JP2559957B2 - Method for producing synthetic resin hollow molded article - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin hollow molding, for example, a double window panel, a double wall daylighting dome, and a relatively large double wall having a double wall as used for a large-sized signboard for internal lighting. The present invention relates to a method for producing a synthetic resin hollow molded article.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a relatively large double-walled hollow plate-like molded body as described above, the following molding method called a double sheet molding method is known.

That is, as shown in FIG. 1, two thermoplastic synthetic resin sheets (1) and (2) are used as molding materials,
Both the seats (1) are sandwiched by the clampers (8) and (9) from above and below with the spacers (7) interposed between the peripheral portions of the sheets.
(2) is supported in parallel and horizontally at a predetermined distance from each other. Then, both sheets (1) and (2) are heated by the heaters (14) and (15) from above and below to be softened, and at the same time compressed air is applied between both sheets from the air nozzle (7a) provided in a part of the spacer (7). As shown in FIG. 2, the two sheets (1) and (2) are blown with each other to pretension the two sheets in a direction in which they are separated from each other. ) Sandwich between them.

In this way, by bringing both molds close to a predetermined closed position, the sheet sandwiching surface (17) at their peripheral edges is formed.
Both sheets (1) and (2) are sandwiched between (18) to join and integrate the peripheral portions thereof, and as shown in FIG. 3, a molding air nozzle (19) provided in at least one mold is provided. A closed space (16) between the seats that penetrates the seat (1)
Both sheets (1) by introducing compressed air of a predetermined pressure into
(2) is brought into close contact with the inner surfaces of the cavities of both molds (3) and (4). At this time, a vacuum is sometimes drawn from the inner surface side of the molding die to assist the sheet in intimate contact with the die.

Next, after cooling while maintaining the internal pressure between both sheets, both sheets (1) are cut by a cutting blade (20).
Cut the joint part (21) at the peripheral edge of (2) at its outer peripheral edge part,
The mold is opened to take out the hollow molded body (A) as shown in FIG.

The molding method as described above is advantageous in that a considerably large molded body (A) can be molded relatively easily as a plate-shaped hollow molded body having an arbitrary shape having a double wall.

[0007]

However, the conventional double sheet molding method as described above has the following problems.

That is, in the heating step of heating both sheets (1) and (2) to the molding temperature, heating heaters (14) and (15) are used.
There is no choice but to perform the heating by the single-sided heating only from the outer surface side of each of the sheets (1) and (2). For this,
Even if a temperature gradient is generated in each sheet (1) and (2) in the thickness direction and a sufficient proper molding temperature is reached on the outer surface side,
It may happen that the molding proper temperature has not yet been reached on the inner surface side.

According to the results of experiments and research conducted by the present inventors,
In the double sheet molding method, in order to obtain a satisfactory finishing accuracy for the molded body (A) and to obtain a sufficient bonding strength at the bonding portion (21), both sheets (1) and (2) are molded by a mold. (3) During the expansion molding operation in which the sheets (1) and (2) are brought into intimate contact with the inner surface, the outer surface temperature T1 and the inner surface temperature T2 are different from the proper molding temperature Tf determined by the material of the sheets (1) and (2). Ideally, at least the heating temperature condition of 5 ° C>Tf-T1> -5 ° C (a) Tf-T2 ≤10 ° C (b) is satisfied.

However, due to the one-sided heating by the heaters (14) and (15), the outer surfaces of the sheets (1) and (2) are heated to a temperature satisfying the condition of the above formula (a) within a relatively short time. However, since the inner surface side is heated depending on the heat conduction in the thickness direction of the sheet, it takes some time to satisfy the above expression (b). Therefore, it is considered to set the heating temperature set by the heaters (14) and (15) to a sufficiently high temperature, for example, a temperature exceeding 2Tf to shorten the required heating time. In this case, Since the outer surface temperature of the sheet becomes too high, the outer surface of the sheet may be discolored due to heat deterioration, and the skin may be roughened due to foaming.

Therefore, in the conventional sheet heating process in the double sheet molding method, the temperature of the heaters (14) and (15) is set to 2 relative to the proper molding temperature Tf of the sheets (1) and (2).
A relatively low temperature below Tf is set, and the heating operation is continued for a relatively long time until the inner surface temperature of the sheet reaches the temperature that satisfies the above expression (b), and then the molding operation must be performed. I didn't get it.

[0012] For example, in the double sheet molding method using a vinyl chloride resin sheet having a thickness of 5.0 mm, the heating temperature of the heaters (14) and (15) is set against the proper molding temperature Tf of the sheet is about 170 ° C. The heating was performed by setting Tm to about 300 ° C. In this case, the temperature rise process of the outer surface temperature T1 and the inner surface temperature T2 of the sheets (1) and (2) is almost as shown in FIG.
As shown in. As shown in the figure, it took about 11 minutes or more to heat the inner and outer surface temperatures of the sheet until the conditions of the expressions (a) and (b) were almost satisfied.

As described above, since the heating requires a relatively long time, the molding cycle is long, the productivity of the molded body (A) is poor, and the consumption of heat energy required for heating is large, which results in a little cost increase. There was a problem that it was hard to come by.

An object of the present invention is to provide a molding method effective for improving the above problems, that is, a method for producing a synthetic resin double-walled hollow body. More simply, the required heating time is shortened, the productivity is improved, and the quality due to excessive outer surface heating or insufficient inner surface heating,
It is an object of the present invention to provide a manufacturing method of a molded product which avoids deterioration of molding accuracy and enables the manufacture of a well-balanced, high-quality and highly accurate molded body.

[0015]

SUMMARY OF THE INVENTION According to the present invention, two thermoplastic synthetic resin sheets are clamped at their peripheral edges with spacers in a manner such that a predetermined closed space is left between them.
After heating both sheets from the outside to soften them, they are sandwiched between a pair of upper and lower molds on the inner side of the clamp position on the peripheral edge, and compressed air is introduced into the closed space between the both sheets to separate them. In the method for producing a hollow molded body which is in close contact with the inner surfaces of both upper and lower molds, the heating step of the sheet comprises After the heating temperature Tm of the heater is set to a temperature between 2Tf and 3Tf with respect to the sheet proper molding temperature Tf and heating is started, the outer surface temperature T1 of both sheets is set to the proper molding temperature while maintaining the temperature range. An initial heating step of continuing heating until a temperature of at least 3/4 Tf or more with respect to Tf is reached; Next, the heating temperature of the heater is gradually decreased with time and the minimum temperature is 1.3 Tf as a lower limit, and the outer surface temperature T1 and the inner surface temperature T2 of each sheet are 5 ° C. higher than the proper molding temperature Tf. Tf−T1> −5 ° C. Tf−T2 ≦ 10 ° C.
The gist is a method for producing a synthetic resin hollow molded article, which is characterized by immediately closing the mold and performing a molding operation.

Except for the heating step, the other molding steps are the same as those of the conventional molding method, and are as described above with reference to FIGS. Therefore, the repetition of the description is omitted.

By the way, the above-mentioned initial heating step in the present invention may be performed while maintaining a predetermined heating temperature during the step, or while gradually lowering the heating temperature of the heater from the initially set maximum temperature. Also good. However, during the initial heating process, the heating temperature condition, that is, 2Tf with respect to the sheet proper heating temperature Tf.
It is necessary to maintain the temperature range of ˜3 Tf. When the heating temperature is set to less than 2Tf, the whole heating process requires a long time, which is not suitable for the intended purpose of the present invention. Conversely, when the heating temperature is set to exceed 3 Tf, discoloration due to heat deterioration on the outer surface of the sheet,
There is a possibility that the skin may be rough due to foaming.

In the initial heating step, the outer surface temperature T1 of the sheet is at least 3/4 T with respect to the proper molding temperature Tf.
The process continues until the temperature reaches f or higher. If the heater heating temperature is lowered to less than 2Tf before reaching the temperature, the amount of heat supplied to the sheet per unit time becomes insufficient and a sufficient softened state is obtained. That is, it takes a relatively long time to reach the temperature near the proper molding temperature Tf. However, it is useless to continue the initial heating step for too long after the outer surface temperature T1 of the sheet reaches 3/4 Tf, and it is rather harmful because it may cause thermal deterioration of the outer surface of the sheet. is there. Therefore, it is desirable that the initial heating step be completed before the outer surface temperature T1 of the sheet reaches a temperature of more than 10 ° C., preferably more than 5 ° C., from the proper molding temperature Tf. .

The gradual heating step may be carried out under a continuous temperature drop operation, or may be carried out under one or a plurality of stepwise temperature drop operations. The point is that the heating temperature of the heater is gradually lowered with time and with the minimum temperature of 1.3 Tf as the lower limit. The minimum temperature of 1.3 Tf is set as the lower limit, because if the heating temperature is lowered to a temperature lower than this, it becomes difficult to reliably maintain the proper molding temperature Tf or its vicinity during molding of the sheet. is there.

At the end of the gradual heating temperature step, the outer surface temperature T1 of the sheet is equal to the molding proper temperature Tf ±.
It is necessary that the temperature is within the range of 5 ° C., and the inner surface temperature T2 is isothermal to the proper molding temperature Tf or within −10 ° C. This is because, when the outer surface temperature T1 and the inner surface temperature T2 deviate from the above ranges, high-accuracy molding becomes difficult as described above.

By the way, in the case where the gradual heating step is carried out under the continuous temperature drop operation like the former among the two methods of carrying out the continuous and stepwise temperature drop, the average temperature thereof is It is desirable to set the descending speed to about 10 to 50 ° C./min. This descent rate is 10 ℃ / m
If it is less than in, the heating becomes excessive and the loss of thermal energy becomes large, so that it becomes of little significance to carry out the gradual heating step. On the contrary, when a rapid heating temperature drop of more than 50 ° C./min is performed, a situation in which the amount of heat supplied from the outer surface side to the sheet is insufficient occurs, resulting in a drawback that the required heating time is long. The most preferable average temperature drop rate is approximately 20 to 40 ° C./min.

On the other hand, when the temperature is lowered stepwise, it is desirable that the lowered temperature, that is, the temperature difference is also set to about 10 to 50 ° C./time. When the temperature difference is less than 10 ° C./time and 50 ° C./time, the same disadvantages as in the case of the continuous lowering operation are derived. The kind of heater used for heating the synthetic resin sheet is particularly limited. Not a thing. Conventionally used nichrome wire heaters, quartz tube sheath heaters, far-infrared ceramic heaters (for example, NGK Insulators Co., Ltd .: trade name "Infrastein"), etc. may be used, but far-infrared radiation type heaters are among them. Therefore, it is preferable to use a system (for example, "quick response heater" manufactured by Asano Laboratory Co., Ltd.) that can quickly and arbitrarily change the amount of heat generated during the heating process.

The rate of temperature rise on the surface of the resin sheet in the heating step varies not only with the heating temperature of the heater, the distance between the heater and the sheet, etc., but also with the ambient temperature and the like and is not always constant. Therefore, in order to properly carry out the present invention, it is desired to continuously measure the surface temperature of the sheet during the heating step and control the heating temperature of the heater based on the measured value. The measurement of the surface temperature as described above is preferably performed by using a non-contact type radiation thermometer, although the method is not particularly limited. However, this surface temperature measurement need only be performed on the outer surface side of the seat facing the heater, and is not necessarily required on the inner surface temperature side. This is because if the outer surface temperature is measured, the inner surface temperature can be almost accurately predicted from the heat transfer coefficient and the heating time specific to the material of the sheet.

In the practice of the present invention, the synthetic resin sheet as a molding material is not particularly limited as long as it is made of a thermoplastic resin. Depending on the application of the hollow molded body, any material is selected and used, but generally a resin sheet having a thickness of about 2 to 10 mm made of, for example, a vinyl chloride resin, an acrylic resin, a polycarbonate resin, or the like is used. . Also, the two resin sheets are
Different materials or different colors may be used.

[0025]

EXAMPLES As synthetic resin sheets (1) and (2) for molding,
A 5.0 mm-thick vinyl chloride resin (manufactured by Tsutsunaka Plastic Industry Co., Ltd .: trade name "Kydak KDG-1200") was used. The proper molding temperature Tf of this sheet is about 170 ° C.
Is.

Then, the two sheets (1) and (2) are
With the spacer (7) interposed between the peripheral portions, the peripheral portions are sandwiched by the clampers (8) and (9) from above and below, and the distance between the sheets (1) and (2) is about 50 mm. The closed space (16) was supported in a parallel and horizontal manner.

Next, the above-mentioned "quick response heater" (product name) (14) is placed above and below both sheets (1) and (2).
(15) was introduced and the sheet was heated from a distance of about 20 cm on both upper and lower surfaces. At this time, as shown in FIG. 2, compressed air is simultaneously introduced into the closed space (16) between the seats (1) and (2) from the air nozzle (7a) provided in a part of the spacer (7), so that both seats The free gravitational deformation of the sheet is prevented and the sheet is pretensioned.

In the above heating step, as shown in FIG. 5, the heaters (14) and (15) are heated to an initial heating temperature of 500.
C., which is twice as high as the molding proper temperature Tf (2Tf) within about 3 minutes and 40 seconds after the start of heating.
The temperature was continuously lowered to 0 ° C., and during this period, the initial heating step (I) was performed. At the end of the initial heating step (I), the outer surface temperature of each of the sheets (1) and (2) is about 170 ° C., which is approximately equal to Tf, and the inner surface temperature is about 125 ° C.
(Preliminary measured temperature).

Then, after the completion of the initial heating step (I), the heating temperature of the heaters (14) and (15) is continuously lowered at an average temperature lowering rate of about 33 ° C./min, and the heating is started from the beginning. When 7 minutes have passed and the temperature has dropped to about 230 ° C,
Thereafter, heating was continued while maintaining this heating temperature. The change states of the outer surface temperature T1 and the inner surface temperature T2 of the sheets (1) and (2) due to this heating were roughly as shown in FIG.

When about 8 minutes have passed after the start of the initial heating step, the outer surface temperature T1 of the sheets (1) and (2) is about 1
73 ° C., and the inner surface temperature T2 reached about 165 ° C. Therefore, up to this point is set as the gradual heating step (II), the heating step is completed, the heaters (14) and (15) are removed, and immediately after that, the sheets (1) and (2) are clamped at their peripheral clamp positions. Inside, a pair of upper and lower molding dies (3) and (4) are brought close to each other, and the sheet clamping portion (1
7) The molding air nozzle (19) provided in at least one mold (3) as shown in FIG. The sheet was penetrated through one of the seats (1) by advancing operation by a drive means (19a) such as a drive cylinder. Subsequently, compressed air is introduced from the air nozzle (19) into the closed space (16) between the sheets (1) and (2), whereby the sheets (1) and (2) are molded into a molding die (3) ( After closely contacting with the inner surface of the cavity of 4), and then performing the required cooling while maintaining this internal pressure, the air nozzle (19) was pulled out and the peripheral edge joint part (21) was cut and removed by the cutting blade (20). . Then, the molds (3) and (4) were opened and the hollow molded body (A) was taken out.

In this hollow molded article (A), the peripheral bonding portion (21) is firmly bonded and integrated, has sufficiently high molding precision, and has a surface portion free from defects such as discoloration due to heat deterioration. It was possible to confirm that it did not have it at all.

[0032]

EFFECTS OF THE INVENTION According to the present invention, depending on the above, when a hollow molded article is manufactured using the vinyl chloride sheet having a thickness of 5 mm shown in the above-mentioned embodiment, the hollow molded article is manufactured by the above-mentioned conventional method. The heating time required until the start of molding was at least 11 minutes, whereas the heating time can be shortened to 8 minutes, and the molding cycle can be shortened to improve productivity and improve molding accuracy. Can be manufactured.

Further, the heat energy consumed can be reduced by shortening the required heating time and the average heating temperature.

Further, since it is possible to eliminate the operation of continuously heating the outer surface of the sheet at a temperature as high as twice as high as the proper molding temperature Tf for a long time, discoloration or other damage due to heat deterioration of the sheet surface can be prevented. Can be reliably prevented,
It is possible to manufacture high quality products.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of a molding apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a main part showing a state during a pretensioning step.

FIG. 3 is a sectional view of a main part showing a state at the time of molding.

FIG. 4 is a cross-sectional view showing an example of a hollow molded body manufactured by the present invention.

FIG. 5 is a graph showing changes in heater temperature and sheet surface temperature in the heating process according to the present invention.

FIG. 6 is a graph showing changes in a heater temperature and a sheet surface temperature in a heating process in a conventional molding method.

[Explanation of symbols]

 (1) (2) ... Resin sheet (3) (4) ... Mold (7) ... Spacer (8) (9) ... Clamper (14) (15) ... Heater (16) ... Closed space (17) ( 18) ... Seating surface (19) ... Air nozzle for molding (21) ... Joined portion (A) ... Hollow molded body

Claims (3)

(57) [Claims] 1. Two thermoplastic synthetic resin sheets are clamped at their peripheral edges with spacers in such a manner that a predetermined closed space is left between them, and the two sheets are heated from the outside to be softened. After that, it is sandwiched between a pair of upper and lower molds on the inner side of the clamp position on the peripheral edge, and compressed air is introduced into the closed space between the two sheets to bring the two sheets into close contact with the inner surfaces of the upper and lower molds. In the manufacturing method, the heating step of the sheet comprises: After the heating temperature Tm of the heater is set to a temperature between 2Tf and 3Tf with respect to the sheet proper molding temperature Tf and heating is started, the outer surface temperature T1 of both sheets is set to the proper molding temperature while maintaining the temperature range. An initial heating step of continuing heating until a temperature of at least 3/4 Tf or more with respect to Tf is reached; Next, the heating temperature of the heater is gradually decreased with time and the minimum temperature is 1.3 Tf as a lower limit, and the outer surface temperature T1 and the inner surface temperature T2 of each sheet are 5 ° C. higher than the proper molding temperature Tf. Tf−T1> −5 ° C. Tf−T2 ≦ 10 ° C.
Next, a method for producing a synthetic resin hollow molded article, characterized in that the mold is immediately closed and a molding operation is performed. 2. The method for producing a synthetic resin hollow molded article according to claim 1, wherein the gradual heating step is performed under a continuous temperature lowering operation at an average temperature lowering rate of 10 to 50 ° C./min. 3. The synthetic resin according to claim 1, wherein the gradual heating step is performed under a stepwise temperature lowering operation of 1 to plural times with a temperature difference of 10 to 50 ° C./time. A method for manufacturing a hollow molded body.