JPS5944206B2 - Netsukaso Seigou Seijyuushishi - Tonokanetsusei Keihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for thermoforming thermoplastic synthetic resin sheets, particularly biaxially oriented thermoplastic synthetic resin sheets.

Heating methods for thermoforming a stretched thermoplastic synthetic resin sheet include a radiation heating method and a contact heating method.

In the former, a heating zone and a forming zone are provided separately, and both edges of the sheet are firmly held, the sheet is heated to an appropriate forming temperature by radiant heating by a heater, and then immediately transferred to the forming zone and formed. . In the latter, heating and shaping generally take place in the same zone. That is, the sheet is pressed against a heated thermal mold plate, heated to an appropriate temperature in a very short time by contact heating, and immediately molded in the same zone. In that case, the periphery of the sheet to be heated is firmly clamped between the formwork and the hot formwork. In this way, in thermoforming a stretched sheet, efforts are made to firmly hold the outer edge of the sheet in order to prevent thermal shrinkage and to heat the molding part as uniformly as possible. As a method for uniformly heating, in the case of radiation heating, for example, Japanese Patent Publication No. 41-16394
As shown in the publication, the heating heater is divided into many sections and precise adjustments are made for each section.

Furthermore, uniform heating is achieved by performing so-called "masking," which involves inserting wire mesh appropriately between the heater and the sheet in areas that are locally overheated to partially block radiant heating. In the case of contact heating, a large number of cartridge heaters are inserted into a metal thermal template, and the inputs thereof are adjusted for each section to equalize the temperature distribution on the thermal template surface. If the material is heated unevenly during the heating process, the parts heated to high temperatures will become thinner, while the parts heated to lower temperatures will become thicker.

In the process where a resin sheet to be molded is firmly held at a certain distance and heated to the molding temperature using a radiation heating method, thinner parts generally have less heat capacity and therefore are always higher in temperature than thicker parts. However, since the proper forming temperature of the sheet is much higher than the temperature at which thermal contraction begins, contraction tension acts, and due to the balance between tensile forces (-), the sheet begins to deform when the temperature exceeds the temperature at which contraction begins. Beyond this point, the value rapidly decreases as the temperature rises, and its value becomes smaller than the shrinkage tension, while the shrinkage tension increases as the temperature rises.Let the tensile strength in the high temperature region a and the low temperature region b be αA, αb, and the contraction tension is βA, respectively.
, βb, then αa×αB, βa>βb and β
Since the relationship b>αa holds true, the high temperature region a is deformed and becomes thinner, and the low temperature region b becomes thicker by that amount. In this way, uneven heating immediately induces variations in wall thickness, which is the biggest obstacle to obtaining a good molded product. The conventional molding method described above, which focuses on uniform heating of a stretched sheet, is based on the premise that the thickness deviation of the resin sheet to be molded is extremely small and that there is no large variation in its thickness.

However, normal resin sheets have a large thickness deviation. For example, commercially available biaxially oriented polystyrene sheets have a thickness of ±5 to ±7% in the extrusion direction and ±10% in the direction perpendicular to the extrusion direction.
A sheet with such a large thickness deviation, which has a thickness deviation of about ±20%, cannot be heated to reduce the occurrence of defective products even if the conventional "masking" technique is employed and heated. Conventionally, the temperature of the resin sheet decreases between heating the resin sheet using a radiation heating method and transferring it to the molding zone for molding, so it is common to heat the resin sheet to a slightly higher temperature in the heating zone. Ta.

For example, as shown in Figure 1, the temperature of the resin sheet increases until it is heated in the heating zone to point A, which is higher than the upper limit Tu of the appropriate molding temperature for the synthetic resin sheet, and then transferred to the molding zone and molded. Even when the resin sheet is cooled to point C, the temperature is set to be higher than the lower limit TL of the appropriate molding temperature for the resin sheet. With such a thermoforming method, a resin sheet with uneven thickness is overheated to point A, which not only tends to make the uneven thickness even worse, but also has the tendency to cause uneven thickness due to overheating of the sheet. The disadvantage was that the orientation of the resin sheet was reversed and the strength of the molded sheet was reduced, resulting in the final product being weak and lacking in strength.

The present inventors have eliminated the drawbacks of the conventional sheet thermoforming methods, and have developed a method for forming sheets with large thickness deviations, for example, ±10 to ±2.
The present invention was completed as a result of studying a method for efficiently producing molded products with excellent appearance and strength even when using a sheet with a thickness unevenness of 0%. .

The object of the present invention is to provide a thermoplastic resin sheet, in particular, a synthetic resin sheet that is uniaxially or biaxially stretched and has a large degree of unevenness in thickness, and which has a uniform wall thickness, excellent strength, and an excellent appearance. Another object of the present invention is to provide a method for efficiently manufacturing excellent deep-drawn molded products. However, the gist of the process is to heat a thermoplastic synthetic resin sheet to an appropriate molding temperature using a radiation heating method, and to place the synthetic resin sheet heated to an appropriate molding temperature into a mold holding frame at the bottom. A mold holding frame in which a female mold is installed, which is provided with air pores and a cooling medium pipe inside, and a plug chamber frame is provided opposite to this mold holding frame, and this plug chamber frame is provided. A plug, a heater for heating the plug chamber, and a blowing pipe are provided in the plug chamber, and the atmosphere in the plug chamber is transferred between the plug chamber and the heated plug chamber, which is heated to around the temperature suitable for molding the synthetic resin sheet, and the heated tightening the synthetic resin sheet between the mold holding frame and the plug chamber frame; pushing the synthetic resin sheet into the female mold by a plug installed in the plug chamber; and pressurizing air into the plug chamber. The present invention relates to a method for heating and molding a thermoplastic synthetic resin sheet, the method comprising the steps of: supplying a molded product to shape the molded product into the shape of a female mold, and immediately cooling the molded product in the female mold. The method of the present invention can be applied to molding thermoplastic synthetic resin sheets, and typical thermoplastic synthetic resins include styrene resins, vinyl chloride resins, and olefin resins, as well as polyamides, polycarbonates, etc. .

These synthetic resins are preferably applied after being uniaxially stretched or biaxially stretched. Hereinafter, embodiments of the present invention will be described in detail based on the drawings, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

FIGS. 2 to 5 show partial cross-sectional views showing steps in carrying out the method of the present invention. In the figure, 1 is a thermoplastic synthetic resin sheet, which is heated to the appropriate temperature for molding the synthetic resin sheet by a heating zone (not shown), and then transferred to a molding zone by a transfer device (not shown). .
The second drawing shows the heated synthetic resin sheet being transferred to the molding zone. The heating method in the heating zone is a radiation heating method. In the case of the contact heating method, since heating is performed in the forming zone, the heated sheet does not cool down at once, so there is no need to employ the method of the present invention. The synthetic resin sheet is heated to the appropriate temperature for molding in the heating zone.

The appropriate molding temperature varies slightly depending on the type of synthetic resin and the thickness of the sheet even for the same type. The type of synthetic resin has a much greater effect on temperature than the thickness of the sheet. The types of synthetic resins and the appropriate molding temperatures are as follows. If the heating in this heating zone exceeds the proper molding temperature of the synthetic resin sheet, the synthetic resin sheet will undergo heat shrinkage, and if the raw material sheet has uneven thickness, the uneven thickness will become worse due to heat shrinkage. However, if the raw material sheet is stretched, it is not preferable because the stretched orientation is restored by overheating and the strength of the formed sheet decreases. The molding zone is a mold holding frame 3 with a female mold 2 installed inside.
It consists of a plug chamber 6 with a plug 7 installed inside, and a plug chamber frame 8. The female mold 2 has a large number of narrow air holes 5 in its bottom, which are connected to an air outlet 12 to be discharged outside the mold. It is preferable that the pores 5 and the outlet 12 have a structure through which compressed air is fed to help release the molded product from the female mold after molding is completed. Female mold 2
A cooling medium piping is provided in the molded part so that a cooling medium can be passed therein to cool the molded product. If the resin sheet is not cooled immediately upon completion of molding, the resin sheet will shrink before the shape of the molded product is determined, resulting in a molded product with poor appearance. For these reasons, it is preferable that the female mold be made of metal such as aluminum alloy. This female mold is installed within the mold holding frame 3. Since the heated synthetic resin sheet is tightened with the plug chamber frame 8, the outer frame of the mold holding frame 3 is preferably set higher than the opening of the female mold. Although the figure shows an example in which one female mold is installed within the mold holding frame 3, it goes without saying that multiple female molds may be installed within the holding frame 3. The mold holding frame in which the female mold is installed is structured so that it can be moved toward and away from the synthetic resin sheet by a drive device (not shown). The plug chamber 6 consists of a hexahedral plug chamber frame 8 with one side open on the outside, and inside the plug chamber 6 is a plug 7 that can be lowered toward the female mold as shown in the drawing. It consists of a heater 9 and a blowing pipe 10 passing through the frame wall of the plug chamber frame 8. The opening of the plug chamber is installed so as to accurately face the mold holding frame 3.
By doing this, when the two are brought close to each other, the synthetic resin sheet 1 can be sandwiched between the plug chamber frame and the mold holding frame and tightened to prevent leakage of compressed air, as shown in Figure 3. . Needless to say, the plug chamber frame 8 is constructed so that it can be moved toward and away from the synthetic resin sheet by a drive device (not shown). A heater 9 for heating the inside of the plug chamber is installed on the inner wall of the plug chamber frame 8. The heater 9 has the function of keeping the air inside the plug room and the plug 7 warm. By installing a heater in the plug chamber in this manner, it is possible to prevent the synthetic resin sheet transferred to the molding zone from cooling down. The plug chamber frame 8 is provided with a blowing pipe 10 that passes through the frame wall and is connected to a compressed air source (not shown). Since the plug chamber frame 8&ζ will be exposed to high temperatures, it goes without saying that metal is preferable. A plug 7 is provided in the plug chamber 6 as shown in the &ζ diagram.

The plug 7 has the function of pushing the synthetic resin sheet, which is tightened between the mold holding frame and the plug chamber frame and heated to a suitable molding temperature, into the female mold cavity 13. The size of the plug 7 is slightly smaller than that of the female mold cavity 13 and has a similar shape. Its material is preferably metal such as aluminum alloy, and its outer surface is preferably mirror-finished. Inside the plug 7, a heater for heating the plug itself may be built in, or a compressed air blowing hole may be bored.
It is also possible to supply compressed air to this from a compressed air source outside the plug chamber. The plug 7 is connected to a plug drive shaft 11, and the plug shaft 11 can be moved up and down in a direction perpendicular to the synthetic resin sheet by a drive device (not shown). The distance between the plug 7 and the bottom of the female mold cavity is 1
It is preferable to be able to approach until the temperature drops below 07I1J1. The drawing shows an example in which one plug is provided for one female mold, but when using a multi-cavity female mold, the number of plugs will depend on the number of molds to be molded. It goes without saying that you can use more. When the heater 9 and the plug 7 have built-in heaters, the atmosphere in the plug chamber needs to be heated by both the heater 9 and the plug 7 to approximately the appropriate temperature for molding the synthetic resin sheet. If the ambient temperature in the plug chamber is too low compared to the proper molding temperature of the synthetic resin sheet, the synthetic resin sheet will be cooled to below the lower limit TL of the proper molding temperature, which may make molding impossible, which is undesirable; If the temperature is too high than the upper limit of the appropriate temperature, overheating may cause uneven thickness of the synthetic resin sheet or change the stretching orientation of the sheet, resulting in a decrease in the strength of the synthetic resin sheet. As shown in Figure 3,
After the synthetic resin sheet is tightened by the mold holding frame and the plug chamber frame, the plug 7 is moved in the direction of the female mold cavity 13 and the synthetic resin sheet is squeezed into the female mold cavity (see Fig. 4).
.

It is preferable to heat the plug 7 in advance to around the appropriate molding temperature of the synthetic resin sheet, since the synthetic resin sheet will not be cooled during this step. FIG. 6 shows the temperature of the synthetic resin sheet in the heating zone and molding zone in the molding process up to now. In the heating zone, the synthetic resin sheet is heated to point D, which is within the appropriate molding temperature. In this case, as shown in FIG. 1, the upper limit T of the appropriate molding temperature. It is not necessary to heat to point A beyond . Subsequently, even when this synthetic resin sheet is transferred to the molding zone, the atmosphere inside the brag chamber in the molding zone is heated to around the appropriate molding temperature for the synthetic resin sheet, so the sheet is heated by radiant heat and cools down. can be prevented. Therefore, the temperature of the synthetic resin sheet can be maintained at the value of point D while reaching point E. At point E, the plug 7 is lowered to squeeze the synthetic resin sheet. In the next step, compressed air is sent from the air inlet 10 installed in the plug chamber to mold the synthetic resin sheet into the shape of a female mold, as shown in FIG.

At this time, if the plug 1 is also provided with air pores, compressed air can be fed in at the same time as it is fed from the air inlet 10. At this time, it is preferable that the temperature of the compressed air sent in is heated to approximately the temperature suitable for molding the synthetic resin sheet. Through the above steps, the molded article 14 formed as shown in FIG.
It contacts the female mold and is immediately cooled to define its shape.

Therefore, cooling of the female mold 2 is performed more preferably when the temperature is adjusted to be as low as possible. Next, plug 7, plug chamber frame 8
is separated from the female mold side, and the molded product is released from the female mold.

Subsequently, the molded product is transferred to a punching zone, where the molded product is punched out from the raw synthetic resin sheet to obtain a molded product. A new synthetic resin sheet heated to the appropriate molding temperature in the heating zone is sent to the molding zone, resulting in the state shown in FIG. 2. If the next molding is performed from this state and the steps already described are performed, continuous molding becomes possible. Although a synthetic resin sheet transfer device is not shown, both ends of the wide and long synthetic resin sheet in the width direction can be held and transferred by pinch chains or clamp chains. The method of the present invention has the following characteristics and has extremely high industrial utility value.

(1) In the conventional thermoforming method, the synthetic resin sheet is heated above the upper limit of the appropriate molding temperature, and even if it is slightly cooled in the molding tube, the sheet does not fall below the lower limit of the suitable molding temperature.

For this reason, sheets with uneven thickness become even more uneven in thickness due to overheating, and the stretching orientation is reversed due to overheating, resulting in the disadvantage that a molded product with excellent appearance and excellent strength cannot be obtained. However, in the method of the present invention, there is no need to heat the synthetic resin sheet above the upper limit of the appropriate molding temperature in the heating zone, and the temperature does not drop below the lower limit of the appropriate molding temperature in the molding zone, so sheets with large thickness unevenness can be used as raw materials. However, a molded product with excellent appearance and strength can be obtained. (2) In the molding zone, if the compressed air as well as the plug is heated to around the proper molding temperature of the synthetic resin sheet, the synthetic resin sheet will not be partially cooled. (3) In the molding zone (since the synthetic resin sheet is maintained at an appropriate molding temperature, preliminary stretching with a plug can be carried out sufficiently and well, making it possible to easily produce deep-drawn molded products). can.

An example of producing a deep-drawn molded product according to the method of the present invention will be shown below. Example Female mold cavity opening size 130mJ1 x 180711J!
1. A square strawberry container mold with bottom wall dimensions of 95u x 145u and depth of 70u was prepared, and a female mold with a large number of air pores drilled around the bottom wall was prepared, and this was molded into a mold with inner dimensions of 180u x 230u.
It was installed in a mold holding frame with a depth of 110 mm.

A plug chamber was provided corresponding to this mold holding frame. The depth of the plug chamber is 100u, and the size of the plug is 7577!1
1! Xl3OUX2OU, and many small far-infrared heaters were installed above the plug room. The plug head was installed at a height of 5u from the bottom of the female mold cavity. The plug is made of metal, has a built-in plug heater, and has a mirror-finished outer surface. The inlet is connected to a source of compressed air. Average wall thickness 0.4577!1W
The biaxially oriented polystyrene sheet was heated to about 130° C. in a radiant heating zone and transferred to a forming zone as shown in FIG.

Then, as shown in FIG. 3, the synthetic resin sheet was tightened between the mold holding frame and the plug chamber frame. At this time, the ambient temperature inside the plug chamber was heated to about 13°C by a heater installed in the plug chamber, and the plug itself was also heated to about 130°C by a heater inside the plug chamber and a heater built into the plug. Subsequently, the synthetic resin sheet was squeezed into the female mold cavity using this plug (see FIG. 4). Immediately after this step, compressed air of 3 Kf/CrA was sent into the plug chamber from the blowing port to mold the synthetic resin sheet along the shape of the female mold. Cooling water was passed through the cooling medium piping of the female mold to maintain the cavity side surface temperature at &O 0 C or lower. The obtained molded product is a square strawberry container.

The wall thickness of this container was measured as follows. Measurements were taken both at the center and at the corners of the sidewalls, in each case starting at the bottom edge of the container and then at 20 ffL intervals upward. The measured values (unit: v!t) are shown in Table 1. When the molded product obtained by this method was observed with the naked eye, it was found to have an extremely excellent appearance.

Furthermore, when the molded product was held in hand and the side wall portion was pressed, there was a considerable repulsive force and the strength was strong. Comparative Example Molding was carried out using the same molding equipment and the same materials as in the above example.

At this time, the sheet was heated to a temperature of 140° C. in the heating zone, sent to a molding zone that had not been heated in advance, the plug temperature was set to 40° C., and the sheet was molded using air pressure of 3 Kf/Cd without any particular heating. The wall thickness distribution of the containers thus obtained was measured in the same manner as in the above example and is shown in Table 2.

When the molded product obtained in this comparative example was visually observed, it was found that the wall thickness distribution was non-uniform, with the upper part of the side wall being thicker and the bottom edge being thinner, and the bottom edges of the corners being particularly thin.

Furthermore, when the molded product was held in hand and the side wall portion was pressed, the side wall became rusty and deformed, and the repulsive force was weak.

[Brief explanation of the drawings] Figure 1 shows that a synthetic resin sheet is heated in the heating zone above the upper limit of the appropriate molding temperature, and when it is transferred to the molding zone, it is slightly cooled and brought to within the upper and lower limits of the suitable molding temperature. A model curve of the temperature of the sheet to be formed is shown. FIGS. 2 to 5 are schematic vertical cross-sectional views showing steps in carrying out the method of the present invention. Figure 2 shows the heated synthetic resin sheet being transferred to the molding zone, Figure 3 shows the synthetic resin sheet being tightened between the mold holding frame and the plug chamber frame, and Figure 4 shows the synthetic resin sheet being moved to the molding zone. FIG. 5 shows the state in which the synthetic resin sheet is squeezed into the female mold cavity by the plug, and the state in which the synthetic resin sheet is molded along the shape of the female mold cavity. FIG. 6 shows a state in which a synthetic resin sheet is heated to a suitable temperature range for molding in a molding zone, maintained within the suitable temperature range for molding when transferred to the molding zone, and subjected to molding according to the method of the present invention. A model curve of a resin sheet is shown. In the figure, 1
is a synthetic resin sheet, 2 is a female mold, 3 is a mold holding frame, 4 is a cooling medium pipe, 5 is an air hole, 6 is a plug chamber, T is a plug, 8 is a plug chamber frame, 9 is a heater, 10 is a blowing pipe, 11 is a plug drive shaft, 12 is a discharge port, and 13 is a molded product.

Claims (1)

[Claims] 1. A process of heating a thermoplastic synthetic resin sheet to an appropriate temperature for molding using a radiation heating method, and placing the synthetic resin sheet heated to an appropriate molding temperature inside a mold holding frame with air pores provided at the bottom. A mold holding frame is provided with a female mold provided with a cooling medium pipe, and a plug chamber frame is provided opposite to this mold holding frame, and within this plug chamber frame there is provided a plug and a plug for indoor heating. A step of transferring the heated synthetic resin sheet to the plug chamber, which is equipped with a heater and a blowing pipe, and in which the atmosphere in the plug chamber is heated to around the appropriate temperature for molding the synthetic resin sheet; and a step of transferring the heated synthetic resin sheet to the mold. A step of tightening the holding frame and the plug chamber frame, a step of pushing the synthetic resin sheet into the female mold by a plug installed in the plug chamber, and a step of supplying compressed air into the plug chamber to tighten the female mold. 1. A method for heating and molding a thermoplastic synthetic resin sheet, comprising the steps of shaping the sheet into a shape and immediately cooling the molded product in the female mold.