Cellulose powder-containing film and method for producing the same

Abstract

To provide a cellulose powder-containing film with low specific gravity, capable of contributing to reduction of environmental burden.SOLUTION: A cellulose powder-containing film comprising, based on 100 pts.mass of the entire cellulose powder-containing film, 20-40 pts.mass of the cellulose powder, 50-70 pts.mass of polyethylene, 3-12 pts.mass of an olefin-based elastomer, and 0.4-4 pts.mass of maleic anhydride-modified polyolefin, the specific gravity thereof being 0.93 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cellulose powder-containing film and a method for producing the same. [Background technology]

[0002] In recent years, waste from synthetic resin products has become a problem, including the problem of marine plastics. Therefore, there is a demand for reducing the amount of synthetic resin used by converting at least a portion of the raw materials used in synthetic resin products, especially those that are discarded after use, to raw materials other than synthetic resin.

[0003] Examples of raw materials other than synthetic resins include cellulose materials such as paper. Cellulose materials are inexpensive and highly recyclable, and are therefore widely used as reinforcing materials for thermoplastic resins and elastomers, which are used to form films and other products. Furthermore, because cellulose materials are biomass materials, blending them into synthetic resin products can result in more environmentally friendly products.

[0004] As an example of a film containing such a cellulose material, Patent Document 1 proposes a cellulose-blended film that contains cellulose powder (A), an olefin resin (B), and a compound having an acid anhydride structure (C), is formed into a film by inflation molding, and satisfies the tensile strength and elongation standards for packaging polyethylene film specified in JIS Z 1702 Type 1A, and has a gloss variation (standard deviation) of 0.1 to 8.0 on the film surface. This document also states that such a cellulose-blended film has the above-mentioned physical properties because the cellulose powder is uniformly dispersed, there are few clumps of cellulose powder on the film surface, and no pinholes occur, making it suitable for use as packaging materials, shopping bags, garbage bags, etc.

[0005] Furthermore, for example, Patent Document 2 proposes a bag film that contains a fiber-resin mixed composition containing 10 to 40 mass% of plant fiber, 10 to 40 mass% of polypropylene, and 20 to 80 mass% of polyethylene, and has a film thickness of 30 to 180 μm. This document describes, with regard to the bag film and its manufacturing method, that a film containing plant fiber, which is a component of paper, and suitable for forming into bags can be obtained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2012-201852 [Patent Document 2] WO2022 / 064772 publication Summary of the Invention [Problem to be solved by the invention]

[0007] The inventions described in the above two documents both use cellulose as a filler in a polyolefin-based film, thereby reducing the amount of petroleum-derived plastic used and contributing to a reduction in the environmental load. However, these documents do not consider the specific gravity of the film at all.

[0008] The specific gravity of cellulose is approximately 1.5, and when used as a filler, the overall film becomes heavier than a film made of polyolefin alone. As a result, when transporting the film itself or products that use the film, CO2 emissions increase compared to films made of polyolefin alone, and there is room for improvement from the perspective of reducing the environmental impact.

[0009] Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a cellulose powder-containing film that has a low specific gravity and can contribute to reducing the environmental load. [Means for solving the problem]

[0010] In order to achieve the above object, the cellulose powder-containing film of the present invention is characterized in that, when the entire cellulose powder-containing film is taken as 100 parts by mass, it contains 20 to 40 parts by mass of the cellulose powder, 50 to 70 parts by mass of polyethylene, 3 to 12 parts by mass of an olefin-based elastomer, and 0.4 to 4 parts by mass of a maleic anhydride-modified polyolefin, and has a specific gravity of 0.93 or less. [Effects of the Invention]

[0011] The cellulose powder-containing film of the present invention, despite containing high-density cellulose powder, has a specific gravity equal to or less than that of a typical LDPE film. Therefore, compared to conventional technologies, it can contribute to reducing CO2 emissions during film transportation and further reduce the environmental load. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows SEM images of the films of Reference Examples 1 and 2 and Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The cellulose powder-containing film (hereinafter simply referred to as "film") of the present invention will be specifically described below. Note that the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0014] <Film> The film of the present invention contains cellulose powder, polyethylene, an olefin-based elastomer such as a propylene-based elastomer, and maleic anhydride-modified polyolefin (hereinafter sometimes referred to as "MA-PO"). The film may further contain other components as necessary.

[0015] <Cellulose powder> The cellulose powder can be produced by using, for example, pulp derived from refined, highly pure cotton linters, wood, bamboo, bagasse, etc., and pulverizing the pulp using a grinder such as a knife mill, a vertical roller mill, or a jet mill to obtain powdered pulp as a raw material, and then classifying the powder to obtain a desired average particle size.

[0016] The average particle size of the cellulose powder is 36 μm or less, preferably 24 μm or less, more preferably 20 μm or less, and even more preferably 18 μm or less. If the average particle size exceeds 36 μm, inflation molding may become difficult. If the average particle size is 36 μm or less, holes due to drawdown during extrusion are eliminated, and the film has excellent formability and toughness.

[0017] The average particle size of the cellulose powder is 6 μm or more, preferably 8 μm or more, and more preferably 10 μm or more. If the average particle size is less than 6 μm, the cellulose powder is bulky, making it difficult to produce the resin composition, which is the raw material for the film, and the film. Furthermore, the surface area of ​​the cellulose powder increases, so it is necessary to increase the amount of compatibilizer to cover it, resulting in poor physical properties of the film. If the average particle size is 6 μm or more, the rigidity of the resin composition is excellent, and the bulkiness of the cellulose powder is reduced, making it easier to produce the resin composition and the film.

[0018] In this specification, the term "average particle size" refers to the 50% particle size (D50), which can be measured as the volume average particle size using a laser diffraction particle size distribution analyzer (a dry particle size distribution analyzer manufactured by Malvern Instruments, trade name: MASTER SIZER 3000) or the like.

[0019] The aspect ratio of the cellulose powder is preferably 2 or less, and more preferably 1.8 or less. During molding such as inflation molding, the cellulose powder tends to be oriented in the MD direction. By setting the aspect ratio to 2 or less, the anisotropy of the orientation of the cellulose powder is reduced and the isotropy is improved.

[0020] The "aspect ratio" refers to the ratio L / D of the long diameter L to the short diameter D of the cellulose powder, and is obtained by observing the cellulose powder with a microscope (for example, a digital microscope manufactured by Keyence Corporation, product name: VHX-7000) and analyzing the obtained images, and then calculating the average aspect ratio for 100 particles.

[0021] Commercially available cellulose powder may be used, such as cellulose microfiber ARBOCEL (registered trademark) manufactured by Rettenmeyer Japan Co., Ltd. and powdered cellulose KC Flock (registered trademark) manufactured by Nippon Paper Industries Co., Ltd.

[0022] The content of cellulose powder is 20 to 40 parts by mass, preferably 25 to 35 parts by mass, when the entire film is taken as 100 parts by mass. If the content of cellulose powder is less than 20 parts by mass, the amount of CO2 reduction will be limited. If the blending amount of cellulose powder exceeds 40 parts by mass, film production, particularly stretching during the film production process, will become difficult.

[0023] <Polyethylene> As the polyethylene, high density polyethylene (HDPE), which is an ethylene homopolymer, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), etc. can be used, and one of these may be used alone or two or more may be used in combination. In particular, it is preferable that the polyethylene contains one or more of low density polyethylene, linear low density polyethylene, and ultra low density polyethylene.

[0024] The polyethylene used is low-density polyethylene (density: 0.900 to 0.930 g / cm 3 Such low-density polyethylene is less likely to lose flexibility even when combined with cellulose powder to form a resin composition, and is easily compatible with elastomers, improving the production stability of the resin composition.

[0025] Furthermore, it is preferable that the polyethylene contains linear low-density polyethylene (LLDPE) or low-density polyethylene obtained using a metallocene catalyst, which improves the stretchability of the resin composition that is the raw material for the film, facilitating film production and advantageously reducing the specific gravity of the film.

[0026] The polyethylene preferably contains ultra-low density polyethylene (ULDPE), which has a specific gravity of less than 0.90 and can effectively reduce the specific gravity of the film.

[0027] The polyethylene content is 50 to 70 parts by mass, preferably 55 to 65 parts by mass, and more preferably 57 to 63 parts by mass, when the entire film is taken as 100 parts by mass. If the polyethylene content is less than 50 parts by mass, the resin composition that is the raw material for the film becomes hard and brittle, and the proportion of cellulose powder increases, making production difficult. If the polyethylene content is more than 70 parts by mass, the proportion of cellulose powder in the film decreases.

[0028] <Olefin elastomer> The olefin-based elastomer is a component that contributes to improving the moldability of the resin composition that is the raw material for the film.

[0029] Specifically, for example, in inflation molding, the cellulose powder is not stretched at all during the primary stretching. In order to improve the moldability of the resin composition, it is important that the resin components other than the cellulose powder follow the cellulose powder during the primary stretching.

[0030] Compared with general thermoplastic resins, olefin-based elastomers have better conformability to cellulose powder during primary stretching. In other words, the inclusion of an olefin-based elastomer reduces the elongational viscosity of the resin composition during cooling (to about 90°C) after primary stretching. Thus, the inclusion of an olefin-based elastomer improves the moldability of the resin composition.

[0031] The olefin elastomers used in the present invention include copolymers or homopolymers mainly composed of an olefin having 3 or more carbon atoms, and copolymers mainly composed of ethylene and an olefin having 3 or more carbon atoms.

[0032] More specifically, examples include propylene-ethylene copolymer, ethylene-propylene-diene terpolymer, etc. The olefin-based elastomer may be used alone or in combination of two or more kinds.

[0033] Furthermore, olefin-based elastomers are generally composed of hard segments that control basic physical properties such as mechanical properties, and soft segments that control elasticity, a rubber-like property. Olefin-based elastomers whose hard segments consist of polypropylene are called propylene-based elastomers, and those whose hard segments consist of polyethylene are called ethylene-based elastomers. Examples of soft segments in olefin-based elastomers include EPDM, EPM, EBM, IIR, hydrogenated styrene butadiene rubber (HSBR), NBR, and acrylic rubber (ACM).

[0034] Furthermore, in terms of excellent moldability, particularly low-temperature moldability, of the resin composition as well as excellent toughness, a copolymer containing propylene as the main component (for example, the above-mentioned "propylene-ethylene copolymer") or a propylene-based elastomer which is a homopolymer of propylene is preferred.

[0035] In the case of a propylene-based elastomer, the content of propylene units relative to all units is preferably 70% by mass to 95% by mass, more preferably 80% by mass to 90% by mass. If the content of propylene units, which are hard segments, is 70% by mass or more, strength is improved, resulting in excellent moldability, while if it is 95% by mass or less, excellent stretchability is obtained due to the elasticity of the soft segments.

[0036] The content of the olefin-based elastomer is 3 to 12 parts by mass, preferably 4 to 10 parts by mass, based on 100 parts by mass of the entire film. If the amount of the olefin-based elastomer is less than 3 parts by mass, the stretchability will be poor. If the amount of the olefin-based elastomer is more than 12 parts by mass, the rigidity of the film will decrease.

[0037] When a propylene elastomer is used as the olefin elastomer, the melt mass flow rate (MFR) of the propylene elastomer is preferably 3 to 16 g / 10 min. When the MFR of the propylene elastomer is 3 g / 10 min or more, the resin composition has excellent moldability and rigidity, and when it is 16 g / 10 min or less, the resin composition has excellent moldability and toughness.

[0038] The melt mass flow rate described above can be obtained by measuring in accordance with the provisions of JIS K 7210-1:2014, and the measurement conditions for the propylene-based elastomer in this application are a temperature of 190°C and a load of 2.16 kg.

[0039] The MFR can be measured under the conditions of a temperature of 230°C and a load of 2.16 kg for general polypropylene-based resins, and a temperature of 190°C and a load of 2.16 kg for general polyethylene-based resins.

[0040] The melting point of the propylene-based elastomer is preferably 50 to 160° C., more preferably 50 to 80° C. If the melting point of the propylene-based elastomer is 50° C. or higher, the toughness of the resin composition will be superior, and if it is 160° C. or lower, the rigidity of the resin composition will be superior.

[0041] The "melting point" refers to the melting initiation temperature on a differential scanning calorimeter (DSC) chart.

[0042] <Maleic anhydride modified polyolefin> MA-PO functions as a compatibilizer and improves the dispersibility of cellulose powder in the film.

[0043] Examples of MA-PO include α-olefin-maleic anhydride copolymers, mixtures of α-olefin polymers and maleic anhydride, and mixtures of α-olefins, α-olefin-maleic anhydride copolymers and maleic anhydride. Examples of α-olefins include ethylene and propylene.

[0044] The MA-PO content is 0.4 to 4 parts by mass, preferably 0.6 to 3 parts by mass, based on 100 parts by mass of the entire film. If the MA-PO content is less than 0.4 parts by mass, the cellulose powder is not sufficiently compatible with the olefin elastomer or polyethylene and aggregates, resulting in poor dispersibility of the cellulose powder and poor moldability. If the MA-PO content is more than 4 parts by mass, the strength and solvent resistance of the film will decrease.

[0045] The melt viscosity of MA-PO is preferably 100 to 15,000 mPa s, and more preferably 200 to 5,000 mPa s. When the melt viscosity of MA-PO is 100 mPa s or higher, the resin composition will have excellent moldability and toughness, and when it is 15,000 mPa s or lower, the resin composition will have excellent rigidity.

[0046] The "melt viscosity" refers to the viscosity measured by a capillary rheometer.

[0047] The acid value of MA-PO is preferably 5 to 150 mgKOH / g, more preferably 30 to 100 mgKOH / g. When the acid value of MA-PO is 5 mgKOH / g or more, the resin composition has excellent moldability, and when it is 150 mgKOH / g or less, the resin composition has excellent appearance.

[0048] The "acid value" refers to a value measured by neutralization titration.

[0049] <Other ingredients> The film may further contain other components in addition to the cellulose powder, polyethylene, olefinic elastomer, and maleic anhydride-modified polyolefin, as needed, such as stabilizers, antioxidants, lubricants, antistatic agents, colorants, and other additives.

[0050] The content of other components when the entire film is taken as 100 parts by mass is preferably 0 parts by mass or more and less than 5 parts by mass, and more preferably 0 parts by mass or more and less than 4 parts by mass.

[0051] The film preferably contains a lubricant as another component. Adding a lubricant to the resin composition, which is the raw material for the film, improves the granulation properties of the resin composition. The lubricant is not particularly limited, but specific examples include stearic acid, zinc stearate, barium stearate, calcium stearate, etc. Furthermore, fatty acid amide compounds such as stearic acid amide and erucic acid amide may also be used.

[0052] When the resin composition contains a lubricant, the amount of lubricant in the resin composition is preferably 2 parts by mass or more but less than 7 parts by mass, and more preferably 3 parts by mass or more but less than 5.4 parts by mass, when the entire resin composition is taken as 100 parts by mass. In a composition that preferably contains a lubricant, if the amount of lubricant is 2 parts by mass or more but less than 7 parts by mass, the effect of improving granulation can be obtained while maintaining other physical properties (e.g., toughness), so the effect of the lubricant can be fully utilized. If the amount of lubricant is less than 2 parts by mass, the effect may not be fully exerted. If the amount of lubricant is 7 parts by mass or more, the dispersibility of the cellulose powder and the physical properties of the film (e.g., toughness) may be reduced.

[0053] <Specific gravity> The specific gravity of the film of the present invention is 0.93 or less, preferably 0.90 or less, and more preferably 0.88 or less. That is, despite containing high-specific-gravity cellulose powder, the film of the present invention has a specific gravity equal to or less than that of a typical LDPE film. Therefore, compared to conventional technologies, this can contribute to reducing CO2 emissions during film transportation and further reduce the environmental load. The specific gravity of the film can be measured in accordance with JIS K 7112 Method D (density gradient tube method).

[0054] <Total light transmittance> The total light transmittance of the film of the present invention measured without containing a colorant is preferably 65% ​​or less, and preferably 30% to 63%. The total light transmittance of the film can be measured in accordance with JIS K7361. Note that "total light transmittance measured without containing a colorant" refers to the total light transmittance of the film in the case of a film that does not contain a colorant, or the total light transmittance measured for a film manufactured using only components other than the colorant in the case of a film that contains a colorant. The greater the amount of voids in the film, the more diffusely reflected light entering the film due to the influence of the voids, resulting in a higher opacity of the film, or in other words, a higher whiteness. The lower the total light transmittance of the film, the higher the opacity and whiteness of the film. The greater the amount of voids in the film, the higher the whiteness of the film and the lower the total light transmittance.

[0055] <haze> The haze of the film of the present invention is preferably 97% or more, more preferably 97.8% or more, from the viewpoint of ensuring high opacity (whiteness) of the film. The haze of the film can be measured in accordance with JIS K7136.

[0056] <Air permeability> The air permeability of the film of the present invention is preferably 35,000 sec / 100 ml or less, and more preferably 1,000 sec / 100 ml or more and 33,000 sec / 100 ml or less. The air permeability of the film can be measured in accordance with JIS P8117. The smaller the air permeability, the greater the air permeability of the film. The smaller the air permeability (the greater the air permeability), the less likely air bubbles will be trapped when the film is attached to a container or the like, improving the suitability for attachment.

[0057] <Application> The uses of the film of the present invention are not intended to be limited, but specific examples include labels attached to containers such as PET bottles and product packaging, outer product packaging bags, shopping bags, garbage bags, etc. The film of the present invention is particularly suitable for labels because it combines sufficient opacity with excellent air permeability. Furthermore, since the film of the present invention has a low specific gravity and floats on water, when used as a label for products made of a non-floating material such as polyethylene terephthalate, the raw material for PET bottles, it has the advantage of facilitating separation during product disposal and recycling.

[0058] <Film manufacturing method> Next, an example of a method for producing the film of the present invention will be described.

[0059] The film according to the present invention can be obtained by, for example and without limitation, subjecting the resin compound to various molding processes, which is obtained by previously kneading and molding the above-mentioned cellulose powder, a portion of the polyethylene, an olefin elastomer, and MA-PO into a resin composition, and then mixing the remaining polyethylene as dilution polyethylene and various optional additives, etc. In this specification, the polyethylene previously blended in the resin composition may be referred to as polyethylene (A), and the polyethylene for dilution may be referred to as polyethylene (B).

[0060] The resin composition is preferably, but not limited to, in the form of a masterbatch, preferably in the form of pellets as a masterbatch, which allows smooth feeding from a hopper to a screw in a process using an extruder, making it suitable for films with various cellulose contents and produced by various molding methods, and easier to handle since it is less likely to scatter than a powder.

[0061] The resin compound may be obtained, for example, by dry-blending the above-mentioned resin composition with polyethylene (B) and the like before charging them into a molding machine, or by charging them into the molding machine in a desired order and kneading them in the molding machine. In this specification, the term "resin compound" is a concept that includes both the above-mentioned dry-blended state and the state in which the resin compound is kneaded in the molding machine.

[0062] The polyethylene (B) may be the same as or different from the polyethylene (A). From the viewpoint of obtaining excellent physical properties of a molded product while ensuring excellent moldability of the resin composition and resin compound, LDPE may be used as the polyethylene (A) and LLDPE may be used as the polyethylene (B).

[0063] The ratio of polyethylene (A) to polyethylene (B) is not particularly limited, and can be appropriately determined as needed to ensure good moldability of the resin composition and resin compound and excellent physical properties of the film.

[0064] <Method of manufacturing resin composition> First, cellulose powder and MA-PO are mixed in a predetermined ratio, and then the resulting mixture is mixed with polyethylene (A), an olefin-based elastomer, and any other components in predetermined ratios. The mixture is melt-kneaded and extruded into strands in a co-rotating twin-screw extruder equipped with a strand die at a predetermined temperature, but is not intended to be limiting, of 150°C or less, preferably 140°C to 150°C, and the extruded mixture is cut to obtain pellets of the resin composition.

[0065] The mixing method may be dry mixing using a super mixer, a Henschel mixer or the like.

[0066] <Film manufacturing method> The film of the present invention can be obtained by molding a resin compound comprising pellets of the above-mentioned resin composition, polyethylene (B), and optional additives using a commonly known molding method.

[0067] For example, when inflation molding is used as the molding method, the resin compound is melt-kneaded in a single-screw extruder at a predetermined temperature, for example, but not limited to, 160°C or lower, preferably 140°C to 160°C, and then introduced into a circular die and extruded, while simultaneously blowing air into the extruded compound to expand it into a film, and the film is then wound up on a take-up roll to obtain the molded product of the present invention.

[0068] The method for producing a film of the present invention preferably includes a step of obtaining a raw film by inflation molding and a step of further stretching the raw film to obtain the film of the present invention. In other words, it is preferable to further stretch the raw film obtained by inflation molding using the above-mentioned resin compound.

[0069] In this specification, the stretching of the resin compound in the process of obtaining the raw film may be referred to as "primary stretching," and the further stretching of the raw film may be referred to as "secondary stretching."

[0070] According to this configuration, by subjecting the raw film to secondary stretching, voids (see Reference Example 1 and Figure 1 described below) are formed between at least a portion of the cellulose powder and components other than the cellulose powder in the film, thereby effectively reducing the specific gravity of the film.

[0071] The method of secondary stretching is not particularly limited, and a generally known method can be used. Specifically, for example, the raw film may be stretched using a device such as a continuous tenter or a batch tenter. The stretching direction is not particularly limited, and may be either the MD direction, which is the resin flow direction during the production of the raw film, or the TD direction, which is a direction perpendicular to the MD direction. Secondary stretching may also be performed in a direction different from either the MD direction or the TD direction. Secondary stretching may also be performed in both the MD direction and the TD direction. In this case, biaxial stretching may be performed in which secondary stretching is performed in either the MD direction or the TD direction, followed by secondary stretching in the other direction.

[0072] The stretching ratio of the secondary stretching is preferably 2 times or more, more preferably 4 times or more, and particularly preferably 4.25 times or more, based on the original film. The higher the stretching ratio, the higher the strength of the film.

[0073] The thickness of the film after the second stretching is preferably 0.15 to 0.83 times the thickness of the original film, more preferably 0.3 to 0.7 times, and even more preferably 0.35 to 0.65 times.

[0074] The thickness of the raw film is not particularly limited, but can be, for example, 60 μm or more and 200 μm or less from the viewpoint of manufacturing stability.

[0075] The thickness of the film after the second stretching can be 30 μm or more and 50 μm or less.

[0076] The film temperature during the secondary stretching may be, for example, normal temperature (room temperature, e.g., 25°C), but is preferably 30°C or higher, more preferably 50°C or higher, and particularly preferably 90°C or higher. By setting the temperature during the secondary stretching to 30°C or higher, the air permeability of the film decreases, i.e., the air permeability of the film improves, and the application suitability of the film improves. [Example]

[0077] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and such modifications are not excluded from the scope of the present invention.

[0078] ≪Material≫ The materials used in this example are listed below. Note that MFR1 is a value measured at a temperature of 190°C and a load of 2.16 kg in accordance with the JIS K 7210-1:2014 standard, and MFR2 is a value measured at a temperature of 230°C and a load of 2.16 kg in accordance with the JIS K 7210-1:2014 standard. (1) Cellulose powder 1 (average particle size: 10 μm, aspect ratio: 1.8, manufactured by Rettenmeyer Japan Co., Ltd., product name: ARBOCEL (registered trademark) UFC100) (2) Cellulose powder 2 (average particle size: 18 μm, aspect ratio: 1.5, manufactured by Rettenmeyer Japan Co., Ltd., product name: ARBOCEL (registered trademark) BE600-10TG) The average particle size of each cellulose powder was measured using a laser diffraction particle size distribution analyzer (Malvern dry particle size distribution analyzer, product name: MASTER SIZER 3000). As described above, the aspect ratio of each cellulose powder was determined by analyzing images of 100 particles using a microscope (Keyence digital microscope, product name: VHX-7000) and the software attached to the microscope, and the average aspect ratio was calculated. (3) Propylene-based elastomer 1 (propylene-ethylene copolymer, ethylene unit content: 16% by mass, MFR1: 1.4 g / 10 min, MFR2: 3 g / 10 min, manufactured by ExxonMobil, trade name: Vistamaxx (registered trademark) 6102FL) (4) Propylene-based elastomer 2 (propylene-ethylene copolymer, ethylene unit content: 6% by mass, MFR2: 10,000 g to 100,000 g / 10 min (actual measurement is impossible, so a converted value based on melt viscosity is listed), melting point: 97°C, manufactured by ExxonMobil, trade name: Vistamaxx (registered trademark) 8880) (5) Low-density polyethylene (linear low-density polyethylene, density: 0.913 g / cm 3 , MFR1: 2g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Evolue (registered trademark) SP1520) (6) MA-PO (olefin wax, α-olefin-maleic anhydride copolymer: 66.8% by mass, α-olefin polymer: 32.9% by mass, maleic anhydride: 0.3% by mass, melting point: 70 to 76°C, melt viscosity: 140 to 210 mPa s, acid value: 95 to 110 mgKOH / g, manufactured by Mitsubishi Chemical Corporation, trade name: Diacarna 30M) (7) Anti-eye burr agent (fatty acid metal salt additive, base polymer: low-density polyethylene (density: 0.9 g / cm 3 ), MFR1: 6.3 g / 10 min, masterbatch containing 10% by mass of magnesium 12-hydroxystearate, manufactured by Katsuta Kako Co., Ltd., product name: AP-600P) (8) Lubricant (zinc stearate, manufactured by NOF Corporation, trade name: Zinc Stearate GP) (9) Anti-foam agent (master pellets containing 65% by mass of calcium oxide as the active ingredient and 35% by mass of LLDPE as the base polymer, manufactured by Ohmi Chemical Industry Co., Ltd., BELL-CML EM)

[0079] Examples 1 to 8 and Comparative Examples 1 to 4 <Preparation of Resin Composition> According to the formulation shown in Table 1, resin compositions were prepared by the following procedure.

[0080] [Table 1]

[0081] First, cellulose powder and MA-PO were mixed in a supermixer to obtain a mixture. Next, the resulting mixture was melt-kneaded with the remaining raw materials (low-density polyethylene (A), propylene-based elastomer, and other materials) in a co-rotating twin-screw extruder at a molding temperature of 150°C and a screw rotation speed of 40 to 120 rpm. The extruded mixture was extruded into strands with a diameter of 2 to 4 mm, and then cut into pellets of the resin composition.

[0082] <Film manufacturing> [Manufacturing raw film] The resulting resin composition pellets, polyethylene (B), and anti-bubble agent were dry-blended in the amounts listed in Table 1. The mixture was melt-kneaded in a single-screw extruder at a molding temperature of 160°C and a screw rotation speed of 60 rpm. The mixture was then introduced into a circular die for inflation molding, cooled and solidified by air cooling, and wound up on a winder. The width of the raw film (the width when the inflation-molded product is folded; i.e., the film is molded into a cylindrical shape with a circumference of 200 mm) was 100 mm, and the thickness was 70 μm or 120 μm. The screw specifications were full flight, L / D: 25, C / R: 3.08.

[0083] The obtained raw film was used as the final cellulose powder-containing film in Comparative Examples 1 to 4. In Examples 1 to 8, the obtained raw film was subjected to the following secondary stretching.

[0084] [Secondary stretching] A 120 mm square film was cut from the raw film and set in a batch tenter (KARO-IV batch tenter manufactured by Bruckner) equipped with a stretching device and a stretching chamber. The stretching device was then moved to the stretching chamber, which had been set to a predetermined temperature ("Film temperature during stretching" in Table 1), and the temperature was raised for a certain period of time (e.g., 60 seconds). After confirming that the sample and stretching device had stabilized at the predetermined temperature, stretching was performed at a predetermined stretch ratio ("MD ratio" and "TD ratio" in Table 1) and stretching speed (e.g., 40% / sec). After stretching was completed, the stretching device was returned to its initial position and left to cool at room temperature, and then removed after it had reached approximately room temperature. In this way, the cellulose powder-containing films of Examples 1 to 8 were obtained.

[0085] The "MD magnification" is expressed as the film length after the second stretching in the MD direction / the original film length, and the "TD magnification" is expressed as the film length after the second stretching in the TD direction / the original film length.

[0086] <Film property measurement> The following measurements were carried out on the films of Examples 1 to 8 and Comparative Examples 1 to 4. The results are shown in Table 1.

[0087] [specific gravity] The specific gravity of the obtained film was measured according to JIS K 7112 D method (density gradient tube method). More specifically, 10 mm × 20 mm test pieces (n = 2) were cut out from the obtained film. The specific gravity of each test piece was then measured, and the average value was taken as the specific gravity of the film. Note that, to avoid the influence of voids present in the stretched film, the measurement of the stretched film was carried out within 1 minute after the test piece had stabilized in the standard solution.

[0088] [Thickness before stretching] The thickness of the film before stretching was measured using a micrometer (Coolant-proof micrometer, manufactured by Mitutoyo Corporation). More specifically, the thickness of the film before stretching was measured at three points in the MD direction, and the average value was used as the thickness of the target film before stretching. The measurement points were set at least 50 mm apart.

[0089] [Thickness after stretching] The thickness of the stretched film was measured using a micrometer (Coolant-proof micrometer, manufactured by Mitutoyo Corporation). More specifically, the thickness of the stretched film was measured at three points in the stretching direction, and the average value was used as the thickness of the target film after stretching. The measurement points were set at least 50 mm apart from each other.

[0090] [Total light transmittance] The total light transmittance of the film was measured in accordance with JIS K7361. More specifically, test pieces were cut out from the film (n = 3). The total light transmittance of each test piece was measured using a haze meter (NDH4000 manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the median value was taken as the total light transmittance of the target film.

[0091] [HAZE] The haze of the film was measured in accordance with JIS K7136. More specifically, three test pieces were cut out from the film. The haze of each test piece was measured using a haze meter (NDH4000 manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the median value was taken as the haze of the film.

[0092] [Air permeability] The air permeability of the film was measured in accordance with JIS P8117. More specifically, test pieces were cut out from the film (n = 3). The air permeability of each test piece was measured using an Oken air permeability tester (EGO2-6 model, manufactured by Asahi Seiko Co., Ltd.), and the median value was taken as the air permeability of the target film.

[0093] [Tensile strength] MD direction (Examples 1, 3 to 8, Comparative Examples 1 to 4) The obtained film was cut into a dumbbell shape (JIS K 6251 dumbbell No. 3, both end width: 25 mm, total length: 100 mm, gauge length: 20 mm, width: 5 mm) extending in the MD direction to prepare a test piece. A tensile test was performed on the test piece in accordance with JIS K7127 at a temperature of 23°C and a relative humidity of 50% RH at a pulling rate of 200 mm / min to measure the tensile strength of the film in the MD direction.

[0094] TD direction (Example 2, Comparative Examples 1 to 4) The obtained film was cut into a dumbbell shape (JIS K 6251 dumbbell No. 3, both end width: 25 mm, total length: 100 mm, gauge length: 20 mm, width: 5 mm) extending in the TD direction to prepare a test piece. A tensile test was performed on the test piece in accordance with JIS K7127 at a temperature of 23°C and a relative humidity of 50% RH at a pulling rate of 200 mm / min to measure the tensile strength of the film in the TD direction.

[0095] <Consideration> As shown in Table 1, the films of Comparative Examples 1 to 4 had a specific gravity of 1.09 or more, while the films of Examples 1 to 8 had a specific gravity of 0.93 or less (specifically, 0.88 or less), indicating that the specific gravity of the film was reduced by secondary stretching.

[0096] Furthermore, compared with the films of Comparative Examples 1 to 4, the films of Examples 1 to 8 have a lower total light transmittance and an increased haze, indicating an increased opacity, ie, an increased whiteness.

[0097] It can be seen that the air permeability is lower and the air permeability is higher in the films of Examples 1 to 3 and 5 to 8 compared to the films of Comparative Examples 1 to 4. Regarding air permeability, the film of Example 4 obtained results similar to those of Comparative Examples 1 to 4. This is thought to be due to the low film temperature during the secondary stretching.

[0098] Also, it was found that the tensile strength in the MD direction or TD direction increased in the films of Examples 1 to 8 compared to the films of Comparative Examples 1 to 4. This indicates that the strength of the film is improved by the secondary stretching.

[0099] ≪Reference Examples 1 and 2≫ The film of Test Example 2d of Japanese Patent Application No. 2023-037948 (cellulose powder content: 30% by mass) was used as the film of Reference Example 1. Further, the film of Example 1 was stretched in the TD direction to obtain the film of Reference Example 2.

[0100] <SEM Observation> Samples were cut out from the films of Reference Example 1 (unstretched), Example 1 (with secondary stretching, MD direction), Example 2 (with secondary stretching, TD direction), and Reference Example 2 (with secondary stretching, TD direction after MD direction stretching), and scanning electron microscope observation (SEM observation) was performed on the plane (sample surface), TD cross-section, and MD cross-section. For the SEM observation of the film of Reference Example 1, SU5000 manufactured by Hitachi High-Tech Corporation was used. For the SEM observation of the films of Example 1, Example 2, and Reference Example 2, Phenom ProX manufactured by Thermo Fisher Scientific was used. The SEM images are shown in Fig. 1. In Fig. 1, the white arrows indicate the MD direction, and the double arrows indicate the stretching direction (however, for the secondary stretching of the film of Reference Example 2 (stretching in the TD direction after stretching in the MD direction), the MD direction is indicated by the double arrows of symbol A, and the TD direction is indicated by the double arrows of symbol B).

[0101] As shown in Figure 1, in the unstretched film of Reference Example 1, cellulose powder is observed protruding from the plane (surface). In the stretched films of Examples 1 and 2 and Reference Example 2, it is clear that the cellulose powder is further protruding and partially peeled off from the resin. When observing the MD and TD cross sections, the cellulose powder and matrix resin are oriented in the stretching direction, and some voids are generated between them, as indicated by the open circles in Figure 1. It is presumed that the generation of these voids reduces the apparent specific gravity of the film. Furthermore, SEM observation of the film of Reference Example 2 reveals that the voids around the cellulose powder are further increased when TD stretching (biaxial stretching) is performed after MD stretching. [Industrial Applicability]

[0102] As explained above, the present invention is suitable for films containing cellulose powder.< / haze>

Claims

1. A cellulose powder-containing film, wherein when the entire cellulose powder-containing film is taken as 100 parts by mass, 20 to 40 parts by mass of the cellulose powder; 50 to 70 parts by mass of polyethylene; 3 to 12 parts by mass of an olefin-based elastomer; and 0.4 to 4 parts by mass of a maleic anhydride-modified polyolefin, A cellulose powder-containing film having a specific gravity of 0.93 or less.

2. The polyethylene comprises linear low-density polyethylene. The cellulose powder-containing film according to claim 1.

3. The average particle size of the cellulose powder is 6 μm or more and 36 μm or less. The cellulose powder-containing film according to claim 1.

4. The aspect ratio of the cellulose powder is 2 or less. The cellulose powder-containing film according to claim 3.

5. a gap exists between at least a portion of the cellulose powder and components other than the cellulose powder in the cellulose powder-containing film; The cellulose powder-containing film according to claim 1.

6. The total light transmittance measured without the colorant is 65% or less. The cellulose powder-containing film according to claim 1.

7. The air permeability is 35,000 sec / 100 ml or less. The cellulose powder-containing film according to claim 1.

8. A method for producing a cellulose powder-containing film according to any one of claims 1 to 7, A step of obtaining a raw film by inflation molding; and further stretching the raw film to obtain the cellulose powder-containing film.

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