JP2004276284A - Method for molding resin molded object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method capable of obtaining a resin molded object having definite high quality. <P>SOLUTION: The method for molding the resin molded object has a first process for preheating a mold 10 to a temperature at least higher than the melting point of a resin R, a second process for filling the mold 10 with the resin R and a third process for moviding the water level of cooling water W for cooling at least the periphery of the mold toward the gate side of the mold 10 from the vent side thereof. By this molding method, the resin molded object having definite high quality can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a molding method for injecting a molten resin into a mold to form a resin molded body having a predetermined shape, and particularly to a resin molded body having no sink marks and uneven surface (flow mark). It relates to a molding method for obtaining.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in molding a resin, a mold is generally controlled to be cooled to an appropriate temperature with cooling water or cooling air during molding in order to obtain a desired resin molded body.
[0003]
Specifically, when controlling the mold cooling rate during resin molding, as shown in FIG. 3, an appropriate cooling circuit 51 is formed in the mold 50, and cooling water or cooling air is provided in the cooling circuit 51. The cooling rate was controlled through (cooling water W in FIG. 3). In the case of this method, a temperature difference occurs between the cooling water and the cooling air (cooling water W in FIG. 3) between the inlet side 51a (area A in the figure) and the outlet side 51b (area B in the figure) of the cooling circuit 51. Would. This is because cooling water and cooling air take heat from the mold 50 while passing through the cooling circuit 51. This temperature difference makes it impossible to cool the resin (shown by R in the drawing) in the mold at a uniform cooling rate as a whole. That is, there is a partial difference in the cooling rate of the resin. This temperature difference is largest at the inlet side 51a and the outlet side 51b of the cooling circuit 51, which has led to the occurrence of problems such as deformation and discoloration of the resin molded body.
[0004]
As a means for improving such a problem, a cooling method has been considered in which the entire mold is placed in a tank and a cooling liquid is supplied to the tank (for example, see Patent Document 1).
[0005]
With this method, it is possible to uniformly cool the outer peripheral surface of the mold with the liquid.
[0006]
[Patent Document 1]
JP-A-7-214563 (page 2-3, FIG. 1)
[Problems to be solved by the invention]
FIG. 4 shows a mold cooling method described in Patent Document 1. The mold cooling device 6 that implements this method fixes a vertically split mold 60 in a state that the mold 60 is slightly floated in a liquid tank 70 via a column 71, and the water supply connected below the liquid tank 70. Cooling water (illustrated by W in the figure) is supplied from a pipe 75 and discharged from a drain pipe 76 above the liquid tank. Further, a pouring pipe 72 for supplying a molten resin (shown by R in the drawing) to the cavity 61 of the mold 60 penetrates the bottom of the liquid tank 70 and is connected to the lower part of the mold. After the resin to be supplied to the mold 60 reaches a specified amount and the filling of the resin is completed, cooling water is supplied from the water supply pipe 75, and the liquid tank 70 is filled with the cooling water to cool the mold 60. . With this method, the cooling rate in the horizontal plane becomes uniform, and uneven cooling in this plane can be eliminated.
[0007]
In the resin molding apparatus provided with such a cooling device 6, when the resin reaches a specified amount, the pressure sensor operates to stop the resin. For this reason, the resin in the mold is solidified after the supply of the resin is stopped, which causes volume shrinkage, which may cause sink marks in the molded body. Further, in the invention described in Patent Document 1, even if the pressurization of the molten resin in the cavity 61 is continued through the pouring pipe 72 in order to compensate for the sinkage during cooling, the molded product is indented. The problem of the occurrence cannot be sufficiently solved. This is because the water supply pipe 75 is set on the gate side, and the lowest temperature cooling water supplied from the water supply pipe 75 mainly reaches the gate 63 side of the mold 60. This is because they are cooled and solidified.
[0008]
When the resin located at the gate 63 is first solidified and the gate 63 is clogged, the pressure of the molten resin is no longer transmitted to the inside of the cavity 61 from that point, so that the resin cannot be supplied to the cavity 61, and Sinking may occur. Therefore, in the molding apparatus including the cooling device 6, sink may occur after molding not only in the portion corresponding to the gate 63 of the mold 60 but also in the entire resin molded body, and a certain quality level is provided. A resin molding cannot be obtained stably.
[0009]
An object of the present invention is to provide a method for molding a resin molded body that can obtain a resin molded body having a certain high quality.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a method for molding a resin molded body according to the present invention includes a first step of preheating a mold at least higher than a melting point of the resin, and a second step of filling the mold with the resin. And a third step of moving the level of the cooling water for cooling at least the periphery of the mold from the vent side to the gate side of the mold while maintaining the pressure inside the mold. .
[0011]
In the cooling process of the mold, the gate side of the mold is finally cooled with the cooling water while keeping the pressure inside the mold, so that the gate side of the mold is cooled before the other parts of the mold. There is nothing. Therefore, there is no possibility that the gate side of the mold is first solidified and the resin is not sufficiently injected into the mold, and the pressure is not applied to cause the sink of the molded body. This makes it possible to obtain a resin molded body having a uniform quality without sink marks and unevenness on the surface.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for molding a resin molded body according to the first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the method for molding a resin molded body according to the first embodiment of the present invention includes a tank 1 made of, for example, stainless steel capable of supplying cooling water from near the bottom surface, This is performed using a mold 10 in which a mold 11 and a lower mold 12 are combined. The cooling circuit is not provided in the mold 10 itself as in the latter conventional example described above, and the mold 10 is cooled uniformly over the entire circumference of the cooling water level as the water level rises. The mold 10 is arranged at a substantially central portion of the tank 1.
[0013]
Subsequently, a method for molding a resin molded body according to the present embodiment will be described in the order of steps.
[0014]
First, the mold 10 is preheated (preheated). This preheating is performed to ensure the fluidity of the thermoplastic resin (shown by R in the figure), and generally, the mold 10 is heated to a temperature higher than the melting point of the resin to be used. In practice, it is preferable to heat to the same temperature as the temperature of the resin to be filled. Preheating the mold in this way increases the time it takes to reach the temperature at which the resin solidifies, does not reduce the fluidity of the resin in the mold, and also controls the cooling rate. It can be easier.
[0015]
Subsequently, the resin is filled into the mold 10 by applying pressure to the resin. The mold 10 includes an upper mold 11 and a lower mold 12, and by appropriately adjusting the surface roughness of the contact surface of the mold (see X in the figure), the resin is removed from the contact surface during the resin filling process. Only the air in the cavity is exhausted without flowing out. The contact surface X forms a vent (exhaust portion) of the mold 10.
[0016]
The pressurized supply of the resin into the mold is continued until the cooling with the cooling water is completed. This is to avoid sink marks after molding. As described above, the cooling water of the mold 10 is started by gradually supplying the cooling water from the water supply pipe 16 into the tank 1 while keeping the pressure inside the mold. At this time, the cooling of the resin near the level of the cooling water in the tank progresses, solidifies, and the volume shrinks. However, the resin filled in the upper portion remains unsolidified because the cooling water has not reached the vicinity of the mold at the periphery thereof. The unsolidified resin moves to a region where the resin is insufficient due to the pressure applied for filling, and the volume reduced by solidification by cooling can be compensated uniformly.
[0017]
When the water level of the cooling water is gradually increased (moved) from the vent side toward the gate 13, the resin in the mold gradually solidifies from below to above. However, the gate 13 which has not yet been affected by the cooling by the cooling water is filled with the resin as appropriate, and a molded body without sink marks due to volume reduction due to solidification is completed.
[0018]
In this embodiment, the cooling water convection in the tank causes the temperature distribution to become low on the vent side (bottom of the tank) and high on the gate side (upper of the tank), so that the gate side hardly solidifies. And aid in the proper cooling of the resin as described above.
[0019]
Next, a method for molding a resin molded body according to a second embodiment of the present invention will be described with reference to the drawings. The method for molding the resin molded article according to the present embodiment is in principle the same as the method for molding the resin molded article according to the above-described first embodiment, except for the configuration of the mold and the cooling water in the mold. Is different from that of the first embodiment.
[0020]
The method for molding a resin molded body according to the second embodiment of the present invention is performed in a state where a mold 20 having a special shape is arranged in the tank 2 as shown in FIG. The mold 20 is a mold for forming a so-called lining that covers a liquid contact surface of a metal pipe through which a fluid flows. The mold is filled with polypropylene (PP) as a resin, and a flange is formed around the entire periphery around both ends. This is a mold for forming a cylindrical lining having a projection.
[0021]
The tank 2 used in the present embodiment is a bottomed cylindrical body made of a metal such as stainless steel as in the case of the first embodiment. A cooling water discharge pipe 3 penetrates the bottom center of the tank 2 from below the tank, and a cooling water supply pipe 4 is provided near the inner wall of the tank 2. Further, the cooling water discharge pipe 3 is provided with an opening / closing valve 3a below the bottom of the tank 2 so that all the cooling water (shown by W in the figure) can be drained after the cooling process is completed.
[0022]
The mold 20 is mounted on the flange plate 22 with a thin annular base plate 21, a thick annular flange plate 22 mounted on the base plate 21, and a space for forming a flange portion of the flange plate 22 and the lining. The tube body M used as a mold and a spacer 23 fitted on the peripheral surface of the tube body M and serving as a heat mass for stabilizing a cooling rate accompanying a rise in the water level of the cooling water. Have. The mold 20 is further placed on top of these molds and has a core 25 having a substantially conical head and a gate 31 mounted on the core 25 and cooperating with the core 25. An upper die 26 to be constituted, a spool bush 27 attached to the upper part of the upper die 26, a nozzle 28 connected to the spool bush 27, having a dish shape and having a resin outflow hole formed in the center, and a nozzle 28 And a cylindrical container 29 which is disposed around the container and stores the resin, and a cylinder head 30 attached to an upper portion of the container 29.
[0023]
As described above, the gate 31 of the mold 20 is formed at the portion sandwiched between the core 25 and the upper mold 26, and the vent 32 of the mold 20 is formed at the portion sandwiched between the flange plate 22 and the tube body M. Is formed.
[0024]
That is, the resin does not leak from the contact surface (vent 32) between the flange plate 22 and the tube body M, but only the air inside the mold is released according to the pressure applied during molding. The air is exhausted from the contact surface to the outside of the mold.
[0025]
Then, using a hydraulic actuator (not shown), the molten resin is filled into the space defined by the cylinder head 30, the container 29, and the nozzle 28 via the injection pipe. Subsequently, by pressing the cylinder head 30 at a constant pressure with a hydraulic cylinder (not shown), the resin accumulated at the upper part of the mold is injected into the mold at a predetermined pressure into the resin hatched space (continuous hatching of a thick line and a thin line) in the mold. It is supposed to be.
[0026]
On the other hand, the cooling water can be drained from the cooling water discharge pipe 3 by opening the on-off valve 3 a provided on the cooling water discharge pipe 3. An appropriate number of slits 21a are formed on the bottom surface of the base plate 21 to efficiently guide the cooling water supplied to the outside of the mold into the inside of the mold. Therefore, the cooling water accumulated outside the mold travels along the slit 21 a of the mold 20 and also accumulates inside the mold 20. Therefore, by opening the open / close valve 4a, the cooling water is supplied from the water supply pipe 4 to the bottom of the tank, and the water level in the tank gradually rises as a whole.
[0027]
The upper end of the drain pipe 3 is located higher than the upper end surface of the lining, and plays a role of forming a lining without sink marks and unevenness (flow mark) on the whole liquid contact surface as described later.
[0028]
Hereinafter, the method for molding a resin molded body according to the present embodiment will be described in the order of each step. In the molding method according to the present embodiment, polypropylene (hereinafter, referred to as “PP”) is used as the resin.
[0029]
First, the entire mold is preheated. This preheating is performed to ensure the fluidity of PP as a resin in the mold, and the entire mold is not shown until 220 ° C., which is higher than the melting point of PP used (about 160 ° C.). Heat in heating tank. The reason for heating to such a temperature is to avoid a decrease in the temperature of the resin in contact with the mold in the present embodiment, thereby reducing the fluidity of the resin.
[0030]
Subsequently, the preheated mold 20 is transferred to a resin molding station by a transfer device (not shown). Note that a tank 2 used for cooling the mold is installed in the transfer station in advance, and the above-described mold 20 is arranged at the bottom of the tank 2. In this operation, the mold 20 is positioned and arranged so that the cooling water discharge pipe 3 protruding into the tank from the bottom of the tank 2 is inserted into the mold 20 as shown in FIG. .
[0031]
Subsequently, the mold 20 is filled with a resin. The supply of the resin into the mold is continued until the cooling of the resin described later is completed. Specifically, after the resin is sufficiently filled in the mold, the pressure in the mold is maintained during the cooling step. This is to avoid the occurrence of sink marks in the resin by compensating for the resin shortage in the mold during cooling, as in the case of the first embodiment. In order to form a lining having an inner diameter of 5 cm and a thickness of 0.4 cm, it takes about 3 minutes, for example, to completely fill the mold with the resin.
[0032]
After the entire mold is filled with the resin, the opening / closing valve 4a of the cooling water supply pipe 4 is opened while the pressure is maintained in the mold from the gate 31 of the mold 2, and the tip of the pipe of the cooling water supply pipe 4 is opened. Cooling water is gradually supplied to the outside of the mold to start cooling of the mold 2.
[0033]
The cooling water accumulated outside the mold flows into the cavity inside the mold through the slit 21a provided in the base plate 21, and the cooling water accumulates inside and outside the mold. Then, the water level of the cooling water accumulated in the cavity inside the mold coincides with the water level of the cooling water accumulated outside the mold, and the portion of the cooling water inside the mold that is lower than the water level is filled. The resin cools rapidly and begins to solidify.
[0034]
In this way, by cooling the inside of the mold at the same time without cooling only the outside of the mold, the inside portion of the lining, which is a molded body, can be cooled at a desired cooling rate. As a result, it is possible to prevent molding defects from appearing inside the lining. Since the inside portion of the lining is an important portion corresponding to the liquid contact portion of the pipe, it can be said that it is technically significant to eliminate such a molding failure of the inside portion of the lining by cooling in this manner.
[0035]
As described above, the cooling of the resin near the level of the cooling water in the tank progresses, solidifies, and the volume shrinks. However, the filled resin located at the top remains unsolidified because the cooling water has not reached the nearby height. The unsolidified resin moves downward due to the holding pressure applied to the mold for filling, and can uniformly compensate for the reduced volume due to solidification due to cooling.
[0036]
Then, if the water level of the cooling water is gradually increased from the direction of the vent 32 to the direction of the gate 31, the resin in the mold gradually solidifies from below to above. However, since the resin is supplied without interruption from the gate 31 that has not yet been affected by the cooling by the cooling water, the reduced volume due to solidification is compensated for by such a resin, and the molded product without sink marks due to the reduced volume due to solidification is removed. Obtainable.
[0037]
Subsequently, when the water level of the cooling water is increased, the water level becomes higher than that of the discharge pipe 3, and the air in the area surrounded by the cooling water and the core 25 inside the mold is discharged through the discharge pipe 3. Everything is exhausted from inside the mold. Then, the cooling water in the tank starts to be continuously discharged due to the siphon phenomenon. Therefore, when the water starts to be discharged by the siphon phenomenon, the open / close valve 3a of the discharge pipe 3 is closed. Thereby, the discharge of the cooling water is temporarily stopped to prevent the cooling water in the tank from being drained.
[0038]
Since the water level of the cooling water inside the mold is higher than the height of the cooling water discharge pipe 3, the length of the cooling water discharge pipe 3 is increased to make the water level higher than the liquid contact portion of the lining formed in the mold. The positional relationship between the core 25 and the upper end of the water supply pipe is specified so as to ascend.
[0039]
That is, the level of the cooling water supplied into the tank rises beyond the upper end of the cooling water discharge pipe 3. Since this water level is higher than the upper end face P of the lining as a molded body in the drawing, the upper end face P of the lining can be cooled reliably. As a result, it is possible to obtain a molded body free from unevenness (flow mark) over the whole liquid contact portion of the lining.
[0040]
Further, as in the above-described embodiment, the temperature distribution becomes low on the vent side (bottom of the tank) and high on the gate side (upper of the tank) due to the convection of the cooling water in the tank, so that the gate side hardly solidifies. Can be made positively. Thus, it assists in suitable cooling of the resin as described above.
[0041]
Subsequently, after a certain cooling time has elapsed, the discharge pipe 3 is opened to discharge all the cooling water in the tank, and the cooling step is completed.
[0042]
Thereafter, the mold 20 is taken out of the tank by a transport device (not shown), and the mold 20 is divided to take out a molded body. Then, the molded body is cut at a predetermined position to obtain a lining for a tubular body.
[0043]
The lining of the tube obtained in this manner has no sink or unevenness of the resin, and maintains high quality especially on the inner peripheral surface which is the liquid contact portion. Therefore, the tube provided with the lining does not have a hole in the lining portion, and therefore, the fluid to be measured does not leak outside the tube.
[0044]
In addition, if the method of molding a resin molded body according to the present embodiment is used, the metal reinforced material such as a reinforcing plate made of a sheet metal having a large number of punched holes is not used for lining, and only the reinforcing filler is contained. An inexpensive and highly durable lining that does not cause sink marks or unevenness on the liquid contact surface can be formed only by the PP that has been used. Therefore, it is possible to contribute to cost reduction of the entire tube.
[0045]
It has been confirmed that the resin used for the molding material in the above embodiment is applicable not only to PP but also to PFA (tetrafluoro-perfluoroalkylvinyl ether resin).
[0046]
In addition, for example, in a molding process of a lining having an inner diameter of 5 cm, a cooling time of about 30 minutes was required for cooling a mold by air cooling as in the related art. It has been found that the time is shortened and greatly contributes to the reduction of the tact time in the lining manufacturing process.
[0047]
In addition, since a lining without sink marks and unevenness could be formed stably, the product yield was remarkably improved as compared with the conventional lining molding method.
[0048]
In the above-described embodiment, the cooling water level gradually rises from the vent side to the gate side around the mold where the gate is located above, but the invention is not necessarily limited to this. Absent. That is, the mold itself is placed in a state of lying horizontally, the gate of the mold is provided on one side in the horizontal direction (for example, rightward), and the cooling water is supplied from the other side of the mold in the horizontal direction (for example, leftward) to the gate. If a structure in which the water level moves in the horizontal direction toward the surface is possible, it can be said that a method of molding a resin molded body using an apparatus having such a structure is also within the scope of the present invention.
[0049]
The medium used for cooling is not limited to water, but may be another liquid such as oil.
[0050]
【The invention's effect】
As described above, the molding method of the resin molded article according to the present invention is such that the gate side of the mold is finally cooled with the cooling water while keeping the inside of the mold in the mold cooling process, The gate side of the mold is not cooled before the rest of the mold. Therefore, there is no possibility that the gate side of the mold is first solidified and the resin is not sufficiently injected into the mold, or the holding pressure does not work, and the molded product does not sink. This makes it possible to obtain a resin molded body having a uniform quality without sink marks and unevenness on the surface.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a mold and a mold cooling device used in a method for molding a resin molded body according to a first embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view illustrating a mold and a mold cooling device used in a method of molding a resin molded body according to a second embodiment of the present invention.
FIG. 3 is a schematic sectional view showing a conventional mold cooling method.
FIG. 4 is a schematic cross-sectional view showing another conventional mold cooling method different from FIG.
[Explanation of symbols]
1, 2 tank 3 discharge pipe 3a opening / closing valve 4 water supply pipe 6 cooling device 10 mold 15 tank 16 water supply pipe 20 mold 21 first mold 21a slit 22 flange plate 23 spacer 25 core 26 upper mold 27 spool bush 28 Nozzle 29 Container 30 Cylinder head 31 Gate 32 Vent 50 Mold 51 Cooling circuit 51a Inlet side 51b Outlet side 60 Mold 61 Cavity 63 Gate 70 Liquid tank 71 Support column 72 Pouring pipe 75 Water supply pipe 76 Drain pipe M Tube body R Resin W cooling water

Claims (1)

A first step of preheating the mold at least above the melting point of the resin;
A second step of filling the resin in the mold;
A resin step of moving the level of cooling water for cooling at least the periphery of the mold from the vent side to the gate side of the mold while maintaining the pressure inside the mold. A method for forming a molded body.

Images