Eggshell powder-containing film and method for producing the same

Abstract

To provide an eggshell powder-containing film which has a simple structure and is deliverable in the form of a film, and a method for producing the same.SOLUTION: An eggshell powder-containing film (1) comprises eggshell powder (2) dispersed in a polyethylene resin (3). In the eggshell powder-containing film (1), an average particle diameter (D) of the eggshell powder (2) is 0.5 μm or more and 3 μm or less, a thickness (W) of the film (1) is 15 μm or more and 200 μm or less, and a content of the eggshell powder (2) in the film (1) is 20% or more and 35% or less in mass ratio.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, the waste problem caused by the excessive use of plastics such as shopping bags has become a global issue, and in Japan, a fee has been introduced for plastic bags as an opportunity to rethink lifestyles. However, not all plastic bags are subject to the fee, and bags that are recognized for their environmental performance and are labeled as such are not subject to the fee.

[0003] On the other hand, from the viewpoint of environmental protection and resource conservation, reuse of industrial waste is being considered. For example, eggshells are one such industrial waste. Eggshells are a biological component, and are considered to have a carbon neutral environmental load and little impact on the environment. In general, eggshells are often powdered and used, and examples of such technologies include JP 2023-2190 A (Patent Document 1) and JP 2020-84033 A (Patent Document 2).

[0004] Patent Document 1 discloses an eggshell powder-containing resin composition that contains eggshell powder having a particle size D50 of 10 μm to 50 μm and a thermoplastic resin. Patent Document 2 discloses a biodegradable resin composition that contains eggshell powder and biodegradable resin powder, each having an average particle size of 0.1 μm to 200 μm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2023-2190 [Patent Document 1] JP 2020-84033 A Summary of the Invention [Problem to be solved by the invention]

[0006] The resin compositions disclosed in Patent Documents 1 and 2 disclose the formation of a film using eggshell powder. However, unlike food trays and the like disclosed as resin compositions, the films are thin and soft, and the structures disclosed in Patent Documents 1 and 2 do not allow the manufacture of films of a quality that can be provided to users.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an eggshell powder-containing film that has a simple structure and can be provided as a film, and a method for producing the same. [Means for solving the problem]

[0008] An eggshell powder-containing film according to one embodiment of the present invention is an eggshell powder-containing film in which eggshell powder is dispersed in polyethylene resin, in which the average particle size of the eggshell powder is 0.5 μm or more and 3 μm or less, the thickness of the film is 15 μm or more and 200 μm or less, and the amount of eggshell powder in the film is 20% or more and 35% or less by mass.

[0009] Preferably, the eggshell powder is uniformly dispersed in the thickness direction and the surface direction.

[0010] Preferably, the polyethylene resin is a virgin resin.

[0011] One embodiment of the present invention relates to a manufacturing method for an eggshell powder-containing film, which is a manufacturing method for producing a film containing eggshell powder, and includes the steps of preparing eggshell powder having an average particle size of 0.5 μm or more and 3 μm or less and polyethylene resin, a mixing step of mixing the eggshell powder with the polyethylene resin in a mass ratio of 20% or more and 35% or less, and a molding step of molding the mixed eggshell powder and polyethylene resin into a film.

[0012] Preferably, the mixing step uses a twin screw extruder having two screws.

[0013] Preferably, the molding step is carried out by an inflation molding method.

[0014] Preferably, the method for producing an eggshell powder-containing film further comprises a drying step of drying the eggshell powder. Effect of the Invention

[0015] According to the eggshell powder-containing film and the manufacturing method thereof of the present invention, a film containing eggshell powder can be provided to users with a simple configuration. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic plan view of the composition of an eggshell powder-containing film according to the present embodiment. [Diagram 2] FIG. 2 is a schematic longitudinal sectional view of the composition of an eggshell powder-containing film according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The eggshell powder-containing film according to the present embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0018] <About the film containing eggshell powder> The eggshell powder-containing film according to the present embodiment is one in which eggshell powder is dispersed in a polyethylene resin. First, the components constituting the eggshell powder-containing film will be described, and then the form of the film will be described in detail.

[0019] (eggshell powder) First, the eggshell powder, which is a component of the film, will be described. The eggshell powder is made by powdering eggshell powder. The eggshell is, for example, the eggshell of a natural or farmed bird, such as a chicken, duck, quail, or ostrich. The eggshell of farmed chickens is in large supply and a constant amount can be secured, making disposal methods difficult. Therefore, it is preferable that the eggshell powder is typically chicken eggshell.

[0020] The eggshell powder may be dried at 90°C to 120°C before or after crushing. The eggshell powder may also contain a calcined eggshell extinguishing powder. To obtain the calcined eggshell extinguishing powder, the eggshell is first calcined for 1 to 60 minutes, for example, at 600°C to 1500°C while introducing carbon dioxide gas or the like. This removes unnecessary organic matter by thermal decomposition. After calcination, water is added to hydrate (extinguish) the eggshell at a temperature of 700°C to 1200°C to obtain a calcined product mainly composed of calcium hydroxide.

[0021] The composition of calcium compounds derived from living organisms is generally calcium carbonate (CaCO3), which is calcined to obtain calcium oxide (CaO). In this embodiment, calcium oxide is hydrated to calcium hydroxide (Ca(OH)2) by performing a predetermined hydration process after calcination. Calcium hydroxide is strongly alkaline, and therefore exhibits effects such as deodorizing, antibacterial, and preservative effects, and also functions as an antibacterial agent. In the above-mentioned drying process and process for obtaining the fire-extinguishing powder, appropriate pulverization is performed, and pulverization is repeated as necessary, thereby reducing the average particle size of the eggshell powder.

[0022] The eggshell powder has an average particle size of 0.5 μm or more and 3 μm or less. If the average particle size is less than 0.5 μm, it is difficult to manufacture the powder itself. If the average particle size exceeds 3 μm, the proportion of the particles in the film thickness of 15 μm to 200 μm or less increases, and when the film is cut, the eggshell powder may be used as a fulcrum to cause the film to split. The average particle size refers to a value measured using an optical microscope or a value obtained by sieving. The 50% diameter (X 50 , D 50The value obtained as the square root of the square root of the

[0023] In this embodiment, it is preferable that the particle size of the eggshell powder is nearly constant, that is, monodisperse, and has a narrow particle size distribution. By making the particle size nearly constant, it is possible to make the mixture with the biodegradable resin powder described later more uniform. For example, uniformity can be used as an index representing the width (narrowness) of the particle size distribution. The uniformity is a value obtained by dividing the 60% particle size under sieve, obtained from the particle size distribution measured by particle size distribution measurement or sieving, by the 60% particle size under sieve, and the closer this value is to 1, the narrower the particle size distribution width is, the uniform particle size is, the less cohesive the particles are, and the particles (powder) have high fluidity. For example, powders with a uniformity of 10 or less, 8 or less, 5 or less, 3 or less, or 2 or less can be used.

[0024] By using sieving, the particle size of the eggshell powder can be measured and the particle size of the eggshell powder (particles) can be made constant (the degree of dispersion (particle size distribution) can be made narrow) at the same time. It is preferable to wash the eggshell (or its pulverized product, etc.) before and after drying when obtaining the eggshell powder, and before and after the firing process when obtaining the fired powder. Washing can remove impurities such as dirt adhering to the eggshell and the eggshell membrane.

[0025] If these impurities or eggshell membrane remain after drying or baking, when they are mixed with a resin (described later) to produce a film, they may cause a decrease in performance, undesired coloring, or an undesirable odor. For example, since eggshell membrane is made of a protein whose main component is keratin (containing sulfur), if it is mixed with a resin while still remaining to produce a resin composition that is then molded, there is a risk of an unpleasant odor due to the sulfur content being generated.

[0026] The conditions for washing are not particularly limited and can be appropriately set depending on the state of the eggshell. For example, the washing can be performed using water at room temperature to about 50°C for about 1 minute to 60 minutes. Washing can also be performed using antibacterial water. Washing can be performed multiple times.

[0027] In these treatment processes, the eggshells or their pulverized products (powder) are appropriately dried as necessary, for example, at a temperature of 70° C. to 120° C. This drying allows the baking and pulverization processes to be carried out quickly after washing, and also reduces the unpleasant odor that adheres to the eggshells. Drying can be carried out multiple times.

[0028] (Polyethylene resin) Next, the polyethylene resin will be described. The polyethylene resin is a thermoplastic resin with a low processing temperature of 95°C to 130°C. The polyethylene resin is preferably a low density polyethylene (a mixture of LLDPE and LDPE). The polyethylene resin is typically in the form of pellets, but may also be in the form of powder.

[0029] It is preferable that the polyethylene resin is a virgin resin. Virgin resin is a resin that is produced using only new materials. A raw material that can be contrasted with virgin resin is regenerated (recycled) resin. Because virgin resin does not contain recycled raw materials, it maintains certain properties and can be used to mold products of uniform quality. Polyethylene resin is reversible, so it deteriorates with use. For this reason, it is said that recycled resin has unstable properties depending on the type, and cannot be used to mold products that maintain quality.

[0030] (Eggshell powder and polyethylene resin blend amount) The amount of eggshell powder in the film is 20% to 35% by mass, preferably 25% to 30%. If the amount of eggshell powder in the film is 25% or more, the film can be provided free of charge when it is molded into a plastic bag. If the amount exceeds 30%, the amount of eggshell powder is too high and cannot be mixed uniformly with the polyethylene resin.

[0031] (film) Finally, the form of the eggshell powder-containing film will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram of the eggshell powder-containing film as viewed from the surface direction, and Figure 2 is a schematic diagram of the same as viewed from the thickness direction.

[0032] The film 1 is a polyethylene resin 3 containing eggshell powder 2 molded into a thin film shape, also called a sheet. Specifically, the thickness W of the film 1 is 15 μm or more and 200 μm or less, and preferably 30 μm or more and 100 μm or less. The film 1 is typically molded into a bag shape, and is specifically provided as a product packaging bag for packaging products. The product packaging bag includes at least a front surface and a back surface, and may be provided with a gusset, a gusset, and a handle depending on the shape of the bag. An example of a product packaging bag is a shopping bag.

[0033] The eggshell powder 2 is uniformly dispersed in the thickness direction and the surface direction. "Uniformly dispersed" means that the content of the eggshell powder 2 is substantially equal in any region in the thickness direction and the surface direction of the film 1. As described above, the average particle size D of the eggshell powder 2 is 0.5 μm or more and 3 μm or less. Meanwhile, the thickness W of the film 1 is 15 μm or more and 200 μm or less. Therefore, for example, five or more particles of the eggshell powder 2 are located in the thickness direction.

[0034] Conventional films containing eggshell powder had noticeable unevenness on the film surface and varied in thickness. Furthermore, when touching the surface of conventional films containing eggshell powder, the film felt as if it was being absorbed, and was uncomfortable to the touch. Therefore, although conventional films containing eggshell powder were able to be formed into a film shape, they had inferior formability compared to films containing 100% synthetic resins such as general polyethylene and polypropylene.

[0035] In contrast, the eggshell powder-containing film of the present embodiment is one in which eggshell powder is dispersed in polyethylene resin, the average particle size of the eggshell powder is 0.5 μm or more and 3 μm or less, the film thickness is 15 μm or more and 200 μm or less, and the amount of eggshell powder in the film is 20% or more and 35% or less by mass, so that a film containing eggshell powder with a simple configuration can be provided to users.

[0036] In addition, because the eggshell powder is uniformly dispersed in both the surface and thickness directions, there are almost no irregularities on the film surface, and the film thickness is uniform, making it possible to achieve a texture that is the same as that of conventional films containing 100% synthetic resin. Furthermore, even when cutting the film to form it into packaging bags, it can be cut accurately in any direction. If the amount of eggshell powder in the film is 25% or more by mass, the film will be recognized as environmentally friendly when processed into plastic shopping bags, and it will be possible to label the film to that effect, making it possible to provide them free of charge.

[0037] <About the manufacturing method of the film containing eggshell powder> The method for producing an eggshell powder-containing film according to the present embodiment includes a preparation step, a drying step, a mixing step, and a molding step. Each step will be described below.

[0038] (preparation process) First, eggshell powder with an average particle size of 0.5 μm or more and 3 μm or less and polyethylene resin are prepared. The eggshell powder is dried and may be 100% eggshell powder that has been subjected to a baking process, or may contain eggshell powder that has been subjected to a combustion process. Examples of polyethylene resin include virgin resin and recycled resin, and it is preferable to use virgin resin. Examples of the form of polyethylene resin include pellets and powder, and it is preferable to use pellets.

[0039] (drying process) Next, the eggshell powder is dried. It is considered that the eggshell powder absorbs moisture from the outside air over time, and the eggshell powder condenses during the mixing process described below. Therefore, it is necessary to dry the eggshell powder immediately before the mixing process. Specifically, the eggshell powder is spread evenly on a tray and set in an electric dryer. The electric dryer blows hot air from holes in its inner wall to electrically dry the contents. The set temperature of the electric dryer is 55°C to 80°C, preferably 60°C to 75°C. The drying time is, for example, about 2 to 3 hours. The drying process is not essential. For example, when the outside air is dry, such as in winter, it is not necessary to perform the drying process.

[0040] (Mixing process) The dried eggshell powder and pellet-shaped polyethylene resin are mixed (compounded) in a mixer and transferred to a twin-screw extruder having two screws. In this case, the mixing ratio of eggshell powder is set to 20% or more and 35% or less by mass. In the twin-screw extruder, the mixture is heated and melted, kneaded, and the eggshell powder is dispersed in the molten polyethylene resin. The melt kneading temperature is preferably 180°C to 260°C.

[0041] After melt-kneading, the melt-kneaded mixture is continuously extruded from a twin-screw extruder to produce a pellet-shaped master batch (concentrated fixed mixture). The shape of the pellets is typically cylindrical, but may also be elliptical or spherical. The size of the pellets is, for example, 2 mm x 2 mm. The size of the pellets is not particularly limited, but can be appropriately set depending on the extruder and molding machine to which they are transferred.

[0042] Instead of the above-mentioned twin-screw extruder, a single-screw extruder having only one screw may be used.

[0043] (molding process) The master batch produced in the mixing process is molded into a film, for example, by inflation molding, a method in which resin is extruded through a metal mold (die) with a ring-shaped gap, and then air is blown in to inflate it to a specified size (inflation), forming it into a tube shape.

[0044] At this time, additives and colorants can be mixed into the master batch. The additives and colorants are preferably of the same size and shape as the master batch produced above. Examples of additives include plasticizers, antioxidants, foaming agents, conductive agents, and flame retardants. By adding additives, functional films can be produced, and by adding colorants, colored films can be produced. If the film containing eggshell powder is transparent, the eggshell can be visually confirmed, so it is preferable that the film is colored opaquely (for example, silver, white, etc.), but this can be selected arbitrarily.

[0045] Instead of inflation molding, the material can also be molded into a film by the T-die casting method (cast molding method). The T-die casting method is a plastic film manufacturing method similar to the inflation molding method, in which a film is manufactured using a T-shaped die with a straight lip (pouring spout) at the tip of the extruder. EXAMPLES

[0046] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these.

[0047] Table 1 shows the evaluation results of the experiments carried out on Invention Examples 1 and 2 and Comparative Examples 1 to 5.

[0048] First, eggshell powder and polyethylene resin were prepared. Scallow Premium R (manufactured by WM) was used as the eggshell powder. This eggshell powder has an average particle size of 0.5 μm or more and 3 μm or less. The eggshell powder contains baked eggshell. The amount of eggshell powder is 20% or more and 35% or less by mass ratio. FS153S (manufactured by Sumitomo) virgin resin was used as the polyethylene resin. Next, eggshell powder and polyethylene resin were charged into the hopper of a twin-screw extruder, and melt-kneaded in the twin-screw extruder to prepare a master batch. The master batch was molded into a film by inflation molding. The film molded in this way was used as Example 1 of the present invention. In Example 1 of the present invention, a drying process was not performed, but the experiment was performed in winter with a humidity of 60% or less.

[0049] The film manufacturing methods of Inventive Example 2 and Comparative Examples 1 to 5 described below were basically the same as Inventive Example 1, but differed as shown in Table 1 below.

[0050] Before mixing the eggshell powder with the polyethylene resin, the eggshell powder alone was subjected to a drying process, which was designated as "Invention Example 2." This drying process was carried out using an electric dryer.

[0051] The mass ratio of eggshell powder was set to 1.5%, and a single-screw extruder was used in the mixing process, making up "Comparative Example 1."

[0052] "Comparative Example 2" was prepared by using scallop powder instead of eggshell powder, setting the mass ratio of scallop powder to 25%, and using a twin-screw extruder in the mixing step of the scallop powder and polyethylene resin.

[0053] "Comparative Example 3" was prepared by setting the mass ratio of eggshell powder to 25%, using recycled resin as the polyethylene resin, and using a twin-screw extruder in the mixing process of the eggshell powder and the polyethylene resin.

[0054] "Comparative Example 4" was prepared by setting the mass ratio of eggshell powder to 25%, using virgin resin as the polyethylene resin, and using a single-screw extruder in the mixing process of the eggshell powder and the polyethylene resin.

[0055] "Comparative Example 5" was prepared by adding 5% by mass of an anti-foaming agent to the components of Comparative Example 4, and using a twin-screw extruder in the mixing process of the eggshell powder and polyethylene resin.

[0056] (Evaluation method) The film condition was confirmed by visually inspecting and touching the film surface for Inventive Examples 1 and 2 and Comparative Examples 1 to 5. Furthermore, the mixing state in the twin-screw extruder or single-screw extruder used in the mixing step was confirmed.

[0057] For the cushioning materials of invention examples 1 and 2 and comparative examples 1 to 5, the surface condition was confirmed and a press compression test and an impact resistance test were conducted under the conditions described above. The results are shown in Table 1. In the evaluation column of Table 1, "◯" indicates that the eggshell powder was uniformly dispersed and the film was of high quality, "△" indicates that the eggshell powder was somewhat condensed, and "×" indicates that the eggshell powder was too condensed and the film was of poor quality, or that the production itself was difficult.

[0058] [Table 1]

[0059] (Evaluation Results) In Example 1 of the present invention, the mixing condition in the twin-screw extruder was good, the film surface was smooth and not rough, and the film was of good quality. In Example 2 of the present invention, the mixing condition in the twin-screw extruder was good, the film surface was not rough, and some aggregation of eggshell powder was observed, but the film was of good quality.

[0060] On the other hand, in Comparative Example 1, the mixing conditions in the single-screw extruder were poor, and the eggshell powder was noticeably aggregated. Although a film was produced, the film had many irregularities on the surface and was of poor quality. This is because, although the amount of eggshell powder was small at 1.5% by mass, the use of a single-screw extruder prevented the eggshell powder and polyethylene resin from being mixed well.

[0061] In Comparative Example 2, there was a foul odor during production and the strength of the film was weak. This was because the scallop shell powder was not roasted, the scallop shell powder itself had low strength, and recycled resin was used as the polyethylene resin.

[0062] In Comparative Example 3, the mixing condition in the twin-screw extruder was poor, and lumps of eggshell powder of about 1 to 5 mm adhered to the screw. Furthermore, the strength of the film was weak. This was because recycled resin was used as the polyethylene resin.

[0063] In Comparative Example 4, the mixing conditions in the single screw extruder were poor, and lumps of eggshell powder of about 1 to 5 mm adhered to the screw. Furthermore, the strength of the film was weak. This was because the eggshell powder and polyethylene resin were not mixed well due to the use of a single screw extruder.

[0064] In Comparative Example 5, the film was produced without any problems, but the eggshell powder aggregated to about 1 to 5 mm on the surface of the film, and the film had low strength. This was because the amount of the bubble inhibitor added was too large.

[0065] From the above results, in Examples 1 and 2 of the present invention, the amount of baked eggshell powder is 20% or more and 35% or less by mass ratio, and virgin polyethylene resin is used. The eggshell powder and polyethylene resin are mixed using a twin-screw extruder, and formed into a film by inflation molding, thereby making it possible to produce a film in which the eggshell powder is uniformly dispersed in the thickness direction and the surface direction. As in Example 2 of the present invention, it is preferable to dry the eggshell powder immediately before mixing the eggshell powder and the polyethylene resin. This is because the eggshell powder absorbs moisture from the external environment over time, even if it is burned during the production of the eggshell powder. This can suppress the aggregation of the eggshell powder and improve the mixing condition of the eggshell powder and the polyethylene resin.

[0066] In the manufacturing method of the present embodiment, the eggshell powder and the polyethylene resin may be melt-kneaded and transferred to the molding machine, or the eggshell powder and the thermoplastic resin may be transferred to the molding machine and melt-kneaded at the same time as molding. The melt-kneading may be performed with a single-screw kneader or a twin-screw kneader.

[0067] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the illustrated embodiment. Various modifications and variations can be made to the illustrated embodiment within the same scope as the present invention or within an equivalent scope. [Explanation of symbols]

[0068] 1. Film containing eggshell powder (film), 2. Eggshell powder, 3. Polyethylene resin.

Claims

1. In an eggshell powder-containing film in which eggshell powder is dispersed in a polyethylene resin, The average particle size of the eggshell powder is 0.5 μm or more and 3 μm or less, The thickness of the film is 15 μm or more and 200 μm or less, The amount of eggshell powder in the film is 20% or more and 35% or less by mass ratio.

2. The eggshell powder-containing film according to claim 1 , wherein the eggshell powder is uniformly dispersed in the thickness direction and the surface direction.

3. The eggshell powder-containing film according to claim 1 or 2, wherein the polyethylene resin is a virgin resin.

4. A method for producing a film containing eggshell powder, comprising the steps of: A step of preparing eggshell powder having an average particle size of 0.5 μm or more and 3 μm or less and a polyethylene resin; A mixing step of mixing the eggshell powder with the polyethylene resin in a mass ratio of 20% to 35%; A method for producing an eggshell powder-containing film, comprising: a molding step of molding the mixed eggshell powder and the polyethylene resin into a film.

5. The method for producing a film containing eggshell powder according to claim 4, wherein a twin-screw extruder having two screws is used in the mixing step.

6. The method for producing a film containing eggshell powder according to claim 4 or 5, wherein the molding step is performed by an inflation molding method.

7. The method for producing an eggshell powder-containing film according to claim 4 or 5, further comprising a drying step of drying the eggshell powder.

Images