JP5370823B2 - Injection foam molding method - Google Patents

Description

The present invention relates to an injection foam molding method for an injection molded product, and in particular, a mold having a plurality of cavities with different product shapes is used to sequentially inject and fill foamable molten resin with a time difference in one injection unit. The foamable molten resin filled by opening the mold is expanded and expanded, or the foamable molten resin filled by not opening the mold is expanded and expanded. The present invention relates to an injection foam molding method for simultaneously molding a plurality of foamed products or a plurality of foamed products and an unfoamed product.

  After injecting and filling molten resin into one of the cavities of a closed mold using a mold having a plurality of cavities, the molten resin is injected and filled into other cavities with a time difference. An injection molding method is disclosed in which the filling of the molten resin into all the cavities is completed, and after the molten resin injected and filled into all the cavities is cooled, the mold is opened and the molded product is taken out. This injection molding method has an effect that a product can be obtained with high productivity using a small injection molding apparatus having a small clamping force. (See Patent Document 1)

  In addition, injection filling and pressure holding processes in each cavity are performed under predetermined injection conditions determined for each cavity, and when injection filling and pressure holding processes in one of the cavities are completed, injection filling to another cavity is performed. An injection molding method is disclosed in which the resin flow at the screw retreating and communicating with each cavity and the resin pressure at the screw tip are released, and the screw stop position after the release is corrected to be the next injection start position. ing. This injection molding method has an effect of stabilizing the filling amount for each cavity and stabilizing the weight and dimensions of the molded product. (See Patent Document 2)

By the way, when a mold having a plurality of cavities is used by the above-described conventional injection molding method and injection foam molding is performed with a foamable molten resin, the screw retreats after injection filling into one cavity, and the resin flow path and screw. Since the resin pressure at the front end is released, the foaming gas is released from the foamable molten resin and defoamed, and a molded product having a predetermined expansion ratio cannot be obtained. In particular, the defoaming was more apparent in the cavity with the rearward injection order, causing foaming magnification, product weight, and shape defects.
And since the conventional injection molding method has a configuration in which a molten resin filling all the cavities is provided in advance at the screw tip and a predetermined required amount is injected for each cavity, the molten resin filled in each cavity is used. Since there is a temperature difference, and the molten resin that fills the cavities in the latter order of filling has a long heat history time, it is difficult to obtain a molded product in which each cavity has a predetermined expansion ratio. It was.

JP-A-1-125212 JP 2004-155071 A

  The present invention has been made in order to solve the above-described problems. A mold having a plurality of cavities having different product shapes is sequentially injected and filled with a foamable molten resin by providing a time difference with one injection unit. The foamable molten resin filled by opening the mold is expanded and expanded, or the foamable molten resin filled by not opening the mold is not foamed. It is an object of the present invention to provide an injection foam molding method capable of simultaneously molding a plurality of foamed products having a predetermined foaming ratio, product weight and shape, or a plurality of foamed products and an unfoamed product.

In order to achieve the above object, the injection foam molding method of the present invention uses a mold having a plurality of cavities with different product shapes to transfer a foamable molten resin containing a foamable gas from one injection unit to different cavities with a time difference. In the injection foam molding method of injecting and filling the foamable molten resin that is sequentially injected and filled, each cavity has an independently driven resin flow path switching means. First, the amount of resin corresponding to the first product cavity volume The foamable molten resin is injected and filled into the first product cavity on the basis of the first injection filling pattern set in advance, and after completion of the injection filling, the resin flow path is closed and the foamable molten resin in the injection unit is filled . with foaming expanding the foamable molten resin filled by extending the retained die back pressure of the metering of the resin quantity corresponding pressure to the second mold cavity volume Subsequently weighed amount of resin corresponding to the second mold cavity volume, the foaming molten resin into the second product cavity based on the second injection filling pattern set predrilled resin flow path to the second molding cavity After injection filling, the resin channel switching means is operated, and the other cavities repeat measurement and injection filling.

In the injection foam molding method of the present invention, in the above-described invention, after the injection filling into the second product cavity, the mold is expanded to expand and expand the filled foamable molten resin. The mold is expanded to expand and expand the filled foamable molten resin. Further, in another injection foam molding method of the above-described invention , a filled foamable molten resin is formed by combining a pattern for expanding a mold after injection filling into the plurality of cavities and a pattern for not expanding the mold. Any product combination that is expanded or not expanded is obtained.

  According to the injection foam molding method of the present invention, when molding a plurality of foam molded articles using a mold having a plurality of cavities having different product shapes, the first product cavity for expanding the cavity after completion of injection filling is used. A foam molded product with excellent surface properties by the high pressure method (full shot method), and the second product cavity that does not expand the cavity after completion of injection filling, sinks into the warp and thick part by full shot of foamable molten resin A foam molded product without a foam or a foam molded product by a low pressure method by short shot of a foamable molten resin, or a non-foamed molded product by applying a holding pressure by full shot of a foamable molten resin It can be obtained by opening and closing operations.

The resin is supplied to each cavity by plasticizing the required amount after filling the previous cavity with the molten resin, then injecting and filling the cavity, and foaming of the foaming agent after completion of filling and during plasticization Therefore, the foaming agent does not foam during the molding operation, and all molded products have a predetermined foaming ratio, product weight, and shape.
In addition, because the molten resin into the second product cavity is selectively expanded after injection filling, the foam molded product has excellent surface properties by the high pressure method (full shot method) even in the second product cavity. Can be obtained at the same time.
In addition, even when an unfoamed molded product is obtained without being expanded after filling with the molten resin, the molten resin can be injected and filled into the cavity without defoaming of the foaming gas. Get.

It is sectional drawing of the metal mold | die and injection molding apparatus which show embodiment of this invention, and has shown the state by which the metal mold | die was closed. FIG. 2 shows an expanded state of the mold cavity of FIG. 1. It is a block diagram explaining the operation | movement process at the time of carrying out injection foam molding with the metal mold | die and molding machine of FIG. It is sectional drawing of the metal mold | die and injection molding apparatus which show other embodiment of this invention.

Embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, an injection molding apparatus 10 according to an embodiment of the present invention includes an injection apparatus having a barrel 11 and a screw 12 that is inserted in the barrel 11 so as to be rotatable and movable in the front-rear direction. The main part is composed of a mold clamping device (not shown) that allows the attached mold 20 to be opened and closed.
Then, the mold clamping device opens and stops with a predetermined size mold in order to expand the cavity after filling the mold 20 with the molten resin, and then the gap between the movable mold and the fixed mold even when an external force is applied. Is provided with a movable platen position holding means for maintaining a constant value.

The mold 20 includes a fixed mold 21 and a movable mold 22, and the first product cavity 24 and the second product cavity 25 are formed by closing the mold 20. The second product cavity 25 is set to have a predetermined volume when the movable mold 22 moves in the mold opening direction and the first product cavity 24 is expanded.
The fixed mold 21 is provided with a resin flow path 23 that communicates with the injection device and supplies molten resin to the first product cavity 24 and the second product cavity 25. The resin flow path 23 includes the first product cavity 24 and the second product cavity. A resin flow path switching means 30 for selectively supplying the molten resin to the cavity 25 is provided. The resin flow path 23 is configured by a hot runner.

The resin flow path switching means 30 includes hydraulic cylinders 31a and 31b, piston rods 32a and 32b, and gate valves 33a and 33b, and is driven and controlled by the control device 35.
When communicating the first product cavity 24, the second product cavity 25 and the resin flow path 23, the controller 35 supplies pressure oil to the rod side of the cylinders 31a, 31b and moves in the direction in which the piston rods 32a, 32b are retracted. When the first product cavity 24, the second product cavity 25, and the resin flow path 23 are shut off, the control means 35 supplies pressure oil to the head side of the cylinders 31a, 31b, and the piston rod 32a, This is done by moving 32b in the pushing direction.
By this operation, the gate valves 33a and 33b move to open and close the resin flow path 23, the first product cavity 24, and the second product cavity 25, and by opening one of the gates and closing the other gate, The resin can be selectively supplied to the cavity. FIG. 1 shows a state in which both gates are closed.

In FIG. 1, the first product cavity 24 and the second product cavity 25 have two cavities. However, the number of cavities provided in the mold is not limited to this, and the third and fourth cavities are not limited thereto. A configuration having a product cavity may also be used.
Further, the switching means 30 of the resin flow path 23 is configured to use a hydraulic cylinder as a driving means for the gate valves 33a and 33b, but is not limited to the hydraulic cylinder, and other driving means such as a pneumatic cylinder is used. May be.
To expand the mold in the means for solving the invention, as shown in the embodiment, the movable core or the slide core incorporated in the movable mold so as to be movable in the mold opening direction is moved in the mold opening direction so that the volume of the cavity is increased. Is expanded from the initial state.

FIG. 2 shows that the first product cavity 25 is fully shot with the legitimate molten resin, and the movable die 22 is retracted by a predetermined expansion stroke S after a predetermined time for forming the skin layer has elapsed. 25 shows a state in which the first product 27 is formed by expanding 25. Further, FIG. 2 shows a state in which the second product cavity is set to a predetermined volume, and the foamable molten resin is filled in the second product cavity 25 to mold the second product 28.
When molding the second product, the position of the movable mold 22 is controlled by the mold clamping device so as to maintain the gap S with the fixed mold 21.

Next, in the injection foam molding method of the embodiment of the present invention, the operation of the injection molding apparatus and the mold will be described with reference to FIG.
First, the movable mold 22 is moved in the direction of the fixed mold 21 and brought into contact therewith to perform mold clamping. The gate valve 33a of the first product cavity 24 and the gate valve 33b of the second product cavity 25 are kept closed.

Next, the gate valve 33a of the first product cavity 24 is opened, and the foamable molten resin is injected and filled into the first product cavity 24 in the injection 1 which is an injection process of the first product.
After the injection 1 is completed, the gate valve 33a is closed, and the mold 20 is held in a clamped state for a predetermined time when the skin layer of the first product is formed. In the injection apparatus, the molten resin in the barrel 11 after the filling is completed. Hold the back pressure at the time of weighing so as not to degas.
Thereafter, the mold clamping device is driven to retract the movable mold 22 by a predetermined stroke S to expand the first product cavity 24 and the second product cavity 25. In the first product cavity 24, the injection-filled molten resin starts to foam, and a first product 27 having a skin layer and foamed inside is obtained, and in this state, cooling is awaited. On the other hand, in the injection apparatus, the screw 12 is driven to plasticize and measure (a) the volume of molten resin to be injected and filled into the second product cavity.

Alternatively, a foamable molten resin having a volume equivalent to the cavity volume is filled, and in addition, a resin amount corresponding to the cooling solidification shrinkage amount of the molten resin is pressure-filled to obtain an unfoamed molded product.
Furthermore, after the injection filling of the foamable molten resin, after waiting for the formation of the skin layer, the mold clamping device is driven to move the movable mold 22 backward by a predetermined stroke S2, and the second product cavity 25 is expanded to foam. It may be inflated. In this case, similarly to the first product 27, a foam molded product having a skin layer and foamed inside is obtained.

  After completion of the metering (a), the gate valve 33b of the second product cavity 25 is opened, and a predetermined amount of foamable molten resin is injected into the second product cavity 25. At this time, the molding method and the properties of the molded product are changed by changing the amount of resin filled in the cavity. That is, when a resin having a volume smaller than the cavity volume is filled, the short shot method is used, and a foamed molded product that compensates the insufficient volume by foaming of the resin is obtained, and the shape of the molded product is rarely limited. On the other hand, when a molten resin having a volume equivalent to the cavity volume is filled, a high pressure method is used, and for example, a molded product with less warpage and deformation and with no shrinkage of the thick part can be obtained.

Next, after the completion of the injection 2, the gate valve 33b is closed and the mold is held in position for a predetermined cooling time. Further, in the injection apparatus, the molten resin in the barrel 11 after completion of filling is held at the back pressure pressure at the time of measurement so as not to degas. Then, the screw 12 is driven to plasticize and measure (b) a volume of molten resin to be injected and filled into the first product cavity to prepare for the next molding cycle.
When the required cooling time for the first molded product 27 and the second molded product 28 is completed, the movable mold 22 is moved in the mold opening direction, and the products 27 and 28 are taken out.
And in an injection process, it controls by predetermined predetermined speed and pressure.

  Another embodiment of the present invention will be described with reference to FIG. The embodiment shown in FIG. 4 is configured such that after the foamable molten resin is filled in the second product cavity, the molded product is obtained by expanding the cavity and foaming the molten resin in the same manner as the first product cavity described above. It is a thing.

As shown in FIG. 4, an injection molding apparatus according to another embodiment of the present invention includes an injection apparatus having a barrel 11 and a screw 12 that is inserted in the barrel 11 so as to be rotatable and movable in the front-rear direction, and a mold 40. And a mold clamping device (not shown) that allows the attached mold 40 to be opened and closed.
Then, after the mold is filled with the molten resin, the mold clamping device opens and stops with a predetermined dimension in order to expand the cavity, and even if an external force is applied, the gap between the movable mold and the fixed mold is kept constant. Position holding means for maintaining the movable platen position is provided.

The mold 40 includes a fixed mold 41 and a movable mold 42, and a first product cavity 44 and a second product cavity 45 are formed by closing the mold.
The fixed mold 41 is provided with a resin flow path 43 that communicates with the injection device and supplies molten resin to the first product cavity 44 and the second product cavity 45. The resin flow path 43 includes the first product cavity 44 and the second product cavity. A resin flow path switching means 50 for selectively supplying molten resin to the cavity 45 is provided. The resin flow path 43 is composed of a hot runner.

The mold 40 includes an expansion means 60 for the second product cavity 45 and a control device 65 for the expansion means 60.
The main part of the expansion means 60 is constituted by a hydraulic cylinder 61, a piston rod 62 and a slide core 63, and is driven and controlled by a control device 65.

The resin flow path switching means 50 includes hydraulic cylinders 51a and 51b, piston rods 52a and 52b, and gate valves 53a and 53b, and is driven and controlled by a control device (not shown).
When communicating the first product cavity 44, the second product cavity 45, and the resin flow path 43, the control means supplies pressure oil to the rod side of the cylinders 51a, 51b to move the piston rods 52a, 52b in the pulling direction. When the first product cavity 44, the second product cavity 45, and the resin flow path 43 are shut off, pressure oil is supplied from the control means to the head side of the cylinders 51a, 51b to move the piston rods 52a, 52b. This is done by moving in the extrusion direction.
By this operation, the gate valves 53a and 53b are moved to open and close the resin flow path 43, the first product cavity 44, and the second product cavity 45, and by opening one of the gates and closing the other gate, The resin can be selectively supplied to the cavity. FIG. 4 shows a state in which both gates are closed.

In FIG. 4, the first product cavity 44 and the second product cavity 45 have two cavities. However, the number of cavities provided in the mold is not limited to this, and the third and fourth cavities are not limited thereto. A configuration having a product cavity may also be used.
The switching means 50 of the resin flow path 43 is configured to use a hydraulic cylinder as the driving means for the gate valves 53a and 53b, but is not limited to the hydraulic cylinder, and other driving means such as a pneumatic cylinder is used. May be.

  Next, operation | movement of the expansion means 60 of the 2nd product cavity 45 is demonstrated. The expansion of the second product cavity 45 is performed after the molten resin is injected and filled into the cavity, similarly to the expansion of the first product cavity 44 described above. Since the expansion of the second product cavity 45 cannot be performed because the thickness of the first product changes when the mold 40 is opened, a configuration using a slide core is adopted.

After the molten resin is injected into the first product cavity to form the skin layer, when opening the movable mold, pressure oil is supplied from the control device 65 to the head side of the hydraulic cylinder 61 of the expansion means 60 and is slid by the piston rod 62. The core 63 is pressed against the fixed mold 41.
Even if the movable die 42 is moved backward in this state and a gap (extended stroke) S is provided between the movable die 42 and the fixed die 41, the volume of the second product cavity 45 can be maintained without change.

Next, molten resin is filled in the second product cavity 45 while the position of the movable mold 42 is maintained, and the formation of a skin layer is awaited. Thereafter, pressure oil is supplied from the controller 65 to the rod side of the hydraulic cylinder 61 of the expansion means 60. And the cavity is expanded by moving the slide core 63 by a predetermined amount in the direction of the movable mold 42 with the piston rod 62. By expanding the cavity, the resin in which the foaming agent is melted can be foamed, and a foamed molded product is obtained.
This method is a high pressure method, and the molded product has a good surface without a swirl mark.

The molding process in the mold shown in FIG. 4 is the same as the process described with reference to FIG. 3 except that a step of forming a skin layer and a step of expanding the cavity are added between the injection 2 of the molten resin into the second product cavity and the cooling step. (That is, the process of the second product and the process of the first product are the same in FIG. 3).
After the mold is opened and the product is taken out, the slide core 63 is moved in the mold closing direction after the next mold clamping process is completed and the movable mold and the fixed mold are in contact with each other. As a result, a second product cavity having a predetermined volume can be formed.
Further, if the control setting is made so that the slide core 63 shown in FIG. 4 is compressed in reverse, the molding operation is similar to the injection compression molding, and an unfoamed molded product with little deformation is obtained.

As described above, according to the injection foam molding method of the present invention, when a plurality of foam molded products are molded using a mold having a plurality of cavities with different product shapes, the cavity is expanded after completion of injection filling. In the first product cavity, the high pressure method (full shot method) is used, and in the second product cavity where the cavity is not expanded after the injection filling is completed, the foamable molten resin is fully shot, so there is no warping or sinking in the thick part. By performing a short shot of a foamed molded product or foamable oil resin, or by applying a holding pressure by performing a full shot, an injection foamed molded product having the characteristics of each molding method, or an injection foamed molded product A combination of normal injection molded products can be obtained by a single mold opening / closing operation.
In the first product cavity, a foam molded product having excellent surface properties can be obtained, and a foam molded product free from warping or sinking in a thick part or a foam molded product by a low pressure method can be obtained by full shot of a foamable molten resin.

After filling the previous cavity with molten resin, the required amount is plasticized and weighed, and then the cavity is injected and filled, and after filling and during plasticization, a back pressure is applied to suppress foaming of the foaming agent. Therefore, the foaming agent does not foam during the molding operation, and all molded articles have a predetermined foaming ratio, product weight, and shape.
In addition, since the molten resin into the second product cavity is configured to be selectively expandable after completion of injection filling, foaming with excellent surface properties by the high pressure method (full shot method) is also applied to the second product cavity. A molded product can be obtained simultaneously.

DESCRIPTION OF SYMBOLS 10 Injection molding apparatus 11 Barrel 12 Screw 20, 40 Mold 21, 41 Fixed mold 22, 42 Movable mold 23, 43 Resin flow path 24, 44 1st product cavity 25, 45 2nd product cavity 27 1st product 28 1st 2. Products 30 and 50 Resin channel switching means 33a and 33b Gate valves 53a and 53b Gate valve 35 Resin channel switching means controller 60 Cavity enlarging means 63 Slide core 65 Cavity enlarging means controller S Expansion stroke

Claims (3)

Using molds with multiple cavities of different product shapes, foamable molten resin containing foamable gas is sequentially injected and filled from one injection unit into different cavities with a time lag, and then the expanded foamable molten resin is expanded and expanded. In this injection foam molding method, each cavity has an independently driven resin flow path switching means, and first measures the amount of resin corresponding to the first product cavity volume and is based on a preset first injection filling pattern. The foamable molten resin is injected and filled into the first product cavity, and after the injection filling is completed , the resin flow path to the first product cavity is closed, and the pressure of the foamable molten resin in the injection unit corresponds to the volume of the second product cavity. It was filled by extending the retained die back pressure of the metering of the amount of resin foaming molten resin with foaming expansion, subsequently a second mold cavity Was weighed amount of resin corresponding to the product, a foamable molten resin into the second product cavity injected and filled on the basis of the second injection filling pattern set predrilled resin flow path to the second molding cavity, below An injection foam molding method in which the resin channel switching means is operated and the other cavities repeat weighing and injection filling. After the injection filling into the second product cavity, the mold is expanded to expand and expand the filled foamable molten resin, and the other cavities are also expanded after the injection filling to expand the filled foamable molten resin. The injection foam molding method according to claim 1, which is expanded. A pattern for expanding the mold after injecting and filling of the plurality of cavities, a combination of a pattern that does not extend the mold, foaming expansion filling foamable molten resin, or obtaining any product combination which does not foamed and expanded claimed Item 2. The injection foam molding method according to Item 1 .

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