Matte polyamide-based film and method for producing the same

Abstract

To provide a matte polyamide-based film which is a stretched film containing particles, and has both desired delustering properties (matte tone) and excellent impact strength and uniformity of the impact strength even under low temperature environment, even though it contains particles, and a method for producing the same.SOLUTION: A polyamide-based film is formed of a resin composition containing 0.5 to 12% of particles and containing a polyamide resin, and satisfies all of (a) glossiness of 50% or less, (b) porosity of 0.4 to 5%, and (c) a ratio (minimum value / maximum value) of a minimum value to a maximum value of film impact strength in n=100 measurement under temperature 5°C atmosphere of 0.5 to 1.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a matte polyamide film and a method for producing the same. [Background technology]

[0002] Polyamide resin films have excellent mechanical and thermal properties and are therefore widely used for packaging a variety of products, particularly for food packaging. To enhance design, there is a demand for frosted glass-like films (matte films) with fine irregularities on the film surface. Matte films reduce the gloss of the film surface (matt effect), blur the visual appearance of the contents, and create a texture reminiscent of Japanese paper, making them popular as high-quality packaging products.

[0003] Methods for processing a film to have a matte finish include, for example, a method of incorporating particles into the film raw material, a method of surface-treating the film after production, etc. Among these, the method of incorporating particles into the film raw material is effective in that it can more reliably obtain a matte effect and the like at a relatively low cost.

[0004] When particles are contained in the film raw material, the resin portion that is in close contact with the particles may peel off due to the stretching stress during the stretching process, causing voids in the film and reducing the mechanical strength of the film. Patent Document 1 discloses a method for controlling the rate of void generation within an appropriate range by adopting specific stretching conditions, thereby preventing a reduction in mechanical strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 119446 Summary of the Invention [Problem to be solved by the invention]

[0006] Although Patent Document 1 makes it possible to obtain a matte film that has a desired matte effect and suppresses the decrease in mechanical strength caused by particles contained in the film, there are cases where the impact strength is locally low in low-temperature environments such as refrigerated environments. In other words, when the number of impact strength measurements in low-temperature environments is increased, the measured impact strength may vary widely.

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a matte polyamide film having a desired matte finish and small variations in impact strength in a low-temperature environment, and a method for producing the same. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the inventors discovered that a matte polyamide film having unique properties can be obtained by a manufacturing method consisting of specific steps, and thus completed the present invention.

[0009] More specifically, by using polyamide resin obtained by polymerizing recycled monomers as a recycled raw material (hereinafter referred to as chemically recycled polyamide resin) and adding a specific amount of particles, we have succeeded in obtaining a matte polyamide film with little variation in impact strength in low-temperature environments.

[0010] That is, the gist of the present invention is as follows. A. A matte polyamide film containing 0.5 to 12% by mass of particles in a polyamide resin, which satisfies all of the following characteristics (1) to (3): (1) Glossiness measured at an incident angle of 20° is 50% or less (2) Porosity: 0.4 to 5% (3) When measured 100 times in an atmosphere at 5°C, the minimum value of the film impact strength is 0.30 J or more, and the ratio of the minimum value to the maximum value (minimum value / maximum value) is 0.5 to 1.0. (b) A matte polyamide film according to (a), characterized in that the polyamide resin contains 10% by mass or more of chemically recycled polyamide resin. (c) A matte polyamide film according to (a) or (b), having a haze of 25% or more. (d) A laminate in which another layer is laminated on the matte polyamide film described in (a) or (b). (e) The laminate according to (d), which includes at least a sealant layer. (f) A laminate according to (d) or (e), wherein the ratio of the minimum value to the maximum value of the film impact strength (minimum value / maximum value) when measured 100 times in an atmosphere at a temperature of 5°C is 0.6 to 1.0. A method for producing the matte polyamide film described in (i) above, comprising the following steps (a) to (c): (a) a step of allowing an unstretched film made of a resin composition containing 0.5 to 12 mass% of polyamide resin and particles containing 10 mass% or more of chemically recycled polyamide resin to absorb water so that the moisture content is 3 to 9 mass%, and then preheating it at a preheating temperature of 180 to 250°C; (b) stretching the unstretched film at a temperature of 170 to 230°C at a stretch ratio of 2.0 to 4.5 in both the longitudinal and transverse directions; (c) A process of heat setting at a temperature of 180 to 230°C A manufacturing method comprising: [Effects of the Invention]

[0011] The film of the present invention has a desired matte finish and exhibits little variation in impact strength even in a low-temperature environment, making it possible to provide a matte polyamide film that is uniformly impact-resistant throughout the film.

[0012] The film of the present invention has excellent designability, impact strength in low-temperature environments, and uniformity of impact strength in low-temperature environments. Therefore, packaging materials containing the film of the present invention are not limited to specific contents and can be used for a wide range of packaging applications, including food, pharmaceuticals, medical devices, cosmetics, chemicals, miscellaneous goods, and electronic components.

[0013] In the film production method of the present invention, since a specific portion of chemically recycled polyamide resin made from waste resin materials is contained as a raw material, it can also contribute to environmental conservation as a sustainable technology. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Matte polyamide film> The matte polyamide film of the present invention (film of the present invention) is a polyamide film containing particles in a polyamide resin.

[0015] <Polyamide resin> The polyamide resin used in the film of the present invention may be any melt-moldable thermoplastic resin having an amide bond (—CONH—) in its molecule, and known or commercially available products can be used. Examples include aliphatic polyamides such as polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polyaminoundecamide (nylon 11), and polylaurylamide (nylon 12); semi-aromatic polyamides such as polyhexamethylene terephthalamide (nylon 6T), polynonanediamine terephthalamide (nylon 9T), and polydecanediamine terephthalamide (nylon 10T); and copolymers and mixtures of these polyamide resins. The polyamide resins can be used alone or in the form of a mixture of two or more types. In the present invention, nylon 6 is particularly preferred because it is easily molded into a film shape.

[0016] The relative viscosity, which is an index of the molecular weight of a polyamide resin, is preferably in the range of 1.5 to 5.0, more preferably 2.5 to 4.0, from the viewpoint of mechanical properties. The relative viscosity is a value measured in 96% by mass sulfuric acid at a concentration of 1 g / dL and a temperature of 25°C.

[0017] The polyamide resin in the present invention preferably includes polyamide resins regenerated by chemical recycling, in addition to polyamide resins obtained using conventional fossil fuel-derived raw materials (particularly virgin monomers), in order to reduce the variation in impact strength in low-temperature environments. The polyamide resin regenerated by chemical recycling (chemically recycled polyamide resin) is obtained by depolymerizing polyamide resin that has become a waste resin material and repolymerizing the resulting regenerated monomer.

[0018] The content of chemically recycled polyamide resin in the polyamide resin must be 10% by mass or more, preferably 30 to 80% by mass, and particularly preferably 40 to 60% by mass, from the viewpoint of reducing variations in impact strength in low-temperature environments.

[0019] The matte polyamide film of the present invention may contain recycled polyamide resin, which is pellets obtained by crushing or remelting waste materials generated during the production of polyamide resin films (e.g., waste materials such as edge trimming waste and slit waste, as well as films that were not commercialized as defective products, etc.). The content of recycled polyamide resin is not limited as long as it does not impair the effects of the present invention.

[0020] <Method for producing chemically recycled polyamide resin> The method for producing the chemically recycled polyamide resin used as the raw material for the film of the present invention is not limited, but can be suitably obtained, for example, by a production method including a step of producing a monomer from a raw material for depolymerization (A) (depolymerization step), a step of producing a chemically recycled polyamide resin by polymerizing a raw material containing the monomer (polymerization step), and a step of refining the chemically recycled polyamide resin (refining step).

[0021] In the depolymerization step, a monomer is regenerated from the raw material for depolymerization (A) (hereinafter referred to as "regenerated monomer"). As the recycled monomer, lactams are particularly preferred, such as ε-caprolactam, enantholactam, capryllactam, lauryllactam, etc. Among these, ε-caprolactam is particularly preferred.

[0022] The type of raw material (A) for depolymerization is not particularly limited, and in addition to various polyamide resins, oligomers of various polyamide resins can also be used. Specifically, the various resins listed as chemically recycled polyamide resins described below can be used. Examples of oligomers include linear units from about dimer to about heptamer, and cyclic units from about dimer to about nonamer. In particular, in the present invention, at least one of a polyamide resin and its oligomer can be suitably used as the raw material for depolymerization (A). In particular, polyamide 6 is a resin substantially composed of ε-caprolactam alone as a monomer unit, and therefore can be suitably used in terms of ease of monomerization and purification / separation. The form of polyamide resin as the raw material (A) for depolymerization may include discharged resin waste, including waste resin from switching between brands during polymerization and waste resin from switching between brands until commercialization of film products, waste waste such as edge trimming waste and slit waste generated during film production, and films that were not commercialized as defective products, etc. The use of such waste materials can contribute to reducing the environmental load. Examples of the form of the oligomer as the raw material for depolymerization (A) include not only highly water-soluble oligomers recovered from the refining water generated during the refining of polyamide resin, but also residues after filtration containing dimers to octamers with low water solubility.

[0023] The method for producing a monomer from the raw material for depolymerization (A) is not particularly limited as long as it can produce a predetermined monomer, but preferably, a depolymerization reaction of the raw material for depolymerization (A) can be adopted. That is, the raw material for depolymerization (A) can be chemically decomposed by the depolymerization reaction to suitably produce a regenerated monomer. The method and conditions for the depolymerization reaction are not particularly limited, and the reaction can be carried out according to known methods. Therefore, for example, a catalyst may or may not be used. The depolymerization may be carried out in the absence of water (dry process) or in the presence of water (wet process). From the viewpoint of productivity, a method in which depolymerization is carried out in hot steam in the presence of a catalyst is particularly preferred. Direct depolymerization of cyclic oligomers, which have low water solubility, is difficult due to the slow hydrolysis rate of the amide bond. However, by subjecting the cyclic oligomers to ring-opening polymerization to form chain molecules and then depolymerizing them under the conditions described above, recycled monomers can be suitably obtained from the cyclic oligomers.

[0024] In the polymerization step, a chemically recycled polyamide resin is produced by polymerizing a raw material containing the recycled monomer. The raw material may be a raw material consisting entirely of recycled monomers, but it is preferable to use virgin monomers in combination. For example, ε-caprolactam (hereinafter referred to as "C-CL") recycled by the depolymerization reaction of polyamide resin can be used in the monomer raw material in a range close to 100 mass%. However, it is preferable to include ε-caprolactam (hereinafter referred to as "V-CL") as a virgin monomer other than C-CL in the monomer raw material. A virgin monomer is the opposite of a recycled monomer and refers to a monomer that has not undergone a polymer depolymerization process. For example, a commercially available monomer can be used as the virgin monomer.

[0025] The chemically recycled polyamide resin produced in the polymerization step may be end-blocked as needed to suppress the generation of monomers during melting. From this perspective, the raw materials may contain additives such as end-blocking agents as needed. The end-blocking agent is not particularly limited, and examples thereof include organic glycidyl esters, dicarboxylic anhydrides, monocarboxylic acids such as benzoic acid, and diamines.

[0026] The polymerization method for obtaining the chemically recycled polyamide resin is not particularly limited, and known methods for polymerizing monomers can be employed. For example, a method can be employed in which ε-caprolactam, water, and benzoic acid as an end-capping agent are mixed, heated and pressurized in a polymerization vessel, and then subjected to a polymerization reaction while reducing the pressure and dehydrating until the desired viscosity is achieved.

[0027] In the refining step, the chemically recycled polyamide resin is refined to remove monomers contained in the chemically recycled polyamide resin and increase the relative viscosity of the chemically recycled polyamide resin to a desired range, thereby providing physical properties suitable for film formation. The refining method is not limited, but it is preferable to immerse the chemically recycled polyamide resin in the form of a molded product such as pellets in hot water at 90 to 100°C for about 15 to 30 hours, so that the relative viscosity (25°C) of the chemically recycled polyamide resin falls within the range of about 2.5 to 4.5. The number of times of refining treatment in the refining step is not particularly limited, but is preferably one or two times from the viewpoint of adjusting the amount of by-products and keeping the relative viscosity within the above range. The chemically recycled polyamide resin after the refining step is preferably dried as needed. The drying conditions are not particularly limited. For example, hot air drying can be performed at about 100 to 130°C for about 10 to 30 hours, but is not limited thereto.

[0028] <particle> The particles used in the present invention are not particularly limited as long as they are particulate. For example, inorganic particles such as calcium carbonate, calcium phosphate, calcium oxalate, silica, titanium dioxide, alumina, barium sulfate, calcium fluoride, and lithium fluoride, and organic particles such as crosslinked polymer particles are preferably used, and these may be used in combination. In addition, inorganic fillers, inorganic pigments, and the like may also be used. Among these, inorganic particles are preferred because they can impart slip properties to the film, and silica is particularly preferred.

[0029] When silica (silica particles) are used as the particles, the silica content in the entire particles is not particularly limited, and is preferably about 50 to 100 mass %, more preferably 80 to 100 mass %, and even more preferably 90 to 100 mass %.

[0030] The average particle size of the particles can be appropriately selected depending on the desired film properties, etc., but from the viewpoint of forming a matte finish and porosity, it is particularly preferable that the average particle size be in the range of 1.0 to 5.0 μm.

[0031] The matte polyamide film of the present invention is made of a polyamide resin containing particles, and the surface of the film has a shape in which some of the particles protrude to a moderate extent, forming protrusions, and the interior of the film has a moderate amount of voids due to the particles. Due to this configuration, the matte polyamide film of the present invention has a matte surface. The protruding particles include not only particles exposed from the film, but also particles that protrude from the film surface while still covered by the film.

[0032] The particles may be particles that have been subjected to a surface treatment using an inorganic or organic surface treatment agent, for example, in order to improve dispersibility, weather resistance, heat resistance, and the like.

[0033] In the film of the present invention, the particles are partially exposed on the surface to form protrusions, which allows the glossiness to be controlled to be low. In particular, the formation of protrusions due to the particles on the surface of the stretched film by stretching reduces the glossiness, allowing a desired matte finish to be obtained.

[0034] The particle content in the film of the present invention must be 0.5 to 12% by mass, preferably 1.0 to 10% by mass, and most preferably 2 to 7% by mass, in order to satisfy the gloss and impact strength in low-temperature environments specified in the present invention. If the particle content in the film is less than 0.5% by mass, the particles will not produce adequate protrusions on the film surface or adequate voids within the film, resulting in a low porosity, which may increase the gloss of the film surface and make it difficult to achieve the desired matte finish. On the other hand, if the particle content exceeds 12% by mass, significant voids will be generated within the film, causing the porosity to exceed 5%, which may result in low impact strength in low-temperature environments.

[0035] <Other ingredients> The film of the present invention may contain additives that are commonly used in films, provided that the effects of the present invention are not impaired. Examples of such additives include lubricants such as ethylene bisstearylamide and calcium stearate, as well as heat stabilizers, antioxidants, weathering agents, flame retardants, plasticizers, and release agents.

[0036] <Film thickness> The thickness of the film of the present invention is not particularly limited as long as it does not impede the effects of the present invention, but it is usually within the range of 10 to 30 μm, and more preferably 12 to 25 μm, particularly from the viewpoint of mechanical properties.

[0037] The properties of the film of the present invention will be described below. <Glossiness> The film of the present invention must have a glossiness of 50% or less as measured at an incident angle of 20°. In particular, the glossiness is preferably 40% or less, and more preferably 30% or less. If the surface glossiness exceeds 50%, the matte finish of the surface becomes insufficient, and the desired matte finish cannot be obtained. The lower limit of the glossiness is not particularly limited, but it is generally sufficient to set it to about 5%.

[0038] <Porosity> The film of the present invention has a moderate amount of voids formed inside the film by the particles, which reduces gloss and effectively reduces the transparency of the film, allowing it to achieve a matte finish. The porosity of the film of the present invention must be 0.4 to 5%, preferably 0.5 to 5%, and more preferably 0.6 to 4.8%. If the porosity is less than 0.4%, there will be few voids inside the film, resulting in a transparent film and making it impossible to achieve the desired matte finish. On the other hand, if the porosity exceeds 5%, there is a risk of a decrease in impact strength in a low-temperature environment or an increase in the variability of impact strength.

[0039] <Haze> The haze of the film of the present invention, which indicates the degree of transparency, is preferably 25% or more, more preferably 30% or more, and most preferably 45% or more. The upper limit of the haze is not particularly limited, but is usually about 95%.

[0040] <Impact strength> The film of the present invention is made from chemically recycled polyamide resin and has a porosity controlled within a specific range, and therefore has excellent impact strength and uniformity of impact strength in a low-temperature environment.

[0041] When the impact strength of the film of the present invention is measured under low-temperature conditions at a temperature of 5°C with n = 100, the minimum impact strength value must be 0.30 J or more, preferably 0.35 J or more, and more preferably 0.40 J or more. If the impact strength is less than 0.30 J, even if a bag can be manufactured using the film of the present invention, the bag will be prone to breakage in a low-temperature environment. For example, if the bag is dropped after refrigeration, it may easily break or crack, causing the contents to spill.

[0042] The ratio (minimum / maximum) of the minimum to maximum impact strength (n=100) in a low-temperature environment must be 0.5 to 1.0, more preferably 0.6 to 1.0, and most preferably 0.7 to 1.0. If the ratio is less than 0.5, it is thought that there will be a local decrease in the impact resistance of the film in a low-temperature environment, which is not practically preferable.

[0043] The mechanism by which the ratio of minimum to maximum impact strength (variation in impact strength) in low-temperature environments is reduced is unknown, but it is speculated that the use of chemically recycled polyamide resin reduces the likelihood of uneven crystalline state occurring during the stretching process, making it less likely for voids inside the film to connect with each other, thereby preventing localized decreases in impact strength.

[0044] <Laminate> The matte polyamide film of the present invention can be used as a laminate with other layers.

[0045] The function and purpose of the layers laminated on the film of the present invention are not particularly limited, and examples thereof include a sealant layer, a barrier layer (gas barrier layer, water vapor barrier layer, etc.), a printed layer, an adhesive layer, a primer layer (anchor coat layer), an antistatic layer, a vapor deposition layer, an ultraviolet absorbing layer, an ultraviolet blocking layer, etc. Any of these layers may be used that are used in known or commercially available laminates. In particular, laminating a sealant layer makes the film suitable for use as a packaging material.

[0046] Examples of resins used for the sealant layer include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, polyethylene / polypropylene copolymer, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid / methacrylic acid copolymer, ethylene-acrylic acid / methacrylic acid ester copolymer, polyvinyl acetate resin, and acid-modified versions of these resins. Polyolefin resins, such as polyethylene, polypropylene, and polyethylene / polypropylene copolymer, are particularly preferred because of their high heat seal strength and the strength of the material itself. These resins may be used alone or in a melt-mix with other resins.

[0047] Examples of methods for forming the sealant layer include a method of laminating a film or sheet made of a sealant resin onto the film of the present invention, a method of extrusion laminating the sealant resin onto the film of the present invention, etc. In the former method, the film or sheet made of the sealant resin may be in an unstretched state or in a stretched state at a low stretch ratio, but in practice, it is preferably in an unstretched state.

[0048] The thickness of the sealant layer is not particularly limited, but is preferably 20 to 100 μm, and more preferably 40 to 70 μm.

[0049] In the present invention, when the impact strength of a laminate obtained by laminating the film of the present invention and a sealant layer under low-temperature conditions of 5°C is measured with n=100, the ratio of the minimum value to the maximum value of the impact strength (minimum value / maximum value) is preferably 0.6 to 1.0, more preferably 0.7 to 1.0, and most preferably 0.8 to 1.0, from the viewpoint of reducing the variation in the impact strength of the laminate.

[0050] <Packaging materials, packaging bags and packaging products> The film of the present invention or a laminate containing the film can be used for various purposes, but is particularly suitable as a packaging material. That is, it can be used as a packaging material for packaging contents. The contents are not limited to, and can include, for example, food and beverages, fruits, juices, drinking water, alcohol, cooked foods, fish paste products, frozen foods, meat products, simmered dishes, rice cakes, liquid soups, seasonings, and various other food and beverages, as well as medical supplies (medical devices), liquid detergents, cosmetics, chemical products, machine parts, electronic parts, and the like.

[0051] The form of the packaging material is not particularly limited, and it can be used, for example, as a packaging bag. As the packaging bag, various types of bags such as a pillow bag, a gusset bag, a stand-up bag, etc. The bag can be formed according to a known method.

[0052] The laminate of the present invention also includes a product (packaged product) in which the contents are packaged in the packaging material or packaging bag as described above. In this case, the packaged state can be, for example, a state in which the contents are sealed from the outside by the packaging material or packaging bag.

[0053] <Method of manufacturing matte polyamide film> The method for producing the film of the present invention comprises the following steps (a) to (c): (a) a step of allowing an unstretched film made of a resin composition containing 0.5 to 12 mass% of polyamide resin and particles containing 10 mass% or more of chemically recycled polyamide resin to absorb water so that the moisture content is 3 to 9 mass%, and then preheating it at a preheating temperature of 180 to 250°C; (b) stretching the unstretched film at a temperature of 170 to 230°C in both the machine direction (MD) and the transverse direction (MD) at a stretch ratio of 2.0 to 4.5 times; (c) A process of heat setting at a temperature of 180 to 230°C The present invention is characterized by comprising:

[0054] (a) Water absorption and preheating process In the water absorption and preheating process, an unstretched film made of a resin composition containing 0.5 to 12 mass% of polyamide resin and particles containing 10 mass% or more of chemically recycled polyamide resin is allowed to absorb water so that the moisture content is 3 to 9 mass%, and then preheated at a temperature of 180 to 250°C.

[0055] Unstretched films can be produced by known methods. For example, they can be produced by melting a resin composition containing particles and chemically recycled polyamide resin, and then molding the resulting melt-kneaded mixture into a film. This can be done using known or commercially available equipment, such as a melt extruder with a T-die. That is, starting materials (e.g., pellet-like raw materials) are first fed into a hopper, plasticized and melted in the melt extruder, and the molten resin is extruded into a sheet from a T-die attached to the tip of the extruder and cooled and solidified by a casting roll. At this time, the polyamide resin is pressed against the casting roll by air to obtain an unstretched film (unstretched sheet).

[0056] The resin composition must contain 0.5 to 12% by mass of particles and 10% by mass or more of the chemically recycled polyamide resin. Resin compositions containing polyamide resins obtained using virgin monomers or recycled resins produced by material recycling can be used, but the various additives listed above can also be incorporated as appropriate. The method for mixing the particles and the additives (hereinafter collectively referred to as "particles, etc.") with the polyamide resin is not limited, and examples include internally adding the particles, etc., at any time before or after the start of polymerization of the polyamide resin; melt-kneading the synthesized polyamide resin and the particles, etc., in a melt extruder; and dry-blending the polyamide resin and the particles, etc., before melting. Among these, the internally adding the particles, etc., at any time after the start of polymerization is preferred from the viewpoint of good dispersibility of the particles, etc., in the film.

[0057] The average thickness of the unstretched film is not particularly limited, but is generally about 60 to 250 μm, and preferably 90 to 235 μm. By setting the thickness within this range, the stretching step can be carried out more efficiently.

[0058] The film of the present invention can be produced by a method in which an unstretched film is allowed to absorb water to a specific moisture content. Specifically, the moisture content of the unstretched film is preferably 3 to 9 mass %, and more preferably 3.5 to 8.5 mass %.

[0059] The method for adjusting the moisture content is not particularly limited as long as it can increase the moisture content of the unstretched film, and may be, for example, any of a method of spraying water or water vapor onto the unstretched film, a method of applying water to the unstretched film with a roller, a method of immersing the unstretched film in water, etc.

[0060] The water is not particularly limited and may be either pure water, tap water, etc. In addition, other components may be dispersed or dissolved in the water as long as they do not impede the effects of the present invention.

[0061] The temperature of the water is not particularly limited, but is preferably set within the range of about 45 to 90°C from the viewpoint of the rate at which the polyamide absorbs water.

[0062] After water absorption, the unstretched film is preheated prior to the stretching step. The preheating temperature is preferably 180 to 250°C, more preferably 200 to 245°C, and particularly preferably 210 to 240°C. Preheating within this temperature range ensures an appropriate void ratio in the film, making it possible to obtain a stretched film with good impact strength even in a low-temperature environment.

[0063] The method for preheating the unstretched film is not limited. For example, a method in which hot air set to the above-mentioned temperature range is blown onto the film traveling through the preheating zone of the stretching machine is preferred. The time for which the unstretched film travels through the preheating zone (preheating time) is preferably 0.5 to 5 seconds.

[0064] (b) Stretching process Next, the stretching step will be described.

[0065] Examples of stretching processes for unstretched films include uniaxial stretching and biaxial stretching, with biaxial stretching being particularly preferred. The biaxial stretching method is not particularly limited, and any of the following methods can be used: a tubular method, a tenter-type simultaneous biaxial stretching method, and a tenter-type sequential biaxial stretching method. The tubular method is advantageous in that the equipment costs are lower than other methods, but it is difficult to improve the film thickness accuracy, and the tenter-type biaxial stretching method is superior in terms of quality stability and dimensional stability. Therefore, the tenter-type biaxial stretching method is preferred as a method for producing the matte polyamide film of the present invention, and the tenter-type simultaneous biaxial stretching method is more preferred from the viewpoint of productivity.

[0066] In the tenter-type simultaneous biaxial stretching method, the stretching stress tends to be higher than in the tubular method, so in order to reduce the stretching stress, it is effective to plasticize the unstretched film by absorbing water to a specific moisture content, then simultaneously stretch the film in the machine direction (MD) and the transverse direction (TD), and then subject the stretched film to a heat setting treatment described below. In other words, the production method of the present invention can exhibit superior effects to the tenter-type simultaneous biaxial stretching method.

[0067] When a tenter-type sequential biaxial stretching method is employed, it is preferable to adjust the unstretched film to a specific moisture content before stretching in the machine direction (MD), stretch in the machine direction (MD), then stretch in the width direction (TD), and then subject the film after stretching in the width direction (TD) to a heat setting treatment as described below.

[0068] Since the film of the present invention contains 10% by mass or more of chemically recycled polyamide resin, as described above, by first adjusting the unstretched film to a specific moisture content and then subjecting it to the stretching and heat-setting processes, the stretching stress during stretching can be suppressed even if the film contains particles, and the resin that is in close contact with the particles can be peeled off due to the stretching stress, which can effectively suppress or prevent the formation of large or numerous voids in the film.

[0069] As described above, by producing a resin composition containing a specific amount of chemically recycled polyamide resin and particles using the production method of the present invention, it is possible to stretch the composition with an appropriate stretching stress, so that the surface of the film has a shape in which some of the particles are appropriately exposed, resulting in protrusions, and the interior of the film has a structure that satisfies a specific porosity due to the particles being appropriately peeled off from the polyamide resin.

[0070] The stretching ratio is 2.0 to 4.5 times in each of the machine direction (MD) and the transverse direction (TD), and it is particularly preferable that the stretching ratio is 2.5 to 4.0 times in both the machine direction (MD) and the transverse direction (TD). By performing stretching within the above-mentioned range of stretching ratio, a film having good mechanical properties can be obtained.

[0071] The stretching ratios in the machine direction (MD) and the transverse direction (TD) may be the same or different. To achieve good stretching with an appropriate stretching stress, it is preferable that the stretching ratio further satisfies the following condition: The ratio of the stretching ratio in the machine direction (MD) to the stretching ratio in the transverse direction (TD) (TD / MD) is preferably 0.9 to 1.2, and more preferably 1.0 to 1.2. Furthermore, the product of the stretching ratio in the machine direction (MD) and the stretching ratio in the transverse direction (TD) (TD×MD) is usually preferably 7 to 16, and more preferably 7.5 to 14.

[0072] The stretching temperature is preferably 170 to 230° C., and particularly preferably 180 to 220° C. By performing stretching within the above temperature range, a film having good mechanical properties can be obtained.

[0073] The stretching temperature of the polyamide film is preferably set within the above range by setting the temperature of the hot air blown onto the film traveling through the stretching zone of the stretching machine within the above range. In this case, the time for which the polyamide film travels through the stretching zone is preferably set to 0.5 to 5 seconds.

[0074] (c) Heat setting process The heat setting process involves subjecting the stretched film to a temperature of 180 to 230°C. The heat setting process involves heat-treating the stretched film while fixing it in the machine direction (MD) and the transverse direction (TD) under a constant tension. Heat setting promotes crystallization of the stretched film and fixes its molecular orientation. Additionally, the voids and surface shape within the stretched film are fixed, improving the dimensional stability of the stretched film and enabling the hot water shrinkage rate of the stretched film to be controlled.

[0075] The heat setting temperature is usually 180 to 230°C, preferably 190 to 230°C, and more preferably 200 to 220°C. By performing the heat setting within this temperature range, a film with good mechanical properties can be obtained. The heat setting time can be appropriately set depending on the heat setting temperature, etc., but is usually preferably about 1 to 10 seconds.

[0076] The method for achieving the heat setting temperature as described above is not particularly limited. Examples of heat setting methods that can be used in the heat setting include a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves. From the viewpoint of achieving uniform and precise heating, a method of blowing hot air is preferred. For example, heat setting can be performed by blowing hot air set to the above-mentioned temperature range onto the film traveling through the heat setting zone of the stretching machine.

[0077] The tension in the heat setting is quantified as a relaxation rate. A relaxation rate of 0% is defined as a case where the stretched film is set to have no slack at all, and the heat setting is usually performed at a relaxation rate of 0% in both the machine direction (MD) and the width direction (TD). That is, the present invention preferably includes a step of performing the heat setting at a relaxation rate of 0% in at least both the machine direction (MD) and the width direction (TD). Specifically, it is preferable to include a step of further heat setting the film biaxially stretched in the stretching step at a temperature of 180 to 230°C with a relaxation rate of 0% in both the machine direction (MD) and the width direction (TD).

[0078] In the present invention, in addition to heat setting at a relaxation rate of 0%, heat setting can also be performed, if necessary, with a certain degree of slack in the stretched film (a relaxation rate exceeding 0%). In the present invention, such heat setting at a relaxation rate exceeding 0% is conveniently referred to as relaxation heat treatment. That is, the heat setting may include a step of heat treatment with a certain degree of slack in the stretched film. In the present invention, relaxation heat treatment can further improve the dimensional stability of the resulting stretched film. The relaxation heat treatment may be performed, for example, in the first, second, or middle stage of the heat setting. The relaxation heat treatment can also be performed in multiple stages.

[0079] The temperature for the relaxation heat treatment may be within the range of the heat setting temperature shown above, but may be the same as or different from the heat setting temperature. The time for the relaxation heat treatment is not particularly limited, but is usually preferably about 1 to 10 seconds.

[0080] When performing a relaxation heat treatment, the relaxation rate in at least one of the machine direction (MD) and the transverse direction (TD) is usually set within a range of about 10% or less, preferably 0.3 to 7%. In the present invention, it is particularly preferable to include a step of performing a relaxation heat treatment in the transverse direction (TD) of the stretched film at a relaxation rate of 0.3 to 7% after heat setting at a relaxation rate of 0%. In this relaxation heat treatment, the relaxation rate in the machine direction (MD) is preferably 0%.

[0081] The matte polyamide film of the present invention may be subjected to a surface treatment such as a corona discharge treatment, if necessary.

[0082] <Method of manufacturing laminate> The method for producing the laminate is not particularly limited, and any of the following can be used: a method of laminating a pre-produced film onto the film of the present invention; a method of forming a coating film by applying a coating liquid for forming a coating film onto the surface of the film of the present invention; and a method of forming a vapor-deposited film by a PVD method, a CVD method, or the like.

[0083] The laminate of the present invention may be subjected to a surface treatment such as corona discharge treatment, if necessary, or may be subjected to a heat treatment such as boiling or retorting. [Example]

[0084] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0085] <Glossiness> Using a GROSS METER GM-26 PRO manufactured by Murakami Color Research Laboratory, the film surface is measured at an incident angle of 20° in accordance with JIS K 7105.

[0086] <Porosity> A cross section of the film is prepared by ion polishing (IP) and observed using a FE-SEM. The SEM image is then processed (automatic binarization with a threshold set at 95) using image analysis software (ImageJ.), the sum of the void areas of the entire cross section of the film is calculated, and the porosity (%) is calculated using the following formula: Porosity (%) = (total void area (μm 2 ) / cross-sectional area of ​​the entire film (μm 2 ))×100

[0087] <Haze> The total light transmittance (Tt) and diffuse transmittance (Td) of the film are measured using a haze meter (NDH 2000) manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K 7105, and the haze is calculated based on the following formula. Haze (%) = (Td / Tt) x 100

[0088] <Impact strength> Using a film impact tester (manufactured by Toyo Seiki Co., Ltd.), the impact strength required to punch a ring-shaped film with a diameter of 7 cm in an atmosphere at a temperature of 5°C was measured. An impact head weighing 30 kg and having a diameter of 12.7 mm (0.5 inches) was used for the measurement. The measurement was carried out 100 times, and the maximum and minimum measured values, the value obtained by dividing the minimum value by the maximum value, and the average value (n = 100) were calculated.

[0089] Base ingredients B2~B4 Film scraps or defective products generated during the production of polyamide resin films and resin scraps (resin waste) containing oligomers generated during the polymerization of polyamide resin were used as the raw material for depolymerization (A). Phosphoric acid was added to the raw material for depolymerization (A), and a depolymerization reaction was carried out under heating using a wet method. After purification by activated carbon treatment, concentration, and distillation, the regenerated ε-caprolactam "C-CL" was recovered. On the other hand, "V-CL" is the virgin monomer ε-caprolactam. C-CL and V-CL were blended in the following ratios (10:90 for B2, 40:60 for B3, and 90:10 for B4), mixed with water and benzoic acid as an end-blocking agent, and then heated, pressurized, depressurized, and dehydrated in a polymerization kettle, followed by polymerization until the target viscosity was achieved. The polymerization time required to achieve the final target viscosity varied depending on the ratio of CL species. The resulting polymer (resin) was pelletized and then refined twice using hot water treatment at 95°C for 10 and 15 hours, followed by drying at 110°C for 20 hours. In this way, polyamide resins (base materials B2 to B4) with a relative viscosity of 3.1 were obtained.

[0090] Base ingredient B1 C-CL, water, and benzoic acid were polymerized in the same manner as in the preparation of base materials B2 to B4, then pelletized, refined twice by hot water treatment, and dried to obtain a polyamide resin (base material B1) with a relative viscosity of 3.0.

[0091] Base ingredient C V-CL, water, and benzoic acid were polymerized in the same manner as in the preparation of base materials B2 to B4, then pelletized, refined twice by hot water treatment, and dried to obtain a polyamide resin (base material C) with a relative viscosity of 3.1.

[0092] Silica-containing master chips M2 to M4 A 30-liter autoclave was charged with 10 kg of ε-caprolactam containing the C-CL and V-CL blended in the following ratios (10:90 for M2, 40:60 for M3, and 90:10 for M4), 1 kg of water, and 520 g of silica (Fuji Silysia Chemical, product name: Sylysia 310P, average particle size 2.7 μm). The mixture was then maintained at 100°C and stirred at that temperature until the reaction system became homogeneous. The mixture was then heated to 260°C with stirring, and a pressure of 1.5 MPa was maintained for 1 hour. The pressure was then released to atmospheric pressure over another hour, and polymerization continued for another hour. Upon completion of polymerization, the reaction product was discharged in the form of strands, cooled, solidified, and cut to obtain pellets composed of polyamide resin. The resulting pellets were then refined in hot water at 95°C for 8 hours to remove unreacted monomers and the like, followed by drying. The obtained polyamide resins (silica-containing master chips M2 to M4) had a relative viscosity of 2.7 and a silica content of 5.4% by mass.

[0093] Silica-containing master chip M1 Using C-CL, water, and silica (manufactured by Fuji Silysia Chemical Ltd., product name: Sylysia 310P, average particle size 2.7 μm) as raw materials, the same steps as those for the silica-containing master chips M2 to M4 were carried out. In this way, a polyamide resin (silica-containing master chip M1) with a relative viscosity of 2.8 was obtained.

[0094] Silica-containing master chip N Using V-CL, water, and silica (manufactured by Fuji Silysia Chemical Ltd., product name: Sylysia 310P, average particle size 2.7 μm) as raw materials, the same steps as for the silica-containing master chips M2 to M4 were carried out. In this way, a polyamide resin (silica-containing master chip N) with a relative viscosity of 2.9 was obtained.

[0095] Example 1 Polyamide resin B2 was mixed with silica-containing master chip M2 so that the monomer usage ratio and particle content were as shown in Table 1, and the mixture was fed into a single-screw extruder set at a cylinder temperature of 260 ° C., extruded through a T-die, and contacted with a cooling roll set at 20 ° C. to obtain an unstretched sheet with a thickness of 150 μm. The unstretched sheet obtained was immersed in a hot water bath adjusted to a water temperature of 65 ° C., and the moisture content of the unstretched sheet was adjusted to 4.5% by mass. Next, the moisture-adjusted unstretched sheet was preheated by blowing hot air at 230 ° C. for 1 second, and then stretched 3 times in the machine direction (MD) and 3.3 times in the transverse direction (TD) using a tenter-type simultaneous biaxial stretching machine adjusted to a temperature of 200 ° C. Next, this stretched film was heat-set by blowing hot air at 210°C for 3 seconds (relaxation rate 0% in both directions), and then it was relaxed at a relaxation rate of 5% only in the transverse direction (TD) while being blown hot air at 210°C for 3 seconds, followed by a relaxation heat treatment.Then, it was cooled to obtain a polyamide film with a thickness of 15 μm.

[0096] Examples 2 to 13 Comparative Examples 1 to 5 A polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 1, except that the raw material types, the ratio of each monomer used, and the silica content were changed to the values ​​shown in Table 1.

[0097] The glossiness, porosity, impact strength in an atmosphere at 5° C. (n=100), and haze were measured for the films obtained in Examples 1 to 13 and Comparative Examples 1 to 5. The results are shown in Table 1.

[0098] [Table 1]

[0099] Example 14 A urethane adhesive (DIC Corporation, Dickdry LX-401A / SP-60) was applied to the surface of the polyamide film obtained in Example 1 in a dry amount of 3.0 g / m 2 The adhesive was then applied so that the adhesive layer was in a thickness of 100 μm, and then heat-treated at 80°C. An unstretched polyethylene film (TUX MCS, 50 μm, manufactured by Mitsui Chemicals Tocello Inc.) was then dry-laminated onto the heat-treated adhesive surface at a nip pressure of 490 kPa on a metal roll heated to 80°C. The adhesive was then subjected to the recommended aging process to obtain a laminated film.

[0100] Examples 15 to 17 Comparative Examples 6 and 7 Laminate films were obtained in the same manner as in Example 14, except that the polyamide films used were changed to those shown in Table 2.

[0101] The impact strength (n=100) was measured in an atmosphere of 5° C. for the laminates obtained in Examples 14 to 17 and Comparative Examples 6 and 7. The results are shown in Table 2.

[0102] [Table 2]

[0103] The polyamide films of Examples 1 to 13 were obtained from resin compositions containing specified amounts of chemically recycled polyamide resin and particles, and therefore satisfied all of the gloss, porosity, minimum value of film impact strength in an atmosphere of 5°C, and ratio of minimum value to maximum value specified in the present invention. That is, these polyamide films had a matte surface, and also had excellent impact strength in a low-temperature environment with small variability in impact strength.

[0104] On the other hand, the polyamide films of Comparative Examples 1 to 3 had a low content of chemically recycled polyamide resin, so the variation in impact strength in a 5°C atmosphere was greater than the specified range, and the impact strength was locally reduced at low temperatures.

[0105] The polyamide film of Comparative Example 4 had a particle content that did not satisfy the range specified in the present invention, and therefore had few protrusions on the film surface and a low film porosity, resulting in a high gloss, low haze, and no desired matte finish.

[0106] The polyamide film of Comparative Example 5 had a particle content exceeding the range specified in the present invention, and therefore had a high porosity. Although the film had a matte finish, the minimum impact strength in a 5°C atmosphere was lower than the specified value, and there was a risk of localized reduction in impact strength in low-temperature environments.

[0107] It can be seen that the laminates of Examples 14 to 17 satisfied the minimum value and the ratio of the minimum value to the maximum value of the film impact strength in an atmosphere of 5° C. specified in the present invention. That is, these laminates had a matte finish with a matte surface, and also had excellent impact strength even in a low-temperature environment, with little variation in impact strength.

[0108] The laminate of Comparative Example 6 was made using a polyamide-based film with a low content of chemically recycled polyamide resin, and therefore had a large variation in impact strength in an atmosphere of 5°C, and the impact strength decreased locally in low-temperature environments.

[0109] The laminate of Comparative Example 7 was a laminate using a polyamide-based film with a high particle content, and therefore had many voids inside the film. Although it had a matte finish, the minimum value of impact strength in an atmosphere of 5°C was lower than the specified range, and the impact strength decreased locally in low-temperature environments.

Claims

1. A matte polyamide film containing particles in an amount of 0.5 to 12% by mass in a polyamide resin, which satisfies all of the following characteristics (1) to (3): (1) Glossiness measured at an incident angle of 20° is 50% or less (2) Porosity: 0.4 to 5% (3) When measured 100 times in an atmosphere at 5°C, the minimum value of the film impact strength is 0.30 J or more, and the ratio of the minimum value to the maximum value (minimum value / maximum value) is 0.5 to 1.

0.

2. 2. The matte polyamide film according to claim 1, wherein the polyamide resin contains 10% by mass or more of a chemically recycled polyamide resin.

3. 3. The matte polyamide film according to claim 1, which has a haze of 25% or more.

4. A laminate comprising the matte polyamide film according to claim 1 or 2 and another layer laminated thereon.

5. The laminate of claim 4 including at least a sealant layer.

6. The ratio of the minimum value to the maximum value of the film impact strength (minimum value / maximum value) when measured 100 times in an atmosphere at a temperature of 5°C is 0.6 to 1.0 The laminate according to claim 4 or 5,

7. A method for producing the matte polyamide film according to claim 1, comprising the following steps (a) to (c): (a) A step of allowing an unstretched film made of a resin composition containing 0.5 to 12 mass% of a polyamide resin containing 10 mass% or more of chemically recycled polyamide resin and particles to absorb water so that the moisture content is 3 to 9 mass%, and then preheating at a preheating temperature of 180 to 250 ° C.; (b) stretching the unstretched film at a temperature of 170 to 230°C at a stretch ratio of 2.0 to 4.5 times in both the length direction and the width direction; (c) A step of heat setting at a temperature of 180 to 230°C A manufacturing method comprising:

Images