JPS6168213A - Rotary molding by rock'n' roll method using crosslinked polyethylene - Google Patents

Abstract

PURPOSE:To obtain the nearly equal rate of crosslinkage of a specified value or above inside and outside a molded piece by blowing heated air applying the rock'n'roll method into a mold in which crosslinked polyethylene is supplied. CONSTITUTION:Crosslinked polyethylene resin material is supplied into a mold 2, biaxial rotation of rocking and rolling actions is given to it and a burner 33 is ignited. After heating, all quantity of the crosslinked polyethylene material is melted and welded into the mold 2. Then, after the rocking action is suspended, the pipe 40 of the heated air blower 37 is inserted from the resin material loading aperture 32 of the mold 2. The crosslinking reaction of crosslinked polyethylene material is acceralated by outside heating and inside heating due to heated air, smoke type gas is exhausted and the crosslinked polyethylene material is cooled. Th crosslinkage rate was about 80% or more and uniform inside and outside the molded piece.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a rotational molding method using crosslinked polyethylene using the rock and roll method.

BACKGROUND OF THE INVENTION In Japan, rotomolded products are mainly made of polyethylene, and particularly large products with a volume of 11,000 m to 300,000 m are molded by the rock'n'roll method. The rock'n'roll method is a method in which molding is performed in an oven while directly heating the mold with a gas burner or the like from the outside of a mold that rotates on two axes.

On the other hand, crosslinked polyethylene is attracting attention as a molding material when molding large products such as those described above.

Cross-linked polyethylene has excellent resilience, outstanding impact strength, and low-temperature durability, so it has a wide range of applications such as large storage tanks, canoes, boats, and containers. When such crosslinked polyethylene is used as a material, it must be heated to about 260° C. to cause a crosslinking reaction. Moreover, this crosslinking reaction must occur throughout the molded article.

For this reason, the crosslinked polyethylene material during molding must be placed under approximately uniform heating conditions as a whole;
The McNeil method is suitable for this purpose. This McNeil method is popular in the United States and other countries.
A rotating mold is stored inside the heating chamber, and within a
This method achieves molding by blowing hot air at 350°C. However, in Japan, it is difficult to find enough space in a normal factory to place a molding machine using the MacNeil method to produce large molded products, and there is only a small amount of space available for things like motorcycle gas tanks, play equipment, chairs, etc. The McNeil method has only been put into practical use for small products and products with special shapes. In addition, a molding machine using the MacNeil method is very expensive, and especially as it becomes larger, the equipment cost becomes several tens of times that of a molding machine using the rock and roll method.

Problems to be Solved by the Invention Therefore, the present invention aims to provide a rotational molding method that can bring about an ideal crosslinking reaction for crosslinked polyethylene while basically using the rock'n'roll method. be.

Crosslinked polyethylene exhibits the most ideal crosslinking reaction at, for example, 260"C, and as the temperature decreases from 260°C, the reaction time becomes longer. Also, when the temperature exceeds 260°C, the reaction becomes too vigorous and "pockets" appear on the resin surface. occurs.

The biggest problem when molding a crosslinked polyethylene material using the rock'n'roll method is that the crosslinking rate varies in the thickness direction of the resulting molded product. More specifically, as mentioned above, the rock'n'roll method uses a method in which the mold is heated only from the outside in an open state without a heating chamber, so the outside surface of the molded product is heated only from the outside. Although it is possible to maintain a temperature of, for example, 260° C. in close contact, the inner surface is constantly exposed to the atmosphere and cooled. Therefore, the humidity inside the molded article becomes extremely low, and the crosslinking rate in that area can only be extremely low, for example, 40% or less.

Therefore, in this invention, 1i is applied to increase the crosslinking rate on the inner surface side of the molded product.

Means for Solving the Problems In this invention, first, the cross-linked polyethylene material is melted by heating the mold from the outside while applying two-axis rotation of rocking and rolling to the mold into which the cross-linked polyethylene material is put. After the mold is fused to the inner surface of the mold, a step of blowing hot air at, for example, 300 to 350° C. into the mold is added.

Effect: According to the present invention, the crosslinking reaction on the inner surface of the molded article can be promoted in response to the blowing of hot air.

Embodiment FIGS. 1 and 2 are a front view and a right side view, respectively, showing molding by the rock'n'roll method used in one embodiment of the present invention. The molding machine 1 includes a mold 2 in the shape of a hollow drum. This mold 2 is given a rocking rotation in the direction shown by the double-headed arrow 3 in FIG. 1, and a rolling rotation in the direction shown by the double-headed arrow 4 in FIG.

In order to give the mold 2 such motion, the mold 2 is held and driven by a structure as described below.

For example, two bearings 7.8 are provided on the factory floor 5, sandwiching the bit 6, and these bearings 7. -8, the main shaft 9 is passed through and is arranged so as to straddle the bit 6. This main shirt]・9 supports substantially the entire weight of the molding machine 1. Main shaft 9
is rotatably supported about its axis relative to a bearing 7.8.

The base frame 10 is fixedly attached to the main shaft 9.
is installed. Base frame 10 has its lower half received in bit 6. Two brackets 11 and 12 are provided on the base frame 1o, and these brackets 11 and 12 control the rotary drive shaft 13.
is rotatably supported around its axis. Near both ends of the rotary drive shafts 1 to 13, rollers 14,
15 is fixedly attached. The rows 514 and 15 engage rotating rings 16 and 17 fixedly provided at both ends of the outer peripheral surface of the mold 2, respectively.

A rotating shaft 18 is parallel to the rotating drive shaft 13.
It is rotatably supported by two brackets provided on the base frame 10.

These two brackets are provided on the base frame 10 at positions corresponding to the aforementioned brackets 11 and 12. One bracket is not shown, but the other bracket is designated as "19" in FIG. Two rollers are also provided on this rotating shaft 11. One roller is r20J in Figure 2.
It is shown in This roller 20 is similar to the roller 15 described above.
At the same time, it engages with one rotating ring 17. and,
The other roller and the aforementioned roller 14 engage the other rotating ring 16 . The mold 2 is held on the base frame 10 by each of these four rollers engaging the rotary ring 16, 17. The rotation drive shaft 13 is rotationally driven by a motor 21.

That is, the motor 21 includes a transmission 22, both of which are fixed on the base frame 10. And, at the end of the rotary drive shaft 23 extending from the transmission@22,
A drive sprocket 24 is provided. On the other hand, a driven sprocket 25 is provided at the end of the rotational drive shaft 13, and this driven sprocket (25 and drive sprocket 2
4, a chain 25 is connected between the two. A rotary drive shaft 1 using such a motor 21 as a drive source
3 gives the mold 2 rolling rotation in the direction of arrow 4.

Another motor 27 is provided at the bottom of the pit 6. Rotational force is transmitted from this motor 27 to a reduction gear 128 , and a crank arm 30 is attached to an output shaft 29 of the reduction gear 28 . A transmission rod 31 is connected between the tip of the crank arm 30 and the base frame 1o. The reciprocating motion of the transmission rod 31 using the motor 27 as a driving source provides the base frame 10 with a rocking motion in three directions of arrows centered on the axis of the main shaft 9.

Of course, the locking action of the base frame 10 also imparts a locking action to the mold 2 which is substantially held thereby.

A resin material inlet 32 is located on one end surface of the mold 2 and on the axis of rotation for rolling rotation.

As a result, this resin material inlet 32 becomes a manhole formed in the upper part of the tank by the mold 2.

A plurality of burners 33 are arranged around the mold 2.

The burner 33 is held at one end of a copper tube 34 that also serves as a gas guide tube. The other end of the copper tube 34 is connected to a header 36 held by a stand 35 extending from the base frame 10.
connected to. The gases supplied up to this header 36 each pass through a copper tube 34 and are combusted at the end of the burner 33 . The heat generated at this time is applied to the outer surface of the mold 2, and the entire surface of the rolling mold 2 is heated uniformly. In addition, since each burner 33 is held by a flexible copper tube 34, it can be placed at any position. This makes it easy to change the position of the burner 33 in response to changes in the size and shape of the mold 2.

FIG. 3 is a front view showing a hot air blowing device 37 used in combination with the molding machine 1 shown in FIGS. 1 and 2. FIG. The hot air blowing device 37 includes an air blower 38 and a heating machine 39, and is configured so that the air generated by the air blower 38 is heated by the heating machine 39. A vibrator 40 is connected to the outlet of the heating 8139. A plurality of through holes 41 are provided in the peripheral wall of the vibrator 40, and hot air is blown out from the vibrator 40 in a radial direction through the through holes 41. The vibrator 40 is provided with a flange 42 that fits into the resin material inlet 32 of the mold 2 described above. Although not shown, the flange 42 may be appropriately provided with an outlet for smoky gas caused by the crosslinking reaction. Such a hot air blowing device 37 is
In order to lift it up to an appropriate height from the floor 5, it is provided on a stand 43 having a predetermined height.

Next, using the molding n1 shown in FIGS. 1 and 2 and the hot air blowing device 37 shown in FIG.
We will introduce an experimental example of molding using L-100).

First, 170 ka of powdered cross-linked polyethylene material is charged into the mold 2 from the resin material input port 32, and the burner 33 is ignited by applying two-axis rotation: rocking motion in the direction of arrow 3 and rolling motion in the direction of arrow 4. did. Note that the direction of rotation of the rolling motion in the four directions of the arrows is reversed at predetermined time intervals.

Thirty minutes after heating, the entire amount of the crosslinked polyethylene powder was melted and fused to the inner surface of the mold 2. From about 35 minutes after heating, water vapor and other gases indicating the vA bridge reaction of the crosslinked polyethylene material began to be discharged from the mold 2 in the form of smoke. 40 minutes after heating, the rocking operation is stopped and only the rolling operation is performed, and as shown in FIG. did. At this time, flange 4
2 is positioned so as to close the resin material input port 32.

In this state, send 1! Hot air is generated by the ll1138 and the heater 39, and the through hole 41 of the vibrator 40 (Fig. 3)
350°C hot air was blown into the mold 2. Note that it is preferable that the flange 42 be provided with a suitable discharge port in order to discharge the hot air blown in this way. As the vibrator 40, this experimental example has a diameter of 3C.
II11 length and 20oCIIl length were used.

The crosslinking reaction of the crosslinked polyethylene material was promoted by the external heating by the burner 33 and the internal heating by the hot air as described above, and smoky gas was violently discharged.

Twenty minutes after blowing hot air, a rapid decrease in exhaust gas was observed, all heating was stopped, and air cooling was performed. After this air cooling state continued for 10 minutes, the rolling operation of the mold 2 was stopped and the molded product was taken out.

As a result of measuring the crosslinking rate using several test pieces of this molded article, it was found that a crosslinking rate of 80% or more was achieved in all parts distributed in the thickness direction of the molded article. Here, it was confirmed that there is no inferiority in comparison with the molded product made by the McNeil method described above.

Effects of the Invention As described above, according to the present invention, while applying the rock'n'roll method which has low equipment cost and low running cost, in order to compensate for the drawbacks of the rock'n'roll method, hot air is By blowing into the inside and outside of the molded product, it is possible to achieve a crosslinking rate of more than a predetermined level (9) almost uniformly inside and outside the molded product. Therefore, it is possible to make molded products such as large storage tanks that take full advantage of the characteristics of crosslinked polyethylene at low cost. In addition, at the time the hot air is blown, the cross-linked polyethylene material is already melted and fused to the inner surface of the mold, so the blowing of hot air makes it possible to melt the cross-linked polyethylene material. The particles will not scatter and will not interfere with proper molding.

[Brief explanation of the drawing]

FIG. 1 shows molding v11 used in one embodiment of the present invention.
FIG. FIG. 2 is a right side view of the molding machine 1 shown in FIG. 1. FIG. 3 is a front view of a hot air blowing device 37 used in combination with the molding machine 1 of FIG. 1. FIG. 4 is a front view showing a state in which the hot air blowing device 37 is combined with the molding 1111. In the figure, 1 is a molding machine, 2 is a mold, 9 is a main shaft, 10 is a base frame, 13 is a rotary drive shaft,
14, 15.20 are rollers, 16° and 17 are rotating rings,
21 and 27 are motors, 32 is a resin material inlet, 33 is a burner, 37 is a hot air blower, 40 is a vibrator, and 41 is a through hole. Mei 1 Figure 2

Claims (3)

[Claims] (1) While applying two-axis rotation (rocking and rolling) to the mold into which the cross-linked polyethylene material has been introduced, the mold is heated from the outside to melt the cross-linked polyethylene material and fuse it to the inner surface of the mold. 1. A rotational molding method using a rock'n'roll method using crosslinked polyethylene, the method comprising blowing hot air into the mold after the mold is brought into a state. (2) In the step of blowing hot air into the mold, the mold is switched to rolling rotation.
Rotational molding method using the rock and roll method using the crosslinked polyethylene described in Section 3. (3) The mold has a resin material inlet located on the rotational axis of rolling rotation, and the hot air has a plurality of through holes in the peripheral wall, and the hot air flows into the mold from the resin material inlet. A rotational molding method using the rock and roll method using the crosslinked polyethylene according to claim 2, which is blown into the crosslinked polyethylene through an inserted vibrator.