JP4770324B2 - Polyamide-based stretched film - Google Patents

Description

  The present invention relates to a stretched gas barrier film.

  As the gas barrier packaging material, a multilayer film using a gas barrier resin such as polyvinylidene chloride (PVDC), ethylene-vinyl alcohol copolymer (EVOH), polyamide or the like as a gas barrier layer is used. Among polyamides, polyamides having a metaxylylene skeleton such as polymetaxylylene adipamide (hereinafter referred to as nylon MXD6) obtained by polycondensation of metaxylylenediamine and adipic acid are treated with boil compared to other gas barrier resins. Further, there is a feature that the gas barrier property is hardly lowered when the retort treatment is performed, and the gas barrier property is rapidly recovered. Taking advantage of this feature, nylon MXD6 has recently been used in the packaging field. For example, a laminated biaxially stretched film including a layer made of a mixture of an aromatic polyamide such as nylon MXD6 and a polyolefin obtained by graft-modifying unsaturated carboxylic acids has been proposed as a packaging film (see Patent Document 1).

Japanese Patent No. 3021854

A film made of nylon MXD6 has an excellent gas barrier property, but has a drawback of low impact resistance and flexibility in an unstretched state. Moreover, there is a drawback that whitening occurs due to moisture absorption or heating. It has already been known that impact resistance and flexibility can be improved to some extent by stretching. It is also known that whitening does not occur by stretching. However, if the draw ratio exceeds 4 times in either the MD or TD direction, the film will break or the transparency and gas barrier properties will deteriorate, so a film with good gas barrier properties and transparency cannot be obtained. There is a problem.
On the other hand, stretched polypropylene films are produced by stretching in the MD and TD directions at a magnification of 5 to 10 times. In order to give gas barrier properties to polypropylene, multilayering with various gas barrier resins has been studied, but when multilayered with nylon MXD6, the nylon MXD6 film breaks at the stretching conditions and stretch ratios adopted for polypropylene. Moreover, since transparency and gas barrier property deteriorate, there exists a problem that a laminated polypropylene film with favorable gas barrier property and transparency cannot be obtained.
An object of the present invention is to provide a polyamide-based film having good gas barrier properties and transparency.

  The present inventors examined the stretchable magnification of a film obtained from a mixture of a polyamide having a metaxylylene skeleton and various resins and the physical properties of the stretched film. As a result, a film obtained from a mixture of a polyamide having a metaxylylene skeleton and an amorphous polyamide resin and / or an ionomer resin does not break even when stretched at a high magnification, which was impossible with a conventional nylon MXD6 film. The present inventors have found that a stretched film having practically sufficient transparency and gas barrier properties can be obtained, and reached the present invention.

  That is, the present invention provides a polyamide containing a diamine constituent unit containing 70 mol% or more of metaxylylenediamine units and a dicarboxylic acid constituent unit containing 70 mol% or more of an α, ω-aliphatic dicarboxylic acid unit having 6 to 12 carbon atoms. The resin (X) and the amorphous polyamide resin (Y) and / or the ionomer resin (Z) are melt-mixed so that the weight ratio X / (Y + Z) is 70/30 to 95/5 to form a film. It is related with the stretched film obtained by extending | stretching this film at a magnification | multiplying_factor exceeding 4 times in at least any direction of MD direction and TD direction.

  According to the present invention, by adding an amorphous polyamide resin and / or an ionomer resin to a polyamide having a metaxylylene skeleton, the resulting film can be stretched at a high magnification without causing breakage, thereby increasing production efficiency. I can do it. The obtained stretched film is excellent in transparency and gas barrier properties. Moreover, even if the boil treatment or the retort treatment is performed, the gas barrier property is hardly deteriorated and the gas barrier property is rapidly recovered, so that it is suitable as a packaging material for foods, pharmaceuticals, industrial chemicals, cosmetics, inks and the like.

  The polyamide resin (X) used in the present invention is obtained by polycondensation of a diamine component and a dicarboxylic acid component, and the metaxylylenediamine unit is 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol. % Or more (each containing 100 mol%) of diamine structural units and C 6-12 α, ω-aliphatic dicarboxylic acid units of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol%. The dicarboxylic acid structural unit which contains the above (each contains 100 mol%) is included.

  The diamine constituent unit may contain a diamine unit other than the metaxylylenediamine unit in an amount of 30 mol% or less, preferably 20 mol% or less, more preferably 10 mol% or less (each including zero). . As diamine units other than the metaxylylenediamine unit, tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2 , 2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine and other aliphatic diamines; 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, 1, 3-diaminocyclohexane, 1,4-diaminocyclohexane, bis (4-aminocyclohexyl) methane, 2,2-bis (4-aminocyclohexyl) propane, bis (aminomethyl) decalin, bis (aminomethyl) ) Alicyclic diamines such as tricyclodecane; diamine units derived from diamines having an aromatic ring such as bis (4-aminophenyl) ether, paraphenylenediamine, paraxylylenediamine, and bis (aminomethyl) naphthalene However, it is not limited to these.

  Examples of the α, ω-aliphatic dicarboxylic acid having 6 to 12 carbon atoms include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, etc. It is preferable to do. Further, in the dicarboxylic acid structural unit, the unit derived from dicarboxylic acid other than the α, ω-aliphatic dicarboxylic acid is 30 mol% or less, preferably 20 mol% or less, more preferably 10 mol% or less (each zero). May be included). Examples of the dicarboxylic acid other than the α, ω-aliphatic dicarboxylic acid include, but are not limited to, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and the like.

The relative viscosity of the polyamide resin (X) is preferably 2.3 to 4.2. The relative viscosity was determined by dissolving 1 g of resin in 100 ml of 96% sulfuric acid and dropping time (t) at 25 ° C. measured with a Cannon-Fenske viscometer, and dropping time of 96% sulfuric acid itself measured similarly (t) The ratio of t0) is shown by the following equation.
Relative viscosity = (t) / (t0)
When the relative viscosity is within the above range, fish eye formation can be avoided due to drawdown, gelation, and the like.

  Moreover, the polyamide resin (X) may contain a unit derived from a small amount of monoamine or monocarboxylic acid used as a molecular weight regulator during production.

  The amorphous polyamide resin (Y) used in the present invention preferably includes a structural unit derived from an aromatic dicarboxylic acid, and more preferably includes a structural unit derived from terephthalic acid and / or isophthalic acid. As long as the amorphous property of the polyamide resin (X) is maintained, the diamine structural unit is not limited, and those containing units derived from hexamethylenediamine can be used. Specific examples of the amorphous polyamide resin (Y) include nylon 6I, nylon 6T, nylon 6IT, nylon 6I6T (I represents isophthalic acid, T represents terephthalic acid), and the like. Examples include acid-copolymerized polyamides, and among these, nylon 6IT is preferable.

  The above-mentioned amorphous polyamide resin (Y) does not show a clear melting point in the differential thermal analysis, and its glass transition point is preferably 50 to 160 ° C. Further, the melt flow rate (MFR) of the amorphous polyamide resin (Y) measured at 230 ° C. under a 2160 g load (ASTM D1238) is preferably 1 to 30 g / min.

  The ionomer resin (Z) used in the present invention is an olefin-free resin in which the side chain carboxyl group of the main chain composed of an olefin unit and an unsaturated carboxylic acid unit is partially neutralized with a metal ion (cross-linked through the metal ion). It is a saturated carboxylic acid copolymer. The olefin unit is preferably an ethylene unit, and the unsaturated carboxylic acid unit is preferably an acrylic acid unit and / or a methacrylic acid unit.

  Specific examples of the ionomer resin (Z) include ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, or ethylene-methacrylic acid-acrylic, in which side chain carboxyl groups are partially neutralized with metal ions. An acid copolymer can be mentioned. The content of acrylic acid units and / or methacrylic acid units in the copolymer is preferably 10 to 20% by weight, more preferably 12%, based on the total amount of ethylene units, acrylic acid units and methacrylic acid units. ~ 18% by weight. When the content is 10% by weight or more, the dispersibility of the ionomer resin (Z) in the polyamide resin (X) is good, and the resulting film has good transparency, which is preferable. When the content is 20% by weight or less, the film can be stretched at a high magnification without breaking, and the production cost of the ionomer resin is low, which is preferable. The content of ethylene units in the copolymer is preferably 80 to 90% by weight, more preferably 82 to 88% by weight, based on the total amount of ethylene units, acrylic acid units and methacrylic acid units.

  The degree of neutralization of the carboxyl groups of the ionomer resin (Z) (the ratio of the number of neutralized carboxyl groups to the total number of carboxyl groups) is preferably 20 to 40%, more preferably 25 to 35%. When the degree of neutralization is 20% or more, the dispersibility of the ionomer resin (Z) in the polyamide resin (X) is good, and the transparency of the obtained film is good, which is preferable. When it is 40% or less, a decrease in melt fluidity of the ionomer resin (Z) can be avoided, and the resulting film has good transparency, which is preferable. The cation component of the neutralized carboxyl group is a metal ion such as zinc, sodium, lithium, potassium, magnesium, calcium, preferably zinc ion and sodium ion, but is not limited thereto. Further, the MFR (ASTM D1238) of the ionomer resin (Z) is preferably 1 to 100 g / min.

In the polyamide resin (X), both the amorphous polyamide resin (Y) and the ionomer resin (Z) may be mixed, or only one of them may be mixed.
When both the amorphous polyamide resin (Y) and the ionomer resin (Z) are mixed, the weight ratio X / (of the sum of the polyamide resin (X) and the amorphous polyamide resin (Y) and the ionomer resin (Z). Y + Z) is preferably 70/30 to 95/5, and more preferably 80/20 to 90/10. The effect of the present invention can be obtained if any one of the amorphous polyamide resin (Y) and the ionomer resin (Z) is mixed. Therefore, the amorphous polyamide resin (Y) and the ionomer resin (Z) may be used in any ratio, and the weight ratio is not particularly limited.

  When the polyamide resin (X) and the amorphous polyamide resin (Y) are mixed, the weight ratio X / Y between the polyamide resin (X) and the amorphous polyamide resin (Y) is preferably 70/30 to 95/5. 80/20 to 90/10 are more preferable. When the amount of the polyamide resin (X) is within the above range, the film can be stretched at a high magnification without breaking. When the amount of the amorphous polyamide (Y) is within the above range, it is possible to avoid deterioration of gas barrier properties and transparency.

  When the polyamide resin (X) and the ionomer resin (Z) are mixed, the weight ratio X / Z of the polyamide resin (X) and the ionomer resin (Z) is preferably 70/30 to 95/5, and 80/20 to 90 / 10 is more preferable. When the amount of the polyamide resin (X) is within the above range, the film can be stretched at a high magnification without breaking. When the amount of the ionomer resin (Z) is within the above range, it is possible to avoid deterioration of gas barrier properties and deterioration of transparency.

  Mixing of the polyamide resin (X), the amorphous polyamide resin (Y) and / or the ionomer resin (Z) may be performed by dry blending the pellets of each component, or by using an extruder in advance. The components may be pelletized after being melt-kneaded.

  In order to improve flexibility and impact resistance, an aliphatic polyamide is added to the mixture of the polyamide resin (X), the amorphous polyamide resin (Y) and / or the ionomer resin (Z) as necessary. It doesn't matter. As the aliphatic polyamide, nylon 6, nylon 66, nylon 6-66, or the like can be used. In addition, an antistatic agent, a lubricant, an antiblocking agent, a stabilizer, a dye, a pigment, and the like may be added to the mixture as necessary. The arbitrarily added resin, additives, and the like may be dry blended, or may be melt kneaded in advance using a single screw or twin screw extruder.

  After the polyamide resin (X), the amorphous polyamide resin (Y) and / or the ionomer resin (Z) are melt mixed and extruded into a film shape, the film is placed in at least one of the MD direction and the TD direction. The stretched film of the present invention can be obtained by stretching at a magnification exceeding 4 times. As for the thickness of this stretched film, 5-40 micrometers is preferable. When the thickness is 5 μm or more, the film can be stretched without breaking, and deterioration of transparency can be prevented. When the thickness is 40 μm or less, the film can be uniformly stretched and uneven thickness can be avoided.

  The stretched film of the present invention can be obtained by stretching a raw film obtained by a film forming method such as a normal T-die method or a cylindrical die method (inflation method). The raw film is preferably produced by melt extrusion at 250 to 290 ° C, more preferably 250 to 270 ° C. When the extrusion temperature is high, decomposition, gel generation, coloring, and foaming occur. As the stretching method, a simultaneous biaxial stretching method or a sequential biaxial stretching method can be used. The stretching is preferably performed at 90 to 160 ° C, more preferably at 110 to 150 ° C. When the stretching temperature is within the above range, poor stretching and whitening can be avoided.

  When the nylon MXD6 single film is stretched 4 times or more in at least one of the MD direction and the TD direction, the film breaks or the transparency and gas barrier properties deteriorate, but the amorphous polyamide resin (Y) and / or Or it becomes possible to extend | stretch by the magnification exceeding 4 times by adding ionomer resin (Z). The draw ratio in the MD direction and / or TD direction is preferably 4.1 to 10 times, more preferably 4.5 to 10 times, and still more preferably 5.1 to 9 times.

  A multilayer film is obtained by combining the stretched film of the present invention comprising a mixed resin of a polyamide resin (X), an amorphous polyamide resin (Y) and / or an ionomer resin (Z), and a film comprising another thermoplastic resin. be able to. For example, by combining with an aliphatic polyamide film, a multilayer film with improved impact resistance and flexibility can be obtained.

  The multilayer film can be produced, for example, by laminating a thermoplastic resin film on the stretched film of the present invention. Lamination may be performed using an adhesive. Moreover, you may laminate a thermoplastic resin film on both surfaces of this stretched film. The thermoplastic resin includes low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, olefin copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, modified Examples thereof include polyolefin resins, and these can be used alone or as a mixture. The thermoplastic resin film may be a single layer or multiple layers, and may be stretched or unstretched. In addition, as an adhesive, a maleic anhydride graft-modified product of polymers such as ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene, linear low-density polyethylene and polypropylene, or these graft-modified products are mainly used. What consists of a composition to be used can be used.

  In addition, a multilayer film obtained by melting and extruding a mixed resin, an adhesive resin, and a thermoplastic resin of a polyamide resin (X), an amorphous polyamide resin (Y) and / or an ionomer resin (Z), and MD A multilayer stretched film can also be obtained by stretching in the direction and / or TD direction at a magnification exceeding 4 times. Also in this case, it can be obtained by stretching a raw film obtained by a film forming method such as a co-extrusion T-die method or a co-extrusion cylindrical die method (inflation method) as in the case of the single-layer stretched film. As the stretching method, a simultaneous biaxial stretching method or a sequential biaxial stretching method can be used. The production of the multilayer stretched film can be carried out under the same stretching conditions (stretching temperature, stretch ratio, etc.) as in the case of the single-layer stretched film.

  The thermoplastic resin used in the multilayer stretched film includes low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, olefin copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate. Examples thereof include copolymers and modified polyolefin resins, and these can be used alone or in a mixture.

  The adhesive resin mainly comprises maleic anhydride graft modified products of polymers such as ethylene-vinyl acetate copolymer, high density polyethylene, low density polyethylene, linear low density polyethylene and polypropylene, or these graft modified products. A composition or the like can be used.

In the laminate film or multilayer stretched film of the present invention, a film made of a mixture of polyamide resin (X), amorphous polyamide resin (Y) and / or ionomer resin (Z) acts as a gas barrier layer.
As the layer structure of the laminate film or multilayer stretched film of the present invention, the gas barrier layer is (A), the adhesive layer is (B), the thermoplastic resin layer is (C), and (A) / (B) / (C 3 types and 3 layers, and (C) / (B) / (A) / (B) / (C) are 3 types and 5 layers, but (A) / (B) A layer configuration of / (A) / (B) / (C) is also possible. The thickness of the A layer is preferably 2 to 50 μm, the thickness of the B layer is 2 to 20 μm, the thickness of the C layer is 10 to 100 μm, and the total thickness of the laminate film and the multilayer stretched film is preferably 30 to 200 μm.

The stretched film, laminate film and multi-layer stretched film of the present invention have little decrease in gas barrier properties and quick recovery of gas barrier properties even when subjected to boil treatment or retort treatment, so processed meat foods, boiled foods, retort foods, etc. It is suitable as a packaging material for food and other various packaging materials.
The opening of the packaging material may be sealed by heat sealing, or may be ligated by a sealing member such as a clip, and is not particularly limited. In the case of a tube-shaped film, it may be cut into a predetermined size and, if necessary, one opening may be heat sealed or ligated for use.

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by the following examples.
The physical properties of the stretched film were measured by the following methods.
(1) Cloudiness value Measured according to ASTM D1003 using a color difference / turbidity measuring instrument (model: COH-300A) manufactured by Nippon Denshoku Industries Co., Ltd.
(2) Oxygen permeability Using an oxygen permeability measuring device (model: OX-TRAN 10 / 50A) manufactured by Modern Controls, the oxygen permeability was measured under the conditions of 23 ° C. and relative humidity of 60% according to ASTM D3985.

Example 1
80 parts by weight of nylon MXD6 (Mitsubishi Gas Chemical Co., Ltd., trade name MX nylon 6007) and 20 parts by weight of amorphous polyamide resin (Mitsui / DuPont Polychemical Co., Ltd., trade name: Sheila PA 3426) , Dry blended to prepare a mixed resin. This was extruded from 260 ° C. to 270 ° C. from an extruder having a cylinder diameter of 20 mm (laboroplast mill manufactured by Toyo Seiki Seisakusho), and a raw film was produced by a T-die-cooling roll method. In order to compare films having different draw ratios, several types of raw film having different thicknesses were prepared so that the film thickness after stretching was the same. The obtained raw film was stretched 4 to 6 times in the MD direction at a stretching temperature of 130 ° C. by using a biaxial stretching device (tenter method) manufactured by Toyo Seisakusho Co., Ltd. to obtain a stretched film. Table 1 shows the transparency (cloudiness value) and oxygen permeability of the stretched film obtained.

Example 2
Stretching in the same manner as in Example 1 except that 5 parts by weight of ionomer resin (manufactured by Mitsui DuPont Polychemical Co., Ltd., trade name: High Milan AM6004) was used instead of the amorphous polyamide resin used in Example 1. A film was prepared. Table 2 shows the transparency (cloudiness value) and oxygen permeability of the stretched film obtained.

Example 3
20 parts by weight of nylon MXD6 (Mitsubishi Gas Chemical Co., Ltd., trade name: MX nylon 6007) and 20 parts by weight of amorphous polyamide resin (Mitsui / DuPont Polychemical Co., Ltd., trade name: SELA PA 3426) Dry blending was performed to prepare a mixed resin for the gas barrier layer. Polypropylene from an extruder with a cylinder diameter of 45 mm (constitutes C layer, manufactured by Nippon Polypro Co., Ltd., trade name: Novatec PP FL6CK), adhesive resin (forms B layer from an extruder with a cylinder diameter of 40 mm, Mitsubishi Chemical ( Co., Ltd., trade name: Modic P513V) and a gas barrier layer mixed resin (constituting the A layer) were extruded at 200 to 210 ° C., 190 to 200 ° C., and 260 to 270 ° C. from an extruder with a cylinder diameter of 30 mm A molten multilayer body (C layer / B layer / A layer) was formed through a feed block, and the molten multilayer body was formed into a multilayer film by a T-die-cooling roll method. In order to compare films with different draw ratios, several types of raw multilayer films having different thicknesses were prepared so that the film thickness after stretching was the same. The obtained multilayer film was uniaxially stretched 4 to 8 times in the MD direction at a stretching temperature of 150 ° C. by a roll type uniaxial stretching machine, and further heat-set to obtain a multilayer stretched film. Table 3 shows the thickness, transparency (cloudiness value), and oxygen permeability of each layer of the multilayer stretched film prepared.

Comparative Example 1
A stretched film was produced in the same manner as in Example 1 except that only nylon MXD6 (trade name MX nylon 6007 manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used. Tables 1 and 2 show the transparency (cloudiness value) and oxygen permeability of the obtained films.

Comparative Example 2
A multilayer stretched film was produced in the same manner as in Example 3 except that only nylon MXD6 (product name: MX nylon 6007, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used as the resin for the gas barrier layer. Table 3 shows the thickness, transparency (cloudiness value), and oxygen permeability of each layer of the multilayer stretched film prepared.

Claims (5)

A polyamide resin (X) containing a diamine constituent unit containing 70 mol% or more of a metaxylylenediamine unit and a dicarboxylic acid constituent unit containing 70 mol% or more of an α, ω-aliphatic dicarboxylic acid unit having 6 to 12 carbon atoms; The mixture obtained by melt-mixing the amorphous polyamide resin ( Y) so that the weight ratio X / Y is 70/30 to 95/5 is extruded into a film shape, and then the film is formed in the MD direction. A stretched film obtained by stretching at a magnification exceeding 6 times in at least one of the TD directions. The amorphous polyamide resin (Y) is at least one hexagon selected from the group consisting of nylon 6I, nylon 6T, nylon 6IT, and nylon 6I6T (where I represents isophthalic acid and T represents terephthalic acid). The stretched film according to claim 1 , which is a methylenediamine-isophthalic acid-terephthalic acid copolymer polyamide. Laminate film including a stretched film and a thermoplastic resin film according to claim 1 or 2. The thermoplastic resin is low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, olefin copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, and modification. The stretched film according to claim 3 , which is at least one resin selected from the group consisting of polyolefin resins. A polyamide resin (X) containing a diamine constituent unit containing 70 mol% or more of a metaxylylenediamine unit and a dicarboxylic acid constituent unit containing 70 mol% or more of an α, ω-aliphatic dicarboxylic acid unit having 6 to 12 carbon atoms; A multilayer film obtained by melt-extruding a mixed resin, an adhesive resin, and a thermoplastic resin each containing a non-crystalline polyamide resin (Y) and having a weight ratio X / Y of 70/30 to 95/5 A multilayer stretched film obtained by stretching at a magnification exceeding 6 times in at least one of the MD direction and the TD direction.