JPS5829222B2 - Method for manufacturing containers made of thermoplastic resin foam sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing containers made of thermoplastic resin foam sheets, and in particular provides an efficient manufacturing method for manufacturing two containers at the same time by a - operation.

Conventionally, various methods for manufacturing pot-shaped containers using thermoplastic resin foam sheets as raw materials are already known.

For example, a polystyrene foam sheet is vacuum-formed or pressure-formed into a pot shape, and the top edge is press-formed to form ribs. Although it is possible to easily produce a large number of pots, the container wall is strongly stretched. Because of this, their strength is low, making it particularly difficult to manufacture containers with deep bottoms.

In order to improve this, a method was devised in which a unidirectionally shrinkable foam sheet is used as a material, formed into a cylindrical body, and then subjected to various operations to obtain a strong pot-shaped container.

However, this only discloses a method for manufacturing one container.

When using a directionally shrinkable foam sheet as a material, many processes are required such as manufacturing the cylindrical body, heating V-ray treatment, forming the bottom and forming the ribs, so it is economically extremely difficult to omit these steps. Meaningful.

As a result of various studies on process abbreviation, the present inventor formed a long cylindrical body equivalent to two containers, left a gap in the center from both ends of the cylindrical body, and inserted a mold, When the foam sheet is heated, the foam sheet contracts toward the central axis of the cylinder and tightly adheres to the peripheral wall of the mold, and the foam sheet in the central gap further contracts toward the central axis and becomes curved. I found out what to do.

By cutting the central part of the shrunken cylindrical body, a crude container is obtained which is tightly attached to two molds, and by forming a bottom and ribs using a known method, a container with good strength can be obtained. The present invention was completed based on the discovery that it can be manufactured efficiently.

That is, in the present invention, when heated, a unidirectionally shrinkable thermoplastic resin foam sheet, which is pre-cut into a rectangle and shrinks more in one direction perpendicular to the other direction than in other directions, is heated. The foamed sheet is bent into a cylindrical shape so as to contract toward the end, and both ends of the foam sheet are joined to form a cylindrical body, and a gap is left in the center from both ends of the cylindrical body to form a circular bottom plate in advance. The foam sheet is heated to a temperature above the softening point and below the melting temperature to shrink the foam sheet toward the central axis of the cylinder, and then mold the foam sheet onto the peripheral side wall of the mold. The method is characterized in that the two containers are molded at the same time by tightly fitting them together, cutting the curved central portion of the foam sheet at the center of both molds, and further heating and compressing the contracted foam sheet to form a bottom portion. The gist of this paper is a method for manufacturing a container made of a thermoplastic resin foam sheet.

The thermoplastic resin foam sheet used in the present invention may be made from, for example, polystyrene, a copolymer of styrene and methyl methacrylate or acrylonitrile, polymethyl methacrylate, polyethylene, polypropylene, polyvinyl chloride, etc. An example is a sheet formed by foaming using an extractor by adding a chemical blowing agent such as abdicarboxylic acid amide or dinitrosopentamethylenetetracine, or an easily volatile blowing agent such as propane, butane, penkune, etc. .

When the foamed sheet used in the present invention is heated to a temperature equal to or higher than the softening point of the foamed sheet, it contracts significantly only in one direction. It is a unidirectionally shrinkable thermoplastic resin foam sheet that has a property of having a very small amount of shrinkage, or not shrinking at all, or expanding slightly without shrinking.

To numerically express an example of the degree of shrinkage of this foam sheet, when heated at 135°C for 5 seconds, the shrinkage rate in one direction is 1% compared to the shrinkage rate in the other direction perpendicular to this direction.
．． It is 5 times or more, and the shrinkage rate in the direction of greater shrinkage is 15 or more.

The thickness of the foamed sheet varies depending on the size of the container, but is preferably in the range of 0.25-2 mm.

Further, the foam sheet used in the present invention has a density of 0.
B/CC or less is preferable.

Among them, those having a density of 0.4-0.06 g/CC are preferably used.

A thermoplastic resin foam sheet having the above properties is cut into a rectangular shape, bent into a cylindrical shape so as to contract toward the center axis of the cylinder when heated, and both ends of the foam sheet are joined to form a cylindrical shape. With the body.

The tube has a length to produce two containers.

That is, the length is the sum of the length of the two molds and the length of the gap in the center.

The molds inserted into both ends of the cylindrical body are generally made of wood, metal such as aluminum, heat-resistant synthetic resin, or the like.

If the desired container has an upper edge larger than the bottom, that is, a container with a tapered side wall, the end of the cylindrical body will rise to the center due to heat contraction of the cylindrical body, and the molded body will not form as per the mold. Sometimes you can't get it.

This can be prevented by, for example, providing parallel portions with equal diameters from the maximum diameter of the taper.

This parallel portion can be used later as a portion where ribs will be formed.

When a mold is inserted into both ends of the cylindrical body and heated to a temperature above the softening point of the foam sheet and below the melting temperature to shrink the cylindrical body toward the central axis of the cylinder, the cylindrical The cylindrical body is first tightly attached to the mold at the parallel portion where the gap between the body and the mold is smallest, and then the cylindrical body is tightly attached to the mold at the tapered portion.

Subsequently, the cylindrical body in the space between both molds and the gap at the center of the cylindrical body further contracts toward the center line, and its cross section curves into a concave lens shape.

If you cut the shrunk cylinder at the most shrunk gap, it will be 2.
A crude product of several containers is obtained.

The bottom of this container is made by making the above-mentioned void part relatively short and a bottom plate is brought into contact with the part of the mold corresponding to the bottom of the container in advance, and after cutting the resin in the void part, it is heated in a female mold for molding. When pressed, the resin in the cut gap is fused to the bottom plate to form the bottom of the container.

The bottom plate is preferably a disk-shaped bottom plate made of the same material as the foamed sheet that does not have heat shrinkability, but may also be paper coated with a pressure-sensitive adhesive.

Ribs can be easily formed on the upper edge of the container by heating and compressing the upper edge in a mold, for example.

Additionally, the upper edge can be curled outward to form ribs that are more palatable.

In the present invention, the bottom part and the ribs can be formed by X-forming without removing the mold from the mold, but of course, it is also possible to mold the bottom part and the ribs by using another mold after taking the mold out. be.

Embodiments of the present invention will be further described below based on the drawings.

FIG. 1 is an elevational view, partially in cross section, of an example of a container obtained by the present invention, and FIGS. 2 to 8 are explanatory views showing embodiments of the manufacturing method thereof.

Arrows in the drawings indicate the direction of contraction of the unidirectionally shrinkable polystyrene foam sheet.

In the figure, 1 is a pot-shaped container obtained by the present invention.

Reference numeral 4 denotes a rib formed on the upper edge of the cup-shaped container 1.

2 is a unidirectionally shrinkable polystyrene foam sheet, the heat shrinkage rate in one direction is 1.5 times or more that the heat shrinkage rate in the other direction perpendicular to this, and the heat shrinkage rate in the direction where the heat shrinkage rate is larger is Heat shrinkage rate is 30% or more, thickness is Q, 4
mm, the density is 0.25 g/cC, and the length is at least slightly larger than the diameter of the parallel portion 6, which is the maximum diameter of the mold 5, in the direction of high heat shrinkage, at least parallel to the mold 5. It has a length that fits into the portion 6 by lQ + u + 15 mm or more, and has a length that can form a void portion 7 of at least 20111111 in the center when molds 5 of the same shape are inserted symmetrically with their bottoms facing each other. It is cut into a rectangular shape so as to correspond to the direction of low heat shrinkage.

Reference numeral 3 denotes a bonding portion where the foamed sheet 2 is rolled into a cylindrical shape with the direction of high heat shrinkage as the circumferential direction and its ends are bonded.

The bonding is preferably carried out by heat fusion, but may also be bonded with an adhesive or the like.

A mold 5 is inserted from both ends of the cylindrical body 8 to which the foamed sheet 2 is joined, as shown in FIG.

The mold 5 is provided with a taper 9, and a parallel portion 6 having the same diameter from the maximum diameter of the taper 9 is provided.

The mold 5 is provided with a ventilation hole 10 penetrating from the top to the bottom, and by reducing the pressure, the bottom plate 1 is inserted into the bottom of the mold 5.
1 is fixed by suction.

When this is put into a heating furnace heated to 150-250°C by hot air, infrared heating, or other heat source, or heated by hot air from the side for 3-10 seconds, the cylindrical body 8 shrinks due to heat as shown in Figure 5. and tightly adheres to the outer surface of the mold 5.

The void portion 7 at the center of the cylindrical body 8 further contracts toward the central axis, and its cross section is formed into a concave lens shape with a narrow center portion.

The heat-shrinked cylindrical body can be heated as it is, or once cooled,
Cut at the center of the gap 7.

By this cutting, two crude foam sheet containers having the same shape are manufactured.

Without removing this from the mold 5, the X mold 5 is used as a male mold for molding, and the female mold 12 for molding fits therein.
is moved by a cylinder or a spring,
The mold is squeezed between the mold 5 and the female mold 12, the cut curved portion 13 of the cylindrical body 8 is pressed and fused to the bottom plate 11, and then the outer periphery of the parallel portion 6 of the mold 5 is and a rib pressing member 1 that fits into the corresponding gap between the female mold 12 for molding.
4 is press-formed along the parallel portion 6 to the uppermost part having a taper 9. At the uppermost part having a taper 9, a strong rib 4 (thickness 3 mm) in which the foamed sheet has changed to the hardness of a low-foamed or non-foamed material is formed. ) is obtained. A pot-shaped container 1 is obtained.

FIGS. 9 to 14 show another manufacturing method and a pot-shaped container obtained by the method. The mold 5 is fitted over the mold 5, and the upper mold 5 is further inserted into the cylindrical body 8 as shown in FIG.

The upper and lower molds 5 have the same shape and are fixed by a rod 15 that moves up and down by the operation of an air cylinder.

Reference numeral 16 denotes a vacuum nozzle, which causes the bottom plate 11 to be attracted to the mold 5 by suctioning and reducing the pressure.

Although not shown, the lower molding die 5 is also vacuumed, /dal 16
10, the cylindrical body 8 contracts and comes into close contact with the outer periphery of the mold 5 when heated from the outside in the state shown in FIG.

The gap portion 7 between the upper and lower molds 5 further contracts toward the central axis of the cylindrical body 8, and the cylindrical body 8 contracts as shown in FIG.

After heating and shrinking the cylindrical body 8, it has a sharp cutting edge 1γ at the tip,
A blade-shaped and suppressing holder having a suppressing holding part 18 in the center,
It is inserted into the gap 7 between the upper and lower molds 5, that is, the center of the curved part 13, and cut.

Next, the suppressing holding part 18 is placed between the cut cylindrical bodies 8, and the upper and lower rods 15 are moved to tightly press the upper and lower forming molds 5 against the pressing holding part 18, thereby folding the contracted cylindrical body. The bent portion comes into close contact with the bottom plate 11 and is bonded to the first
A pot-shaped container as shown in FIGS. 3 and 14 is formed.

As described above, the present invention enables two containers to be obtained at the same time from a unidirectionally shrinkable thermoplastic resin foam sheet, and the number of steps such as cutting the foam sheet and heat-shrinking the cylindrical body is halved, and the containers can be manufactured efficiently. can be manufactured.

[Brief explanation of the drawing]

The drawings are for illustrating embodiments of the present invention, and FIG. 1 is an elevational view, partially in cross section, of an example of a pot-shaped container obtained by the present invention, and FIGS. 2 to 8 illustrate the manufacturing method thereof. FIG. 2 is an explanatory diagram showing an embodiment. 9 to 14 are explanatory views showing embodiments of another manufacturing method. The main symbols in the drawings are as follows. 1...Cop-shaped container, 2...Unidirectionally shrinkable polystyrene foam sheet, 3...Joint part,
4...Rib, 5-...Mold, 6...
...Parallel part, 7...Gap part, 8...
...Cylindrical body, 9...Taper 11...
・Bottom plate, 13...Curved part, 15...Rod,
16...Vacuum, nozzle, 17...Blade tip, 18...Press holding part.

Claims (1)

[Claims] 1. A unidirectionally shrinkable thermoplastic resin foam sheet that has been torn into a rectangular shape in advance, which shrinks more in one direction perpendicular to the other direction than in other directions when heated, becomes a cylinder when heated. Curved into a cylindrical shape so as to contract toward the central axis of
Both ends of the foam sheet are joined to form a cylindrical body, and a mold for a container is inserted into the cylindrical body, with a circular bottom plate attached in advance, leaving a gap in the center from both ends of the cylindrical body. The foamed sheet is heated to a temperature above its softening point and below its melting temperature to shrink the foamed sheet toward the central axis of the cylinder and tightly adhere it to the peripheral side wall of the mold, thereby forming a curved shape in the center of the drawing mold. A method for manufacturing a container made of a thermoplastic resin foam sheet, comprising cutting the center portion of the foam sheet, heating and compressing the contracted foam sheet to form a bottom portion, and molding two containers at the same time. . 2. Thermoplastic resin foam according to claim 1, which uses a unidirectionally shrinkable thermoplastic resin foam sheet that can shrink by at least 10% or more in the outer circumferential direction toward the central axis of the cylindrical body when heated. Method for manufacturing sheet containers. 3. The method for manufacturing a container made of a thermoplastic resin foam sheet according to claim 1 or 2, wherein the thermoplastic resin foam sheet is a polystyrene foam sheet. 4. After tightly attaching the cylindrical body to the peripheral side wall of the mold and cutting the center part of the curved foam sheet in the center of the drawing mold, remove it from the mold and insert the bottom plate in another pair of male and female molds. A method for manufacturing a container made of a thermoplastic resin foam sheet according to claim 1, which comprises forming a container made of a thermoplastic resin foam sheet. 5. The cylindrical body is tightly attached to the peripheral side wall of the mold, and after cutting the central part of the curved foam sheet in the center of the drawing mold, ribs are formed on the upper edge of the container. A method for producing a container made of a thermoplastic resin foam sheet according to item 1.