foam sheet

Abstract

A foam sheet, relating to the field of foam manufacturing, comprises: a cross-linked resin layer, an independent pore layer, and an open-cell layer; the independent pore layer has closed and non-communicating pores; the open-cell layer has cavities communicating with the outside of the foam sheet; the open-cell layer is located on at least one of the upper and lower surfaces of the foam sheet distributed along its thickness direction; the average number of pores T / R of the foam sheet parallel to the thickness direction satisfies: 1.5 ≤ T / R ≤ 10; the average pore diameter of the independent pore layer parallel to the thickness direction is 100 μm to 500 μm. The foam sheet of this application embodiment has excellent shock absorption and cushioning performance.

Description

Technical Field

[0001] This application relates to the field of foam manufacturing technology, and more particularly to a foam sheet. Background Technology

[0002] With the rapid development of mobile communication technology and the widespread use of smartphones, mobile phones are no longer limited to just making calls; they have become indispensable multimedia playback tools in people's daily lives. Especially regarding the sound quality of mobile phones, users are becoming increasingly demanding, expecting a high-quality experience similar to professional audio equipment. However, when playing music or making calls at high volumes, existing smartphones often experience unnecessary resonance and vibration of the back cover due to speaker vibration. This not only interferes with the purity of sound quality and reduces listening comfort but may also accelerate the aging of internal components, shortening the overall lifespan of the phone. In particular, the dual-speaker stereo speaker systems commonly used in recent years, while improving the stereo effect, also increase the risk of resonance and may even cause airtightness problems, such as sound leakage—a key element in excellent acoustic cavity design.

[0003] Traditionally, foam has been used as a shock-absorbing material due to its excellent cushioning performance and durability, which can alleviate the impact and vibration experienced by internal components of a mobile phone to some extent. The pore structure in foam absorbs and dissipates sound waves through its internal cellular structure, and through vibration and friction loss mechanisms, it can play a role in sound insulation and vibration reduction. However, in practical applications, pure foam materials face many challenges: while the shock-absorbing effect theoretically increases with the number of layers in a single or multi-layer independent pore structure, it also brings problems such as increased thickness and increased compressive stress. Under continuous compression, the pores are prone to excessive deformation, leading to a decrease in shock-absorbing performance, and the permanent deformation after compression is also large, affecting its long-term effectiveness. In addition, although open-pore foam performs well in terms of cushioning performance, it is not good at controlling the vibration of the gas cavity generated when the speaker is working, and cannot effectively prevent the airflow vibration from being transmitted to the back cover of the phone, which may even aggravate the vibration of the outer shell.

[0004] Therefore, the industry urgently needs to develop a new solution that can effectively suppress the transmission of speaker vibrations to the back cover of the phone. Utility Model Content

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0006] This application provides a foam sheet material with excellent shock absorption and cushioning performance. It can not only effectively reduce the vibration of the gas cavity, but also has small permanent deformation after compression, and the shock absorption performance has long-term effectiveness.

[0007] This application provides a foam sheet comprising: a cross-linked resin layer, an independent pore layer, and an open-cell layer; the independent pore layer has closed and non-communicating pores; the open-cell layer has cavities communicating with the outside of the foam sheet; the open-cell layer is located on at least one of the upper and lower surfaces of the foam sheet distributed along the thickness direction.

[0008] The average number of pores in the foam sheet parallel to the thickness direction is T / R, and T / R satisfies:

[0009] 1.5≤T / R≤10;

[0010] Where T is the thickness of the foam sheet, and R is the average pore diameter of the foam sheet in the direction parallel to the thickness. The units of T and R are the same.

[0011] The average pore diameter of the independent pore layer is between 100 μm and 500 μm in the direction parallel to the thickness.

[0012] In some embodiments of this application, the pore size difference of the independent pore layer parallel to the thickness direction is ≤650μm;

[0013] The thickness of the foam sheet is from 0.15 mm to 4.5 mm, and the thickness range of the foam sheet is ≤0.1 mm.

[0014] In some embodiments of this application, the thickness of the foam sheet is 0.15 mm to 3 mm.

[0015] In some embodiments of this application, the thickness of the foam sheet is 0.15 mm to 1.2 mm.

[0016] In some embodiments of this application, the opening ratio of the surface of the opening layer is ≥90%.

[0017] In some embodiments of this application, the opening ratio of the surface of the opening layer is ≥95%.

[0018] In some embodiments of this application, the porosity between the independent pore layer and the open-pore layer is ≤20%.

[0019] In some embodiments of this application, the crosslinked resin layer is in contact with the independent pore layer, and the open-pore layer is in contact with the independent pore layer.

[0020] In some embodiments of this application, the foam sheet includes:

[0021] A cross-linked resin layer, a layer with independent pores, and a layer with open pores are arranged in the following order: cross-linked resin layer, layer with independent pores, and layer with open pores; or...

[0022] Two cross-linked resin layers, two independent pore layers, and one open-cell layer are arranged in the following order: cross-linked resin layer, independent pore layer, cross-linked resin layer, independent pore layer, and open-cell layer; or

[0023] One cross-linked resin layer, two independent pore layers, and two open-pore layers are arranged in the following order: open-pore layer, independent pore layer, cross-linked resin layer, independent pore layer, and open-pore layer.

[0024] The foam sheet of this embodiment includes an independent pore layer and an open-cell layer. The open-cell layer provides excellent cushioning performance; it can undergo adaptive deformation under compression, allowing the independent pore layer to maintain a stable shape and possess good shock absorption performance. The independent pore layer effectively absorbs sound waves and attenuates vibrations, while avoiding enhanced sound wave reflection caused by continuous pores. Therefore, when the foam sheet of this embodiment is filled into the back cover of a mobile phone, it can effectively suppress the resonance phenomenon of the back cover within different frequency ranges.

[0025] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0026] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0027] Figure 1 This is a schematic diagram of the structure of a foam sheet as an exemplary embodiment of this application;

[0028] Figure 2 for Figure 1 The image shown is an optical microscope image of the actual foam sheet.

[0029] Figure 3 A schematic diagram of another foam sheet structure, which is an exemplary embodiment of this application;

[0030] Figure 4 for Figure 3 The image shown is an optical microscope image of the actual foam sheet.

[0031] Figure 5 A schematic diagram of the structure of another foam sheet as an exemplary embodiment of this application;

[0032] Figure 6 This is a schematic diagram of a closed-hole and a through-hole structure. Detailed Implementation

[0033] This application describes several embodiments, but these descriptions are exemplary and not limiting, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0034] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application can also be combined with any conventional features or elements to form unique technical solutions. Any feature or element of any embodiment can also be combined with features or elements from other technical solutions to form another unique technical solution. Therefore, it should be understood that any feature shown and / or discussed in this application can be implemented individually or in any suitable combination. Therefore, the embodiments are not limited except by the limitations imposed by the appended claims and their equivalents. Furthermore, various modifications and changes can be made within the scope of the appended claims.

[0035] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation of the claims. Moreover, the claims concerning the method and / or process should not be limited to the steps performed in the written order, and those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0036] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0037] This application provides a foam sheet. Figure 1 This is a schematic diagram of the structure of a foam sheet as an exemplary embodiment of this application; Figure 2 for Figure 1 The image shown is an optical microscope image of the actual foam sheet. Figure 3 A schematic diagram of another foam sheet structure, which is an exemplary embodiment of this application; Figure 4 for Figure 3 The image shown is an optical microscope image of the actual foam sheet. Figure 5 This is a schematic diagram of the structure of another foam sheet as an exemplary embodiment of this application.

[0038] The foam sheet is formed from cross-linked polyolefin resin, such as Figures 1 to 5 As shown, the foam sheet includes: a cross-linked resin layer 10, an independent pore layer 20, and an open-cell layer 30; the cross-linked resin layer 10 is formed of unfoamed cross-linked polyolefin resin; the independent pore layer 20 is formed of foamed cross-linked polyolefin resin, and the independent pore layer 20 has closed and non-communicating pores 21 formed by foaming; the open-cell layer 30 is formed of foamed cross-linked polyolefin resin, or is formed of both foamed and unfoamed cross-linked polyolefin resin, and the open-cell layer 30 has cavities 31 communicating with the outside of the foam sheet; the open-cell layer 30 is located on at least one of the upper and lower surfaces of the foam sheet distributed along the thickness direction.

[0039] The initial temperature of the first stage of the thermogravimetric (TG) analysis of the foam sheet was between 150°C and 400°C.

[0040] The average number of pores in the foam sheet parallel to the thickness direction (i.e., the ZD direction) is T / R, and T / R satisfies:

[0041] 1.5≤T / R≤10;

[0042] Where T is the thickness of the foam sheet, and R is the average pore diameter of the foam sheet in the ZD direction. The units of T and R are the same.

[0043] The average pore diameter of the independent pore layer in the ZD direction is 100 μm to 500 μm.

[0044] The foam sheet of this embodiment includes an independent pore layer and an open-cell layer. The open-cell layer provides excellent cushioning performance; it can undergo adaptive deformation under compression, allowing the independent pore layer to maintain a stable shape and possess good shock absorption performance. The independent pore layer effectively absorbs sound waves and attenuates vibrations, while avoiding enhanced sound wave reflection caused by continuous pores. Therefore, when the foam sheet of this embodiment is filled into the back cover of a mobile phone, it can effectively suppress the resonance phenomenon of the back cover within different frequency ranges.

[0045] In some embodiments of this application, the pores in the independent pore layer are uniformly distributed and independent of each other, which is beneficial to achieving effective sound wave absorption and vibration attenuation.

[0046] Open-hole / closed-hole structure

[0047] Closed-cell foam can absorb and dissipate sound waves through its internal closed-cell structure, and can play a certain role in sound insulation and vibration reduction through vibration and friction loss mechanisms. However, under continuous compression, the closed cells are prone to excessive deformation, leading to a decrease in vibration damping performance. Moreover, the permanent deformation after compression is also large, affecting its long-term effectiveness.

[0048] While the perforated foam performs well in terms of cushioning, it is inadequate in controlling the vibration of the air cavity generated when the speaker is working. It cannot effectively prevent the airflow vibration from being transmitted to the back of the phone, and may even aggravate the vibration of the casing.

[0049] The foam sheet material of this application embodiment integrates closed-cell and open-cell structures. The pores in the independent pore layers are closed and do not communicate with each other, i.e., closed-cell; the cavities in the open-cell layers are connected to the outside of the foam sheet, i.e., open-cell. When this novel foam material is compressed, the open-cell layers first undergo adaptive deformation, thereby allowing the subsequent independent pore layers to maintain a relatively stable shape, significantly reducing the occurrence of permanent compression deformation.

[0050] The initial temperature of the first weightlessness stage in TG analysis

[0051] This temperature typically corresponds to the point at which the material begins to experience significant mass loss.

[0052] If the starting temperature of the first weight loss stage is too low, it means that the resin will begin to lose mass at a low processing temperature, which will affect the strength of the pore structure and the pore size distribution of the foam material, and affect the shock absorption performance.

[0053] First, if the starting temperature of the first weight loss stage in the TG analysis of the foam sheet is too low, the structural strength of the pores will decrease during the high-temperature foaming process, making it prone to "bubble coalescing." This leads to a larger pore size difference, overall pore unevenness, and a reduction in the cushioning and shock absorption performance of the foam material. Second, if the starting temperature of the first weight loss stage is low, the material's stability is poor, and performance degradation is likely to occur during use. Gas in the independent pores is more likely to escape during compression, resulting in poor permanent compression deformation performance of the foam sheet, which is detrimental to maintaining stable shock absorption performance during long-term use.

[0054] The higher starting temperature of the first stage of weightlessness reflects a more stable material structure. The resulting porous structure is less susceptible to changes in ambient temperature, which is beneficial to the long-term stability and durability of the damping material. However, an excessively high starting temperature of thermal weight loss indicates that the material may have a higher degree of cross-linking or a more regular molecular structure, which will significantly affect the flexibility of the material's molecular chains. This will make it difficult or impossible for the material to absorb the energy generated by vibration through the movement or rotation of chain segments, resulting in a weakening of the sound insulation and vibration damping performance of the foamed material.

[0055] The starting temperature of the first weight loss stage in the thermogravimetric analysis of the foam sheet in this application embodiment is in the range of 150°C to 400°C. It has good pore strength, uniform and stable pore structure, low permanent compression deformation, and can provide long-term stable sound insulation and vibration reduction effect.

[0056] In the embodiments of this application, the average number of pores in the ZD direction of the foam sheet is T / R, and T / R can satisfy:

[0057] 1.5≤T / R≤10;

[0058] Where T is the thickness of the foam sheet, and R is the pore diameter of the foam sheet in the ZD direction.

[0059] For example, T / R can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10.

[0060] If the T / R ratio is too small, the increase in compressive stress will rise rapidly with the increase in compressive stress during the compression process, and the compression curve will not be smooth. If the T / R ratio is too large, the pores are prone to excessive deformation under continuous compression, which will lead to a decrease in shock absorption performance. Moreover, the permanent deformation after compression will also be large, affecting its long-term effectiveness.

[0061] In some embodiments of this application, the thickness of the foam sheet can be from 0.15mm to 4.5mm. For example, the thickness of the foam sheet can be from 0.15mm to 3mm; or, for another example, the thickness of the foam sheet can be from 0.15mm to 1.2mm. Still other examples include the thickness of the foam sheet being 0.15mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, or 4.5mm.

[0062] In some embodiments of this application, the average density of the foam sheet can be 0.025 g / cm³. 3 Up to 0.1 g / cm 3 When the average density of the foam sheet is 0.025 g / cm³ 3 Up to 0.1 g / cm 3 This helps to control the size and uniformity of pores.

[0063] In some embodiments of this application, the average pore diameter of the independent pore layer in the ZD direction is 100μm to 500μm, the pore diameter range is ≤650μm, and the thickness range of the foam sheet is ≤0.1mm. Meeting these conditions is beneficial to controlling the uniformity of pores and enhancing the cushioning and shock absorption effect of the foam sheet.

[0064] To further improve the softness of the foam sheet and control the shedding problem during subsequent processing, the degree of crosslinking of the foam sheet is preferably 10% to 60%.

[0065] In some embodiments of this application, the open-cell ratio of the open-cell layer surface of the foam sheet is ≥90%, preferably ≥95%. When the open-cell ratio of the open-cell layer surface is ≥90%, it is beneficial to have a smooth compression curve, which can provide excellent cushioning performance. When compressed, the open-cell layer can undergo adaptive deformation, allowing the independent pore layer to maintain a stable shape and possess good shock absorption performance.

[0066] In some embodiments of this application, the porosity between the independent pore layer and the open-cell layer of the foam sheet is ≤20%. When the porosity is >20%, the open-cell layer deforms excessively when compressed, the independent pore layer cannot maintain a stable shape, and the shock absorption performance is reduced.

[0067] In the description of this application, the term "through pores" in the context of "porosity" is distinguished from the concept of independent pores (also known as closed pores) in an independent pore layer. Independent pores refer to pores within a material that are independent, each pore being separated by a closed membrane and not interconnected with other pores, such as... Figure 6 As shown in Figure B, a through-pore refers to a pore within a material that is not completely separated by a sealed membrane, and has at least one channel connecting it to other pores, such as... Figure 6 The pore A in the image is shown.

[0068] In some embodiments of this application, the compressive stress of the foam sheet under 15% compression deformation can be from 1 kPa to 50 kPa; the compressive stress under 70% compression deformation can be from 25 kPa to 700 kPa.

[0069] In some embodiments of this application, when the compression deformation of the foam sheet varies in the range of 15% to 70%, the maximum increase in compressive stress is 10 kPa to 60 kPa for every 1% increase in compression deformation.

[0070] Here, each 1% increase in compressive deformation refers to an increase in compressive deformation according to the pattern of 15%, 16%, 17%, 18%, ... 70%; the "increase in compressive stress" is relative to the compressive stress corresponding to the previous 1% compressive deformation.

[0071] When the compression deformation of the foam sheet increases by 1%, the maximum increase in compressive stress is within the range of 10KPa to 60KPa. This is beneficial for the foam sheet to maintain a close and low compressive strength under different compression levels. When the foam sheet is filled into the back cover of the mobile phone, it can protect the internal components of the mobile phone from damage.

[0072] In some embodiments of this application, such as Figures 1 to 5 As shown, the cross-linked resin layer 10 is in contact with the independent pore layer 20, and the open-pore layer 30 is in contact with the independent pore layer 20. The open-pore layer 30 can be obtained by opening a portion of the independent pore layer 20, or by opening a portion of the independent pore layer 20 and the entire cross-linked resin layer, but the opening does not destroy the integrity of the pores in the independent pore layer 20.

[0073] In some embodiments of this application, such as Figure 1 and Figure 2 As shown, the foam sheet may include:

[0074] A cross-linked resin layer 10, an independent pore layer 20, and an open-cell layer 30 are arranged in the order of cross-linked resin layer 10, independent pore layer 20, and open-cell layer 30.

[0075] In some embodiments of this application, such as Figure 3 and Figure 4 As shown, the foam sheet may include:

[0076] Two cross-linked resin layers 10, two independent pore layers 20, and one open-cell layer 30 are arranged in the following order: cross-linked resin layer 10, independent pore layer 20, cross-linked resin layer 10, independent pore layer 20, and open-cell layer 30.

[0077] In some embodiments of this application, such as Figure 5 As shown, the foam sheet may include:

[0078] One cross-linked resin layer 10, two independent pore layers 20 and two open-pore layers 30 are arranged in the order of open-pore layer 30, independent pore layer 20, cross-linked resin layer 10, independent pore layer 20 and open-pore layer 30.

[0079] In some embodiments of this application, the crosslinked polyolefin resin can be a crosslinking product of one or more polyolefin resin raw materials. The foam sheets in the embodiments of this application are formed using easily crosslinked polyolefin resins, which possess excellent heat resistance, weather resistance, and mechanical strength, and can maintain a stable structural morphology and good cushioning and shock absorption performance under long-term pressure and high and low temperature environments. The aforementioned polyolefin resin can achieve a crosslinking degree of 10% to 60% through any one or more crosslinking methods selected from chemical crosslinking, covalent crosslinking, ionic crosslinking, interpenetrating networks, thermoplastic dynamic crosslinking, electron beam radiation crosslinking, gamma-ray radiation crosslinking, ultraviolet light crosslinking, enzyme-catalyzed crosslinking, and hydrothermal crosslinking.

[0080] Polyolefin resins

[0081] In some embodiments of this application, the polyolefin resin raw material may include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and ethylene-butene copolymer, etc., preferably polyethylene resin.

[0082] The choice of polyethylene resin is not particularly limited, and includes, but is not limited to, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene. Optionally, ethylene-α-olefin copolymers with ethylene as the main component can also be selected, wherein the α-olefin is selected from α-olefins having 2 to 12 carbon atoms, such as propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3-ethyl-1-pentene, 1-octene, 1-decene, and 1-undecene. The number of such α-olefins can be only one, or two or more. The above selection of polyethylene resins can be used alone or in combination of two or more. Low-density polyethylene is preferred.

[0083] Examples of polypropylene resins include propylene homopolymers, propylene-ethylene copolymers, propylene-ethylene-α-olefin copolymers, and propylene-α-olefin copolymers. They can be used individually or in combination of two or more. Specifically, examples of α-olefins constituting propylene-α-olefin copolymers include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene, with α-olefins having 6-12 carbon atoms being preferred. For propylene copolymers, the propylene content in the copolymer is 50 wt% or more.

[0084] Rubber and / or thermoplastic elastomers may also be further added to polyolefin resins. These rubbers and / or thermoplastic elastomers have a glass transition temperature below 20°C. Specific examples include: natural or synthetic rubbers such as natural rubber, polyisobutylene, isoprene rubber, butyl rubber, chloroprene rubber, and nitrile rubber; olefin elastomers such as ethylene-vinyl acetate copolymer, polybutene, polyisobutylene, and chlorinated polyethylene; styrene elastomers such as styrene-isoprene-styrene copolymer (SIS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-butadiene-styrene copolymer (SIBS), and their hydrogenated polymers; thermoplastic polyester elastomers; thermoplastic polyurethane elastomers; and thermoplastic acrylic elastomers. The number of these rubbers and / or thermoplastic elastomers may be only one, or two or more.

[0085] In some embodiments of this application, the crosslinked polyolefin resin may be a crosslinking product of at least two polyolefin resin raw materials.

[0086] It should be noted that, regardless of the type of polyolefin resin selected, whether or not elastomer materials are added, or whether or not other functional additives are added, after blending the polyolefin matrix resin, the mass fraction of the n-hexane extract is preferably 1% to 8.5%, the tensile strength can be 15MPa to 35MPa, the elongation can be 500% to 900%, and the softening temperature (Vicat softening point) is 70℃ to 100℃.

[0087] The properties of resins are influenced by their chemical composition and microstructure, which determine their performance in different applications.

[0088] n-Hexane extract

[0089] Hexane extracts refer to components in resins that are soluble in hexane; these components are typically low-molecular-weight compounds. These substances can affect the resin's irradiation crosslinking and melt foaming processes, thus influencing the structural strength of the pores and the onset temperature of thermal weight loss in the foamed material.

[0090] In polyolefin resins, n-hexane extract refers to the soluble substance obtained by extracting a polyolefin resin sample with n-hexane as a solvent under certain conditions (see Chinese National Standard GB / T5009.58-2003).

[0091] The components of this soluble substance may include: 1. Unreacted monomers: ethylene or other monomers that may not have been fully polymerized during the production of polyolefin resins; 2. Low molecular weight polymers: polyethylene fragments with relatively low molecular weight formed during the polymerization reaction; 3. Catalyst residues: catalysts used in the polymerization reaction and their byproduct residues, etc.

[0092] The effect of low molecular weight polymers on the crosslinking of polyolefin resins: Crosslinking of polyolefin resins mainly occurs between the main chain molecules of the polyolefin resin, rather than on the oligomer molecules. Excessive low molecular weight polymer content may interfere with the main chain crosslinking, leading to reduced melt strength and large pores. Excessive low molecular weight polymer content will result in poor melt flowability of the resin, which will have a certain impact on the process flow. When the low molecular weight polymer content is appropriate, the molecular weight distribution of the crosslinked polyolefin resin is uniform and the main chain crosslinking is more complete, resulting in better tensile strength, compressive strength, resilience, etc.

[0093] Tensile strength and elongation of polyolefin resin raw materials

[0094] Tensile strength refers to the maximum stress that a material can withstand under tensile load. When the strength of the resin is too low, the possibility of open pores appearing in the cross-linked resin layer during foaming increases, making it impossible to form a complete cross-linked resin layer structure. The pore wall structure formed by foaming high-strength resin usually has higher strength as well. However, when the strength of the pore wall structure is too high, the binding force on the bubble expansion process will also increase, and the average number of pores T / R in the ZD direction may be too small.

[0095] In some embodiments of this application, the tensile strength of the polyolefin resin raw material can be from 15 MPa to 35 MPa, and the elongation can be from 500% to 900%.

[0096] Strength of polyolefin resin raw materials: including tensile strength and shear strength.

[0097] The high strength of polyolefin resin raw materials means that their foamed materials have a stronger ability to resist damage under cutting forces. High-strength foamed materials are less likely to break during the cutting process, resulting in cleaner cuts, but may also lead to increased cutting resistance, requiring greater cutting forces or sharper cutting tools.

[0098] Hardness of polyolefin resin raw materials: High-strength foamed materials often have relatively high hardness, which leads to faster tool wear during cutting and makes chip shedding more difficult to control.

[0099] Elongation / Ductility: High elongation of polyolefin resins indicates that they can undergo significant deformation under tension without immediately breaking. Such foamed materials can better adapt to the pressure distribution of the cutting tool during cutting, resulting in a smoother cutting process and less chip loss. High elongation is usually associated with good toughness. Foamed materials with good toughness are less prone to brittle fracture during cutting, instead forming continuous chips with a certain thickness, which helps reduce chip generation.

[0100] High-strength but low-elongation foamed materials tend to generate a large number of fine debris during cutting. These debris are difficult to collect and may affect their use in electronic devices.

[0101] Foamed materials with moderate strength and high elongation produce relatively intact chips during cutting, which are easy to clean and recycle, while reducing the risk of damage to equipment and molds.

[0102] Vicat softening point of polyolefin resin raw materials

[0103] The Vicat softening point of a resin measures the temperature at which it transitions from a solid state to a state with a certain degree of plasticity when heated; it can also be called the softening temperature. The Vicat softening point reflects the resin's thermal stability and operating temperature range. Generally, the higher the molecular weight and the higher the degree of cross-linking of the resin, the higher its Vicat softening point. Resins with lower softening points generally form denser cross-linked networks more easily, but their ability to trap gas generated in the pores during foaming is weaker. Selecting a resin with a suitable Vicat softening point makes it easier to control the pore structure of the foamed material within the designed range.

[0104] In some embodiments of this application, the Vicat softening point of the mixed resin can be from 70°C to 100°C.

[0105] Impact on softness: Polyolefin resins with low Vicat softening points may exhibit softer properties at or slightly above room temperature. If the Vicat softening point is high, the foamed material will remain relatively hard at room temperature, providing more support.

[0106] Impact on Compression Curve: The Vicat softening point affects the compression increment and resilience of foamed materials. Materials with lower Vicat softening points deform more easily during compression, resulting in a flatter compression curve, while materials with higher Vicat softening points exhibit stronger compression resistance and slower deformation.

[0107] Impacts on Vibration Damping, Sound Insulation, and Cushioning Performance: The vibration damping, sound insulation, and cushioning capabilities of foamed materials are closely related to their softness, hardness, and elasticity. Resins with low Vicat softening points, after foaming, are generally more effective at absorbing and dispersing external forces due to their softness and malleability, providing excellent vibration damping. For sound insulation applications, soft materials can better seal gaps and prevent sound transmission.

[0108] During processing, if the Vicat softening point is too low, the heat generated during cutting can easily damage the open-cell structure, resulting in unstable thickness of the foamed sheet. Moreover, the friction during cutting may cause more material to fall off, making it easier to generate debris. It is also difficult to create holes when needle punching. If the Vicat softening point is too high, the foaming ratio will be low, the softness will be reduced, and the resilience will be poor, but the cutting may be cleaner and more efficient with less debris.

[0109] Impact on thermal stability: Resins with higher Vicat softening points generally have better thermal stability. The foamed products can maintain good morphological stability and mechanical properties at high temperatures. Resin foam materials with high Vicat softening points have relatively good dimensional stability and durability under long-term heat or stress, and are not easily deformed or degraded due to temperature changes.

[0110] Pore ​​uniformity: A high Vicat softening point may result in low resin flow during foaming, affecting gas diffusion and pore structure formation, which may lead to problems such as uneven pores and density distribution deviation.

[0111] This application embodiment also provides a method for preparing the foam sheet as described above, the method comprising:

[0112] Polyolefin resin raw materials are mixed with foaming agents and optional functional additives, and then extruded to obtain shaped sheets.

[0113] The shaped sheet is cross-linked modified and foamed to form a cross-linked resin layer and an independent pore layer with pores, thereby obtaining a foamed sheet comprising a cross-linked resin layer, an independent pore layer and a cross-linked resin layer in sequence.

[0114] An opening is made on at least one side of the foamed sheet to form the open layer, thereby obtaining the foamed sheet.

[0115] In some embodiments of this application, the step of creating an opening in at least one side of the foamed sheet to form the open-cell layer includes: removing a cross-linked resin layer and a portion of the independent pore layer from one side of the foamed sheet, exposing a portion of the pores in the independent pore layer, such that a portion of the pores in the independent pore layer is converted into a cavity communicating with the outside, and a portion of the independent pore layer having the cavity is converted into the open-cell layer.

[0116] In some embodiments of this application, the step of creating an opening layer on at least one side of the foamed sheet includes:

[0117] A cavity communicating with the outside is formed on at least one side of the foamed sheet, the cavity extending into the independent pore layer, such that a portion of the independent pore layer having the cavity and the cross-linked resin layer penetrated by the cavity are transformed into the open-cell layer.

[0118] In some embodiments of this application, the preparation method further includes: after obtaining the foamed sheet, but before opening a hole on at least one side of the foamed sheet,

[0119] Multiple foamed sheets are combined together to obtain composite sheets;

[0120] The step of creating an opening layer by making a hole on at least one side of the foamed sheet includes: creating an opening layer by making a hole on at least one side of the composite sheet.

[0121] Furthermore, two foamed sheets can be thermally laminated together first, and holes can be made on the top and bottom surfaces or a single surface of the laminated foamed sheet.

[0122] In some embodiments of this application, the mixing of the polyolefin resin raw material with a foaming agent and optional functional additives includes:

[0123] At least two polyolefin resin raw materials are blended and modified by extrusion to obtain a mixed resin;

[0124] The mixed resin is mixed with a foaming agent and optionally a functional additive.

[0125] In some embodiments of this application, the preparation method may include:

[0126] At least two polyolefin resin raw materials are blended and modified by extrusion to obtain a mixed resin;

[0127] The mixed resin is mixed with a foaming agent and optionally a functional additive, and then extruded to obtain a shaped sheet.

[0128] The shaped sheet is cross-linked modified and foamed to form a cross-linked resin layer and an independent pore layer with pores, thereby obtaining a foamed sheet comprising a cross-linked resin layer, an independent pore layer and a cross-linked resin layer in sequence.

[0129] An opening is made on at least one side of the foamed sheet to form the open layer, thereby obtaining the foamed sheet.

[0130] In some embodiments of this application, the preparation method may include:

[0131] Polyolefin resin raw materials are mixed with foaming agents and optional functional additives, and then extruded to obtain shaped sheets.

[0132] The shaped sheet is cross-linked modified and foamed to form a cross-linked resin layer and an independent pore layer with pores, thereby obtaining a foamed sheet comprising a cross-linked resin layer, an independent pore layer and a cross-linked resin layer in sequence.

[0133] Multiple foamed sheets are combined together to obtain composite sheets;

[0134] An opening is made on at least one side of the composite sheet to form the opening layer, thereby obtaining the foam sheet.

[0135] In some embodiments of this application, before extruding the polyolefin resin raw material, other functional additives can be added according to actual needs to further improve the various properties of the polyolefin foam sheet. For example, antioxidants, antibacterial agents, colorants, antistatic agents and fillers can be added.

[0136] Antioxidants include, for example, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 4,4'-dioctyl diphenylamine, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, antioxidant B225, antioxidant 445, and antioxidant MBA. 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 4,4'-dioctyl diphenylamine are further preferred.

[0137] Resins undergo high temperatures during compounding, modification, and foaming. High-temperature oxidation leads to molecular chain breakage, affecting the thermogravimetric initiation temperature and pore structure stability of the foam. Adding antioxidants to the resin prevents or delays this oxidation process. Antioxidants capture free radicals generated during polymer chain breakage, preventing further free radical chain reactions and thus preventing further degradation. Studies show that their free radical-capturing ability eliminates free radicals during electron beam irradiation crosslinking, weakening the resin's crosslinking structure and reducing gel content. Therefore, antioxidants with less impact on electron beam irradiation crosslinking modification, such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 4,4'-dioctyldiphenylamine, are preferred in the formulation.

[0138] The specific steps for each process are as follows:

[0139] Blending modification

[0140] In the blending modification step, the blending modification can be carried out in an extruder to obtain a mixed resin.

[0141] Extrusion molding

[0142] In the extrusion molding step, polyolefin resin, mixed resin, foaming agent, and functional additives are passed through the extruder head to form a continuous sheet with a specific thickness.

[0143] Crosslinking

[0144] In this embodiment of the application, after the polyolefin resin is extruded and molded, a gelation reaction process, i.e. a crosslinking modification reaction, is carried out. Crosslinking can be carried out using currently known technologies, such as chemical crosslinking, covalent crosslinking, ionic crosslinking, interpenetrating networks, thermoplastic dynamic crosslinking, electron beam radiation crosslinking, gamma-ray radiation crosslinking, ultraviolet light crosslinking, enzyme-catalyzed crosslinking, and hydrothermal crosslinking, or any one or more of these methods. Preferably, the crosslinking modification method is selected from any one or two of chemical crosslinking and electron beam radiation crosslinking.

[0145] More preferably, the crosslinking modification is performed via electron beam radiation crosslinking, which involves irradiating the resin sheet with ionizing radiation such as electron beams, alpha rays, beta rays, and gamma rays. The irradiation dose of the ionizing radiation is adjusted to achieve the desired degree of crosslinking in the resulting foamed sheet, for example, 10 Mrad to 30 Mrad, preferably 12 Mrad to 28 Mrad, and more preferably 16 Mrad to 21 Mrad. The energy of the irradiation crosslinking affects the crosslinking rate, typically selected as 1.0 MeV to 3.0 MeV, preferably 1.2 MeV to 2.8 MeV, and more preferably 1.5 MeV to 2.5 MeV.

[0146] The amount of ionizing radiation exposure affects the cross-linking structure of resins. When the ionizing radiation exposure is too low, the cross-linking of the resin is too low, which leads to a lower starting temperature in the first weight loss stage of the thermogravimetric analysis (TG) test of the foamed resin. At the same time, it can cause excessively large and uneven pores during the foaming process, an increase in the porosity of the independent pore layer, and a thinning of the cross-linked resin layer, or even the appearance of holes. When the ionizing radiation exposure is too high, it can increase the possibility of resin molecular weight chain breakage and degradation.

[0147] As a chemical crosslinking agent, any substance previously used in the manufacture of foams is acceptable, without particular limitation. Specific examples include dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, cumyl hydroperoxide, tert-butyl hydroperoxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylhexane, 4,4-di(tert-butylperoxy)valerate, α,α'-bis(tert-butylperoxy)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3, and tert-butylperoxy, etc. The content of the crosslinking aid is preferably 0.1% to 2 wt% based on the total weight of the polyolefin resin raw material.

[0148] Atmospheric pressure high temperature foaming

[0149] The cross-linked sheet-like polyolefin resin composition is heated to cause a thermally decomposable blowing agent to foam. For example, a blowing agent with a decomposition temperature higher than the melting temperature of the resin is used. For instance, an organic or inorganic chemical blowing agent with a decomposition temperature of 160°C to 270°C is used.

[0150] Examples of organic foaming agents include azodicarbonamide, metal salts of azodicarboxylic acid (such as barium azodicarboxylic acid), azobisisobutyronitrile and other azo compounds, nitroso compounds such as N,N'-dinitrospentamethylenetetramine, hydrazinyldicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazine), toluenesulfonylhydrazine and other derivatives, and aminourea compounds such as toluenesulfonylaminourea.

[0151] Examples of inorganic foaming agents include ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous sodium citrate.

[0152] Among these foaming agents, from the viewpoints of obtaining microbubbles and from the viewpoints of economy and safety, azo compounds and nitroso compounds are preferred, azodicarbonamide, azobisisobutyronitrile, and N,N'-dinitrospentamethylenetetramine are more preferred, and azodicarbonamide is even more preferred. Azodicarbonamide is preferred. Thermally decomposable foaming agents can be used alone or in combination of two or more types.

[0153] Regarding the amount of thermally decomposable foaming agent added, relative to 100 parts by weight of polyolefin resin raw material, the thermally decomposable foaming agent is preferably 6 to 15 parts by weight, and the ash content is ≤1%.

[0154] The content of foaming agent affects the pore size and distribution of foamed sheets. If the content of foaming agent is too low, the average number of pores in the ZD direction (T / R) will be too small, resulting in high compressive stress and poor cushioning and shock absorption performance of the foamed sheet. If the content of foaming agent is too high, the heat generated during foaming will be too large, the formation of pores will be difficult to control, resulting in open-cell structure in the cross-linked resin layer, or even breakage of the foamed sheet, making it impossible to produce foamed sheets with a thickness of less than 1.2 mm.

[0155] The ash in the foaming agent will remain in the pores after the foaming agent decomposes. If the ash content is too high, it will increase the amount of foam shedding when the foam vibrates. The ash content in the foaming agent needs to be controlled within 1%.

[0156] The temperature for heating and foaming varies depending on the decomposition temperature of the thermally decomposable foaming agent. When using azo compound foaming agents, the foaming temperature is typically between 140°C and 300°C, preferably between 160°C and 260°C.

[0157] In addition, foaming aids can be added to help regulate the decomposition temperature and decomposition rate of the foaming agent. Foaming aids compatible with azo foaming agents include urea-based, phosphate-based, organic acid-based, and metal salt-based foaming aids, preferably metal salt-based foaming aids, and more preferably zinc salt foaming aids such as zinc oxide, stearic acid, and zinc stearate.

[0158] In some embodiments of this application, the perforation method may include any one or more of cutting, needle punching, abrasion, chemical etching, laser drilling, high-pressure water jet cutting, hot pressing, and mechanical stretching perforation. These perforation methods can form a uniformly distributed perforated layer with a certain degree of air permeability without compromising the overall strength and acoustic performance of the foam sheet.

[0159] During the cutting process, to ensure a smooth, impurity-free, and uneven surface on the foamed sheet, the foamed material is fed into a pressure roller with a pressure adjusted to 0.2 MPa to 0.8 MPa to maintain the sheet's flatness before cutting. The cutting machine is set to a wire cutting speed of 100 mm / s to 5000 mm / s to ensure a smooth cut surface and prevent damage to the pore structure. The cooling water flow rate is set to 5 L / min to 10 L / min, and the temperature to 5°C to 30°C to reduce heat accumulation during cutting and prevent material melting or deformation. The traction force is controlled to 10 N to 50 N, and the traction speed to 0.5 m / min to 5 m / min, resulting in a foamed sheet with a cross-linked resin layer, an independent pore layer, and an open-cell layer.

[0160] In the needle punching process, in order to ensure that the surface of the foamed sheet is flat, free of impurities and uneven, the gap of the needle punching rollers can be adjusted so that the puncture depth is 50μm to 100μm, the needle diameter is 0.08mm to 0.12mm, and the center distance between the needles is 0.4mm to 0.6mm. The foamed material passes through the needle punching machine, and the numerous fine needles on the needle plate quickly penetrate the material to form a continuous pore structure.

[0161] In the abrasion step, the foamed material can be brought into contact with a surface abrasive roller with a mesh size of 80 at a linear speed of 20 m / min to 50 m / min. The speed of the abrasive roller is 1 m / min to 5 m / min, and the pressure between the foamed material and the abrasive roller is 0.1 MPa to 0.3 MPa. The surface abrasive roller breaks down the cross-linked resin layer of the foamed material to form an open-cell structure.

[0162] This application also provides the use of the foam sheet as a shock-absorbing material as described above.

[0163] In some embodiments of this application, the use may include: filling the cavity with the foam sheet to reduce airflow vibration in the cavity.

[0164] This application embodiment also provides a display component, the display component including: a display panel, a middle frame and a back cover, the display panel, the middle frame and the back cover forming an inner cavity, the inner cavity communicating with the outside of the display component; the inner cavity is filled with foam sheet;

[0165] The foam sheet is formed of cross-linked polyolefin resin and includes: a cross-linked resin layer, an independent pore layer, and an open-cell layer; the cross-linked resin layer is formed of unfoamed cross-linked polyolefin resin; the independent pore layer is formed of foamed cross-linked polyolefin resin, and the independent pore layer has closed and non-communicating pores formed by foaming; the open-cell layer is formed of foamed cross-linked polyolefin resin, and the open-cell layer has cavities communicating with the outside of the foam sheet; the open-cell layer is located on at least one of the upper and lower surfaces of the foam sheet distributed along the thickness direction.

[0166] The starting temperature of the first stage of the thermogravimetric analysis of the foam sheet is between 150°C and 400°C.

[0167] The average number of pores in the ZD direction of the foam sheet is T / R, and T / R satisfies:

[0168] 1.5≤T / R≤10;

[0169] Where T is the thickness of the foam sheet, and R is the average pore diameter of the foam sheet in the ZD direction. The units of T and R are the same.

[0170] The average pore diameter of the independent pore layer in the ZD direction is 100 μm to 500 μm.

[0171] In some embodiments of this application, the display component further includes at least one of a speaker, a vibration motor, and a circuit board;

[0172] The speaker is located in the inner cavity; the foam sheet is filled between the speaker and the middle frame and / or between the speaker and the back cover;

[0173] The vibration motor is located in the inner cavity; the foam sheet is filled between the vibration motor and the middle frame and / or between the vibration motor and the back cover;

[0174] The circuit board is located in the inner cavity; the foam sheet is filled between the circuit board and the middle frame and / or between the circuit board and the back cover.

[0175] In some embodiments of this application, the display component may include a housing with a cavity, a speaker located in the cavity, and a foam sheet filling the cavity. The speaker is fixed within a frame, and the cavity in front of the frame transmits sound to the outside of the display component through a sound outlet, while the cavity behind the frame communicates with the air inside the display component through a ventilation hole. The foam sheet is die-cut into a certain shape and fixed in part or all of the cavity by compression or polymer adhesive.

[0176] For example, the foam sheet of this application embodiment can be used in the following mobile phone parts:

[0177] 1. Used between the speaker and the phone casing, it can help fix the position of the speaker, prevent the speaker from shifting or loosening due to long-term vibration, maintain stable sound quality, absorb and disperse the vibration energy of the speaker, and prevent this energy from being directly transmitted to the phone casing, thereby reducing resonance.

[0178] 2. Circular shock-absorbing foam used around the base of the vibration motor: Located between the vibration motor and the phone casing, it absorbs the vibration generated when the motor is working, reduces noise, prevents the casing from resonating, and ensures that the motor is securely installed and extends its service life.

[0179] 3. Used as a shock-absorbing pad for full bonding on the back of the circuit board: Located between the circuit board (e.g., PCB motherboard) and the mobile phone casing, on the back or edge of the circuit board, using shock-absorbing foam sheets to isolate the circuit board from vibration directly transmitted to the casing, reducing the potential risk of damage to the components on the circuit board.

[0180] 4. Used as cushioning foam embedded around the camera module to prevent motor vibration from affecting the delicate optical components and maintain shooting stability;

[0181] 5. Used between the phone battery and the back cover or mid-frame: Used between the battery and the phone's back cover or mid-frame to absorb vibrations and prevent the battery from moving inside the phone or being damaged by vibrations.

[0182] 6. For use at the contact point between the mobile phone screen and the frame: In order to avoid abnormal screen display or noise caused by vibration, the foam sheet of this application embodiment can be set as a shock-absorbing material at the edge of the screen.

[0183] This application also provides an electronic product, which includes the display device described above.

[0184] In some embodiments of this application, the electronic products may include: smart mobile communication devices, laptops, liquid crystal displays, OLED displays, e-books, tablet terminals, gaming devices, cameras, wearable electronic devices, etc.

[0185] The technical solutions of the embodiments of this application are further illustrated below through exemplary models of foam sheets and their preparation process.

[0186] The foam sheets in the following examples and comparative examples have the following characteristics: Figure 1 The structure shown is obtained by the following method.

[0187] Example 1

[0188] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 40 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0189] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 10.5 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 0.5 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0190] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 17.3 Mrad to crosslink the resin sheet;

[0191] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0192] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0193] Example 2

[0194] This embodiment modifies the shaped sheet material through chemical crosslinking.

[0195] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC), 40 parts by weight of polyolefin elastomer A (DOW AFFINITY™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) were blended together. ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0196] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 10.5 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 0.5 parts by weight of antioxidant 4,4'-dioctyl diphenylamine, and 2 parts by weight of dicumyl peroxide and then extruded into sheets by twin-screw extruder.

[0197] (3) Foaming: The cross-linked modified sheet obtained in step (2) is heated to decompose and foam the foaming agent. The heating temperature is 220°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0198] (4) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.2MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 1000 mm / s, a cooling water flow rate of 5L / min and a temperature of 5℃, a traction force of 10N and a traction speed of 5m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0199] Example 3

[0200] (1) Blending modification of resin: 20 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 20 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 60 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 8.35%, a tensile strength of 19.3MPa, an elongation of 860%, and a softening temperature of 89.3℃.

[0201] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 10.5 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 0.5 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0202] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 18.5 Mrad to crosslink the resin sheet;

[0203] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0204] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.8MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 100 mm / s, a cooling water flow rate of 5L / min and a temperature of 28℃, a traction force of 30N and a traction speed of 0.5m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0205] Example 4

[0206] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 40 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0207] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 5 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.2 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 0.2 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0208] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 19.7 Mrad to crosslink the resin sheet;

[0209] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0210] (5) Needling of foamed sheet: The foamed sheet is fed into the needle punching machine. The gap of the needle punching roller is adjusted so that the puncture depth is 80μm, the diameter of the needle is 0.1mm, and the center distance between the needles is 0.2 to 0.5mm. The foamed material passes through the needle punching machine, and the numerous fine needles on the needle plate quickly penetrate the material to form a continuous pore structure.

[0211] Example 5

[0212] (1) Blending modification of resin: 80 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 10 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 10 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 1.25%, a tensile strength of 16.7MPa, an elongation of 580%, and a softening temperature of 95.7℃.

[0213] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 15.6 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.8 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 0.8 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0214] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 20.3 Mrad to crosslink the resin sheet;

[0215] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0216] (5) Abrasion of foamed sheet: The foamed material comes into contact with a surface sanding roller with a mesh size of 80 through a linear speed of 40m / min. The speed of the sanding roller is 3m / min. The pressure between the foamed material and the sanding roller is 0.2MPa. The surface sanding roller and the foamed sheet have relative displacement, which destroys the cross-linked resin layer of the foamed material to form an open-cell structure.

[0217] Example 6

[0218] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 40 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0219] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 10.5 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 0.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 0.5 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0220] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 17.3 Mrad to crosslink the resin sheet;

[0221] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming. The surfaces of the two foamed sheets are pressed together by a hot air composite machine while they are molten to form a foamed sheet with a five-layer structure of cross-linked resin layer / independent pore layer / cross-linked resin layer / independent pore layer / cross-linked resin layer.

[0222] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet A is obtained by cutting 0.5mm off the upper surface of the foam sheet. The other surface of the foam sheet A is obtained by cutting 0.5mm off the upper surface of the foam sheet in the same way.

[0223] Comparative Example 1

[0224] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 40 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together.™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0225] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) and 10.5 parts by weight of the foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%) are mixed evenly and then extruded into sheets by a twin-screw extruder.

[0226] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 17.3 Mrad to crosslink the resin sheet;

[0227] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0228] (5) Needle punching of foamed sheet: The foamed sheet is fed into the needle punching machine. The gap of the needle punching roller is adjusted so that the puncture depth is 80μm, the diameter of the needle is 0.1mm, and the center distance between the needles is 0.5mm. The foamed material passes through the needle punching machine, and the numerous fine needles on the needle plate quickly penetrate the material to form a continuous pore structure.

[0229] Comparative Example 2

[0230] (1) Blending modification of resin: 40 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 40 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 20 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 3.52%, a tensile strength of 25.7MPa, an elongation of 650%, and a softening temperature of 93.5℃.

[0231] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) and 10.5 parts by weight of the foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%) are mixed evenly and then extruded into sheets by a twin-screw extruder.

[0232] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 10.3 Mrad to crosslink the resin sheet;

[0233] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0234] (5) Abrasion opening of foamed sheet: The foamed material comes into contact with a surface sanding roller with a mesh size of 80 through a linear speed of 40m / min. The speed of the sanding roller is 3m / min. The pressure between the foamed material and the sanding roller is 0.2MPa. The surface sanding roller and the foamed sheet have relative displacement, which destroys the cross-linked resin layer of the foamed material to form an open structure.

[0235] Comparative Example 3

[0236] (1) Blending modification of resin: 10 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 10 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 80 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 10.05%, a tensile strength of 13.7MPa, an elongation of 1000%, and a softening temperature of 63℃.

[0237] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) and 15.6 parts by weight of the foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%) are mixed evenly and then extruded into sheets by a twin-screw extruder.

[0238] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 15.6 Mrad to crosslink the resin sheet;

[0239] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 265°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0240] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0241] Comparative Example 4

[0242] (1) Blending modification of resin: 90 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 10 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 0.95%, a tensile strength of 16.5 MPa, an elongation of 550%, and a softening temperature of 95.5 °C.

[0243] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 18.7 parts by weight of foaming agent sodium bicarbonate (gas generation of 115 ml / g and ash content of 4.3%), 1.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 1.5 parts by weight of antioxidant 4,4'-dioctyl diphenylamine and then extruded into sheets by twin-screw extruder.

[0244] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 23.7 Mrad to crosslink the resin sheet;

[0245] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 290°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0246] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0247] Comparative Example 5

[0248] (1) Blending modification of resin: 90 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 10 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™PF 1140G) was fed into a twin-screw extruder to obtain a mixed resin; the mass fraction of the n-hexane extract of the mixed resin was 0.95%, the tensile strength was 16.5 MPa, the elongation was 550%, and the softening temperature was 95.5℃; (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) was mixed with 8.5 parts by weight of the foaming agent azodicarbonamide (gas generation was 216 ml / g, ash content was 0.5%) and then extruded into a sheet by a twin-screw extruder;

[0249] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 23.7 Mrad to crosslink the resin sheet;

[0250] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 290°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0251] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0252] Comparative Example 6

[0253] (1) Blending modification of resin: 10 parts by weight of low-density polyethylene (Sinopec LD100-AC) and 10 parts by weight of polyolefin elastomer A (DOW AFFINITY) were blended together. ™ PF 1140G) and 80 parts by weight of polyolefin elastomer B (SK Solumer) ™ The mixture (875L) was fed into a twin-screw extruder to obtain a mixed resin; the mixed resin had a hexane extract mass fraction of 10.05%, a tensile strength of 13.7MPa, an elongation of 1000%, and a softening temperature of 63℃.

[0254] (2) Sheet forming: 100 parts by weight of the mixed resin obtained in step (1) are mixed with 15.6 parts by weight of foaming agent azodicarbonamide (gas generation of 216 ml / g and ash content of 0.5%), 1.5 parts by weight of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and 1.5 parts by weight of antioxidant 4,4'-dioctyldiphenylamine and then extruded into sheets by twin-screw extruder.

[0255] (3) Crosslinking modification: The sheet obtained in step (2) is subjected to irradiation crosslinking with an irradiation dose of 16.1 Mrad to crosslink the resin sheet;

[0256] (4) Foaming: The cross-linked modified sheet obtained in step (3) is heated to decompose and foam the foaming agent. The heating temperature is 205°C to obtain a foamed sheet. The two sides of the foamed sheet are unfoamed cross-linked resin layers, and the middle is an independent pore layer with pores formed by foaming.

[0257] (5) Foam sheet cutting: The foam sheet is fed into the pressure roller, and the roller pressure is adjusted to 0.6MPa to keep the sheet flat before cutting. The cutting machine is set to a wire cutting speed of 500 mm / s, a cooling water flow rate of 5L / min and a temperature of 20℃, a traction force of 40N and a traction speed of 3m / min. The foam sheet is obtained by cutting 0.2mm off the upper surface of the foam sheet.

[0258] The performance of the foamed sheets prepared in the above embodiments and comparative examples was tested according to the following methods.

[0259] 1. Thickness and thickness range

[0260] The thickness of the foamed sheet was tested according to the Chinese national standard GB / T 40872-2021. Simultaneously, the thickness was measured at 50 arbitrary points, and the difference between the maximum and minimum values ​​was taken as the thickness range. Only the central area of ​​the sample (≥5mm from the edge) was measured during the test. The sample needed to be conditioned for at least 24 hours at a temperature of (23±2)℃ and a relative humidity of (50±10)%.

[0261] 2. Density

[0262] In accordance with the provisions of Chinese National Standard GB / T 40872-2021.

[0263] 3. Average pore diameter and pore diameter range in the ZD direction

[0264] The interface pores of the foamed material after liquid nitrogen brittle fracture treatment were observed using a scanning electron microscope. At least 5 observation areas were randomly selected, and the diameters of all intact pores in the area parallel to the thickness direction (i.e., the ZD direction) were counted. The average pore diameter in the ZD direction was calculated. The number of intact pores in the selected observation area was between 20 and 100.

[0265] Stomatal diameter range is the average of the difference between the maximum and minimum stomatal diameters in the five observation areas.

[0266] 4. Degree of crosslinking

[0267] a. Take a 100mg sample from the foam sheet and accurately weigh the sample A (mg).

[0268] b. Wrap the sample in a 200-mesh metal mesh, then immerse the mesh-wrapped sample in xylene at 120°C and let it stand for 24 hours. The insoluble matter can be collected within the metal mesh through filtration; after vacuum drying, accurately weigh the insoluble matter B (mg).

[0269] c. Calculate the degree of crosslinking (mass%):

[0270] Degree of crosslinking (mass%) = 100% × (B / A).

[0271] 5. Porosity

[0272] The surface of the open layer of the foam sheet was observed using a scanning electron microscope. At least 5 observation areas were randomly selected, and the total number of pores and through holes in all areas were counted to calculate the porosity. The number of pores in the selected observation areas ranged from 20 to 100.

[0273] For needle-punched samples, since the resin cross-linking layer is relatively intact, it is impossible to observe the independent pore layer connected to the open pore layer. It is necessary to cut off the resin cross-linking layer before observing the through pores.

[0274] 6. The starting temperature of the first weight loss stage in thermogravimetric (TG) analysis

[0275] (1) Prepare the sample to be tested. Place the sample in an oven at 105°C and keep it for 30 minutes to remove moisture or other volatile components from the sample. Transfer it to a desiccator and cool it to room temperature.

[0276] (2) The sample mass is 5 ± 0.5 mg and it is evenly distributed at the bottom of the crucible; place the sample crucible in the sample chamber of the TG instrument.

[0277] (3) During the test, air is introduced at a rate of 150 ml / min to ensure that the sample is tested in a controlled atmosphere; the temperature is controlled by program and heated from 30°C to 800°C at a rate of 10 K / min.

[0278] (4) During the entire heating process, the instrument continuously records the mass change of the sample and generates a mass-temperature curve (TG curve); the curve shows the mass change of the sample at different temperatures, reflecting the thermal stability, decomposition behavior and composition of the material;

[0279] (5) On the TG curve, the temperature at which the curve begins to deviate from the baseline is the starting temperature of the first weightlessness stage.

[0280] 7. Opening ratio

[0281] The surface of the open layer of the foam sheet was observed using a scanning electron microscope. At least 5 observation areas were randomly selected, and the number of intact pores and the number of damaged pores in all areas were counted. The open pore ratio was calculated as: number of damaged pores / (number of intact pores + number of damaged pores) * 100%. The number of pores in the selected observation area was between 20 and 100.

[0282] 8. Compressive stress at 15% and 75% compression deformation

[0283] The test shall be conducted in accordance with the Chinese National Standard GB / T 18942.1. The specimen thickness shall be at least 10 mm; for thinner materials, the specimens shall be stacked at least to a thickness of 10 mm. Before the test begins, a prestress of (100±10) Pa shall be applied to the specimen. After the preload is completed, the compression measurement system shall be zeroed. The test shall be performed by compressing the specimen at a rate of (50±10)% of its initial thickness per minute. The compressive stress at the first compression of 15% and 75% deformation shall be measured. The maximum increment of compressive stress by 1% increase in compression ratio shall be read from the compressive stress curve.

[0284] 9. Vibration chip shedding quantity test

[0285] If the pore structure is damaged during the opening process, the debris in the pores may fall off during use and affect the normal function of electronic products. The test counts the number of debris that falls off the pores by means of vibration.

[0286] The testing procedure involves placing a 50cm x 50cm sample on a vibration platform, setting the vibration frequency to 2000Hz, and vibrating for 30 minutes. After the test, the sample is flipped over and vibrated for another 30 minutes. The number of debris larger than 10μm that falls off the sample after vibration is observed and counted using an electron magnifying glass. A score of ≤10 debris is rated as excellent, 10 < debris < 30 debris is rated as good, and >30 debris is rated as poor.

[0287] 10. Vibration damping performance

[0288] The damping performance of a material is evaluated using the minimum damping coefficient over a temperature range of 0℃ to 35℃. When the damping coefficient is >0.5, the damping effect is rated as excellent; when 0.08 < damping coefficient ≤0.5, the damping effect is rated as good; and when the damping coefficient ≤0.08, the damping effect is rated as poor.

[0289] Test method for minimum damping coefficient from 0℃ to 35℃:

[0290] The damping coefficient of the foamed material was tested using Dynamic Mechanical Analysis (DMA) under the following conditions: temperature range: -10℃ to 50℃; heating rate: 5℃ / min; frequency: 1 Hz; amplitude: 0.1 mm; DMA temperature scan mode was selected, and a compression fixture was used. The foamed material was cut to a size and shape suitable for the fixture test and fixed in the DMA equipment fixture. The parameters of the DMA equipment were set according to the test conditions. The temperature scan test was started according to the predetermined temperature range and heating rate. During the test, data on storage modulus, loss modulus, and damping coefficient were collected. The damping coefficient as a function of temperature obtained from the test was smoothed using Savitzky-Golay filtering, and the mean of three consecutive data points was taken as the effective value to find the minimum value of the damping coefficient in the range of 0℃ to 35℃.

[0291] 11. Compression permanent deformation rate

[0292] The compression set of the sample was tested according to the method specified in Chinese National Standard GB / T 6669-2008, at a temperature of (25±2)℃, compressing 50%±4% of the sample thickness, and for a compression time of (22±0.2)h.

[0293] A measured compressive permanent deformation of less than 30% is considered excellent, greater than or equal to 30% and less than 40% is considered good, and greater than 40% is considered poor.

[0294] Table 1 Performance of foamed sheets

[0295]

[0296] As can be seen, the foam sheet of this application embodiment has good cushioning and shock absorption performance. When compressed, it can undergo adaptive deformation without excessive deformation, which would lead to a decrease in shock absorption performance. Moreover, the permanent deformation after compression is appropriate, which can maintain long-term effective cushioning and shock absorption performance.

[0297] In this embodiment, the starting temperature of the first weight loss stage of the thermal weight loss analysis of the foam sheet is between 150°C and 400°C. This temperature can make the pores uniform and have high structural strength, giving the foam sheet a certain degree of softness and improving the cushioning and shock absorption performance of the foam sheet. It can also ensure the performance stability of the foam sheet, maintain the permanent compression deformation performance, and thus maintain long-term effective cushioning and shock absorption performance.

[0298] The average number of pores in the ZD direction of the foam sheet in this application embodiment satisfies the following T / R: 1.5≤T / R≤10; a relatively gentle compression curve can be obtained, thereby providing excellent cushioning and shock absorption performance, and the permanent deformation after compression will not be too large, so as to maintain long-term effective cushioning and shock absorption performance.

[0299] In addition, the average density of the foam sheet is 0.025 g / cm³. 3 Up to 0.1 g / cm 3 The independent pore layer has a pore diameter of 100μm to 500μm in the ZD direction, the open pore ratio on the surface of the open pore layer is ≥90%, the porosity between the independent pore layer and the open pore layer is ≤20%, the compressive stress under 15% compression deformation is 1Kpa to 50Kpa, the compressive stress under 70% compression deformation is 25Kpa to 700Kpa, and when the compression deformation varies from 15% to 75%, the maximum increment of compressive stress for every 1% increase in compression deformation is 10KPa to 60KPa. All of these are beneficial to improving the cushioning, shock absorption performance and permanent deformation after compression of the foam sheet.

[0300] When the compression deformation of the foam sheet in this embodiment varies from 15% to 75%, for every 1% increase in compression deformation, the maximum increase in compressive stress is 10 kPa to 60 kPa, which is beneficial for the foam sheet to maintain good cushioning performance in the event of vibration.

[0301] The comparative foam sheet exhibits poor cushioning performance, shock absorption performance, or permanent deformation after compression due to inappropriate parameters in the thermogravimetric analysis, including the starting temperature of the first weight loss stage, the average number of pores (T / R) in the ZD direction, the average density, the average pore diameter in the ZD direction, the degree of crosslinking, the proportion of open pores on the surface of the open layer, the porosity, the compressive stress at 15% or 75% compression deformation, or the maximum increment of compressive stress when the compression deformation varies from 15% to 75%.

[0302] While the embodiments disclosed in this application are as described above, the content is merely for the purpose of facilitating understanding of this application and is not intended to limit this application. Any person skilled in the art to which this application pertains may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in this application; however, the scope of protection of this application shall still be determined by the scope defined in the appended claims.

Claims

1. A foam sheet, characterized in that, include: Cross-linked resin layer, independent pore layer and open-cell layer; The independent pore layer has closed and non-interconnected pores; The perforated layer has a cavity that communicates with the outside of the foam sheet; The perforated layer is located on at least one of the upper and lower surfaces of the foam sheet, which are distributed along the thickness direction; The average number of pores in the foam sheet parallel to the thickness direction is T / R, and T / R satisfies: 1.5≤T / R≤10; Where T is the thickness of the foam sheet, and R is the average pore diameter of the foam sheet in the direction parallel to the thickness. The units of T and R are the same. The average pore diameter of the independent pore layer is between 100 μm and 500 μm in the direction parallel to the thickness.

2. The foam sheet according to claim 1, characterized in that, The pore size difference of the independent pore layer parallel to the thickness direction is ≤650μm; The thickness of the foam sheet is from 0.15 mm to 4.5 mm, and the thickness range of the foam sheet is ≤0.1 mm.

3. The foam sheet according to claim 2, characterized in that, The thickness of the foam sheet is 0.15 mm to 3 mm.

4. The foam sheet according to claim 3, characterized in that, The thickness of the foam sheet is 0.15 mm to 1.2 mm.

5. The foam sheet according to claim 1, characterized in that, The perforation ratio on the surface of the perforated layer is ≥90%.

6. The foam sheet according to claim 5, characterized in that, The perforation ratio on the surface of the perforated layer is ≥95%.

7. The foam sheet according to claim 1, characterized in that, The porosity between the independent pore layer and the open pore layer is ≤20%.

8. The foam sheet according to any one of claims 1 to 7, characterized in that, The cross-linked resin layer is in contact with the independent pore layer, and the open-pore layer is in contact with the independent pore layer.

9. The foam sheet according to claim 8, characterized in that, The foam sheet includes: A cross-linked resin layer, a layer with independent pores, and a layer with open pores are arranged in the following order: cross-linked resin layer, layer with independent pores, and layer with open pores; or... Two cross-linked resin layers, two independent pore layers, and one open-cell layer are arranged in the following order: cross-linked resin layer, independent pore layer, cross-linked resin layer, independent pore layer, and open-cell layer; or One cross-linked resin layer, two independent pore layers, and two open-pore layers are arranged in the following order: open-pore layer, independent pore layer, cross-linked resin layer, independent pore layer, and open-pore layer.

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