Multiple-pore-forming stretched film

Abstract

The present invention provides a multiple-pore-forming film that contains a biodegradable resin, has excellent pore-forming processibility, suppresses distortion due to hot water treatment, and has excellent resistance to pore shrinkage due to hot water treatment when pores are formed. This multiple-pore-forming stretched film contains a biodegradable resin and exhibits an area shrinkage rate of 1.0-15.0% after being immersed in water at 100°C for 5 minutes.

Description

Stretched film for making porous

[0001] The present invention relates to a stretched film for forming pores, etc.

[0002] When extracting tea from tea leaves, bags such as tea bags are sometimes used. When water comes into contact with the tea leaves inside the tea bag, tea components are extracted from the tea leaves. For this reason, materials that can be used as porous filter media are used for the bags, and nonwoven fabrics are commonly used. However, because nonwoven fabrics are an aggregate of fibers, they cause diffuse reflection of light and have low transparency. Therefore, it is not possible to observe the movement of the tea leaves inside the bag, especially during hot water extraction, and this does not meet the taste preferences of tea lovers.

[0003] Patent Document 1 proposes making a polylactic acid film porous and using it as the extraction bag. If the film is made of a resin such as polylactic acid, it is possible to increase transparency and, since it is biodegradable, it is easy to dispose of.

[0004] Utility Model Registration No. 3243795

[0005] The inventors focused on biodegradable resin films and conducted research on the extraction bags. They discovered that hot water can cause the film to fold and become sticky, that holes made in the biodegradable resin film to impart water permeability and filterability are not always uniform, and that the holes shrink when exposed to hot water. All of these problems impair filterability, water permeability, and design.

[0006] The present invention aims to provide a porous film that contains a biodegradable resin, has excellent perforation processability, is suppressed in distortion due to hot water treatment, and has excellent resistance to hole reduction due to hot water treatment when holes are made.

[0007] In view of the above problems, the present inventors have conducted extensive research and found that the above problems can be solved by a stretched film for porous formation that contains a biodegradable resin and has an area shrinkage rate of 1.0% to 15.0% after immersion in water at 100°C for 5 minutes. Based on this finding, the present inventors have conducted further research and have completed the present invention. That is, the present invention includes the following aspects.

[0008] Item 1. A stretched film for forming pores, which contains a biodegradable resin and has an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes.

[0009] Item 1A. Use for making porous a stretched film that contains a biodegradable resin and has an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes.

[0010] Item 1B. Use of a stretched film containing a biodegradable resin and having an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes for producing a porous stretched film.

[0011] Item 2. The stretched film for porosity formation or use according to Item 1, wherein the content of the biodegradable resin relative to 100% by mass of the stretched film for porosity formation is 70% by mass or more.

[0012] Item 3. The stretched film for forming pores or the use thereof according to Item 1 or 2, wherein the biodegradable resin contains polylactic acid.

[0013] Item 4. The stretched film for porosity formation or use thereof according to Item 3, wherein the content of the polylactic acid relative to 100% by mass of the stretched film for porosity formation is 70% by mass or more.

[0014] Item 5. The stretched film for porosity formation or use according to any one of Items 1 to 4, wherein the area shrinkage rate is 1.0% or more and 10.0% or less.

[0015] Item 6. Melting point in DSC measurement оｎｓｅｔ and melting point ｅｎｄｓｅｔ difference (melting point ｅｎｄｓｅｔ -Melting point оｎｓｅｔ Item 6. The stretched film for porosity formation or use according to any one of Items 1 to 5, wherein the temperature (Tc) of the stretched film for porosity formation is 18.0°C or higher and 19.2°C or lower.

[0016] Item 7. The stretched film for forming pores or the use thereof according to any one of Items 1 to 6, which has a thickness of 10 μm or more.

[0017] Item 8. The stretched film for forming pores or the use thereof according to any one of Items 1 to 7, which is a biaxially stretched film.

[0018] Item 9. The stretched film for forming pores or use thereof according to any one of Items 1 to 8, which is for a porous filter material.

[0019] Item 10. The stretched film for making porous or its use according to any one of Items 1 to 9, which is for use in a water-permeable packaging material.

[0020] Item 11. The stretched film for making porous according to Item 10, or its use, for use in a thermo-permeable, hydrophilic packaging material.

[0021] Item 12. A porous stretched film containing a biodegradable resin and having an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes.

[0022] According to the present invention, it is possible to provide a porous film that contains a biodegradable resin, has excellent perforation processability, is suppressed in distortion due to hot water treatment, and has excellent resistance to hole reduction due to hot water treatment when holes are drilled.

[0023] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0024] In this specification, the term "to" in a numerical range means "greater than or equal to" or "less than or equal to." That is, the expression "α to β" means "greater than or equal to α and less than or equal to β," or "greater than or equal to β and less than or equal to α," and includes both α and β as a range.

[0025] In the present specification, when an upper limit and a lower limit are separately described, any range formed by combining the described upper limit and lower limit is also disclosed in the present specification.

[0026] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0027] In one aspect, the present invention relates to a stretched film for pore formation (sometimes referred to as the "stretched film of the present invention" in this specification) that contains a biodegradable resin and has an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes.

[0028] The biodegradable resin is not particularly limited as long as it is a resin that can be ultimately decomposed to carbon dioxide by the decomposition action of living organisms (especially microorganisms) and can be used to obtain a stretched film. Examples of biodegradable resins include polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), 3-hydroxybutyrate-co-3-hydroxyhexanoate polymer (PHBH), and polybutylene succinate (PBS).

[0029] The biodegradable resin may be one type alone or two or more types.

[0030] Among biodegradable resins, polylactic acid is particularly preferred from the viewpoints of its suitability for producing stretched films and ease of adjusting the above-mentioned areal shrinkage rate within a predetermined range. The stretched film of the present invention particularly preferably contains polylactic acid as the biodegradable resin. The type of polylactic acid is not particularly limited, and a wide variety of known polylactic acids can be used, including polylactic acid obtained by condensation polymerization of lactic acid components as raw material monomers. The polylactic acid can contain either or both of the optical isomers of L-lactic acid (L-form) and D-lactic acid (D-form).

[0031] The melting point of polylactic acid is preferably, for example, 110°C to 200°C. In this case, it becomes easy to adjust the stretching ratio. The melting point of polylactic acid is preferably 120°C to 190°C, more preferably 130°C to 185°C, and even more preferably 140°C to 180°C.

[0032] The glass transition temperature of polylactic acid is not particularly limited, and can be, for example, from -40°C to 70°C, and more preferably from 0°C to 70°C.

[0033] In the present invention, the melting point and glass transition temperature of polylactic acid are values ​​measured using a differential scanning calorimeter (for example, Diamond DSC, power compensation type DSC manufactured by Perkin-Elmer).

[0034] The melt mass flow rate of polylactic acid is not particularly limited. In order to ensure that the fluidity of the resin is within an appropriate range and that a desired stretched film can be easily produced, the melt mass flow rate of polylactic acid is preferably 0.5 g / 10 min to 15 g / 10 min, more preferably 1 g / 10 min to 10 g / 10 min, and even more preferably 2 g / 10 min to 10 g / 10 min. The melt mass flow rate referred to in this specification refers to a value measured in accordance with JIS K-7210 (1999) at 230°C and 21.18 N.

[0035] The number average molecular weight (Mn) of the biodegradable resin (particularly polylactic acid) is preferably 80,000 to 200,000, more preferably 90,000 to 150,000, and even more preferably 100,000 to 130,000. The weight average molecular weight (Mw) of the biodegradable resin (particularly polylactic acid) is preferably 150,000 to 350,000, more preferably 170,000 to 300,000, and even more preferably 190,000 to 240,000. By setting the molecular weight below the upper limit of the above range, molecular entanglement (pseudo crosslinking points) is suppressed, and by setting the molecular weight above the lower limit of the above range, molecular movement is suppressed, thereby suppressing the degree of crystallization. By appropriately adjusting the upper and lower limits, the degree of shrinkage can be more appropriately adjusted.

[0036] The molecular weight distribution (Mw / Mn) of the biodegradable resin (particularly polylactic acid) is preferably 2.50 or less, more preferably 2.20 or less, even more preferably 2.00 or less, and even more preferably 1.85 or less. By setting the molecular weight distribution within the above range, low molecular weight components do not become excessive, and the degree of shrinkage can be more appropriately adjusted. The lower limit of the molecular weight distribution is, for example, 1.20, preferably 1.40, more preferably 1.50, and even more preferably 1.60.

[0037] The number average molecular weight, weight average molecular weight, and molecular weight distribution of the biodegradable resin are values ​​measured according to the method described in the Examples below.

[0038] The method for producing polylactic acid is not particularly limited, and for example, a wide variety of known production methods can be employed. Polylactic acid can also be obtained from commercial products. Representative commercial products of polylactic acid include "4032D" (melting point 163°C) manufactured by NatureWorks, and "L175" (melting point 175°C), "LX175" (melting point 155°C), and "LX930" (melting point 130°C) manufactured by Total Corbion.

[0039] The polylactic acid may be one type alone or two or more types.

[0040] The stretched film of the present invention may contain other additives in addition to the resin component containing the biodegradable resin, as long as the effects of the present invention are not impaired. Examples of such additives include heat stabilizers, antioxidants, organic and inorganic lubricants, chlorine scavengers, antistatic agents, antifogging agents, and hydrolysis inhibitors.

[0041] In the stretched film of the present invention, the additive may be coated on the surface of the resin layer, or may be present in a mixed state with the resin in the resin layer (in the case of a multi-layer film, at least one layer (e.g., an outer layer that forms the film surface, an inner layer that does not form the film surface, etc.)). In the former case (coating), the coating layer may optionally contain coating components such as a binder resin and a solvent. In addition, in the case of coating, the timing of coating may be either before or after stretching.

[0042] Biodegradable resins such as polylactic acid may be prone to static electricity, and in such cases, it is preferable to incorporate an antistatic agent among the above additives. In the stretched film of the present invention, the antistatic agent may be coated on the surface of the resin layer, or may be present in a mixed state with the resin in the resin layer (in the case of a multi-layer film, at least one layer (e.g., an outer layer that forms the film surface, an inner layer that does not form the film surface, etc.)). In the former case (coating), the coating layer may optionally contain coating components such as a binder resin and a solvent. In addition, in the case of coating, the timing of coating may be either before or after the stretching treatment.

[0043] The antistatic agent may be a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, or a nonionic antistatic agent. These antistatic agents may be used alone or in combination of two or more.

[0044] Examples of the cationic antistatic agent include primary amine salts, secondary amine salts, tertiary amine salts, fatty acid amide amine salts, quaternary ammonium salts, alkyl trialkylene glycol ammonium salts, alkyl ether ammonium salts, benzalkonium salts, benzethonium salts, pyridinium salts, imidazolinium salts, etc. Among these, quaternary ammonium salts are preferred, and polyoxyethylene trialkyl ammonium nitrate is particularly preferred.

[0045] Examples of the nonionic antistatic agent include esters having 5 to 25 carbon atoms, such as propylene glycol mono-fatty acid esters, ethylene glycol mono-fatty acid esters, glycerin mono-fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, methyl glycoside fatty acid esters, alkyl polyglucosides, polyoxyethylene mono-fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and polyoxyethylene sorbitol fatty acid esters; ethers having 5 to 25 carbon atoms, such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene cholesterol, polyoxyethylene cholestanol, polyoxyethylene polyoxypropylene alkyl ethers, and polyoxyethylene polyoxypropylene glycol; and amides, such as polyoxyethylene fatty acid amides, alkyl diethanolamides, and alkylamine oxides. Among these, esters having 5 to 25 carbon atoms are preferred, and polyoxyethylene mono-fatty acid esters are particularly preferred.

[0046] Examples of the anionic antistatic agent include carboxylates, sulfonates, sulfates, and phosphates, and specific examples include alkali metal or alkaline earth metal salts such as alkyl ether carboxylates, fatty acid amide ether carboxylates, acyl lactates, N-acyl glutamates, N-acyl methyl alanines, N-acyl sarcosines, N-acyl-ω-amino acid salts, alkanesulfonates, α-olefin sulfonates, α-sulfofatty acid methyl ester salts, acyl isethionates, alkyl sulfosuccinates, alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, N-acyl methyl taurates, formalin condensation sulfates, alkyl sulfates, alkyl ether sulfates, alkyl aryl ether sulfates, fatty acid alkanolamide sulfates, fatty acid monoglyceride sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, alkyl aryl ether phosphates, and fatty acid amide ether phosphates. Of these, alkyl sulfonates are preferred.

[0047] Examples of the amphoteric antistatic agent include aminopropionic acid, carboxybetaine having 5 to 20 carbon atoms, sulfobetaine, and the like.

[0048] The stretched film of the present invention contains a biodegradable resin as a main component. In this specification, "containing a biodegradable resin as a main component" means that the stretched film contains 50% by mass or more of the biodegradable resin relative to the entire stretched film (100% by mass of the stretched film). The content of the biodegradable resin relative to 100% by mass of the stretched film of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 99% by mass or more, even more preferably 99.9% by mass or more, and particularly preferably 100% by mass. In one embodiment, the upper limit of the biodegradable resin content relative to 100% by mass of the stretched film of the present invention is, for example, 100%, 99.9%, 99%, 95%, or 90% by mass.

[0049] The content of the biodegradable resin relative to 100% by mass of the resin components contained in the stretched film of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more, especially more preferably 99.9% by mass or more, and particularly preferably 100% by mass.

[0050] The content of polylactic acid relative to 100% by mass of the stretched film of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more, especially more preferably 99.9% by mass or more, and particularly preferably 100% by mass. In one embodiment, the upper limit of the content of polylactic acid relative to 100% by mass of the stretched film of the present invention is, for example, 100%, 99.9%, 99%, 95%, or 90% by mass.

[0051] The content of polylactic acid relative to 100% by mass of the resin components contained in the stretched film of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more, especially more preferably 99.9% by mass or more, and particularly preferably 100% by mass.

[0052] The number average molecular weight (Mn) of the resin component contained in the stretched film of the present invention is preferably 80,000 to 200,000, more preferably 90,000 to 150,000, and even more preferably 100,000 to 130,000. The weight average molecular weight (Mw) of the resin component contained in the stretched film of the present invention is preferably 150,000 to 350,000, more preferably 170,000 to 300,000, and even more preferably 190,000 to 240,000. By setting the molecular weight at or below the upper limit of the above range, molecular entanglement (pseudo-crosslinking points) is suppressed, and by setting the molecular weight at or above the lower limit of the above range, molecular movement is suppressed, thereby suppressing the degree of crystallization. By appropriately adjusting the upper and lower limits, the degree of shrinkage can be more appropriately adjusted.

[0053] The molecular weight distribution (Mw / Mn) of the resin component contained in the stretched film of the present invention is preferably 2.50 or less, more preferably 2.20 or less, even more preferably 2.00 or less, and even more preferably 1.85 or less. By setting the molecular weight distribution within the above range, low molecular weight components do not become excessive, and the degree of shrinkage can be more appropriately adjusted. The lower limit of the molecular weight distribution is, for example, 1.20, preferably 1.40, more preferably 1.50, and even more preferably 1.60.

[0054] The number average molecular weight, weight average molecular weight, and molecular weight distribution of the resin component are values ​​measured according to the method described in the Examples below.

[0055] The stretched film of the present invention has an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100° C. for 5 minutes, which allows the film to exhibit the following properties: excellent drilling processability, suppressed distortion due to hot water treatment, and excellent resistance to hole shrinkage due to hot water treatment when holes are drilled.

[0056] From the viewpoint of the above-mentioned properties, the area shrinkage rate is preferably 1.0% or more and 12.0% or less, more preferably 1.0% or more and 10.0% or less, even more preferably 1.0% or more and 8.0% or less, still more preferably 1.0% or more and 6.0% or less, particularly preferably 1.2% or more and 4.0% or less, and particularly preferably 1.2% or more and 3.0% or less. The area shrinkage rate can be, for example, 1.0% or more, 1.1% or more, 1.2% or more, 1.3% or more, 1.4% or more, or 1.5% or more, and can be, for example, 12.0% or less, 10.0% or less, 8.0% or less, 6.0% or less, 4.0% or less, or 3.0% or less.

[0057] The area shrinkage rate is a value measured according to the method described in the section [Area Shrinkage Rate] in the Examples section below.

[0058] The stretched film of the present invention preferably has a melting point as measured by DSC. оｎｓｅｔ and melting point ｅｎｄｓｅｔ difference (melting point ｅｎｄｓｅｔ -Melting point оｎｓｅｔ ) is 18.0° C. or more and 19.2° C. or less. This makes it easier to adjust the area shrinkage rate within a predetermined range.

[0059] The difference is preferably 18.0° C. or more and 19.0° C. or less, more preferably 18.0° C. or more and 18.8° C. or less, and even more preferably 18.0° C. or more and 18.6° C. or less. The difference can be, for example, 17.8° C. or more, 18.0° C. or more, 18.1° C. or more, or 18.2° C. or more, and can be, for example, 19.2° C. or less, 19.0° C. or less, 18.9° C. or less, 18.7° C. or less, or 18.5° C. or less.

[0060] The difference is calculated based on the melting point of the examples described later. оｎｓｅｔ , melting point ｅｎｄｓｅｔ The values ​​are measured according to the method described in the column.

[0061] The stretched film of the present invention may be a uniaxially stretched film obtained by stretching in one direction, or a biaxially stretched film obtained by stretching in two directions. When the stretched film of the present invention is a biaxially stretched film, it is preferably a biaxially stretched film stretched in both the MD and TD directions.

[0062] The stretched film of the present invention may have a single layer structure or a multilayer structure. When the stretched film of the present invention has a multilayer structure, for example, other layers may be provided on one or both sides of the polylactic acid layer. The stretched film of the present invention preferably has a single layer structure.

[0063] The thickness of the stretched film of the present invention is not particularly limited, but from the viewpoint of ensuring a certain strength, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. From the viewpoint of ensuring transparency, the thickness is preferably 50 μm, more preferably 30 μm, and even more preferably 25 μm or less. When the stretched film of the present invention has the above-mentioned multilayer structure, the thickness of the stretched film of the present invention means the total value of the thicknesses of each layer.

[0064] The number average molecular weight (Mn) of the stretched film of the present invention is preferably 80,000 to 200,000, more preferably 90,000 to 150,000, and even more preferably 100,000 to 130,000. The weight average molecular weight (Mw) of the stretched film of the present invention is preferably 150,000 to 350,000, more preferably 170,000 to 300,000, and even more preferably 190,000 to 240,000. By setting the molecular weight at or below the upper limit of the above range, molecular entanglement (pseudo crosslinking points) is suppressed, and by setting the molecular weight at or above the lower limit of the above range, molecular movement is suppressed, thereby suppressing the degree of crystallization. By appropriately adjusting the upper and lower limits, the degree of shrinkage can be more appropriately adjusted.

[0065] The molecular weight distribution (Mw / Mn) of the stretched film of the present invention is preferably 2.50 or less, more preferably 2.20 or less, even more preferably 2.00 or less, still more preferably 1.90 or less, and particularly preferably 1.86 or less. By setting the molecular weight distribution within the above range, low molecular weight components do not become excessive, and the degree of shrinkage can be more appropriately adjusted. The lower limit of the molecular weight distribution is, for example, 1.20, preferably 1.40, more preferably 1.50, even more preferably 1.60, still more preferably 1.70, and particularly preferably 1.80.

[0066] The crystallinity of the stretched film of the present invention is preferably 35 to 45%, more preferably 35 to 43%, even more preferably 36 to 43%, still more preferably 36 to 42%, and particularly preferably 37 to 41%. By setting the crystallinity at or below the upper limit of the above range, drilling processability can be better adjusted, and by setting the crystallinity at or above the lower limit of the above range, crystallization is less likely to proceed during hot water immersion, and the areal shrinkage rate can be suppressed and adjusted to a more appropriate range.

[0067] The thickness, number average molecular weight, weight average molecular weight, molecular weight distribution, crystallinity, and degree of molecular orientation of the stretched film of the present invention are values ​​measured according to the methods described in the Examples below.

[0068] The stretched film of the present invention preferably has transparency. The total light transmittance of the stretched film of the present invention is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The upper limit of this value is 100%. The haze of the stretched film of the present invention is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0069] The method for producing the stretched film of the present invention is not particularly limited, and for example, a wide variety of known production methods can be used. For example, the stretched film of the present invention can be produced by extruding a resin raw material containing at least a biodegradable resin to obtain a resin sheet, and then stretching this resin sheet. This production method is abbreviated as "Production Method A."

[0070] The resin raw material used in production method A may contain various additives as needed.

[0071] The resin raw material can be prepared by, for example, the same method as known preparation methods, and examples thereof include a method in which resin pellets, powder, etc. are dry-blended using a batch mixer such as a tumbler or a mixer, or a continuous metering mixer; or a method in which resin pellets, powder, etc. are supplied to a kneader, optionally together with other resin pellets, powder, and / or additives, and melt-kneaded to obtain a melt-blend resin composition; Among these, melt-kneading is preferred to prepare the resin raw material.

[0072] As the kneader used for melt kneading, a known kneader can be used, and a single-screw type, a twin-screw type, or a multi-screw type having more than two screws can be used. Furthermore, in the case of a screw type having two or more screws, either a co-rotating or counter-rotating kneading type can be used. A co-rotating twin-screw type kneader is preferred because it is easy to knead the biodegradable resin.

[0073] The kneading temperature for melt kneading is preferably in the range of 200°C to 300°C, more preferably 220°C to 280°C. To prevent deterioration of the resin during melt kneading, an inert gas such as nitrogen can be purged. The melt-kneaded resin can be pelletized to an appropriate size using a commonly known granulator to obtain melt blend resin composition pellets.

[0074] In production method A, a resin sheet can be obtained using the resin raw material obtained as described above. Specifically, the resin raw material is supplied to an extruder, heated and melted, and, if necessary, fine foreign matter and the like is removed using a filter or the like, and then the melt is extruded into a sheet shape through a T-die, thereby obtaining a resin sheet.

[0075] The extruder used to obtain the resin sheet can be, for example, a wide variety of known extruders. There are no limitations on the screw type of the extruder, and a single-screw type, twin-screw type, or multi-screw type with more than one screw may be used. When the resin raw materials are prepared by dry blending, using a twin-screw type or multi-screw type with more than one screw tends to provide excellent mixing and dispersion. The extrusion temperature is preferably in the range of 200°C to 300°C, more preferably 220°C to 280°C. To prevent thermal degradation of the resin during extrusion, an inert gas such as nitrogen can be purged.

[0076] The melt-extruded resin sheet is formed into a sheet by a known method, for example, by adhering it to at least one metal drum set at a temperature of 25 to 120°C using an air knife or other rolls, or by static electricity, and the resin sheet is obtained as a so-called raw sheet. The temperature of the metal drum is more preferably 30 to 80°C, and even more preferably 35 to 55°C.

[0077] The production method A may further include a lamination step as necessary. For example, when a stretched film having the layer b formed on one or both sides of the layer a is to be obtained, the production method A preferably includes a lamination step.

[0078] In the lamination step, for example, a wide variety of conventional lamination methods can be used, including films obtained by laminating using a co-extrusion method, a lamination method, a heat sealing method, etc.

[0079] Specifically, when producing a stretched film having a laminated structure, two or more dry-blended and / or melt-blended resin compositions (each resin composition may have the same or different composition) are co-extruded to obtain a resin sheet having a laminated structure, and the resin sheet having such a laminated structure can be stretched. Alternatively, a stretched film having a laminated structure can be produced by laminating a monolayer stretched film with another film. Alternatively, a stretched film having a laminated structure can be produced by stretching a multilayer unstretched film (each layer may have the same or different resin composition) obtained by laminating two or more layers of unstretched films extruded as monolayers together.

[0080] Examples of the coextrusion method include a pre-die lamination method in which molten resins are brought into contact in a feed block before a mold, an in-die lamination method in which they are brought into contact along a path inside a mold, for example, a multi-manifold die, an out-die lamination method in which they are discharged from multiple concentric lips and brought into contact, etc. For example, in the case of the in-die lamination method, a multi-layer die such as a three-layer multi-manifold die can be used to form a three-layer structure of layer b / layer a / layer b, consisting of a surface layer (skin layer: layer b) and a core layer (intermediate layer: layer a).

[0081] Examples of lamination methods include extrusion lamination, which uses equipment for melt extrusion molding used in the T-die method to extrude a film of molten resin directly onto another film to form a laminated film.

[0082] Examples of heat sealing methods include an external heating method in which a heated metal body is pressed against multiple bonded films from the outside of the films, and the conducted heat melts and bonds the films, and an internal heating method in which high-frequency radio waves or ultrasound are used to generate heat in the films and bond them.

[0083] In the manufacturing method A, the above lamination methods can be used alone or in combination.

[0084] As described above, when production method A includes a lamination step, the resin sheet can have a laminated structure, and when production method A does not include a lamination step, the resin sheet has a single-layer structure. By performing the stretching described below using a resin sheet having a single-layer structure, a biaxially stretched film consisting of layer a can be obtained. When performing the stretching described below using a resin sheet having a laminated structure, a multilayer biaxially stretched film including at least layer a can be obtained.

[0085] In manufacturing method A, a resin sheet (raw sheet) having the above-described single-layer or laminated structure is stretched. As the stretching method, known methods such as stretching between rolls with different peripheral speeds, a tenter method, and a tubular method can be used. The stretching direction can be uniaxial stretching, biaxial stretching, or biaxial stretching in an oblique direction, and in the case of biaxial or more stretching, both sequential stretching and simultaneous stretching are applicable. Among these, simultaneous biaxial stretching by a tenter method, sequential biaxial stretching by a tenter method, and sequential biaxial stretching in which longitudinal (flow, MD) stretching between rolls with different peripheral speeds is followed by transverse (width, TD) stretching by a tenter method are preferred, as they facilitate the production of the desired biaxially stretched film. Below, a method for obtaining the biaxially stretched film of the present invention by sequential biaxial stretching will be described, but the method is not limited thereto.

[0086] In the sequential biaxial stretching method, it is preferable to adjust the stretching temperature and stretch ratio depending on the melting point and glass transition temperature of the resin used. First, a resin sheet (raw sheet) is maintained at a temperature of preferably 50 to 130°C, more preferably 60 to 100°C, and even more preferably 65 to 85°C, and is stretched in the longitudinal direction by preferably 2 to 5 times, more preferably 2.5 to 4 times, by passing it between rolls with different peripheral speeds or by a tenter method. By adjusting the longitudinal stretching ratio to around 3 times, for example, 2.5 to 3.4 times, preferably 2.7 to 3.2 times, and more preferably 2.8 to 3.2 times, the above-mentioned area shrinkage ratio is easily obtained. Subsequently, the stretched film is stretched in the transverse direction by preferably 2 to 5 times, more preferably 2.5 to 4 times, by a tenter method, at a temperature of preferably 50 to 130°C, more preferably 60 to 100°C, and even more preferably 65 to 85°C. The above-mentioned area shrinkage percentage can be easily achieved by adjusting the transverse stretching ratio to about 3 times, for example, 2.5 to 3.4 times, preferably 2.7 to 3.2 times, and more preferably 2.8 to 3.2 times. The film is then subjected to a heat treatment, such as a relaxation treatment and a heat setting treatment, before being wound up. The wound film is then subjected to an aging treatment, preferably in an atmosphere of about 20 to 45°C, and then cut to the desired product width.

[0087] The relaxation treatment is preferably performed under conditions in which the transversely stretched film is relaxed at about 65° C. to 85° C. (more preferably 70 to 80° C.) In addition, in such relaxation treatment, the relaxation rate is preferably 1 to 8%, more preferably 2 to 7%, even more preferably 3 to 7%, and still more preferably 4 to 6%, from the viewpoint of making it easier to obtain the above-mentioned area shrinkage rate.

[0088] From the viewpoint of facilitating the achievement of the above-mentioned area shrinkage percentage, the heat setting conditions are preferably a temperature of 110°C to 150°C, more preferably 120 to 145°C, even more preferably 125 to 145°C, still more preferably 130 to 145°C, and particularly preferably 135 to 145°C, and a time of 10 to 80 seconds (more preferably 15 to 60 seconds, and even more preferably 20 to 40 seconds). By adjusting at least one of the conditions of the stretching ratio, relaxation treatment, and heat setting, it becomes easy to adjust the tear strength to within a predetermined numerical range.

[0089] The stretched film of the present invention is a film for making porous, i.e., a film to be used after being made porous. Making porous refers to processing a film so that holes penetrating the film are uniformly distributed over most of the film surface (e.g., 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 100% of the total film area). The diameter of the holes in the porous film is preferably 200 to 800 μm, more preferably 300 to 500 μm, from the viewpoints of preventing leakage of contents such as tea leaves to the outside of the bag when the film is made into a bag shape, and of achieving excellent permeability between the liquid inside the bag containing the extracted components of the contents and the liquid outside the bag, thereby enabling smooth liquid exchange. From the same viewpoint, the number of holes in the porous film is preferably 30 to 100 / cm. ２ , more preferably 50 to 90 pieces / cm ２ is.

[0090] The stretched film of the present invention can be suitably used as a porous filter material or a water-permeable packaging material, more specifically, as a bag-shaped product such as a tea bag, which is immersed in an extraction solvent (water, particularly hot water) to produce an extract (e.g., tea) from the contents (e.g., tea leaves).

[0091] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0092] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0093] Example 1: Luminy (registered trademark) LX175 (manufactured by Total Corbion PLA, polylactic acid) was prepared as polylactic acid, and the polylactic acid was introduced into a single-screw extruder through a hopper, melted, and extruded through a single-layer die. The extruded resin layer was cooled and solidified while being pressed by air pressure using an air knife onto a cooling drum controlled at 45°C, to obtain a raw sheet.

[0094] The obtained raw sheet was stretched using a Bruckner batch-type biaxial stretching machine KARO. The stretching method was a sequential biaxial stretching method in which the sheet was stretched in the longitudinal direction and then in the transverse direction. After preheating in an oven set at 75 ° C, the sheet was stretched in the longitudinal direction (MD direction) at a stretching speed of 6 times / second to 3.0 times, and then further stretched in the transverse direction (TD direction) at a stretching speed of 1 time / second to 3.15 times. In the same oven, a relaxation treatment was performed at a relaxation rate of 5% (this resulted in a final TD direction stretching ratio of 3.0 times), and the sheet was stretched in the transverse direction to 3 times, and then heat-set at 140 ° C for 30 seconds, after which it was removed from the oven and cooled to room temperature to obtain a biaxially stretched film with a thickness of 20 μm.

[0095] Example 2 A biaxially stretched film was obtained in the same manner as in Example 1, except that the thickness was changed to 16 μm.

[0096] Example 3 A biaxially stretched film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 135°C.

[0097] Example 4 A biaxially stretched film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 130°C.

[0098] Example 5 A biaxially stretched film was obtained in the same manner as in Example 1, except that the relaxation rate was changed to 2% and the heat setting temperature was changed to 130°C.

[0099] Comparative Example 1 A biaxially stretched film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 100°C.

[0100] Comparative Example 2 A biaxially stretched film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 100° C. and the thickness was changed to 16 μm.

[0101] Comparative Example 3 A biaxially stretched film was obtained in the same manner as in Example 1, except that the relaxation rate was changed to 2% and the heat setting temperature was changed to 100°C.

[0102] Comparative Example 4 A biaxially stretched film was obtained in the same manner as in Example 1, except that the stretching ratios in both the longitudinal and transverse directions were changed to 3.5 times.

[0103] Comparative Example 5 Luminy (registered trademark) LX175 (polylactic acid, manufactured by Total Corbion PLA) was melted and formed into a film by a casting method, to obtain a film having a thickness of 20 μm.

[0104] [Film Thickness] The thickness of the biaxially stretched film was measured using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu Co., Ltd. in accordance with JIS-C2330 (2024).

[0105] [Molecular Weight and Molecular Weight Distribution of Film] The molecular weight and molecular weight distribution of the biaxially stretched film were measured and calculated by GPC under the following conditions: Apparatus: HLC-8220 (manufactured by Tosoh Corporation), Column: PLgel 5 μm MiniMIX-D, Temperature: 40° C., Solvent: Chloroform, Flow Rate: 0.35 mL / min. 1 mL of a 0.1% by mass sample was injected, and the number average molecular weight (Mn) and weight average molecular weight (Mw) of polylactic acid were calculated from the molecular weight distribution of the film (= polylactic acid) measured under the above conditions using a molecular weight calibration curve prepared using a monodisperse polystyrene standard sample. The molecular weight distribution was determined by dividing Mw by Mn.

[0106] [Film Crystallinity] The crystallinity of the biaxially stretched film was measured as follows. Approximately 5 mg of the film was weighed out, placed in an aluminum sample holder, and set in a PerkinElmer power compensation DSC. Measurement was performed over a range from 30°C to 210°C at a temperature rise rate of 10°C / min under a nitrogen flow. The heat of exotherm at the crystallization peak was subtracted from the heat of endotherm at the melting peak observed during the temperature rise, and the result was divided by the theoretical heat of fusion of perfectly crystalline polylactic acid (93.6 J / g) to determine the crystallinity (%) of the film.

[0107] [Area Shrinkage Rate] The area shrinkage rate was measured as follows. The film was cut into a 5 cm x 5 cm square and immersed in hot water at 100°C for 5 minutes. The area shrinkage rate was calculated using the following formula: (area before immersion - area after immersion) / area before immersion x 100 = area shrinkage rate (%).

[0108] [Melting point оｎｓｅｔ , melting point ｅｎｄｓｅｔ ] Melting point оｎｓｅｔ , melting point ｅｎｄｓｅｔThe measurement was carried out as follows. A PerkinElmer Diamond DSC with power compensation was used. Approximately 5 mg of the film was weighed out, placed in an aluminum sample holder, and set in the DSC device. Under a nitrogen flow, the temperature was raised from 30°C to 210°C at a rate of 10°C / min. The melting curve was measured, and the temperature at which the melting peak began to appear was taken as the melting point. ｏｎｓｅｔ The temperature at which the melting peak ends is called the melting point ｅｎｄｓｅｔ Based on the measured values, the melting point оｎｓｅｔ and melting point ｅｎｄｓｅｔ (= melting point ｅｎｄｓｅｔ -Melting point оｎｓｅｔ ) was calculated.

[0109] [Evaluation of Drilling Processability] Drilling processability was evaluated as follows. The film was passed through a hot-needle perforator (Hot-needle perforator, PM5, manufactured by AFS) set to a perforated roll temperature of 210°C at a line speed of 30 m / min to perform drilling. The test results were applied to evaluate drilling processability according to the following evaluation criteria. (Evaluation criteria) A: Holes are drilled uniformly. B: Holes are not drilled uniformly.

[0110] [Evaluation of resistance to hole shrinkage due to hot water treatment] Resistance to hole shrinkage due to hot water treatment was evaluated as follows. The film was cut into a 5 cm x 5 cm square and a hole was punched in the center. The film or sheet was immersed in hot water at 100°C for 5 minutes. The hole shrinkage rate was measured using the following formula: (hole diameter before immersion - hole diameter after immersion) / hole diameter before immersion x 100 The measured values ​​were applied to the following evaluation criteria to evaluate resistance to hole shrinkage due to hot water treatment. (Evaluation criteria) A: The pore size reduction rate due to hot water treatment was less than 5%. B: The pore size reduction rate due to hot water treatment was 5% or more but less than 15%. C: The pore size reduction rate due to hot water treatment was 15% or more.

[0111] Table 1 shows the production conditions and the measurement and evaluation results for the biaxially stretched films of Examples and Comparative Examples 1 to 4 and the film of Comparative Example 5.

[0112]

[0113] In Table 1, "Not measurable" for Comparative Example 5 indicates that the film was folded and stuck due to the hot water treatment, making it impossible to measure. On the other hand, no distortion of the film due to the hot water treatment was observed in the biaxially stretched films of Examples and Comparative Examples 1 to 4.

[0114] From Table 1, it can be seen that a stretched film having an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes has excellent perforation processability, suppresses distortion due to hot water treatment, and has excellent resistance to hole shrinkage due to hot water treatment when a hole is made.

Claims

1. A stretched film for making porous, which contains a biodegradable resin and has an area shrinkage rate of 1.0% to 15.0% after immersion in water at 100°C for 5 minutes.

2. The stretched film for forming pores according to claim 1, wherein the content of the biodegradable resin relative to 100% by mass of the stretched film for forming pores is 70% by mass or more.

3. The oriented film for forming pores according to claim 1, wherein the biodegradable resin contains polylactic acid.

4. The stretched film for forming pores according to claim 3, wherein the content of said polylactic acid is 70% by mass or more relative to 100% by mass of said stretched film for forming pores.

5. The oriented film for forming pores according to claim 1, wherein the area shrinkage rate is 1.0% or more and 10.0% or less.

6. Melting point in DSC measurement оｎｓｅｔ and melting point ｅｎｄｓｅｔ difference (melting point ｅｎｄｓｅｔ -Melting point оｎｓｅｔ 2. The stretched film for forming pores according to claim 1, wherein the temperature (Tc) of the stretched film is 18.0°C or higher and 19.2°C or lower.

7. The stretched film for forming pores according to any one of claims 1 to 6, which has a thickness of 10 µm or more.

8. The oriented film for forming pores according to any one of claims 1 to 6, which is a biaxially oriented film.

9. The stretched film for forming pores according to any one of claims 1 to 6, which is used for a porous filter material.

10. The stretched film for making porous according to any one of claims 1 to 6, which is used for a water-permeable packaging material.

11. The stretched film for forming pores according to claim 10, which is used for a thermo-permeable and hydrophilic packaging material.

12. A porous stretched film containing a biodegradable resin and having an area shrinkage rate of 1.0% or more and 15.0% or less after immersion in water at 100°C for 5 minutes.