Stretched film for creating porous structures

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

[Technical Field]

[0001] This invention relates to stretched films for porous materials, etc. [Background technology]

[0002] When obtaining 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 leaves. For this reason, the material used for the bag is a porous filter material, and nonwoven fabric is generally used. However, since nonwoven fabric is an aggregate of fibers, it causes diffuse reflection of light and has low transparency. Therefore, it is not possible to observe the movement of the tea leaves inside the bag, especially during hot water extraction, and thus it cannot meet the needs of such preferences.

[0003] Patent Document 1 proposes using a porous polylactic acid film as the bag for the extraction described above. A resin film such as polylactic acid can be made more transparent and is biodegradable, making it easy to dispose of. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Utility Model Registration No. 3243795 Gazette [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors focused on biodegradable resin films and, while conducting research on the extraction bags described above, discovered that the film sometimes becomes folded and adheres when exposed to hot water, that when holes are made in the biodegradable resin film to impart water permeability and filtration properties, the holes are not always uniform, and that the holes sometimes shrink when in contact with hot water. All of these problems impair filtration, water permeability, and aesthetic appeal.

[0006] The present invention aims to provide a porous film that contains a biodegradable resin, has excellent drilling properties, suppresses distortion due to hot water treatment, and has excellent resistance to hole shrinkage due to hot water treatment after drilling. [Means for solving the problem]

[0007] In view of the above problems, the inventors diligently conducted research and found that a porous stretchable film containing a biodegradable resin and having an area shrinkage rate of 1.0% to 15.0% after immersion in water at 100°C for 5 minutes can solve the above problems. Based on this finding, the inventors furthered their research and completed the present invention. That is, the present invention encompasses the following aspects.

[0008] Item 1. A stretched film for porous construction containing a biodegradable resin, wherein the area shrinkage rate after immersion in water at 100°C for 5 minutes is 1.0% or more and 15.0% or less.

[0009] Item 1A. Use of stretched film containing biodegradable resin and having an area shrinkage rate of 1.0% to 15.0% after immersion in water at 100°C for 5 minutes, for the purpose of creating porosity.

[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 the manufacture of a porous stretched film.

[0011] Item 2. The porous stretched film or use described in Item 1, wherein the content of the biodegradable resin is 70% by mass or more per 100% by mass of the porous stretched film.

[0012] Item 3. The stretched porous film or use according to item 1 or 2, wherein the biodegradable resin contains polylactic acid.

[0013] Item 4. The porous stretched film or use described in Item 3, wherein the content of polylactic acid is 70% by mass or more per 100% by mass of the porous stretched film.

[0014] Item 5. The stretched film for porosification or use according to any one of Items 1 to 4, wherein the area shrinkage ratio is not less than 1.0% and not more than 10.0%.

[0015] Item 6. Melting point in DSC measurement оnset and melting point endset difference (melting point endset - melting point оnset ) is not less than 18.0°C and not more than 19.2°C, the stretched film for porosification or use according to any one of Items 1 to 5.

[0016] Item 7. The stretched film for porosification or use according to any one of Items 1 to 6, wherein the thickness is 10 µm or more.

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

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

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

[0020] Item 11. The stretched film for porosification or use according to Item 10, which is for a hot water-permeable packaging material.

[0021] Item 12. A porosified stretched film containing a biodegradable resin, and having an area shrinkage ratio of not less than 1.0% and not more than 15.0% after immersion in water at 100°C for 5 minutes. Effects of the Invention

[0022] According to the present invention, there can be provided a film for porosification that contains a biodegradable resin, is excellent in punching processability, has suppressed distortion caused by hot water treatment, and is excellent in resistance to hole shrinkage caused by hot water treatment when holes are punched therein. Mode for Carrying Out the Invention

[0023] In this specification, the terms “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.”

[0024] In this specification, the "~" in numerical ranges means "greater than or equal to" and "less than or equal to." That is, the notation α~β means α or greater and β or less, or β or greater and α or less, and the range includes α and β.

[0025] Where upper and lower limits are stated separately in this specification, ranges formed by any combination of the stated upper and lower limits are also disclosed in this specification.

[0026] In identifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein.

[0027] In one aspect, the present invention relates to a stretched porous film (which may also be referred to as "the stretched film of the present invention" in this specification) 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.

[0028] Biodegradable resins are not particularly limited as long as they are resins that can be decomposed to carbon dioxide by biological processes (especially by microorganisms) and can be used to produce stretched films. 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 a single type or two or more types.

[0030] Among biodegradable resins, polylactic acid is particularly preferred because it is suitable for the production of stretched films and because the area shrinkage rate can be easily adjusted 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 for example, known polylactic acid can be widely applied. For example, known polylactic acid such as polylactic acid obtained by condensation polymerization of lactic acid components as raw material monomers can be widely used. The polylactic acid may contain only one optical isomer of L-lactic acid (L-isomer) and D-lactic acid (D-isomer), or both.

[0031] The melting point of polylactic acid is preferably, for example, 110°C to 200°C. In this case, it is easier 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, -40°C to 70°C, with 0°C to 70°C being more preferable.

[0033] In this invention, the melting point and glass transition temperature of polylactic acid are values ​​measured using a differential scanning calorimeter (e.g., an input-compensated DSC, DiamondDSC, manufactured by Perkin-Elmer).

[0034] The melt mass flow rate of polylactic acid is not particularly limited. Preferably, the melt mass flow rate of polylactic acid is 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, in that the resin fluidity is within an appropriate range and the desired stretched film can be easily produced. In this specification, the melt mass flow rate refers to the value measured at 230°C and 21.18 N in accordance with JIS K-7210 (1999).

[0035] The number-average molecular weight (Mn) of the biodegradable resin (especially 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 (especially 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. As a result of 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 (especially 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, the amount of low molecular weight components is not excessive, and the degree of shrinkage can be adjusted more appropriately. 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, known production methods can be widely adopted. Polylactic acid can also be obtained from commercially available products. Representative commercially available polylactic acid products include NatureWorks' "4032D" (melting point 163°C), TotalCorbion's "L175" (melting point 175°C), "LX175" (melting point 155°C), and "LX930" (melting point 130°C).

[0039] Polylactic acid can be a single type 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 hindered. Examples of such additives include heat stabilizers, antioxidants, organic and inorganic lubricants, chlorine scavenging agents, 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 it may be present in a mixed state with the resin in the resin layer (in the case of a multilayer, at least one layer (e.g., an outer layer that constitutes the film surface, an inner layer that does not constitute the film surface, etc.)). In the former case (coating), the coating layer may optionally contain coating components such as a binder resin or a solvent. Also, in the case of coating, the timing of coating may be either before or after the stretching process.

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

[0043] Examples of the above-mentioned antistatic agents include cationic antistatic agents, anionic antistatic agents, amphoteric antistatic agents, and nonionic antistatic agents. These antistatic agents may be used individually or in combination of two or more types.

[0044] Examples of the cationic antistatic agents mentioned above include primary amine salts, secondary amine salts, tertiary amine salts, fatty acid amidoamine salts, quaternary ammonium salts, alkyltrialkylene glycol ammonium salts, alkyl ether ammonium salts, benzalkonium salts, benzethonium salts, pyridinium salts, and imidazolinium salts. Among these, quaternary ammonium salts are preferred, and polyoxyethylene trialkylammonium nitrate is particularly preferred.

[0045] Examples of the above-mentioned nonionic antistatic agents include esters with 5 to 25 carbon atoms such as propylene glycol monofatty acid esters, ethylene glycol monofatty acid esters, glycerin monofatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, methyl glycoside fatty acid esters, alkyl polyglucosides, polyoxyethylene monofatty acid esters, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and polyoxyethylene sorbitol fatty acid esters; ethers with 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, alkyldiethanolamides, and alkylamine oxides. Among these, esters with 5 to 25 carbon atoms are preferred, and polyoxyethylene monofatty acid esters are particularly preferred.

[0046] Examples of the above-mentioned anionic antistatic agents include carboxylates, sulfonates, sulfates, and phosphates. Specifically, 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 methylalaninates, N-acyl sarcosineates, N-acyl-ω-amino acid salts, alkanesulfonates, α-olefin sulfonates, α-sulfo fatty acid methyl esters, acyl isethionates, alkyl sulfosuccinates, alkyl sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, N-acyl methyl taurates, formalin condensation sulfates, alkyl sulfates, alkyl ether sulfates, alkylaryl ether sulfates, fatty acid alkanolamide sulfates, fatty acid monoglyceride sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, alkylaryl ether phosphates, and fatty acid amide ether phosphates. Among these, alkyl sulfonates are preferred.

[0047] Examples of the above-mentioned amphoteric antistatic agents include aminopropionic acid, carboxybetaine with 5 to 20 carbon atoms, and sulfobetaine.

[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 (relative to 100% by mass of the stretched film). The biodegradable resin content 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, particularly more preferably 99.9% by mass or more, and especially preferably 100% by mass. In one embodiment, the upper limit of the biodegradable resin content is, for example, 100% by mass, 99.9% by mass, 99% by mass, 95% by mass, or 90% by mass relative to 100% by mass of the stretched film of the present invention.

[0049] The biodegradable resin content relative to 100% by mass of the resin component 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, even more preferably 95% by mass or more, particularly preferably 99% by mass or more, particularly more preferably 99.9% by mass or more, and especially preferably 100% by mass.

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

[0051] The polylactic acid content of the stretched film of the present invention relative to 100% by mass of the resin component 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, particularly more preferably 99.9% by mass or more, and especially 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 to be below the upper limit of the above range, molecular entanglement (pseudo-crosslinking points) is suppressed, and by setting the molecular weight to be above the lower limit of the above range, molecular movement is suppressed, thereby suppressing the degree of crystallization. As a result of appropriately adjusting the upper and lower limits, the degree of shrinkage can be adjusted more appropriately.

[0053] The molecular weight distribution (Mw / Mn) of the resin components 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, the amount of low molecular weight components is not excessive, and the degree of shrinkage can be adjusted more appropriately. 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 components are values ​​measured according to the method described in the examples below.

[0055] The stretched film of the present invention exhibits an area shrinkage rate of 1.0% to 15.0% after immersion in 100°C water for 5 minutes. This allows the film to exhibit excellent drilling processability, suppression of distortion due to hot water treatment, and excellent resistance to hole shrinkage due to hot water treatment after drilling.

[0056] From the viewpoint of the above 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, still more preferably 1.0% or more and 8.0% or less, even more preferably 1.0% or more and 6.0% or less, particularly preferably 1.2% or more and 4.0% or less, and most preferably 1.2% or more and 3.0% or less. Further, 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 described later.

[0058] The stretched film of the present invention preferably has a melting point in DSC measurement оnset and a 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 easy to adjust the area shrinkage rate within a predetermined range.

[0059] The above 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 still more preferably 18.0°C or more and 18.6°C or less. Further, the above 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 above difference is a value measured according to the method described in the section [Melting point оnset , melting point endset in the examples described later.

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

[0062] The stretched film of the present invention may have a single-layer structure or a multi-layer structure. If the stretched film of the present invention has a multi-layer 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 is preferably 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 level of 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. In the case where the stretched film of the present invention has the multilayer structure described above, the thickness of the stretched film of the present invention refers to the sum 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 to be below the upper limit of the above range, molecular entanglement (pseudo-crosslinking points) is suppressed, and by setting the molecular weight to be above the lower limit of the above range, molecular movement is suppressed, thereby suppressing the degree of crystallization. As a result of appropriately adjusting the upper and lower limits, the degree of shrinkage can be adjusted more appropriately.

[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, even more preferably 1.90 or less, and particularly preferably 1.86 or less. By setting the molecular weight distribution within the above range, the amount of low molecular weight components is not excessive, and the degree of shrinkage can be adjusted more appropriately. 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, even more preferably 1.70, and particularly preferably 1.80.

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

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

[0068] The stretched film of the present invention is preferably transparent. 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%. Furthermore, 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 manufacturing the stretched film of the present invention is not particularly limited, and for example, known manufacturing methods can be widely employed. For example, the stretched film of the present invention can be manufactured by extruding a resin sheet obtained from a resin raw material containing at least a biodegradable resin, and then stretching this resin sheet. Such a manufacturing method will be abbreviated as "Manufacturing Method A".

[0070] The resin raw materials used in manufacturing method A may include various additives as needed.

[0071] The method for preparing the resin raw material can be the same as known preparation methods, for example, by dry blending resin pellets or powders using a batch-type mixing device such as a tumbler or mixer, or a continuous weighing-type mixing device; or by supplying resin pellets or powders together with other resin pellets or powders and / or additives as needed to a kneader and melt-kneading to obtain a melt-blended resin composition; and so on. Among these, it is preferable to prepare the resin raw material by melt-kneading.

[0072] For the mixing process, any known mixing machine can be used, and a single-screw type, a twin-screw type, or a multi-screw type with more than one screw may be used. Furthermore, in the case of a twin-screw type with two or more screws, either co-rotating or staggered rotation mixing types may be used. A twin-screw mixing machine with co-rotating screws is preferred because it facilitates the mixing of biodegradable resins.

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

[0074] In manufacturing 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, minute foreign matter is removed using a filter or the like. Then, the resin sheet can be obtained by melt-extruding it into a sheet shape from a T-die.

[0075] For obtaining the resin sheet, any known extruder can be widely used. There are no restrictions on the screw type of the extruder; a single-screw type, a twin-screw type, or a multi-screw type with more than one screw may be used. When the resin raw material is prepared using the dry blend described above, using a twin-screw type or a multi-screw type with more than one screw tends to provide better mixing and dispersibility. The extrusion temperature is preferably in the range of 200°C to 300°C, and more preferably 220°C to 280°C. To prevent thermal degradation of the resin during extrusion, purging with an inert gas such as nitrogen can be performed.

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

[0077] Manufacturing method A may further include a lamination step as needed. For example, when the goal is to obtain a stretched film in which layer b is formed on one or both sides of layer a, it is preferable that manufacturing method A includes a lamination step.

[0078] In the lamination process, for example, conventional lamination methods can be widely used, and examples of films obtained by lamination using methods such as co-extrusion, lamination, and heat sealing can be used.

[0079] Specifically, when manufacturing a stretched film having a laminated structure, a resin sheet having a laminated structure can be obtained by co-extruding two or more dry blend and / or melt blend resin compositions (the composition of each resin composition may be different or the same), and then stretching such a resin sheet having a laminated structure. Alternatively, a stretched film having a laminated structure can also be manufactured by laminating a single-layer stretched film with another film. Furthermore, a stretched film having a laminated structure can also be manufactured by stretching a multilayer unstretched film (the composition of the resin composition constituting each layer may be different or the same) obtained by laminating two or more unstretched films extruded as single layers together.

[0080] Examples of the aforementioned co-extrusion methods include pre-die lamination, in which the molten resin is brought into contact within a feed block in front of the mold; in-die lamination, in which contact occurs within a path inside the mold, such as a multi-manifold die; and off-die lamination, in which the molten resin is extruded and brought into contact from multiple concentric lips. For example, in the in-die lamination method, a multilayer die such as a 3-layer multi-manifold die can be used to create a three-layer structure consisting of a surface layer (skin layer: layer b) and a core layer (intermediate layer: layer a), such as layer b / layer a / layer b.

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

[0082] Heat sealing methods include external heating methods, in which a heated metal object is pressed against multiple films to be bonded together from the outside of the films, and the conducted heat melts and bonds the films, and internal heating methods, in which heat is generated in the films using high-frequency radio waves or ultrasound to bond them.

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

[0084] As described above, if manufacturing method A includes a lamination process, the resin sheet can have a laminated structure, and if manufacturing method A does not include a lamination process, the resin sheet has a single-layer structure. By performing the stretching described later using a resin sheet having a single-layer structure, a biaxially oriented film consisting of layer a can be obtained. When performing the stretching described later using a resin sheet having a laminated structure, a multilayer biaxially oriented film having at least layer a can be obtained.

[0085] In manufacturing method A, the resin sheet (raw material sheet) having the single-layer or laminated structure described above is stretched. As for the stretching method, known methods such as stretching between rolls with a difference in peripheral speed, the tenter method, and the tubular method can be used. As for the stretching direction, uniaxial stretching, biaxial stretching, and diagonal biaxial stretching are possible, and for stretching in two or more axes, both sequential stretching and simultaneous stretching are applicable. Of these, the simultaneous biaxial stretching method using the tenter method, the sequential biaxial stretching method using the tenter method, and the sequential biaxial stretching method, in which the longitudinal (flow, MD) stretching is performed between rolls with a difference in peripheral speed and then the transverse (width, TD) stretching is performed using the tenter method are preferred because they make it easier to obtain the desired biaxially oriented film. The method for obtaining the biaxially oriented film of the present invention by the sequential biaxial stretching method will be described below, but is not limited thereto.

[0086] In the sequential biaxial stretching method, it is preferable to adjust the stretching temperature and stretching ratio according to the melting point and glass transition temperature of the resin used. First, the resin sheet (raw material sheet) is kept at a temperature of preferably 50 to 130°C, more preferably 60 to 100°C, and even more preferably 65 to 85°C, and stretched in the longitudinal direction by preferably 2 to 5 times, more preferably 2.5 to 4 times, by passing it between rolls with a difference in peripheral speed, or by the 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 area shrinkage rate can be 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, at a temperature of preferably 50 to 130°C, more preferably 60 to 100°C, and even more preferably 65 to 85°C, using the tenter method. By adjusting the transverse 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 area shrinkage rate can be easily obtained. After that, the film is subjected to a heat treatment, which includes a relaxation treatment and a heat setting treatment, before being wound up. The wound film can be subjected to an aging treatment in an atmosphere of preferably 20 to 45°C, and then cut to the desired product width.

[0087] The conditions for the relaxation treatment are preferably such that the film after transverse stretching is relaxed at approximately 65°C to 85°C (more preferably 70°C to 80°C). Furthermore, in such a relaxation treatment, the relaxation rate is preferably 1 to 8%, more preferably 2 to 7%, even more preferably 3 to 7%, and even more preferably 4 to 6%, from the viewpoint of easily obtaining the above-mentioned area shrinkage rate.

[0088] The conditions for the heat-setting treatment are preferably 110°C to 150°C, more preferably 120°C to 145°C, even more preferably 125°C to 145°C, even more preferably 130°C to 145°C, and most preferably 135°C to 145°C for 10 to 80 seconds (15 to 60 seconds is more preferable, and 20 to 40 seconds is even more preferable) from the viewpoint of easily obtaining the above area shrinkage rate. By adjusting at least one of the above conditions of stretching ratio, relaxation treatment and heat-setting treatment, it becomes easy to adjust the tear strength to a predetermined numerical range.

[0089] The stretched film of the present invention is a film for porosity, that is, a film intended for use after porosity has been created. Porosity refers to a process in which holes penetrating the film are uniformly distributed over most of the film surface (for example, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 100% of the total film surface). The diameter of the holes in the porosity is preferably 200 to 800 μm, more preferably 300 to 500 μm, from the viewpoint of preventing leakage of contents such as tea leaves from the bag when the film is made into a bag shape, and ensuring excellent permeability between the liquid inside the bag containing the extracted components of the contents and the liquid outside the bag, allowing for smooth liquid exchange. From a similar viewpoint, the number of holes in the porosity is preferably 30 to 100 holes / cm². 2 Comfortably 50-90 pieces / cm 2 That is the case.

[0090] The stretched film of the present invention can be suitably used as a porous filter material and a water-permeable packaging material. More specifically, it can be suitably used as a bag-like material, such as a tea bag, used to produce an extract (e.g., tea) from contents (e.g., tea leaves) by immersing it in an extraction solvent (water, especially hot water).

[0091] In identifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein. [Examples]

[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® LX175 (manufactured by Total Corbion PLA, Inc., polylactic acid) was prepared as the polylactic acid, fed from a hopper into a single-screw type extruder, melted, and extruded through a single-layer die. The extruded resin layer was cooled and solidified on a cooling drum controlled at 45°C while being pressed with air pressure using an air knife to obtain a raw material sheet.

[0094] The obtained raw material sheets were stretched using a Bruckner KARO batch-type biaxial stretcher. The stretching method was a sequential biaxial stretching method, where the sheets were stretched longitudinally and then transversely. After preheating the oven to a set temperature of 75°C, the sheets were stretched longitudinally (MD direction) at a stretching speed of 6 times / second to 3.0 times their original thickness, and then transversely (TD direction) at a stretching speed of 1 time / second to 3.15 times their original thickness. A relaxation treatment with a relaxation rate of 5% was performed in the same oven (resulting in a final TD direction stretching ratio of 3.0 times), the sheets were stretched transversely to 3 times their original thickness, and then heat-set at 140°C for 30 seconds. After being removed from the oven and cooled to room temperature, a biaxially oriented film with a thickness of 20 μm was obtained.

[0095] (Example 2) A biaxially oriented film was obtained using the same method as in Example 1, except that the thickness was changed to 16 μm.

[0096] (Example 3) A biaxially oriented film was obtained using the same method as in Example 1, except that the heat-setting temperature was changed to 135°C.

[0097] (Example 4) A biaxially oriented film was obtained using the same method as in Example 1, except that the heat-setting temperature was changed to 130°C.

[0098] (Example 5) A biaxially oriented film was obtained using the same method as in Example 1, except that the relaxation rate was changed to 2% and the heat-fixing temperature was changed to 130°C.

[0099] (Comparative Example 1) A biaxially oriented film was obtained using the same method as in Example 1, except that the heat-fixing temperature was changed to 100°C.

[0100] (Comparative Example 2) A biaxially oriented film was obtained using the same method as in Example 1, except that the heat-fixing temperature was changed to 100°C and the thickness was changed to 16 μm.

[0101] (Comparative Example 3) A biaxially oriented film was obtained using the same method as in Example 1, except that the relaxation rate was changed to 2% and the heat-fixing temperature was changed to 100°C.

[0102] (Comparative Example 4) A biaxially oriented film was obtained using the same method as in Example 1, except that the stretching ratio in both the longitudinal and transverse directions was changed to 3.5 times.

[0103] (Comparative Example 5) Luminy® LX175 (manufactured by Total Corbion PLA, made from polylactic acid) was melted and a film was formed by casting to obtain a film with a thickness of 20 μm.

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

[0105] [Molecular weight and molecular weight distribution of the film] The molecular weight and molecular weight distribution of the biaxially oriented film were measured and calculated using GPC under the following conditions. Apparatus: HLC-8220 (manufactured by Tosoh Corporation), Column: PLgel 5μm MiniMIX-D, Temperature: 40℃ Solvent: Chloroform, Flow rate: 0.35 mL / min A 0.1% by mass sample was injected at a concentration of 1 mL, 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 created with monodisperse polystyrene standard samples. The molecular weight distribution was defined as Mw divided by Mn.

[0106] [Degree of crystallinity of the film] The degree of crystallinity of the biaxially oriented film was measured as follows: Approximately 5 mg of film was weighed out, placed in an aluminum sample holder, and set in a PerkinElmer input-compensated DSC. Measurements were taken from 30°C to 210°C under a nitrogen flow at a heating rate of 10°C / min. The degree of crystallinity (%) of the film was determined by subtracting the exothermic amount of the crystallization peak from the endothermic amount of the melting peak observed during heating, and dividing by the theoretical heat of fusion of perfect polylactic acid crystals (93.6 J / g).

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

[0108] [Melting point оnset , melting point endset ] melting point оnset , melting point endset The melting point was measured as follows: A PerkinElmer "Input Compensated DSC Diamond DSC" was used. Approximately 5 mg of film was weighed out, placed in an aluminum sample holder, and set in the DSC instrument. Under a nitrogen flow, the temperature was increased 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 defined as the melting point. onset The melting point is the temperature at which the melting peak ends. endset Based on the measured values, the melting point оnset and melting point endset The difference (= melting point) endset - Melting point оnset ) was calculated.

[0109] [Evaluation of drilling machinability] The perforation processability was evaluated as follows: The film was passed through a hot-needle perforator (AFS, PM5) set to a perforated roll temperature of 210°C at a line speed of 30 m / min to perform the perforation process. The perforation processability was evaluated by applying the test results to the evaluation criteria below. (Evaluation Criteria) A: The holes are made uniformly. B: The holes are not made uniformly.

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

[0111] Table 1 shows the manufacturing conditions and measurement and evaluation results for the biaxially oriented films of Examples and Comparative Examples 1-4, as well as the film of Comparative Example 5.

[0112] [Table 1]

[0113] In Table 1, the "unmeasurable" result for Comparative Example 5 indicates that the film became folded and adhered due to the hot water treatment, making measurement impossible. On the other hand, no distortion of the biaxially oriented films in the Examples and Comparative Examples 1-4 was observed due to the hot water treatment.

[0114] Table 1 shows that stretched films with an area shrinkage rate of 1.0% to 15.0% after immersion in 100°C water for 5 minutes exhibit excellent drilling properties, suppress distortion due to hot water treatment, and have excellent resistance to hole shrinkage due to hot water treatment after drilling.

Claims

1. A stretched film for porous formation, It contains polylactic acid, and its surface shrinkage rate after immersion in water at 100°C for 5 minutes is 1.0% or more and 15.0% or less, and The polylactic acid content is 70% by mass or more relative to 100% by mass of the porous stretched film. Stretched film for creating porous structures.

2. The porous stretched film according to claim 1, wherein the content of biodegradable resin is 90% by mass or more relative to 100% by mass of the porous stretched film.

3. The porous stretched film according to claim 1, wherein the content of polylactic acid relative to 100% by mass of the porous stretched film is 90% by mass or more.

4. The stretched porous film according to claim 1, wherein the area shrinkage rate is 1.0% or more and 10.0% or less.

5. Melting point in DSC measurement оｎｓｅｔ and melting point ｅｎｄｓｅｔ The difference (melting point) ｅｎｄｓｅｔ - Melting point оｎｓｅｔ The porous stretched film according to claim 1, wherein the temperature is 18.0°C or higher and 19.2°C or lower.

6. A porous stretched film according to any one of claims 1 to 5, having a thickness of 10 μm or more.

7. A porosity-enhancing stretched film according to any one of claims 1 to 5, which is a biaxially oriented film.

8. A porous stretched film according to any one of claims 1 to 5, for use as a porous filter material.

9. A porous stretched film according to any one of claims 1 to 5, for use as a water-permeable packaging material.

10. A porous stretched film according to claim 9, for use as a heat-permeable water packaging material.

11. A porous stretched film, It contains polylactic acid, and its surface shrinkage rate after immersion in water at 100°C for 5 minutes is 1.0% or more and 15.0% or less, and The polylactic acid content is 70% by mass or more relative to 100% by mass of the porous stretched film. Porous stretched film.

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