Laser-printable film and packaging using same

Abstract

[Problem] To provide a film that can be subject to detailed printing by a laser, the film having high transparency and exceptional thickness variation. At the same time, to provide directly printed packaging in which the film is used. [Solution] A polyamide film characterized in having at least one layer that can be laser-printed upon, a pigment that enables printing by laser irradiation being contained within all the layers of the film in an amount of 100-3000 ppm inclusive, and the thickness variation in either the longitudinal direction or the width direction being 0.1-20% inclusive.

Description

[Technical field]

[0001] The present invention relates to a film suitable for use in packaging including markings such as printed characters, etc. In particular, the present invention relates to a polyamide-based film that can be printed with a laser, and also relates to packaging including corresponding lids and labels. [Background technology]

[0002] Conventionally, packaging has been used for distribution goods such as food, medicine, and industrial products. Many of these packaging not only protect the contents, but also display information about the product name, production date, raw materials, etc. As a means of such display, for example, as described in Patent Document 1, a label (tack label) in which an adhesive is applied to the back side of a base material that can be printed by ink or thermal transfer has been widely used. A tack label is attached to a release paper (backing paper) with information printed on the front side, which will be the display surface, in advance, and is peeled off from the backing paper and attached to the package when used. Since the backing paper after the tack label is attached is no longer needed, the amount of waste increases by the amount of label used. In addition, label users must have labels with different display contents depending on the type of content, and as the number of types of content increases, label management becomes complicated, and there is a risk of label misapplication. Furthermore, it is usually necessary to have extra inventory in case of a shortage of labels, and when the production and sale of the content ends, the label is discarded because it has no use. In this way, tack labels have various disadvantages.

[0003] In order to solve the above problems, Patent Document 2 discloses a thermal film having a thermal recording layer. The film of Patent Document 2 changes color due to heat, and therefore becomes a package with display performance by itself. Therefore, it is not necessary to use the above-mentioned tack label. In addition, by incorporating a printer such as a thermal printer into the process of making a package using a film such as that of Patent Document 2, bag making and displaying can be completed in one process, which contributes to labor saving and cost reduction. Due to these advantages, a method of printing directly on the package itself has become popular recently. However, if a thermal layer is provided on the base film, there is a concern that the thermal layer will peel off due to friction with the outside, so a protective layer is usually provided on top of the thermal layer (on the surface side). Coating is widely used as a means of providing these functional layers. Coating at least involves the processes of application, drying, and winding, so the number of processes increases for each functional layer, and productivity decreases. Furthermore, since these functional layers contain particles, there is also a problem that transparency decreases depending on the layer thickness.

[0004] Meanwhile, in recent years, in addition to the above-mentioned inks and heat, laser-triggered technologies have become widespread as display (printing) means. For example, Patent Document 3 discloses a laser-printable multilayer laminate film in which the printing layer includes a layer made of an ink composition that can be printed with laser light. By using this film, the part irradiated with the laser changes color and becomes printable. However, a multilayer laminate film such as the film in Patent Document 3, like the film in Patent Document 2, needs to have a printing layer on the film substrate, so the problems of layer peeling and reduced productivity have not been solved.

[0005] Patent Document 4 discloses an additive for laser marking made of bismuth oxide. By kneading this additive into plastic, the part irradiated with the laser changes color, making it possible to print. Normally, plastic alone does not react to lasers, but this additive is excited by the energy of the laser and can discolor the plastic. Since the additive exists inside the film, it is useful in that peeling of the functional layer, which occurs with coating, is unlikely to occur. However, since the additive is a metal particle, there remains a problem of reducing the transparency of the film, as with the above coating. The present inventors also discovered a problem that when particles are kneaded into the film, thickness unevenness becomes large when the film is stretched. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-362027 A [Patent Document 2] JP 2017-209847 A [Patent Document 3] JP 2017-196896 A [Patent Document 4] International Publication No. 2014 / 188828 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to solve the problems of the prior art as described above. That is, the present invention aims to provide a film that has high transparency, is excellent in thickness unevenness, and allows clear printing by laser. At the same time, the present invention aims to provide a package that is directly printed using this film. [Means for solving the problem]

[0008] The present invention comprises the following configurations. 1. It has at least one layer that can be printed by laser irradiation, A polyamide film characterized in that the entire film layer contains 100 ppm to 3000 ppm of a pigment that enables printing by laser irradiation, the haze is 1% to 30%, and the thickness unevenness in either the longitudinal direction or the transverse direction is 0.1% to 20%. 2. The polyamide film according to 1., characterized in that the pigment that can be printed by laser irradiation contains a metal, and the metal contains at least one of the following elements: bismuth, gadolinium, neodymium, titanium, antimony, tin, or aluminum in the form of a simple substance or an oxide thereof. 3. The polyamide film according to either 1 or 2, wherein the thickness of the layer that can be printed by laser irradiation is from 5 μm to 100 μm. 4. The polyamide film according to any one of 1 to 3, wherein the color b* value is from -1 to 6. 5. The polyamide film according to any one of 1 to 4, further comprising a layer which cannot be printed by laser irradiation on at least one of the layers adjacent to the layer which can be printed by laser irradiation. 6. A polyamide film according to any one of 1. to 5., characterized in that the heat shrinkage rate after exposure to 140° C. hot air for 30 minutes in either the longitudinal direction or the width direction is −0.5% or more and 10% or less. 7. A packaging body including a lid material or a label using the polyamide film according to any one of 1. to 6. 8. The packaging material according to claim 7, characterized in that at least a portion of the packaging material is printed. Effect of the Invention

[0009] The film of the present invention has high transparency, is excellent in thickness unevenness, and can be clearly printed by laser. At the same time, it is an object of the present invention to provide a package directly printed with this film. [Brief description of the drawings]

[0010] [Figure 1] Image printed by irradiating the film of Example 1 with a laser DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The polyamide film of the present invention will now be described. The polyamide film of the present invention has at least one layer that can be printed by laser irradiation, and has the following preferred characteristics and configuration.

[0012] 1. Raw materials that make up the film 1.1. Pigments for laser marking In order to make the film of the present invention laser printable, it is necessary to add a pigment (hereinafter, sometimes simply referred to as pigment) that has the function of discoloring the film by laser irradiation. Usually, the polyamide resin constituting the film itself hardly reacts to laser light, so it cannot be printed by laser irradiation. The pigment is excited by the energy of the laser light and carbonizes the surrounding polyamide resin (preferable conditions for laser irradiation will be described later). In addition to carbonizing the polyamide resin, some types of pigments themselves change to black. These single or combined color changes make it possible to print on the film. Considering the accuracy of printing on the film, it is preferable to use a pigment that also changes color by itself.

[0013] The type of pigment may be any of the metals or metal oxides of bismuth, gadolinium, neodymium, titanium, antimony, tin, and aluminum. The particle size of the pigment is preferably 0.1 μm or more and 10 μm or less. If the particle size of the pigment is less than 0.1 μm, the color change during laser irradiation may be insufficient. If the particle size exceeds 10 μm, the haze of the film is likely to exceed 30% and the color b value is likely to exceed 2. The particle size is more preferably 0.5 μm or more and 9 μm or less. As pigments that satisfy these conditions, "TOMATEC COLOR" (manufactured by Tokan Material Technology Co., Ltd.), "Iriotec (registered trademark)" (manufactured by Merck Performance Materials Co., Ltd.), etc. are commercially available, and these can be used preferably.

[0014] The amount of pigment added to the laser printable layer must be between 100 ppm and 3000 ppm. If the amount of pigment added is less than 100 ppm, the laser print density will be insufficient, which is undesirable. On the other hand, if the amount of pigment added exceeds 3000 ppm, the film's haze, color value, and thickness unevenness will tend to exceed the specified range, which is undesirable. The effect of adding pigment on haze and color value occurs not only because the pigment itself is colored, but also because the pigment particles scatter light. In addition, when the film is stretched, the thickness unevenness of the film worsens if the film contains pigment particles. The influence on the thickness unevenness of the film is considered to be due to the fact that the stretching stress decreases when the film containing the pigment particles is stretched. The amount of pigment added is more preferably 150 ppm or more and 2950 ppm or less, and even more preferably 200 ppm or more and 2900 ppm or less. In the present invention, the amount of pigment required to be added when calculated per all layers of the film may be 100 ppm or more and 3000 ppm or less. When layers other than the laser-printed layer are provided, the amount of pigment calculated per all layers of the film is calculated to be less than the amount of the laser-printed layer. However, in the present invention, the majority (50% or more) of the total layer thickness is composed of the laser-printed layer, and if the thickness of the other layers is increased, the laser-printed layer becomes too thin in comparison, sacrificing printing accuracy, so that the amount of pigment calculated per all layers of the film may be close to the amount of pigment contained in the laser-printed layer.

[0015] The method of blending the laser pigment into the polyamide resin constituting the film of the present invention can be, for example, added at any stage of resin production. In addition, a method of blending a slurry of particles dispersed in a solvent with a polyamide-based resin raw material using a vented kneading extruder and a method of blending particles and polyamide using a kneading extruder are also included. Among these, a method of blending particles and polyamide using a kneading extruder (master batching) is preferred.

[0016] 1.2.Types of polyamide raw materials The polyamide raw material constituting the film of the present invention is not particularly limited, and can be freely used within the scope of the present invention. Examples of the polyamide raw material include one resin selected from polycapramide (nylon 6), polyhexamethylene adipamide (nylon 66), caprolactam / lauryl lactam copolymer (nylon 6 / 12), caprolactam / hexamethylene diammonium adipate copolymer (nylon 6 / 66), ethylene ammonium adipate / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon 6 / 66 / 610), metaxylylene diamine and adipic acid polymer (MXD-6), and hexamethylene isophthalamide / terephthalamide copolymer (amorphous nylon), or a mixed resin in which two or more of these are mixed. In addition, an adhesive modification layer can be provided on the surface of the film made of the above-mentioned resins. Examples of materials for the adhesion modifying layer include acrylic resins, water-soluble or water-dispersible polyester resins, and hydrophobic polyester resins graft-copolymerized with acrylic resins.

[0017] The lower limit of the relative viscosity (RV) of the polyamide resin as a raw material is preferably 2.2, more preferably 2.3. If it is less than the above, the crystallization rate may be too fast, making biaxial stretching difficult. On the other hand, the upper limit of the RV of the polyamide resin is preferably 4, more preferably 3.9. If it exceeds the above, the load on the extruder may become too high, and productivity may decrease. The relative viscosity in the present invention refers to the value measured at 25°C using a solution in which 0.5 g of the polymer is dissolved in 50 ml of 97.5% sulfuric acid.

[0018] 1.3.Additives other than laser pigments Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, coloring inhibitors, ultraviolet absorbers, and lubricants (antiblocking agents), may be added to the polyamide resin constituting the film of the present invention as necessary. Of these, it is preferable to add a lubricant that improves the slipperiness of the film to at least the outermost layer of the film. As the lubricant, any one may be selected, such as fine particles of silica or the like, or low molecular weight compounds such as fatty acid amides, alkyl sulfonates, stearic acids, and erucic acid amides. As a method for incorporating additives into the polyamide resin constituting the film of the present invention, for example, they can be added at any stage in the production of the polyamide resin, but a method in which the additives and polyamide are blended using a kneading extruder is preferred.

[0019] 2. Film layer structure 2.1. Layer configuration The film of the present invention must have at least one layer that can be printed by laser irradiation (hereinafter referred to as laser printable layer) containing the pigment described in 1.1. "Pigment for laser marking". The layer structure of the film may be a single layer of only the laser printable layer, or layers other than the laser printable layer may be laminated. As described above, laser printing is achieved by carbonizing the polyamide resin that constitutes the laser printable layer. Therefore, if the film has a single layer structure of only the laser printable layer, the printed part tends to feel rough to the touch when touched with a finger or the like. Therefore, it is preferable to laminate a layer that does not react to laser irradiation on at least one side of the laser printable layer, since this makes it difficult for differences in the touch caused by the laser printing to occur. The most preferable layer structure is a two-type three-layer structure in which the laser printable layer is sandwiched (as the central layer) between layers that do not react to laser irradiation. The film of the present invention may also be provided with a layer that has been subjected to corona treatment, coating treatment, flame treatment, etc., in order to improve the printability and slipperiness of the film surface, and any of these may be provided within the scope of the present invention. When the film has a layer structure of two types and three layers, the central layer is a laser printable layer, and the outermost layer can be made to contain a lubricant or be subjected to corona treatment, for example, so that each layer has a different function.

[0020] In addition, the film of the present invention may be provided with characters or patterns other than the printing by laser irradiation in order to improve the design of the packaging material. Known materials such as ink for gravure printing and ink for flexographic printing can be used as materials for forming these characters and patterns. The number of printed layers may be one layer or multiple layers. In order to improve the design by printing in multiple colors, it is preferable to have a printed layer consisting of multiple layers. The printed layer may be located either on the outermost layer or in an intermediate layer.

[0021] 2.2.Thickness of laser marking layer The thickness of the laser-printed layer is preferably 5 μm or more and 100 μm or less. If the thickness of the laser-printed layer is less than 5 μm, the print density when irradiated with laser light decreases, making the characters difficult to see, which is not preferable. On the other hand, if the thickness of the laser-printed layer exceeds 100 μm, the haze and color value tend to exceed the specified range, which is not preferable. The thickness of the laser-printed layer is more preferably 10 μm or more and 95 μm or less, and even more preferably 15 μm or more and 90 μm or less.

[0022] 3. Film characteristics 3.1. Haze The film of the present invention preferably has a haze of 1% or more and 30% or less. If the haze exceeds 30%, the transparency of the film is lost, and not only the visibility of the contents is poor when the film is used as a package, but also the characters obtained by laser irradiation are difficult to see, which is not preferable. In contrast to the conventionally disclosed technology of discoloration by simple laser marking, the film of the present invention requires high clarity because the characters obtained by laser irradiation must be readable. The haze is more preferably 25% or less, and even more preferably 20% or less. On the other hand, the lower the haze value, the more preferable it is because the transparency is improved, but in the technical level of the present invention, the lower limit is 1%, and even if the lower limit is 2%, it is sufficient for practical use.

[0023] 3.2.Color b* value The film of the present invention preferably has a color b* value of -1 or more and 6 or less. The color b* value represents the yellowness of the film, and the higher the value, the greater the yellowness. If the color b* value exceeds 6, the color tone of the film will be more yellowish. If such a film is used, for example, after printing processing, the color tone of the print will be more yellow than originally expected, and the design will be deteriorated, which is undesirable. The color b* value is more preferably 5.8 or less, and even more preferably 5.6 or less. On the other hand, the color b* value has a lower limit of -1 in the technical level of the present invention, and even if the lower limit is -0.8, it is sufficient for practical use.

[0024] 3.3. Thickness unevenness The thickness unevenness of the film of the present invention is preferably 0.1% or more and 20% or less in either the longitudinal direction or the transverse direction. The thickness unevenness here refers to the value obtained by dividing the difference between the maximum value and the minimum value by the average value when the thickness of the film is measured over an arbitrary length using a continuous contact thickness meter. The smaller the thickness unevenness value, the better the thickness accuracy. If the thickness unevenness exceeds 20%, it is undesirable because it is likely to cause winding defects such as wrinkles, sagging, and unevenness when wound into a roll. The thickness unevenness is more preferably 18% or less, and even more preferably 16% or less. On the other hand, the lower limit of the thickness unevenness is 0.1% in the technical level of the present invention. A lower limit of the thickness unevenness of 1% is sufficient. It is more preferable that the thickness unevenness is within the above-mentioned range in both the longitudinal direction and the transverse direction.

[0025] 3.4.Thickness The total thickness of the film of the present invention is preferably 8 μm or more and 200 μm or less. If the film thickness is thinner than 8 μm, the film is difficult to handle and difficult to handle during secondary processing such as printing, which is not preferable. On the other hand, the film thickness may exceed 200 μm, but is not preferable because the weight of the film used increases and the chemical cost increases. The film thickness is more preferably 13 μm or more and 195 μm or less, and even more preferably 18 μm or more and 190 μm or less.

[0026] 3.5.Heat shrinkage rate The heat shrinkage rate of the film of the present invention after exposure to 140°C hot air for 30 minutes in either the longitudinal or transverse direction is preferably -0.5% or more and 10% or less. If the heat shrinkage rate exceeds 10%, the film is likely to deform during processing including heating such as heat sealing, which is not preferable. The upper limit of the heat shrinkage rate is more preferably 9.8% or less, and more preferably 9.6% or less. On the other hand, the lower the heat shrinkage rate, the more preferable it is, but the lower limit is -0.5% according to the technical level of the present invention. Even if the lower limit of the heat shrinkage rate is -0.3%, it is sufficient for practical use. It is more preferable that the heat shrinkage rate is within the above range in both the longitudinal and transverse directions.

[0027] 4. Film manufacturing conditions 4.1. Raw material mixing and supply In producing the polyamide film of the present invention, as described above in "1. Raw materials constituting the film", it is necessary to make the film contain a pigment that can be printed by laser irradiation. Since it is preferable to use the pigment as a master batch, two or more raw materials are usually mixed. Conventionally, when two or more raw materials are mixed and fed into an extruder, there is a problem that the supply of raw materials varies (segregates), which worsens the thickness unevenness. In order to prevent this and to make the thickness unevenness within the specified range in the present invention, it is preferable to install an agitator in the piping or hopper directly above the extruder to uniformly mix the raw materials and then melt extrude them.

[0028] 4.2.Melt extrusion The film of the present invention can be obtained by supplying the raw materials described in 1. "Raw materials constituting the film" to an extruder by the method described in 4.1. "Mixing and supplying raw materials" above, melt-extruding the raw materials from the extruder to form an unstretched film, and stretching it by a predetermined method described below. When the film includes a laser-printed layer and other layers, the timing of laminating each layer may be either before or after stretching. When laminating before stretching, it is preferable to adopt a method in which the resins that are the raw materials for each layer are melt-extruded by separate extruders and joined using a feed block or the like in the middle of the resin flow path. When laminating after stretching, it is preferable to adopt a lamination method in which films formed separately are bonded together with an adhesive, or an extrusion lamination method in which a molten polyamide resin is poured on the surface layer of a single or laminated film to laminate it. From the viewpoint of productivity, a method in which each layer is laminated before stretching is preferable.

[0029] Known methods can be used for melt extrusion of raw material resin, and a method using an extruder equipped with a barrel and a screw is preferred. Any existing method such as a T-die method or a tubular method can be used for extrusion. The extrusion temperature is preferably 220°C or more and 350°C or less. If the extrusion temperature is less than 220°C, the melt viscosity of the polyamide resin becomes too high, the extrusion pressure increases, and the filter in the melt line is deformed, which is not preferred. If the heating temperature exceeds 350°C, the thermal decomposition of the resin progresses, and breakage is likely to occur during stretching, which is not preferred.

[0030] In addition, a higher shear rate when the resin is discharged from the die mouth is preferable because it reduces thickness unevenness in the width direction of the film (especially the maximum concave portion). A higher shear rate stabilizes the pressure when the resin is discharged from the T-die outlet. The preferred shear rate is 100 sec -1 More preferably, 150 sec -1 More than 170 sec, especially preferred -1 That's all. A higher draft ratio is preferable because it reduces thickness unevenness in the longitudinal direction, but if the draft ratio is too high, resin residue will adhere to the resin outlet of the die, reducing productivity, so a draft ratio that is too high is not preferable. The shear rate at the die outlet can be calculated using the following formula (1). γ=6Q / (W×H 2 ) ···Formula (1) γ: Shear rate (sec -1 ) Q: Amount of raw material discharged from the extruder (cm 3 / sec) W: width of the die outlet opening (cm) H: Length of the die outlet opening (lip gap) (cm)

[0031] Thereafter, the film melted by extrusion is quenched to obtain an unstretched film. As a method for quenching the molten resin, a method in which the molten resin is cast from a die onto a rotating drum and quenched and solidified to obtain a substantially unoriented resin sheet can be suitably adopted. The film may be produced by any of the following methods: non-stretching, uniaxial stretching (stretching in at least one of the longitudinal (length) direction and the transverse (width) direction), and biaxial stretching. The following description focuses on the sequential biaxial stretching method of longitudinal stretching and transverse stretching, in which longitudinal stretching is carried out first and transverse stretching is then carried out.

[0032] 4.3. First (longitudinal) stretching For stretching in the first direction (longitudinal or longitudinal direction), the unstretched film may be introduced into a longitudinal stretching machine in which a plurality of roll groups are arranged in series. For longitudinal stretching, it is preferable to preheat the film with a preheating roll until the film temperature reaches 30°C to 150°C. If the film temperature is lower than 30°C, it is difficult to stretch the film when stretched in the longitudinal direction, and breakage is likely to occur, which is not preferable. If the film temperature is higher than 150°C, the film is likely to stick to the roll, and the film is likely to wrap around the roll or the roll is likely to become dirty due to continuous production, which is not preferable. In addition, if the temperature is higher than 150°C, the film will crystallize, and it will also be difficult to stretch the film when stretched in the longitudinal direction, and breakage may occur. The film temperature on the preheating roll is more preferably 35°C to 145°C, and even more preferably 40°C to 140°C. When the film temperature reaches 30°C to 150°C, the film is stretched longitudinally. The longitudinal stretching ratio is preferably 1 to 10 times. Since 1 times means that no longitudinal stretching is performed, the longitudinal stretching ratio is 1 to obtain a uniaxially stretched film, and 1.1 times or more is required to obtain a biaxially stretched film. If the longitudinal stretching ratio is 1.1 times or more, the film can be oriented in the longitudinal direction to increase its mechanical strength. On the other hand, the upper limit of the longitudinal stretching ratio can be any number of times, but if the longitudinal stretching ratio is too high, the film becomes difficult to stretch transversely and breaks easily, so it is preferably 5 times or less. The longitudinal stretching ratio is more preferably 1.5 times to 4.5 times, and even more preferably 2 times to 4 times.

[0033] 4.4.Second (lateral) stretching After the first (longitudinal) stretching, the film is preferably transversely stretched at a stretch ratio of about 3 to 6 times at 30° C. to 180° C. in a tenter while both ends in the width direction (direction perpendicular to the longitudinal direction) of the film are held by clips. Before the transverse stretching, it is preferable to preheat the film, and the preheating may be performed until the film surface temperature reaches 25° C. to 175° C. As with longitudinal stretching, if the transverse stretching ratio is 1.1 times or more, molecular orientation can be imparted to the film in the width direction to increase the mechanical strength. The upper limit of the transverse stretching ratio can be any number of times, but if the stretching ratio is too high, transverse stretching becomes difficult and breakage is likely to occur, so it is preferably 6 times or less. The transverse stretching ratio is more preferably 3.5 times or more and 5.5 times or less, and even more preferably 4 times or more and 5 times or less. After the transverse stretching, it is preferable to pass the film through an intermediate zone where no active heating operation is performed. Since the temperature in the next final heat treatment zone is higher than that in the transverse stretching zone of the tenter, if an intermediate zone is not provided, the heat (hot air itself or radiant heat) from the final heat treatment zone will flow into the transverse stretching process. In this case, the temperature in the transverse stretching zone is not stable, and not only will the thickness unevenness of the film easily exceed 25%, but physical properties such as the thermal shrinkage rate will also vary. Therefore, it is preferable to pass the film after the transverse stretching through the intermediate zone for a predetermined time and then perform the final heat treatment. In this intermediate zone, it is important to block the accompanying flow caused by the running of the film and the hot air from the transverse stretching zone and the final heat treatment zone so that when a strip of paper is hung down without the film passing through it, the paper hangs down almost completely in the vertical direction. The passing time through the intermediate zone is sufficient for about 1 to 5 seconds. If it is shorter than 1 second, the length of the intermediate zone is insufficient and the heat blocking effect is insufficient. On the other hand, it is preferable for the intermediate zone to be long, but if it is too long the equipment will become large, so about 5 seconds is sufficient.

[0034] 4.5.Heat Treatment After passing through the intermediate zone, the film is preferably heat-treated at 130°C or more and 250°C or less in the heat treatment zone. Heat treatment promotes crystallization of the film, which makes it easier to reduce the heat shrinkage rate caused in the stretching process. If the heat treatment temperature is less than 130°C, it is difficult to keep the heat shrinkage rate at 10% or less, which is not preferred. On the other hand, if the heat treatment temperature exceeds 250°C, it is unpreferable because the haze tends to exceed 30%. The heat treatment temperature is more preferably 135°C or more and 245°C or less, and even more preferably 140°C or more and 240°C or less.

[0035] The time to pass through the heat treatment zone is preferably 2 to 20 seconds. If the time is less than 2 seconds, the film will pass through the heat treatment zone before the surface temperature of the film reaches the set temperature, making the heat treatment meaningless. The longer the time to pass through, the greater the effect of the heat treatment, so a time of 5 seconds or more is more preferable. However, if the time to pass through is to be longer, the equipment will become larger, so for practical purposes, a time of 20 seconds or less is sufficient. During heat treatment, the thermal shrinkage in the width direction can be reduced by shortening the distance between the clips of the tenter at any desired ratio (relaxation in the width direction). Therefore, in the final heat treatment, it is preferable to perform relaxation in the width direction in the range of 0% to 20% (a relaxation rate of 0% means that no relaxation is performed). Although the higher the relaxation rate in the width direction, the lower the shrinkage in the width direction, the upper limit of the relaxation rate (shrinkage rate in the width direction of the film immediately after transverse stretching) is determined by the raw material used, the stretching conditions in the width direction, and the heat treatment temperature, so relaxation cannot be performed beyond this limit. In the film of the present invention, the upper limit of the relaxation rate in the width direction is 20%. In addition, during heat treatment, it is also possible to shorten the distance between the clips in the longitudinal direction at any desired ratio (relaxation in the longitudinal direction).

[0036] 4.6. Cooling After passing through the heat treatment zone, the film is preferably cooled in a cooling zone using cooling air at 10° C. to 30° C. for a passage time of 2 to 20 seconds. Then, both ends of the film are cut and removed while being wound up to obtain a film roll.

[0037] 5.Gas barrier layer The film of the present invention may be provided with a gas barrier layer mainly made of an inorganic thin film. In the following description, the film of the present invention provided with a gas barrier layer is referred to as a "gas barrier layer laminate."

[0038] 5.1. Characteristics of gas barrier layer laminate 5.1.1.Water vapor transmission rate The gas barrier laminate using the film of the present invention has a water vapor permeability of 0.1 [g / (m 2 ·d)] or more than 5[g / (m 2 The water vapor permeability is preferably 5 [g / (m 2 · d)] is not preferable because when used as a package containing contents, the shelf life of the contents will be shortened. On the other hand, the water vapor permeability is 0.1 [g / (m 2 If the gas barrier properties are less than 0.1 [g / (m d)], the shelf life of the contents will be longer, which is preferable. However, the current state of the art requires a gas barrier properties of less than 0.1 [g / (m d)]. 2 The lower limit of water vapor permeability is 0.2 [g / (m 2 ·d)] is sufficient for practical use. The upper limit of water vapor permeability is 4.8 [g / (m 2 ·d)] is preferable, and 4.6 [g / (m 2 It is more preferable that the above formula (d) is used.

[0039] 5.1.2.Oxygen permeability The gas barrier laminate using the film of the present invention has an oxygen permeability of 0.05 [cc / (m 2 ·d·atm)] or more 4[cc / (m 2 The oxygen permeability is preferably 4 [cc / (m 2 ·d·atm)] is undesirable because it shortens the shelf life of the contents. On the other hand, if the oxygen permeability is 0.05 [cc / (m 2If the oxygen permeability is less than 0.05 [cc / (m 2 The lower limit of oxygen permeability is 0.05 [cc / (m 2 ·d·atm)] is sufficient for practical use. The upper limit of oxygen permeability is 3.8 [cc / (m 2 d atm)], and 3.6 [cc / (m 2 It is more preferable that the sintering temperature is 100°C or less.

[0040] 5.2. Raw material type and composition of gas barrier layer The raw material type of the gas barrier layer is not particularly limited, and conventionally known materials can be used, and can be appropriately selected according to the purpose to satisfy the desired gas barrier properties, etc. Examples of raw material types of the gas barrier layer include metals such as silicon, aluminum, tin, zinc, iron, and manganese, and inorganic compounds containing one or more of these metals, and examples of the corresponding inorganic compounds include oxides, nitrides, carbides, and fluorides. These inorganic substances or inorganic compounds may be used alone or in combination. In particular, silicon oxide (SiOx) and aluminum oxide (AlOx) are preferably used alone (monomeric body) or in combination (binary body) because the transparency of the film provided with the gas barrier layer can be improved. When the inorganic compound component is composed of a binary body of silicon oxide and aluminum oxide, the content of aluminum oxide is preferably 20% by mass or more and 80% by mass or less, and more preferably 25% by mass or more and 70% by mass or less. When the content of aluminum oxide is 20% by mass or less, the density of the gas barrier layer decreases, and the gas barrier properties may decrease, which is not preferable. Furthermore, if the content of aluminum oxide is 80 mass % or more, the flexibility of the gas barrier layer decreases, making it more susceptible to cracking, which may result in a decrease in gas barrier properties, which is undesirable. The oxygen / metal element ratio of the metal oxide used in the gas barrier layer is preferably 1.3 or more and less than 1.8, since this reduces the variation in gas barrier properties and ensures consistently excellent gas barrier properties. The oxygen / metal element ratio can be determined by measuring the amounts of oxygen and metal elements by X-ray photoelectron spectroscopy (XPS) and calculating the oxygen / metal element ratio.

[0041] 5.3.Method of forming gas barrier layer The method of forming the gas barrier layer is not particularly limited, and known manufacturing methods can be adopted as long as the object of the present invention is not impaired. Among known manufacturing methods, it is preferable to adopt a vapor deposition method. Examples of vapor deposition methods include PVD methods (physical vapor deposition methods) such as vacuum deposition, sputtering, and ion plating, or CVD (chemical vapor deposition). Among these, vacuum deposition and physical vapor deposition are preferable, and vacuum deposition is particularly preferable from the viewpoint of production speed and stability. As a heating method in the vacuum deposition method, resistance heating, high-frequency induction heating, electron beam heating, etc. can be used. In addition, oxygen, nitrogen, water vapor, etc. may be introduced as a reactive gas, or reactive vapor deposition using means such as ozone addition and ion assist may be used. In addition, the film formation conditions may be changed as long as the object of the present invention is not impaired, such as applying a bias to the substrate, raising or cooling the substrate temperature, etc. The method for forming a gas barrier layer by the vacuum deposition method is described below. When forming a gas barrier layer, the film of the present invention is transported to a gas barrier layer manufacturing apparatus via a metal roll. An example of the configuration of the gas barrier layer manufacturing apparatus includes an unwinding roll, a coating drum, a winding roll, an electron beam gun, a crucible, and a vacuum pump. The film is set on the unwinding roll, passes through the coating drum, and is wound up by the winding roll. The film pass line (inside the gas barrier layer manufacturing apparatus) is depressurized by a vacuum pump, and the inorganic material set in the crucible is evaporated by a beam emitted from an electron gun and is deposited on the film passing through the coating drum. During deposition of the inorganic material, heat is applied to the film, and tension is also applied between the unwinding roll and the winding roll. If the temperature applied to the film is too high, not only does the film undergo large thermal shrinkage, but it also becomes softer, making it more likely to undergo elongation deformation due to tension. Furthermore, the temperature drop (cooling) of the film after the deposition process becomes large, and the amount of shrinkage (different from thermal shrinkage) after expansion becomes large, which is undesirable because cracks occur in the gas barrier layer and it becomes difficult to achieve the desired gas barrier properties. On the other hand, the lower the temperature applied to the film, the more preferable it is because deformation of the film is suppressed, but the amount of evaporation of the inorganic material decreases, which reduces the thickness of the gas barrier layer, and there is a concern that the desired gas barrier properties may not be achieved. The temperature applied to the film is preferably 100°C or higher and 180°C or lower, more preferably 110°C or higher and 170°C or lower, and even more preferably 120°C or higher and 160°C or lower.

[0042] 6. Overcoat layer 6.1.Types of overcoat layers The film of the present invention or the gas barrier laminate using the film of the present invention (collectively referred to as the base film in this section 6.) may be provided with an overcoat layer for the purpose of improving scratch resistance, further gas barrier properties, etc., on top of the gas barrier layer mentioned in "5. Gas Barrier Layer" above. The type of overcoat layer is not particularly limited, but a conventionally known material such as a composition consisting of a urethane resin and a silane coupling agent, a compound consisting of an organosilicon and its hydrolyzate, or a water-soluble polymer having a hydroxyl group or a carboxyl group can be used, and can be appropriately selected according to the purpose to satisfy the desired gas barrier properties, etc. In addition, the overcoat layer may contain one or more additives for the purpose of imparting antistatic properties, UV absorbency, coloring, thermal stability, slip properties, etc., within the scope of the present invention, and the types and amounts of the additives can be appropriately selected depending on the desired purpose.

[0043] 6.2. Method for forming overcoat layer When forming the overcoat layer, the substrate film is transported to a coating facility via a metal roll. Examples of the equipment configuration include an unwinding roll, a coating step, a drying step, and a winding step. During overcoating, the laminate set on the unwinding roll is passed through a metal roll and undergoes a coating step and a drying step, and is finally guided to a winding roll. The coating method is not particularly limited, and a conventionally known method such as a gravure coating method, a reverse coating method, a dipping method, a low coating method, an air knife coating method, a comma coating method, a screen printing method, a spray coating method, a gravure offset method, a die coating method, and a bar coating method can be adopted and appropriately selected according to the desired purpose. Among these, the gravure coating method, the reverse coating method, and the bar coating method are preferred from the viewpoint of productivity. As the drying method, one or more heating methods such as hot air drying, hot roll drying, high frequency irradiation, infrared irradiation, and UV irradiation can be used in combination. In the drying process, the substrate film is heated and tension is applied between metal rolls. If the temperature at which the substrate film is heated in the drying process is too high, not only will the substrate film undergo large thermal shrinkage, but it will also soften, making it easier for elongation deformation due to tension to occur, and cracks will easily occur in the gas barrier layer of the substrate film. Furthermore, the temperature drop (cooling) of the laminate after the drying process will be large, and the amount of shrinkage (different from thermal shrinkage) after expansion will be large accordingly, which is undesirable because cracks will occur in the gas barrier layer and overcoat layer, making it difficult to achieve the desired gas barrier properties. On the other hand, the lower the temperature at which the substrate film is heated, the more preferable it is because deformation of the substrate film is suppressed, but the solvent of the coating liquid will be difficult to dry, which raises concerns that the desired gas barrier properties will not be achieved. The temperature at which the substrate film is heated is preferably 60°C or higher and 200°C or lower, more preferably 80°C or higher and 180°C or lower, and even more preferably 100°C or higher and 160°C or lower.

[0044] 7.Lamination with other films The polyamide-based film of the present invention can be laminated with another polyamide-based film or a film made of another material, as long as it does not deviate from the gist of the present invention. The resin type of the film made of another material is not particularly limited, and examples thereof include polyolefin resin, polyester resin, polystyrene resin, etc., and may contain these in a composite form. In addition, the film to be laminated with the polyamide-based film of the present invention may include a gas barrier layer in at least a part. The raw material type of the gas barrier layer is not particularly limited, and conventionally known materials can be used, and can be appropriately selected according to the purpose to satisfy the desired gas barrier properties, etc. Examples of the raw material type of the gas barrier layer include metals such as silicon, aluminum, tin, zinc, iron, and manganese, and inorganic compounds containing one or more of these metals, and examples of the corresponding inorganic compounds include oxides, nitrides, carbides, and fluorides. These inorganic substances or inorganic compounds may be used alone or in combination.

[0045] 8. Packaging structure and manufacturing method The polyamide film of the present invention or a laminate of the polyamide film of the present invention and another film (collectively referred to as "the film of the present invention" in this section 8) can be suitably used as a package. Examples of the package include bags made by heat sealing such as vertical pillow bags, horizontal pillow bags, and gusset bags, and fusion-cut bags made by fusion-cut sealing. Furthermore, the package also includes a lid material for a plastic container and a bottle label formed into a cylindrical shape by a center seal. The film of the present invention can be made into a bag by itself, but may be laminated with other materials. Usually, adhesiveness is required to form a package, so it is preferable to laminate another layer having sealing properties. Examples of the other layer include, but are not limited to, an unstretched film containing polyethylene terephthalate as a constituent component, an unstretched, uniaxially or biaxially oriented film containing another amorphous polyester as a constituent component, an unstretched, uniaxially or biaxially oriented film containing nylon as a constituent component, an unstretched, uniaxially or biaxially oriented film containing polypropylene as a constituent component, an unstretched, uniaxially or biaxially oriented film containing polyethylene as a constituent component, and the like. The packaging material may be at least partially composed of the film of the present invention. The film of the present invention may be provided on any layer of the packaging material, but in consideration of the visibility of the print, it is not preferable to place an opaque film on the outer side of the film of the present invention. The method for producing a packaging material having the film of the present invention is not particularly limited, and any conventionally known production method can be used, such as heat sealing using a heat bar (heat jaw), adhesion using a hot melt, or center sealing using a solvent.

[0046] 9. Laser types Examples of the type (wavelength) of the laser to be irradiated to the film of the present invention include CO2 laser (10600 nm), YAG laser (1064 nm), YVO4 laser (1064 nm), fiber laser (1090 nm), green laser (532 nm), and UV laser (355 nm). These laser types are not particularly limited and can be used as desired within the scope of the present invention. Among the above, the use of YAG laser, YVO4 laser, fiber laser, green laser, and UV laser is preferred, and the use of Nd:YAG laser, fiber laser, green laser, and UV laser is particularly preferred. Packaging materials having the film of the present invention can be suitably used as packaging materials for various items such as food, medicines, and industrial products. EXAMPLES

[0047] Next, the present invention will be specifically described using examples and comparative examples. However, the present invention is not limited to the embodiments of the examples, and can be appropriately modified without departing from the spirit of the present invention. <Polyamide raw materials> [Raw material A] As polyamide A, nylon 6 (nylon 6 manufactured by Toyobo Co., Ltd., RV2.8, containing 4000 ppm of fine powder synthetic amorphous silica having an average particle size of 2.5 μm and 2% by mass of ε-caprolactam monomer) was used.

[0048] [Raw material B] As polyamide B, nylon MXD6 (Nylon MXD6, RV2.2, manufactured by Toyobo Co., Ltd.) was used.

[0049] [Mixing example 1] Polyamide A and laser pigment "IRIOTEC (registered trademark) 8825" (manufactured by Merck Performance Materials) were mixed (dry blended) in a weight ratio of 95:5 to obtain polyamide C in the same manner as in Blending Example 1.

[0050] [Mixing example 2] The above polyamide A and laser pigment "TOMATEC COLOR42-920A (main component Bi2O3)" (manufactured by Tokan Material Technology Co., Ltd.) were mixed (dry blended) in a weight ratio of 95:5 and fed into a screw extruder for melting and mixing. This molten resin was continuously discharged from a strand die in a cylindrical shape and cut with a strand cutter to obtain chip-shaped polyamide D.

[0051] [Table 1]

[0052] [Example 1] Polyamide A and polyamide C were mixed in a mass ratio of 95:5 as the raw materials for the laser-printable layer (layer A), and polyamide A was used alone (100%) as the raw material for the other layer (layer B). The mixed raw materials for layers A and B were fed into separate screw extruders, and both layers A and B were melted at 275°C and extruded from a T-die at a shear rate of 280sec-1. An agitator was attached directly above the extruder, and the mixed raw materials were fed into the extruder while being stirred by this agitator. The molten resins were joined by a feed block in the middle of the flow path and discharged from the T-die, and cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The flow path of the molten resin was set so that the central layer of the laminated film was layer A and both outermost layers were layer B (a two-type, three-layer structure of B / A / B), and the discharge amount was adjusted so that the thickness ratio of layers A and B was 90 / 10 (B / A / B=5 / 90 / 5). The unstretched laminated film obtained after cooling and solidifying was introduced into a longitudinal stretching machine having a series of rolls, preheated on a preheating roll until the film temperature reached 60°C, and then stretched 3.3 times.

[0053] The film after longitudinal stretching was introduced into a transverse stretching machine (tenter), preheated at 80°C for 5 seconds, and then stretched 4.0 times in the width direction (transverse direction) at 100°C. The film after transverse stretching was introduced directly into the intermediate zone and passed through in 1.0 second. In the intermediate zone of the tenter, hot air from the heat treatment zone and hot air from the transverse stretching zone were blocked so that when a rectangular piece of paper was hung down without the film passing through, the piece of paper would hang down almost completely in the vertical direction. The film then passed through the intermediate zone and was guided to the heat treatment zone where it was heat treated at 220°C for 7 seconds. At the same time as the heat treatment, the clip interval in the film width direction was narrowed to perform a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled with 30°C cooling air for 5 seconds. Both edges were cut and removed, and the film was wound into a roll with a width of 400 mm, thereby continuously producing a biaxially stretched film with a thickness of 15 μm over a specified length. The properties of the obtained film were evaluated by the above-mentioned method. The production conditions and evaluation results are shown in Table 2.

[0054] [Examples 2 to 6] In the same manner as in Example 1, polyamide films were continuously produced by changing the mixing conditions of the raw materials, the extrusion conditions, the longitudinal stretching temperature, the longitudinal stretching ratio, the transverse stretching temperature, the transverse stretching ratio, and the heat treatment temperature. The film of Example 5 has a two-layer structure of two types of layers, A and B (thickness ratio A / B=80 / 20), and the film of Example 6 is a single-layer film with only layer A. The production conditions and evaluation results of each film are shown in Table 2.

[0055] [Example 7] In Example 7, a gas barrier layer was laminated on one side of the film roll of Example 5 to continuously produce a gas barrier laminate to obtain a roll. Specifically, aluminum was used as the deposition source, and aluminum oxide (AlOx) was laminated on one side of the film by vacuum deposition while introducing oxygen gas in a vacuum deposition machine. The thickness of the gas barrier layer was 10 nm. The manufacturing conditions and evaluation results of the obtained laminate are shown in Table 2.

[0056] [Example 8] In Example 8, a gas barrier layer was laminated on one side of the film roll of Example 1 to continuously produce a gas barrier laminate, and then an overcoat layer was continuously produced on the gas barrier layer to obtain a roll. Specifically, a gas barrier layer was laminated on one side of the film by a vacuum deposition method using aluminum oxide (AlOx) and silicon oxide (SiOx) as deposition sources. The thickness of the gas barrier layer was 30 nm. A solution in which a tetraethoxysilane hydrolysis solution and polyvinyl alcohol were mixed in a ratio of 50:50 was continuously applied to the gas barrier layer side of this laminate, and then the laminate was introduced into a drying oven set at a temperature of 120° C. and a wind speed of 15 m / sec to continuously form an overcoat layer. The thickness of the overcoat layer was 300 nm. Table 2 shows the manufacturing conditions and evaluation results of the obtained laminate.

[0057] [Comparative Examples 1 to 4] In Comparative Examples 1 to 4, polyamide films were continuously produced by varying the mixing conditions of the raw materials, the extrusion conditions, the longitudinal stretching temperature, the longitudinal stretching ratio, the transverse stretching temperature, the transverse stretching ratio, and the heat treatment temperature in the same manner as in Example 1. The film in Comparative Example 1 does not contain a laser marking pigment. The production conditions and evaluation results of each film are shown in Table 2.

[0058] <Film evaluation method> The film was evaluated as follows. The measurement sample was taken from the center of the film width. If the longitudinal and width directions cannot be immediately determined because the area of ​​the film is small, etc., it is sufficient to determine the longitudinal and width directions temporarily and measure the film. There is no particular problem even if the provisionally determined longitudinal and width directions are 90 degrees different from the true directions.

[0059] [Film thickness] A sample was cut out of the film to A4 size (21.0 cm x 29.7 cm). The thickness of this sample was measured at 10 different points using a micrometer, and the average thickness (μm) was calculated.

[0060] [Type and amount of laser-marking pigment contained in all layers of film] Quantitative determination of Nd, Bi, Sb, Sn, and P 0.1 g of sample was precisely weighed into a Teflon (registered trademark) container of a microwave sample decomposition device (Anton Paar, Multiwavepro), 6 mL of concentrated nitric acid was added, and the device was placed in a dedicated lid and outer container. Heat treatment was performed in the device for 60 minutes at a final temperature of 200 ° C. Then, the treated liquid was cooled to room temperature and placed in a 50 mL digital tube, and the Teflon (registered trademark) container after treatment was washed with ultrapure water and placed in the same tube to a constant volume of 50 mL, and a measurement sample was prepared. Then, the treated liquid was measured with a high-frequency inductively coupled plasma emission spectrometer (Hitachi High-Tech Science, SPECTROBLUE), and the amount of metal elements in the sample was quantified using a calibration curve created with a standard solution of the target element. The element content in the sample was A (ppm), the element concentration in the pretreatment solution was B (mg / L), and the element concentration in the blank test solution (measurement blank) was C (mg / L), and the amount of metal elements in 0.1 g of sample was calculated using the following formula (2). A=(BC)×50 / 0.1 Formula (2)

[0061] - Quantitative analysis of other metal elements 0.1 g of the sample was weighed into a platinum crucible and pre-carbonized on a hot plate up to 400 ° C. Then, ashing was performed for 8 hours at 550 ° C. using an electric furnace FO610 manufactured by Yamato Scientific Co., Ltd. After ashing, 3 mL of 6.0 N hydrochloric acid was added, acid decomposition was performed on a hot plate at 100 ° C., and heat treatment was performed until the hydrochloric acid was completely evaporated. After completion of acid decomposition, the volume was adjusted to a constant value using 20 mL of 1.2 N hydrochloric acid. Then, the treated solution was measured with a high-frequency inductively coupled plasma emission spectrometer (SPECTROBLUE manufactured by Hitachi High-Tech Science Corporation), and the amount of metal elements in the sample was quantified using a calibration curve prepared with a standard solution of the target element. The element content in the sample was A (ppm), the element concentration in the pretreatment solution was B (mg / L), and the element concentration in the blank test solution (measurement blank) was C (mg / L), and the amount of metal elements in 0.1 g of the sample was calculated using the following formula (3). A=(BC)×20 / 0.1 Formula (3)

[0062] [Hayes] The measurement was performed in accordance with JIS-K-7136 using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) The measurement was performed twice, and the average value was calculated.

[0063] [Color b* value] The b* value was measured for one film sample by the reflection method using a spectrophotometer (ZE-6000, manufactured by Nippon Denshoku Co., Ltd.).

[0064] [Longitudinal thickness variation] The film was sampled in a roll shape with a length of 11 m in the longitudinal direction and a width of 40 mm, and the thickness was continuously measured along the longitudinal direction of the film (measurement length: 10 m) at a measurement speed of 5 m / min. using a continuous contact thickness meter manufactured by Micron Measurement Instruments Co., Ltd. The maximum thickness during measurement was defined as Tmax., the minimum thickness as Tmin., and the average thickness as Tave., and the thickness unevenness in the longitudinal direction of the film was calculated using the following formula (4). Thickness unevenness = {(Tmax.-Tmin.) / Tave.} × 100 (%) Equation (4)

[0065] [Thickness unevenness in the width direction] The film was sampled in a wide strip of 40 mm in the longitudinal direction and 500 mm in the transverse direction, and the thickness was continuously measured along the width of the film sample at a measurement speed of 5 m / min. (measurement length: 400 mm) using a continuous contact thickness meter manufactured by Micron Measurement Instruments Co., Ltd. The maximum thickness during measurement was Tmax., the minimum thickness was Tmin., and the average thickness was Tave. The thickness unevenness in the transverse direction of the film was calculated from the above formula 4.

[0066] [Heat shrinkage rate] A piece was cut to a width of 10 mm and a length of 250 mm in the longitudinal and transverse directions, marked at 200 mm intervals, and the spacing (A) between the marks was measured under a constant tension of 5 gf. The film was then heat-treated at 140°C for 30 minutes under no load, after which the spacing (B) between the marks was measured under a constant tension of 5 gf, and the thermal shrinkage was calculated using formula (5). The thermal shrinkage in the longitudinal and transverse directions was calculated based on the thermal shrinkage thus determined. Heat shrinkage rate (%) = {(AB) / A} × 100 Formula (5)

[0067] [Tensile breaking strength] In accordance with JIS K7113, a rectangular film sample was prepared with a measurement direction of 140 mm and a direction perpendicular to the measurement direction (film width direction) of 20 mm. Using a universal tensile tester "Autograph AG-Xplus" (Shimadzu Corporation), both ends of the test piece were held with chucks for 20 mm on each side (distance between chucks: 100 mm), and a tensile test was performed under conditions of an ambient temperature of 23°C and a tensile speed of 200 mm / min. The strength (stress) at tensile break was taken as the tensile breaking strength (MPa). The measurement directions were the longitudinal and transverse directions.

[0068] [Water vapor permeability] The water vapor permeability was measured according to JIS K7126 B method. Using a water vapor permeability measuring device (PERMATRAN-W3 / 33MG manufactured by MOCON), the water vapor permeability was measured in the direction in which the moisture-conditioning gas permeated from the heat seal layer side under an atmosphere of a temperature of 40°C and a humidity of 90% RH. Before the measurement, the sample was left in an environment of a humidity of 65% RH for 4 hours to condition the moisture.

[0069] [Oxygen permeability] The oxygen permeability was measured according to JIS K7126-2. Using an oxygen permeability measuring device (OX-TRAN 2 / 20 manufactured by MOCON), the oxygen permeability was measured in the direction in which oxygen permeates from the heat seal layer side under an atmosphere of 23 degrees Celsius and 65% RH. Before the measurement, the sample was left in an environment of 65% RH for 4 hours to condition the humidity.

[0070] [Printing evaluation by laser irradiation (visual inspection)] The film was irradiated with a laser to print the letters "abc," and the print density was evaluated visually. A 355 nm ultraviolet (UV) laser marker (MD-U1000, Keyence Corporation) was used as the printer, and the laser was irradiated under the following conditions: laser power 40%, scan speed 1000 mm / sec, pulse frequency 40 kHz, spot variable -20. The print density was evaluated according to the following criteria. Judgment: 〇 Characters can be visually recognized. Judgment: × Characters cannot be visually recognized

[0071] [Table 2]

[0072] [Film manufacturing conditions and evaluation results] All of the films of Examples 1 to 8 had excellent physical properties as shown in Table 2, and good evaluation results were obtained. On the other hand, the results of Comparative Examples 1 to 4 were all unfavorable for the following reasons. Comparative Example 1 did not contain a laser pigment, and therefore no printing was observed even when irradiated with a laser. In Comparative Example 2, the laser-printed layer was as thick as 125 μm, so the haze and color b* value exceeded the prescribed ranges, and the appearance was no longer suitable for use as a packaging material. In Comparative Example 3, the laser pigment concentration was as high as 0.4% and the metal (Bi) was contained at 3,300 ppm, so the thickness unevenness in the longitudinal and transverse directions exceeded 20%. Therefore, when the film was wound into a roll, wrinkles occurred due to the poor thickness unevenness. In Comparative Example 4, no stirrer was used when the raw material was melt-extruded, and the shear rate was low, so that the thickness unevenness in the longitudinal direction worsened. [Industrial Applicability]

[0073] The polyamide film of the present invention can provide a film that has high transparency, is excellent in thickness unevenness, and can be clearly printed by a laser, and can therefore be suitably used for applications such as labels, etc. At the same time, a package directly printed with this film can be provided.

Claims

1. The substrate has at least one layer that can be printed by laser irradiation, the layer that can be printed by laser irradiation is a stretched film layer, A polyamide-based film characterized in that a pigment that enables printing by laser irradiation is contained in the entire film layer at 100 ppm to 3000 ppm, a haze is 1% to 30%, and thickness unevenness in either the longitudinal direction or the width direction is 0.1% to 20%.

2. 2. The polyamide film according to claim 1, characterized in that the pigment that can be printed by laser irradiation contains a metal, and the metal contains at least one of the following elements: bismuth, gadolinium, neodymium, titanium, antimony, tin, and aluminum in the form of a simple substance or an oxide thereof.

3. 3. The polyamide film according to claim 1, wherein the thickness of the layer on which printing can be performed by laser irradiation is from 5 μm to 100 μm.

4. 4. The polyamide film according to claim 1, wherein the color b* value is from -1 to 6.

5. 5. The polyamide film according to claim 1, further comprising a layer which cannot be printed by laser irradiation on at least one of the layers adjacent to the layer which can be printed by laser irradiation.

6. 6. The polyamide film according to claim 1, wherein the heat shrinkage rate after exposure to 140° C. hot air for 30 minutes in either the longitudinal direction or the transverse direction is −0.5% or more and 10% or less.

7. A packaging material comprising a cover material or a label using the polyamide film according to any one of claims 1 to 6.

8. 8. The package according to claim 7, characterized in that at least a portion of the package is printed.

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