JPH05179048A - Prefoaming of foamable resin particle - Google Patents

Abstract

PURPOSE:To carry out the subject prefoaming of foamable resin particles while reducing the variation of foaming and stabilizing the weight of the product by detecting the level of the upper surface of the foamable resin particles by an elevatably attached level meter and controlling the expansion rate. CONSTITUTION:In prefoaming of foamable resin particles by a batch-system prefoaming machine, this machine is equipped with an elevatable level meter 6 capable of detecting the level of the upper surface of the foamable resin particles so as to detect the level of the upper surface rising accompanying foaming by the level meter 6. The above-mentioned level meter 6 is also designed so as to rise following elevation of the level of the upper surface and the blow rate of a heating medium is controlled according to the rate of elevation. Thus, the objective prefoaming of the foamable resin particles is carried out.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for pre-expanding expandable resin particles.

[0002]

2. Description of the Related Art As a method for pre-expanding expandable thermoplastic resin particles (referred to as expandable resin particles in the present invention), there are batch method, continuous method and the like. Among these, in the batch type pre-foaming method, in the can body of the pre-foaming machine, a predetermined amount of expandable resin particles as a raw material is charged, and the particles are heated by a heating medium such as steam to expand and foam, A general method is to take out this batchwise.

The pre-foaming machine used in this batch-type pre-foaming method is generally provided with a level meter for detecting the upper surface level of the expandable resin particles, and the upper surface level of the expandable resin particles rises with foaming. The desired level of foaming is obtained by sensing that the level has reached a certain level by the level meter.

However, in this pre-foaming, it is important to control so as not to cause the fluctuation of the foaming (magnification) between the batches as well as the fluctuation of the foaming between the beads in the pre-foaming machine. Conventionally, foaming (magnification)
As a means for controlling the above, two level gauges are fixedly provided at two positions, an uppermost position and a position slightly lower than the uppermost position, and when the lower level meter senses the upper surface level, [1 ] Narrow the amount of steam blown in (JP-A-3-13307)
No.), [2] Steam is stopped and hot air is blown in (JP-A-3-133).
08), [3] once cooled and then reheated (JP-A-3-13).
1635), and so on.

[0005]

However, in the above-mentioned conventional control method, since the level meter is fixedly provided, the time required for the upper surface level to reach the level meter at the upper position depends on the material. Depending on the product type, the time after manufacturing the raw material, the target magnification, the amount of heating medium blown, the amount of cooling air blown, etc., this will cause variations in foaming in the foaming machine, which will be classified during granulation and This causes a variation in product weight of the foamed molded product using the foamed particles, resulting in a defective product.

[0006] In particular, the expandable resin particles contain a gas which is a foaming agent in the expandable resin particles, which tends to diffuse into the atmosphere over time and change the foamability, so that the heating medium changes over time with the raw material. It was necessary to manually adjust the blowing amount and cooling air blowing amount.

In view of the above, according to the present invention, as a batch type pre-expanding method of expandable resin particles, it is possible to reduce the variation in the expansion (magnification) between batches and in the pre-expanding machine, and to stabilize the product weight. It is intended to provide a method for obtaining pre-expanded particles capable of obtaining an expanded molded article.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for pre-expanding expandable resin particles, in which the upper surface level of expandable resin particles is sensed by a level meter to control the expansion ratio.
In order to solve the above-mentioned problems, a level meter that detects the upper surface level of the expandable resin particles is provided so that it can move up and down, and the upper surface level that rises with foaming is detected by this level meter and It is characterized in that the meter is made to follow the rise of the upper surface level, and the blowing amount of the heating medium is controlled according to the rising speed.

In this pre-expansion, the upper surface level of the expandable resin particles rises with foaming, and the rising speed is proportional to the foaming speed. Therefore, the foaming speed can be automatically controlled by causing the level meter for detecting the upper surface level to follow the increase of the upper surface level accompanying the foaming and controlling the blowing amount of the heating medium according to the rising speed.

For example, when the rising speed of the level meter, which follows the rising of the upper surface level due to foaming, is faster than the rising speed corresponding to the standard foaming speed, the blowing amount of the heating medium is reduced to delay foaming, and vice versa. When the rising speed is slow, the blowing amount of the heating medium is increased to accelerate the foaming. As a result, the foaming speed can be controlled to approximately correspond to the standard foaming speed during the period from the start of foaming until the upper surface level reaches the predetermined foaming ratio, and the foaming ratio can be averaged to reduce the variation in foaming. Can be made

Further, in the above pre-foaming method, the optimum state of the foaming rate is stored in the controller in advance, and the blowing amount of the heating medium is controlled while the level meter follows so as to match it. In this case, the rising speed of the upper surface level of the expandable resin particles, that is, the foaming speed can be automatically controlled to the optimum foaming state.

Further, in the above pre-foaming method, it is detected that a level meter that follows the rise of the upper surface level of the expandable resin particles has passed a preset point,
The blowing amount of the heating medium can also be adjusted.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 schematically shows a batch type pre-foaming machine for carrying out the method of the present invention. In the figure, (1)
Is a can body of the pre-foaming machine, and (2) is an inlet for the expandable resin particles impregnated with a foaming agent, which is provided above the can body (1). (3) is an outlet for the pre-expanded particles after the pre-expansion, to which a particle feeding means (3a) is connected. Reference numeral (4) shows a supply pipe of steam as a heating medium, and (4a) shows a valve for supplying the heating medium, which is opened / closed by a signal from a controller described later. Although not shown, a supply pipe (4a) for heating medium is provided with a supply pipe with a valve for cooling air for temperature adjustment. Further, inside the can body (1), a stirring device (not shown) with stirring blades, which is appropriately driven by a driving means, is provided at a position near the bottom.

The side wall of the can body (1) is provided with a vertically long viewing window (5) extending from a lower position near the bottom to an upper limit position. Reference numeral (6) is a level meter for detecting the upper surface level of the expandable resin particles put into the can body (1), and the upper surface of the expanded resin particles is passed through the inspection window (5) at the side of the inspection window (5). It is provided to sense the level.

The level meter (6) can be moved up and down along the viewing window (5) and its position can be controlled according to the setting of the foaming ratio and the like. As a means for this, in the case of the illustrated embodiment, the support portion (6a) of the level meter (6) is screwed into a vertically arranged screw rod (7), and this screw rod (7) is used as a speed reducing device or power transmission. The level meter (6) is connected to a driving means (8) such as a motor via a means and drives the driving means (8) to rotate the screw rod (7).
Is provided so that it can be moved up and down and can be stopped at any position.

As the level meter (6), a commonly used one such as a phototube type, an ultrasonic type, a tuning fork type and a float type can be used. The position of the level meter (6) is basically provided outside the can body (1) as described above, but even inside the can body (1), it does not interfere with the stirring device. Any sensor that is not adversely affected by the atmosphere in the can body (1) can be installed.

As the drive means (8) of the level meter (6), various motors such as a servomotor, a stepping motor, a geared motor with a clutch brake can be used, and a screw rod (7) as shown in the figure can be used. Besides, it can be implemented by a rack and a pinion, and various other means. It is also possible to provide it so that it can be moved up and down by an air actuator or an oil actuator.

The drive means (8) and the controller (10) for controlling the supply of the heating medium are, for example, a level meter (6).
Each time when the upper surface level is sensed, the sensing means receives the sensing signal to drive the driving means (8) to raise the level meter (6) by a fixed distance so as to follow the rising of the upper surface level and at regular time intervals. The rising speed is extracted by comparing the position of No. 1 with a preset position, and a signal is sent to the heating medium supply valve (4a) according to the rising speed, and the valve (4a) is opened / closed for heating. It is provided so as to control the blowing amount of the medium. Normally, when the rising speed is faster than the speed value set according to the optimum foaming speed, the blowing amount is decreased, and when the rising speed is slow, the blowing amount is increased. At the same time, a signal is also sent to the valve of the temperature control cooling air supply pipe to increase or decrease the amount of cooling air blown. Further, when the level meter (6) reaches the set upper limit position, the valve (4a) is set to be closed.

The pre-foaming method of the present invention is carried out by using the above-mentioned pre-foaming machine.
First, the foamable resin particles, which are the raw material impregnated with the foaming agent, were added to the can with a charging amount calculated by the internal volume of the can body (1) at the upper limit of movement of the level meter (6) and the target expansion ratio. Put into the body (1), while stirring with a stirrer,
Steam as a heating medium is blown from the lower part to heat and expand the expandable resin particles to foam them.

At this time, the level meter (6) is initially located at the lower limit, and as the expandable resin particles foam and the upper surface level rises, the level meter (6) senses the upper surface level and based on the detection signal. The drive means (8) is driven to move upward.

Then, information that the rising speed is fast (or slow) is taken into the controller (10) by the sensing signal from the level meter (6), and the valve (4a) is opened / closed to throttle the blowing amount of the heating medium. Output (or increase) output. Alternatively, it outputs such that the amount of cooling air blown in is increased (or throttled).

When the upper surface level of the expandable resin particles reaches the upper limit of the movement of the level meter (6), the blowing of the heating medium is stopped and the expandable resin particles are taken out from the can body (1) of the pre-expanding foaming machine. ..

(Example) A continuous batch type prefoaming machine (Model SKK-110 manufactured by Sekisui Koki Seisakusho Co., Ltd.) was remodeled, and as shown in FIG. ) From the lower position of 1) from the mounting position of the normal level meter (6)
It was provided to the position up to 00 mm. A photoelectric tube was used as the level meter (6), and a stepping motor and a screw rod were used to move the level meter (6) composed of this photoelectric tube.

When the level meter (6) senses the upper surface level, the level meter (6) rises by 1 cm and the position of the level meter (6) is compared with the initially set position at intervals of 10 seconds. If the difference, that is, the difference in rising speed, is positive, the amount of steam blown into the heating medium is reduced, and if it is negative, the amount of steam blown is preprogrammed in the controller.

The expandable polystyrene was foamed using the above apparatus. Decide the amount of raw material input with a target magnification of 50 times,
I programmed the time to reach the target magnification to be 3 minutes. When the foaming test was performed 5 times in this way,
The actual average foaming time was 2 minutes 54 seconds, and the maximum difference from the set time was 8 seconds.

Next, when the target ratio was set to 60 times and the amount of raw material charged was changed and a foaming test was conducted in the same manner, the average actual foaming time was 3 minutes and 5 seconds, and the maximum difference from the set time was 9 minutes.
It was seconds. In addition, as a result of measuring the variation of foaming in all batches, it was very good.

[0028]

As described above, according to the pre-foaming method of the present invention, the level meter that follows the rise of the upper surface level, that is, the blowing amount of the heating medium is controlled according to the rising speed of the upper surface level. By automatically controlling the foaming rate, it is possible to average the foaming ratio, and it is possible to obtain a foamed molded product with a stable product weight, in which not only the variation between batches but also the variation in foaming in the pre-foaming machine is reduced.

Further, since the blowing amount of the heating medium can be automatically controlled according to the foaming speed, the blowing amount of the heating medium can be adjusted by manual operation every time even if the expandable resin particles having different expandability are used. It is not necessary to always obtain stable pre-expanded particles.

Further, even if the target expansion ratio is changed, it is possible to always obtain stable pre-expanded particles without manually adjusting the blowing amount of the heating medium.

[Brief description of drawings]

FIG. 1 is a front view showing an outline of a pre-foaming machine used for carrying out the present invention.

[Explanation of symbols]

 (1) Can body of pre-foaming machine (2) Foaming resin particle input port (3) Pre-foaming particle discharge port (4) Heating medium supply pipe (4a) Heating medium supply valve (5) Viewing window ( 6) Level meter (7) Screw rod (8) Drive means (10) Controller

Claims (4)

[Claims] 1. A predetermined amount of expandable resin particles is charged into a can of a pre-foaming machine, heated and foamed by a heating medium blown into the can, and the level of the expandable resin particles is sensed by a level meter. A pre-expansion method for expandable resin particles that controls the expansion ratio.A level meter that detects the upper surface level of the expandable resin particles is provided so that it can move up and down, and the upper surface level that rises with foaming is measured by this level meter. A method for pre-expanding expandable resin particles, characterized in that the level meter is made to follow the rise of the upper surface level and the blowing amount of the heating medium is controlled in accordance with the rising speed. 2. The pre-expansion method for expandable resin particles according to claim 1, wherein when the rising speed of the level meter that follows the increase in the upper surface level of the expandable resin particles is fast, the blowing amount of the heating medium is reduced, A pre-foaming method, characterized in that when the rising speed is slow, the blowing amount of the heating medium is increased. 3. The method for pre-expanding expandable resin particles according to claim 1, wherein an optimum state of the foaming rate is stored in a controller in advance, and the heating medium is followed while being followed by a level meter so as to match it. A method for pre-foaming, which comprises controlling the amount of blowing. 4. The pre-expansion method for expandable resin particles according to claim 1, wherein a level meter that follows an increase in the upper surface level of the expandable resin particles detects that the level meter has passed a preset point. The pre-foaming method is characterized in that the blowing amount of the heating medium is adjusted.