JPH09277371A - Vacuum molding apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly heat a sheet material to be molded and to perfectly prevent the generation of wrinkles or raindrops in the sheet material to produce a good molded product. SOLUTION: An endless belt 13 is provided between a heating roll 10 and a cooling drum 11 under tension. A sheet material 14 to be molded is preheated by a preheating roller 15 to be closely brought into contact with the surface of the belt 13 by a pressure contact roller 16. A mold 17 is arranged under the belt 13 in a freely liftable manner. Air in the cavity 17a of the mold 17 is excluded to mold the sheet material 14 into the shape of the cavity 17a.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a vacuum forming apparatus and method for producing a simple container such as a yogurt container from a thermoplastic resin sheet.

[0002]

2. Description of the Related Art In the so-called vacuum forming technique, a sheet material made of a thermoplastic resin is heated and softened by an appropriate heating device, and this is applied to the surface of a mold having many small holes for vacuum suction. After fixing and sealing so that air does not leak from between the sheet material and the mold, the air in the cavity of the mold is rapidly exhausted through the small holes, and the shape of the mold cavity is formed on the sheet material. Reverse transcription is performed. Therefore, it is important to heat the sheet material to a uniform temperature in advance in order to obtain a good molded product by such molding technology. If there is uneven heating temperature distribution, uneven thickness (wall thickness) It causes defects such as unevenness).

Conventionally, in this type of vacuum forming apparatus, an oven type and a heating plate type are known as means for heating a sheet material.

In the oven type apparatus, both sides of the sheet material to be molded in the width direction are clamped and the sheet material is heated by passing through a heating atmosphere such as an oven. However, the temperature of the heated sheet material rises. As it softens and stretches, the central part hangs downward due to its own weight, and if the degree of drooping is significant, wrinkles may occur in the molded product when molding with a mold.

Also, the area of the oven is usually 1 width.
The length of the oven is less than a few meters, but the oven is heated by several tens to hundreds or more of ceramic or metal casting heaters with a considerable distance (10 to 20 cm) above and below the sheet material to be molded, and The temperature of each heater can be adjusted independently. In addition, the total heating can be adjusted proportionally, and the total capacity of the heater is from several 10 Kw to 100 K.
Some exceed w. This is a very uneconomical heating method because the capacity is such that the sheet is completely carbonized if all the energy is absorbed by the sheet material to be molded.
Further, because of such temperature control of indirect heating (radiant heat and air heat transfer), adjustment is performed while visually checking the sheet material and observing the molded product, and the adjuster requires considerable experience and skill. .

On the other hand, the heating plate type has good thermal efficiency, but for heating the heating plate type, a large number of heating bodies are installed below the heating plate and it is necessary to individually control them in the oven type. It was the same.

In the heating plate type apparatus, as shown in FIG. 4, first, the sheet material 1 is placed on the upper surface of the heating plate 2 (see FIG. 1A), and the mold 3 is lowered. The outer peripheral edge of the sheet material 1 is firmly clamped between the heating platen 2 and the heating platen 2, and then compressed air is introduced from the small holes 3a provided in the mold 3 to heat the sheet material 1 by this air pressure. The sheet material 1 is heated by closely pressing the surface of the board 2 (see the same figure).
(b)). Then, next, the small holes 3a are released to atmospheric pressure (or vacuum is introduced), and compressed air is introduced from a large number of vent holes 2a provided in the heating plate 2 to move the sheet material 1 into the cavity of the mold 3. After pressing against the surface and molding (Fig.
(c)) Finally, the mold 3 is raised to take out the molded product ((d) of the same figure).

However, in such a heating plate type apparatus, when the sheet material 1 is pressed against the surface of the heating platen 2 by air pressure and heated in FIG. An air layer remains between the surface of the heating platen and the sheet material in that part does not adhere, resulting in insufficient heating, resulting in raindrop-like spots (rain drop) on the molded product. was there.

Therefore, conventionally, the surface of the heating platen is roughened to facilitate the evacuation and movement of the sheet material during heating, or the temperature of the heating platen is adjusted according to the heat shrinkage rate of the sheet material. To alleviate the occurrence of raindrops.

However, in general, a heated sheet material expands due to thermal expansion and its area increases. Therefore, in a heating plate type apparatus, the outer peripheral edge of the sheet material is nipped and adhered between the heating plate and the die, and then compressed air is applied. In other words, the heating plate type device expands the area of the sheet material after fixing the outer periphery, so the sheet material stretches and becomes slack. It is unavoidable that the surface of the heating platen rises from the surface of the heating plate to some extent, and the contact between the sheet material and the heating plate is impaired to cause uneven heating.
This was an unavoidable phenomenon due to the principle of the heating plate type that the outer circumference was clamped and heated.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to uniformly heat a sheet material to be molded, and to prevent wrinkles and raindrops in the sheet material. An object of the present invention is to provide a vacuum forming apparatus and method which can be completely prevented and can produce a good molded product.

Another object of the present invention is to improve the thermal efficiency of the vacuum forming apparatus.

[0013]

In order to achieve the above-mentioned object, in the vacuum forming apparatus of the present invention, the endless belt is heated, and the sheet material is adhered and held so that the sheet material is stuck to the surface of the endless belt. Decided to heat up.

Therefore, the vacuum forming apparatus according to claim 1 is an endless belt, a belt heating means for heating the belt, a means for bringing a sheet material to be formed into close contact with the surface of the belt, and a surface of the belt. A mold that can be moved in and out of
An exhaust means for exhausting the air in the cavity of the mold is provided.

In this case, as described in claim 2, the belt heating means may be configured as means for heating the roller for stretching the belt. As another belt heating means, a sheath heater may be arranged so as to face the belt, or a roller dedicated to heating may be provided to press the belt against the belt.

Further, in the vacuum forming method according to the third aspect, the endless belt is heated and the sheet material to be molded is closely held on the surface of the belt, and the surface of the sheet material opposite to the belt side is held. The mold is brought into close contact with the mold, the air in the cavity of the mold is exhausted, and the shape of the cavity is inverted and transferred to the sheet material.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a vacuum forming apparatus according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view schematically showing a vacuum forming device.

In the drawing, reference numeral 10 is a cylindrical heating drum, which is arranged laterally so that the central axis of the cylinder is horizontal and is supported so as to be rotatable about the central axis. There is. The inside is hollow, and the heating medium is circulated. As the heating medium, heating oil, steam, pressurized hot water, etc. can be adopted.

Reference numeral 11 denotes a cooling drum of the same shape and size which is arranged in parallel with the heating drum 10. The cooling water is circulated inside. And the cooling drum 11
A rotary drive device composed of a motor 12 is attached to the rotary shaft of, and the cooling drum 11 is intermittently rotationally driven counterclockwise as will be described later in detail. Although the belt can be cooled only by natural heat radiation, circulating cooling water through the cooling drum is effective in preventing overheating of the belt during long-term continuous operation.

Numeral 13 is an endless belt stretched between the heating drum 10 and the cooling drum 11 and is formed by joining a metal strip plate of stainless steel or the like in a loop shape. Ventilation holes 13a having a diameter of 0.5 mm are formed in a lattice pattern at intervals of 10 mm over the entire surface. The belt material may be a heat-resistant polymer material or the like. Also, the diameter of the drum should be 500 to 20 times the thickness of the belt so that excessive stress is not applied to the belt 13.
It is preferable to set the belt 13 to about 100 times.
Of the heating drum 10 and the cooling drum 11 have an outer diameter of 1 m. The distance between the vent holes provided in the belt 13 is preferably about 5 to 20 mm, and the diameter thereof is 0.
About 2 to 2 mm is good.

In the present embodiment, the heating temperature of the heating drum 10 is controlled so that the surface temperature of the belt 13 is 150 ° C., and the cooling drum 11 is controlled so that the surface temperature of the belt 13 is 60 ° C. Cooling is controlled.

Reference numeral 14 is a sheet material to be molded, which is a polystyrene sheet in the present embodiment, and is continuously supplied to the right from a supply roll (not shown) arranged on the left side in the figure. It is supposed to be done.

Reference numeral 15 is a preheating roller for heating the sheet material 14 from above and below, and the inside thereof is hollow,
Like the heating drum, a heating medium is circulated. However, the heating temperature is controlled to a slightly lower temperature of 70 ° C. so that the sheet material 14 can be peeled off easily from the surface of the preheating roller 15.

Numeral 16 is a pressure roller for adhering the sheet material 14 preheated by the preheating roller 15 to the surface of the belt 13, which is made of heat resistant rubber having appropriate elasticity and is suitable for the surface of the belt 13. It is pressed with a strong urging force.

Reference numeral 17 denotes a metal mold for molding the sheet material 14, which is vertically movable by a hydraulic cylinder 18 attached to the bottom surface while keeping the horizontal state, and has an upper surface. A plurality of female-shaped cavities 17a in which the shape of a desired molded product is reversed are recessed. Although three cavities 17a are shown in the drawing as 3 cavities × 3 columns = 9 cavities,
In reality, more, for example, 8 × 8 columns = 64 may be formed.

As shown in FIG. 2, on the inner wall surface of each cavity 17a, a small hole 17 for venting air which communicates with the back surface of the mold 17 is formed.
Many holes b are provided, and many small holes are provided especially at the corners of the cavity 17a.
After being grouped together in the internal communication passage 19b, they are connected to the accumulator 21b via the valve 20b. On the other hand, a large number of small holes 17c are provided in a row on the outer peripheral edge of the die 17, and these are connected to the communication passage 19c inside the die 17.
After being grouped together, they are connected to an accumulator 21c via a valve 20c. 22b, 2
2c is a one-way valve, and 23 is a vacuum pump.

Next, the operation of the vacuum forming apparatus of this embodiment having the above structure will be described. FIG. 3 is a side sectional view sequentially showing the operation of the vacuum forming apparatus.

Now, as shown in FIG. 3A, the sheet material 14 to be molded is in a state of being adhered to and adhered to the surface of the belt 13. The temperature of the belt 13 is 150 ° C. in the left side portion in contact with the heating drum 10, 145 ° C. in the central portion directly above the mold 17, and 60 ° C. in the right side portion in contact with the cooling drum 11. The sheet material 14 also has a temperature substantially equal to this.

Next, as shown in FIG. 3B, the hydraulic cylinder 18 is driven to raise the die 17. Then, mold 1
7 pushes up the lower surface of the belt 13 so that the sheet material 14 is sandwiched between the mold 17 and the belt 13.

Next, the valve 20c is opened and a vacuum is introduced into the small hole 17c at the outer peripheral edge of the mold 17. As a result, the sheet material 14 is in a state of being adsorbed to the outer peripheral edge of the mold 17.
In this state, the hydraulic cylinder 18 is operated to slightly lower the die 17. At this time, the dimension for lowering the mold may be about 0.2 mm.

Then, the sheet material 14 is, as shown in FIG.
While being adsorbed to the outer peripheral edge of the mold 17, that portion is peeled off from the surface of the belt 13, and the belt 13 and the sheet material 1
A gap 24 is formed between the four.

Here, the valve 20b is opened and the small hole 17
A vacuum is introduced into b and the air in the cavity 17a is exhausted. Then, the sheet material 14 becomes a mold 17 as shown in FIG.
It is pressed against the inner wall surface of the cavity 17a, is almost instantaneously stretch-molded, and is molded into a shape in which the cavity 17a is inverted and transferred.

Next, as shown in FIG. 3 (e), when the mold 17 is lowered to the lower end, the sheet material 14 is released from the cavity 17a so as to be released from the mold. At the time of releasing the mold, a structure may be adopted in which compressed air is introduced from the back surface side of the mold 17 into the small holes 17b. Next, the motor 12 is rotated to feed the belt 13 counterclockwise for a predetermined length of one shot. The formed sheet material 14 is sequentially sent to the right side, and a final product is obtained through post-processes such as trimming.

When the belt 13 is fed counterclockwise, the sheet material 14 is continuously supplied from the left side in the drawing. The sheet material 14 has already been preheated by the preheating roller 15,
It is a little softened, and it is in a state of being expanded due to some thermal expansion. The pressure roller 16 is pressed against the surface of the belt 13 so that the belt 13 is in close contact with the surface of the belt 13. Sheet material 14
The part of the belt 13 that is pressed against the surface of the belt 13 is instantly heated by the high temperature of the belt 13 to cause elongation,
This elongation is eliminated by being squeezed out by the pressure contact roller 16, so that air does not enter between the sheet material 14 and the belt 13. In other words, the belt member 1 does not have slack or wrinkles on the sheet material 14 and is in a completely adhered state.
Attached to 3.

[0035]

As described above, according to the vacuum forming apparatus of the present invention, the endless belt is heated, and the sheet material is adhered and held on the surface so that the sheet material is heated. Therefore, the sheet material is attached to the belt and heated in a completely adhered state without slack or wrinkle. That is, since there is no gap between the sheet material and the belt, heating unevenness does not occur at all, and the sheet material can be uniformly heated. As a result, it is possible to produce a good molded product without causing defects such as wrinkles and rain drops in the molded product.

Further, when the sheet material on which the character graphic is printed in advance is used, since the sheet material does not hang down as in the conventional oven type apparatus, the printing pattern can be made with high accuracy on the die. There is an advantage that it is possible to align the positions.

Further, compared with the conventional oven type or heating plate type apparatus, the thermal efficiency can be greatly improved.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a vacuum forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a mold of the vacuum forming apparatus of FIG.

FIG. 3 is a view showing an operation of the vacuum forming apparatus of FIG. 1, and is a side sectional view taken along the center of the mold.

FIG. 4 is a diagram illustrating a heating plate type device according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 sheet material 2 heating plate 2a ventilation hole 3 mold 3a small hole 10 heating drum 11 cooling drum 12 motor 13 belt 13a ventilation hole 14 molded sheet material 15 preheating roller 16 pressure contact roller 17 mold 17a cavity 17b, 17c small hole 18 Hydraulic cylinder 19b, 19c Communication passage 20b, 20c Valve 21b, 21c Accumulator 22b, 22c One-way valve 23 Vacuum pump 24 Gap

Claims (3)

[Claims] 1. An endless belt, a belt heating means for heating the belt, a means for bringing a sheet material to be molded into close contact with the surface of the belt, and a mold capable of coming into contact with and separating from the surface of the belt. A vacuum forming apparatus comprising: exhaust means for exhausting air in the cavity of the mold. 2. The vacuum forming apparatus according to claim 1, wherein the belt heating means is means for heating a roller that stretches the belt. 3. The endless belt is heated, a sheet material to be molded is closely held on the surface of the belt, and a mold is brought into close contact with the surface of the sheet material opposite to the belt side.
A vacuum forming method, characterized in that the air in the cavity of the mold is exhausted and the shape of the cavity is reversely transferred to the sheet material.