JP2008302665A - Hot runner device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot runner device capable of making a temperature difference larger even though the distance between a nozzle and a mold is short. <P>SOLUTION: The hot runner device attached to a mold 2 and for injecting a molten resin into a cavity 6 of the mold 2 has a nozzle body 20 injecting the resin while being pushed to the mold 2 and insulation members 30, 40 and 50 arranged between the nozzle body 20 and the mold 2. The insulation members contact with the nozzle body 20 in a first contact part and contact with the mold 2 in a second contact part. The length of a heat transfer channel along the insulation member between the first contact part and the second contact part is longer than the direct distance between the nozzle body 20 and the mold 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hot runner apparatus, and more particularly to a hot runner apparatus used for injection molding of thermoplastic resin.

  A hot runner device used for injection molding of a thermoplastic resin is a device for quickly filling a resin into a mold cavity and preventing a runner from being formed in a molded product. Since the formation of the runner can be prevented, the trouble of removing the runner after molding can be saved, and the molding efficiency can be increased.

  In the hot runner apparatus, the resin in the nozzle is held in a high-temperature molten state by heating the nozzle body with a heater. On the other hand, the resin filled in the mold cavity needs to be quickly cooled so as to reach a temperature at which it can be taken out (a temperature at which it solidifies), and the mold cavity is cooled so as to have a low temperature. . Therefore, temperature control is performed so that the cavity-side mold has a temperature equal to or lower than the resin solidification temperature and the nozzle of the hot runner apparatus has a temperature equal to or higher than the melting temperature of the resin with respect to the gate position where the nozzle contacts the mold.

  For example, generally, the mold cooling temperature is 100 ° C. or lower, and the resin melting temperature is 200 ° C. or higher. In such a case, it is necessary to maintain a large temperature difference of 100 ° C. or more between minute distances across the gate position.

  In the hot runner apparatus, it is necessary to open and close the gate so that the resin does not leak when the mold is opened. As a gate opening / closing method, there are an open gate method in which the gate hole is covered with a solidified resin without providing any opening / closing mechanism, and a valve gate method in which a valve is mechanically inserted into the gate hole and closed. In recent years, a valve gate system is often used.

  In any of the above methods, the nozzle portion is strongly pressed against the mold so that the molten resin does not leak from the gate to the outside even when the pressure of the molten resin flowing through the gate is applied. Therefore, the nozzle body and the fixed mold have portions where metal parts are in contact with each other, and heat conduction through the contact portion causes a temperature increase on the cavity side and a temperature decrease on the nozzle side. It was.

  When the mold temperature on the cavity side becomes high, the resin is not sufficiently cooled and solidified within a predetermined time, and there is a possibility that a stringing phenomenon may occur when the mold is opened. Further, when the temperature of the nozzle body is lowered, a part of the molten resin in the nozzle is solidified, and this solidified resin is melted by the molten resin at the time of filling the next resin and filled together into the cavity. However, if the amount of the solidified resin is large, there is a possibility that it will enter the cavity without being melted. If this already solidified resin enters the cavity, for example, when a preform material for a PET bottle is formed, a whitening phenomenon occurs.

  In recent years, in order to increase the molding efficiency, the cooling time tends to be shortened to shorten the molding cycle. For this purpose, it is necessary to shorten the cooling time by setting the mold temperature lower. Therefore, the temperature difference between the nozzle of the hot runner device and the mold cavity is increasing. As a result, the problem is how to maintain the temperature difference between the nozzle body and the stationary mold, which has not been a major problem in the past, at an appropriate value.

  As a conventional technique, the tip of the nozzle is directly in contact with the mold, but this part of the mold is made of a material having a low thermal conductivity, the tip of the nozzle is not in contact with the mold, and the position away from the nozzle tip. There is a method of making contact. The former has the disadvantage that the tip of the nozzle cools directly. On the other hand, if the latter is largely separated, there is a problem that the structure becomes large and resin leakage is unavoidable.

  Therefore, it has been proposed to provide a seal ring around the nozzle so that the leaking resin is sealed in the gap so that the resin functions as a heat insulating layer (see, for example, Patent Document 1). Patent Document 1 also discloses a technique for providing an air insulation gap between the nozzle and the mold to insulate the nozzle and the mold.

In addition, there has been proposed a seal ring provided around the nozzle in a shape that reduces the misalignment of the nozzle (see, for example, Patent Document 2).
Japanese Patent No. 2842240 Japanese Patent No. 3160890

  The methods described in Patent Documents 1 and 2 described above have a problem that the gap to the seal ring is relatively large and the maintenance work for removing the resin leaking into the gap is complicated. Moreover, if the diameter of the seal ring is reduced in order to reduce this gap, there is a problem that heat of the nozzle body is easily transferred to the mold.

  In order to solve such problems, the tip of the nozzle is brought into direct contact with the mold. A small heater is incorporated at the very tip of the nozzle, the gate is closed, and the resin in the solidified nozzle is immediately before the next filling. A method of remelting with a small heater is also conceivable. However, in order to incorporate a small heater at the very tip of the nozzle, there is a problem that the structure of the nozzle becomes complicated and the apparatus becomes expensive.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a hot runner apparatus that can take a large temperature difference even if the distance between the nozzle and the mold is short.

  To achieve the above object, according to the present invention, there is provided a hot runner device for injecting molten resin into a mold cavity, which is attached to a mold, and is pressed against the mold. A nozzle main body for injecting resin, and a heat insulating member provided between the nozzle main body and the mold, and the heat insulating member is in contact with the nozzle main body at a first contact portion, and The length of the heat transfer channel along the heat insulating member between the first contact portion and the second contact portion is such that the nozzle body and the die are in contact with each other. A hot runner device is provided that is longer than the linear distance between the two.

  According to the present invention, since the heat insulating member is provided between the nozzle body and the mold, a large temperature difference can be provided between the nozzle body and the mold. Therefore, the temperature of the mold can be reduced while keeping the temperature of the nozzle body at the melting temperature of the resin. Thereby, cooling time is shortened and a molding cycle can be shortened.

  First, a hot runner apparatus to which the present invention is applicable will be described with reference to FIG. FIG. 1 is a sectional view showing the overall configuration of a hot runner apparatus to which the present invention is applicable.

  The hot runner apparatus shown in FIG. 1 is a valve gate type hot runner apparatus, and is configured to be attached to the fixed mold 2. The fixed mold 2 and the movable mold 4 form a cavity 6 into which molten resin is injected. The hot runner apparatus includes a nozzle unit 8, a resin supply unit 10 that supplies molten resin to the nozzle unit 8, and a driving unit 14 that drives a valve pin 12 for opening and closing the gate.

  The nozzle unit 8 includes a nozzle body 20 in which a passage of molten resin is formed, and a heater 22 that is provided around the nozzle body 20 and heats the nozzle body 20. A molten resin passage 20a is formed in the center of the nozzle body 20, and the valve pin 12 extends in the passage 20a. The tip of the valve pin 12 functions as a valve that opens and closes the gate hole 2 a connected to the cavity of the mold 2.

  The valve pin 12 extends through the resin supply unit 10, and its upper end is connected to the shaft 14 a of the drive unit 14. The drive unit 14 forms a hydraulic cylinder, and the shaft 14a can be driven by hydraulic pressure. Therefore, the valve pin 12 can be driven by driving the shaft 14 a of the drive unit 14. Thereby, the gate hole 2a of the fixed mold 2 can be opened and closed. The drive unit 14 is formed with two hydraulic cylinders in series. By driving the upper hydraulic cylinder, the valve pin 12 can be reciprocated up and down. Further, by driving the lower hydraulic cylinder, it is possible to apply a further pressing force to the valve pin 12 when the gate hole 2 a is closed by the valve pin 12.

  When pouring the molten resin into the cavity 6, the valve pin 12 is raised to open the gate hole 2a, so that the molten resin flows from the passage 20a into the cavity 6 through the gate hole 2a. When the cavity 6 is filled with molten resin, the valve pin 12 is lowered, and the tip of the valve pin 12 is inserted into the gate hole 2a, thereby closing the gate hole 2a. In this state, the tip of the valve pin 12 protrudes slightly into the cavity 6 or stops on the same surface as the outer peripheral surface of the cavity 6. Further, when used in a mold for taking out a molded product in the forward / backward direction of the valve pin 12, with the valve pin 12 and the gate hole 2a overlapping, the tip of the valve pin 12 is stopped at a position where it is drawn from the cavity 6. Also good.

  In FIG. 1, the nozzle body 20 of the nozzle portion 8 is attached to the fixed mold 2. A metal seal ring 24 is provided between the lower end of the nozzle body 20 and the fixed mold 2. The seal ring 24 is provided to seal the molten resin by being sandwiched between the nozzle body 20 and the stationary mold 2 when the nozzle body 20 is attached to the stationary mold 2. Since the seal ring 24 contacts both the nozzle body 20 maintained at a high temperature because the molten resin flows and the fixed mold 2 maintained at a low temperature so as to solidify the molten resin, the heat of the nozzle body 20 is reached. Moves to the fixed mold 2 through the seal ring 24. Therefore, in order to increase the temperature difference between both sides of the seal ring 24, it is necessary to reduce the temperature gradient when heat is conducted through the seal ring 24. That is, it is preferable to form the seal ring 24 with a material having low thermal conductivity.

  Here, the seal ring 24 will be described in detail. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the portion where the seal ring 24 in FIG. 1 is provided.

  As described above, the seal ring 24 is disposed between the nozzle body 20 and the fixed mold 2 and functions as a spacer. The seal ring 24 also has a positioning function when the nozzle body 20 is attached to the fixed mold 2. That is, by positioning the nozzle body 20 with respect to the gate hole 2a of the fixed mold 2 with high accuracy, when the tip of the valve pin 12 protrudes from the nozzle, the tip of the valve pin 12 is accurately aligned with the gate hole 2a of the fixed mold. The gate hole 2a can be closed by fitting well. Since the valve pin 12 is retracted while filling the cavity 6 with the molten resin (in FIG. 2, the molten resin leaks into the gap 26 between the nozzle body 20 and the fixed mold 2. .

  While the nozzle body 20 is kept at a high temperature, the stationary mold 2 is cooled by cooling water flowing through a cooling water channel (not shown) and is kept at a low temperature in order to cool and solidify the resin in the cavity 6. ing. Therefore, when the gate hole 2a is closed by the valve pin 12, the tip of the valve pin 12 also comes into contact with the low temperature stationary mold 2 and the temperature is lowered. The temperature at the tip of the nozzle body 20 also tends to decrease due to heat transfer through the seal ring 24.

  Therefore, when the heat of the heater 22 does not reach the tip sufficiently, the temperature of the tip portion of the nozzle body 22 may cause the resin to solidify near the tip of the molten resin passage 20a. On the other hand, the heat of the nozzle body 20 and the heater 22 flows to the fixed mold 2 through the seal ring 24 and the fixed mold is heated, and the cooling / solidification of the resin in the cavity 6 may be delayed. is there.

  In order to avoid the above problems, a material having as low a thermal conductivity as possible is used for the seal ring 24. However, since the seal ring 24 is also required to have strength, there is a limit to using a material other than metal. is there. Also, increasing the diameter of the seal ring 24 to a position away from the gate position is structurally limited and cannot exceed the nozzle diameter. Further, when the gap 26 becomes large, the amount of resin leakage increases and maintenance becomes difficult.

  The heater 22 is preferably provided as far as possible to the tip of the nozzle body 20, but the heat may flow to the stationary mold 2 through the seal ring 24 to raise the temperature. The limit is just before the seal ring 24.

  The heat of the nozzle body 20 heated by the heater 22 is transmitted to the low temperature stationary mold 2 through the seal ring 24. Here, it is known that the amount of heat q per unit time moved by heat conduction is proportional to the heat conductivity k and the temperature gradient dT / dx (temperature difference / distance). Therefore, in order to reduce the amount of heat transferred from the nozzle body 20 to the fixed mold 2, the thermal conductivity of the seal ring 24 may be reduced or the temperature gradient may be reduced.

  Since the seal ring 24 is pressed between the nozzle body 20 and the fixed mold 2, rigidity and strength are also required. Therefore, a relatively brittle ceramic or the like cannot be used as the material of the seal ring 24, and a metal is used, so that it is difficult to significantly reduce the thermal conductivity. Further, the outer shape of the nozzle body 20 is as small as about 30 mm, and a large space cannot be secured in the portion to which the nozzle body 20 is attached. Therefore, the size of the seal ring 24 is increased to reduce the temperature gradient (that is, the distance is reduced). It is also difficult to make it larger.

  Therefore, in the present invention, by devising the shape of the seal ring in a limited space, the heat transfer distance by the seal ring is lengthened, the temperature gradient is reduced, the heat conduction is reduced, and it is used as a heat insulating member. . Thereby, the temperature drop of the front-end | tip part of the nozzle main body 20 and the temperature rise of the stationary mold 2 can be suppressed, and the temperature difference between the front-end | tip part of the nozzle main body 20 and the stationary mold 2 is maintained large. Can do.

  Next, a hot runner apparatus according to a first embodiment of the present invention will be described with reference to FIG. FIG. 3 is an enlarged cross-sectional view of a portion provided with a seal ring of the hot runner apparatus according to the first embodiment of the present invention. The hot runner apparatus according to the first embodiment of the present invention is a device in which the shape of the seal ring is devised, and the portions other than the seal ring are the same as those of the hot runner apparatus shown in FIG.

  In FIG. 3, the seal ring 30 functioning as a heat insulating member has an elongated cross section compared to the seal ring 24 shown in FIG. 2, and the width of the heat transfer channel is reduced. Since FIG. 3 is a cross-sectional view, the overall shape of the seal ring 30 is such that a hollow cone is cut into a ring.

  Since the seal ring also needs an alignment function, one end 30a of the seal ring 30 contacts the nozzle body 20 in the vertical and horizontal directions, and the other end 30b also contacts the fixed mold 2 in the vertical and horizontal directions. To do. If the portion where one end 30a of the seal ring 30 contacts the nozzle body 20 is a first contact portion, and the portion where the other end 30b of the seal ring 30 contacts the stationary mold 2 is a second contact portion, A distance L1 between the contact portion and the second contact portion is longer than a distance L0 between the outer periphery of the nozzle body 20 and the inner periphery of the fixed mold 2. Therefore, the length (corresponding to L1) of the heat transfer channel formed by the seal ring 30 is longer than the length (corresponding to L0) of the heat transfer channel of the seal ring 24 shown in FIG. The temperature gradient in the ring 30 is small.

  Further, when the seal ring 30 shown in FIG. 3 is compared with the seal ring 24 shown in FIG. 2, the seal ring 30 shown in FIG. Therefore, since the seal ring 30 shown in FIG. 3 has a smaller heat transfer channel area and a larger thermal resistance, the temperature difference between both ends 30a and 30b can be increased.

  Next, a hot runner apparatus according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is an enlarged sectional view of a portion provided with a seal ring of the hot runner apparatus according to the first embodiment of the present invention. The hot runner apparatus according to the second embodiment of the present invention is a device in which the shape of the seal ring is devised, and the portions other than the seal ring are the same as the hot runner apparatus shown in FIG.

  In FIG. 4, the seal ring 40 functioning as a heat insulating member is formed with narrow grooves 42 and 44 from the outer peripheral side and the inner peripheral side in cross section as compared with the seal ring 24 shown in FIG. 2. As a result, the seal ring 40 has a shape in which an elongated portion in the cross section meanders by repeating a U-turn twice, and its one end 40a contacts the nozzle body 20 in the vertical direction and the horizontal direction, and the other end 40b also It is in contact with the fixed mold 2 in the vertical direction and the horizontal direction.

  If the portion where one end 40a of the seal ring 40 contacts the nozzle body 20 is a first contact portion, and the portion where the other end 40b of the seal ring 40 contacts the stationary mold 2 is a second contact portion, the first contact portion A distance L2 along the seal ring 40 between the contact portion and the second contact portion is longer than a distance L0 between the outer periphery of the nozzle body 20 and the inner periphery of the fixed mold 2. Therefore, the length (corresponding to L2) of the heat transfer channel formed by the seal ring 40 is longer than the length (corresponding to L0) of the heat transfer channel of the seal ring 24 shown in FIG. The temperature gradient in the seal ring 40 is about 1/3.

  As described above, compared to the seal ring 24 shown in FIG. 2, the seal ring 40 according to the present embodiment has a shape that fits in the same space, but the heat transfer channel can be about three times as long, The temperature gradient can be reduced to about 1/3.

  Since the seal ring 40 is a small annular member, when it is difficult to form the grooves 42 and 44, the seal ring 40 is divided into several parts as in the third embodiment below. It is good also as assembling after forming.

  Next, a hot runner apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is an enlarged cross-sectional view of a portion provided with a seal ring of a hot runner apparatus according to a third embodiment of the present invention. The hot runner apparatus according to the third embodiment of the present invention is a device in which the shape of the seal ring is devised, and the portions other than the seal ring are the same as those of the hot runner apparatus shown in FIG.

  In FIG. 5, the seal ring 50 functioning as a heat insulating member has a shape in which an elongated portion in a cross section meanders by repeating a U-turn twice in the vertical direction, as the seal ring 40 shown in FIG. 4 is rotated by 90 °. One end 50a is in contact with the nozzle body 20 in the vertical and horizontal directions, and the other end 50b is also in contact with the fixed mold 2 in the vertical and horizontal directions.

  If the portion where one end 50a of the seal ring 50 contacts the nozzle body 20 is a first contact portion, and the portion where the other end 50b of the seal ring 50 contacts the stationary mold 2 is a second contact portion, A distance L3 along the seal ring 50 between the contact portion and the second contact portion is longer than a distance L0 between the outer periphery of the nozzle body 20 and the inner periphery of the fixed mold 2. Therefore, the length (corresponding to L3) of the heat transfer channel formed by the seal ring 40 is longer than the length of the heat transfer channel (corresponding to L0) of the seal ring 24 shown in FIG. The temperature gradient is also getting smaller.

  As shown in FIG. 5, the seal ring 50 is divided into three parts, and the three parts are combined to form one seal ring 50. As described above, the seal ring is divided into a plurality of portions to form a seal ring having a complicated shape.

  Further, the seal ring 50 has a shape in which a plurality of rings are overlapped to form a U-turn in the vertical direction as a whole shape, and is difficult to deform with respect to loads from the vertical and horizontal directions. Therefore, even if the nozzle body 20 is pressed toward the fixed mold 2 with a large load, the deformation of the seal ring 50 is suppressed to be small, and the position of the nozzle body 20 with respect to the fixed mold 2 can be accurately maintained.

  FIG. 6 is an enlarged cross-sectional view of a part of the seal ring 50 in FIG. A part of the seal ring shown in FIG. 6 is a connection part between one part forming the seal ring 50 and the other part. When the width in the cross section of one portion forming the seal ring 50 is x1, x2 corresponding to the width of the contact portion at the connection portion is smaller than x1. This means that the area of the heat transfer channel formed by the seal ring 50 is small at the connection portion. Therefore, the thermal resistance is increased at the connecting portion, and the temperature difference between the both ends 50a and 50b of the seal ring 50 can be increased.

  As described above, according to each of the above-described embodiments, the seal ring 30, 40, 50 functioning as a heat insulating member is provided between the nozzle body 20 and the fixed mold 2, and thus the nozzle body 20 and the fixed mold are provided. A large temperature difference can be provided between the two. Therefore, the temperature of the fixed mold 2 can be reduced while keeping the temperature of the nozzle body 20 at the melting temperature of the resin. Thereby, cooling time is shortened and a molding cycle can be shortened.

  In addition, although each above-mentioned Example demonstrated as a valve gate type hot runner apparatus, this invention is applicable also to an open gate type hot runner system.

It is sectional drawing which shows the whole structure of the hot runner apparatus which can apply this invention. It is an expanded sectional view which shows the vicinity of the part provided with the seal ring shown in FIG. It is an expanded sectional view of the part in which the seal ring of the hot runner apparatus by 1st Example of this invention was provided. It is an expanded sectional view of the part in which the seal ring of the hot runner apparatus by 2nd Example of this invention was provided. It is an expanded sectional view of the part in which the seal ring of the hot runner apparatus by 3rd Example of this invention was provided. It is sectional drawing to which a part of seal ring in FIG. 5 was expanded.

Explanation of symbols

2 Fixed mold 2a Gate hole 4 Movable mold 6 Cavity 8 Nozzle part 10 Resin supply part 12 Valve pin 14 Drive part 20 Nozzle body 22 Heater 24, 30, 40, 50 Seal ring 26 Clearance 42, 44 Groove

Claims (6)

A hot runner device attached to a mold for injecting molten resin into the mold cavity,
A nozzle body for injecting resin while being pressed against the mold;
A heat insulating member provided between the nozzle body and the mold,
The heat insulating member is in contact with the nozzle body at a first contact portion, and is in contact with the mold at a second contact portion,
The length of the heat transfer channel along the heat insulating member between the first contact portion and the second contact portion is longer than a linear distance between the nozzle body and the mold. Hot runner device. The hot runner device according to claim 1,
The hot runner apparatus is characterized in that the heat insulating member has a meandering cross section. The hot runner device according to claim 2,
The hot runner apparatus according to claim 1, wherein the heat insulating member is a member in which a circumferential groove is formed in an annular member. The hot runner device according to claim 2,
The hot runner apparatus, wherein the heat insulating member is formed by combining a plurality of members. The hot runner device according to claim 1,
The hot runner apparatus, wherein the heat transfer channel of the heat insulating member has a non-uniform width. The hot runner device according to claim 5,
The heat insulating member is formed by combining a plurality of members,
The heat transfer channel is formed across the plurality of members,
The hot runner apparatus characterized in that the width of the contact portion between the adjacent members is smaller than the width of the heat transfer channel formed in each of the members.

Images