JP4917795B2 - Biaxially stretched laminated film and method for producing the same - Google Patents

Description

  The present invention relates to a polyamide-based laminated film and a method for producing the same, and in particular, when water is absorbed into an unstretched film prior to simultaneous biaxial stretching, water is absorbed so that the layer made of polyglycolic acid is maintained in an amorphous state. Regarding the method.

  In general, polyamide resin films are excellent in mechanical properties, optical properties, thermal properties, gas barrier properties, toughness, pinhole resistance, flex resistance, etc., and are widely used mainly for packaging applications, especially food packaging applications. Has been. In particular, in a field where gas barrier properties are required, a film in which polymetaxylylene adipamide or saponified ethylene-vinyl acetate copolymer is laminated on polyamide is used. However, these laminated films have a problem that the gas barrier property is lowered under high humidity, and their use is limited such that they cannot be used for packaging foods with high water activity.

  On the other hand, polyglycolic acid (PGA) is being developed as a new material whose gas barrier property does not deteriorate under high humidity. For example, Patent Document 1 discloses a multilayer film of polyglycolic acid and a thermoplastic resin. However, in this document, only a method for inflating a parison is described as a method for producing a multilayer film when polyamide is used as a thermoplastic resin, and an industrially applicable production method is not disclosed.

In addition, when a multilayer film composed of a polyamide layer and a polyglycolic acid layer is produced by applying normal polyamide film production conditions in which an unstretched film is absorbed and then biaxially stretched simultaneously, the polyglycolic acid crystallinity Is very high, the polyglycolic acid layer is likely to be crystallized, and stretching may be difficult.
JP 2003-305817 A

  An object of the present invention is to provide a laminated film composed of a polyamide layer and a polyglycolic acid layer and a method for producing the same, and more specifically, in absorbing the laminated film prior to simultaneous biaxial stretching, It is to provide a method of absorbing water without crystallizing the acid.

As a result of intensive studies to solve the above problems, the inventors of the present invention have made it possible to absorb polyamide at a specific temperature and time for a laminated film of polyamide and polyglycolic acid, without causing polyglycolic acid to crystallize. The inventors have found that water can be absorbed up to a moisture content suitable for stretching, and completed the present invention. That is, the gist of the present invention is as follows.
(1) An unstretched laminated film in which at least one layer mainly made of polyglycolic acid and a layer mainly made of polyamide are laminated is absorbed in a hot water tank, and then includes preheating, stretching and heat treatment steps. A method for producing a biaxially stretched laminated film in which axial stretching is performed , wherein the water absorption time (t seconds) and the polyglycolic acid half crystallization time (tc seconds) at the water absorption temperature satisfy the following formula: A method for producing a biaxially stretched laminated film.
t <tc / 2
20 <t <300
(2) A biaxially stretched laminated film produced by the above production method having an oxygen permeability of 100 ml / (m ² · day · MPa) or less at 20 ° C. and 100% RH atmosphere.

  By absorbing water under specific conditions when water is absorbed into an unstretched film prior to simultaneous biaxial stretching, the polyamide layer can be controlled to a moisture content suitable for stretching without crystallizing the polyglycolic acid layer. A stretched laminated film having excellent uniformity of physical properties in the width direction can be easily produced. Therefore, the industrial utility value of the laminated film produced by the present invention is extremely high.

Next, the present invention will be described in detail. In the present invention, polyglycolic acid is a (co) polymer or a mixture thereof containing 60 mol% or more of a repeating structure (—O—CH ₂ —CO—), preferably a repeating structure (—O—CH ₂ —). A (co) polymer containing 80 mol% or more of CO-) or a mixture thereof.
As a component to be copolymerized or mixed with polyglycolic acid, an aliphatic polyester composed of a diol and a dicarboxylic acid typified by poly (ethylene succinate), poly (butylene succinate), poly (butylene succinate cobutylene adipate) and the like And poly (lactic acid), poly (3-hydroxybutyric acid), poly (3-hydroxyvaleric acid), poly (6-hydroxycaproic acid) and other polyhydroxycarboxylic acids, poly (ε-caprolactone) and poly (δ valerolactone) Representative poly (ω-hydroxyalkanoates), alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, poly (butylene succinate cobutylene terephthalate) and poly (butylene adipate cobutylene terephthalate) Other, polyesteramides, polyestercarbonates, polyketones, ethylene oxalate, polysaccharides starch and the like.
In addition, polyglycolic acid has a resin, such as polyolefin, elastomer, ionomer, lubricant, pigment, heat stabilizer, antioxidant, weathering agent, flame retardant, plasticizer, mold release, as long as the performance of the film is not impaired. An agent can also be blended.

  In the present invention, polyamide is a melt-moldable thermoplastic resin having an amide bond (—CONH—) in the molecule, and is composed of polycapramide (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexa Examples include methylene sebacamide (nylon 610), polyaminoundecamide (nylon 11), polylauryl amide (nylon 12), and copolymers and mixtures thereof. Nylon 6 is particularly preferable. 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 biaxially stretched laminated film of the present invention is composed of at least two types of layers, a layer (X) mainly composed of polyglycolic acid and a layer (Y) mainly composed of polyamide. The content of polyglycolic acid in the X layer is preferably 80% by mass or more, and more preferably 90% by mass or more. Gas barrier property falls that content of polyglycolic acid is less than 80 mass%. On the other hand, the polyamide content in the Y layer is preferably 85% by mass or more, and more preferably 95% by mass or more. If the polyamide content is less than 85% by mass, characteristics of the polyamide such as toughness and pinhole resistance may be impaired.

  The typical layer structure of the biaxially stretched laminated film of the present invention includes troubles caused by physical properties such as strength and gas barrier properties of the obtained laminated film, film breakage during film production, and low glass transition temperature of polyglycolic acid. In order to avoid this, it is desirable that the X layer is not an external surface layer, and a three-layer structure of Y / X / Y is preferable. The thickness of the X layer is preferably 6 to 40% of the total thickness, and more preferably 10 to 30%. When the thickness of the X layer is less than 6% of the total thickness, the gas barrier property is deteriorated, and when it exceeds 40%, crystallization of polyglycolic acid is liable to occur at the time of water absorption and the stretchability is deteriorated.

  Moreover, as a layer structure of the biaxially stretched laminated film of the present invention, a five-layer structure of Y / Z / X / Z / Y using a Z layer made of an adhesive is more preferable. The resin used as the Z layer only needs to have a high interlayer adhesion between the X layer and the Y layer, and examples thereof include polymers such as modified polyolefin, ethylene-vinyl acetate copolymer, ionomer, polyurethane, and epoxy resin. . The thickness of the Z layer is preferably 0.5 to 4 μm, and more preferably 0.5 to 2 μm. If the thickness is less than 0.5 μm, the adhesion may be insufficient, and application is difficult. If this thickness exceeds 4 μm, the cost is high, which is disadvantageous from an economical viewpoint.

  The thickness of the biaxially stretched laminated film of the present invention is not particularly limited as long as the thickness of each layer is in the above range, but is usually preferably 10 to 50 μm when used as a flexible packaging material. If the thickness is thin, it is difficult to achieve both strength properties and gas barrier properties. If the thickness is thick, the performance becomes excessive and the cost performance deteriorates.

  As a method for forming an unstretched laminated film, a known method can be used. For example, several types of resin constituting each layer are melted in separate extruders, stacked on a multilayer structure in a feed block, and then extruded from a die (mono-manifold type), or several types of molten resin A multi-manifold method or the like can be used in which a multi-layer structure is extruded in a die in a die. The multi-manifold method is preferable because the thickness accuracy of each layer is high. After coextrusion from a die, an unstretched laminated film is obtained by quenching on a cooling roll.

  In the present invention, it is necessary to introduce the unstretched laminated film into a hot water tank and perform water absorption treatment under the following conditions. By performing this water absorption treatment, the polyamide layer is plasticized, the stretching stress is reduced, and simultaneous biaxial stretching in the next step is facilitated. Moreover, the temperature rise of the polyglycolic acid layer is suppressed due to latent heat of vaporization in the preheating zone of the stretching machine, and an effect of preventing crystallization can be obtained.

  In the present invention, the water absorption temperature and the water absorption time (t) in the hot water tank are closely related to the semi-crystallization time (tc) of polyglycolic acid. Here, the half crystallization time (tc) is defined as follows. First, 15 mg of polyglycolic acid is weighed in an aluminum pan, and is heated to 270 ° C. at a rate of 300 ° C./min using a differential scanning calorimetry (DSC) device to melt. Immediately cool to the measurement temperature at a rate of 300 ° C./min and hold. Time measurement is started when the measurement temperature is reached, and the time at which the crystallization exothermic peak top observed in the DSC curve is reached is defined as the half crystallization time. The DSC apparatus may be any apparatus as long as the heating rate is 300 ° C./min or higher and the cooling rate using liquid nitrogen, liquid helium, or the like is 300 ° C./min or higher. For example, manufactured by Perkin-Elmer DSC unit DSC7 etc. can be used.

  The water absorption time (t) needs to be less than half of the polyglycolic acid half crystallization time (tc) at the water absorption temperature. By setting the water absorption time (t) within this range, crystallization can be suppressed to such an extent that polyglycolic acid can be subjected to stretching during water absorption. At the same time, the water absorption time (t) needs to be 20 to 300 seconds. When the water absorption time (t) is less than 20 seconds, the moisture content is insufficient, the stretching stress becomes high, the bowing becomes large, and the physical properties in the width direction of the obtained film become non-uniform. In order to increase the moisture content, water is absorbed at a high temperature. However, since it exceeds 1/2 of the half crystallization time (tc), it cannot be crystallized and stretched. When the water absorption time (t) exceeds 300 seconds, it is necessary to lengthen the hot water tank or slow down the sheet passing speed, which is inferior in productivity.

  The temperature of the hot water tank is preferably 45 to 75 ° 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 75 ° C., not only polyglycolic acid but also polyamide will be crystallized, making stretching difficult.

The moisture content of the unstretched laminated film after water absorption is preferably 3 to 9%. The moisture content of the unstretched laminated film refers to the proportion of moisture contained in the whole unstretched laminated film, and the mass W of the sample piece cut out from the unstretched laminated film after water absorption, and at 80 ° C. under reduced pressure. It is obtained by the following formula from the mass Wd after drying for 24 hours. If the moisture content is less than 3%, the stretching stress becomes high, the bowing becomes large, and the physical properties in the width direction of the obtained film become non-uniform. If it exceeds 9%, neck stretching tends to occur and thickness spots are likely to occur.
Moisture content (%) = (W−Wd) / W × 100

  The unstretched laminated film subjected to the water absorption treatment in this way can be easily stretched under normal simultaneous biaxial stretching conditions. That is, the end of the film is gripped with a clip and stretched 2.0 to 4.0 times in the longitudinal and transverse directions at a preheating temperature of 50 to 180 ° C and a stretching temperature, respectively, and the stretched film is heat treated at 150 to 220 ° C. In addition, 1-8% relaxation treatment is applied in the lateral direction. When the preheating temperature and the stretching temperature are less than 50 ° C., the polyamide layer cannot be stretched. When the preheat temperature and the stretching temperature exceed 180 ° C., the evaporation rate of absorbed water becomes too fast and the film temperature becomes high. It becomes difficult to stretch. When the heat treatment temperature is less than 150 ° C., the shrinkage rate is increased and the dimensional stability is poor, and when it exceeds 220 ° C., the operability is lowered due to troubles such as fusing.

The biaxially stretched laminated film thus obtained has no defects in the layer made of polyglycolic acid, and has an oxygen permeability of 100 ml / (m ² · day · MPa) or less in an atmosphere of 20 ° C. and 100% RH. It can be.

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) Raw material nylon 6: A1030BRF manufactured by Unitika Ltd.
Polyglycolic acid: 20 kg of glycolide was charged into a reaction kettle and dried at room temperature for about 30 minutes while blowing nitrogen gas. Next, 4 g of SnCl ₄ .6.5H ₂ O was added as a catalyst, and polymerization was carried out by maintaining at 170 ° C. for 2 hours while blowing nitrogen gas. After completion of the polymerization, the reaction kettle is cooled to room temperature, and the bulk polymer taken out from the reaction kettle is pulverized into fine particles of about 3 mm or less and dried under reduced pressure at about 150 ° C. and about 0.1 kPa overnight to remove residual monomers. Thus, polyglycolic acid was obtained. (Semi-crystallization time (tc) at each measurement temperature:> 10000 seconds (40 ° C.), 2680 seconds (50 ° C.), 320 seconds (60 ° C.), 74 seconds (70 ° C.), 44 seconds (80 ° C.))
Adhesive: Bond First 2B manufactured by Sumitomo Chemical Co., Ltd.
(2) Measurement method (2-1) Half crystallization time (tc)
Using DSC DSC7 manufactured by Perkin-Elmer, 15 mg of polyglycolic acid was weighed in an aluminum pan and heated to 270 ° C. at a rate of 300 ° C./min to be melted. Immediately cooled to the measurement temperature at a rate of 300 ° C./min and held. Time measurement was started when the measurement temperature was reached, and the time when the exothermic peak top of crystallization observed in the DSC curve was reached was defined as the half crystallization time.
(2-2) Moisture content (%)
It calculated | required by following Formula from the mass Wd of the sample piece cut out from the unstretched laminated | multilayer film after non-water absorption, and the mass Wd after drying it at 80 degreeC under pressure reduction for 24 hours.
Moisture content (%) = (W−Wd) / W × 100
(2-3) Thickness spots (%)
The thickness of the stretched film was measured at intervals of 5 mm in the width direction, and was determined from the maximum value Dmax, minimum value Dmin, and average value Dave of the thickness by the following formula.
Thickness unevenness (%) = (Dmax−Dmin) ÷ Dave × 100
(2-4) Oxygen permeability OX-TRAN 2/20 manufactured by Modern Control was used and measured under the conditions of 20 ° C. and 100% RH. (Unit: ml / (m ² · day · MPa) / (1 sheet thickness))

Example 1
Using a coextrusion T die for 3 types and 5 layers, nylon 6 is extruded from the first extruder at 250 ° C. (Y layer), polyglycolic acid is extruded from the second extruder at a temperature of 250 ° C. (X layer), The adhesive was extruded from the third extruder at a temperature of 250 ° C. (Z layer), and the film laminated in the order of Y / Z / X / Z / Y with a multi-manifold type die was controlled to a surface temperature of 10 ° C. The film was brought into close contact with the cooling drum and quenched to obtain an unstretched laminated film having a thickness of each layer of Y / Z / X / Z / Y = 50/10/30/10/50 μm and a total thickness of 150 μm. The obtained unstretched laminated film was introduced into a water tank adjusted to 50 ° C. and subjected to water absorption treatment for 180 seconds. At this time, the water absorption of the unstretched film was 6.2%. A biaxially stretched laminate with a preheating temperature of 140 ° C and a stretching temperature of 140 ° C is simultaneously biaxially stretched 3 times in the longitudinal direction and 3.3 times in the transverse direction, and heat treated at a temperature of 200 ° C and a relaxation rate of 5%. A film was obtained. The oxygen permeability of the obtained film was measured and shown in Table 1.

Examples 2-4, Comparative Examples 1-4
The same procedure as in Example 1 was performed except that the water absorption conditions were changed as shown in Table 1.

Claims (4)

Primarily a layer comprising the polyglycolic acid, the unstretched laminated film in which a layer mainly composed of a polyamide are laminated one by at least one layer, after being water in a hot water bath, preheated and a simultaneous biaxial stretching comprising stretching and heat treatment step A method for producing a biaxially stretched laminated film, wherein the water absorption time (t seconds) and the polyglycolic acid half-crystallization time (tc seconds) at the water absorption temperature satisfy the following formula: A method for producing a stretched laminated film.
t <tc / 2
20 <t <300 The method for producing a biaxially stretched laminated film according to claim 1, wherein the moisture content of the unstretched laminated film after water absorption is 3 to 9%. The method for producing a biaxially stretched laminated film according to claim 1 or 2, wherein the temperature of the hot water tank is 45 to 75 ° C. The biaxially stretched laminated film produced by the production method according to any one of claims 1 to 3, wherein the oxygen permeability in an atmosphere of 20 ° C and 100% RH is 100 ml / (m ² · day · MPa) or less.