Anti-falling rubber coating structure of double-color injection molding product and preparation method thereof

Abstract

The invention belongs to the technical field of injection molding products, and particularly relates to a double-color injection molding product anti-falling rubber coating structure which comprises a base body and a rubber coating layer coating the surface of the base body, a plurality of triangular inverted-buckle protrusions are arranged on the surface of the base body, and embedded grooves matched with the triangular inverted-buckle protrusions are formed in the corresponding positions of the rubber coating layer. Two base angles of each triangular inverted buckle bulge face the direction of the rubber coating layer, and a vertex angle is in acute angle connection with the surface of the base body. The interface bonding force between the rubber coating layer and the base body is remarkably enhanced through geometric interlocking design, a mechanical meshing structure is formed by the triangular back-off protrusions on the surface of the base body and the embedded grooves of the rubber coating layer, the peel strength of the triangular back-off protrusions and the embedded grooves of the rubber coating layer is improved by 30%-50% compared with a traditional plane structure, and the problem that the rubber coating layer is prone to falling off is effectively solved; meanwhile, the inverted buckle structure and the base body are subjected to synchronous injection molding, additional machining steps are not needed, the production process is simplified, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of injection molding products, and particularly relates to an anti-shedding encapsulation structure for a two-color injection molding product and a preparation method thereof. Background Art

[0002] In the field of injection-molded automotive parts, two-shot injection molding is widely used in automotive NVH products and electronic device housings, as it combines the functional properties of different materials (such as the structural strength of a hard plastic base and the cushioning and sealing properties of a soft plastic overmolding layer). However, existing technologies suffer from insufficient interfacial bonding strength between the overmolding layer and the base, making it prone to peeling and seriously impacting product reliability.

[0003] Traditional solutions primarily improve bonding strength through mechanical retaining structures (such as slides and elastic parts) or by increasing the roughness of the contact surface. However, these methods have significant drawbacks: mechanical retaining structures require additional components, leading to complex product structures and increased production costs; methods that increase roughness (such as sandblasting and chemical etching) face challenges such as limited bonding strength improvement, poor process stability, and potential damage to the substrate surface properties. Furthermore, existing technologies struggle to accommodate the universal needs of different material combinations (such as hard and soft adhesives), limiting the application and expansion of two-shot injection molding products in complex working conditions. Summary of the Invention

[0004] The object of the present invention is to provide an anti-shedding encapsulation structure for a double-color injection molded product to solve the problems existing in the background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: an anti-falling encapsulation structure for a two-color injection molded product, comprising a base and an encapsulation layer coated on the surface of the base, a plurality of triangular inverted protrusions being provided on the surface of the base, and the encapsulation layer forming an engaging groove adapted to the triangular inverted protrusions at corresponding positions, the two bottom corners of the triangular inverted protrusions facing the direction of the encapsulation layer, and the top angle being connected to the surface of the base at an acute angle.

[0006] Preferably, the vertex angle of the triangular inverted protrusion is 30°-60°.

[0007] Preferably, the base body and the rubber coating are injection molded from different materials, the base body is made of thermoplastic plastic, and the rubber coating is made of elastomeric material.

[0008] Preferably, the thermoplastic material includes PA and the elastomeric material includes EVA or TPU.

[0009] Preferably, the triangular undercut protrusion is injection-molded synchronously with the base, and the height of the protrusion is flush with the surface of the base.

[0010] A method for preparing an anti-shedding encapsulation structure for a two-color injection molded product, characterized by comprising the following steps: (1) Mold cavity processing: Process a triangular concave structure on the cavity surface of the injection mold. The top angle of the concave is 30°-60°, and the depth of the triangular concave in the mold is flush with the target substrate depth; (2) One-shot injection molding: using thermoplastic plastic to perform one-shot injection molding on the mold of step (1) to form a base with a triangular boss; (3) Secondary overmolding: The substrate is placed in a two-color injection mold, and the elastomer material is injected to fill the gap between the triangular bosses. After curing, an overmolding layer is formed that fits in with the triangular undercut protrusions.

[0011] Preferably, the thermoplastic is PA, and the elastomeric material is EVA or TPU.

[0012] Preferably, the mold temperature for the primary injection molding in said step is 80-110° C., and the injection molding pressure is 8-12 MPa; the mold temperature for the secondary encapsulation in said step is 8-20° C., and the injection molding pressure is 8-15 MPa.

[0013] The beneficial effects of the present invention are as follows: the present invention significantly enhances the interfacial bonding force between the encapsulation layer and the substrate through a geometric interlocking design; the triangular undercut protrusions on the surface of the substrate and the interlocking grooves of the encapsulation layer form a mechanical interlocking structure, which increases the peeling strength between the two by 30%-50% compared with the traditional planar structure, effectively solving the problem of easy falling off of the encapsulation layer; at the same time, the undercut structure and the substrate are injection molded simultaneously, without the need for additional processing steps, simplifying the production process and reducing production costs.

[0014] This structure is suitable for a variety of material combinations, such as the hard and soft combinations of thermoplastic PA and elastomeric materials EVA and TPU, and can be widely used in automotive accessories, electronic equipment casings and other fields. After the encapsulating material is secondary injection molded to fill the boss gap and solidify, it forms a tightly fitted integrated structure with uniform and reliable bonding force, combining material adaptability and structural stability to meet the long-term use requirements under complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram of the present invention; Figure 2 This is an enlarged view of the fit between the triangular undercut and the rubber layer; Figure 3 This is the design drawing of the base mold. DETAILED DESCRIPTION

[0016] In the description of the present disclosure, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present disclosure.

[0017] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this disclosure, unless otherwise specified, "plurality" means two or more.

[0018] In the description of this disclosure, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," "connect," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections, electrical connections, or communication connections; they may refer to direct connections or indirect connections through an intermediate medium; they may refer to internal communication between two components or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this disclosure based on specific circumstances.

[0019] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0020] like Figure 1 Figure 1 shows an anti-slip encapsulation structure for two-shot injection molded products. A method for fabricating such an anti-slip encapsulation structure for two-shot injection molded products is also described. This structure consists of a substrate 1 and an encapsulation layer 2. Its core lies in numerous triangular undercut protrusions 3 distributed on the substrate surface, with matching recesses 4 formed in the encapsulation layer. This geometric interlocking design significantly enhances the interfacial bonding between the encapsulation layer and the substrate. The acute apex angles of the undercuts (connected to the substrate surface at an acute angle) form a "wedge-shaped locking" structure. When the encapsulation is peeled off by external forces, the inclined surfaces of the triangular protrusions exert a force perpendicular to the interface, preventing it from detaching (based on the principle of geometric interlocking). A smaller apex angle increases the force component, but the substrate strength must be considered (a too small apex angle can easily cause the protrusions to break).

[0021] During the preparation process, Example 1: Taking automotive NVH (noise, vibration and harshness) control components as an example (such as engine hood gasket) 1. Mould design and processing: Based on product design requirements, we design and manufacture a two-shot injection mold. Using precision machining techniques (such as CNC milling and EDM) we create an array of evenly distributed triangular bosses on the mold cavity surface (corresponding to the area of ​​the base body that requires encapsulation) during the first injection molding (base molding).

[0022] The geometric parameters of the triangular boss are set to: the top angle is 45°. The density of the boss arrangement is adjusted according to the required bonding force, and is usually designed to set a boss every 1.5-2cm. The bottom edge direction of the boss should avoid being parallel to the expected main force direction of the rubber layer (for example, it can be designed to be staggered or at a certain angle to the force direction) to optimize the anti-peeling performance. The mold material should be selected from steel with good wear resistance (such as H13), and ensure that the surface finish of the boss area meets the demoulding requirements (see Appendix Figure 3 ).

[0023] 2. One-shot injection molding (matrix molding): Nylon (PA66) is selected as the base material. This material has high strength, rigidity and heat resistance, and is suitable for high-temperature and high-pressure components.

[0024] Dry the PA66 pellets at 120°C for more than 4 hours to ensure that the moisture content is less than 0.1%.

[0025] Set the injection molding machine parameters: barrel temperature 260-300℃, mold temperature 80-110℃, injection pressure 8-12MPa, holding pressure 40-80MPa. The injection and holding times are determined according to the product size.

[0026] Injection molding is performed. The molten PA66 fills the mold cavity, simultaneously forming a triangular boss structure on the mold cavity surface and dense triangular undercut protrusions on the substrate surface. After cooling, the mold is opened to obtain a PA66 substrate with triangular undercut protrusions.

[0027] 3. Matrix transfer and secondary injection molding (encapsulation layer molding): The primary-molded PA66 substrate is accurately placed into the corresponding secondary molding cavity of the two-shot injection mold using a robot, manual rotation, or direct rotation of the two-shot mold. The mold design must ensure precise positioning of the substrate and that the encapsulated area aligns perfectly with the boss area of ​​the primary mold.

[0028] Ethylene-vinyl acetate copolymer (EVA, Shore A 60-70) is selected as the encapsulation material. EVA has good elasticity, flexibility, shock absorption properties and compatibility with PA.

[0029] Set the secondary injection molding parameters: barrel temperature 80-110℃, mold temperature 8-20℃ (usually lower than the primary injection mold temperature, which is conducive to rapid cooling and shaping of EVA), injection pressure 8-15MPa, and holding pressure 3-6MPa.

[0030] Perform secondary injection molding. The molten EVA is injected into the mold, tightly wrapping the target area surface of the PA66 matrix and fully flowing into all the gaps between the triangular undercut protrusions on the matrix surface (see attached Figure 1 、 2 ). Under the action of injection molding pressure and temperature, after the EVA cools and solidifies, a triangular fitting groove is formed, which is precisely complementary to the undercut protrusion of the substrate, achieving strong mechanical interlocking.

[0031] 4. Cooling and demoulding: Keep the mold closed to allow the rubber layer to fully cool and solidify. The cooling time is determined by the thickness of the product and the characteristics of the EVA.

[0032] After the mold is opened, the ejector mechanism ejects the final two-shot molded product. Thanks to the rational design of the triangular undercut protrusion (a 45° vertex angle is within the optimal range) and the good elasticity of the EVA material, the product can be smoothly demolded without damaging the undercut structure or the rubber layer.

[0033] Tests have shown that the peel strength of the encapsulation layer of the PA66 / EVA two-color component using this triangular inverted structure is about 40% higher than that of a traditional structure with the same material combination but a smooth surface. This significantly improves the long-term reliability of the product in a vibration environment during transportation and effectively prevents the encapsulation layer from falling off.

[0034] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A double-color injection molded product anti-shedding encapsulation structure, characterized by: The invention comprises a base body (1) and an encapsulating layer (2) coated on the surface of the base body (1), wherein the surface of the base body (1) is provided with a plurality of triangular undercut protrusions (3), and the encapsulating layer (2) forms an engaging groove (4) adapted to the triangular undercut protrusions (3) at corresponding positions, wherein the two bottom corners of the triangular undercut protrusions (3) face the direction of the encapsulating layer (2), and the top corners are connected to the surface of the base body (1) at an acute angle.

2. The anti-shedding encapsulation structure for double-color injection molded products according to claim 1, characterized in that: The vertex angle of the triangular undercut protrusion (3) is 30°-60°.

3. The anti-shedding encapsulation structure for double-color injection molded products according to claim 1, characterized in that: The base body (1) and the rubber coating layer (2) are injection-molded from different materials; the base body (1) is made of thermoplastic plastic, and the rubber coating layer (2) is made of elastomeric material.

4. The anti-shedding encapsulation structure for double-color injection molded products according to claim 3, characterized in that: The thermoplastic material includes PA (polyamide), and the elastomeric material includes EVA (ethylene-vinyl acetate copolymer) or TPU (thermoplastic polyurethane).

5. The anti-shedding encapsulation structure for double-color injection molded products according to claim 1, characterized in that: The triangular undercut protrusion (3) is injection-molded synchronously with the base (1), and the height of the protrusion is flush with the surface of the base (1).

6. A method for preparing the anti-shedding encapsulation structure of a double-color injection molded product according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Mold cavity processing: a triangular concave structure is processed on the cavity surface of the injection mold, wherein the top angle of the concave is 30°-60°, and the depth of the triangular concave in the mold is flush with the depth of the target substrate (1); (2) One-step injection molding: using thermoplastic plastic to injection mold the base (1), so that the triangular boss is simultaneously molded into a triangular undercut protrusion (3) on the surface of the base (1); (3) Secondary encapsulation molding: The primary molded base (1) is placed in a two-color injection mold, and the encapsulation material is injected to fill the gap of the triangular undercut protrusion (3) and solidified to form an interlocking groove (4) that matches the triangular undercut protrusion (3), thereby obtaining an encapsulation layer (2).

7. The preparation method according to claim 6, characterized in that: The thermoplastic material is PA, and the elastomer material is EVA or TPU.

8. The preparation method according to claim 6, characterized in that: In the step (2), the mold temperature for the primary injection molding is 80-110° C., and the injection molding pressure is 8-12 MPa; in the step (3), the mold temperature for the secondary encapsulation molding is 8-20° C., and the injection molding pressure is 8-15 MPa.

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