Preparation method of polyurethane synthetic leather with high air permeability

Abstract

The invention discloses a preparation method of polyurethane synthetic leather with high air permeability, and belongs to the technical field of polyurethane synthetic leather, the preparation method comprises the following steps: S1, uniformly mixing and stirring waterborne polyurethane resin, a foaming agent, a chain extender, an antioxidant, an antibacterial agent and a toughening filler to obtain a core layer mixed solution; s2, uniformly mixing and stirring isocyanate, polyether polyol, dimethylformamide, a plasticizer, a catalyst and a wear-resistant filler to obtain a surface layer mixed solution; s3, uniformly coating the surface of one layer of breathable film with the core layer mixed liquid, and then covering the surface of the core layer mixed liquid with the other layer of breathable film, wherein the core layer mixed liquid and the two layers of breathable films jointly form a sandwich structure; s4, uniformly coating two surfaces of the sandwich structure with the surface layer mixed solution, heating for reaction, keeping the temperature for a period of time after the reaction is finished, cooling, and taking out to obtain the polyurethane synthetic leather; the polyurethane synthetic leather provided by the invention has good air permeability.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane synthetic leather, and in particular to a method for preparing polyurethane synthetic leather with high air permeability. Background Art

[0002] Natural leather, also known as genuine leather, is a natural polymer material obtained from animal skin after physical and chemical processing such as depilation and tanning. It is widely used in footwear, furniture and other fields due to its softness, comfort, durability and breathability. Since genuine leather is produced from animal epidermis and its output is limited, it cannot meet the growing needs of mankind. Therefore, synthetic leather is often used to replace natural leather. However, some synthetic leathers currently have defects such as poor air permeability and poor softness. After synthetic leather is made into footwear, furniture and other products, synthetic leather with poor air permeability can easily cause users to feel stuffy during use, and water vapor can easily accumulate inside the product, leading to bacterial growth and reduced product durability. Especially in the field of footwear, footwear with poor air permeability can cause stuffiness, and synthetic leather with poor softness can affect the comfort of the product.

[0003] Based on the above situation, a Chinese patent with announcement number CN113186731A discloses a high-elastic PU synthetic leather structure and its preparation process, wherein the synthetic leather comprises a base fabric, a spray layer and a transparent film, wherein the spray layer and the transparent film each comprise two layers, the two spray layers are respectively disposed on the upper side and the lower side of the base fabric, the spray layer is disposed between the base fabric and the transparent film, and the base fabric and the transparent film are both adhered to the spray layer; the above synthetic leather has good elasticity and can improve the comfort of the product to a certain extent, but the surface of the synthetic leather is covered with a transparent film, and the transparent film has relatively good density, which affects the penetration of gas molecules such as water vapor into the synthetic leather, resulting in poor air permeability of the synthetic leather. After the synthetic leather is used as a shoe material, furniture and other products, the product is likely to cause the user to feel stuffy during use, and water vapor is likely to accumulate inside the product, resulting in bacterial growth and reduced product durability, so the synthetic leather still has room for improvement. Summary of the invention

[0004] In view of the technical defects existing in the background technology, the present invention proposes a method for preparing a polyurethane synthetic leather with high air permeability, which solves the above technical problems and meets the actual needs. The specific technical scheme is as follows: A method for preparing a highly breathable polyurethane synthetic leather comprises the following steps: S1, mixing and stirring the waterborne polyurethane resin, the foaming agent, the chain extender, the antioxidant, the antibacterial agent, and the toughening filler to obtain a core layer mixed liquid; S2, mixing isocyanate, polyether polyol, dimethylformamide, plasticizer, catalyst, and wear-resistant filler to obtain a surface layer mixed liquid; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of breathable film, another layer of breathable film is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of breathable film together form a sandwich structure; S4, evenly coating the surface layer mixture on both sides of the sandwich structure and then heating to react, keeping the mixture warm for a period of time after the reaction is completed, cooling and taking it out to obtain a polyurethane synthetic leather; In step S4, the core layer mixed liquid reacts to form a core layer foam, and the surface layer mixed liquid reacts to form a surface layer leather. The polyurethane synthetic leather is composed of surface layer leather, breathable film, core layer foam, breathable film, and surface layer leather in sequence in the thickness direction.

[0005] As a further technical solution of the present invention, in step S1, the core layer mixed liquid includes the following components in mass percentage: 85%~93% of waterborne polyurethane resin, 1%~2% of foaming agent, 1%~4% of chain extender, 0.1%~1% of antioxidant, 1%~3% of antibacterial agent, and 2%~5% of toughening filler.

[0006] As a further technical solution of the present invention, the chain extender is selected from one or more of ethylene glycol, propylene glycol, ethylenediamine, and isophoronediamine; and the foaming temperature of the foaming agent is 80-100°C.

[0007] As a further technical solution of the present invention, the antioxidant is selected from one or more of antioxidant (1010), antioxidant (1076), and antioxidant (1135).

[0008] As a further technical solution of the present invention, the antibacterial agent is selected from one or more of inorganic silver ion antibacterial agents, inorganic zinc ion antibacterial agents, pyridine antibacterial agents, and quaternary ammonium salt antibacterial agents.

[0009] As a further technical solution of the present invention, the toughening filler is selected from one or more of micron-sized calcium carbonate, micron-sized silicon dioxide, micron-sized talc, micron-sized titanium dioxide, and micron-sized barium sulfate.

[0010] As a further technical solution of the present invention, in step S2, the surface layer mixed liquid includes the following components in mass percentage: 40%~55% isocyanate, 20%~30% polyether polyol, 15%~25% dimethylformamide, 0.5%~1% plasticizer, 0.1%~0.5% catalyst, and 2%~5% wear-resistant filler.

[0011] As a further technical solution of the present invention, the plasticizer is selected from one of diallyl succinate, dibutyl phthalate, dibutyl phthalate, and polysiloxane.

[0012] As a further technical solution of the present invention, the wear-resistant filler is selected from one or more of nylon fiber, aramid fiber and polyester fiber.

[0013] As a further technical solution of the present invention, in step S4, the heating temperature is 90-120°C, and the insulation temperature is 50-80°C.

[0014] The beneficial effects of the present invention are: The polyurethane synthetic leather of the present invention is provided with a core layer foam body inside, which can make the inside of the polyurethane synthetic leather more elastic and softer, and is conducive to improving the use comfort of the polyurethane synthetic leather. The core layer foam body is formed by wrapping the core layer mixed liquid with two layers of breathable films and heating and foaming. During the heating and foaming process, the molding reactions of the two surface leathers are carried out simultaneously. The gas generated by the foaming agent during foaming will carry moisture to form water vapor that penetrates the breathable film to promote the foaming of the surface layer mixed liquid, so that a certain pore structure is formed inside the surface leather. The water vapor can also make the surface leather form more microporous structures, thereby improving the air permeability of the polyurethane synthetic leather. DETAILED DESCRIPTION

[0015] The implementation mode of the present invention is described below in conjunction with relevant embodiments. The implementation mode of the present invention is not limited to the following embodiments, and the present invention relates to relevant necessary components in the technical field, which should be regarded as the known technology in the technical field and can be known and mastered by the technical personnel in the technical field.

[0016] A method for preparing a highly breathable polyurethane synthetic leather comprises the following steps: S1, mixing and stirring the waterborne polyurethane resin, the foaming agent, the chain extender, the antioxidant, the antibacterial agent, and the toughening filler to obtain a core layer mixed liquid; S2, mixing isocyanate, polyether polyol, dimethylformamide, plasticizer, catalyst, and wear-resistant filler to obtain a surface layer mixed liquid; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of breathable film, another layer of breathable film is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of breathable film together form a sandwich structure; S4, evenly coating the surface layer mixture on both sides of the sandwich structure and then heating to react, keeping the mixture for a period of time after the reaction is completed, cooling and taking out to obtain the polyurethane synthetic leather; In step S4, the core layer mixed liquid reacts to form a core layer foam, and the surface layer mixed liquid reacts to form a surface layer leather. The polyurethane synthetic leather is composed of the surface layer leather, the breathable film, the core layer foam, the breathable film, and the surface layer leather in the thickness direction.

[0017] The polyurethane synthetic leather produced by the present invention has good air permeability, in order to solve the defect of insufficient air permeability of some current polyurethane synthetic leathers, and the polyurethane synthetic leather of the present invention has good softness and elasticity, the shoes, furniture and other products produced by the polyurethane synthetic leather can avoid the feeling of stuffiness during use through good air permeability, and provide users with a soft and elastic touch, thereby improving the comfort of the products.

[0018] Regarding the preparation method of the polyurethane synthetic leather of the present invention, in step S1, the core layer mixed liquid includes the following components by mass percentage: 85%~93% of waterborne polyurethane resin, 1%~2% of foaming agent, 1%~4% of chain extender, 0.1%~1% of antioxidant, 1%~3% of antibacterial agent, and 2%~5% of toughening filler; in addition to the polyurethane resin, the waterborne polyurethane resin also includes but is not limited to the following components: isocyanate, oligomer polyol, crosslinking agent, solvent, thickener, film-forming aid, the waterborne polyurethane resin has a coating property similar to that of the coating, and the core layer mixed liquid obtained by mixing and stirring the waterborne polyurethane resin with the foaming agent, chain extender, antioxidant, antibacterial agent, and toughening filler has similar coating properties. After the core layer mixed liquid is coated on the surface of an appropriate substrate, the components in the waterborne polyurethane resin can be reacted by heating and foamed under the action of the foaming agent, thereby forming a core layer foam.

[0019] In step S2, the surface layer mixture includes the following components in percentage by mass: 40% to 55% isocyanate, 20% to 30% polyether polyol, 15% to 25% dimethylformamide, 0.5% to 1% plasticizer, 0.1% to 0.5% catalyst, and 2% to 5% wear-resistant filler; after the surface layer mixture is coated on the surface of an appropriate substrate, the isocyanate and the polyether polyol can react to form polyurethane molecules under the combined action of heating and a catalyst, wherein the catalyst is preferably stannous octoate, and during the reaction, the isocyanate can react with water molecules in the environment to generate carbon dioxide gas, thereby initiating the formation of foam so that the polyurethane molecules form a stable three-dimensional network structure, thereby forming a surface layer leather, and dimethylformamide is used as a solvent in the surface layer mixture to dissolve the components to form a uniform solution system, and dimethylformamide can form a film on the surface of the surface layer leather, making the surface of the surface layer leather smooth, waterproof, breathable and having good mechanical strength.

[0020] In step S3, the breathable membrane is preferably a polytetrafluoroethylene elastic breathable membrane. When the elastic breathable membrane is stretched by an external force, the pore size of the air permeable structure on its surface will increase, which can improve the gas passage efficiency. Polytetrafluoroethylene is a high-temperature resistant material. The breathable membrane made of polytetrafluoroethylene can maintain stable performance in an environment above 200°C. The sandwich structure wraps the core layer mixed liquid inside with two layers of breathable membranes, which is convenient for the subsequent isolation of the core layer mixed liquid and the surface layer mixed liquid through the breathable membrane, so that the core layer mixed liquid and the surface layer mixed liquid react separately in a heated environment to avoid mixing of the components of the two and affecting the normal reaction. The breathable membrane serves as a carrier for connecting the core layer foam and the surface layer leather inside the polyurethane synthetic leather, and has a plurality of breathable micropores on its surface, which can ensure that the gas penetrates the polyurethane synthetic leather normally, thereby ensuring the breathability of the polyurethane synthetic leather.

[0021] In step S4, the surface layer mixture is evenly coated on both sides of the sandwich structure to form a five-layer structure consisting of the surface layer mixture, the breathable film, the core layer mixture, the breathable film, and the surface layer mixture in the thickness direction. The five-layer structure is placed in a sealed space and heated to 90-120°C to make the core layer mixture and the surface layer mixture react respectively. The core layer mixture reacts between the two layers of breathable film to form a polyurethane molecular chain. Since the foaming temperature of the foaming agent is 80-100°C, the foaming agent will decompose to generate gas to form a three-dimensional structure of the polyurethane molecular chain, and in the reaction process, the chain is extended. The agent increases the molecular weight of polyurethane and improves the strength of the core layer foam after foaming. The core layer mixture undergoes a high-rate foaming reaction under the action of the foaming agent. The core layer foam after foaming has a rich pore structure. The core layer foam can improve the softness and elasticity of the polyurethane synthetic leather and improve the comfort of use of the polyurethane synthetic leather. When the polyurethane synthetic leather is squeezed by external force, the gas inside the core layer foam will be squeezed into the surface leather through the surface of the breathable film, and air can circulate between the surface leather and the external environment, thereby improving the breathability of the polyurethane synthetic leather.

[0022] Furthermore, the five-layer structure is placed horizontally and suspended in a sealed space for reaction. A certain amount of gas will be generated during the foaming reaction of the core layer mixed liquid. In a high-temperature environment, these gases will carry the moisture in the water-based polyurethane resin to form water vapor. Part of the water vapor will move toward the surface layer mixed liquid on the upper surface through the air permeable holes of the breathable membrane. The water vapor provides moisture for the surface layer mixed liquid reaction as a foaming agent, thereby foaming to form a surface layer leather with a certain foaming ratio. The surface layer leather is set as the upper layer leather, and the surface layer mixed liquid on the lower surface is foamed by the water vapor in the sealed environment. A small amount of water vapor that penetrates the breathable membrane and moves downward is used as a foaming agent to foam, thereby forming a surface leather with a lower foaming ratio, and the surface leather is set as the lower leather; the foaming ratio of the lower leather is lower than that of the upper leather, the pore structure inside the upper leather is richer and has better softness and elasticity, and more water vapor will penetrate the breathable membrane and enter the surface mixed liquid during the formation of the upper leather, so that the film on the surface of the upper leather can form more microporous structures and have better air permeability, while the internal structure of the lower leather is tighter, and its mechanical strength and the waterproofness of the surface film are better.

[0023] It should be further explained that the above five-layer structure is heated to 90-120°C for reaction, and the heating is used to promote the reaction of the core layer mixed liquid and the surface layer mixed liquid respectively, and ensure that the foaming agent can foam normally during the reaction; the temperature for insulation after the reaction is 50-80°C, and the insulation process can ensure the complete reaction and make the structure of the polyurethane molecular chain more stable, thereby improving the durability of the polyurethane synthetic leather.

[0024] The upper layer of the polyurethane synthetic leather based on the above structure has better softness, elasticity and air permeability, so the upper layer of leather is usually used as the side in contact with the human body. For example, in shoes made of polyurethane synthetic leather, the upper layer of leather is located inside the shoe material, making the shoe material more comfortable and breathable to wear, while the lower layer of leather is located on the outer surface of the shoe material, making the shoe material more durable through good mechanical strength, and the better waterproofness of the lower layer of leather can also prevent external liquids from penetrating into the inside of the shoe material.

[0025] In summary, the polyurethane synthetic leather of the present invention is provided with a core layer foam body inside, which can make the inside of the polyurethane synthetic leather elastic and softer, and is conducive to improving the comfort of use of the polyurethane synthetic leather. The core layer foam body is formed by wrapping the core layer mixed liquid with two layers of breathable membranes and heating and foaming. During the heating and foaming process, the molding reactions of the two surface leathers are carried out simultaneously. The gas generated by the foaming agent during foaming will carry moisture to form water vapor that penetrates the breathable membrane to promote the foaming of the surface layer mixed liquid, so that a certain pore structure is formed inside the surface leather. The water vapor can also make the surface leather form more microporous structures, thereby improving the air permeability of the polyurethane synthetic leather.

[0026] As one of the preferred embodiments of the present invention, the chain extender is selected from one or more of ethylene glycol, propylene glycol, ethylenediamine, and isophoronediamine. The foaming ratio of the core layer foam is relatively high, which makes the internal structure relatively loose. The chain extender can chemically react with components such as isocyanate and polyether polyol in the polyurethane reaction system to quickly extend the chain and increase the length of the polyurethane molecular chain after the reaction, thereby improving the strength of the core layer foam and preventing the polyurethane synthetic leather from being easily torn and delaminated under the action of external force; ethylene glycol, propylene glycol, ethylenediamine, and isophoronediamine can all be used as chain extenders in the core layer foam reaction system to improve the flexibility, strength, aging resistance and other properties of the core layer foam.

[0027] As one of the preferred embodiments of the present invention, the antioxidant is selected from one or more of antioxidant (1010), antioxidant (1076), and antioxidant (1135). The antioxidant can prevent the core layer mixed liquid from being scorched during the reaction process, and can also improve the stability of the core layer foam in a high temperature environment, and prevent the core layer foam from undergoing oxidation reaction during storage or use, thereby ensuring the structural stability of the core layer foam. Antioxidant (1010), antioxidant (1076), and antioxidant (1135) can all be used as antioxidants for the core layer foam, which is beneficial for improving the stability of the internal structure of the polyurethane synthetic leather and improving the durability of the polyurethane synthetic leather.

[0028] As one of the preferred embodiments of the present invention, the antibacterial agent is selected from one or more of inorganic silver ion antibacterial agents, inorganic zinc ion antibacterial agents, pyridine antibacterial agents, and quaternary ammonium salt antibacterial agents. The core layer foam has a rich pore structure. When the polyurethane synthetic leather is circulated with the outside air, water vapor is easily retained inside the core layer foam, causing bacteria to breed and produce odor, and even causing the polyurethane synthetic leather to become moldy and cracked. The antibacterial agent improves the antibacterial properties of the polyurethane synthetic leather by killing bacteria and preventing bacteria from multiplying inside the core layer foam; inorganic silver ion antibacterial agents, inorganic zinc ion antibacterial agents, pyridine antibacterial agents, and quaternary ammonium salt antibacterial agents can all be used as antibacterial agents for the core layer foam, which can improve the safety of products made of polyurethane synthetic leather.

[0029] As one of the preferred embodiments of the present invention, the toughening filler is selected from one or more of micron-sized calcium carbonate, micron-sized silicon dioxide, micron-sized talc, micron-sized titanium dioxide, and micron-sized barium sulfate. The foaming ratio of the core layer foam is relatively high, which makes the internal structure relatively loose. The toughening filler can increase the mechanical strength, toughness and other properties of the core layer foam, and prevent the polyurethane synthetic leather from being easily torn and delaminated under the action of external force; micron-sized calcium carbonate, micron-sized silicon dioxide, micron-sized talc, micron-sized titanium dioxide, and micron-sized barium sulfate can all be used as toughening fillers for the core layer foam, which is beneficial to improving the flexibility and durability of the polyurethane synthetic leather.

[0030] As one of the preferred embodiments of the present invention, the plasticizer is selected from one of dipropylene succinate, dibutyl phthalate, dibutyl phthalate, and polysiloxane. The plasticizer can improve the flexibility and processing performance of the surface leather, so that the surface leather can withstand long-term bending, extrusion and other usage environments and maintain structural stability, and make the surface leather have a better touch as a human body contact surface; dipropylene succinate, dibutyl phthalate, dibutyl phthalate, and polysiloxane can all be used as plasticizers for the surface leather, which is beneficial to improving the durability and comfort of polyurethane synthetic leather.

[0031] As one of the preferred embodiments of the present invention, the wear-resistant filler is selected from one or more of nylon fiber, aramid fiber, and polyester fiber. The surface leather serves as the surface structure of the polyurethane synthetic leather. The wear-resistant filler can increase the wear resistance of the surface leather. The wear-resistant filler adopts fibrous material. The internal structure of the surface leather is interconnected through the fiber material, so that the surface leather is not prone to peeling, cracking, etc. under the action of external force, and the surface leather has higher mechanical strength. Nylon fiber, aramid fiber, and polyester fiber can all be used as wear-resistant fillers for the surface leather, which is beneficial to improving the wear resistance and durability of the polyurethane synthetic leather.

[0032] The present invention is further described below by way of examples and comparative examples.

[0033] Example 1

[0034] S1, mixing 88.5% of waterborne polyurethane resin, 1% of foaming agent, 4% of ethylene glycol, 0.5% of antioxidant (1010), 2% of inorganic silver ion antibacterial agent, and 4% of micron-grade calcium carbonate in percentage by mass and stirring to obtain a core layer mixed solution; S2, mixing 43% of isocyanate, 30% of polyether polyol, 21% of dimethylformamide, 0.8% of dipropylene succinate, 0.2% of stannous octoate, and 5% of nylon fiber by mass and stirring to obtain a surface layer mixture; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of polytetrafluoroethylene elastic breathable membrane, another layer of polytetrafluoroethylene elastic breathable membrane is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of polytetrafluoroethylene elastic breathable membrane together form a sandwich structure; S4. The surface layer mixture is evenly coated on both sides of the sandwich structure and then gradually heated to 100°C for reaction. After the reaction is completed, the mixture is kept at 60°C for a period of time and then cooled to obtain a polyurethane synthetic leather.

[0035] Example 2

[0036] S1, mixing 89% of waterborne polyurethane resin, 1.5% of foaming agent, 3% of ethylene glycol, 0.5% of antioxidant (1010), 2% of inorganic silver ion antibacterial agent, and 4% of micron-grade calcium carbonate in percentage by mass and stirring to obtain a core layer mixed solution; S2, mixing 49% of isocyanate, 25% of polyether polyol, 21.5% of dimethylformamide, 0.8% of dipropylene succinate, 0.2% of stannous octoate, and 3.5% of nylon fiber by mass and stirring to obtain a surface layer mixture; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of polytetrafluoroethylene elastic breathable membrane, another layer of polytetrafluoroethylene elastic breathable membrane is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of polytetrafluoroethylene elastic breathable membrane together form a sandwich structure; S4. The surface layer mixture is evenly coated on both sides of the sandwich structure and then gradually heated to 100°C for reaction. After the reaction is completed, the mixture is kept at 60°C for a period of time and then cooled to obtain a polyurethane synthetic leather.

[0037] Example 3

[0038] S1, mixing 89.5% of waterborne polyurethane resin, 2% of foaming agent, 3% of ethylene glycol, 0.5% of antioxidant (1010), 2% of inorganic silver ion antibacterial agent, and 3% of micron-grade calcium carbonate in percentage by mass and stirring to obtain a core layer mixed solution; S2, mixing 55% of isocyanate, 20% of polyether polyol, 22% of dimethylformamide, 0.8% of dipropylene succinate, 0.2% of stannous octoate, and 2% of nylon fiber by mass and stirring to obtain a surface layer mixture; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of polytetrafluoroethylene elastic breathable membrane, another layer of polytetrafluoroethylene elastic breathable membrane is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of polytetrafluoroethylene elastic breathable membrane together form a sandwich structure; S4. The surface layer mixture is evenly coated on both sides of the sandwich structure and then gradually heated to 100°C for reaction. After the reaction is completed, the mixture is kept at 60°C for a period of time and then cooled to obtain a polyurethane synthetic leather.

[0039] Comparative Example 1 S1, mixing and stirring 95% of waterborne polyurethane resin, 1.5% of foaming agent, 1% of ethylene glycol, 0.5% of antioxidant (1010), and 2% of inorganic silver ion antibacterial agent in percentage by mass to obtain a core layer mixed solution; S2, mixing 49% of isocyanate, 25% of polyether polyol, 21.5% of dimethylformamide, 0.8% of dipropylene succinate, 0.2% of stannous octoate, and 3.5% of nylon fiber by mass and stirring to obtain a surface layer mixture; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of polytetrafluoroethylene elastic breathable membrane, another layer of polytetrafluoroethylene elastic breathable membrane is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of polytetrafluoroethylene elastic breathable membrane together form a sandwich structure; S4. The surface layer mixture is evenly coated on both sides of the sandwich structure and then gradually heated to 100°C for reaction. After the reaction is completed, the mixture is kept at 60°C for a period of time and then cooled to obtain a polyurethane synthetic leather.

[0040] Comparative Example 2 S1, mixing 89% of waterborne polyurethane resin, 1.5% of foaming agent, 3% of ethylene glycol, 0.5% of antioxidant (1010), 2% of inorganic silver ion antibacterial agent, and 4% of micron-grade calcium carbonate in percentage by mass and stirring to obtain a core layer mixed solution; S2, mixing 49% of isocyanate, 25% of polyether polyol, 21.5% of dimethylformamide, 0.8% of dipropylene succinate, 0.2% of stannous octoate, and 3.5% of nylon fiber by mass and stirring to obtain a surface layer mixture; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of polytetrafluoroethylene film, another layer of polytetrafluoroethylene film is covered on the surface of the core layer mixed liquid, the core layer mixed liquid and the two layers of polytetrafluoroethylene film together form a sandwich structure, wherein the polytetrafluoroethylene film adopts a non-breathable film structure; S4. The surface layer mixture is evenly coated on both sides of the sandwich structure and then gradually heated to 100°C for reaction. After the reaction is completed, the mixture is kept at 60°C for a period of time and then cooled to obtain a polyurethane synthetic leather.

[0041] The polyurethane synthetic leathers obtained in all the above examples and comparative examples were tested for air permeability, moisture permeability, breaking strength, elongation, and peel strength. The test results are shown in Table 1 below:

[0042] Table 1 The data in Table 1 are explained. The air permeability and moisture permeability mainly test the efficiency of gas, water vapor and other molecules penetrating the polyurethane synthetic leather. The polyurethane synthetic leather with higher air permeability and moisture permeability can better circulate with the outside air during use, and can better discharge moisture, thereby reducing the stuffiness during use of the product made of the polyurethane synthetic leather. The breaking strength and peeling strength mainly test the mechanical strength of the polyurethane synthetic leather. The polyurethane synthetic leather with higher breaking strength and peeling strength has better durability. The breaking strength of the polyurethane synthetic leather is mainly affected by the mechanical properties of the surface leather, while the peeling strength is mainly affected by the mechanical properties of the core foam. The elongation mainly tests the flexibility and elasticity of the polyurethane synthetic leather. Good flexibility and elasticity can provide users with better touch and improve the comfort of the product made of the polyurethane synthetic leather during use.

[0043] Analyzing the data in Table 1, in Examples 1-3, the air permeability and moisture permeability are mainly affected by the amount of foaming agent added in the core layer mixture, because when the amount of foaming agent added increases, more gas will be produced during the reaction, thereby increasing the foaming ratio of the core layer foam and the surface leather, and forming more microporous structures in the surface leather; the breaking strength and elongation are mainly affected by the addition ratio of isocyanate to polyether polyol in the core layer mixture, wherein the higher the amount of isocyanate added, the higher the breaking strength of the surface leather, and the higher the amount of polyether polyol added, the higher the softness of the surface leather, thereby having a higher elongation; the peel strength is mainly affected by the mechanical strength of the core layer foam, wherein the higher the amount of ethylene glycol as a chain extender and the nano-scale calcium carbonate as a toughening filler added, the higher the mechanical strength of the core layer foam can be.

[0044] Comparative Example 1 is based on Example 2, and the amount of chain extender added in the core layer mixed liquid is reduced and the toughening filler is eliminated, so that the fracture strength of the polyurethane synthetic leather in Comparative Example 1 is reduced to a certain extent, and the peel strength is significantly reduced; Comparative Example 2 is based on Example 2, and the polytetrafluoroethylene elastic breathable membrane is replaced with a polytetrafluoroethylene film, so that the water vapor generated by the foaming agent during the reaction is difficult to penetrate the polytetrafluoroethylene film into the surface layer mixed liquid, so that the foaming ratio of the surface layer leather is reduced, thereby making the internal structure of the surface layer leather more compact. Therefore, the fracture strength of the polyurethane synthetic leather in Comparative Example 2 is improved to a certain extent, while the elongation is reduced to a certain extent, and the polytetrafluoroethylene film has a significant effect of isolating the polyurethane synthetic leather from the outside world, resulting in a significant reduction in the air permeability and moisture permeability of the polyurethane synthetic leather. It can be seen that the use comfort of the polyurethane synthetic leather is poor.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a highly breathable polyurethane synthetic leather, characterized in that: The following steps are involved: S1, mixing and stirring the waterborne polyurethane resin, the foaming agent, the chain extender, the antioxidant, the antibacterial agent, and the toughening filler to obtain a core layer mixed liquid; S2, mixing isocyanate, polyether polyol, dimethylformamide, plasticizer, catalyst, and wear-resistant filler to obtain a surface layer mixed liquid; S3, after the core layer mixed liquid is evenly coated on the surface of a layer of breathable film, another layer of breathable film is covered on the surface of the core layer mixed liquid, and the core layer mixed liquid and the two layers of breathable film together form a sandwich structure; S4, evenly coating the surface layer mixture on both sides of the sandwich structure and then heating to react, keeping the mixture warm for a period of time after the reaction is completed, cooling and taking it out to obtain a polyurethane synthetic leather; In step S4, the core layer mixed liquid reacts to form a core layer foam, and the surface layer mixed liquid reacts to form a surface layer leather. The polyurethane synthetic leather is composed of surface layer leather, breathable film, core layer foam, breathable film, and surface layer leather in sequence in the thickness direction.

2. The method for preparing a highly breathable polyurethane synthetic leather according to claim 1, characterized in that: In step S1, the core layer mixed liquid includes the following components by mass percentage: 85% to 93% of waterborne polyurethane resin, 1% to 2% of foaming agent, 1% to 4% of chain extender, 0.1% to 1% of antioxidant, 1% to 3% of antibacterial agent, and 2% to 5% of toughening filler.

3. The method for preparing a highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The chain extender is selected from one or more of ethylene glycol, propylene glycol, ethylenediamine, and isophoronediamine; the foaming temperature of the foaming agent is 80-100°C.

4. The method for preparing a highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The antioxidant is selected from one or more of antioxidant (1010), antioxidant (1076), and antioxidant (1135).

5. The method for preparing a highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The antibacterial agent is selected from one or more of inorganic silver ion antibacterial agents, inorganic zinc ion antibacterial agents, pyridine antibacterial agents, and quaternary ammonium salt antibacterial agents.

6. The method for preparing highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The toughening filler is selected from one or more of micron-sized calcium carbonate, micron-sized silicon dioxide, micron-sized talcum powder, micron-sized titanium dioxide, and micron-sized barium sulfate.

7. The method for preparing highly breathable polyurethane synthetic leather according to claim 1, characterized in that: In step S2, the surface layer mixture includes the following components in percentage by mass: 40% to 55% isocyanate, 20% to 30% polyether polyol, 15% to 25% dimethylformamide, 0.5% to 1% plasticizer, 0.1% to 0.5% catalyst, and 2% to 5% wear-resistant filler.

8. The method for preparing highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The plasticizer is selected from one of diallyl succinate, dibutyl phthalate, dibutyl phthalate and polysiloxane.

9. The method for preparing highly breathable polyurethane synthetic leather according to claim 1, characterized in that: The wear-resistant filler is selected from one or more of nylon fiber, aramid fiber and polyester fiber.

10. The method for preparing highly breathable polyurethane synthetic leather according to claim 1, characterized in that: In step S4, the heating temperature is 90-120°C, and the insulation temperature is 50-80°C.

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