Preparation method of fluoride-free hydrolysis-resistant knurling polyurethane synthetic leather

Abstract

The invention discloses a preparation method of fluorine-free hydrolysis-resistant knurling polyurethane synthetic leather, which comprises the following steps: preparing wet-process polyurethane resin for leather by adopting PTMG (polytetramethylene glycol) with proper polymerization degree as a chain extender through a pre-polymerization process, preparing soft hydrolysis-resistant wet-process polyurethane resin by adopting bio-based poly-farnesyl alcohol as a main raw material through an insufficient method, and preparing the fluorine-free hydrolysis-resistant knurling polyurethane synthetic leather by adopting a high-temperature-resistant wet-process polyurethane resin. The two components are matched to optimize and balance the embossing performance and the thickness retention rate, the finally obtained soft hydrolysis-resistant polyurethane synthetic leather product is soft and glutinous in hand feeling and good in hydrolysis resistance, the thickness reaches the standard, and embossing is clear and does not rebound; a fluorine-containing water repellent does not need to be added, and the method is simple in process, low in cost and energy consumption and excellent in product performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane synthetic leather, and specifically relates to a wet-process polyurethane resin for soft hydrolysis-resistant leather, a preparation method thereof, and an application in the preparation of fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather. Background Art

[0002] With the development of the economy, people's requirements for environmental protection have become increasingly strict. In February 2023, the European Chemicals Agency issued a proposal to restrict perfluoroalkyl and polyfluoroalkyl substances, which lays the foundation for the EU's approach to banning the production and import of more than 10,000 persistent chemicals. This restriction will have a significant impact on dozens of industries such as textiles, consumer cookware, and medical devices, requiring the replacement of these substances in thousands of products, or else facing the complete removal of the products from the market. Fluorine-containing substances can cause soil and drinking water pollution, and this pollution is persistent, bioaccumulative, and toxic, and cannot be decomposed even in waste incineration, and can only be burned at temperatures above 1000 °C.

[0003] In polyurethane synthetic leather products, sometimes in order to improve the hydrolysis resistance of the synthetic leather, a fluorine-containing water repellent is added to improve the service life of the synthetic leather. However, with the issuance of the EU ban, the related products of polyurethane synthetic leather enterprises have been severely impacted, so most manufacturers choose to switch to fluorine-free water repellents.

[0004] For example, patent document CN111057211A discloses a wet-process polyurethane resin for synthetic leather with high hydrolysis resistance and high peel strength and fluorine-free, and a preparation method thereof, which is composed of two components A and B in a weight ratio of 1:30 to 20. Component A includes: 36% to 50% of diphenylmethane-4,4-diisocyanate, 27% to 37% of castor oil, 6.5% to 10.5% of methanol, and 12% to 20% of N,N-dimethylformamide; Component B includes: 9% to 11% of diphenylmethane-4,4-diisocyanate, 5.5% to 7.5% of polytetrahydrofuran ether glycol, 1% to 2% of polypropylene glycol, 6% to 10% of polyester diol, 2% to 2.5% of ethylene glycol, and 70% to 73% of N,N-dimethylformamide; a polyurethane resin with a solid content of 45% to 50% is prepared. The polyurethane resin of this document has the characteristics of good film-forming property, good hydrolysis resistance, and high strength, and does not contain fluorine elements.

[0005] Patent document CN111926579A discloses a fluorine-free anti-siphon high-density synthetic leather and a production method thereof, in which a fluorine-free filler, water repellent, color paste, etc. are added during the preparation of the base.

[0006] Patent document CN118344934A discloses a bio-based fluorine-free water repellent for synthetic leather and its preparation method. By reacting a bio-based polyol with a special isocyanate, a multi-functional capped intermediate is obtained; then, the multi-functional capped intermediate is used to obtain a bio-based long carbon chain end extending outward through transesterification to obtain a bio-based fluorine-free water repellent. The water repellent in this document is fluorine-free and more easily degradable, with low carbon and environmental protection, meeting the concepts of green chemistry and renewable energy.

[0007] According to the existing literature search and as shown in the above literature, currently, fluorine-free polyurethane synthetic leather mainly focuses on high-density space leather. For example, patent document CN111057211A makes the polyurethane form a cross-linked network structure by adding multi-functional castor oil, and at the same time adds polyether polyol to further improve its hydrolysis resistance. The most crucial point is that the solid content of the polyurethane resin is made 45% - 50%, making the pores of the synthetic leather small enough. When the polyurethane synthetic leather is soaked in an aqueous solution of 10% NaOH for 24 hours, the lye is not easily permeated into the synthetic leather, which helps to improve its hydrolysis resistance. However, this method is commonly used in high peel strength shoe leather, such as all sports shoes are made by this method. This kind of synthetic leather has a high peel strength, a hard hand feeling, but poor embossing properties, and the elasticity of the synthetic leather is also not good.

[0008] In recent years, raw material suppliers in South Korea, Japan, and Germany have successively launched fluorine-free water repellents. However, through a large number of experiments, it has been proved that the water repellent effects of these fluorine-free water repellents are far inferior to those of fluorine-containing water repellents. In the same synthetic leather, when 0.5 parts of fluorine-containing water repellent are added, after soaking in alkali for 24 hours, the physical properties of the synthetic leather basically do not change. However, when 1.5 parts of fluorine-free water repellent are added, after soaking in alkali for 24 hours, the surface of the synthetic leather will completely rot. If the content of polyether polyol added to the polyurethane resin is too high, it is easy to cause a decrease in the peel strength of the synthetic leather, an increase in the pore size, and the synthetic leather is prone to surface rotting.

[0009] Almost all of the existing fluorine-free hydrolysis-resistant polyurethane synthetic leather is high-solid content (33% - 35% solid content) used on sports shoe leather, with a stiff hand feeling and unable to be embossed. Almost all of the existing soft and embossable resins are not hydrolysis-resistant, and even if they are hydrolysis-resistant, it is only after adding fluorine-containing water repellents. To meet the requirements of downstream customers, the present invention has developed a soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather and applied it to the field of ball leather to meet the specifications for export to Europe. After literature search and market research, there is no such type of synthetic leather on the market yet. Summary of the Invention

[0010] The object of the present invention is to provide a wet-process polyurethane resin for soft hydrolysis-resistant leather, its preparation method, and its application in the preparation of fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather. By introducing bio-based diols into the polyurethane resin and designing a reasonable reaction process and leather-making method, a polyurethane synthetic leather with a soft handfeel, good embossing performance, fluorine-free, and no change in physical properties after being soaked in 10% NaOH aqueous solution for 24 hours is prepared.

[0011] To achieve the above object, the technical solution of the present invention is as follows.

[0012] The first object of the present invention is to provide a soft hydrolysis-resistant wet-process polyurethane resin, which is made from the following raw materials by mass fraction: 16% - 28% of polyol A, 0.002% - 0.01% of antioxidant, 0.0002% - 0.001% of phosphoric acid, 2% - 15% of isocyanate A, 0.3% - 4% of chain extender A, 0.01% - 0.04% of methanol, 0.01% - 0.04% of anti-sticking and anti-reducing agent, and the balance is solvent;

[0013] The solid content of the soft hydrolysis-resistant wet-process polyurethane resin is 29% - 32%, and the viscosity is 27 - 35 cps / 25 °C (preferably 29 - 32 cps / 25 °C);

[0014] The polyol A is a bio-based polyol with a weight-average molecular weight of 2500 - 3500, or a combination of this bio-based polyol and one or more of polybutylene adipate diol, polycarbonate diol, and polytetrahydrofuran ether diol with a weight-average molecular weight of 1000 - 4000, wherein the bio-based polyol accounts for more than 65% of the total mass of the polyols; the bio-based polyol is formed by free radical polymerization of bio-based farnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) to form a linear chain polymer, with hydroxyl groups retained at both ends, and its structural formula is as follows:

[0015] HO-[CH2CH=C(CH3)CH2CH2CH2CH=C(CH3)CH2CH2CH2CH=C(CH3)]-CH2OH;

[0016] For example, the bio-based polyols Krasol F3000 polyol and Krasol F3100 polyol of Total CrayValley Company. This bio-based polyol has a multi-side chain structure, making the prepared polyurethane resin have good hydrophobicity, chemical resistance, elastic softness, and low-temperature performance of the synthetic polyurethane main resin; the bio-based source of the bio-based farnesol is Brazilian sandalwood;

[0017] The isocyanate A is at least one of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane-4,4-diisocyanate; the chain extender A is at least one of ethylene glycol, 1,4-butanediol, and neopentyl glycol;

[0018] The solvent is N,N-dimethylformamide and / or N,N-dimethylacetamide; the antioxidant is at least one of pentaerythritol ester antioxidants, such as antioxidant 1010 and antioxidant 618; the anti-sticking and viscosity-reducing auxiliary is malic acid or / and phthalic anhydride.

[0019] The preparation method of the soft hydrolysis-resistant wet-process polyurethane resin includes the following steps:

[0020] S1, Mix polyol A, part of isocyanate A, antioxidant, phosphoric acid, and part of the solvent evenly. The molar ratio R of cyanate group (-NCO) to hydroxyl group (-OH) is 0.2 - 0.9 (preferably 0.85); carry out a prepolymerization reaction at 70 - 80 °C. After the NCO value in the system is qualified, obtain polyurethane prepolymer A;

[0021] S2, Add chain extender A to polyurethane prepolymer A and stir evenly. Then add the remaining isocyanate A and the remaining solvent in batches for viscosity increase. After the viscosity of the system meets the standard, add methanol for capping, and then add the anti-sticking and viscosity-reducing auxiliary and stir evenly to obtain the soft hydrolysis-resistant wet-process polyurethane resin.

[0022] The second object of the present invention is to provide a wet-process polyurethane resin for leather, which is made of the following raw materials by mass fraction: polyol B 11% - 21%, antioxidant 0.002% - 0.01%, phosphoric acid 0.0002% - 0.001%, isocyanate B 1% - 10%, chain extender B 1% - 6%, methanol 0.01% - 0.04%, anti-sticking and viscosity-reducing auxiliary 0.01% - 0.04%, and the balance is solvent;

[0023] The solid content of the wet-process polyurethane resin for leather is 23% - 27% (preferably 25%), and the viscosity is 18 - 22 cps / 25 °C;

[0024] The polyol B is one or a combination of poly(tetrahydrofuran) glycol (PTMG), poly(butylene adipate) glycol (PBA), polypropylene glycol (PPG), and poly-modified propylene glycol with a molecular weight of 1000 - 4000; the poly-modified propylene glycol is one or a combination of EO-capped at the end (named PPG-1) and EO-embedded in the middle chain segment (named PPG-2);

[0025] The isocyanate B is one or a combination of more than one of 4,4-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane-4,4-diisocyanate (HMDI);

[0026] The chain extender B is polytetrahydrofuran diol with a weight average molecular weight of 220 to 230 (hereinafter simply referred to as PTMG-225); Through a large number of experiments, the applicant found that when using small molecule diols (such as ethylene glycol, butanediol, pentanediol, etc.) as chain extenders, due to their short molecular chains, the intermolecular force in the polyurethane molecular chain is relatively strong, and the crystallinity of the hard segment region is too strong, resulting in too high hardness and resilience of the resin, and poor embossing performance with unclear patterns; In this application, PTMG-225 with a slightly larger molecular weight is used as the chain extender, which weakens the crystallinity of the hard segment region of the polyurethane resin, reduces the hardness and resilience of the resin, and is beneficial to improving the embossing performance, with deep and non-rebounding patterns;

[0027] The solvent is N,N-dimethylformamide and / or N,N-dimethylacetamide; The antioxidant is at least one of pentaerythritol ester antioxidants, such as antioxidant 1010 and antioxidant 618; The anti-sticking and anti-adhesion aid is malic acid or / and phthalic anhydride.

[0028] The preparation method of the wet-process polyurethane resin for leather includes the following steps:

[0029] D1, Mix the polyol B, isocyanate B, antioxidant, phosphoric acid, and part of the solvent evenly, and the molar ratio R of the cyanate group (-NCO) to the hydroxyl group (-OH) is 1 to 1.1; Carry out a prepolymerization reaction at 70 to 80 °C, and after the viscosity of the system reaches 10 to 13 cps / 25 °C, obtain the polyurethane prepolymer B;

[0030] D2, Add the chain extender B to the polyurethane prepolymer B and stir evenly, then add the isocyanate in batches in small amounts many times to increase the viscosity, and add the solvent to dilute;

[0031] D3, When the viscosity of the system meets the standard, add methanol for end-capping, and then add the anti-sticking and anti-adhesion aid, and stir evenly to obtain the wet-process polyurethane resin for leather.

[0032] The third object of the present invention is to provide a preparation method of a fluorine-free, hydrolysis-resistant, and embossable polyurethane synthetic leather, including the following steps:

[0033] (1) Dissolve the soft hydrolysis-resistant wet-process polyurethane resin in a solvent to obtain an impregnating solution, impregnate a non-woven fabric, squeeze out the excess resin, and iron it to obtain a base fabric; (2) Mix the wet-process polyurethane resin for leather, the soft hydrolysis-resistant wet-process polyurethane resin, the solvent DMF, and a coloring agent evenly and defoam to obtain a coating material; (3) Coat the coating material on the surface of the base fabric obtained in step (1), and then place it in a coagulation bath for coagulation; (4) Wash and dry the base fabric;

[0034] In the said step (1), the mass ratio of the soft hydrolysis-resistant wet-process polyurethane resin to the solvent DMF is 1:(2 - 4); the extrusion thickness after impregnating the non-woven fabric is 0.4 - 0.8 mm; the moisture content of the base fabric is controlled at 30% - 50%.

[0035] In the said step (2), the mass ratio of the wet-process polyurethane resin for leather to the soft hydrolysis-resistant wet-process polyurethane resin is 1:9 - 2:3, the addition amount of the solvent DMF is 45% - 60% of the total mass of the two resins, and the addition amount of the coloring agent is 0.3% - 0.5% of the total mass of the two resins;

[0036] In the said step (3), the coating thickness of the mixed liquid on the surface of the base fabric is 1.6 - 2.2 mm, and the coagulation time is 15 - 20 min; the coagulation bath is a mixed liquid of DMF and water, and the DMF concentration is 20% - 25%.

[0037] In the said step (4), the drying temperature of the base fabric is 90 - 120 °C.

[0038] The present invention also provides a fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather prepared by the above method. The fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather can be directly embossed, and it can be hot-pressed for 5 - 10 s at 160 - 180 °C and 0.35 - 0.7 MPa using a low-temperature embossing machine. The preferred embossing conditions are hot-pressing for 6 s at 165 °C and 0.48 MPa.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] The wet-process polyurethane resin for leather of the present invention is prepared by a prepolymerization process using PTMG with an appropriate degree of polymerization as a chain extender, and has strong crystallinity and a low foaming rate, but has a poor embossing effect; while the soft and hydrolysis-resistant wet-process polyurethane resin is prepared by the under-amount method using polyfarnesol with a multi-side chain structure, has a soft and fleshy feel, a good foaming effect, is easy to emboss, but has a high thickness loss rate. For example, it is easy to press a 20-mm thick synthetic leather into a 12-mm thick one; however, by impregnating the base fabric with the soft and hydrolysis-resistant wet-process polyurethane resin and then scraping and coating the surface layer with a combination of it and the wet-process polyurethane resin for leather, the embossing performance and thickness retention rate can be optimized and balanced. The finally obtained soft and hydrolysis-resistant polyurethane synthetic leather product not only has a soft and glutinous feel and good hydrolysis resistance, but also has a qualified thickness and clear embossing without rebound; it does not require the addition of a fluorine-containing water repellent and can meet the environmental protection specifications for the export of polyurethane synthetic leather to the European Union. The method of the present invention has a simple process, low cost and energy consumption, excellent product performance, and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 are synthetic leather samples prepared in Examples 1 to 3.

[0042] Figure 2 are synthetic leather samples prepared in Comparative Examples 1, 2 and 6.

[0043] Figure 3 are synthetic leathers prepared in Comparative Examples 3 and 5.

[0044] Figure 4 is the pulverization of the synthetic leather prepared in Comparative Example 4 after 24-hour hydrolysis resistance test.

[0045] Figure 5 is a picture of a qualified fluorine-free hydrolysis-resistant synthetic leather after 24-hour hydrolysis resistance test. DETAILED DESCRIPTION OF THE INVENTION

[0046] Those of ordinary skill in the art in this technical field should recognize that this embodiment is only used to illustrate the present invention and is not used to limit the present invention. As long as changes and variations are made to the embodiment within the scope of the implementation of the present invention, they can be within the scope of the claims of the present invention.

[0047] The raw materials used in the following examples and comparative examples of the present invention are as follows:

[0048] Example 1

[0049] Preparation of wet-process polyurethane resin for leather: S1. Put 190 parts of PTMG-1000 (parts by mass, the same below), 190 parts of PBA-2000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 397 parts of solvent DMF into a four-necked flask. Connect a mechanical stirrer and a thermocouple to the flask mouth and stir evenly. S2. Put 49.6 parts of isocyanate TDI into the reaction flask, heat up to 70 °C, and the reaction increases viscosity until the resin viscosity is 10 cps / 25 °C. S3. Add 363 parts of DMF and 70.76 parts of PTMG-225 to the reaction flask, stir evenly, and then add 78.6 parts of isocyanate MDI. Continuously dilute with DMF as the viscosity increases. The amount of diluted DMF used is 978 parts. S4. When the resin viscosity reaches 18 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-viscosity reducing auxiliary agent malic acid, and continue stirring for 1 h to complete packaging, named PU-1.

[0050] Preparation of soft hydrolysis-resistant wet-process polyurethane resin: S1. Put 267 parts of polyol Krasol3000, 89 parts of polyol PBA-3000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 262 parts of solvent DMF into the reaction flask, stir evenly, and then add 25.2 parts of isocyanate MDI, and react at 70 °C for 1 h. S2. Put 374.7 parts of solvent DMF and 15 parts of chain extender EG into the reaction flask and stir evenly, then add 64.9 parts of isocyanate MDI and react at 70 °C to increase viscosity. Continuously dilute with DMF during the viscosity increase process (the diluted DMF is 442 parts). S3. When the resin viscosity reaches 27 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-viscosity reducing auxiliary agent malic acid, and continue stirring for 1 h to complete packaging, named PU-2.

[0051] Preparation of fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather: (1) Dissolve 100 parts of PU-2 in 200 parts of solvent DMF to act as an impregnating solution for impregnating spunlace non-woven fabric. The extrusion thickness is 0.4 mm, and then iron it flat, controlling the moisture content to be 30% to obtain a base fabric; (2) Mix 10 parts of PU-1, 90 parts of PU-2, 60 parts of solvent DMF and 0.3 part of color powder evenly and defoam to obtain a coating material; coat the coating material on the surface of the base fabric, and the coating thickness is 1.6 mm, and then place it in a coagulation tank of a mixed solution of DMF and water for coagulation, and the DMF concentration is 20%; (3) After coagulation for 15 min, carry out extrusion washing and dry it in an oven at 90 °C to obtain fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather.

[0052] Send the above-mentioned fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather into a low-temperature embossing machine, and carry out embossing at a temperature of 165 °C and a pressure of 0.48 MPa for 6 s.

[0053] Example 2

[0054] Preparation of wet-process polyurethane resin for leather: S1, Put 127 parts of PPG-1-2000 (parts by mass, the same below), 127 parts of PPG-4000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 397 parts of solvent DMF into a four-necked flask. Connect a mechanical stirrer and a thermocouple to the flask mouth and stir evenly. S2, Put 23.8 parts of isocyanate MDI into the reaction flask, heat up to 70 °C, and the reaction increases viscosity until the resin viscosity is 11.5 cps / 25 °C. S3, Add 363 parts of DMF and 139 parts of PTMG-225 to the reaction flask, stir evenly, then add 154.4 parts of isocyanate MDI. As the viscosity increases, continuously dilute with DMF, and the amount of diluted DMF used is 957 parts. S4, When the resin viscosity reaches 20 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-viscosity reducing auxiliary agent malic acid, and continue to stir for 1 h to be packaged, named PU-1.

[0055] Preparation of soft hydrolysis-resistant wet-process polyurethane resin: S1, Put 194 parts of polyol Krasol3100, 82 parts of polyol PBA-3000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 262 parts of solvent DMF into the reaction flask, stir evenly, and then add 20.5 parts of isocyanate HMDI, and react at 80 °C for 4.5 h. S2, Put 374.7 parts of solvent DMF and 41 parts of chain extender 1,4-BG into the reaction flask and stir evenly, then add 117.1 parts of isocyanate MDI and react at 70 °C to increase viscosity. During the viscosity increase process, continuously dilute with DMF (the diluted DMF is 427 parts). S3, When the resin viscosity reaches 30 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-viscosity reducing auxiliary agent malic acid, and continue to stir for 1 h to be packaged, named PU-2.

[0056] Preparation of fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather: (1) Dissolve 100 parts of PU-2 in 300 parts of solvent DMF, act as an impregnating solution for impregnating spunlace non-woven fabric, extrude to a thickness of 0.6 mm, and then iron it flat, control the moisture content to be 40%, to obtain a base fabric; (2) Mix 20 parts of PU-1, 80 parts of PU-2, 55 parts of solvent DMF and 0.4 part of color powder evenly and defoam to obtain a coating material; coat the coating material on the surface of the base fabric, the coating thickness is 2 mm, and then place it in a coagulation tank of a mixed solution of DMF and water for coagulation, and the DMF concentration is 23%; (3) After coagulation for 17 min, carry out extrusion washing and dry in an oven at 110 °C to obtain fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather.

[0057] Feed the above-mentioned fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather into a low-temperature embossing machine, and perform embossing at a temperature of 165 °C and a pressure of 0.48 MPa for 6 s.

[0058] Example 3

[0059] Preparation of wet-process polyurethane resin for leather: S1, Put 210 parts of PPG-2-2000 (parts by mass, the same below), 210 parts of PTMG-1000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 397 parts of solvent DMF into a four-necked flask. Connect a mechanical stirrer and a thermocouple to the flask mouth and stir evenly. S2, Put 54.8 parts of isocyanate TDI into the reaction flask, heat up to 70 °C, and the reaction becomes viscous until the resin viscosity is 13 cps / 25 °C. S3, Add 363 parts of DMF and 95 parts of PTMG-225 to the reaction flask, stir evenly, then add 105.5 parts of isocyanate MDI, and continuously dilute with DMF as the viscosity increases. The amount of diluted DMF used is 1270 parts. S4, When the resin viscosity reaches 22 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-sticking and viscosity-reducing auxiliary agent malic acid, and continue to stir for 1 h to obtain the product, which is named PU-1.

[0060] Preparation of soft hydrolysis-resistant wet-process polyurethane resin: S1, Put 200 parts of polyol Krasol3100, 76 parts of polyol PTMG-1000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 262 parts of solvent DMF into the reaction flask, stir evenly, then add 27 parts of isocyanate IPDI, and react at 80 °C for 6 h. S2, Put 399 parts of solvent DMF and 47.38 parts of chain extender NPG into the reaction flask and stir evenly, then add 119.03 parts of isocyanate MDI and react at 70 °C to increase viscosity. During the viscosity increase process, continuously dilute with DMF (the diluted DMF is 437 parts). S3, When the resin viscosity reaches 35 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-sticking and viscosity-reducing auxiliary agent malic acid, and continue to stir for 1 h to obtain the product, which is named PU-2.

[0061] Preparation of fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather: (1) Dissolve 100 parts of PU-2 in 400 parts of solvent DMF to serve as an impregnating solution for impregnating the water-jet non-woven fabric. The extrusion thickness is 0.8 mm, and then iron it flat. Control the moisture content to be 50% to obtain the base fabric. (2) Mix 40 parts of PU-1, 60 parts of PU-2, 45 parts of solvent DMF and 0.5 part of color powder evenly and defoam to obtain the coating material. Coat the coating material on the surface of the base fabric with a coating thickness of 2.2 mm, and then place it in a coagulation tank of a mixed solution of DMF and water for coagulation. The DMF concentration is 25%. (3) After coagulation for 20 min, carry out extrusion washing and dry it in an oven at 120 °C to obtain the fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather.

[0062] Feed the above-mentioned fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather into a low-temperature embossing machine and carry out embossing at a temperature of 165 °C and a pressure of 0.48 MPa for 6 s.

[0063] Example 4

[0064] Preparation of wet-process polyurethane resin for leather: S1, Put 232 parts of PTMG-3000 (parts by mass, the same below), 232 parts of PBA-2000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 397 parts of solvent DMF into a four-necked flask. Connect a mechanical stirrer and a thermocouple to the flask mouth and stir evenly. S2, Put 48.3 parts of isocyanate MDI into the reaction flask, heat up to 70 °C, and the reaction increases viscosity until the resin viscosity is 10 cps / 25 °C. S3, Add 363 parts of DMF and 31 parts of PTMG-225 to the reaction flask, stir evenly and then add 34.4 parts of isocyanate MDI. Continuously dilute with DMF as the viscosity increases. The amount of diluted DMF used is 978 parts. S4, When the viscosity of the resin reaches 18 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes and then add 0.5 part of anti-sticking and viscosity-reducing auxiliary agent malic acid, and continue to stir for 1 h to be packaged and named PU-1. The rest is the same as Example 1.

[0065] Example 5

[0066] Preparation of soft hydrolysis-resistant wet-process polyurethane resin: S1, Put 180 parts of polyol Krasol3100, 72 parts of polyol PTMG-1000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 262 parts of solvent DMF into a reaction flask, stir evenly, then add 28.05 parts of isocyanate MDI, and react at 70 °C for 1 h. S2, Put 399 parts of solvent DMF and 49 parts of chain extender 1,4-BG into the reaction flask and stir evenly, then add 140.8 parts of isocyanate MDI and react at 70 °C to increase viscosity. During the viscosity increase process, continuously dilute with DMF (the diluted DMF is 438 parts). S3, When the viscosity of the resin reaches 35 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-tackifying and anti-sticking auxiliary malic acid, and continue to stir for 1 h to complete packaging, named PU-2. The rest is the same as in Example 3.

[0067] Example 6

[0068] Preparation of soft hydrolysis-resistant wet-process polyurethane resin: S1, Put 260 parts of polyol Krasol3000, 133 parts of polyol PBA-3000, 0.2 part of antioxidant 1010, 0.02 part of phosphoric acid and 262 parts of solvent DMF into a reaction flask, stir evenly, then add 27.8 parts of isocyanate MDI, and react at 70 °C for 1 h. S2, Put 374.7 parts of solvent DMF and 10 parts of chain extender 1,4-BG into the reaction flask and stir evenly, then add 32.7 parts of isocyanate MDI and react at 70 °C to increase viscosity. During the viscosity increase process, continuously dilute with DMF (the diluted DMF is 448 parts). S3, When the viscosity of the resin reaches 27 cps / 25 °C, add 0.5 part of terminator methanol, stir for 15 minutes, then add 0.5 part of anti-tackifying and anti-sticking auxiliary malic acid, and continue to stir for 1 h to complete packaging, named PU-2. The rest is the same as in Example 1.

[0069] Comparative Example 1

[0070] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 1 is prepared basically the same as in Example 1, except that: instead of using the wet-process polyurethane resin for leather, directly use the soft hydrolysis-resistant wet-process polyurethane resin to prepare the synthetic leather required by the present invention, and the rest remains unchanged.

[0071] Comparative Example 2

[0072] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 2 is prepared basically the same as in Example 1, except that: Preparation of the wet-process polyurethane resin for leather: In step S2, put 49.6 parts of isocyanate TDI into a reaction flask, heat up to 70 °C, react to increase viscosity until the resin viscosity is 3 cps / 25 °C. The rest remains unchanged.

[0073] Comparative Example 3

[0074] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 3 was prepared in basically the same manner as in Example 1, except that in the preparation of the soft hydrolysis-resistant wet-process polyurethane resin: PTMG-2000 was used to replace 267 parts of polyol Krasol3000 in an equimolar amount, and the rest remained unchanged.

[0075] Comparative Example 4

[0076] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 4 was prepared in basically the same manner as in Example 1, except that in the preparation of the soft hydrolysis-resistant wet-process polyurethane resin: S1, 178 parts of polyol Krasol3000 and 178 parts of polyol PBA-3000 were used to replace 267 parts of polyol Krasol3000 and 89 parts of polyol PBA-3000, and the rest remained unchanged.

[0077] Comparative Example 5

[0078] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 5 was prepared in basically the same manner as in Example 1, except that in the preparation of the soft hydrolysis-resistant wet-process polyurethane resin: S3, 10 parts of PU-1, 90 parts of PU-2, 70 parts of solvent DMF and 0.3 part of color powder were mixed evenly, defoamed and reserved for use, and the rest remained unchanged.

[0079] Comparative Example 6

[0080] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather provided by Comparative Example 5 was prepared in basically the same manner as in Example 1, except that in the preparation of the soft hydrolysis-resistant wet-process polyurethane resin: S3, 10 parts of PU-1, 90 parts of PU-2, 30 parts of solvent DMF and 0.3 part of color powder were mixed evenly, defoamed and reserved for use, and the rest remained unchanged.

[0081] The soft fluorine-free hydrolysis-resistant embossable polyurethane synthetic leathers obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were compared in terms of the softness and hardness of their handfeel; the flatness of the surface and the quality of the embossing performance. Under the constant temperature condition of 27°C, they were soaked in a 10% NaOH aqueous solution for 24 h to examine their hydrolysis-resistant physical properties; in the present invention, the hydrolysis-resistant retention rate was used to quantify the hydrolysis-resistant performance, that is, for the same leather sample, the peel strength was measured once before soaking in alkali and once again after soaking in alkali, and the retention rate of the peel strength was calculated. The higher the retention rate, the better the hydrolysis-resistant performance. The above test results are listed in Table 1.

[0082] Table 1 shows the physical property tests of Examples 1 to 6 and Comparative Examples 1 to 6

[0083]

[0084] It can be seen from the test results in Table 1 that Examples 1 and 3 have the best soft feel, surface smoothness, embossing and hydrolysis resistance, while the proportion of polyols used in Examples 2, 4, 5 and 6 is close to the upper and lower limits specified in the present invention, that is, the proportion of polyol components is too high or too low. The high content of polyols causes the synthetic leather to coagulate slowly and has poor foaming properties during the coagulation process, so the synthetic leather feels softer (not as good as Examples 1 and 3). The low content of polyols causes the synthetic leather to coagulate faster. During the coagulation process, the epidermis coagulates first, while the interior coagulates slowly and has poor foaming properties, so the feel is also softer, that is, it is slightly harder than Examples 1 and 3. The embossing effect of the synthetic leather prepared in Examples 1 to 6 is as follows: Figure 1 As shown, the pattern is deep, clear and full.

[0085] The physical properties of Comparative Examples 1 to 6 are obviously inferior to those of Examples 1 to 3. This is because:

[0086] In Comparative Example 1, when preparing synthetic leather, no wet polyurethane resin for leather was added, and water washing was adjusted (to remove DMF in synthetic leather), so that the synthetic leather had poor DMF removal, resulting in poor surface flatness and hard hand feeling of the synthetic leather; the intermediate prepolymer viscosity of Comparative Example 2 was low, resulting in poor foaming performance and hard hand feeling when preparing synthetic leather; in Comparative Example 6, too little solvent DMF was added during the mixing process, resulting in poor DMF removal during water washing of the synthetic leather, pockmarked surface, and hard hand feeling. The synthetic leather prepared in Examples 1, 2 and 6 is as follows: Figure 2 As shown, due to the poor DMF removal performance of the synthetic leather, a small amount of DMF remains in the synthetic leather. During the drying process, a small amount of DMF will damage the surface of the synthetic leather, making the surface uneven, so the surface brightness is poorer than that of Examples 1 to 6. Since the surface is not flat, the embossing is unevenly applied to some areas, so the embossing performance is poor, and the pattern is shallow and not clear enough.

[0087] In Comparative Example 3, PTMG-2000 was used in an equivalent molar amount to replace 267 parts of polyol Krasol3000, so that the synthetic leather solidified faster, and the surface of the prepared synthetic leather was bubbling, which made the leather surface easy to peel and damage. In Comparative Example 5, too much DMF was added when preparing the synthetic leather ingredients, so that the synthetic leather solidified too quickly and bubbling appeared on the surface. The synthetic leather prepared in Comparative Examples 3 and 5 is as follows Figure 3 shown.

[0088] In Comparative Example 4, the amount of bio-based polyol Krasol3000 was less than 65%, so that the surface of the prepared synthetic leather was powdered after a 24-hour hydrolysis resistance test, and the water resistance was unqualified. Figure 4 The pictures of the products (qualified products) of Examples 1 to 3 after 24h hydrolysis resistance test are as follows: Figure 5 As shown, there is no chalking or discoloration, and there is a slight gloss change.

Claims

1. A soft hydrolysis-resistant wet-process polyurethane resin, characterized in that, It is made of the following raw materials by mass fraction: 16% - 28% of polyol A, 0.002% - 0.01% of antioxidant, 0.0002% - 0.001% of phosphoric acid, 2% - 15% of isocyanate A, 0.3% - 4% of chain extender A, 0.01% - 0.04% of methanol, 0.01% - 0.04% of anti-sticking and viscosity-reducing agent, and the balance is solvent; the solid content of the soft hydrolysis-resistant wet-process polyurethane resin is 29% - 32%, and the viscosity is 27 - 35 cps / 25°C; The polyol A is a bio-based polyol with a weight-average molecular weight of 2500 - 3500, or a combination of this bio-based polyol and one or more of polybutylene adipate diol, polycarbonate diol, and polytetrahydrofuran ether diol with a weight-average molecular weight of 1000 - 4000, wherein the bio-based polyol accounts for more than 65% of the total mass of the polyols; the bio-based polyol is a linear chain polymer formed by free radical polymerization of bio-based farnesol, with hydroxyl groups retained at both ends; the chain extender A is at least one of ethylene glycol, 1,4-butanediol, and neopentyl glycol.

2. The soft hydrolysis-resistant wet-process polyurethane resin according to claim 1, characterized in that The isocyanate A is at least one of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane-4,4-diisocyanate; the solvent is N,N-dimethylformamide and / or N,N-dimethylacetamide; the antioxidant is at least one of pentaerythritol ester antioxidants; the anti-sticking and viscosity-reducing agent is malic acid or / and phthalic anhydride.

3. The preparation method of the soft hydrolysis-resistant wet-process polyurethane resin according to claim 1, characterized in that, It includes the following steps: S1, Mix polyol A, part of isocyanate A, antioxidant, phosphoric acid, and part of the solvent evenly, and the molar ratio R of cyanate group to hydroxyl group is 0.2 - 0.9; carry out a prepolymerization reaction at 70 - 80°C, and after the NCO value in the system is qualified, obtain polyurethane prepolymer A; S2, Add chain extender A to polyurethane prepolymer A and stir evenly, then add the remaining isocyanate A and the remaining solvent in batches for viscosity increase. After the viscosity of the system meets the standard, add methanol for capping, and then add the anti-sticking and viscosity-reducing agent and stir evenly to obtain the soft hydrolysis-resistant wet-process polyurethane resin.

4. A wet-process polyurethane resin for leather, characterized in that, It is made of the following raw materials by mass fraction: 11% - 21% of polyol B, 0.002% - 0.01% of antioxidant, 0.0002% - 0.001% of phosphoric acid, 1% - 10% of isocyanate B, 1% - 6% of chain extender B, 0.01% - 0.04% of methanol, 0.01% - 0.04% of anti-sticking and viscosity-reducing agent, and the balance is solvent; the solid content of the wet-process polyurethane resin for leather is 23% - 27%, and the viscosity is 18 - 22 cps / 25°C; the chain extender B is polytetrahydrofuran diol with a weight-average molecular weight of 220 - 230.

5. The wet-process polyurethane resin for leather according to claim 4, wherein The polyol B is a combination of one or more of polytetrahydrofuran diol, polybutylene adipate diol, polypropylene glycol, and poly-modified propylene glycol with a molecular weight of 1000 - 4000; the poly-modified propylene glycol is a combination of one or two of end-capped with EO and EO embedded in the middle chain segment.

6. The wet-process polyurethane resin for leather according to claim 4, characterized in that, The isocyanate B is one or a combination of more than one of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane-4,4-diisocyanate; The solvent is N,N-dimethylformamide and / or N,N-dimethylacetamide; the antioxidant is at least one of pentaerythritol ester antioxidants; the anti-sticking and viscosity-reducing aid is malic acid or / and phthalic anhydride.

7. The wet-process polyurethane resin for leather according to claim 4, characterized in that, The preparation method of the wet-process polyurethane resin for leather comprises the following steps: D1, Mix polyol B, isocyanate B, antioxidant, phosphoric acid, and a part of the solvent evenly. The molar ratio R of isocyanate group to hydroxyl group is 1 to 1.1; carry out a prepolymerization reaction at 70 to 80 °C. After the viscosity of the system reaches 10 to 13 cps / 25 °C, obtain polyurethane prepolymer B; D2, Add chain extender B to polyurethane prepolymer B and stir evenly. Then add isocyanate in batches in small amounts many times to increase the viscosity, and add DMF for dilution; D3, When the viscosity of the system meets the standard, add methanol for capping, and then add the anti-sticking and viscosity-reducing aid, and stir evenly to obtain the wet-process polyurethane resin for leather.

8. A preparation method of a fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather, characterized in that, Comprises the following steps: (1) Dissolve the soft hydrolysis-resistant wet-process polyurethane resin in a solvent to obtain an impregnating solution, impregnate non-woven fabric, squeeze out the excess resin, and iron it flat to obtain a base fabric; (2) Mix the wet-process polyurethane resin for leather, the soft hydrolysis-resistant wet-process polyurethane resin, solvent DMF, and a colorant evenly and defoam to obtain a coating material; the mass ratio of the wet-process polyurethane resin for leather to the soft hydrolysis-resistant wet-process polyurethane resin is 1:9 to 2:3; (3) Coat the coating material on the surface of the base fabric obtained in step (1), and then place it in a coagulation bath for coagulation; (4) Wash and dry the base fabric.

9. The preparation method of the fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather according to claim 8, characterized in that, In the step (1), the mass ratio of the soft hydrolysis-resistant wet-process polyurethane resin to solvent DMF is 1:(2 to 4); the extrusion thickness after impregnating the non-woven fabric is 0.4 to 0.8 mm; the moisture content of the base fabric is controlled at 30% to 50%; In the step (2), the addition amount of solvent DMF is 45% to 60% of the total mass of the two resins, and the addition amount of the colorant is 0.3% to 0.5% of the total mass of the two resins; In the step (3), the coating thickness of the mixed liquid on the surface of the base fabric is 1.6 to 2.2 mm, and the coagulation time is 15 to 20 min; the coagulation bath is a mixed liquid of DMF and water, and the DMF concentration is 20% to 25%; In the step (4), the drying temperature of the base fabric is 90 to 120 °C.

10. A fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather prepared by the method according to claim 9.

11. For the fluorine-free hydrolysis-resistant embossable polyurethane synthetic leather according to claim 10, directly carry out embossing, and use a low-temperature embossing machine to hot-press at 160 to 180 °C and 0.35 to 0.7 MPa for 5 to 10 s.

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