Screw cap

Abstract

Provided is an unprecedented screw cap which can be well recycled as a paper product and can also be used in the same manner as a conventional plastic cap. The screw cap contains pulp and a binder. The ratio of the pulp to the binder is: pulp:binder = 50-80 mass%:20-50 mass%.

Description

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[0001] The present invention relates to a screw cap.

[0002] For example, screw caps used for PET bottles, glass bottles, etc. as disclosed in Patent Document 1 are generally made of plastic (made of polyethylene or polypropylene), but due to the increasing awareness of environmental problems in recent years, alternatives to other materials with better environmental and recyclable properties are being considered.

[0003] Japanese Patent Application Laid-Open No. 2015-63317

[0004] The present invention has been made in view of the above-described current situation, and aims to provide a never-before-existing screw cap that contains pulp as a main component, can be recycled well as a paper product, and can be used in the same manner as a conventional plastic cap.

[0005] The gist of the present invention will be described.

[0006] The first aspect of the present invention is a screw cap containing pulp and a binder, wherein the ratio of the pulp to the binder is pulp: binder = 50% by mass or more and 80% by mass or less: 20% by mass or more and 50% by mass or less.

[0007] Further, the second aspect of the present invention relates to a screw cap according to the first aspect, wherein the pulp has a fiber length of 0.3 mm or more and 2.5 mm or less and a fiber width of 15 μm or more and 32 μm or less.

[0008] Further, the third aspect of the present invention relates to a screw cap according to the second aspect, wherein the pulp contains dry-refined wood pulp.

[0009] Further, the fourth aspect of the present invention relates to a screw cap according to the first aspect, wherein the binder contains at least one of starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and polysaccharides extracted from seaweeds.

[0010] Furthermore, a fifth aspect of the present invention relates to a screw cap characterized in that, in the second aspect, the binder contains at least one of the following: starch, polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed.

[0011] Furthermore, a sixth aspect of the present invention relates to a screw cap characterized in that, in the third aspect, the binder contains at least one of the following: starch, polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed.

[0012] Furthermore, a seventh aspect of the present invention relates to a screw cap characterized in that, in any of the fourth to sixth aspects, the binder contains at least one of alginic acid, carrageenan, and agar as polysaccharides extracted from seaweed.

[0013] Furthermore, an eighth aspect of the present invention relates to a screw cap characterized in that, in any of the first to sixth aspects, the surface roughness Ra is 1 μm or more and 20 μm or less.

[0014] Furthermore, the ninth aspect of the present invention relates to a screw cap characterized in that, in the seventh aspect, the surface roughness Ra is 1 μm or more and 20 μm or less.

[0015] Furthermore, the tenth aspect of the present invention relates to a screw cap formed by injection molding a molding material containing the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less, in any of the first to sixth aspects.

[0016] Furthermore, an eleventh aspect of the present invention relates to a screw cap, characterized in that, in the seventh aspect, a molding material containing the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less is formed by injection molding.

[0017] Furthermore, a twelfth aspect of the present invention relates to a screw cap, characterized in that, in the eighth aspect, a molding material comprising the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less is formed by injection molding.

[0018] Furthermore, a thirteenth aspect of the present invention relates to a screw cap formed by injection molding a molding material containing the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less, in the ninth aspect.

[0019] As described above, the present invention provides a screw cap that is primarily made of pulp, is highly recyclable as a paper product, and can be used in the same way as conventional plastic caps.

[0020] A preferred embodiment of the present invention will be briefly described by illustrating its operation.

[0021] The screw cap according to the present invention is formed from a material in which pulp and a binder are blended in a predetermined ratio, making it recyclable as a paper product.

[0022] Furthermore, like plastic caps, it can be suitably used as a screw cap for PET bottles, glass bottles, etc., and it also has a unique soft appearance and texture that resembles paper.

[0023] Furthermore, the ratio of the opening torque to the closing torque becomes larger, resulting in an anti-loosening effect and excellent sealing and airtightness. This is presumed to be due to the fact that the voids formed after molding by the above material are crushed and crimped during closing.

[0024] Specific embodiments of the present invention will be described below.

[0025] This embodiment is a screw cap containing pulp and a binder (a lid member having a female threaded portion formed on its inner surface that screws onto the male threaded portion of the mouth of a PET bottle or glass bottle, etc.), wherein the ratio of pulp to binder is pulp:binder = 50% by mass or more and 80% by mass or less:20% by mass or more and 50% by mass or less.

[0026] Specifically, this embodiment is formed by injection molding a molding material that is created by mixing and kneading pulp, a binder, water, and an auxiliary agent, and then molding it into a predetermined shape (for example, pellets or tablets).

[0027] Natural fibers can be used as pulp. Examples include wood pulp such as papermaking pulp, dissolved pulp, mercerized pulp, and fluff pulp; non-wood pulp obtained from cotton, linters, flax, Manila hemp, sisal hemp, bagasse, kenaf, straw, etc.; recycled paper pulp obtained from recycled paper; and plant-based materials such as rice husks and wood flour. In addition, lyocell fibers, which are refined cellulose fibers, and rayon fibers, which are regenerated natural cellulose fibers, can also be used within the category of natural fibers.

[0028] As the wood pulp, softwood pulp, hardwood pulp, or a mixture of both in a predetermined ratio can be used. When mixing hardwood pulp and softwood pulp, the ratio is preferably set to 20:80 to 80:20, and more preferably 50:50. Furthermore, it is preferable to use pulp with a fiber length of 0.3 mm to 2.5 mm and a fiber width of 15 μm to 32 μm.

[0029] In this embodiment, softwood pulp with a fiber length of 0.3 mm to 2.5 mm and a fiber width of 15 μm to 32 μm is used. The ratio of pulp to binder is pulp:binder = 50% to 80% by mass:20% to 50% by mass, preferably pulp:binder = 60% to 75% by mass:25% to 40% by mass. If the pulp content is less than 50% by mass, molding defects may occur in the screw threads of the cap, making it impossible to close the cap. If it exceeds 80% by mass, molding may not be possible at all, which is undesirable.

[0030] Furthermore, wood pulp that has been dry-processed may be used as the pulp. Specifically, wood pulp that has been dry-processed using a general dry-processing machine (for example, one comprising a defibration section that applies mechanical shear force to cellulose fibers to dissolve them, and a screen having a number of openings of a predetermined diameter through which the defibrated material passes) may be included in the components other than water in an amount of, for example, 30% by mass or more.

[0031] Dry-defibrated wood pulp refers to so-called cellulose fibers that have been defibrated by a dry-defibration machine, with a fiber length of 0.3 mm or more and 1.2 mm or less. Specifically, in the case of softwood pulp, the fiber length is 0.5 mm or more and 1.2 mm or less (preferably 0.65 mm or more and 1.05 mm or less) and the fiber width is 25 μm or more and 32 μm or less. In the case of hardwood pulp, the fiber length is 0.3 mm or more and 0.8 mm or less (preferably 0.49 mm or more and 0.64 mm or less) and the fiber width is 15 μm or more and 25 μm or less.

[0032] Furthermore, the product may contain both dry-fibrillated wood pulp and unfibrillated wood pulp. For example, the product may contain 30% to 70% by mass of dry-fibrillated wood pulp and 10% to 40% by mass of unfibrillated wood pulp among the components other than water.

[0033] Furthermore, un-defibrated wood pulp refers to wood chips that have been chemically pulped (for example, pulping by Kraft pulping), and in the case of softwood pulp, the fiber length is generally greater than 2.0 mm, and in the case of hardwood pulp, the fiber length is generally greater than 0.8 mm.

[0034] Furthermore, softwood pulp and hardwood pulp can be combined as appropriate, and may include dry-fiberized softwood pulp and unfiberized hardwood pulp, or dry-fiberized hardwood pulp and unfiberized softwood pulp.

[0035] In this embodiment, the fiber length refers to the average fiber length, and the fiber width refers to the average fiber width. The average fiber length and average fiber width can be measured using a fiber length measuring instrument (for example, the L&W Fiber Tester Plus manufactured by ABB).

[0036] As a binder, at least one of the following can be used: starch, polyvinyl alcohol (PVA), carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed. As the starch, corn starch, potato starch, or rice flour can be used. In this example, corn starch is used. In addition, in this example, polyvinyl alcohol is further included to make the surface smooth.

[0037] Furthermore, at least one of alginic acid, carrageenan, and agar can be used as the polysaccharide extracted from seaweed.

[0038] Furthermore, small amounts of additives such as zinc stearate (St-Zn) as a mold release agent and amolden as a fungicide may be included. For example, the mixture may contain 0.5% to 3% by mass of a mold release agent and 0.05% to 0.5% by mass of a fungicide, relative to 100% by mass of the components other than water and additives (pulp + binder).

[0039] The molding material in this embodiment contains, as components other than water and auxiliary agents (with pulp + binder accounting for 100% by mass), 50% to 80% by mass of pulp and 20% to 50% by mass of a water-soluble binder. Specifically, it contains 50% to 80% by mass of pulp, 5% to 45% by mass of starch, and 5% to 15% by mass of polyvinyl alcohol.

[0040] Furthermore, the moisture content of the molding material (the percentage of water relative to the total molding material) is set to be between 20% by mass and 60% by mass.

[0041] The molding material of this embodiment can be obtained by kneading a mixture of wood pulp, starch, polyvinyl alcohol, and an auxiliary agent with water (while heating) until the moisture content is between 20% by mass and 60% by mass.

[0042] If the moisture content of the shaped material after kneading (including in the form of pellets or tablets) is less than 20% by mass, the fluidity of the shaped material will significantly decrease, making shaping difficult, which is not preferable. Also, if the moisture content exceeds 60% by mass, shaping is difficult due to the low viscosity, and during injection molding, a long time is required for the degassing and release of water vapor, resulting in a long time for shaping and a decrease in production efficiency, which is not preferable.

[0043] This example can be manufactured by filling the above-mentioned shaped material into a heated injection mold, vaporizing and removing the added water, drying and solidifying it, and then taking it out. During drying and solidification, minute voids are formed due to the evaporation of internal moisture (evaporation of water vapor). When taking it out of the mold, it is possible to demold by forced extraction or rotating the core of the mold, but it is preferable to demold by grasping it from the outside with a cap removal machine (robot hand) etc. and rotating it (because it is difficult to adopt a mechanism for rotating the core since the mold temperature is 180°C or higher).

[0044] The surface roughness Ra of the screw cap shaped as described above is 1 μm or more and 20 μm or less (generally 4 μm or more in the experimental examples described later).

[0045] Since this example is configured as described above, it can be recycled as a paper product by being formed of a material in which pulp and a binder are blended at a predetermined ratio.

[0046] Also, similar to plastic caps, it can be suitably used as a screw cap for PET bottles, glass bottles, etc., and furthermore, it has a unique soft appearance and feel presenting the texture of paper.

[0047] Moreover, the ratio of the opening torque to the closing torque becomes large, and an anti-loosening effect is exerted, enabling good sealing performance and airtightness.

[0048] Therefore, this example is a screw cap that can be recycled well as a paper product with pulp as the main component, and can also be used in the same way as a conventional plastic cap.

[0049] Experiments 1 to 3 that support the effects of this example will be described.

[0050] [Experiment 1] The surface roughness, surface appearance, and opening torque of screw caps (outer diameter approximately 58 mm, inner diameter approximately 56 mm, height approximately 15 mm, thread height approximately 0.5 mm, screw standard: DIN168 GL56) were manufactured by mixing predetermined amounts of pulp (NBKP (coniferous pulp), defibrated pulp or powdered pulp (Sanyo Chemical Co., Ltd. #4000 pure pulp FP-150)) and binder (starch and PVA) as shown in Tables 1 and 2, and adjusting the molding material to a predetermined moisture content (approximately 35%), and then placing it into an injection molding machine (Nissei Plastic Industrial Co., Ltd. NEX5000).

[0051] Table 1 shows Experimental Examples 1 to 4, and Table 2 shows Comparative Examples 1 to 5. The experimental examples are those in which the pulp and binder formulations are within the numerical range of the above-described embodiment. The comparative examples are those in which the pulp and binder formulations are outside the above-described numerical range, as well as examples made of plastic and stainless steel, which are not pulp molded products.

[0052] Surface roughness was measured in accordance with JIS B0633 (the surface roughness Ra, representing the arithmetic mean roughness, and the surface roughness Rz, representing the maximum height, were calculated from the measured roughness curve). The surface appearance was evaluated visually. For the opening torque, the opening torque (the torque required to turn the screw cap in the opening direction from the closed position) was measured for closing torques from 0.5 N to 3.0 N in 0.5 N increments. A digital torque meter TNP-5 manufactured by NIDEK Corporation was used for torque measurement.

[0053]

[0054]

[0055] Tables 1 and 2 show that in all experimental examples, the surface roughness was significantly greater than that of the plastic cap in Comparative Example 4 and the stainless steel cap in Comparative Example 5 (both outer and inner surfaces), and the appearance resembled that of paper (surface roughness Ra was 1 μm or more, and Rz was 30 μm or more).

[0056] Furthermore, for Comparative Examples 1 to 3, which had formulations outside the numerical range of this embodiment, Comparative Examples 1 and 3 could not be molded, and Comparative Example 2 could be molded but broke during closure, making torque measurement impossible.

[0057] Furthermore, regarding the opening torque, in all experimental examples it exceeded 60% of the closing torque. At closing torques of 0.5 N and 1.0 N, the experimental example and comparative examples 4 and 5 were roughly equivalent, but at closing torques of 1.5 N or higher, it was confirmed that the opening torque was greater than that of comparative examples 4 and 5. As mentioned above, this is presumed to be due to the formation of minute voids in the molding material according to this embodiment during drying and solidification due to the evaporation of internal moisture (evaporation of water vapor), and these voids formed by the molding material are crushed and crimped during closing.

[0058] From the above, it was confirmed that by using a formulation within the numerical range of the above-described embodiment, it is possible to realize a screw cap that exhibits a unique paper-like texture and has excellent airtightness and sealing properties.

[0059] [Experiment 2] The oil and water resistance of screw caps (outer diameter approximately 58 mm, inner diameter approximately 56 mm, height approximately 15 mm, thread height approximately 0.5 mm, screw standard: DIN168 GL56) were evaluated by putting a molding material (manufactured by Nissei Plastic Industrial Co., Ltd., NEX5000) made by mixing predetermined amounts of pulp (NBKP (coniferous pulp) or defibrated pulp) and binder (starch and PVA) as shown in Table 3, and adjusting the moisture content to a predetermined level (approximately 35%) into an injection molding machine (Nissei Plastic Industrial Co., Ltd., NEX5000).

[0060] Experimental Examples 5 and 6 are examples in which the pulp and binder formulations are within the numerical range of the above-described embodiment. The comparative example is Comparative Example 5 (stainless steel cap) from Experiment 1.

[0061] The oil resistance test was conducted by dropping various commercially available oils (castor oil, sesame oil, butter, lard, grease (concentration 2), and moisturizing cream) onto the inside of the screw cap and observing the penetration of the droplets after 0.5 hours, 1 hour, 2 hours, 4 hours, 8 hours, and 24 hours (maintained at 23°C during the test).

[0062] The water resistance test involved filling the inside of the screw cap with water and measuring the increase in weight after 24 hours as the amount of water absorbed. The water absorption rate was calculated by dividing the amount of water absorbed by the weight of the screw cap in its dry state before the test.

[0063]

[0064] Table 3 shows that experimental examples 5 and 6 did not absorb any oil for 24 hours, demonstrating sufficient oil resistance and confirming that they can be used as caps for storage containers of various oils.

[0065] Furthermore, in Experimental Examples 5 and 6, even when continuously exposed to water for 24 hours, water penetration was limited, and although there was some deformation, the caps did not collapse, confirming that they are practical for use as caps for bottles and jars used to store beverages and other items in an upright position.

[0066] [Experiment 3] The aroma was evaluated when a screw cap was attached to a commercially available 200ml glass bottle container that had been prepared by mixing predetermined amounts of pulp (NBKP (coniferous pulp) or defibrated pulp) and binder (starch and PVA) as shown in Table 4, and adjusting the molding material to a predetermined moisture content (approximately 35%), and then putting it into an injection molding machine (NEX5000 manufactured by Nissei Plastic Industrial Co., Ltd.).

[0067] Experimental Examples 7 and 8 show cases where the opening of a 200 ml container was closed with a screw cap in which the pulp and binder composition was within the numerical range of this embodiment described above. Comparative Example 6 shows an example where the opening was closed with the stainless steel lid that came with the 200 ml container, and Comparative Example 7 shows an example where the opening of the 200 ml container was not closed.

[0068] In the fragrance test, 5g of undiluted fragrance solution was placed in 200ml containers of each experimental example and comparative example, and kept in a 60°C atmosphere for 6 hours. The scent was then checked both inside and outside the containers, and evaluated based on the intensity of the scent (◎: strong scent, ○: noticeable scent, △: faint scent, ×: no scent), the amount of fragrance released, and the rate of release. The intensity of the scent was evaluated by sensory evaluation.

[0069]

[0070] Table 4 shows that in Comparative Example 6, no fragrance leaked out to the outside and no volatilization occurred. In Comparative Example 7, the fragrance evaporated and dissipated. In contrast, Experimental Examples 7 and 8 were able to seal the inside to the extent that the fragrance did not weaken, while allowing a faint fragrance to evaporate gradually on the outside. This demonstrated a characteristic (sustained release) not found in conventional cap materials.

[0071] This sustained release property can be adjusted by changing the thickness of the cap, applying a coating, or attaching foil. Therefore, the screw cap according to this embodiment makes it possible to realize unprecedented products, such as air fresheners that can be used while the opening remains closed.

Claims

1. A screw cap comprising pulp and a binder, characterized in that the ratio of pulp to binder is pulp:binder = 50% by mass or more and 80% by mass or less:20% by mass or more and 50% by mass or less.

2. The screw cap according to claim 1, characterized in that the pulp has a fiber length of 0.3 mm or more and 2.5 mm or less and a fiber width of 15 μm or more and 32 μm or less.

3. The screw cap according to claim 2, characterized in that the pulp includes dry-fiberized wood pulp.

4. The screw cap according to claim 1, characterized in that the binder contains at least one of the following: starch, polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed.

5. The screw cap according to claim 2, characterized in that the binder contains at least one of the following: starch, polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed.

6. The screw cap according to claim 3, characterized in that the binder contains at least one of starch, polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, and polysaccharides extracted from seaweed.

7. A screw cap according to any one of claims 4 to 6, characterized in that the binder contains at least one of alginic acid, carrageenan, and agar as polysaccharides extracted from seaweed.

8. A screw cap according to any one of claims 1 to 6, characterized in that the surface roughness Ra is 1 μm or more and 20 μm or less.

9. A screw cap according to claim 7, characterized in that the surface roughness Ra is 1 μm or more and 20 μm or less.

10. A screw cap according to any one of claims 1 to 6, characterized in that it is formed by injection molding a molding material containing the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less.

11. The screw cap according to claim 7, characterized in that it is formed by injection molding a molding material containing the pulp and the binder in the above proportions and having a moisture content of 20% by mass or more and 60% by mass or less.

12. The screw cap according to claim 8, characterized in that it is formed by injection molding a molding material containing the pulp and the binder in the above proportions and having a moisture content of 20% by mass or more and 60% by mass or less.

13. The screw cap according to claim 9, characterized in that it is formed by injection molding a molding material containing the pulp and the binder in the aforementioned proportions and having a moisture content of 20% by mass or more and 60% by mass or less.

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