Polyurethane composite coating for leather waterproofing and preparation method thereof

Abstract

The invention belongs to the technical field of polyurethane coatings, and particularly relates to a polyurethane composite coating for leather waterproofing and a preparation method of the polyurethane composite coating. The polyurethane composite coating is prepared from the following raw materials in parts by weight: 90 to 100 parts of waterborne polyurethane resin, 1 to 5 parts of modified dopamine, 5 to 10 parts of lauric acid, 0.5 to 3 parts of dispersing agent, 0.1 to 0.5 part of defoaming agent and 30 to 40 parts of water. The modified dopamine interacts with the waterborne polyurethane to form a tight network structure, and the network structure can limit the permeation effect of water molecules. The lauric acid as a long-chain fatty acid can reduce the surface tension of the coating, so that the coating is easier to spread and wet on the leather surface. And the modified dopamine and lauric acid are matched for use, so that the waterproof performance of the coating can be enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane coatings, and in particular relates to a polyurethane composite coating for leather waterproofing and a preparation method thereof. Background Art

[0002] With the development of science and technology, leather is increasingly used. However, the lack of water resistance of leather itself limits its wider application potential to a certain extent. In order to overcome this limitation, the industry generally adopts the strategy of applying a protective film on the surface of leather to improve its overall performance. Among the many protective film materials, polyurethane (full name polyurethane) has become one of the first choices due to its excellent mechanical properties.

[0003] Polyurethane (full name polyurethane) is a polymer material with excellent mechanical properties formed by polyols and polyisocyanates through polycondensation reaction. The structure of polyurethane coating contains urethane bonds, ester bonds, ether bonds, urea bonds, allomethyl ester bonds, biuret bonds, acylurea bonds and unsaturated fatty chains, etc. Therefore, it has various excellent properties, such as high tensile strength, wide hardness range, good tear strength, good heat sealing, strong adhesion, etc., and is widely used in surface protection coatings, architectural coatings, automotive coatings and other fields. However, polyurethane coatings have poor wear resistance, average water resistance, and poor mechanical properties, which can easily cause the coating formed after construction to break under external forces such as friction.

[0004] The catechol group contained in the dopamine molecule gives it excellent adhesion properties. This adhesion allows dopamine to adhere tightly to the surfaces of various substrates, including metal, glass, polymers, and wood. In waterproof coatings, this adhesion of dopamine can significantly improve the bonding force between the coating and the substrate, thereby enhancing the waterproof effect of the coating.

[0005] Lauric acid, also known as dodecanoic acid, is a saturated fatty acid. It is a white needle-shaped crystal at room temperature with a slight laurel oil aroma. It is present in many vegetable oils, but the main ones with higher content include coconut oil (45%~52%), palm oil (44%~52%), babassu seed oil (43%~44%), etc. Lauric acid has good chemical stability and biodegradability. Studies have found that lauric acid may be used as a surfactant, emulsifier or dispersant to improve the dispersibility, stability and construction performance of waterproof coatings.

[0006] Based on the above background, the present invention provides a novel polyurethane composite coating for leather waterproofing. Summary of the invention

[0007] The first object of the present invention is to provide a polyurethane composite coating for leather waterproofing, wherein the polyurethane composite coating has excellent waterproofing and mechanical properties.

[0008] The second object of the present invention is to provide a method for preparing a polyurethane composite coating for leather waterproofing, which is simple and easy to practice.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: A polyurethane composite coating for leather waterproofing, comprising the following raw materials in parts by weight: 90-100 parts of waterborne polyurethane resin, 1-5 parts of modified dopamine, 5-10 parts of lauric acid, 0.5-3 parts of dispersant, 0.1-0.5 parts of defoamer, and 30-40 parts of water; The preparation process of the modified dopamine is as follows: adding oxidized sodium alginate to a dopamine aqueous solution for reaction, and after the reaction is completed, purifying to obtain the modified dopamine.

[0010] Preferably, the mass ratio of dopamine to oxidized sodium alginate is 1:(1-3), and the reaction time is 6-10 hours.

[0011] Preferably, the preparation process of the oxidized sodium alginate is as follows: A sodium periodate aqueous solution is added to a sodium alginate aqueous solution to obtain a mixed solution; after adjusting the pH of the mixed solution, the mixture is reacted at room temperature in the dark, and then ethylene glycol is added to terminate the reaction. After the reaction is completed, the reaction solution is dialyzed and freeze-dried to obtain the product.

[0012] Preferably, the molar ratio of the sodium alginate to the sodium periodate is 1:(2-4); the mass concentration of the sodium alginate aqueous solution is 1-3%, and the mass concentration of the sodium periodate aqueous solution is 1-3%.

[0013] Preferably, the average molecular weight of the sodium alginate is 10-20 KDa.

[0014] Sodium alginate is a natural high molecular weight polysaccharide extracted from deep-sea brown algae. Sodium periodate, as an oxidant, can oxidize the hydroxyl groups in sodium alginate to generate new functional groups such as aldehyde groups or carboxyl groups. The present invention reacts dopamine with oxidized sodium alginate, and the amino groups in dopamine can react with the aldehyde groups or carboxyl groups in the oxidized sodium alginate, thereby realizing the modification of dopamine. A network structure can be formed between the sodium alginate in the modified dopamine and the aqueous polyurethane, and the hydrogen bonding between the amino groups, phenolic hydroxyl groups in dopamine and the hydroxyl groups of the aqueous polyurethane makes the network structure more compact, and this network structure can limit the penetration of water molecules, thereby improving the waterproofness of the coating. At the same time, the enhancement of the network structure also helps to improve the mechanical properties of the coating, such as tensile strength and toughness.

[0015] Preferably, the pH of the mixed solution is adjusted to 4-5; and the reaction time is 8-10 hours.

[0016] Preferably, the dispersant is selected from one of TEGO Dispers 760W, FLOSPERSETM 3000N, and BYK-191; and the defoamer is glycerol polyether defoamer GP330 or polyoxypropylene polyoxyethylene glycerol ether GPE-3000.

[0017] The method for preparing the above-mentioned polyurethane composite coating for leather waterproofing comprises the following steps: According to the raw material ratio, water-based polyurethane resin, modified dopamine, lauric acid and water are stirred and mixed uniformly to obtain mixture A; dispersant and defoaming agent are added to mixture A, stirred and mixed uniformly to obtain mixture B, and mixture B is evenly coated on the leather surface, and after drying and curing, the mixture is obtained.

[0018] Preferably, the curing temperature is 80-90°C.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly: (1) The present invention creatively provides a novel polyurethane composite coating for leather waterproofing, which comprises waterborne polyurethane, modified dopamine, lauric acid and other components. Modified dopamine interacts with waterborne polyurethane to form a tight network structure, which can limit the penetration of water molecules. Lauric acid, as a long-chain fatty acid, can reduce the surface tension of the coating, making it easier to spread and wet on the leather surface. The modified dopamine and lauric acid are used in combination to enhance the waterproof performance of the coating.

[0020] In addition, the phenolic hydroxyl groups in the modified dopamine and the long-chain fatty acid groups in lauric acid also jointly enhance the adhesion between the coating and the leather, making the coating stronger. The enhancement of the network structure and the improvement of the adhesion jointly act on the mechanical properties of the coating, giving it higher tensile strength and toughness.

[0021] (2) The present invention tests the properties of the obtained polyurethane composite coating, and the polyurethane composite coating has excellent waterproof properties and mechanical properties, wherein the water contact angle θ is greater than 157.3°, the tensile strength is greater than 11.5 MPa, the elongation at break is greater than 656%, and the adhesion is greater than 5.5 MPa. DETAILED DESCRIPTION

[0022] The technical scheme of the present invention is further described below in conjunction with specific embodiments. However, it should be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the present invention. The specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0023] The waterborne polyurethane resin in the embodiment of the present invention is a waterborne polyurethane resin (AH-1704B-2) with a solid content of 30±1% and a viscosity of ≥100 mPa.s.

[0024] Example Example 1 A polyurethane composite coating for leather waterproofing is composed of the following raw materials in parts by weight: 94 parts of waterborne polyurethane resin, 2 parts of modified dopamine, 8 parts of lauric acid, 1 part of TEGO Dispers 760W, 0.4 parts of glycerol polyether defoamer GP330, and 33 parts of water.

[0025] The preparation process of the modified dopamine is as follows: According to the molar ratio of sodium alginate to sodium periodate of 1:3, a 2% sodium periodate aqueous solution was added to a 2% sodium alginate aqueous solution (average molecular weight of sodium alginate is 15KDa) to obtain a mixed solution; the pH of the mixed solution was adjusted to 4.5, and the mixture was reacted at room temperature in the dark for 9 hours, and then ethylene glycol was added to terminate the reaction. After the reaction was completed, the reaction solution was dialyzed and freeze-dried to obtain oxidized sodium alginate; According to the mass ratio of dopamine to oxidized sodium alginate of 1:2, the oxidized sodium alginate was added to the dopamine aqueous solution to carry out reaction for 8 hours. After the reaction was completed, the reaction solution was dialyzed for 48 hours and freeze-dried to obtain modified dopamine.

[0026] The preparation method of the above-mentioned polyurethane composite coating for leather waterproofing, the specific preparation process is as follows: According to the raw material ratio, the water-based polyurethane resin, modified dopamine, lauric acid and water were stirred and mixed at a speed of 200 r / min to obtain a mixture A; TEGO Dispers 760W and glycerol polyether defoamer GP330 were added to the mixture A, and the mixture was stirred and mixed at a speed of 200 r / min to obtain a mixture B, and the mixture B was evenly coated on the leather surface, dried, and cured at 80° C. to form a film, so as to obtain a polyurethane composite coating.

[0027] Example 2 The invention discloses a polyurethane composite coating for leather waterproofing. The polyurethane composite coating is composed of the following raw materials in parts by weight: 90 parts of waterborne polyurethane resin, 1 part of modified dopamine, 5 parts of lauric acid, 0.5 parts of FLOSPERSETM 3000N, 0.1 parts of polyoxypropylene polyoxyethylene glycerol ether GPE-3000, and 30 parts of water.

[0028] The preparation process of the modified dopamine is as follows: According to the molar ratio of sodium alginate to sodium periodate of 1:2, a sodium alginate aqueous solution with a mass concentration of 3% was added to a sodium alginate aqueous solution with a mass concentration of 1% (the average molecular weight of sodium alginate is 10KDa) to obtain a mixed solution; the pH of the mixed solution was adjusted to 5, and the mixture was reacted at room temperature in the dark for 8 hours, and then ethylene glycol was added to terminate the reaction. After the reaction was completed, the reaction solution was dialyzed and freeze-dried to obtain oxidized sodium alginate; According to the mass ratio of dopamine to oxidized sodium alginate of 1:1, the oxidized sodium alginate was added to the dopamine aqueous solution to carry out the reaction for 10 hours. After the reaction, the reaction solution was dialyzed for 48 hours and freeze-dried to obtain modified dopamine.

[0029] The preparation method of the above-mentioned polyurethane composite coating for leather waterproofing, the specific preparation process is as follows: According to the raw material ratio, water-based polyurethane resin, modified dopamine, lauric acid and water are stirred and mixed at a speed of 200 r / min to obtain a mixture A; FLOSPERSETM 3000N and polyoxypropylene polyoxyethylene glycerol ether GPE-3000 are added to the mixture A, and the mixture is stirred and mixed at a speed of 200 r / min to obtain a mixture B, and the mixture B is evenly coated on the leather surface, dried, and cured at 85°C to form a film, so as to obtain a polyurethane composite coating.

[0030] Example 3 A polyurethane composite coating for leather waterproofing is composed of the following raw materials in parts by weight: 100 parts of waterborne polyurethane resin, 5 parts of modified dopamine, 10 parts of lauric acid, 3 parts of BYK-191, 0.5 parts of glycerol polyether defoamer GP330, and 40 parts of water.

[0031] The preparation process of the modified dopamine is as follows: According to the molar ratio of sodium alginate to sodium periodate of 1:4, a sodium alginate aqueous solution with a mass concentration of 1% was added to a sodium alginate aqueous solution with a mass concentration of 3% (the average molecular weight of sodium alginate is 20KDa) to obtain a mixed solution; the pH of the mixed solution was adjusted to 4, and the mixture was reacted at room temperature in the dark for 10 hours, and then ethylene glycol was added to terminate the reaction. After the reaction was completed, the reaction solution was dialyzed and freeze-dried to obtain oxidized sodium alginate; According to the mass ratio of dopamine to oxidized sodium alginate of 1:3, the oxidized sodium alginate was added to the dopamine aqueous solution to react for 6 hours. After the reaction, the reaction solution was dialyzed for 48 hours and freeze-dried to obtain modified dopamine.

[0032] The preparation method of the above-mentioned polyurethane composite coating for leather waterproofing, the specific preparation process is as follows: According to the raw material ratio, the water-based polyurethane resin, modified dopamine, lauric acid and water are stirred and mixed at a speed of 200 r / min to obtain a mixture A; BYK-191 and glycerol polyether defoamer GP330 are added to the mixture A, and the mixture is stirred and mixed at a speed of 200 r / min to obtain a mixture B, and the mixture B is evenly coated on the leather surface, dried, and cured at 90°C to form a film, so as to obtain a polyurethane composite coating.

[0033] Comparative Example Comparative Example 1 A polyurethane composite coating for leather waterproofing, the polyurethane composite coating is composed of the following raw materials in parts by weight: 94 parts of waterborne polyurethane resin, 2 parts of modified dopamine, 8 parts of tannic acid, 1 part of TEGO Dispers 760W, 0.4 parts of glycerol polyether defoamer GP330, and 33 parts of water, and the rest is consistent with Example 1.

[0034] Comparative Example 2 A polyurethane composite coating for leather waterproofing, the polyurethane composite coating is composed of the following raw materials in parts by weight: 94 parts of waterborne polyurethane resin, 2 parts of modified dopamine, 1 part of TEGO Dispers 760W, 0.4 parts of glycerol polyether defoamer GP330, and 33 parts of water, and the rest is consistent with Example 1.

[0035] Comparative Example 3 A polyurethane composite coating for leather waterproofing, the polyurethane composite coating is composed of the following raw materials in parts by weight: 94 parts of waterborne polyurethane resin, 2 parts of dopamine, 8 parts of lauric acid, 1 part of TEGO Dispers 760W, 0.4 parts of glycerol polyether defoamer GP330, and 33 parts of water, and the rest is consistent with Example 1.

[0036] Experimental example The polyurethane composite coatings obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests: Waterproof test: The water contact angle θ of the leather surface was measured using a JC2000C dynamic contact angle meter. Each group of measurements was repeated 5 times. The experimental results of each group were the average of the 5 test results. The results are shown in Table 1. Tensile strength: refer to GB / T 19250-2013, each group is measured 5 times, each group of experimental results is the average of 5 test results, the results are shown in Table 1; Elongation at break: refer to GB / T 19250-2013, each group is measured 5 times, and each group of experimental results is the average of 5 test results. The results are shown in Table 1; Adhesion: refer to GB / T 5210-2006, each group of measurements were repeated 5 times, each group of experimental results is the average of 5 test results, the results are shown in Table 1.

[0037] Table 1 The water contact angle value is one of the important indicators to measure the waterproof performance of the material surface. If the water contact angle θ is less than 90°, it means that the material is hydrophilic; if the water contact angle θ is greater than 90° and less than 150°, it means that the material is hydrophobic; if the water contact angle θ is greater than 150°, it means that the material is super hydrophobic.

[0038] It can be seen from Table 1 that the polyurethane composite coatings obtained in Examples 1-3 have excellent waterproof properties, the waterproof properties of the polyurethane composite coatings obtained in Comparative Example 1 are second, and the waterproof properties of the polyurethane composite coatings obtained in Comparative Example 2 are the worst. Analysis shows that Comparative Example 1 uses tannic acid instead of lauric acid, Comparative Example 2 omits lauric acid, and Comparative Example 3 uses dopamine instead of modified dopamine. The above results show that the combination of lauric acid and modified dopamine can improve the waterproof properties of the material. This may be because a network structure can be formed between the sodium alginate in the modified dopamine and the aqueous polyurethane, and the hydrogen bonding between the amino group, phenolic hydroxyl group in dopamine and the hydroxyl group of the aqueous polyurethane makes the network structure more compact. This network structure can limit the penetration of water molecules, thereby improving the waterproof properties of the coating. Lauric acid, as a long-chain fatty acid, can reduce the surface tension of the coating, making it easier to spread and wet on the leather surface. Therefore, the use of modified dopamine in combination with lauric acid enhances the waterproof properties of the coating.

[0039] The polyurethane composite coatings obtained in Examples 1-3 also have excellent mechanical properties and adhesion, the mechanical properties of the polyurethane composite coatings obtained in Comparative Example 1 are second, and the mechanical properties of the polyurethane composite coatings obtained in Comparative Example 2 are the worst. Combining the differences in the composition of the polyurethane composite coatings in Examples 1-3 and Comparative Examples 1-3, it is known that the combined use of lauric acid and modified dopamine can improve the mechanical properties and adhesion of the material. This may be attributed to the hydrogen bonding between the phenolic hydroxyl groups in the modified dopamine and the waterborne polyurethane, which enhances the network structure and the long-chain fatty acid groups of lauric acid, and also jointly enhances the adhesion between the coating and the leather, making the coating more firm. The enhancement of the network structure and the improvement of adhesion act together on the mechanical properties of the coating, giving it higher tensile strength and toughness.

[0040] In summary, the present invention reacts dopamine with oxidized sodium alginate, and the amino group in dopamine can react with the aldehyde group or carboxyl group in the oxidized sodium alginate, thereby realizing the modification of dopamine. A network structure can be formed between the sodium alginate in the modified dopamine and the aqueous polyurethane, and the hydrogen bonding between the amino group, phenolic hydroxyl group in dopamine and the hydroxyl group of the aqueous polyurethane makes the network structure more compact, and this network structure can limit the penetration of water molecules, thereby improving the waterproofness of the coating. At the same time, the enhancement of the network structure also helps to improve the mechanical properties of the coating, such as tensile strength and toughness.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. On the basis of the present invention, some modifications or replacements may be made thereto, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of protection claimed by the present invention.

Claims

1. A polyurethane composite coating for leather waterproofing, characterized in that: The invention comprises the following raw materials in parts by weight: 90-100 parts of waterborne polyurethane resin, 1-5 parts of modified dopamine, 5-10 parts of lauric acid, 0.5-3 parts of dispersant, 0.1-0.5 parts of defoamer and 30-40 parts of water; The preparation process of the modified dopamine is as follows: adding oxidized sodium alginate to a dopamine aqueous solution for reaction, and after the reaction is completed, purifying to obtain the modified dopamine.

2. The polyurethane composite coating for leather waterproofing according to claim 1, characterized in that: The mass ratio of dopamine to oxidized sodium alginate is 1:(1-3), and the reaction time is 6-10 hours.

3. The polyurethane composite coating for leather waterproofing according to claim 1, characterized in that: The preparation process of the oxidized sodium alginate is as follows: A sodium periodate aqueous solution is added to a sodium alginate aqueous solution to obtain a mixed solution; after adjusting the pH of the mixed solution, the mixture is reacted at room temperature in the dark, and then ethylene glycol is added to terminate the reaction. After the reaction is completed, the reaction solution is dialyzed and freeze-dried to obtain the product.

4. The polyurethane composite coating for leather waterproofing according to claim 3, characterized in that: The molar ratio of the sodium alginate to the sodium periodate is 1:(2-4); the mass concentration of the sodium alginate aqueous solution is 1-3%, and the mass concentration of the sodium periodate aqueous solution is 1-3%.

5. The polyurethane composite coating for leather waterproofing according to claim 4, characterized in that: The average molecular weight of the sodium alginate is 10-20 KDa.

6. The polyurethane composite coating for leather waterproofing according to claim 3, characterized in that: The pH of the mixed solution is adjusted to 4-5; and the reaction time is 8-10 hours.

7. The polyurethane composite coating for leather waterproofing according to claim 1, characterized in that: The dispersant is selected from one of TEGODispers 760W, FLOSPERSETM 3000N and BYK-191; the defoamer is glycerol polyether defoamer GP330 or polyoxypropylene polyoxyethylene glycerol ether GPE-3000.

8. The method for preparing the polyurethane composite coating for leather waterproofing according to claim 1, characterized in that: The following steps are involved: According to the raw material ratio, water-based polyurethane resin, modified dopamine, lauric acid and water are stirred and mixed uniformly to obtain mixture A; dispersant and defoaming agent are added to mixture A, stirred and mixed uniformly to obtain mixture B, and mixture B is evenly coated on the leather surface, and after drying and curing, the mixture is obtained.

9. The method for preparing the polyurethane composite coating for leather waterproofing according to claim 8, characterized in that: The curing temperature is 80-90°C.

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