.
In addition, for the formation of the barrier layer (Y) by applying the coating material for forming the barrier layer, the barrier layer (Y ) May be formed. However, in consideration of the cost and the adhesion between the polyamide film (X) and the barrier layer (Y), a coating for forming the barrier layer is applied before the stretching process, and the polyvinylidene chloride copolymer is coated by the stretching process. An in-line coat that forms a film is preferred.

  The temperature of the step of evaporating and drying the moisture of the coating for forming the barrier layer is preferably 70 ° C. to 150 ° C., more preferably in the range of 80 ° C. to 120 ° C. where the film forming property of the polyvinylidene chloride copolymer is good. It is. When the drying temperature is less than 70 ° C., the film-forming property is deteriorated, and when it exceeds 150 ° C., the temperature of the coating material for forming the barrier layer is excessively increased and a phenomenon such as bumping occurs, making it difficult to obtain a uniform film. The moisture evaporation drying process may be divided into different temperature distributions, and the time taken for the treatment process showing the highest temperature among them is the thickness of the unstretched film or polyvinylidene chloride copolymer, the barrier layer forming coating It is arbitrarily selected depending on the solid content and specific heat. The time is usually 0.01 to 120 seconds, preferably 1 to 80 seconds. If it is less than 0.01 seconds, the water layer evaporating property of the coating material for forming the barrier layer tends to be poor, or the film formation of the polyvinylidene chloride copolymer tends to be insufficient. Further, if it exceeds 120 seconds, in some cases, the crystallization of the polyamide film (X) is promoted too much, so that it is impossible to produce a stretched film, or the adhesiveness to the barrier layer (Y) tends to be disadvantageous. There is.

  The method for applying the polyvinylidene chloride copolymer barrier layer-forming coating to the polyamide film (X) is not particularly limited, but gravure roll coating, reverse roll coating, wire bar coating, air knife coating, die coating, curtain Usual methods such as die coating can be used.

  Next, it extends | stretches on the conditions of (1-b). An unstretched film that has been subjected to water absorption treatment, has a moisture content of 3 to 9%, and is coated with a polyvinylidene chloride copolymer film, grips the edges of the film with clips, MD direction and TD direction It is preferable to stretch 2.0 to 4.0 times. The draw ratio is preferably 2.5 to 3.8 times, and the ratio of the draw ratio in the MD direction to the draw ratio in the TD direction (TD / MD) is preferably 0.9 to 1.2. preferable.

  And the preheating temperature at the time of extending | stretching needs to be 180-250 degreeC, It is preferable to set it as 200-245 degreeC among these, More preferably, it is 210-240 degreeC. When the preheating temperature is less than 180 ° C., the amount of heat for evaporating moisture in the film is reduced. For this reason, the stretching stress increases, the bowing increases, and the porosity increases. Moreover, since it becomes difficult to obtain the film temperature required for stretching, neck stretching occurs or cutting frequently occurs. When the temperature exceeds 250 ° C., the evaporation rate of absorbed water becomes too fast. Therefore, since the film temperature becomes too high, crystallization of the polyamide proceeds and stretching becomes difficult.

  In addition, in order to preheat a polyamide film to said temperature, it is preferable to carry out by setting the temperature of the hot air sprayed on the film which drive | works the preheating zone of a extending machine to said temperature range. And it is preferable that the time (preheating time) for which the polyamide film travels in the preheating zone is 0.5 to 5 seconds.

  About extending | stretching temperature, 170-230 degreeC is required, It is preferable to set it as 180-220 degreeC, More preferably, it is 190-210 degreeC. When the stretching temperature is less than 170 ° C., it is difficult to obtain a uniform film temperature in the TD direction, and neck stretching or poor thickness occurs, or cutting frequently occurs. On the other hand, when the stretching temperature exceeds 230 ° C., the film temperature becomes too high, so that draw stretching is performed, and the molecular orientation is difficult to be performed, so that the impact strength and the strong elongation decrease.

  The biaxially stretched film is subsequently heat treated to fix the biaxial orientation. The temperature condition for this heat setting requires a temperature of 180 to 230 ° C, preferably 195 to 220 ° C, more preferably 205 to 215 ° C. The heat fixing treatment time is preferably 1 to 10 seconds, and the relaxation rate in the width direction is preferably in the range of 0.3 to 7%. By performing such heat setting (relaxation heat treatment), the dimensional stability of the matte-like barrier polyamide film can be enhanced.

  When the heat setting treatment temperature is less than 180 ° C., the dimensional stability of the film deteriorates, the oblique difference in hot water shrinkage exceeds 2.5%, or the barrier layer (Y) made of a polyvinylidene chloride copolymer The barrier property is lowered due to inferior dissolution and fusion property, and the adhesion between the polyamide film (X) and the barrier layer (Y) is lowered. On the other hand, when the heat setting treatment temperature exceeds 230 ° C., thermal deterioration of the film occurs, and impact strength and high elongation decrease. Furthermore, due to troubles such as fusing during heat setting treatment, the operability is lowered, or all the crystal nuclei of the polyvinylidene chloride copolymer are dissolved, resulting in poor brushing resistance.

  In order to set the stretching temperature and heat setting temperature as described above, it is preferable to set the temperature of the hot air blown to the film running in the stretching zone or heat setting zone of the stretching machine within the above temperature range.

  A surface treatment such as a corona discharge treatment may be applied to the polyamide film (X) or the barrier layer (Y) of the matte-like barrier polyamide film of the present invention, if necessary.

  The matte-like barrier polyamide film of the present invention can be made into various laminated films by laminating a resin layer such as a sealant.

  The resin used as the sealant is low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polyethylene / polypropylene copolymer, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid. / Methacrylic acid copolymer, ethylene-acrylic acid / methacrylic ester copolymer, polyvinyl acetate resin, etc., polyethylene, polypropylene, polyethylene / polypropylene copolymer, etc. with high heat seal strength and material strength The polyolefin resin is preferred. These resins may be used alone, or may be copolymerized or melt-mixed with other resins, or may be further acid-modified.

As a method of laminating the sealant layer to the matte-like barrier polyamide film, a film or sheet made of a sealant resin is laminated to the matte-like gas barrier polyamide film via an adhesive, or the sealant resin is applied to the matte-like gas barrier polyamide film. Examples include extrusion lamination. In the former method, the film or sheet made of the sealant resin may be in an unstretched state or in a stretched state at a low magnification, but practically preferably in an unstretched state.
When applying the adhesive to the matte-like barrier polyamide film, either the polyamide film (X) or the barrier layer (Y) may be used, but when the laminated film is processed into a packaging bag, It is preferable to apply an adhesive to the surface of the barrier layer (Y) so that the polyamide film (X) is on the outside.

  Although the thickness of a sealant layer is not specifically limited, It is preferable that it is 20-100 micrometers, and it is more preferable that it is 40-70 micrometers.

  A packaging bag can be produced by using the matte-like barrier polyamide film of the present invention. This packaging bag is, for example, a food / beverage product, fruit, juice, drinking water, liquor, cooked food, marine product, frozen product Contents such as foods, meat products, boiled foods, rice cakes, liquid soups, seasonings, other various foods and drinks, liquid detergents, cosmetics, and chemical products can be filled and packaged.

  Next, the present invention will be described more specifically with reference to examples. In addition, the raw material and measurement method which were used for evaluation of an Example and a comparative example are as follows.

(1) Glossiness (%)
The surface of the obtained polyamide film having a multilayer structure was measured at an incident angle of 20 ° according to JIS K 7105, using MURAKAMI Color Technology Laboratory Co., Ltd. (GROSS METER GM-26 PRO).
(2) Porosity (%)
Using the obtained polyamide film having a multilayer structure, a cross section of the film was prepared by ion polishing (IP), and the cross section was observed by FE-SEM. The SEM image is subjected to image processing (automatic binarization processing with a threshold value 95 setting) using image analysis software (ImageJ.), And the total void area of the cross section of the entire film is calculated. (%) Was calculated.
Porosity (%) = (total void area (μm ² ) / cross-sectional area of the entire film (μm ² )) × 100
(3) Impact strength (J)
By measuring the impact strength required for punching a ring-shaped film having a diameter of 7 cm in an atmosphere of 20 ° C. using a film impact tester (manufactured by Toyo Seiki Co., Ltd.) using the obtained polyamide film having a multilayer structure. went. For the measurement, an impact head having a weight of 30 kg and a diameter of 12.7 mm (0.5 inch) was used.

(4) Diagonal difference in hot water shrinkage rate Measured and calculated by the method described above.
(5) Oxygen permeability Using the obtained polyamide film having a multilayer structure, using an oxygen barrier measuring device (OX-TRAN 2 / 20MH) manufactured by Mocon, based on JIS K7126-2 method, a temperature of 20 ° C, The oxygen permeability was measured in an atmosphere with a relative humidity of 65%.
(6) Water vapor transmission rate According to the method described in JIS K-7129, at a temperature of 40 ° C. and a humidity of 90% RH, PERMATRAN-W 3/33 manufactured by Mocon Co. The water vapor transmission rate was measured. The unit is g / (m ² · day).

(7) Moisture content (%) in the production method
It calculated | required by following Formula from the mass Wd of the sample piece cut out from the unstretched film after water absorption, and the mass Wd after drying it at 80 degreeC under pressure reduction for 24 hours.
Moisture content (%) = (W−Wd) / W × 100
(8) Tensile strength / elongation The obtained polyamide film having a multilayer structure was measured using Autograph AG-1 (manufactured by Shimadzu Corporation). The test piece was a strip having a width of 10 mm and a length of 150 mm, the cell used was 100 kg, the test speed was 500 mm / min, and the chuck interval was 100 mm.
For both tensile strength and tensile elongation, specimens were collected in the length direction (MD) and width direction (TD) of the film, respectively.

(9) Thickness measurement Using the obtained multilayered polyamide film, the thickness of 0.5 μm or more is a commercially available digital thickness gauge (contact thickness gauge, trade name: Ultra High Precision Deci Microhead MH-15M, Japan (Optical Co., Ltd.). On the other hand, the thickness of less than 0.5 μm was measured by gravimetric analysis (the weight measured value of a film of a certain area was divided by the area and further divided by the specific gravity of the composition).
(10) Stretchability Productivity was evaluated when production was continuously performed for 24 hours under the production conditions shown in each example. In the case where the number of breaks of the film produced at the time of stretching was 1 or less, it was evaluated as ○, when the number of cuts was 2 to 4 was evaluated as Δ, and when the number of cuts was 5 or more, it was evaluated as ×. Regarding the condition of evaluation x, the operability is very low, and stable production of the product is difficult.

[Raw materials]
[Silica-containing master chip (M1)]
10 kg of ε-caprolactam, 1 kg of water, and 500 g of silica (manufactured by Fuji Silysia Chemical Co., Ltd., product name: Silicia 310P, average particle size of 2.7 μm) are put into a 30 liter autoclave and maintained at 100 ° C. The reaction system was stirred at that temperature until the reaction system became uniform. Subsequently, the mixture was heated to 260 ° C. with stirring, maintained at a pressure of 1.5 MPa for 1 hour, released to normal pressure over an additional hour, and polymerized for an additional hour. When the polymerization was completed, the reaction product was discharged into a strand, cooled, solidified, and then cut to obtain a polyamide resin pellet. Next, the pellets were refined with dry heat at 95 ° C. for 8 hours to remove unreacted monomers and the like, and then dried. The relative viscosity of the obtained polyamide resin was 2.7, and the silica content was 5.2% by mass.

[Silica master chip (M2)]
10 kg of ε-caprolactam, 1 kg of water, and 1.5 kg of silica (manufactured by Fuji Silysia Chemical Co., Ltd., product name: Silicia 310P, average particle size of 2.7 μm) are put into an autoclave having a volume of 30 liters, and 100 ° C. The mixture was stirred at that temperature until the reaction system became homogeneous. Subsequently, the mixture was heated to 260 ° C. with stirring, maintained at a pressure of 1.5 MPa for 1 hour, released to normal pressure over an additional hour, and polymerized for an additional 1.5 hours. When the polymerization was completed, the reaction product was discharged into a strand, cooled, solidified, and then cut to obtain a polyamide resin pellet. Next, the pellets were refined with dry heat at 95 ° C. for 8 hours to remove unreacted monomers and the like, and then dried. The relative viscosity of the obtained polyamide resin was 2.6, and the silica content was 15.6% by mass.

・ Barrier layer forming paint (latex) (1)
85 parts by weight of water, 0.15 parts by weight of sodium alkyl sulfonate and 0.10 parts by weight of sodium persulfate were charged into a pressure-resistant reaction vessel subjected to glass lining, and after degassing, the temperature of the contents was maintained at 55 ° C. . In a separate container, 97 parts by mass of vinylidene chloride, 2 parts by mass of methyl acrylate, and 1 part by mass of acrylic acid were weighed and mixed to prepare a monomer mixture. In the reaction vessel, 10 parts by mass of the monomer mixture was charged and the reaction was allowed to proceed with stirring. After confirming that the reaction almost proceeded by lowering the internal pressure of the reaction vessel, 10 parts by weight of sodium alkyl sulfonate in 15% by weight aqueous solution was injected, and then the remaining amount of the monomer mixture was continuously added for 15 hours. A fixed amount was added. To the obtained monomer mixture, 15% by mass aqueous sodium alkyl sulfonate was added so that the liquid surface tension at 20 ° C. was 42 mN / m, to obtain a barrier layer forming coating material (I).

・ Barrier layer forming paint (latex) (2)
L536B (solid content concentration: 50% by mass) polyvinylidene chloride latex manufactured by Asahi Kasei Chemicals

Example 1
A silica-containing master chip M1 was mixed with nylon 6 resin (manufactured by Unitika Ltd., trade name: A1030BRF, relative viscosity 3.1) so that the silica content shown in Table 1 was obtained, and the cylinder temperature was set to 260 ° C. The unstretched film with a thickness of 150 μm was obtained by feeding to a shaft extruder, extruding from a T-die, and contacting with a cooling roll having a set temperature of 20 ° C. The obtained unstretched film was immersed in a hot water layer adjusted to 65 ° C. so that the moisture content was 3.5%.
Next, the barrier layer-forming paint (1) is applied to one side of the unstretched film by an air knife coating method, and dried for 30 seconds with an infrared irradiator at a temperature of 110 ° C. Was evaporated to dryness.

  Next, the unstretched film coated with this barrier layer-forming coating (1) was preheated by blowing hot air at 230 ° C. for 1 second, and was adjusted in the MD direction by a tenter type simultaneous biaxial stretching machine adjusted to a temperature of 200 ° C. 3 times and 3.3 times in the TD direction. Subsequently, while hot air at 210 ° C. was blown on the stretched sheet for 3 seconds, it was relaxed by 5% in the TD direction to perform heat setting treatment. And it cooled and obtained the polyamide film of the multilayer structure which consists of a 15-micrometer-thick polyamide film (X) and a 1.2-micrometer-thick barrier layer (Y).

Examples 2-9, Comparative Examples 5-11
A polyamide film (X) having a thickness of 15 μm and a thickness of 1.2 μm were obtained in the same manner as in Example 1 except that the moisture content, preheating temperature, stretching temperature, and heat setting temperature of the unstretched sheet were changed to the values shown in Table 1. A polyamide film having a multilayer structure composed of the barrier layer (Y) was obtained.

Example 10
A polyamide film (X) having a thickness of 15 μm and a barrier layer having a thickness of 1.2 μm were obtained in the same manner as in Example 2 except that the mixing amount of the silica-containing master chip M1 was changed so as to obtain the silica content shown in Table 1. A polyamide film having a multilayer structure composed of (Y) was obtained.

Examples 11 and 12, Comparative Example 12
A polyamide film (X) having a thickness of 15 μm was used in the same manner as in Example 2 except that the mixing amount of the silica-containing master chip M2 was changed using the silica-containing master chip M2 so that the silica content shown in Table 1 was obtained. A polyamide film having a multilayer structure composed of a barrier layer (Y) having a thickness of 1.2 μm was obtained.

Example 13
Except for changing the thickness of the unstretched sheet to 250 μm, the same procedure as in Example 2 was performed, and a multilayer structure comprising a polyamide film (X) having a thickness of 25 μm and a barrier layer (Y) having a thickness of 1.2 μm was used. A polyamide film was obtained.

Example 14
A polyamide film having a multilayer structure comprising a polyamide film (X) having a thickness of 15 μm and a barrier layer (Y) having a thickness of 1.2 μm is carried out in the same manner as in Example 2 except that the coating material for forming a barrier layer (2) is used. Got.

Examples 15-18, Comparative Example 15
Except for changing the thickness of the barrier layer (Y) to Table 1, it was carried out in the same manner as in Example 2 to obtain a polyamide film (X) having a thickness of 15 μm and a polyamide film having a multilayer structure composed of the barrier layer (Y). .

Comparative Example 1
A polyamide film having a multilayer structure composed of a polyamide film (X) having a thickness of 15 μm and a barrier layer (Y) having a thickness of 1.2 μm was obtained in the same manner as in Example 2 except that the silica-containing master chip M1 was not mixed. It was.

Comparative Example 2
A polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 2, except that the barrier layer-forming coating material (1) was not applied to the unstretched film.

Comparative Example 3
A multilayer comprising a polyamide film (X) having a thickness of 15 μm and a barrier layer (Y) having a thickness of 1.2 μm, except that the unstretched sheet was stretched without being immersed in the warm water layer. A polyamide film having a constitution was obtained.

Comparative Example 4
Except for changing the thickness of the unstretched sheet to 250 μm, the same procedure as in Comparative Example 3 was performed, and a multilayer structure comprising a polyamide film (X) having a thickness of 25 μm and a barrier layer (Y) having a thickness of 1.2 μm was used. A polyamide film was obtained.

Comparative Example 13
A single shaft in which a silica-containing master chip M1 is mixed with nylon 6 resin (manufactured by Unitika, trade name: A1030BRF, relative viscosity 3.1) so that the silica content shown in Table 1 is obtained, and the cylinder temperature is set to 260 ° C. It was supplied to an extruder, extruded from a T die, and contacted with a cooling roll having a set temperature of 20 ° C. to obtain an unstretched sheet having a thickness of 150 μm. Next, this unstretched film was stretched in the MD direction at a temperature of 55 ° C. and a stretch ratio of 2.5 by a longitudinal stretching machine composed of heating roller groups having different peripheral speeds. Next, the barrier layer-forming paint (1) is applied to the longitudinally stretched film by an air knife coating method, and dried for 30 seconds with an infrared irradiator at a temperature of 110 ° C. Was evaporated to dryness.

  Next, the film coated with the barrier layer-forming paint (1) is introduced into a tenter, preheated by blowing hot air of 60 ° C. for 1 second in the preheating portion, and then stretched at a temperature adjusted to 80 ° C. The film was stretched in the TD direction at a stretch ratio of 4 times. Subsequently, while hot air at 210 ° C. was blown on the stretched sheet for 3 seconds, it was relaxed by 5% in the TD direction to perform heat setting treatment. And it cooled and obtained the polyamide film of the multilayer structure which consists of a 15-micrometer-thick polyamide film (X) and a 1.2-micrometer-thick barrier layer (Y).

Comparative Example 14
Except that the draw ratio was changed to 3 times in the MD direction and 3.3 times in the TD direction, the same procedure as in Comparative Example 13 was performed, and the polyamide film (X) having a thickness of 15 μm and the barrier layer (Y) having a thickness of 1.2 μm were formed. A polyamide film having a multilayer structure was obtained.

  Table 1 shows the production conditions in Examples 1 to 18 and Comparative Examples 1 to 15, the characteristic values of the obtained polyamide film having a multilayer structure, and the evaluation results of stretchability.

  In Examples 1 to 18, since the specific production conditions were satisfied, the obtained polyamide film having a multilayer structure satisfies all of the characteristic values (1) to (6) defined in the present invention. It had a matte surface with a matte surface and was excellent in impact strength, dimensional stability, oxygen barrier property, and water vapor barrier property.

On the other hand, in Comparative Example 1, since a polyamide resin not containing silica was used, the obtained polyamide film having a multilayer structure had high glossiness and did not have a matte tone.
In Comparative Example 2, since the barrier layer (Y) was not formed, the required oxygen permeability and water vapor permeability could not be obtained. In Comparative Examples 3 to 5, since the moisture content of the unstretched film was too low, the stretching stress was increased, and the resulting polyamide film having a multilayer structure had a large difference in the hot water shrinkage rate and the porosity was high. The impact strength was low. Furthermore, the stretchability was also poor. In Comparative Examples 6 to 11, any one of the preheating temperature, the stretching temperature, and the heat setting temperature was not in a suitable range, and thus the characteristic values (2) to (4) defined in the present invention were not satisfied. Moreover, in the comparative example 12, since the polyamide resin with much silica content was used, the porosity became large and the impact strength was low. Furthermore, the tensile strength and tensile elongation were low, and the stretchability was also poor. In Comparative Examples 13 to 14, since the moisture content of the unstretched film was low and the preheating temperature and the stretching temperature were both low, the oblique difference in hot water shrinkage ratio was large and the porosity was high. In Comparative Example 15, since the thickness of the barrier layer (Y) was too thin, the obtained polyamide film having a multilayer structure did not satisfy the characteristic values (5) to (6) defined in the present invention. .

Claims (3)

A polyamide film having a multilayer structure including a polyamide film (X) made of a polyamide resin containing silica and a barrier layer (Y),
A mat-like barrier polyamide film characterized by simultaneously satisfying the following conditions (1) to (6):
(1) Glossiness is 50% or less (2) Porosity of film is 0.1 to 5%
(3) Impact strength measured at 20 ° C. is 0.35 J or more. (4) The difference in hot water shrinkage between the direction of 45 degrees and the direction of 135 degrees with respect to the film width direction (TD direction) is 2. 0.05% or less (5) Oxygen permeability at 20 ° C. under 65% RH, 100 ml / m ² · day · MPa or less (6) Water vapor permeability at 40 ° C. under 90% RH, 20 g / m ² · day or less The matte-like barrier polyamide film according to claim 1, wherein the barrier layer (Y) is formed of a polyvinylidene chloride copolymer. A method for producing a matte-like barrier polyamide film according to claim 1 or 2, wherein the steps (1) and (2) are sequentially performed.
(1) A barrier layer-forming coating material comprising a polyvinylidene chloride copolymer on at least one surface of an unstretched film after water absorption in a hot water tank so that the moisture content of the unstretched film is 3 to 9%. Apply.
(2) Preheating is performed at a preheating temperature of 180 to 250 ° C., stretching is performed at a temperature of 170 to 230 ° C., and heat setting is further performed at a temperature of 180 to 230 ° C.