JP4230044B2 - Manufacturing method of plastic molded product and injection mold - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plastic molded product and an injection mold, and in particular, a method for manufacturing a plastic molded product that is long like a roof rail and has an enlarged cross-sectional shape in the middle in the length direction. About.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an injection molding method that is widely used as a molding method for plastic molded products is a molding having a long and abrupt enlarged change portion A having a cross-sectional shape in the middle in the length direction, such as a roof rail 40 shown in FIG. It is also used for goods. The enlarged change part A in the roof rail 40 is located between the mounting legs 41 and 41 and the intermediate part 42 at both ends of the roof rail 40, and the thickness j of the intermediate part 42 is larger than the thickness k of the mounting legs 41 and 41 at both ends. It is considered large. Reference numeral 43 denotes an intermediate leg. In the production of such a molded product, an injection mold 50 as shown in FIG. 5 is used, and molten resin P is injected and filled into the cavity 53 from the runner 51 through the gate 52, and the plastic molded product is cooled and cured. Demold. Reference numeral 54 denotes a lower cavity surface, 55 denotes an upper cavity surface, and 58 denotes a columnar portion for forming a roof rail mounting hole.
[0003]
By the way, in a normal general injection mold, the molten resin injected into the cavity from the gate flows while in contact with the cavity surface, fills the cavity, and becomes a molded product having a good surface. The injection molding die 50 for a molded product made of a long product as described above and whose cross-sectional shape expands in the middle in the length direction has the following problems.
[0004]
That is, in the injection mold 50, the gate 52 is provided at one end in the length direction of the cavity 53 so that the gate mark is not conspicuous in the molded product, and the enlarged change portion of the cavity cross section is located in front of the gate 53. A 'will be located. As a result, when the molten resin P injected from the gate 52 into the cavity 53 reaches the enlarged change portion A ′ of the cavity 53, the molten resin P that has been rectified by the substantially uniform cavity cross section in the vicinity of the gate 52 until then. The air flow begins to be extremely disturbed at the beginning of the flow, and an air pocket (air pool) 56 is formed near the upper cavity surface 55 of the enlarged change portion A ′ in the cavity 53, and the air left in the air pocket 56 is molded. Disperses on the surface of the product and causes defects such as flow marks and surface peeling on the molded product.
[0005]
In addition, the molten resin P traveling in the cavity 53 is cooled in contact with the cavity surface at the edge portion orthogonal to the flow direction M, and the solidification progresses faster, so the viscosity is higher than that in the central portion away from the cavity surface. It becomes difficult to flow. The difference between the solidification speed and the flow velocity in the vicinity of the cavity surface and in the central portion of the molten resin P increases as the distance from the gate 52 increases, and defects such as surface peeling are easily caused in the obtained molded product. Therefore, in the case of having the cavity 53 that is long in the forward direction of the gate 52, such as the mold 50 for the roof rail, there is a problem that the molded product is more likely to be defective.
[0006]
As a means for solving the above problem, as shown in the molding die 60 shown in FIG. 6, a protrusion 61 for restricting the flow of the injected molten resin P is erected on the lower mold cavity surface 64 near the cavity expansion changing portion B. Can be considered. The protrusion 61 causes the molten resin P injected from the gate 62 into the cavity 63 to flow while expanding and colliding with the protrusion 61 when passing through the cavity expansion changing portion B. Therefore, the resin P is sufficiently filled even in a portion where the cross section of the cavity 63 widens, so that it is possible to prevent the flow mark from being generated on the surface of the molded product molded by the upper cavity surface 65. become.
[0007]
However, in the case where the protrusion 61 is provided, as can be seen from FIG. 6, the molten resin P collides with the protrusion 61 and moves forward while being diverted to both sides and the upper side of the protrusion 61. Since the merging occurs again in front of the required amount with respect to the portion 61, an air pool is likely to occur near the surface 61a on the opposite side of the gate 62 of the projecting portion 61 at the time of merging. It may cause a new problem that the aesthetics deteriorate. In particular, in a molded product in which the back surface of the molded product is also a design surface, such as a roof rail, a decrease in the appearance of the back surface is unfavorable because it impairs the commercial value. Furthermore, since the concave portion by the protrusion 61 is formed on the rear surface of the molded product after demolding, there is also a problem that the appearance of the rear surface is impaired by the concave portion and the strength of the molded product is lowered.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and provides a method for producing a plastic molded product and an injection mold therefor in which a plastic molded product having a good appearance can be obtained without flow marks or surface peeling.
[0009]
[Means for Solving the Problems]
That is, the invention of the manufacturing method of the plastic molded product is that when the molten resin is injected from the gate into the cavity of the injection mold to manufacture the plastic molded product, the injection mold is placed at one end in the longitudinal direction of the cavity. A gate is formed, and the cavity is formed such that the thickness of the intermediate cavity between both ends is larger than the thickness of the end cavity located at the end in the length direction, and the cross-sectional shape is enlarged by the intermediate cavity. And a cross-sectional enlarged change part whose thickness is enlarged and changed in the middle of the transition from the end cavity to the intermediate cavity, and the gate is located between the start of injection and the middle of injection. projecting a projection for flow restriction from the cavity surface into a cavity in the cross section expansion change of the way from the end cavity to said intermediate section cavity The molten resin flow restriction is performed so that the molten resin flows while colliding with the protrusion, and then the molten resin flow restriction is released until the end of injection by retracting the flow restriction protrusion from the cavity. It is characterized by that.
[0010]
Further, the invention of the mold is an injection mold having a projection for restricting the flow of injection molten resin protruding from the cavity surface into the cavity, wherein a gate is formed at one end in the length direction of the cavity, The thickness of the intermediate cavity between both ends is formed larger than the thickness of the end cavity located at the end in the vertical direction, and the cross-sectional shape is increased at the intermediate cavity. A cross-section enlarged change portion whose thickness is enlarged and changed in the middle of the transition to the intermediate cavity, and the flow restricting protrusion is moved from the end cavity where the gate is located to the intermediate cavity in the middle It is characterized in that it is provided so as to protrude into and retract from the cavity of the transverse cross-section enlarged change portion.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic partial cross-sectional view showing immediately after the start of injection of an injection mold according to one embodiment of the present invention, FIG. 2 is a schematic partial cross-sectional view of the injection mold showing a retracted state of a protrusion during injection, and FIG. It is a general | schematic fragmentary top view of the lower mold | type concerning this Example.
[0012]
An injection mold 10 shown in FIGS. 1 and 2 is used to form a roof rail having the same shape as the molded article shown in FIG. 4, and includes a lower mold 11 and an upper mold 21, and includes a runner 13 and a gate. G and cavity C. The lower mold 11 has a lower cavity surface 12 of the cavity C, the upper mold 22 has an upper cavity surface 22 of the cavity C, and the cavity C is formed by the lower cavity surface 12 and the upper cavity surface 22 by a closed mold. Form.
[0013]
The gate G is for introducing the molten resin P into the cavity C at the time of injection molding. The gate G is located on one end side of the cavity C and passes through the cavity C and the runner 13. In the figure, reference numeral 18 denotes a columnar portion provided on the lower cavity surface 12 to form a roof rail mounting hole.
[0014]
The cavity C is a long shape having a shape corresponding to the roof rail, and the thickness (height) of the intermediate cavity C2 between both ends is higher than the thickness (height) of the end cavity C1 located at the end in the length direction (longitudinal direction) L. ) Is formed large, and the cross-sectional shape is large in the intermediate cavity C2.
[0015]
Further, as shown in FIG. 3, the flow restricting protrusion 30 of the injection molten resin P in the direction M in which the injection molten resin P proceeds from the gate G (the direction toward the end of the cavity C opposite to the gate G). Is provided so as to be able to advance and retreat from the lower cavity surface 12 of the cavity C toward the upper cavity surface 22 in a direction orthogonal to the cavity length direction L, whereby the protrusion 30 tip 30a protrudes and retracts with respect to the cavity C. Has been made possible. The protrusion 30 is protruded and retracted by the advance / retreat apparatus 31. The forward / backward device 31 of this example is composed of a hydraulic cylinder device provided upward on the lower die 11 and is connected to a control device (not shown) outside the molding die 10, and the protrusion 30 is placed on the upper die cavity surface 22 at a predetermined time. It is designed to move forward and backward.
[0016]
The protrusion 30 collides with the molten resin P injected into the cavity C and slows the forward speed of the molten resin P, and spreads the flow of the molten resin P in a direction perpendicular to the length direction of the cavity C. By providing the protrusion 30 so as to protrude from the lower cavity surface 12 through which the injection molten resin P flows, the flow of the molten resin can be reliably controlled.
[0017]
The width w1 of the protrusion 30 is not less than the diameter (width) d of the gate G and smaller than the width w2 of the cavity C where the protrusion 30 is located, and the protrusion 30 tip 30a and the upper cavity in the protruding state A gap e is left between the surfaces 22. The protrusion 30 of this embodiment is a flat plate, and the w1 is 15 mm, w2 is 30 mm, and d is 2.5 mm. Further, as shown in FIG. 2, when the protrusion 30 tip 30a is retracted to the lower mold cavity surface 12, the shape of the tip 30a of the protrusion 30 is the same as that of the cavity surface 12a around the protrusion 30 tip 30a. It is set as the shape which becomes one, and the recessed part by the protrusion 30 trace is not formed in the back surface of the molded product obtained. In addition, the protrusion 30 is not limited to this example, and may be a cylindrical shape (pin shape) or the like.
[0018]
Further, it is preferable that the position of the flow restricting projection 30 be located near a portion where the cross-sectional shape of the cavity C perpendicular to the length direction L of the cavity C changes and expands in front of the gate G. The enlarged change portion C3 is a position where the flow of the molten resin P injected from the gate G to the cavity C is disturbed, and is an efficient position for improving the flow of the molten resin P. In this example, it is located in the cross-sectional enlarged change portion C3 where the thickness changes during the transition from the end cavity C1 to the intermediate cavity C2. When the protrusion 30 for restricting the flow is provided in the inclined portion of the lower cavity surface 12 as in this example, the flow is more restricted if it protrudes perpendicularly to the lower inclined surface. Become effective.
[0019]
Next, a method for producing a plastic molded product of the present invention using the mold will be described with reference to the drawings. First, as shown in FIG. 1, the mold 10 is closed, and a molten resin P is injected into the cavity C from a gate G located at one end of the cavity C through an runner 13 from an injection device (not shown). At this time, the flow restricting projection 30 is projected into the cavity C in advance in the enlarged change portion C3, and the molten resin P injected into the cavity C flows when passing through the enlarged change portion C3 of the cavity. It is made to flow while colliding with the restricting protrusion 30.
[0020]
The molten resin P that has collided with the flow restricting protrusion 30 advances while spreading in a direction perpendicular to the length direction L of the cavity C, and is controlled so as to slow down the advance speed toward the other end of the cavity C. Therefore, when entering the intermediate cavity C2 having an enlarged cross-sectional shape from the end cavity C1 on the gate G side, it sufficiently expands into the cavity C and generates an air pocket near the upper cavity surface 22 above the enlarged change part C3. Can be prevented.
[0021]
Next, during the injection, as shown in FIG. 2, the flow restricting projection 30 is retracted by the operation of a control device (not shown), retracted from the cavity C, and the flow of the molten resin P until the end of the injection. Release the regulation. As a result, air pockets can be prevented from being generated near the surface 30b on the side opposite to the gate G of the protrusion 30 in the protruding state, and a molded product having a good back surface is formed. Furthermore, since the protrusion tip 30a is flush with the lower cavity surface 12 when the flow restricting protrusion 30 is retracted, it is possible to prevent the recess of the protrusion 30 from being formed on the back surface of the molded product. . The time point when the flow restricting projection 30 is retracted is an appropriate time point before the end of injection, and is set according to the shape of the cavity, the total injection time, and the like. In this example, with respect to the total injection time of 7.5 seconds, the restricting protrusion 30 was retracted at a time point of 1.0 second from the start of injection to be flush with the lower cavity surface 12.
[0022]
After completion of the injection, the mold resin is opened after a predetermined time has elapsed and the molten resin in the cavity C is cooled and hardened, and the molded product is removed. The obtained molded article is excellent in aesthetics without any fear of peeling off the flow mark or the surface, having a good appearance on the back surface, and having no recess due to the flow restricting protrusion trace.
[0023]
【The invention's effect】
As illustrated and described above, according to the method of manufacturing a plastic molded product of the present invention, the flow restricting protrusion protrudes from the cavity surface into the cavity at the cross-sectional enlarged change portion from the start of injection to the middle of injection. The flow is regulated by causing the injection molten resin to collide with the protrusion, and then the resin flow restriction is released from the withdrawal of the flow restriction protrusion from the cavity until the end of the injection. The resin could be satisfactorily filled, and the problems caused by the flow restricting projection protruding into the cavity until the end of injection could be eliminated, and a plastic molded product having excellent appearance could be obtained.
[0024]
Further, according to the injection mold of the present invention, the flow restricting projection is provided so as to protrude into and retract from the cavity of the transverse cross section enlarged change portion. When the injection is performed, the flow restricting projection is protruded into the cavity from the start of injection to the middle of injection to restrict the flow of the molten resin, and then the flow restricting protrusion is retracted from the cavity until the end of injection to restrict the flow of the molten resin. The release can be performed, whereby a plastic molded article having a good appearance can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a schematic partial cross-sectional view showing immediately after the start of injection of an injection mold according to one embodiment of the present invention.
FIG. 2 is a schematic partial cross-sectional view of an injection mold showing a protruding part retracted state during injection.
FIG. 3 is a schematic partial plan view of a lower mold according to this embodiment.
FIG. 4 is a perspective view showing a general roof rail.
FIG. 5 is a schematic partial sectional view showing an embodiment of a conventional injection mold.
FIG. 6 is a schematic partial sectional view showing an injection mold as a premise of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Injection mold 11 Lower mold 12 Lower cavity surface 21 Upper mold 22 Upper cavity surface 30 Flow control protrusion 30a Flow control protrusion tip 40 Roof rail C Cavity C3 Cavity enlargement change part P Molten resin G Gate L Length direction

Claims (5)

When manufacturing a plastic molded product by injecting molten resin from the gate into the cavity of the injection mold,
The injection mold has the gate (G) formed at one end in the length direction (L) of the cavity (C),
In the cavity (C), the thickness of the intermediate cavity (C2) between both ends is larger than the thickness of the end cavity (C1) located at the end in the length direction (L), and the cross-sectional shape is The cross section enlarged change portion (C3) which is enlarged in the intermediate cavity (C2) and whose thickness is enlarged and changed during the transition from the end cavity (C1) to the intermediate cavity (C2). Have
During the period from the start of injection to the middle of injection, the flow control is performed in the cross sectional enlarged change portion (C3) in the middle from the end cavity (C1) where the gate (G) is located to the intermediate cavity (C2). The protrusion (30) is protruded from the cavity surface into the cavity, and the flow of the molten resin is regulated so as to flow while the molten resin collides with the protrusion (30).
Next, the flow restriction of molten resin is released until the end of injection by retracting the flow restricting projection (30) from the cavity, and the method for producing a plastic molded product is characterized in that:   The method for producing a plastic molded product according to claim 1, wherein the flow restricting projection (30) is projected from the lower cavity surface (12) of the cavity.   The method for producing a plastic molded product according to claim 1 or 2, wherein the tip of the protrusion is flush with the cavity surface when the flow restricting protrusion (30) is retracted. In an injection mold having a protrusion for restricting the flow of injection molten resin protruding from the cavity surface into the cavity,
A gate (G) is formed at one end in the longitudinal direction of the cavity (C),
In the cavity (C), the thickness of the intermediate cavity (C2) between both ends is larger than the thickness of the end cavity (C1) located at the end in the length direction (L), and the cross-sectional shape is The cross section enlarged change portion (C3) which is enlarged in the intermediate cavity (C2) and whose thickness is enlarged and changed during the transition from the end cavity (C1) to the intermediate cavity (C2). Have
The flow restricting protrusion (30) is moved into the cavity of the cross-sectional enlarged change portion (C3) on the way from the end cavity (C1) where the gate (G) is located to the intermediate cavity (C2) . An injection mold characterized by being provided so as to be retractable from a protrusion and a cavity.   The injection mold according to claim 4, wherein the flow restricting projection (30) protrudes from the lower cavity surface (12) of the cavity.

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