JPH0428526A - Plug of plug-assist molding equipment in molding of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To obtain a plug, which does not leave a flaw to the inner surface of a deep-drawing vessel, by composing the plug pushing a thermoplastic resin sheet toward a mold of a base material consisting of a heat-insulating material and a lubricating layer formed onto the surface of the base material. CONSTITUTION:In the plug 10, a molded form using wood and wood powder as main materials or an article formed of a material having heat-resistant properties and heat retaining properties such as felt is adopted as a base material 11 first, and a lubricating layer 12 consisting of fluoroplastics is formed on the surface of the base material 11. Since the base material has heat-resistant properties as a whole, the plug 10 does not rob of heat from a sheet even when the sheet as a softened synthetic-resin deep drawing vessel is abutted. Since the plug 10, the surface of which is covered with the lubricating layer 12 made up of fluoroplastics, etc., the plug 10 does not damage the inner surface of the deep drawing vessel composed of the sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a plug used in a plug-assist molding device for forming a so-called deep-drawn container by compressed air or vacuum forming a thermoplastic resin sheet. .

(Prior art) A transparent thermoplastic resin sheet as shown in Figures 8-A and 8-B was deep-drawn to form a container for storing vegetables such as cherry tomatoes and side dishes such as pickles. Things are buzzing on the market. Such deep-drawn containers are made of thermoplastic resin,
The sheet was heated to soften it, and then formed onto a predetermined mold surface by air pressure or vacuum forming. Deep-drawn containers of this type have traditionally been made of materials such as polystyrene and vinyl chloride, but these materials pose a pollution problem when disposed of as waste. Therefore, it is no longer used much.

Instead, thermoplastic resin sheets (hereinafter simply referred to as sheets) such as polyethylene terephthalate (PET, especially A-PET) and polypropylene have been used as materials for deep-drawn containers in recent years, but these materials Although it has excellent oil resistance and heat resistance, it becomes soft and sticky during the molding process.
This makes it easier to stick to the mold for molding (or the plug described below).

By the way, in order to deep-draw a container, it is necessary to actively draw the softened sheet into the mold, since the bottom peripheral wall of the container will be thinner than the rest and have areas with less rigidity if only the power of vacuum or compressed air is used. A so-called plug-assist molding method or device is used in which the material is pressed in and molded. A so-called plug is used in this plug assist molding method or device to push the sheet. This kind of plug (3
0), as shown in Figures 7-A to 7-D, literally forms the sheet (40) that has been heated and sent to the mold (31) in a softened state as follows. It is helpful. That is, as shown in Figure 7A, this plug (30) begins to move downward relative to the center of the sheet (40) that has been softened and placed at a predetermined position in the mold (31). −
As shown in Figure B, it comes into contact with the center of the sheet (40) and pushes it down into the mold (31). Furthermore, the plug (30) that moved downward stopped just before the sheet (40) came into contact with the mold surface of the mold (31) shown in Figure 7-C, and then this plug (30) stopped. In this state, the sheet (40) is pressed against the mold surface of the mold (31) by compressed air or vacuum, and a container as shown in FIGS. 8-A and 8-B is formed.

Even if the plug (30) as described above is employed, various problems remain in the completed deep-drawn container.

This is because the two synthetic resin sheets (40) are forcibly formed into a container as shown in FIGS. 8-A and 8-B. For example, Japanese Patent Publication No. 1-29693 discloses that in order to solve vertical cracks in containers, [In a method for manufacturing deep-drawn containers biaxially stretched from a sheet made of polyethylene terephthalate by the plug assist method, the diameter of the plug is Alternatively, the circumferential direction of the upper side wall of a deep drawn container is characterized in that the width is 80% or less of the inner diameter of the mold, and the upper side wall is expanded in diameter in the lateral direction. Birefringence Δn=n, which is represented by the difference between the refractive index n in the circumferential direction and the refractive index n in the thickness direction, in a cross section parallel to and perpendicular to the side wall surface.

- A method for producing a deep-drawn polyester container with excellent impact resistance, wherein nt is at least 0.05. ” technology has already been proposed.

However, there are other problems that must be solved when using this plug (30). It is a "scar" on the inner surface of the deep-drawn container formed using the plug (30). These "scratches" are most often caused by the state of the surface of the plug (30) being directly transferred to the thermoplastic resin sheet;
30) If the material is a cloth grain pattern, a wood grain pattern, or metal, the polished pattern is directly transferred to the sheet side. In particular, this type of plug (30) is made of a softened sheet (
40) into the mold (31),
As shown in Fig. 7-B and Fig. 7-C, this plug (30) not only contacts the softened sheet (40), but also has its tip at its tip due to the need for deep drawing.
0). At this time, the sheet (
40) has also been softened, so that scratches J due to the aforementioned patterns existing at the tip of the plug (30) remain on the inner surface of the completed deep-drawn container. This "scar"
This can literally be fatal if you want to make the container transparent so that the contents can be seen clearly and beautifully. Such a phenomenon cannot be solved simply by rounding the tip of the plug (30), especially in the case of the sheet (40) made of a material that becomes sticky when softened as described above. This is something that is noticeable.

Therefore, when the present inventors use this type of plug to form a deep-drawn container, what conditions are necessary for the plug in order to prevent damage to the inner surface of the container? As a result of considering whether this is the case, I came to know that the following conditions exist.

(2) The plug, especially its head surface, does not come into direct contact with the seat (40) or has sufficient sliding properties against the seat (40). This plug stretches the sheet (40), so at that time, make sure that the plug is not in direct contact with the sheet (40).
Alternatively, if the sheet (40) is sufficiently slidable, the sheet (40) will not be damaged when being stretched.

■The sheet (40) is made of various materials, but if the sheet (40) becomes sticky when softened, a plug that does not stick to the sheet (40) due to its adhesive force may be used. It would be good if it were. This is because it is naturally expected that if the sheet (40) adhered to the plug is stretched, it will be damaged.

■The plug must have a certain degree of heat resistance. Sheet to be stretched by plug (40)
is pre-softened by residual heat,
This softened state is necessary until it is molded by the mold (31). Therefore, the preheated sheet (4
If the plug were to absorb the heat of 0), the sheet (40) would be hardened at that point, making it impossible to mold it with the mold (31).

The inventors of the present invention have conducted various studies on how to create a plug that satisfies the above conditions ① to ②.
The present invention was completed.

(Problem to be Solved by the Invention) The present invention has been made based on the above-mentioned circumstances, and the problem to be solved is that when forming a deep-drawn container using a plug, "Scars" that occur on the inside of
It is.

The object of the invention described in the first claim is that even if the sheet (40) comes into direct contact with the sheet (40), the softening heat will not be absorbed.
) to provide a plug that can slide sufficiently against the inner surface of a deep-drawn container and does not leave any scratches on the inner surface of a deep-drawn container. Furthermore, an object of the invention according to the second claim is to provide a plug that does not leave any damage on the inner surface of a deep-drawn container by preventing the softened sheet (40) from coming into direct contact with the plug. .

(Means and operations for solving the problem) In order to solve the above problem, the means taken by the invention described in the first claim are explained by adding the symbols used in the examples. This plug is used in a plug-assist molding device that manufactures containers by subjecting a plastic resin sheet to compressed air or vacuum forming processing using a mold, and presses the thermoplastic resin sheet toward the mold. (11) and a lubricating layer (12) formed on the surface of the base material (11).
0) J.

Therefore, in this plug (10), the base material (1
As for 1), as shown in the examples below, a molded body mainly made of wood or wood flour, or a body made of a material with heat insulating and heat retaining properties such as felt is used, and the surface is coated with fluororesin. Since the lubricating layer (12) is formed, the entire structure has heat insulating properties. As a result, even if the sheet (40), which is to be a deep-drawn container made of softened synthetic resin, comes into contact with the plug (10), the plug (10) will not transfer heat from the sheet (40).

Therefore, this plug (lO) has at least a seat (4
The sheet (40) is kept in a softened state until the sheet (40) completely adheres to the inner surface of the mold (31).

Further, the surface of this plug (lO) is covered with a lubricating layer (12) made of fluororesin or the like.

As a result, the plug (10) has sufficient lubricity for the sheet (40) and stretches the sheet (40) evenly and smoothly. Therefore, even if the sheet (40) comes into contact with the plug (10), the plug (lO) will not damage the inner surface of the deep-drawn container made of the sheet (40).

On the other hand, the means taken by the invention according to the second claim is similarly ``used in a plug assist molding apparatus for manufacturing containers by subjecting a thermoplastic resin sheet to air pressure or vacuum forming processing using a mold, In the plug that presses the material toward the mold, the plug is composed of a base material (21), a protrusion ring (22) integrally formed at the tip of the base material (21) and protruding in an annular shape, and the base material (21). A vent hole (23) formed in the material (21) to introduce compressed air into the protruding ring (22).
This is a plug (20) J characterized by comprising:

In other words, according to this plug (20), this plug (20)
When the sheet (40) softened by 0) is pushed into the mold (31), air from a compressed air supply device (not shown) is constantly blown toward the sheet (40). In other words, as shown in Figure 5,
In this plug (20), from the ventilation hole (23) formed in the base material (21), the tip, that is, the sheet (40
Air is always supplied to the protruding ring (22) located on the ) side, and this air always flows outward from between the tip of the protruding ring (22) and the seat (40) to form an air layer. That's what I'm doing. Because this air layer always exists between the tip of the protruding ring (22) and the sheet (40), even if the plug (20) is pushed into the mold (31),
The seat (40) never comes into contact with the plug (20).

Therefore, this plug (20) can move the sheet (40) into the mold (
31) Since the plug (20) does not come into direct contact with the sheet (40) when it is pushed into the container, there is no possibility that the plug (20) will damage or leave damage to the inner surface of the deep-drawn container completed by the sheet (40). There isn't. Of course, the ventilation holes (2
The air supplied into the protruding ring (22) through (3) is heated to about the softening point of (40).

(Example) Next, the invention according to each claim will be described in detail according to the example shown in the drawings.

FIG. 1-A of K-5 shows a sectional view of a plug (10) according to the first claim, and this plug (10) has a size that can be accommodated in the mold (31) with plenty of room. base material (11), and a lubricating layer (11) integrally formed on the surface of this base material (11).
12).

The base material (11) of this plug (10) is mainly made of felt or wood flour and molded into the shape shown in the figure.
12) to prevent falling off.

Of course, as the material for this base material (11), as long as it satisfies the conditions such as heat insulation, ceramic mixed materials,
Alternatively, a material such as FRP containing glass fiber may be used. The plug (10) is formed by cutting out a lump formed from the above material into a predetermined shape. In other words, a so-called syntactic foam was used and cut out to form the plug (IO).

In this example, a fluororesin film was used as the lubricating layer (12). This fluororesin film (manufactured by Nitto Electric Industry Co., Ltd.; trade name Nidoflon NO.900)
0) uses one with a thickness of 0.2III11,
It was integrated on the outer periphery of the base material (11) as shown in Figure 1-A. In addition, the thickness of the fluororesin film for forming this lubricating layer (12) is preferably as thin as possible in order to ensure sufficient heat retention or heat insulation properties of the plug (10).
Further, in consideration of the coating on the base material (11), it is better to have a thicker coating, but the thickness may be appropriately selected as necessary. This integration is achieved by heat-pressing the lubricating layer (12) onto the base material (11).
11).

Using the plug (lO) of the present invention configured as described above, a completely transparent sheet (40) made of polyethylene terephthalate with a thickness of 0.35 mm is used to make the − side 11
A square container with a depth of 40IIm is formed at 0+nm, and a square container of the same shape is formed using a conventional plug with felt attached to the surface of a water mass of the same shape as the base material (11). However, when both were visually inspected, no damage was found in the container formed using the plug (1O) of the present invention. On the other hand, in containers formed using conventional plugs, cloudy parts were present especially on the peripheral wall near the bottom. When this cloudy area was closely observed, it was found that many thin scratch patterns were formed, which were found to be scratches caused by the transfer of patterns that had existed on the plug surface.

In addition, buckling strength tests were conducted on both materials, and the results were as shown in the table below.

(Left below) Measurement of buckling strength at 0 force and diameter 40H (Kg) It is clear from this table that at least the buckling strength increases by about 40% when using the plug (10) of the present invention. This is what happens.

Furthermore, the first -
When the wall thicknesses at the measurement locations shown in Figure C were compared and measured, the results shown in Figure 1-B were obtained. In the figure, the plug (10) according to the present invention is indicated by A-----, and the conventional plug is indicated by α-1. For reference, the state of a container formed without using any plug of this type is shown below. From this measurement result, it can be understood that the container formed using the plug (IO) according to the present invention is relatively homogeneous compared to the case where the conventional plug is used. In particular, at measurement locations 7 to 9, the thickness of the conventional plug is thicker than the others, whereas when the plug (10) of the present invention is used, the thickness at the other measurement locations is more similar to that of the conventional plug. I know that the situation is.

Figure 2 shows a second embodiment of the plug (10) according to the first claim, and the difference between this plug (10) and the first embodiment is that the lubricating layer (12) is the base material (11)
It is formed by coating the fluororesin directly on the surface. That is, in this plug (lO), the base material (11) is made of a material that can sufficiently withstand the temperature (180°C to 280°C) at which the fluororesin is baked and coated and does not change, such as ceramic, glass, or heat-resistant resin. Alternatively, it may be formed using plaster or a mixture thereof.

The surface of this base material (11) is coated with a fluororesin using a brimer.

Good results similar to those described above were obtained in a container formed by the plug (10) constructed as described above.

Figures 3 and 4 show a plug (10
) is shown in the third embodiment. In this case, in order to ensure heat insulation, a cup-shaped metal (aluminum in this example) is used as the base material (11), and its interior is hollow (naturally containing air). It is something. As for the surface lubricating layer (12), a fluororesin sheet may be attached, or the base material (11
) also has heat resistance, so baking may be performed by coating with fluororesin.

and Fence ■1 Fig. 5, Fig. 6-A, and Fig. 6-H show a plug (20) according to the second claim.

This plug (20) does not directly contact the sheet (40) with its tip, but the sheet (40) is inserted into the mold (31).
), and its structure is fundamentally different from that of the plug (10) according to the first claim. The outline of this plug (20) is shown in Fig. 5,
This plug (20) consists of a base material (21) and a base material (2).
It consists of a protruding ring (22) formed in 1) and a vent hole (23) formed in the base material (21) to guide heated slightly pressurized air into the protruding ring (22). . Then, due to the flow of air supplied into the protruding ring (22) from the ventilation hole (23), this and the sheet (40) are brought into contact with the tip of the protruding ring (22), as shown in FIG. It forms an air layer that prevents contact.

This plug (20) is specifically shown in Figure 6-A and Figure 6.
- It is constructed as shown in Figure B, and the base material (21) is formed of a predetermined material (in this case, it does not necessarily have to be a heat insulating material), and the base material (21) is A circular protruding ring (22) is formed at the tip. In addition, in this example, the ventilation hole (23) is connected to the base material (
The ventilation hole (23) has a dispersion plate (21) at the inner end of the protruding ring (22).
4) is installation. This distribution plate (24) has ventilation holes (
23) The heated low pressure air supplied from the protruding ring (
22), thereby stabilizing the flow of air flowing out from the tip of the protruding ring (22).

Of course, an air supply device (not shown) is connected to this plug (20), and this air supply device heats the sheet (40) to an extent that maintains its softened state.
And air is supplied under increased pressure.
This heated low-pressure air is supplied to the plug (2
0) into the protruding ring (22) through the ventilation hole (23). In this example, this plug (
The air from the air supply device (not shown) connected to 20) has a pressure of 0°2 kg/cm' to 3,
Okg/cm' and its temperature is 50℃~12
It is in the range of 0°C.

Using the plug (20) configured as described above, while blowing out heated slightly pressurized air from the tip of the protruding ring (22), the plug (20) is fed at a feeding speed of 100 mm/sec to 500 mm/sec. When a deep-drawn container as shown in Fig.-B was formed, no cloudy parts, that is, no scratches were formed on the inner surface of the container. Moreover, its buckling strength was also sufficient.

In addition, at the tip of the protruding ring (22) of this plug (20),
If a film made of a fluororesin having excellent lubricating properties and wear resistance, such as the lubricating layer (12) in the first aspect, is formed, it can be expected that the effect will be further improved.

(Effect of the invention) As detailed above, first of all, the plug (1
In 0), the base material (11) is made of a material with excellent heat insulation properties, and a lubricating layer (12) with lubricity and wear resistance is formed on its surface. When the molding method is carried out, the finished deep-drawn container can be made intact.

In particular, in this plug (10), the base material (11) is made to have excellent heat insulation properties by limiting its material or changing its structure.
40) without taking heat from it to harden it.
This also allows the completed deep-drawn container to remain intact. This plug (10) does not require constant preheating.

On the other hand, in the plug (20) according to the second claim, since the plug (20) is configured so that heated slightly pressurized air can be constantly supplied from the tip of the protruding ring (22), the seat (40) by the plug (20) is ) into the mold (31), the plug (20) and the sheet (40) can be prevented from coming into direct contact with each other. Therefore, with this plug (20), the completed deep-drawn container can be completely intact.

[Brief explanation of drawings]

Figure 1-A is a sectional view of the plug according to the first claim;
Figure B is a graph comparing the wall thickness distribution in each part of a deep-drawn container formed using this plug and a conventional plug, and Figure 1-C is the measurement location shown in Figure 1-8. FIG. 2 is a cross-sectional view showing another embodiment of the plug according to the first claim, FIG. 3 is a cross-sectional view of the plug showing still another embodiment, and FIG. is a partial enlarged sectional view of the rV-rV line section in FIG. 3, FIG. 5 is a sectional view showing the schematic structure of the plug according to the second claim, FIG. Figure 6-B is a bottom view of the same. Figure 7-A, Figure 7-B, Figure 7-C, and Figure 7-D are cross-sectional views showing the plug assist molding method in this order, and Figure 8-A.
The figure is a sectional view of the deep-drawn container to be formed, and FIG. 8-B is a perspective view thereof. Explanation of symbols IO...Plug, 11...Base metal, 12...Lubricating layer, 20...Plug, 21...Base metal, 22...Protruding ring, 23...Thread pore, 30... plug, 31... type, 40... sheet. that's all

Claims (1)

[Claims] 1) Used in a plug assist molding device that forms a container by subjecting a thermoplastic resin sheet to air pressure or vacuum molding using a mold, and presses the thermoplastic resin sheet toward the mold. 1. A plug comprising a base material made of a heat insulating material and a lubricating layer formed on the surface of the base material. 2) In a plug used in a plug assist molding device that forms a container by subjecting a thermoplastic resin sheet to air pressure or vacuum molding using a mold, the plug presses the thermoplastic resin sheet toward the mold. , consisting of a base material, a protruding ring integrally formed at the tip of the base material and protruding in an annular shape, and a ventilation hole formed in the base material for introducing compressed air into the protruding ring. A plug characterized by: