Waterborne polyurethane, preparation method thereof and application of waterborne polyurethane in printing adhesive cement

Abstract

The invention relates to the technical field of polyurethane, and particularly discloses waterborne polyurethane, a preparation method thereof and application of the waterborne polyurethane in printing adhesive cement. The preparation method of the waterborne polyurethane comprises the following steps: S1, at 98-102 DEG C, carrying out heat preservation reaction on 170-180 parts by weight of polyol, 45-55 parts by weight of isocyanate and 5-10 parts by weight of 1, 4-butanediol for 1.5-2.5 hours, then adding 25-35 parts by weight of acetone and 0.08-0.12 part by weight of a catalyst, and continuously carrying out heat preservation reaction until the content of NCO in a system is 0.8-1.2%; s2, adding 515-525 parts of acetone into a system obtained in S1, cooling to 45 DEG C or below, adding 4-6 parts of sulfonate, continuously stirring for 25-35 minutes, then adding 280-320 parts of water, emulsifying for 5-10 minutes, adding 35-45 parts of a diaminocarboxylic acid aqueous solution after emulsification is finished, and uniformly mixing; and S3, carrying out reduced pressure distillation on the system obtained in the step S2, adjusting the pH value of the system to be neutral, and filtering to obtain the waterborne polyurethane. The polyurethane provided by the invention can be used for printing rubber cement, and has the advantage of prolonging the opening time of the printing rubber cement.

Description

Technical Field

[0001] The present application relates to the technical field of polyurethanes, and more specifically, to a waterborne polyurethane, a preparation method thereof, and an application thereof in printing pastes. Background Art

[0002] Due to its excellent mechanical properties and chemical properties, such as folding resistance, flex resistance, high resilience, excellent adhesion fastness, etc., waterborne polyurethane is widely used in the printing process of textiles such as shoe materials and clothing. Due to the reasons of the printing process, it is often required that the waterborne polyurethane used in printing pastes has the characteristics of high solid content and fast thickening speed. Therefore, the molecular structure of this type of waterborne polyurethane is usually linear. However, the linear structure results in a lack of necessary crosslinking during the curing of the printing paste, so that its water resistance and solvent resistance after drying and film formation are often poor.

[0003] In order to improve this problem, in the actual use process, generally about 5wt% of isocyanate curing agent is added to the printing paste, and the isocyanate curing agent is a hydrophilic modified isocyanate curing agent. By introducing hydrophilic groups, the curing agent molecules can be evenly dispersed in the paste, so as to fully crosslink with the waterborne polyurethane molecules, achieving a good curing effect, and further improving the water resistance, solvent resistance and other properties of the rubber film.

[0004] However, in this curing system, due to the too high activity of the isocyanate curing agent, it will quickly react with the waterborne polyurethane after being added to the printing paste. Especially at a relatively high ambient temperature (≥35°C), generally "dead paste" will be formed after 3-4 hours. If the prepared slurry cannot be used up within the specified time, it can only be scrapped, resulting in a large amount of waste and loss. Therefore, researchers consider using milder curing agents to replace the isocyanate curing agent, such as polycarbodiimide or aziridine, etc. However, in order to meet the requirements of high solid content for the waterborne polyurethane used in printing pastes, sulfonates with strong hydrophilicity (such as sulfonates containing hydroxyl or amino groups) are often used as dispersants, making the existing waterborne polyurethane unable to form a good curing effect with mild curing agents such as polycarbodiimide or aziridine, thus affecting the various properties of the printing paste after film formation. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a high-solid-content waterborne polyurethane containing side carboxyl groups in the molecular main chain, a preparation method thereof, and an application thereof in printing pastes, and uses the rapid crosslinking reaction between carboxyl groups and polycarbodiimide or aziridine to achieve an ideal curing state.

[0006] The first aspect of the present application is to provide a preparation method of a high-solid-content waterborne polyurethane containing side carboxyl groups, adopting the following technical scheme: A preparation method of aqueous polyurethane, comprising the following steps: S1. At a temperature of 98 - 102 °C, keep 170 - 180 parts by weight of polyol, 45 - 55 parts by weight of isocyanate and 5 - 10 parts by weight of 1,4 - butanediol for heat - preservation reaction for 1.5 - 2.5 h, then add 25 - 35 parts by weight of acetone and 0.08 - 0.12 parts by weight of catalyst and continue heat - preservation reaction until the NCO content in the system is 0.8 - 1.2%; S2. Add 515 - 525 parts by weight of acetone to the system obtained in S1 and cool it to below 45 °C, then add 4 - 6 parts by weight of sulfonate and stir continuously for 25 - 35 min, then add 280 - 320 parts by weight of water for emulsification for 5 - 10 min. After the emulsification is completed, add 35 - 45 parts by weight of aqueous solution of diamino - carboxylic acid and mix evenly; S3. Carry out vacuum distillation on the system obtained in step S2 and adjust the pH value of the system to neutral, then filter to obtain aqueous polyurethane.

[0007] In a preferred embodiment, the diamino - carboxylic acid is one of 2,4 - diamino - butyric acid, 2,5 - diamino - valeric acid, 2,6 - diamino - caproic acid.

[0008] In a preferred embodiment, the sulfonate is sodium N - (2 - aminoethyl) ethanesulfonate.

[0009] In a preferred embodiment, the polyol is composed of polytetrahydrofuran ether diol, polycaprolactone diol and polyethylene glycol with a weight ratio of (26 - 28):(6 - 8):1.

[0010] The second aspect of the present application is to provide an aqueous polyurethane obtained by the preparation method as described above, and the structure of the aqueous polyurethane is as follows:

[0011] The third aspect of the present application is to provide a printing paste. By weight, the printing paste comprises 87 - 92 parts of the aqueous polyurethane obtained in claim 5, 0.1 - 0.2 parts of pH regulator, 2.0 - 4.0 parts of deionized water, 0.5 - 1.0 parts of defoamer, 0.3 - 0.5 parts of surfactant, 0.4 - 0.8 parts of wetting agent, 0.2 - 0.4 parts of leveling agent, 2.0 - 3.0 parts of humectant, 0.5 - 1.5 parts of white carbon black, and 1.5 - 2.5 parts of thickener.

[0012] In a preferred embodiment, when the printing paste is used, 5% by weight of polycarbodiimide or aziridine curing agent based on the weight of the printing paste is added.

[0013] In a preferred embodiment, the storage time of the printing paste at room temperature is ≥ 24 h.

[0014] In summary, the present application includes at least one of the following beneficial technical effects: In the present application, sulfonate is used as a hydrophilic group to prepare aqueous polyurethane. By adding diamino carboxylic acid in the post-chain extension preparation stage, carboxyl groups are introduced into the resin by using the reaction between amino groups and isocyanate groups, and a sulfonic acid-type aqueous polyurethane resin containing carboxyl functional groups is obtained. Since the diamino carboxylic acid is added after the formation of polyurethane particles, the introduction of carboxylic acid does not affect the particle size of the polyurethane particles and the solid content of the polyurethane, which can ensure the application of the aqueous polyurethane in the printing paste. At the same time, due to the presence of carboxyl groups in the aqueous polyurethane, after adding polycarbodiimide or aziridine curing agent to the printing paste, the aqueous polyurethane and polycarbodiimide or aziridine can achieve the effect of extending the activation period, so that the system has a longer open time, which can exceed 24 h, even reach 48 h, and can be used at a relatively high ambient temperature ≥ 30 °C. Moreover, the aqueous polyurethane and polycarbodiimide or aziridine in the present application have good curing effects. Specific embodiments

[0015] The following further elaborates on the present application with reference to examples. When the raw materials used in the examples and comparative examples of the present application are not specifically stated, they can all be obtained commercially.

[0016] Due to the linear structure of the aqueous polyurethane molecules, the printing paste lacks necessary crosslinking during curing. Therefore, in actual use, a hydrophilic-modified isocyanate curing agent is added to the printing paste. However, the isocyanate curing agent has high activity and a fast reaction rate with the aqueous polyurethane. After preparation, the printing paste will form a dead paste after 3 - 4 h. If it cannot be used up in time, a large amount of loss will be caused. In order to solve this problem, the inventor of the present invention adds a milder curing agent, polycarbodiimide or aziridine, to the preparation of the printing paste, and at the same time prepares an aqueous polyurethane containing carboxyl groups. After the two are used in combination, a cross-linked system of aqueous polyurethane - carbodiimide with a long activation period can be obtained. Compared with the aqueous polyurethane - isocyanate cross-linked system, the open time of this system can exceed 24 h, even reach 48 h, and it can also be used at an ambient temperature above 30 °C. In addition to having a long activation period, its drying and curing effects are also good.

[0017] In the present application, the diamino carboxylic acid is one of 2,4-diaminobutyric acid, 2,5-diaminopentanoic acid, and 2,6-diaminohexanoic acid, and the achieved effects are basically the same. In the following examples, 2,6-diaminohexanoic acid is used as an example for illustration.

[0018] The structure of the aqueous polyurethane prepared in the present application is as follows: Among them, PU is the main chain of polyurethane resin.

[0019] Example 1 A method for preparing aqueous polyurethane, comprising the following steps: S1. Add 17 kg of polyol into a reaction kettle, stir and heat to 125 ± 2 °C, and dehydrate for 30 min under a vacuum of -0.095 MPa; the polyol is composed of polytetrahydrofuran ether diol (Mn = 2000), polycaprolactone diol (Mn = 2000), and polyethylene glycol (Mn = 1000) with a weight ratio of 26:6:1; S2. Cool down to below 60 °C, add 4.5 kg of isophorone diisocyanate, then heat up to 100 ± 2 °C and keep the temperature for 1 h, then dropwise add 0.5 kg of 1,4-butanediol, continue to keep the temperature for 1 h, then add 2.5 kg of acetone and 0.008 kg of organic bismuth catalyst and continue to keep the temperature until the NCO content in the system is 0.8 - 1.2%; S3. Add 51.5 kg of acetone to the system obtained in S2 and cool down to below 45 °C, then add 0.4 kg of sodium N-(2-aminoethyl)-2-aminoethanesulfonate and stir continuously for 25 min, then add 28 kg of water and emulsify for 5 - 10 min. After emulsification, add 3.5 kg of 2,6-diaminohexanoic acid aqueous solution (concentration 10 wt%) and mix evenly; S4. Carry out vacuum distillation on the system obtained in step S3 and adjust the pH value of the system to neutral, then filter with a 180 - 200 mesh filter cloth to obtain carboxyl-containing aqueous polyurethane, and the solid content of this aqueous polyurethane is 50.2%.

[0020] Example 2 A method for preparing aqueous polyurethane, comprising the following steps: S1. Add 17.5 kg of polyol into a reaction kettle, stir and heat to 125 ± 2 °C, and dehydrate for 30 min under a vacuum of -0.095 MPa; the polyol is composed of polytetrahydrofuran ether diol (Mn = 2000), polycaprolactone diol (Mn = 2000), and polyethylene glycol (Mn = 1000) with a weight ratio of 27:7:1; S2. Cool down to below 60 °C, add 5.0 kg of isophorone diisocyanate, then heat up to 100 ± 2 °C and keep the temperature for 1 h, then dropwise add 0.8 kg of 1,4-butanediol, continue to keep the temperature for 0.5 h, then add 3.0 kg of acetone and 0.01 kg of organic bismuth catalyst and continue to keep the temperature until the NCO content in the system is 0.8 - 1.2%; S3. Add 52.0 kg of acetone to the system obtained in S2, cool it down to below 45°C, add 0.5 kg of sodium ethylenediamine ethanesulfonate, stir continuously for 25 min, then add 30 kg of water and emulsify for 5 - 10 min. After the emulsification is completed, add 4.0 kg of 2,6-diaminohexanoic acid aqueous solution (concentration: 10 wt%) and mix evenly. S4. Subject the system obtained in step S3 to vacuum distillation and adjust the pH value of the system to neutral. Then filter it with a 180 - 200 mesh filter cloth to obtain a carboxyl-containing aqueous polyurethane, and the solid content of this aqueous polyurethane is 50.5%.

[0021] Example 3 A preparation method of aqueous polyurethane, comprising the following steps: S1. Add 18 kg of polyol to a reaction kettle, stir and heat to 125 ± 2°C, and dehydrate for 30 min under a vacuum of -0.095 MPa; the polyol consists of polytetrahydrofuran ether diol (Mn = 2000), polycaprolactone diol (Mn = 2000), and polyethylene glycol (Mn = 1000) with a weight ratio of 28:8:1. S2. Cool down to below 60°C, add 5.5 kg of isophorone diisocyanate, then heat up to 100 ± 2°C and keep the temperature for 1 h. Then drip 1.0 kg of 1,4-butanediol, continue to keep the temperature for 1.5 h, and then add 3.5 kg of acetone and 0.012 kg of organic bismuth catalyst and continue to keep the temperature until the NCO content in the system is 0.8 - 1.2%. S3. Add 52.5 kg of acetone to the system obtained in S2, cool it down to below 45°C, add 0.6 kg of sodium ethylenediamine ethanesulfonate, stir continuously for 25 min, then add 32 kg of water and emulsify for 5 - 10 min. After the emulsification is completed, add 3.5 kg of 2,6-diaminohexanoic acid aqueous solution (concentration: 10 wt%) and mix evenly. S4. Subject the system obtained in step S3 to vacuum distillation and adjust the pH value of the system to neutral. Then filter it with a 180 - 200 mesh filter cloth to obtain a carboxyl-containing aqueous polyurethane, and the solid content of this aqueous polyurethane is 50.3%.

[0022] Comparative Example 1 A preparation method of aqueous polyurethane, which is different from Example 1 in that in step S3, 2,6-diaminohexanoic acid aqueous solution is not added, and the others are the same as in Example 1.

[0023] Apply the aqueous polyurethanes obtained in the above Examples 1 - 3 and the control example to printing pastes, specifically as follows: Application Example 1 A preparation method of a printing paste, comprising the following steps: Add 8.7 kg of the waterborne polyurethane obtained in Example 1 to a stirring kettle, start stirring, and then add 0.01 kg of a pH regulator (2-amino-2-methyl-1-propanol, commercially available under the brand name AMP-95), 0.2 kg of deionized water, 0.05 kg of an organosilicon defoamer, 0.03 kg of a surfactant, 0.04 kg of a wetting agent, 0.02 kg of a leveling agent, 0.2 kg of a humectant (diethylene glycol), and 0.05 kg of silica white. After continuous stirring for 30 min, add 0.15 kg of a thickener to obtain the printing paste; wherein the surfactant uses Coatex P30 dispersant, and the product indexes are as follows: The chemical composition is sodium polycarboxylate, the appearance is a yellow transparent liquid, the active ingredient is 42 ± 1%, the pH value is 7.5 ± 1 @ 20 °C, the specific gravity is 1.31 ± 0.02 g / ml @ 20 °C, and the compatibility: easily soluble in water; The wetting agent uses an environment-friendly PE-100, and the chemical name is a mixture of C12-14 fatty alcohol polyoxyethylene ethers. The product indexes are as follows: The appearance is a colorless to light yellow liquid, the active ingredient is 83-87%, the density is 0.97-1.03 g / cm3, the pH (5% aqueous solution) is 5.0-8.0, the cloud point (1% aqueous solution) is 73-79, and the solidification temperature < 10 °C; The leveling agent uses BYK-333, and the chemical composition is polyether-modified polydimethylsiloxane, and the density (20 °C) is 1.04 g / ml.

[0024] Application Example 2 A preparation method of a printing paste, comprising the following steps: Add 9.2 kg of the waterborne polyurethane obtained in Example 1 to a stirring kettle, start stirring, and then add 0.02 kg of a pH regulator (2-amino-2-methyl-1-propanol, commercially available under the brand name AMP-95), 0.4 kg of deionized water, 0.1 kg of an organosilicon defoamer, 0.05 kg of a surfactant, 0.08 kg of a wetting agent, 0.04 kg of a leveling agent, 0.3 kg of a humectant (diethylene glycol), and 0.15 kg of silica white. After continuous stirring for 30 min, add 0.25 kg of a thickener to obtain the printing paste; wherein the surfactant uses Coatex P30 dispersant, and the product indexes are as follows: The chemical composition is sodium polycarboxylate, the appearance is a yellow transparent liquid, the active ingredient is 42 ± 1%, the pH value is 7.5 ± 1 @ 20 °C, the specific gravity is 1.31 ± 0.02 g / ml @ 20 °C, and the compatibility: easily soluble in water; The wetting agent uses an environment-friendly PE-100, and the chemical name is a mixture of C12-14 fatty alcohol polyoxyethylene ethers. The product indexes are as follows: The appearance is a colorless to light yellow liquid, the active ingredient is 83-87%, the density is 0.97-1.03 g / cm3, the pH (5% aqueous solution) is 5.0-8.0, the cloud point (1% aqueous solution) is 73-79, and the solidification temperature < 10 °C; The leveling agent uses BYK-333, and its chemical composition is polyether-modified polydimethylsiloxane, with a density (20°C) of 1.04 g / ml.

[0025] Application Example 3 A preparation method of a printing paste, which is different from Application Example 1 in that the aqueous polyurethane uses the aqueous polyurethane obtained in Example 2, and the others are the same as Application Example 1.

[0026] Application Example 4 A preparation method of a printing paste, which is different from Application Example 1 in that the aqueous polyurethane uses the aqueous polyurethane obtained in Example 3, and the others are the same as Application Example 1.

[0027] Application Comparative Example 1 A preparation method of a printing paste, which is different from Application Example 1 in that the aqueous polyurethane uses the aqueous polyurethane obtained in Comparative Example 1, and the others are the same as Application Example 1.

[0028] Performance Detection Add 5% of polycarbodiimide curing agent by weight of the printing paste to the printing pastes obtained in the above Application Examples 1-4, and add 5% of hydrophilically modified isocyanate curing agent (commercially available, with specific properties of NCO content 21±0.5%, viscosity at 23°C: 1200-1800 mPa·s, free HDI monomer ≤0.15%, density about 1.16 g / ml) by weight of the printing paste to the printing paste obtained in Application Comparative Example 1. Then test the pot life of the aqueous polyurethane resin-polycarbodiimide cross-linking system and the aqueous polyurethane resin-isocyanate cross-linking system, as well as the physical properties of the cured coating. The test results are shown in Table 1.

[0029] The pot life refers to the time when the printing paste can be used without gelling after adding the curing agent.

[0030] Table 1 Performance Detection Results of Printing Paste It can be seen from Table 1 that: After applying the aqueous polyurethane obtained in Examples 1-3 of the present application to the printing paste, the printing pastes obtained in Application Examples 1-4 can reach non-gelling within 48 hours at an ambient temperature of 25°C, having a relatively long open time, which can ensure that the prepared printing paste is fully used up within this time period, reducing the loss cost of the printing paste. In addition, the cured coatings of the printing pastes obtained in Application Examples 1-4 of the present application do not crack after folding 200,000 times at room temperature and do not crack after folding 50,000 times under the condition of -20°C, indicating that the printing paste coatings obtained in the present application have good bending resistance at normal and low temperatures, and the tensile strength is greater than 5 kgf / cm, the ultraviolet resistance is 4.5 levels, and the yellowing resistance is 5.0 levels, indicating that the cured printing paste layer in the present application has good adhesion fastness on the base fabric, and at the same time has good ability to resist ultraviolet damage and the ability to resist heat oxygen / air damage.

[0031] Compared with Application Example 1, in Application Comparative Example 1, when no carboxyl group is added in the preparation of the aqueous polyurethane and the curing agent adopts an isocyanate curing agent, the reaction of the system in Application Comparative Example 1 is fast, resulting in a significant reduction in the open time of Application Comparative Example 1 compared to the open time of the present application, and the rubber film is relatively hard, resulting in poor low-temperature bending resistance.

[0032] The embodiments of the specific implementation manners are all preferred embodiments of the present application, and do not limit the protection scope of the present application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing waterborne polyurethane, characterized in that: The following steps are involved: S1. At a temperature of 98-102° C., 170-180 parts by weight of polyol, 45-55 parts by weight of isocyanate and 5-10 parts by weight of 1,4-butanediol are reacted for 1.5-2.5 hours, and then 25-35 parts by weight of acetone and 0.08-0.12 parts by weight of catalyst are added and the reaction is continued until the NCO content in the system is 0.8-1.2%; S2, add 515-525 parts by weight of acetone to the system obtained in S1 and cool to below 45°C, then add 4-6 parts by weight of sulfonate and continue stirring for 25-35 minutes, then add 280-320 parts by weight of water and emulsify for 5-10 minutes, after the emulsification is completed, add 35-45 parts by weight of diaminocarboxylic acid aqueous solution and mix evenly; S3, subjecting the system obtained in step S2 to reduced pressure distillation and adjusting the pH value of the system to neutral, and then filtering to obtain waterborne polyurethane.

2. The method for preparing an aqueous polyurethane according to claim 1, characterized in that: The diamino acid carboxylic acid is one of 2,4-diaminobutyric acid, 2,5-diaminopentanoic acid and 2,6-diaminohexanoic acid.

3. The method for preparing an aqueous polyurethane according to claim 1, characterized in that: The sulfonate salt adopts sodium ethylenediamine ethanesulfonate.

4. The method for preparing an aqueous polyurethane according to claim 1, characterized in that: The polyol is composed of polytetrahydrofuran ether diol, polycaprolactone diol and polyethylene glycol in a weight ratio of (26-28): (6-8):

1.

5. A waterborne polyurethane obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The structure of the waterborne polyurethane is as follows: Among them, PU is the main chain of polyurethane resin.

6. A printing paste, characterized in that: In parts by weight, the printing paste comprises 87-92 parts of the water-based polyurethane obtained in claim 5, 0.1-0.2 parts of a pH regulator, 2.0-4.0 parts of deionized water, 0.5-1.0 parts of a defoaming agent, 0.3-0.5 parts of a surfactant, 0.4-0.8 parts of a wetting agent, 0.2-0.4 parts of a leveling agent, 2.0-3.0 parts of a moisturizing agent, 0.5-1.5 parts of white carbon black, and 1.5-2.5 parts of a thickener.

7. A printing paste according to claim 6, characterized in that: When the printing paste is used, 5% of the weight of the printing paste is added with polycarbodiimide or aziridine curing agent.

8. A printing paste according to claim 7, characterized in that: The printing paste is added with polycarbodiimide or aziridine curing agent, and the storage time at room temperature is ≥24h.

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