JP2011000814A - Stringing preventing hot sprue bush and injection molding mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot sprue bush not generating a phenomenon causing defects such as stringing or silver streaks of molded products without needing to apply special machining to a mold and without needing special strict molding conditions.SOLUTION: A heater 13 is arranged in a part of the hot sprue bush 10 and the hot sprue bush 10 is attached to a part. A cooling part 17 by a fixed side mold plate 2 in which cooling water channels 6 are arranged is arranged, and a sprue hole 12 which is a passage of a molten resin is formed so that a cross sectional area perpendicular to a flowing direction of the molten resin is the same or increases over the whole length of the sprue hole or of the combination of the same part and the increasing part.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot sprue bush to be attached to an injection mold using a resin material and an injection mold, and more particularly to a string pulling prevention hot sprue that can prevent the occurrence of string pulling when the mold is opened. The present invention relates to a bush and an injection mold.

  In injection molding using a resin material, molten resin injected from an injection nozzle of an injection molding machine is filled into a cavity via, for example, a sprue, a runner, and a gate, and the filled molten resin is cooled and solidified, and after mold opening Removed from the mold.

  By the way, in the mold opening process in a series of molding processes, when the molten resin part in the nozzle hole of the injection nozzle and the solidified resin part in the sprue hole of the sprue bush are separated at a part having a temperature gradient at the boundary part. In addition, a so-called “string drawing” phenomenon may occur in which the separated portion on the molten resin portion side is stretched to form a thread.

  When the molding resin formed into a thread is adhered in the cavity, streaky traces are formed on the surface of the molded product in the next molding cycle, and the appearance of the product is impaired.

  Further, if the molding resin formed into a thread form adheres to the parting surface of the mold, the parting surface of the mold may be scratched or corners may be damaged during mold clamping. Further, a gap is generated on the parting surface, and the molten resin flows, and becomes a burr of a molded product, which deteriorates the appearance of the product as described above. At the same time, the dimension of the cavity is increased, and the dimensional accuracy of the molded product may be lowered.

  Therefore, the following injection molding has been proposed as a method for preventing the occurrence of the yarn drawing phenomenon that is a cause of defects of such molded products.

  As shown in FIG. 8, an air outlet 62 is provided on the side of the injection nozzle 60 in the vicinity of the contact portion between the tip of the injection nozzle 60 and the tip of the sprue bush 61 of the injection molding machine. A cooling water channel 63 is provided on the bush 61 side.

  Then, the cooling water is supplied to the cooling water passage 63 to maintain the state where the sprue bush 61 is cooled to an appropriate temperature, and after filling the molds 64 and 65 with the molten resin, the cooling air is injected from the air outlet 62 to the injection nozzle. It cools by spraying on the outer surface near the front-end | tip part of 60. FIG.

  As a result, the tip of the injection nozzle 60 is rapidly cooled to cool the high-temperature molten resin in the nozzle hole to the cooling solidification temperature, and the solidified resin in the molten resin part and the sprue hole 66 in the nozzle hole when the mold is opened. The yarn pulling phenomenon in which the boundary portion with the portion 67 is stretched with the movement of the movable side mold plate 65 to form a thread is prevented (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-48288

  By the way, in the yarn pulling prevention method in which the dies 64 and 65 and the sprue bush 61 are configured as described above, it is necessary to process the dies 64 and 65 and the sprue bush 61 to provide the air passage 68 and the cooling water passage 63, respectively. As the number of processing steps increases, the manufacturing period becomes longer and the manufacturing cost increases.

  In addition to the molds 64 and 65 and the sprue bush 61, it is necessary to provide a cooling air circulation path and a cooling water circulation path each including a cooler, and temperature control management for them is also required. As a result, the cooling circulation mechanism and its temperature control mechanism are arranged, which leads to further cost increase.

  Further, by cooling the tip portion of the injection nozzle 61, the molten resin at that portion is solidified to close the nozzle hole, and until the solidified resin that closed the nozzle hole is melted by heating the nozzle in the next molding cycle. The mold resin cannot be injected into the mold. For this reason, the molding cycle becomes longer, the production efficiency is lowered, and the manufacturing cost is increased.

  As an injection molding method other than the above, it is noted that the resin material for forming the sprue does not contribute as a molded product, and there is a molding method for reducing the loss of the resin material by shortening the length of the sprue as much as possible. It is known as injection molding by a mold using a hot spruce bush as shown in FIG. 9 (known technique).

  In this injection molding, the hot sprue bush 80 has one end connected to a nozzle hole (not shown) of the injection nozzle of the molding machine and the other end connected to the runner 83 of the molds 81 and 82. The heater 85 for keeping the temperature of the molten resin flowing in the sprue hole 84 constant, the temperature sensor 86 for temperature detection for controlling the temperature of the heater 85, and the end on the runner 83 side in the sprue hole 84 It comprises a cooling part 87 for cooling and solidifying the molten resin in the part.

  The present inventor has intensively studied the yarn drawing phenomenon. As a result, when the injection nozzle of the injection molding machine and the sprue bush come into contact with each other, the thread drawing phenomenon is a narrowing in which the cross-sectional area of the hole becomes small along the flow direction of the molten resin at the connecting portion between the nozzle hole and the sprue bushing. It has been estimated that this occurs due to shear heat generated when the molten resin passes through this constriction.

  Hot spruce bushes of various structures have been put into practical use, but most of them have the sprue hole 84 in the cross-sectional area of the sprue hole 84 along the flow direction of the molten resin, as described in the above-mentioned prior literature. In the cooling process, a molten resin portion of a molded resin is formed on the injection nozzle side in the sprue hole 84, and a cooling solidified portion is formed on the runner 83 side. The

  Even in the injection molding using the hot sprue bush 80 having such a configuration, when the molten resin passes through the narrowed portion 88 of the sprue hole 84, shear heat is generated, and the resin temperature in that portion rises above the set temperature. Even if it is intended to cool to the solidification temperature at the time of mold opening after cooling, it is pulled along with the movement of the movable side mold plate 82 without being lowered to the solidification temperature due to the temperature rise due to heat generation, and is elongated into a long thread shape. This causes a troublesome phenomenon called “stringing”. Further, the heat generated by the constricted portion may cause a syllabus streak and may cause an appearance defect of the molded product.

  Strict molding conditions are required to prevent the occurrence of such problems, and time and technology are required for the heater mounting position and temperature setting, and a great deal of labor is required for temperature control and temperature management.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to perform stringing or drawing without requiring special processing of the mold and without requiring particularly strict molding conditions. An object of the present invention is to provide a hot sprue bush and an injection mold that do not cause a phenomenon that causes defects in a molded product such as sylvathreak.

  In order to solve the above-mentioned problem, the invention described in claim 1 of the present invention is a hot sprue bush attached to an injection mold provided with cooling means, and the hot sprue bush is partially heated. And a part provided with a cooling part by the injection mold, and the sprue hole provided in the hot sprue bushing and serving as a passage for the molten resin extends in the flow direction of the molten resin over its entire length. The vertical cross-sectional area is the same and increases along the flow direction of the molten resin, and is formed by any one of a combination of the same portion and the increasing portion. To do.

  The invention described in claim 2 of the present invention is characterized in that, in claim 1, the heating means is located on the upstream side in the flow direction of the molten resin, and the cooling part is located on the downstream side. To do.

  Moreover, the invention described in claim 3 of the present invention is that, in any one of claims 1 and 2, a temperature sensor is attached to the hot sprue bush, and the temperature detected by the temperature sensor is adjusted. Based on this, the heating temperature by the heating means is controlled.

  The invention described in claim 4 of the present invention has the hot sprue bush according to any one of claims 1 to 3, and the sprue hole fills the cavity with a molten resin through a runner. An injection mold having a molten resin passage, wherein the runner has the same inner diameter as the sprue hole or a larger inner diameter than the sprue hole.

  The hot sprue bush of the present invention includes a heating part and a cooling part, and a sprue hole serving as a passage for the molten resin has a cross-sectional area perpendicular to the flowing direction of the molten resin along the flowing direction of the molten resin. It was formed by any one of a combination of the same part and an increasing part so as to be the same and to increase.

  As a result, there is no occurrence of shear heating when the molten resin flows in the sprue hole in the molding resin injection process, and the molding resin in the sprue hole in the mold opening process after the cooling process is the boundary between the heating and melting part and the cooling and solidifying part. In this case, the yarns are separated without causing a stringing phenomenon.

  In other words, it is possible to prevent the occurrence of sprue stringing at the time of mold opening by limiting the shape of the sprue hole without requiring special processing of the mold and without requiring special strict molding conditions. As a result, various problems caused by stringing can be avoided.

  Further, since the sprue hole does not have a constricted portion, the pressure loss is reduced. Accordingly, in the injection molding using the hot sprue bush of the present invention, the injection pressure can be reduced, and the range of combinations of injection molding condition settings can be increased. In addition, the molding cycle can be accelerated.

It is sectional drawing of embodiment which concerns on this invention. It is process explanatory drawing of embodiment which concerns on this invention. It is explanatory drawing about the temperature distribution of the principal part of an Example and a comparative example. It is process explanatory drawing of a comparative example. It is explanatory drawing of other embodiment. Similarly, it is explanatory drawing of other embodiment. It is explanatory drawing which concerns on the application example of this invention. It is explanatory drawing which concerns on a prior art example. Similarly, it is explanatory drawing which concerns on a prior art example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 7 (the same reference numerals are given to the same portions). The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. Unless stated to the effect, the present invention is not limited to these embodiments.

  1 is a cross-sectional view of an embodiment according to the present invention, FIG. 2 is an explanatory diagram of a process of the embodiment, FIG. 3 is an explanatory diagram of a temperature distribution of a main part of an example and a comparative example, and FIG. 5, FIG. 5 and FIG. 6 are explanatory views of other embodiments, and FIG. 7 is an explanatory view according to an application example of the present invention.

  The embodiment shown in FIG. 1 shows a state in which the hot sprue bush of the present invention is attached to an injection mold. The mold adopts a two-sheet mold (two-plate mold) divided into a fixed mold (cavity plate) 2 and a movable mold (core plate) 3 by a parting line 1.

  In addition, the code | symbol 4 shows a locating ring, hereafter, 5 is a fixed-side mounting plate, 6 is a cooling water channel, 7 is a runner, 10 is a hot sprue bush.

  The hot sprue bush 10 extends from the nozzle touch part 11 to which the injection nozzle (not shown) of the injection molding machine abuts, the nozzle touch part 11 to the runner 7, and the runner 7 of the molten resin injected from the injection nozzle. A sprue hole 12 serving as a flow path, a heater 13 which is disposed on the outer peripheral surface of the hot sprue bush 10 including the sprue hole 12 and heats the molding resin passing through the sprue hole 12, and a temperature for controlling the temperature of the heater 13 A temperature sensor 14 for detection is provided.

  The fixed-side template 2 is provided with a sprue bush fitting hole 15 for attaching the hot sprue bush 10. The inner surface of the sprue bush fitting hole 15 is in contact with the end 16 on the nozzle touch portion 11 side and the end 17 on the runner 7 side of the hot sprue bush 10 with the hot sprue bush 10 attached. The hot sprue bush 10 is supported on the stationary side template 2 by the contact portions.

  Therefore, a gap 18 is formed between the sprue bushing fitting hole 15 and the hot sprue bush 10 except for two contact portions with the hot sprue bush 10, and the heater 13 is formed in the gap 18. And the temperature sensor 14 is arrange | positioned.

  Moreover, the sprue hole 12 of the hot sprue bush 10 has the same cross-sectional area over the entire length from the nozzle touch part 11 to the runner 7.

  Next, an injection molding process using the mold having the hot sprue bush 10 having the above-described configuration will be described with reference to FIG. FIG. 2 shows a fixed side mold plate 2, a movable side mold plate 3 and a hot sprue bush 10 which constitute the main part of the present invention.

  First, in the mold clamping step (a), the fixed-side mold plate 2 and the movable-side mold plate 3 to which the hot sprue bush 10 is attached are clamped with a predetermined pressure across the parting line 1 and the hot sprue bush 10 The sprue hole 12 and the runner 7 are in communication. The hot sprue bush 10 is set to a predetermined heating temperature in advance by the heater 13 and the temperature sensor 14. At the same time, cooling water is circulated in advance in a cooling water passage (not shown) provided in the fixed-side mold plate 2 so that the fixed-side mold plate 2 is set to a predetermined cooling temperature and the movable-side mold plate 3 is also used. The cooling means (not shown) is activated in advance, and the movable side template 3 is also set to a predetermined cooling temperature. The inner diameter of the sprue hole 12 was φ6, and the inner diameter of the runner 7 was φ8.

  In the next injection step (b), the injection nozzle (not shown) of the molding machine comes into contact with the nozzle touch part (not shown) of the hot sprue bush 10 and the nozzle hole (not shown) and the sprue hole 12. Are connected, and the molten resin (molded resin) 30 injected from the injection nozzle flows through the sprue hole 12 of the hot sprue bush 10 and fills the cavity (not shown) via the runner 7 and the gate. . At this time, the heat from the heater 13 whose temperature is controlled based on the temperature detected by the temperature sensor 14 is conducted through the hot sprue bush 10 and moves to the molten resin 30 flowing through the sprue hole 12. It is maintained at a predetermined temperature.

  In the next cooling step (c), the end 17, the runner 7, the gate, and the cavity on the runner 7 side of the hot sprue bush 10 that are in contact with the fixed side mold plate 2 are fixed side mold plate 2 and movable side mold plate. 3 is cooled by the cooling means 3, the end portion 17 becomes a cooling portion of the hot sprue bush 10, and the portion of the hot sprue bush 10 that forms a gap 18 with the sprue bushing fitting hole 15 of the stationary side template 2 is a heater. The heated state is maintained by 13.

  Therefore, as shown in the embodiment of FIG. 3, the temperature distribution of the molding resin in the sprue hole 12 immediately before the mold opening process after the mold cooling for a predetermined time is as follows. 2 has a temperature gradient at the boundary between the region C of the end portion (cooling unit) 17 in contact with the region 2 and the region H of the heating unit where the gap 18 is formed by the hot sprue bush 10 and the fixed-side template 2. become. That is, the state of the molding resin is different across the boundary between the region C and the region H, the H region on the gap 18 side is in a heated and melted state, and the C region on the runner 7 side is in a cooled and solidified state.

  By the way, the temperature distribution of the comparative example of FIG. 3 shows the temperature distribution immediately before the mold opening process of the molding resin in the sprue hole having the narrowed portion in the above-described injection molding (known technique). The temperature distribution of the part is greatly different from that of the example. The cause of the difference in temperature distribution in the temperature gradient portion and the phenomenon resulting from the difference will be described in detail later.

  In the next mold opening step (d), when the movable side mold plate 3 is moved and separated from the fixed side mold plate 2, the molding resin in the sprue hole 12 is separated at the boundary between the heated and melted state and the cooled and solidified state. The sprue 31 cooled and solidified is held on the movable side mold plate 3 together with the molded product and separated from the fixed side mold plate 2.

  In the next mold release step (e), the molded product is removed from the movable side mold plate 3. The molded product at this time is formed in a state where the sprue 31, the runner 32, the gate, and the product are integrated.

  Here, the temperature distribution of the molding resin in the sprue hole 12 immediately before the mold opening process shown in FIG. 3 and the separation state of the molding resin in the sprue hole 12 in the mold opening process will be described. The temperature distribution of the comparative example of FIG. 3 is the temperature distribution immediately before the mold opening process after the cooling process in the injection molding using the conventional known hot sprue bush shown in FIG. 9, and the example is the hot spruce bush of the present invention. It is the temperature distribution just before the mold opening process in the injection molding using this. In the comparative example and the example, both the sprue hole 12 and the inner diameter of the runner 7 are the same as those in the example, and the comparative example is provided with a narrowed portion.

  As can be seen from FIG. 3, in the temperature distribution of the example and the comparative example, a remarkable difference is recognized in the temperature gradient at the boundary between the heated and melted portion of the molding resin in the sprue hole 12 and the cooled and solidified portion, In the example, the temperature distribution at the boundary between the heating and melting part of about 250 ° C. and the cooling and solidification part of about 120 ° C. changes at a substantially constant change rate, whereas in the comparative example, the heating and melting part of about 250 ° C. Shows a temperature distribution having a portion at about 280 ° C., which is higher than the temperature at 250 ° C. in the heating and melting portion, at the boundary portion between the portion and the cooling and solidification portion at about 120 ° C. Further, in the temperature distribution in the length direction of the sprue hole 84, for example, a position at 200 ° C. is a position farther from the parting line 1 than in the comparative example.

  This is because the sprue hole 12 of the hot sprue bush 10 of the embodiment has a cross-sectional area perpendicular to the flow direction of the molten resin over the entire length from the nozzle touch part 11 where the injection nozzle of the molding machine abuts to the runner of the mold. The temperature distribution after the cooling process of the molding resin in the sprue hole is formed only by heating by the heater and cooling by the fixed side template, whereas the hot sprue bush of the comparative example The 80 sprue holes 84 have a constricted portion 88 whose cross-sectional area decreases from the nozzle touch portion 89 along the flow direction of the molten resin, and the temperature distribution after the cooling process of the molded resin in the sprue hole 84 is the heater. This is probably because the molten resin is formed by an abnormally high temperature due to shear heat generation when passing through the constricted portion 88 together with the heating by 85 and the cooling by the fixed-side mold plate 81.

  That is, in the temperature distribution of the molding resin in the sprue hole 84 of the comparative example, the molten resin passes through the narrowed portion 88 of the sprue hole 84 at a temperature higher (about 280 ° C.) than the heating and melting portion (about 250 ° C.). This is due to shear heat generation.

  As a result, in the comparative example, in the mold opening process after the cooling process, as shown in FIGS. 4A and 4B, the temperature of the narrowed portion 88 of the molding resin in the sprue hole 84 does not fall down to the solidification temperature. In accordance with the movement of the movable side mold plate 81 when the mold is opened, the thread drawing 90 is generated in the separation part (a), and the thread drawing 90 remains in the spur 91 of the molded product after the mold release (FIG. 4B). (See figure). On the other hand, in the embodiment, in the mold opening process after the cooling process, the separation part of the molding resin in the sprue hole due to the movement of the movable side mold plate reaches the solidification temperature sufficiently because the temperature drop rate during the cooling process is fast. Thus, the stringing phenomenon does not occur in the separation part.

  In order to prevent stringing from occurring in the molded resin separation portion in the sprue hole in the mold opening process, the sprue hole has a portion with a small cross-sectional area along the flow direction of the molten resin as described above. It is a condition not to. Therefore, in addition to the case where the sprue hole has the same cross-sectional area over the entire length as in the present embodiment, the sprue hole 12 is crossed from the nozzle touch part to the middle as shown in FIG. The sprue hole 12 is formed so that the sprue hole 12 has a cross-sectional area that is the same as that of the sprue hole 12 as shown in FIG. Even when formed so as to gradually increase over the entire length from the portion 11 to the runner 7, it is possible to prevent stringing.

  That is, by not providing the sprue hole with a portion having a small cross-sectional area along the flow direction of the molten resin, it becomes possible to prevent the threading of the sprue during mold opening.

  Such thread pulling prevention at the time of mold opening can be achieved by applying the above-described hot sprue bushing configuration to the hot tip bushing attached to the runnerless mold also in the runnerless mold of FIG.

  In this case, the hot chip bushing 40 is provided with a heating means (heater) 41 and is cooled by a mold (fixed side mold plate) 43 provided with a cooling means (cooling water channel) 42 to which the hot chip bushing 40 is attached. A portion 44 is provided, and the molten resin passage 45 of the hot tip bushing 40 is formed in a shape that does not have a constricted portion, and is configured so that no shearing heat is generated when the molten resin flows.

  As described above, the hot sprue bushing of the present invention includes a heating part and a cooling part, and the sprue hole serving as a passage for the molten resin has a cross-sectional area perpendicular to the flow direction of the molten resin over the entire length. It was formed so as to be the same along the flow direction, or to increase, or to be a combination of the same part and the increasing part.

  In the above-described embodiment, the inner diameter of the sprue hole 12 is φ6, and the inner diameter of the runner 7 is φ8. However, when the inner diameter of the runner and the inner diameter of the sprue hole are the same φ8, In either case where the inner diameter of the runner was φ10 and the inner diameter of the sprue hole was φ6, it was possible to prevent stringing.

  As a result, there is no shear heating when the molten resin flows through the sprue hole in the injection process, and in the mold opening process after the cooling process, the molding resin in the sprue hole is drawn at the boundary between the heat melting part and the cooling solidification part. Separation without causing a phenomenon.

  In other words, it is possible to prevent the occurrence of sprue stringing at the time of mold opening by limiting the shape of the sprue hole without requiring special processing of the mold and without requiring special strict molding conditions. As a result, various problems caused by stringing can be avoided.

1 Parting line 2 Fixed side plate (cavity plate)
3 Movable side plate (core plate)
4 Locating Ring 5 Fixed Side Mounting Plate 6 Cooling Channel 7 Runner 10 Hot Sprue Bush 11 Nozzle Touch Part 12 Sprue Hole 13 Heater 14 Temperature Sensor 15 Sprue Bushing Fitting Hole 16 End 17 End (Cooling Part)
18 Gap 30 Molten resin (molded resin)
31 sprue 32 runner 40 hot tip bushing 41 heating means (heater)
42 Cooling means (cooling water channel)
43 Mold (fixed side template)
44 Cooling section 45 Passage

Claims (4)

A hot sprue bush attached to an injection mold provided with a cooling means,
The hot sprue bush is partly provided with heating means and partly provided with a cooling part by the injection mold,
The sprue hole provided in the hot sprue bush and serving as a passage of the molten resin has the same cross-sectional area along the flow direction of the molten resin over the entire length of the sprue hole perpendicular to the flow direction of the molten resin, and A hot sprue bush characterized by being formed by any one of a combination of the same part and an increasing part so as to increase.   The hot sprue bush according to claim 1, wherein the heating unit is located on the upstream side in the flow direction of the molten resin, and the cooling unit is located on the downstream side.   The temperature sensor is attached to the said hot sprue bush, The heating temperature by the said heating means is controlled based on the temperature detected by the said temperature sensor, Either 1 or 2 characterized by the above-mentioned. Hot sprue bush described in An injection mold having the hot sprue bush according to any one of claims 1 to 3, wherein the sprue hole has a molten resin passage through which a molten resin is filled into a cavity through a runner,
An injection mold, wherein the runner has an inner diameter that is the same as or larger than the sprue hole.

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