Solvent-free flexible paper, preparation method, regenerated flexible paper and application

Abstract

The invention discloses solvent-free flexible paper, a preparation method of the solvent-free flexible paper, regenerated flexible paper and application of the regenerated flexible paper. The solvent-free flexible paper comprises powder base materials and a binding agent with a multi-stage network structure, wherein the binding agent comprises a first-stage network structure wrapping the surfaces of the powder base materials and a second-stage network structure connected between the powder base materials. According to the embodiment of the invention, the solvent-free flexible paper does not need to consume water resources and solvents.

Description

Solvent-free flexible paper and its preparation method, recycled flexible paper and its applications Technical Field

[0001] This application relates to a solvent-free flexible paper and its preparation method, as well as recycled flexible paper and its applications. Background Technology

[0002] Dry papermaking, a related technology, refers to a papermaking method that uses air as a carrier for pulp fibers, deposits a thin layer of fibers on a forming wire, and then uses an adhesive to bond and form paper. Compared with wet papermaking, it has the advantages of saving water resources and reducing air pollution.

[0003] However, dry papermaking in related technologies still uses pulp as raw material, which consumes a large amount of water resources and generates a large amount of wastewater. Summary of the Invention

[0004] This application provides a solvent-free flexible paper and its preparation method, as well as recycled flexible paper and its application, which can avoid consuming water resources and solvents.

[0005] In a first aspect, embodiments of this application provide a solvent-free flexible paper, which includes a powder substrate and an adhesive having a multi-level network structure. The adhesive includes a primary network structure coated on the surface of the powder substrate and a secondary network structure connected between the powder substrates.

[0006] The solvent-free flexible paper of this application has good mechanical properties, and the preparation process does not require water and / or non-aqueous solvents, which can reduce environmental pollution.

[0007] In some embodiments, the primary network structure and the secondary network structure independently include interlocking adhesive fibers.

[0008] In some embodiments, based on solvent-free flexible paper, the powder substrate accounts for 75% to 99% by mass, and the binder accounts for 1% to 25% by mass.

[0009] In some embodiments, based on solvent-free flexible paper, the powder substrate accounts for 85% to 97% by mass, and the binder accounts for 3% to 15% by mass.

[0010] In some embodiments, the mass ratio of powder substrate to binder is 99:1 to 75:25.

[0011] In some embodiments, the mass ratio of powder substrate to binder is 97:3 to 85:15.

[0012] In some embodiments, the Dv50 of the powder substrate is 200 mesh to 10000 mesh.

[0013] In some embodiments, the Dv50 of the powder substrate is 500 mesh to 3000 mesh.

[0014] In some embodiments, the Dv10 of the powder substrate is 10000~20000 mesh.

[0015] In some embodiments, the Dv90 of the powder substrate is 150-200 mesh.

[0016] In some embodiments, when the elastic modulus of the powder substrate is 0.1 to 8 GPa, the mass ratio of the powder substrate to the binder is 97:3 to 70:25.

[0017] In some embodiments, when the elastic modulus of the powder substrate is 10~30 GPa, the mass ratio of the powder substrate to the binder is 99:1~85:15.

[0018] In some embodiments, when the Dv50 of the powder substrate is 5000~10000 mesh, the mass ratio of the powder substrate to the binder is 95:5~75:25.

[0019] In some embodiments, when the Dv50 of the powder substrate is 200 to 5000, the mass ratio of the powder substrate to the binder is 98:2 to 80:20.

[0020] In some embodiments, the powder substrate comprises natural organic powder particles and / or natural inorganic powder particles.

[0021] In some embodiments, natural organic powder particles include one or more of natural wood powder particles, straw powder particles, agricultural processing by-product powder particles, fruit and nut shell powder particles, and animal shell powder particles.

[0022] In some embodiments, natural inorganic powder particles include mineral powder particles.

[0023] In some embodiments, the mineral powder particles include one or more of silicates, carbonates, oxides, sulfides, and phosphates.

[0024] In some embodiments, the natural wood powder particles include one or more of the following: pine powder, cypress powder, fir powder, poplar powder, nanmu powder, elm powder, oak powder, oak powder, walnut powder, cherry powder, mahogany powder, teak powder, reed powder, spotted bamboo powder, weeping bamboo powder, money bamboo powder, green bamboo powder, rattan bamboo powder, purple bamboo powder, stone bamboo powder, dragon pearl bamboo powder, and bean bamboo powder.

[0025] In some embodiments, the straw powder particles include one or more of rice straw powder, corn straw powder, wheat straw powder, rapeseed straw powder, barley straw powder, oat straw powder, soybean straw powder, broad bean straw powder, and pea straw powder.

[0026] In some embodiments, the agricultural processing by-product powder particles include one or more of the following: rice husk powder, corn cob powder, sweet potato vine powder, peanut vine / shell powder, potato vine powder, pumpkin vine powder, loofah vine powder, sugarcane bagasse powder, and cassava bagasse powder.

[0027] In some embodiments, the fruit and nut shell powder particles include one or more of pistachio shell powder, macadamia nut shell powder, hazelnut shell powder, chestnut shell powder, acorn shell powder, pine nut shell powder, and walnut shell powder.

[0028] In some embodiments, the animal shell powder particles include one or more of shrimp shell powder, eggshell, crab shell powder, and seashell powder.

[0029] In some embodiments, the adhesive includes one or more of polytetrafluoroethylene, polyethylene, polypropylene, polylactic acid, thermoplastic polyurethane, copolymers of ethylene and tetrafluoroethylene, and copolymers of hexafluoropropylene and tetrafluoroethylene.

[0030] In some embodiments, the solvent-free flexible paper also includes additives, including one or more of reinforcing agents, flame retardants, and fillers.

[0031] In some embodiments, the reinforcing agent includes one or more of starch, modified starch, carboxymethyl cellulose, chitosan, and chopped fibers.

[0032] In some embodiments, the flame retardant includes aluminum hydroxide.

[0033] In some embodiments, the filler includes one or more of talc, calcium carbonate, titanium dioxide, kaolin, amorphous silica, silicate, aluminum trihydroxy, barium sulfate, and calcium sulfate.

[0034] In some embodiments, the thickness of the solvent-free flexible paper is 30~5000μm.

[0035] In some embodiments, the basis weight of solvent-free flexible paper is 35~300 g / mm². 2 .

[0036] In some embodiments, the density of solvent-free flexible paper is 0.700~1.200 g / cm³. 3 .

[0037] In some embodiments, the surface roughness of the solvent-free flexible paper is 120~300 nm.

[0038] In some embodiments, the contact angle of the solvent-free flexible paper surface is 70° to 100°.

[0039] In some embodiments, the wet tensile strength of solvent-free flexible paper is 0.4~1.0 N / mm. 2 .

[0040] In some embodiments, the elastic modulus of solvent-free flexible paper is 30~80 GPa.

[0041] In some embodiments, the tensile strength of the solvent-free flexible paper is 1~12 MPa.

[0042] In some embodiments, the tensile toughness of solvent-free flexible paper is 1800~30000 J. m -2 .

[0043] In some embodiments, the porosity of the solvent-free flexible paper is 20% to 50%.

[0044] In some embodiments, the average pore size of the solvent-free flexible paper is 120~170 nm.

[0045] In some embodiments, solvent-free flexible paper is obtained by mixing and rolling a powder substrate and a binder.

[0046] Secondly, embodiments of this application provide a recycled flexible paper made from solvent-free flexible paper according to the first aspect. The recycled flexible paper includes a paper powder substrate and an adhesive having a multi-level network structure. The adhesive includes a primary network structure coated on the surface of the paper powder substrate and a secondary network structure disposed between the paper powder substrates.

[0047] Thirdly, embodiments of this application provide a method for preparing solvent-free flexible paper according to the first aspect. The preparation method includes: providing a powder substrate, the powder substrate comprising natural organic powder particles and / or natural inorganic powder particles; mixing the powder substrate and a binder according to a predetermined ratio to obtain a mixture, the mixing speed being 300~20000 rpm, the time being 3~25 min, and the temperature being 20~80℃; and rolling the mixture to obtain solvent-free flexible paper.

[0048] In some embodiments, the mixing process includes ball milling and / or kneading.

[0049] In some embodiments, the ball milling speed is 300~1000 rpm and the processing time is 10~15 min.

[0050] In some embodiments, the mixing speed is 3000~20000 rpm, the temperature is 20~80℃, and the processing time is 3~10 min.

[0051] In some embodiments, the mixing process includes ball milling and intensive mixing. The intensive mixing process has a rotation speed of 3000~10000 rpm, a temperature of 50~80℃, and a processing time of 5~10 min. The ball milling process has a rotation speed of 300~500 rpm and a processing time of 10~13 min.

[0052] In some embodiments, the rolling process further includes extruding the mixture and then folding the extruded mixture in half; the extrusion and folding processes are performed alternately multiple times.

[0053] In some embodiments, when the elastic modulus of the powder substrate is 0.1~8 GPa, the number of folding treatments is 20~50.

[0054] In some embodiments, when the elastic modulus of the powder substrate is 10~30 GPa, the number of folding treatments is 10~30.

[0055] In some embodiments, the method for preparing the powder substrate includes: pulverizing the raw material containing the powder substrate to obtain the powder substrate.

[0056] Fourthly, embodiments of this application provide the application of a solvent-free flexible paper of the first aspect and / or a recycled flexible paper of the second aspect as thermally conductive paper, flame-retardant paper, waterproof paper, electromagnetic shielding paper, insulating paper, conductive paper, or microwave absorbing paper. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 shows a scanning electron microscope image of solvent-free flexible paper provided in Embodiment 1 of this application, where the scale bar is 10 μm.

[0059] Figure 2 shows a scanning electron microscope image of solvent-free flexible paper provided in Embodiment 1 of this application, where the scale bar is 2 μm.

[0060] Figure 3 shows a comparison of the tensile strength of the solvent-free flexible paper provided in Embodiment 1 of this application in a wet state and an initial state.

[0061] Figure 4 shows a scanning electron microscope (SEM) image of the solvent-free flexible paper provided in Embodiment 1 of this application, where A and B are SEM images at different positions.

[0062] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0063] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0064] Many specific details are set forth in the following description in order to provide a full understanding of this application, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0065] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the solvent-free flexible paper, its preparation method, recycled flexible paper, and its applications. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of providing a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0066] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0068] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0069] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0070] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0071] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0072] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0073] Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C.

[0074] In related technologies, dry papermaking still uses fiber as the main component, and fiber extraction involves cooking, washing, and pulping processes. These processes consume a lot of water and generate a large amount of wastewater.

[0075] In view of this, this application provides a solvent-free flexible paper and its preparation method, as well as recycled flexible paper and its application, which can avoid consuming water resources and solvents.

[0076] This application provides a solvent-free flexible paper. Solvent-free means that no water and / or other solvents are consumed during the preparation of the flexible paper, and no solvent remains in the flexible paper.

[0077] The solvent-free flexible paper provided in this application includes a powder substrate and an adhesive having a multi-level network structure. The adhesive includes a primary network structure coated on the surface of the powder substrate and a secondary network structure connecting the powder substrates.

[0078] The solvent-free flexible paper of this application embodiment includes a powder substrate and a binder. The powder substrate constitutes the skeleton of the solvent-free flexible paper, and the binder can fix and connect different powder substrate skeletons. Compared with related dry-process and / or wet-process paper, the use of water resources and / or solvents can be avoided. On the one hand, it can reduce the possibility of paper aging caused by solvent evaporation, thereby improving the durability of solvent-free flexible paper; on the other hand, it can also save water resources and reduce the impact of solvent evaporation on the environment and human health. Compared with the fibers formed from pulp in related technologies, the powder substrate has the characteristics of wide availability and simple acquisition, especially the ability to directly crush and recycle agricultural waste; at the same time, the powder substrate has better mechanical properties than fibers.

[0079] Binders with multi-level network structures include primary and secondary network structures. As shown in Figure 4, both the primary and secondary network structures are formed by interwoven binder fibers, and the secondary network structure can also serve as a component unit of the primary network structure; that is, the secondary network structure can constitute the binder fibers of the primary network structure. Specifically, the primary network structure coats the surface of the powder substrate, encapsulating multiple powder substrates to form a composite structure where the primary network structure acts as a net, covering multiple powder substrates. The secondary network structure connects the powder substrates, linking adjacent powder substrates to form a planar adhesive network with the powder substrate as its core. This reduces the possibility of slippage of the powder substrate in various directions, improving the mechanical properties of solvent-free flexible paper.

[0080] In some embodiments, the primary network structure and the secondary network structure independently include interlocking adhesive fibers.

[0081] The primary network structure includes overlapping first adhesive fibers, which may include interwoven longitudinal and transverse lines to form a net structure, thereby partially or fully covering one or more powder substrates; the secondary network structure includes overlapping second adhesive fibers, which may include longitudinal and transverse lines to form a planar adhesive network, thereby bonding adjacent powder substrates.

[0082] In some embodiments, based on solvent-free flexible paper, the powder substrate accounts for 75% to 99% by mass, and the binder accounts for 1% to 25% by mass.

[0083] Based on solvent-free flexible paper, the mass percentage of powder substrate is independently selected from any value or a range between any two of 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 98%.

[0084] Based on solvent-free flexible paper, the mass percentage of the adhesive is independently selected from any value or a range between any two of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0085] Adhesive fibers can coat the surface of powder substrates, encapsulating multiple powder substrates to form a composite structure in which a primary network structure acts as a fishing net, encapsulating multiple powder substrates. Adhesive fibers can also connect powder substrates to each other, linking adjacent powder substrates to form a planar adhesive network with the powder substrate as the core.

[0086] Powder substrates and binders with appropriate mass ratios can better form primary and secondary network structures, thereby improving mechanical properties while reducing costs.

[0087] The mass percentage of the binder can be obtained by acquiring the TG thermogravimetric curve.

[0088] Optionally, based on solvent-free flexible paper, the powder substrate accounts for 85% to 97% by mass, and the binder accounts for 3% to 15% by mass.

[0089] In some embodiments, the mass ratio of powder substrate to binder is 99:1 to 75:25. For example, it can be 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, 89:11, 88:12, 87:13, 86:14, 85:15, 84:16, 83:17, 82:18, 81:19, 80:20, 79:21, 78:22, 77:23, 76:24, 75:25, or any range of the above values.

[0090] Powder substrates and binders with appropriate mass ratios can better form primary and secondary network structures, thereby improving mechanical properties while reducing costs.

[0091] Optionally, the mass ratio of powder substrate to binder is 97:3 to 85:15.

[0092] In some embodiments, the Dv50 of the powder substrate is 200 mesh to 10000 mesh. For example, it can be 200 mesh, 300 mesh, 400 mesh, 500 mesh, 600 mesh, 700 mesh, 800 mesh, 900 mesh, 1000 mesh, 1100 mesh, 1200 mesh, 1300 mesh, 1400 mesh, 1500 mesh, 1600 mesh, 1700 mesh, 1800 mesh, 1900 mesh, 2000 mesh, 2100 mesh, 2200 mesh, 2300 mesh, 2400 mesh, 2500 mesh, 2600 mesh, 2700 mesh. Mesh, 2800 mesh, 2900 mesh, 3000 mesh, 3100 mesh, 3200 mesh, 3300 mesh, 3400 mesh, 3500 mesh, 3600 mesh, 3700 mesh, 3800 mesh, 3900 mesh, 4 000 mesh, 4100 mesh, 4200 mesh, 4300 mesh, 4400 mesh, 4500 mesh, 4600 mesh, 4700 mesh, 4800 mesh, 4900 mesh, 5000 mesh, 5100 mesh, 5200 mesh , 5300 mesh, 5400 mesh, 5500 mesh, 5600 mesh, 5700 mesh, 5800 mesh, 5900 mesh, 6000 mesh, 6100 mesh, 6200 mesh, 6300 mesh, 6400 mesh, 65 00 mesh, 6600 mesh, 6700 mesh, 6800 mesh, 6900 mesh, 7000 mesh, 7100 mesh, 7200 mesh, 7300 mesh, 7400 mesh, 7500 mesh, 7600 mesh, 7700 mesh, 7800 mesh, 7900 mesh, 8000 mesh, 8100 mesh, 8200 mesh, 8300 mesh, 8400 mesh, 8500 mesh, 8600 mesh, 8700 mesh, 8800 mesh, 8900 mesh, 9000 mesh mesh, 9100 mesh, 9200 mesh, 9300 mesh, 9400 mesh, 9500 mesh, 9600 mesh, 9700 mesh, 9800 mesh, 9900 mesh, 10000 mesh, or a range consisting of any of the above values.

[0093] The powder substrate with a suitable Dv50 in the embodiments of this application can reduce defects in solvent-free flexible paper, thereby improving the mechanical properties of solvent-free flexible paper.

[0094] Optionally, the Dv50 of the powder substrate is 500 mesh to 3000 mesh.

[0095] In some embodiments, the Dv10 of the powder substrate is 10,000 to 20,000 mesh, and the Dv90 of the powder substrate is 150 to 200 mesh.

[0096] The Dv10 of the powder substrate can be 10,000 mesh, 11,000 mesh, 12,000 mesh, 13,000 mesh, 14,000 mesh, 15,000 mesh, 16,000 mesh, 17,000 mesh, 18,000 mesh, 19,000 mesh, 20,000 mesh, or any range of the above values.

[0097] The Dv90 of the powder substrate can be 150 mesh, 160 mesh, 170 mesh, 180 mesh, 190 mesh, 200 mesh, or any combination of the above values.

[0098] Powder substrates with appropriate particle size distribution can allow small-diameter powder substrates to fill the gaps between large-diameter powder substrates, thereby improving the mechanical properties of flexible paper.

[0099] Dv10, Dv50, and Dv90 represent the particle size corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively. Measurements can be performed using conventional methods. A cross-section of flexible paper can be prepared using a cross-section polisher (such as the JEOL IB-09010CP argon ion cross-section polisher), and the microstructure of the cross-section can be mapped using a scanning electron microscope (e.g., ZEISS Sigma 300) to obtain a SEM image. Based on the obtained SEM image, multiple (e.g., more than 5) test areas are selected and statistically analyzed using Nano Measurer particle size distribution software. At least 50 powder substrate particles can be observed in each test area to determine the particle size distribution.

[0100] Different particle sizes of powder substrates require different levels of cohesion and adhesion, thus necessitating the use of appropriate amounts of binder. In some embodiments, when the Dv50 of the powder substrate is 5000~10000 mesh, the mass ratio of powder substrate to binder is 95:5~75:25.

[0101] In other embodiments, when the Dv50 of the powder substrate is 200 to 5000, the mass ratio of the powder substrate to the binder is 98:2 to 80:20.

[0102] In some embodiments, when the elastic modulus of the powder substrate is 0.1 to 8 GPa, the mass ratio of the powder substrate to the binder is 97:3 to 70:25.

[0103] Elastic modulus, usually referring to Young's modulus, is a key mechanical parameter characterizing a powder substrate's resistance to elastic deformation. Different types of powder substrates have different elastic moduli, and in order to better form a multi-level network structure, powder substrates with different elastic moduli require binders with different mass ratios.

[0104] In other embodiments, when the elastic modulus of the powder substrate is 10~30 GPa, the mass ratio of the powder substrate to the binder is 99:1~85:15.

[0105] In some embodiments, the powder substrate includes natural organic powder particles and natural inorganic powder particles.

[0106] Natural organic powder particles include forestry "three residues", such as sugarcane bagasse from the sugar industry, agricultural straw, wetland reeds, and recycled waste paper. Among them, agricultural straw refers to the stems and leaves remaining after crops such as rice, wheat, and corn have matured and been threshed.

[0107] The powder substrates used in this application are widely available, which can reduce costs and improve the recycling rate of waste.

[0108] In some embodiments, natural organic powder particles include one or more of natural wood powder particles, straw powder particles, agricultural processing by-product powder particles, fruit and nut shell powder particles, and animal shell powder particles.

[0109] Optionally, the natural wood powder particles include one or more of the following: pine powder, cypress powder, fir powder, poplar powder, nanmu powder, elm powder, oak powder, oak wood powder, walnut powder, cherry powder, mahogany powder, teak powder, reed powder, spotted bamboo powder, weeping bamboo powder, golden bamboo powder, green bamboo powder, rattan bamboo powder, purple bamboo powder, carnation powder, dragon pearl bamboo powder, and bean bamboo powder; the straw powder particles include one or more of the following: rice straw powder, corn straw powder, wheat straw powder, rapeseed straw powder, barley straw powder, oat straw powder, soybean straw powder, broad bean straw powder, and pea straw powder. The range includes various agricultural crop processing by-product powder particles, such as rice husk powder, corn cob powder, sweet potato vine powder, peanut vine / shell powder, potato vine powder, pumpkin vine powder, loofah vine powder, sugarcane bagasse powder, and cassava bagasse powder; fruit and nut shell powder particles, such as pistachio shell powder, macadamia nut shell powder, hazelnut shell powder, chestnut shell powder, acorn shell powder, pine nut shell powder, and walnut shell powder; animal shell powder particles, such as shrimp shell powder, eggshell powder, crab shell powder, and seashell powder; and in some embodiments, natural inorganic powder particles include mineral powder particles.

[0110] Optionally, the mineral powder particles include one or more of silicates, carbonates, oxides, sulfides, and phosphates.

[0111] In some embodiments, the adhesive includes one or more of polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polylactic acid (PLA), thermoplastic polyurethane (TPU), copolymers of ethylene and tetrafluoroethylene, and copolymers of hexafluoropropylene and tetrafluoroethylene.

[0112] The adhesive used in this application is a fiberizable adhesive that forms a three-dimensional network fiber structure under mechanical force (such as shearing or stretching). Different powder substrates can be fixedly connected through the formed adhesive fibers, thereby enabling the formation of solvent-free flexible paper. For example, when the adhesive is polytetrafluoroethylene (PTFE), PTFE can undergo crystal slip along the c-axis under shear load, thereby forming a high aspect ratio nanofiber structure; then, under the action of mechanical force in different directions, a network fiber structure is formed, which then bonds the powder substrate to obtain paper.

[0113] In some embodiments, the solvent-free flexible paper also includes additives, the surface of which is coated with a primary network structure and secondary network structures are connected between the additives.

[0114] The solvent-free flexible paper of this application embodiment also includes additives that can improve various properties of the paper, such as dry strength, wet strength, smoothness, whiteness, opacity, and water resistance. The additives can be mixed with the powder substrate and fixedly bonded under the action of a binder with a multi-level network structure. For example, by adding inorganic flame retardants such as metal hydroxides including aluminum hydroxide, metal oxides including antimony oxide, and organic flame retardants including nitrogen-based, phosphorus-based, and halogen-based flame retardants, a solvent-free flexible paper with flame-retardant properties can be obtained; similarly, by adding microwave-absorbing materials including graphene and ferrite, a solvent-free flexible paper with microwave-absorbing properties can be obtained; and by adding conductive materials including metal sheets, a solvent-free flexible paper with conductive properties can be obtained.

[0115] Optionally, the additives include one or more of reinforcing agents, flame retardants, and fillers.

[0116] Optionally, the reinforcing agent includes one or more of starch, modified starch, carboxymethyl cellulose, chitosan and chopped fibers, the flame retardant includes aluminum hydroxide, and the filler includes one or more of talc, calcium carbonate, titanium dioxide, kaolin, amorphous silica, silicate, aluminum trihydroxy, barium sulfate and calcium sulfate.

[0117] In some embodiments, the thickness of the solvent-free flexible paper is 30~5000μm. For example, it can be 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, 1500μm, 2000μm, 2500μm, 3000μm, 3500μm, 4000μm, 4500μm, 5000μm, or any range of the above values.

[0118] The solvent-free flexible paper with a suitable thickness according to the embodiments of this application can have excellent mechanical properties, and the thickness of the solvent-free flexible paper can be controlled by adjusting the roller spacing during the rolling process.

[0119] In some embodiments, the basis weight of solvent-free flexible paper is 35~300 g / mm². 2 For example, it can be 35g / mm. 2 40g / mm 2 50g / mm 2 60g / mm 2 70g / mm 2 80g / mm 2 90g / mm 2 100g / mm 2 120g / mm 2 140g / mm 2 160g / mm 2 180g / mm 2 200g / mm 2 220g / mm 2 240g / mm 2 260g / mm 2 280g / mm 2 300g / mm 2 or a range consisting of any of the above values.

[0120] Paper basis weight refers to the mass of paper per unit area. The solvent-free flexible paper with a suitable basis weight in the embodiments of this application can possess excellent mechanical properties.

[0121] In some embodiments, the density of solvent-free flexible paper is 0.700~1.200 g / cm³. 3 For example, it can be 0.700 g / cm³. 3 0.800g / cm 3 0.900g / cm 3 1.000g / cm 31.100g / cm 3 1.200g / cm 3 or a range consisting of any of the above values.

[0122] Paper density refers to the mass of a unit volume of paper. It reflects the compactness of the powder matrix inside the paper and directly affects key properties such as paper hardness, strength, air permeability, and printability.

[0123] In some embodiments, the surface roughness of the solvent-free flexible paper is 120~300 nm.

[0124] In some embodiments, the porosity of the solvent-free flexible paper is 20% to 50%.

[0125] In some embodiments, the average pore size of the solvent-free flexible paper is 120~170 nm.

[0126] The solvent-free flexible paper of this application embodiment has fewer defects, thus reducing porosity and roughness, and thereby improving mechanical properties.

[0127] Optionally, the surface roughness of the solvent-free flexible paper is independently selected from any value or a range between 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, and 300nm.

[0128] Optionally, the porosity of the solvent-free flexible paper is independently selected from any value or a range between any two of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, and 50%.

[0129] Optionally, the average aperture of the solvent-free flexible paper is independently selected from any value of 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, or a range between any two.

[0130] In some embodiments, the contact angle of the solvent-free flexible paper surface is 70° to 100°. For example, it can be 70°, 75°, 80°, 85°, 90°, 95°, 100°, or any range of the above values.

[0131] The wetting angle is the angle between the solid-liquid interface, through the liquid interior, and at the gas-liquid interface at the junction of solid, liquid, and gas phases. In this application, the wetting angle refers to the contact angle of water on the surface of paper.

[0132] In some embodiments, the wet tensile strength of solvent-free flexible paper is 0.4~1.0 N / mm. 2 For example, it can be 0.4 N / mm. 2 0.5N / mm 2 0.6N / mm 2 0.7N / mm 2 0.8N / mm 2 0.9N / mm 2 1.0 N / mm 2 or a range consisting of any of the above values.

[0133] The solvent-free flexible paper of this application has an interwoven network structure of binder fibers on its surface, which can improve the hydrophobicity of the surface of the solvent-free flexible paper and has higher wet strength compared with traditional wet paper that relies on hydrogen bonding.

[0134] In some embodiments, the elastic modulus of solvent-free flexible paper is 30~80 GPa.

[0135] In some embodiments, the tensile strength of the solvent-free flexible paper is 1~12 MPa.

[0136] In some embodiments, the tensile toughness of solvent-free flexible paper is 1800~30000 J. m -2 .

[0137] The solvent-free flexible paper of this application embodiment has excellent mechanical properties.

[0138] Optionally, the elastic modulus of the solvent-free flexible paper is independently selected from any value or a range between 30 GPa, 35 GPa, 40 GPa, 45 GPa, 50 GPa, 55 GPa, 60 GPa, 65 GPa, 70 GPa, 75 GPa, and 80 GPa.

[0139] Optionally, the tensile strength of the solvent-free flexible paper is independently selected from any value or a range between 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, and 12 MPa.

[0140] Optionally, the fracture toughness of the solvent-free flexible paper is independently selected from 1800J. m -2 1900J m -2 、2000J m -2 、3000J m -2 、4000J m -2 、5000J m -2 、6000J m -2 、7000J m -2 、8000J m -2 、9000J m -2 、10000J m -2 、11000J m -2 、12000J m -2 、13000J m -2 、14000J m -2 、15000J m -2 、16000J m -2 、17000J m -2 、18000J m -2 、19000J m -2 、20000J m -2 、21000J m -2 、22000J m -2 、23000J m -2 、24000J m -2 、25000J m -2 、26000J m -2 、27000J m -2 、28000J m -2 、29000J m -2 、30000J m -2Any value in the range or any value between the two.

[0141] In some embodiments, solvent-free flexible paper comprises a powder substrate, a binder having a multi-level network structure, and additives. The binder includes a primary network structure coating the surface of the powder substrate and / or additives and a secondary network structure connecting the powder substrate and / or additives.

[0142] Related technologies indicate that paper containing solvents will volatilize and release VOCs such as benzene, toluene, and formaldehyde, polluting the environment and harming human health; it will also cause defects such as pinholes and orange peel texture in the coating, reducing the surface smoothness of the paper; and it will also accelerate paper aging, such as aging caused by the hydrolysis of ester solvents to produce acid.

[0143] The solvent-free flexible paper of this application embodiment is composed of a powder substrate, binder, and additives, and contains no solvents. Compared with related technologies that contain solvents, it can reduce environmental pollution and improve product safety and durability.

[0144] In some embodiments, solvent-free flexible paper is obtained by mixing and rolling a powder substrate and a binder.

[0145] In this embodiment, the powder substrate and the binder are mixed to pre-fiberize the binder, forming a primary primary network structure on the surface of the powder substrate and a primary secondary network structure between the powder substrates. The premix is ​​then rolled to further stretch the binder fibers, thereby forming a multi-level network structure.

[0146] This application also provides a recycled flexible paper, which includes a paper powder substrate and an adhesive having a multi-level network structure. The adhesive includes a primary network structure coated on the surface of the paper powder substrate and a secondary network structure disposed between the paper powder substrates.

[0147] The paper powder substrate in the recycled flexible paper of this application embodiment can be derived from recycled solvent-free flexible paper; or it can be recycled conventional paper, such as wet-process paper, dry-process paper, etc.

[0148] In this embodiment, the recycled flexible paper uses a binder with a multi-level network structure to fix the paper powder substrate, which has higher water resistance than traditional wet-process paper that relies on hydrogen bonding, thereby improving the mechanical properties of the recycled flexible paper.

[0149] In some embodiments, appropriate additives may be added to improve the relevant properties of recycled flexible paper, such as dry strength, wet strength, smoothness, whiteness, opacity, and water resistance. The additives can be mixed with the paper powder substrate and fixedly bonded by a binder with a multi-level network structure.

[0150] This application also provides a method for preparing solvent-free flexible paper, the method comprising: providing a powder substrate, the powder substrate comprising natural organic powder particles and natural inorganic powder particles; mixing the powder substrate and a binder according to a predetermined ratio to obtain a mixture, the mixing speed being 300~20000 rpm, the time being 3~25 min, and the temperature being 20~80℃; and rolling the mixture to obtain solvent-free flexible paper.

[0151] In this embodiment, the powder substrate and the binder are mixed to pre-fiberize the binder, forming a primary primary network structure on the surface of the powder substrate and a primary secondary network structure between the powder substrates.

[0152] In this embodiment, the mixture is subjected to roll pressing, which further fiberizes the binder fibers, thereby forming a multi-level network structure. Roll pressing can be performed by extruding with rollers, or by folding the material in half and then performing a secondary extrusion after extruding with rollers.

[0153] Compared to pulp in related technologies, the powder substrate of this application has the advantages of being widely available and easy to obtain, and in particular, it can recycle agricultural waste.

[0154] The solvent-free flexible paper preparation method of this application embodiment, compared with related dry and / or wet paper, can avoid the use of water resources and solvents. On the one hand, it can reduce the possibility of paper aging caused by solvent evaporation, thereby improving the durability of solvent-free flexible paper; on the other hand, it can also save water resources and reduce the impact of solvent evaporation on the environment and human health.

[0155] In some embodiments, the mixing process includes ball milling and / or kneading.

[0156] Internal mixing refers to the process of uniformly mixing, dispersing, and chemically reacting multi-component materials by generating shearing, extrusion, and friction through the rotation of a rotor in a closed, high-temperature environment.

[0157] Both intensive mixing and ball milling processes can uniformly mix the powder substrate and the binder, so that the binder can evenly fix and connect the skeleton formed by the powder substrate.

[0158] In the embodiments of this application, only grinding treatment may be performed, only mixing treatment may be performed, or mixing treatment may be performed first and then ball milling treatment may be performed.

[0159] In other embodiments, the mixing process includes first performing a mixing process followed by a ball milling process.

[0160] First, the mixing process makes the mixture of powder substrate and binder more loose. Then, the ball milling process allows the binder to be better pre-fiberized, forming a primary primary network structure on the surface of the powder substrate and a primary secondary network structure between the powder substrates.

[0161] In some embodiments, the ball milling speed is 300~1000 rpm and the processing time is 10~15 min.

[0162] The ball milling process with appropriate parameters in the embodiments of this application can make the powder substrate and binder mix more evenly, thereby enabling the binder fibers to better coat the powder substrate.

[0163] Optionally, the rotational speed of the ball milling process is independently selected from any value or a range between 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, and 1000 rpm.

[0164] Optionally, the processing time is independently selected from any value of 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, or a range between any two.

[0165] In some embodiments, the mixing speed is 3000~20000 rpm, the temperature is 20~80℃, and the processing time is 3~10 min.

[0166] The embodiments of this application feature a mixing process with appropriate parameters, which allows the binder to be uniformly and fully stretched in all directions, thereby improving the integrity of the fiber network framework and thus enhancing the coating effect on the powder substrate.

[0167] Optionally, the mixing speed is independently selected from 3000 rpm, 3200 rpm, 3400 rpm, 3600 rpm, 3800 rpm, 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm, 5000 rpm, 5200 rpm, 5400 rpm, 5600 rpm, 5800 rpm, 6000 rpm, 6200 rpm, 6400 rpm, 6600 rpm, 6800 rpm, 7000 rpm, 7200 rpm, 7400 rpm, and 7600 rpm. The value can be any value from 7800rpm, 8000rpm, 8200rpm, 8400rpm, 8600rpm, 8800rpm, 9000rpm, 9200rpm, 9400rpm, 9600rpm, 9800rpm, 10000rpm, 11000rpm, 12000rpm, 13000rpm, 14000rpm, 15000rpm, 16000rpm, 17000rpm, 18000rpm, 19000rpm, or 20000rpm, or a range between any two.

[0168] Optionally, the mixing temperature is independently selected from any value or a range between 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, and 80°C.

[0169] Optionally, the mixing time is independently selected from any value of 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or any range between both.

[0170] In order to form a more complete multi-level network structure, in some embodiments, the rolling process also includes extruding the mixture and then folding the extruded mixture in half; the extrusion and folding processes are repeated multiple times.

[0171] In this embodiment, the binder can be further fiberized through roll pressing to form a complete multi-level network structure. Roll pressing also includes first extruding the mixture, typically using a roll press, to further fiberize the binder and form a complete multi-level network structure; then folding the mixture in half further enhances the integrity of the multi-level network structure.

[0172] The squeezing and folding processes can be alternated multiple times. For example, after squeezing, folding can be performed, then squeezing again, and then folding again, and so on, multiple times.

[0173] To better form a multi-level network structure, powder substrates with different elastic moduli require different numbers of folding processes. In some embodiments, when the elastic modulus of the powder substrate is 0.1~8 GPa, the number of folding processes is 20~50. In other embodiments, when the elastic modulus of the powder substrate is 10~30 GPa, the number of folding processes is 10~30.

[0174] In some embodiments, the method for preparing the powder substrate includes: pulverizing the raw material containing the powder substrate to obtain the powder substrate.

[0175] The relevant technologies typically use pulp as the source of paper fibers. However, the pulp preparation process involves cooking and washing, which consumes a large amount of water resources and generates a large amount of wastewater, as well as a large amount of energy.

[0176] This application embodiment obtains the powdered substrate by directly crushing the raw material containing the powdered substrate. This allows paper production to no longer rely on paper fibers, thus eliminating the need for cooking and washing processes, thereby reducing wastewater generation and saving water and energy. Simultaneously, it allows the raw materials for papermaking to be no longer limited to traditional papermaking wood such as softwood rice and hardwood, enabling the full recycling and utilization of waste materials such as straw.

[0177] The following examples describe the disclosure of this application in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0178] Example 1: Bamboo powder (Dv50:5000 mesh) and polytetrafluoroethylene (PTFE) binder were mixed at a mass ratio of 95:5. The mixture was ball-milled at 300 rpm for 11 minutes, then extruded under the action of a roller press, and then folded. The extrusion and folding processes were repeated 45 times to obtain solvent-free flexible paper.

[0179] The preparation and performance testing methods of solvent-free flexible paper in Comparative Examples 1 and 2 are the same as those in Example 1, except that the ball milling parameters are different. The specific parameters are detailed in Table 1.

[0180] Performance testing: Density test method: Weigh the paper m using an electronic balance, cut a certain area of ​​paper, measure the thickness and calculate the volume V. The formula for calculating the density of paper is ρ=m / V.

[0181] Tensile strength test method: Tested according to the international standard for paper tensile strength testing, ISO 1924-2. See Table 1 for specific structure.

[0182] Test method for fracture toughness: Reference (P. Mäkelä, C. Fellers, An analytic procedure for determination of fracture toughness of paper materials. Nord.Pulp Pap. Res. J. 27, 352-360 (2012) doi:10.3183 / npprj-2012-27-02-p352-360.).

[0183] Cobb paper ink absorption Test method: Cobb The absorbency value is an important indicator for evaluating the water absorption of paper and paperboard, and its test method follows international standards (such as ISO 535 or GB / T 1540). This test measures the amount of water absorbed per unit area of ​​a paper sample under specified time and pressure, thus simulating the paper's resistance to liquids during printing or use. The test procedure is briefly described as follows: Instrument preparation: A Cobb absorbency tester is used. Its main components are an open metal cylinder with an inner diameter of 112.8 mm (corresponding to a test area of ​​100 cm²), a pressure cap, a rubber pad no smaller than the cylinder opening, and a balance accurate to 0.001 g.

[0184] Sample preparation: Cut the paper sample into a circle or square much larger than the test area and place it on a rubber pad. Ensure the test side is facing up, then press it tightly with a metal cylinder and cap to form a leak-free test area.

[0185] Water addition test: Quickly pour 100 mL (i.e., water level of 10 mm) of distilled water or a specific liquid conforming to the standard into the cylinder. Start timing from the moment the water contacts the paper sample and maintain the test time for 60 seconds.

[0186] Finishing and Drying: After 60 seconds, quickly empty the water from the cylinder. Remove the cylinder and immediately blot away any remaining water on the surface of the paper sample with highly absorbent paper or cloth. This step must be done quickly to prevent the paper from absorbing more water.

[0187] Weighing and Calculation: Before water absorption (m) ) and after water absorption (m Immediately weigh the paper sample. (Cobb) The value is calculated using the following formula: Cobb = (m - m ) / A, where A is the test area (usually 0.01 m² or 100 cm²). The calculation result is usually expressed in g / m². Too high ink absorbency of the cardboard: Ink penetrates too deeply, which may cause the printed pattern to be dull, not vibrant enough, or even show through to the back of the paper. Too low ink absorbency of the cardboard: The ink remains on the surface and dries too slowly, which can easily cause smudging of the printed matter and is also not conducive to high-speed printing. Ink absorbency Cobb A value of 15-30 can produce paper with good printing and writing effects.

[0188] Table 1

[0189] As shown in the table, in Comparative Examples 1 and 2, the ball milling time was either too short or too long, resulting in insufficient or excessive fiberization (the fibers lost their ability to continue stretching), thus failing to form a multi-level network structure. In contrast, the solvent-free flexible paper of this application embodiment has a multi-level network structure and exhibits excellent mechanical properties.

[0190] The experimental procedures for Examples 1-1 to 1-4 are basically the same as those for Example 1, except that the ratio of powder substrate to binder is different. See Table 2 for details.

[0191] Table 2

[0192] As shown in the table, with the decrease in the mass ratio of binder, the density, tensile strength, and tensile toughness of solvent-free flexible paper decrease, while the ink absorption of solvent-free flexible paper increases. Therefore, a binder with an appropriate mass ratio can enable solvent-free paper to better balance mechanical properties and printing and writing performance.

[0193] The experimental procedures for Examples 2-1 to 2-4 are basically the same as those for Example 1, the difference being the particle size of the powder substrate. See Table 3 for details.

[0194] Table 3

[0195] As shown in the table, the particle size of the powder substrate can affect the multi-level network structure of solvent-free flexible paper, and thus affect the mechanical properties of solvent-free flexible paper.

[0196] The experimental procedures for Examples 3-1 to 3-8 are basically the same as those for Example 1, except that the elastic modulus of the powder substrate and the ratio of the powder substrate to the binder are different. See Tables 4 and 5 for details.

[0197] Table 4

[0198] As shown in the table, a low binder content affects the multi-level network structure of solvent-free flexible paper, resulting in lower mechanical properties.

[0199] Table 5

[0200] As shown in the table, a low binder content affects the multi-level network structure of solvent-free flexible paper, resulting in lower mechanical properties.

[0201] Example 4-1: Bamboo powder (Dv50: 5000 mesh) as the substrate was mixed with polytetrafluoroethylene (PTFE) binder at a mass ratio of 95:5. The mixture was first kneaded at 80°C and 3000 rpm for 10 minutes, then ball-milled at 300 rpm for 11 minutes, followed by extrusion under the action of a roller press, and then folded in half. The extrusion and folding processes were repeated 30 times to obtain solvent-free flexible paper.

[0202] Table 6

[0203] As shown in the table, performing intensive mixing followed by ball milling can improve the mechanical properties of solvent-free flexible paper.

[0204] The experimental steps of Examples 5-1 to 5-6 are the same as those of Example 1, except that the powder substrate and the number of folding treatments are different.

[0205] Table 7

[0206] As shown in the table, applying different numbers of contact cycles to powder substrates with different elastic moduli can better form a multi-level network structure, thereby improving the mechanical properties of solvent-free flexible paper.

[0207] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A solvent-free flexible paper, characterized in that, The solvent-free flexible paper includes a powder substrate and an adhesive having a multi-level network structure. The adhesive includes a primary network structure covering the surface of the powder substrate and a secondary network structure connecting the powder substrates.

2. The solvent-free flexible paper according to claim 1, characterized in that, The primary network structure and the secondary network structure independently include the adhesive fibers that overlap each other.

3. The solvent-free flexible paper according to claim 1 or 2, characterized in that, Based on the solvent-free flexible paper, the powder substrate accounts for 75% to 99% of the mass, and the binder accounts for 1% to 25% of the mass. Optionally, the powder substrate accounts for 85% to 97% of the mass, and the binder accounts for 3% to 15% of the mass.

4. The solvent-free flexible paper according to any one of claims 1-3, characterized in that, The mass ratio of the powder substrate to the binder is 99:1 to 75:25, and can be selected as 97:3 to 85:

15.

5. The solvent-free flexible paper according to any one of claims 1-4, characterized in that, The powder substrate has a Dv50 of 200 mesh to 10000 mesh, optionally 500 mesh to 3000 mesh; and / or, the powder substrate has a Dv10 of 10000 to 20000 mesh; and / or, the powder substrate has a Dv90 of 150 to 200 mesh.

6. The solvent-free flexible paper according to any one of claims 1-5, characterized in that, When the elastic modulus of the powder substrate is 0.1~8 GPa, the mass ratio of the powder substrate to the binder is 97:3~70:25; and / or, when the elastic modulus of the powder substrate is 10~30 GPa, the mass ratio of the powder substrate to the binder is 99:1~85:

15.

7. The solvent-free flexible paper according to any one of claims 1-6, characterized in that, When the Dv50 of the powder substrate is 5000~10000 mesh, the mass ratio of the powder substrate to the binder is 95:5~75:25; and / or, when the Dv50 of the powder substrate is 200~5000, the mass ratio of the powder substrate to the binder is 98:2~80:

20.

8. The solvent-free flexible paper according to any one of claims 1-7, characterized in that, The powder substrate includes natural organic powder particles and / or natural inorganic powder particles.

9. The solvent-free flexible paper according to claim 8, characterized in that, The natural organic powder particles include one or more of natural wood powder particles, straw powder particles, agricultural crop processing by-product powder particles, fruit and nut shell powder particles, and animal shell powder particles; and / or, the natural inorganic powder particles include mineral powder particles, optionally, the mineral powder particles include one or more of silicates, carbonates, oxides, sulfides, and phosphates.

10. The solvent-free flexible paper according to claim 9, characterized in that, The natural wood powder particles include one or more of the following: pine powder, cypress powder, fir powder, poplar powder, nanmu powder, elm powder, oak powder, oak wood powder, walnut powder, cherry wood powder, mahogany powder, teak powder, reed powder, spotted bamboo powder, weeping bamboo powder, golden bamboo powder, green bamboo powder, rattan bamboo powder, purple bamboo powder, carnation powder, dragon pearl bamboo powder, and bean bamboo powder. The straw powder particles include rice straw powder, corn straw powder, wheat straw powder, rapeseed straw powder, barley straw powder, oat straw powder, soybean straw powder, broad bean straw powder, and pea straw powder. The powder particles are one or more of the following: soybean straw powder; the agricultural crop processing by-product powder particles include one or more of the following: rice husk powder, corn cob powder, sweet potato vine powder, peanut vine / shell powder, potato vine powder, pumpkin vine powder, loofah vine powder, sugarcane bagasse powder, and cassava bagasse powder; the fruit and nut shell powder particles include one or more of the following: pistachio shell powder, macadamia nut shell powder, hazelnut shell powder, chestnut shell powder, acorn shell powder, pine nut shell powder, and walnut shell powder; and the animal shell powder particles include one or more of the following: shrimp shell powder, eggshell, crab shell powder, and seashell powder.

11. The solvent-free flexible paper according to any one of claims 1-10, characterized in that, The adhesive includes one or more of polytetrafluoroethylene, polyethylene, polypropylene, polylactic acid, thermoplastic polyurethane, copolymers of ethylene and tetrafluoroethylene, and copolymers of hexafluoropropylene and tetrafluoroethylene.

12. The solvent-free flexible paper according to any one of claims 1-11, characterized in that, The solvent-free flexible paper also includes additives, which include one or more of reinforcing agents, flame retardants, and fillers.

13. The solvent-free flexible paper according to claim 12, characterized in that, The reinforcing agent includes one or more of starch, modified starch, carboxymethyl cellulose, chitosan, and chopped fibers; and / or, the flame retardant includes aluminum hydroxide; and / or, the filler includes one or more of talc, calcium carbonate, titanium dioxide, kaolin, amorphous silica, silicates, aluminum trihydroxy, barium sulfate, and calcium sulfate.

14. The solvent-free flexible paper according to any one of claims 1-13, characterized in that, The solvent-free flexible paper satisfies at least one of conditions (1) to (11): (1) the thickness of the solvent-free flexible paper is 30~5000μm; (2) the basis weight of the solvent-free flexible paper is 35~300g / mm. 2 (3) The density of the solvent-free flexible paper is 0.700~1.200 g / cm³. 3 (4) The surface roughness of the solvent-free flexible paper is 120~300nm; (5) The contact angle of the surface of the solvent-free flexible paper is 70°~100°; (6) The wet tensile strength of the solvent-free flexible paper is 0.4~1.0N / mm. 2 (7) The elastic modulus of the solvent-free flexible paper is 30~80 GPa; (8) The tensile strength of the solvent-free flexible paper is 1~12 MPa; (9) The fracture toughness of the solvent-free flexible paper is 1800~30000 J. m -2 (10) The porosity of the solvent-free flexible paper is 20%~50%; (11) The average pore size of the solvent-free flexible paper is 120~170nm.

15. The solvent-free flexible paper according to any one of claims 1-14, characterized in that, The solvent-free flexible paper is obtained by mixing the powder substrate and the binder and then rolling them.

16. A recycled flexible paper made from the solvent-free flexible paper according to any one of claims 1-15, characterized in that, The recycled flexible paper includes a paper powder substrate and a binder with a multi-level network structure. The binder includes a primary network structure covering the surface of the paper powder substrate and a secondary network structure disposed between the paper powder substrates.

17. A method for preparing solvent-free flexible paper according to any one of claims 1-15, characterized in that, The preparation method includes: providing a powder substrate, the powder substrate comprising natural organic powder particles and / or natural inorganic powder particles; mixing the powder substrate and a binder according to a predetermined ratio to obtain a mixture, wherein the mixing speed is 300~20000 rpm, the time is 3~25 min, and the temperature is 20~80℃; and the mixture is subjected to roll pressing to obtain solvent-free flexible paper.

18. The preparation method according to claim 17, characterized in that, The mixing process includes ball milling and / or internal mixing; optionally, the ball milling process has a rotation speed of 300~1000 rpm and a processing time of 10~15 min; optionally, the internal mixing process has a rotation speed of 3000~20000 rpm, a temperature of 20~80℃, and a processing time of 3~10 min.

19. The preparation method according to claim 18, characterized in that, The mixing process includes ball milling and internal mixing. The internal mixing process has a rotation speed of 3000~10000 rpm, a temperature of 50~80℃, and a processing time of 5~10 min. The ball milling process has a rotation speed of 300~500 rpm and a processing time of 10~13 min.

20. The preparation method according to any one of claims 17-19, characterized in that, The rolling process further includes extruding the mixture and then folding the extruded mixture in half; the extrusion and folding processes are performed alternately multiple times.

21. The preparation method according to any one of claims 17-20, characterized in that, When the elastic modulus of the powder substrate is 0.1~8 GPa, the number of folding treatments is 20~50; and / or, when the elastic modulus of the powder substrate is 10~30 GPa, the number of folding treatments is 10~30.

22. The preparation method according to any one of claims 17-21, characterized in that, The method for preparing the powder substrate includes: pulverizing the raw material containing the powder substrate to obtain the powder substrate.

23. The use of any solvent-free flexible paper according to any one of claims 1-15 and / or the recycled flexible paper according to claim 16 as thermally conductive paper, flame-retardant paper, waterproof paper, electromagnetic shielding paper, insulating paper, conductive paper or microwave absorbing paper.

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