JP7581773B2 - Container member and manufacturing method thereof, container cap and container body - Google Patents

Description

This disclosure relates to container members and their manufacturing methods, as well as container caps and container bodies.

In recent years, plastic molded products are being used in all kinds of everyday items and industrial products around us. As plastic molded products have become more versatile due to improved quality and reduced costs, the demand for plastic molded products is increasing. On the other hand, as seen in the problem of marine plastic waste, attention has been focused on the impact of microplastics on environmental pollution, and there is a growing trend to move away from plastic and to refrain from using plastic products.

When it comes to disposable plastic containers for food and daily necessities, there is a growing demand from users to reduce the amount of petroleum-based plastic used. In response to these demands, efforts are being made to reduce the amount of plastic used by using plant-based resins as part of the raw material, utilizing recycled plastic materials, and improving dimensions and shapes.

Foam molding is known as a means of reducing the weight of plastic molded products. Foam molding can be broadly divided into chemical foam molding and physical foam molding. Chemical foam molding uses a foaming agent, while physical foam molding uses a fluid in a supercritical state (hereinafter referred to as "supercritical fluid molding"). Chemical foam molding has issues such as concerns about the negative impact of the foaming agent on the environment and contamination of the mold. Supercritical fluid molding does not have such concerns. Supercritical fluid molding has traditionally been applied to relatively large industrial products such as automobile part molding and office equipment. In recent years, with the improvement of supercritical fluid generation technology and resin composition kneading technology, the application of supercritical fluid molding to high-cycle injection molding has been considered. Patent documents 1 to 3 disclose food containers manufactured by supercritical fluid molding.

Patent No. 6085729 Patent No. 6430684 JP 2020-040690 A

The inventors carried out various supercritical fluid moldings using various molds in order to broaden the scope of application of supercritical fluid molding. As a result, they discovered that as the degree of foaming increases, defects such as minute sink marks and foaming marks (swirl marks) tend to occur on the surface of the molded body. If a container is constructed using container components with surface defects, even if they are minute, liquid leakage or air leakage may occur depending on the type of content.

The present disclosure provides a container member that is lightweight due to foaming and can achieve excellent sealing properties, and a manufacturing method thereof. The present disclosure also provides a container cap and a container body that are lightweight due to foaming and can achieve excellent sealing properties.

One aspect of the present disclosure relates to a method for manufacturing a container member. This manufacturing method includes the steps of (A) injecting a first molten resin composition containing a resin material into a cavity of a mold, (B) injecting a second molten resin composition containing a resin material and a supercritical fluid into the cavity of the mold while the molded body obtained through the step (A) is placed in the cavity, and (C) foaming the second molten resin composition in the cavity by reducing the pressure. The container member obtained through the step (C) has a dense layer made of a cured product of the first molten resin composition and a foamed layer made of a cured product of the second molten resin composition and having a plurality of voids derived from the supercritical fluid.

The container member obtained through step (C) constitutes a container together with other members. For example, if the container member is a container cap, the other member is a container body that contains the contents. If the container member is a container body that has a flange portion provided around the periphery of the opening, the other member is a lid material that abuts against this flange portion.

The dense layer formed in the above step (A) has an abutment portion against other members that constitute the container together with the container member. This abutment portion is constituted by the dense layer. Therefore, even if the surface of the foamed layer formed through step (C) has appearance defects such as sink marks or foaming marks caused by foaming, excellent sealing properties can be achieved.

The dense layer is in contact with at least a portion of the surface of the foam layer, and it is preferable that the interface between the dense layer and the foam layer has irregularities. The irregularities at the interface between these layers can contribute to improving the adhesion between these layers. The interface may be intentionally provided with irregularities.

The foam layer may have through holes penetrating in the thickness direction, and the through holes may be filled with a first resin material. By filling the through holes with the first resin material, a portion made of the first resin material (the dense layer) can be partially exposed on the surface of the container member. For example, by forming the shape of the through holes in a plan view into a product logo or the like, a logo or the like that has a different texture, gloss, or color from the foam layer can be provided on the surface of the container member. Furthermore, the through holes in the foam layer and the first resin material filled therein can contribute to improving the adhesion between the dense layer and the foam layer.

An example of a container member according to the present disclosure is a cap for a container that contains liquid or the like. The container cap according to the present disclosure comprises a top surface portion having an inner ring portion on the inner surface side, and a side surface portion extending from the peripheral portion of the top surface portion in a direction away from the top surface portion, a dense layer made of a first resin material and including the inner ring portion, and a foam layer made of a second resin material and having a plurality of voids derived from a supercritical fluid. The inner ring portion is a portion that fits into the opening of the container body. Since the inner ring portion is composed of a dense layer, excellent sealing properties can be achieved.

Another example of a container member according to the present disclosure is a container body that constitutes a container together with a lid. The container body according to the present disclosure includes an opening, a dense layer made of a first resin material that constitutes a flange portion provided around the periphery of the opening and that constitutes the inner surface of the container body, and a foam layer made of a second resin material that has a plurality of voids derived from a supercritical fluid and that constitutes the outer surface of the container body. The flange portion is the portion that the lid material abuts against. For example, the lid material is attached to the flange portion by heat sealing to ensure the hermeticity of the container. Since the flange portion is made of a dense layer, excellent hermeticity can be achieved.

In the present disclosure, the foam layer and the dense layer are preferably made of the same type of resin material. By using the same type of resin material for these layers, the container member, container cap, and container body can be made into a mono-material, which contributes to promoting the recycling of resin materials.

According to the present disclosure, a container member and a manufacturing method thereof are provided that are lightweight due to foaming and can achieve excellent sealing performance. In addition, according to the present disclosure, a container cap and a container body are provided that are lightweight due to foaming and can achieve excellent sealing performance.

FIG. 1 is a cross-sectional view that illustrates a schematic diagram of one embodiment of a container cap according to the present disclosure. FIG. 2 is a cross-sectional view that typically illustrates the interface between a dense layer and a foam layer in the container cap shown in FIG. FIG. 3(a) is a plan view that shows a schematic diagram of another embodiment of a container cap according to the present disclosure, and FIG. 3(b) is a cross-sectional view taken along line bb in FIG. 3(a). FIG. 4 is a cross-sectional view that illustrates one embodiment of a container body according to the present disclosure.

The following describes in detail the embodiments of the present disclosure. Here, a container cap (screw cap) is used as an example of a container member. Note that the present invention is not limited to the following embodiments.

<Container cap and method of manufacturing same>
1 is a cross-sectional view showing a container cap according to the present embodiment. The container cap 10 shown in this figure (hereinafter sometimes simply referred to as "cap 10") is manufactured through the following steps.
(A) A step of injecting a first molten resin composition containing a resin material into a cavity of a mold.
(B) A process of injecting a second molten resin composition containing a resin material and a supercritical fluid into a cavity of a mold while the molded body obtained through the above process (A) is placed in the cavity.
(C) foaming the second molten resin composition in the cavity by reducing the pressure.
The cap 10 manufactured by this method includes a dense layer L1 made of a cured product of a first molten resin composition (first resin material) and a foamed layer L2 made of a cured product of a second molten resin composition (second resin material) and having a plurality of voids derived from a supercritical fluid. Note that the series of steps (B) to (C) can be carried out, for example, using a MuCell injection molding machine ("MuCell" is a registered trademark of Trexel Co. Ltd.) (see Patent Documents 1 and 2).

The cap 10 is known as a screw cap. The cap 10 comprises a top surface portion 1 and a side surface portion 2 that hangs down from the periphery of the top surface portion 1. An inner ring portion 1a that fits inside the opening of the container body is provided on the inside surface of the top surface portion 1. A screw thread 2a that corresponds to the screw thread (not shown) of the opening of the container body is provided on the inside of the side surface portion 2.

The thickness of the cap 10 is, for example, 1 to 2 mm. The thickness of the cap 10 here means the sum of the thickness of the dense layer L1 (excluding the part where the inner ring part 1a and the thread 2a are provided) and the thickness of the foam layer L2. The thickness of the dense layer L1 (excluding the part where the inner ring part 1a and the thread 2a are provided) is, for example, 0.3 to 0.7 mm, and may be 0.4 to 0.6 mm. By making the dense layer L1 have such a thickness, the strength of the cap 10 can be sufficiently ensured. The thickness of the foam layer L2 is, for example, 0.3 to 1.7 mm, and may be 0.4 to 1.6 mm or 0.5 to 1.5 mm. By making the foam layer L2 have such a thickness, the effect of weight reduction by foaming can be sufficiently obtained. Note that, if the thickness of the cap 10 is made thicker than 2 mm, the dense layer L1 and the foam layer L2 may be made thicker than the above upper limit value.

Figure 2 is a cross-sectional view showing a schematic of the interface between dense layer L1 and foam layer L2 in cap 10. As shown in Figure 2, interface F between dense layer L1 and foam layer L2 may have irregularities. Such irregularities can be formed by intentionally providing a rib shape in dense layer L1 or foam layer L2, or by applying an embossing process to the mold surface. By increasing the surface area of interface F, the adhesion (welding strength) between dense layer L1 and foam layer L2 can be further improved.

The dense layer L1 and the foam layer L2 may be made of the same type of resin material or different types of resin materials. From the viewpoint of promoting recycling of the cap 10, it is preferable that the dense layer L1 and the foam layer L2 are made of the same type of resin material. That is, when the material of the dense layer L1 is PET (polyethylene terephthalate), it is preferable that the material of the foam layer L2 is also PET. When the material of the dense layer L1 is PP (polypropylene), it is preferable that the material of the foam layer L2 is also PP. When the material of the dense layer L1 is PE (polyethylene), it is preferable that the material of the foam layer L2 is also PE. Note that the color of the dense layer L1 may be different from the color of the foam layer L2 by two-color molding.

Each step in the manufacturing method for the cap 10 is described below.

[Step (A)]
A molded body is produced by injecting a first molten resin composition containing a resin material into a cavity of a mold. This molded body becomes the dense layer L1 of the cap 10. Step (A) can be carried out by ordinary injection molding.

[Step (B)]
First, a molten resin composition containing a resin material and a supercritical fluid is prepared. Examples of the resin material include polypropylene resin and polyethylene resin. Examples of the supercritical fluid include carbon dioxide, nitrogen, argon, and helium. According to the study by the present inventors, when the supercritical fluid is carbon dioxide, the molten resin composition is prepared by adding preferably 1 to 4 parts by mass, more preferably 2 to 3 parts by mass of carbon dioxide in a supercritical state to 100 parts by mass of the resin material. When the carbon dioxide content of the molten resin composition is 1 part by mass or more, it is easy to form a sufficiently uniform foam layer over the entire top surface portion 1, and weight reduction by foaming tends to be achieved. On the other hand, when the carbon dioxide content of the molten resin composition is 4 parts by mass or less, excessive foaming tends to be suppressed.

When the supercritical fluid is nitrogen, the molten resin composition is prepared by adding preferably 0.1 to 1.2 parts by mass, more preferably 0.3 to 0.7 parts by mass, of supercritical nitrogen per 100 parts by mass of the resin material. When the nitrogen content of the molten resin composition is 0.5 parts by mass or more, it tends to be easier to form a sufficiently uniform foamed layer over the entire foamed layer L2, and weight reduction through foaming can be achieved. On the other hand, when the nitrogen content of the molten resin composition is 1.0 part by mass or less, excessive foaming tends to be suppressed.

When the resin material used is polypropylene resin, the temperature of the molten resin composition (screw cylinder temperature) is preferably about 210 to 230°C. When the resin material used is polyethylene resin, this temperature is preferably about 220 to 240°C. When this temperature is above the lower limit, the resin flows easily within the cavity, while when it is below the lower limit, for example, there is a tendency to suppress burning of the resin.

The molten resin composition may contain components other than the resin material and the supercritical fluid. That is, the molten resin composition may further contain, for example, a filler, a colorant, an antistatic agent, an antioxidant, etc., as necessary. According to this embodiment, the top surface portion 1 can be made white by the voids caused by foaming, so the molten resin composition may contain a white pigment of 2 mass% or less based on the mass of the molten resin composition, or may not contain a white pigment.

A foam layer L2 is formed so as to cover a portion of the surface of the molded body (dense layer L1) obtained through the above step (A). This step can be carried out by insert molding using a supercritical fluid. That is, with the molded body obtained through the above step (A) placed in the cavity of a mold, a molten resin composition is injected into the cavity through the gate of the mold.

When the molten resin composition is introduced into the cavity, the pressure is reduced, causing the air bubble cells to grow and independent air bubbles to form in the resin composition. The injection speed is preferably 100 to 300 mm/sec, and more preferably 150 to 200 mm/sec. An injection speed of 100 mm/sec or more tends to make it easier for the resin to reach the end of the flow, and tends to suppress the occurrence of short shots. On the other hand, an injection speed of 300 mm/sec or less tends to suppress the occurrence of burrs in the cap 10. According to the study by the present inventors, when the resin material is polyethylene resin and the supercritical fluid is nitrogen, it is preferable to set the injection speed in multiple stages. That is, it is more preferable to set the initial injection speed to 250 to 300 mm/sec, and to reduce the second-stage injection speed to 150 to 200 mm/sec.

In this embodiment, from the viewpoint of sufficiently promoting foaming in the cavity, it is not necessary to carry out a process of applying pressure to the cavity after filling the cavity with the molten resin composition (pressure holding). In this embodiment, from the viewpoint of forming a sufficiently thin foam layer L2, it is preferable not to carry out a process called "core back" for reducing the pressure in the cavity. Core back is a process of moving the movable part of the mold to expand the volume of the cavity before the molten resin filled in the cavity has finished solidifying (see Patent Document 1). In this embodiment, as described above, foaming can be caused in the cavity by the pressure reduction caused by the introduction of the molten resin composition into the cavity.

When the temperature of the cap 10 drops to about 30 to 60°C, the cap 10 is removed from the mold. The foam layer L2 having voids resulting from foaming is formed, which reduces the weight and the amount of plastic material used. The formation of voids preferably reduces the weight by 3% or more by mass compared to a molded body without voids (a normal injection molded body).

Although the embodiment of the present disclosure has been described above, the present invention is not limited to the above embodiment. For example, as shown in FIG. 3(a) and FIG. 3(b), the foam layer L2 may have through holes 5 penetrating in the thickness direction, and the first resin material constituting the dense layer L1 may be filled in the through holes 5. By filling the through holes 5 with the first resin material, the portion made of the first resin material (the dense layer L1) can be partially exposed on the surface of the container cap 20. As shown in FIG. 3(a), by making the shape of the through holes 5a, 5b, and 5c in a plan view into the logo of the product ("ABC" in FIG. 3(a) indicates the logo), a logo having a texture, glossiness, or color different from that of the foam layer L2 can be provided on the surface of the container cap 20. In addition, the through holes 5 in the foam layer L2 and the first resin material filled therein may contribute to improving the adhesion between the dense layer L1 and the foam layer L2. As shown in Figures 3(a) and 3(b), from a design perspective, a logo (ABC) may be displayed on the surface of the recess 1b provided in the center of the top surface 1.

In the above embodiment, a container cap is given as an example of a container member, but the present invention is not limited thereto. For example, packaging containers such as stoppered caps, trays, and cups may be manufactured by the manufacturing method according to the above embodiment. The contents of the packaging container may be food or non-food. FIG. 4 is a cross-sectional view showing a cup (container body) that constitutes a container together with a lid material. The cup 30 shown in this figure is composed of a dense layer L1 and a foam layer L2. The dense layer L1 constitutes the flange portion 12 provided on the periphery of the opening 11 and constitutes the inner surface of the cup 30. The foam layer L2 constitutes the outer surface of the cup 30. The flange portion 12 is an abutment portion against the lid material 15. Since the flange portion 12 is composed of the dense layer L1, excellent sealing properties can be achieved. The container composed of the cup 30 and the lid material 15 is sold in a state in which pudding, jelly, etc. are contained.

The thickness of the cup 30 is, for example, 1 to 2 mm. The thickness of the cup 30 here means the sum of the thickness of the dense layer L1 (excluding the flange portion 12) and the thickness of the foamed layer L2. The thickness of the dense layer L1 (excluding the flange portion 12) is, for example, 0.3 to 0.7 mm, and may be 0.4 to 0.6 mm. By making the dense layer L1 have this thickness, the strength of the cup 30 can be sufficiently ensured. The thickness of the foamed layer L2 is, for example, 0.3 to 1.7 mm, and may be 0.4 to 1.6 mm or 0.5 to 1.5 mm. By making the foamed layer L2 have this thickness, the effect of weight reduction by foaming can be sufficiently obtained. Note that, if the thickness of the cup 30 is made thicker than 2 mm, the dense layer L1 and the foamed layer L2 may be made thicker than the above upper limit value, and if the thickness of the cup 30 is made thinner than 1 mm, the dense layer L1 and the foamed layer L2 may be made thinner than the above lower limit value.

In the above embodiment, the container cap has a two-layer structure of dense layer L1 and foam layer L2 as a whole, but for example, only the inner ring portion 1a and its surroundings may have a two-layer structure of dense layer L1 and foam layer L2. The other portions may be foamed resin bodies having multiple voids derived from the supercritical fluid, which can provide a further weight reduction effect.

1...top surface, 1a...inner ring portion, 1b...recess, 2...side surface, 2a...thread, 5a, 5b, 5c...through hole, 10, 20...container cap (container member), 11...opening, 12...flange portion, 15...lid material, 30...cup (container body, container member), F...interface, L1...dense layer, L2...foam layer.

Claims (6)

(A) injecting a first molten resin composition containing a resin material into a cavity of a mold;
(B) a step of injecting a second molten resin composition containing a resin material and a supercritical fluid into a cavity of a mold while the molded body obtained through the step (A) is placed in the cavity;
(C) foaming the second molten resin composition in the cavity by a reduction in pressure caused by the introduction of the second molten resin composition into the cavity , and maintaining the volume of the cavity without expanding until the second molten resin composition filled in the cavity is solidified ;
Including,
A method for manufacturing a container member, wherein the container member obtained through the (C) process comprises a dense layer consisting of a cured product of the first molten resin composition, and a foamed layer consisting of a cured product of the second molten resin composition and having a plurality of voids derived from a supercritical fluid. a dense layer made of a first resin material;
a foamed layer made of a second resin material and having a plurality of voids derived from a supercritical fluid;
A container member comprising :
the dense layer has an abutment portion for contacting another member constituting a container together with the container member,
The foam layer has through holes penetrating in a thickness direction,
The through hole is filled with the first resin material . the dense layer is in contact with at least a portion of a surface of the foam layer,
The container member according to claim 2 , wherein an interface between the dense layer and the foamed layer has irregularities. 4. The container member according to claim 2, wherein the dense layer and the foamed layer are made of the same type of resin material. A top surface portion having an inner ring portion on an inner surface side;
A side surface portion extending from a peripheral portion of the top surface portion in a direction away from the top surface portion;
A screw thread provided on the inside of the side surface;
A container cap comprising:
a dense layer made of a first resin material and including the inner ring portion;
a foamed layer made of a second resin material and having a plurality of voids derived from a supercritical fluid;
Equipped with
The thread is formed by the dense layer,
A container cap , wherein the dense layer constitutes an inner surface of the top surface portion, and the dense layer is exposed in a region of the inner surface of the top surface portion that is surrounded by the inner ring portion . A container body that constitutes a container together with a lid material,
An opening;
a dense layer made of a first resin material, constituting the entire flange portion provided around the periphery of the opening and constituting the inner surface of the container body;
a foam layer made of a second resin material, having a plurality of voids derived from the supercritical fluid, and constituting an outer surface of the container body;
A container body comprising:

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