Method for producing bag film from fiber-resin mixed composition

Abstract

Provided is a method for producing a film that includes a vegetable fiber and is suitable for molding a bag.　The method for producing a film for a bag comprises a molding step for molding, by inflation molding, a fiber resin mixed composition containing: 10-40 mass% of a vegetable fiber; 10-40 mass% of polypropylene; and 20-80 mass% of polyethylene. A pellet of the mixed composition of the vegetable fiber and polypropylene and a pellet of the polyethylene are dry-blended and put into a hopper of the inflation molding, thereby molding at a mass ratio of the fiber resin mixed composition.

Description

[Technical Field]

[0001] The present invention relates to a bag film using a fiber-resin mixed composition containing wood fiber, polyethylene, and polypropylene, and a method for producing the same. [Background technology]

[0002] A variety of plastic resins and molding techniques have been investigated and put to practical use. Such plastic resins are also widely used in packaging containers and the like. However, due to issues such as marine pollution caused by microplastics and the use of petroleum resources, efforts are being made to reduce the amount of plastic resin used. For example, the following technology has been disclosed as a material that uses paper.

[0003] Patent Document 1 discloses a paper-containing resin composition for molding obtained by mixing a low combustion heat component whose main component is paper and a high combustion heat component whose main component is a thermoplastic synthetic resin whose combustion heat is higher than that of the paper, wherein the low combustion heat component is mainly composed of paper powder having a particle size of 50 μm or more and 200 μm or less, the composition contains more than 50 wt % and not more than 70 wt % of the low combustion heat component and more than 30 wt % and less than 50 wt % of the high combustion heat component, and the weight percentages of the low combustion heat component and the high combustion heat component in the composition have the relationship low combustion heat component > high combustion heat component.

[0004] Patent Document 2 discloses a foamed material having a large number of bubbles inside, characterized in that the foamed material is composed of 20 to 40 weight % polyolefin synthetic resin, 40 to 60 weight % paper powder, 20 to 30 weight % hydrophilic polymer, and water mixed into a high-temperature molten material obtained by mixing the synthetic resin, the paper powder, and the hydrophilic polymer under heating, wherein the weight ratio of the water to the molten material is in the range of 10 to 30 weight %, and the water vaporizes inside the molten material, forming a large number of bubbles inside the molten material while expanding the molten material to a given magnification, and the hydrophilic polymer forms a membrane that encapsulates the bubbles.

[0005] Patent Document 3 discloses a molding composition formed from a polyolefin-based thermoplastic synthetic resin and paper, obtained by mixing the synthetic resin with the paper, wherein the paper has an average particle size of 30 to 80 μm and is a paper powder that does not contain chlorine or fluorescent brighteners, the weight ratio of the synthetic resin to the total weight of the molding composition is in the range of 25 to 80 wt %, the weight ratio of the paper powder to the total weight of the molding composition is in the range of 20 to 75 wt %, and the paper powder is dispersed approximately uniformly in the synthetic resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-181511 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-041041 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-073504 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Documents 1 to 3 relate to technologies that use powdered paper. By using naturally derived paper, this technology can contribute to carbon offsets more than products that primarily use plastic resins. However, products manufactured using such compositions have been limited to thick products such as cases, cups, trays, and cutlery that can be molded by injection molding or the like. Furthermore, film-like products such as bags have not been molded. This is thought to be because the fibers of the paper components contained in the film tend to become breakage points when molded into bags or other products, making continuous molding difficult, as well as the difficulty of controlling the molding temperature.

[0008] Under such circumstances, an object of the present invention is to provide a film that contains plant fibers, which are components of paper, and is suitable for forming bags. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have found that the following inventions meet the above objectives, thereby completing the present invention.

[0010] <1> A method for producing a bag film, comprising a molding step of molding a fiber-resin mixed composition containing 10 to 40% by mass of plant fiber, 10 to 40% by mass of polypropylene, and 20 to 80% by mass of polyethylene by inflation molding. <2> The pellets of the mixed composition of the plant fiber and the polypropylene and the pellets of the polyethylene are dry-blended and then charged into a hopper of the inflation molding to form a fiber-resin mixed composition in a mass ratio. <1> A method for producing the bag film described in 1. <3> The molding step is performed at an extrusion temperature of 160 to 200°C. <1> or <2> A method for producing the bag film described in 1. <4> The film thickness is 30 to 180 μm. <1> ~ <3> 1. A method for producing a bag film according to any one of the preceding claims. <5> The aforementioned <1> ~ <4> 1. A method for producing a bag, comprising a processing step of forming a welded portion at the bottom seal or the side seal using the bag film according to any one of the preceding items. <6> A bag film containing a fiber-resin mixed composition containing 10 to 40% by mass of vegetable fiber, 10 to 40% by mass of polypropylene, and 20 to 80% by mass of polyethylene, and having a film thickness of 30 to 180 μm. <7> The aforementioned <6> A bag having a planar portion of the bag film described in 1 and a welded portion of the bag film. [Effects of the Invention]

[0011] According to the present invention, a film containing plant fibers, which are components of paper, and suitable for forming into bags can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an inflation molding apparatus that can be used in the manufacturing method of the present invention. [Figure 2] 1 is an image showing a part of the manufacturing process of a film according to an embodiment of the present invention. [Figure 3] 1 is an image showing a part of the manufacturing process of a film according to an embodiment of the present invention. [Figure 4] 1 is an image of a bag film produced by the manufacturing method of the present invention. [Figure 5] 1 is an enlarged image of a surface portion of a bag film manufactured by the manufacturing method of the present invention. [Figure 6] 1 is an image of the inside of a bag film manufactured by the manufacturing method of the present invention when unfolded. [Figure 7] 10 is an image of another bag made according to an embodiment of the present invention. [Figure 8] 10 is an enlarged image of the surface portion of another bag manufactured according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail an embodiment of the present invention, but the following description of the constituent elements is one example (typical example) of an embodiment of the present invention, and the present invention is not limited to the following content unless the gist of the present invention is changed. Note that when the expression "to" is used in this specification, it is used as an expression that includes the numerical values ​​before and after it.

[0014] [Method of manufacturing bag film of the present invention] The method for producing a bag film of the present invention includes a molding step of molding 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 by inflation molding. In this application, the method for producing a bag film of the present invention may be simply abbreviated as "the manufacturing method of the present invention." According to the production method of the present invention, a film containing plant fibers, which are components of paper, and suitable for forming into bags can be obtained.

[0015] [Bag film of the present invention] The bag film of the present invention contains a fiber-resin mixed composition containing 10 to 40 mass% of vegetable fiber, 10 to 40 mass% of polypropylene, and 20 to 80 mass% of polyethylene, and has a film thickness of 30 to 180 μm. The bag film of the present invention contains plant fibers, which are components of paper, and is suitable for forming bags. Note that the bag film of the present invention can be manufactured by the manufacturing method of the present invention in this application, and the corresponding configurations in this application can be used interchangeably.

[0016] In an attempt to mold a film using paper components, the inventors attempted to mold a film using a blown film extrusion machine using pellets of a mixed composition of plant fiber and polypropylene. However, when attempting to mold pellets of this mixed composition into a film, they found that the extrusion pressure was too high, the pellets extruded in pieces from the extrusion port, and the resulting thickness variations and holes during expansion and stretching were difficult to achieve. However, they accidentally discovered that a homogeneous film could be obtained by using polyethylene in combination with the polypropylene, which typically has a different extrusion temperature than polypropylene and is not sufficiently mixed when mixed in a blown film extrusion machine, resulting in unevenness.

[0017] The inventors dry-blended pellets of a mixed composition of plant fiber and polypropylene (first pellets) with polyethylene pellets (second pellets), then added them to a hopper and subjected them to inflation molding. Surprisingly, they were able to obtain a homogeneous film suitable for use as a bag film. This film has a paper-like appearance due to the dispersed plant fiber, and is surrounded by a thin, light-diffusing film of dispersed polyethylene and polypropylene.

[0018] [Fiber-resin mixed composition] The fiber-resin mixed composition of the present invention is a mixture of plant fiber, polypropylene, and polyethylene. This mixed composition also includes a dry blend (so-called dry blend) of pellets containing premixed components and pellets containing other components. For example, a dry blend of pellets (first pellets) of the plant fiber and polypropylene mixed composition and pellets (second pellets) of polyethylene is preferred.

[0019] [Plant fiber] The fiber-resin mixed composition contains 10 to 40% by mass of plant fibers. The plant fibers can be natural plant fibers used in paper, etc. The natural plant fibers can be stem fibers, fruit fibers, leaf fibers, etc. In particular, fibers used in paper can be widely used. The plant fibers can be appropriately defibrated and used. Virgin pulp can be used as this fiber. From the perspective of contributing to recycling and environmental conservation, and because they are easily dispersed in film, it is effective to use fibers derived from waste paper, etc. Furthermore, waste paper-derived fibers are easily shortened and defibrated through multiple papermaking processes and uses, and are therefore suitable for dispersion with polypropylene and polyethylene.

[0020] The plant fiber content in the fiber-resin mixed composition is preferably 12% by mass or more, more preferably 15% by mass or more. If the plant fiber content is too low, it may be difficult to mix with polyethylene and polypropylene. The plant fiber content may be 35% by mass or less, 30% by mass or less, or 28% by mass or less. If the plant fiber content is excessively high, it may be difficult to obtain a sheet or film with a stable shape in heat molding such as inflation molding. Furthermore, when the inflation-molded film is molded into a bag or the like, processing by welding may become unstable.

[0021] [polypropylene] The fiber-resin mixed composition contains 10 to 40 mass % of polypropylene, which may be block polymerized polypropylene, random polymerized polypropylene, homopolymerized polypropylene, metallocene catalyst polypropylene, or modified polypropylene.

[0022] The polypropylene content in the fiber-resin mixed composition is preferably 12% by mass or more, more preferably 15% by mass or more. If the polypropylene content is too low, it may be difficult to mix with plant fibers and polyethylene. The polypropylene content may be 35% by mass or less, 30% by mass or less, or 28% by mass or less. If the polypropylene content is excessive, the plant fibers derived from the natural environment will relatively decrease. Furthermore, it may become less easily mixed with polyethylene, resulting in uneven appearance and physical properties, which may deteriorate the quality.

[0023] [polyethylene] The fiber-resin mixed composition contains 10 to 80 mass% of polyethylene. The polyethylene may be low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, metallocene-catalyzed polyethylene, or modified polyethylene. It is particularly preferable to use low-density polyethylene or linear low-density polyethylene, which are suitable for molding into a film.

[0024] The polyethylene may be a plant-derived plastic polyethylene. The plant-derived plastic polyethylene may be made from sugarcane or other raw materials. For example, Green Polyethylene (trademark) from Braskem (headquarters: Brazil) may be used. The use of such plant-derived plastics can reduce the amount of fossil fuel used and the amount of carbon dioxide emitted in the production process. Furthermore, the biomass content in bag films made of the fiber-resin mixture composition can be improved.

[0025] The polyethylene content in the fiber-resin mixed composition is more preferably 15% by mass or more, and can be 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the polyethylene content is too low, it may be difficult to mix with plant fibers and polypropylene. The polyethylene content may be 70% by mass or less, or 60% by mass or less. If the polyethylene content is excessively high, the plant fibers derived from the natural environment will relatively decrease. Furthermore, molding processability may decrease, resulting in uneven appearance and physical properties, which may deteriorate the quality.

[0026] As partially described above, the fiber resin composition can be prepared by pre-mixing plant fibers, polypropylene, and a portion of polyethylene and pelletizing them by melt molding or the like. This can be pellets of plant fibers and polypropylene and / or polyethylene. A pre-mix of plant fibers and polypropylene can be used. Such a mixture of plant fibers and polypropylene may be referred to as first pellets. The mixing ratio of plant fibers to polypropylene in the first pellets (plant fibers:polypropylene) can be 10:40 to 40:10, 10:20 to 20:10, 10:15 to 15:10, or 10:12 to 12:10, in terms of mass ratio. The plant fibers and polypropylene can be approximately equal in ratio, with the plant fibers accounting for a larger proportion.

[0027] [Other ingredients] The fiber-resin mixed composition of the present invention may contain components other than plant fibers, polypropylene, and polyethylene (hereinafter referred to as "other components"). The proportion of plant fibers, polypropylene, and polyethylene in the fiber-resin mixed composition ("plant fibers + polypropylene + polyethylene" / fiber-resin mixed composition) is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. The upper limit of this proportion may be 100% by mass, or may be 99.5% by mass or less, or 99% by mass or less. Other components that can be used include plasticizers, weathering agents, colorants, and biomass, which are used in blown film molding of polyolefin-based resins. Examples of biomass that can be used include compositions containing rice flour, such as Rice Resin®, compositions containing starch derived from potatoes, such as NuPlastiQ®, and compositions containing bamboo flour.

[0028] [Blown film molding] The manufacturing method of the present invention includes a molding step using inflation molding, which is a film-forming technique in which a resin is extruded into a tube shape from an extruder and softened, and then gas is blown into the extruded resin to inflate it and the extruded resin is taken up.

[0029] FIG. 1 shows an outline of the structure of an inflation molding apparatus. The inflation molding apparatus 10 is a device for forming a film 1 by inflation molding. A fiber-resin mixed composition is charged from a hopper 21, and a motor 22 rotates to rotate a screw 23, which extrudes the composition from a die 24. During this extrusion, a gas such as air is blown from the bottom to the top of the die 24 as shown by the arrow in FIG. 1, thereby inflating the film 1 and forming it. The inflated film 1 is taken up onto a roll 4 via a guide 3, rollers 31, 32, and 33.

[0030] The ratio of the fiber-resin mixed composition can be a predetermined ratio when it is charged into the hopper 21. From the viewpoints of the stability of the mixed ratio and ease of charging into the hopper 21, it is preferable to dry-blend the pellets and charge them into the hopper.

[0031] [Extrusion temperature] The extrusion temperature of the blown film molding die 24 is preferably 160 to 200°C. Generally, polypropylene for blown film molding is extruded at a relatively low temperature of around 150°C, while polyethylene for blown film molding is extruded at around 180°C, resulting in different extrusion temperatures. Even if one of these conditions or an intermediate condition is used, the difference in fluidity is too great to allow for sufficient mixing. However, the present invention uses a fiber-resin mixed composition with a predetermined ratio, which unexpectedly allows for the polyethylene and polypropylene to be formed into a film in a dispersed and mixed state.

[0032] In this molding, as described above, the manufacturing method of the present invention preferably performs molding at an extrusion temperature of 160 to 200°C at the die 24. The extrusion temperature can be set appropriately taking into consideration the extrusion pressure, the molecular weight of the resin, the mixing ratio, the film thickness, etc. It is more preferably 170°C or higher, and even more preferably 175°C or higher. Furthermore, 195°C or lower is more preferable. If the extrusion temperature is too low, the extrusion pressure may become too high, which may prevent extrusion or dispersion. If the extrusion temperature is too high, deterioration due to heating may occur, resulting in coloration, etc. The extrusion temperature at the die 24 is set to a predetermined temperature, and the temperature of the flow path corresponding to the screw 23 from the hopper 21 to the die 24 is increased in stages.

[0033] The thickness of the film to be formed is preferably 30 to 180 μm. The thickness of the film can be adjusted by adjusting the extrusion rate, the size of the opening of the die 24, the take-up speed, etc. If the film thickness is too thin, the plant fibers will be larger than the film thickness and will become areas where stress is concentrated, making molding difficult, thickness unevenness will make winding difficult, and there is a risk of them becoming breakage points when formed into a bag. If the film thickness is too thick, the rigidity will be too high and the film may not be suitable for inflation molding. The upper limit of the film thickness may be 150 μm or less, 120 μm or less, or 100 μm or less. The lower limit of the film thickness may be 35 μm or more, or 40 μm or more.

[0034] [Bag forming] The bag film produced by the manufacturing method of the present invention can be processed into bags using inflation-molded film bag-forming techniques such as bottom sealing, side sealing, attachment of peripheral components, and printing. Although the film contains plant fibers, it also contains polyethylene and polypropylene, which are uniformly dispersed. Therefore, the film is suitable for continuous manufacturing using thermoplastic resin molding and processing methods such as heat sealing. By utilizing these film properties, bags can be made with a flat portion of the bag film and a welded portion of the bag film (see Figure 4). [Example]

[0035] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not changed.

[0036] [Materials etc.] Mixed composition (a): "MAPKA (registered trademark) "KM-MB51-WP"" (Environmental Management Research Institute Co., Ltd.) general-purpose grade, paper content 51% by mass, polypropylene content 49% by mass, density: 1.15 kg / cm 3 (JIS K7112), MFR: 0.1g / 10min (JIS K7210 230℃, 2.16kg) LLDPE (a): Metallocene LLDPE Evolue (registered trademark) "SP2520" (Prime Polymer Co., Ltd.) Density: Approximately 925 kg / m 3 (JIS K7112) LLDPE(b): Rotren LLDPE “Q1018N” (QATOFIN Company Limited) LLDPE(c): Green polyethylene (trademark) "SLL118 / 21" (Braskem), MFR (190 / 2.16) (measurement standard D1238) 1g / 10min, density 0.918g / cm 3 , biomass ratio 87%

[0037] [Manufacturing equipment] The main specifications of the inflation molding device used in the production test are as follows: Die: 250mm Tube / sheet compatible Raw roll width: 600mm~1200mm Thickness guide: 20μm~150μm Extrusion rate: 80kg / h~110kg / h Take-up speed: 8m / min~80m / min Gusset folding width: Maximum 100mm Winding device: Maximum winding diameter φ600mm Maximum weight 150kg

[0038] [Example 1] 1) Test composition: Mixed composition (a), LLDPE (a), and LLDPE (b) were mixed in pellet form to prepare a test composition for molding. The composition of the test composition is shown in Table 1. Each test composition was blown into a film using the blown film molding machine (manufacturing machine) described above. The production conditions were a die extrusion temperature of 191°C, a cooling blower frequency of 38 Hz, and a tension of 1.2 kgf. The target film thickness was 70 μm and the film width was 820 mm.

[0039] For all of the test compositions (1) to (3), a film having a thickness of approximately 70 μm, which corresponds to the target thickness, could be stably formed into a winding length of 1000 m. Figure 2 shows an image of the area around the die (see die 24 in Figure 1) during the production of test composition (1). Figure 3 shows the film being transported by guide rolls for winding after that. Thus, bag films could be stably produced by the production method according to the present invention.

[0040] [Table 1]

[0041] [Comparative Example 1] An attempt was made to blow-film extrusion using the mixed composition (a) alone under the conditions similar to those in Example 1. Since the mixed composition (a) does not contain polyethylene but does contain polypropylene, the die extrusion temperature was raised stepwise by 10°C from 160°C to 190°C, which corresponds to the general extrusion temperature for polypropylene, but the extrusion test was carried out. However, the mixed composition could not be expanded by blowing, and a film could not be formed at any temperature.

[0042] [Bag film molding (1)] A single layer film cut from the film molded in Example 1 above was processed to produce a bag. Photographs of the bag are shown in Figures 4 to 6. The bag was folded from the center, with the folded portion serving as the bottom side. The bottom side was folded in by approximately 6 cm using a gusset. The edge on the opposite side to the bottom side served as the opening side, and to improve the strength of the opening, it was folded inward by approximately 6 cm using a gusset. In addition, a loop approximately 3 cm wide and 28 cm long was attached by welding near the center of the opening side. Side seals were then welded and cut to a width of approximately 40 cm (the length in the conveying direction) to obtain a bag.

[0043] As shown in Figure 4, the bag has a width w of approximately 40 cm (in the direction of film flow) and a height h of approximately 30 cm (in the width direction of the film). As shown in the enlarged view of Figure 5, the bag has a texture similar to that of Japanese paper, with paper fibers dispersed throughout. As shown in Figure 6, the handle is reinforced by gusseting, allowing the bottom to be used at a wider width.

[0044] [Bag film molding (2)] In accordance with Example 1, a film of test composition (1) molded into a tubular shape with a film thickness of 70 μm and a width (w) of 30 cm was used to form a bag by bottom sealing. The bag made using test composition (1) is shown in Figure 7. This bag was molded into a bag shape with a width (w) of 30 cm and a height (h) of 51 cm, with an oval cutout for the handle. When the film is molded into a bag by inflation molding, the flow direction of the film corresponds to the height (h) of the bag. The upper end in the height (h) direction is the fusion part with the bag in the previous flow direction, and the lower end is the fusion part with the bag (film) in the subsequent flow direction. A fusion part was provided 1 cm above the bottom of the fusion part at the lower end. This bag is used as a bag with the upper end as the opening, the left and right sides as the closed parts utilizing the tubular molding achieved by inflation molding, and the fusion part at the lower end as the closed part at the bottom.

[0045] This bag was filled with two 1kg dumbbells (2kg total) and hung by the handle. After leaving it for 24 hours, the dumbbells did not fall, and the bag remained strong and unbroken. Furthermore, yellow, blue, and black patterns and thin black text were printed near the center of the surface, and they were printed well. Figure 8 shows a close-up image of the surface of this bag. This image was taken with the contrast enhanced. The surface and film of this bag are white, and components believed to be plant fibers derived from recycled paper are uniformly dispersed throughout the surface and film, giving it a texture similar to Japanese paper. Its appearance is reminiscent of natural ingredients and its design is excellent.

[0046] [Example 2] 1) In accordance with Example 1, a test composition having the following composition was prepared and a film was produced. Test composition: 40 parts by mass of the mixed composition (a), 50 parts by mass of LLDPE (a), and 10 parts by mass of LLDPE (c) were mixed in pellet form to prepare a test composition for molding.

[0047] The obtained film was used to form a bag. This bag had excellent mechanical properties and an excellent appearance, similar to the bag of Example 1. Furthermore, the biomass content was approximately 28.7% in total, which means that biomass was effectively utilized. Furthermore, the bag was safe, meeting the standards of Food Sanitation Act No. 370. [Industrial Applicability]

[0048] The manufacturing method of the present invention can be used for industrial production of bags and is therefore industrially useful. [Explanation of symbols]

[0049] 1 film 10 Molding equipment 21 Hopper 22 Motor 23 Screw 24 nozzle 3 Guide 31, 32, 33 Roller 4 rolls

Claims

1. 15 to 28% by mass of vegetable fiber, 12 to 28% by mass of polypropylene; A fiber resin mixed composition containing 40 to 70 mass% of polyethylene, The method includes a molding step of molding by inflation molding at an extrusion temperature of 160 to 200°C, pellets of the mixed composition of the plant fiber and the polypropylene and pellets of the polyethylene are dry-blended and charged into a hopper of the inflation molding machine, thereby molding the fiber-resin mixed composition into a mass ratio; The total amount of the plant fiber, the polypropylene, and the polyethylene in the fiber-resin mixed composition is 95% by mass or more, A method for producing a bag film having a film thickness of 30 to 180 μm.

2. The plant fiber comprises virgin pulp, The method for producing a bag film according to claim 1 , wherein the polyethylene contains a plant-derived plastic. (Excluding bag films containing graphite and / or α-olefin copolymers containing side chains and acidic groups.)

3. A method for producing a bag, comprising a processing step of forming a welded portion at the bottom seal or the side seal using the bag film according to claim 1 or 2.

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