JP3814956B2 - Thermoplastic resin foam molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a foam molding method for thermoplastic resins such as styrene resins such as polystyrene, olefin resins such as polyethylene and polypropylene, and more specifically, thermoplastic resin foaming by an in-mold foam molding method using a bead method. The present invention relates to a body molding method.
[0002]
[Prior art]
The thermoplastic resin foam molding method as described above, that is, the in-mold foam molding method by the bead method includes (1) a filling step, (2) a heating step, (3) a cooling step, (4) a mold releasing step, Such a series of steps is continuously performed as one cycle. In the (1) filling step, the foamed resin beads pre-foamed as needed are filled into a molding space of a die composed of a female die and a male die, and in the (2) heating step, the gold The resin beads filled in the mold forming space are heated by a heating medium introduced into the mold to be foamed and fused. Generally, for example, saturated water vapor is used as a heating medium for foaming and fusing resin beads in the (2) heating step. (2) In the heating step, a male mold and a female mold are used. Steam pressure and heating time during heating to meet the quality requirements of the molded product while detecting the pressure of the steam supplied to each mold steam chamber on the moving side and the fixed side constituting the secondary pressure Is set and molding is performed automatically. This (2) heating step is further divided into fine heating steps such as one-side heating, reverse one-side heating, and double-sided heating (main heating), and the heating method in each of these heating steps, that is, steam to the mold The supply amount control method plays an important role in the foaming and fusion of resin beads, and also in the length of molding time in one cycle, and many proposals have been made.
[0003]
For example, Japanese Patent Application Laid-Open No. 62-216734 discloses a method for controlling a steam valve so as to pulsate steam supplied to a mold steam chamber, thereby shortening a molding cycle and achieving uniform melting. It is described that the attachment is performed and the consumption of the heating medium can be reduced. Japanese Patent Application Laid-Open No. 61-171326 discloses a heating method in the heating process, in which first, saturated steam flows from the fixed side to the moving side, and then one reverse heating, in which steam flows from the moving side to the fixed side. High-quality molding by controlling the vapor pressure setting in each heating process, such as double-sided heating that keeps the pressure on the fixed side and moving side constant, to the individual pressure required for each process. That the product can be obtained and the amount of steam used can be saved.
[0004]
However, in the conventional techniques as described above, in any case, the installed steam valve and the control method are not fully utilized, and excessive facilities are used to perform heating necessary for foam molding. Need. That is, in the method described in Japanese Patent Application Laid-Open No. Sho 62-216734, the main purpose is to make the steam spread as evenly as possible to the resin peas in the molding space by pulsating the heated steam. It has not succeeded in supplying steam into the mold in a short time. In the case of one-side heating or reverse one-side heating, the set pressure of the mold steam chamber is considerably lower than the set pressure during double-sided heating, for example, one-side heating; 0.2 kg / cm ² G, For heating: 0.4 kg / cm ² G, double-sided heating: 0.7 kg / cm ² G. For this reason, in the method described in Japanese Patent Application Laid-Open No. 61-171326, for example, in order to set three types of pressures as described above, it is necessary to provide individual pressure control equipments according to the respective heating stages. As a result, the equipment becomes complicated and expensive, and the maintenance of the equipment becomes troublesome. Further, in the one-side heating or the reverse one-side heating, the opening degree of the steam valve is always nearly 100%, and the amount of steam supplied to the mold is large. However, in the case of double-sided heating, when the steam chamber pressure approaches the set value, the steam valve operates to control the mold steam pressure so that it does not exceed the set value, and the opening of the steam valve is set. The amount of steam supplied gradually decreases before reaching the value, and as a result, the time until the pressure in the mold steam chamber reaches the set value becomes longer, and the molding cycle is shortened. The current situation is that the expected effect is not necessarily obtained.
[0005]
[Problems to be solved by the invention]
Therefore, in view of the above-described method for molding a thermoplastic resin foam in the mold, the present invention provides a molding method capable of shortening the molding cycle by improving the temperature rise rate during heating. .
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have found that the appropriate temperature for foaming and fusing the thermoplastic resin particles correlates with the pressure of the steam in the steam chamber because of the property of saturated steam as the heating medium. The rapid increase in the pressure of the steam supplied to the mold at the initial stage of the heating process, particularly the double-sided heating, quickly increases the mold temperature necessary for molding, that is, the temperature of the thermoplastic resin particles. As a result, it was considered that the molding cycle was shortened. As a result of extensive research on this point, steam was supplied with the steam valve fully open at a certain time in the initial stage of the heating process, particularly in the initial stage of double-sided heating, and then met the quality requirements of the molded product. Thus, by controlling to a predetermined constant value, the steam heating time in the thermoplastic resin molding method was greatly shortened, and the molding cycle was shortened.
[0007]
That is, the in-mold foam molding method for a thermoplastic resin foam according to the present invention has two steps for setting the pressure of steam supplied to the mold during heating in the double-sided heating process, and sets the first set value to two steps. By setting steam higher than the set value for the first stage, supplying steam to the mold at the first stage set value at the beginning of heating, then switching to the second set value and supplying steam to the mold, the amount of steam supplied to the mold, a large amount supplied to the initial duplex heated and then is characterized in performing the double-sided heating by controlling the supply amount of vapor pressure with a preset target. Thereby, in the initial stage of double-sided heating, a large amount can be instantaneously supplied to rapidly increase the steam pressure in the steam chamber, and then the steam supply amount can be controlled according to the set value of the steam chamber. Moreover, it is preferable to switch the set value of the vapor pressure supplied to the mold from the first stage to the second stage with a timer. Further, it is preferable that the first-stage vapor pressure is set by a high-pressure air regulator, and the second-stage vapor pressure is set by a low-pressure air regulator.
[0008]
The method for molding a thermoplastic resin foam according to the present invention as described above can be carried out using an existing molding machine. Specifically, in addition to the pressure regulator air regulator that has been used in the past, the pressure regulator air regulator for high pressure is installed in parallel on the steam valve of the molding machine currently in production. In addition, a timer for switching between the conventional air regulator (for low pressure) and the newly added high pressure air regulator may be provided. That is, the molding method of the present invention can be easily carried out with an existing molding machine by newly providing the high-pressure air regulator and the timer one by one on each of the fixed side and moving side molds. . As a result, in the conventional double-sided heating process, the initial first-stage pressure setting value by the high-pressure air regulator and the second-stage pressure setting by the low-pressure air regulator are used. The amount of saturated steam supplied to the mold during heating can be instantaneously increased in large quantities at the initial stage of heating to rapidly increase the steam pressure in the steam chamber, Subsequently, heating can be performed by controlling the set value of the steam chamber, and the steam heating time can be greatly shortened.
[0009]
[Action]
When the pressure in the steam chamber at the time of double-sided heating set in advance to meet the quality requirements of the molded product is, for example, 0.7 kg / cm ² G when the set pressure at the time of molding the styrene resin foam is a conventional method Then, since the pressure of the steam supplied to the mold has been controlled to 0.7 kg / cm ² G by the steam valve from the beginning of the double-sided heating, the opening rate of the steam valve is the rate of increase of the steam pressure in the steam chamber. so as not to exceed 0.7 kg / cm ² G is a set value of the target, gradually decreases from a previous to reach 0.7 kg / cm ² G, the rising speed of the pressure of the steam chamber is suppressed, As a result, it took a long time to reach the set pressure. On the other hand, according to the present invention, the set pressure in the first stage at the initial stage of double-sided heating is set to a pressure higher than the target set pressure of 0.7 kg / cm ² G, for example, 1.0 kg / cm ² G. In the initial stage of double-sided heating, the steam valve set to 1.0 kg / cm ² is in a substantially fully open state, and a large amount of steam is instantaneously supplied into the mold through the steam valve. The vapor pressure rises rapidly to near the original target of 0.7 kg / cm ² G. Next, the set pressure of the steam valve is switched to 0.7 kg / cm ² G, which is the original target value, so that the mold vapor pressure in double-sided heating is 0.7 kg / cm ² according to the quality requirements of the molded product. G is maintained. Thus, according to the molding method of the present invention, the rise time of the mold vapor pressure to the set pressure is shortened as compared with the conventional method, and as a result, the molding time for the entire process of one cycle is shortened.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. However, this is merely an example of the present invention, and the present invention is not limited thereto.
[0011]
FIG. 1 is a schematic view of an in-mold foam molding machine for carrying out the method for molding a thermoplastic resin foam according to the present invention. In the figure, reference numeral 1 denotes a molding die, which is composed of a moving-side core die 10 and a fixed-side cavity die 20, and is formed between both dies 10 and 20. A space 2 is formed, and steam chambers 11 and 21 are provided in each of the core mold 10 and the cavity mold 20 on the back side of the molding space 2. Each of the steam chambers 11 and 21 is connected and connected to the steam source 4 and the steam pipes 12 and 22 via the steam pressure regulating valves 13 and 23 in the middle, and the core-type steam chamber 11 and the cavity-side steam chamber 21 Drain pipes 81 and 82 are connected to each other. Furthermore, the cavity mold 20 is provided with a filling machine 6 for filling resin beads as raw materials into the molding space, an eject pin (not shown), and the like.
[0012]
Pressure regulating means 14 and 24 are provided in the steam pressure regulating valves 13 and 23 respectively provided in the middle of the core side steam piping 12 and the cavity side steam piping 22. The pressure adjusting means 14 and 24 are configured such that secondary side steam is introduced from the core side steam chamber 11 and the cavity side steam chamber 21 through the secondary side pressure pipes 18 and 28, and each pressure adjusting means 14 and 24 are connected to the valve opening air source 5. Conventionally, each of the pressure adjusting means 14 and 24 is provided with one pressure adjusting air regulator as a pressure adjusting air source, and gold introduced from the secondary side pressure pipes 18 and 28 is provided. The opening of the steam pressure regulating valves 13 and 23 is adjusted by the steam pressure in the mold steam chambers 11 and 21 and the air pressure preset in the air regulator and the air pressure supplied from the valve opening air source 5. The amount of water vapor supplied into the steam chambers 11 and 21 was adjusted. On the other hand, in the present invention, as shown in the figure, the three-way switching valves 15 and 25 are connected to the pressure regulating means 14 and 24, and the first-stage steam is connected to each of the three-way switching valves 15 and 25. The high-pressure air regulators 16 and 26 for setting the pressure and the low-pressure air regulators 17 and 27 for setting the second-stage vapor pressure are provided in parallel, and the high-pressure air regulator 16 on the core side and the low-pressure air regulator 16 The air regulator 17 and the cavity-side high-pressure air regulator 26 and the low-pressure air regulator 27 are provided so as to be switched by timers T ₁ and T ₂ , respectively.
[0013]
The molding method of the plastic resin foam of the present invention by the above-described foam molding machine will be briefly described. First, in (1) the filling step, the molding space 2 formed by the core mold 10 and the cavity mold 20 is entered. The resin beads are filled from the filling machine 6. Next, (2) in the heating step, the cavity side drain pipe 82 is closed, while the core side drain pipe 81 is opened, steam is supplied from the cavity side steam pipe 22 to the cavity side steam chamber 21 to perform one heating. Do. Next, the core side drain pipe 81 is closed, while the cavity side drain pipe 82 is opened, steam is supplied from the core side steam pipe 12 to the core side steam chamber 11 to perform reverse one-side heating. Thereafter, with both the core side drain pipe 81 and the cavity side drain pipe 82 closed, both the core side steam chamber 11 and the cavity side steam chamber 21 are connected from both the core side steam pipe 12 and the cavity side steam pipe 22, respectively. Steam is simultaneously supplied to the both sides to perform double-sided heating. At the initial stage of this double-sided heating, the steam pressure regulating valves 13 and 23 provided in the middle of the steam pipes 12 and 22 are respectively pressure regulating means 14 and 24. Are controlled by high-pressure air regulators 16, 26 set higher than the mold-set vapor pressure of air regulators 16, 17, and 26, 27 connected in parallel to the three-way switching valves 15, 25, respectively, By supplying steam from the steam source 4 to the respective steam chambers 11 and 21 with the steam pressure regulating valves 13 and 23 being substantially fully open, a large amount of steam is instantaneously supplied at the initial stage of heating. , The vapor pressure in 21 rises rapidly. Next, when a predetermined time set by the timers T ₁ and T ₂ elapses, the pressure is switched to the low pressure air regulators 17 and 27 set to the mold vapor pressure, and the inside of each of the steam chambers 11 and 21 is the quality of the molded product. Steam is subsequently supplied from the steam source 4 until a steam pressure preset to meet the requirements is reached. Thereafter, heat retention is performed for a predetermined time while the mold vapor pressure is at the set value. Next, (3) in the cooling step, the cooling water is sprayed from the cooling water inlet pipes 71 and 72 provided in the steam chambers 11 and 21 of the core mold 10 and the cavity mold 20 to the back side of the molding space 2. Then, the mold and the molded product in the molding space 2 are cooled with water. After this water cooling, there is a case where a so-called vacuum forming method is performed in which the inside of the steam chambers 11 and 21 is decompressed through the drain pipes 81 and 82 and the cooling water is effectively cooled using the latent heat of vaporization of the cooling water. Then, in the (4) mold release step after cooling, the core mold 10 that is the moving mold is retracted and the molded product is taken out from the molding space 2 by the action of an eject pin (not shown).
[0014]
The method for molding a thermoplastic resin foam according to the present invention is performed as described above. When molding a polystyrene foam using the molding machine shown in FIG. 1, when the set pressure for double-sided heating requires 0.7 kg / cm ² G, double-sided heating by high-pressure air regulators 16 and 26 The initial set pressure is 1.0 kg / cm ² G, and after 2 seconds from the start of double-sided heating with timers T ₁ and T ₂ , the original set pressure for double-sided heating set with low-pressure air regulators 17 and 27 When the molding was switched to a certain 0.7 kg / cm ² G, the double-sided heating time was 8 seconds compared to the case of the conventional method in which 0.7 kg / cm ² G was set from the initial stage of double-sided heating. To 5 seconds.
[0015]
Furthermore, in the conventional method, the total time for one-side heating and one-side heating is generally set to 20 seconds. However, in the above embodiment of the present invention, the initial steam chamber set pressure during double-sided heating is increased, and both sides are heated. Since the rate of pressure increase at the initial stage of heating became faster, it was found that a predetermined molded product quality could be obtained even if the total time of one-side heating and reverse one-side heating was reduced to 10 seconds. As a result, the total heating time in the heating step can be shortened from 28 seconds to 15 seconds, and an industrially remarkable high cycle of molding can be achieved.
[0016]
In addition, although this invention is as above-mentioned, the means like following (1) and (2) can also be considered for the large amount blowing of the vapor | steam in the initial stage of double-sided heating. However, both of these have difficulties. On the other hand, the method described above is the best method without such difficulties.
(1) Although it is conceivable to use a large capacity steam valve and supply a large amount of saturated steam from the initial stage of double-sided heating, it is difficult to finely control the steam pressure according to the set pressure, which is good Adjustment tends to be difficult.
(2) Instead of using the high-pressure air regulator and the low-pressure air regulator as described above, increase the number of steam valves and open all the steam valves in the first stage to supply a large amount of steam instantaneously. In the second stage, the same effect as in the case of the air regulator can be obtained by controlling the set pressure by closing some of the steam valves. However, in this case, the control becomes complicated and the cost tends to increase.
On the other hand, in the above embodiment, the existing molding machine is provided with only two types of air regulators, a high pressure air regulator for pressure adjustment and a low pressure air regulator, and a timer for switching between them. Good molding cycle shortening effect can be obtained. This is a great advantage for companies that use the same molding machine to produce thermoplastic resin foam.
[0017]
【The invention's effect】
As described above, according to the method for molding a thermoplastic resin foam according to the present invention, the heating time can be significantly shortened, and as a result, the molding cycle can be shortened to significantly improve the production efficiency. Moreover, this method can be easily implemented using an existing molding machine, and is very useful industrially.
[Brief description of the drawings]
FIG. 1 is a schematic view of a molding machine used in a method for molding a thermoplastic resin foam according to the present invention.
[Explanation of symbols]
1: Mold for molding, 2: Molding space,
4: Steam source, 5: Air source for valve opening,
10: Core mold, 11: Core side steam chamber,
12: Core side steam piping, 13: Core side steam pressure regulating valve,
14: Core side pressure adjusting means, 15: Three-way switching valve,
16: Air regulator for high pressure, 17: Air regulator for low pressure,
18: Core side secondary pressure piping,
20: Cavity mold, 21: Cavity side steam chamber,
22: Cavity side steam piping, 23: Cavity side steam pressure regulating valve,
24: Cavity side pressure adjusting means, 25: Three-way selector valve,
26: Air regulator for high pressure, 27: Air regulator for low pressure,
28: Secondary pressure piping on the cavity side,
71, 72: Cooling water inlet pipe, 81, 82: Drain pipe.

Claims (3)

In the in-mold foam molding method for a thermoplastic resin foam, the pressure setting of the steam supplied to the mold during heating in the double-sided heating process is set to two stages, and the first stage setting value is set to be higher than the second stage setting value. Supply steam to the mold at the initial stage of heating by supplying steam to the mold at the first set value, then switching to the second set value and supplying steam to the mold amounts, a large amount supplied to the initial duplex heated and then preset molding method of a thermoplastic resin foam which is characterized in that the two-sided heating by controlling the supply amount of the vapor pressure of the target. 2. The molding method according to claim 1 , wherein the set value of the vapor pressure supplied to the mold is switched from the first stage to the second stage with a timer. 3. The molding method according to claim 2 , wherein the first stage vapor pressure is set by a high pressure air regulator, and the second stage vapor pressure is set by a low pressure air regulator.

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