JP4079362B2 - Molding method of resin molding - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a molding method for injecting molten resin into a mold to form a resin molded body having a predetermined shape, and in particular, a resin molded body that eliminates sink marks and surface irregularities (flow marks). The present invention relates to a molding method for obtaining.
[0002]
[Prior art]
Conventionally, in order to obtain a desired resin molded body in molding a resin, it is generally performed to cool the mold to an appropriate temperature with cooling water or cooling air during molding.
[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 formed 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 between the cooling water and the cooling air (cooling water W in FIG. 3) occurs between the inlet side 51a (region A in the drawing) and the outlet side 51b (region B in the drawing) of the cooling circuit 51. End up. This is because cooling water or cooling air takes heat from the mold 50 while passing through the cooling circuit 51. Due to this temperature difference, the resin in the mold (shown by R in the figure) cannot be cooled at a uniform cooling rate as a whole. That is, a cooling difference is partially generated in the cooling rate of the resin. This temperature difference is greatest on the inlet side 51a and the outlet side 51b of the cooling circuit 51, which leads to the occurrence of defects such as deformation and discoloration of the resin molded body.
[0004]
As a means for improving such a problem, a cooling system is 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, the outer peripheral surface of the mold can be evenly cooled with the liquid.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 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 for carrying out this method has a mold 60 that can be divided into upper and lower parts fixed in a liquid tank 70 in a state of being slightly floated via a support 71 and connected to the lower side of the liquid tank 70. Cooling water (shown by W in the figure) is supplied from the pipe 75, and the cooling water is discharged from the drain pipe 76 at the top of the liquid tank. A pouring pipe 72 for supplying molten resin (shown by R in the figure) to the cavity 61 of the mold 60 passes through the bottom of the liquid tank 70 and is connected to the lower part of the mold. Then, after the resin supplied to the mold 60 reaches the specified amount and the filling of the resin is completed, the cooling water is supplied from the water supply pipe 75 and the mold 60 is cooled by filling the liquid tank 70 with the cooling water. . With this method, the cooling rate in the horizontal plane is uniform, and uneven cooling in this plane can be eliminated.
[0007]
The resin molding apparatus provided with such a cooling device 6 is configured to stop the resin by operating the pressure sensor when the resin reaches a specified amount. For this reason, volume shrinkage due to solidification of the resin in the mold after the resin supply is stopped may cause sink marks in the molded body. Further, in the invention described in Patent Document 1, even if the pressurization to the molten resin in the cavity 61 is continued through the pouring pipe 72 in order to compensate for the sink during cooling, the molded body may be damaged. The problem that it occurs cannot be solved sufficiently. This is because the water supply pipe 75 is set on the gate side, and the cooling water having the lowest temperature supplied from the water supply pipe 75 mainly reaches the gate 63 side of the mold 60, so that the resin on the gate side is the first. This is because it is cooled and solidified.
[0008]
Thus, when the resin located in the gate 63 is first solidified and the gate 63 is clogged, the pressure of the molten resin is not transmitted to the inside of the cavity 61 from that point, and the resin cannot be supplied to the cavity 61, so Sink may occur. For this reason, in the molding apparatus provided with such a cooling device 6, sink marks may occur after molding not only on the portion corresponding to the gate 63 of the mold 60 but also on the entire resin molded body, which has a certain quality level. A resin molding cannot be obtained stably.
[0009]
The objective of this invention is providing the molding method of the resin molding which can obtain the resin molding provided with fixed high quality.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, a molding method for a resin molded body according to the present invention is as follows.
A first step of preheating the mold at least higher than the melting point of the resin;
A second step of filling the mold in the tank with resin;
After the mold is sufficiently filled with the resin, while maintaining the pressure in the mold and continuing to fill the resin , at least the cooling water level for cooling the periphery of the mold is changed from the vent side to the gate side of the mold. And a third step of gradually supplying cooling water into the tank so as to move toward the tank .
[0011]
In the mold cooling process, after the resin in the tank is sufficiently filled with resin, the mold gate side is finally cooled with cooling water while keeping the pressure inside the mold and continuing to fill the resin. In order to make sure that at least the cooling water level for cooling the mold periphery moves from the vent side to the gate side of the mold, the cooling water is gradually supplied into the tank. The gate side is not cooled before the other part of the mold. Therefore, sufficient resin injected into the mold gate side of the mold solidifies earlier never Kunar such made. Also, after the resin was sufficiently filled in the mold placed in the tank, the mold side was cooled with cooling water at the end while holding the inside of the mold and continuing to fill the resin . The holding pressure does not act , and there is no possibility of sink marks of the molded body due to the resin not being filled at that time . As a result, it is possible to obtain a resin molded product having a constant quality without sink or unevenness on the surface.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for molding a resin molded body according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a molding method of 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 the vicinity of the bottom surface, It implements using the metal mold | die 10 formed by the type | mold 11 and the lower mold | type 12 couple | bonding. Note that the mold 10 itself is not provided with a cooling circuit as in the latter conventional example, so that the mold 10 is uniformly cooled over the entire circumference of the water level as the level of the cooling water rises. A mold 10 is disposed at a substantially central portion of the tank 1.
[0013]
Then, the molding method of the resin molding concerning this embodiment is demonstrated in the order of the process.
[0014]
First, the mold 10 is preheated (preliminarily heated). 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 used. In practice, it is preferable to heat to the same temperature as the temperature of the resin to be filled. By preheating the mold in this way, it takes longer to reach the temperature at which the resin solidifies, the resin fluidity in the mold does not deteriorate, and in addition to this, the cooling rate is also controlled. Can be made easier.
[0015]
Subsequently, pressure is applied to the resin to fill the mold 10 with the resin. The mold 10 is composed of an upper mold 11 and a lower mold 12, and by appropriately adjusting the surface roughness of the mold contact surface (see X in the figure), the resin is removed from the contact surface in the resin filling process. Only the air in the cavity is exhausted without flowing out. The contact surface X forms a vent (exhaust part) of the mold 10.
[0016]
The pressurized supply of resin into the mold is continued until cooling with cooling water is completed. This is to avoid sink marks after molding. In this way, cooling of the mold 10 is started by gradually supplying cooling water from the water supply pipe 16 into the tank 1 while maintaining the pressure inside the mold. At this time, the resin in the vicinity of the water level of the cooling water in the tank is cooled and solidified to shrink the volume. However, the resin filled in the upper part remains unsolidified because the cooling water does not reach the height near the periphery of the mold. This unsolidified resin moves to the resin deficient region due to the pressure applied for filling, and solidifies by cooling, so that the reduced volume can be compensated evenly.
[0017]
And if the water level of a cooling water is raised (moved) little by little toward the gate 13 from a vent side, resin in a metal mold will also be solidified gradually from the bottom to the upper part in connection with this. However, the resin is appropriately compensated from the gate 13 which has not yet been affected by the cooling water, and a molded body free from sinks due to volume reduction due to solidification is obtained.
[0018]
In this embodiment, the cooling water is convected in the tank, so that the temperature distribution becomes low on the vent side (bottom of the tank) and high on the gate side (top of the tank), and the gate side is hard to solidify. Which can be made automatically and assists in suitable cooling of the resin as described above.
[0019]
Then, the molding method of the resin molding concerning the 2nd Embodiment of this invention is demonstrated based on drawing. The molding method of the resin molding according to the present embodiment is in principle the same as the molding method of the resin molding according to the first embodiment described above, but the configuration of the mold and the cooling water in the mold are as follows. The cooling region by 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 carried out in a state where a specially shaped mold 20 is arranged in a tank 2 as shown in FIG. The mold 20 is a mold for forming a so-called lining that covers the wetted surface of a metal tube through which a fluid flows, and this mold is filled with polypropylene (PP) as a resin, and flanges are formed around both ends. It is a metal mold | die for forming the cylindrical lining provided with the protruding part.
[0021]
The tank 2 used in this embodiment is composed of 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 from the bottom of the tank 2 at the bottom center of the tank 2, and a cooling water supply pipe 4 is provided in the vicinity of the inner wall of the tank 2. 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 placed on the flange plate 22 in a state where a thin annular base plate 21, a thick annular flange plate 22 placed on the base plate 21, and a space for forming the flange portion of the flange plate 22 and the lining are secured. And a pipe body M that is used as a mold, and a spacer 23 that is fitted to the peripheral surface of the pipe body M and serves as a thermal mass for achieving a constant cooling rate as the cooling water level rises. Have. The mold 20 is further placed on top of these molds, and a core 25 having a substantially conical head and a gate 31 mounted on the top of the core 25 in cooperation with the core 25. The upper die 26, the spool bush 27 attached to the upper portion of the upper die 26, the nozzle 28 which is coupled to the spool bush 27 and has a dish shape and has a resin outflow hole formed in the center, and the nozzle 28 Is provided with a cylindrical container 29 for storing resin, and a cylinder head 30 attached to the upper part of the container 29.
[0023]
The gate 31 of the mold 20 is formed at a portion sandwiched between the core 25 and the upper mold 26 as described above, and the vent 32 of the mold 20 is a portion sandwiched between the flange plate 22 and the tubular body M. Is formed.
[0024]
In other words, 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 affected by the pressure applied during molding. The gas is exhausted from the contact surface to the outside of the mold.
[0025]
Then, a molten resin is filled into a space defined by the cylinder head 30, the container 29, and the nozzle 28 through an injection pipe using a hydraulic actuator (not shown). Subsequently, the cylinder head 30 is pushed at a constant pressure by a hydraulic cylinder (not shown), and the resin accumulated in the upper part of the mold is injected into the resin hatched space (continuous hatching of thick and thin lines) in the mold at a predetermined pressure. It has come to be.
[0026]
On the other hand, the cooling water can drain the cooled cooling water from the pipe 3 by opening an opening / closing valve 3 a provided in the cooling water discharge pipe 3. Note that 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 mold. Therefore, the cooling water collected on the outside of the mold is transferred to the inside of the mold 20 through the slit 21 a of the mold 20. Therefore, by opening the on-off valve 4a, 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 drainage pipe 3 is positioned above the upper end surface of the lining, and plays the role of forming a lining without sink marks or unevenness (flow marks) on the entire wetted surface as described later.
[0028]
Hereinafter, the molding method of the resin molded body according to the present embodiment will be described in the order of each process. 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 the resin PP in the mold, and the entire mold is not shown up to 220 ° C., which is higher than the melting point of the PP used (about 160 ° C.). Heat in the heating tank. The reason for heating to such a temperature is to avoid that the temperature of the resin in contact with the mold is lowered in this 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). In addition, the tank 2 used for mold cooling is installed in advance in the transfer station, and the above-described mold 20 is disposed at the bottom of the tank 2. Incidentally, in this task, arranging while positioning the mold 20 so that the cooling water discharge pipe 3 projecting from the bottom of the tank 2 in the tank is inserted into the die 20 as shown in FIG. 2 .
[0031]
Subsequently, the mold 20 is filled with 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 continuously maintained during the cooling process. This is to avoid the occurrence of sink marks in the resin by making up for the resin shortage in the mold during cooling as in the case of the first embodiment. It should be noted that it takes about 3 minutes as an example to form a lining having an inner diameter of 5 cm and a thickness of 0.4 cm until the entire mold is filled with the resin.
[0032]
After filling the entire mold with resin, the opening / closing valve 4a of the cooling water supply pipe 4 is opened while pressure is maintained in the mold from the gate 31 of the mold 2, and the pipe tip of the cooling water supply pipe 4 is opened. The cooling of the mold 2 is started by gradually supplying cooling water to the outside of the mold.
[0033]
The cooling water collected outside the mold flows into the cavity inside the mold via the slit 21a provided in the base plate 21, and the cooling water accumulates inside and outside the mold. And the water level of the cooling water collected in the cavity inside the mold and the water level of the cooling water collected outside the mold are matched, and the lower part of the cooling water level is filled in the mold. The resin cools rapidly and begins to solidify.
[0034]
In addition, by cooling the inside of the mold at the same time without cooling only the outside of the mold as described above, the inner 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 on the inner portion of the lining. In addition, since the inner part of the lining is an important part corresponding to the liquid contact part of the tube, it can be said that it is technically significant to eliminate the molding defect of the inner part of the lining by cooling in this way.
[0035]
As described above, the resin in the vicinity of the water level of the cooling water in the tank is solidified as the cooling proceeds and the volume shrinks. However, the filled resin located in the upper part remains unsolidified because the cooling water has not reached the height in the vicinity thereof. This unsolidified resin moves downward by holding pressure applied to the mold for filling, and solidifies by cooling, so that the reduced volume can be compensated evenly.
[0036]
And if the water level of a cooling water is raised little by little from the direction of the vent 32 to the direction of the gate 31, the resin in a metal mold will also be solidified gradually from the downward direction to the upward direction. However, since the resin is supplied without interruption from the gate 31 that has not yet been affected by the cooling with the cooling water, the volume reduction due to solidification is compensated with the resin, and a molded body free from sink due to the volume reduction due to solidification is obtained. Obtainable.
[0037]
Subsequently, when the water level of the cooling water is raised, the water level becomes higher than that of the discharge pipe 3, and the air in the region surrounded by the cooling water inside the mold and the core 25 passes through the discharge pipe 3. Everything is exhausted from the mold. And the cooling water in a cage | basket begins to be discharged | emitted continuously by a siphon phenomenon. Therefore, the opening / closing valve 3a of the discharge pipe 3 is closed when water begins to be discharged due to the siphon phenomenon. This temporarily stops the cooling water discharge so that the cooling water in the tank does not drain.
[0038]
Since the cooling water level inside the mold is higher than the height of the cooling water discharge pipe 3, the water level is higher than the wetted part of the lining formed in the mold by increasing the length of the cooling water discharge pipe 3. The positional relationship between the core 25 and the upper end of the water supply pipe is specially defined so as to rise.
[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 the water level is higher than the upper end surface P in the figure of the lining which is a molded body, the upper end surface P of the lining can be reliably cooled. As a result, it is possible to obtain a molded body in which unevenness (flow mark) does not occur over the entire liquid contact portion of the lining.
[0040]
Moreover, the temperature distribution becomes low on the vent side (bottom of the tank) and high on the gate side (top of the tank) due to the convection of the cooling water in the tank as in the above embodiment, and the gate side is hard to solidify. Can be made positively. Therefore, it helps the preferred 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 basket, and the cooling process is terminated.
[0042]
Thereafter, the mold 20 is taken out from the tank by a conveying device (not shown), the mold 20 is divided, and the molded body is taken out. And a molded object is cut | disconnected in a predetermined position and the lining for pipes is obtained.
[0043]
The tube lining thus obtained does not have resin sink marks or unevenness, and maintains a high quality especially on the inner peripheral surface which is a liquid contact portion. For this reason, the pipe body provided with such a lining does not have a hole in the lining portion, and therefore the fluid to be measured does not leak out of the pipe body.
[0044]
Further, if the molding method of the resin molded body according to the present embodiment is used, only the reinforcing filler is contained without using a metal reinforcing material such as a reinforcing plate made of a sheet metal in which many punched holes are formed for the lining. A low-priced and durable lining that does not cause sink marks or unevenness on the wetted surface can be formed by using only PP. Therefore, it can contribute to the cost reduction of the whole tubular body.
[0045]
In the above-described embodiment, it has been confirmed that the resin used for the molding material is applicable not only to PP but also to PFA (tetrafluoride-perfluoroalkyl vinyl ether resin).
[0046]
In addition, for example, in the molding process of the lining having an inner diameter of 5 cm, it takes about 30 minutes to cool the mold by air cooling as in the prior art. However, when the above method is used, the mold cooling takes about 15 minutes. It has been found that it is shortened and greatly contributes to the reduction of the tact time of the lining manufacturing process.
[0047]
Moreover, since the lining without sink marks and unevenness could be stably formed, the yield of the product was significantly improved as compared with the conventional lining molding method.
[0048]
In the above-described embodiment, the description has been given based on the configuration in which the coolant level gradually rises from the vent side to the gate side around the mold with the gate on top, but the present invention is not necessarily limited thereto. Absent. That is, the mold itself is placed in the horizontal direction, the mold gate is provided in one horizontal direction (for example, the right direction), and the cooling water is supplied from the other horizontal direction (for example, the left direction) to the gate. If a structure in which the water level moves in the horizontal direction 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, and may be other liquids such as oil.
[0050]
【The invention's effect】
As described above, the molding method of the resin molded body in the present invention, in the cooling process of the mold after the resin is filled sufficiently encased within the mold in a bath, holding pressure resin in the mold In order to ensure that the gate side of the mold is finally cooled with cooling water while continuing to fill the mold , at least the water level of the cooling water that cools the mold periphery is moved from the vent side of the mold toward the gate side. Since the cooling water is gradually supplied into the tank, the gate side of the mold is not cooled before the other part of the mold. Therefore, sufficient resin injected into the mold gate side of the mold solidifies earlier never Kunar such made. Also, after the resin was sufficiently filled in the mold placed in the tank, the mold side was cooled with cooling water at the end while holding the inside of the mold and continuing to fill the resin . it is not to or cause shrinkage to the molded body by pressure-holding has not been carried out the filling of the resin in Rutotomoni that such does not act. As a result, it is possible to obtain a resin molded product having a constant quality without sink or 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 showing a mold and a mold cooling device used in a method for molding a resin molded body according to a second embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a conventional mold cooling method.
FIG. 4 is a schematic cross-sectional view showing a conventional mold cooling method different from FIG. 3;
[Explanation of symbols]
1, 2 Tank 3 Discharge pipe 3a Open / close 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 Die 51 Cooling circuit 51a Inlet side 51b Outlet side 60 Die 61 Cavity 63 Gate 70 Liquid tank 71 Post 72 Pouring pipe 75 Water supply pipe 76 Drain pipe M Pipe body R Resin W Cooling water

Claims (1)

A first step of preheating the mold at least higher than the melting point of the resin;
A second step of filling the mold in the tank with resin;
After the mold is sufficiently filled with the resin, while maintaining the pressure in the mold and continuing to fill the resin , at least the cooling water level for cooling the periphery of the mold is changed from the vent side to the gate side of the mold. And a third step of gradually supplying cooling water into the tank so as to move toward the tank .

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