TWM679385U - Injection structure of reverse compression molded foam - Google Patents

Abstract

The injection method for reverse-pressure molding of foam provided by this invention includes: a first mold portion; a second mold portion movable between a mold-closing position joined with the first mold portion and a mold-opening position separated from the first mold portion; a mold chamber defined by the first mold portion and the second mold portion when joined, located between the joined first mold portion and the second mold portion; a perforated runner recessed in the first mold portion from one side; a perforated buffer space recessed in the first mold portion from the other side, communicating with the runner 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 runner.

Description

Injection structure of reverse compression molded foam

This work relates to polymer processing technology, and in particular to an injection structure for a reverse-pressure molded foam.

In the field of polymer processing technology, the process of converting solid polymer raw materials into a flowable liquid phase using heat 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 external shape, is a well-known processing technology.

In response to the different needs of various products, many innovative technologies have been developed to study the above-mentioned processing techniques. Among them, the conventional technology for single-phase melts formed by mixing and plasticizing supercritical fluid as a physical foaming agent with the molecular raw materials is designed to avoid premature foaming caused by a sudden drop in pressure below the critical pressure when the melt is filled into the mold chamber. This is achieved by filling the mold chamber with an appropriate amount of gas to create a suitable air pressure before filling, and using this air pressure to create a counter-pressure on the subsequently filled single-phase melt. This ensures that the single-phase melt is subjected to a counter-pressure higher than atmospheric pressure when it is filled into the mold chamber, thus suppressing the formation of gas nuclei and overcoming the aforementioned premature foaming problem.

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 runner, the cross-sectional area of its flow path changes drastically. Since the fluid's hydromechanical state differs across these cross-sectional areas, the instantaneous expansion of the cross-sectional area causes a decrease in flow velocity and dynamic pressure when the single-phase melt enters the spacious mold chamber from the narrow runner. In the localized areas where the cross-sectional area changes, namely near the gate through which the gating system communicates with the mold chamber and the mold chamber space adjacent to the gate, the hydrostatic pressure of the fluid in these localized areas will increase significantly. In particular, after filling is completed, the single-phase melt present in these areas may be retained due to excessive hydrostatic pressure, resulting in incomplete foaming of the foamed article at the location corresponding to these localized areas after subsequent foaming and molding.

Therefore, the main purpose of this invention 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.

Therefore, in order to achieve the above objectives, the present invention implements an injection method for reverse compression molding of foamed materials. This method controls how a single-phase melt, which is a mixture of polymer raw material melt and supercritical fluid and has been plasticized, flows in a flow channel to reduce the fluctuation range of the fluid pressure when the single-phase melt enters the mold chamber, thereby avoiding the occurrence of local stress residue.

That is, the injection method for reverse-pressure molding of foam provided by this invention includes: a single-phase melt containing a supercritical fluid polymer raw material composition is injected under an injection pressure to flow 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.

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.

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.

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.

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

The injection structure for reverse-molded foam provided in this invention can be used to realize the above-mentioned injection method for reverse-molded foam in order to obtain the expected effect.

The main technical feature of the injection structure of the reverse-pressure molded foam is that the shape of the conventionally set gate on the mold is improved so that when the gate 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 properties of flow rate and pressure during the flow process in the gate, thereby achieving different negative pressure gradients as described above. Structurally, the injection structure of the reverse-pressure molded foam includes: a first mold portion; a second mold portion movable between a mold-closing position that is joined 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 joined, located between the joined first mold portion and the second mold portion; a perforated runner recessed into the first mold portion from one side; and a perforated buffer space recessed into the first mold portion from the other side, communicating with the runner 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 runner.

The ratio between the inner diameter of the buffer zone space and the inner diameter of the gating can be changed according to the needs of different polymer raw material compositions. The inner diameter of the buffer zone space can be between 120% and 200% of the inner diameter of the gating, or it can be other different ratios outside this range.

Here are two preferred embodiments of this invention, illustrated with diagrams for detailed explanation.

The injection method and structure for reverse-pressure molded foam provided in a preferred embodiment of this invention are characterized by the fact that, in polymer injection molding technology, a single-phase melt formed by mixing a hot-melted polymer raw material with a supercritical fluid, after being driven by injection pressure, flows unidirectionally in a flow channel and, before entering the mold cavity, exhibits a localized flow state adjacent to the mold cavity. Specifically, the foam can be a shoe midsole.

Please refer to Figure 1. The injection molding method for this reverse-pressure molded foam includes the following steps:

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

A flow channel is defined by connecting the respective specific spaces of a known device such as an injection barrel, nozzle, and mold. For example, the flow channel is defined by connecting different specific spaces such as the screw groove space inside the injection barrel, the front cavity of the injection barrel, the flow channel inside the nozzle, and the runner provided in the mold to form a continuous flow space.

A fixed or non-fixed injection pressure is applied to the single-phase melt present 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 channel, 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.

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 inner mold chamber of the mold at a filling flow rate and a filling pressure. Both the filling pressure and the counter pressure formed by the gas already present in the mold chamber at the beginning of filling are greater than the atmospheric pressure, so as to maintain the single phase 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. At the same time, during the flow of the single-phase melt from the midstream position to the filling position, there is a second negative pressure gradient with an absolute slope value that is lower than the first negative pressure gradient. This allows the single-phase melt to be filled into the mold chamber in a relatively gentle state, so as to avoid the supercritical fluid in the single-phase melt from undergoing phase change due to excessively fast flow rate or excessive local pressure drop during filling.

Please refer to the specific example shown in Figure 2. 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 is 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 the absolute value of the slope of the first negative pressure gradient between the upstream position (A) and the midstream position (B), which 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 diagram further illustrates that when the single-phase melt enters the larger mold chamber at the filling position (C), its pressure drops to the same level as the existing back pressure in the mold chamber (70 MPa in the diagram) immediately after the adjacent widening section (i.e., the section from C to D in the diagram).

To ensure that the absolute value of the slope of the second negative pressure gradient is different 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-multiples of 10, such as 141%, 164%, or even 172.3%. This range is merely a preferred embodiment and does not cover the entire scope of the present invention. Therefore, even if the range is exceeded, it should still be protected by this patent application within the scope of its application.

Referring to Figure 3, 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).

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 plate-shaped and are mounted on conventional vertical or horizontal clamping devices to be 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 in the mold-closing position, 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 in the mold-opening position, 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.

The gating system (50) is recessed in the shape of a straight hole on the side of the first mold part (20) that is not used to merge with 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 merge with the second mold part (30), and is connected to the gating system (50) at one end and to the mold chamber (40) at the other end, with the gate (70) defined by the orifice at the other end. In one feasible embodiment, the buffer space (60) and the gating system (50) can be coaxial.

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

In accordance with the aforementioned method embodiments, the runner (50) and the buffer 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 connection between the runner (50) and the buffer space (60) is defined as the midstream position, and the location of the gate (70) is defined as the mold filling position. In this process, the single-phase melt is driven by the injection pressure into the runner (50) and then fills the mold chamber (40) through the buffer space (60), thereby achieving the pressure and flow rate control effect disclosed in the aforementioned method embodiments, and thus ensuring the quality of the final molded product.

(A): Upstream position (B): Midstream position (C): Filling position (10): Injection structure of reverse compression molded foam (20): First mold (30): Second mold (40): Mold chamber (50): Runner (60): Buffer space (70): Gate

Figure 1 is a flowchart of the method disclosed in a preferred embodiment of the present invention. Figure 2 is an example diagram of the pressure and flow rate distribution of the method disclosed in a preferred embodiment of the present invention. Figure 3 is a plan view of the article disclosed in another preferred embodiment of the present invention.

(10): Injection structure of reverse compression molded foam

(20): First module

(30): Second module

(40): Mold Chamber

(50): Watering the road

(60): Buffer space

(70): Pouring saliva

Claims (4)

An injection structure for a reverse-pressure molded foam includes: a first mold portion; a second mold portion movable between a mold-closed position joined with the first mold portion and a mold-opening position separated from the first mold portion; a mold chamber defined by the first mold portion and the second mold portion when joined, located between the joined first mold portion and the second mold portion; a perforated runner recessed into the first mold portion from one side; and a perforated buffer space recessed into the first mold portion from the other side, communicating with the runner 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 runner. The injection structure for the reverse-pressure molded foam as described in claim 1, wherein the orifice axis of the buffer space is coaxial with the orifice axis of the gating system. The injection structure of the reverse-pressure molded foam as described in claim 2, wherein the buffer space is a straight hole with a single inner diameter. The injection structure of the reverse-pressed foam as described in claim 1, 2 or 3, wherein the inner diameter of the buffer zone space is between 120% and 200% of the inner diameter of the runner.