Closed-cell foaming material for backpack equipment

Abstract

The invention discloses a closed-cell foam material for backpack equipment, the closed-cell foam material is composed of matrix resin and an elastomer component, the matrix resin is an ethylene-vinyl acetate copolymer in which the content of a vinyl acetate structural unit is 5%-15%; the closed-cell foaming material has the overall density of 0.05-0.08 g / cm < 3 >, and the average diameter of internal cells is not larger than 200 microns; the closed cell foam material exhibits a compression set rate of less than 5%. According to the closed-cell foaming material for the backpack equipment provided by the invention, light weight, high resilience and deformation resistance are realized through collaborative design of materials and a process.

Description

Technical Field

[0001] This invention relates to the field of polymer foam composite materials technology, and specifically to a closed-cell foam material for backpack equipment. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) foam is widely used in footwear, packaging, and sports protective gear due to its lightweight and excellent cushioning properties. In carrying equipment (such as backpacks), EVA is often considered as a core material for the back panel or cushioning padding. However, traditional EVA foam materials used in this field have inherent performance contradictions, making it difficult to meet the comprehensive requirements of comfort, support, and durability in high-end carrying equipment. Specifically, to obtain sufficient support to prevent the load from compressing the user's back, traditional EVA materials often use a high vinyl acetate (VA) content (usually greater than 15%), but this results in high material hardness and an excessively high elastic modulus, failing to fully conform to the body's curves under pressure. Conversely, if the VA content is reduced (less than 10%) to pursue a softer feel, the material becomes too soft, lacking support and failing to provide proper back protection. Furthermore, traditional EVA foam materials mostly use chemical foaming processes, resulting in large and closed cell sizes, leading to low density (e.g., <0.10 g / cm³). 3 It has poor resilience, high compression set, and short service life. At the same time, although high VA content or the addition of a large amount of chemical additives can improve softness, it is often accompanied by the problem of volatile organic compound residues. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and to provide a closed-cell foam material for backpack equipment, which achieves lightweight, high resilience and deformation resistance through the synergistic design of materials and processes.

[0004] To achieve the above objectives, the various embodiments of the present invention employ the following technical solutions, but are not limited to the following solutions:

[0005] The first technical solution relates to a closed-cell foam material for backpack equipment, comprising a matrix resin and an elastomer component, wherein the matrix resin is an ethylene-vinyl acetate copolymer with a vinyl acetate structural unit content of 5%-15%; the closed-cell foam material has a density of 0.05-0.08 g / cm³. 3 The overall density is low, and the average diameter of its internal pores is no greater than 200 μm; closed-cell foam materials exhibit a compression set of less than 5%.

[0006] The second technical solution is based on the first technical solution, wherein the elastomer component includes rubber and polyolefin elastomer, wherein the rubber is selected from natural rubber or styrene-butadiene rubber.

[0007] The third technical solution is based on the second technical solution, wherein the content of polyolefin elastomer in the material is 10-20 parts by weight, based on 100 parts by weight of ethylene-vinyl acetate copolymer.

[0008] The fourth technical solution is based on the first technical solution, wherein the elastomer component includes thermoplastic polyurethane elastomer particles and polyether ester elastomer.

[0009] The fifth technical solution is based on the first technical solution, wherein the closed-cell foam material also contains 1%-2% by mass of hollow glass microspheres, and the particle size of the hollow glass microspheres is 10-20μm.

[0010] The sixth technical solution is based on the first technical solution, wherein the closed-cell foam material has a uniform closed-cell structure formed by a supercritical fluid foaming process.

[0011] The seventh technical solution is based on the sixth technical solution, wherein the residual amount of volatile organic compounds in the closed-cell foam material is less than 3 mg / kg.

[0012] The eighth technical solution is based on any one of the first to seventh technical solutions, wherein the Shore A hardness of the closed-cell foam material after foaming is 35-45.

[0013] As can be seen from the above description of the various embodiments of the present invention, compared with the prior art, the various embodiments of the present invention have the following beneficial effects:

[0014] In the first technical solution and related embodiments, the matrix resin is an ethylene-vinyl acetate copolymer with a vinyl acetate structural unit content of 5%-15%, combined with an elastomer component in the matrix resin, forming the rigid skeleton and tough network of the material. The low VA content provides the necessary initial rigidity and resistance to deformation, while the introduction of the elastomer gives the material better resilience and toughness, solving the problem of traditional high-VA EVA materials being too hard. The overall density is 0.05-0.08 g / cm³. 3 Together with the average diameter of the internal pores, which is no greater than 200 μm, the microstructure of the material is defined. Ultra-low density ensures lightweight construction, and the ultra-fine pores (no greater than 200 μm) mean a dense, uniform, and robust microporous network is formed at low density. This gives the material high specific strength and high resilience, providing physical support and comfort. The compression set is less than 5%, far superior to traditional foamed materials, exhibiting excellent fatigue resistance and durability, preventing collapse during long-term use and extending its service life.

[0015] In the second technical solution and related embodiments, the elastomer is a blend of rubber (natural / styrene-butadiene) and polyolefin elastomer (POE). The rubber provides the material with flexibility and tear resistance, while the POE enhances low-temperature toughness and high resilience. The two complement the low-VA content EVA matrix resin to achieve a balance of mechanical properties in terms of hardness and elasticity.

[0016] In the third technical solution and related embodiments, the amount of polyolefin elastomer (POE) added is in the range of 10-20 parts by weight. POE can fully form a flexible network without destroying the rigid skeleton of the matrix, ensuring that the material can obtain high resilience while the compression set rate can still be stably below 5%.

[0017] In the fourth technical solution and related embodiments, an embodiment of an elastomer is provided. The elastomer is a blend of thermoplastic polyurethane elastomer (TPU) particles and polyether ester elastomer. TPU provides excellent resilience and tear resistance, while polyether ester elastomer enhances the material's weather resistance. This combination is suitable for applications with more stringent requirements for durability and resistance to high and low temperatures, thus expanding the scope of application of the present invention.

[0018] In the fifth technical solution and related embodiments, surface-modified hollow glass microspheres are added, further reducing the overall density of the material on the basis of the original low density. At the same time, by adjusting the surface modifier of the hollow glass microspheres (such as a silane coupling agent), compatibility with the EVA matrix is ​​ensured, without affecting the support.

[0019] In the sixth technical solution and related embodiments, a supercritical fluid (CO2 or N2) foaming process is adopted. Utilizing the excellent permeability and nucleation ability of supercritical fluids, a much finer and more uniform closed-cell structure (average diameter ≤0.3mm) can be generated compared to traditional chemical foaming. This is a key process guarantee for achieving low density, high resilience, and high specific strength.

[0020] In the seventh technical solution and related embodiments, the supercritical fluid foaming process is a purely physical foaming process (supercritical N2), which avoids the use of chemical foaming agents, reduces the residual volatile organic compounds in the back panel to an extremely low level (<3mg / kg), improves the environmental protection level and safety of the product, and meets the highest standards of the EU REACH regulation.

[0021] In the eighth technical solution and related embodiments, the Shore A hardness is 35-45, which ensures that the material has sufficient stiffness to provide effective support, while also ensuring softness and comfort when in contact with the human body. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise expressly defined, the use of terms such as "first," "second," or "third" in the claims and description of this invention is for distinguishing different objects, not for describing a specific order.

[0024] Unless otherwise expressly defined, the use of directional terms such as "center," "lateral," "longitudinal," "horizontal," "vertical," "top," "bottom," "inner," "outer," "upper," "lower," "front," "rear," "left," "right," "clockwise," and "counterclockwise" in the claims and description of this invention is merely for the convenience of describing the invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention.

[0025] Unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" used in the claims and description of this invention should be interpreted broadly, that is, any connection in which there is no displacement relationship or relative rotation relationship between the two parties, including non-removable fixed connection, detachable fixed connection, integral connection, and fixed connection by other means or components.

[0026] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0027] A closed-cell foam material for backpack equipment comprises a matrix resin and an elastomer incorporated within the matrix resin. The matrix resin is an ethylene-vinyl acetate copolymer (EVA) with a vinyl acetate (VA) structural unit content of 5%-15%. Unlike conventional backplates using high VA content (>15%) EVA, this low VA content design imparts higher crystallinity and initial modulus to the material, providing a robust skeletal support for the backplate and forming the basis for achieving low permanent deformation. In a preferred embodiment, the VA content is 8%-12%, achieving a better balance between rigidity, toughness, and processing fluidity.

[0028] Elastomer components are incorporated into the matrix resin to overcome the potential brittleness of low-VA and EVA resins and improve resilience. There are two main options for the elastomer components:

[0029] The first preferred embodiment comprises a rubber and a polyolefin elastomer (POE). The rubber can be natural rubber or styrene-butadiene rubber, providing excellent flexibility and tear resistance; the POE enhances low-temperature toughness and high resilience. Both complement the low-VA-content EVA matrix resin, achieving a balance of mechanical properties in terms of hardness and elasticity. In one specific embodiment, the amount of POE added is 10-20 parts by weight, for example, 15 parts by weight (15 phr), based on 100 parts by weight of EVA.

[0030] The second alternative involves an elastomer component comprising thermoplastic polyurethane (TPU) elastomer particles and a polyether ester elastomer. TPU provides excellent resilience and tear resistance, while the polyether ester elastomer enhances the material's weather resistance. This combination is suitable for applications with more stringent requirements for durability and resistance to high and low temperatures, thus expanding the applicability of this invention.

[0031] Lightweight filler (optional): To further reduce density, 1%-2% by mass of hollow glass microspheres can be dispersed and added to the above matrix. The particle size of these hollow glass microspheres is preferably 10-20 μm, and their surface is modified with a silane coupling agent to ensure compatibility with the EVA matrix and not affect the support.

[0032] Closed-cell foam materials are manufactured using a supercritical fluid foaming process, where the supercritical fluid is either supercritical carbon dioxide or supercritical nitrogen. By employing supercritical fluid (CO2 or N2) foaming technology, and utilizing the excellent permeability and nucleation ability of supercritical fluids, a finer and more uniform closed-cell structure (average diameter ≤0.3mm) can be generated compared to traditional chemical foaming.

[0033] In a preferred embodiment, supercritical foaming technology combining physical and chemical foaming is used to replace traditional purely chemical foaming. By controlling the foaming temperature and the amount of foaming agent, the foam cells are made finer and more uniform, and the foam walls are thicker and more rigid. This solves the problems of soft material and insufficient support caused by low density and low VA content, while also reducing chemical residues and improving environmental friendliness.

[0034] As an alternative to supercritical fluid foaming, which is a purely physical foaming process, the residual volatile organic compounds (VOCs) in the material are below 3 mg / kg. By replacing the carbon dioxide used in the original physical foaming process with supercritical nitrogen, which has a lower diffusion coefficient, it can form finer pores (0.1-0.3 mm in diameter), further improving the material's toughness. Furthermore, nitrogen is widely available and cheaper, making it suitable for large-scale production. In this embodiment, the supercritical fluid foaming process is a purely physical foaming process (supercritical CO2 or N2), completely avoiding the use of chemical foaming agents and reducing the residual VOCs in the backsheet to extremely low levels (<3 mg / kg), improving the product's environmental friendliness and safety, and meeting the highest standards of the EU REACH regulation.

[0035] Through the foaming process described above, the material is made with an overall density of 0.05-0.08 g / cm³. 3 This is a closed-cell foam. Its internal pores are uniform and fine, with an average diameter not exceeding 200 micrometers (μm), for example, up to approximately 160 μm. This high-density, fine closed-cell structure is key to the material's high specific strength and high resilience. The material exhibits excellent resistance to permanent deformation, with a compression set of less than 5%, and in a preferred embodiment as low as 3%-4%; it also possesses suitable hardness, with a Shore A hardness typically between 35-45, for example, approximately 38 Shore A, ensuring a balance between support and a comfortable feel.

[0036] In this embodiment, the matrix resin is an ethylene-vinyl acetate copolymer with a vinyl acetate structural unit content of 5%-15%, combined with an elastomer component in the matrix resin to form the rigid skeleton and tough network of the material. The low VA content provides the necessary initial rigidity and resistance to deformation, while the introduction of the elastomer gives the material better resilience and toughness, solving the problem of traditional high-VA EVA materials being too hard. The overall density is 0.05-0.08 g / cm³. 3 Together with the average diameter of the internal pores, which is no greater than 200 μm, the microstructure of the material is defined. Ultra-low density ensures lightweight construction, and the ultra-fine pores (no greater than 200 μm) mean a dense, uniform, and robust microporous network is formed at low density. This gives the material high specific strength and high resilience, providing physical support and comfort. The compression set is less than 5%, far superior to traditional foamed materials, exhibiting excellent fatigue resistance and durability, preventing collapse during long-term use and extending its service life.

[0037] The following uses compression molding as an example to illustrate the method for preparing the closed-cell foam material of this application.

[0038] 1. Preparation of the main slurry: Accurately weigh each component according to the formula. In a typical embodiment, 100 parts by weight of ethylene-vinyl acetate copolymer (EVA) resin particles with a vinyl acetate (VA) content of 8%, 15 parts by weight of polyolefin elastomer (POE) particles, and necessary processing aids (such as 0.5-1.5 parts by weight of crosslinking agent DCP, 1-3 parts by weight of foaming aid zinc oxide) and 1-2 parts by weight of surface-modified hollow glass microspheres are added to a high-speed mixer. During the mixing process, an appropriate amount of water (e.g., 5%-15% of the total dry weight) is added to fully wet and mix the components to form a uniform wet mixture.

[0039] 2. Preparation of pre-foamed slurry with foaming agent: In another container, 8 parts by weight of a chemical foaming agent (e.g., azodicarbonamide AC) are mixed with a certain amount of water, and the mixture is stirred into a uniform and fine foam slurry by high-speed mechanical stirring or a special foaming device. This step aims to pre-disperse the foaming agent in the water and form a large number of microbubble nuclei, which helps to ensure the uniformity of subsequent foaming.

[0040] 3. Mixing and Internal Mixing: The main slurry prepared in step 1 and the foaming agent pre-foaming slurry prepared in step 2 are thoroughly mixed to form the final foamable slurry. This slurry is then injected into an internal mixer. Inside the mixer, the materials are plasticized and mixed under a certain temperature (e.g., 80-120℃) and shear force, and the moisture gradually evaporates, ultimately forming a uniform film preform with a certain degree of plasticity. This preform is then sheeted while hot and cooled to obtain the film ready for use.

[0041] 4. High-Temperature Molding Foaming: Based on the required thickness and shape of the final product, weigh the cooled film according to the specified proportions and place it into a flat vulcanizing mold preheated to the foaming and crosslinking temperature (e.g., 160-180℃). After mold closing, heat the film at a set temperature (e.g., 170-175℃) and pressure. During this process, the chemical foaming agent in the film decomposes upon heating to generate gas, while the material crosslinks and solidifies, foaming and molding under the constraint of the mold to form a foamed sheet with a closed-cell structure.

[0042] 5. Cooling, Shaping, and Post-processing: After foaming and cross-linking, the mold is held under pressure for cooling. After cooling to a suitable temperature, the mold is demolded to obtain a shaped closed-cell foamed material sheet. Subsequently, according to product design requirements, the large sheet is cut into specific sizes and shapes to obtain the closed-cell foamed material described in this invention.

[0043] Alternative to purely physical foaming: If environmental friendliness is a priority (VOC < 3 mg / kg), chemical foaming agents can be omitted in step 1, relying entirely on the supercritical fluid (such as N2) in steps 3-4 as the sole foaming medium. By controlling the pressure, temperature, and depressurization rate of the supercritical fluid, uniformly foamed materials meeting the density and cell size requirements can also be obtained.

[0044] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A closed-cell foam material for carrying equipment, characterized in that, The closed-cell foam material is composed of a matrix resin and an elastomer component, wherein the matrix resin is an ethylene-vinyl acetate copolymer with a vinyl acetate structural unit content of 5%-15%; the closed-cell foam material has a density of 0.05-0.08 g / cm³. 3 The overall density is such that the average diameter of the internal pores is no greater than 200 μm; the closed-cell foam material exhibits a compression set of less than 5%.

2. The closed-cell foam material for carrying equipment as described in claim 1, characterized in that, The elastomer component comprises rubber and polyolefin elastomer, wherein the rubber is selected from natural rubber or styrene-butadiene rubber.

3. The closed-cell foam material for carrying equipment as described in claim 2, characterized in that, The content of the polyolefin elastomer in the closed-cell foam material is 10-20 parts by weight, based on 100 parts by weight of the ethylene-vinyl acetate copolymer.

4. The closed-cell foam material for carrying equipment as described in claim 1, characterized in that, The elastomer component comprises thermoplastic polyurethane elastomer particles and polyether ester elastomer.

5. A closed-cell foam material for carrying equipment as described in claim 1, characterized in that, The closed-cell foam material also contains 1%-2% by mass of hollow glass microspheres, the particle size of which is 10-20 μm.

6. A closed-cell foam material for carrying equipment as described in claim 1, characterized in that, The closed-cell foam material has a uniform closed-cell structure formed by a supercritical fluid foaming process.

7. A closed-cell foam material for carrying equipment as described in claim 6, characterized in that, The residual amount of volatile organic compounds in the closed-cell foam material is less than 3 mg / kg.

8. A closed-cell foam material for carrying equipment as described in any one of claims 1 to 7, characterized in that, The Shore A hardness of the closed-cell foam material after foaming is 35-45.