Patent Application
20230321954
The present invention relates to a laminated film used in the packaging fields of foods, pharmaceuticals, and industrial products and the like.
More specifically, the present invention relates to a laminated film including an inorganic thin film layer and a protective layer in this order on a substrate film layer using a polyester resin recycled from PET bottles. The laminated film has excellent barrier properties, adhesiveness, and processability.
In recent years, regulations for reducing the use of disposable plastics have been strengthened in various countries including Europe. In this background, there are growing international awareness of resource circulation and aggravated waste problems in emerging countries. Therefore, for plastic packaging materials required for foods and pharmaceuticals and the like, environment-responsive products are required from the viewpoint of 3R (recycle, reuse, reduce).
Examples of performances required for the above-mentioned environmentally friendly packaging material include: the packaging material is made of a recycled material; the packaging material has gas barrier performance capable of blocking various gases and extending the best-before expiration date; and the packaging material has a material with a less environmental load (for example, no organic solvent is used, and the amount of the material used itself is small).
A polyester resin recycled from PET bottles is known as a typical recycled material, and a technique is known, in which a polyester film for a covering label having less trouble due to static electricity is formed of a polyester resin derived from PET bottles having a small oligomer content without deteriorating productivity and quality (see, for example, Patent Document 1). As environmental regulations increase in the future, demand for such film applications is expected to increase.
On the other hand, in food applications requiring blocking of various gases such as water vapor and oxygen, a gas barrier laminated body in which a metal thin film made of aluminum or the like, and an inorganic thin film made of an inorganic oxide such as silicon oxide or aluminum oxide are formed on the surface of a substrate film made of plastic is generally used. Among them, a laminated body in which a thin film made of an inorganic oxide (inorganic thin film layer) such as silicon oxide, aluminum oxide, or a mixture thereof is formed does not require the use of aluminum foil and is transparent, whereby the contents thereof can be confirmed. Therefore, the laminated film is widely used.
For the gas barrier film composed of the recycled material and the inorganic thin film as described above, a laminated film exhibiting good gas barrier properties when formed as a gas barrier laminated film including an inorganic thin film layer and a sealant layer has been proposed. The laminated film contains a polyester resin recycled from PET bottles, and has low heat shrink properties and small thickness unevenness (for example, Patent Document 2). However, such a conventional technique has been insufficient for applications where higher barrier performance is required. Retort resistance performance and film processing suitability have not been discussed. Furthermore, the inorganic thin film layer is disadvantageously broken by physical damage such as bending, which is apt to cause deteriorated barrier properties.
As means for maintaining barrier properties and adhesiveness even after retorting, it has been reported that a coating layer composed of an oxazoline group-containing water-soluble polymer is provided between a substrate film and an inorganic thin film layer formed by, for example, a vapor-deposition method (see, for example, Patent Document 3). The provision of the coating layer between the substrate film and the inorganic thin film can also be continuously performed while a film of the substrate is formed. Thus, it can be expected that the provision makes costs far lower than the formation of the protective layer on the inorganic thin film. However, in the case of the above constitution, the coating layer itself has no gas barrier properties so that only the inorganic thin film layer mainly contributes to the gas barrier properties, whereby the constitution has a problem that the laminated body is not sufficient in gas barrier properties. In the above-described conventional technique, a substrate having a small environmental load is not used in consideration, which has a concern that the environment load is large.
As means for improving the barrier properties of a film including an inorganic thin film, an attempt has been made in which a protective layer having gas barrier properties is further provided on the inorganic thin film. Suggested has been, for example, a method in which a water-soluble polymer, an inorganic lamellar compound, and a metal alkoxide or a hydrolyzate thereof are coated on an inorganic thin film to form a composite of an inorganic substance containing the inorganic lamellar compound and the water-soluble polymer on the inorganic thin film by a sol-gel method, and a laminated body in which an inorganic thin film is coated with a metaxylylene group-containing polyurethane (see, for example, Patent Document 4). However, the provision of the protective layer increases the number of processing steps, which has a concern in terms of a cost increase and an environmental load. In order to improve the barrier performance by the protective layer, it is necessary to use a protective layer having a film thickness equal to or greater than a certain film thickness or a special coating material, which also disadvantageously causes the cost increase and the environmental load. In the above-described conventional technique, a substrate having a small environmental load is not used in consideration, which has a concern that the environment load is large.
In Patent Document 2 described above, there is room for improvement in the gas barrier properties of the inorganic thin film layer, and retort properties and processing suitability are not studied. In Patent Document 3 described above, there is room for improvement in the gas barrier performance of the inorganic thin film layer, and the environment load is not considered. In Patent Document 4 described above, the environment load is not considered.
The present invention has been made in view of the problems of the conventional techniques.
That is, an object of the present invention is to provide an environment-responsive laminated film including a coating layer and an inorganic thin film layer on a substrate film layer using a polyester resin recycled from PET bottles. The laminated film is excellent in barrier performance, can maintain barrier properties and adhesiveness even after a severe wet heat treatment such as retort sterilization, and is excellent in processability.
The present inventors have found that the barrier properties of an inorganic thin film layer can be improved by controlling the surface hardness of an environment-responsive substrate film using a polyester resin recycled from PET bottles, further have found that the barrier properties and adhesiveness of the laminated film can be maintained even after a severe wet heat treatment such as retorting by providing a coating layer between a substrate and the inorganic thin film layer, and have completed the present invention.
That is, the present invention comprises the following components.
The present invention makes it possible to provide a laminated film which is excellent in gas barrier properties of an inorganic thin film layer and is excellent in barrier properties and adhesiveness even after a severe wet heat treatment such as retort sterilization while using a recycled material. Moreover, the laminated film of the present invention provides few processing steps, is excellent in processability, and can be easily produced, whereby a gas barrier film excellent in both economic efficiency and production stability and having homogeneous characteristics can be provided.
The following is a detailed description of the present invention.
[Substrate Film Layer]
In the present invention, as described later, a recycled polyester resin regenerated from PET bottles containing an isophthalic acid component as an acid component is preferably used as a raw material for a substrate film. Therefore, the substrate film is composed of a mixed resin of a recycled polyester resin and a virgin raw material, that is, an unrecycled resin, and the intrinsic viscosity of the resin constituting the film means a value obtained by measuring the intrinsic viscosity of the mixed resin constituting the film. The lower limit of the intrinsic viscosity of the resin constituting the film obtained by measuring the substrate film is preferably 0.58 dl/g, and more preferably 0.60 dl/g. When the intrinsic viscosity is less than 0.58 dl/g, the intrinsic viscosity of the recycled resin composed of PET bottles often exceeds 0.68 dl/g, and when the viscosity is reduced at the time of producing a film using the recycled resin, poor thickness unevenness may occur, which is not preferable. The film may be colored, which is not preferable. The upper limit is preferably 0.70 dl/g, and more preferably 0.68 dl/g. When the intrinsic viscosity exceeds 0.70 dl/g, the resin is less likely to be discharged from an extruder, whereby the productivity may be lowered, which is not preferable.
The lower limit of the thickness of the substrate film is preferably 8 μm, more preferably 10 μm, and still more preferably 12 μm. If the thickness is less than 8 μm, the strength of the film may be insufficient, which is not preferable. The upper limit is preferably 200 μm, more preferably 50 μm, and still more preferably 30 μm. If the thickness exceeds 200 μm, the film becomes too thick, which may cause difficult processing. It is not preferable that the thickness of the film increases from the viewpoint of an environmental load, and it is preferable to reduce the volume as much as possible.
The lower limit of the refractive index of the substrate film in the thickness direction is preferably 1.4930, and more preferably 1.4940. If the refractive index is less than 1.4930, orientation is not sufficient, and therefore a lamination strength may not be obtained. The upper limit is preferably 1.4995 and more preferably 1.4980. If the refractive index exceeds 1.4995, the orientation of the plane may collapse to cause insufficient mechanical characteristics, which is not preferable.
The lower limit of the heat shrinkage rate of the substrate film treated at 150° C. for 30 minutes in the machine direction (sometimes referred to as MD) and the transverse direction (sometimes referred to as TD) is preferably 0.1%, and more preferably 0.3%. If the heat shrinkage rate is less than 0.1%, the improvement effect may be saturated, and the film may be mechanically brittle, which is not preferable. The upper limit is preferably 3.0%, and more preferably 2.5%. If the heat shrinkage rate exceeds 3.0%, pitch deviation and the like may occur due to dimensional change during processing such as printing, which is not preferable. If the heat shrinkage rate exceeds 3.0%, shrinkage and the like in the transverse direction may occur due to dimensional change during processing such as printing, which is not preferable.
A recycled polyester resin derived from PET bottles containing an isophthalic acid component as an acid component is preferably used as a raw material for a substrate film. The crystallinity of a polyester used for PET bottles is controlled in order to improve the bottle appearance, and as a result, a polyester containing 10 mol % or less of an isophthalic acid component may be used. The contained isophthalic acid causes the crystal structure of the polyester to collapse, which contributes to the flexibility of the substrate. By controlling the flexibility, a surface on which an inorganic thin film is easily laminated can be provided.
The lower limit of the amount of a terephthalic acid component in all dicarboxylic acid components constituting the polyester resin contained in the substrate film is preferably 95.0 mol %, more preferably 96.0 mol %, still more preferably 96.5 mol %, and particularly preferably 97.0 mol %. If the amount is less than 95.0 mol %, crystallinity is deteriorated, whereby the heat shrinkage rate may increase, which is not so preferable. The upper limit of the amount of the terephthalic acid component in the polyester resin contained in the film is preferably 99.5 mol %, and more preferably 99.0 mol %. Many of the recycled polyester resins derived from PET bottles contain dicarboxylic acid components typified by isophthalic acid besides terephthalic acid, whereby the amount of the terephthalic acid component constituting the polyester resin in the film exceeding 99.5 mol % consequently makes it difficult to produce a polyester film containing a recycled resin at a high rate, which is not so preferable.
In the present invention, it is important to control the amount of an isophthalic acid component relative to a total dicarboxylic acid component constituting the polyester resin contained in the substrate film for imparting flexibility for exhibiting barrier performance. The lower limit is preferably 0.5 mol %, more preferably 0.7 mol %, still more preferably 0.9 mol %, and particularly preferably 1.0 mol %. Recycled polyester resins derived from PET bottles contain a large amount of an isophthalic acid component, whereby the amount of the isophthalic acid component constituting the polyester resin in the film of less than 0.5 mol % consequently makes it difficult to produce a polyester film containing a recycled resin at a high rate, which is not so preferable. The flexibility of the surface is reduced, and the inorganic thin film layer is apt to be subjected to a stress load when the inorganic thin film layer is laminated, whereby the barrier performance may be deteriorated. The upper limit of the amount of the isophthalic acid component in all the dicarboxylic acid components constituting the polyester resin contained in the film is preferably 5.0 mol %, more preferably 4.0 mol %, still more preferably 3.5 mol %, and particularly preferably 3.0 mol %. If the amount exceeds 5 mol %, crystallinity is deteriorated, whereby the heat shrinkage rate may increase, which is not so preferable. When the substrate becomes too soft, the inorganic thin film cannot follow the change, whereby the barrier performance may be deteriorated. By setting the content rate of the isophthalic acid component within the above range, a surface on which the inorganic thin film layer is easily deposited is obtained due to the softening effect of the substrate surface, and as a result, good barrier properties can be exhibited.
The upper limit of the intrinsic viscosity of the recycled resin derived from PET bottles is preferably 0.90 dl/g, more preferably 0.80 dl/g, still more preferably 0.77 dl/g, and particularly preferably 0.75 dl/g. If the intrinsic viscosity exceeds 0.9 dl/g, the resin is less likely to be discharged from an extruder, whereby the productivity may be lowered, which is not so preferable.
The lower limit of the content rate of the polyester resin recycled from PET bottles in the film is preferably 50% by weight, more preferably 65% by weight, and still more preferably 75% by weight. If the content rate is less than 50% by weight, the content rate is low for utilization of the recycled resin, which is not so preferable in terms of contribution to environmental protection. The amount of the isophthalic acid component is reduced, whereby the lamination of the inorganic thin film layer may be unable to exhibit superior flexibility. Meanwhile, the upper limit of the content rate of the polyester resin recycled from PET bottles is 95% by weight, preferably 90% by weight, more preferably 85% by weight. If the content rate exceeds 95% by weight, it is sometimes impossible to sufficiently add a lubricant or an additive such as inorganic particles for improving the function as a film, which is not so preferable. A polyester resin recycled from PET bottles may be used as a master batch (a resin contained in a high concentration) used when a lubricant or an additive such as inorganic particles is added for improving the function as a film.
As the kind of the lubricant, inorganic lubricants such as silica, calcium carbonate, and alumina, and also organic lubricants are preferable, and silica and calcium carbonate are more preferable. By these lubricants, transparency and slippage can be exhibited. The average particle diameter of the particles to be the lubricant is preferably within a range of 0.05 to 3.0 μm as measured by the Coulter counter.
The lower limit of the lubricant content rate in the substrate film is preferably 0.01% by weight, more preferably 0.015% by weight, and still more preferably 0.02% by weight. If the content rate is less than 0.01% by weight, the slippage may be deteriorated. The upper limit of the lubricant content rate is preferably 1% by weight, more preferably 0.2% by weight, and still more preferably 0.1% by weight. If the lubricant content rate exceeds 1% by weight, transparency may be deteriorated, which is not so preferable.
A method for producing the substrate film used in the laminated film of the present invention is not particularly limited, but for example, the following production method is recommended. It is important to set a temperature for melting and extruding a resin in an extruder. The basic idea is that (1) deterioration is suppressed by extrusion at a temperature as low as possible, since a polyester resin used for PET bottles contains an isophthalic acid component, and (2) the polyester resin has a portion that melts at a high temperature or a high pressure or the like in order to sufficiently and uniformly melt an intrinsic viscosity or a fine highly crystalline portion. Addition of the isophthalic acid component leads to deterioration in the tacticity of a polyester and a decrease in the melting point. Therefore, extrusion at a high temperature results in a significant decrease in melt viscosity or deterioration by heat, and also in a decrease in the mechanical strength and an increase in foreign matters resulting from the deterioration. Sufficient melt-kneading is impossible merely by lowering the extrusion temperature, which may result in problems of an increase in thickness unevenness and foreign matters such as fish eyes. From the above, examples of a recommended production method include a method of using two extruders in tandem, a method of increasing the pressure in a filter part, or a method of using a screw having a high shear force for a part of a screw constitution.
The lower limit of the set temperature of the resin melting part in the extruder (excluding the maximum set temperature of the compression part of the screw in the extruder) is preferably 270° C., and the upper limit thereof is preferably 290° C. If the set temperature is lower than 270° C., extrusion is difficult, and if the temperature exceeds 290° C., the resin may be deteriorated, which is not so preferable.
The lower limit of the highest set temperature in the compression part of the screw in the extruder is preferably 295° C. In a polyester resin used for PET bottles, crystals having a high melting point (260° C. to 290° C.) often exist in terms of transparency. An additive and a crystallization nucleating agent and the like are added, and unevenness in the fine melting behavior is observed in the resin material. If the highest set temperature is lower than 295° C., it is difficult to sufficiently melt them, which is not so preferable. The upper limit of the highest set temperature in the compression part of the screw in the extruder is preferably 310° C. If the highest set temperature exceeds 310° C., the resin may be deteriorated, which is not so preferable.
The lower limit of the time for the resin to pass the region at the highest set temperature in the compression part of the screw in the extruder is preferably 10 seconds, and more preferably 15 seconds. If the time is shorter than 10 seconds, the polyester resin used for PET bottles cannot be sufficiently melted, which is not so preferable. The upper limit of the time is preferably 60 seconds, and more preferably 50 seconds. If the time exceeds 60 seconds, the resin is apt to be deteriorated, which is not so preferable. By setting the extruder in such ranges, a film reduced in thickness unevenness, foreign matters such as fish eyes, and coloration can be obtained even if a large amount of a polyester resin recycled from PET bottles is used.
The resin melted in this manner is extruded in a sheet-like form on a cooling roll, and then biaxially stretched. The stretching method may be a simultaneous biaxial stretching method, but a sequential biaxial stretching method is particularly preferable. These make it easy to satisfy productivity and quality required in the present invention.
A method for stretching the film in the present invention is not particularly limited, but the following points are important. In order to stretch a resin having an intrinsic viscosity of 0.58 dl/g or more and containing an isophthalic acid component, ratios and temperatures in the machine direction (MD) stretching and transverse direction (TD) stretching are important. If the MD stretch ratio and the temperature are not appropriate, a stretching force is not uniformly applied, and the orientation of molecules is insufficient, which may result in an increase in thickness unevenness or insufficient mechanical characteristics. The film may be broken in the next TD stretching step, or thickness unevenness may be extremely increased. If the TD stretch ratio and the temperature are not appropriate, the film may not be uniformly stretched; balance of the vertical and transverse orientation may be deteriorated; and the mechanical characteristics may be insufficient. When the next heat setting step is performed in the state that the thickness unevenness is significant or the molecular chain orientation is insufficient, relaxation cannot be uniformly performed, which causes problems of more significant thickness unevenness and insufficient mechanical characteristics. Therefore, it is basically recommended that in the MD stretching, stretching is performed step by step by performing temperature adjustment described below, and in the TD stretching, stretching is performed at an appropriate temperature so that the orientation balance is not extremely deteriorated. The present invention is not limited to the following aspects, but will be described with an example.
A machine direction (MD) stretching method is preferably a roll stretching method or an IR heating method.
The lower limit of the MD stretching temperature is preferably 100° C., more preferably 110° C., and still more preferably 120° C. Even if the MD stretching temperature is lower than 100° C., and a polyester resin with an intrinsic viscosity of 0.58 dl/g or more is stretched to orient molecules in the machine direction, the film is broken in the next transverse stretching step or an extreme thickness defect is caused, which is not preferable. The upper limit of the MD stretching temperature is preferably 140° C., more preferably 135° C., and still more preferably 130° C. If the MD stretching temperature exceeds 140° C., the orientation of molecular chains becomes insufficient, whereby mechanical characteristics may become insufficient, which is not so preferable.
The lower limit of the MD stretch ratio is preferably 2.5 times, more preferably 3.5 times, and still more preferably 4 times. Even if the MD stretch ratio is less than 2.5 times, and a polyester resin having an intrinsic viscosity of 0.58 dl/g or more is stretched to orient molecules in the machine direction, the film may be broken in the next transverse stretching step or an extreme thickness defect may be caused, which is not so preferable. The upper limit of the MD stretch ratio is preferably 5 times, more preferably 4.8 times, and still more preferably 4.5 times. If the MD stretch ratio exceeds 5 times, the effect of improving a mechanical strength and thickness unevenness may be saturated, which is not so meaningful.
The MD stretching method may be the above-mentioned one-stage stretching, but the film is preferably stretched in two or more stages. Stretching in two or more stages makes it possible to well stretch a polyester resin having a high intrinsic viscosity and derived from a recycled resin containing isophthalic acid, which provides reduced thickness unevenness, and an improved lamination strength and mechanical characteristics.
The lower limit of the MD stretching temperature in the first stage is preferably 110° C., and more preferably 115° C. If the MD stretching temperature is lower than 110° C., heat is insufficient, whereby vertical stretching cannot be sufficiently performed, resulting in poor flatness, which is not preferable. The upper limit of the MD stretching temperature in the first stage is preferably 125° C., and more preferably 120° C. If the MD stretching temperature exceeds 125° C., the orientation of molecular chains may become insufficient and mechanical characteristics may be deteriorated, which is not so preferable.
The lower limit of the MD stretch ratio in the first stage is preferably 1.1 times, and more preferably 1.3 times. If the MD stretch ratio is 1.1 times or more, finally, a polyester resin having an intrinsic viscosity of 0.58 dl/g or more can be sufficiently stretched in the machine direction by weak stretching in the first stage, and accordingly, the productivity can be improved. The upper limit of the MD stretch ratio in the first stage is preferably 2 times, and more preferably 1.6 times. If the MD stretch ratio exceeds 2 times, the orientation of molecular chains in the machine direction is too high, whereby the stretching may become difficult in the second stage or thereafter and the film may have significant thickness unevenness, which is not so preferable.
The lower limit of the MD stretching temperature in the second stage (or final stage) is preferably 110° C., and more preferably 115° C. If the MD stretching temperature is 110° C. or higher, a polyester resin having an intrinsic viscosity of 0.58 or more can be sufficiently stretched in the machine direction and can be stretched in the transverse direction in the next step, so that the thickness unevenness in the vertical and transverse directions can be reduced. The upper limit of the MD stretching temperature is preferably 130° C., and more preferably 125° C. If the MD stretching temperature exceeds 130° C., crystallization is promoted, whereby the transverse stretching may become difficult or the thickness unevenness may become significant, which is not so preferable.
The lower limit of the MD stretch ratio in the second stage (or final stage) is preferably 2.1 times, and more preferably 2.5 times. Even if the MD stretch ratio is less than 2.1 times, and a polyester resin having an intrinsic viscosity of 0.58 or more is stretched to orient molecules in the machine direction, the film may be broken in the next transverse stretching step or an extreme thickness defect may be caused, which is not so preferable. The upper limit of the MD stretch ratio is preferably 3.5 times, and more preferably 3.1 times. If the MD stretch ratio exceeds 3.5 times, the orientation in the machine direction is too high, whereby the stretching may be impossible in the second stage or thereafter and the film may have significant thickness unevenness, which is not so preferable.
The lower limit of the TD stretching temperature is preferably 110° C., more preferably 120° C., and still more preferably 125° C. If the TD stretching temperature is lower than 110° C., the stretching stress in the transverse direction is increased, whereby the film may be broken or the thickness unevenness may become extremely significant, which is not so preferable. The upper limit of the TD stretching temperature is preferably 150° C., more preferably 145° C., and still more preferably 140° C. If the TD stretching temperature exceeds 150° C., the orientation of molecular chains does not increase, whereby mechanical characteristics may be deteriorated, which is not so preferable.
The lower limit of the transverse direction (TD) stretch ratio is preferably 3.5 times, and more preferably 3.9 times. If the stretch ratio is less than 3.5 times, molecular orientation is weak, whereby a mechanical strength may become insufficient, which is not so preferable. The orientation of molecular chains in the machine direction is significant and the balance between the vertical and transverse directions is deteriorated to make the thickness unevenness significant, which is not so preferable. The upper limit of the TD stretch ratio is preferably 5.5 times, and more preferably 4.5 times. If the TD stretch ratio exceeds 5.5 times, the film may be broken, which is not so preferable.
In order to obtain the substrate film used for the laminated film of the present invention, it is desirable to appropriately set conditions for heat setting continuously performed in a tenter after the completion of the TD stretching and for the subsequent cooling of the film to room temperature. As compared with a common polyethylene terephthalate film containing no isophthalic acid, a polyester film containing a recycled resin derived from PET bottles and containing isophthalic acid has low crystallinity, is apt to be melted in an ultra-fine level, and has a poor mechanical strength. Therefore, when the polyester film is exposed to high temperatures under strain abruptly after completion of stretching, or when the polyester film is abruptly cooled under strain after completion of heat setting at high temperatures, a tensile force balance in the transverse direction is disordered due to an inevitable temperature difference in a film transverse direction, which results in thickness unevenness and defective mechanical characteristics. Meanwhile, when the heat setting temperature is lowered to deal with the phenomenon, a sufficient lamination strength may not be obtained. In the present invention, it is recommended to perform steps of heat setting 1 at a slightly low temperature, heat setting 2 (as necessary, heat setting 3) at a sufficiently high temperature, and thereafter, gradual cooling to lower the temperature to room temperature after the completion of stretching. However, the present invention is not limited to this method, and other recommended methods include a method of controlling the film tension correspondingly to the velocity of hot air in the tenter and the temperatures in the respective zones; a method of performing heat treatment at a relatively low temperature in a furnace with a sufficient length after the completion of stretching; and a method of relaxing the film by heat rolls after the completion of the heat setting.
As one example, a method by controlling the tenter temperature will be described. Heat settings 1, 2, and 3 are arranged in order from the upstream side in the film machine direction of a heat setting zone in the tenter.
The lower limit of the temperature in the heat setting 1 is preferably 160° C., and more preferably 170° C. If the temperature is lower than 160° C., the heat shrinkage rate finally increases, and deviation and shrinkage may be caused at the time of processing, which is not so preferable. The upper limit of the temperature is preferably 215° C., and more preferably 210° C. If the temperature exceeds 215° C., the film is abruptly exposed to a high temperature, whereby the thickness unevenness may become significant or the film may be broken, which is not so preferable.
The lower limit of the time for the heat setting 1 is preferably 0.5 seconds, and more preferably 2 seconds. If the time is shorter than 0.5 sec, the film temperature increase may be insufficient. The upper limit of the time is preferably 10 seconds, and more preferably 8 seconds. If the time exceeds 10 seconds, productivity may be deteriorated, which is not so preferable.
The lower limit of the temperature in the heat setting 2 is preferably 220° C., and more preferably 227° C. If the temperature is lower than 220° C., the heat shrinkage rate may become significant, whereby deviation and shrinkage may be caused at the time of processing, which is not so preferable. The upper limit of the temperature is preferably 240° C., and more preferably 237° C. If the temperature exceeds 240° C., the film may be melted, or even if not melted, the film may be fragile, which is not so preferable.
The lower limit of the time for the heat setting 2 is preferably 0.5 seconds, and more preferably 3 seconds. If the time is shorter than 0.5 seconds, the film may be apt to be broken at the time of heat setting, which is not so preferable. The upper limit of the time is preferably 10 seconds, and more preferably 8 seconds. If the upper limit of the time exceeds 10 seconds. sagging may occur to result in thickness unevenness, which is not so preferable.
The lower limit of the temperature in the case where the heat setting 3 is performed as necessary is preferably 205° C., and more preferably 220° C. If the temperature is lower than 205° C., the heat shrinkage rate may become significant, and deviation whereby shrinkage may be caused at the time of processing, which is not so preferable. The upper limit of the temperature is preferably 240° C., and more preferably 237° C. If the temperature exceeds 240° C., the film may be melted, or even if not melted, the film may be fragile, which is not so preferable.
The lower limit of the time in the case where the heat setting 3 is performed as necessary is preferably 0.5 seconds, and more preferably 3 seconds. If the time is shorter than 0.5 seconds, the film may be apt to be broken at the time of heat setting, which is not so preferable. The upper limit of the time is preferably 10 seconds, and more preferably 8 seconds. If the time exceeds 10 seconds, sagging may occur to cause thickness unevenness, which is not so preferable.
TD relaxation may be carried out at any point in the heat setting. The lower limit thereof is preferably 0.5%, and more preferably 3%. If the lower limit is less than 0.5%, the heat shrinkage rate particularly in the transverse direction becomes significant, whereby deviation and shrinkage may be caused at the time of processing, which is not so preferable. The upper limit thereof is preferably 10%, and more preferably 8%. If the upper limit exceeds 10%, sagging may occur to cause thickness unevenness, which is not so preferable.
The lower limit of the gradual cooling temperature after the TD heat setting is preferably 90° C., and more preferably 100° C. If the gradual cooling temperature is lower than 90° C., the film contains isophthalic acid, whereby the thickness unevenness may become significant because of shrinkage by abrupt temperature change or the film may be broken, which is not so preferable. The upper limit of the gradual cooling temperature is preferably 150° C., and more preferably 140° C. If the gradual cooling temperature exceeds 150° C., a sufficient cooling effect may not be obtained, which is not so preferable.
The lower limit of the gradual cooling time after the heat setting is preferably 2 seconds, and more preferably 4 seconds. If the gradual cooling time is shorter than 2 seconds, a sufficient gradual cooling effect may not be obtained, which is not so preferable. The upper limit thereof is preferably 20 seconds, and more preferably 15 seconds. The gradual cooling time exceeding 20 seconds is apt to be disadvantageous in terms of productivity, which is not so preferable.
The upper limit of the haze per thickness of the substrate film layer in the present invention is preferably 0.66%/μm, more preferably 0.60%/μm, and still more preferably 0.53%/μm. When the substrate film layer having a haze of 0.66%/μm or less is subjected to printing, the quality of printed characters and images is improved.
The substrate film layer in the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, or surface roughening treatment, as long as the object of the present invention is not impaired, and may be subjected to known anchor coating treatment, printing, or decoration or the like.
A layer made of another material may be laminated on the substrate film layer in the present invention. As the method, the layer may be laminated on the substrate film layer after or during the production of the substrate film layer.
[Inorganic Thin Film Layer]
In the laminated film having gas barrier properties of the present invention, an inorganic thin film layer is provided on the surface of the substrate film. The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as the material can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and mixtures of silicon oxide and aluminum oxide are preferable. In this composite oxide, silicon oxide and aluminum oxide are preferably mixed at such a mixing ratio that the concentration of Al is within a range of 20 to 70% by mass in terms of metal content by mass. If the concentration of Al is less than 20% by mass, the barrier properties against water vapor may be deteriorated. Meanwhile, If the concentration of Al exceeds 70% by mass, the inorganic thin film layer tends to be harder, whereby the film may be broken during secondary processing such as printing or lamination to cause deteriorated gas barrier properties. When the Al concentration is 100% by mass, the water vapor barrier performance is good, but the inorganic thin film layer is made of a single material, whereby the surface of the inorganic thin film layer tends to be smooth. The inorganic thin film layer has poor slipperiness, whereby defects (wrinkles and acnes and the like) in processing are apt to occur. The silicon oxide as used herein is various silicon oxides such as SiO and SiO2, or a mixture thereof, and the aluminum oxide as used herein is various aluminum oxides such as A10 and Al2O3, or a mixture thereof.
The film thickness of the inorganic thin film layer is normally 1 to 100 nm, and preferably 5 to 50 nm. If the film thickness of the inorganic thin film layer is less than 1 nm, satisfactory gas barrier properties may be less likely to be obtained. Meanwhile, even if the film thickness exceeds 100 nm such that the inorganic thin film layer is excessively thickened, the gas barrier properties-improving effect equivalent to such increase in the thickness cannot be obtained, and such a film thickness is rather disadvantageous in terms of flex resistance and production cost.
The method for forming the inorganic thin film layer is not particularly limited, and known vapor-deposition methods, for example, physical vapor-deposition methods (PVD methods) such as a vacuum vapor-deposition method, a sputtering method, and an ion plating method, or chemical vapor-deposition methods (CVD methods) may be adopted as appropriate. Hereinafter, a typical method for forming the inorganic thin film layer will be described by taking a silicon oxide-aluminum oxide based thin film as an example. For example, in the ease of adopting a vacuum vapor-deposition method, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, or the like is preferably used as a vapor-deposition raw material. Normally, particles are used as these vapor-deposition raw materials. In this case, the size of each particle is desirably a size that does not change the pressure during vapor-deposition, and a preferable particle size is 1 mm to 5 mm. For heating, systems such as resistive heating, high frequency induction heating, electron beam heating, and laser heating can be adopted. It is also possible to adopt reactive vapor-deposition in which oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, or water vapor or the like is introduced as a reaction gas or a means such as ozone addition or ion assist is used. Furthermore, film production conditions such as applying a bias to a body to be vapor-deposited (laminated film to be vapor-deposited) and heating or cooling the body to be vapor-deposited can also be optionally changed. Similarly, the vapor-deposition materials, the reaction gases, the application of a bias to the body to be vapor-deposited, and the heating/cooling and the like can be changed even when a sputtering method or a CVD method is adopted.
In the present invention, the surface hardness (flexibility) is controlled by the content of isophthalic acid in the substrate film. By setting the surface hardness within a predetermined range, the inorganic thin film layer is likely to be deposited on the substrate due to its flexibility, whereby a coating film excellent in barrier performance is obtained. The surface hardness is preferably 60 to 120 N/mm2. The surface hardness is more preferably 65 N/mm2 or more, still more preferably 70 N/mm2 or more, and particularly preferably 75 N/mm2 or more, and more preferably 115 N/mm2 or less, still more preferably 110 N/mm2 or less, and particularly preferably 105 N/mm2 or less. If the surface hardness of the laminated film exceeds 120 N/mm2, the flexibility of the surface is reduced, and the inorganic thin film layer is apt to be subjected to a stress load when the inorganic thin film layer is laminated, whereby the barrier performance may be deteriorated. Meanwhile, when the surface hardness is less than 60 N/mm2, the film becomes too soft, and the inorganic thin film cannot follow the change, whereby the barrier performance may be deteriorated. It is not preferable also from the viewpoint of processing suitability described later.
[Coating layer]
In the laminated film of the present invention, a coating layer can be provided between the substrate film layer and the inorganic thin film layer for the purpose of securing gas barrier properties and lamination strength after retorting, and slipperiness for improving processing suitability. Examples of the resin composition used for the coating layer provided between the substrate film layer and the inorganic thin film layer include compositions obtained by adding epoxy-based, isocyanate-based, melamine-based, oxazoline-based, and carbodiimide-based curing agents and the like to urethane-based, polyester-based, acryl-based, titanium-based, isocyanate-based, imine-based, and polybutadiene-based resins and the like. These resin compositions used for the coating layer preferably contain a silane coupling agent having at least one or more organic functional groups. The organic functional groups include alkoxy groups, amino groups, epoxy groups, isocyanate groups, etc. By the addition of the silane coupling agent, the lamination strength after retorting is further improved.
Among the resin compositions used for the coating layer, it is preferable to use a resin containing an oxazoline group or a carbodiimide group, and it is more preferable to use a mixture of an acrylic resin and a urethane-based resin in addition to these resins. These functional groups have high affinity with the inorganic thin film, and can react with a metal hydroxide and an oxygen deficiency portion of an inorganic oxide that is generated during formation of the inorganic thin film layer, whereby firm adhesion to the inorganic thin film layer is exhibited. An unreacted functional group present in a coating layer can react with a carboxylic acid terminal that is generated by hydrolysis of the substrate film layer and the coating layer, thereby forming cross-links.
In the present invention, the adhesion amount of the coating layer is preferably 0.010 to 0.200 (g/m2). This makes it possible to uniformly control the coating layer, and as a result, the inorganic thin film layer can be densely deposited. The cohesive force inside the coating layer is improved, and the adhesion between the respective layers of the substrate film-coating layer-inorganic thin film layer is also improved, whereby the water-resistant adhesiveness of the coating layer can be improved. The adhesion amount of the coating layer is preferably 0.015 (g/m2) or more, more preferably 0.020 (g/m2) or more, and still more preferably 0.025 (g/m2) or more, and preferably 0.190 (g/m2) or less, more preferably 0.180 (g/m2) or less, and still more preferably 0.170 (g/m2) or less. If the adhesion amount of the coating layer exceeds 0.200 (g/m2), the cohesive force inside the coating layer becomes insufficient, whereby good adhesion may not be exhibited. Since the uniformity of the coating layer is also deteriorated, defects occur in the inorganic thin film layer, whereby the gas barrier properties may be deteriorated. Furthermore, when the coating layer is thick, the softening effect of the substrate is weakened, leading to deterioration in gas barrier properties. Moreover, the production cost increases, which is economically disadvantageous. Meanwhile, if the film thickness of the coating layer is less than 0.010 (g/m2), the substrate cannot be sufficiently coated, whereby sufficient gas barrier properties and interlayer adhesion may not be obtained.
The method for forming the coating layer is not particularly limited, and, for example, conventionally known methods such as coating methods can be adopted. Examples of suitable methods among the coating methods include an off-line coating method and an in-line coating method. For example, in the case of an in-line coating method that is performed in a step of producing a substrate film layer, as conditions for drying and a heat treatment during coating, although depending on a coating thickness or conditions of an apparatus, it is preferable to send the substrate film to a stretching step in a perpendicular direction immediately after coating and to perform drying in a pre-heating zone or a stretching zone in the stretching step. In such a case, normally, the temperature is preferably set to about 50 to 250° C.
Examples of the solvent (solvating medium) used when the coating method is used include aromatic solvents such as benzene and toluene; alcohol-based solvents such as methanol and ethanol; ketone-based solvents such as acetone and methyl ethyl ketone; ester-based solvents such as ethyl acetate and butyl acetate; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.
In the present invention, the surface hardness (flexibility) is controlled by the content of isophthalic acid in the substrate film. By setting the surface hardness within a predetermined range, the coating layer is likely to permeate and be deposited on the substrate due to its flexibility, and as a result, a uniform coating film is obtained. The surface hardness of the coating layer surface side of the film obtained by laminating the coating layer on the substrate film is preferably 120 N/mm2 or less. The surface hardness is preferably 115 N/mm2 or less, more preferably 110 N/mm2 or less, and still more preferably 105 N/mm2 or less. When the surface hardness of the laminated film exceeds 120 N/mm2, the flexibility of the surface is reduced, which makes it difficult to obtain the permeation effect of the coating layer. The lower limit value of the surface hardness is preferably 60 N/mm2, more preferably 65 N/mm2, still more preferably 70 N/mm2, and particularly preferably 75 N/mm2. Also in a laminated film in which an inorganic thin film layer described later is further laminated on the coating layer, the preferred range of the surface hardness on the inorganic thin film layer surface side is the same as the above range.
As described above, the barrier performance can be expected to be improved by softening the surface hardness, but accordingly, there is a concern that the slipperiness is deteriorated. When the slipperiness is poor, wrinkles may be formed at the time of winding in a vapor-deposition deposition or coating/laminating step, small convex defects (acnes) may occur due to the film being caught at the time of winding, or blocking may occur, resulting in troubles. In the present invention, by controlling the surface roughness of the laminated film, proper slipperiness can be imparted to the surface of the substrate while the flexibility of the substrate is maintained, and as a result, a film excellent in also processability can be obtained. Regarding the surface roughness of the film, an average roughness Ra in a 2-μm square region is preferably 2.0 to 6.0 nm, as observed by an atomic force microscope (AFM). As a result, minute unevenness is imparted to the surface, and as a result, good slipperiness is obtained. The roughness is preferably 2.5 to 5.5 nm, more preferably 3.0 to 5.0 nm, and still more preferably 3.5 to 4.5 nm. When the roughness exceeds 6 nm, the inorganic thin film layer is not uniformly laminated due to the unevenness, and as a result, the gas barrier properties may be deteriorated. Meanwhile, when the roughness is less than 2 nm, the film is flat, whereby the slipperiness is deteriorated.
Examples of the method for setting the surface roughness to the above-mentioned range include a surface treatment such as application of a coating layer or a corona treatment. Among them, from the viewpoint of being capable of simultaneously imparting water-resistant adhesiveness and slipperiness, it is preferable to apply the coating layer. The roughness of the coating layer can be adjusted by changing the mixing ratio of two or more kinds of materials to change the dispersibility of the resin, changing the adhesion amount of the coating layer, or changing a solvent to be diluted at the time of preparing a coating liquid.
The coefficient of static friction has and the coefficient of dynamic friction μd of the inorganic thin film layer surface/coating layer surface of the laminated film of the present invention are preferably within a range of 0.20 to 0.40. The coefficient of static friction has and the coefficient of dynamic friction μd are more preferably 0.275 to 0.375, and still more preferably 0.30 to 0.35. When the slipperiness of the laminated film exceeds 0.40, wrinkles or acnes occur at the time of winding the film. Meanwhile, when the slipperiness is less than 0.20, the film may slip to cause winding deviation.
[Protective layer]
In the present invention, when gas barrier performance is further required or processing such as printing is required, a protective layer can also be provided on the inorganic thin film layer. The metal oxide layer is not a completely dense film, but has minute deficient portions dotted therein. By applying a specific resin composition for a protective layer described later onto the metal oxide layer to form a protective layer, a resin contained in the resin composition for a protective layer permeates the deficient portions of the metal oxide layer, which accordingly provides an effect of stabilizing the gas barrier properties. In addition, by using a material having gas barrier properties also for the protective layer itself, the gas barrier performance of the laminated film may also be significantly improved. However, it should be noted that the provision of the protective layer causes a cost increase due to an increase in the number of steps, and an environment load depending on a material to be used. It should also be noted that the protective layer changes the above-mentioned surface roughness.
The adhesion amount of the protective layer is preferably 0.10 to 0.40 (g/m2). This makes it possible to uniformly control the protective layer in coating, resulting in a film having less coating unevenness and defects. The cohesive force of the protective layer itself is improved, and the adhesion between the inorganic thin film layer and the protective layer is also firm. The adhesion amount of the protective layer is preferably 0.13 (g/m2) or more, more preferably 0.16 (g/m2) or more, and still more preferably 0.19 (g/m2) or more, and preferably 0.37 (g/m2) or less, more preferably 0.34 (g/m2) or less, and still more preferably 0.31 (g/m2) or less. If the adhesion amount of the protective layer exceeds 0.400 (g/m2), the gas barrier properties are improved, but the cohesive force inside the protective layer is insufficient, and the uniformity of the protective layer is also deteriorated, whereby unevenness and defects may occur in the coating appearance, or the gas barrier properties and the adhesiveness may not be sufficiently exhibited. Meanwhile, if the film thickness of the protective layer is less than 0.10 (g/m2), sufficient gas barrier properties and interlayer adhesion may not be obtained.
As the resin composition used for the protective layer formed on the surface of the inorganic thin film layer of the laminated film of the present invention, resins such as a urethane-based resin, a polyester-based resin, an acryl-based resin, a titanium-based resin, an isocyanate-based resin, an imine-based resin, and a polybutadiene-based resin and the like can be used and curing agents such as an epoxy-based resin, an isocyanate-based resin, and a melamine-based resin may be further added.
In particular, the urethane resin is preferably contained because, in addition to barrier performance due to high cohesiveness of a urethane bond itself, a polar group interacts with the inorganic thin film layer and also has flexibility due to the presence of its amorphous portion, so that damage to the inorganic thin film layer can be suppressed even when a flexing load is applied.
(Urethane Resin)
The glass transition temperature (Tg) of the urethane resin used in the present invention is preferably 100° C. or higher, more preferably 110° C. or higher, and still more preferably 120° C. or higher from the viewpoint of improvement in the barrier properties due to the cohesive force. However, in order to exhibit an adhesion force, a flexible resin having excellent flexibility and a Tg of 100° C. or lower may be mixed with the urethane resin. In that case, the addition ratio of the flexible resin is preferably within a range of 0 to 80%. The addition ratio is more preferably within a range of 10 to 70%, and still more preferably within a range of 20 to 60%. If the addition ratio is within the above range, both the cohesive force and the flexibility can be achieved, whereby the barrier properties and the adhesion are improved. If the addition ratio exceeds 80%, the film becomes too soft, which may lead to deterioration in barrier performance.
A urethane resin containing an aromatic or aromatic-aliphatic diisocyanate component as a main constituent component is more preferably used as the urethane resin from the viewpoint of improving the gas barrier properties thereof.
Among them, it is particularly preferable that the urethane resin contains a metaxylylene diisocyanate component. The use of the resin allows an effect of stacking between its aromatic rings to further increase the cohesive force of the urethane bonds. Consequently, good gas barrier properties are obtained.
In the present invention, the proportion of the aromatic or aromatic-aliphatic diisocyanate in the urethane resin is preferably set to 50 mol % or more (50 to 100 mol %) in 100 mol % of the polyisocyanate component (F). The total proportion of the aromatic or aromatic-aliphatic diisocyanate is preferably 60 to 100 mol %, more preferably 70 to 100 mol %, and still more preferably 80 to 100 mol %. As such resins, “TAKELAC (registered trademark) WPB” series commercially available from Mitsui Chemicals, Inc. can be suitably used. If the total proportion of the aromatic or aromatic-aliphatic diisocyanate is less than 50 mol %, good gas barrier properties may not be obtained.
In the urethane resin used in the present invention, various cross-linking agents such as a silicon-based cross-linking agent may be blended as long as the gas barrier properties are not impaired for the purpose of improving the cohesive force and the wet heat resistant adhesiveness of the film. Examples of the cross-linking agent include a silicon-based cross-linking agent, an oxazoline compound, a carbodiimide compound, and an epoxy compound. Among them, the water-resistant adhesiveness to the inorganic thin film layer can be particularly improved by blending a silicon-based cross-linking agent. From this viewpoint, a silicon-based cross-linking agent is particularly preferable. In addition, an oxazoline compound, a carbodiimide compound, and an epoxy compound and the like may be used in combination as the cross-linking agent.
The coating method of the resin composition for a protective layer is not particularly limited as long as it is a method of coating the film surface to form a layer. For example, normal coating methods such as gravure coating, reverse roll coating, wire bar coating, and die coating can be employed.
When the protective layer is formed, it is preferable to apply the resin composition for a protective layer and then heat and dry the resin composition, and the drying temperature at that time is preferably 110 to 190° C., more preferably 130 to 185° C., and still more preferably 150 to 180° C. If the drying temperature is lower than 110° C., insufficient drying may occur in the protective layer, or the formation of the protective layer does not proceed, whereby a cohesive force and water-resistant adhesiveness may be deteriorated, resulting in deterioration in barrier properties and hand tearability. Meanwhile, if the drying temperature exceeds 190° C., heat is excessively applied to the film, whereby the film may become brittle to cause a decreased puncture strength, or the film may shrink to cause deteriorated processability. In particular, by drying at 150° C. or higher, and preferably 160° C. or higher, the formation of the protective layer effectively proceeds, which provides a further increased adhesion area between the resin of the protective layer and the inorganic thin film layer, so that the water-resistant adhesiveness can be improved. If the solvent in the protective film is first volatilized under relatively low temperature conditions of 90° C. to 110° C. immediately after coating, and the protective film is then dried at 150° C. or higher, a uniform film can be obtained, which is particularly preferable. In addition to drying, it is also more effective to perform additional heat treatment in a low temperature range as much as possible in order to advance the formation of the protective layer.
As described above, the laminated film of the present invention includes the substrate containing the polyester resin derived from PET bottles containing isophthalic acid and having a low environmental load, whereby the laminated film is excellent in gas barrier performance before a treatment. Furthermore, the laminated film includes the coating layer, whereby the laminated film can maintain its barrier properties and adhesiveness to the inorganic thin film layer even after a severe wet heat treatment.
When the laminated film of the present invention is used as a packaging material, it is preferable to form a laminated body formed a heat sealable resin layer called a sealant. The heat sealable resin layer is usually provided on the inorganic thin film layer, but may be provided on the outer side of the substrate film layer (the surface opposite to the surface on which the coating layer is formed). The heat sealable resin layer is usually formed by an extrusion lamination method or a dry lamination method. The thermoplastic polymer forming the heat sealable resin layer may be any thermoplastic polymer as long as it can sufficiently exhibit sealant adhesiveness, and polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, and ionomer resins and the like can be used.
For the adhesive layer used in the present invention, a general-purpose adhesive for lamination can be used. For example, it is possible to use solvent (free) type, aqueous type, and hot melt type adhesives containing poly(ester) urethane-based, polyester-based, polyamide-based, epoxy-based, poly(meth)acrylic-based, polyethyleneimine-based, ethylene-(meth)acrylic acid-based, polyvinyl acetate-based, (modified) polyolefin-based, polybutadiene-based, wax-based, and casein-based materials and the like as a main component. Among them, a urethane-based or polyester-based material is preferable in consideration of moist heat resistance that can withstand retorting and flexibility that can follow the dimensional changes of each substrate. As a method for laminating the adhesive layer, for example, the adhesive layer can be coated by a direct gravure coating method, a reverse gravure coating method, a kiss coating method, a die coating method, a roll coating method, a dip coating method, a knife coating method, a spray coating method, a fountain coating method, and other methods. The coated amount after drying is preferably 1 to 8 g/m2 in order to exhibit sufficient adhesiveness after retorting. The coated amount is more preferably 2 to 7 g/m2, and still more preferably 3 to 6 g/m2. If the coated amount is less than 1 g/m2, it is difficult to bond the film on the entire surface, whereby the adhesive force decreases. If the coated amount is more than 8 g/m2 or more, it takes time to completely cure the film, and unreacted substances are apt to remain, whereby the adhesive force decreases.
Furthermore, in the laminated film of the present invention, at least one or more printed layers and other plastic substrates and/or paper substrates may be laminated between the inorganic thin film layer or the substrate film layer and the heat sealable resin layer, or on the outer side thereof.
As a printing ink for forming the printed layer, an aqueous or solvent-based resin-containing printing ink can be preferably used. Herein, examples of a resin used in the printing ink include an acrylic resin, a urethane-based resin, a polyester-based resin, a vinyl chloride-based resin, a vinyl acetate copolymer resin, and mixtures thereof. The printing ink may contain known additives such as an anti-static agent, a light blocking agent, an ultraviolet absorber, a plasticizer, a lubricant, a filler, a coloring agent, a stabilizer, a lubricant, an antifoaming agent, a cross-linking agent, an anti-blocking agent, and an antioxidant. The printing method of forming the printed layer is not particularly limited, and known methods such as an offset printing method, a gravure printing method, and a screen printing method may be used. For drying the solvent after printing, known drying methods such as hot wind drying, hot roll drying, and infrared drying may be used.
The laminated body of the present invention preferably has an oxygen transmission rate of 15 ml/m2·d·MPa or less under conditions of 23° C. and 65% RH before and after retorting from the viewpoint of exhibiting good gas barrier properties. Furthermore, by controlling composition and adhesion amount of the inorganic thin film layer, the oxygen transmission rate can be set to preferably 12.5 ml/m2·d·MPa or less, and more preferably 10 ml/m2·d·MPa or less. The oxygen transmission rate exceeding 15 ml/m2·d·MPa makes it difficult to cope with applications requiring high gas barrier properties. Meanwhile, if the oxygen transmission rate before and after retorting is less than 1 ml/m2·d·MPa in any case, the barrier performance is excellent, but a residual solvent is less likely to outwardly permeate the bag, whereby the amount of the residual solvent transferred to the contents may relatively increase, which is not preferable. The lower limit of the oxygen transmission rate is preferably 1 ml/m2·d·MPa or more.
The laminated body of the present invention preferably has a water vapor transmission rate of 2.0 g/m2·d or less under conditions of 40° C. and 90% RH before and after retorting from the viewpoint of exhibiting good gas barrier properties. Furthermore, by controlling composition and adhesion amount of the inorganic thin film layer, the water vapor transmission rate can be set to preferably 1.5 g/m2·d or less, and more preferably 1.0 g/m2·d or less. The water vapor transmission rate exceeding 2.0 g/m2·d·MPa makes it difficult to cope with applications requiring high gas barrier properties. Meanwhile, if the water vapor transmission rate before and after retorting is less than 0.1 g/m2, the barrier performance is excellent, but a residual solvent is less likely to outwardly permeate the bag, whereby the amount of the residual solvent transferred to the contents may relatively increase, which is not preferable. The lower limit of the water vapor transmission rate is preferably 0.1 g/m2·d or more.
The laminated body of the present invention preferably has a wet lamination strength of 1.0 N/15 mm or more, more preferably 1.5 N/15 mm or more, and still more preferably 2.0 N/15 mm or more under conditions of 23° C. and 65% RH before and after retorting. If the lamination strength is less than 1.0 N/15 mm, peeling occurs due to a flexing load or liquid contents, whereby the barrier properties may be deteriorated, or the contents may leak. Furthermore, hand tearability may be deteriorated.
Hereinafter, the present invention will be described in more detail by way of Examples, but is not limited to the examples described below. Various evaluations were performed by the following measurement methods.
(1) Intrinsic Viscosity (IV) of Raw Material Resin and Resin Constituting Substrate Film
A sample was vacuum-dried at 130° C. all day and all night, and then pulverized or cut. 80 mg of the obtained sample was accurately weighed, and heat-dissolved at 80° C. for 30 minutes in a mixed solution of phenol/tetrachloroethane=60/40 (volume ratio). The mixture was heat-dissolved at 80° C., and then cooled to normal temperature. The mixed solvent prepared at the above ratio was added in a measuring flask to adjust the total volume to 20 ml, followed by performing measurement at 30° C. (unit: dl/g). An Ostwald viscometer was used to measure the intrinsic viscosity.
(2) Content Rate of Terephthalic Acid and Isophthalic Acid Components Contained in Raw Material Polyester and Polyester Constituting Substrate Film
A sample solution was prepared by dissolving a raw material polyester resin or a polyester film in a solvent in which chloroform D (manufactured by Yurisoppu Co., Ltd.) and trifluoroacetic acid Dl (manufactured by Yurisoppu Co., Ltd.) were mixed at 10:1 (volume ratio). Then, NMR of protons in the prepared sample solution was measured using an NMR apparatus (nuclear magnetic resonance analyzer: GEMINI-200 manufactured by Varian) under the measurement conditions of a temperature of 23° C. and an integration number of 64. In the NMR measurement, the peak intensity of predetermined protons was calculated, and the content rates (mol %) of the terephthalic acid component and the isophthalic acid component in 100 mol % of acid components were calculated.
The thicknesses of films were measured in accordance with JIS K7130-1999 A method using a dial gauge.
Sampling was carried out in a width of 10 mm in the substrate film and marked lines were put at 200 mm interval at room temperature (27° C.). The interval of the marked lines (L0) was measured. Then, the film was sandwiched between papers, placed in a hot air oven controlled at a temperature of 150° C., and treated for 30 minutes. Thereafter, the sample was taken out, and the interval (L) of the marked lines was then measured to calculate a heat shrinkage rate from the following formula. Samples are collected for both a machine direction and a transverse direction.
Heat shrinkage rate (%)={(L0−L)/L0}×100
The refractive index (Nz) in the thickness direction was determined according to JIS K7142 using an Abbe's refractometer NAR-1T (manufactured by ATAGO Co., Ltd.). Sodium D ray was employed as a light source; a test piece having a refractive index of 1.74 was used; and methylene iodide was used as an intermediate liquid.
For laminated films (after lamination of thin films) obtained in Examples and Comparative Examples, a film thickness composition was measured by a calibration curve prepared in advance using an X-ray fluorescence analyzer (“ZSX100e” manufactured by Rigaku Corporation). The conditions of an excited X-ray tube were 50 kV and 70 mA.
In each of Examples and Comparative Examples, each laminated film obtained at the stage of laminating a coating layer on a substrate film was used as a sample. A test piece of 100 mm×100 mm was cut out from this sample. A coating layer was wiped with 1-methoxy-2-propanol or dimethylformamide. From a change in the mass of the film before and after wiping, the adhesion amount of the coating layer was calculated.
The surface hardness of the laminated film was measured with use of a dynamic ultra-microhardness tester (“DUH-211” manufactured by Shimadzu Corporation). Specifically, a diamond triangular pyramid indenter (Berkovich type) having an intercristal angle of 115° was used on the protective layer surface of the laminated film alone fixed and held on a glass plate with an adhesive, so as to perform a hardness measurement test by the loading-unloading test, and the obtained martens hardness was defined as the value of the surface hardness. Test conditions included a test force of 1.0 mN, a loading rate of 0.02 mN/second, and a holding time of 2 seconds. The value of the hardness measured under the present conditions was 0.3 μm or more as an indentation depth, which was sufficiently greater than the thickness of the coating layer or the inorganic thin film layer, and was interpreted to represent the surface hardness of the substrate.
The surface roughness of the laminated film was measured with use of a scanning probe microscope (SPM) (“SPM9700” manufactured by Shimadzu Corporation) (cantilever: OMCL-AC200TS available from Olympus Corporation was used, observation mode: phase mode). Specifically, an SPM image was obtained in a viewing angle of 2-μm square on the film surface. In the obtained image, inclination correction, which was a function of a software attached to the SPM, was used so as to perform inclination correction in X-, Y-, and Z-directions, and thereafter the value of an arithmetic average roughness was calculated. The arithmetic average roughness Ra was a value obtained by removing a surface undulation component longer than a predetermined wavelength from a cross-sectional curve by a high-pass filter, extracting only a reference length in the direction of the average line of a roughness curve obtained thereby from the roughness curve, taking an X axis in the direction of the average line of the extracted portion and a Y axis in the direction of a vertical magnification ratio, and two-dimensionally expanding a value obtained by the following formula when the roughness curve is represented by y=f(X).
Ra=1/L∫L0 |f(x)|dx L: reference length
The coefficient of static friction has and the coefficient of dynamic friction μd of the vapor-deposited surface and the non-vapor-deposited surface of the film were measured in a humidity atmosphere of 50% RH according to the ASTM-D-1894 method.
[Production of Laminated Bodies]
A nylon film (“N1100” manufactured by Toyobo Co., Ltd.) having a thickness of 15 μm was bonded onto the laminated body obtained in each of Examples and Comparative Examples by a dry lamination method using a urethane-based two-liquid-component curable adhesive (“Takelac (registered trademark) A525S” manufactured by Mitsui Chemicals, Inc. and “Takenate (registered trademark) A50”) were blended at a ratio of 13.5:1 (mass ratio)). Then, a non-stretched polypropylene film (“P1146” manufactured by Toyobo Co., Ltd.) having a thickness of 70 μm as a heat sealable resin layer was bonded onto the nylon film by a dry lamination method using the same urethane-based two-liquid-component curable adhesive as described above. The resultant was aged at 40° C. for 4 days to obtain a gas barrier laminated body for evaluation (hereinafter, sometimes referred to as “laminated body A”). Each of the thicknesses of the adhesive layers formed of the urethane based two-liquid-component curable adhesive after drying was about 4 μm.
The normal oxygen transmission rate of the laminated body produced in the above [Production of Laminated Bodies] was measured in an atmosphere of a temperature of 23° C. and a humidity of 65% RH using an oxygen transmission rate measurement apparatus (“OX-TRAN (registered trademark) 1/50” manufactured by MOCON) in accordance with JIS-K7126 B method. The oxygen transmission rate was measured in a direction in which oxygen permeated from the substrate film side to the heat sealable resin layer side of the laminated body.
Meanwhile, the laminated body produced in the above [Production of Laminated Bodies] was subjected to a wet heat treatment in which the laminated body was held in hot water at 130° C. for 30 minutes, and dried at 40° C. for 1 day (24 hours). The oxygen transmission rate (after retorting) of the obtained laminated body after the wet heat treatment was measured in the same manner as described above.
For the laminated bodies produced in the above [Production of Laminated Bodies], the normal water vapor transmission rate was measured in an atmosphere of a temperature of 40° C. and a humidity of 90% RH using a water vapor transmission rate measurement apparatus (“PERMATRAN-W 3/33 MG” manufactured by MOCON) in accordance with JIS-K 7129 B method. The water vapor transmission rate was measured in a direction in which water vapor permeated from the heat sealable resin layer side of the laminated body toward the substrate film side.
Meanwhile, the laminated body produced in the above [Production of Laminated Bodies] was subjected to a wet heat treatment in which the laminated body was held in hot water at 130° C. for 30 minutes, and dried at 40° C. for 1 day (24 hours). The water vapor transmission rate (after retorting) of the obtained laminated body after the wet heat treatment was measured in the same manner as described above.
The laminated body produced above was cut into a test piece having a width of 15 mm and a length of 200 mm, and a lamination strength (normal state) was measured using a Tensilon universal material testing machine (“Tensilon UMT-II-500 type” manufactured by Toyo Baldwin Co., Ltd.) under the conditions of a temperature of 23° C. and a relative humidity of 65%. In the measurement of a lamination strength, a tensile speed was set to 200 mm/min, and a strength was measured when water was applied between the laminated film layer and the heat sealable resin layer of each of the laminated films obtained in Examples and Comparative Examples, and peeling was performed at a peeling angle of 90 degrees.
Meanwhile, the laminated body produced as described above was subjected to retorting for 30 minutes in which the laminated body was held in pressurized hot water at a temperature of 130° C. Immediately thereafter, a test piece was cut out from the obtained laminated body after retorting in the same manner as described above, and a lamination strength (after retorting) was measured in the same manner as described above.
Regarding a film roll after winding when the laminated body described in each of Examples and Comparative Examples was subjected to vapor-deposition processing, the presence or absence of four items of wrinkles, acnes, winding deviation, and blocking was examined, and the film roll with no defect was evaluated as good, the film roll with any one defect was evaluated as average, and the film roll with two or more defects was evaluated as poor.
Hereinafter, coating liquids used in the present Examples and Comparative Examples will be described in detail. The coating liquids were used in Examples 1 to 7 and Comparative Example 1 to 5, and shown in Table 1.
[Carbodiimide-Based Cross-Linking Agent (A)]
As a carbodiimide-based cross-linking agent, commercially available “Carbodilite (registered trademark) SV-02” manufactured by Nisshinbo Chemical Inc.; solid content: 40%) was prepared.
[Oxazoline Group-Containing Resin (B)]
As an oxazoline group-containing resin, commercially available water-soluble oxazoline-group-containing acrylate (“EPOCROS (registered trademark) WS-300” manufactured by Nippon Shokubai Co., Ltd.; solid content: 10%) was prepared. The oxazoline group amount in this resin was 7.7 mmol/g.
[Acrylic Resin (C)]
As an acrylic resin, a commercially available acrylic ester copolymer emulsion having a concentration of 25% by mass (“Movinyl (registered trademark) 7980” manufactured by Nichigo-Movinyl Co. Ltd.) was prepared. The acid value (theoretical value) of the acrylic resin was 4 mgKOH/g.
[Urethane Resin (D)]
As a urethane resin, a commercially available polyester urethane resin dispersion (“Takelac (registered trademark) W605” manufactured by Mitsui Chemicals, Inc., solid content: 30%) was prepared. This urethane resin had an acid value of 25 mgKOH/g, and a glass transition temperature (Tg) of 100° C., which was measured by DSC. The proportion of its aromatic or aromatic-aliphatic diisocyanates was 55 mol % of the whole of its polyisocyanate components, the proportion being measured by 1H-NMR.
As a silane coupling agent, commercially available “KBM903 (registered trademark)” manufactured by Shin-Etsu Chemical Co., Ltd., solid content 100%) was prepared. In use, the silane coupling agent was diluted with water to obtain a 2% aqueous solution.
[Urethane Resin (F)]
In a four-neck flask equipped with a stirrer, a Dimroth condenser, a nitrogen introducing pipe, a silica gel drying pipe, and a thermometer, 143.95 parts by mass of methaxylylene diisocyanate, 25.09 parts by mass of 4,4′-methylenebis(cyclohexyl isocyanate), 28.61 parts by mass of ethylene glycol, 5.50 parts by mass of trimethylolpropane, 12.37 parts by mass of dimethylolpropionic acid, and 120.97 parts by mass of methyl ethyl ketone as a solvent were mixed. The mixture was stirred at 70° C. under a nitrogen atmosphere to confirm that the reaction solution had reached a predetermined amine equivalent. Next, the temperature of the reaction solution was decreased to 35° C., and 9.14 parts by mass of triethylamine was then added to the reaction solution to obtain a polyurethane prepolymer solution. Next, 794.97 parts by mass of water was added to a reaction vessel equipped with a homodisper allowing high-speed stirring, and the temperature was adjusted to 15° C. The polyurethane prepolymer solution was added thereto and dispersed in the water while stirred and mixed at 2000 min-1. An amine aqueous solution obtained by mixing 22.96 parts by mass of 2-[(2-aminoethyl)amino]ethanol and 91.84 parts by mass of water was added thereto, and then an amine aqueous solution obtained by mixing 2.38 parts by mass of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (product name; KBM-603 manufactured by Shin-Etsu Chemical Co., Ltd.) and 9.50 parts by mass of water was added thereto to perform a chain extension reaction. Thereafter, methyl ethyl ketone and a part of water were removed under reduced pressure to obtain a polyurethane dispersion (E) having a solid content of 25% by mass and an average particle diameter of 70 nm. The Si content (according to charge calculation) of the obtained polyurethane dispersion (D-1) was 1200 mg/1 kg, and the methaxylylene group content (according to charge calculation) was 32% by mass.
[Coating Liquid 1 Used for Coating Layer]
Materials were mixed at the following blending ratio to prepare a coating liquid (resin composition for coating layer).
[Coating Liquid 2 used for Coating Layer]
Materials were mixed at the following blending ratio to prepare a coating liquid (resin composition for coating layer).
[Coating Liquid 3 used for Coating Layer]
Materials were mixed at the following blending ratio to prepare a coating liquid (resin composition for coating layer).
[Coating Liquid 4 Used for Coating Layer]
Materials were mixed at the following blending ratio to prepare a coating liquid (resin composition for coating layer).
Hereinafter, a method for producing a laminated film used in each of Examples and Comparative Examples will be described. The laminated films were used in Examples 1 to 7 and Comparative Example 1 to 4, and shown in Table 1.
(Preparation of Polyester Resin Recycled from PET Bottles)
A recycled polyester raw material was obtained by washing PET bottles for beverages to remove foreign matters such as remaining beverage, thereafter melting flakes obtained by pulverizing the PET bottles by an extruder, further changing the filter with a filter having a smaller mesh size, then separating the fine foreign matters by filtration twice, and then separating the fine foreign matters by third filtration using a filter with the smallest mesh size of 50 μm. The obtained resin had a composition of terephthalic acid/isophthalic acid//ethylene glycol=97.0/3.0//100 (mol %), and the intrinsic viscosity of the resin was 0.70 dl/g. This resin was defined as a polyester A.
(Production of Substrate Film)
A substrate film was produced using a polyethylene terephthalate resin made of terephthalic acid//ethylene glycol=100//100 (mol %) as a polyester B and having an intrinsic viscosity of 0.62 dl/g, and a master batch containing, as a polyester C, the polyester B and 0.3% of amorphous silica having an average particle diameter of 1.5 μm. The respective raw materials were dried at 125° C. under reduced pressure of 33 Pa for 8 hours. A mixture obtained by mixing these raw materials so that A/B/C became 70/20/10 (weight ratio) was charged into a single screw extruder. The resin temperature was set to 280° C. from the extruder to a melt line, a filter, and a T-die. The resin temperature was set to 305° C. for 30 seconds from the starting point of a compression part of a screw of the extruder, and thereafter to 280° C. again.
The melt extruded out of the T-die was brought into close contact with a cooling roll to obtain an un-stretched sheet. Then, the un-stretched sheet was stretched (MD1) 1.41 times in the machine direction with rolls heated to 118° C. and having different circumferential speeds, and further stretched (MD2) 2.92 times in the machine direction with rolls heated to 128° C. and having different circumferential speeds. The vertically stretched sheet was introduced to a tenter, and one surface of the film was coated with the coating liquid 1 by a fountain bar coating method. The sheet was introduced to the tenter while being dried, preheated at 121° C., and thereafter transversely stretched 4.3 times at 131° C. Then, for heat setting, the sheet was subjected to a treatment at 180° C. without relaxation (0%) for 2.5 seconds (TS1), thereafter to a treatment at 231° C. with 5% of relaxation for 3.0 seconds (TS2), and further to a treatment at 222° C. without relaxation for 2.5 seconds (TS3). Then, the sheet was cooled in the same tenter at 120° C. for 6.0 seconds, and finally wound with a winder to obtain a biaxially stretched polyester film having a thickness of 12 μm.
Laminated films were similarly produced and evaluated except that the blending amounts of the polyesters A, B, and C or the coating liquids of the coating layer as shown in Table 1 were changed in preparing the substrate film layers described in Examples and Comparative Examples.
Hereinafter, a method for producing an inorganic thin film layer used in each of Examples and Comparative Examples will be described. The inorganic thin film layers were used in Examples 1 to 7 and Comparative Examples 1 to 5, and shown in Table 1.
(Formation of Inorganic Thin Film Layer M-1)
As an inorganic thin film layer M-1, aluminum oxide was vapor-deposited on the substrate film layer. In the method of vapor-depositing aluminum oxide on the substrate film layer, a film is set on the unwinding side of a continuous type vacuum vapor-deposition apparatus, caused to travel via a cooling metal drum, and wound. At this time, the pressure of the continuous type vacuum vapor-deposition apparatus was reduced to 10-4 Torr or less. Metal aluminum having a purity of 99.99% was loaded in a crucible made of alumina from the lower portion of the cooling drum. The metal aluminum was heated and evaporated. While oxygen was supplied into the vapor to perform an oxidization reaction, aluminum oxide was deposited onto the film to form an aluminum oxide film having a thickness of 10 nm.
<Formation of Inorganic Thin Film Layer M-2>
As an inorganic thin film layer M-2, a composite oxide layer of silicon dioxide and aluminum oxide was formed on a substrate film layer by an electron beam vapor-deposition method. Particulate SiO2 (purity: 99.9%) and Al2O3(purity: 99.9%) having a size of about 3 mm to 5 mm were used as a vapor-deposition source. The film thickness of the inorganic thin film layer (SiO2/Al2O3 composite oxide layer) in the film (inorganic thin film layer/coating layer-containing film) obtained as described above was 13 nm. The composition of the composite oxide layer was SiO2/Al2O3(mass ratio)=60/40.
As described above, laminated films including the coating layer and the inorganic thin film layer on the substrate film was produced. The obtained laminated films were subjected to evaluations. The results are shown in Table 2.
The present invention makes it possible to provide a laminated film which is excellent in gas barrier properties of an inorganic thin film layer and is excellent in barrier properties and adhesiveness even after a severe wet heat treatment such as retort sterilization while using a recycled material. Moreover, the laminated film of the present invention provides few processing steps, and can be easily produced, whereby a gas barrier film excellent in both economic efficiency and production stability and having homogeneous characteristics can be provided.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-027457 | Feb 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/005630 | 2/16/2021 | WO |
