JPS6014567Y2 - Heating device for thermoplastic resin sheet molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heater device suitable for thermoforming a thermoplastic resin sheet, particularly a biaxially stretched thermoplastic resin sheet.

Heating methods for thermoforming a stretched thermoplastic 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 is immediately transferred to the forming zone for forming.

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 to prevent thermal shrinkage and to heat the forming part as uniformly as possible.

As a method for uniformly heating, in the case of radiation heating, for example, as shown in Japanese Patent Publication No. 16394/1983,
The heaters are divided into many categories, and precise adjustments are made for each category.

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 their input is adjusted for each section in order to equalize the temperature distribution on the thermal template surface.

If the material is heated unevenly during the heating process, the parts that are heated to high temperatures will become thinner, while the parts that are heated to lower temperatures will become thicker.

Generally, 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 have less heat capacity and therefore always reach a higher temperature than thicker parts.

However, since the proper forming temperature of the sheet is considerably 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.

The tensile strength decreases rapidly with increasing temperature beyond the softening point, and its value becomes smaller than the shrinkage tension, while the shrinkage tension increases with increasing temperature.

Let αa and αb be the tensile strength in high temperature region a and low temperature region
1. Also, if the pre-compression tensions are βa and βb, respectively, then αa × αb1βa>βb, and the relationship βb>αa holds, so the high-temperature area a deforms and becomes thinner, and the low-temperature area becomes thinner by that amount. It becomes thick.

In this way, uneven heating immediately induces variations in wall thickness,
This is the biggest obstacle to obtaining good molded products.

Based on the above reasons, in the thermoforming of stretched sheets that is currently in practical use, a method that focuses on uniformly heating the sheet to prevent changes in the thickness of the sheet is adopted.

The conventional thermoforming method described above, which focuses on uniform heating of stretched sheets, is based on the premise that the sheet to be formed has extremely small deflection and that there is no large variation in its thickness.

However, ordinary resin sheets have a large degree of deflection; for example, commercially available biaxially oriented polystyrene sheets have ±5 to ±7% in the extrusion direction and ±1 in the direction perpendicular to the extrusion direction.
Sheets with thickness deviations of about 0 to ±20% and such large deflections cannot reduce the occurrence of defective products even if conventional masking methods are employed and heated.

Even when using a sheet with a large deviation in thickness, for example, a sheet with a degree of deflection of ±10 to ±20%, a method for efficiently producing a good molded product is to make the capacity of the heaters the same on the top and bottom, and to stir or stir the hot air. A circulating method has been proposed (for example, see Japanese Patent Publication No. 43-5558), but even with this method, it is difficult to heat the ends (edges) in the width direction of the resin sheet in the same way as the center. Moreover, hot air leaks from the insertion gap of the resin sheet and hits the molded product that has already been transferred to the molded product punching section, deforming the molded product.

The inventors of the present invention have overcome the drawbacks of the sheet thermoforming method described above, and have developed a method that has a large degree of deflection, for example, ±10 to ±2.
As a result of studying an apparatus that can efficiently produce good molded products even when a sheet having a degree of deflection of 0% is used, the present invention was completed.

An object of the present invention is to provide a heater device for thermoforming that can uniformize temperature distribution and efficiently produce good molded products even when a thermoplastic resin sheet with a large degree of deflection is used.

However, the gist of this is that in a heating device that constitutes a heating section for a molded plate of a thermoplastic resin sheet in which a heating section, a molding section, and a molded product punching section are sequentially arranged, the heater of the heating device is an on-off type electric This heater is installed on both the upper and lower sides of the heated resin sheet that is inserted and transferred into the heating device, and the upper heater is installed parallel to the direction of transfer of the heated resin sheet. The heaters are arranged so that the heat generation capacity increases toward the ends in the width direction of the resin sheet, and are arranged at least 10 cm away from the heated resin sheet, and the lower heaters are arranged at right angles to the conveying direction of the heated resin sheet. The total heat capacity is 50% or less of the total heating capacity of the upper heater, and the amount of heat generated on the inlet and outlet sides of the heated resin sheet is increased, and each heater is maintained at an appropriate temperature for molding the resin sheet when turned on. The applied voltage is set to +5 to +20% higher than the applied voltage required to maintain the temperature, and when it is off, the applied voltage is set to -5 to -25% lower than the applied voltage required to maintain the appropriate temperature. The present invention relates to a heating device for a thermoplastic resin sheet molded plate.

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 the gist thereof is exceeded.

Fig. 1 is a longitudinal cross-sectional view showing an example of a molding machine incorporating a heating device according to the present invention, Fig. 2 is a longitudinal cross-sectional side view of the section lined by FIG. 3B is a bottom view showing a model of an example of heater arrangement; FIG. 3B is a plan view showing a model of an example of heater arrangement in a bottom heater; FIG. FIG. 3 is a partial electrical circuit diagram when temperature adjustment is performed.

In the figure, 1 is a thermoplastic resin sheet to be molded, 2.3 is a guide roll, 4 is a preparation roll, 5 is a chain gear, and 6
is a bottle chain or clamp chain, 7 is a top heating furnace, 8 is a bottom heating furnace, 9 is a top heater, 10 is a bottom heater, 11 is a temperature sensing part for temperature adjustment, 12 is a formwork, 13 is a mold, 14 is a Formwork drive cylinder, 15 is a pressure plate, 16
17 is a hole for inserting a heater, 17 is a pressure plate fixing base, 18 is a pressure plate fixing plate, 19 is an air hole, 20 is an air pipe, 21 is an exhaust hole, 22 is an exhaust pipe, and 23 is a molded product.

In the heating device according to the present invention, heaters are provided on both the upper and lower surfaces of the resin sheet to be heated, which is inserted into the heating section (see FIG. 1).

The upper surface heaters provided in the upper surface heating furnace are arranged parallel to the conveying direction of the heated resin sheet (see Figs. 2 and 3).
(See Figure A).

If the top heater has a structure that connects from the inlet side to the outlet side of the heated resin sheet, such as a tube heater, for example, the temperature at the center of the heater will be high and the temperature at both ends will be low, resulting in an unfavorable temperature distribution. Therefore, Figure 3A
As illustrated in a-L a-2t a-39a-4?
Short heaters a-5 and a-6 are connected in parallel in parallel to the resin sheet transport direction.

b-1 to b-6, c-1 to c-6, d-1 to d-6, e
The same applies to -1 to e-6.

The width of the upper surface heaters is preferably changed depending on the width of the resin sheet to be heated, but in any case, it is preferable to arrange the upper heaters so that the width is larger than the width of the resin sheet to be heated.

This is to correct the fact that the temperature of the heated resin sheet tends to be lower at both ends (edges) and to make it ideal.

FIG. 2 and FIG. 3A show an example in which the heaters at both ends of the five rows of heaters (rows a and e) are located outside beyond the width of the resin sheet to be heated.

In the heating device according to the present invention, it is preferable that the capacity (wattage) of the upper surface heater increases toward the ends (edges) in the width direction of the resin sheet.

This is because when the capacities of the heaters are the same, the temperature tends to rise in the central part where the heaters are installed adjacent to each other.
It is easy to maintain the temperature, but heaters installed on the edge side of the resin sheet are easily absorbed by the clamps that hold the edge of the sheet, and are easily affected by the temperature of the outside air. This is because it is difficult for the temperature to rise compared to the other parts, and it is difficult to maintain the temperature constant.

In order to achieve uniform temperature rise and uniform heating with normal heating equipment,
For example, as in the device described in Japanese Utility Model Publication No. 48-27250, it is necessary to change the set voltage of heating heaters with uniform capacity using variable resistors connected to each heater, but this method requires considerable experience and skill. It has the disadvantage of being necessary.

According to experiments conducted by the present inventors, if the capacity of the top heater installed in the top heating furnace is set low at the center of the resin sheet, and the capacity of the heater installed at the ear side of the resin sheet is set high, the above-mentioned It was found that the defects could be eliminated.

For example, place the top heater 10 degrees above the surface of the heated resin sheet.
When provided in 5 rows with cm separation, the capacity ratio of the heaters in each row is 1.0 in the center (row C), 1 in rows b and d, and 2.0 in rows a and e. It was found that it is preferable to

This eliminates the complexity of adjusting the temperature while adjusting each set voltage using a variable resistor.

Note that if the upper surface heater is placed too close to the resin sheet to be heated, a temperature distribution will occur in the resin sheet, so the upper surface heater is provided at least 10 cm or more away from the surface of the resin sheet to be heated.

Note that it is desirable that the height of the upper surface heater from the surface of the resin sheet to be heated can be adjusted within the upper surface heating furnace.

The above-described top heater is preferably covered with a metal box on the outside as shown in FIG.

Preferably, the inside of the metal box is designed to reflect heat rays.

It is preferable to cover the outside of the metal box with a heat insulating material to reduce heat radiation.

In the above-mentioned top heating furnace, a temperature-regulating temperature sensing element is installed approximately in the center thereof.

Connect this to a temperature regulator and synchronize it with the stepless voltage regulator (■) to adjust the applied voltage.

The lower heaters provided in the lower heating furnace of the heating device according to the present invention are arranged perpendicular to the direction of conveyance of the heated resin sheet.

This is to prevent heating spots from occurring on the heated resin sheet.

The total heating capacity of the bottom heaters arranged in this way, that is, the wattage per unit area, is an amount equivalent to 50% or less of the total heating capacity (wattage per unit area) of the top heaters, especially 10 to 30%. Particularly preferred is a range corresponding to %.

The reason why it is preferable to use a large capacity upper heater and a small capacity lower heater is because when the resin sheet to be heated is transferred into the heating furnace, the lower surface of the resin sheet is heated by the lower heater. The heated air rises and traps heat, causing the temperature to rise and the bottom side of the resin sheet to become overheated.On the other hand, the temperature on the top side of the resin sheet decreases from the bottom side when the resin sheet is transferred into the heating furnace. Heat is cut off, and the temperature of the temperature-adjusting thermosensor drops below the set temperature, which causes the heating heater to turn on, increasing overheating by the bottom heater, making temperature regulation even more difficult; This is because when the rising airflow exits to the molding section side, it is possible to eliminate the problem of the hot airflow hitting the molded article that has already been sent to the molded article punching section and deforming the molded article.

As shown in FIG. 2, the width of the lower heater is set so that it fits within the chain clamp that clamps both ears of the resin sheet to minimize heating of the chain.

The capacity of the bottom heater is the inlet side heater (f-1 in Figure 3B) and the outlet side heater (f-1 in Figure 3B) of the resin sheet to be heated.
It is arranged so that the capacity of f-2) becomes large.

The capacity of the heaters provided on the inlet and outlet sides is increased by the heaters provided in the center (g-1 and g-2 in Figure 3B).
) is made larger than that because there are no heaters adjacent to each other at both ends of the inlet and outlet sides, and because they are easily cooled by outside air, a heater with a large capacity is provided in advance.

According to experiments conducted by the present inventors, when four bottom heaters are provided in a bottom heating furnace as shown in FIGS. 1 and 3B, an inlet side heater f-1 and an outlet side heater f −
It has been found that it is preferable to set the capacity of heaters g-1 and g-2 in the center to 0.5, assuming that the capacity of heaters g-1 and g-2 is 1.0.

Heaters that can be used as the bottom heater include tube heaters and sheath heaters.

The outer periphery of the bottom heater must be covered with a metal box, as shown in Figure 2.

The inside of this metal box is preferably designed to reflect heat rays, and the outside is preferably covered with a heat insulating material to reduce heat radiation.

The length of the heating device composed of an upper heating furnace and a lower heating furnace is usually preferably 3 to 5 shots.

The drawing shows an example of a length that can heat three shots.

The heating device according to the present invention controls the temperature using an on-off electric control method.

At this time, the applied voltage when turned on is +5 to 50% higher than the applied voltage required to maintain the appropriate temperature for molding the resin sheet.
Set the value to +25% higher.

Further, the applied voltage during off-time is set to a value lower by -5 to -25% than the applied voltage required to maintain the appropriate temperature.

This is an on-off type! In the air control method, when the heater switch is on, the temperature tends to rise, and when the switch is off, the temperature tends to drop, and the fluctuation in the temperature actually applied to the heated resin plate becomes large. This is to make it as small as possible.

The appropriate temperature at which a resin sheet can be molded varies depending on the type of resin, the thickness of the sheet, etc., but is approximately within the following range and is determined through experiments.

Polystyrene 115-135°C Polyethylene 110-130°C Polypropylene 160-180°C Vinyl chloride 100-160°C The applied voltage to maintain the appropriate temperature for molding the resin sheet is determined as follows. .

That is, while the stepless voltage regulator PT is initially adjusted manually and the resin sheet is manually molded, the balance between the temperature and the stepless voltage regulator PT is recorded.

In this way, the relationship between the temperature inside the heating furnace and the scale of the stepless voltage regulator circle is tabulated.

Next, the applied voltage at the appropriate temperature at which the resin sheet determined by the experiment can be molded is determined from the table.

Based on this applied voltage, set the applied voltage when on to a value that is +5 to +25% higher than the applied voltage required to maintain the appropriate temperature, and set the applied voltage when off to maintain the appropriate temperature. Set the value to be -5 to -25% lower than the required applied voltage.

Next, the temperature will be adjusted automatically.

There are no particular restrictions on the thermoplastic resin sheet that can be heated and molded using the heating device according to the present invention, but styrene resins, olefin resins, vinyl chloride resins, polyamides, and other thermoplastic resins can be formed by calendering or extrusion molding. Stretched or unstretched sheets produced by the method are common.

The present invention has the following characteristics, and its industrial utility value is extremely large.

■ When heating a resin sheet to be heated using a conventionally known device that divides the heated resin sheet into multiple compartments, there is a limit to the feed rate of the resin sheet, and the temperature in the center of each compartment becomes high. The disadvantage is that the resin sheet cannot be heated uniformly.

However, in the heating device according to the present invention, since a device without partition walls is used, there is no restriction on the feeding amount of the resin sheet, and uniform heating can be easily performed.

(2) In the heating device according to the present invention, since the heaters are arranged in a cross-shape so as to face each other vertically, it is possible to heat the resin plate to be heated without causing temperature unevenness.

■ In the heating device according to the present invention, the voltage applied to the upper heater and the lower heater is set in advance in the range of ±5 to ±25% of the applied voltage necessary to maintain the appropriate temperature for molding the resin sheet. Since the temperature is controlled at the same time, temperature fluctuations during molding can be kept within an extremely small range.

■ In the heating device according to the present invention, the upper surface heater is separated from the resin sheet to be molded by at least 10 cm, and the upper surface heater and the lower surface heater are set to a preferable value in advance, so temperature adjustment is easy and operation is easy. No skill is required.

Hereinafter, a process of heating and molding a resin sheet using the heating device according to the present invention will be described.

The raw resin sheet wound into a roll is transferred to a guide roll 2.
and 3, and sent to the heating section.

The sheet is guided to a bin chain or a clamp chain by an adjustment roll 4, and once the sheet has been sent, it is prevented from returning.

The bin chain 6 is linked by a chain gear (sprocket) 5 to an intermittent sheet conveying device (not shown), and conveys the sheet of bone to a required area.

The resin sheet transferred in this way is heated within the heating device.

An example of the heating device is shown in detail as follows.

(a) Length of top heating furnace outer box...90- Width of outer box...600171111 Power source...200 volt heater...Infrastein heater (manufactured by Nippon Insulator: far infrared heater) ) was installed as shown in Figure 3A.

The center distance between each heater is in the sheet transport direction. (For example, from a-1 to a-2 direction) 150m++t, sheet width direction (e.g. from a-1 to b- 1 direction) was set at 100 mm.

The installed position is on the side of the seat. Up to 10 hours and up to 15 to 100% It has an adjustable structure.

The capacity of the heater was as shown in Table 1 below.

(b) Length of bottom heating furnace outer case...90 (ha) Width of outer case...35- Power source...200 volt heater...3077m x 3oMn x 35-meter sheathed heater It was installed as shown in Figure 3B.

The distance between the heated resin sheet and the heated resin sheet is 50 questions. Ta.

The capacity of the heater was as shown in Table 2 below.

Table 2 (Unit: Wattage when applied voltage is 200 volts) f-1
g-1g-2f-2 400200200400 Total capacity of the bottom heater: 1.2KW Total heating capacity of the bottom heater: 3.5KW/rIl (corresponds to 25% of the total heating capacity of the top heater.

) (c) Temperature adjustment method All rows of top heaters are connected in parallel.

For example, connect a-1 to a-6 in parallel and connect this to R
□.

b-1 to b-6 are connected in parallel in the same way, and this is shown in Figure 4 R.
Set it to 2.

Thereafter, the C, d, and e columns are connected in the same manner.

R2-R7 are not shown in FIG.

Lower surface heaters f-1 and f-2 are connected in parallel as R6, not shown, and g-1 and g-2 are connected in parallel as R7, not shown.

Use two stepless voltage regulator ports for each of R1-R7, and set the on-state voltage using PT-i to PT-7, and the off-state voltage using PT-i' to PT7'. ,
Adjustment can be made by an on-off switch CR operating in unison with the temperature regulator ATC.

CR-1 to CR-7 are all shown as dashed lines in FIG. 4 (however, CR-4 to CR-7 are not shown).

), the electromagnetic selector switch CR is activated to synchronize the temperature by operating the temperature regulator R31 connected to the temperature sensitive body TC (corresponding to the number 11 in FIG. 1).

That is, when the indicated temperature of the heating furnace is lower than the set temperature, the temperature control relay switch R3 built in the temperature regulator R3 is connected and turned on, and the electromagnetic changeover switch CR is activated. .

The electromagnetic changeover switch CR is designed to be able to switch seven circuits at the same time.

Using the heating device described above, a biaxially oriented polystyrene sheet with a thickness of 0.25 mm (the thickness variation of the sheet should be ± in the width direction).
12%, ±5% in the extrusion direction.

) The applied voltage when heating is as follows.

First, by the method described above, the applied voltage necessary to maintain the temperature at which the raw resin sheet can be molded was determined, and the values for each heater were as shown in Table 3 below.

Table 3 (Unit: Volt) abcdefg 130 120 110 120 130 100 9
5 Based on the applied voltages in Table 3, the set voltages for on and off were determined as shown in Table 4 below.

Table 4 When the heater is on 40 30 20 30 40 10 00 When it is off 20 10 00 10 20 0 0 When the applied voltage of each heater is set as shown in Table 4, the temperature inside the heating furnace (temperature control temperature sensor TC temperature) is 250
kept at ℃.

The temperature of the resin sheet changes depending on the thickness of the sheet, the residence time of the sheet in the heating furnace, etc.

The biaxially stretched polystyrene sheet was intermittently sent to a heating furnace and heated for a residence time in the heating furnace of 9 seconds.

When heated under roller conditions, the sheet temperature will be within ±2.
The temperature could be controlled within 5°C.

The heated resin sheets are sequentially transferred to the molding section.

When the transfer is completed, the mold 12 is lowered, the resin sheet is clamped between the mold 12 and the pressure plate 15, compressed air is immediately sent from the air pipe 20, and the compressed air that passes through the air pores 19 molds the resin sheet. Press into mold 13.

At this time, the air inside the mold is removed from the exhaust hole 21 and the exhaust pipe 22.
is discharged through.

After cooling and solidifying the resin sheet in the mold, the mold frame 12
is raised and transferred to the molded product punching process.

This molding process could be performed at an extremely high speed of 20 shots per minute.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional side view showing an example of a molding machine incorporating the heating device according to the invention, and FIG.
- Figure 3A is a bottom view showing a model of an example of the arrangement of heaters in the top heater, and Fig. 3B is a plan view showing a model of an example of the arrangement of heaters in the bottom heater. FIG. 4 is a partial electric circuit diagram when the heater of the heating device according to the present invention is connected and the temperature is adjusted. 1... Thermoplastic resin sheet to be molded, 2° 3... Guide roll, 4... Adjustment roll, 5... Chain gear, 6... Bin chain or clamp chain, 7...
...Top surface heating furnace, 8...Bottom surface heating furnace, 9...Top surface heater, 10...Bottom surface heater, 11...Temperature control temperature sensitive body, 12...Formwork, 13... Molding mold, 14・
...Formwork drive cylinder, 15...Pressure plate, 16...
・Hole for inserting heater, 17...Pressure plate fixing base, 18・
... Pressure plate fixing plate, 19 ... Air pore, 2o ... Air piping, 21 - Exhaust hole, 22 ... Exhaust pipe, 23
···Molding.

Claims (1)

[Scope of utility model registration request] In a heating device constituting a heating section of a thermoplastic resin sheet molding machine in which a heating section, a molding section, and a molded product punching section are sequentially arranged, the heater of the heating device is of an on-off type electric control system, and The heaters are provided on both the upper and lower sides of the heated resin sheet that is inserted and transferred into the heating device, and the upper heaters are arranged parallel to the direction in which the heated resin sheet is transported, and the upper heaters are arranged parallel to the direction in which the heated resin sheet is transported, and the upper heaters are arranged at the ends of the resin sheet in the width direction. The heat generation capacity increases as it goes closer to the heated resin sheet.
The lower heaters are arranged at a distance of 0C771 or more, the lower heaters are arranged at right angles to the conveying direction of the heated resin sheet, and the total heat capacity thereof is 50% or less of the total heating capacity of the upper heaters,
The amount of heat generated on the inlet and outlet sides of the heated resin sheet is increased, and when each heater is turned on, the applied voltage + 5 is required to maintain the appropriate temperature for molding the resin sheet.
The applied voltage is set to ~ +20% higher, and when off, it is -5 to -25% higher than the applied voltage required to maintain the proper temperature.
A heating device for a thermoplastic resin sheet molding machine, characterized by being set at a low applied voltage.