Polyurethane composite material and preparation method and application thereof

Abstract

The application provides a polyurethane composite material and a preparation method and application thereof, and the polyurethane composite material comprises a polyurethane resin and natural fiber powder; the preparation raw material of the polyurethane resin comprises the following components in parts by weight: polyol 30-50 parts, isocyanate 30-60 parts, plasticizer 2-8 parts, catalyst 0.01-0.3 parts and water 0.5-4 parts; and the particle size of the natural fiber powder is 400-900 mu m. The polyurethane synthetic leather prepared from the polyurethane composite material has the characteristics of silent rubbing, excellent performance and high peeling strength.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane materials technology, specifically relating to a polyurethane composite material, its preparation method, and its application. Background Technology

[0002] Polyurethane materials made using polyurethane foaming technology have a porous structure, which gives them some noise reduction and sound insulation properties. However, existing polyurethane foams only utilize the physical properties of polyurethane to absorb sound and thus reduce noise. The noise reduction is still poor and needs improvement.

[0003] CN115376480A discloses a high-efficiency noise-reducing and sound-insulating polyurethane foam and its insulation components. The high-efficiency noise-reducing and sound-insulating polyurethane foam includes a polyurethane foam board with an internal cavity containing a filling core. The filling core consists of, in sequence, a honeycomb board, a first noise-reducing board, a second noise-reducing board, glass wool felt, and a fiberboard. End caps are integrally connected to both ends of the polyurethane foam board, and the ends of the end caps are rolled up with arc-shaped notches. The high-efficiency noise-reducing and sound-insulating polyurethane foam provided by this technical solution has a stable pore structure, essentially a closed-cell structure, exhibiting not only excellent heat insulation performance but also good freeze-thaw resistance and sound absorption.

[0004] CN214084107U discloses a high-sound-absorbing polyurethane foam automotive interior panel. The panel includes a mounting shell and a buffer inner panel. The buffer inner panel is located at the top of the mounting shell; a bottom layer is located at the bottom of the mounting shell, on which a polyurethane sound-absorbing layer is placed; an upper layer is located at the bottom of the mounting shell above the polyurethane sound-absorbing layer; sound-absorbing holes are formed in the center of the buffer inner panel; sliding telescopic rods are located on both sides of the lower surface of the buffer inner panel; the bottom of the sliding telescopic rods is connected to a limit plate; and sound-absorbing strips are located on the side wall of the inner cavity of the mounting shell below the buffer inner panel. This technical solution isolates external sound by setting a polyurethane sound-absorbing layer at the bottom of the mounting shell, achieving a sound insulation effect, keeping the vehicle interior quiet, and improving interior comfort.

[0005] CN110229303A discloses a polyurethane sound-absorbing material for automobiles based on soybean oil polyols and its preparation method. The components and their mass fractions of the polyurethane sound-absorbing material are as follows: 35-45 parts soybean oil polyol, 80 parts polyether polyol, 1.2-1.8 parts foam stabilizer, 1.0-2.0 parts foaming agent, 1.5 parts catalyst, 4.5 parts crosslinking agent, and 40-50 parts polyisocyanate. The polyurethane sound-absorbing material for automobiles provided by this invention can achieve an average sound absorption coefficient of 0.588 at low frequencies and has good sound insulation performance.

[0006] Polyurethane synthetic leather is commonly used in various commercial products and is classified into soft polyurethane synthetic leather (mainly for clothing) and hard polyurethane synthetic leather (mainly for athletic shoes). The specific type of polyurethane synthetic leather depends on its mechanical properties and the nature of its raw materials, such as the type and molecular weight of the polyols. Soft polyurethane synthetic leather has many advantages, such as good flexibility, good cushioning, reversible deformation, high durability during use, and good sound absorption properties due to the presence of voids, channels, or gaps in its structure. When sound waves flow through the open pores of soft synthetic leather, the friction between the airflow and the bubble walls converts sound energy into heat energy. As people's living standards improve, higher demands are placed on polyurethane synthetic leather. For example, when making clothing, shoes, or bags from synthetic leather, it is necessary to ensure that the polyurethane synthetic leather does not make an annoying sound when rubbed together.

[0007] Therefore, there is a need to develop a type of polyurethane synthetic leather that is silent when rubbed. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a polyurethane composite material, its preparation method, and its applications. Polyurethane synthetic leather made from the aforementioned polyurethane composite material exhibits characteristics such as silent rubbing, excellent performance, and high peel strength.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a polyurethane composite material, the polyurethane composite material comprising polyurethane resin and natural fiber powder;

[0011] The raw materials for preparing the polyurethane resin include the following components by weight: 30-50 parts of polyol (e.g., 32, 34, 36, 38, 40, 42, 44, 46, or 48 parts, etc.), 30-60 parts of isocyanate (e.g., 33, 36, 39, 42, 45, 48, 51, 54, or 57 parts, etc.), 2-8 parts of plasticizer (e.g., 3, 4, 5, 6, or 7 parts, etc.), 0.01-0.3 parts of catalyst (e.g., 0.05, 0.1, 0.15, 0.2, or 0.25 parts, etc.), and 0.5-4 parts of water (e.g., 1, 1.5, 2, 2.5, 3, or 3.5 parts, etc.).

[0012] The particle size of the natural fiber powder is 400-900μm (e.g., 450μm, 500μm, 550μm, 600μm, 650μm, 700μm, 750μm, 800μm or 850μm, etc.).

[0013] In this invention, the performance of polyurethane synthetic leather made from polyurethane composite materials is related to the composition of polyurethane resin and natural fiber powder in the polyurethane composite material, as well as the pore structure of the produced polyurethane synthetic leather. By setting the raw materials and content of polyurethane resin preparation and combining it with natural fiber powder, the performance of polyurethane composite materials is improved, thereby improving the mechanical properties or sound absorption properties of polyurethane synthetic leather made from polyurethane composite materials. It features silent rubbing, excellent performance, and high peel strength.

[0014] Preferably, the polyol includes any one or a combination of at least two of polyoxypropylene ether diol, polycyclic tetrahydrofuran ether diol, polybutylene adipate diol, or polyethylene adipate diol.

[0015] Preferably, the weight-average molecular weight of the polyol is 1000 to 4000, such as 1300, 1600, 1900, 2200, 2500, 2800, 3100, 3400 or 3700.

[0016] In this invention, the weight-average molecular weight of the polyol is 1000-4000. If the weight-average molecular weight of the polyol is too small, it will not be easy to foam and the resulting polyurethane synthetic leather will have small pores. If the weight-average molecular weight of the polyol is too large, the foaming will be larger, meaning that the surface of the resulting polyurethane synthetic leather will be thinner and the surface will be easily worn through when rubbed.

[0017] Preferably, the isocyanate includes any one or a combination of at least two of diphenylmethane diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), toluene diisocyanate, or isophorone diisocyanate.

[0018] Preferably, the plasticizer includes any one or a combination of at least two of the following: silicone softener, castor oil, epoxidized soybean oil, or epoxidized butyl furfuryl oleate.

[0019] Preferably, the catalyst comprises any one or a combination of at least two of N-ethylmorpholine, organobismuth, dibutyltin dilaurate, or triethanolamine.

[0020] Preferably, the mass of the natural fiber powder is 5% to 20% of the mass of the polyurethane resin, for example, 7%, 9%, 11%, 13%, 15%, 17% or 19%.

[0021] In this invention, the mass of the natural fiber powder is 5% to 20% of the mass of the polyurethane resin. If the percentage of the natural fiber powder to the polyurethane resin is too small, it will not achieve a good sound absorption effect; if the percentage of the natural fiber powder to the polyurethane resin is too large, more fiber powder will float on the surface of the made polyurethane synthetic leather, increasing the resistance when rubbing, i.e., it will not be able to be rubbed.

[0022] In a second aspect, the present invention provides a method for preparing a polyurethane composite material as described in the first aspect, the method comprising the following steps:

[0023] (1) Natural fibers are treated with alkali and ground to obtain natural fiber powder;

[0024] (2) Mix the polyurethane resin and the natural fiber powder obtained in step (1) to obtain a polyurethane composite material.

[0025] The mass concentration of alkali in the alkaline solution in step (1) is 5wt%-20wt%, for example, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, or 19wt%.

[0026] In this invention, unlike glass fiber, mica, or talc, natural fibers possess excellent strength properties, good thermal performance, low cost, low density, non-corrosiveness, and biodegradability. However, natural fibers also have drawbacks such as hydrophilic structure, low thermal stability, low dimensional stability, incompatibility with certain polymer matrices, and poor interfacial bonding. To eliminate these drawbacks, this invention employs alkali treatment of natural fibers. Alkali treatment leads to a reduction in the weight of natural fibers because it removes non-cellulose compounds such as hemicellulose, lignin, wax, and pectin from the natural fibers. Consequently, more reactive groups are formed on the alkali-treated surface, improving the compatibility between the alkali treatment and the polymer matrix. The natural fiber powder obtained in step (1) exhibits good compatibility with polyurethane resin. This invention improves the mechanical properties or sound absorption properties of polyurethane synthetic leather made from polyurethane composites by using biodegradable natural fibers to prepare polyurethane composites. Furthermore, it makes the preparation method of polyurethane composites safe and environmentally friendly, reducing dependence on petrochemical materials.

[0027] Preferably, the natural fiber includes rice straw.

[0028] Preferably, the alkaline solution comprises sodium hydroxide solution and / or potassium hydroxide solution.

[0029] Preferably, the temperature of the alkaline treatment is 0 to 50°C, such as 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or 45°C.

[0030] Preferably, the alkaline treatment time is 10 to 60 minutes, such as 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, or 55 minutes.

[0031] Preferably, the alkaline treatment further includes water washing and drying steps.

[0032] Preferably, the drying temperature is 30-80℃ (e.g., 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or 75℃, etc.), and the drying time is 10-24h (e.g., 12h, 14h, 16h, 18h, 20h or 22h, etc.).

[0033] Preferably, the method for preparing the polyurethane resin includes the following steps: mixing polyol, isocyanate, plasticizer, catalyst and water, reacting to obtain the polyurethane resin.

[0034] Preferably, the mixing comprises mixing a polyol, a plasticizer, a catalyst and water, and then adding an isocyanate.

[0035] Thirdly, the present invention provides a polyurethane synthetic leather, which is prepared from a polyurethane composite material as described in the first aspect.

[0036] This invention proposes for the first time a polyurethane synthetic leather that is silent when rubbed. This polyurethane synthetic leather is characterized by being silent when rubbed, and does not produce annoying noise when rubbed, which is significantly different from existing polyurethane synthetic leathers on the market. It has broad application prospects in many fields, such as the manufacture of bags, clothing or shoes.

[0037] Fourthly, the present invention provides a method for preparing polyurethane synthetic leather as described in the third aspect, the method comprising the following steps: first coating a release paper surface with a polyurethane composite material as described in the first aspect, drying, second coating a release paper surface with a polyurethane composite material as described in the first aspect, attaching a base fabric, pressing, and drying again to obtain the polyurethane synthetic leather; the thickness of the first coating is 1-2 mm, for example 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, or 1.9 mm, etc.

[0038] Preferably, the thickness of the second coating is 0.1 to 0.5 mm, such as 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm or 0.45 mm.

[0039] Preferably, the drying and re-drying temperatures are each independently between 90 and 140°C, for example, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, or 135°C.

[0040] Preferably, the drying and re-drying times are each independently 10 to 30 minutes, for example 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes or 28 minutes.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This invention improves the mechanical and sound absorption properties of polyurethane synthetic leather by setting the raw materials and content of polyurethane resin and combining it with natural fiber powder. The resulting polyurethane synthetic leather does not produce annoying noise when rubbed together, exhibits excellent performance, and has high peel strength. The addition of natural fiber powder to the polyurethane composite material promotes sustainable development and is environmentally friendly. The preparation method of the polyurethane composite material and polyurethane synthetic leather is simple, cost-effective, and energy-efficient, resulting in a product with excellent performance and promising application prospects. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0044] The sources of some components in the examples and comparative examples are as follows:

[0045] Example 1

[0046] This embodiment provides a polyurethane composite material, its preparation method, and its application. The polyurethane composite material includes polyurethane resin and natural fiber powder, wherein the mass of the natural fiber powder is 20% of the mass of the polyurethane resin.

[0047] The raw materials for preparing the polyurethane resin include the following components by weight: 50 parts of polyol (polyethylene ether diol, weight average molecular weight of 1000), 60 parts of isocyanate (diphenylmethane diisocyanate), 2 parts of plasticizer (organosilicon softener, brand: SY-4139, manufacturer: Jiangxi Sanyue), 0.3 parts of catalyst (N-ethylmorpholine), and 0.5 parts of water.

[0048] The preparation method of the polyurethane composite material includes the following steps:

[0049] (1) Soak waste rice straw in a 5% sodium hydroxide solution for 60 minutes at a temperature of 50°C. Then wash it continuously with distilled water until the sodium hydroxide in the rice straw is completely removed. Then dry it in a 30°C oven for 24 hours and leave it at room temperature for 24 hours. Finally, grind it with a ball mill to obtain natural fiber powder and screen out natural fiber powder with a length of 400-500 μm.

[0050] (2) Mix 50 parts by weight of polyol, 2 parts by weight of plasticizer, 0.3 parts by weight of catalyst and 0.5 parts by weight of water in a beaker and stir continuously. Then add 60 parts by weight of isocyanate to the beaker and stir at room temperature for 30 seconds. Then add 22.5 parts by weight of natural fiber powder obtained in step (1) and stir evenly to obtain the polyurethane composite material.

[0051] A polyurethane synthetic leather, the preparation method of which includes the following steps: first coating the surface of release paper with the above-mentioned polyurethane composite material, the thickness of the first coating being 1 mm, then drying in a 90°C oven for 10 min; second coating the above-mentioned polyurethane composite material on the dried polyurethane composite material foam layer, the thickness of the second coating being 0.1 mm; attaching a base fabric, pressing it, and drying it again in a 90°C oven for 10 min; peeling off the release paper to obtain the polyurethane synthetic leather.

[0052] Example 2

[0053] This embodiment provides a polyurethane composite material, its preparation method, and its application. The polyurethane composite material includes polyurethane resin and natural fiber powder, wherein the mass of the natural fiber powder is 13% of the mass of the polyurethane resin.

[0054] The raw materials for preparing the polyurethane resin include the following components by weight: 40 parts of polyol (polyethylene adipate diol, weight average molecular weight of 4000), 50 parts of isocyanate (MDI, manufacturer: Wanhua Chemical), 5 parts of plasticizer (castor oil, manufacturer: BASF), 0.01 parts of catalyst (bismuth quinocetate, Shandong Rongxin Chemical), and 4 parts of water.

[0055] The preparation method of the polyurethane composite material includes the following steps:

[0056] (1) Soak waste rice straw in a 15% sodium hydroxide solution for 30 minutes at a temperature of 25°C. Then wash it continuously with distilled water until the sodium hydroxide in the rice straw is completely removed. Then dry it in a 50°C oven for 15 hours and leave it at room temperature for 24 hours. Finally, grind it with a ball mill to obtain natural fiber powder and screen out natural fiber powder with a length of 600-700 μm.

[0057] (2) Mix 40 parts by weight of polyol, 5 parts by weight of plasticizer, 0.01 parts by weight of catalyst and 4 parts by weight of water in a beaker and stir continuously. Then add 50 parts by weight of isocyanate to the beaker and stir at room temperature for 30 seconds. Then add 13 parts by weight of natural fiber powder obtained in step (1) and stir evenly to obtain the polyurethane composite material.

[0058] A polyurethane synthetic leather, the preparation method of which includes the following steps: first coating the surface of release paper with the above-mentioned polyurethane composite material, the thickness of the first coating being 1.5 mm, then drying it in an oven at 110°C for 20 min; second coating the above-mentioned polyurethane composite material on the dried polyurethane composite material foam layer, the thickness of the second coating being 0.3 mm; attaching a base fabric, pressing it, and drying it again in an oven at 110°C for 20 min; peeling off the release paper to obtain the polyurethane synthetic leather.

[0059] Example 3

[0060] This embodiment provides a polyurethane composite material, its preparation method, and its application. The polyurethane composite material includes polyurethane resin and natural fiber powder, wherein the mass of the natural fiber powder is 20% of the mass of the polyurethane resin.

[0061] The raw materials for preparing the polyurethane resin include the following components by weight: 30 parts of polyol (polycyclic tetrahydrofuran ether diol, with a weight average molecular weight of 2000), 30 parts of isocyanate (toluene diisocyanate), 8 parts of plasticizer (epoxidized soybean oil), 0.2 parts of catalyst (triethanolamine), and 2 parts of water.

[0062] The preparation method of the polyurethane composite material includes the following steps:

[0063] (1) Soak waste rice straw in a 20% sodium hydroxide solution for 10 minutes at 0°C, then wash it continuously with distilled water until the sodium hydroxide in the rice straw is completely removed. Then dry it in an 80°C oven for 10 hours and leave it at room temperature for 24 hours. Finally, grind it with a ball mill to obtain natural fiber powder, and screen out the natural fiber powder with a length of 800-900μm.

[0064] (2) Mix 30 parts by weight of polyol, 8 parts by weight of plasticizer, 0.2 parts by weight of catalyst and 2 parts by weight of water in a beaker and stir continuously. Then add 30 parts by weight of isocyanate to the beaker and stir at room temperature for 30 seconds. Then add 3.5 parts by weight of natural fiber powder obtained in step (1) and stir evenly to obtain the polyurethane composite material.

[0065] A polyurethane synthetic leather, the preparation method of which includes the following steps: first coating the surface of release paper with the above-mentioned polyurethane composite material, the thickness of the first coating being 2 mm, then drying in an oven at 140°C for 30 min; second coating the above-mentioned polyurethane composite material on the dried polyurethane composite material foam layer, the thickness of the second coating being 0.5 mm; attaching a base fabric, pressing it, and drying it again in an oven at 140°C for 30 min; peeling off the release paper to obtain the polyurethane synthetic leather.

[0066] Example 4

[0067] This embodiment provides a polyurethane composite material, its preparation method, and its application. The only difference between this embodiment and Example 1 is that diphenylmethane diisocyanate is replaced with the same mass of isophorone diisocyanate. Otherwise, they are the same as in Example 1.

[0068] Example 5

[0069] This embodiment provides a polyurethane composite material, its preparation method, and its application. The only difference between this embodiment and Embodiment 1 is that the weight of the natural fiber powder is adjusted to 26 parts by weight, and the mass of the natural fiber powder is 23% of the mass of the polyurethane resin. Otherwise, it is the same as Embodiment 1.

[0070] Comparative Example 1

[0071] This comparative example provides a polyurethane composite material, its preparation method, and its application. The only difference between this example and Example 1 is that the mass concentration of sodium hydroxide in the sodium hydroxide solution is adjusted to 2 wt%, while the rest is the same as Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a polyurethane composite material, its preparation method, and its application. The only difference between this example and Example 1 is that the weight of the catalyst is adjusted to 0.6 parts, while the rest is the same as Example 1.

[0074] Comparative Example 3

[0075] This comparative example provides a polyurethane composite material, its preparation method, and its application. The only difference between this example and Example 1 is that the screening in step (1) is adjusted to screen out natural fiber powder with a length of 2000-2100 μm. Otherwise, it is the same as Example 1.

[0076] Comparative Example 4

[0077] This comparative example provides a polyurethane composite material, its preparation method, and its application. The only difference between this example and Example 1 is that the thickness of the first coating in the preparation method of polyurethane synthetic leather is adjusted to 3 mm, while the rest is the same as Example 1.

[0078] The polyurethane synthetic leather provided in the above embodiments and comparative examples was tested using the following specific test methods:

[0079] Peel strength: Tested in accordance with GB / T 3903.3-2011.

[0080] Rub test: Rub the polyurethane synthetic leather together and listen to the sound it makes to test whether there is any sound when rubbing.

[0081] The test results are shown in Table 1 below:

[0082] Table 1. Physical properties of polyurethane synthetic leather

[0083]

[0084] As shown in Table 1, the polyurethane synthetic leather provided in Examples 1-5 is silent when rubbed together and has a peel strength of 63-110N.

[0085] Compared to Example 1, if the percentage of natural fiber powder to polyurethane resin is too high (Example 5), the surface of the polyurethane synthetic leather becomes too rough and difficult to rub. If rubbing is intensified, the surface of the polyurethane synthetic leather is easily damaged. Therefore, it can be seen that when the percentage of natural fiber powder to polyurethane resin in this invention is within a specific range, the polyurethane synthetic leather prepared has better performance.

[0086] Compared with Example 1, if the mass concentration of alkali in the alkaline solution is too low (Comparative Example 1), there will be a sound when rubbing and the peel strength will be reduced. This is because if the mass concentration of alkali in the alkaline solution is too low, the non-cellulose compounds in the rice straw cannot be removed, which will affect the physical properties of the polyurethane synthetic leather produced.

[0087] Compared with Example 1, if the weight fraction of the catalyst is too large (Comparative Example 2), there will be a sound when rubbing and the peel strength will be reduced. This is because if the weight fraction of the catalyst is too large, the reaction to produce polyurethane resin will be too fast, which will easily produce a variety of side reactions and thus affect the physical properties of the polyurethane synthetic leather.

[0088] Compared with Example 1, if the particle size of the natural fiber powder is too large (Comparative Example 3), it will affect the physical properties of the obtained polyurethane synthetic leather, making a sound when rubbed and reducing the peel strength.

[0089] Compared with Example 1, if the thickness of the first coating is too large (Comparative Example 4), there will be a sound when rubbing and the peel strength will be reduced. This is because the thickness of the first coating is too large, which affects the curing of the polyurethane composite material. The curing is incomplete, which in turn affects the physical properties of the polyurethane synthetic leather.

[0090] The applicant declares that the present invention illustrates a polyurethane composite material, its preparation method, and its application through the above embodiments. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A polyurethane synthetic leather, characterized by, The polyurethane synthetic leather is prepared from a polyurethane composite material, which includes polyurethane resin and natural fiber powder. The raw materials for preparing the polyurethane resin include the following components by weight: 30-50 parts of polyol, 30-60 parts of isocyanate, 2-8 parts of plasticizer, 0.01-0.3 parts of catalyst, and 0.5-4 parts of water. The particle size of the natural fiber powder is 400-900 μm; The natural fiber powder accounts for 5% to 20% of the mass of the polyurethane resin. The polyurethane composite material is prepared by the following method, which includes the following steps: (1) Natural fibers are treated with alkali and ground to obtain natural fiber powder; (2) Mix the polyurethane resin and the natural fiber powder obtained in step (1) to obtain a polyurethane composite material; The mass concentration of alkali in the alkaline solution in step (1) is 5 wt%-20 wt%, the alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution, and the natural fiber includes rice straw; The polyurethane synthetic leather is prepared by the following method, which includes the following steps: first coating the surface of release paper with polyurethane composite material, drying, second coating with polyurethane composite material, attaching a base fabric, pressing, and drying again to obtain the polyurethane synthetic leather; The thickness of the first coating is 1~2 mm; The thickness of the second coating is 0.1~0.5 mm; The drying and re-drying temperatures are each independently 90~140℃, and the times are each independently 10~30 min.

2. The polyurethane synthetic leather according to claim 1, characterized in that, The polyols include any one or a combination of at least two of the following: polypropylene ether diol, polytetrahydrofuran ether diol, polybutylene adipate diol, or polyethylene adipate diol.

3. The polyurethane synthetic leather according to claim 1, characterized in that, The weight-average molecular weight of the polyol is 1000~4000.

4. The polyurethane synthetic leather according to claim 1, characterized in that, The isocyanate includes any one or a combination of at least two of diphenylmethane diisocyanate, toluene diisocyanate, or isophorone diisocyanate.

5. The polyurethane synthetic leather according to claim 4, characterized in that, The diphenylmethane diisocyanate includes diphenylmethane-4,4'-diisocyanate.

6. The polyurethane synthetic leather according to claim 1, characterized in that, The plasticizer includes any one or a combination of at least two of the following: silicone softener, castor oil, epoxidized soybean oil, or epoxidized butyl furfuryl oleate.

7. The polyurethane synthetic leather according to claim 1, characterized in that, The catalyst comprises any one or a combination of at least two of N-ethylmorpholine, organobismuth, dibutyltin dilaurate, or triethanolamine.

8. The polyurethane synthetic leather according to claim 1, characterized in that, The temperature for the alkaline treatment is 0~50℃.

9. The polyurethane synthetic leather according to claim 1, characterized in that, The alkaline treatment time is 10-60 minutes.

10. The polyurethane synthetic leather according to claim 1, characterized in that, The alkaline treatment also includes water washing and drying steps.

11. The polyurethane synthetic leather according to claim 10, characterized in that, The drying temperature is 30~80℃, and the drying time is 10~24 h.

12. The polyurethane synthetic leather according to claim 1, characterized in that, The preparation method of the polyurethane resin includes the following steps: mixing polyol, isocyanate, plasticizer, catalyst and water, reacting to obtain the polyurethane resin.

13. A method for preparing polyurethane synthetic leather according to any one of claims 1-12, characterized in that, The preparation method includes the following steps: first coating the surface of the release paper with polyurethane composite material, drying, second coating with polyurethane composite material, attaching the base fabric, pressing, and drying again to obtain the polyurethane synthetic leather; The thickness of the first coating is 1~2 mm; The thickness of the second coating is 0.1~0.5 mm; The drying and re-drying temperatures are each independently 90~140℃, and the times are each independently 10~30 min.

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