Injection molding of an inverse compression molded foam

Abstract

The utility model provides an injection structure of back pressure forming foaming object, it includes: a first mould part, a second mould part can be in a with the first mould part is combined the die closing position, and a with the first mould part is separated the die opening position between activity, by the first mould part with the second mould part in the die room defined when the combination, between the first mould part and the second mould part each other, a hole -like runner, from the first mould part one side recessed in the first mould part, a hole -like buffer space, from the first mould part other side recessed in the first mould part, with the runner communication with one end, and with the die room communication with the other end orifice definition a sprue, wherein, the inner diameter of buffer space is greater than the inner diameter of the runner.

Description

Technical Field

[0001] This utility model relates to polymer processing technology, and in particular to an injection structure for a reverse-pressure molded foam. Background Technology

[0002] In the field of polymer processing technology, the existing processing technology involves converting solid polymer raw materials into a flowable liquid phase using thermal energy, and then filling the flowable polymer melt into a mold chamber of a specific shape through physical means such as injection or extrusion, thereby giving the molded item its appearance shape.

[0003] In response to the different needs of various products, many innovative technologies for the above-mentioned processing techniques have been revealed. Among them, the single-phase melt formed by mixing and plasticizing the molecular raw material with supercritical fluid as a physical foaming agent has been addressed by conventional technology to avoid premature foaming caused by a sudden drop in pressure below the critical pressure when it is filled into the mold chamber. Before filling, the mold chamber is filled with an appropriate amount of gas to form a suitable gas pressure. This gas pressure then forms a counter-pressure on the subsequently filled single-phase melt. As a result, when the single-phase melt is filled into the mold chamber, it is subjected to a counter-pressure higher than atmospheric pressure, which suppresses the formation of gas nuclei and thus overcomes the aforementioned premature foaming problem.

[0004] Although the aforementioned reverse pressure molding technology can solve the problem of premature foaming, when the single-phase melt enters the mold chamber through the sprue on the mold, the cross-sectional area of ​​its flow path changes drastically. The fluid dynamics are different in different cross-sectional areas, which causes the flow velocity and dynamic pressure to decrease when the single-phase melt enters the open mold chamber from the narrow sprue due to the instantaneous expansion of the cross-sectional area. At the same time, in the local area where the cross-sectional area changes, that is, near the gate through which the sprue communicates with the mold chamber and in the mold chamber space adjacent to the gate, the hydrostatic pressure in this local area will increase significantly at the microscopic level. Especially after filling, the single-phase melt in this area may be stuck due to excessive hydrostatic pressure, which may lead to incomplete foaming of the foamed article at the position corresponding to this local area after subsequent foaming molding. Utility Model Content

[0005] Therefore, the main objective of this utility model is to provide an injection structure for reverse-pressure molded foam, which can be used to implement an injection method for reverse-pressure molded foam, thereby improving the quality of the finished foam and avoiding incomplete foaming defects caused by excessive local stress residue in a limited area due to the injection process.

[0006] Therefore, in order to achieve the above objectives, the injection method for reverse-pressure molding foam of this utility model controls how a single-phase melt, which is a mixture of polymer raw material melt and supercritical fluid and plasticized, flows in a flow channel to reduce the fluctuation of fluid pressure when the single-phase melt enters a mold chamber, thereby avoiding the occurrence of local stress residue.

[0007] That is, the injection method for reverse-pressure molded foam provided by this utility model includes: a single-phase melt containing a supercritical fluid polymer raw material composition is injected at an injection pressure and flows in a flow channel along a unidirectional flow direction, and a first negative pressure gradient exists between an upstream position and a midstream position during the flow process in the flow channel, wherein the single-phase melt has a midstream flow velocity and a midstream pressure at the midstream position; and its main technical feature is that after the single-phase melt continues to flow along the flow direction from the midstream position to a filling position, it is filled into a mold chamber of a mold at a filling flow velocity lower than the midstream flow velocity and a filling pressure lower than the midstream pressure.

[0008] Furthermore, the flow of the single-phase melt from the midstream position to the mold filling position is subject to a second negative pressure gradient, and the absolute value of the slope of the second negative pressure gradient is different from the absolute value of the slope of the first negative pressure gradient.

[0009] The absolute value of the slope of the second negative pressure gradient is less than the absolute value of the slope of the first negative pressure gradient.

[0010] To achieve the above-mentioned different negative pressure gradients, the first cross-sectional area of ​​the flow channel between the upstream position and the midstream position can be made smaller than the second cross-sectional area of ​​the flow channel between the midstream position and the filling position, perpendicular to the flow direction.

[0011] Furthermore, to prevent the single-phase melt from foaming prematurely in the mold chamber, the filling pressure and the counter-pressure formed by the gas already present in the mold chamber at the start of filling can both be greater than atmospheric pressure.

[0012] The injection structure for reverse-pressure molded foam provided by this utility model can be used to realize the above-mentioned injection method for reverse-pressure molded foam to achieve the expected effect.

[0013] The main technical feature of the injection structure of the reverse pressure molded foam is that the shape of the sprue set on the mold in the prior art is improved so that when the sprue receives the plasticized single-phase melt supplied by the external device and supplies it to the mold chamber, the single-phase melt changes its physical performance of flow rate and pressure during the flow process in the sprue, thereby achieving different negative pressure gradient performance as described above. Structurally, the injection molding structure of the reverse-pressure molded foam includes: a first mold portion; a second mold portion movable between a mold-closing position that is combined with the first mold portion and a mold-opening position that is separated from the first mold portion; a mold chamber defined by the first mold portion and the second mold portion when they are combined, located between the combined first mold portion and the second mold portion; a perforated sprue recessed in the first mold portion from one side; and a perforated buffer space recessed in the first mold portion from the other side, communicating with the sprue at one end and with a gate defined by an orifice at the other end, communicating with the mold chamber; wherein the inner diameter of the buffer space is larger than the inner diameter of the sprue.

[0014] As a preferred embodiment of the above technical solution, preferably, the hole axis of the buffer zone space and the hole axis of the gating system are coaxial.

[0015] As a preferred embodiment of the above technical solution, the buffer zone space is preferably a straight hole with a single inner diameter.

[0016] The ratio between the inner diameter of the buffer zone and the inner diameter of the runner can be changed according to the needs of different polymer raw material compositions. The inner diameter of the buffer zone can be between 120% and 200% of the inner diameter of the runner, or it can be other different ratios outside this range. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a preferred embodiment of the method provided by this utility model.

[0019] Figure 2 This is an example diagram showing the pressure and flow velocity distribution of a method provided in a preferred embodiment of the present invention.

[0020] Figure 3 This is a plan view of an article provided in another preferred embodiment of the present invention.

[0021] Among them, (A) upstream position; (B) midstream position; (C) filling position; (10) injection structure of reverse pressure molded foam; (20) first mold part; (30) second mold part; (40) mold chamber; (50) sprue; (60) buffer zone space; (70) gate. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0023] The following are two preferred embodiments of the present invention, described in detail with reference to the accompanying drawings.

[0024] The injection method and structure for reverse-pressure molded foam provided in a preferred embodiment of this utility model are technically characterized by the following: In polymer injection molding technology, a single-phase melt formed by mixing hot-melted polymer raw materials with supercritical fluid flows unidirectionally in a flow channel under injection pressure, and before entering the mold chamber, it exhibits a localized flow state adjacent to the mold chamber. Specifically, the foam can be a product after foaming, and may include, but is not limited to, shoe midsoles, shoe outsoles, slippers, sporting goods, etc.

[0025] Please see Figure 1 As shown, the injection molding method for this reverse-pressure molded foam includes the following steps:

[0026] The polymer composition is formed by melting solid polymer raw materials by heating, mixing it with supercritical fluid formed by inert gases such as nitrogen or carbon dioxide in a supercritical state, and then plasticizing it to form a single-phase melt.

[0027] The flow channel is defined by connecting conventional devices such as injection barrels, nozzles, and molds together through their respective specific spaces. For example, the flow channel is defined by connecting different specific spaces such as the screw groove space in the injection barrel, the front cavity of the injection barrel, the flow channel inside the nozzle, and the sprue provided in the mold to form a continuous flow space.

[0028] A fixed or non-fixed injection pressure is applied to the single-phase melt existing in the flow channel, allowing the single-phase melt to flow in the flow channel along a unidirectional flow direction. Between an upstream position and a midstream position in the flow process of the single-phase melt, there exists a first negative pressure gradient. That is, the pressure of the single-phase melt will gradually decrease as the flow distance increases. In other words, when the single-phase melt is located at the upstream position, there will be an upstream flow velocity and an upstream pressure. Similarly, when it is located at the midstream position, there will also be a midstream flow velocity and a midstream pressure, and the midstream pressure will be less than the upstream pressure.

[0029] Subsequently, as the single-phase melt passes through the midstream position, it is continuously subjected to the injection pressure and continues to flow along the flow direction. At a filling position, it is filled into the internal mold chamber at a filling flow rate and a filling pressure. Both the filling pressure and the back pressure formed by the gas already present in the mold chamber at the start of filling are greater than atmospheric pressure, thus maintaining the single-phase nature of the single-phase melt. Furthermore, the filling flow rate is lower than the midstream flow rate, and the filling pressure is also lower than the midstream pressure. Simultaneously, during the flow of the single-phase melt from the midstream position to the filling position, there exists a second negative pressure gradient with a slope absolute value smaller than the first negative pressure gradient. This allows the single-phase melt to be filled into the mold chamber in a relatively gentle state, preventing phase changes in the supercritical fluid within the single-phase melt that might occur during filling due to excessively high flow rates or excessive local pressure drops.

[0030] Please see Figure 2 In the specific example shown in the figure, the pressure of the single-phase melt at the upstream position (A) is 120 MPa and the flow rate is 300 mm / s. At the midstream position (B), the pressure drops to 85 MPa and the flow rate to 250 mm / s. At the filling position (C), the pressure is 80 MPa and the flow rate is 150 mm / s. The figure also shows that the absolute value of the slope of the first negative pressure gradient between the upstream position (A) and the midstream position (B) is greater than the absolute value of the slope of the second negative pressure gradient between the midstream position (B) and the filling position (C), and the flow rate is also significantly reduced. The figure further indicates that when the single-phase melt enters the larger mold chamber at the filling position (C), its pressure drops to equal the existing back pressure in the mold chamber (70 MPa in the figure) immediately after the immediate widening section (i.e., section C to D in the figure).

[0031] To ensure that the absolute value of the slope of the second negative pressure gradient differs from that of the first negative pressure gradient, one possible technique is to make the first cross-sectional area of ​​the flow channel between the upstream position and the midstream position smaller than the second cross-sectional area of ​​the flow channel between the midstream position and the filling position. Furthermore, the second cross-sectional area can be between 120% and 200% of the first cross-sectional area. Specific values ​​within this range can be multiples of 10, such as 130%, 140%, 150%, 160%, 170%, 180%, and 190%, or any non-multiple value such as 141%, 164%, or even 172.3%. This range is merely a preferred embodiment and does not cover the entire scope of the technical features of this utility model. Therefore, even if the range is exceeded, it should still be protected by this utility model within the scope of the claims in this application.

[0032] Please see Figure 3 As shown, in order to realize the injection method of the reverse-pressure molded foam, the present invention provides an injection structure (10) for the reverse-pressure molded foam in another specific embodiment. The injection structure (10) for the reverse-pressure molded foam mainly includes a first mold part (20), a second mold part (30), a mold chamber (40), a runner (50), a buffer space (60), and a gate (70).

[0033] The first mold part (20) and the second mold part (30) jointly define the mold chamber (40). However, since this part belongs to the conventional multi-piece mold technology that has been used for many years, generally speaking, the first mold part (20) and the second mold part (30) are usually in the form of plates and are installed on conventional vertical or horizontal clamping devices. They are driven by conventional clamping devices so that they can move back and forth between a mold closing position where they are joined together and a mold opening position where they are separated. When the mold is closed, the mold chamber (40) is located between the first mold part (20) and the second mold part (30) that are joined together, and is sealed as a closed space inside the mold. Conversely, when the mold is open, the mold chamber (40) is open due to the separation of the first mold part (20) and the second mold part (30). Such technical contents are well known and used in the field of shoe midsole molding and forming technology, so this case does not intend to elaborate on them.

[0034] The runner (50) is recessed in the shape of a straight hole on the side of the first mold part (20) that is not used to join the second mold part (30). The buffer space (60) is also recessed in the shape of a straight hole on the side of the first mold part (20) that is used to join the second mold part (30), and one end is connected to the runner (50), while the other end is connected to the mold chamber (40), and the gate (70) is defined by the opening at the other end. In one feasible embodiment, the buffer space (60) and the runner (50) can be coaxial.

[0035] It is particularly noteworthy that the main technical feature of this embodiment is that the inner diameter of the hole in the buffer zone space (60) is larger than the inner diameter of the hole in the gating channel (50), so that the flow rate of the fluid can be reduced after entering the buffer zone space (60) from the gating channel (50), and the pressure drop is also reduced.

[0036] Corresponding to the aforementioned method embodiments, the runner (50) and the buffer zone space (60) are part of the flow channel. The orifice at the inlet end of the runner (50) is further defined as the upstream position, the position where the runner (50) and the buffer zone space (60) are connected is defined as the midstream position, and the position where the gate (70) is located is defined as the mold filling position. Thus, the single-phase melt is driven by the injection pressure to enter the runner (50) and fill the mold chamber (40) through the buffer zone space (60). In the process of flow, the pressure and flow rate control effect disclosed in the aforementioned method embodiments is achieved, thereby ensuring the quality of the final molded product.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. An injection structure for a reverse-pressure molded foam, characterized in that, Includes: First module; A second mold part can move between a mold-closing position that is combined with the first mold part and a mold-opening position that is separated from the first mold part; A mold chamber defined by the first mold and the second mold when they are combined is located between the combined first mold and the second mold; A perforated sprue is recessed into the first mold portion from one side; A perforated buffer space is recessed into the first mold part from the other side of the first mold part, with one end connected to the runner and the other end defined as a gate and connected to the mold chamber. The inner diameter of the buffer zone is larger than the inner diameter of the gating channel.

2. The injection structure of the reverse-pressure molded foam according to claim 1, characterized in that, The bore axis of the buffer zone space is coaxial with the bore axis of the gating system.

3. The injection molding structure of the reverse-pressure molded foam according to claim 2, characterized in that, The buffer zone has the shape of a straight hole with a single inner diameter.

4. The injection molding structure of the reverse-pressure molded foam according to claim 1, 2 or 3, characterized in that, The inner diameter of the buffer zone is between 120% and 200% of the inner diameter of the gating system.

Images