JP2007261186A - Injection molding method for resin molding product and injection mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent surface sink from occurring at a surface sink occurrence portion such as a thick-walled part of a resin molding product by pressing a melt resin in a cavity even at the dwell completion stage. <P>SOLUTION: A molten resin R is injected and filled in the cavity 6 of an injection molding die 1. A tubular pin 13 and an insertion pin 17 movably inserted in the tubular pin 13 are advanced and operated toward a recessed part 5b formed on a molding surface 5a of a second type 5 so as to respond to the back surface of the vicinity of the surface sink occurrence portion of an instrument panel to press the molten resin R. At the dwell completion stage when a resin solidified layer R1 is formed at the portion contacting to the molding surfaces 3a, 5a of the injection molding die 1, only the insertion pin 17 is further advanced and operated to burst through the resin solidified layer R1 with the insertion pin 17, and press the molten resin R in the inside of the resin solidified layer R1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of an injection molding method and injection mold of a resin molded product, and specifically relates to measures for preventing sink marks.

In general, when a resin molded product is injection-molded, a molten resin injected and filled in a cavity is held to compensate for volume shrinkage due to cooling and solidification. Even if the pressure is maintained in this manner, if the resin molded product has a thick portion, the surface of the resin molded product corresponding to the thick portion may have a sink due to a difference in thermal contraction with the surrounding area. The concave portion is formed on the molding surface of the injection mold so as to correspond to the back surface in the vicinity of the thick wall portion of the resin molded product, and the molten resin is injected and filled into the cavity of the injection mold, and then the above-mentioned at the pressure holding stage. By moving the pin into the recess, the molten resin in the cavity is pressed with the pin to flow in the vicinity of the thick part, and the resin molding corresponding to the thick part is compensated for the volume decrease due to the progress of cooling and solidification. It prevents the sink marks on the surface of the product.
JP-A-9-104035 (paragraph 0014 column, FIGS. 1 and 2)

  However, even if the pin is advanced into the recess in the vicinity of the thick portion as in Patent Document 1, the molten resin is solidified thereafter, which is not sufficient as a measure for preventing the sink. Therefore, it is conceivable to advance the pin at the end of the pressure holding, but the molten resin in the cavity is cooled and solidified at an earlier stage due to the mold temperature than the inside, in contact with the molding surface of the mold. At the end of pressure holding, a hard resin solidified layer stands at the tip of the pin, and the pin cannot press the molten resin inside to flow near the thick part. Sinking occurs on the surface of the resin molding.

  The present invention has been made in view of such a point, and the object of the invention is to press the molten resin in the cavity even at the end of the pressure holding and cause sink marks at the sink generation site such as the thick part of the resin molded product. It is to ensure that it does not occur.

  In order to achieve the above object, the present invention is characterized in that the pin for pressing the molten resin has an inner and outer double structure, and the advance timing of each pin is set appropriately.

  Specifically, the present invention is directed to an injection molding method for a resin molded product and an injection mold, and the following solution is taken.

  That is, the invention according to claim 1 relates to the former injection molding method, in which a molten resin is injected and filled into a cavity of an injection mold, and then movable into the tubular pin and the tubular pin. In the initial stage of pressure holding, the inserted insertion pin is operated to advance toward the concave portion formed on the molding surface of the injection mold so as to correspond to the back surface in the vicinity of the sink portion of the resin molded product. Press the molten resin, and then, at the pressure holding end stage where the resin solidified layer is formed at the part in contact with the molding surface of the mold, only the insertion pin is further advanced to solidify the resin with the insertion pin. It is characterized in that the molten resin inside the resin solidified layer is pressed through the layer.

  The invention described in claims 2 and 3 relates to the latter injection mold, and among them, the invention described in claim 2 includes a first mold for molding a resin molded product surface, and the first mold. And a second mold that molds the back surface of the resin molded product. The concave surface is formed on the molding surface of the second mold so as to correspond to the back surface in the vicinity of the sinking portion of the resin molded product. On the back side, a tubular pin and an insertion pin movably inserted in the tubular pin are disposed so as to be able to move forward and backward. Both the tubular pin and the insertion pin are attached by an urging means at the initial stage of pressure holding. At the end of the pressure-holding stage when the resin-solidified layer is formed at the portion in contact with the molding surface of the mold, the operating means is operated to advance toward the concave portion and press the molten resin in the cavity. The resin solidified layer at the part that contacts the molding surface of the second mold by further advancing operation Break through, characterized in that it is configured to press the molten resin inside the resin solidified layer.

  The invention described in claim 3 is characterized in that, in the invention described in claim 2, the tip of the insertion pin is formed with a sharp tip.

  According to the first aspect of the present invention, the molten resin is pressed by the advancing operation of the tubular pin and the insertion pin to compensate for the volume decrease due to the progress of the cooling and solidification in the initial stage of pressure holding, and in the subsequent pressure holding end stage. As the insertion pin moves forward, it breaks through the resin solidified layer at the part in contact with the molding surface of the mold and presses the internal molten resin to compensate for the volume decrease due to the progress of cooling and solidification at the end of pressure holding. It is possible to prevent the occurrence of sink marks at the sink generation site of the resin molded product.

  According to the second aspect of the present invention, it is possible to reliably prevent the occurrence of sink marks at the sink generation site of the resin molded product with a simple mold structure in which the pin has a double inner / outer structure.

  According to the invention which concerns on Claim 3, a resin solidified layer can be pierced reliably with a small operating force.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 6 shows a vehicle instrument panel P as a resin molded product. A front defroster air outlet p1 extending in the vehicle width direction is formed at the vehicle body front end side of the instrument panel P, and a side defroster air outlet p2 is formed at both ends in the vehicle width direction. As shown in an enlarged view in FIG. 7, a rib p3 is integrally projected on the back surface side of the opening peripheral edge of each side defroster air outlet p2, and has a hole p4 on the back surface in the vicinity of the rib p3. Two circular fillet portions p5 are integrally projected. In addition, two component mounting bosses p6 are integrally protruded with a gap in the middle of the vehicle panel in the vehicle rear end side on the back surface of the instrument panel P, and a hole is formed on the back surface in the vicinity of the boss p6. Two circular fillet portions p5 having p4 are integrally projected. Since the rib p3 and the boss p6 are formed thicker than the general portion, there is a large difference in thermal shrinkage between the molten resin and the general portion, and if no measures are taken, the instrument corresponding to the rib p3 and the boss p6 Sinking occurs on the surface of panel P.

  The instrument panel P is injection molded by an injection mold 1 as shown in FIGS. The injection mold 1 is a first mold 3 that is a fixed mold that molds the surface of the instrument panel P, and a second mold that is a movable mold that is arranged opposite to the first mold 3 and molds the back surface of the instrument panel P. 5 and a cavity 6 is formed between the molding surface 3a of the first mold 3 and the molding surface 5a of the second mold 5 when the injection mold 1 is closed. On the molding surface 5a of the second mold 5, a recess 5b is formed so as to correspond to the back surface in the vicinity of the rib p3 and the boss p6 in the vicinity of the sink generation portion of the instrument panel P. A pin insertion hole 7 comprising a small diameter hole 7a and a large diameter hole 7b is formed through the bottom surface of the recess 5b, and an air slider 9 as an operating means having a rod 9a at the outer end of the large diameter hole 7b. Is attached to be able to advance and retreat, and a bush 11 is inserted into the large-diameter hole 7b.

  A tubular pin 13 having an insertion hole 13a is inserted into the small-diameter hole portion 7a so as to be able to advance and retreat, and is arranged on the back side of the concave portion 5b. A flange 13b and a protrusion 13c are integrally formed at the proximal end of the tubular pin 13. Projected. A first spring 15 as an urging means is mounted between the flange 13b and the bush 11, and the tubular pin 13 is constantly urged in the direction approaching the recess 5b by the spring force of the first spring 15. The flange 13b is brought into contact with the step 7c at the boundary between the small-diameter hole 7a and the large-diameter hole 7b of the pin insertion hole 7 so that the tip is at the bottom surface level of the recess 5b. Is positioned. An elastic body such as rubber may be used instead of the first spring 15.

  In the tubular pin 13, an insertion pin 17 having a sharp tip 17a formed at the tip is movably inserted, whereby the tubular pin 13 and the insertion pin 17 are connected to the back side of the recess 5b. Is arranged. The proximal end side of the insertion pin 17 is formed to have a slightly smaller diameter than the distal end side, and a step portion 17b is formed at the boundary between the two. On the other hand, the insertion hole 13a of the tubular pin 13 is also formed with a large diameter at the front end side and a small diameter at the base end side with the flange 13b as a boundary, and a step portion 13d is formed at the boundary between the two, and the step portion 17b of the insertion pin 17 is formed. By engaging with the step portion 13 d of the tubular pin 13, the insertion pin 17 is prevented from dropping from the insertion hole 13 a of the tubular pin 13. A male screw portion 17c is formed at the base end of the insertion pin 17, and a nut 19 is screwed into the male screw portion 17c so that the spring seat 21 inserted at the base end of the insertion pin 17 does not fall off. ing. Between the spring receiving seat 21 and the flange 13b of the tubular pin 13, a second spring 23 as an urging means is shrunk so as to surround the protrusion 13c, and the insertion pin 17 is connected to the second spring. The stepped portion 17b is pressed and engaged with the stepped portion 13d of the tubular pin 13 by being constantly urged in the direction away from the recessed portion 5b by the spring force of 23, and the tapered portion 17a protrudes from the distal end of the tubular pin 13 to face the recessed portion 5b. Not.

  The spring force of the first spring 15 is stronger than the spring force of the second spring 23. For example, when the injection pressure of the molten resin R is 40 to 50 MPa and the holding pressure is 20 MPa, the spring force of the first spring 15 is The spring force of the second spring 23 is set to 20 MPa in the compressed state.

  The tubular pin 13 and the insertion pin 17 are both urged by the spring force of the first spring 15 to advance toward the concave portion 5b and press the molten resin R in the cavity 6 at the initial stage of pressure holding. (See FIG. 3), the insertion pin 17 is moved by the advancing operation of the air slider 9 at the pressure-holding end stage where the resin solidified layer R1 is formed at the portion in contact with the molding surfaces 3a and 5a of the injection mold 1. It is configured to be further advanced by being struck to protrude into the concave portion 5b, pierce the resin solidified layer R1 in a portion in contact with the molding surface 5a of the second mold 5 and press the molten resin R inside the resin solidified layer R1. Has been.

  Next, the procedure for molding the instrument panel P by the injection mold 1 configured as described above will be described. In addition, the number attached | subjected in the parenthesis below shows the order of a shaping | molding process.

  (1) As shown in FIG. 1, the second mold 5 is moved closer to the first mold 3 to close the injection mold 1. In this mold closed state, the tubular pin 13 is moved forward toward the recess 5b side of the second mold 5 by the spring force of the first spring 15, and the tip is positioned at the bottom surface level of the recess 5b. The insertion pin 17 presses and engages the stepped portion 17b with the stepped portion 13d of the tubular pin 13 by the spring force of the second spring 23, and the tapered portion 17a protrudes from the distal end of the tubular pin 13 and faces the recessed portion 5b. .

  (2) As shown in FIG. 2, the molten resin R is injected and filled from the gate (not shown) into the cavity 6 of the injection mold 1 in the above-mentioned mold closed state. In this example, since the injection pressure of the molten resin R is slightly higher than the spring force of the first spring 15, the tubular pin 13 and the insertion pin 17 are both moved backward by the injection pressure of the molten resin R.

  (3) As shown in FIG. 3, since the spring force of the first spring 15 is superior to the holding pressure at the initial stage of holding pressure, both the tubular pin 13 and the insertion pin 17 are recessed portions of the second mold 5. Advances toward 5b. In this example, the flange 13b of the tubular pin 13 is slightly separated from the step 7c of the pin insertion hole 7 due to the balance between the spring force and the holding pressure of the first spring 15, and the tip of the tubular pin 13 is at the bottom level of the recess 5b. Is slightly lower than. The molten resin R is pressed by the advancing operation of the tubular pin 13 and the insertion pin 17 to compensate for the volume decrease due to the progress of cooling and solidification in the initial stage of pressure holding. The molten resin R in the cavity 6 is cooled and solidified at an early stage due to the influence of the mold temperature from the inside of the first mold 3 and the second mold 5 in contact with the molding surfaces 3a and 5a, and the resin solidified layer R1 on the outside. Is formed, but the inside is in a molten state although solidification proceeds.

  (4) As shown in FIG. 4, at the pressure holding end stage, the solidification of the molten resin R progresses further, the cross-sectional area of the molten resin R portion becomes smaller, and the pressure holding from the gate goes to the whole. It will not reach. At this stage, the air slider 9 is moved forward to advance the rod 9a. As a result, the base end of the insertion pin 17 is hit by the rod 9a, and only the insertion pin 17 is further advanced against the spring force of the second spring 23 to protrude into the recess 5b. The tapered portion 17a breaks through the resin solidified layer R1 at the portion in contact with the molding surface 5a of the mold 5, and the tapered portion 17a enters the molten resin R. The advance operation of the insertion pin 17 presses the molten resin R inside the resin solidified layer R1, and compensates for the volume decrease due to the progress of cooling and solidification at the pressure holding end stage.

  (5) In this state, as shown in FIG. 5, the instrument panel P is obtained after the molten resin R is completely cooled and solidified. In the vicinity of the rib p3 and the boss p6 on the back surface of the instrument panel P, as shown in FIG. 7, a solid portion p5 solidified in the concave portion 5b is formed. A hole portion p4 is formed by the tip portion of 17. Thereafter, the air slider 9 is retracted to retract the rod 9a, the second mold 5 is retracted to open the injection mold 1 and the instrument panel P is removed from the second mold 5 with an ejector pin (not shown). Type. Thereby, the tubular pin 13 and the insertion pin 17 are returned to the state of FIG. 1 by the spring force of the first spring 15 and the second spring 23.

  As described above, in this embodiment, the molten resin R is pressed by the advancing operation of the tubular pin 13 and the insertion pin 17 to compensate for the volume decrease due to the progress of cooling and solidification in the initial stage of pressure holding, and the subsequent pressure holding. At the end stage, the insertion pin 17 protrudes into the recess 5b, so that the resin solidified layer R1 at the portion in contact with the molding surface 5a of the second mold 5 is pierced to press the internal molten resin R, and the pressure holding end stage is reached. Since the volume decrease due to the progress of cooling and solidification is compensated, it is possible to prevent the occurrence of sink marks on the surface of the instrument panel P corresponding to the ribs p3 and the bosses p6 that are the sink generation sites of the instrument panel P.

  Moreover, in this embodiment, it is possible to reliably prevent the surface sink of the instrument panel P corresponding to the ribs p3 and the bosses p6 with a simple mold structure in which the pins have a double structure inside and outside.

  Furthermore, in this embodiment, the resin solidified layer R1 can be pierced reliably with a small operating force by the tapered portion 17a formed at the tip of the insertion pin 17.

  It should be noted that the tubular pin 13 may be protruded into the recess 5b together with the insertion pin 17 at the initial stage of pressure retention in the above embodiment, and the insertion pin 17 is not provided in the cavity 6 at the stage of completion of pressure retention. You may make it project so that it may reach.

  The present invention is useful as a method for preventing sink marks in an injection molding method of a resin molded product and an injection mold.

It is sectional drawing which shows the injection mold in a mold closed state. It is sectional drawing which shows the injection mold in the state which injected and filled the molten resin in the cavity, and retracted both the tubular pin and the insertion pin with the injection pressure. It is sectional drawing which shows the injection mold of the state which operated the tubular pin and the insertion pin toward the recessed part, and pressed the molten resin in the pressure-holding initial stage. At the end of the pressure holding state, only the insertion pin is further advanced to project into the recess, and the resin solidified layer at the part in contact with the molding surface of the second mold is pierced to press the molten resin inside the resin solidified layer. It is sectional drawing which shows an injection mold. It is sectional drawing which shows the injection mold in the state by which the molten resin completely solidified in the cavity and the instrument panel was injection-molded. It is a perspective view of an instrument panel. It is the expansion perspective view which looked at the waste part around the side defroster air blower outlet from the back side of the instrument panel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection mold 3 1st type | mold 3a, 5a Molding surface 5 2nd type | mold 5b Recess 6 Cavity 9 Air slider (operation means)
13 Tubular pin 15 First spring (biasing means)
17 Insertion Pin 17a Tapered Part P Instrument Panel (Resin Molded Product)
R Molten resin R1 Resin solidified layer

Claims (3)

Injecting and filling molten resin into the cavity of the injection mold,
Next, the injection mold is molded so that the tubular pin and the insertion pin that is movably inserted in the tubular pin correspond to the back surface in the vicinity of the sinking portion of the resin molded product at the initial stage of pressure holding. Press the molten resin to advance toward the recess formed on the surface,
Thereafter, at the pressure holding end stage where the resin solidified layer is formed at the part in contact with the molding surface of the mold, only the insertion pin is further advanced to break through the resin solidified layer with the insertion pin. A method for injection molding a resin molded product, comprising pressing a molten resin inside the layer. A first mold that molds the surface of the resin molded product, and a second mold that is arranged opposite to the first mold and molds the back surface of the resin molded product,
A concave portion is formed on the molding surface of the second mold so as to correspond to the back surface in the vicinity of the sinking portion of the resin molded product,
On the back side of the recess, a tubular pin and an insertion pin that is movably inserted into the tubular pin are arranged so as to be movable forward and backward.
Both the tubular pin and the insertion pin are energized by the energizing means in the initial stage of pressure holding and advance toward the recess to press the molten resin in the cavity,
In the stage where the resin solidified layer is formed at the part in contact with the molding surface of the mold, the insertion pin is further advanced by the operating means to break through the resin solidified layer at the part in contact with the molding surface of the second mold. An injection mold for a resin molded product, wherein the molten resin inside the resin solidified layer is pressed. In the injection mold of the resin molded product according to claim 2,
An injection mold for a resin-molded product, characterized in that a tapered portion with a sharp tip is formed at the tip of the insertion pin.

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