Method for producing eggshell powder-containing resin composition having Anti-bacterial properties, impact resistance and flexibility

Abstract

The purpose of the present invention is to provide: an eggshell powder-containing resin composition having excellent impact resistance and flexibility even if the proportion of eggshell powder in the eggshell powder-containing resin composition is high; and a method for producing same.　Provided are: an eggshell powder-containing resin composition which contains an eggshell powder and a resin, wherein the eggshell powder is a fired eggshell powder having an average particle diameter of 4-10 μm, and preferably 4-7 μm, and a particle circularity of 0.6-1; and a method for producing an eggshell powder-containing resin composition which contains an eggshell powder and a resin, wherein the eggshell powder is a fired eggshell powder having an average particle diameter of 4-10 μm, and preferably 4-7 μm, and a particle circularity of 0.6-1, and the method has a step for mixing the fired eggshell powder, a resin and a surfactant.

Description

Method for producing eggshell powder-containing resin composition having antibacterial properties, impact resistance and flexibility

[0001] The present invention relates to an eggshell powder-containing resin composition having antibacterial properties, impact resistance and flexibility.

[0002] In recent years, recycling and upcycling technologies have been attracting attention worldwide as part of efforts to create a sustainable society based on the SDGs. One of these issues is the disposal of eggshells. Eggshells are approximately 94% calcium carbonate, with the remaining content including magnesium carbonate, calcium phosphate, trace amounts of organic matter, and trace amounts of water. For this reason, eggshells have been proposed as an environmentally friendly, biodegradable plastic when mixed with resins such as polypropylene.

[0003] However, in order for a plastic molded product to be considered combustible waste, at least 51% of the total content must be naturally derived, and there have been practical problems with this, such as the difficulty of molding when the proportion of eggshell in the resin composition is high, and the generation of hydrogen sulfide originating from the eggshell membrane that adheres to the inside of the eggshell. Therefore, in order to solve these problems, various resin compositions containing eggshell have been proposed.

[0004] For example, Japanese Patent Application Laid-Open No. 2022-152310 discloses a method for producing a synthetic resin molded product, which comprises mixing a molding material made of pellets of polypropylene resin kneaded with eggshell powder with a powder deodorant, melting and kneading the mixed molding material obtained by mixing the molding material with the powder deodorant, and injection molding the mixed molding material to form a molded product (Patent Document 1).

[0005] Furthermore, Japanese Patent Laid-Open Publication No. 2022-24250 discloses an eggshell powder resin composition that contains a resin component and eggshell powder in a weight ratio of 50:50 to 10:90, and further contains a deodorizing component that removes hydrogen sulfide, an odorous component of the eggshell powder (Patent Document 2).

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 2020-84033 discloses a method for producing a biodegradable resin composition, which includes a step of mixing eggshell powder with a biodegradable resin powder, and a step of melt-kneading the mixture after the mixing step, wherein the eggshell powder and the biodegradable resin powder each have an average particle size of 0.1 μm to 200 μm, and the ratio of their average particle sizes is within ±1000% (Patent Document 3).

[0007] Furthermore, Japanese Patent No. 6764210 discloses an eggshell powder-containing thermoplastic resin composition containing two groups of eggshell powder with different particle sizes in a mass ratio of 50:50 to 10:90, with the ratio of eggshell powder to the total mass being 50 / 100 or more, and a molded article using the same (Patent Document 4).

[0008] JP 2022-152310 A JP 2022-24250 A JP 2020-84033 A Japanese Patent No. 6764210 A

[0009] It is known that baked eggshells themselves have a high pH and can sterilize and deodorize in a short time. Therefore, by blending them into a resin composition, it is possible to create a resin composition with antibacterial properties. However, conventional eggshell powder-containing resin compositions have the problem that increasing the amount of eggshell powder makes molding more difficult, and the resulting molded products tend to crack and become brittle.

[0010] Furthermore, in order to remove eggshell membranes adhering to eggshells, conventionally, the eggshells are agitated in hot water to remove the eggshell membranes, then crushed, washed again, and dried at a temperature of about 20 to 200°C under vacuum or about 100 to 400°C under normal pressure, requiring many steps, which poses a problem in terms of production costs.

[0011] Furthermore, research and development of conventional eggshell powder-containing resin compositions has tended to be carried out with the aim of increasing the eggshell content, and there is still room for improvement in their mechanical properties, such as impact resistance and flexibility.

[0012] Therefore, an object of the present invention is to provide an eggshell powder-containing resin composition that has excellent impact resistance and flexibility even when the proportion of eggshell powder in the eggshell powder-containing resin composition is high, and a method for producing the same.

[0013] The present inventors conducted various studies to solve the above-mentioned problems and found that the above-mentioned problems can be solved by using baked eggshells as eggshells and adjusting the average particle size and circularity of the baked eggshells.

[0014] The present invention was made based on this finding and provides an eggshell powder-containing resin composition containing eggshell powder and a resin, wherein the eggshell powder is baked eggshell powder having an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and a particle circularity of 0.6 to 1.

[0015] The present invention also provides a method for producing an eggshell powder-containing resin composition containing eggshell powder and a resin, the method comprising the steps of: using baked eggshell powder, where the eggshell powder has an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and has particle circularity adjusted to 0.6 to 1; and mixing the baked eggshell powder with a resin and a surfactant.

[0016] According to the eggshell powder-containing resin composition and the method for producing an eggshell powder-containing resin composition of the present invention, it is possible to provide an eggshell powder-containing resin composition, pellets, and resin molded products with improved impact resistance and flexibility.

[0017] An embodiment of the present invention will be described in detail. In the eggshell powder-containing resin composition according to the embodiment of the present invention, the eggshell powder is baked eggshell powder having an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and a particle circularity of 0.6 to 1.

[0018] The baked eggshell powder used in this embodiment is obtained by baking eggshells at high temperatures, and there are no particular restrictions on its origin as long as it is avian, but in consideration of ease of acquisition, cost, etc., eggshells derived from chicken eggs are preferred.

[0019] Calcination can be carried out in a rotary kiln or a general calcination furnace. Calcination conditions are between 800 and 1200°C for 1 to 5 hours. The pH varies depending on the calcination temperature; for example, when calcined at 600°C, the pH is 9.2, and when calcined at 910°C, the pH is 12.5. The higher the pH, the greater the expected antibacterial properties, so when high antibacterial properties are required, it is preferable to use calcined eggshell powder calcined at a higher temperature.

[0020] The baked eggshell powder has had the egg membrane removed during its production process, and when it is made into a resin composition, pellets, or molded resin product, it does not emit a hydrogen sulfide odor caused by the eggshell membrane. The production process is not particularly limited, but for example, the eggshell membrane is separated from the eggshell by agitating the eggshell with the eggshell membrane attached using wind power. The eggshell from which the eggshell membrane has been separated is then baked, and the baked eggshell powder is preferably used.

[0021] The baked eggshell powder used in this embodiment has a particle average diameter and circularity within a specified range. Here, "average diameter" is synonymous with the average particle diameter and refers to the 50% particle diameter (D50%) measured by a laser diffraction / scattering method (Microtrack method). In this embodiment, a laser analysis / scattering particle size distribution measuring device (LA950-V2 manufactured by Horiba, Ltd.) was used to measure the average particle diameter.

[0022] "Circularity" is an index used to evaluate how close an object or particle is to a circle. Circularity is usually expressed in the range of 0 to 1, with the closer to 1 the shape is to a circle. The general definition is: circularity = 4π (area) / (perimeter) ２ In practice, the measurement can be performed using a sonic vibration sieving measuring instrument (Robot Sifter RPS-105M (trademark) manufactured by Seishin Enterprise Co., Ltd.).

[0023] In this embodiment, from the viewpoint of impact resistance and flexibility, the circularity is preferably closer to 1. Specifically, the circularity is preferably 0.6 to 1, more preferably 0.7 to 1, and even more preferably 0.8 to 1.

[0024] In this embodiment, "impact resistance" is synonymous with the item evaluated by the Charpy impact properties of plastics (JIS K7111-1:2012), and refers to the durability of a material against external impact. Furthermore, "flexibility" is synonymous with the item evaluated by tensile elongation (JIS K7161-2014), and refers to the degree of softness. The baked eggshell powder-containing resin composition according to this embodiment is characterized in that the resulting resin molded product has excellent impact resistance and flexibility, even when the eggshell powder content is relatively high.

[0025] The amount of baked eggshell powder in the baked eggshell powder-containing resin composition of this embodiment varies depending on the type and application of the resin molded product, but to create an environmentally friendly plastic, the baked eggshell powder content is set to 51% or more. Adding baked eggshell powder can impart antibacterial properties to the resin composition, pellets, and molded resin products. However, if the content exceeds 80% by weight, molding becomes difficult and impact resistance and flexibility decrease, so the upper limit is set to 80% by weight.

[0026] The type of the "synthetic resin" is not particularly limited and can be appropriately selected depending on the purpose and application. That is, either a synthetic resin or a biodegradable resin can be selected, and if it is a synthetic resin, either a thermoplastic resin or a thermosetting resin can be selected.

[0027] Examples of thermoplastic resins include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl acetate (PVAc), polyurethane (PUR), Teflon (registered trademark) (polytetrafluoroethylene, PTFE), ABS resin (acrylonitrile butadiene styrene resin), acrylic (PMMA), and polyamide (PA).

[0028] Examples of thermosetting resins include phenolic resin (PF), epoxy resin (EP), melamine resin (MF), urea resin (UF), unsaturated polyester resin (UP), alkyd resin, silicone resin, polyurethane (PUR), and thermosetting polyimide (PI).

[0029] Furthermore, examples of biodegradable resins include polylactic acid (PLA), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polylactic acid / polycaprolactone copolymer, polyglycolic acid (PGA), polylactic acid / polyether copolymer, butanediol / long-chain dicarboxylic acid copolymer, polybutylene adipate / terephthalate (PBAT), polytetramethylene adipate-co-terephthalate, polyethylene terephthalate succinate (PETS), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polyvinyl alcohol (PVA), and starch polyester.

[0030] Other raw materials such as colorants, fillers, surfactants, etc. can be added to the eggshell powder-containing resin composition according to this embodiment, as long as the effects of the present invention are not impaired, or depending on the purpose or application.

[0031] The eggshell powder-containing resin composition according to this embodiment is preferably formed into granular pellets from the viewpoints of handling, transportation, storage, etc. The eggshell powder-containing resin composition according to this embodiment can be formed into pellets by a method similar to a general method for forming pellets of resin compositions, such as using an extruder.

[0032] The pellets are then molded into a resin molded product as appropriate for the purpose and application. The molding method may be a resin molding method using a screw, such as injection molding, blow molding (hollow molding, blow molding), or extrusion molding, or a resin molding method not using a screw, such as casting, vacuum molding / pressure molding, compression molding, press molding, or hand layup.

[0033] Next, we will explain the method for producing an eggshell powder-containing resin composition containing eggshell powder and a resin. The method for producing an eggshell powder-containing resin composition according to this embodiment uses baked eggshell powder, which has an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and has a particle circularity of 0.6 to 1, and includes the steps of mixing the baked eggshell powder with a resin and a surfactant.

[0034] The baked eggshell powder used in this embodiment, which has an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and a particle circularity of 0.6 to 1, has had the egg membrane removed during the manufacturing process, and when it is made into a resin composition, pellets, or molded resin product, it does not emit the hydrogen sulfide odor caused by the eggshell membrane. The manufacturing process is not particularly limited, but for example, after cracking an egg, the eggshell with the attached eggshell membrane is washed and completely dried, and then pre-pulverized. The pre-pulverized eggshell is then agitated in a specific device using wind power, allowing the eggshell membrane to be sucked out from the top of the device due to the difference in specific gravity, thereby separating the eggshell membrane from the eggshell.

[0035] The eggshells from which the eggshell membranes have been separated are then calcined in a rotary kiln or a general calcination furnace at 800 to 1200°C for 1 to 5 hours to obtain calcined eggshells. The calcined eggshells are then pulverized, and by changing the impeller used to pulverize the calcined eggshell powder, the particles are adjusted to an average diameter of 4 to 10 μm, preferably 4 to 7 μm, and a circularity of 0.6 to 1, ultimately obtaining the desired powdered calcined eggshell powder. Such calcined eggshell powder can be commercially available, for example, calcined eggshell fine powder calcium manufactured by M-Tech Co., Ltd.

[0036] The eggshell powder obtained as described above is preferably surface-treated with a surfactant to enhance its dispersibility in resin. The surfactant may be, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant, such as a higher fatty acid salt, a higher fatty acid amide, or a higher fatty acid ester.

[0037] Other raw materials such as colorants, fillers, surfactants, etc. may be added within a range that does not impair the effects of the present invention or depending on the purpose and application. The mixture is then pelletized by the method described above to form a resin molded product.

[0038] 1. Preparation of Resin Composition Containing Burned Eggshell Powder Commercially available finely powdered calcined eggshell calcium (chicken eggshell, manufactured by M-Tech Co., Ltd.) with three different average particle sizes (A: 3.5 μm, B: 4.0 μm, C: 5.5 μm, D: 6.0 μm, E: 7.0 μm, F: 10.0 μm, G: 15.0 μm) was prepared as the burned eggshell powder. The average particle sizes were measured using a laser analysis / scattering particle size distribution analyzer (LA950-V2 manufactured by Horiba, Ltd.).

[0039] For the baked eggshell powder C (average particle size 5.5 μm) above, three different roundnesses (H: 0.4, I: 0.6, J: 0.75, K: 0.8) were prepared by changing the impeller used to pulverize the baked eggshells. The roundness was measured using an ultrasonic vibration sieving measuring device (Robot Sifter (trademark) RPS-105M, manufactured by Seishin Enterprise Co., Ltd.).

[0040] 59% by weight of each of these baked eggshell powders was surface-treated with 1% surfactant (stearic acid) according to the method described in JP 2002-146182 A. This was mixed with 40% by weight of polyethylene (PE) and pelletized using a twin-screw extruder. The resulting pellets were then molded using an injection molding machine to produce resin molded products using baked eggshell powder with different mode diameters and circularity. These were used as test pieces (A to G) and subjected to the physical property tests described below.

[0041] 2. Physical Property Tests (1) Study of Impact Resistance and Flexibility Due to Differences in Average Diameter Using the test pieces A to G described above, impact resistance and flexibility were studied in the following manner. That is, Charpy impact resistance (JIS K7111-2012) was measured as a test item to confirm impact resistance, and tensile elongation (JIS K7161-2014) was measured as a test item to confirm flexibility. A higher Charpy impact value indicates higher impact resistance, and a higher tensile elongation value indicates higher flexibility.

[0042] The results are shown in Table 1. When the focus was on the average particle size, it was found that smaller particles were superior in impact resistance and flexibility.

[0043]

[0044] (2) Study on Impact Resistance and Flexibility Due to Differences in Circularity Using the test pieces H to K, impact resistance and flexibility were studied in the same manner as in (1) above.

[0045] The results are shown in Table 2. It was found that even when the average particle diameter was the same at 5.5 μm, differences in circularity caused differences in the Charpy and tensile elongation. As a result of this test, it was found that particles with a higher circularity (closer to 1) had better flexibility and impact resistance.

[0046]

Claims

1. An eggshell powder-containing resin composition containing eggshell powder and a resin, wherein the eggshell powder is baked eggshell powder having an average particle diameter of 4 to 10 μm, preferably 4 to 7 μm, and a particle circularity of 0.6 to 1.

2. The eggshell powder-containing resin composition according to claim 1, wherein the resin is a synthetic resin or a biodegradable resin.

3. Pellets made primarily from the eggshell powder-containing resin composition according to claim 1 or 2.

4. A resin molded product made primarily from the material claimed in claim 3.

5. A method for producing an eggshell powder-containing resin composition containing eggshell powder and a resin, the method comprising the steps of: using baked eggshell powder in which the eggshell powder has an average particle diameter of 4 to 7 μm and a particle circularity of 0.6 to 1; and mixing the baked eggshell powder with a resin and a surfactant.

6. The method for producing an eggshell powder-containing resin composition according to claim 5, wherein the resin is a synthetic resin or a biodegradable resin.

7. A method for producing pellets, further comprising a step of curing the eggshell powder-containing resin composition according to claim 5 or 6 to form pellets.

8. A method for producing a resin molded product, further comprising the step of molding the pellets according to claim 7 into a resin molded product.

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