JP2024018783A - Metal mold for injection molding and resin molding method - Google Patents

Abstract

To provide a metal mold for injection molding capable of molding even a thin wall molded article having a convex by suppressing a manufacturing cost of a metal mold, and suppressing degradation of a thin wall molded article.SOLUTION: A metal mold 10 for injection molding forms a resin molded article having a convex and a flat part by injecting molten resin into a cavity 13 formed between a core mold 12 and a cavity mold 14, where the cavity 13 comprises: a convex space part 13A which forms a convex; a flat space part 13B which forms a flat part around the convex; and a guide zone space part 13C which is formed for at least one of the convex space part 13A and the flat space part 13B, and has a wall thickness thicker than the convex space part 13A and the flat space part 13B, where the guide zone space part 13C comprises a convex-surrounding guide zone space part 13X which contacts a boundary part between the convex space part 13A and the flat space part 13B, and circulates the boundary part, and the cavity mold 14 is equipped with a gate 16 for injecting molten resin for the guide zone space part 13C.SELECTED DRAWING: Figure 1

Description

The present invention relates to an injection mold and a resin molding method.

Conventionally, vacuum forming technology has been known as a technology for molding various relatively thin resin molded products (hereinafter also simply referred to as "molded products"), such as egg cartons. Since vacuum forming technology uses a resin material that has been processed in advance into a sheet shape having a predetermined wall thickness, it is relatively easy to mold a thin molded product.

However, in the vacuum forming technique, it is necessary to process the resin material into a sheet shape in advance, and therefore, there is a problem that the resin material is limited to resin materials that can be obtained in a sheet-like state. In addition, since the sheet-shaped resin material is stretched over a frame, heated, and attached to a mold using vacuum suction to form the product, the bent parts of the molded product are stretched and become thinner and brittle, making it difficult to maintain the dimensional accuracy of the wall thickness. This is difficult, and there are problems such as the difficulty of making the wall thickness very thin for molded products with complex shapes that have many irregularities.

Injection molding technology is also well known as a technology for molding resin molded products. Injection molding technology is a mold formed inside an injection mold (hereinafter also simply referred to as a "mold"), which is made by melting a resin material and processing a metal block to provide a flow path for the molten resin. The space (hereinafter also referred to as "cavity") is injected and filled with molten resin, cooled and solidified, and then the separable mold members that make up the mold are separated to open the molding space (hereinafter referred to as "cavity"). , also referred to as "mold opening"), is a technique for molding a molded product by removing the molded product. For example, Patent Document 1 discloses a mold in which a gate (pinpoint gate) that is an entrance from a runner to a molding space is formed.

Compared to vacuum forming technology, injection molding technology does not cause stretching at bent parts, it is molded according to the shape of the mold cavity, has high dimensional accuracy, and does not cause the strength of the molded product to be compromised at bent parts. It has the advantage of not being In addition, injection molding technology, unlike vacuum molding technology, can be used with many types of resin materials, and even used resin materials such as polypropylene (PP) can be collected, remelted, and reused, making it more environmentally friendly. It also has the advantage of being able to suppress the load.

However, with injection molding technology, it is necessary to pour molten resin into every corner of the cavity to fill it, so the difficulty of molding often depends on the shape and dimensions of the molded product, especially those with relatively thin walls and dimensions. For molded products with a large surface area or complex shapes with a complex mixture of flat parts and uneven parts, there are many factors that prevent the smooth flow of molten resin. There is a problem in that it is relatively difficult to fill the resin to the end of the cavity without any gaps.

Further, in Patent Document 2, the present inventor has made a proposal that leads to solving the above-mentioned problems in injection molding technology. Patent Document 2 discloses a complex-shaped shock absorber that is molded using a mold and has a mixture of flat parts and convex parts.

According to the buffer technology disclosed in Patent Document 2, it has been shown that it is possible to form a relatively thin molded product having a thickness of about 0.4 mm. In the mold used for the buffer body of Patent Document 2, an induction band (a rib-shaped portion in the molded product) extending from the gate surrounds a cavity portion corresponding to the convex portion of the buffer body, and the induction band further extends from the gate. It is formed so as to branch out and climb up the portion corresponding to the convex portion. According to the proposal in Patent Document 2, compared to the case without such an induction band, the flow of molten resin in the portion corresponding to the convex part of the buffer body becomes smoother, the number of gates can be reduced accordingly, and the number of gates in the convex part can be reduced. It is said to have the effect of suppressing molding defects that occur.

Utility Model Publication No. 6-5929 JP2020-097433A

However, through subsequent prototyping experiments and research by the present inventor, it has been found that the effect of suppressing molding defects occurring in convex portions as described above can be obtained for specific shapes such as the shock absorber structure of Patent Document 2. Although this has been confirmed, it is not easy to determine the optimal positional relationship between the part corresponding to the convex part in the cavity and the guide band for general molded product shapes with thin walls and complex convex parts. It became clear.

Patent Document 2 does not disclose any method for reducing the flow path resistance of the cavity bending portion at the boundary between the flat part of a molded product having a convex portion and the convex portion, and therefore, the technique proposed in Patent Document 2 Even if the method is used, there still remains the problem that repeated trial and error is required to determine the appropriate mold shape including the arrangement of the guide band, resulting in high costs.

The present invention has been made by focusing on the above-mentioned problem, and even if the molded product is relatively thin and large in size, or the molded product has a complex shape with a complex mixture of flat parts and uneven parts, The purpose of the present invention is to provide a mold that can simplify the number and arrangement of gates, suppress mold manufacturing costs, and suppress deterioration in the quality of molded products, as well as molded products molded using such molds. do.

The injection mold according to aspect 1 of the present invention has a core mold and a cavity mold, and the core mold and the cavity mold are overlapped, and the injection mold is formed between the core mold and the cavity mold. An injection mold for molding a resin molded product having a convex part and a flat part by injecting molten resin into a cavity, the cavity having a convex space part in which the convex part is molded, and a convex part space part in which the convex part is molded; a planar space forming the planar part around the part; and an induction band formed in at least one of the protrusion space and the planar space and having a wall thickness greater than that of the protrusion space and the planar space. a space, the guide band space includes a guide band space that goes around the convex part in contact with a boundary between the convex space and the planar space, and the cavity type includes: A gate for injecting molten resin is provided in the guide zone space.

According to the above configuration, the molten resin injected from the gate into the guide zone space of the cavity has a flow path thicker than the convex space or the plane space, and therefore flows more easily than the convex space or the plane space. Through the guide band space having a space with low road resistance, the end of the guide band space that goes around the plane space and the convex space at a point away from the gate is quickly reached. In addition, since the end of the flow path with low flow resistance along the guide zone space is connected to the high flow path resistance part, after the molten resin is filled up to the end of the guide zone space, the flow path continues. Pressure is accumulated in the molten resin inside the induction zone space in accordance with the applied injection pressure.

As a result, the molten resin flows under relatively high pressure into the horizontally adjacent planar space and convex space along the guide band space, and spreads around the mold without the guide band space. Compared to the above, the filling property is better, and as a result, defects such as short circuits are less likely to occur, and high-quality thin-walled molded products can be molded.

In the above configuration, from the viewpoint of flow path resistance, the guide band space is mainly formed in a planar space where a relatively straight flow path can be secured, but depending on the dimensions and shape of the molded product, the guide band space may The space portion may be formed in the convex space portion, or may be formed in both the planar space portion and the convex space portion. Furthermore, from the viewpoint of efficiently arranging the guide band network starting from the gate, it is desirable to provide the gate for injecting the molten resin into the guide band space at the position of the guide band space formed in the planar space. Depending on the size and shape of the molded product, any number of guide strips can be provided at any position in the guide band space.

Further, according to the above configuration, the guide band space includes the convex part circumference guide band space part that is in contact with the convex part foot part and goes around the convex part foot part, so that the convex part circumference guide band space part is made of molten resin. The entire length of the guiding band space around the convex part plays the role of a film gate to the convex part space, and as a result, the flow of the molten resin from the plane space part to the convex part space is blocked and the flow path is blocked. This reduces the flow-inhibiting effect of the bending portion of the flow path at the base of the convex portion, which is a factor that increases resistance. Therefore, compared to a mold that does not have such a guide band space around the convex portion, defects such as short circuits in the convex portion are less likely to occur, and a thin-walled molded product of high quality can be molded. Note that it is desirable that the corners of the flow path bending portion have an R shape (roundness) on both the inner peripheral wall surface and the outer peripheral wall surface.

In the injection molding mold according to Aspect 2 of the present invention, in Aspect 1, residual gas remaining in at least one of the core mold and the cavity mold is discharged from the top of the convex space. Equipped with a residual gas exhaust section.

According to the above configuration, by including the convex part circumference guide band space part in which the guide band space part goes around in contact with the base part of the convex part, in addition to improving the filling property of the molten resin into the convex part space part, At least one of the core type and the cavity type is equipped with a residual gas discharge part that discharges residual gas from the top of the convex space, and thereby the residual gas staying near the top of the convex space is removed. Since the discharge part discharges the residual gas to the outside of the mold as appropriate, the residual gas concentrated near the top of the convex space is suppressed from being excessively compressed and becomes high pressure, which obstructs the flow of the molten resin. The filling properties of the molten resin into the parts are further improved.

In the present invention, the residual gas discharge part may have any structure or shape as long as it has a gas flow path that penetrates from the cavity to the outside of the mold through which the molten resin cannot pass and through which the residual gas can pass. However, for example, it may include a gas vent hole provided in at least one of the core mold and the cavity mold and reaching the top of the convex space from the outer surface of the mold, and a plug member detachably inserted into the gas vent hole. The plug member is a rod-shaped member in which the entire outer peripheral surface of at least the portion that contacts the top of the convex space is in close contact with the entire inner peripheral surface of the gas vent hole, and the outer peripheral surface of the closely-contacted portion of the rod-shaped member and the gas vent hole are in contact with each other. A gas flow path may be formed between the inner circumferential surface through which the molten resin cannot pass, but through which residual gas can pass.

In addition, in the present invention, when a gas vent hole is used as the residual gas exhaust section, a vacuum device is connected to the outlet of the gas vent hole, and the residual gas discharged from the gas vent hole is sucked by the vacuum device. Evacuation of residual gas from the top of the space may be facilitated.

As aspect 3 of the present invention, a resin molding method may be configured in which a resin molded article is molded using the injection mold described in aspect 1 above. As described in Aspect 1, the resin molding method having the above configuration can provide a high-quality resin molded product in which deterioration in quality due to distortion, insufficient filling, discoloration, etc. in the molded product is suppressed.

According to the present invention, even in a thin-walled molded product having a convex portion, the degree to which the flow of molten resin in the cavity is inhibited due to the convex portion is alleviated, thereby reducing the injection pressure of the molten resin. It becomes possible to obtain good cavity filling properties even when the molded product is molded, and furthermore, by this low-pressure molding, it becomes possible to reduce pressure distortion or burrs remaining inside the molded product.

In addition, by providing leeway in the molding conditions in this way, it is possible to reduce the number of mold prototypes required to ensure sufficient filling properties, suppress mold manufacturing costs, and even with thin-walled molded products. It is possible to provide a mold and a molded product that can be molded while suppressing quality deterioration.

FIG. 3 is a cross-sectional view illustrating the injection molding die according to the present embodiment, with the cross section taken along the line AA' in FIG. 2 turned upside down. FIG. 2 is a bottom view illustrating the cavity mold of the injection mold according to the present embodiment, viewed from the side where the cavity is formed. It is a perspective view explaining other examples of a plug member.

Embodiments of the present invention will be described below. In the description of the drawings below, the same or similar parts are denoted by the same or similar symbols. However, the drawings are schematic, and the relationship between the thickness and planar dimensions, the ratio of the thickness of each device and each member, etc. differ from the reality. Therefore, the specific thickness and dimensions should be determined with reference to the following explanation. Furthermore, the drawings include portions that differ in dimensional relationships and ratios.

<Thin-wall molding technology>
Before explaining the configuration of the injection mold according to this embodiment, first, the thin-wall molding technique will be explained.

In the following description of the present invention, the term "cavity mold" refers to a mold in which the molding space inside the mold is filled with molten resin, and the molded product can be removed from the cavity after it has cooled and solidified. is mainly divided into two parts. Of these mold parts, the one that is connected to the molten resin injection nozzle of the injection molding machine and has a gate that is the outlet for discharging the molten resin into the cavity. Means mold parts.

Furthermore, the term "core mold" refers to the mold part that is opposed to the "cavity mold" among the two divided mold parts.

In addition, "flow path resistance" refers to physical factors such as the viscosity of the molten resin injected into the cavity as a fluid, and physical factors such as the distance, wall thickness, bending, width change, etc. along the flow of the molten resin in the cavity. It refers to the acting force that obstructs the flow of molten resin due to shape factors.

Moreover, "thickness" means the dimension of the shortest axis of a cross section perpendicular to the flow path direction of the molten resin in a cavity or a molded product. Also, "thin wall" means that because the "flow path resistance" along the flow of molten resin inside the cavity is large, the molten resin reaches the end of the cavity and fills the entire cavity before it cools and loses fluidity. This refers to the wall thickness in a cavity or molded product that is relatively difficult to use, and does not mean that the wall thickness is below a certain thickness.

Furthermore, the term "thin-walled molded product" means a molded product with a "thin" wall thickness. Furthermore, "thin-wall molding technology" refers to resin molding technology that has been specially devised to stably mold "thin-wall molded products" that are relatively difficult to fill with molten resin.

In addition, the "induction zone" is a band-shaped flow path provided in the cavity so that the flow path resistance of the molten resin injected into the cavity is particularly low in a specific direction, and the cavity in this flow path portion The thickness is thicker than the cavity thickness at the surrounding area, and the end of this channel part is connected to a part where the cavity thickness is thinner than this channel part, or ends up to the mold wall surface. It means a channel that extends and ends at a dead end (hereinafter, the section where the cavity thickness is thinner than the channel section of this "guidance zone" is also referred to as the "thin wall section").

In addition, the gate is usually provided at a position where the molten resin is directly injected into the induction zone flow path, and the induction zone flow path starts from this gate position and extends along the flow path to the thinner part farthest from the gate position. The position where the connection ends is the end of the flow path. Therefore, if a gate is located in the middle of continuous guide band channels, two guide band channels are provided from the gate position to both sides, and the guide band channels are , it is possible to branch or merge along the way.

Furthermore, in the case of a molded product, the term "convex part" means a part that is concave or protrusive in a direction perpendicular to the main plane part of the molded product, and a concave part or a protruding part is a part that is concave or protrusive along the concavo-convex surface of the molded product. It is formed with a relatively thin wall thickness, and in the case of a cavity, it means any part of the uneven shape of the cavity formed by overlapping the corresponding uneven parts of the cavity mold and the core mold. In addition, "the base of a convex part" in the case of a molded product means the boundary part between the convex part and the flat part, and in the case of a cavity, it means the boundary part between the convex part space part and the flat part. . Furthermore, the term "protrusion-circling guide band space" means a cavity space that forms a guide band that is in contact with the base of the protrusion.

In addition, in the present invention, the term "convex part" means, as shown in the above definition, when a molded product has a flat part that serves as a reference, a concave part with respect to that flat part. Used as a general term for the part that is present and the part that protrudes. Furthermore, in a cavity for molding a molded product, the uneven shape is formed according to the unevenness of the cavity mold and the core mold, but there is no rule as to which is the recessed part and which is the protruding part. Similarly to the concave and convex portions of molded products, the term "convexities" is used generically without distinguishing between the two.

In addition, "residual gas" refers to the gas that exists in the cavity during the process of filling the cavity with molten resin, and is added to the air that exists in the cavity from the beginning and when the injection of molten resin starts. It consists of the air and volatile components of resin that were present in the runner and sprue.

In addition, "short" means that when molten resin is injected into a cavity to fill it, the molten resin cools and solidifies before it reaches the end of the cavity, or the discharge of "residual gas" is delayed and the residual gas This refers to a phenomenon in which a part of a molded product is insufficiently filled due to reasons such as solidification before the molten resin is filled into the part.

Generally, during injection molding of molded products, residual gas exists in the cavity, and as the molten resin injected from the gate fills the cavity, the residual gas is driven away from the gate. The residual gas pressure acts to stop the flow of the molten resin, which is one reason for reducing the filling speed.

On the other hand, the injected molten resin is cooled from the part that touches the low-temperature mold wall inside the cavity, and eventually loses its fluidity and solidifies, so that filling no longer progresses. For this reason, in injection molding, the time required for the molten resin injected into the cavity to solidify and the time required for the molten resin to exhaust all residual gas and completely fill the cavity (hereinafter also referred to as "cavity filling time"). ), and if the latter time is longer, a short circuit, which is one of the defects caused by insufficient filling, will occur.

The cavity filling time is determined by the difference between the injection pressure at the gate that is the starting end of the molten resin flow path in the cavity and the pressure of the residual gas in contact with the tip of the flowing molten resin (hereinafter, this pressure difference is also referred to as "flowing pressure"). The smaller the length, the longer it will be.

In addition to the general properties of injection molding as described above, when molding thin-walled products, the cross-sectional area per unit width of the flow path is narrower than that of thick-walled products, and the residual gas tends to be under high pressure. , the increase in flow path resistance is one of the factors that increases the cavity filling time.

Therefore, if the discharge speed of the residual gas is slow, the residual gas will be compressed by the injection of the molten resin and become high pressure, which will lower the flow pressure and become a factor that inhibits filling.At the same time, the temperature will rise due to the adiabatic compression of the residual gas, and the molten resin will be There is also a risk of burning the resin by exceeding its ignition point. Due to the combination of flow path resistance and flow pressure behavior, the cavity filling time tends to be longer in thin-walled molded products than in thick-walled molded products. This is a major reason why thin-wall molding is difficult.

As mentioned above, in thin-wall molding, it is unavoidable that the flow path resistance is high and the residual gas becomes high pressure. The scope is gradually being expanded.

As one such technological development, induction band technology has been developed.

When filling a cavity with molten resin using an induction band, compared to the case where the molten resin is filled sequentially from the gate part into thin-walled parts with high flow path resistance without using an induction band, it is easier to fill the parts away from the gate. The molten resin can reach and fill thin-walled parts with a relatively short delay, making it easy to mold thin-walled molded products.

<Configuration of injection mold>
As shown in FIG. 1, the injection molding die 10 according to this embodiment is an injection molding die 10 having a core mold 12 and a cavity mold 14. The core mold 12 and the cavity mold 14 are overlapped, and molten resin is injected into the cavity 13 (molding space) formed between the core mold 12 and the cavity mold 14, thereby forming a mold having a convex part and a flat part. The product is molded. The injection mold 10 also includes a gate 16 and a residual gas exhaust section 18 .

(cavity)
The cavity 13 according to this embodiment includes a convex space 13A, a plane space 13B, and a guide band space 13C. In this embodiment, the thickness of the cavity 13 is about 0.4 mm, but it can be changed as appropriate in the present invention. The convex space portion 13A forms a convex portion of the molded product. The planar space portion 13B forms a planar portion around the convex portion of the resin molded product. The guide band space 13C has a band shape, is formed in the convex space 13A and the plane space 13B, and has a space that is thicker than the convex space 13A and the plane space 13B. In the present invention, the guide band space may be provided in either the convex space or the plane space. In addition, in this embodiment, the guide band space 13C is formed up to the middle part between the bottom and the top of the convex space 13A, as shown in FIGS. 1 and 2, but in the present invention, When the guide band space is provided in the convex space, it may be formed at any position from the bottom to the top of the convex space depending on the shape of the convex.

(Protrusion surrounding guidance zone space)
The protrusion-circulating guide band space 13X according to the present embodiment branches from the guide band space 13C, contacts the base of the protrusion that is the boundary between the protrusion space 13A and the planar space 13B, and is located at the base of the protrusion. Going around the department. The convex part circumference guide band space 13X is arranged so as to go around the entire circumference of the convex part foot of each convex part space part 13A. In addition, in the present invention, the convex part circumference guiding band space may be made to go around only a part of the base of the convex part, taking into consideration the wall thickness, the height of the convex part, etc. The section may be divided into multiple locations and arranged to go around.

As shown in FIG. 2, the surface of the cavity mold 14 facing the core mold includes a convex space corresponding portion 14A corresponding to the convex space portion 13A, a planar space corresponding portion 14B corresponding to the planar space portion 13B, and a guide band space. It has a guide band space corresponding part 14C corresponding to the part 13C, and a convex part circulating guide band space corresponding part 14X corresponding to the convex part circulating guide band space part 13X. Although FIG. 2 shows an example in which the number of convex space corresponding parts 14A is four, in the present invention, the number of convex space corresponding parts can be changed to one or more as appropriate.

Further, in the present invention, by providing the convex part surrounding guide band space, this convex part surrounding guide band space functions as a molten resin pool, and the entire length of the convex part surrounding guide band space part is the film to the convex part space. The flow inhibiting effect of the curved part of the flow path at the base of the convex part, which plays the role of a gate and, as a result, obstructs the flow of molten resin from the planar space to the convex part, increasing the flow resistance. Reduce the number of deaths. In addition, the corners formed in the cavity due to the bending of the base of the convex part and the contact of the convex circumferential guide band space with the base of the convex part are rounded to reduce the flow-disturbing factors at the corners. This is desirable.

(Gate)
In this embodiment, the gate 16 injects molten resin into the guide zone space 13C. The type of gate 16 is a pin gate. Note that in the present invention, other types of gates such as tunnel gates may be employed.

(Residual gas discharge part)
In this embodiment, the residual gas discharge section 18 is a gas vent hole 18A and a plug member 18B. In addition, in this invention, a residual gas discharge part is not limited to this. For example, the parting surface may be used as a residual gas outlet. Specifically, depending on the shape of the molded product, the mold can be designed so that the parting line passes through the apex of the convex portion, and the parting surface can be used as an outlet for residual gas.

Further, in this embodiment, the residual gas discharge portion 18 is formed in both the cavity mold 14 and the core mold 12. In the present invention, the residual gas discharge part 18 may be formed only in the core mold 12 or only in the cavity mold 14. Further, in the present invention, the residual gas discharge section is not essential.

(Gas vent hole)
The gas vent hole 18A according to this embodiment is a hole that penetrates from the outside of the mold to the top of the convex space 13A, and one end thereof opens at the top of the convex space 13A.

However, in the present invention, the opening position of the gas vent hole may be arranged at any position between the top of the convex space and the gate. The gas vent hole 18A according to this embodiment discharges residual gas from the top of the convex space 13A.

In this embodiment, the opening of the gas vent hole 18A facing the molded product has a circular shape with a diameter of about 2.0 mm. Note that in the present invention, the dimensions and shape of the opening can be changed as appropriate. The shape of the gas vent hole can be set to any geometric shape, such as a polygon or an ellipse.

(Plug member)
The plug member 18B according to this embodiment is provided in a state in which it is detachably inserted into the gas vent hole 18A. The plug member 18B is a cylindrical member that is in close contact with the inner periphery of the gas vent hole 18A. The plug member 18B has a shaft and a head (flange) whose diameter is larger than the shaft. Although not shown, the head can be detachably fixed to the mold using screws or the like. The outer diameter of the cylindrical shaft of the plug member 18B is approximately equal to the inner diameter of the gas vent hole 18A. In the present invention, the shape of the plug member is not limited to a cylindrical shape, but may be other shapes such as a prismatic shape depending on the shape of the gas vent hole.

Since the plug member 18B according to this embodiment can be removed from the gas vent hole 18A, it is easy to clean the plug member 18B and the gas vent hole 18A when not molded.

A gas flow path 20 having an opening diameter through which the molten resin cannot pass and which allows the residual gas to pass is formed on the outer circumferential surface of the cylindrical material of the plug member 18B according to this embodiment. The opening diameter according to this embodiment is approximately 2/100 mm. In addition, in the present invention, the opening diameter is not limited to this, and an appropriate opening diameter may be determined depending on the type of resin material used for molding, the temperature of the molten resin, molding conditions such as injection pressure, the length and flexibility of the gas flow path, etc. In contrast, when designing a mold, an appropriate opening diameter can be arbitrarily determined by taking these factors into consideration.

(Gas flow path)
The gas flow path 20 illustrated in FIG. 1 is formed by bringing the outer surface of the plug member 18B into close contact with the inner surface of the gas vent hole 18A, and between the inner surface of the gas vent hole 18A and the outer surface of the shaft portion of the plug member 18B. has been done.

In this embodiment, the gas flow path 20 provided on the outer surface of the shaft portion of the plug member 18B facing the inner surface of the gas vent hole 18A has a planar shape parallel to the axial direction of the plug member 18B, as shown in FIG. It is said that there is a gap between When the gas flow path 20 provided on the outer surface of the shaft portion of the plug member 18B is a planar gap parallel to the axial direction, the cylindrical material as the material is cut to a predetermined thickness on a plane parallel to the axial direction. Accordingly, the plug member 18B according to this embodiment can be easily manufactured.

In addition, in the present invention, as shown in FIG. 3, the gas flow path 20 may be configured by, for example, a plurality of linear vertical grooves 18B1 extending along the axial direction of the cylindrical material. In addition, in the present invention, the gas flow path is not limited to a planar or cylindrical gap along the axial direction or a linear vertical groove, but for example, the outer peripheral surface of a cylindrical material is sandblasted and randomly bent. A gas flow path may be formed by combining a plurality of flow paths.

Note that, as shown in FIG. 3, the head of the plug member is not essential in the present invention, and the plug member may have only a shaft portion.

Furthermore, in the present invention, the groove width of the vertical groove 18B1 as the gas flow path 20 illustrated in FIG. The shapes and dimensions of the subsequent gas flow paths may be arbitrary. For example, the diameters of each gas flow path may be expanded to expand toward the outside, which is the outlet of the residual gas, or each vertical groove may be formed by a groove along the outer periphery. The grooves may be in communication.

(Air injection mechanism)
Although not shown, in the injection mold 10 according to the present embodiment, a flow path whose other end is connected to an air injection device (not shown) is connected to the outlet of the gas vent hole 18A. There is. In the injection molding process, after cooling and solidification of the molten resin is completed and the mold is opened, the air injection device is activated and air is injected from the outlet of the gas vent hole 18A toward the outer surface of the convex part of the molded product. By doing so, the molded product stuck to the core mold 12 or the cavity mold 14 can be extruded and released from the mold using air pressure.

In addition, in the present invention, in addition to the gas vent hole, an air injection hole, one end of which is connected to an air injection device and communicates with a flow path, can be arbitrarily placed at an arbitrary position of at least one of the core mold and the cavity mold. The molded product stuck to the core mold or cavity mold can be pushed out and released from the mold using air pressure. Note that such air injection holes are provided in the core mold or the cavity mold, which is the side to which the molded product sticks when the mold is opened, which is determined depending on the shape of the molded product, the selection of the mold dividing surface, and the like.

(Bypass path mechanism)
Further, in the injection molding die 10 according to the present embodiment, gas vent holes 18A are formed in the core mold and the cavity mold 14, and inside the core mold 12 and the cavity mold 14, although not shown, there are A bypass path is formed that branches off from the middle of the gas vent hole 18A. That is, one end of the bypass passage communicates with the gas flow passage 20 at a position slightly upstream of the head of the plug member 18B that is in close contact with the gas vent hole 18A, and the other end of the bypass passage communicates with the outside of the mold. , exhaust residual gas to the outside air.

Moreover, the bypass path is provided in a state where it branches toward the side surface direction of the core mold and cavity mold 14 from the middle of the gas vent hole 18A. In addition, in the present invention, by appropriately providing a bypass path, the outlet for discharging the residual gas to the outside air is not limited to the position of the top of the convex portion, but can be provided at any position.

(Resin molded product)
By using the injection molding die 10 according to the present embodiment, a molded product including a convex portion and a flat portion formed around the lower portion of the convex portion can be molded. The mark of the gas vent hole provided in the mold is formed on the top of the convex part of the molded product, and the mark of the gate 16 is formed on the flat part. In addition, the molded product molded by the resin molding method performed using the injection mold 10 has an induction band (circulating around the convex part) that touches the boundary between the convex part and the flat part and runs along the boundary part. A rib is formed as a trace of the guide band space 13X).

(effect)
According to the injection mold 10 according to the present embodiment, the molten resin first has a flow path thicker than the convex space 13A and the plane space 13B, so that the molten resin flows into the convex space 13A and the plane space 13B. It is injected into the cavity 13 through the gate 16 provided at the position of the guide band space 13C, which has a space with a lower flow path resistance than 13B. The injected molten resin then quickly reaches the end of the guide zone space 13C at a point away from the gate 16 (that is, the point where the flow path resistance of the flow path is high thereafter).

On the other hand, at the time when the molten resin reaches the end of the guide band space C, the planar space 13B and the convex space 13A, which have high flow path resistance and are adjacent to the guide band space 13C, are not filled with much molten resin. There is no state. However, when the molten resin reaches the end of the guide zone space C, the flow of the molten resin is blocked in an area with high flow path resistance, and as a result, the molten resin pressure inside the guide zone space C is accumulated. The molten resin penetrates and spreads along the guide band space C to the adjacent plane space 13B and convex space 13A at the same time, so the quality is improved compared to a mold without the guide band space 13C. Capable of molding high-quality thin-walled products.

Further, according to the present embodiment, the molten resin injected from the gate 16 into the guide band space 13C adjacent to the planar space 13B flows down the guide band space 13C adjacent to the planar space 13B, and flows down the guide band space 13C adjacent to the planar space 13B. It reaches the base of the convex part, which is the boundary between the part 13B and the convex space part 13A, and flows into the convex part surrounding guide band space part 13X branched from the guide band space part 13C, and from there flows into the convex part space part 13A to the top. Go ahead and fill it up.

Since the convex part surrounding guiding band space part 13X is provided in contact with the bent part formed by the plane space part 13B and the convex part space part 13A, the plane space part 13B and the convex part space part 13A are formed. It has the function of expanding the flow path at the bent portion, and has the effect of reducing flow path resistance due to bending of the flow path.

Further, a protrusion-circling guide band space 13X is provided around the base of the protrusion, and the pressure of the molten resin in the protrusion-circling guide band space 13X is accumulated to be approximately close to the liquid pressure at the gate position. As a result, the convex part surrounding guide band space 13X acts like a film gate for the convex part space 13A, and the filling property of the convex part space is improved, so that the convex part in contact with the base part of the convex part A thin-walled molded product of high quality can be molded compared to the case where there is no circulating guide band space 13X.

Further, according to the present embodiment, the residual gas discharge part 18 that discharges residual gas is located at the top of the convex space 13A. Therefore, the residual gas inside the cavity 13 tends to concentrate at the top of the convex space 13A due to the flow pressure of the molten resin, but the residual gas inside the cavity concentrated at the top passes through the residual gas discharge section 18. , released to the outside of the mold. As a result, it is possible to suppress deterioration in quality of the molded product due to gas burning, short-circuiting, warping, etc. caused by residual gas.

Further, according to the present embodiment, the residual gas is appropriately discharged to the outside of the mold by the residual gas discharge section 18, so that the residual gas concentrated at the top of the convex space 13A is prevented from being excessively pressurized. suppressed. Along with this, the molding pressure required to fill the cavity with molten resin can also be lowered, reducing the pressure burden on the molding machine, making it possible to use a smaller molding machine, and reducing costs. I can contribute.

Further, according to the present embodiment, the gate 16 is arranged not at the top of the convex space 13A but at the guide band space 13C provided adjacent to the plane space 13B. For this reason, for example, in the cavity 13, a flow path formed by the guide zone space 13C extending from one gate 16 is branched into a plurality of flow paths also formed by the guide zone space, and the branched flow paths are A plurality of convex space portions 13A can be arranged on the downstream side.

That is, compared to the conventional method in which a gate 16 is provided at the top of each convex space 13A, even if a molded product has a plurality of convex portions, a plurality of gates 16 are provided in accordance with the number of convex portions. No need to place it in a mold. Therefore, the configuration of the runner for supplying the molten resin to the gate 16 in a well-balanced manner is relatively simple, and the cost of designing and manufacturing the mold can be reduced.

Further, according to the present embodiment, appropriate degassing can be performed by appropriately replacing and using plug members 18B having different residual gas discharge performance depending on the type of resin and the amount of residual gas. In addition, the residual gas discharge path needs to be cleaned from time to time because the volatile components of the molten resin become tar-like and gradually become dirty and clogged. It is easy to clean.

Further, according to the present embodiment, by communicating the flow path connected to the air injection device with the outlet of the gas vent hole 18A, after the mold opening process is completed, the molded product is moved into the injection molding mold by the wind pressure of the air. It can be extruded from the mold 10 and released.

Further, according to the present embodiment, when releasing the molded product by air injection pressure using the gas vent hole 18A of the molded product, compared to the case of releasing the molded product using an ejector pin, it is easier to release the molded product. The molded product will not be damaged by mechanical impact.

Further, according to the present embodiment, residual gas in the cavity 13 can be sucked from the gas vent hole 18A by communicating a flow path (not shown) connected to a vacuum device with the outlet of the gas vent hole 18A. becomes possible. As a result, the efficiency of exhausting residual gas in the cavity is improved, and deterioration in quality of the molded product due to gas burns, short circuits, warping, etc. caused by residual gas can be suppressed.

Further, according to the resin molding method using the injection mold 10 according to the present embodiment, even a thin molded product can be molded efficiently and with high quality.

<Additional notes>
Based on the present embodiment described above, the present invention will be additionally explained below as an additional note.

(Consideration of prior art)
Generally, residual gas exists inside the cavity, and the pressure of the residual gas inside the cavity is approximately atmospheric pressure at the stage when the injection of molten resin begins, but as the injection of the molten resin progresses, the pressure increases. Rise. On the other hand, as the molten resin occupies the space inside the cavity, some of the residual gas in the cavity is pushed by the molten resin and passes through the small gap that exists on the parting surface of the mold, and enters the mold. It is discharged to the outside.

However, the gap between the molds is very narrow to the extent that the molten resin cannot leak out, and therefore the rate of discharge of residual gas is usually relatively slow. Therefore, the pressure of the residual gas in the cavity will continue to increase until the residual gas is finally completely exhausted or until the injection of the molten resin is stopped. Further, the pressure of the residual gas within the cavity acts as a force to stop the flow of the injected molten resin within the cavity.

This increase in the internal pressure of the residual gas obstructs the flow of molten resin within the cavity, resulting in insufficient filling, resulting in partial wall thickness shortages, uneven wall thickness, or not being filled with molten resin at all. This is a cause of short circuits, which are the parts that do not occur. Further, when the residual gas is adiabatically compressed and the pressure increases, the gas temperature also rises, and eventually exceeds the ignition point of the molten resin, causing the surface of the resin to burn. That is, there also arises a problem that the quality of the thin-walled molded product deteriorates.

Patent Document 1 does not disclose anything regarding the resistance of the flow path of molten resin in the cavity and the influence of residual gas when injection molding a molded product. Therefore, the technique of Patent Document 1 alone cannot solve the problem of deterioration in quality of molded products caused by high flow path resistance in injection molding and delayed discharge of residual gas.

Further, as a result of study by the present inventor regarding the technique of Patent Document 2, it was confirmed that it is possible to improve the filling property of the molten resin during injection molding by providing an induction band within the cavity. However, it has been found that sufficient quality may not be obtained depending on the shape and dimensions of the molded product, such as the thinness of the wall and the number of convex portions.

In injection molding of a molded product having a convex part as shown in Patent Document 2, as a method of suppressing the increase in pressure of residual gas in the cavity portion corresponding to the convex part, for example, a gate that is the starting point of the flow of molten resin is used. , a method of arranging the mold at a position corresponding to the top of the convex portion is conceivable.

However, according to this method, it is necessary to arrange all the gates at mold positions corresponding to the tops of the convex portions, so as the number of convex portions increases, the number of gates also increases. For example, if the molded product is an egg carton, ten or more protrusions are usually required in one molded product, and if the lid is also integrally molded, nearly twice that number is required. The number of gates is required. Along with this, it becomes necessary to stretch runners according to the arrangement of the gates, which makes it difficult to balance the injection between the gates, and also makes the mold complex and increases the processing burden of the mold. As a result, there is a problem in that the manufacturing cost of the mold increases.

(Protrusion surrounding guidance zone space)
In the present invention, as a result of prototype production and research by the inventor, in injection molding of a thin-walled molded product with a complex shape with irregularities, when trying to fill the molten resin to the end of the cavity according to the shape, the cross-sectional area of the flow path It was found that the passage resistance was high due to the passage being longer than that of the previous one, and the passage having many bends, which reduced the filling performance.

Therefore, first, a gate is provided in the guide band space formed in a part of the planar space, and the guide band space is used as a pseudo runner to spread the molten resin near the base of the convex part, which is the largest bending part. Further, a guide band space around the convex part is provided, which is preferably provided around the entire circumference of the base of the convex part, but depending on the shape of the molded product, there is no room to provide a guide band space part. In some cases, a convex circumference guide band space may be provided in a part of the convex base, and this convex circumference guide band space guides the molten resin around the convex base, and the convex circumference is guided by the convex circumference guide band space. The guide band space is used as a pseudo film gate, and the molten resin accumulated in the guide band space surrounding the convex part is injected into the thin wall part of the convex part from the foot of the convex part. Design the cavity structure of the mold.

In addition, in the arrangement of the convex part surrounding guide band space, if the convex part is large and the molten resin is insufficiently filled into the thin part of the convex part, the convex part is branched from the convex part surrounding guide band space part. It is also possible to provide a guide band space that climbs up the side wall of the section.

Further, the convex part surrounding guide band space is formed so as to be in contact with the base part of the convex part, and desirably is formed astride the convex part wall surface, and more preferably, the convex part surrounding guide band space part and the convex part wall surface are formed. The boundaries between the two do not have corners and are connected by smooth curved surfaces. In addition, if it is not possible to provide the convex circumference guiding band space in contact with the convex base depending on the shape of the molded product, the distance from the convex circumferential guiding band space to the convex base should be It is sufficient that the convex portions are sufficiently close to each other so that the flow path resistance in the convex portions does not become a major hindrance to filling the convex portions with the molten resin.

By adopting such a mold structure, the flow path resistance of the flow path from the gate to the tip of the convex part is significantly lower than that when the convex part surrounding guide band space is not used, which is particularly effective in thin-wall molding. A means for solving the problem of poor filling of the convex portions is provided.

In addition, when the flow path resistance during filling with molten resin is lowered, the injection pressure of the molten resin can also be lowered, and therefore the liquid pressure of the molten resin is also lowered, resulting in a state of low-pressure molding, so residual gas is removed from the mold. Combined with the idea of discharging the gas to the outside, this has the effect of suppressing the build-up of residual gas pressure.

In addition, if the pressure of the residual gas does not become too high, the temperature of the residual gas will not exceed the ignition point of the molten resin due to adiabatic compression, which will prevent gas burning defects and prevent distortions caused by high pressure from remaining in the molded product. Furthermore, since the pressure burden is reduced, molding can be performed using a small molding machine, which has the effect of reducing costs.

In addition, by providing a residual gas exhaust hole at the top of the convex portion, it is possible to further reduce the pressure of the residual gas, and as a result, the repulsive force of the residual gas is reduced, reducing the flow path resistance. As in the case where the pressure is lowered, filling properties are improved, low-pressure molding becomes possible, and effects such as suppression of gas burns and distortion and miniaturization of the molding machine can be obtained.

The key point of the present invention, which is to provide a convex circumferential guiding band space in contact with the base of the convex part, is a technique for improving the flow path resistance of the bent part of the convex part. The proposal to provide the above is a technique for improving the discharge of residual gas in the convex portion, and both of them have the effect of improving the filling performance of the convex portion and suppressing the increase in pressure of the residual gas in the entire cavity.

In addition to the above-mentioned effects, the effects obtained by suppressing the high pressure of the residual gas include suppressing the generation of burrs due to the residual gas pressure, and suppressing the injection pressure of molten resin to a low level. In addition, the stress applied when the resin solidifies is reduced, warping and deformation of the molded product is also suppressed, and the cooling time required to correct warp and deformation can be shortened, shortening the molding cycle. The lower injection pressure makes it possible to downsize the injection molding machine and reduce costs.The lower injection pressure also reduces the mold clamping force, increasing the ability to discharge residual gas from the parting surface, which further reduces the amount of residual gas. Effects such as being able to keep the pressure low can be obtained.

From this specification, the aspects described in the following aspects 1 to 3 are conceptualized and included in the present invention.

The injection mold according to aspect 1 of the present invention has a core mold and a cavity mold, and the core mold and the cavity mold are overlapped, and the injection mold is formed between the core mold and the cavity mold. An injection mold for molding a resin molded product having a convex part and a flat part by injecting molten resin into a cavity, the cavity having a convex space part in which the convex part is molded, and a convex part space part in which the convex part is molded; a planar space forming the planar part around the part; and an induction band formed in at least one of the protrusion space and the planar space and having a wall thickness greater than that of the protrusion space and the planar space. a space, the guide band space includes a guide band space that goes around the convex part in contact with a boundary between the convex space and the planar space, and the cavity type includes: A gate for injecting molten resin is provided in the guide zone space.

According to the above configuration, the molten resin injected from the gate into the guide zone space of the cavity has a flow path thicker than the convex space or the plane space, and therefore flows more easily than the convex space or the plane space. Through the guide band space having a space with low road resistance, the end of the guide band space that goes around the plane space and the convex space at a point away from the gate is quickly reached. In addition, since the end of the flow path with low flow resistance along the guide zone space is connected to the high flow path resistance part, after the molten resin is filled up to the end of the guide zone space, the flow path continues. Pressure is accumulated in the molten resin inside the induction zone space in accordance with the applied injection pressure.

As a result, the molten resin flows under relatively high pressure into the horizontally adjacent planar space and convex space along the guide band space, and spreads around the mold without the guide band space. As a result, defects such as short circuits are less likely to occur, and high-quality thin-walled molded products can be molded.

In the above configuration, from the viewpoint of flow path resistance, the guide band space is mainly formed in a planar space where a relatively straight flow path can be secured, but depending on the dimensions and shape of the molded product, the guide band space may The space portion may be formed in the convex space portion, or may be formed in both the planar space portion and the convex space portion. Furthermore, from the viewpoint of efficiently arranging the guide band network starting from the gate, it is desirable to provide the gate for injecting the molten resin into the guide band space at the position of the guide band space formed in the planar space. Depending on the size and shape of the molded product, any number of guide strips can be provided at any position in the guide band space.

Further, according to the above configuration, the guide band space includes the convex part circumference guide band space part that is in contact with the convex part foot part and goes around the convex part foot part, so that the convex part circumference guide band space part is made of molten resin. The entire length of the guiding band space around the convex part plays the role of a film gate to the convex part space, and as a result, the flow of the molten resin from the plane space part to the convex part space is blocked and the flow path is blocked. This reduces the flow-inhibiting effect of the bending portion of the flow path at the base of the convex portion, which is a factor that increases resistance. Therefore, compared to a mold that does not have such a guide band space around the convex portion, defects such as short circuits in the convex portion are less likely to occur, and a thin-walled molded product of high quality can be molded. Note that it is desirable that the corners of the flow path bending portion have an R shape (roundness) on both the inner peripheral wall surface and the outer peripheral wall surface.

In the injection molding mold according to Aspect 2 of the present invention, in Aspect 1, residual gas remaining in at least one of the core mold and the cavity mold is discharged from the top of the convex space. Equipped with a residual gas exhaust section.

According to the above structure, the guide band space includes a convex part circumference guide band space that comes into contact with the base of the convex part, thereby improving the filling performance of the molten resin into the convex part space. In addition, at least one of the core mold and the cavity mold is provided with a residual gas exhaust part that discharges residual gas from the top of the convex space, which further improves the filling performance of the molten resin into the convex space. .

In addition, in the present invention, the residual gas discharge part is, for example, a gas vent hole that is provided in at least one of the core mold and the cavity mold and reaches the top of the convex space from the outer surface of the mold, and a gas vent hole that is detachably attached to the gas vent hole. The plug member is a rod-shaped member whose entire outer circumferential surface, at least in the portion that contacts the top of the convex space, is in close contact with the entire inner circumferential surface of the gas vent hole, and the close contact portion of the rod-shaped member is A gas flow path may be formed between the outer circumferential surface and the inner circumferential surface of the gas vent hole through which the molten resin cannot pass, but through which residual gas can pass.

In addition, in the present invention, when a gas vent hole is used as the residual gas exhaust section, a vacuum device is connected to the outlet of the gas vent hole, and the residual gas discharged from the gas vent hole is sucked by the vacuum device. Evacuation of residual gas from the top of the space may be facilitated.

As aspect 3 of the present invention, a resin molding method may be configured in which a resin molded article is molded using the injection mold described in aspect 1 above.
As described in aspect 1, the resin molded product having the above configuration can provide a high quality resin molded product in which deterioration in quality due to distortion, insufficient filling, discoloration, etc. in the molded product is suppressed.

<Other embodiments>
Although the present invention has been described by the embodiments disclosed above, the statements and drawings that form part of this disclosure should not be understood as limiting the present invention. The present invention includes embodiments in which each of the embodiments described above is appropriately combined, and various embodiments not described above, and the technical scope of the present invention can be understood from the above description. It is determined only by matters specifying the invention in the claims.

10 Injection mold 12 Core mold 13 Cavity 13A Convex space 13B Planar space 13C Guide band space 13X Convex circumferential guide band space 14 Cavity mold 14A Convex space corresponding part 14B Planar space corresponding part 14C Induction band Space corresponding part 14X Convex part circumferential guide band space corresponding part 16 Gate 18 Residual gas discharge part 18A Gas vent hole 18B1 Vertical groove 18B Plug member 20 Gas flow path

Claims (3)

It has a core mold and a cavity mold, and the convex part and the flat part are formed by overlapping the core mold and the cavity mold and injecting molten resin into the cavity formed between the core mold and the cavity mold. An injection mold for molding a resin molded product having
The cavity is formed in a convex space part in which the convex part is formed, a plane space part in which the flat part is formed around the convex part, and at least one of the convex part space part and the planar space part. , comprising a guiding band space having a thickness thicker than the convex space and the plane space,
The guide band space includes a convex-circling guide band space that is in contact with a boundary between the convex space and the planar space and goes around the boundary;
The cavity type includes a gate in the guide zone space for injecting molten resin.
Mold for injection molding. At least one of the core mold and the cavity mold is provided with a residual gas exhaust part that discharges residual gas remaining at the top from the top of the convex space.
The injection mold according to claim 1. A resin molding method for molding a resin molded product using the injection mold according to claim 1.