Method and mould for manufacturing multicomponent parts in which at least one of the components is liquid silicone

Abstract

The present invention relates to a method and mould (1) applied to the manufacture of parts in two ("2k") or more distinct components, at least one of which is a silicone rubber. Said mould (1) comprises a system with injection channels (11 and 12), moulding zones (6) and moving elements (14) that move in two different states: initially, there is space for the injection of the first component (15) and the secondary injection channel (12) is closed; subsequently, after the injection of the first component (15) and the movement of the moving element (14), space opens up for the injection of the second material (16) and the primary injection channel (11) closes. Said mould (1) has angled surfaces (9) the angles of which, with the movement of the moving components, compress protuberances in the moulded part with the first component (17), helping to reduce burrs during the injection of the second material.

Description

METHOD AND MOLD FOR MANUFACTURING MULTI-COMPONENT PARTS IN WHICH AT LEAST ONE OF THE COMPONENTS IS LIQUID SILICONE

[0001] The present invention relates to a method and mold for injecting multicomponent parts, that is, parts made up of two (“2k”) or more materials, namely, these components being: liquid silicone (LSR) combined with liquid silicone, liquid silicone combined with thermoplastic polymer or other combinations between elastomeric materials and polymers with distinct properties or colors, in which the injections of both components occur without opening the mold.

[0002] The state of the art presents some examples of techniques for manufacturing multicomponent polymer parts, primarily in two different materials, known as "2k" (2k) molds. Many of the presented methods, however, require opening the mold and transferring the part to another molding zone. Therefore, a limitation of this methodology is the high cycle times and increased costs associated with robotic systems, due to the need to handle the parts between the injection processes of each component.

[0003] To reduce part handling times, devices were developed that, after a quick mold opening, realign the molding zones, allowing the injection of new layers of material. One example is patent application US5026265A by Toshiyuki Kanai and Nobuo Shinnoh, published on July 25, 1991, which discloses a system for molding parts with multiple layers of polymeric materials, with the second material adhering to the grooves in the surface of the first material. In this device, the process utilizes three main mold parts, designated Z, W, and Y. Z represents the cavity and is attached to the injection machine's moving plate. W and Y represent the bushings, and are attached to a plate that moves perpendicular to the machine's opening axis. First, the first material is injected into the molding region formed between parts Z and W.Subsequently, the mold opens, bushing Y moves to the position previously occupied by bushing W, the mold is closed, and the second component is injected, forming the final multicomponent part. However, a limitation of this methodology is the need to open the mold to realign the two molding zones (bushing and cavity). This process increases cycle times, presents disadvantages regarding material adhesion, and requires additional components. Another example is patent application PT 103381 B, by Paulo Juliano Pereira da Silva Araújo, published on May 31, 2007, which discloses a support system for multicomponent injection molds. Such molds are capable of injecting parts into multiple components by utilizing rotating movable components or "sides."However, rotary molds have the disadvantage of having a greater number of components, being larger, requiring greater material consumption in their manufacture and only being suitable for use in larger injection machines.

[0004] Patent application US11155011B2, by Kota Nakashima, published on August 1, 2019, describes a mold that does not require an opening for the injection of two or more materials. The process is accomplished through the movement of elements in bushings, often referred to as "core-backs." A limitation of this invention is that it is only applicable to thermoplastic materials, which, during the injection process, have viscosities up to four orders of magnitude greater than liquid silicones. This difference in viscosity causes the liquid silicone to flow through undesirable areas and leads to the creation of burrs, which ultimately discourages the use of moving components in molds that work with this type of elastomeric material.

[0005] Furthermore, none of the methods present in the state of the art provide solutions for the distribution of temperatures throughout the mold, which may result in the clogging of the injection nozzles and damage to the system.

[0006] In cases where this method is used only for the injection of two different liquid silicones, it is known that both molding zones and their respective plates must be heated to temperatures between 120 and 180°C, and there may be a cooled plate (4), around 20°C, to prevent premature curing of the material in the nozzles, also cooled, and in the injection channels (11 and 12). In these situations, both injection channels, primary (11) and secondary (12) are used for silicone injection.

[0007] In cases where this method is used for the injection of a liquid silicone and a thermoplastic, it is known that one of the injection channels must be used for the injection of the thermoplastic material while the other must be used for the injection of the silicone. Usually, the primary injection channel (11) is the channel through which the thermoplastic is injected, and the secondary injection channel (12) is the channel through which the silicone is injected. However, this description is only intended to exemplify a nomenclature normally applied to the channels, not excluding situations in which the injection sequence is changed, injecting silicone through the primary injection channel (11) and thermoplastic through the secondary injection channel (12).

[0008] Therefore, while silicone must be at low temperatures, typically below 30°C, in the secondary sprue (12) and heated within the molding zones (6) to temperatures between 120 and 180°C, the thermoplastic must be at high temperatures in the primary sprue (11), above 300°C, and cooled within the molding zones (6). Therefore, the high temperature of the primary sprue (11), used for the thermoplastic material, ends up generating significant heat transfer to elements that should be cooled. These cooled elements include the cooled plates (4), the nozzles, and the secondary sprue (12). In addition to reducing the system's energy efficiency, such heat transfer can also cause unwanted curing of the silicone and damage to the injection system and mold. Advantageous Effect of the Invention

[0009] To address the problems currently present in the prior art, the present method and mold offer the advantage of developing a manufacturing process, preferably by injection, for parts in which at least one of the components is liquid silicone. To this end, a moving element (14) is used, and both components are injected without opening the mold (1). Furthermore, thermal insulation systems, such as insulating sheets and blankets, are used to reduce heat transfer between the heated and cooled zones of the mold (1), increasing the energy efficiency of the process and reducing the likelihood of downtime for maintenance and cleaning of solidified material outside the molding zones (6). Furthermore, the molding zones (6) may have angled faces (9) that create protruding contours in the part molded with the first component (17).Said protruding contours (17) cause part of the part composed of the first component (15) to be compressed, during the movement of the mobile element (14), against the walls of the molding zones. In this way, said compressed region acts as a sealing material, preventing leaks and, consequently, reducing the creation of burrs in the part of the part injected with the second component (16).

[0010] The present invention will be explained in detail with the aid of the drawings and the indications present therein:

[0011] For the purpose of promoting an understanding of the principles according to the embodiments of the present invention, reference will be made to the embodiments illustrated in the figures and to the language employed to describe them. In any event, it should be understood that there is no intention to limit the scope of the present invention to the content of the figures. Any subsequent changes or modifications to the inventive features illustrated herein, as well as any additional applications of the principles and embodiments of the invention illustrated, which would normally occur to one skilled in the art having possession of this description, are considered within the scope of the claims of the present invention.

[0012] Therefore, the figures constitute examples of application of the methodology and mold described in the present invention.

[0013] [Fig. 1] Represents a three-dimensional, isometric view of the mold, highlighting the injection channels for each of the materials; the primary injection channel (11) and the secondary injection channel (12), the fixed sides (2) and mobile side (3), the interface or system (13), which allows the movement of the mobile element (14), and the cooled plates (4) and heated plates (5), on the fixed side;

[0014] [Fig. 2] A side view, in section, of the mold with the molding zones (6), highlighting the bushing (8) and the cavity (7), the injection channel of the first, primary component, (11), the injection channel of the second, secondary component, (12), the mobile element (14), the system or interface (13) that moves the mobile element, and the extraction system (10) formed by extraction plates and extractors, preferably with a cylindrical body and conical head;

[0015] [Fig. 3] A side view, in section, of the mold with the mobile element (14) advanced due to the position, also advanced, of the system or interface (13) that moves such component. Also noteworthy are the angled faces (9) in the molding zones (6), created to reduce leaks during the injection of the second component;

[0016] [Fig. 4] A side view, in section, of the mold with the movable element (14) recessed due to the position, also recessed, of the system or interface (13) that moves such component;

[0017] [Fig. 5] A side view, in section, of the mold during extraction of the part, highlighting the advanced position of the extraction system (10);

[0018] [Fig. 6] A detailed view of the mold region featuring angled faces (9), which act as geometries capable of helping to reduce material leakage during the injection of the second component. This face produces protruding contours (17) in the part of the part molded with the first component, when the mobile element is in the advanced position, and then compresses it when the mobile element is withdrawn;

[0019] [Fig. 7] A detailed view, at different stages of the injection process, of the region of the molded part that presents the geometry to reduce leaks consisting of protruding contours (17). In a first stage, only the part of the part composed of the first component (15) was injected; subsequently, during the injection of the part of the part composed of the second component (16), the region with protruding contours (17) is compressed. Finally, after opening the mold, the compressive forces cease and the region with protruding contours (17) returns, totally or partially, to its original state;

[0020] [Fig. 8] Shows an example of a final part molded in two components (15 and 16), showing a three-dimensional, isometric view and two side views, in section, highlighting the injection point (18) of the first component (15) and the injection point (19) of the second component (16). In each of the side views, a stage of the injection is shown, with a stage in which only the first component (15) was molded and a stage in which both components (15 and 16) were molded.

[0021] The said method and mold (1) consists of an injection system through which the controlled flow of the polymeric material occurs associated with a set of elements that form a fixed side (2) and a mobile side (3), as shown in figures 1 and 2.

[0022] The injection system includes two channels: a primary channel (11) for injecting the first material, equipped with systems for closing the respective channel; and a secondary channel (12) for injecting the second material, equipped with a second closing system. Each of these closing systems is capable of allowing or stopping the flow of material from an injection unit. Said channels (11 and 12) may both be cold runners, for injecting liquid silicone, or one of them may be hot runners, for injecting thermoplastics.

[0023] Said mold (1) includes one or more molding zones (6), composed of cavities (7) and bushings (8), and in the case exemplified in figure 2, the cavity is present on the fixed side (2). The molding zones (6) have mobile elements (14) that, under the action of the movement of a mechanism or system (13), move, allowing two different states in the bushing. Said system or interface (13) is preferably of the hydraulic, pneumatic or electric type.

[0024] In the state defined as the first state, a mobile element (14), located on the fixed side (2) or on the mobile side (3) of the mold (1), is in the advanced position, allowing space only for injection of the part of the final part composed of the first component (15), through the first injection channel (11), and the injection channel of the second component (12) is completely closed. This state is shown in figure 3.

[0025] In the state defined as the second state, after partial or total injection of the part of the part composed of the first component (15), a mobile element (14), located on the fixed side (2) or on the mobile side (3) of the mold (1), moves, partially or totally, until it reaches a recessed position, so that space is opened for the injection of the second component (16), by means of the second injection channel (12), and the first injection channel (11) is totally or partially closed. This state is shown in figure 4.

[0026] Depending on the characteristics of the different injected materials, there may or may not be a time interval between the end of the first stage and the beginning of the second. This time interval corresponds to the time required for the solidification of the part composed of the first component (15). If there is no such time interval or if the injection channel of the first component (11) is not completely closed after the beginning of the second stage, a small degree of mixing occurs between the two components, contributing to their adhesion. At the end of the second stage, it is always necessary to wait a period of time for the injected part to solidify, allowing its extraction.

[0027] Adjusting the position of the mobile element (14), between the forward and fully recessed positions, allows adjustment of the layer thickness of the second component (16), representing a technical advantage when rapid changes need to be made to the final part.

[0028] In said molding zones (6), angled faces (9) may also be associated, with angles between 0 and 60º in relation to the mold opening axis, such that they mold in the first component (15) protruding contours (17) capable of reducing the probability of creating burrs due to material leakage during injection. Figure 6 exemplifies a situation in which the withdrawal movement of the mobile element (14) causes a part of the bushing (8) to also be withdrawn and make room for the injection of the second component (16). During such movement, some of the areas with said protruding contours (17), previously molded with the first component (15), are compressed against the walls of the molding areas (6) and function as a sealing material, preventing leaks and, consequently, reducing the creation of burrs in the part of the part injected with the second component (16). The angled faces (9) have walls with an inclination, in relation to the mold opening axis, between 0 and 60º.Figure 7 illustrates the compression process during part molding. The first layer of the part, molded in the first component (15), has protruding contours (17) that are compressed against the walls of the molding zones (6) while the second material is injected to form the second layer of the part (16); at the end of both injections, the part is extracted and the zone with an angled wall (17) returns partially or completely to its original position.

[0029] Once the injection and solidification process of both materials in the part is complete, the part is extracted, as shown in Figure 5. In Figure 5, the extraction system (10) is preferably mechanical, driven by extractor plates that move cylindrical body and conical head extractors. However, this extraction system can also operate through the use of air valves, suction systems, automation, or other means that allow the parts to be removed from the molding zones.

[0030] Regarding the injection process, when injecting liquid silicones (LSR), this type of material is prepared and injected cold, at temperatures between 15 and 30°C, using an injection unit and a nozzle with an injection channel. Within the mold, this material solidifies when heated. Thermoplastics, on the other hand, are injected hot, using an injection unit and a heated nozzle with an injection channel, and solidify when cooled within the mold.

[0031] Therefore, for two-component injection to be possible, it is necessary to ensure the correct temperatures in the different parts of the mold that are in contact with the nozzles in which the injection channels are located.

[0032] In cases where two different liquid silicones are injected, it is known that both molding zones and their respective sheets must be heated to temperatures between 120 and 180ºC, and there may be a cooled sheet (4) at around 20ºC to prevent premature curing of the material in the nozzles, also cooled, and in the primary and secondary injection channels (11 and 12). Between a heated sheet (5) and a cooled sheet (4) there must be insulation structures, such as insulating sheets.

[0033] When injecting liquid silicone and a thermoplastic, the silicone must be at low temperatures in the secondary injection runner (12) and heated within the molding zones (6) to temperatures between 120 and 180°C; the thermoplastic must be at high temperatures in the primary injection runner (11), above 300°C, and cooled within the molding zones (6). Therefore, the high temperature of the nozzles and primary injection runner (11) ends up generating significant heat transfer to elements that should be cooled. These cooled elements include the cooled plates (4), the nozzles, and the secondary injection runner (12). In addition to reducing the system's energy efficiency, this heat transfer can also cause unwanted curing of the silicone and damage to the injection system and mold.Therefore, there must be insulation structures between the heated plates (5) and cooled plates (4) and there must also be other insulation structures between: each of the nozzles and the plates to which they are attached, for example, through the use of insulation blankets; or between the nozzles, for example, with the insertion of insulation structures in the walls of the plates that separate them; or with the insulation only of the nozzle for the injection of silicone in relation to the plates to which it is attached.

[0034] Finally, there may also be gaps between heated plates (5) and cooled plates (4) that allow the flow of liquids that condense, due to the different temperatures in the mold, and deposit close to the nozzles used for injection.

[0035] Therefore, the present method and mold present advantageous applications for the injection of a wide range of two-component parts, in which at least one of the materials used is liquid silicone (LSR). Among the various uses, Figure 8 presents an example of an application, in which a sponge is injected into two different types of silicone and the injection point (18) of the first component (15) is hidden by the second material (16).

[0036] Figure 8 is intended to exemplify a possible product preferably made by the method described in the present invention. Both Figure 8 and the other figures and examples should not be seen, therefore, as limitations to the objective of the present invention, but rather as complements to its scope. List of references

[0037] 1. Mold;

[0038] 2. Fixed side of the mold;

[0039] 3. Moving side of the mold;

[0040] 4. Cooled plate on the fixed side of the mold;

[0041] 5. Heated plate on the fixed side of the mold;

[0042] 6. Molding zones;

[0043] 7. Cavity;

[0044] 8. Bushing;

[0045] 9. Angled faces, in the molding area;

[0046] 10. Part extraction system;

[0047] 11. First component injection channel, or primary channel;

[0048] 12. Second component injection channel, or secondary channel;

[0049] 13. Mechanism, interface or system that allows the movement of the mobile element;

[0050] 14. Mobile element;

[0051] 15. Part of the final piece composed of the first component;

[0052] 16. Part of the final piece composed of the second component;

[0053] 17. Protruding contour, in the part molded with the first component.

[0054] 18. Injection point of the first component;

[0055] 19. Injection point of the second component; Patent Literature

[0056] Patent Application US5026265A; by Toshiyuki Kanai and Nobuo Shinnoh, published July 25, 1991.

[0057] Patent Application PT 103381 B; by Paulo Juliano Pereira da Silva Araújo, published on May 31, 2007.

[0058] Patent Application US11155011B2, by Kota Nakashima, published on August 1, 2019;

Claims

Method for injecting parts into two or more components, at least one of the components being a silicone rubber, manufactured in a mold (1), characterized by comprising stages in which: In a first state, a mobile element (14), located on the fixed side (2) or on the mobile side (3) of the mold (1), is in the advanced position, allowing space only for injection of the first component (15), by means of the first injection channel (11), and the injection channel of the second component (12) is completely closed; In a second state, after partial or total injection of the first component (15), a mobile element (14), located on the fixed side (2) or on the mobile side (3) of the mold (1), moves, partially or completely, until reaching a recessed position, so that space is opened for injection of the second component (16), by means of the second injection channel (12), and the first injection channel (11) is completely or partially closed. Method, according to claim 1, characterized in that the displacement of the mobile element (14), the injection of the first component (15) and the injection of the second component (16) of the part are carried out without opening the mold (1). Method, according to claim 1, characterized in that the retraction displacement of the mobile element (14) is preferably in a direction parallel or perpendicular to the mold opening and in the opposite direction to the molding zones (6). Method, according to claim 1, characterized in that the advance displacement of the mobile element (14) is preferably in a direction parallel or perpendicular to the mold opening and in the direction of the molding zones (6). Mold, for the injection of parts in two or more components, at least one of the components being a silicone rubber, characterized by having: fixed side (2); mobile side (3); mobile element (14); injection channel of the first component (11); injection channel of the second component (12); bushing (8); cavity (7); extraction system (10); Mold, according to claim 5, characterized in that the fixed (2) and mobile (3) sides have molding zones (6) composed of one or more bushings (8) and cavities (7). Mold, according to claim 5, characterized in that the molding zones (6) present angled faces (9), with angles between 0 and 60º in relation to the mold opening axis, which create protruding contours in the part of the part molded with the first component (17). Mold, according to claim 5, characterized in that after the displacement of the mobile element (14), the protruding contours (17) have dimensions, in the plane perpendicular to the mold opening axis, greater than the distance between the cavity wall (7) and the bushing wall (8). Mold, according to claim 5, characterized by having heated plates and cooled plates, as well as cooled injection channels and heated injection channels, so that, between heated plates or components and cooled plates or components there are thermal insulation structures, preferably consisting of insulating plates or insulation blankets. Mold, according to claim 5, characterized by there being gaps with a width between 1 and 10 millimeters that create ducts between the injection nozzles and the lower surface of the mold, allowing the flow of liquids originating from condensation.

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