Secondary mold pressing process of perforated supercritical foaming insole

Abstract

The invention belongs to the field of shoemaking processes, and particularly relates to a secondary mould pressing process of a perforated supercritical foaming insole, which comprises the following steps: drying a thermoplastic material; the dried foaming particles are subjected to high-temperature melting injection molding to form small blanks; under the protection atmosphere of carbon dioxide and nitrogen, carrying out supercritical foaming treatment on the small blank, raising the temperature, maintaining the pressure, and then rapidly releasing the pressure to form a semi-finished product of the foaming material; in the vertical placement state, when the semi-finished foaming material is placed into the mold cavity, the preset through holes of the semi-finished foaming material are connected with the rigid shaping columns in a sleeving mode, and then heating softening and cooling shaping are conducted, so that the semi-finished foaming material is subjected to mold pressing to form a half-midsole piece with a pattern through hole structure; and the two half midsole pieces which are formed through respective mold pressing and punching are bonded through an adhesive to form the whole midsole. According to the invention, the manufacturing of the full-through three-dimensional perforated structure of the environment-friendly thermoplastic material can be realized, a chemical foaming agent is completely abandoned, and 100% material recoverability is achieved.

Description

Technical Field

[0001] This invention relates to the field of shoe manufacturing technology, and in particular to a secondary molding process for a perforated supercritical foam midsole. Background Technology

[0002] Current midsole manufacturing processes generally employ one-time injection foaming technology to create perforated structures. This process has the following drawbacks: 1. Uneven molecular chain orientation during high-pressure injection foaming process leads to a significant deterioration in the finished product's resistance to compression deformation and its rebound efficiency. 2. In order to maintain structural integrity, excessive filling of raw materials is required, resulting in the product density generally exceeding 0.25g / cm³, which does not conform to the trend of lightweight design; 3. This process relies on chemical foaming agents such as azodicarbonamide, which not only produces harmful byproducts such as ammonia during decomposition, but also causes cross-linking degradation of materials during recycling due to foaming agent residue, which seriously violates the principles of green manufacturing.

[0003] These technological bottlenecks have severely hampered the development of high-performance, sustainable midsoles. Summary of the Invention

[0004] The purpose of this invention is to provide a secondary molding process for perforated supercritical foamed midsoles to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a secondary molding process for a perforated supercritical foamed midsole, comprising the following steps: a. Drying step: The thermoplastic material is dried to form foamed granules; b. Injection molding preform step: The dried foamed granules are melted and injection molded into preforms at high temperature; c. Supercritical foaming step: Under the protective atmosphere of carbon dioxide and nitrogen, the heated injection-molded preform is subjected to supercritical foaming treatment. The temperature is raised and pressure is maintained, and then the pressure is quickly released to form a semi-finished foamed material. d. Molding and perforation molding steps: When the foamed material semi-finished product is placed into the mold cavity in a vertical position, its pre-set perforations will form a precise fit with the rigid shaping column fixed in the mold cavity. Then, it is heated to soften and cooled to shape, so as to mold the foamed material semi-finished product into a semi-bottom part with a patterned perforated structure. e. Assembly and bonding steps: The two half midsole pieces, which have been molded and perforated, are bonded together with adhesive to form a whole midsole.

[0006] Preferably, the thermoplastic material is one or more of TPU, nylon elastomer, and TPEE.

[0007] Preferably, in step a, the drying process specifically involves placing the thermoplastic material into a drying cylinder and drying it at a temperature of 80°C to 120°C for 4 to 6 hours.

[0008] Preferably, in step b, the processing step of the injection preform is as follows: the dried foamed granules are poured into the injection molding machine and heated and injection molded at a temperature of 180℃~220℃ for 1min~3min.

[0009] Preferably, in step c, the supercritical foaming process specifically involves: placing the heated injection-molded preform into a supercritical foaming reactor, injecting carbon dioxide and nitrogen gas at a pressure of 35 MPa to 55 MPa, heating to 120°C to 150°C, maintaining the pressure for 3 to 5 hours, and then rapidly depressurizing through the exhaust valve of the supercritical foaming reactor.

[0010] Preferably, in step d, the heating temperature is 130℃~160℃, the heating time is 500s~800s, and the cooling time is 500s~800s.

[0011] Preferably, the rigid shaping column is a shaped iron rod.

[0012] Preferably, the adhesive is glue.

[0013] As can be seen from the above description of the structure of the present invention, compared with the prior art, the present invention has the following advantages: This invention provides a secondary molding process for perforated supercritical foam midsoles. Through a synergistic process of injection molding preforms, supercritical foaming, and molding perforation, it enables the manufacture of midsoles with a fully perforated three-dimensional structure using environmentally friendly thermoplastic materials. This process completely eliminates chemical foaming agents and achieves 100% material recyclability. Compared to traditional iP injection molding, the product density is reduced by 80% to 200%, and the rebound rate is increased to over 80%. At the same time, it breaks through the limitation of existing supercritical technology, which can only produce semi-perforated or fitted perforations, forming a functional perforated system that combines a gradient microporous structure with high breathability, thus promoting the development of high-performance sustainable midsoles. Attached Figure Description

[0014] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a process diagram of a secondary molding process for a perforated supercritical foamed midsole according to the present invention; Figure 2 This is a top view of the mold cavity for a secondary molding process of a perforated supercritical foamed midsole according to the present invention; Figure 3This is a front view of the mold cavity for a secondary molding process of a perforated supercritical foamed midsole according to the present invention; Figure 4 This is a left view of the mold cavity for a secondary molding process of a perforated supercritical foamed midsole according to the present invention. Figure 5 This is a photograph of a preform for a secondary molding process of a perforated supercritical foamed midsole according to the present invention. Figure 6 Photograph of a semi-finished foam material for a secondary molding process of a perforated supercritical foamed midsole according to the present invention. Figure 7 This is a photograph of a semi-midsole part from the secondary molding process of a perforated supercritical foamed midsole according to the present invention. Figure 8 This is a photograph of two and a half midsole pieces bonded together using a secondary molding process for a perforated supercritical foamed midsole according to the present invention.

[0015] In the diagram: 1. Baking material; 2. Injection preform; 3. Supercritical foaming; 4. Compression molding with perforation; 5. Assembly and bonding; 6. Shaping iron rod; 7. Mold cavity. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0017] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Example 1 refer to Figures 1 to 8 A secondary molding process for a perforated supercritical foam midsole includes the following steps: a. Drying Step 1: Place the TPU material into a drying drum and dry it at 80℃ for 4 hours to form foamed granules; b. Injection preform step 2: Pour the dried foamed granules into the injection molding machine and heat them at 180℃ for 1 minute to form a preform; c. Supercritical foaming step 3: The heated injection-molded preform is placed in a supercritical foaming kettle, and carbon dioxide and nitrogen gas at a pressure of 35 MPa are injected. The temperature is raised to 120°C and the pressure is maintained for 3 hours. Then, the pressure is quickly released through the exhaust valve of the supercritical foaming kettle to form a semi-finished foamed material. d. Molding and perforation step 4: When the foamed material semi-finished product is placed into the mold cavity 7 in a vertical position, its pre-set perforation will form a precise fit with the fixed iron rod 6 inside the mold cavity 7. Then, it is heated and softened at 130℃ for 500s and cooled and shaped for 500s to mold the foamed material semi-finished product into a semi-bottom part with a patterned perforated structure. e. Assembly and bonding step 5: The two half midsole pieces, which have been molded and perforated, are glued together to form a whole midsole.

[0019] Example 2 refer to Figures 1 to 8 A secondary molding process for a perforated supercritical foam midsole includes the following steps: a. Drying Step 1: Place the nylon elastomer material into a drying drum and dry it at 100℃ for 5 hours to form foamed granules. b. Injection preform step 2: Pour the dried foamed granules into the injection molding machine and heat them at 200℃ for 2 minutes to form a preform; c. Supercritical foaming step 3: The heated injection-molded preform is placed in a supercritical foaming kettle, and carbon dioxide and nitrogen gas at a pressure of 45 MPa are injected. The temperature is raised to 135°C and the pressure is maintained for 8 hours. Then, the pressure is quickly released through the exhaust valve of the supercritical foaming kettle to form a semi-finished foamed material. d. Molding and perforation step 4: When the foamed material semi-finished product is placed into the mold cavity 7 in a vertical position, its pre-set perforation will form a precise fit with the fixed iron rod 6 in the mold cavity 7. Then, it is heated and softened at 145℃ for 650s and cooled and shaped for 650s to mold the foamed material semi-finished product into a semi-bottom part with a patterned perforated structure. e. Assembly and bonding step 5: The two half midsole pieces, which have been molded and perforated, are glued together to form a whole midsole.

[0020] Example 3 refer to Figures 1 to 8 A secondary molding process for a perforated supercritical foam midsole includes the following steps: a. Drying Step 1: Place the TPEE material into a drying drum and dry it at 120℃ for 6 hours to form foamed granules; b. Injection preform step 2: Pour the dried foamed granules into the injection molding machine and heat them at 220℃ for 3 minutes to form a preform; c. Supercritical foaming step 3: The heated injection-molded preform is placed in a supercritical foaming kettle, and carbon dioxide and nitrogen gas at a pressure of 55 MPa are injected. The temperature is raised to 150°C and the pressure is maintained for 5 hours. Then, the pressure is quickly released through the exhaust valve of the supercritical foaming kettle to form a semi-finished foamed material. d. Molding and perforation step 4: When the foamed material semi-finished product is placed into the mold cavity 7 in a vertical position, its pre-set perforation will form a precise fit with the fixed iron rod 6 inside the mold cavity 7. Then, it is heated and softened at 160℃ for 800s and cooled and shaped for 800s to mold the foamed material semi-finished product into a semi-bottom part with a patterned perforated structure. e. Assembly and bonding step 5: The two half midsole pieces, which have been molded and perforated, are glued together to form a whole midsole.

[0021] This invention utilizes a synergistic process of injection molding preforms, supercritical foaming, and compression molding to achieve the manufacture of midsoles with a fully perforated three-dimensional structure using environmentally friendly thermoplastic materials. This process completely eliminates chemical foaming agents and achieves 100% material recyclability. Compared to traditional iP injection molding, the product density is reduced by 80% to 200%, and the rebound rate is increased to over 80%. It also overcomes the limitations of existing supercritical technology, which can only produce semi-perforated or fitted perforations, forming a functional perforated system that combines a gradient microporous structure with high breathability, thus promoting the development of high-performance sustainable midsoles.

[0022] Table 1 - Performance of the midsoles prepared in Examples 1, 2, and 3 (room temperature testing)

[0023] As can be seen from Table 1, the method of the present invention reduces the density of the prepared midsole by 80% to 200% and increases the rebound rate to over 80%. It can overcome the limitations of existing supercritical technology, which can only produce semi-perforated or fitted perforations, and form a functional perforated system that combines gradient microporous structure and high breathability, thus promoting the development of high-performance sustainable midsoles.

[0024] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A secondary molding process for a perforated supercritical foamed midsole, characterized in that, Includes the following steps: a. Drying step: The thermoplastic material is dried to form foamed granules; b. Injection molding preform step: The dried foamed granules are melted and injection molded into preforms at high temperature; c. Supercritical foaming step: Under the protective atmosphere of carbon dioxide and nitrogen, the heated injection-molded preform is subjected to supercritical foaming treatment. The temperature is raised and pressure is maintained, and then the pressure is quickly released to form a semi-finished foamed material. d. Molding and perforation molding steps: When the foamed material semi-finished product is placed into the mold cavity in a vertical position, its pre-set perforations will form a precise fit with the rigid shaping column fixed in the mold cavity. Then, it is heated to soften and cooled to shape, so as to mold the foamed material semi-finished product into a semi-bottom part with a patterned perforated structure. e. Assembly and bonding steps: The two half midsole pieces, which have been molded and perforated, are bonded together with adhesive to form a whole midsole.

2. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: The thermoplastic material is one or more of TPU, nylon elastomer, and TPEE.

3. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: In step a, the specific steps for processing the material to be dried are as follows: the thermoplastic material is placed into a drying cylinder and dried at a temperature of 80℃~120℃ for 4h~6h.

4. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: In step b, the specific steps for processing the injection preform are as follows: the dried foamed granules are poured into the injection molding machine and heated and injection molded at a temperature of 180℃~220℃ for 1min~3min.

5. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: In step c, the supercritical foaming process is as follows: the heated injection-molded preform is placed in a supercritical foaming reactor, carbon dioxide and nitrogen gas at a pressure of 35 MPa to 55 MPa are injected, the temperature is raised to 120°C to 150°C, the pressure is maintained for 3 to 5 hours, and then the pressure is quickly released through the exhaust valve of the supercritical foaming reactor.

6. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: In step d, the heating temperature is 130℃~160℃, the heating time is 500s~800s, and the cooling time is 500s~800s.

7. The secondary molding process for the perforated supercritical foamed midsole according to claim 1, characterized in that: The rigid shaping column is a shaped iron rod.

8. The secondary molding process for a perforated supercritical foamed midsole according to claim 1, characterized in that: The adhesive is glue.

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