JPH03173631A - Expansion molding method for thermoplastic synthetic resin - Google Patents

Abstract

PURPOSE:To stably obtain a molded body of high quality at a high cycle in low steam consumption by detecting foaming pressure at the time of final heating by a digital surface pressure gauge to stop the supply of steam on the basis of the detected pressure at a required point within a set range. CONSTITUTION:After a mold is filled with raw material beads, heated steam is supplied to a jacket part from a medium (steam) supply pipe 4 and introduced into the mold from a steam introducing opening to heat the molding space of the mold to about 105-120 deg.C and the raw material beads are plasticized and further foamed to be mutually welded by internal pressure and formed into a integrated product. At this time, foaming pressure (mold pressure) is detected by a digital surface pressure gauge 2 and, when the detected pressure reaches the predetermined set value determined within a range of a set value of 0.60-1.00kg/cm<2>, the supply of steam is stopped and heating is controlled to obtain stable foaming pressure. When the raw material beads are foamed under heating and the integral welding thereof advances, the mold is preliminarily cooled according to a usual technique and a product is cooled by the supply of a cooling medium such as cooling water and, after the mold is reduced in pressure to remove drain, the product is demolded to be taken out.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves filling a mold with pre-foamed thermoplastic synthetic resin particles, such as expanded polystyrene resin particles, and heating the mold by supplying steam. The present invention relates to a molding method for obtaining a foamed synthetic resin molded product having a controlled skin thickness and a constant desired quality.

(Prior art) Foamed molded products made from foamable thermoplastic synthetic resins such as foamed polystyrene, foamed polyethylene, and rigid foamed polyurethane are known for their excellent heat retention, cushioning effect, chemical stability, toughness, and low apparent specific gravity. Due to these characteristics, it is widely used as a packaging material for various foodstuffs, machinery and equipment, etc.

Conventionally, such molded bodies are usually made by placing pre-foamed resin particles (hereinafter referred to as , raw material beads) are filled, steam is supplied into the mold to heat the mold, and the raw material beads are further foamed and plasticized to fuse and stop each other, and then cooled to harden and stabilize the resin. It is manufactured by a method in which the molded body is taken out from the open mold, and is disclosed in Japanese Patent Publication No. 61-45490, Japanese Patent Application Laid-Open No. 60-116432, and Japanese Patent Application Laid-Open No. 62-1989.
Some molding examples are disclosed in Japanese Patent No. 267129 and the like.

Among them, the method described in Japanese Patent Publication No. 61-45490 involves filling pre-foamed raw material beads into a pair of molds, and degassing them through small ventilation holes in the molds via a conduit connected to a decompression device. The air inside the mold is removed by an operation of replacing the air with steam supplied from a steam supply pipe, and then steam is supplied into the mold from the steam supply pipe to foam and fuse the raw material beads in the mold. This method improves the degree of fusion between the beads of a foamed synthetic resin molded product, improves the quality of the molded product, and is effective in shortening the molding cycle. .

However, despite the effectiveness of the above method,
It was found that the following problems remained. In other words, heating efficiency is improved by removing air from the mold (even if it were, fusion progresses from the surface to the inside, so the faster the surface fusion speed is, the less steam flows into the interior). As a result, it is not possible to maintain the same fusion rate between the inside and the surface layer, leading to an imbalance in the fusion rate between the surface layer and the center of the molded product, making it difficult to produce a product with a stable and constant quality. This means that it is difficult to obtain.

Therefore, the inventors of the present invention have made repeated studies to improve the problem.
As a result, in particular, prior to heating and fusing the raw material beads by supplying steam, the beads are preheated by introducing steam at a temperature at which the fusing of the raw material beads does not proceed into the mold, and then air is removed by a vacuum suction operation. We have previously proposed a method in which the water is drained, and then steam is supplied from a large-diameter supply pipe to slow down the progress of surface fusion to heat fusion at once, followed by cooling.

By the way, while the development of each of the above methods is progressing,
A surface pressure gauge is used as a guide to determine the heating time and degree of fusion, and an analog surface pressure gauge is generally used to control the pressure.For pressure control, the chamber pressure is detected and the heating process is canted midway through. In addition to this method, there is also a method of controlling preheating steps such as one-sided heating using the surface pressure gauge to save energy, but these methods have not yet been put to practical use.

(Problems to be Solved by the Invention) However, in the conventional foam molding method, the temperature of the mold before molding always varies due to changes in temperature and seasons, so a constant heating efficiency cannot be obtained. There is a problem that the degree of fusion always varies in the surface skin layer, and it also varies depending on the type of raw materials, foaming conditions, and maturity of pre-foamed beads, making it impossible to obtain products with a constant quality cycle. In order to obtain molded products with consistent quality, it was found that some form of heating control is extremely important in foam molding.

The present invention focuses on the above-mentioned fact, and in response to this, uses a digital surface pressure meter that can detect the foaming pressure with high precision, detects the foaming pressure, and controls the heating to produce high-quality molded products in a high cycle. The purpose is to stably obtain steam with low steam consumption.

(Means for Solving the Problems) That is, the feature of the present invention that meets the above object is that basically, pre-foamed thermoplastic raw material beads are filled into a mold, preheated, and then molded. In this method, a foamed synthetic resin molded article is obtained by supplying steam to perform main heating, heating and fusing the raw material beads, and then cooling and releasing the mold. The purpose is to control the heating by detecting the pressure using a surface pressure gauge and stopping the steam supply at a required point within the set pressure range based on the detected pressure.

Further, in the above molding method, the present invention performs preheating by introducing steam at a temperature at which the fusion of the raw material beads does not proceed into the mold after filling the raw material beads, and then stops the heating when the mold temperature is 100 to 105 °C, and then Bead resin temperature 100-105
℃, and during main heating, the foaming pressure (mold pressure) was detected by a digital blood pressure monitor and the pressure was 0.60 to 1.00.
It is characterized in that when the required set pressure is within the range of kg/cJ, the supply of steam is stopped and heating is controlled.

In steam foam molding, the present invention detects the mold temperature during the process from the mold release process after molding to the filling blowback, that is, the mold temperature at the time of mold release, and uses a computer to determine the preheating time depending on the temperature level. Another feature is that the temperature of the mold before main heating is kept constant by adjustment.

(Function) When performing foam molding using the above foam molding method of the present invention,
After preheating the raw material beads, steam drainage is extracted by reducing the pressure using a vacuum suction operation as necessary, and gases such as butane are vented, increasing the efficiency of subsequent main heating and heating and melting with a relatively small amount of steam. During this main heating, the foaming pressure is detected as the mold pressure using a digital surface pressure gauge, and when this reaches the required set value, the steam supply is stopped and heating control is performed to stabilize the temperature. Obtain foaming pressure to improve molding cycle and quality stability.

Furthermore, by controlling the resin temperature during preheating and one-sided heating to 100 to 105°C, the heating efficiency during main heating is improved together with the vacuum effect in the next step.

Furthermore, as described in claim 3, the temperature of the mold at the time of mold release is detected and the temperature of the mold before heating is kept constant by adjusting the preheating time, thereby improving the stability of the molding cycle and the stability of quality. Further increase.

Hereinafter, specific embodiments of the present invention will be described.

(Example) The figure schematically shows an apparatus for implementing the method of the present invention, in which (1) is a mold, (2) is a pressure gauge consisting of a high-precision digital surface pressure gauge, (3) is a thermometer, and (4) is a pressure gauge consisting of a high-precision digital surface pressure gauge. ) is a steam supply pipe, and the steam supply pipe (4) is provided with an on-off valve (5), and the pressure and temperature detected by the digital surface pressure gauge (2) and thermometer (3) are input. The valves are sequentially opened and closed by a sequencer (6) which controls the opening and closing of the valves.

The sequence in foam molding in this case and the sequencer and human power elements in each step are as follows.

■ Filling T (temperature) ■ Blow bank (returning the remaining raw material beads in the feeder) T ■ Preheating T ■ One-sided heating T or P (pressure) ■ Vacuum suction T ■ Main heating (1) T ■ Main heating (2) T or P ■ Pre-cooling ■ Water cooling [phase] Vacuum suction ■ Cooling @ Thus, during mold release, firstly, raw material beads, such as expandable polystyrene beads, which have been pre-foamed into the molding space (7) by the supply means, are , or polyethylene beads,
Expandable polyolefin beads such as polypropylene beads are supplied and filled, and the excess is blown back.

In particular, polysretin beads are preferably used in the present invention. The pre-expansion ratio of these raw material beads is usually 30 to 9.
A magnification of approximately 0 times, most practically a magnification of approximately 60 times, is used.

After filling the raw material beads, heated steam is supplied to the outer mantle from the medium (steam) supply pipe, and the steam is introduced into the mold from the steam introduction opening to heat the inside of the molding space to about 105 to 120°C. While the raw material beads are plasticized, they are further foamed and fused together by internal pressure to form an integral product. In the present invention, prior to supplying the main heating steam, the raw material beads are melted in advance. The beads are preheated by briefly introducing steam at a temperature at which deposition does not proceed, that is, below 105°C, preferably from 100 to 105°C. In this case, steam is introduced into one mold to heat the mold, and then the steam is introduced into the mold.

If the steam temperature exceeds 105° C., surface fusion may proceed, so it is important that the steam temperature is lower than that.

Thus, when the above-mentioned preheating progresses and the mold temperature reaches the corresponding required temperature of 100 to 105°C, the steam supply is stopped, while heating is stopped, and the mold is heated using a vacuum pump, large capacity vacuum pump, vacuum tank, etc. Inside, remove air and water to remove gas such as butane and condensed water. At this time, avoid lowering the temperature of the raw material beads as much as possible.

In this way, the raw material beads that have been preheated, deaerated, and dehydrated are then subjected to main heating at 112°C depending on the amount of raw material beads.
℃~115℃, respectively, to form heat fusion and surface skin by supplying steam at the corresponding temperature. Initially, steam is introduced only from the side to control surface skin fusion, and the skin layer is thinned.
B. - Finally, the fusion is completed.

At this time, the foaming pressure (mold pressure) is detected with a digital surface pressure gauge, and the set value is 0.60 to 1.00 kg/cffl.
When a predetermined set value determined within the range is reached, the steam supply is stopped and heating control is performed to obtain stable foaming pressure.

1- After heating and foaming and fusion-stopping progresses, the product is cooled by pre-cooling and supplying a refrigerant such as cooling water according to the usual method, and then the inside of the mold is depressurized and the C drain is removed. The product is removed from the mold and taken out. At this time, the mold temperature at the time of mold release is detected and the preheating time is adjusted via a calculator to keep the mold temperature constant during the next heating and foaming process.

Test examples conducted to confirm the effects of the method of the present invention are listed below.

Test Example 1 Using an aluminum mold, expanded polystyrene resin particles containing butane gas (trade name Kaneka I?L, expansion ratio 554'f) were used.
) are the raw material beads, and the following molding control sequence is performed: ], Filling 30 seconds 2, Blow hack 3 3, Preheating 2 4, One side heating 6 5, Vacuum 20 2 6, Main heating (1) 6 7, Gravity ■ Heat (2) 11 8, Pre-cooling 2 9, Water cooling 3 10, Vacuum cooling 1 11, Normal cooling 60 12 Following the sequential process consisting of mold release, the resin temperature during heating was set to 10
Controlled at 0 to 105°C, the block size was 1000 x 2000 x 5 based on the conditions shown in Table 1 below.
A foamed molded article of 00-1 was produced.

On the other hand, for comparison, foam molded products of the same size were similarly produced without controlling the resin temperature, with heating temperatures of 85° C. (low temperature) and 112° C. (high temperature), respectively.

The quality of each obtained molded body is also shown in Table 1.

Table 1 below shows that by controlling the resin temperature, the heating efficiency of the inventive example is improved compared to Comparison 1. Also, compared to Comparison 2, air circulation to the center is better, and the surface It can be seen that there are fewer defects in the quality of the core and the center, and that the skin layer is in good condition.

3 4 Test Example 2 Using an aluminum mold, using expanded polystyrene resin particles (trade name Kaneka FM, expansion ratio 58 times) as raw material beads, the block size was adjusted according to the molding control sequence of Test Example 1 under the conditions shown in Table 2 below. 1゜00×2000×
Five consecutive shots of 500 n+ foam molded articles were produced.

At this time, the foaming pressure was detected using a high-precision digital surface pressure gauge in the second main heating step, and the foaming pressure set value was reached (0.72kg/
cnT), main heating 2 was cut midway.

On the other hand, as a comparative example, heating and foaming was carried out under normal timer control without detecting the foaming pressure.

(Comparison 3) The results of comparing the quality of both obtained molded bodies are also shown in Table 2 below.

From Table 2 above, it is understood that the molding cycle and quality stability of the products according to the present invention are increased by 5% due to heating control based on foaming pressure detection.

Test Example 3 Using an aluminum mold, using expanded polystyrene resin particles (product name SKO, expansion ratio 80 times) as raw material beads, block size 9 was formed based on the same molding control sequence as above.
00 x 1800 x 400 The dragon foam molded product was molded in five continuous shots under the molding conditions shown in Table 3 below.

For comparison, foam molded products were molded under the same conditions except that the preheating time was not adjusted depending on the mold temperature during mold release.

In the table, in both Invention Example 3 and Control Example, the mold temperature before molding was controlled constant, but in the Control Example, steam supply was stopped by a timer, while in Invention Example 3, steam supply was controlled by surface pressure. This is the case if you stop. In addition, Comparison 4 and Comparison 5 are those in which the preheating time is constant without using mold temperature control.
The timer cut was used for comparison 5, and the surface pressure cut was used for comparison 5.

Table 3 also shows the results of comparing the quality of the foam molded products obtained by each of the above methods.

7 - As can be seen from Table 3 above, the stability of the molding cycle and product quality is increased by detecting the mold temperature during mold release and adjusting the preliminary time. Furthermore, it has been confirmed that the molding cycle time becomes even more stable when used in combination with the basic technology of the present invention, which detects foaming pressure using a high-precision digital surface pressure gauge and controls heating.

(Effects of the Invention) As described below, in the foam molding of thermoplastic synthetic resin, the foaming pressure is detected by a high-precision digital surface pressure gauge during main heating, and based on this, the required pressure within a predetermined pressure range is It is basically based on stopping the steam and controlling the heating in terms of 0.60. When the required set value of the set pressure control range of ~1.00 kg/cJ is reached, the steam is stopped to maintain the foaming pressure in a stable state and control the molded body skin thickness, which has the most influence on the quality cycle. This makes the molding cycle significantly more stable than in the past, and is expected to have the remarkable effect of improving the stability of product quality.

In addition to the above-mentioned effects, the invention as set forth in claim 2 has the effect of increasing the vacuum effect in the next step and further improving the main heating efficiency by controlling the resin temperature during heating to 100 to 105'C.

Furthermore, in addition to the above-mentioned effects, the invention as claimed in claim 3 makes it possible to control the skin thickness with high accuracy because the mold temperature before heating is kept constant, and in combination with control by foaming pressure.
This has the effect of making the fusion rate of the surface portion and the center portion uniform and close to each other, thereby further improving the stability of the quality of molding cycle 2.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing an overview of the implementation status of the method of the present invention. (1)...mold, (2)...Digital pressure gauge, (3)...Thermometer, (4)...Steam supply pipe, (5)...Opening/closing valve, (6)...Sequencer (7)...Molding space.

Claims (1)

[Claims] 1. Pre-foamed thermoplastic raw material beads are filled into a mold, preheated, and then main heating is performed by supplying steam into the mold to fuse the raw material beads. In the method of obtaining a foamed synthetic resin molded body by cooling and releasing the mold, the foaming pressure during the main heating is detected by a digital surface pressure gauge, and the steam supply is stopped at a required point in the set pressure range based on the detected pressure. , a foam molding method for thermoplastic synthetic resin characterized by controlling heating. 2. In the molding method according to claim 1, the temperature of the raw material beads during preheating is controlled at 100 to 105°C, and during main heating, in the range of 0.60 to 1.00 kg/cm^2,
A foam molding method for thermoplastic synthetic resin characterized by stopping steam introduction and controlling heating when the foaming pressure setting value of a digital surface pressure gauge is reached. 3. The molding method according to claim 2, further characterized in that the temperature of the mold before main heating is kept constant by detecting the mold temperature at the time of mold release and adjusting the preheating time via a calculator. Foam molding method for thermoplastic synthetic resin.