JP5980598B2 - Biaxially stretched polyamide film and method for producing the same - Google Patents

Description

The present invention relates to a polyamide film having excellent pinhole resistance and gas barrier properties, and a method for producing the same.

  Vinylidene chloride copolymers are widely used in food packaging and industrial films because of the excellent gas barrier properties of the film formed.

  Patent Document 1 discloses a method for pre-coating a vinylidene chloride copolymer on a polyamide film to impart gas barrier properties. The film obtained by this method has excellent gas barrier properties, and has both boil heat resistance and brushing resistance.

International Publication No. 2009/069307 Pamphlet

  However, the polyamide film in Patent Document 1 has an inadequate aspect particularly in pinhole resistance under low temperature use, and there is room for improvement.

  As a method for improving pinhole resistance at low temperatures, it is known to add an ethylene copolymer or the like. However, when such measures are taken, wrinkles occur in the water absorption process before pre-coating, and In this coating process, there was a problem that application failure occurred and production became difficult.

  On the other hand, when stretching without performing water absorption treatment, the problem of wrinkles in the water absorption step can be avoided, but the followability of the coating film during stretching is poor, cracks are easily generated, and even if a film is formed, There were drawbacks such as insufficient laminate strength and barrier performance, or poor uniformity of physical properties in the width direction of the film.

  In addition, when post-coating a vinylidene chloride copolymer on a stretched film, a post-treatment process is required, which raises a problem of cost increase.

  The present invention more economically provides a polyamide film having both excellent gas barrier properties and pinhole resistance.

  As a result of intensive studies, the inventors of the present invention have limited the amount of ethylene copolymer added and the water absorption treatment conditions of the unstretched film before coating the vinylidene chloride copolymer, without impairing operability. It has been found that pinhole resistance can be imparted to a gas barrier film produced by a pre-coating method, which has been considered difficult, and has led to the present invention.

That is, the gist of the present invention is as follows.
(1) A film having a resin layer containing a vinylidene chloride copolymer on at least one side of a biaxially stretched polyamide film containing 2 to 5% by mass of an ethylene copolymer, and 1000 at 5 ° C. A biaxially stretched polyamide film characterized in that the number of pinholes in a repeated bending fatigue test is 10 or less.
(2) The biaxially stretched polyamide film according to (1), wherein the oxygen permeability in an atmosphere of 20 ° C. and 85% RH is 100 ml / m ^{2 ·} d · MPa or less. The biaxially stretched polyamide film according to (1) or (2), wherein
(4) The moisture content of an unstretched polyamide film containing 2 to 5% by mass of an ethylene copolymer in warm water not exceeding 50 ° C. is adjusted to 2 to 7% by mass, and then the vinylidene chloride copolymer is adjusted. The method for producing a biaxially stretched polyamide film according to any one of (1) to (3), wherein a latex containing is applied, dried and then simultaneously biaxially stretched.

  According to the present invention, a biaxially stretched polyamide film excellent in gas barrier properties and pinhole resistance can be obtained economically without impairing operability.

  Hereinafter, the present invention will be described in detail.

  The polyamide film in the present invention is one in which a resin layer made of a vinylidene chloride copolymer is formed on at least one surface of a polyamide film containing a predetermined amount of an ethylene copolymer.

  The polyamide in the present invention is a melt-moldable linear polymer compound having an amide bond —CONH— in the molecule, and includes polycapramide (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene. Examples are sebacamide (nylon 610), polyaminoundecamide (nylon 11), polylaurimide (nylon 12), and copolymers thereof. Of these, polycapramide (nylon 6) is particularly preferred in terms of productivity and performance.

  The ethylene copolymer in the present invention is not particularly limited, but a terpolymer of ethylene / acrylic acid ester / maleic anhydride, an ethylene / (meth) acrylic acid copolymer, or an ionomer thereof is a polyamide. The compatibility is good and can be mentioned as a suitable example.

  The melt index (measurement conditions: 190 ° C., 21.2 N load) of the ethylene copolymer according to JIS K7210 is 0.1 to 60 g / 10 minutes, preferably 1 to 50 g / 10 minutes. . When the melt index is lower than 0.1 g / 10 min, the compatibility with the polyamide becomes insufficient, and the pinhole resistance and transparency are likely to deteriorate. Conversely, even if it is higher than 60 g / 10 minutes, the same tendency is observed. Further, from the viewpoint of preventing wrinkle generation in a water absorption treatment tank described later, a product having a high softening temperature, specifically, a product having a Picad softening point temperature of 50 ° C. or higher is preferable.

  In the present invention, the polyamide film serving as the base contains 2 to 5% by mass of an ethylene copolymer. When the amount of the ethylene copolymer is more than 5% by mass, wrinkles are generated in the water absorption tank of the unstretched film at the time of production, and the transparency of the obtained film is deteriorated. Moreover, the production amount of the gel at the time of melting increases, the film appearance deteriorates, the filter pressurization speed of the extruder increases, and the production efficiency deteriorates. When the amount of the ethylene copolymer is less than 2% by mass, the pinhole resistance performance of the resulting film is insufficient.

  If necessary, generally known additives such as antioxidants, lubricants, crystal nucleating agents, antistatic agents and the like can be added to the base polyamide film.

  A resin layer containing a vinylidene chloride copolymer is formed on the polyamide film of the present invention. Although it does not specifically limit as a vinylidene chloride type copolymer, In order to adjust performance, the mixture of 2 or more types of vinylidene chloride type copolymers is used suitably.

  A particularly preferable mixture of vinylidene chloride copolymers is a mixture of two or more kinds of vinylidene chloride copolymers to which no thermal crosslinking agent is added, and one of the vinylidene chloride copolymers is a crystal of the same. While melting | fusing point is 170 degreeC or more and 210 degrees C or less, 25-45 mass parts is contained with respect to 100 mass parts of vinylidene chloride type | system | group copolymer mixtures.

  The vinylidene chloride copolymer is obtained by polymerizing 50 to 99% by mass of vinylidene chloride as a raw material and 1 to 50% by mass of one or more other monomers copolymerizable with vinylidene chloride by a known emulsion polymerization method. To obtain a latex dispersed in the medium. When the proportion of the copolymerizable monomer is less than 1% by mass, plasticization inside the resin becomes insufficient, the film-forming property of the film is deteriorated, and when the proportion of the monomer exceeds 50% by mass. Gas barrier properties are reduced. The higher the ratio of vinylidene chloride, the higher the vinylidene chloride copolymer having a higher crystalline melting point.

  Examples of monomers that can be copolymerized with vinylidene chloride include, for example, vinyl chloride; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; methyl methacrylate Methacrylic acid esters such as glycidyl methacrylate; acrylonitrile, methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid; These monomers can be used alone or in combination of two or more.

  In the particularly preferred vinylidene chloride copolymer mixture described above, one kind of vinylidene chloride copolymer is mainly added to improve brushing resistance, and constitutes a vinylidene chloride copolymer mixture. Among the two or more types of vinylidene chloride copolymers, it exhibits the highest crystalline melting point. The crystal melting point is preferably in the range of 170 ° C. or higher and 210 ° C. or lower, more preferably in the range of 180 ° C. or higher and 210 ° C. or lower, from the viewpoints of the melt-fusing properties, gas barrier properties, and brushing resistance of the coating. Moreover, it is preferable that the crystalline melting point of this vinylidene chloride type | system | group copolymer is below the maximum temperature of the heat processing in a film manufacturing process.

  As described above, the higher the ratio of vinylidene chloride, the higher the crystalline melting point of the vinylidene chloride copolymer. Thus, the vinylidene chloride copolymer having a melting point of 170 ° C. or higher and 210 ° C. or lower has a ratio of vinylidene chloride. Is preferably polymerized in a ratio close to the above-mentioned upper limit, for example, in a range in which vinylidene chloride is 95 to 99 parts by mass. On the other hand, other vinylidene chloride copolymers to be mixed with a vinylidene chloride copolymer having a melting point of 170 ° C. or higher and 210 ° C. or lower are required to form a continuous film under film production conditions. For this reason, it is not preferable that the vinylidene chloride ratio is too high. Usually, those having a vinylidene chloride ratio of 80 to 95 parts by mass can be preferably used.

  The proportion of the vinylidene chloride copolymer having a crystal melting point of 170 ° C. or more and 210 ° C. or less is 25 to 25 parts by mass with respect to 100 parts by mass of the vinylidene chloride copolymer mixture from the viewpoint of brushing resistance and film forming properties. It is preferably 45 parts by mass.

  The vinylidene chloride copolymer can be used in combination with other resins. Examples of other resins include ethylene-vinyl acetate copolymer, (meth) acrylic ester copolymer, methyl methacrylate-butadiene-styrene copolymer, acrylonitrile copolymer, methyl vinyl ether-maleic anhydride copolymer. Etc. These resins can be used alone or in combination of two or more.

  It is preferable that the vinylidene chloride copolymer is not copolymerized with a so-called thermal crosslinking agent that does not react at room temperature and undergoes a crosslinking reaction with high heat, generally 100 ° C. or higher. Note that the thermal crosslinking agent can be said to be a thermal crosslinking agent only after it is copolymerized in such an amount as to exhibit its function, and in order to exhibit a remarkable crosslinking effect, an amount exceeding 0.1% by mass is required. In the above, “there is no thermal crosslinking agent added” means that the copolymerization amount of the thermal crosslinking agent is 0.1% by mass or less.

Specific examples of such a thermal cross-linking agent include epoxy groups such as glycidyl methacrylate and methylol methacrylate; melamine groups; methylolated or methylmethylol compounds thereof; oxolin groups. When the thermal cross-linking agent is copolymerized with the vinylidene chloride copolymer, the thermal cross-linking reaction proceeds to a high degree, thereby lowering the elasticity of the coating layer and lowering the adhesion with the base film.

  If desired, one or more additives such as pigments, antioxidants, antistatic agents, ultraviolet absorbers, lubricants, and preservatives can be added to the vinylidene chloride copolymer.

  The resin layer containing a vinylidene chloride copolymer can be obtained by applying a latex containing a vinylidene chloride copolymer to a base film and drying it.

  The solid content concentration of the latex containing the vinylidene chloride copolymer can be changed depending on the specifications of the coating apparatus and the drying / heating apparatus, but is preferably in the range of 10 to 70% by mass, more preferably It is the range of 30-55 mass%. If it is less than 10% by mass, a problem that a long time is required in the drying step tends to occur. On the other hand, if it exceeds 70% by mass, film formation proceeds during storage and the liquid pot life is shortened, and problems with coating properties tend to occur.

  The method of applying the latex containing the vinylidene chloride copolymer is not particularly limited, but a usual method such as gravure roll coating, reverse roll coating, wire bar coating, air knife coating, die coating, curtain die coating, etc. may be used. it can.

  In the biaxially stretched polyamide film of the present invention, the thickness of the resin layer containing the vinylidene chloride copolymer is preferably 0.1 to 3.0 μm, more preferably 0.5 to 2.0 μm. preferable. When the film thickness is less than 0.1 μm, the gas barrier property is likely to be lowered, and when it exceeds 3.0 μm, the film forming property is lowered and the appearance of the film is easily impaired.

  After applying a latex containing a vinylidene chloride copolymer, a resin layer is formed through a process of evaporating and drying the moisture of the latex by hot air blowing with a dryer or irradiation of infrared rays and heat fusion. The temperature of the water evaporation drying step is preferably 70 to 150 ° C, and more preferably in the range of 80 to 120 ° C where the film-forming property of the vinylidene chloride copolymer latex is good. When the drying temperature is less than 70 ° C., the film-forming property is lowered, and when it exceeds 150 ° C., the temperature of the latex is greatly increased, and a phenomenon such as bumping appears and it becomes 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 base film and the vinylidene chloride copolymer layer, the solid content of the latex and the specific heat. It is arbitrarily selected by etc. The time is usually 0.01 to 120 seconds, preferably 1 to 80 seconds. When the time is less than 0.01 seconds, the water vaporization property of the vinylidene chloride copolymer latex tends to be inferior, or the film formation of the vinylidene chloride copolymer mixture layer tends to be insufficient. On the other hand, if it exceeds 120 seconds, crystallization of the polyamide resin may be promoted too much to make it impossible to produce a stretched film, or the adhesion to the latex film tends to be reduced.

  As the biaxial stretching method of the polyamide film, a simultaneous biaxial stretching method that can suppress the crystallinity of the film immediately before the final stretching step is preferable. The simultaneous biaxial stretching condition is usually 70 to 230 ° C., preferably 100 to 230. When adjusting the moisture to the above-mentioned range, the range of the stretching temperature of 170 to 230 ° C. at which the temperature of the sheet rapidly rises and softens with the completion of the evaporation of moisture can suppress the progress of crystallization of the unstretched sheet. Therefore, it is more preferable. In general, the draw ratio is preferably 2 to 4 times in the longitudinal and transverse directions.

  Subsequently, the film after biaxial stretching is heat-set at 150 to 250 ° C., preferably 190 to 230 ° C. under tension or relaxation within 30%. At this time, if the maximum temperature of the heat setting treatment is less than 150 ° C., the dimensional stability of the stretched film is inferior, the melt-bonding property of the vinylidene chloride copolymer layer is inferior, the gas barrier property is lowered, There exists a tendency for adhesiveness with a base film to fall. In addition, if the temperature exceeds 250 ° C., the polyamide resin reaches the melting point or more and melts, making it impossible to manufacture, or dissolving the crystal nuclei of the vinylidene chloride copolymer, thereby impairing the brushing resistance effect. Or

  A preferred method for producing the biaxially stretched polyamide film of the present invention is to adjust the moisture content of the unstretched film to 2 to 7% by mass in warm water not exceeding 50 ° C., and then contains a vinylidene chloride copolymer. It includes applying a latex, drying, and simultaneously biaxial stretching.

  In the said manufacturing method, it is necessary to set water absorption treatment conditions so that the moisture content of the unstretched polyamide film just before apply | coating a vinylidene chloride copolymer mixture may be 2-7 mass%, Preferably it is 3-6 mass%. There is. When the water absorption is less than 2% by mass, the stretching stress at the time of simultaneous biaxial stretching increases, and the trouble of film breakage increases. In addition, stress strain with the vinylidene chloride copolymer film tends to occur, and the interlaminar adhesion with the substrate film tends to decrease. In addition, if the water absorption exceeds 7% by mass, wrinkles occur in the film during the water absorption treatment, so troubles may occur in the coating process of the vinylidene chloride copolymer, and the wrinkled part becomes a coating defect, resulting in a product collection. The rate gets worse.

  It is preferable that the hot water temperature of the water absorption treatment tank does not exceed 50 ° C. When it exceeds 50 ° C., the stiffness of the film is lowered and wrinkles are likely to occur. In particular, care is required because wrinkles are more likely to occur as the concentration of the ethylene copolymer added increases. If the water absorption temperature is kept low, the generation of wrinkles can be suppressed. However, if it is too low, it takes a long time to obtain a predetermined moisture content, and measures such as extending the water absorption tank and reducing the production rate are necessary. This is not a good idea. The range of 45-50 degreeC is preferable.

  The biaxially stretched polyamide film of the present invention needs to have 10 or less pinholes in a 1000 times repeated bending fatigue test under an atmosphere of 5 ° C. If the number of pinholes exceeds 10, the strength of the package is insufficient, and in particular, problems such as leakage of contents occur due to pinholes resulting from bending fatigue at low temperatures. The method of the repeated bending fatigue test will be described later.

  The biaxially stretched polyamide film of the present invention can be suitably used for applications such as food packaging materials, electrical insulating materials, and general industrial materials.

Next, the present invention will be specifically described by way of examples.
The property evaluation methods and film materials in the examples and comparative examples are as follows.

<Evaluation method>

(1) Repeated bending fatigue test Fed. Shown in MIL-B-131F. Test Method Std. No. According to Method 2017 of 101C, bending was performed 1000 times in a 5 ° C. atmosphere by a so-called gel bot tester, and the number of pinholes generated in the film was counted.

(2) Gas barrier property Using an oxygen barrier measuring device (OX-TRAN 2/20) manufactured by Mocon, oxygen permeability was measured in an atmosphere at a temperature of 20 ° C and a relative humidity of 85%.
In practice, the oxygen permeability is preferably 100 ml / m ^{2 ·} d · MPa or less, more preferably 75 ml / m ^{2 ·} d · MPa or less.

(3) Moisture content of polyamide unstretched film The unstretched film immediately after exiting the water absorption tank was collected, put in a weighing bottle, dried, and the moisture content was calculated from the weight change before and after drying.

(4) Crystalline melting point of vinylidene chloride copolymer Using a differential scanning calorimeter (DSC: DSC-60, manufactured by PERKIN ELMER), 2 mg of a dry film of vinylidene chloride copolymer latex was transferred at a constant rate (10 ° C / min. ) From the peak of the endothermic peak of the chart obtained when the temperature is raised from room temperature to 230 ° C.

(5) Presence / absence of wrinkles The state of the film in the tank during the water absorption treatment was visually observed and evaluated.
○: Wrinkles are not observed.
X: Wrinkles are observed.

(6) Coat appearance The film formation state of the vinylidene chloride copolymer was visually observed and evaluated (1 m ² ).
○: No crack occurred in the film.
X: One or more cracks were generated in the film.

<Raw material>

・ Nylon 6
Unitika A1030BRF
・ Ethylene copolymer
(A) Nippon Polyethylene Corporation: Lexpearl ET230X
Ternary copolymer of ethylene, n-butyl acrylate and maleic anhydride Melt index: 7.8 (JIS K7210 190 ° C., 21.2 N load condition)
(B) Mitsui DuPont Polychemical Co., Ltd .: High Milan 1652
Ionomer of ethylene / methacrylic acid copolymer (ionic species: zinc)
Melt index: 5.5 (JIS K7210 190 ° C, 21.2N load condition)

<Preparation of vinylidene chloride copolymer mixture>

Vinylidene chloride copolymer latex (A-1)
In a pressure-resistant reaction vessel with glass lining at room temperature, 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 and degassed. 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. 10 parts by mass of the monomer mixture was charged into the reaction vessel, and the reaction was allowed to proceed under stirring. After confirming that the reaction almost proceeded by lowering the internal pressure of the reaction vessel, 10 parts by mass of a 15% by mass aqueous solution of sodium alkyl sulfonate was injected, and then the remaining total amount of the monomer mixture was added over 15 hours. A constant amount was added continuously. As a result, latex was obtained. To the obtained latex, 15% by mass aqueous sodium alkyl sulfonate was added so that the liquid surface tension at 20 ° C. was 42 mN / m. The polymerization yield at this time was 99.9%, and the composition of the obtained vinylidene chloride copolymer latex was almost equal to the charging ratio. The solid content concentration of the latex was 51% by mass. The crystal melting point measured by DSC was 190 ° C.

Vinylidene chloride copolymer latex (B-1)
The compounding quantity in another container mentioned above was changed into 90 mass parts of vinylidene chloride, 9 mass parts of methyl acrylate, and 1 mass part of acrylic acid. Otherwise, a vinylidene chloride copolymer latex was obtained in the same manner as described above. The solid content concentration of the latex was 51% by mass. The crystal melting point measured by DSC was 140 ° C.

Example 1
Mixing of vinylidene chloride copolymer latex Latex A-1 and latex B-1 were stirred and mixed to obtain a mixed latex. Here, the vinylidene chloride copolymer of A-1 was 35 parts by mass with respect to 100 parts by mass of the total amount of vinylidene chloride copolymer contained in the mixed latex.

  Ethylene copolymer (A) is 3.5% by mass, average particle size relative to nylon 6 (A1030BRF manufactured by Unitika Co., Ltd.) having a relative viscosity of 3.0 measured at 25 ° C. in 96% concentrated sulfuric acid at 25 ° C. The agglomerated silica having a diameter of 2 μm was mixed so as to be 0.08% by mass, melt-kneaded with an extruder set at 250 ° C., and pelletized.

  Next, this pellet was melt-extruded by an extruder equipped with a T-die set at 260 ° C. and cooled on a cooling roll having a surface temperature of 20 ° C. to obtain an unstretched film having a thickness of 150 μm. Next, this unstretched film was subjected to water absorption treatment for 100 seconds in a water absorption tank set at 48 ° C., and adjusted to a moisture content of 6% by mass.

  The mixed latex was applied to the untreated surface of this unstretched film by an air knife coating method, and was subjected to a drying treatment for 30 seconds with an infrared irradiator at a temperature of 110 ° C. to evaporate and dry the water in the latex.

  The unstretched film coated with this latex was guided to a simultaneous biaxial stretching machine at a temperature of 220 ° C. and subjected to simultaneous biaxial stretching at a magnification of 3.0 times in length and 3.3 times in width. Subsequently, a heat setting treatment for 6 seconds at a temperature of 215 ° C. and a relaxation treatment of 5% in the transverse direction were performed, and after cooling the film surface temperature to 40 ° C. or lower, the film was wound on a winder, and the film thickness was 15 μm. A polyamide film coated with a 1.2 μm thick vinylidene chloride copolymer mixture was obtained.

Examples 2-3
A polyamide film coated with a vinylidene chloride copolymer mixture was obtained in the same manner as in Example 1 except that the amount of ethylene copolymer A added to nylon 6 was changed as shown in Table 2.

Example 4
A polyamide film coated with a vinylidene chloride copolymer mixture was obtained in the same manner as in Example 1 except that ethylene copolymer B was used as the ethylene copolymer added to nylon 6.

Table 2 shows the evaluation results of the films obtained in Examples 1 to 4.

Comparative Examples 1-2
A polyamide film coated with a vinylidene chloride copolymer mixture was obtained in the same manner as in Example 1 except that the amount of ethylene copolymer A added to nylon 6 was changed as shown in Table 2. Table 2 shows the gas barrier properties and pinhole resistance of the obtained film.
In Comparative Example 1, the number of pinholes increased because the amount of the ethylene copolymer added was small.
On the other hand, in Comparative Example 2, since the amount of the ethylene copolymer added was large, wrinkles were generated in the water absorption treatment tank, and a good coat film could not be formed.

Comparative Example 3
A polyamide film coated with a vinylidene chloride copolymer mixture was obtained in the same manner as in Example 1 except that the unstretched film was not subjected to water absorption treatment. The water absorption of the unstretched film immediately before coating was 1% by mass. For this reason, since the crack had arisen in the coat film after extending | stretching, the film was not evaluated.

Comparative Example 4
An attempt was made to obtain a polyamide film coated with a vinylidene chloride copolymer mixture in the same manner as in Example 1 except that the water absorption time of the unstretched film was 180 seconds. Since the water absorption rate was too high, wrinkles were generated in the water absorption treatment tank, and subsequent coating could not be performed.

Comparative Example 5
An attempt was made to obtain a polyamide film coated with a vinylidene chloride copolymer mixture in the same manner as in Example 1 except that the hot water temperature in the water absorption treatment tank was 52 ° C. Although the water absorption rate of the unstretched film was 6.7% by mass, the warm water temperature exceeded 50 ° C., which caused wrinkles on the running film, and subsequent coating could not be performed.

Claims (4)

A film having a resin layer containing a vinylidene chloride copolymer on at least one side of a biaxially stretched polyamide film containing 2 to 5% by mass of an ethylene copolymer, and is repeatedly bent 1000 times in an atmosphere of 5 ° C. A biaxially stretched polyamide film characterized in that the number of pinholes in a fatigue test is 10 or less. 2. The biaxially stretched polyamide film according to claim 1, wherein the oxygen permeability in an atmosphere of 20 ° C. and 85% RH is 100 ml / m ^{2 ·} d · MPa or less. The biaxially stretched polyamide film according to claim 1 or 2, wherein the polyamide is a polycapramide. Latex containing a vinylidene chloride copolymer after adjusting the moisture content of the unstretched polyamide film containing 2-5% by mass of an ethylene copolymer in warm water not exceeding 50 ° C. to 2-7% by mass. The method for producing a biaxially stretched polyamide film according to any one of claims 1 to 3, wherein a biaxially stretched film is applied and dried at the same time.