JP7558564B2 - Plastic container lids made from recycled plastic - Google Patents

Description

The present invention relates to plastic molded products such as plastic containers and container lids, and in particular to plastic molded products made using plastic waste.

In recent years, recycling of containers and packaging has progressed, and for plastic molded products, attempts to recycle waste materials reproduced during the manufacturing process (pre-consumer materials) and materials collected after use by consumers (post-consumer materials) are becoming more widespread. Recycling methods include material recycling, in which waste plastic is melted and pelletized to be used again as plastic material, and chemical recycling, in which waste plastic is chemically treated and used as a chemical raw material. Of these, material recycling is a promising recycling method because it places less strain on the environment, is inexpensive, and is highly efficient in use.

However, plastic products are not made from the same materials. There are a variety of materials, including olefin-based materials such as polyethylene and polypropylene, ester-based materials such as polystyrene, and materials with high mechanical strength known as engineering plastics such as polyacetal, polyamide, and polycarbonate. Some materials are suitable for material recycling, while others are not. Material recycling can be achieved relatively easily if the raw plastic materials that make up the waste are suitable for material recycling, but materials that are collected as waste are often mixed with materials that are not suitable for material recycling, and many plastic products are made by mixing multiple materials or composite materials such as elastomers, and in this case, even if they are pelletized and reused, they may not meet the characteristics required for the intended plastic molded product.

In other words, in material recycling, if the recycled plastic material does not meet the characteristics required for the desired plastic product, true recycling cannot be achieved.

In response to these problems, Patent Document 1 discloses a technology that improves the impact resistance and flexibility of recycled plastic products by adding 1 to 50% by weight of elastic polymers such as recycled rubber, styrene butadiene rubber, ethylene-propylene rubber, styrene butadiene styrene block polymer, and styrene isoprene styrene block polymer to recycled plastics that contain polyethylene resin, polypropylene resin, and polystyrene resin, for a total of 50 to 99% by weight of the recycled plastic.

JP 2009-1693 A

Currently, most plastic materials collected as waste are polyethylene (PE) and polypropylene (PP), with smaller amounts of polyacetal (POM) and polybutylene terephthalate (PBT). When POM or PBT is added to PE or PP and pelletized to use as recycled plastic material for molding, molding is possible, but it has been found that the characteristics (physical properties) of the molded product are different from those of recycled plastic molded products that do not contain POM or PBT, and may not be suitable for the intended use. For example, when manufacturing a container lid as a molded product, the container lid is required to not easily fall off the container when fitted to the container, that is, to have an appropriate pull-out load and not break when dropped. However, adding hard resins such as POM or PBT makes it prone to cracking when dropped and is unsuitable as a lid material.

The present invention has been made to solve the above problems, and aims to provide molded products made from waste plastics suitable for containers and container lids, and in particular to provide molded products that meet specified performance standards using waste plastic materials including POM, PBT, etc.

The plastic molded product of the present invention, which solves the above problems, is a plastic molded product obtained by injection molding a plastic raw material containing plastic waste, characterized in that the plastic waste contains polyethylene and/or polypropylene as a main material, polybutyl terephthalate and/or polyacetal resin as a secondary material, and the plastic raw material contains polyethylene and an olefin-based thermoplastic elastomer () as an additive resin. Metallocene plastomer and/or metallocene polyethylene are particularly preferred as the additive resin.

The plastic container lid material of the present invention is obtained by injection molding plastic raw materials including plastic waste, the plastic waste contains polyethylene and/or polypropylene as a main material, polybutyl terephthalate and/or polyacetal resin as a secondary material, the plastic raw materials further contain additive resins, and is characterized in that there were zero occurrences of cracks during a drop test (5°C, dropped from a height of 70 cm, 10 samples). The drop height of 70 cm in this drop test is based on the average height of an average person's waist or the average height of a table on which a plastic container is placed. The temperature is set to 5°C in winter, which is harsher than room temperature.

According to the present invention, by using plastic waste material containing polyethylene and/or polypropylene as the main material and polybutyl terephthalate and/or polyacetal resin as the secondary material, it is possible to provide a plastic molded product with a good balance between flexibility and hardness. In particular, it is possible to provide a plastic molded product that has the performance required for a lid material.

FIG. 1 shows the structure of a lid material produced in an embodiment, with the upper part being a cross-sectional view of the lid material and the lower part being a view from the opening side of the lid.

The following describes embodiments of the plastic molded product and lid material of the present invention.

The plastic molded product (including the lid material) of the present invention is manufactured by injection molding using waste plastic material (recycled material) as the plastic raw material and adding an additive resin to it.

Plastic waste includes recycled plastic products after use and waste materials that remain when injection molding is performed during the process of manufacturing plastic molded products and are left over when the molded product is removed from the mold. Primary materials include polyethylene, polypropylene, and mixtures of these. Secondary materials include engineering plastics such as polyacetal resin and polybutylene phthalate, and mixtures of these.

The ratio of PE to PP and the ratio of POM to PBT in the mixture are not particularly limited, but the ratio of the secondary material to the main material is preferably 70:30 to 90:10 by weight, and the secondary material is preferably less than 30% by weight, and more preferably 25% by weight or less. If the amount of secondary material exceeds 30% by weight, the shock absorption properties decrease, and even if an additive resin is added, the material is more likely to crack when dropped or otherwise subjected to shock at low temperatures.

As the additive resin, it is preferable to use polyethylene or an olefin elastomer, and LDPE, LLDPE, or their α-olefin polymers are more preferable. In particular, polyethylene synthesized by a metallocene catalyst (metallocene polyethylene) and polyethylene-α-olefin copolymers (metallocene plastomers) obtained by copolymerizing α-olefins such as butene-1, hexene-1, and 4-methylpentene-1 with polyethylene by a metallocene catalyst are preferable. Metallocene polyethylene and metallocene plastomers have fewer branches and are more flexible and rigid than ordinary polyethylene (LDPE). By adding them as additive resins, it is possible to improve the impact resistance of plastic waste materials that contain the above-mentioned high mechanical strength engineering plastics as secondary materials. However, if too much additive resin is added, it is more likely to crack when impacted. In addition, when the plastic molded product is a lid material for a container, it is required that it does not come off the container when holding the lid, that is, that the pull-out load is high, but if the additive resin exceeds 30% by weight, the pull-out load tends to decrease.

Therefore, the amount of added resin should preferably not exceed 30% by weight, and more preferably be 25% by weight or less, based on 100% by weight of the plastic waste. The lower limit of the amount added is preferably 10% by weight or more, and more preferably be more than 10% by weight.

The plastic molded product of the present invention basically uses the above-mentioned plastic waste material and additive resin as plastic materials, but may also contain plastic materials other than recycled plastics and resins other than PE and PP, such as PA (nylon) and SBC (styrene-based thermoplastic elastomer).
Furthermore, known additives such as pigments, ultraviolet absorbers, and antistatic agents may be added.

The plastic molded products of the present invention are made by crushing plastic materials (plastic waste) separated by type of resin from plastic waste using a crusher (e.g., a resin dumpling pressure) and feeding them to a normal injection molding machine together with added resins. After crushing, the plastic waste may be melted and pelletized. In some cases, plastic waste is supplied without separating the PP and PE, and such plastic waste can also be used. Additives are added as necessary to granular (including powdered) or pelletized plastic waste, and the plastic is fed to a normal injection molding machine. The injection molding conditions vary depending on the shape and structure of the molded product, but molding can be performed under the same conditions as the injection molding conditions for normal PE and PP.

For example, if the molded product is a relatively small part such as a container lid, the mold temperature is set to 60°C, the holding pressure is set to 30-50 MPa, etc., and the injection molded product can be obtained with a cycle time of 15-30 seconds/set.

The plastic molded product of the present invention is molded using waste plastic materials with different properties and additive resins, and can provide a molded product with excellent impact resistance that is not inferior to products using PP or PE alone, compared to products that use only plastics with different properties. In particular, when the plastic molded product is a lid for a container, a product with the appropriate pull-out load required for the lid can be obtained. The pull-out load refers to the load required when an external force is applied to the lid when the lid is fitted to the container, and the lid will not come off the container just by holding it, but can be removed from the container by applying an appropriate force, so an appropriate pull-out load is required in relation to the container.

As an example, as shown in Figure 1, in a lid material 10 (diameter: 34.8 mm, height: 34.8 mm, thickness: 1.3 mm, weight: approximately 3.5 g) with a protrusion 11 on the inner periphery that engages with a recess formed on the outer periphery of the mouth of a container, when the lid material is fitted to the container, the container is fixed with the bottom side, and the lid material is pulled up at a predetermined pulling speed (200 mm/min), the load (pull-out load) at which the lid material comes out of the container is preferably 50 N or more and 70 N or less. This makes it possible to provide a lid material that will not easily come off even when the container is lifted by holding only the lid material, for a container with a total weight of approximately 250 g including the container and contents.

In addition, because it has excellent impact resistance, it will not break or crack even if it is hit by an object or dropped under normal use conditions. Specifically, when a lid material with the above structure is dropped to the floor from a height of 70 cm at a low temperature (5°C), zero cracks occur in 10 samples.

As described above, according to the present invention, multiple types of plastic waste can be used to provide plastic products with good properties, particularly lids for containers. This increases the recycling efficiency of plastic waste compared to recycling only PE or PP, and significantly reduces the amount of waste material disposed of.

Below, we will explain an example in which the plastic molded product of the present invention is used as a container lid material. In the following explanation, "%" means "% by weight" unless otherwise specified.

1. Production of Lid Material <Example 1>
As plastic waste materials, recycled molded products and waste materials generated during injection molding were collected, and a mixed material of PE and PP (unsorted material): main material A, and a mixed material of PBT and POM (unsorted material): secondary material B were each crushed into powder (granules), and then 80% material A and 20% material B were mixed to create the plastic raw material for injection molding.

Metallocene polyethylene (product name: Harmolex, manufactured by Japan Polyethylene Co., Ltd.) and metallocene-based polyethylene (product name: Kernel, manufactured by Japan Polyethylene Co., Ltd.) were mixed in a weight ratio of 90:10, and this was added as additive resin C at 10% to 100% of the plastic waste.

The plastic raw material with the added resin was injection molded under the molding conditions of mold temperature: 60°C, cycle time: 16.4 seconds/set, and holding pressure: 40 MPa to produce a container lid material (diameter: 34.8 mm, height: 34.8 mm, thickness: 1.3 mm, weight: approximately 3.5 g) with the shape shown in Figure 1. This lid material fits onto the container by engaging the protrusions on the inner surface with the recesses of the container.

<Examples 2 to 4>
The addition ratio of the additive was changed as shown in Table 1, but otherwise the same procedure as in Example 1 was followed to carry out injection molding to produce container lid materials.

Example 5
The additive was added at a ratio of 30% to 100% of the plastic waste material, and injection molding was carried out in the same manner as in Example 1 to produce a container lid material. However, the conditions for injection molding were a cycle time of 34.5 seconds and a holding pressure of 45 MPa.

Example 6
The same plastic waste material as in Example 1 (main material A + secondary material B) was used, and 10% of metallocene-based polyethylene (product name: Harmolex, manufactured by Japan Polyethylene Corporation) was added as additive resin C to 100% of this plastic waste material. Injection molding was performed in the same manner as in Example 1 to produce a container lid material.

Example 7
The same plastic waste material as in Example 1 (main material A + secondary material B) was used, and 10% of metallocene plastomer (product name: Kernel, manufactured by Japan Polyethylene Corporation) was added as additive resin C to 100% of this plastic waste material. Injection molding was performed in the same manner as in Example 1 to produce a container lid material.

<Comparative Example 1>
A container lid material was produced by injection molding using 100% plastic waste material, which was a mixture of 90% recycled PP and 10% POM, without adding any additional resin. The conditions for injection molding were cycle time: 25.8 seconds/set, and holding pressure: 35 MPa.

<Comparative Example 2>
A container lid material was produced by injection molding using the same plastic waste material as in Example 1 without adding any additives. The conditions for injection molding were a cycle time of 25.8 seconds/set and a holding pressure of 35 MPa.

<Comparative Example 3>
The ratio of main material A to auxiliary material B was changed to main material A: 70%, auxiliary material B: 30%, but otherwise injection molding was performed in the same manner as in Example 1 to produce a container lid material.

<Reference example 1, reference example 2>
Using only the main material A, a container lid material was produced by injection molding.

2. Evaluation of Molded Products A visual evaluation of solvent resistance, a pull-out load evaluation, and a drop test were performed on the container lid materials produced in Examples 1 to 6 and Comparative Examples 1 to 3. In addition, a pull-out load evaluation and a drop test were performed on Reference Examples 1 and 2.

For the visual evaluation of solvent resistance, an application test was conducted in which the surface of the molded product was wiped with a cloth soaked in alcohol (left for 24 hours after application), and an immersion test was conducted in which the product was immersed in a container of alcohol for three days. The appearance was then visually observed to confirm the occurrence of "silver" (surface haze). The results were given as "X" for even one of the 10 samples, and "O" for none.

In the drop test, the molded products were dropped upside down from heights of 50cm, 60cm, and 70cm above the floor (P tile) at room temperature (RT) and 5°C, and the lid material was visually observed to see if any cracks occurred. The results were rated as "Good" if none of the 10 samples had any cracks, "Good" if at least one crack was found but not all, and "Poor" if 80% or more of the samples had cracks.

The removal load was measured at room temperature and at 37°C, when the lid was fitted to the container, the container was fixed with the bottom side up, and the lid was pulled up at a speed of 200 mm/min. It is important that the lid does not come off easily when the container is lifted or moved by holding only the lid during use, and the standard (reference specification) for removal load in the container manufacturing industry is said to be 50 N or more, even in a high temperature environment (37°C).

The evaluation results of the above molded products are shown in Table 2.

As shown in Reference Examples 1 and 2, when only the main material PP (Reference Example 1) or PP + PE (Reference Example 2) is used, both the drop test and pull-out load show excellent results. In contrast, as shown in Comparative Examples 1 and 2, when 10% or more of a secondary material (POM or PBT) is mixed, the pull-out load decreases and the material becomes more susceptible to cracking when dropped.

On the other hand, the molded products of Examples 1 to 7, which were made by mixing the main material and the secondary material and adding an additive resin, all showed better results in the pull-out load and drop test than those of Comparative Examples 1 and 2.

Specifically, in the drop test, at room temperature, no cracks occurred in any of the samples except for Comparative Example 3, but at 5°C, cracks occurred in Comparative Examples 2 and 3 when dropped from 60 cm. Also, in Example 1, which contains 10% added resin, cracks occurred 2 to 3 times out of 10 in a drop test from 70 cm, demonstrating that it is preferable for the amount of added resin to exceed 10%.

With regard to the pull-out load (37°C), all of the examples except for Example 5 showed high values of 50N or more (above the reference standard), but Comparative Example 1 showed about 42N, and Comparative Examples 2 and 3 showed values of 40N or less. Moreover, Example 5, in which the amount of added resin was 30%, also showed a pull-out load of 40N or less, and it was found that it is preferable to set the amount of added resin to not exceed 30% when using it as a lid material.

Furthermore, a comparison between Example 1 and Comparative Example 3 showed that even if the amount of added resin was the same (10%), if the amount of secondary material (PBT/POM) was large, the required performance as a lid material was insufficient in both the drop test and pull-out load, and it was found that the amount of PBT and POM in the waste material was preferably less than 30%.

Furthermore, it was confirmed that the molded products of Examples 1 to 7 all had good solvent resistance to alcohol. On the other hand, as shown in Table 2, "silver" was confirmed on the top surface of the lid material of the molded products of Comparative Examples 1 and 2. In Comparative Examples 2 and 3, the amount of PBT in the total plastic material was high, and it is believed that the "silver" occurred due to insufficient drying of the PBT.

10: Lid material, 11: Protrusion

Claims (5)

A lid material for plastic containers obtained by injection molding a plastic raw material including plastic waste,
The plastic waste material contains polyethylene and/or polypropylene as a main material and polyacetal resin as a secondary material;
The plastic raw material contains, as an additive resin, one or more selected from polyethylene and/or olefin-based thermoplastic elastomers in an amount of 10% by weight or more and less than 30% by weight based on 100% by weight of the plastic waste material;
A lid material for plastic containers, characterized in that it produces zero cracks during a drop test (5°C, dropped from a height of 70 cm, 10 samples). The plastic container lid material according to claim 1 ,
A lid for plastic containers, characterized in that the removal load (37°C) when the lid for containers is fitted onto the container is 50N or more. The plastic container lid material according to claim 1,
A lid material for plastic containers, characterized in that the secondary material contains polyacetal resin and polybutyl terephthalate. The plastic container lid material according to claim 1 or 3 ,
A lid material for plastic containers, characterized in that the proportion of the main material in the plastic waste is 70% by weight or more and 90% by weight or less, and the proportion of the secondary material is 10% by weight or more and 30% by weight or less. The plastic container lid material according to claim 1 ,
A lid material for plastic containers, characterized in that the added resin is metallocene polyethylene and/or metallocene plastomer.

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