JPH06190912A - Forming method for foamed polyethylene terephthalate sheet - Google Patents

Abstract

PURPOSE:To uniformize the wall thickness and crystallization of a sheet formed product and manufacture of product of superior quality by performing the double-side vacuum molding of a preheated and softened sheet by means of a molding die with a couple of molds, at least one of which is heated up to more than the crystallization temperature. CONSTITUTION:A crystalline foamed polyethylene terephthalate sheet (foamed PET sheet) 2 is heat softened to the state of being moldable but not accelerating the crystallization of the foamed PET sheet 2 by oven heaters 1a and 1b. As the oven heaters 1a and 1b, for example, an infrared ray heater or the like is used. A heating mold 3 consists of a combination of a couple of a male mold disposed below a sheet formed product 22 formed by a sheet 21 and a female mold disposed above the sheet formed product 22 facing the male mold. The heat softened sheet 21 is double-side vacuum molded and foamed by using the heating mold 3 with at least one of the male and female molds is heated up to the crystallization temperature or over. Crystallization is accelerated in the heated state in the mold 3 to manufacture a molded product 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a foamed polyethylene terephthalate sheet, and more particularly to a molding method for obtaining a molded article used as a packaging container having heat resistance, humidity resistance and strength. It is a thing.

[0002]

2. Description of the Related Art Conventionally, polyethylene terephthalate sheet (hereinafter referred to as "PET sheet") molded articles are
It is known that by heating above the crystallization temperature (about 130 ° C.) to increase the crystallinity, a material having excellent heat resistance, humidity resistance and strength can be obtained.

As a method for molding this PET sheet, P
The ET sheet is heated to a temperature above its glass transition temperature (75 ° C.) and below its crystallization temperature (130 ° C.), and this sheet is thermoformed, and then, while maintaining its formed shape, it is above its crystallization temperature and its melting point (258). A method of obtaining a molded product by heating to (° C.) or lower has been proposed (see Japanese Patent Publication No. 4-29529). And, usually, the thermoformed sheet molded article,
To retain its shape, it is repressed by a pair of cooling dies after thermoforming.

In the thermoforming in this molding method, in order to improve the adhesion between the sheet and the mold cavity surface of the mold, pressure molding is performed using a pair of heating molds to such an extent that the mold release is not impaired. Alternatively, a means for forming by vacuum suction or compressed air supply from one surface of a pair of heating dies is adopted.

[0005]

However, in the above molding method, when a foamed PET sheet is used,
There were the following problems. The foamed PET sheet re-foams when heated, but its thickness may vary greatly depending on the elapsed time of the raw fabric or the heating state, which may cause variations in the wall thickness of the molded product, and defective molding is likely to occur.

Further, since the foamed PET sheet is foamed, its heat conduction is poor and it takes a long time to crystallize in the mold, resulting in a long molding cycle and poor productivity. By the way, in order to make the thickness of these molded products uniform and shorten the crystallization time, it is conceivable to set the mold clearance small and increase the contact pressure from both sides of the sheet molded product.

However, in this case, the releasability is remarkably deteriorated, and at the time of releasability, the sheet molded article partially adheres strongly to the mold cavity surface, rather causing deformation failure and lowering productivity. Become. On the other hand, in the case where the heat-softening sheet is thermoformed by vacuum forming or pressure forming from one surface of the pair of heating molds, in addition to the above problems, a molded product having a wall thickness according to the mold clearance can be obtained. There was a problem that it would be difficult. That is, vacuum suction or the like from one surface of the mold is performed in order to bring the sheet molded product into close contact with the mold cavity surface of one of the molds without any gap to improve heat conduction from the mold. As a result, refoaming of the sheet molded product is suppressed. Therefore, the sheet molded product is
A gap is created between the mold and the mold that is not in close contact, and as a result,
This is because the thickness of this gap portion becomes thin.

In view of the above circumstances, an object of the present invention is to
It is an object of the present invention to provide a method for molding a foamed PET sheet, which can stabilize the quality and improve the productivity of a molded article made of the foamed PET sheet.

[0009]

In order to solve the above-mentioned problems, a method for forming a foamed PET sheet according to the present invention is to heat and soften a crystalline foamed polyethylene terephthalate sheet at a temperature not higher than its crystallization temperature. To promote crystallization in a heated state in the mold after performing double-sided vacuum molding to foam in the mold by using a molding mold in which at least one of a pair of molds is heated to a crystallization temperature or higher. It is characterized by.

[0010]

According to the method for molding a foamed PET sheet of the present invention having the above-mentioned structure, the crystalline foamed PET sheet is heated to a temperature not higher than its crystallization temperature, so that it can be molded without promoting crystallization. Is softened to. Since this heat-softening sheet is molded using a molding mold in which at least one of the pair of molds is heated to the crystallization temperature or higher, crystallization is promoted.

Since the inside of the sheet-molded product molded by this molding die is depressurized by double-sided vacuum molding in which vacuum is sucked from both sides of the mold, theoretically the inside of the foam bubbles of the sheet-formed product reaches a vacuum pressure. Foaming is accelerated up to. As a result, the sheet molded product is foamed in the mold to fill the mold clearance, and the wall thickness of the molded product can be made uniform.

Crystallization of the sheet molded product can be promoted uniformly and quickly because the sheet molded product is uniformly foamed by double-sided vacuum forming and the sheet molded product is evenly contacted with the mold cavity surface. Since foaming of the sheet-formed product is promoted by double-sided vacuum forming, it can be performed faster than the rate at which the sheet-formed product starts to crystallize and cure due to heat conduction from the heating mold. That is, the sheet-formed product is crystallized in the heated state in the mold after foaming in the mold.

Next, after releasing the vacuum suction from both surfaces of the mold, the mold is released. The release of this molded product from the mold is carried out by in-mold foaming without press pressure to secure the wall thickness of the sheet molded product, so the adhesion of the sheet molded product to the mold is weak. The mold release can be performed easily and quickly. On the other hand, when only one side of the pair of molding dies is used as a heating mold, crystallization is promoted on one side of the sheet molded product and crystallization is suppressed on the other side, and crystallization and crystallization of the sheet molded product are performed. At the same time, rigidity is given by suppression. This makes it possible to omit re-pressing with a cooling mold for maintaining the shape of the sheet-formed product in a later step.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of a molding process using a method for molding a foamed polyethylene terephthalate sheet (hereinafter referred to as “foamed PET sheet”) of an embodiment of the present invention, and FIG. 2 is used for this molding method. The schematic diagram of the heating die 3 and the cooling die 9 is shown.

In the molding step shown in FIG. 1, the pre-heating zone A for heating and softening the expanded PET sheet 2 fed from the roll-shaped sheet S into a moldable state without promoting crystallization,
Heat-softened sheet 21 that has been heat-softened in the preheating zone A
And the cooling zone C for cooling the sheet molded product 22 molded in the molding zone B to near room temperature in order to impart rigidity to the molding zone B. Then, in each zone, the sheet is fed to each zone without error by using the chain clamp 5 or the like which is a highly accurate feeding mechanism.

In the preheating zone A, the sheet 2 is provided above and below the expanded PET sheet 2 fed from the roll sheet S.
Oven heaters 1a, 1 arranged in non-contact with
b is a station for heating and softening the foamed PET sheet 2 to a moldable state without promoting crystallization by the oven heaters 1a and 1b. As the oven heaters 1a and 1b, for example, an infrared heater or the like is used, and the radiant heat heats the foamed PET sheet 2 to a temperature not lower than the glass transition point (75 ° C.) and before crystallization is promoted. The sheet surface temperature is preferably set in the range of 110 to 140 ° C. That is, if the sheet surface temperature is lower than 110 ° C, it takes time to soften by heating, and if it is higher than 140 ° C, the foamed PE is heated.
This is because crystallization of the T sheet 2 may be promoted and the surface may be hardened.

In place of the oven heaters 1a and 1b, a plurality of sets of heating plates provided vertically and horizontally are used to form the PET foam.
The sheet 2 may be sandwiched and brought into contact with each other for preheating. The molding zone B is provided with the heating mold 3 as a molding mold shown in FIG. 2, and is a station for molding the heat-softened heat-softened sheet 21 and for promoting foaming and crystallization.

As shown in FIG. 2, the heating mold 3 includes a male mold 31 disposed below a sheet molded product 22 on which the sheet 21 is molded, and a sheet molded product 22 facing the male mold 31. Is a pair in which a female mold 32 arranged above is combined, and is a so-called match mold in which the sheet molded product 22 is brought into contact with the male and female mold cavity surfaces. Male 31
Is a convex portion 33 heated to promote crystallization of the sheet molded product 22, a heater plate 34a for heating the convex portion 33,
It is provided with a lower mounting plate 82a and a lower platen 83a that support the convex portion 33 and the heater plate 34a. The convex portion 33 is provided with a plurality of vacuum suction holes H for reducing the pressure inside the mold. A vacuum pump P is connected to the hole H through a pipe K, and the vacuum pump P is controlled to operate when the heating mold 3 is clamped. This vacuum pressure is -5
It is set in the range of 50 to -650 m / m Hg. Convex part 3
The heater 3 is heated by the heater plate 34a directly attached to the lower surface of the heater 3 with bolts or the like. The heating temperature of the convex portion 33 is
At a crystallization temperature of the PET resin (135 ° C.) or higher and at a softening point (25
8 ° C.), preferably 160 to
It is set in the range of 220 ° C. That is, this heating temperature is 1
This is because if it is lower than 60 ° C., it becomes difficult to promote crystallization of the sheet molded product 22, and if it is higher than 220 ° C., the sheet molded product 22 adheres to the mold 3 and becomes difficult to be released. Two cartridge heaters 37a are embedded in the heater plate 34a. In addition, this cartridge heater 37a
The number of is not particularly limited as long as the convex portion 33 is uniformly heated, and an appropriate number can be used. Also, the heater plate 34
As a, other known heating means such as one in which a nichrome wire is directly buried can be used. A lower attachment plate 82a is attached to the lower portion of the heater plate 34a via a base 81a, and a lower platen 83 is attached to the lower surface of the lower attachment plate 82a.
a is attached. The base 81a is for making it difficult for heat to be transferred from the heater plate 34a to the lower mounting plate 82a and the lower platen 83a. Furthermore, in the lower mounting plate 82a,
Cooling water, cooling oil, or the like may be circulated to make it difficult for heat to be transferred to the lower platen 83a. The heat is not transmitted to the lower platen 83a in this way.
When the lower platen 83a is thermally expanded, the male die 31 and the female die 32
This is to prevent this thermal expansion, because it causes backlash and eventually defective molding. The lower platen 83a is fixed to a lower press board E1 to which a cooling mold 9 described later is attached. The lower press board E1 is connected to a rod of a cylinder 6a that can move back and forth. By driving the cylinder 6a, the male die 31
The whole can be moved up and down.

On the other hand, the female die 32 is the convex portion 3 of the male die 31.
3, the heater plate 34a, the base 81a, the lower mounting plate 82a, and the lower platen 8 are provided.
Cartridge heater 37b having the same configuration as 3a
Heater plate 34b, base 81b, and upper mounting plate 82 in which is embedded
b and an upper platen 83b. Further, the upper platen 83b is also fixed to an upper press board E2 to which a cooling die 9 to be described later is attached, and the upper press board E2 is also movable back and forth so that the entire female die 32 can move up and down. The rod of the cylinder 6b is connected.

The clearance of one heating die 3 made of these male and female dies is set to such a dimension that the sheet molded product 22 contacts the mold cavity surface. The matching time during which the heating mold 3 is clamped and matched with the sheet molded product 22 is about 6 to 15 seconds. FIG. 3 is a schematic view of a forming process in which the sheet-formed product 22 is vacuum-formed on both sides in the forming zone B. With reference to FIG. 3, when the sheet molded product 22 is molded by the heating mold 3, the sheet molded product 22 and the concave portion 35 of the female mold 32 are clamped with a gap therebetween (see FIG. See 1).). And
When the vacuum pump P is operated and vacuum is sucked from both sides of the die 3, the inside of the die is depressurized, and the sheet molded product 22 is foamed in the die with the full die clearance (see FIG. 3 (2)). This in-mold foaming is theoretically accelerated until the inside of the foamed cells of the sheet molded product 22 reaches a vacuum pressure. However, in the case of excessive foaming, since the cells are closed cells, a negative pressure may be applied after the mold is released to cause the sheet molded product 22 to shrink. Therefore, the thickness is about three times the thickness before molding and the density is about 1/10. It is preferable to use foaming up to. In this state, if the sheet molded product 22 and the mold 3 are matched for a while, the sheet molded product 22
Crystallization is accelerated. As described above, since the foaming of the sheet molded product 22 is promoted by the double-sided vacuum forming,
The heat conduction from the heating die 3 can be performed at a speed faster than the rate at which the sheet molded product 22 starts to crystallize and cure. That is, the sheet molded product 22 is crystallized after foaming in the mold. Next, after the operation of the vacuum pump P is stopped and the vacuum suction from both surfaces of the mold 3 is released, the cylinders 6a and 6b are driven to release the heating mold 3. In order to secure the thickness of the sheet molded product 22, this demolding is performed by in-mold foaming without applying a pressing pressure, and since the adhesive force of the sheet molded product 22 to the mold 3 is weak, it is easy to And it can be done quickly.

The cooling zone C is provided with the cooling mold 9 shown in FIG. 2, and is a station for re-pressing the sheet molded product 22 molded in the above-mentioned molding zone B to cool it to around room temperature. . The cooling mold 9 is a pair of a male mold 91 and a female mold 92, and is attached to the lower press plate E1 and the upper press plate E2 to which the male mold 31 and the female mold 32 of the heating mold 3 are attached. The male die 91 and the female die 92 are attached so as to be adjacent to the heating die 3. The male die 91 includes a convex portion 93 having the same shape as the convex portion 33 of the heating mold 3, a cooling plate 94a,
The base 91a and the lower platen 92a are provided. Male 9
The convex portion 93 of No. 1 does not have the vacuum suction hole H like the convex portion 33 of the heating mold 3, but the cooling plate 94a attached to the lower surface thereof.
Is cooled by. Although not shown, water or oil is circulated in the cooling plate 94a so as to keep the temperature of the convex portion 93 constant, and cools the sheet molded product 22 molded by the heating mold 3. To give rigidity. Specifically, this temperature is preferably set in the range of 20 to 80 ° C., and if it is lower than 20 ° C., there is a risk that the heat of the heating die 3 arranged next to the temperature will be absorbed.
If the temperature is higher than 80 ° C., the softened state is maintained beyond the glass transition point (75 ° C.) of the foamed PET resin, and the sheet molded product 22 is easily deformed. The cooling plate 94a has a base 91.
A lower platen 92a is attached via a, and the lower platen 92a is fixed to the lower press board E1.

The female die 92 is provided with a concave portion 95 corresponding to the convex portion 93 of the male die 91, a cooling plate 94a,
The base 91a and the lower platen 92a are provided with a cooling plate 94b having the same configuration as that of the base 91b and the upper platen 92b. The upper platen 92b is fixed to the upper press board E2. The cooling mold 9 represses and cools the sheet molded product 22 that has been molded by the heating mold 3, whereby rigidity is imparted to the sheet molded product 22 and its shape is maintained. Become.

Then, the sheet molded product 22 whose shape is held by the cooling mold 9 is cut into each molded product 23 by the pair of cutters 4a and 4b connected to the cylinder 7, and is recovered as a product. By repeating the above molding process, a molded product made of the foamed PET sheet is manufactured.

As described above, according to the foamed PET sheet molding method of the above-described embodiment, since the sheet molded product 22 molded by the pair of heating molds is vacuum-molded on both sides, the mold clearance is fully filled. Inside is foamed. After that, the sheet molded product 22 is promoted to be crystallized while being heated in the mold.
As a result, the thickness and crystallization of the sheet molded product 22 can be made uniform, and the molded product 23 of excellent quality can be obtained.
Can be obtained. Moreover, since the foaming speed and the crystallization speed of the sheet molded product 22 can be increased by performing the double-sided vacuum forming, the molding cycle can be shortened and the productivity can be improved. In addition, since the adhesive force between the sheet molded product 22 and the mold 3 is weakened by the in-mold foaming without applying a pressing pressure, the sheet molded product 22 can be released easily and quickly. The cycle can be shortened and productivity can be improved.

Since the molded product thus obtained has excellent heat resistance, humidity resistance and strength, it is used as various packaging containers. As the foamed PET sheet 2, one having an expansion ratio of about 1.5 to 15 times is preferably used, that is, if the expansion rate is 1.5 times or less, the rigidity is poor and the heating die 3 is deformed at the time of releasing. There is a risk of
In addition, if it is 15 times or more, the foaming is so high that it takes time to crystallize up to the central portion of the sheet.

Further, either one of the male die 31 and the female die 32 of the heating die 3 may be used as a cooling die. In this case, the sheet molded product 21 can be crystallized and rigidity can be imparted at the same time by suppressing the crystallization, and the cooling die 9 for maintaining the shape in the subsequent step is not necessary, and repressing can be omitted. Thereby, productivity can be further improved.

Further, the heating die 3 and the cooling die 9 are provided.
May have a built-in clamp for holding the sheet molded product 22 at a fixed position so that the sheet molded product 22 can be smoothly released. Further, in this embodiment, the heating die 3 and the cooling die 9 are attached to the same lower press plate E1 and upper press plate E2, but they may be attached to different press plates.

Furthermore, the heating die 3 and the cooling die 9
Both may be provided with a large number of convex portions 33, 93 and concave portions 35, 95 on one surface, and various other design changes may be made without departing from the scope of the present invention.
Next, the following tests were conducted by the method for molding the foamed PET sheet shown in FIG. Test Example A molded product made of a foamed PET sheet was manufactured under the following conditions. Sheet specifications: Crystalline foamed polyethylene terephthalate sheet Sheet weight: 400 g / m ² Sheet thickness: 1.5 mm Secondary thickness after heating: 3.1 mm Mold dimension Length: 743 mm Width: 600 mm Heating plate dimension: 370 x 600 mm Cooling dimension: 370 × 600mm Heating mold temperature: 180 ° C (both male and female molds) Cooling mold temperature: 40 ° C Number of heating molds: 5 × 3 = 15 Number of cooling molds: 5 × 3 = 15 Molded product Size Caliber: 82mm Bottom diameter: 70mm Depth: 35mm Mold clearance: 2.0mm Molding method: Match mold molding / double-sided vacuum molding Comparative example Other than the single-sided vacuum molding of the female mold only,
A molded product made of a foamed PET sheet was manufactured in the same manner as in the above test example. <Evaluation> Regarding the crystallization rate in the mold in the above-mentioned test examples and comparative examples, as shown in FIG. 4, the average value of the crystallinity at the points a, b and c of the ● part of the molded product 23. (%) Is taken as the vertical axis, and the matching time (seconds) when the mold is clamped and the sheet molded product matches the mold is taken as the horizontal axis. The molded product obtained in the test example is-△-, and the comparative example is The graph obtained by plotting the molded product obtained in 1. as-○-is shown in FIG. The target value of crystallinity is 25%.

Further, in the above test examples and comparative examples,
Table 1 shows the variation in the wall thickness of the molded product, the crystallinity of the molded product, and the molding cycle with respect to the set value of 2 mm. The molding cycle is the time from the start of mold clamping of the heating mold to the end of mold release.

[0030]

[Table 1]

From the results shown in FIG. 5 and Table 1, it was found that the test example was superior to the comparative example in all cases.

[0032]

As described above, according to the method for molding a foamed PET sheet of the present invention, a sheet molded product molded by a pair of molding dies is vacuum-molded on both sides and foamed in the mold with a full mold clearance. After that, crystallization is promoted by keeping the heated state in the mold. As a result, the thickness and crystallization of the sheet molded product can be made uniform, and a molded product having excellent quality can be obtained.

Further, by performing the double-sided vacuum forming, the foaming rate and the crystallization rate of the sheet-formed product can be increased, so that the forming cycle can be shortened and the productivity can be improved. In addition, it is formed by in-mold foaming without pressing pressure, and the adhesive force between the sheet molded product and the mold is weak, and the mold release of the sheet molded product can be performed easily and quickly, thus shortening the molding cycle. The productivity can be improved.

On the other hand, when only one side is used as a heating mold, crystallization of the sheet molded product and rigidity impartment by suppressing crystallization can be performed simultaneously, and repressing by a cooling mold for shape retention in a later step can be omitted. be able to. Thereby, productivity can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a forming step in a method for forming a foamed PET sheet according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a heating mold and a cooling mold used in the molding method of FIG.

FIG. 3 is a schematic view showing a process of double-sided vacuum forming in a heating mold.

FIG. 4 is a view showing a portion where a crystallinity of a molded product is measured.

FIG. 5 is a graph showing a crystallization rate of a sheet molded product in a heating mold.

[Explanation of Codes] A Preheating Zone B Molding Zone C Cooling Zone 2 Foamed PET Sheet 21 Heat Softening Sheet 22 Sheet Molded Product 23 Molded Product 3 Heating Mold (Molding Mold) 9 Cooling Mold

Claims (1)

[Claims] 1. A molding die in which a crystalline foamed polyethylene terephthalate sheet is heated and softened at a temperature not higher than its crystallization temperature, and at least one of a pair of molds is heated to a temperature not lower than the crystallization temperature. A method for forming a foamed polyethylene terephthalate sheet, which comprises performing double-sided vacuum forming to foam in a mold, and then promoting crystallization while being heated in the mold.