Method for shaping PU (polyurethane) uppers

Abstract

The invention discloses a PU (polyurethane) upper surface shaping method which comprises the following steps: putting a PU upper surface material into a mold, and carrying out preheating treatment at 80-120 DEG C for 30-90 seconds; the pressure of 0.5 MPa to 1.5 MPa is applied to the preheated PU upper, and the pressure is kept for 60 seconds to 180 seconds; and cooling and shaping are conducted, the cooling temperature is 15-25 DEG C, and the cooling time is 120-300 seconds. According to the shaping method for the PU upper surface, the PU upper surface material can be uniformly and properly softened through the preheating link. By means of the structure, materials can smoothly flow and fully fill all corners of the mold during subsequent pressurization, common appearance defects such as wrinkles and holes in the traditional technology are effectively avoided, the uppers are made to present flat, smooth and attractive appearance, and the visual quality of products is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of footwear manufacturing technology, and in particular to a method for shaping PU material uppers. Background Technology

[0002] Polyurethane (PU) is widely used in the production of upper materials due to its excellent properties, such as good elasticity, abrasion resistance, chemical corrosion resistance, and ease of processing and molding. The molding process of PU uppers plays a crucial role in the quality and performance of the final product, directly affecting the appearance, comfort, and durability of the shoe.

[0003] Traditional methods for shaping PU uppers have several shortcomings. In terms of temperature control, early processes often lacked precise temperature regulation. During the preheating stage, excessively high temperatures can cause the PU material to soften prematurely or even decompose, damaging its internal structure and affecting the strength and stability of the upper. Conversely, excessively low temperatures prevent the material from reaching a suitable softening state, hindering its flow and filling of the mold during subsequent pressure shaping, resulting in incomplete upper forming and defects such as wrinkles and holes. Improper temperature control during cooling also affects upper quality. Too rapid cooling can create internal stress in the material, causing deformation or cracking; too slow cooling prolongs the production cycle and reduces production efficiency.

[0004] Applying pressure is also a challenge in traditional processes. Previously, a single-stage pressure application was often used, which makes it difficult to precisely control the pressure and duration. Insufficient pressure prevents the PU material from adhering tightly to the mold, resulting in poor shaping; excessive pressure can cause over-extrusion of the material, leading to uneven thickness and even damage to the mold. Furthermore, single-stage pressure application cannot adequately accommodate the deformation characteristics of the PU material at different stages, failing to achieve the desired shaping effect.

[0005] In terms of molds, traditional molds have limited material and structural design. Ordinary molds have poor heat dissipation performance, resulting in uneven temperature transfer during preheating and cooling, leading to inconsistent shaping of different parts of the upper surface and affecting product quality stability. Furthermore, the lack of effective surface treatment measures allows PU material to easily adhere to the mold during the shaping process, making demolding difficult, damaging the upper surface, and reducing the mold's lifespan.

[0006] Furthermore, traditional processes often neglect the post-treatment of the upper after molding. After molding, the internal structure of PU material is not yet fully stable. If it is not properly treated, problems such as dimensional changes and performance degradation may occur during use, affecting the overall quality and lifespan of the shoes.

[0007] Therefore, it is necessary to provide a new method for shaping PU material uppers to solve the above-mentioned technical problems. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention provides a method for shaping PU material upper surface.

[0009] The present invention provides a method for shaping PU material upper, comprising the following steps:

[0010] S1: Place the PU upper material in the mold and preheat it at 80-120℃ for 30-90 seconds;

[0011] S2: Apply a pressure of 0.5-1.5MPa to the preheated PU surface and maintain it for 60-180 seconds;

[0012] S3: Cooling and shaping, cooling temperature is 15-25℃, cooling time is 120-300 seconds.

[0013] Preferably, the preheating temperature in step S1 is 90-110°C and the preheating time is 45-75 seconds.

[0014] Preferably, the pressure in step S2 is 0.8-1.2 MPa, and the holding time is 90-150 seconds.

[0015] Preferably, the cooling temperature in step S3 is 18-22°C and the cooling time is 150-240 seconds.

[0016] Preferably, the mold in step S1 is an aluminum alloy mold, and the surface of the mold is provided with breathable micropores with a diameter of 0.1-0.3mm.

[0017] Preferably, the inner surface of the mold is coated with a release agent, which is a silicone oil-based release agent, and the coating thickness is 5-15 μm.

[0018] Preferably, the pressure in step S2 is applied in two stages: in the first stage, the pressure is increased to 0.5-0.8 MPa at a rate of 0.1-0.3 MPa / s and maintained for 30-60 seconds; in the second stage, the pressure is increased to 1.0-1.5 MPa at a rate of 0.05-0.15 MPa / s.

[0019] Preferably, post-treatment is also included: placing the shaped PU surface in an environment of 40-60℃ for aging treatment for 2-4 hours.

[0020] Preferably, the relative humidity of the aging treatment environment is controlled at 40-60%.

[0021] Preferably, the PU upper material comprises the following components: 60-80 wt% polyurethane resin, 10-20 wt% plasticizer, 2-5 wt% stabilizer, and 1-3 wt% colorant.

[0022] Compared with related technologies, the PU material upper shaping method provided by the present invention has the following beneficial effects:

[0023] This invention provides a method for shaping PU material uppers. Through a preheating process, the PU upper material is softened uniformly and precisely. This allows the material to flow smoothly and fully fill all corners of the mold during subsequent pressurization, effectively avoiding appearance defects such as wrinkles and holes common in traditional processes. The upper has a flat, smooth, and aesthetically pleasing appearance, greatly improving the visual quality of the product.

[0024] The pressurization process employs a two-stage pressure application method. The first stage applies pressure gradually at an appropriate rate, allowing the material to adapt to the pressure and undergo initial deformation adjustment. The second stage further increases the pressure based on the material's characteristics, ensuring the upper better conforms to the mold during shaping, with even and reasonable stress distribution across all parts. This phased pressure application method fully considers the deformation characteristics of PU material at different pressure stages, enabling precise shaping of the upper and significantly improving its dimensional accuracy and shape stability, ensuring that the uppers of every pair of shoes meet a highly consistent quality standard.

[0025] The cooling and shaping stage, through controlled cooling temperature and methods, allows the PU material to shrink slowly and evenly during cooling, effectively reducing the generation of internal stress. This avoids problems such as deformation and cracking of the upper surface caused by internal stress, further consolidating the shaping effect of the upper surface and ensuring that it maintains good shape and performance during long-term use.

[0026] In terms of production efficiency, this method achieves more precise time control in preheating, pressurization, and cooling, ensuring the quality requirements of each step while avoiding unnecessary time waste. This allows for the production of more products per unit of time, greatly improving production efficiency and reducing production costs.

[0027] The mold is made of aluminum alloy, which has excellent heat dissipation properties, allowing it to quickly reach the required temperature during preheating and cooling. This ensures uniform temperature transfer, resulting in consistent shaping of all parts of the upper and improving product quality stability. The micropores on the mold surface help expel air during pressurization, allowing the PU material to better fill the mold and reducing molding defects caused by residual air, further improving molding efficiency and quality. Simultaneously, the silicone-based release agent coated on the inner surface of the mold effectively reduces adhesion between the material and the mold, making demolding easier and smoother. This not only protects the upper surface from damage but also extends the mold's lifespan, reducing replacement frequency and costs.

[0028] Furthermore, the added post-processing steps provide a strong guarantee for improved product quality. Aging the shaped PU upper stabilizes the material's internal molecular structure, eliminates residual stress, and further enhances the upper's dimensional stability and physical properties. The aging-treated upper is better resistant to external factors such as temperature and humidity changes during subsequent processing and use, and is less prone to deformation and aging, thus extending the shoe's lifespan and improving the overall product quality. Moreover, the optimization of the PU upper material composition gives the material better processing performance during the shaping process, better adapting to the various process requirements of this shaping method, laying the foundation for producing high-quality PU uppers. Attached Figure Description

[0029] Figure 1 A flowchart illustrating the PU material upper shaping method provided by this invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Example 1

[0032] In the specific implementation process, such as Figure 1 As shown, a method for shaping a PU material upper surface includes the following steps:

[0033] Materials preparation:

[0034] The selected PU upper material contains the following components: 70wt% polyurethane resin, 15wt% plasticizer, 3wt% stabilizer, and 2wt% colorant. After accurately weighing each component according to the specified proportions, they are placed in a high-speed mixer and mixed for 15 minutes at 800 rpm to ensure thorough and uniform dispersion, thus obtaining the PU upper material to be shaped.

[0035] Mold preparation:

[0036] An aluminum alloy mold is used, with 0.2mm diameter micropores on its surface for ventilation. Before use, the mold is cleaned to remove surface oil and impurities. Then, a silicone oil-based release agent is applied to the inner surface of the mold using a spray gun, with the coating thickness controlled at 10μm to ensure smooth demolding of the PU upper material after setting.

[0037] Preheating treatment:

[0038] The prepared PU upper material is placed in an aluminum alloy mold coated with release agent, and then the mold is placed in a preheating oven and preheated at 95°C for 60 seconds. During preheating, the PU upper material gradually softens, and the molecular chains become active, preparing it for subsequent pressure setting. The selection of preheating temperature and time is based on research into the properties of PU material; 95°C allows the PU material to reach a suitable degree of softening, and the 60-second preheating time ensures uniform heating of the material.

[0039] Pressure setting:

[0040] After preheating, the mold is transferred to a hydraulic press to apply pressure to the preheated PU surface. The pressure is applied in two stages:

[0041] Phase 1: Increment the pressure to 0.6 MPa at a rate of 0.2 MPa / s and hold for 45 seconds. In this phase, the lower pressure and slower incretion rate allow the PU material to gradually adapt to the pressure, avoiding internal defects caused by sudden high pressure.

[0042] Second stage: Pressurize to 1.2 MPa at a rate of 0.1 MPa / s and hold for 120 seconds. The higher pressure in this stage allows the PU material to fully fill the mold cavity, forming an accurate side panel shape, while also promoting the rearrangement of the molecular structure inside the material, improving the shaping effect.

[0043] Cooling and shaping:

[0044] After pressure setting, the mold is removed from the hydraulic press and placed in a cooling device. The cooling temperature is set to 20°C, and the cooling time is 180 seconds. During the cooling process, the PU material gradually solidifies, and its molecular structure stabilizes, thus fixing the shape of the surface. The cooling temperature of 20°C and the cooling time of 180 seconds ensure that the material is fully cooled while avoiding stress generated inside the material due to excessively rapid cooling.

[0045] Post-processing:

[0046] The shaped PU upper was removed from the mold and placed in an environment of 50℃ for aging treatment for 3 hours, with the relative humidity controlled at 50%. Aging treatment further stabilizes the molecular structure of the PU material, eliminates internal residual stress, and improves the dimensional stability and physical properties of the upper. After aging treatment, all performance indicators of the PU upper reached excellent levels, with a smooth and flat surface, accurate shape, and no obvious deformation.

[0047] Example 2

[0048] Materials preparation:

[0049] The selected PU upper material has the following composition: 65wt% polyurethane resin, 18wt% plasticizer, 4wt% stabilizer, and 3wt% colorant. The components are added to a twin-screw extruder and melt-blended at 160°C. The resulting material is then granulated using a pelletizer and injection molded into the desired PU upper material.

[0050] Mold preparation:

[0051] An aluminum alloy mold was used, with micropores on the mold surface having a diameter of 0.1 mm. After cleaning and drying the mold, a silicone oil-based release agent was applied to the inner surface of the mold by brushing, with a coating thickness of 8 μm. Care was taken to apply the release agent evenly during brushing to avoid accumulation or uneven coating.

[0052] Preheating treatment:

[0053] Place the PU upper material into the mold, and then place the mold into a hot air circulating oven for preheating. Set the preheating temperature to 90℃ and the preheating time to 75 seconds. The hot air circulating oven provides uniform hot air, ensuring that the PU material is heated more evenly. The 90℃ preheating temperature and 75-second preheating time ensure that the material reaches the appropriate softening state.

[0054] Pressure setting:

[0055] Place the preheated mold on the hydraulic press and apply pressure in the following two stages:

[0056] Phase 1: Increase the pressure to 0.5 MPa at a rate of 0.15 MPa / s and hold for 60 seconds. This slow pressure increase helps the PU material gradually adapt to the pressure, reducing the formation of internal defects.

[0057] Second stage: Increase pressure to 1.0 MPa at a rate of 0.08 MPa / s and hold for 150 seconds. Higher pressure and appropriate holding time allow the PU material to better fill the mold, forming a precise upper shape, while improving the material's density.

[0058] Cooling and shaping:

[0059] After pressurization, the mold is quickly transferred to a cooling water tank for cooling. The cooling water temperature is controlled at 18℃, and the cooling time is 240 seconds. Water cooling can quickly remove heat from the mold and PU material, allowing the material to solidify and set rapidly. The cooling temperature of 18℃ and the cooling time of 240 seconds ensure that the material is fully cooled, improving the setting effect.

[0060] Post-processing:

[0061] The shaped PU upper is removed from the mold and placed in a constant temperature and humidity chamber for aging treatment. The aging treatment temperature is 45℃, the time is 4 hours, and the relative humidity is controlled at 45%. After aging treatment, the dimensional stability of the PU upper is further improved, and the surface quality is better, meeting the requirements of high-quality footwear products.

[0062] Example 3

[0063] Materials preparation:

[0064] Prepare PU upper material with the following components: 75wt% polyurethane resin, 12wt% plasticizer, 2.5wt% stabilizer, and 1.5wt% colorant. Place all components into an internal mixer and mix at 150℃ for 10 minutes to ensure thorough and uniform mixing. Then, pass the mixture through a two-roll mill to obtain a PU upper material sheet of uniform thickness.

[0065] Mold preparation:

[0066] An aluminum alloy mold is used, with 0.3mm diameter micropores on the mold surface for ventilation. The mold is polished to make its surface smooth, then cleaned and dried. A silicone oil-based release agent is sprayed onto the inner surface of the mold using a spraying device, with a coating thickness of 12μm, ensuring that the release agent evenly covers the mold surface.

[0067] Preheating treatment:

[0068] After cutting the PU upper material sheet to the appropriate size, place it into the mold, and then put the mold into an infrared heating furnace for preheating. The preheating temperature is set to 105℃, and the preheating time is 50 seconds. The infrared heating furnace has the characteristics of fast heating speed and high thermal efficiency, which can make the PU material reach the preheating temperature in a short time. The preheating temperature of 105℃ and the preheating time of 50 seconds can make the material soften to a suitable degree, which is convenient for subsequent pressure shaping.

[0069] Pressure setting:

[0070] Place the preheated mold on the hydraulic press and apply pressure in the following two stages:

[0071] First stage: Apply pressure at a rate of 0.25 MPa / s to 0.7 MPa and hold for 35 seconds. This rapid pressure application allows the PU material to quickly adhere to the mold surface, reducing the formation of air bubbles.

[0072] Second stage: Pressurize to 1.4 MPa at a rate of 0.12 MPa / s and hold for 100 seconds. The higher pressure allows the PU material to flow and fill fully in the mold, forming a precise sidewall shape, while improving the mechanical properties of the material.

[0073] Cooling and shaping:

[0074] After pressurization, the mold is placed in a cooling duct for cooling. The cooling air temperature is 22℃, and the cooling time is 150 seconds. Air cooling ensures that the mold and PU material are cooled evenly, preventing material deformation caused by excessively rapid local cooling. The cooling temperature of 22℃ and the cooling time of 150 seconds ensure that the material is fully cooled and set.

[0075] Post-processing:

[0076] The PU upper surface, after being removed from the mold and shaped, is placed in an environment of 55℃ for 2.5 hours for aging treatment, with the relative humidity of the aging treatment environment controlled at 55%. After aging treatment, the performance of the PU upper surface is further optimized, with better elasticity and wear resistance, meeting the needs of different application scenarios.

[0077] Example 4

[0078] Materials preparation:

[0079] The selected PU upholstery material has the following composition: 60wt% polyurethane resin, 20wt% plasticizer, 5wt% stabilizer, and 1wt% colorant. All components are placed in a reaction vessel and mixed under nitrogen protection at a stirring speed of 300 rpm for 30 minutes to ensure thorough and uniform reaction. The resulting PU upholstery material is then extruded using an extruder.

[0080] Mold preparation:

[0081] An aluminum alloy mold was used, with 0.15mm diameter micropores on the mold surface for ventilation. The mold was polished to achieve a surface roughness of Ra0.8, followed by cleaning and drying. A silicone oil-based release agent was applied to the inner surface of the mold using a dip-coating method, with a coating thickness of 6μm. After dip-coating, the mold was placed in a ventilated area to air dry.

[0082] Preheating treatment:

[0083] Place the PU sidewall material into the mold, and then place the mold into a microwave heating device for preheating. The preheating temperature is set to 100℃, and the preheating time is 40 seconds. Microwave heating is characterized by uniform heating and fast speed, which can make the PU material reach the preheating temperature in a short time. The preheating temperature of 100℃ and the preheating time of 40 seconds can ensure that the material softens evenly, preparing it for subsequent pressure shaping.

[0084] Pressure setting:

[0085] Place the preheated mold on the hydraulic press and apply pressure in the following two stages:

[0086] Phase 1: Increase the pressure to 0.55 MPa at a rate of 0.1 MPa / s and hold for 50 seconds. This slow pressure increase helps the PU material gradually adapt to the pressure, preventing internal cracks caused by sudden pressure changes.

[0087] Second stage: Increase pressure to 1.1 MPa at a rate of 0.06 MPa / s and hold for 130 seconds. Higher pressure allows the PU material to better fill the fine parts of the mold, forming a precise surface shape, while also increasing the material's density and strength.

[0088] Cooling and shaping:

[0089] After pressurization, the mold is immersed in cooling oil at a temperature of 19°C for 200 seconds. Oil cooling allows for rapid cooling of both the mold and the PU material, while reducing stress generated during cooling. The 19°C cooling temperature and 200-second cooling time ensure sufficient cooling and setting of the material, improving the quality of the setting process.

[0090] Post-processing:

[0091] The PU upper surface, after being shaped and removed from the mold, is placed in a constant temperature and humidity chamber for aging treatment. The aging treatment temperature is 40℃, the time is 3.5 hours, and the relative humidity is controlled at 40%. After aging treatment, the dimensional stability and physical properties of the PU upper surface are significantly improved, meeting the requirements for long-term use.

[0092] Example 5

[0093] Materials preparation:

[0094] Prepare the PU upper material with the following components: 80wt% polyurethane resin, 10wt% plasticizer, 2wt% stabilizer, and 3wt% colorant. Place all components into a high-speed mixer and mix for 10 minutes at 1000 rpm. Then, injection mold the mixture into the desired PU upper material using an injection molding machine.

[0095] Mold preparation:

[0096] An aluminum alloy mold is used, with 0.25mm diameter micropores on the mold surface for ventilation. The mold is sandblasted to give it a certain degree of surface roughness, followed by cleaning and drying. A silicone oil-based release agent is then sprayed onto the inner surface of the mold using a spraying device, with a coating thickness of 14μm, ensuring uniform coverage of the mold surface and improving demolding performance.

[0097] Preheating treatment:

[0098] The PU upper material is placed into the mold, and then the mold is placed in a far-infrared heating furnace for preheating. The preheating temperature is set to 110℃, and the preheating time is 30 seconds. The far-infrared heating furnace allows the PU material to be heated from the inside out, resulting in more uniform heating. The preheating temperature of 110℃ and the preheating time of 30 seconds can quickly soften the material, making it easier to pressurize and shape it later.

[0099] Pressure setting:

[0100] Place the preheated mold on the hydraulic press and apply pressure in the following two stages:

[0101] First stage: Increase pressure to 0.8 MPa at a rate of 0.3 MPa / s and hold for 30 seconds. This rapid increase in pressure allows the PU material to quickly adhere to the mold surface, reducing the formation of bubbles and defects.

[0102] Second stage: Increase pressure to 1.5 MPa at a rate of 0.15 MPa / s and hold for 90 seconds. The higher pressure allows the PU material to be fully compacted in the mold, forming a precise surface shape, while improving the material's mechanical properties and wear resistance.

[0103] Cooling and shaping:

[0104] After pressurization, the mold is placed in a cooling water bath for cooling. The cooling water temperature is controlled at 21℃, and the cooling time is 160 seconds. Water cooling can quickly remove heat from the mold and PU material, allowing the material to solidify and set rapidly. The cooling temperature of 21℃ and the cooling time of 160 seconds ensure that the material is fully cooled, improving the setting effect.

[0105] Post-processing:

[0106] The PU upper was removed from the mold and placed in an environment of 60℃ for 2 hours for aging treatment, with the relative humidity of the aging treatment environment controlled at 60%. After aging treatment, the performance of the PU upper was further stabilized, meeting the stringent requirements of high-quality footwear products.

[0107] The PU material upper shaping method of the present invention can effectively improve the shaping effect of PU material upper by precisely controlling the parameters of each step such as preheating, pressure shaping, cooling shaping and post-processing, and optimizing the selection of mold and PU upper material, thereby improving the quality and performance of footwear products.

[0108] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for shaping PU material uppers, characterized in that, Includes the following steps: S1: Place the PU upper material in the mold and preheat it at 80-120℃ for 30-90 seconds; S2: Apply a pressure of 0.5-1.5MPa to the preheated PU surface and maintain it for 60-180 seconds; S3: Cooling and shaping, cooling temperature is 15-25℃, cooling time is 120-300 seconds.

2. The method for shaping PU material upper surface according to claim 1, characterized in that: The preheating temperature in step S1 is 90-110℃, and the preheating time is 45-75 seconds.

3. The method for shaping PU material upper surface according to claim 1, characterized in that: The pressure in step S2 is 0.8-1.2 MPa, and the holding time is 90-150 seconds.

4. The method for shaping PU material upper surface according to claim 1, characterized in that: The cooling temperature in step S3 is 18-22℃, and the cooling time is 150-240 seconds.

5. The method for shaping PU material upper surface according to claim 1, characterized in that: The mold mentioned in step S1 is an aluminum alloy mold with ventilation micropores on its surface, the pore diameter being 0.1-0.3mm.

6. The method for shaping a PU material upper surface according to claim 5, characterized in that: The inner surface of the mold is coated with a release agent, which is a silicone oil-based release agent, and the coating thickness is 5-15 μm.

7. The method for shaping PU material upper surface according to claim 1, characterized in that: The pressure in step S2 is applied in two stages: in the first stage, the pressure is increased to 0.5-0.8 MPa at a rate of 0.1-0.3 MPa / s and maintained for 30-60 seconds; in the second stage, the pressure is increased to 1.0-1.5 MPa at a rate of 0.05-0.15 MPa / s.

8. The method for shaping PU material upper surface according to claim 1, characterized in that: It also includes post-treatment: placing the shaped PU surface in an environment of 40-60℃ for aging treatment for 2-4 hours.

9. A method for shaping a PU material upper surface according to claim 8, characterized in that: The relative humidity of the aging treatment environment is controlled at 40-60%.

10. The method for shaping a PU material upper surface according to claim 1, characterized in that: The PU upper material comprises the following components: 60-80 wt% polyurethane resin, 10-20 wt% plasticizer, 2-5 wt% stabilizer, and 1-3 wt% colorant.

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