JP7702121B2 - Synthetic resin molded product and method for manufacturing synthetic resin molded product - Google Patents

Description

The present invention relates to a synthetic resin molded product containing eggshell powder and a method for producing the synthetic resin molded product.

In recent years, as shown in Patent Document 1, the incineration or landfill disposal of petroleum-derived synthetic resin products at the time of disposal has been cited as a cause of global warming and soil pollution, and awareness of environmental improvement has increased.
Attention is now being paid to using biological materials that have traditionally been disposed of as waste, such as eggshells and seashells, to reduce the proportion of synthetic resins used.

Patent Document 1 shows that fine calcium hydroxide powder made by baking eggshells or shells at high temperatures and adding water, fine calcium carbonate powder from eggshells or shells, or fine powder of fibrous materials such as wood chips and paper are mixed and kneaded in a resin composition (thermoplastic resin, thermosetting resin) in a specified ratio to produce a powder-containing resin composition. It is then proposed to use this powder-containing resin composition as a material to manufacture antibacterial food products such as chopsticks and spoons.

Patent Document 2 also describes a method for removing proteins from calcareous materials of biological origin and a resin composition containing solid calcium carbonate obtained by this method. It also describes mixing a resin base material (resin matrix) made of one or both of a thermoplastic resin and a thermosetting resin with crushed eggshells, which is calcium carbonate.

Patent Document 2 explains that when egg white and egg shell membrane remain in the eggshell upon cracking an egg, and this eggshell is used as a filler for a resin, etc., pyrolysis products of the remaining proteins are generated as by-products, and have an unpleasant odor derived from sulfide compounds such as hydrogen sulfide.
In addition, a method has been proposed to remove the cause of unpleasant odors in the process of producing calcium carbonate, and a method has been shown in which a biologically derived calcareous material containing calcium carbonate as the main component is immersed in an alkaline hydroxide aqueous solution of 2.5 mol/L or more to hydrolyze and remove proteins in the calcareous material. Also, a method of removing eggshell membrane has been shown in which eggshell membrane is decomposed using a sodium hydroxide aqueous solution of 0.5 mol/L at 90°C.

Furthermore, technology relating to calcium-containing batch pellets and molded bodies using these pellets is shown in Patent Document 3. Patent Document 3 lists, as pellet-shaped products, calcium carbonate powder made by pulverizing materials selected from eggshells, seashells, and coral shells, or calcium oxide powder made by calcining and pulverizing materials selected from eggshells, seashells, and coral shells, and melt-kneading materials containing thermoplastic resin.

Meanwhile, Patent Document 4 proposes a technology related to deodorants for various malodorous gases such as ammonia, amines, and mercaptans, in addition to hydrogen sulfide, which has the unpleasant odor described above. As shown in Patent Document 4, a product for removing the malodorous gases is a white deodorant, which is a fine white powder made of tightly bound particles of zinc oxide (ZnO) and aluminum oxide and/or silicon oxide (silicon dioxide SiO ₂ ). It is also shown that this white deodorant is thermally stable up to about 400°C and can be added to plastics.

Patent Document 5 also shows a deodorizing device, which has a deodorizing device main body made of an injection-molded synthetic resin containing a deodorizing agent whose main components are silicon dioxide and zinc oxide. As mentioned above, it is described as a deodorizing device that removes malodorous gases, and shows that the adsorption sites of bases derived from zinc oxide can adsorb acidic malodorous substances such as hydrogen sulfide and methyl mercaptan, and the adsorption sites of acids derived from silicon dioxide can adsorb basic malodorous substances such as ammonia and trimethylamine.

JP 2018-062579 A JP 2011-184269 A Utility Model Registration No. 3230019 Japanese Patent Application Publication No. 63-246167 Utility Model Registration No. 3156575

In producing synthetic resin molded products, adding eggshell powder made by finely crushing eggshells to a synthetic resin material to form various molded products is in line with the aim of reducing the proportion of petroleum-derived chemical synthetic resins used, which is useful in preventing the depletion of petroleum resources, as well as reducing _CO2 generated during the production of petroleum-based materials and the amount of _CO2 generated during incineration.

As such, it has been proposed to manufacture synthetic resin molded products using synthetic resin material and eggshell powder as the main molding materials, as shown in the above-mentioned Patent Documents 1, 2, 3, etc. In one specific example of this manufacturing method, a molding material consisting of pellets of thermoplastic resin kneaded with eggshell powder is prepared in advance, and when continuously manufacturing molded products, this molding material is fed into an injection molding machine and melted in a heater barrel equipped with an in-line screw, and the molten molding material is injected to injection-mold the molded product.

When it comes to eggshell powder, the manufacturing process requires a great deal of effort to ensure that no protein components, such as eggshell membranes and egg whites, remain. And the reality is that eggshell powder that is combined with synthetic resin materials for use in pellets, although not all eggshell powder products, is highly likely to be contaminated with finely powdered eggshells that still contain protein components.

As a result, when pelletized molding material is used in injection molding, there is a problem in that the molded product produced has a sulfur smell.

However, there are currently no known methods for adding deodorants to the molding material to solve the problem of molded products emitting bad odors.

In view of the above circumstances, the present invention aims to reduce the level of sulfur odor and other odors emitted from molded products obtained by injection molding using a molding material made by kneading eggshell powder with polypropylene resin and pelletizing it, thereby improving the marketability of molded products that contain eggshell powder.

The present invention has been made in consideration of the above problems, and aims to solve the above problems by providing a synthetic resin molded product that contains polypropylene resin, eggshell powder, and a powder deodorant, the eggshell powder and the powder deodorant being mixed in the polypropylene resin.

In the above invention, the powder deodorant can be a mixture of amorphous silica powder and zinc oxide powder.

The other invention solves the above problems by providing a method for manufacturing a synthetic resin molded product, which comprises mixing a granular 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 granular molding material with the powder deodorant, and injecting the mixed molding material into the polypropylene resin molten by the melting and kneading, with the eggshell powder and the powder deodorant mixed in the polypropylene resin, to injection mold the molded product.

In the present invention, the powder deodorant can be a mixture of amorphous silica powder and zinc oxide powder.

In addition, in the present invention, it is preferable that the mixed molding material contains 1% by weight of powder deodorant relative to 100% by weight of granular molding material.

In addition, in the present invention, when mixing the eggshell powder and polypropylene resin in the granular molding material, it is preferable that the mixing ratio of the polypropylene resin is at least 40% by weight, where the granular molding material is taken as 100% by weight.

According to the present invention, eggshell powder and a powder deodorant are mixed in the polypropylene resin of the synthetic resin molded product, and the inclusion of eggshell powder has the effect of suppressing the generation of bad odors even in the presence of substances that cause bad odors such as sulfur odors.

According to another invention, even if general-purpose pellets are used, in which the mixing ratio is 60% by weight of eggshell powder and 40% by weight of polypropylene resin relative to 100% by weight of the molding material, it is possible to obtain a molded product in which the generation of unpleasant odors such as sulfur odors is suppressed.

FIG. 2 is an explanatory diagram showing a schematic diagram of polypropylene resin pellets and eggshell powder of molding materials. FIG. 2 is an explanatory diagram illustrating the order of a molding step, a melt-kneading step, and an injection step of a mixed molding material in the present invention. FIG. 11 is an explanatory diagram showing a mixed molding material according to another embodiment.

The present invention will now be described in detail based on the embodiment shown in Figures 1 to 3. Below, a molded product is molded by the method of the embodiment of the present invention. To briefly explain this embodiment, first, a molding material 4 consisting of pellets 3 made by kneading eggshell powder 2 with polypropylene resin 1, and powder deodorant 5 are prepared. Then, the molding material 4 and powder deodorant 5 are mixed to create a mixed molding material 6. After this, the mixed molding material 6 is put into an injection molding machine to melt and knead it, and the product (molded item) is injection molded by this injection molding machine.

Figure 1 shows a pellet 3, which is the molding material 4, and shows the components of the molding material. This molding material 4 is made by kneading polypropylene resin 1 with eggshell powder 2, and extruding it with an extrusion molding machine to form a granule. With regard to the blending of polypropylene resin 1 and eggshell powder 2, the blending ratio of polypropylene resin 1 is 40% by weight when molding material 4 is taken as 100% by weight. In other words, eggshell powder 2 is 60% by weight, and polypropylene resin 1 is 40% by weight.

Additives may be added when extruding molding material 4, but in that case the amount of additive is small and does not change the blending ratio of polypropylene resin 1 and eggshell powder 2 in molding material 4.

Eggshell powder 2 is made by washing eggshells to remove the eggshell membrane and egg white, then drying the eggshells, and pulverizing them into a powder after drying. Polypropylene resin 1 and eggshell powder 2 are then mixed and fed into an extrusion molding machine as described above, where the molten polypropylene resin 1 and eggshell powder 2 are kneaded together and extruded into pellets.

Typically, eggshell powder 2 is made by collecting discarded eggshells from food factories and the like, and it is sufficient if the protein components such as eggshell membrane and egg white can be easily removed from the eggshells. However, with regard to pellets containing eggshell powder currently on the market, there is a possibility that eggshell powder from which the protein components have not been completely removed may be mixed in.
In the present invention, even when pellets containing eggshell powder from which protein has not been completely removed are used for molding, a method is devised to suppress the emission of a sulfur odor from the molded product.

(Mixed molding material preparation stage A)
Therefore, in the present invention, when a molded product is obtained by injection molding using a molding material 4, first there is a step (mixed molding material preparation step A) of mixing the molding material 4 with the powder deodorant 5. Then, as shown in Fig. 2, it is followed by a mixed molding material melting and kneading step B in which the mixed molding material 6 prepared by mixing the molding material 4 with the powder deodorant 5 is melted and kneaded.

(Mixed molding material melt kneading stage B)
When melting and kneading the mixed molding material 6 that has passed through the mixed molding material preparation stage A, this mixed molding material 6 is filled into an injection molding machine 7, and the molding material 4 and the powder deodorant 5 of the mixed molding material 6 are melted and kneaded in the heating barrel (a heating cylinder with a screw) of this injection molding machine 7.

(Mixed molding material injection stage C)
The mixed molding material 6 that has passed through the mixed molding material melt-kneading stage B continues to the mixed molding material injection stage C in which it is injected by the injection molding machine 7, and the melt-kneaded mixed molding material 6 is injected to injection mold a molded product.
The molded article thus obtained contains polypropylene resin 1, eggshell powder 2, and powder deodorant 5, with eggshell powder 2 and powder deodorant 5 being mixed in polypropylene resin 1.

The powder deodorant 5 is a mixture of powdered amorphous silica (SiO ₂ ) and powdered zinc oxide (ZnO). The particle size is set to 10 μm or less. The powder deodorant 5 is preferably mixed at a mixing ratio of 1% by weight with respect to 100% by weight of the molding material 4.

In the above-mentioned mixing step A of mixing the molding material, the molding material 4 and the powder deodorant 5 are mixed using a tumbler and mixed for about 30 to 40 minutes.

In this embodiment, the mixed molding material 6 obtained by mixing is fed into an injection molding machine 7, and a tray is molded by injection molding.

In the present invention, the mixed molding material melt-kneading step B, in which the mixed molding material 6 obtained by mixing in a tumbler is melt-kneaded, is carried out using an injection molding machine as described above, but is not limited to an in-line screw type injection molding machine.

When molding the molded product, the process goes through the mixed molding material mixing stage A and the mixed molding material melt-kneading stage B, followed by injection molding to obtain the molded product, so that in the molded tray, the mixture of eggshell powder 2 and powder deodorant 5 is uniform within the polypropylene resin 1, as described above.

Therefore, even if particulate eggshell powder 2 that gives off a sulfur odor is present in any part of the molded product, the powder deodorant 5 is located nearby and can absorb the sulfur odor components to prevent the odor from spreading.

The intake of malodorous components by the powder deodorant 5 is not limited to the sulfur odor components emitted from the eggshell powder 2. As explained in Patent Document 4 about the white deodorant made of silicon dioxide and zinc oxide, the adsorption sites of the base derived from zinc oxide can adsorb acidic malodorous substances such as hydrogen sulfide and methyl mercaptan, and the adsorption sites of the acid derived from silicon dioxide can adsorb basic malodorous substances such as ammonia and trimethylamine.

In the embodiment, the powder deodorant 5 is described as a mixture of amorphous silica powder and zinc oxide powder, but the powder deodorant 5 is not limited to the mixture. The powder deodorant 5 may release a deodorant component that has the effect of decomposing malodorous components, and the deodorant component may act to decompose malodorous components such as the sulfur odor emitted from the eggshell powder.

When the molded product is a tray, the non-slip sheet can be placed on the bottom surface of the core mold of the molding die (corresponding to the area where tableware and the like are placed) and injection molding can be performed using the in-mold molding method. In this case, a tray can be molded with the non-slip sheet tightly attached.

As described above, the blending ratio of polypropylene resin 1 and eggshell powder 2 in molding material 4 is 60% by weight of eggshell powder 2 and 40% by weight of polypropylene resin 1 when molding material 4 is 100% by weight. If it is considered that the strength of the molded product injection molded with mixed molding material 6 using molding material 4 with this blending ratio is insufficient, the blending ratio of polypropylene resin in the molded product can be increased, for example, by preparing molding material 4 in which the blending ratio of eggshell powder 2 and polypropylene resin 1 is increased.

(Increase in polypropylene resin content)
In addition, in the present invention, while using molding material 4 containing 60% by weight of eggshell powder 2 and 40% by weight of polypropylene resin 1, it is possible to increase the blending ratio of polypropylene resin 1 in the molded product by the following method.

To increase the blending ratio of polypropylene resin 1 in the molded product, the molding material 4 (60% by weight of eggshell powder, 40% by weight of polypropylene resin), the powder deodorant 5, and pellets 8 (molding material for adjusting the blending ratio) consisting only of polypropylene resin 1 are mixed to prepare the mixed molding material 6, and the molded product is obtained using this mixed molding material 6 through the mixed molding material preparation stage A, the mixed molding material melt-kneading stage B, and the mixed molding material injection stage C as described above.

In the above method, the blending ratio of polypropylene resin 1 in the components of the molded product is increased, so the degree to which odors such as sulfur odors are perceived from the eggshell powder portion can be further reduced. In this case, there is no need to prepare a new molding material 4 with a different blending ratio of eggshell powder 2 and polypropylene resin 1, and odors such as sulfur odors can be easily reduced.

In cases where it is necessary to further reduce the level of unpleasant odors such as sulfur odor, the injection molded product is heat-treated at a fixed temperature for a fixed time. As a specific example of this heat treatment, the tray (an example of the above molded product) is placed in a large dryer (box type) with several dozen trays stacked alternately so that hot air can be blown over the entire tray, creating gaps between the trays to allow the hot air to easily pass through the gaps.
By heating the molded product after injection molding at a constant temperature for a fixed period of time in this manner, it is possible to further prevent the emission of unpleasant odors such as sulfur odors.

1... Polypropylene resin 2... Eggshell powder 3... Pellets (molding material)
4: Molding material 5: Powder deodorant 6: Mixed molding material 7: Injection molding machine 8: Pellets consisting of polypropylene resin only A: Mixed molding material preparation stage B: Mixed molding material melt kneading stage C: Mixed molding material injection stage

Claims (4)

The present invention includes a polypropylene resin, an eggshell powder, and a powder deodorant, the eggshell powder and the powder deodorant being mixed in the polypropylene resin,
1. A synthetic resin molded product, wherein the powder deodorant is a mixture of amorphous silica powder and zinc oxide powder . a granular molding material consisting of pellets of polypropylene resin kneaded with eggshell powder is mixed with a powder deodorant, the mixed molding material obtained by mixing the granular molding material with the powder deodorant is melt-kneaded, and the mixed molding material is injected into the polypropylene resin molten by the melt-kneading so that the eggshell powder and the powder deodorant are mixed together to injection-mold a molded product ;
2. A method for producing a synthetic resin molded product, wherein the powder deodorant is a mixture of amorphous silica powder and zinc oxide powder . 3. The method for producing a synthetic resin molded product according to claim 2 , wherein the mixed molding material contains 1% by weight of the powder deodorant relative to 100% by weight of the granular molding material. 4. The method for producing a synthetic resin molded product according to claim 2 or 3 , wherein in the blending of the eggshell powder and polypropylene resin in the granular molding material, the blending ratio of the polypropylene resin is at least 40% by weight based on 100% by weight of the granular molding material.

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