Mechanical gradient bionic skin multilayer injection mold and forming method

Abstract

The invention provides a mechanical gradient bionic skin multi-layer injection mold and a forming method. The mechanical gradient bionic skin multi-layer injection mold comprises a fixed mold plate and a movable mold plate. The mold core slides in the center of the movable mold plate in the cavity, a groove corresponding to a product in shape is formed in the fixed mold plate, and an initial cavity is formed between the mold core and the bottom face of the groove. According to the method, a special mold with a movable mold core is adopted, biomimetic materials with different hardness and elasticity moduli are sequentially injected into the same cavity by accurately controlling mold closing, injection molding and mold opening actions, and one-time forming from epidermis to dermis and subcutaneous tissue is achieved. The bionic skin with the structure of'soft epidermis-tough dermis-elastic subcutaneous tissue 'and the mechanical property in gradient change is manufactured in a one-time forming period by accurately controlling mold actions and a multi-material sequential injection molding process, industrialization is easy, and more reliable ergonomic data is provided for design of safety protection and military equipment.

Description

Technical Field

[0001] This invention relates to the field of biomimetic material preparation and advanced injection molding technology, specifically a multi-layer injection mold and molding method for biomimetic skin with mechanical gradient. Background Technology

[0002] In fields such as automotive collision testing, drone impact testing, aerospace human factors engineering, and individual soldier protective equipment testing, bionic skin is needed to accurately simulate the biomechanical response of human tissue under impact, laceration, puncture, and extreme environments. Currently, bionic skin used for such testing is mostly made from a single homogeneous material or assembled by bonding different components later. Homogeneous materials cannot simulate the natural differences in hardness, elastic modulus, and coefficient of friction of skin in different parts of the human body (such as the forearm and chest), resulting in significant deviations between test data and real human biomechanical responses. Furthermore, later bonding methods suffer from weak adhesion, easy delamination, complex processes, and difficulty in achieving continuous transitions in interlayer properties, making interfaces prone to becoming structural weak points during testing.

[0003] Existing multi-layer injection molding technology is mostly used to manufacture appearance parts or simple structural parts, and lacks special processes and control methods for biomimetic skin, which requires internal mechanical gradients and high biosimulation characteristics. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a multi-layer injection mold and molding method for biomimetic skin with mechanical gradients. Through mold design and motion control, as well as a multi-material sequential injection molding process, biomimetic skin with a structure of "soft epidermis-tough dermis-elastic subcutaneous tissue" and gradient mechanical properties can be manufactured in a single molding cycle. This invention provides a mechanical gradient biomimetic skin multilayer injection mold, including a fixed mold plate and a moving mold plate; the moving mold plate has a cavity in the center, and the mold core slides in the cavity through a slider base connected to the rear end; the fixed mold plate is provided with a runner, a gate and a groove corresponding to the product shape connected in sequence, and an initial cavity is formed between the mold core and the bottom surface of the groove.

[0005] In a further improvement, the moving template has multiple chambers arranged vertically, each chamber containing an independently controlled mold core, and the fixed template has several grooves that match the positions of the mold cores.

[0006] This invention also provides a method for multi-layer injection molding of biomimetic skin with mechanical gradient, using a multi-layer injection mold for biomimetic skin with mechanical gradient, comprising the following steps: 1) Select the materials for each layer according to the usage requirements and set the injection temperature, pressure, speed, and core movement sequence and stroke for each layer; 2) Skin layer injection molding: Close the mold and inject a low-hardness, high-elasticity first thermoplastic elastomer material into the cavity to form the skin layer; 3) Cavity switching and dermal layer injection: When the surface layer material is semi-cured or in a thermoplastic state, drive the mold core backward to expand the cavity volume, and inject a second thermoplastic elastomer material with high toughness and medium to high hardness to form the dermal layer; 4) Subcutaneous tissue layer injection molding: In the semi-cured state of the dermal material, the mold core is driven back again to inject a low-density, high-elasticity third material to form the subcutaneous tissue layer; 5) Cooling and demolding: After the molded part is cooled in a controlled manner, it is opened and ejected.

[0007] Further improvements include: step 2) the Shore hardness of the first thermoplastic elastomer material is A5–25; step 3) the Shore hardness of the second thermoplastic elastomer material is A40–70; and step 4) the third material is low-density thermoplastic polyurethane foam or silicone rubber foam. The first and second thermoplastic elastomer materials are one or more of thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), or silicone rubber.

[0008] In a further improvement, the retraction stroke of the mold core is 0.5–3.0 mm. The mold core retracts for the first time within 1–10 seconds after the skin layer injection is completed, and retracts for the second time within 5–15 seconds after the dermis layer injection is completed.

[0009] Further improvements include an injection molding temperature of 180–210°C and an injection speed of 30–70 cm³ / s for the epidermis; an injection molding temperature of 190–220°C and an injection speed of 60–100 cm³ / s for the dermis; and an injection molding temperature of 160–190°C and an injection speed of 20–50 cm³ / s for the subcutaneous tissue.

[0010] Further improvements include a mold temperature of 40–60°C, a skin layer holding time of 3–8 seconds, and an overall cooling time of 20–50 seconds.

[0011] The beneficial effects of this invention are as follows: 1. By precisely controlling the mold movements and using a multi-material sequential injection molding process, a biomimetic skin with a structure of "soft epidermis-tough dermis-elastic subcutaneous tissue" and gradient changes in mechanical properties can be manufactured in a single molding cycle.

[0012] 2. The obtained biomimetic skin sample has a thinner dermis and subcutaneous tissue in the cheekbone area, resulting in higher overall hardness; while the dermis and subcutaneous tissue in the cheek area are thicker, resulting in greater overall softness. A continuous gradient of hardness and elastic modulus exists from the epidermis to the dermis, with strong interlayer bonding and no delamination, successfully simulating the regional mechanical and structural gradient characteristics of facial skin.

[0013] 3. This method effectively solves the technical bottleneck of heterogeneous skin preparation. The prepared gradient skin has strong interlayer bonding force, and the process can be realized on a regular injection molding machine, making it easy to industrialize.

[0014] 4. This skin can significantly improve the effectiveness of biomechanical response testing in scenarios such as extreme temperatures, drone cuts, car collisions, evaluation of military bulletproof vest backings, and aerospace ejection seat impacts, providing more reliable ergonomic data for the design of safety protection and military equipment. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a process flow diagram of the present invention; Figure 2 A schematic diagram of the mold closing state structure with a retractable mold core; Figure 3 This is a schematic diagram of the cavity expansion after the mold core retracts; Figure 4 This is a schematic diagram of a cross-sectional structure of a biomimetic skin with a mechanical gradient. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a multi-layer injection mold for biomimetic skin with mechanical gradient, such as... Figure 2 and Figure 3 As shown, it includes a fixed template 1 and a moving template 2; the moving template 2 has a cavity 7 in the center, and the mold core 4 slides in the cavity 7 through the slider base 3 connected at the rear end; the fixed template 1 is provided with a runner 8, a gate 5 and a groove corresponding to the shape of the product connected in sequence, and the mold core 4 and the bottom surface of the groove form an initial cavity 6.

[0019] As an improvement, the moving template 2 is provided with multiple chambers 7 along the vertical direction, each chamber is provided with an independently controlled mold core 4, and the fixed template 1 is provided with several grooves that match the position of the mold core 4.

[0020] The injection molding process used in this invention is as follows: Figure 1 As shown, the details are as follows: The method includes the following steps: 1. Mold preparation and parameter setting: Use a special mold with a retractable mold core, and set the injection temperature, pressure, speed, and the timing and stroke of the mold core movement for each layer of material.

[0021] 2. Epidermal layer injection molding: Close the mold and inject a low-hardness, high-elasticity first thermoplastic elastomer material into the cavity to form the epidermal layer of biomimetic skin.

[0022] 3. Cavity Switching and Dermal Layer Injection: With the outer skin material semi-cured or in a thermoplastic state, the cavity volume is expanded by driving the mold core backward. Subsequently, a second thermoplastic elastomer material with high toughness and medium-to-high hardness is injected to form the dermal layer. The two layers of materials are thermally fused at the interface to achieve a strong bond.

[0023] 4. Subcutaneous tissue layer injection molding: In the semi-cured state of the dermal material, the mold core is driven back again to inject a low-density, high-elasticity third material (such as TPU foam or silicone rubber foam) to form the subcutaneous tissue layer.

[0024] 5. Cooling and demolding: The molded part is cooled in a controlled manner, then the mold is opened and the final product is ejected.

[0025] The present invention will be specifically described below through three embodiments. Example

[0026] Take the fabrication of a bionic skin that simulates the forearm area as an example.

[0027] Molds and materials: Use such as Figure 2 The special injection mold shown is used for the outer skin layer. The outer skin layer is made of transparent thermoplastic polyurethane (TPU) with a Shore hardness of A15, the dermal layer is made of reinforced TPU with a Shore hardness of A50 (containing 5% nano-silica filler), and the subcutaneous tissue layer is made of low-density TPU foam material (density 0.3 g / cm³).

[0028] Process: 1. Close the mold, and set the mold temperature to 45°C.

[0029] 2. The TPU skin layer is injected into the initial cavity at 195°C and medium speed (50 cm³ / s) through the runner and gate, with a thickness of 0.3 mm. It is then held under pressure and cooled for 5 seconds to form the skin layer attached to the mold core (3).

[0030] 3. Control the mold core to retract precisely by 1.5mm (the mold state here is as follows) Figure 3This allows the initial cavity to separate from the bottom of the groove, expanding to form a connected cavity for filling the dermis.

[0031] 4. Immediately inject the dermal TPU layer into the enlarged cavity at a high speed (80 cm³ / s) at 205°C.

[0032] 5. Control the mold core to retract 1.0 mm again, and inject TPU foam into the subcutaneous tissue layer (175°C, 30 cm³ / s).

[0033] 6. After holding the pressure and cooling for 30 seconds, open the mold and eject the product.

[0034] Results: The obtained three-layer bionic skin sample has strong interlayer bonding, no interface, and a smooth hardness gradient from the surface to the interior, which conforms to the mechanical characteristics of forearm skin. Example

[0035] Molds and materials: The mold structure is the same as in Example 1, except that the thickness of the dermis and subcutaneous tissue layers is increased. The epidermal layer material is TPU with a Shore A hardness of 20, the dermis layer is filled TPU with a Shore A hardness of 55, and the subcutaneous tissue layer is low-density silicone rubber foam (density 0.25 g / cm³).

[0036] Process: 1. Close the mold, and set the mold temperature to 50℃.

[0037] 2. The TPU skin layer is injected into the initial cavity at 200°C and medium speed (40cm³ / s) through the runner and gate, with a thickness of 0.4mm. It is then held under pressure and cooled for 6 seconds to form the skin layer attached to the mold core.

[0038] 3. Control the mold core to retract precisely by 2.5mm, so that the initial cavity is separated from the bottom surface of the groove, and the cavity is expanded to form a connected cavity for filling the dermis layer.

[0039] 4. Immediately inject the dermal TPU layer into the enlarged cavity at a high speed (70 cm³ / s) at 210°C.

[0040] 5. Control the mold core to retract 1.5mm again, and inject TPU foam into the subcutaneous tissue layer (180°C, 25cm³ / s).

[0041] 6. After holding the pressure and cooling for 40 seconds, open the mold and eject the product.

[0042] Results: The dermis and subcutaneous tissue layers of the sample were significantly thickened, and the overall elasticity and cushioning performance were enhanced, simulating the structural characteristics of chest skin. Example

[0043] To demonstrate the ability of the method of the present invention to achieve regionalized mechanical properties of biomimetic skin, taking the preparation of a piece of skin simulating a facial area as an example, the skin needs to simultaneously simulate the high-hardness cheekbone area and the relatively soft cheek area.

[0044] Molds and materials: Using a mold with the same basic structure as Example 1 (e.g.) Figure 2 (As shown), but its telescopic mold core has been modified into two independently controllable sub-mold core units. On the moving template of the mold, along the perpendicular to Figure 2 Two independently controllable mold cores are arranged side-by-side along the cutting direction. Their front faces are aligned with continuous grooves on the fixed mold plate to form a complete cavity. The control circuits of the two components are independent, and the programmable controller can differentiate their retraction stroke and timing settings.

[0045] The outer skin layer is made of silicone rubber with a Shore A hardness of 5-10, and the dermal layer is made of filled TPU with a Shore A hardness of 50-55.

[0046] Process: 1. Close the mold, and set the mold temperature to 50°C.

[0047] 2. The skin layer TPE-S is injected into the initial cavity (6) at a low speed (35 cm³ / s) through the gating system (5,8) at 185°C, and then held under pressure and cooled for 6 seconds.

[0048] 3. Control the mold core A in the cheekbone area to move back 0.8 mm, forming a dermal filling cavity in the corresponding area; simultaneously control the mold core B in the cheek area to move back 2.0 mm, forming a dermal filling cavity in the corresponding area.

[0049] 4. Immediately inject the dermal TPU layer into the enlarged cavity at 215°C and high speed (90 cm³ / s).

[0050] 5. Control the mold core A in the cheekbone area to move back 0.3mm again to form a subcutaneous tissue filling cavity in the corresponding area; simultaneously control the mold core B in the cheek area to move back 1.2mm to form a subcutaneous tissue filling cavity in the corresponding area.

[0051] 6. Subcutaneous tissue layer injection molding: Low-density silicone rubber foam is injected into the subcutaneous tissue cavity at 180°C at a rate of 30 cm³ / s.

[0052] 7. After holding the pressure and cooling for 35 seconds, open the mold and eject the product.

[0053] Effect: The obtained bionic skin samples, such as Figure 4As shown, the dermis and subcutaneous tissue are thinner in the cheekbone area, resulting in higher overall firmness; while the dermis and subcutaneous tissue are thicker in the cheek area, resulting in greater overall softness. The interlayer bonding is strong, with no delamination, successfully simulating the regional mechanical and structural gradient characteristics of facial skin.

[0054] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, for the device embodiments, the above descriptions are merely preferred embodiments of the present invention. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple, and relevant parts can be referred to the descriptions of the method embodiments. The above descriptions are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, without departing from the principle of the present invention, should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-layer injection mold for biomimetic skin with mechanical gradient, characterized in that: It includes a fixed template (1) and a moving template (2); the moving template (2) has a cavity (7) in the center, and the mold core (4) slides in the cavity (7) through the slider base (3) connected to the rear end; the fixed template (1) is provided with a flow channel (8), a gate (5) and a groove corresponding to the shape of the product connected in sequence, and the mold core (4) and the bottom surface of the groove form an initial cavity (6).

2. The multi-layer injection mold for biomimetic skin with mechanical gradient according to claim 1, characterized in that: The moving template (2) has multiple chambers (7) arranged in the vertical direction. Each chamber is equipped with an independently controlled mold core (4). The fixed template (1) has several grooves that match the position of the mold core (4).

3. A method for multi-layer injection molding of biomimetic skin with mechanical gradient, characterized in that: The method of using the biomimetic skin multilayer injection mold with mechanical gradient as described in claim 1 includes the following steps: 1) Select the materials for each layer according to the usage requirements and set the injection temperature, pressure, speed, and core movement sequence and stroke for each layer; 2) Skin layer injection molding: Close the mold and inject a low-hardness, high-elasticity first thermoplastic elastomer material into the cavity to form the skin layer; 3) Cavity switching and dermal layer injection: When the surface layer material is semi-cured or in a thermoplastic state, drive the mold core backward to expand the cavity volume, and inject a second thermoplastic elastomer material with high toughness and medium to high hardness to form the dermal layer; 4) Subcutaneous tissue layer injection molding: In the semi-cured state of the dermal material, the mold core is driven back again to inject a low-density, high-elasticity third material to form the subcutaneous tissue layer; 5) Cooling and demolding: After the molded part is cooled in a controlled manner, it is opened and ejected.

4. The mechanical gradient biomimetic skin multilayer injection molding method according to claim 1, characterized in that: Step 2) The Shore hardness of the first thermoplastic elastomer material is A5–25; Step 3) The Shore hardness of the second thermoplastic elastomer material is A40–70; Step 4) The third material is low-density thermoplastic polyurethane foam or silicone rubber foam.

5. The mechanical gradient biomimetic skin multilayer injection molding method according to claim 4, characterized in that: The first thermoplastic elastomer material and the second thermoplastic elastomer material are one or more of thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), or silicone rubber.

6. The mechanical gradient biomimetic skin multilayer injection molding method according to claim 1, characterized in that: The retraction stroke of the mold core is 0.5–3.0 mm; the mold core retracts for the first time within 1–10 seconds after the skin layer injection is completed, and retracts for the second time within 5–15 seconds after the dermis layer injection is completed.

7. The mechanical gradient biomimetic skin multilayer injection molding method according to claim 1, characterized in that, The injection molding temperature for the epidermal layer is 180–210°C, and the injection speed is 30–70 cm³ / s; the injection molding temperature for the dermal layer is 190–220°C, and the injection speed is 60–100 cm³ / s; the injection molding temperature for the subcutaneous tissue layer is 160–190°C, and the injection speed is 20–50 cm³ / s.

8. The mechanical gradient biomimetic skin multilayer injection molding method according to claim 1, characterized in that, The mold temperature is 40–60°C, the skin layer holding time is 3–8 seconds, and the overall cooling time is 20–50 seconds.

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