JP4410611B2 - Foam cap for polyethylene terephthalate bottle-type container and method for producing the same - Google Patents

Description

  The present invention relates to a cap having a cap nut shape capable of repeatedly opening and closing a mouth opening of a polyethylene terephthalate bottle-type container (hereinafter referred to as “pet bottle”) and a method for manufacturing the cap.

  The PET bottle has a male threaded portion on the outer peripheral surface of the mouth, and is configured so that the mouth opening can be repeatedly opened and closed by a cap made of polyolefin nut having a female threaded portion that can be screwed onto the male threaded portion. Has been. PET bottles are widely used as packaging containers, and used PET bottles are separated, collected and recycled according to the provisions of the Containers and Packaging Recycling Law.

  In the separate collection and recycling of PET bottles, it is necessary to separate and remove foreign substances other than polyethylene terephthalate mixed in the separately collected PET bottles so that foreign substances other than polyethylene terephthalate do not enter. When PET caps are mixed with polyolefin caps, sorting by wind sorting becomes difficult, resulting in high recycling costs.

  Therefore, it is conceivable to make the cap made of polyethylene terephthalate. However, since polyethylene terephthalate is hard and not elastic, when the cap is screwed into the screw portion of the mouth portion, the outer peripheral edge portion of the mouth opening and the cap There may be a gap between them and the contents may leak out.

  In the invention disclosed in Patent Document 1, as shown in FIG. 6, it occurs when the cap 110 is screwed into the mouth portion 102 with respect to the polyethylene terephthalate cap 110 used to open and close the mouth portion 102 of the PET bottle 101. As a leakage preventing material 120 that seals the gap between the outer peripheral edge of the mouth opening and the cap 110, a laminate in which a polyethylene terephthalate film 122 is laminated on a base 121 made of foamed polyethylene terephthalate is used.

  However, in the above-described conventional technology, an increase in cost due to a leakage preventing material that is a separate component from the cap is inevitable. Further, there is an unsolved problem that when the cap is tightened excessively, either the male screw portion of the mouth portion or the female screw portion of the cap may be lost.

On the other hand, in Patent Document 2, an unfoamed molded product is molded in advance, and the unfoamed molded product is stored in a sealed container that is housed in a cavity of a foaming mold and then clamped, and then a supercritical fluid is stored in the unsealed container. Production of a thermoplastic foam-molded article, wherein the foam-molded article is infiltrated into a foam-molded article and then expanded to a shape that follows the cavity of the foam-molded mold by foaming due to vaporization of the supercritical fluid. A method is disclosed.
Japanese Patent Laid-Open No. 10-139061 JP 2002-59449 A

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and can reduce the cost of separating and recycling PET bottles, and can be used for a bottle-type container made of polyethylene terephthalate having sufficient sealing properties. An object of the present invention is to provide a foam cap and a method for producing the same.

  In order to achieve the above object, the foam cap for a polyethylene terephthalate bottle-type container of the present invention is a bag having a female screw part that can be detachably screwed into a male screw part provided in the mouth part of the polyethylene terephthalate bottle-type container. A nut-like foam cap, wherein the foam cap is made of a polyethylene terephthalate foam.

  The method for producing a foam cap for a polyethylene terephthalate bottle-type container according to the present invention is similar to the foam cap for a polyethylene terephthalate bottle-type container according to claim 1, wherein the foam cap is intended. A step of forming a non-foamed cap made of polyethylene terephthalate having a reduced size corresponding to the expansion ratio, and a cavity that regulates the shape of the foamed cap when the non-foamed cap is clamped, and the cavity and the outside A step of clamping the mold in a state where it is accommodated in the cavity of a split-type foaming mold having a communication hole communicating with the mold, and storing the mold-clamped foaming mold in a pressure vessel to heat the unfoamed cap While supplying the supercritical fluid into the pressure vessel and infiltrating the unfoamed cap, the pressure is reduced and the supercritical fluid is introduced. It characterized by having a a foaming process of expanding into a shape to follow the cavity by the foaming due to vaporization of the fluid.

  Since this invention is comprised as mentioned above, there exists an effect described below.

  Since it is made of a polyethylene terephthalate foam, it is elastically deformed so that the outer peripheral edge of the opening of the PET bottle and the foam cap are brought into close contact with each other without any gap therebetween. Further, the twist of the female thread portion and the twist of the male thread portion of the mouth portion of the PET bottle are in close contact with each other, and the sealing performance is significantly improved.

  In addition, it is not necessary to separate and remove the cap from the PET bottles that are separately collected and recycled, and the separation and recycling cost can be reduced.

  As a result of diligent research to solve the above-mentioned problems, it is possible to combine moderate elasticity and strength by foam molding using a supercritical fluid similar to the foam molding product manufacturing method disclosed in Patent Document 2 as a foaming agent. The knowledge that the foam cap which has can be manufactured was acquired. The present invention has been made based on the above findings.

  An embodiment of a foam cap for a PET bottle according to the present invention will be described.

  As shown in FIG. 1, a plastic bottle 30 that is a polyethylene terephthalate bottle-type container is provided with a male thread portion 31 a on the outer peripheral surface of a mouth portion 31 that is a spout.

  The foam cap 1 has a cap nut shape, has a female screw portion 1a that can be screwed into the male screw portion 31a of the mouth portion 31 of the plastic bottle 30, and is made of a polyethylene terephthalate foam. For this reason, when the female thread part 1a of the foam cap 1 is screwed and tightened to the male thread part 31a of the mouth part 31 of the PET bottle 30, it is elastically deformed, and even if a large tightening force is not applied, the mouth part 31 A gap does not occur between the opening edge and the foam cap, and the threads of the male screw portion 31a and the female screw portion 1a are in close contact with each other, and the sealing performance is good.

  Next, an embodiment of a method for producing a foam cap for a PET bottle according to the present invention will be described.

  In the present embodiment, a convex mold 2 and a concave mold 3 (see FIG. 2), which are split-type foaming molds having cavities that regulate the outer surface of the foam cap 1 that is the final molded product at the time of mold clamping, are used. In the convex mold 2 and the concave mold 3, the screw forming portion 2 a side of the convex mold 2 is inserted into the concave cavity of the concave mold 3, and both ends of the through hole 6 of the convex mold 2 are positioned in the through holes 5 on the left and right walls of the concave mold 3. The mold is clamped by inserting the fixing pin 4 from one through hole 5 to the other through hole 5.

  The convex mold 2 and the concave mold 3 have communication holes (not shown) that allow the inside of the cavity to communicate with the outside even when the mold is clamped, so that a supercritical fluid described later can be introduced into the cavity from the outside. Has been.

  (1) An unfoamed cap 11 made of polyethylene terephthalate having a reduced size that is similar to the foam cap 1 made of a polyethylene terephthalate foam, which is the final molded product, and that matches the expected foaming ratio of the foam cap 1. Is molded by a known molding method such as injection molding.

  In this step, the expansion ratio of the foam cap 1 can be changed by changing the size (reduction dimension) of the non-foam cap 11.

  (2) Next, as shown in FIG. 2, the non-foamed cap 11 obtained in the step (1) is foamed between the cavity surface of the convex mold 2 and the concave mold 3 and the outer surface of the non-foamed cap 11. Is arranged so that a gap for expansion is generated, and the fixing pin 4 is inserted from one through hole 5 to the other through hole 5 as described above, and clamping is performed.

  (3) After the above (2), the mold-clamped foaming mold is stored in the pressure vessel 20, and then the lid 21 is closed and airtight as shown in FIG.

  (4) After (3) above, the supercritical fluid generator 23 introduces the supercritical fluid state into the pressure vessel 20.

  As the supercritical fluid, an inert gas such as carbon dioxide, nitrogen, argon, neon, or helium may be used. Among these, carbon dioxide is preferable because it does not have a very high use temperature and pressure, and has good permeability.

  (5) After the above (4), the temperature of the non-foamed cap 11 is maintained within the range from the crystallization temperature to the melting point and exposed to the supercritical fluid for a predetermined time, so that the supercritical fluid is unfoamed. Infiltrate the inside of the body cap 11.

  In this step, if the temperature of the unfoamed cap 11 is lower than the crystallization temperature, the number of minute bubbles generated during foaming described later is too small. The higher the temperature of the unfoamed cap 11 is, the shorter the permeation time of the supercritical fluid into the unfoamed cap 11 is. However, when the melting point is exceeded, the unfoamed cap 11 starts to melt and the desired shape cannot be maintained.

  (6) After the above (5), as shown in FIG. 4, the pressure inside the pressure vessel 20 is reduced, and the supercritical fluid that has permeated the unfoamed cap 11 is vaporized into a large amount of fine bubbles. The cap 1 is foamed and then cooled.

  (7) After the above (6), the foam cap 1 is taken out together with the convex mold 2 and the concave mold 3 which are clamped by opening the lid 21 of the pressure vessel 20, and the fixing pin 4 is pulled out as shown in FIG. The mold is opened, and then the foam cap 1 is removed from the screw forming portion 2a of the convex mold 2.

  A non-foamed cap was injection-molded by using an injection molding machine (J100-EP, manufactured by Nippon Steel Works, Ltd.) using polyethylene terephthalate (manufactured by Kuraray Co., Ltd., grade: Kurapet 1030, melting point 255 ° C.) as a molding material.

  After storing and sealing the unfoamed cap so that there is a gap between the cavity surface of the foamed mold composed of convex and concave molds and the outer surface of the unfoamed cap, it is housed in a pressure vessel and sealed, Supercritical carbon dioxide (20 Mpa, 250 ° C.) was supplied from a supercritical fluid generator (manufactured by Takumina) and held for 5 minutes. Subsequently, the pressure was released, the foam was expanded and expanded in a shape following the cavity, cooled, and the mold was opened, and a foam cap made of expanded polyethylene terephthalate was taken out.

(Leakage test)
Water was put into a commercially available 500 ml PET bottle, and a foam cap made of foamed polyethylene terephthalate was screwed onto the screw portion of the mouth and sealed, and the mouth portion was left facing for 3 days. There was no liquid leakage by visual observation.

  Moreover, even if the weight before and after the liquid leak test was measured, there was no change in weight.

(Drop test)
The PET bottle with the foam cap made of polyethylene terephthalate was turned upside down and dropped from a height of 1.2m so that the foam cap made of polyethylene terephthalate hits the floor surface. There wasn't.

It is a typical fragmentary sectional view of the state where the foam cap by one embodiment was screwed together to the mouth of a PET bottle. It is explanatory drawing which shows 1 process of the manufacturing method of the foam cap by one Embodiment. It is explanatory drawing which shows the process of infiltrating a supercritical fluid to a non-foamed cap after the process shown in FIG. It is explanatory drawing which shows the process of decompressing and making it foam after the process shown in FIG. It is explanatory drawing which shows the process of opening a convex mold and a concave mold, and taking out a foam cap. It is a typical fragmentary sectional view of the state where the cap by one conventional example was screwed together to the mouth of a PET bottle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Foam cap 1a Female thread part 2 Convex type 2a Thread formation part 3 Concave type 4 Fixing pin 5, 6 Through-hole 11 Non-foamed cap 11a Female thread part 20 Pressure vessel 21 Lid 22 Supply port 23 Supercritical fluid generator 24 Valve

Claims (2)

A cap nut-like foam cap having a female screw portion (1a) that can be detachably screwed into a male screw portion (31a) provided in a mouth portion (31) of a polyethylene terephthalate bottle-shaped container (30),
The foam cap for a bottle type container made of polyethylene terephthalate, wherein the foam cap is made of a polyethylene terephthalate foam. A step of forming a non-foamed cap made of polyethylene terephthalate having a reduced size corresponding to a desired foaming ratio of the foam cap, which is similar to the foam cap for a polyethylene terephthalate bottle-type container according to claim 1. When,
A state in which the non-foamed cap is accommodated in the cavity of a split-type foaming mold having a cavity that regulates the shape of the foam cap when the mold is clamped and a communication hole that communicates the cavity and the outside. The process of clamping with
The mold-clamped foaming mold is housed in a pressure vessel, and while heating the unfoamed cap, a supercritical fluid is supplied into the pressure vessel to penetrate the unfoamed cap, and then the pressure is reduced. And a foaming step of expanding into a shape that follows the cavity by foaming by vaporization of the supercritical fluid. A method for producing a foam cap for a polyethylene terephthalate bottle-type container.

Images